ELECTROCHEMICAL CARBON DIOXIDE UTILIZATION

A process for producing glycerol carbonate can include providing an electrolyte including CO2 and glycerol in an electrochemical reaction unit, and applying an electrochemical potential between an anode and a cathode immersed in the electrolyte to electrochemically transform the CO2 and glycerol into glycerol carbonate. Providing reduced viscosity and/or certain temperature conditions can advantageously enhance production. The CO2 can be supplied via a CO2-loaded stream obtained from an absorption reactor, or as a gas phase, into the electrochemical reaction unit. The resulting reaction mixture can be processed by solvent extraction of the glycerol carbonate, while the recovered glycerol can be recycled for reuse in electrochemical reactions. Systems including an electrochemical reaction unit, an extractor, an optional absorption reactor, an optional water removal unit, and an optional CO2 gas recycle assembly, is also described.

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Description
TECHNICAL FIELD

The technical field generally relates to CO2 capture and utilization to produce chemical compounds, such as glycerol carbonate.

BACKGROUND

Various methods exist to capture, process, and chemically transform CO2 into other compounds. However, incorporation of CO2 into useful chemicals is in many cases energy intensive or very slow via solar chlorophyll reactions. The capture and utilization of CO2 is a particularly relevant issue in the context of environmental impacts of CO2 emissions and the challenges in converting CO2 into useful products. Greenhouse gas emissions are responsible for global warming and carbon dioxide is a major greenhouse gas. Carbon dioxide is primarily generated from fossil fuel combustion, biomass combustion and certain industrial and manufacturing processes, such as cement, iron and steel and various chemicals.

A renewable fuel which minimizes greenhouse gas emissions is biodiesel. Biodiesel production and its use has been steadily increasing. Glycerol is a by-product of the biodiesel production process and there has been some difficulty in utilizing or converting the glycerol into value-added products. One potential value-added product is glycerol carbonate, which has many potential applications as a versatile building block for various compounds (e.g., as an intermediate in the manufacture of colours, varnishes, cosmetics, pharmaceuticals, glues, etc.). Glycerol carbonate is a bifunctional compound that can be employed as solvent, additive, monomer, chemical intermediate, or as a component of gas-separation membranes, for example.

Glycerol carbonate can be prepared from glycerol by various different methods. One method is the reaction of glycerol with urea using catalysts, such as c-zirconium phosphate or mixed oxides HTc-Zn derived from hydrotalcite. There are other starting chemicals which can also produce glycerol carbonate.

Another method for the production of glycerol carbonate is carbonation of glycerol with carbon dioxide (see Equation 1).

For example, glycerol has been reacted with carbon dioxide at 453 K and 5 MPa while catalyzed by n-Bu2Sn(OMe)2, resulting in a glycerol carbonate yield of about 5.72% (see C. Vieville, J. W. Yoo, S. Pelet, Z. Mouloungui, Catal. Lett. 56 (1998) 245-247). In another example, a 35% yield of glycerol carbonate was obtained from glycerol and carbon dioxide in methanol by using 1 mol % nBu2SnO as the catalyst for 4 h at 13.8 MPa and 120° C. (see J. George, Y. Patel, S. M. Pillai, P. Munshi, J. Mol. Catal. A: Chem. 304 (2009) 1-7). These publications generally indicate that production of glycerol carbonate via chemical reactions is slow and energy intensive. In particular, the direct addition of CO2 to glycerol in previous work appeared to result in poor yield and/or requires challenging operating conditions, such as high pressures (e.g., 13.8 MPa).

Other review papers (e.g., P. U. Okoye and B. H. Hameed in Renewable and Sustainable Energy Reviews 53 (2016) 558-574) have remarked on the problems of catalyst decay due to factors such as leaching, contaminants, deposition in active sites, and high temperatures. Catalyst deactivation and the associated regeneration requirements can be problematic and can increase energy and cost of catalyst-based processes. Thus, the chemical carboxylation synthesis route for the production of glycerol carbonate has a number of challenges. The production of glycerol carbonate via chemical reaction synthesis requires a catalyst which is subject to rapid degradation.

While the reaction of CO2 and glycerol to produce glycerol carbonate appears to have potential in terms of availability of the reactants, this reaction is limited by thermodynamics and the conditions required for direct chemical synthesis requires catalysts, high temperatures and pressure conditions, which complicate and reduce the feasibility of the process. Even with such conditions, the reaction has been seen to be kinetically slow.

U.S. Pat. No. 8,845,875 (Teamey et al.) discloses a compartmentalized electrochemical cell having a separator dividing the cathodic compartment from the anodic compartment. Carbon dioxide can be provided in a catholyte in the cathodic compartment while an alcohol can be provided in an anolyte in the anodic compartment, and an electrical potential between the anode and the cathode can then be provided to produce first and second products from the respective compartments. The product pairs generated by the electrochemical cell can be acetic acid and formaldehyde, hydrogen and formaldehyde, or carbon monoxide and formaldehyde, for example. Various other product compounds can be produced by this compartmentalized electrochemical cell.

There are therefore various challenges related to the efficient production of glycerol carbonate and other organic products from carbon dioxide.

SUMMARY

In some implementations, there is provided a process for producing glycerol carbonate, comprising: providing an electrolyte comprising CO2 and glycerol in an electrochemical reaction unit; and applying an electrochemical potential between an anode and a cathode immersed in the electrolyte to electrochemically transform the CO2 and glycerol into glycerol carbonate.

In some implementations, the electrolyte comprises water. In some implementations, the electrolyte comprises monovalent cations such that the CO2 is at least partly in the form of dissolved CO2 and dissolved bicarbonate/carbonate ions of the monovalent cations. In some implementations, the monovalent cations comprise potassium. In some implementations, the monovalent cations comprise sodium.

In some implementations, the process includes providing the electrolyte at an electrolyte temperature of at least 40° C., between about 35° C. and about 120° C., or between 35° C. and about 50° C.

In some implementations, the process includes reducing an electrolyte viscosity by heating the electrolyte and/or diluting the electrolyte. In some implementations, the electrolyte viscosity is controlled below 300 cP.

In some implementations, the anode is composed of nickel. In some implementations, the anode comprises a nickel coating. In some implementations, the anode and the cathode are composed of and/or coated with non-noble metal that is in contact with the electrolyte. In some implementations, the anode and/or cathode include one or more materials as described in further detail herein.

In some implementations, the process includes producing a loaded solution comprising dissolved CO2; and supplying the loaded solution to the electrochemical reaction unit. In some implementations, producing the loaded solution comprises: supplying a CO2-containing gas to an absorption reactor; supplying an absorbent solution to the absorption reactor; directly contacting the CO2-containing gas and the absorbent solution in the absorption reactor to cause the CO2 gas to dissolve in the absorbent solution and form bicarbonate/carbonate ions; and withdrawing the loaded solution from the absorption reactor.

In some implementations, the absorbent solution comprises water, potassium and glycerol. In some implementations, the absorption reactor is a bubble column reactor.

In some implementations, the absorption reactor is operated at temperature conditions between 15° C. and 60° C., or between 15° C. and 40° C. In some implementations, the absorption reactor is operated at temperature conditions between 20° C. and 30° C. In some implementations, the absorption reactor is operated at substantially atmospheric pressure conditions.

In some implementations, the process also includes separating the glycerol carbonate from the electrolyte. In some implementations, separating the glycerol carbonate from the electrolyte comprises: withdrawing a reaction mixture comprising the electrolyte and the glycerol carbonate from the electrochemical reaction unit; subjecting the reaction mixture to solvent extraction by contacting the reaction mixture with a solvent capable of solubilizing the glycerol, to produce: a glycerol carbonate depleted fraction comprising glycerol; and a glycerol carbonate enriched fraction comprising the solvent.

In some implementations, the solvent extraction comprises: supplying the reaction mixture and a solvent to an extractor to promote the transfer of the glycerol carbonate into the solvent phase; and removing the glycerol carbonate depleted fraction and the glycerol carbonate enriched fraction from the extractor.

In some implementations, the reaction mixture and the solvent are passed counter-currently with respect to each other in the extractor. In some implementations, the solvent comprises an alcohol. In some implementations, the solvent comprises propanol. In some implementations, the solvent comprises isopropanol.

In some implementations, the process includes subjecting the glycerol carbonate enriched fraction to solvent recovery to produce a recovered solvent fraction and a glycerol carbonate fraction. In some implementations, the process includes recycling at least a portion of the recovered solvent fraction back into to the solvent extraction. In some implementations, the solvent recovery comprises distillation. In some implementations, the solvent recovery is performed in a packed distillation column.

In some implementations, the process includes recovering glycerol from at least a portion of the glycerol carbonate depleted fraction. In some implementations, recovering glycerol comprises supplying the glycerol carbonate depleted fraction to an evaporator to produce a condensate stream and a glycerol enriched stream.

In some implementations, the process includes supplying at least a portion of the glycerol enriched stream back into the absorption reactor as at least part of the absorbent solution. In some implementations, the process includes adding a glycerol make-up stream to the glycerol enriched stream upstream of the absorption reactor to form the absorbent solution.

In some implementations, the process includes mixing the electrolyte while the electrochemical potential is applied between the anode and the cathode to induce fluid flow therebetween. In some implementations, the mixing is performed by a mixing element disposed within the electrochemical reaction unit.

In some implementations, the electrolyte is free of amine-based and/or carbamate-forming compounds. In some implementations, the electrolyte consists essentially of the glycerol, the CO2 in the form of a CO2/carbonic-acid/bicarbonate/carbonate system, and potassium or sodium cations, and water. In some implementations, the electrolyte is basic; the electrolyte may have a pH between 8 and 14, or between 10 and 14. In some implementations, the electrolyte is neutral or slightly acidic.

In some implementations, the process includes performing the electrochemical reaction at a reaction temperature up to 100° C. or up to 120° C. In some implementations, the process includes performing the electrochemical reaction at a reaction temperature that is below a boiling point of any component of the electrolyte. In some implementations, the process includes performing the electrochemical reaction without pressurization.

In some implementations, the process may include maintaining, monitoring and/or controlling pH before, during and/or after the electrochemical reaction, for example by adding a base (e.g., KOH).

In some implementations, there is provided a system for producing glycerol carbonate, comprising:

    • an electrochemical reaction unit comprising:
      • a reaction chamber;
      • an anode and a cathode disposed within the reaction chamber;
      • an inlet for providing an electrolyte comprising glycerol and CO2 into the reaction chamber;
      • a power source coupled to the anode and the cathode, and configured to create an electric potential therebetween to induce electrochemical reduction and oxidation reactions, and thereby produce a reaction mixture comprising glycerol carbonate; and
      • an outlet for releasing the reaction mixture;
    • an extractor comprising:
      • a reaction mixture inlet in fluid communication with the outlet of the electrochemical reaction unit for receiving the reaction mixture;
      • a solvent inlet receiving a solvent capable of solubilizing glycerol carbonate;
      • an extraction chamber in fluid communication with the reaction mixture inlet and the solvent inlet, and configured to enable direct contact between the reaction mixture and the solvent to enable the glycerol carbonate to dissolve into the solvent, and thereby produce a glycerol carbonate depleted fraction comprising glycerol and a glycerol carbonate enriched fraction comprising the solvent;
      • a first outlet for releasing the glycerol carbonate enriched fraction; and
      • a second outlet for releasing the glycerol carbonate depleted fraction;
    • an absorption reactor comprising:
      • a gas inlet for receiving a CO2-containing gas;
      • a liquid inlet for receiving an absorbent solution comprising glycerol, a carbonate salt and material derived from the glycerol carbonate depleted fraction;
      • an absorption chamber in fluid communication with the gas inlet and the liquid inlet, and configured to enable direct contact between the CO2-containing gas and the absorbent solution to form a loaded absorbent;
      • an absorbent outlet for releasing the loaded absorbent and being in fluid communication with the inlet of the electrochemical reaction unit such that the loaded absorbent forms at least part of the electrolyte.

In some implementations, the system also includes a solvent recovery unit coupled to the second outlet of the extractor for receiving the glycerol carbonate depleted fraction and producing a recovered solvent stream and a glycerol enriched stream.

In some implementations, the system also includes an evaporator coupled to the solvent recovery unit for receiving the glycerol enriched stream and producing a condensate stream and a glycerol-containing stream that forms part of the absorbent solution.

In some implementations, the system also includes a mixer coupled to the evaporator for receiving the glycerol-containing stream and also receiving a glycerol make-up stream to mix the same and form the absorbent solution.

In some implementations, the system also includes a dilution unit for diluting the electrolyte and/or the loaded absorbent to a dilution level sufficient to provide an electrolyte viscosity below 500 cP within the reaction chamber of the electrochemical reaction unit.

In some implementations, the system also includes a heater for heating the electrolyte and/or the loaded absorbent to a temperature sufficient to provide an electrolyte viscosity below 500 cP within the reaction chamber of the electrochemical reaction unit.

In some implementations, the system also includes at least one feature or unit enabling performing a step, as described for the process above and/or herein.

In some implementations, there is provided an electrochemical process for integrating CO2 into an ionisable organic compound to form a reaction product, comprising: providing an electrolyte comprising the ionisable organic compound, a salt, and the CO2 in the form of a CO2/carbonic-acid/bicarbonate/carbonate system; and applying an electrochemical potential between an anode and a cathode immersed in the electrolyte to induce simultaneous electrochemical reduction and oxidation reactions of the CO2 and the ionisable organic compound, respectively, and form the reaction product.

In some implementations, the ionisable organic compound comprises an alcohol and the reaction product comprises a carbonate ester. In some implementations, the ionisable organic compound comprises glycerol and the reaction product comprises a glycerol carbonate. In some implementations, the salt comprises potassium carbonate. In some implementations, the salt comprises sodium carbonate. In some implementations, the electrolyte comprises an alkaline metal hydroxide prepared with dissolved CO2.

In some implementations, the alcohol comprises methanol and the carbonate ester compound comprises dimethyl carbonate. In some implementations, the alcohol comprises a diol or a triol or a combination thereof. In some implementations, the alcohol comprises an aryl or an alkyl group.

In some implementations, the electrochemical process includes one or more features as described herein.

In some implementations, there is provided a process for producing glycerol carbonate, comprising providing an electrolyte comprising CO2 and glycerol in an electrochemical reaction unit; electrochemically reducing the CO2 to promote formation of glycerol carbonate in the electrolyte; and controlling electrolyte viscosity sufficiently low to enable free fluid flow of the electrolyte.

In some implementations, controlling the electrolyte viscosity comprises heating the electrolyte above a threshold temperature. In some implementations, the threshold temperature is 30° C., 35° C., or 40° C.

In some implementations, controlling the electrolyte viscosity comprises diluting the electrolyte above a dilution threshold. In some implementations, the dilution is performed with water. In some implementations, the dilution threshold is at least 5 vol % water, 10 vol % water, 15 vol % water, 20 vol % water, or 25 vol % water.

In some implementations, controlling the electrolyte viscosity is performed so as to provide the electrolyte viscosity below 600 cP, 500 cP, 400 cP, 300 cP, 250 cP, 200 cP or 150 cP.

In some implementations, the process also includes providing the electrolyte, an anode and a cathode in a common reaction chamber; and applying an electrochemical potential between the anode and the cathode immersed in the electrolyte to enable electrochemical reduction and oxidation reactions of the CO2 and glycerol, respectively.

In some implementations, there is provided an electrochemical process for integrating CO2 into an ionisable organic compound to form a reaction product, comprising: providing an electrolyte comprising the ionisable organic compound, a salt, and the CO2 in the form of a CO2/carbonic-acid/bicarbonate/carbonate system; applying an electrochemical potential between an anode and a cathode immersed in the electrolyte to induce simultaneous electrochemical reduction and oxidation reactions of the CO2 and the ionisable organic compound, respectively, and form the reaction product; and controlling electrolyte viscosity sufficiently low to enable free fluid flow of the electrolyte.

In some implementations, controlling the electrolyte viscosity comprises heating the electrolyte above a threshold temperature. In some implementations, the threshold temperature is 30° C., 35° C., or 40° C. In some implementations, controlling the electrolyte viscosity comprises diluting the electrolyte above a dilution threshold. In some implementations, the dilution is performed with water. In some implementations, the dilution threshold is at least 5 vol % water, 10 vol % water, 15 vol % water, 20 vol % water, or 25 vol % water. In some implementations, controlling the electrolyte viscosity is performed so as to provide the electrolyte viscosity below 600 cP, 500 cP, 400 cP, 300 cP, 250 cP, 200 cP or 150 cP.

In some implementations, the ionisable organic compound comprises an alcohol and the reaction product comprises a carbonate ester. In some implementations, the ionisable organic compound comprises glycerol and the reaction product comprises a glycerol carbonate. In some implementations, the salt comprises potassium carbonate.

In some implementations, the ionisable organic compound has a viscosity of at least 3900 cP at 10° C., at least 1400 cP at 20° C., and/or at least 600 cP at 30° C.; and the

In some implementations, the electrolyte is basic, and may have a pH between 8 and 14 or between 10 and 14.

In some implementations, the electrochemical reaction is performed at a reaction temperature up to 100° C. The electrochemical reaction may be done at a reaction temperature that is below a boiling point of any component of the electrolyte. The electrochemical reaction may be done without pressurization.

In some implementations, there is provided a method of producing glycerol carbonate including simultaneous electrochemical reduction of CO2 and oxidation of glycerol within a common electrolyte fluid, and allowing contact between electrochemical reaction products to form a reaction mixture comprising the glycerol carbonate. The method can also include one or more features as described herein.

It is also noted that, in some implementations, the process can be adapted such that the ionisable organic compound can include an amine to electrochemically produce a carbonate+NH3 product and/or a carbamate+water product, and can include a thiol compound (R—S—H) to electrochemically produce a carbonate+H2S produce and/or thioether+water product. The ionisable organic compound can also be a mixture of multiple reactants disclosed herein to electrochemically produce a mixture of products.

In some implementations, there the processes and/or systems provide an electrolyte comprising dissolved CO2 and glycerol in an electrochemical reaction unit; and an electrochemical potential is applied between electrodes (an anode and a cathode) immersed in the electrolyte to electrochemically transform the dissolved CO2 and glycerol into glycerol carbonate. Any additional features as described herein, such as subsequent extraction steps, introducing the CO2 as part of a solution or in gas phase, and the like, can be added to such process.

For certain implementations, CO2 is introduced to the electrochemical cell as a gas. The CO2 can be provided by injecting gaseous CO2 directly into the electrolyte. The gaseous CO2 can be injected in the form of bubbles, that can be injected at a bottom of the electrochemical reaction unit. The gaseous CO2 can be part of a gas stream containing other components, or relatively pure CO2. The other components can consist of inert components and optional trace components. The gaseous CO2 can be provided with a gas temperature for heating the electrolyte, i.e., a temperature that is above the initial electrolyte temperature. The gaseous CO2 can be injected via a gas diffuser. The gaseous CO2 can also be injected into a bottom of the electrochemical reaction unit in spaced-apart relation from the anode and the cathode. The CO2 can also be introduced via a gas permeable membrane that is in contact with the electrolyte.

In some implementations, there can be a step of removing water from the glycerol carbonate depleted fraction to produce a glycerol enriched stream. The water removal can also be performed on or another process stream to remove water from the overall system. The step of removing water can be performed by evaporation, and/or by dehydration by contacting the glycerol carbonate depleted fraction with an absorbent material that absorbs a portion of the water to produce a water-loaded absorbent material. When a dehydrator is used, the process can also include separating the water-loaded absorbent material from the glycerol enriched stream, subjecting the water-loaded absorbent material to regenerating to remove water therefrom and produce regenerated absorbent material, and reintroducing the regenerated absorbent material for contacting the glycerol carbonate depleted fraction.

In some implementations, particularly when CO2 gas is introduced into the electrolyte, the electrolyte is mildly acidic with a pH between about 5 and about 7, and/or the electrochemical reaction unit is operated at a pressure between about 0 bar and about 5 bars or between about 1 bar and about 4 bars.

As mentioned above, there may be a step of removing water from a process stream at least part of which is used as at least part of the electrolyte. The step of removing water can be performed on the glycerol carbonate depleted fraction to produce a water-depleted glycerol enriched stream. The step of removing water can be performed on a liquid solution prior to feeding the same into the electrochemical reaction unit. The liquid solution can be the loaded absorbent produced by the absorption reactor. The step of removing water can be performed on the reaction mixture withdrawn from the electrochemical reaction unit prior to the solvent extraction. The step of removing water can be performed by evaporation or by contacting the glycerol carbonate depleted fraction with an absorbent material that absorbs a portion of the water to produce a water-loaded absorbent material. In the latter case, the process can include separating the water-loaded absorbent material from the glycerol enriched stream, subjecting the water-loaded absorbent material to regenerating to remove water therefrom and produce regenerated absorbent material, and reintroducing the regenerated absorbent material for contacting the glycerol carbonate depleted fraction.

In terms of the system, it can include a water removal unit coupled to the solvent recovery unit for receiving the glycerol enriched stream and producing a glycerol-containing stream that is depleted in water and forms part of the absorbent solution. The water removal unit can include an evaporator that produces a condensate stream and the glycerol-containing stream, and/or a dehydrator comprising absorbent material that contacts the glycerol enriched stream and absorbs a portion of the water therefrom to produce a water-loaded absorbent material and the glycerol-containing stream. The dehydrator can comprise a contact vessel in which the absorbent material contacts the glycerol enriched stream, and a regeneration vessel that receives the water-loaded absorbent material, removes water therefrom and returns regenerated absorbent material back into the contact vessel.

In some implementations, the water removal unit configured for removing water from a process stream at least part of which is used as at least part of the electrolyte; the water removal unit is configured to receive the glycerol enriched stream to produce the glycerol-containing stream that is depleted in water; the water removal unit is configured to receive the loaded absorbent produced by the absorption reactor prior to feeding into the electrochemical reaction unit; and the water removal unit is configured to receive the reaction mixture withdrawn from the electrochemical reaction unit prior to the solvent extraction. The water removal unit can include an evaporator or a dehydrator. the dehydrator can include a contacting vessel comprising absorbent material that contacts the process stream and absorbs water therefrom, and produces a water-loaded absorbent material. The dehydrator can also include a regeneration vessel coupled to the contacting vessel for receiving the water-loaded absorbent material and regenerating the same to produce regenerated absorbent material for reintroduction into the contacting vessel. The regeneration vessel can be configured to regenerate the water-loaded absorbent material by heating.

The system can also include, in some embodiments, a CO2 gas recycle assembly coupled to the electrochemical reaction unit, and configured to receive unreacted CO2 gas from the electrochemical reaction unit and recycle at least a portion of the recovered unreacted CO2 gas back into the electrochemical reaction unit.

In some implementations, there is provided a system for producing glycerol carbonate, comprising:

    • an electrochemical reaction unit comprising:
      • a reaction chamber;
      • an anode and a cathode disposed within the reaction chamber;
      • an inlet for providing an electrolyte comprising glycerol into the reaction chamber;
      • a gas inlet for providing CO2 gas into the reaction chamber;
      • a power source coupled to the anode and the cathode, and configured to create an electric potential therebetween to induce electrochemical reduction and oxidation reactions, and thereby produce a reaction mixture comprising glycerol carbonate; and
      • an outlet for releasing the reaction mixture;
    • an extractor comprising:
      • a reaction mixture inlet in fluid communication with the outlet of the electrochemical reaction unit for receiving the reaction mixture;
      • a solvent inlet receiving a solvent capable of solubilizing glycerol carbonate;
      • an extraction chamber in fluid communication with the reaction mixture inlet and the solvent inlet, and configured to enable direct contact between the reaction mixture and the solvent to enable the glycerol carbonate to dissolve into the solvent, and thereby produce a glycerol carbonate depleted fraction comprising glycerol and a glycerol carbonate enriched fraction comprising the solvent;
      • a first outlet for releasing the glycerol carbonate enriched fraction; and
      • a second outlet for releasing the glycerol carbonate depleted fraction;
    • a CO2 gas source coupled to the gas inlet for providing CO2 gas into the reaction chamber.

In some implementations, the gas inlet comprises a gas distributor configured to inject CO2 bubbles into the electrolyte. The gas distributor can be arranged at a bottom of the electrochemical reaction unit. There can be a gas permeable membrane that is in contact with the electrolyte, and wherein the gas inlet is configured to supply the CO2 via the gas permeable membrane into the electrolyte. The gas permeable membrane can be sandwiched with the electrode.

In some implementations, there is also a solvent recovery unit coupled to the second outlet of the extractor for receiving the glycerol carbonate depleted fraction and producing a recovered solvent stream and a glycerol enriched stream. There can also be one or more water removal units, mixer, dilution unit, heater, CO2 gas recycle assembly and other elements as described above.

Embodiments of the techniques disclosed herein can provide various advantages, at least some of which are as follows: reducing or eliminating the need for intense process conditions, such as high temperatures and/or pressures; reducing or eliminating the need for catalysts and their associated degradation and regeneration issues; facilitating the use of renewable, efficient and/or available sources of energy in the form of electrical energy; providing production processes that have enhanced kinetics and/or yield; and providing production processes that are efficient, economical, flexible and/or versatile.

The electrochemical process can include a number of features, such as a single compartment for accommodating the electrolyte and electrodes such that the electrochemical reactions occur within a common volume of electrolyte; an integrated production system that includes a CO2 gas absorption reactor, an electrochemical reaction unit, and a product extraction unit to thereby generate reactant and product streams and facilitate reuse of certain components; and/or viscosity control techniques that may leverage dilution and/or heating to provide an electrolyte viscosity that is low enough to facilitate free fluid flow, mixing and movement of reactants during the electrochemical reactions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram with chemical reaction formula showing the production of glycerol carbonate.

FIG. 2 is a process flow diagram of an example process implementation.

FIG. 3 is a side plan view of an experimental setup of an electrochemical cell where the electrodes are nickel and the electrolyte includes methanol, potassium carbonate, and 18-crown-6.

FIG. 4 is a side plan view of an experimental setup of an electrochemical cell where the electrodes are nickel and the electrolyte includes glycerol and potassium carbonate.

FIG. 5 is a side plan view of an experimental setup of an electrochemical cell where the electrodes are nickel and the electrolyte includes glycerol, potassium carbonate, and water.

FIG. 6 is a schematic of various applications of glycerol carbonate.

FIG. 7 is a graph of temperature versus glycerol viscosity.

FIG. 8 is a graph of voltage versus current.

FIG. 9 is another graph of voltage versus current.

FIG. 10 is a graph of gas flow rate versus current.

FIG. 11 is another graph of gas flow rate versus current.

FIG. 12 illustrates graph results from Liquid Chromatography-Mass Spectrometry (LC-MS) analysis of spent electrolyte.

FIG. 13 is a further graph of gas flow rate versus current.

FIG. 14 is yet a further graph of gas flow rate versus current.

FIG. 15 is a process flow diagram of another example process implementation.

FIG. 16 is a process flow diagram of another example process implementation.

FIG. 17 is a process flow diagram of another example process implementation, which notably includes direct addition of CO2 gas into the electrochemical cell.

FIG. 18 is a process flow diagram of another example process implementation.

FIG. 19 is a process flow diagram of an example electrochemical cell with CO2 gas recycle.

FIG. 20 is a process flow diagram of another example electrochemical cell with a CO2 gas permeable membrane.

 DETAILED DESCRIPTION

Electrochemical fixation of carbon dioxide with an ionisable organic compound (e.g., glycerol) to form a value-added product such as glycerol carbonate can facilitate efficient incorporation of carbon dioxide within product compounds at reasonable operating conditions. Electrochemical conversion was found to have a high conversion and low cost due to lower operating temperatures and use of non-noble catalysts, for example. Electrochemical fixation can be further enhanced by using renewable energy to power the electrochemical reactions.

In some implementations, the process can be used to couple carbon dioxide with organic species that can be electrochemically oxidized at a cathode while carbon dioxide as a carbonate is simultaneously reduced in the same electrolyte at an anode. The coupling of the carbon dioxide and organic compound, facilitated by their respective electrochemical reduction and oxidation, in a common electrolyte results in the formation of a new organic species with the carbon from the carbon dioxide as an integral part of the structure. The new organic species can then be separated from the electrolyte by various methods. This process can facilitate avoiding the energy cost of directly rebuilding carbon dioxide molecules into complex structures in a stepwise fashion. By selecting suitable organic structures, carbon dioxide can be more favorably electrochemically added to the organic molecule to create new value-added products. The electrochemical coupling process uses the production of both reduced and oxidized species in close proximity to initiate the reaction without the need for catalysts or high temperature or pressure conditions.

Electrochemical formation of glycerol carbonate from glycerol and potassium carbonate has been demonstrated without the high cost of the conditions required for conventional chemical processes. Such carbon fixation, which uses captured carbon dioxide, can facilitate closing the greenhouse emissions loop, hence reducing greenhouse accumulation in the atmosphere. The electrochemical formation of glycerol carbonate can provide various advantages compared to current processes which have performance challenges due to low conversion efficiency (e.g., 30% at 475° C.) and high costs associated with heating, pressurizing, and use of noble metal catalysts.

Referring to FIG. 1, a glycerol carbonate production system is illustrated and can include several integrated units to convert CO2 and glycerol into glycerol carbonate. FIG. 1 shows that certain optional reactor types and operating conditions can be used for certain unit operations. It should be understood that other reactor types and operating conditions can also be used. The overall glycerol carbonate production system can include an electrochemical reaction unit, which may be a parallel plate electrolyzer operated at ambient temperature and pressure conditions and converts CO2 (which is preferably present in the form of a CO2/carbonic-acid/bicarbonate/carbonate system in the electrolyte) and glycerol into glycerol carbonate. A more detailed description of the electrochemical reaction unit and its operation will be provided further below.

Referring now to FIG. 2, the overall glycerol carbonate production system 10 will be described in greater detail. Reference can also be made to FIG. 1, which provides complementary information regarding an embodiment of the overall system. FIG. 2 shows the overall system 10 which can include an electrochemical reaction unit 12, a separation unit 14 for separating the glycerol carbonate from the other compounds, a CO2 absorption reactor 16 for producing a loaded absorbent that includes dissolved CO2.

Referring still to FIG. 2, CO2-containing gas 18 can be supplied to the CO2 absorption reactor 16 along with a lean absorbent 20 for direct contact with the gas. The CO2 can dissolve and be captured by the absorbent to form a loaded absorbent 22 and a CO2-depleted gas 24. The absorbent can be an aqueous solution and can also include glycerol. Alternatively, glycerol could be added to the loaded absorbent 22 after exiting the absorption reactor 16 and prior to entering the electrochemical reaction unit 12. Another alternative is to add glycerol into the electrochemical reaction unit 12 separately from the loaded absorbent 22. In one preferred scenario, the absorbent is an aqueous solution including potassium or sodium carbonate. The absorption reactor 16 can take the form of various reactor types and configurations, such as a bubble column, a packed column, a spray tower, or a combination thereof. The reactor type may be selected based on the process operating conditions, e.g., the partial pressure of the CO2 gas, the CO2 content of the gas, the temperature conditions, and so on. The CO2 absorption reactor 16 can be coupled to a gas source (not illustrated), which may generate combustion emissions or other CO2-containing gas streams.

FIG. 2 further illustrates that the loaded absorbent 22 is supplied to the electrochemical reaction unit 12. The loaded absorbent 22 can thus form the electrolyte of the electrochemical reaction unit 12 in which an anode 26 and a cathode 28 are immersed. The electrodes 26, 28 are thus immersed in the electrolyte within a reaction chamber defined by an enclosure that includes side walls and a base, where the reaction chamber is configured to allow free fluid flow of the electrolyte. In some scenarios, the reaction chamber of the electrochemical reaction unit 12 includes no internals or separation membrane or the like, thus facilitating free movement of the electrolyte.

The electrodes are coupled to a power source 30 configured to create an electric potential between the electrodes. Applying the electric potential enables the glycerol and the CO2/carbonic-acid/bicarbonate/carbonate system within the electrolyte to undergo an electrochemical transformation to produce glycerol carbonate. The resulting reaction mixture 32 within the electrochemical reaction unit 12 can then be withdrawn and sent for further processing, which may include extraction of the glycerol carbonate from the rest of the mixture 32. During the electrochemical reaction, gas can be liberated and a gas outlet stream 34 can be released from the electrochemical reaction unit 12. The gas outlets stream 34 can be further treated or stored, if desired, and may also be recycled back into the process in some scenarios.

In some implementations, the electrodes 26, 28 may be composed of or coated with nickel or similar material. Preferably, the electrodes are composed of or coated with non-noble metal(s). It should be noted that other electrode compositions can be used and selected based on the reactants, the electrolyte composition, and the desired product. For example, implementations of the techniques described herein could be used in conjunction with carbon electrodes, titanium coated electrodes, gold coated electrodes, stainless steel, dimensionally stable anodes (DSA), copper electrodes, etc. In some implementations, the electrodes could be a combination of different metal or materials (e.g., bimetallic catalysts such as Cu—Ni, Cu—Zn, Zn—Ni; tri-metallic or multi-metallic catalysts such as Cu—Zn—Ni; and/or composite materials where metals such as Cu or Ni are impregnated onto some porous materials like activated carbon to boost surface area and hence activity.

Still referring to FIG. 2, the reaction mixture 32 that includes glycerol carbonate and, optionally, includes other compounds (e.g., unreacted potassium carbonate, potassium hydroxide, and water) is supplied to a separation unit 14 for separating the glycerol carbonate and recovering recyclable materials back into the process. It should be noted that when a single or main product (e.g., glycerol carbonate) is targeted, the separation unit 14 can be configured and operated to recover the product as a substantially isolated stream. Alternatively, when a mixture of products are targeted, such as a mixture of different alkylene carbonates resulting from different alcohol reactants, the separation unit 14 can be designed and operated accordingly to recover a mixed product stream.

FIG. 2 illustrates that the separation unit 14 can include multiple sub-units, such as a solvent extractor 36 followed by a distillation column 38. The solvent extractor 36 can receive the reaction mixture 32 and a solvent stream 40 (e.g., composed of isopropanol), where the solvent stream is selected for extracting the product (e.g., glycerol carbonate) from the mixture 32, to thereby produce a product enriched fraction 42 and a product depleted fraction 44. The product enriched fraction 42 can include a substantial portion of the glycerol carbonate that is dissolved in the solvent, while the product depleted fraction 44 can include water, potassium carbonate, potassium hydroxide, glycerol and little to no glycerol carbonate.

The product enriched fraction 42 can then be supplied to a solvent recovery unit, which may be the distillation column 38, to produce a recovered solvent component 46 and a product stream 48 (e.g., glycerol carbonate product). The recovered solvent component 46 can then be recycled back to the solvent extractor 36. It should be noted that various other devices can be used as part of the separation unit 14 for recovering one or more desired products from the reaction mixture 32 removed from the electrochemical reaction unit 12. FIG. 6 illustrates various end uses and applications for glycerol carbonate. When the product stream 48 is glycerol carbonate, it can be further processed to prepare the final commercial product for sale, which can in some cases be based on the end use.

Referring back to FIG. 2, the product depleted fraction 44 can be recycled back into the process, particularly when it includes unreacted reactants (e.g., glycerol) or components that are used in the electrochemical reaction units 12, such as potassium salt. Depending on its composition and the upstream unit operations, the product depleted fraction 44 may be subjected to additional treatment prior to recycling. For example, the product depleted fraction 44 can be supplied to an evaporator 50 to produce a condensate stream 52 and a reactant enriched stream 54 which, in turn, can be supplied to a tank or mixer 56 to be combined with a make-up glycerol stream 58 and further make-up stream(s) 60 which may include other reactants or compounds desired for the process (e.g. salts). The resulting combined stream 62 can be supplied as part or all of the lean absorbent 20 fed to the absorption reactor 16.

While FIGS. 1 and 2 illustrate embodiments of a system for production of glycerol carbonate from CO2 and glycerol, it should be understood that such a system can be used and/or adapted for use with reactants other than glycerol to produce other products that incorporate CO2. For example, the ionisable organic compound can include at least one alkyl or aryl alcohol to produce a carbonate ester having the following formula I:

where R1 and R2 can be the same or different, and can each be selected from an alkyl group (e.g., C1 to C10) that is linear or branched, and an aryl group (e.g., phenyl). Regarding potential R groups, a general case may be the first atom being C which is bound to the oxygen, and the R group can be an alkyl group with some additional functional group(s) on the other carbon molecules such as —C═O— or —C—OH; an allyl group (—CH═CH—R′) where R′ can be alkyl or —H; or alkyne (—C≡C—R″) where R″ can be alkyl or —H. In addition, the carbonate ester can have a closed ring structure according to the following formula II:

where R3 and R4 can be the same or different, and can each be selected from hydrogen, an alkyl group (e.g., C1 to C10) that is linear or branched, an aryl group (e.g., phenyl), or a functional group such as —R, —OH, —COOH, —NH2, etc.

Furthermore, the ionisable organic compound can include an amine to produce a carbamate product. For amines, a C—N bond may break (forming carbonate+NH3) or an N—H bond may break (forming carbamate+water), with the N—H bond cleavage being more favorable with basic solutions. Another alternative is thiols (R—S—H), where a C—S bond could break (forming organic carbonate+H2S) or an S—H could break (forming thioether+water). Again, S—H bond cleavage would be more favorable in basic solutions that would extract H+.

A variety of ionisable organic species may be carbonated using techniques described herein. Alcohols are an example. Organic hydroxides can also be ionized and hence may also be able to be electrochemically carbonated. The following ionisable species may be used in the process or an adapted version thereof: Organic hydroxides such as quaternary ammonium hydroxides (R4N+ OH—), quaternary phosphonium hydroxides (R4P+ OH—), and tertiary sulfonium hydroxides (R3S+ OH—); these organic hydroxides may be collectively referred to as onium hydroxides. In both quaternary ammonium hydroxides and quaternary phosphonium hydroxides, there are four alkyl/aryl groups attached to nitrogen or phosphorus atoms. Some examples are tetrabutyl-ammonium hydroxide, benzyltriethylammonium hydroxide, and n-butyltriphenylammonium hydroxide. In the case of sulfonium hydroxides, there are three groups attached to the sulfur atom.

In addition, while aqueous systems have been investigated, techniques described herein may be adapted for purely organic phase systems. In addition, in some environmental applications, the organic compound may be a contaminant such that carbonation of the contaminant makes it inert or facilitates its extraction.

A relevant factor is the economic feasibility of the process. Glycerol has an unusually low price due to oversupply, and the product glycerol carbonate has a high value because it is difficult to produce chemically, leading to an unusual combination and notable advantages for the electrochemical processes described herein for producing glycerol carbonate.

Referring back to FIG. 1, it should be noted that some implementations of the process make use of carbon dioxide that has been dissolved and ionized, and thus takes the form of a CO2/carbonic-acid/bicarbonate/carbonate system in the electrolyte liquid. The electrochemical reaction uses the carbonate/bicarbonate ions as raw materials to be coupled with an ionisable organic compound, such as glycerol. FIG. 1 illustrates that the carbonate/bicarbonate ions are formed in an absorption reactor (e.g., bubble column) where CO2 gas is dissolved and ionized within an absorbent solution that preferably includes water, potassium carbonate, the ionisable organic compound at conditions (temperature, pressure, pH, etc.) favoring the ionization of the CO2.

In some implementations, the pH of the solution is basic (pH>7) and is preferably between about 8 and about 14, or between about 10 and about 14, depending on various factors including CO2 solubility in the medium of the electrolyte. Due to the limited solubility of CO2 in electrolyte, the solution is preferably kept basic to keep CO2 in the solution by forming CO32− and HCO3−. In general, the more basic the solution, the easier CO2 can stay in solution and not escape as CO2 gas. In other words, since CO2 is being used as a reactant, the pH should be favorable for adsorption and stability of the carbonate/bicarbonate ions. In some scenarios, pH between about 5 and about 8 could be used, and the process could be managed in various ways to provide adequate CO2 electrode contacting characteristics such as with the use of a gas diffusion membrane or gas diffusion electrode common in fuel cell technology. Various electrochemical reaction unit configurations and reactor types can be used, some of which are illustrated in the figures.

The electrochemical techniques described herein facilitate the addition of CO2 into existing ionisable organic molecules, thereby reducing the energy required and allowing for the production of value-added products. Two examples have been demonstrated and are reported herein. First, the addition of CO2 (from dissolved carbonate) to methanol enabled the electrochemically promoted formation of dimethyl carbonate and acetic acid. Second, the formation of glycerol carbonate was enabled the electrochemically promoted addition of CO2 (from dissolved carbonate) to glycerol. In the second example, the product value exceeds the reactant value and energy consumed by at least 400%. The products have been confirmed by liquid chromatography with a mass spectrometer detector operated by Biozone™ (Centre for Applied Bioengineering Research at the University of Toronto's Faculty of Applied Science and Engineering). The electrochemical route is facilitated by supplying a voltage difference between two electrodes with an electrolyte that has the organic reactant and dissolved CO2 in the form of carbonate. It is also noted that a third example used the addition of CO2 in gas phase into the electrolyte.

In the example using glycerol, the only substantial organic product was glycerol carbonate. Glycerol carbonate is a high value product with a market price of around 8100 US$/ton. Due to its high cost, it is not widely used in commercial applications. However, if glycerol carbonate can be produced efficiently from glycerol, it will have a large potential to be used as a substitute for petro-derivative compounds.

In some implementations, the electrochemical process includes viscosity control and/or viscosity reduction of the electrolyte within the chamber of the electrochemical reaction unit, particularly where one or more of the reactants has an elevated viscosity and inhibits mixing. It has been found that a challenge in using glycerol, for example, is its high viscosity. The viscosity of glycerol varies significantly with temperature. In order to achieve enhanced mixing and fluid movement within the electrochemical reaction unit and/or accelerated dissolution of potassium carbonate into the glycerol, controlling viscosity can be performed. The viscosity control can thus lead to higher conversion to glycerol carbonate.

One method of controlling viscosity is by manipulating the temperature. One can also determine an optimum operating temperature as heating costs rise significantly with temperature. FIG. 7 illustrates the relation between glycerol viscosity and temperature. It can be seen that an increase in temperature from 0° C. to 40° C. results in a drastic reduction in viscosity of glycerol, whereas an increase from 40° C. to 70° C. has a minimal effect on reducing viscosity. Thus, the electrolyte within the electrochemical reaction unit can be heated or controlled within a temperature range that facilitates low viscosity properties of the electrolyte. When the electrolyte consists essentially of glycerol and potassium carbonate with little to no water, the temperature control can be done so that the temperature is above 30° C., 35° C., 40° C. or 45° C., for example. The temperature control can also be done so that the electrolyte has a resulting viscosity that is reduced by at least 50%, 60%, 70%, 80% or 90% compared to ambient temperature conditions (20° C.). The temperature control can be performed by operating the absorption reactor at a sufficiently high temperature, by pre-heating the loaded absorbent before introduction into the electrochemical reaction unit, and/or by heating the electrolyte within the electrochemical reaction unit before and/or during the reaction (e.g., using a heating jacket, internal heating elements, etc.).

Nevertheless, the electrochemical reactions could be performed at higher temperatures, e.g., up to about 100° C., depending on the stability and properties of the component of the electrolyte. In the case of glycerol, for example, it is quite heat tolerant and operating at temperatures up to 100° C. could be done without pressurization and therefore could be performed under cost-effective conditions. In some implementations, the upper temperature limit that is used is below the boiling point of any components in the electrolyte and facilitates operation without pressurization of the electrochemical reaction unit.

Another method of controlling viscosity is by manipulating the composition of the electrolyte. For example, the water content of the electrolyte can be increased in order to decrease the overall viscosity. The electrolyte can be diluted with water at various points in the process to achieve a desired viscosity range. The dilution level may be at least 5 vol %, 10 vol %, 15 vol %, 20 vol % or 25 vol % water, for example. In addition, the water dilution can be balanced with temperature, energy consumption and reaction performance (e.g., yield and rate) to enhance the overall performance and economics of producing the product (e.g., glycerol carbonate).

The viscosity of the electrolyte can be controlled or varied based on a combination of variables, including composition (e.g., dilution) and temperature. In some scenarios, the viscosity of the electrolyte is provided or controlled below a threshold value of 600 cP, 500 cP, 400 cP, 300 cP, 250 cP, 200 cP or 150 cP, for example.

In some implementations, the electrochemical process includes solubility control with respect to the dissolved CO2 system (e.g., potassium carbonate based system) in the ionisable organic compound (e.g., glycerol) to facilitate enhanced conversion yield of glycerol to glycerol carbonate, for example. Potassium carbonate will be able to dissolve faster in glycerol at higher temperatures due to lower glycerol viscosity. Thus, the carbonate salt solubility can be taken into account for enhancing production of glycerol carbonate from glycerol. Table 1 below shows physical characteristics of glycerol and potassium carbonate solution at varied ratios. A molar ratio of 1:3.5 of potassium carbonate to glycerol was determined to be the solubility limit to achieve a clear solution.

TABLE 1 Mixing Ratios of Potassium Carbonate and Glycerol Ratio Appearance 1:1 Turbid White Liquid 1:2 Colourless liquid with some solid 1:3 Colourless liquid with little solids 1:3.5 Colourless liquid 1:4 Colourless liquid 1:5 Colourless liquid 1:6 Colourless liquid 1:10 Colourless liquid 1:20 Colourless liquid 1:50 Colourless liquid 1:75 Colourless liquid 1:100 Colourless liquid

As will be discussed in relation to FIGS. 2 and 15 to 18 in particular, there are several possible process configurations that can be used for the electrochemical production methods described herein.

Referring to FIG. 15, the following table provides a legend for the reference characters as well as some example operating condition information.

Label Description 101 Glycerol 102 CO2 103 Mixer (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 100 atm) 104 Recycled Glycerol, K2CO3, KOH, H2O 105 Glycerol, K2CO3, KOH, H2O 106 Bubble Column Reactor (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 100 atm) 201 Glycerol, K2CO3, KOH, H2O 202 Dehydrator (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 100 atm) 203 Water absorbent + H2O 204 Water absorbent 205 Heater (Temp. Range: 25° C.-1000° C., Pressure: Vacuum - 100 atm) 206 H2O 207 Glycerol, K2CO3, KOH, H2O 208 Electrochemical Cell (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 1000 atm) 301 Glycerol Carbonate, Glycerol, K2CO3, KOH, H2O 302 Solvent Extractor (Temp. Range: −50° C.-200° C., Pressure: Vacuum - 100 atm) 303 Solvent + Glycerol Carbonate 304 Vacuum Distillation (Temp. Range: −50° C.-300° C., Pressure: Vacuum - 1 atm) 305 Recycled Solvent 306 Glycerol Carbonate

Referring to FIG. 16, the following table provides a legend for the reference characters as well as some example operating condition information.

Label Description 401 Glycerol 402 CO2 403 Mixer (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 100 atm) 404 Recycled Glycerol, K2CO3, KOH, H2O 405 Glycerol, K2CO3, KOH, H2O 406 Bubble Column Reactor (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 100 atm) 501 Glycerol, K2CO3, KOH, H2O 502 Electrochemical Cell (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 1000 atm) 503 Glycerol Carbonate, Glycerol, K2CO3, KOH, H2O 504 Solvent Extractor (Temp. Range: −50° C.-200° C., Pressure: Vacuum - 100 atm) 505 Solvent + Glycerol Carbonate 506 Vacuum Distillation (Temp. Range: −50° C.-300° C., Pressure: Vacuum - 1 atm) 507 Recycled Solvent 508 Glycerol Carbonate 601 Glycerol, K2CO3, KOH, H2O 602 Dehydrator (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 100 atm) 603 Water absorbent + H2O 604 Heater (Temp. Range: 25° C.-1000° C., Pressure: Vacuum - 100 atm) 605 Water absorbent 606 H2O

Referring to FIG. 17, the following table provides a legend for the reference characters as well as some example operating condition information.

Label Description 701 CO2 702 Glycerol 703 Mixer (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 100 atm) 704 Recycled Glycerol, K2CO3, KOH, H2O 705 Glycerol, K2CO3, KOH, H2O 706 Electrochemical Cell (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 1000 atm) 801 Glycerol Carbonate, Glycerol, K2CO3, KOH, H2O 802 Solvent Extractor (Temp. Range: −50° C.-200° C., Pressure: Vacuum - 100 atm) 803 Solvent + Glycerol Carbonate 804 Vacuum Distillation (Temp. Range: −50° C.-300° C., Pressure: Vacuum - 1 atm) 805 Recycled Solvent 806 Glycerol Carbonate 901 Glycerol, K2CO3, KOH, H2O 902 Dehydrator (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 100 atm) 903 Water absorbent + H2O 904 Heater (Temp. Range: 25° C.-1000° C., Pressure: Vacuum - 100 atm) 905 Water absorbent 906 H2O

Referring to FIG. 18, the following table provides a legend for the reference characters as well as some example operating condition information.

Label Description 1001 Glycerol 1002 CO2 1003 Mixer (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 100 atm) 1004 Recycled Glycerol, K2CO3, KOH, H2O 1005 Glycerol, K2CO3, KOH, H2O 1006 Bubble Column Reactor (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 100 atm) 1101 Glycerol, K2CO3, KOH, H2O 1102 Electrochemical Cell (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 1000 atm) 1103 Glycerol Carbonate, Glycerol, K2CO3, KOH, H2O 1104 Dehydrator (Temp. Range: 0° C.-100° C., Pressure: Vacuum - 100 atm) 1105 Water Absorbent + H2O 1106 Heater (Temp. Range: 25° C.-1000° C., Pressure: Vacuum - 100 atm) 1107 Water Absorbent 1108 H2O 1201 Glycerol Carbonate, Glycerol, K2CO3, KOH, H2O 1202 Solvent Extractor (Temp. Range: −50° C.-200° C., Pressure: Vacuum - 100 atm) 1203 Solvent + Glycerol Carbonate 1204 Vacuum Distillation (Temp. Range: −50° C.-300° C., Pressure: Vacuum - 1 atm) 1205 Recycled Solvent 1206 Glycerol Carbonate

In some implementations, one or more of the operation conditions of the process of system described herein is within 5%, 10%, 15% or 20% (plus or minus) of the corresponding operating condition mentioned in one of the above four tables.

FIG. 15 illustrates a process configuration that is similar to that of FIG. 2, but a dehydrator is employed instead of an evaporator and at a different location, i.e., in between the absorber and the electrochemical unit instead of in between the solvent extractor and the absorber. More regarding the dehydrator will be discussed further below. In addition, the process configurations of FIGS. 15, 16 and 18 use a loaded absorbent solution that is formed in a CO2 gas absorber and is fed into the electrochemical reaction unit as a liquid solution. In contrast, the process configuration of FIG. 17 includes the direct injection of CO2-containing gas into the electrochemical reaction unit.

In general, a water removal unit can be provided in the process in order to remove water and maintain the water balance, given that water is generated in the process (e.g., 2KOH+CO2→K2CO3+H2O). The water removal unit can include one or more units located at one or more locations in the process, operating based on one or more water removal mechanisms. For example, the water removal unit can include an evaporator as illustrated in FIG. 2, and it can be located in between the solvent extractor and the mixer or absorber. The evaporator removes the water by heating the solution and causing water to evaporate and be collected as condensate. Alternatively, the water removal unit can include a dehydrator that includes absorbent materials (e.g., silicalite, zeolites, and so on, which may be in powder or particulate form). The water can be absorbed by the absorbent materials and then be separated from the rest of the liquid. The water-loaded absorbent materials can then be treated (e.g., by heating or other mechanisms) in order to remove the water and regenerate the absorbent materials for reuse in the dehydrator. The dehydrator can include a water removal vessel (e.g., unit 202 in FIG. 15) coupled to a regenerator vessel (e.g., unit 205 in FIG. 15) that receives the water-loaded particles for regeneration (i.e., water depletion) and then sends the particles back into the water removal vessel. The dehydrator system can be advantageous over the evaporator system due to reduced energy consumption, as the evaporator can have high energy demands for heating and vaporizing the water.

The water removal unit can be located at various locations, as shown in FIGS. 2 and 15 to 18. For instance, the water removal unit can be in between the solvent extractor and the absorber or between the solvent extractor and the mixer (as per FIGS. 2, 16 and 17); the water removal unit can be in between the absorber and the electrochemical reaction unit (as per FIG. 15); and/or the water removal unit can be in between the electrochemical reaction unit and the solvent extractor (as per FIG. 18). The location of the water removal unit can be selected based on several factors, such as the quantity or flow rate of the stream from which water is removed, the impact of water on downstream unit operations, and so on. In some cases, there may be multiple water removal units, that may be the same or different from each other.

In the embodiment illustrated in FIG. 17, the CO2-containing gas 701 is supplied directly into the electrochemical cell 706. It is noted that the CO2-containing gas can be from various sources, and can be a substantially pure CO2 gas or a mixed gas stream. When relatively pure CO2 is used, the CO2 gas can be obtained from a CO2 scrubbing operation, notably the CO2 gas released from the regenerator. Various other sources of CO2 gas can also be used. When the CO2-containing gas is a mixed gas stream, the other gas components are preferably predominantly inert, such a nitrogen, although trace amounts of other components may be present. In addition, mixed gases with other reactive components could be used and the reaction products could be handled accordingly, e.g., by subjecting the output to appropriate separation processes. Preferably, gas and reaction product components that could cause fouling of the electrodes or electrolyte or unwanted by-products could be removed prior to introducing the CO2-containing gas into the electrochemical cell. In such cases, a gas pre-treatment unit may be provided to remove contaminants from the CO2-containing gas prior to introduction into the electrochemical cell.

The CO2-containing gas can be supplied via a gas inlet line directly into the electrolyte of the electrochemical cell, for example via a sparger, diffuser or other type of distribution device that may generate gas bubbles. The gas bubbles can be provided so as to be relatively small and distributed within the volume of the electrolyte, for enhanced mass transfer. The injected CO2 gas may be in the form of bubbles of a desired or pre-determined size, and the CO2 gas injection rate may also be such that there is a desired concentration of CO2 available for the electrochemical reaction.

In addition, the electrochemical cell can be configured such that the CO2-containing gas is injected into the electrolyte at certain locations to promote good distribution and availability of the CO2 for the electrochemical reactions. In one configuration, the gas inlet is provided at the bottom of the electrochemical cell and the gas bubbles flow upward through the electrolyte, while the electrodes extend from the top of the cell into the electrolyte and are spaced away from the bottom. An example of this arrangement is shows in FIG. 19.

In some implementations, a portion of the CO2 gas is released from the electrolyte during operation of the unit, and can be collected via a gas outlet line that may be provided at the top of the electrochemical cell. The collected CO2 gas can then be recycled back into the cell and/or collected in a separate holding tank for reuse in a subsequent electrochemical reaction. An example of this arrangement is shows in FIG. 19, and more regarding this recycling will be discussed below.

It is also noted that a combination of the process configurations can be used, e.g., where CO2 is introduced into the electrochemical reaction unit by both injecting/adding CO2 gas and introducing a liquid solution that includes a CO2/bicarbonate/carbonate system. The relative proportions of the gas phase and liquid phase CO2 can be provided and adjusted as desired.

Referring now to FIG. 19, the electrochemical reaction unit 12 can include a CO2 gas recycle assembly 70 for recycling CO2 gas that did not react in the unit 12. For example, the CO2 gas recycle assembly 70 can include a gas outlet 72 at the top of the vessel for receiving CO2 gas, and a recycle line 74 for supplying the gas back into the feed. A CO2 gas holding tank 76 can also be provided. FIG. 19 illustrates an embodiment where CO2-containing gas is fed directly into the electrochemical reaction unit 12 via a gas feed line 78 from a CO2-containing gas source 80. In this illustration, the CO2-containing gas is fed via a distributor 82 that bubbles the gas into the electrolyte (E), preferably at the bottom of the vessel. This type of gas recycling assembly can be particularly advantageous when CO2 gas bubbles are directly injected into the electrolyte, as shown in FIG. 19, since more CO2 gas may flow up and out of the reaction zone compared to other configurations where a CO2/carbonate solution is supplied to the electrochemical reaction unit. A control system 81 can be used to control the gas recycling and the proportion of recycled CO2 and initial CO2-containing gas that are used to provide the gas feed stream that is supplied into the cell 12 via the feed line 78.

FIG. 20 illustrates an alternative configuration of the electrochemical reaction unit 12 in which the CO2-containing gas 78 is fed into a gas chamber 82 that is in fluid communication with a gas permeable membrane 84, which is adjacent to the electrode. For instance, the electrode and the membrane can be sandwiched together, and the electrode can have a mesh-like structure or another type of liquid permeable structure that allows electrolyte to contact and moisten the gas permeable membrane 84. In this configuration of the electrochemical reaction unit 12, a recycle CO2 gas recycle assembly 70 similar to the one of FIG. 19 is not necessary. The membrane 84 can the larger, smaller or the same size as the electrode.

Implementations described herein facilitate various advantages, including mitigation of environmental impacts and conservation of the environment. For instance, the utilization of CO2 can convert this greenhouse gas into a useful product and the utilization of glycerol aids in using a by-product of the biodiesel industry, which in turn facilitates a reduction of fossil fuel use. In addition, operating the process at milder conditions can further facilitate mitigating energy consumption.

EXAMPLES & EXPERIMENTATION

Carbon dioxide is not very reactive because it is fully oxidized. Instead of trying to reduce CO2 and build useful larger organic molecules from this state, the described electrochemical process shows that CO2 (as a carbonate ion) can be coupled to higher molecular weight organic species even at low temperatures. Instead of chemically driving the reaction via high-temperature gas phase catalysis, the reaction is conducted as an oxidation/reduction coupling. In this scenario, a limitation is that the organic molecule is capable of being ionisable. Alcohols are potential reactants. By using a membrane-free electrolytic cell where the compounds are free to flow within the electrolyte, the organic molecule can be oxidized while the carbon dioxide (as carbonate ion) can be reduced, thus producing favorable conditions for coupling. While this simple description is not strictly mechanistically correct, the outcome is a carbonated organic species and the conversion of CO2. Various embodiments are demonstrated in the following examples.

Example 1: Methanol+K2CO3+18-Crown-6 Ether

FIG. 3 shows the sealed electrolysis cell used to synthesize dimethyl carbonate and ethanoic acid from methanol, potassium carbonate and 18-crown-6 ether. The cathode is the electrically negative terminal while the anode is the electrically positive terminal. The electrolyte consists of potassium carbonate dissolved in methanol and 18-crown-6 (to boost potassium carbonate solubility) ether, for this example the mix is 1:1:20 molar ratio of potassium carbonate:18-crown-6 ether:methanol.

The electrolysis is performed by applying direct current (DC) voltage across the cathode and the anode, under varying electrical current and voltage, with the electrolyte stirred under room temperature. During electrolysis, gas (mainly due to water electrolysis to form hydrogen and oxygen) evolves from the surfaces of both the electrodes. The gas is directed to a bubble flowmeter where the volumetric flow rate of the mixture is measured based on the time taken for the bubble to move by certain volume.

The formation of both dimethyl carbonate and acetic acid is confirmed by Liquid Chromatography-Mass Spectrometry (LC-MS) analysis of the spent electrolyte which identifies both dimethyl carbonate and acetic acid as major products.

Example 2: Glycerol+K2CO3

FIG. 4 shows the sealed electrolysis cell used to synthesize glycerol carbonate from glycerol and potassium carbonate. The cathode is the electrically negative terminal while the anode is the electrically positive terminal. The electrolyte consists of potassium carbonate dissolved in glycerol, in this example the mix is 1:4 molar ratio of potassium carbonate:glycerol.

The electrolysis is performed by applying direct current (DC) voltage across the cathode and the anode, under varying electrical current and voltage, with the electrolyte heated to reduce viscosity (in this case up to 90° C.) and stirred. During electrolysis, gas (mainly due to water electrolysis to form hydrogen and oxygen) evolves from the surfaces of both the electrodes. The gas is directed to a bubble flowmeter where the volumetric flow rate of the mixture is measured based on the time taken for the bubble to move by certain volume.

The formation of glycerol carbonate is confirmed by Liquid Chromatography-Mass Spectrometry (LC-MS) analysis of the spent electrolyte which identifies glycerol carbonate as a major product.

Example 3: Glycerol+K2CO3+Water

FIG. 5 shows the sealed electrolysis cell used to synthesize glycerol carbonate from glycerol and potassium carbonate with water dilution. The cathode is the electrically negative terminal while the anode is the electrically positive terminal. The electrolyte consists of water-diluted potassium carbonate dissolved in glycerol, in this example the mix is the 1:4 molar potassium carbonate:glycerol, diluted with 20% (by volume) of water.

The electrolysis is performed by applying direct current (DC) voltage across the cathode and the anode, under varying electrical current and voltage, with the electrolyte stirred (no heating since viscosity reduced by water addition) under room temperature. During electrolysis, gas (mainly due to water electrolysis to form hydrogen and oxygen) evolves from the surfaces of both the electrodes. The gas is directed to a bubble flowmeter where the volumetric flow rate of the mixture is measured based on the time taken for the bubble to move by certain volume.

The formation of glycerol carbonate is confirmed by Liquid Chromatography-Mass Spectrometry (LC-MS) analysis of the spent electrolyte which identifies glycerol carbonate as a major product. The above examples show that the electrochemical process uses a common electrolyte (no separator or membrane) and produces a product which has incorporated a carbonate molecule into the ionisable organic species. This process is efficient and can be operated at room temperatures and pressures.

Example 4: Impact of Dilution, Temperature on Glycerol+K2CO3

Additional information and details regarding experiments are provided below:

Experimental Setup Details

In terms of the experimental setup, the carbonation of glycerol under defined operating conditions was carried out in the apparatus illustrated in FIG. 5. A 250 ml Erlenmeyer flask with a side outlet was utilized to contain the mixture and placed on top of a hot plate. A magnetic stirrer was placed within the flask to ensure good mixing during the experiment.

Two nickel based electrodes were used. Two wire leads were thread through a rubber stopper (sized to plug the top of the flask) and connected to one electrode each. Plastic silicon glue was used to seal the wires passing through the stopper to prevent gas leakage. The wires were connected to positive and negative terminals of a DC power supply. The electrodes are identified in FIG. 5 as the cathode (positive) and anode (negative) based on the charge. Clear rubber tubing was used to connect the side outlet to a 10 ml pipette, which acts as the flow meter to measure the gas flowrate. This was filled with standard liquid soap solution to measure bubble rise rate (gas flowrate) during the electro-synthesis reaction. A temperature gun was used to measure the temperature of the mixture.

Example 5: Direct Gas Contacting Electrochemical Reaction

In this example, CO2 was directly introduced into the electrochemical reactor as a gas. In using CO2 gas directly in this manner, the process flow diagram could have various similar features as illustrated in FIG. 2 but would not require the gas absorption process equipment. The electrolyte used was a mixture containing 4M glycerol+1M K2CO3+10% Vol water. Nickel gauze was used for both the anode and cathode. A current of 3.1 amps was passed through the electrolyte in the reactor for 2 hours. The gas was introduced into the bottom of the reactor via a gas inlet tube with a gas diffuser at a rate of 75 mL CO2 per minute. At the end of the experiment the electrolyte was analyzed and 10.4 g of glycerol carbonate were found to have been produced from an initial 74 g of glycerol. This is a 14% conversion. The best results were obtained for the direct gas injection in terms of higher reaction yield (more glycerol carbonate being produced).

Experimental Procedure Details

The procedure can be divided into three primary sections: sample preparation, experimental testing, and product analysis. For sample preparation, two different samples were produced to identify the viability of producing glycerol carbonate at favourable conditions. Using literature data present for the solubility of potassium carbonate in glycerol, a molar ratio of 1:3.5 (potassium carbonate to glycerol) for a clear solution when mixed together at elevated temperature for two hours. This is the literature solubility limit identified; however, it was difficult to obtain efficient and effective mixing at this ratio at the laboratory scale. The ratio was then increased to 1:4, and mixed on the hot plate at 80° C. for approximately four hours to obtain a clear solution. This solution is highly viscous at room temperature, and thus to facilitate continuous mixing, the mixture was maintained at elevated temperature. A large batch of this solution was produced and the first test sample consisted purely of this mixture, while the second sample had 20% by volume deionized water added in order to reduce the viscosity to facilitate mixing at room temperature.

For both experiments of the two samples, 200 ml of solution was transferred to the flask in the testing apparatus. The temperature of the solution for sample one was increased to 90° C., while the second sample was maintained at room temperature. The magnetic stirrer was turned on for good mixing. Soap was added to the flowmeter such that it was below the gas inlet, and this also allowed priming of the flowmeter. The DC power was turned on, and an increase in the temperature was observed to between 95-100° C. and 50-55° C. for sample one and two, respectively. Initially, the current was kept higher at 0.5 A to allow the reaction to initiate and a bubble rise was observed.

For sample one, reaction measurements were taken at 0.1 A with 0.1 A increment up to 0.7 A. The runs were repeated twice more at a starting point of 0.11 A and 0.12 A. The gas bubble rise rate was measured along with the voltage and temperature. Due to the high viscosity, mixing was non-uniform, hence the temperature was measured at the top and bottom of the solution and averaged.

For sample two, the same reaction measurements were taken at 0.2 A with 0.2 A increment up to 1.4 A. The runs were repeated with a starting point of 0.21 A up to 1.21 A. This sample was able to operate up to higher current due to the water percentage, which significantly reduced the viscosity of the solution, and therefore the resistance. Due to uniform mixing, the temperature was measured in the center of the solution at the start and end of the experiment. In both experiments, the voltage was measured at the start and end of each run and averaged.

For product analysis, sample one was diluted with deionized water to 1 μM and analyzed using LC-MS (Liquid Chromatography-Mass Spectroscopy). In addition, propanoic acid was used to protonate the mixture to identify the presence of anions due to the color change. Table below summarizes the experimental procedure of the two (2) tests.

TABLE 2 Summary of Test Sample Conditions Sample One Sample Two Potassium Carbonate:Glycerol 4:1 4:1 Molar Ratio Water (% vol) 0 20 Temperature (° C.) 90 22 Pressure (atm) 1 1 Current Range (A) 0.1-0.7 0.2-1.4 Product Analysis LC-MS Acid addition

Summary of Observations

It was noticed that as the reaction proceeded, the solution in both experiments progressed to a darker colour and eventually a near black colour. The color progression over the course of the experiment was generally from clear to cloudy to yellowish to brownish to dark brown-blackish. Both experiments were conducted over a 2 hour period and resulted in generally identical end products in terms of colour. In the case of sample one, the reaction rapidly proceeded shortly after the current was turned on and the colour began to change. With sample two, however, it appeared to take longer for the glycerol carbonate formation to initiate. There was no gas release for the first 30 minutes after the DC current was applied, whereas in sample one, it commenced soon after. There was still a reaction taking place in sample one indicated by bubbling and froth formation on the anode. In both reactions, there was a reaction taking place at the anode characterized by bubbling and froth formation at that electrode. Sample one was highly viscous and hence did not mix well with the magnetic stirrer in contrast to sample two, which mixed well due to the dilution with water.

Results and Analysis

The results obtained were plotted and analysed to identify factors affecting the reaction rate for both experiments. Refer to Tables 3 and 4 for detailed results.

TABLE 3 Test Results from Experiment One Theoretical Water Split Gas Gas Gas Flow Tavg Current Vavg Vol Total Flow Flowrate Ratio Trial # (° C.) (A) (V) (ml) time (s) (ml/s) (ml/s) (Actual/Theoretical) 1 90 0.1 5.065 5 283.410 0.018 0.023 0.762 1 96.5 0.2 7.05 5 155.660 0.032 0.047 0.681 1 99 0.3 8.7 5 110.180 0.045 0.071 0.638 1 96.5 0.4 10.385 5 83.410 0.060 0.094 0.636 1 97 0.5 11.925 5 66.480 0.075 0.118 0.637 1 98.25 0.6 13.235 5 56.180 0.089 0.142 0.626 1 98.25 0.7 14.19 5 46.180 0.108 0.166 0.653 2 99.3 0.11 3.765 5 355.000 0.014 0.026 0.539 2 97.45 0.21 5.505 5 188.730 0.026 0.050 0.534 2 97.65 0.31 7.51 5 115.930 0.043 0.073 0.589 2 97.95 0.41 9.4 5 84.250 0.059 0.097 0.612 2 97.5 0.51 11.105 5 67.060 0.075 0.121 0.619 2 97.7 0.61 12.56 5 55.080 0.091 0.144 0.629 2 98.55 0.71 13.75 5 47.000 0.106 0.168 0.632 3 98.85 0.12 3.85 5 430.260 0.012 0.028 0.408 3 98.35 0.22 5.765 5 196.130 0.025 0.052 0.489 3 98.55 0.32 7.71 5 111.360 0.045 0.076 0.592 3 98.05 0.42 9.715 5 85.630 0.058 0.099 0.587 3 98.2 0.52 11.505 5 65.310 0.077 0.123 0.622 3 98 0.62 12.98 5 53.960 0.093 0.147 0.632 3 98.05 0.72 14.175 5 46.330 0.108 0.170 0.633

TABLE 1 Test Results from Experiment Two Theoretical Gas water split Gas Flow Tavg Current Vavg Vol Total Flow gas flow Ratio Trial # (° C.) (A) (V) (ml) time (s) (ml/s) rate (ml/s) (Actual/Theoretical) 1 55.75 0.2 3.385 5 288.960 0.017 0.042 0.413 1 52.55 0.4 5.02 5 95.850 0.052 0.083 0.628 1 51.1 0.6 6.63 5 60.600 0.083 0.124 0.665 1 50.55 0.8 8.315 5 44.530 0.112 0.165 0.680 1 50.365 1 10.075 5 34.380 0.145 0.206 0.705 1 50.15 1.2 11.78 5 27.880 0.179 0.247 0.725 1 50.7 1.4 13.17 5 24.000 0.208 0.289 0.721 2 49.55 0.21 3.92 5 322.360 0.016 0.043 0.359 2 47.45 0.41 5.785 5 92.660 0.054 0.084 0.644 2 46.65 0.61 7.94 5 57.480 0.087 0.124 0.699 2 45.95 0.81 10.2 5 42.680 0.117 0.165 0.711 2 46.3 1.01 11.985 5 33.230 0.150 0.206 0.732 2 46.5 1.21 13.655 5 26.930 0.186 0.247 0.753

The parameters analysed were voltage, current and gas flowrate. The voltage was plotted against the current for each experiment as illustrated in FIG. 8 and FIG. 9, respectively.

There is a linear correlation between voltage and current. As per Ohm's law, voltage is directly proportional to the product of current and resistance. The voltage versus current profile for test 1 has a larger gradient implying a larger resistance than observed from test 2. Higher resistance can be due in part to higher viscosity of the fluid. The water dilution in test 2 helps reduce the viscosity of the solution hence reducing the resistance. The y-intercept for test 1 is larger than test 2 suggesting a larger voltage required for experimental start-up. This is primarily due to the test 1 sample being more viscous than the test 2 sample. However, due to a lower concentration of glycerol and potassium carbonate used in test 2, there was a slower reaction rate observed. There appears to be a greater deviation between the individual runs in test 2 as opposed to test 1. Based on the R2 values for the tests, test 1 runs are 2% more precise than runs for test 2. This is a relatively small deviation and can be attributed to human error.

FIG. 10 and FIG. 11 illustrate the gas flowrate versus the current through the electrodes. There is a positive correlation as gas flowrate increases with current. This was due to an increase in gas liberation at the anode. This however does not necessarily signify an increase in reaction rate as it could imply a greater dissociation of carbonate ions leading to CO2 release or due to water-splitting reaction using the water produced from the glycerol carbonation reaction. During the experiment itself, a faster change in colour from colourless to dark brown was observed with an increase in current suggesting a faster reaction rate. It is important to note that for both the tests, similar gas flowrates were observed at the same amperage. This implies that water content in the mixture does not substantially affect the gas liberation rate. The presence of water alters the reaction rate between the glycerol and the carbonate ions thereby resulting in varied rates of colour change for both the tests.

The high viscosity of glycerol makes dissolving potassium carbonate quite challenging. This was due at least in part to the inability of performing adequate mixing. The high viscosity was also a hindrance to the reaction itself due to the carbonate ions being unable to mix and react with the glycerol medium. The strategy employed was to control temperature as a means to lower the viscosity and facilitate mixing. The relation between temperature and viscosity of glycerol is illustrated in FIG. 7. A 1:1 ratio of glycerol to potassium carbonate is practically possible and optimal to maximize glycerol carbonation production, and more importantly, CO2 consumption. However, dissolving potassium carbonate in glycerol is a time-consuming, energy intensive process that may not be economically attractive especially when producing glycerol carbonate on a commercial scale. The addition of water helps address this issue by significantly lowering the viscosity of glycerol at ambient temperatures, and potentially allowing higher solubility of potassium carbonate. The addition of water makes the process less energy intensive and more economical as heat is not required to dissolve potassium carbonate into glycerol. The water however reduces the solute/solvent concentration due to the addition of water thereby reducing the reaction rate. This was confirmed by test 2 which took a longer time to change colour from colourless to dark brown.

Literature reports that glycerol carbonate is colourless. Tests 1 and Test 2 yield a dark brown solution which was not consistent with literature. Upon conducting an LC-MS test, glycerol carbonate was confirmed to be the dominant compound in the sample. The results from the LC-MS test are shown in FIG. 12. The test displays one major peak with the component having a molecular mass of 117.0179 g, which is essentially the molecular mass of glycerol carbonate (118 g) without a proton since the test was a negative test. As per the analysis conducted after the experiment, it was hypothesized that the dark brown colour occurs due to the reaction illustrated below:

The dark brown colour was hypothesized to form due to the formation of the potassium glycerol carbonate salt. A propanoic acid test was conducted to confirm the presence of potassium glycerol carbonate salt and potassium hydroxide as per the above reaction scheme. In terms of the colour of the product solution before and after the acid test, the solution before was a brownish-reddish color and the solution after was a yellowish color. There was a significant reduction in the brown colour after addition of acid, confirming the presence of glycerol carbonate ions. The acid donates protons to the solution which are used up by the glycerol anions to produce glycerol carbonate. Glycerol carbonate is colourless which explains the colour transition from dark brown to lighter brown/dark yellow. Acid could be added to the mixture produced in the electrochemical reaction unit, if conversion of the salt to the corresponding alcohol is desired.

In addition, without gas chromatography or analysis, it was difficult to identify the types of gases being liberated from the process. The gas flow rate was compared to the theoretical production rate of gases from water-splitting to partially characterize the outlet gases. For both tests, the gas flow ratio increases with current (see FIG. 13 and FIG. 14), which indicates that higher amounts of gas was liberated with increasing current supply. It was hypothesized that the primary gas released from both tests was from water spitting, but there can be release of some carbon dioxide from decomposition of carbonate ions. The water-splitting is highly favoured at low current, non-intensive conditions, and produces a large amount of gases. Thus, if the measured gas flowrate were greater than the theoretical gas flowrate due to water-splitting, this would indicate with certainty that carbon dioxide was being released and possibly water vapour (provided the conditions for evaporation). At present it is difficult to determine with certainty the types of gases being liberated from the reaction.

The results of these accelerated experiments as a mode for demonstrating electro-synthesis of glycerol carbonate were positive, and include at least the following notable findings:

    • Potassium carbonate can be readily electro-synthesized with glycerol to produce glycerol carbonate with nickel-based electrodes.
    • Molar ratios of ≥3.5 of glycerol to potassium carbonate are required to produce a clear solution.
    • The glycerol and potassium carbonate mixture has a high viscosity, hence elevated temperature, dilution, or another viscosity reducing method facilitates mixing of the solution.
    • Glycerol viscosity drops drastically when the temperature is increased to 40° C.
    • Addition of 20% by volume water to the glycerol+potassium carbonate solution reduces the viscosity sufficiently to allow good mixing at room temperature and still synthesize glycerol carbonate.

Therefore, glycerol carbonate can be electro-synthesized at room temperature and atmospheric pressure conditions using potassium carbonate.

Carbon dioxide, potassium carbonate and glycerol conversion experiments provide proof of concept for an efficient electrochemical route to glycerol carbonate and potentially other organic compounds that integrate carbonate(s). Preferred or optimum operating conditions as well as economics of the process can be further investigated to assess embodiments of the process, some of which facilitate closing the greenhouse gas loop and result in a decrease in the accumulation of greenhouse gases in the atmosphere.

Based on the experimental results and observations, further enhancements may include at least one of the following:

    • Determining the solubility of potassium carbonate in glycerol and water solvent at different compositions in order to bring the potassium carbonate to glycerol ratio as close to unity as possible.
    • Measure and assess viscosity at varying compositions of a mixture of glycerol, potassium carbonate, and water.
    • Measure yield of glycerol carbonate while controlling current, temperature, water content, and glycerol to potassium carbonate molar ratios.
    • Determine optimal composition of water, glycerol, and potassium carbonate for sufficient conversion and minimal reaction inhibition.
    • Analyse the process using supercritical carbon dioxide as opposed to potassium carbonate and compare the two processes based on economic criteria and yield.
    • Evaluate the rate of formation of glycerol carbonate using a pressurized system to determine optimal pressure for high yield and rate.
    • Perform the experiments using a range of catalysts as seen in literature to determine the catalyst favouring highest conversion of glycerol to glycerol carbonate. For instance the Purosiv catalyst was identified to yield a conversion of 32%.
    • The LC-MS test should be run with a pure glycerol carbonate sample as a reference when comparing test run samples with each other.
    • Confirm the reaction mechanisms and kinetics in order to optimize the glycerol conversion process.
    • Vary the electrode and catalyst sizes to determine the optimum electrode diameter required to produce economically viable glycerol carbonate.

It should be noted that while various embodiments are described above in relation to potassium carbonate, glycerol and water, various other embodiments may employ different carbonate salts (e.g., sodium), different ionisable organic compounds (e.g, other alcohols, etc.), and different dilution agents or solvents that are mixed with the reactants to form the electrolyte. In addition, various electrode compositions can be used in the electrochemical reaction unit, and the overall process can include various unit operations for separating products, recovering by-products, recycling reactants or other compounds, and/or generating the electrolyte that is supplied to the electrochemical reaction unit.

Claims

1. A process for producing glycerol carbonate, comprising:

providing an electrolyte comprising CO2 and glycerol in an electrochemical reaction unit; and
applying an electrochemical potential between an anode and a cathode immersed in the electrolyte to electrochemically transform the CO2 and glycerol into glycerol carbonate.

2. The process of claim 1, wherein the electrolyte comprises water and monovalent cations such that the CO2 is at least partly in the form of dissolved CO2/bicarbonate/carbonate ions of the monovalent cations.

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4. The process of claim 2, wherein the monovalent cations comprise potassium.

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6. The process of claim 1, further comprising providing the electrolyte at an electrolyte temperature of at least 40° C.

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8. The process of claim 1, further comprising reducing an electrolyte viscosity by heating the electrolyte and/or diluting the electrolyte.

9. The process of claim 1, further comprising controlling an electrolyte viscosity below 300 cP.

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15. The process of claim 1, further comprising:

producing a loaded solution comprising the CO2; and
supplying the loaded solution to the electrochemical reaction unit; and
wherein producing the loaded solution comprises: supplying a CO2-containing gas to an absorption reactor; supplying an absorbent solution to the absorption reactor; directly contacting the CO2-containing gas and the absorbent solution in the absorption reactor to cause the CO2 gas to dissolve in the absorbent solution and form bicarbonate/carbonate ions; and withdrawing the loaded solution from the absorption reactor.

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17. The process of claim 15, wherein the absorbent solution comprises water, potassium and glycerol, and the absorption reactor is operated at temperature conditions between 15° C. and 40° C.

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22. The process of claim 1, wherein CO2 is introduced to the electrochemical cell as a gas by injecting gaseous CO2 directly into the electrolyte in the form of bubbles.

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29. The process of claim 22, wherein the gaseous CO2 is provided with a gas temperature for heating the electrolyte.

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33. The process of claim 1, further comprising separating the glycerol carbonate from the electrolyte, comprising:

withdrawing a reaction mixture comprising the electrolyte and the glycerol carbonate from the electrochemical reaction unit;
subjecting the reaction mixture to solvent extraction by contacting the reaction mixture with a solvent capable of solubilizing the glycerol, to produce; a glycerol carbonate depleted fraction comprising glycerol; and a glycerol carbonate enriched fraction comprising the solvent.

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35. The process of claim 33, wherein the solvent extraction comprises:

supplying the reaction mixture and a solvent to an extractor to promote the transfer of the glycerol carbonate into the solvent phase; and
removing the glycerol carbonate depleted fraction and the glycerol carbonate enriched fraction from the extractor.

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40. The process of claim 35, further comprising subjecting the glycerol carbonate enriched fraction to solvent recovery to produce a recovered solvent fraction and a glycerol carbonate fraction; and recycling at least a portion of the recovered solvent fraction back into to the solvent extraction.

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44. The process of claim 35, further comprising recovering glycerol from at least a portion of the glycerol carbonate depleted fraction, wherein recovering glycerol comprises supplying the glycerol carbonate depleted fraction to an evaporator to produce a condensate stream and a glycerol enriched stream; removing water from the glycerol carbonate depleted fraction to produce a glycerol enriched stream; and supplying at least a portion of the glycerol enriched stream back into the absorption reactor as at least part of the absorbent solution.

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54. The process of claim 1, wherein the electrolyte is free of amine-based and/or carbamate-forming compounds.

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65. The process of claim 33, further comprising removing water from the glycerol carbonate depleted fraction and using at least part of the removed water is used as at least part of the electrolyte.

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73. A system for producing glycerol carbonate, comprising:

an electrochemical reaction unit comprising: a reaction chamber; an anode and a cathode disposed within the reaction chamber; an inlet for providing an electrolyte comprising glycerol and dissolved CO2 into the reaction chamber; a power source coupled to the anode and the cathode, and configured to create an electric potential therebetween to induce electrochemical reduction and oxidation reactions, and thereby produce a reaction mixture comprising glycerol carbonate; and an outlet for releasing the reaction mixture;
an extractor comprising: a reaction mixture inlet in fluid communication with the outlet of the electrochemical reaction unit for receiving the reaction mixture; a solvent inlet receiving a solvent capable of solubilizing glycerol carbonate; an extraction chamber in fluid communication with the reaction mixture inlet and the solvent inlet, and configured to enable direct contact between the reaction mixture and the solvent to enable the glycerol carbonate to dissolve into the solvent, and thereby produce a glycerol carbonate depleted fraction comprising glycerol and a glycerol carbonate enriched fraction comprising the solvent; a first outlet for releasing the glycerol carbonate enriched fraction; and a second outlet for releasing the glycerol carbonate depleted fraction;
an absorption reactor comprising: a gas inlet for receiving a CO2-containing gas; a liquid inlet for receiving an absorbent solution comprising glycerol, a carbonate salt and material derived from the glycerol carbonate depleted fraction; an absorption chamber in fluid communication with the gas inlet and the liquid inlet, and configured to enable direct contact between the CO2-containing gas and the absorbent solution to form a loaded absorbent; an absorbent outlet for releasing the loaded absorbent and being in fluid communication with the inlet of the electrochemical reaction unit such that the loaded absorbent forms at least part of the electrolyte.

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117. An electrochemical process for integrating CO2 into an ionisable organic compound to form a reaction product, comprising:

providing an electrolyte comprising the ionisable organic compound, a salt, and the CO2 in the form of a CO2/carbonic-acid/bicarbonate/carbonate system;
applying an electrochemical potential between an anode and a cathode immersed in the electrolyte to induce simultaneous electrochemical reduction and oxidation reactions of the CO2 and the ionisable organic compound, respectively, and form the reaction product.

118. The process of claim 117, wherein the ionisable organic compound comprises an alcohol and the reaction product comprises a carbonate ester.

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128. The process of claim 117, further comprising controlling the electrolyte viscosity comprising diluting the electrolyte above a dilution threshold of at least 15 vol % water and providing the electrolyte viscosity below 300 cP.

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Patent History
Publication number: 20190186027
Type: Application
Filed: Aug 11, 2017
Publication Date: Jun 20, 2019
Inventors: Donald KIRK (Caledon), Hui Huang HOE (Toronto)
Application Number: 16/324,872
Classifications
International Classification: C25B 3/10 (20060101); C25B 15/02 (20060101); C25B 15/08 (20060101);