METHOD FOR PRODUCTION OF SUCCINIC ACID AND SULFURIC ACID BY PAIRED ELECTROSYNTHESIS

Abstract

A method for the production of succinic acid and sulfuric acid by paired electrolytic synthesis is disclosed in the present invention. The method is described as following: in cathodic compartment of an electrochemical cell separated with cation exchange membrane, maleic acid or maleic anhydride is used as raw material, sulfuric acid as the cathodic reactant and the supporting electrolyte of the reaction system, succinic acid is thus synthesized by the electro-reduction reaction at cathode. In anodic compartment, the aqueous sulfuric acid solution containing iodide ion is used as electrolyte, iodide ion is anodized to form I2 and I3−. SO2 gas is fed into the circulated anolyte, reacting with I2 and I3− to form sulfuric acid and regenerate iodide ion. Simultaneously the evaporated hydroiodic acid and distilled water are returned to the anolyte circulation system. The cell voltage and the cost of production are reduced significantly.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent Application No. PCT/CN2011/072346, with an international filing date of Mar. 31, 2011, designating the United States, now pending, and further claims priority benefits to Chinese Patent Application No. 201010137720.4, filed Apr. 1, 2010. The contents of all of the aforementioned applications, including any intervening amendments thereto, are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for production of succinic acid and sulfuric acid by paired electrosynthesis.

2. Description of the Related Art

Succinic acid is an important chemical raw material which is colorless or white crystalline, odorless and sour taste. It is widely used in the fields of pharmaceuticals, pesticides, fine chemicals and alkyd resin. In recent years, succinic acid has been widely used in the fields of biodegradable plastics, polybutylene succinate (PBS), and organic coatings etc.

There are three main methods to synthesize succinic acid: chemical synthesis, biological conversion and electrolysis method.

At present, most of succinic acid for industrial use is produced by chemical synthesis method which includes oxidation and catalytic hydrogenation. Although those technologies have been developed and applied practically, there are still many problems existing such as the uncontrollable side reactions, low yield, low purity of the product, high requirement in operation and usage of expensive catalyst, etc. Furthermore, there is serious environmental pollution in its production process.

In recent years, the method of producing succinic acid with bacterial or microbial fermentation has become a research focus worldwide because it uses starch, glucose, milk and other waste as raw material. However, a large amount of research still needs to be investigated and completed, such as low extraction efficiency, low production and conversion rate, high production cost, generation of a large amount of wastewater, etc. It is estimated that more than 10 tons of wastewater is generated in producing 1 ton of succinic acid. Therefore, it is hard to meet the requirement of industrial production. At present, the biological conversion technology is still limited to the laboratory scale and needs much more time to be commercialized.

Succinic acid can be also produced by electrolytic reduction method in which maleic acid or maleic anhydride is used as the reactant. The production of succinic acid with electrolytic technology had been industrialized in 1930s. After nearly 80 years of development of the technology, the electrolytic synthesis technology becomes more and more mature, leading to accomplish higher conversion ratio, yield, purity and current efficiency in producing succinic acid. In the meantime, zero discharge of wastewater is reached by recycling mother liquor. Therefore, the electrolytic technology has been considered as a green chemical synthesis technology.

According to the literature, the electrolytic technology of succinic acid production can be fulfilled in two ways named as membrane technique and membrane-free technique. At present, the membrane-free technique has been adopted widely, as indicated in the patents 200710047530.1 (Chinese patent application), 200610148269. x(Chinese patent application), etc. The electrooxidation reaction with oxygen evolution has almost always been adopted as the anodic reaction in most present industrial production of succinic acid in which PbO₂ anode is chosen as anode material. However, the disadvantage in this method is that the cell voltage is high, the life of PbO₂ anode is short and the initial investment of the anode is high. Other than oxygen evolution reaction, it was also reported that the electro-oxidation reaction of glyoxal to glyoxylic acid had been adopted as the anodic reaction (Fine Chemicals, Chinese journal, 1997, 14(5), 56˜57), but the yields of glyoxylic acid and succinic acid are both relatively low.

In the present invention, a new technology for electrolytic synthesis of succinic acid and sulfuric acid is disclosed. The principle of the technology is based on the paired electrolytic synthesis, in which succinic acid is formed by the electro-reduction of maleic acid (or maleic anhydride) and the redox couple of I⁻/I₂ is used as anodic mediator to produce sulfuric acid. Sulfuric acid is obtained in the anolyte circulation system through the redox reaction of I₂ (or I₃⁻) with sulfur dioxide gas fed into the anolyte from outside. Iodine (or I₃⁻) is generated through the electrooxidation reaction of iodide. Therefore, the present invention is a novel technology in producing succinic acid and sulphuric acid at the same time with paired electrolytic technology.

SUMMARY OF THE INVENTION

The present invention discloses a technical solution for producing succinic acid and sulfuric acid with paired electrolytic synthesis. By selecting suitable anodic reaction, the cell voltage and the cost of production are reduced significantly, the current efficiency is high and the electrolyte is recycled. Meantime, the problems of short lifetime of anode and environmental pollution are solved.

In order to solve the above technique problems, a technical solution adopted in the present invention is as following.

A technical solution in producing succinic acid and sulfuric acid with paired electrolytic synthesis, said solution is: using maleic acid or maleic anhydride as raw material of the cathodic reaction, sulfuric acid as the cathodic reactant and the supporting electrolyte of the reaction system; the anolyte and cathloyte compartments in the electrochemical cell are separated each other with cation-exchange membrane; the reaction occurred on the cathode is described as the following equations:

As the electrolytic reaction in the cathodic compartment proceeds to a certain degree, succinic acid is generated by post-processing catholyte. The technicians in this field can monitor the extent of the reaction according to the electricity consumed theoretically.

In the anodic compartment, sulfuric acid solution containing iodide ion is used as anolyte, iodide ion is anodized to form I₂ and I₃⁻, and SO₂ gas is fed into the anolyte continuously which is circulated within the system. Sulfuric acid is produced and iodide ion is regenerated through the redox reaction of I₂ and I₃⁻, with sulfur dioxide. When the concentration of sulfuric acid in the anolyte reaches a certain degree, the anolyte is post-processed to obtain higher concentration sulfuric acid. Simultaneously, evaporated hydroiodic acid and the distilled water are isolated and returned to the anolyte circulation system.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of accompanying drawings will be provided below.

FIG. 1 is a schematic diagram of an experimental apparatus applied in the current invention embodiment, where: 1-anode, 2-cathode, 3-anolyte tank, 4-catholyte tank, 5-cation exchange membrane, 6-flow controlling valve, 7-electrolyte circulation pump, 8-SO₂ inlet.

FIG. 2 is the process flow diagram of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Detailed description will be given below in conjunction with accompanying drawings.

In anodic compartment, the aqueous sulfuric acid solution containing iodide ion is used as the electrolyte and the sulfur dioxide gas is fed into the anolyte circulation system, the following electrooxidation reaction takes place.

2I⁻→I₂+2e (or 3I⁻→I₃⁻→2e)  (1)

In the above anodic reaction, the iodide ion is regenerated through the following chemical redox reaction of I₂ and I₃⁻ with SO₂ or H₂SO₃. In the meantime, sulfuric acid is produced as well. The reactions can be expressed as the followings.

I₂+SO₂+2H₂O═H₂SO₄+2HI  (2)

H₂SO₃+I₂+H₂O=4H⁺+2I⁻+SO₄²⁻  (3)

I₃⁻+SO₂+2H₂O=4H⁺+3I⁻+SO₄²⁻  (4)

In the anodic compartment, sulphur dioxide gas is fed into the anolyte where sulfurous acid is formed through the reaction of SO₂ and water.

A cation exchange membrane is used to separate the electrochemical cell adopted in the present invention. In said electrochemical cell, the anode materials resistant to the corrosion in strongly acidic solution containing iodide are used as the anode, as preferred, graphite and DSA electrode (RuO₂—TiO₂/Ti anode). The cathode materials with high overpotential of hydrogen evolution are employed as cathode, as preferred, lead and lead alloys. The distance between the cathode and anode is kept as short as possible, as preferred, 5˜50 mm.

In the reaction process of the present invention, the preferred conditions are: the concentration of reactants in the cathodic compartment is controlled as following: sulfuric acid 0.5˜3 mol/L, maleic acid 0.5˜3 mol/L; the concentration of reactants in the anolyte is controlled as following: sulfuric acid 0.5˜7 mol/L, iodide ion 0.5˜4 mol/L. The molar ratio of the total of I₂ and I₃⁻, generated through the anodic reaction to SO₂ fed from the outside is controlled at 1:(1˜1.5). The preferred current density of the cathode and anode is 300˜1200 A/m² and 300˜1500 A/m², respectively.

The electrolysis process of the present invention is operated using batch-type and continuous-type modes. Said continuous-type mode is carried out as following: adding reactants needed continuously, taking part of electrolyte out of the system for post-processing after the electrolysis reaction reaches a certain degree, returning the mother liquor from the post-processing to the electrolyte system after supplementing raw material; said batch-type mode is operated as follows: adding catholyte in one time or several times, feeding SO₂ to the anolyte continuously, replacing the electrolyte with fresh electrolyte when the electrolysis reaction reaches a certain degree, post-processing the electrolyte containing reaction products, supplementing raw material in the post-processed electrolyte and using it as fresh electrolyte.

The post-processing method of the catholyte in the present invention is as following: cooling the catholyte, filtering the cooled catholyte to get succinic acid crystal, rinsing the succinic acid crystal and drying it to obtain succinic acid product. The mother liquor generated in filtering is returned to the catholyte circulation system after supplementing maleic acid or maleic anhydride. As a result, the yield of succinic acid is increased, the consumption of raw material is reduced, and the cost of production is decreased. In the meantime, green production is achieved.

The post-processing method of the anolyte in the present invention is as following: post-processing the anolyte to get concentrated sulfuric acid after the concentration of sulfuric acid reaches a certain degree, in the meantime, returning the evaporated hydroiodic acid and steam to the anolyte circulation system.

In addition, the temperature of the electrolyte has a large influence on the electrolysis reaction because the solubility of succinic acid increases with the temperature of the electrolyte. When the temperature of the electrolyte is too low, large amount of succinic acid will precipitate to form crystal during the process of electrolysis, leading to the increase of the cell voltage and affecting the electrolysis reaction. However, high temperature of the electrolyte will damage the equipment of electrolysis and shorten the life of membrane. The reaction temperature is maintained at 20˜70° C., as preferred, 30˜50° C.

The experimental equipment used in the present invention includes: a cation membrane-separated electrochemical cell, an anolyte tank and an catholyte tank. Said electrochemical cell is separated into anodic compartment installed with anode and cathodic compartment installed with cathode. Said electrochemical cell could be assembled and connected in mono-polar or bi-polar way. The inlet port of said anodic compartment is set at the bottom and connected to the outlet port of the anolyte tank through pump and flow controlling valve. The outlet of said anodic compartment is set at the top and connected to the inlet port of the anolyte tank, constituting an anolyte circulation system. The inlet port of said cathodic compartment is set at the bottom and connected to the outlet port of the catholyte tank at the bottom through pump and flow controlling valve. The outlet of cathodic compartment is set at the top and connected to the inlet port of catholyte tank, constituting a catholyte circulation system. In the present invention, there are two ways for sulfur dioxide gas to be fed into the anolyte circulation system: one is to feed sulfur dioxide gas into the anodic compartment directly where an oxidation-reduction reaction takes place, the other is to feed sulfur dioxide gas into the anolyte tank where the oxidation-reduction reaction takes place.

Compared with the related art, the beneficial results of the present invention include: (1) reducing the energy consumption of succinic acid electrolytic synthesis significantly by adopting appropriate paired anodic and cathodic reactions, (2) decreasing the initial investment and production cost by using inexpensive anode material, overcoming the problem of short lifetime of anode, (3) providing a new wet technology to produce sulfuric acid at low temperatures, (4) increasing current efficiency, recycling electrolyte and achieving green production. The technology of the present invention is suitable for industrial scale production.

Example 1

A mono-polar membrane-separated electrochemical cell is used. Graphite and lead are used as anode and cathode, respectively. The apparent area of both the anode and the cathode is 50 cm². The distance between the anode and the cathode is 40 mm. A homogeneous cation exchange membrane made of polyvinylidene fluoride (F101 type) is used in the cell.

The electrolytic technological parameters are chosen as follows: the initial concentration of KI and sulfuric acid in the anodic compartment is 1 mol/L, the initial concentration of sulfuric acid and maleic anhydride in the cathodic compartment is 1 mol/L, the temperature of the electrolyte is controlled at the range of 30˜35° C. The electrolyte in the anolyte and cathodic compartments is circulated through pump set on their respective tank. The total amount of anolyte and catholyte is 3 liters, respectively. SO₂ gas is fed into the anodic compartment. Slight excess of SO₂ gas is kept to ensure that the solution in the anodic compartment remains green yellow (not brown). The current density of the electrolysis reaction is 1000 A/m², and the average cell voltage is 2.38 V.

After 10 hours at constant current density, the electrolysis reaction is stopped, and the catholyte is taken out for post-processing. After post-treatment which includes cooling, crystallization, filtration, rinsing with icy deionized water and drying, 68.4 g succinic acid is obtained finally. The cathodic current efficiency is calculated to be 95.1%.

Example 2

A mono-polar membrane-separated electrochemical cell is used. Graphite and lead are used as anode and cathode, respectively. The apparent area of both the anode and the cathode is 50 cm². The distance between the anode and the cathode is 40 mm. A homogeneous cation exchange membrane made of polyvinylidene fluoride (F101 type) is used in the cell.

The electrolytic technological parameters are chosen as follows: the anolyte in the anodic compartment is the anolyte after electrolysis reaction in Example 1, the catholyte in the cathodic compartment is the mother liquor of the catholyte in Example 1. The initial concentration of maleic acid in the catholyte is adjusted to be 1 mol/L by supplementing maleic anhydride. The temperature of the electrolyte is controlled at the range of 50˜55° C. Other technological parameters are the same as those in Example 1. The average cell voltage is 2.26 V.

After 5 hours at constant current density, the electrolysis reaction is stopped, and the catholyte is taken out for post-processing. After post-treatment which includes cooling, crystallization, filtration, rinsing with icy deionized water and drying, 51.1 g succinic acid is obtained finally. The cathodic current efficiency is calculated to be 94.2%.

Example 3

A mono-polar membrane-separated electrochemical cell is used. DSA and lead are used as anode and cathode, respectively. The apparent area of both the anode and the cathode is 50 cm². The distance between the anode and the cathode is 20 mm. A homogeneous cation exchange membrane made of Nafion 117 is used in the cell.

The electrolytic technological parameters are chosen as follows: the anolyte in the anodic compartment is the anolyte after electrolysis reaction in Example 2, the catholyte in the cathodic compartment is the mother liquor of the catholyte in Example 2. The initial concentration of maleic acid in the catholyte is adjusted to be 1.2 mol/L by supplementing maleic anhydride. The temperature of the electrolyte is controlled at the range of 30˜35° C. SO₂ gas is fed into the anolyte tank. Other technological parameters are the same as those in Example 1. The average cell voltage is 1.38 V.

After 10 hours at constant current density, the electrolysis reaction is stopped, and the catholyte is taken out for post-processing. After post-treatment which includes cooling, crystallization, filtration, rinsing with icy deionized water and drying, 52.2 g succinic acid is obtained finally. The cathodic current efficiency is calculated to be 94.9%.

Example 4

A mono-polar membrane-separated electrochemical cell is used. Graphite and lead are used as anode and cathode, respectively. The apparent area of both the anode and the cathode is 100 cm². The distance between the anode and the cathode is 15 mm. A homogeneous cation exchange membrane made of Nafion 117 is used in the cell.

The electrolytic technological parameters are chosen as follows: the anolyte in the anodic compartment is the anolyte after electrolysis reaction in Example 3, the catholyte in the cathodic compartment is the mother liquor of the catholyte in Example 3. The initial concentration of maleic acid in the catholyte is adjusted to be 0.8 mol/L by supplementing maleic acid. The temperature of the electrolyte is controlled at the range of 40˜45° C. SO₂ gas is fed into the anodic compartment. The current density of the anode and the cathode is controlled at 750 A/m². Other technological parameters are the same as those in Example 1. The average cell voltage is 1.59V.

After 2 hours at constant current density, the electrolysis reaction is stopped, and the catholyte is taken out for post-processing. After post-treatment which includes cooling, crystallization, filtration, rinsing with icy deionized water and drying, 31.2 g succinic acid is obtained finally. The cathodic current efficiency is calculated to be 94.5%.

Example 5

A mono-polar membrane-separated electrochemical cell is used. Graphite and lead are used as anode and cathode, respectively. The apparent area of both the anode and the cathode is 100 cm². The distance between the anode and the cathode is 15 mm. A homogeneous cation exchange membrane made of Nafion 117 is used in the cell.

The electrolytic technological parameters are chosen as follows: the anolyte in the anodic compartment is the anolyte after electrolysis reaction in Example 4, the catholyte in the cathodic compartment is the mother liquor of catholyte in Example 4. The initial concentration of maleic acid in the catholyte is adjusted to be 0.8 mol/L by supplementing maleic acid. The temperature of the electrolyte is controlled at the range of 50˜55° C. SO₂ gas is fed into the anodic compartment. The current density of the anode and the cathode is controlled at 1200 A/m². Other technological parameters are the same as those in Example 1. The average cell voltage is 1.64V.

After 2 hours at constant current density, the electrolysis reaction is stopped, and the catholyte is taken out for post-processing. After post-treatment which includes cooling, crystallization, filtration, rinsing with icy deionized water and drying, 49.7 g succinic acid is obtained finally. The cathodic current efficiency is calculated to be 94.1%.

After the above five examples (from Example 1 to Example 5) are finished, the anolyte is taken out for analysis. The results show the concentration of sulfate in the anolyte is 1.83 mol/L, the total average anodic current efficiency is calculated to be 96.56%. The anolyte is taken out to be concentrated. After the volume of the anolyte is reduced to 1 L by evaporating, the concentration of sulfuric acid is found to be 5.49 mol/L. The evaporated substances are collected and returned to the anolyte circulation system after cooling.

Claims

1. A method for the production of succinic acid and sulfuric acid by paired electrolytic synthesis comprising: inside cathodic compartment of an electrochemical cell separated with cation exchange membrane, maleic acid or maleic anhydride is used as raw material, sulfuric acid as the cathodic reactant and the supporting electrolyte of the reaction system, succinic acid is thus synthesized by the electro-reduction reaction at cathode. When the extent of electrolysis reaction reaches a certain degree, catholyte is taken out and post-processed to obtain succinic acid. In anodic compartment, the aqueous sulfuric acid solution containing iodide ion is used as electrolyte, iodide ion is anodized to form I2 and I3−. SO2 gas is fed into the circulated anolyte, reacting with I2 and I3− through redox reaction to form sulfuric acid and regenerate iodide ion in anolyte. When the concentration of sulfuric acid in the anolyte reaches a certain degree, the anolyte is taken out to be concentrated to obtain sulfuric acid of high concentration. Simultaneously, the hydroiodic acid and the distilled water evaporated from the anolyte are returned to the anolyte circulation system.

2. The method of claim 1, wherein inside said electrochemical cell, graphite or titanium-supported RuO2—TiO2 electrode is used as anode, lead or lead alloys as cathode. The distance between the cathode and the anode is 5˜50 mm.

3. The method of claim 1, wherein during the process of electrolysis reaction, the concentration of reactants in said catholyte is controlled as following: sulfuric acid 0.5˜3 mol/L, maleic acid 0.5˜3 mol/L; the concentration of reactants in said anolyte as following: sulfuric acid 0.5˜7 mol/L, iodide ion 0.5˜4 mol/L. The molar ratio of the total amount of I2 and I3− generated through the anodic reaction to SO2 fed from outside is controlled at 1:(1˜1.5).

4. The method of claim 3, wherein the current density of cathode and anode is controlled at 300˜1200 A/m2 and 300˜1500 A/m2, respectively.

5. The method of claim 1, wherein the post-processing of said catholyte after electrolysis reaction comprising: said catholyte thus obtained is cooled, precipitated, filtered, rinsed, dried to obtain succinic acid; the mother liquor from filtration is returned to said cathodic compartment after supplementing maleic acid or maleic anhydride.

6. The method of claim 1, wherein the temperature of said electrolysis reaction is controlled at the range of 20-70° C.

7. The method of claim 1, wherein the temperature of said electrolysis reaction is controlled at the range of 30-50° C.

8. The method of claim 1, wherein said paired electrolytic synthesis is operated in two modes: batch-type and continuous-type.