Biodesulfurization of hydrocarbons

Abstract

A process for converting organic sulfur compounds contained in liquid hydrocarbons to elemental sulfur. The liquid hydrocarbons are solubilized in an organic solvent and reacted in the presence of a biocatalyst and hydrogen. The organic solvent is a nucleophilic solvent having a pKa greater than about 2, an electrophilic solvent having a pKa more negative than about −2, or mixtures thereof. The biocatalyst may be supported on a Lewis acid. Elemental sulfur is removed from the liquid hydrocarbons. Liquid hydrocarbons treated in accordance with this process have significantly reduced concentrations of organic sulfur compounds and thus reduced viscosity.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a process for removing organic sulfur compounds from hydrocarbons, and more particularly, to a process for converting organic sulfur compounds that are contained in a liquid hydrocarbon, to elemental sulfur by contacting the hydrocarbon with an organic solvent and hydrogen in the presence of a biocatalyst and thereafter removing the elemental sulfur.

[0003] 2. Description of Related Art

[0004] Many crude oils that are produced from subterranean environs, transported via tubulars, such as pipelines, risers, casing and tubing, and ultimately refined contain organic sulfur compounds. These processes are interfered with and/or complicated due to the corrosive nature and the high viscosity of such sulfur compounds, especially heterocyclic sulfur compounds, and the fouling of catalyst utilized in petroleum refining that is attributable to such sulfur compounds. Further, many countries have enacted legislation reducing the amount of sulfur that may be present in gasoline and other fuels refined from crude oil in an attempt to reduce sulfur emissions to the atmosphere from burning such fossil fuels. As worldwide reserves of clean burning, low sulfur hydrocarbons are increasingly being depleted, attention has turned to finding methods of reducing the sulfur content of lower grade, relatively high sulfur containing crude oils so as to facilitate the transportation and refining thereof.

[0005] One method that has been proposed involves the use of a biocatalyst that alters the sulfur-bearing heterocycles in crude oil by cleaving carbon-sulfur bonds and/or joining polar substituents to the sulfur heteroatom and/or the hydrocarbon framework. In this manner, the viscosity and the sulfur content of the crude oil is reduced and the sulfur is converted to elemental sulfur and/or hydrogen sulfide which can be more easily separated from crude oil. This method generally involves reacting a crude oil with a biocatalyst in the presence of an aqueous solvent and hydrogen. Recently, it has been proposed to utilize an organic solvent, such as dimethylformamide (DMF) as an organic solvent in this method. However, rates of biodesulfurization using such an organic solvent are quite slow, especially for relatively high molecular weight crude oil molecules. Thus, a need exists for process for desulfurizing crude oil using an organic solvent and a biocatalyst that results in relatively high rates of sulfur conversion.

SUMMARY OF THE INVENTION

[0006] To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, one characterization of the present invention is a process for converting organic sulfur compounds contained in liquid hydrocarbons. This process comprises reacting organic sulfur compounds contained in liquid hydrocarbons in the presence of a biocatalyst, hydrogen and an organic solvent thereby converting the organic sulfur compounds to elemental sulfur. The organic solvent is selected from the group consisting of a nucleophilic solvent having a pKa greater than about 2, an electrophilic solvent having a pKa more negative than about −2, or mixtures thereof.

[0007] In another characterization of the present invention, a process is provided for removing organic sulfur compounds from liquid hydrocarbons. The process comprises a) contacting liquid hydrocarbons containing organic sulfur compounds with an organic solvent, said solvent solubilizing said liquid hydrocarbons, and b) reacting the liquid hydrocarbons that are solubilized in the organic solvent in the presence of a biocatalyst and hydrogen thereby converting the organic sulfur compounds to elemental sulfur. The organic solvent is selected from the group consisting of a nucleophilic solvent having a pKa greater than about 2, an electrophilic solvent having a pKa more negative than about −2, or mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and, together with the description, serve to explain the principles of the invention.

[0009] In the drawings:

[0010] FIG. 1 is a schematic flow diagram of one embodiment of the process of the present invention;

[0011] FIG. 2 is a schematic flow diagram of another embodiment of the process of the present invention;

[0012] FIG. 3 is a graph that depicts the boiling point distribution for crude oil desulfurized in a slurry of organic solvent (N-buytlamine) and biocatalyst as a function of the amount of crude oil distilled;

[0013] FIG. 4 is a graph that depicts the boiling point temperature for crude oil desulfurized in a slurry of organic solvent (methyl ethyl ketone) and biocatalyst as a function of the amount of crude oil distilled;

[0014] FIG. 5 is a graph that depicts the conversion rate of organic sulfur initially present in a crude oil to elemental sulfur in the presence of a biocatalyst as a function of solvent nature (pKa);

[0015] FIG. 6 is a graph that depicts the crude oil viscosity as a function of the organic to elemental sulfur conversion;

[0016] FIG. 7 is a graph that depicts the amount of organic sulfur initially present in a crude oil that is converted in the presence of a biocatalyst to elemental sulfur as a function of the amount of biocatalyst that is immobilized on a support; and

[0017] FIG. 8 is a graph that depicts the amount of elemental sulfur removed by using a solvent/crude oil mixture with water as a function of the molar ratio of wash water to solvent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In accordance with one embodiment of the present invention, a nucleophilic and/or electrophilic organic solvent(s) is introduced via line or conduit 5 into a hydrocarbon stream, for example crude oil, heavy crude oil, bitumen, or a refined fraction of crude oil, which is transported in line or conduit 1. The hydrocarbon stream is substantially completely solubilized in the organic solvent. Hydrogen gas from any suitable source (not illustrated) is also introduced via line or conduit 3 into the mixture of the hydrocarbon stream in organic solvent in line 1. The resultant mixture of hydrocarbon, organic solvent and hydrogen is transported via line 1 into or near the bottom of a reactor 10. Reactor 10 contains a packed bed 12 of biocatalyst dispersed on a support. The biocatalyst used in accordance with the present invention is a microorganism such as that available from Finnerty Enterprises Inc., Athens, Ga. In reactor 10, organic sulfur compounds that are present in the hydrocarbon stream are converted into elemental sulfur at a temperature of less than about 165° F. While not wishing to be bound by any particular mechanism or theory and although not completely understood, the conversion of organic sulfur compounds to elemental sulfur in the reactor is believed to occur in accordance with two overall chemical mechanisms wherein R1, R2, R3, and R4 represent hydrocarbon constituents. Organic sulfides are converted in accordance with reaction A and organic thiophenes are converted in accordance with reaction B.

R1S R2+H2→R1H+R2H+S  (A)

[0019] 1

[0020] The organic solvent having treated hydrocarbons solubilized therein and elemental sulfur is removed from reactor 10 via line or conduit 16 and is introduced into the lower end of contactor 20 and counter currently contacted with wash water from any suitable source (not illustrated). The wash water is introduced into contactor 20 via line or conduit 24 in an amount of from about 10 to about 20 moles of wash water per mole of solvent. The organic solvent and elemental sulfur are solubilized in the wash water. The treated hydrocarbons having a reduced sulfur content are removed from contactor 20 via line 26 for transportation and/or further processing. This solution is removed from contactor 20 via line or conduit 22 and transported to distillation vessel 30 wherein the solution is heated to separate the organic solvent in the form of vapor from a remaining water and sulfur slurry. The vaporous solvent is removed from distillation vessel 30 via line or conduit 5 and cools and condenses to liquid form while being recycled in line 5 for introduction into the feed hydrocarbon stream as previously discussed. The aqueous sulfur slurry is removed from distillation vessel 30 via line 32 and introduced into a separator 40 wherein sulfur is either phase separated or filtered from the water, heated and removed as a liquid product via line or conduit 42. The water is then recycled via line or conduit 24 to contactor 20.

[0021] In accordance with another embodiment of the process of the present invention as illustrated in FIG. 2, a stirred tank reactor 80 is utilized in lieu of packed bed reactor 10. Biocatalyst is introduced via line or conduit 92 into the mixture of hydrocarbon, organic solvent and hydrogen that is introduced via line 1 into reactor 80. Reactor 80 is provided with any suitable means, such as a rotating blade 82, to maintain a substantially uniform dispersion of biocatalyst, hydrocarbon, organic solvent and hydrogen in reactor 80. The reacted mixture is transported via line 16 from reactor 80 to settler 90 wherein the biocatalyst is separated from the mixture and returned to reactor 80 via line 92, pump 94 and line 1. The organic solvent having treated hydrocarbons solubilized therein and elemental sulfur is then transported via line 96 and introduced into the lower end of contactor 20 for processing as described with respect to FIG. 1.

[0022] In accordance with the present invention, applicant has discovered that utilizing certain organic solvent(s), which has been selected in accordance with parameters set forth below, unexpectedly results in very high conversions of organic sulfur compounds to elemental sulfur in extremely short periods of time.

[0023] The organic solvent utilized in the process of the present invention is an electron donating solvent, i.e. nucleophilic or basic, an electron accepting solvent, i.e. electrophilic or acidic, or a combination thereof. It is believed that nucleophilic solvents catalyze organic sulfur conversion in accordance with reaction A above, while electrophilic solvents catalyze organic sulfur conversion that occurs in accordance with reaction B above. Thus, where the hydrocarbon liquid to be treated contains primarily organic sulfides, a nucleophilic solvent should be employed in the process of the present invention. Where the liquid hydrocarbon to be treated contains primarily organic thiopenes, a electrophilic solvent should be used. The relative nature of an electrophilic or nucleophilic solvent is noted by the equilibrium constant (pKa) of a given solvent. As is evident to a skilled artisan, pKa values for a given solvent are typically obtained from an authoratative text, for example “Organic Solvents: Physical Properties and Methods of Purification”, John A. Riddick and William B. Bunger, published by Wiley Interscience (3rd edition; 1970). For nucleophilic solvents, the pKa increases in the positive direction from a value of 0 with increasing electron donating capability. For electrophilic solvents, the pKa decreases from a value of 0 with increasing electron accepting capability. Nucleophilic solvents suitable for use in accordance with the process of the present invention are those having a pKa value greater than about 2, more particularly greater than about 6 and most particularly greater than about 10, while electrophilic solvents suitable for use in accordance with the process of the present invention are those having a pKa value more negative than about −2, more particularly more negative than about −6 and most particularly more negative than about −10. Suitable nucleophilic solvents include N-butylamine, diethylamine, butanediamine, ethylenimine, toluene, pyridine, aniline and acetophenone, while suitable electrophilic solvents include methylethylketone, pyrrole, benzaldehyde.

[0024] Where the liquid hydrocarbon to be treated contains both organic sulfides and thiopenes in significant quantities, a combination of nucleophilic and electrophilic solvents that are selected in accordance with the parameters outlined herein may be employed in the process of the present invention. In such instances, it is also suitable to use an amphiprotic solvent, i.e. a solvent that contains both electron donating and electron accepting groups in one solvent molecule. An example of an amphiprotic solvent is ethanolamine. One potential disadvantage with employing both an amphiprotic solvent or a nucleophilic solvent and an electrophilic solvent is the potential for these solvents to exchange electrons between each other thus reducing their effectiveness in converting organic sulfur compounds. Accordingly, in such instances, it is preferred to use a nucleophilic solvent in conjunction with a Lewis acidic support for the biocatalyst, such as that commercially available from Alcoa Industrial Chemicals under the trade name designation HiQ Alumina® and DD2. It is believed that the acid support catalyzes reaction B thereby increasing the rate of conversion of organic thiopenes. The support should be selected to have a relatively high degree of Lewis acidity.

[0025] It will be evident to a skilled artisan that conversion of organic sulfides and/or thiopenes to elemental sulfur in accordance with the process of the present invention concomitantly results in viscosity reduction of the treated liquid hydrocarbon which assists in the transportation and further treatment of such liquid hydrocarbon.

[0026] The following examples demonstrate the practice and utility of the present invention, but are not to be construed as limiting the scope thereof.

EXAMPLE 1

[0027] A crude oil produced from the Oregon Basin field in Wyoming was combined with N-butylamine solvent and a biocayalyst (from Finnerty Enterprises Inc., Athens, Ga.) and desulfurized in a slurry reactor at a temperature of 158° F. for a period of one hour. Hydrogen gas was supplied to the reactor at a partial pressure of 1200 to 1400 psig. The concentration of the biocatalyst was 3.75 wt % of the crude oil and the concentration of crude oil in the solvent was 40 wt %. The reactant slurry was removed from the reactor and the biocatalyst was separated from the slurry by centrifugation. The treated crude oil was washed with water to remove the solvent and elemental sulfur and then distilled. A virgin sample of the Oregon Basin crude oil was also distilled for comparative purposes. As evident from the results of this distillation that are illustrated in FIG. 3, significant increases in the boiling point distribution data, as compared to the virgin crude oil, were obtained, i.e. larger amounts of product components were distilled for any given boiling point. The largest increase occurred for the toluene component of crude oil, i.e. 231° F. It is believed that nucleophilic solvents, e.g. N-butylamine, make the biocatalyst pore wall more electronegative, thus catalyzing reaction A and yielding lower boiling R1H and R2H components, e.g. toluene being an R1H or R2H component.

EXAMPLE 2

[0028] A crude oil produced from the Oregon Basin field in Wyoming (same as Example 1) was combined with methyl ethyl ketone (solvent) and a biocatalyst (from Finnerty Enterprises Inc., Athens, Ga.) and desulfurized in a slurry reactor at a temperature of 72-75° F. for a period of two and one half hours. Hydrogen gas was supplied to the reactor at a partial pressure of 1200 to 1400 psig. The concentration of the biocatalyst was 2.10 wt % of the crude oil and the concentration of crude oil in the solvent was 40 wt %. The reactant slurry was removed from the reactor and the biocatalyst was separated from the slurry by centrifugation. The treated crude oil was washed with water to remove the solvent and elemental sulfur and then distilled. A virgin sample of the Oregon Basin crude oil was also distilled for comparative purposes. As evident from the results of this distillation which are illustrated in FIG. 4, an electrophilic solvent, e.g. methyl ethyl ketone, did not yield any significant change in the boiling point distribution data, i.e. substantially equal amounts of product components were distilled for any given boiling point. This result would be expected for reaction B where component molecular weights are not significantly changed due to the reaction.

EXAMPLE 3

[0029] A crude oil produced from the Oregon Basin field in Wyoming (same as use in Examples 1 and 2) was combined with a solvent and a biocatalyst (from Finnerty Enterprises Inc., Athens, Ga.) and desulfurized in a slurry reactor at a temperature of 158-165° F. for a period varying from 0.8 to 2.3 hours depending upon the run. Hydrogen gas was supplied to the reactor at a partial pressure of 1200 to 1400 psig. The concentration of the biocatalyst was 2.10 wt % of the crude oil and the concentration of crude oil in the solvent was 40 wt %. The reactant slurry was removed from the reactor and the biocatalyst was separated from the slurry by centrifugation. The treated crude oil was washed with water to remove the solvent and elemental sulfur. The conversion rate of organic sulfur to elemental sulfur was measured using X-ray and differential scanning colorimetry techniques. This procedure was repeated using four different solvents. One solvent, methyl ethyl ketone (MEK) is electrophilic, two solvents, pyridine (PY) and N-butylamine (NBA), are nucleophilic and a fourth solvent, a 50/50 blend of NBA and MEK, has a nucleophilic nature. This procedure was also repeated without using a solvent. The results of these reactions, which are graphically illustrated in FIG. 5, indicate that the greater the electrophilic nature (−pKa value) or the nucleophilic nature (+pKa value) of the organic solvent utilized in the process of the present invention, the greater the rates of conversion of organic sulfur that is obtained. Acceptable rates of conversion are those greater than about 0.01 hr−1.

EXAMPLE 4

[0030] A crude oil produced from the Oregon Basin field in Wyoming was combined with a solvent and a biocatalyst (from Finnerty Enterprises Inc., Athens, Ga.) and desulfurized in a slurry reactor at a temperature of 72-75° F. for a period of 1.0 to 2.5 hours depending upon the run. Hydrogen gas was supplied to the reactor at a partial pressure of 1200 to 1400 psig. The concentration of the biocatalyst was 2.10 wt % of the crude oil and the concentration of the crude oil in the solvent was 40%. The reactant slurry was removed from the reactor and the biocatalyst was separated from the slurry by centrifugation. The treated crude oil was washed with water to remove the solvent and elemental sulfur. The percentage of organic sulfur converted to elemental sulfur was measured using x-ray and differential scanning colorimetry techniques. The viscosity of the desulfurized crude oil was also measured by a capillary flow tube technique. This procedure was repeated using N-butylamine and methyl ethyl ketone as the solvent and without using a solvent. The results are plotted in FIG. 6. It is evident from these results that the viscosity reduction achieved from desulfurizing crude oil in accordance with the process of the present invention is independent of whether a nucleophilic or electrophilic solvent is employed.

EXAMPLE 5

[0031] A crude oil produced from the Oregon Basin field in Wyoming was combined with N-butylamine solvent and fed to a reactor packed with a biocatalyst dispersed on a support. The biocatalyst was from Finnerty Enterprises Inc., Athens, Ga. Two separate catalyst supports were used in different runs. One support was a 50/50 weight percentage blend of a high Lewis acidity support available under the trade name designation HiQ®-7219CC and a lower Lewis acidity support available under the trade name designation DD2 from Alcoa Industrial Chemicals. The other support was consisted entirely of the DD2 low Lewis acidity support. The crude and solvent resided in the packed bed reactor at 145-150° C. for a period of from 0.5 to 2 hours. Hydrogen gas was supplied to the reactor at a partial pressure of 541 to 1383 psig. The concentration of the biocatalyst was 21.1 wt % of the total catalyst and support weight when the blended HiQ®/DD2 support was utilized and 16.7 wt % of the total catalyst and support weight when the DD2 support was used. The treated crude oil was removed from the reactor and washed with water to remove the solvent and elemental sulfur. The percentage of organic sulfur converted to elemental sulfur was measured using x-ray and differential scanning colorimetry techniques. This procedure was repeated using a catalyst which was employed in previous runs, using a different catalyst, or using a different catalyst support. As clearly indicated by the results that are illustrated in FIG. 7, using a catalyst having a higher Lewis acidity support resulted in significant increases in organic sulfur conversion. In addition, using higher catalyst concentrations increased organic to elemental sulfur conversion. Parameters not effecting organic sulfur conversion were crude oil concentration in the solvent, hydrogen partial pressure and residence time.

EXAMPLE 6

[0032] Samples of an Oregon Basin crude oil that was desulfurized in accordance with the present invention using butanediamine (BDA) or ethanolamine (EA) as the organic solvent were washed at 70-75° F. to remove solvent and elemental sulfur therefrom. The molar ratio of water to solvent present in the desulfurized crude was varied in different runs to determine the effect thereof. As illustrated by the results in FIG. 8, a molar ratio of between about 10 to about 20 moles of wash water per mole of solvent resulted in the greatest amount of elemental sulfur being removed from the desulfurized crude oil. In accordance with the present invention, use of organic solvents with two polar functions, such as BDA or EA, result in greater amounts of elemental sulfur being removed from the desulfurized crude oil than use of mono polar solvents, such as NBA or MEK.

[0033] While the foregoing preferred embodiments of the invention have been described and shown, it is understood that the alternatives and modifications, such as those suggested and others, may be made thereto and fall within the scope of the invention.

Claims

1. A process for converting organic sulfur compounds contained in liquid hydrocarbons comprising:

reacting organic sulfur compounds contained in liquid hydrocarbons in the presence of a biocatalyst, hydrogen and an organic solvent selected from the group consisting of a nucleophilic solvent having a pKa greater than about 2, an electrophilic solvent having a pKa more negative than about −2, or mixtures thereof thereby converting said organic sulfur compounds to elemental sulfur.

2. The process of claim 1 wherein said nucleophilic solvent has a pKa greater than about 6.

3. The process of claim 1 wherein said nucleophilic solvent has a pKa greater than about 10.

4. The process of claim 1 wherein said sulfur compounds are sulfides and said organic solvent is N-butylamine.

5. The process of claim 1 wherein said step of reacting is performed at a temperature of about 165° F. or less.

6. The process of claim 1 wherein said electrophilic solvent has a pKa more negative than about −6.

7. The process of claim 1 wherein said electrophilic solvent has a pKa more negative than about −10.

8. The process of claim 1 wherein said sulfur compounds are thiopenes and said organic solvent is methylethylketone.

9. The process of claim 1 wherein said biocatalyst is dispersed on a support.

10. The process of claim 9 wherein said support exhibits Lewis acidity.

11. A process for removing organic sulfur compounds from liquid hydrocarbons comprising:

a) contacting liquid hydrocarbons containing organic sulfur compounds with an organic solvent, said solvent solubilizing said liquid hydrocarbons and being selected from the group consisting of a nucleophilic solvent having a pKa greater than about 2, an electrophilic solvent having a pKa more negative than about −2, or mixtures thereof;

b) reacting said liquid hydrocarbons that are solubilized in said organic solvent in the presence of a biocatalyst and hydrogen thereby converting said organic sulfur compounds to elemental sulfur.

12. The process of claim 11 further comprising:

c) contacting said organic solvent and said liquid hydrocarbons after the step of reacting with water thereby solubilizing said elemental sulfur and said organic solvent into said water.

13. The process of claim 12 wherein said organic solvent and said liquid hydrocarbons are contacted with between about 10 to about 20 moles of said water per mole of said organic solvent.

14. The process of claim 12 further comprising:

d) removing said organic solvent from said water and said elemental sulfur; and

e) recycling said organic solvent to step a).

15. The process of claim 14 further comprising:

f) separating said sulfur from said water; and

g) recycling said water from which said sulfur is separated to step c).

16. The process of claim 11 wherein said nucleophilic solvent has a pKa greater than about 6.

17. The process of claim 11 wherein said nucleophilic solvent has a pKa greater than about 10.

18. The process of claim 11 wherein said sulfur compounds are sulfides and said organic solvent is N-butylamine.

19. The process of claim 11 wherein said step of reacting is performed at a temperature of about 165° F. or less.

20. The process of claim 11 wherein said electrophilic solvent has a pKa more negative than about −6.

21. The process of claim 11 wherein said electrophilic solvent has a pKa more negative than about −10.

22. The process of claim 11 wherein said sulfur compounds are thiopenes and said organic solvent is methylethylketone.

23. The process of claim 11 wherein said biocatalyst is dispersed on a support.

24. The process of claim 23 wherein said support is a Lewis acid.

25. The process of claim 11 wherein said liquid hydrocarbons are crude oils.