Polysiloxane scrubbing liquid for removing tar-like compounds

Abstract

Tar-like components can be removed from gas streams resulting from gasification of coal, waste or biomass by contacting the gas with a liquid organic aryl polysiloxane. The polysiloxane preferably contains alkyl groups and aryl groups, and is in particular a polymethyl polyphenyl polysiloxane. The gas comprises one or more of hydrogen, carbon monoxide, carbon dioxide, and methane.

Claims

1. A process of clarifying a gas stream comprising tar-like or tar-constituting components comprising aromatic compounds having 6 or more carbon atoms, the process comprising contacting the gas stream with a liquid organic aryl polysiloxane as a washing liquid.

2. The process according to claim 1, wherein the polysiloxane comprises an average of between 0.2 and 1.8 C5-C14 aryl group per silicon atom.

3. The process according to claim 1, wherein the polysiloxane comprises an average of between 0.5 and 1.5 C5-C10 aryl group and between 0.5 and 1.5 C1-C4 alkyl group per silicon atom.

4. The process according to claim 1, wherein the polysiloxane has a molar weight between 700 and 7000 Da.

5. The process according to claim 1, wherein the polysiloxane is a polymethylphenyl-siloxane or a poly-diphenyl-dimethyl-siloxane.

6. The process according to claim 1, wherein the tar-like components comprise polycyclic aromatic compounds having 9-18 carbon atoms.

7. The process according to claim 1, wherein the gas stream, prior to contacting with the polysiloxane, is treated with a scrubbing liquid comprising aromatic hydrocarbons, at a temperature of between 150 and 900° C.

8. The process according to claim 1, wherein the gas stream, prior to contacting with the polysiloxane, is subjected to an electrostatic filter.

9. The process according to claim 1, wherein the gas stream originates from the gasification of biomass, organic waste, coal or a combination thereof.

10. The process according to claim 1, wherein the gas stream, prior to contacting with the polysiloxane, is subjected to an aerosol scavenger.

11. The process according to claim 1, wherein the gas stream comprises one or more of hydrogen, carbon monoxide, carbon dioxide, methane and nitrogen.

12. The process according to claim 11, wherein the gas stream comprises at least 30 vol. % of one or more of hydrogen, methane and carbon monoxide.

13. The process according to claim 1, wherein the gas stream is contacted with the polysiloxane at a temperature between 30 and 150° C. at atmospheric pressure.

14. The process according to claim 13, wherein the gas stream is contacted with the polysiloxane at a temperature between 60 and 120° C., at atmospheric pressure.

15. The process according to claim 13, further comprising heating the polysiloxane to a temperature which is higher than the temperature used in the contacting step.

16. The process according to claim 15, wherein, at constant pressure, the higher temperature is at least 50° C. above the temperature used in the contacting step.

17. The process according to claim 16, wherein, at constant pressure, the higher temperature is between 80 and 120° C. above the temperature used in the contacting step.

18. The process according to claim 13, further comprising depressurising the polysiloxane to a pressure which is lower than the pressure used in the contacting step.

19. The process according to claim 18, wherein, at constant temperature, the lower pressure is at least 5.6 times lower than the pressure use in the contacting step.

20. The process according to claim 19, wherein, at constant temperature, the lower pressure is between 8 and 16 times lower than the pressure used in the contacting step.

Description

DESCRIPTION OF THE FIGURE

(1) The accompanying FIGURE shows a gas cleaning system according to the invention.

EXAMPLE

(2) A substitute natural gas (SNG) containing 13 vol % methane, 2 vol % nitrogen, 32 vol % carbon monoxide, 18 vol % carbon dioxide, 28% vol % hydrogen and 4 vol % ethene and containing about 11-12 g/Nm.sup.3 of C8-C16 (poly)aromatic hydrocarbons, was subjected to absorption using either a conventional aliphatic hydrocarbon derived from mineral oil or a commercial polymethylphenylsiloxane (PMPS) as an absorption liquid, and the absorption liquid was subsequently stripped using air.

(3) The setting of the absorber and stripper were as follows in both cases: Temperature absorber=80° C. Temperature stripper=180° C. Gas flow stripper=16 1/min (˜1 Nm.sup.3/h) Oil flow absorber/stripper32 2.1 1/min

(4) The tests were performed 4 times and the results were averaged. Table 1 below shows the concentrations (in mg/Nm.sup.3) and removal rates for the hydrocarbons up to pyrene. Benzene and toluene were omitted as they could not be precisely measured. Tar components of a level below 50 mg/Nm.sup.3 (in both columns) were also omitted.

(5) Continued operation using the aliphatic hydrocarbon oil resulted in a significant loss of about 6 g oil per m.sup.3 of scrubbed gas, whereas the loss of the polysiloxane was negligible (<0.5 g/m.sup.3). The hydrocarbon oil turns brown and eventually black and starts smelling after a few scrubbing cycles, whereas the polysiloxane oil remains clear and essentially colourless after prolonged operation.

(6) TABLE-US-00001 TABLE 1 Removal rate of tar components by aliphatic oil vs. polysiloxane oil Mineral Oil PMPS Abs Abs Re- Abs Abs Re- in out moval in out moval Ethylbenzene 14 2 87% 66 7 90% m/p-Xylene 59 10 84% 110 23 79% o-Xylene + Styrene 791 83 89% 1169 163 86% Phenol 510 34 93% 404 7 98% Indene 2478 17 99% 1219 6 99% m/p-Cresol 40 3 94% 62 17 73% Naphthalene 5978 103 98% 4746 20 100%  2-Methylnaphthalene 225 7 97% 346 1 100%  1-Methylnaphthalene 132 4 97% 191 0 100%  Biphenyl 99 1 99% 160 0 100%  Acenaphthene 307 11 96% 492 6 99% Fluorene 133 10 93% 286 1 100%  Phenanthrene 202 19 90% 536 2 100%  Anthracene 26 2 94% 71 0 100%  Fluoranthene 56 9 85% 149 1 99% Pyrene 33 2 94% 100 1 99%