Two-stage gas washing method applying sulfide precipitation and alkaline absorption
Disclosed is a method relating to hydrocarbon production by gasification of carbonaceous material, for example, a two-stage gas washing method as a part of gas refining. Disclosed is a method for hydrogen sulfide and carbon dioxide removal from synthesis gas produced by gasification. Disclosed is a use of a combination of two chemical wash approaches. The process can be utilized as a part of biomass to liquid (BTL) process.
1. A method for washing hydrogen sulfide and carbon dioxide from a gas obtainable by gasification of a carbonaceous biomass, the method comprising:
a) contacting the gas with a first absorbent solution comprising transition metal ions in acidic aqueous solution, wherein the transition metal ions include copper, zinc, iron, cobalt or a mixture thereof;
b) binding hydrogen sulfide present in the gas to said first absorbent solution;
c) recovering the gas from step b);
d) contacting the recovered gas from step c) with a second absorbent solution comprising an alkaline absorbent;
e) binding carbon dioxide present in the recovered gas from step c) to said second absorbent solution; and
f) recovering the gas obtained from step e).
2. The method according to claim 1 , wherein the concentration of the transition metal ions in the first absorbent solution is less than about 1000 ppm w , calculated from a weight of the first absorbent solution.
3. The method according to claim 1 , wherein the transition metal ions comprise copper.
4. The method according to claim 1 , wherein the contacting of the gas with the first absorbent solution takes place at a temperature from 10 to 80° C. and at a pressure from 1 to 50 bar.
5. The method according to claim 1 , wherein the contacting of the gas with the second absorbent solution takes place at a temperature from 10 to 80° C.
6. The method according to claim 1 , wherein the contacting of the gas with the second absorbent solution takes place at substantially the same temperature and/or substantially the same pressure as the contacting of the gas with the first absorbent solution.
7. The method according to claim 1 , wherein an H 2 S level of the gas recovered from step f) is less than 20 ppb.
8. The method according to claim 1 , wherein said first and/or second absorbent solution is/are regenerated after gas recovery.
9. A method for producing hydrocarbons or derivatives thereof from a biomass raw material, the method comprising:
i) gasifying the biomass raw material in the presence of oxygen to produce a gas comprising carbon monoxide, carbon dioxide, hydrogen, water and hydrocarbons;
ii) optionally conducting a tar reforming step;
iii) optionally removing tar components from the gas;
iv) optionally adjusting a hydrogen-to-carbon monoxide ratio;
v) washing hydrogen sulfide and carbon dioxide from the gas comprising carbon monoxide, carbon dioxide, hydrogen, water and hydrocarbons by conducting the method according to claim 1 ;
vi) converting in a synthesis reactor at least a part of the carbon monoxide and hydrogen contained in the gas into a product including a hydrocarbon composition or derivatives thereof; and
vii) recovering the hydrocarbon composition or derivatives thereof.
10. The method according to claim 9 , further comprising conducting COS hydrolysis prior to step v).
11. The method according to claim 1 , wherein the alkaline absorbent includes an amine, carbonate, aqueous CaO solution or a combination thereof.
12. The method according to claim 1 , wherein the second absorbent solution is applied as an aqueous amine wash, carbonate wash, carbonate precipitation or a combination thereof.
13. The method according to claim 1 , wherein the concentration of the transition metal ions in the first absorbent solution is less than about 100 ppm w , calculated from a weight of the first absorbent solution.
14. The method according to claim 1 , wherein the transition metal ions comprise copper from CuSO 4 .
15. The method according to claim 1 , wherein the contacting of the gas with the second absorbent solution takes place at a temperature from 20 to 40° C.
16. The method according to claim 1 , wherein an H2S level of the gas recovered from step f) is less than 1 ppb.
17. The method according to claim 9 , wherein the transition metal ions comprise copper.
18. The method according to claim 4 , wherein the contacting of the gas with the second absorbent solution takes place at substantially the same temperature and/or the same pressure as the contacting of the gas with the first absorbent solution.
19. The method according to claim 5 , wherein the contacting of the gas with the second absorbent solution takes place at substantially the same temperature and/or the same pressure as the contacting of the gas with the first absorbent solution.
20. The method according to claim 3 , wherein the alkaline absorbent includes an amine, carbonate, aqueous CaO solution or a combination thereof.
21. The method according to claim 1 , wherein the first absorbent solution has a pH of about 1 to 6.5.
22. The method according to claim 1 , wherein the first absorbent solution has a pH of about 1 to 5.
23. The method according to claim 1 , wherein the first absorbent solution consists essentially of transition metal ions in acidic aqueous solution.
24. The method according to claim 1 , wherein the first absorbent solution consists of water and CuSO 4 .