Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy... – Treating gas – emulsion – or foam
Patent
1997-12-23
1999-11-02
Redding, David A.
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
Treating gas, emulsion, or foam
423226, 4232421, 4235192, 423544, 423563, 4235762, 4352891, A61L 901
Patent
active
059768681
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the treatment of a gas containing hydrogen sulphide and optionally other pollutants, the gas being washed in a first gas scrubber with an alkaline wash liquid and the spent wash liquid being treated in a first aerobic reactor with oxygen in the presence of sulphide-oxidising bacteria and the effluent from the first aerobic reactor being re-used as wash liquid and elementary sulphur formed during the treatment with oxygen being removed from the effluent.
A process of this type is disclosed in International Patent Application WO 92/10270. This process is suitable for the removal of hydrogen sulphide (H.sub.2 S) and optionally other reduced sulphur compounds, such as mercaptans and carbon disulphide, or for the removal of sulphur dioxide (SO.sub.2).
A disadvantage of the known method is that small amounts of sulphate are produced during the biological oxidation of sulphide and that no solution is provided for preventing the undesired accumulation thereof. The known method is also not suitable for the removal of other pollutants which can be present in addition to H.sub.2 S, such as ammonia (NH.sub.3), hydrocyanic acid (HCN), sulphur dioxide (SO.sub.2), carbonyl sulphide (COS) and/or carbon disulphide (CS.sub.2).
A process has now been found for the treatment of gases, which allows removal of hydrogen sulphide without appreciable residues and which also allows other undesirable gaseous components frequently encountered, such as ammonia, hydrocyanic acid, sulphur dioxide, carbon disulphide or carbonyl sulphide, to be removed without separate pretreatment or post-treatments and associated installations being required for this. The process produces only solid elementary sulphur and, if the gas to be treated also contains nitrogen compounds such as NH.sub.3 or HCN, molecular nitrogen (N.sub.2), both of which can be used or discharged without any drawbacks. The process is particularly suitable for the treatment of fuel gases (natural gas, coal gas) and other gases which are usefully used after treatment. The process is also suitable for the treatment of gases which will no longer be used and ultimately will be discharged, optionally after burning off, such as flue gases and industrial gases, for example Claus off-gases (gases which are produced during the reaction of high concentrations of H.sub.2 S with SO.sub.2 with the formation of elementary sulphur).
The process according to the invention is characterised in that the effluent from the first aerobic reactor, from which sulphur has been separated off, is treated in an anaerobic reactor with sulphate-reducing bacteria and returned to the first aerobic reactor.
As a result of the use of the anaerobic reactor connected downstream of the aerobic reactor, the sulphate which leaves the aerobic reactor is reduced to sulphide. When the gas to be treated contains sulphur dioxide in addition to hydrogen sulphide, this sulphur dioxide (in the form of sulphite or sulphate) is reduced to sulphide as well.
The bacteria which are active for reduction of sulphate and sulphite and other oxidised sulphur compounds in the anaerobic reactor (designated here as sulphate-reducing bacteria) are, for example, bacteria of the genera Desulfovibrio, Desulfotomaculum, Desulfomonas, Desulfobulbus, Desulfobacter, Desulfococcus, Desulfonema, Desulfosarcina, Desulfobacterium and Desulfuromonas. Bacteria of this type are available without any problem from diverse anaerobic cultures and/or grow spontaneously in the anaerobic reactor.
Reduction equivalents (electron donors) are needed for the biological reduction in the anaerobic reactor. Suitable electron donors are, inter alia, hydrogen, carbon monoxide, lower alcohols (for example methanol and ethanol) and other organic substances which can easily be oxidised by biological means, such as acetate, propionate, glucose, sucrose, starch and the like.
The sulphide-containing effluent from the anaerobic reactor is recycled to the aerobic reactor, where the sulphide is again largely converted into elementary sul
REFERENCES:
patent: 5269929 (1993-12-01), Sublette et al.
patent: 5354545 (1994-10-01), Buisman
patent: 5366633 (1994-11-01), Buisman
"Exploiting nature's sulphur cycle", Sulphur Metabolizing Bacteria, Sulphur No. 235, Nov. 1994, pp. 59-63, 65-67 and 69.
Paques Bio Systems B.V.
Redding David A.
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