Liquid purification or separation – Processes – Treatment by living organism
Patent
1999-01-25
2000-12-05
Smith, Duane
Liquid purification or separation
Processes
Treatment by living organism
210622, 95156, 423220, 42324311, 435266, C02F 334, B01D 1900
Patent
active
06156205&
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for the purification of gas containing hydrogen sulphide and possibly other contaminants, in which process use is made of sulphide-oxidising bacteria.
BACKGROUND OF THE INVENTION
International Patent Application WO 92/10270 discloses a process for the purification of a gas containing hydrogen sulphide, in which the gas is scrubbed in a gas scrubber with an alkaline scrubbing liquid, the scrubbing liquid used is treated in an aerobic reactor with oxygen in the presence of sulphur-oxidising bacteria the effluent from the aerobic reactor is used again as scrubbing liquid and the elemental sulphur formed during the treatment with oxygen is separated from the effluent. The process is suitable for the removal of hydrogen sulphide (H.sub.2 S) and other reduced sulphur compounds, such as mercaptans and carbon disulphide, or for the removal of sulphur dioxide (SO.sub.2). For H.sub.2 S removal, the pH is kept between 8 and 9 by means of buffering compounds. The sulphur-oxidising bacteria used include the genera Thiobacillus and Thiomicrospira.
A disadvantage of this known process is that relatively large quantities of scrubbing liquid are necessary in order to absorb the hydrogen sulphide effectively. The known process is also unsuitable for the removal of other contaminants which may be present in addition to H.sub.2 S, such as carbonyl sulphide (COS).
SUMMARY OF THE INVENTION
It has now been found that biological conversion of sulphide to elemental sulphur can be performed at high pH using selected autotrophic sulphide-oxidising bacteria. As a result of the higher pH, the required quantity of scrubbing liquid is substantially reduced and the required equipment can therefore be smaller and less expensive. The new bacteria to be used according to the invention are effective at a pH above 9 up to about 11, in particular at a pH of 9.2 to 10.5. The bacteria to be used especially have a pH optimum above 9.0.
The biological oxidation of hydrogen sulphide and carbonyl sulphide using the autotrophic alkaliphilic bacteria predominantly results in the production of elemental sulphur, with some thiosulphate being formed as a byproduct.
It has further been found that thiosulphate can be converted to polythionate efficiently and with an increase in pH by a treatment in the presence of oxygen or a nitrogen oxide using thiosulphate-oxidising bacteria. Such thiosulphate-oxidising bacteria may include known sulphur-oxidisers, such as those of the genera Thiobacillus and Thiomicrospira, or heterotrophic bacteria. The term polythionate is used herein to comprise trithionate (S.sub.3 O.sub.6.sup.2-), tetrathionate (S.sub.4 O.sub.6.sup.2-), and possibly higher polythionate (S.sub.n O.sub.6.sup.2-, n>4) species. The absorption of H.sub.2 S, COS (carbonyl sulphide) and other sulphur compounds by the scrubbing solution can be improved by using the solution containing the polythionate ions obtained in this way, with the result that these contaminants can be removed from gases more efficiently and with less scrubbing liquid. The process essentially yields only solid elemental sulphur. The optional bacterial thiosulphate-oxidising treatment can be performed simultaneously with the sulphide-oxidising treatment--if oxygen is used as the thiosulphate-oxidising agent--, but preferably the oxidation of thiosulphate is performed subsequently in a separate stage.
The process according to the invention is particularly suitable for the purification of fuel gas, coal gas, Claus-plant off-gases, chemical gases, process gases and other gases containing COS, and gases which are under pressure. Examples of gases which are under pressure are fuel gas (for example, 30 bar) and natural gas (for example, 70 bar).
As a consequence of the relatively high pH, less scrubbing liquid is needed than in known biological processes for the removal of sulphur compounds. The quantity of scrubbing liquid needed can further be reduced as a consequence of the presence of polythionate in the scrubbing liqui
REFERENCES:
patent: 1832325 (1931-11-01), Rosenstein
patent: 5354545 (1994-10-01), Buisman
patent: 5366633 (1994-11-01), Buisman
patent: 5401657 (1995-03-01), Jones et al.
patent: 5480550 (1996-01-01), Sublette
patent: 5508014 (1996-04-01), Rai
patent: 5637220 (1997-06-01), Buisman
by Vedenina et al., "ATP synthesis by heterotrophic bacteria during the oxidation of thiosulfate to tetrathionate", Chemical Abstracts Service, Columbus, Ohio, 1993.
Buisman Cees Jan Nico
Janssen Albert Jozef Hendrik
Kuenen Joannes Gijsbrecht
Robertson Lesley Anna
Sorokin Dimitri Yuri
Paques Bio Systems B.V.
Prince Fred
Smith Duane
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