Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Sulfur or sulfur containing component
Patent
1993-05-10
1995-06-20
Langel, Wayne
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Sulfur or sulfur containing component
4232452, 423437R, C01B 1700, C01B 3120
Patent
active
054259290
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of recovering substantially pure CO.sub.2 from a fermentation gas polluted with organic compounds and with sulphur compounds.
In various processes, gas streams are obtained which contain substantial amounts of CO.sub.2. In particular when brewing beer, fermenting grapes, and in distilleries, large amounts of CO.sub.2 -containing gas are developed which is polluted with organic compounds and with sulphur compounds. The value of this gas, however, is considerable because it is obtained by a natural process and can be properly applied in the beverage industry, e.g. for making carbonated soft drinks or beer.
Since the gas also contains substantial amounts of impurities in the form of organic compounds such as ethanol, and sulphur compounds such as H.sub.2 S and DMS (dimethyl sulphide), it is necessary to purify the gas before it is used. The gas also contains non-condensable gases such as oxygen and nitrogen, which gases must also be removed at least partially.
The presence of the sulphur compounds in the gas gives an unpleasant smell and/or taste, e.g. in mineral water if this is provided with unpurified or insufficiently purified CO.sub.2.
Up to the present this fermentation gas has been purified nearly exclusively by washing with water, compression, and cooling to remove the major part of the water, removing the organic and sulphur impurities by adsorption at an activated carbon filter, further drying the gas and condensating the CO.sub.2 to reduce the content of non-condensable gases.
U.S. Pat. No. 4,699,642 discloses a method of preparing substantially pure, liquid CO.sub.2 for use in the beer brewing process. According to this patent, purification is also effected by adsorption.
This system has the drawback that the risk of a breakthrough of impurities is rather great. In practice, it has also been found that additional measures must be taken regularly to avoid this risk. A breakthrough of impurities is not desirable because of the smell and/or taste problems when CO.sub.2 is used in beverages.
The object of this invention is to provide a method of recovering substantially pure CO.sub.2 from a fermentation gas polluted with organic compounds and with sulphur compounds.
According to the invention this method comprises washing the gas with water or an aqueous solution under such conditions that the gas contains no more than 2.5, preferably no more than 1.25 ppm organic impurities, oxidizing the oxidizable impurities, removing the major part of the water, and drying the CO.sub.2 to the desired water content.
Surprisingly, it has been found that this simple method gives a purified CO.sub.2 having a content of sulphur-containing impurities of not more than 2 ppb calculated as H.sub.2 S.
The amounts of organic impurities and sulphur impurities have been calculated on the basis of parts by volume per volume.
Crucial points of the method according to the invention are, inter alia, the very thorough washing of the gas, followed by the oxidation with an aqueous solution of an oxidator. As compared with the known methods based on the adsorption of the impurities at activated carbon, the method according to the invention is very simple. Since no adsorption stage is present, the method can be carried out continuously with fewer appliances in a simpler process.
Surprisingly, it is possible to eliminate the concentrations of impurities, very low as they are, by oxidation, despite a low dosage of active chlorine of 0.5.times.10.sup.-4 to 3.0.times.10.sup.-4 wt. % in the solution. In the method according to the invention it has also been found that substantially no trihalomethane and/or ethyl acetate is formed, as can be expected of a combination of wet washing and oxidation with chlorine compounds.
BRIEF DESCRIPTION OF DRAWING
The accompanying FIGURE diagrammatically shows an installation for carrying out the method according to the invention.
Gas streams that can be purified according to the invention are, inter alia, the CO.sub.2 -containing gas streams from the brewing of beer, f
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patent: 1519932 (1924-12-01), Reich
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patent: 1968899 (1934-08-01), Nathan
patent: 4551325 (1985-11-01), Alesandrini et al.
John H. Perry, Chemical Engineers' Handbook, Fourth Edition (1972), McGraw-Hill Book Co., pp. 18-25, 18-26.
Patent Abstracts of Japan-vol. 6, No. 131 (C-114) (1009)-Jul. 17, 1982.
Jansen Karel R. J.
van Oeveren Pieter W.
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