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Process to remove carbonyl sulfide from LPG. (General Developments).

A patent has been issued (Patent No. 6,334,949, Jan. 1, 2002) to two NIST scientists for a process that selectively removes carbonyl sulfide, a potentially problematic impurity, from liquefied petroleum gas (LPG). NIST scientists in Boulder discovered the carbonyl sulfide process accidentally, while researching the extraction of metals. Commercial sources of LPG are composed primarily of propane, and provide fuel gas for outdoor grills, recreational vehicles, and rural residences and businesses. In addition to propane, LPG may contain butane, ethane, but also some unfavorable impurities that can ultimately form corrosive products. One such impurity is carbonyl sulfide, or COS. This compound is of concern because in the presence of water, it can hydrolyze to form hydrogen sulfide, a deadly and corrosive gas not permitted in commercial LPG.

While conducting research on the extraction of metals with supercritical fluid extraction, the scientists discovered that the common supercritical fluid solvent carbon dioxide forms a stable complex with a macro-cyclic organic molecule called p-tertiary-butylcalix[4]arene. Their work with infrared spectrophotometry indicated that this might be an inclusion complex. The similarity of the molecular structures of carbon dioxide and carbonyl sulfide prompted tests with COS. As with [CO.sub.2], a very stable complex was obtained with COS.

Additional work demonstrated a new process that selectively removes carbonyl sulfide from LPG. Since calix[4]arene is a stable material, the new process has the potential of decreasing costs to LPG suppliers and processors. Current methods of removing COS from LPG all suffer from major drawbacks. For example, molecular sieve processes require large bed sizes and very short cycle times, and reactions with metal oxides result in a nonregenerable waste product. P-tertiary- butylcalix[4]arene, on the other hand, can be regenerated, and has a strong interaction with COS. A process based on this material has the potential of removing COS at both low and trace levels. This is a thermally stable compound that can be used to very high temperatures.

CONTACT: Thomas J. Bruno, (303) 497-5158;
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Article Details
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Publication:Journal of Research of the National Institute of Standards and Technology
Geographic Code:1USA
Date:Jul 1, 2002
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