Catalytic processes sweetening

Sweetening is an efficient catalytic process for the removal of sulfur present as mercaptans in light oils. Even when present in very small quantities, mercaptans cause foul odor, deterioration of additives in finished products and are corrosive. They are oxidized to innocuous disulfides by air under caustic condition and in the presence of cobalt phtalocyanine catalyst [1]. In industrial process, the use of caustic soda solution leads nevertheless to environmental problems in the refinery. 

Sweetening of petroleum products implies the removal of dissolved free sulfur and its compounds like hydrogen sulfide, and mercaptans in order that the product has no bad odour and does not tend to cause corrosion. The removal of these is accomplished by oxidation processes, solvent processes or catalytic desulfurization processes. 

As with sweetening the design process for removal of CO2 is very similar to that of dehydration. Special consideration is given to the presence of O2 in the feed and in some cases it is found necessary to catalytically remove the oxygen. 

The production of COS in the front end reaction furnace presents special problems since sulfur in this form may be difficult to remove in the downstream catalytic beds under conditions that are optimal for the Claus redox reaction between H2S and SO COS (and CS2) were known to be generated from hydrocarbon impurities carried over in the acid gas feed thus the efficiency of the up-stream sweetening process became an important factor. The reaction of CO2, a common constituent of the acid gas feed, with H2S and/or sulfur under furnace temperature conditions has also been shown to be an important source of COS. 

Sulfur removal, as practiced in various refineries, can take several forms for instance, concentration in refinery products such as coke (Table 7-1), hydrode-sulfurization, or chemical removal (acid treating and caustic treating, i.e., sweetening or finishing processes). Nevertheless, the desulfurization of petroleum is almost universally accomplished by the catalytic reaction of hydrogen with the sulfur-containing constituents of petroleum to produce hydrogen sulfide that can be readily separated from the liquid products (Chapter 9). 

The catalytic oxidation of sulfur-containing compounds has been studied mostly on the examples of thioethers and thiols, which are most often encountered in petrochemical industry. Elimination of the foul odor arising from thiols (mercaptans) contained in some oils ("sweetening") is mostly carried out by oxidation of thiols to disulfides. The oxidation of sulfur salts is also of practical importance in the processing of sulfide ores and handling the... 

Although catalytic desulfurization differs vitally from what have been termed sweetening processes, it serves the same purpose and in addition is able to remove more stable sulfur compounds than those involved in plain sweetening. The gum content of cracked gasoline is also reduced by the process. When operated at 1000 F rather than the customary 750 F... 

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