UOP Merox process

K. M. Brown, Commercial Kesults with UOP MEROX Process for Mercaptan Extraction in US. and Canada, UOP Booklet 267, UOP, Inc., Des Plaines,... 

Sweetfrac A process for removing sulfur compounds from naphtha. The process is essentially the UOP Merox process, positioned upstream of the naphtha splitter in conventional petroleum refining. 

Any mercaptans boiling below 80°C are also readily dissolved in alkaline solutions (Eq. 18.32). A common process for the removal of dissolved mercaptans of this kind, especially from catalytically cracked gasoline and liquefied petroleum gas, is the Universal Oil Products (UOP) Merox process that also uses caustic soda for extraction. In this process, however, the mercaptans are then oxidized to disulfides using air assisted by a metal complex catalyst dissolved in the caustic soda (Eq. 18.34). 

Production of cresols and xylenols from spent caustic washes of the petroleum refineries has been confined mostly to the Untied States since cresolates feedstocks have been inadequate in other countries. Besides as a result of use of UOP s Merox process of sweetening which does not use NaOH solution, or of hydrotreating process, less and less cresols... 

In 1958, UOP introduced a catalyst based process to accelerate the oxidation of mercap-tans to disulfides at or near ambient temperature. The process, which is licensed by UOP as the Merox process, is used to remove mercaptans from liquid or gaseous hydrocarbon streams. It operates by either converting the mercaptans to less objectionable disulfides in the flowing stream or removing the mercaptans with a caustic wash and then converting them to disulfides (Staehle et al., 1984). Only the approach involving both caustic absorption and subsequent oxidation to disulfides is applicable to gas purification. 

Although the Merox process is plicable to gases, most units have been designed to process liquid hydrocarbons. As of January, 1991, more than 1,450 Merox units of all types had been commissioned (UOP, 1992A). 

Two undesirable aspects of FCC naphtha quaUty are that it may contain unacceptably high amounts of foul smelling mercaptans, and that its thermal stabiUty may be too low. Mercaptans are usually found in the light FCC naphtha and may be removed or converted to sulfides and disulfides by a sweetening process such as Merox, developed by UOP. Thermal stabiUty is improved in sweetening processes through removal of cresyUc and naphthenic acids. It may be further improved by clay treating and by addition of oxidation inhibitors such as phenylene diamine. 

Merox [Mercaptan oxidation] A process for removing mercaptans from petroleum fractions by extracting them into aqueous sodium hydroxide and then catalytically oxidizing them to disulfides using air. The catalyst is an organometallic compound, either a vanadium phthalocyanine supported on charcoal, or a sulfonated cobalt phthalocyanine. Developed by UOP in 1958 and widely licensed by 1994, more than 1,500 units had been built, worldwide. Unzelman, G. H. and Wolf, C. J., in Petroleum Processing Handbook, Bland, W. F. and Davidson, R. L., Eds., McGraw-Hill, New York, 1967, 3-128. 

Mercaptans are converted in disulfides by oxidative dehydrogenation. The reaction is carried out for sweetening hydrocarbons, such as jet fuel gasoline kerosine and gas oil. The reaction is catalysed by a mixture of transitional metals as Cu, Mn, Fe and Co with activated carbon as catalyst carrier. The process is developed by UOP under the trade name MEROX [15-17]... 

T.A. Verachtert, G.F, Asselin and B.E. Staehle, Merox treatment of kerosine, UOP Process Division Technology Conference, September, (1982). 

UOP Inc., 1992A, Merox, Gas Processing Handbook 92, Hydro. Process., April, p. 120. 

---