Cobalt molybdate desulfurization

Molybdenum salts used as catalysts include cobalt molybdate for hydrogen treatment of petroleum stocks for desulfurization, and phospho-molybdates to promote oxidation. Compounds used for dyes are sodium, potassium, and ammonium molybdates. With basic dyes, phosphomolyb-dic acid is employed. The pigment known as molybdenum orange is a mixed crystal of lead chromate and lead molybdate. Sodium molybdate, or molybdic oxide, is added to fertilizers as a beneficial trace element. Zinc and calcium molybdate serve as inhibitory pigments in protective coatings arid paint for metals subjected to a corrosive atmosphere. Compounds used to produce better adherence of enamels are molybdenum trioxide and ammonium, sodium, calcium, barium, and lead molybdates. 

Examination of the reaction products indicated that the primary products of reaction were probably butadiene and H2S. The rates of hydrogenation of butadiene and butene were found to be consistent with the amounts appearing in the reaction products (provided, in the case of cobalt molybdate catalyst, that H2S was present to simulate reaction conditions). The results support the view that C-S bond cleavage is the first step in thiophene desulfurization, rather than hydrogenation of the ring. 

It may be that on cobalt molybdate, olefins can adsorb on sites other than the desulfurization sites. If so, it would be in accordance with conclusions reached by Hammar (14), and would also explain the selective poisoning reported with nitrogen compounds and CO (17, 20), which are strongly adsorbed reversible poisons like H2S (2, 17). These poisons offer one of the few ways at present available of improving selectivity and so lowering hydrogen consumption when desulfurizing olefinic feeds. 

Carbonyl sitlfide may be formed ditring natural gas treatment by the reaction of hydrogen sitlfide and carbon dioxide and this can be difficult to remove completely using zinc oxide alone. This is not a problem if a bed of cobalt molybdate catalyst is included in the desulfurizer. It has been shown that lead oxide is an efficient absorbent of earboityl sulfide so the natural lead oxide impurity in some zinc oxides may promote absorption, espeeially if traees of water vapour are present to hydrolyze the carbonyl sulfide. 

Impregnation of cobalt and molybdenum (without sodium) increases largely the isomerizing activity of the catalyst the /3-pinene is then completely converted. The catalysts prepared with sodium molybdate and sodium hydroxide (Co-Mo-Na and Na-Co-Mo-Na) have lower isomerizing activities while their HDS activities are significantly increased. As in the case of alumina supported catalysts the sulfided CoMo phase protected by a double layer of alkaline ions on the carbon support gives the best results in HDS of /3-pinene. The behaviour of this catalyst was examined in desulfurization of the turpentine oil (40% a-pinene, 25% /3-pinene, 25% A -carene and 10% camphene + dipentene + myrcene, 1500 ppm S). The results are recorded in Table 6. 

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