Processing of spent hydrorefining catalysts by selective chlorination
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I.
INTRODUCTION
CATALYSTS containing valuable metals such as Co, Ni, and Mo are widely used in the oil industries and especially for the hydrodesulfurization of petroleum fractions. The lifetime of hydrodesulfurization catalysts is about 3 years, m During the hydrorefining operations, the catalysts are contaminated either by compounds of elements such as S, C, V, Fe, Si, or the elements themselves, and traces of As, P, etc. The origin of these compounds is either the petroleum fractions themselves or the construction materials of different unit operations during their processing and/or regeneration. These catalysts could be classified into three types according to the active phases' base metals: Co-Mo, Ni-Mo, and (Co and Ni)-Mo, all supported by alumina or silicoaluminate. The typical composition of a hydrodesulfurization catalyst is 3 to 5 pct CoO or NiO, 11 to 16 pct MOO3, and the balance alumina or silicoalurninate. Besides the recovery of valuable metals that are currently imported, the recycling of these solid wastes could contribute to environmental protection. The European Community (EC) petroleum industries generate some 10,000 tons per year of spent hydrorefining catalysts. The majority of published work on the recovery of valuable metals from spent catalysts deals first with roasting to eliminate the catalysts' S and C contents, before subjecting them to hydrometallurgical or pyrometallurgical treatments. The roasting conditions are important because they influence the recovery rates of the metals during these treatments. This article is a summary of investigations on the optimization of the roasting parameters and the selective chlorination of roasted spent catalysts. I. G A B A L L A H , Senior Researcher, Laboratoire Environment et Miu&alurgie, associated with the Centre National de la Recherche Scientifique, Mineral Processing and Environmental Engineering team, and M. DJONA, Researcher, are with the Institut National Polytechnique de Lorraine, 54501 Vandoeuvre, France. Manuscript submitted July 6, 1993.
METALLURGICAL AND MATERIALS TRANSACTIONS B
II.
LITERATURE REVIEW
A bibliographical study t2] based on some 70 articles dealing with the recovery of valuable metals from spent catalysts revealed that the main tendency is to use hydrometallurgical processes. However, it appears that the valuable metals' recovery rates are generally lower than those obtained by selective chlorination. Only a few articles are devoted to the chlorination of the spent catalysts. Jong and Siemens from the United States Bureau of Mines 131studied the chlorination of spent catalysts roasted at 400 ~ in N2 for 30 minutes, using a chlorinating gas mixture of C12 + CO or C12 + air at 450 ~ for 30 minutes in a fluidized bed reactor. The solid residue was hydrolyzed, and the filtrate was submitted to solvent extraction for the recovery of Ni. The authors revealed that the recovery rates are about 89 pct of Mo and 83 pct of Ni using C12 + air, with the extraction of 4 pct of A1203.
Welsh and Piquet t4] describe a pretreatment
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