GB735145A - Improvements in or relating to method for reactivating a platinum and/or palladium catalyst - Google Patents

Abstract

A platinum and/or palladium catalyst on which is deposited carbonaceous material is reactivated by treatment at an elevated temperature with an oxygen-containing gas having an oxygen partial pressure of about 5 to about 200 lbs. per square inch absolute. The temperature may be 700-1600 DEG F., preferably 700-1250 DEG F. At oxygen partial pressures of 5-15 lbs. per square inch, temperatures of 1050-1600 DEG F. are preferred. Times of reactivation are 10 minutes to 500 hours. A pretreatment may be given, e.g. for 1-15 minutes at 600-1250 DEG F., with a gas having an oxygen partial pressure of 0.07-1.5 lbs. per square inch. After reactivation the catalyst may be treated at 400-1200 DEG F. with hydrogen or recycle gas from a hydroforming process, in order to remove oxygen. The invention is particularly applicable to catalysts which have been used for hydroforming hydrocarbons, but reference is also made to processes involving dehydrogenation, hydrogenation, hydrogenolysis, cracking, hydrocracking, isomerization, oxidation, aromatization, cyclization, hydrodesulphurization, hydrocarbon synthesis, dealkylation, hydrodechlorination, dehydroxylation, alkylation, polymerization, and hydrogen exchange. The processes may involve the use of fixed, moving, or fluidized beds of catalyst. Suitable catalysts are prepared by mixing a carrier with a solution or suspension of an ammine complex of platinum or palladium, the potassium salt of chloroplatinic or chloropalladic acid, the acids themselves, or platinic or palladic sulphide, drying, and calcining or reducing. The ammine complex may be prepared by reacting ammonia or a substituted ammonia, e.g. an alkylamine, alkyldiamine, quinoline, pyridine, hydrazo compound or hydroxylamine, with a halide, nitrate, sulphate, sulphite, nitrite, or oxyhalide of platinum or palladium. Mercury, zinc, or cadmium, or compounds thereof, may be present in the catalyst as activating agents; suitable compounds are the oxides, hydroxides, chlorides, chlorates, bromides, nitrates, sulphates, sulphites, carbonates, bicarbonates, oxychlorides, fluorides, iodides, phosphates, phosphites, and acetates of these metals. An alcohol or ketone, e.g. methanol, ethanol, propanol, butanol, acetone, glycol, or benzyl alcohol, may be added as a promoting agent during the preparation of the catalyst. Combined fluorine or chlorine may also be present. Suitable carriers are silica, alumina, titania, charcoal, thoria, zirconia, pumice, kieselguhr, fuller's earth, magnesia, silica-alumina, and silica-magnesia. The catalyst may contain 0.01-15 per cent (preferably 0.5-2 per cent) by weight of platinum or palladium. In an example, catalyst is prepared by peptizing precipitated alumina gel with acetic acid, and mixing with a complex prepared by reacting platinum chloride with ammonia. This catalyst was used for hydroforming naphtha, with periodic regeneration using a gas containing 2-8 per cent of oxygen, but eventually lost activity and selectivity. Treatment with hydrogen and mixing with freshly calcined alumina did not effect appreciable reactivation. On passing a stream of dried oxygen through the catalyst at 700-900 DEG F. for 84 hours at atmospheric pressure, the original activity and selectivity were substantially restored.