GB798712A - Improvements in or relating to recovery of platinum group metal from catalyst - Google Patents

Abstract

Platinum group metal is recovered from a catalyst containing also aluminium oxide and carbonaceous deposits by calcining the catalyst in the presence of an oxygen-containing gas to burn off the carbonaceous deposits, then treating with aluminium chloride vapour in a stripping zone at 93-870 DEG C. and removing from the stripping zone vapours containing volatile platinum group metal compounds. The process is especially suitable for recovering platinum from a catalyst which has been used in a hydrocarbon conversion operation. In a preferred process, the spent catalyst is heated in air at 370-870 DEG C. for 1-12 hours or more and then subjected to magnetic separation to remove iron. Washing the catalyst follows, using water or an aqueous solution containing acetic acid, nitric acid, phosphoric acid, sulphuric acid, hydrochloric acid, sodium hydroxide, ammonium hydroxide, or a surface-active agent; acetone, chloroform, ether, carbon tetrachloride, and alcohol are alternative washing agents. The catalyst is dried at 93-870 DEG C. in air, chlorine, carbon monoxide, or carbon dioxide and then subjected to treatment with vaporous aluminium chloride. The vapour may be passed through the catalyst, or the catalyst may be mixed with aluminium chloride, or a solution thereof, and heated; another method is to treat the catalyst with phosphorus pentachloride vapours which react with the alumina to form aluminium chloride. The aluminium chloride vapour may be formed by heating aluminium chloride, by contacting alumina with carbon monoxide and chlorine or with carbon tetrachloride, or by contacting a mixture of alumina and carbon with chlorine; in use the aluminium chloride vapours may be diluted with helium, nitrogen, chlorine, carbon dioxide, or carbon monoxide; oxygen is excluded, for example by providing a bed of charcoal at the entrance to the stripping zone. The vaporous product from the stripping zone is contacted with water or an aqueous solution of aluminium chloride, which may contain hydrochloric acid. When platinum is being recovered, a solution of platinum chloride is formed which is treated with a reducing agent, e.g. aluminium metal, hydrazine hydrate, or stannous chloride, to form metallic platinum. In examples, platinum is recovered from an alumina-platinum catalyst and palladium from an alumina-palladium catalyst. Other platinum group metals referred to are iridium, rhodium, ruthenium, and osmium; the catalyst may also contain silica or combined halogen.