Improvements in catalysts for the catalytic production of polymers

摘要

A catalyst for the polymerization of olefins comprises chromium oxide deposited on or otherwise associated with alumina, silica, alumina-silica, thoria, or zirconia, at least part of the chromium being in the hexavalent state, and the catalyst also containing strontium oxide which retards the decomposition of hexavalent chromium compounds. The chromium content of the catalyst is preferably 0.1-10 per cent and the amount of strontium oxide may be equivalent to 0.2-4 gram atoms of strontium per gram atom of chromium. Suitable carriers are synthetic alumina gel, bauxite, activated alumina, silica gel, acid-treated clays, and silica-alumina cracking catalyst. The catalyst may be prepared by treating the carrier with aqueous solutions or suspensions of chromium and strontium compounds, either successively or simultaneously, and then heating and calcining; dispersion media other than water, e.g. ethanol, pentanol, or acetone, may be used. Another method of preparation is coprecipitation of the oxides with the support. Chromium and strontium compounds which may be used are the oxides, nitrates, and acetates, chromic acid, chromic chloride or sulphate, and strontium carbonate, hydroxide, chromate, or dichromate. The catalyst may be activated by treatment with dry air at 750-1000 DEG F. After use the catalyst may be washed with a paraffinic solvent to remove deposited polymer, treated with an inert gas, e.g. nitrogen, at 700-1100 DEG F. for 1 hour, and then with an oxidizing gas to burn off carbonaceous deposits. Specification 790,195 also is referred to.ALSO:Olefins are polymerized in the presence of a catalyst comprising chromium oxide (at least part of the chromium being in the hexavalent state) deposited on or otherwise associated with alumina, silica, alumina-silica, thoria, or zirconia, and containing strontium oxide as a stabilizer, in order to avoid or retard decomposition of the hexavalent chromium compounds (see Group III). The olefins polymerized and the conditions of polymerization are as disclosed in Specification 804,641. Specification 790,195 also is referred to.