GB587378A - Improvements in or relating to the manufacture of ethylene - Google Patents

Abstract

Ethylene is produced directly under pressure by subjecting ethanol to contact with a dehydration catalyst at a pressure between 350 and 1500 atmospheres and at high temperature preferably 300-600 DEG C., and if desired cooling and/or scrubbing the ethylene obtained. The ethylene produced is contacted with an ethylene polymerization catalyst while still at an elevated temperature and pressure to produce polymerization products. Dehydration catalysts include acid catalysts such as phosphoric acid which may be suspended on an inert porous material such as coke or pumice, cadmium phosphate, and inorganic catalysts such as alumina and activated clays. Polymerization catalysts include oxygen, peroxides such as hydrogen peroxide, alkyl and acyl peroxides and alkyl hydroperoxides; per acids and their salts such as persuccinic acid, alkali persulphates, percarbonates and perborates, amine oxide, hydrazine, oximes; and organo-metallic compounds such as lithium butyl. For oxygen catalyst the polymerization temperature is greater than 100 DEG C., and the pressure exceeds 500 atmospheres. For catalysts such as per compounds, the temperature is preferably 60 DEG to 150 DEG C. and the pressure 70 to 1000 atmospheres. It is advantageous to use the same pressure for dehydration and polymerization. Some cooling of the dehydration products is generally necessary and the crude ethylene should be separated from the dehydration catalyst. Liquid polymerization products are obtained when temperatures of 300-400 DEG C. and pressures of 50-100 atmospheres are employed. Interpolymers with compounds having carbon-carbon double bonds may also be obtained by adding such compounds after dehydration. Dehydration is preferably conducted in a hot reaction zone such as a tubular reaction vessel and the dehydration products are then passed continuously through a cooler and then into a second reaction zone for polymerization. In examples: (1) dehydration is effected at 310 DEG C. and 1500 atmospheres pressure with orthophosphoric acid as catalyst; (2) using the same catalyst dehydration is carried out at 300 DEG C. and 300 atmospheres. The temperature is lowered to 120 DEG C. and polymerization is effected in the presence of benzoyl peroxide. Specifications 317,500, [Class 2 (iii)], 471,590, 497,643, 578,584 and 8070/40 (as open to inspection under Sect. 91) are referred to. In the first Provisional Specification, the dehydration catalysts also include concentrated sulphuric acid and caustic soda and the dehydration pressure is above 50 atmospheres. The second Provisional Specification states that dehydration and polymerization may be carried out simultaneously.