GB1148967A - A process for the preparation of ethylene - Google Patents

Abstract

1,148,967. Ethylene. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. 31 July, 1967 [2 Aug., 1966], No. 35039/67. Heading C5E. Ethylene is produced by a two-stage cracking process in which a hydrocarbon oil boiling below 250‹ C., e.g. straight-run naphtha, is first catalytically hydrocracked, the hydrocarbon products being then separated and thermally cracked in the presence of steam to yield ethylene which is separated. Suitable conditions for the first stage are 200-500‹ C., 10-500 atm. pressure, a space velocity of 0À1-10 vol/vol/hour and a hydrogen-oil volume ratio of 150-5000:1. The catalyst may comprise a metal of Group IB, VI B or VIII of the Mendeleef Periodic Table and/or an oxide and/or sulphide thereof supported on a solid acidic refractory carrier, and preferably containing chlorine and/or fluorine. A preferred catalyst is Pd or Pt on a molecular sieve, e.g. mordenite, treated with a hydrohalic acid. The products from the first stage may be water-washed to remove impurities such as H 2 S and ammonium compounds, and then distilled to separate a hydrocarbon mixture, mainly C 2-5 alkanes, which is passed to the second stage. Suitable conditions for the second stage are: 600-900‹ C., 1-2 atm. pressure, 0À2-5 seconds residence time and 0À1-10 kg. steam/kg. hydrocarbons. The product of the second stage is water-cooled, separated and dried, freed from hydrogen which is recycled, and then fractionated to separate first methane, then product ethylene, then ethane which is recycled to the second cracking stage, and finally higher hydrocarbons. The two-stage process increases ethylene yield over a conventional one-stage thermal cracking.