GB818823A - Improvements in and relating to the production of hydrocarbons - Google Patents

Abstract

Olefines principally ethylene and some propylene and acetylene are produced by vaporizing a hydrocarbon distillate and heating it to at least 650 DEG C., mixing it with steam heated to at least 1200 DEG C., passing the mixed vapours through an isolated soaking zone with a contact time of up to 0.7 second, e.g. 0.005-0.25 second, and quenching the product within 0.5-4 seconds. Suitable feedstocks are C4-C8 paraffinic petroleum fractions boiling in the range -12 DEG to 170 DEG C. The steam may be heated by a pebble heater and introduced to the pyrolysis chamber, made of refractory brickwork, at one or more points where it is mixed with the hydrocarbon heated to 650-700 DEG C. The steam to hydrocarbon weight ratio may be between 5 : 1 and 0.4 : 1. Propylene is produced in significant amounts if the steam is heated to 1200-1300 DEG C. giving a mixed temperature of 800-900 DEG C., at steam temperatures of above 1300 DEG C. the ethylene yield is increased. In the examples a straight run naphtha, boiling range 50-150 DEG C., is (1) heated to 690 DEG C. and mixed with three times its weight of steam at 1370 DEG C. for a contact time of 0.25 second to give a gaseous product containing 22 molar per cent of ethylene and 10-11 molar per cent of acetylene with methane and hydrogen; (2) treated as in (1) except for a contact time of 0.1 second; the gaseous product contained calculated in terms of total carbon in the gas, 27 per cent of ethylene, 12 per cent acetylene and 5 per cent propylene with higher hydrocarbons, methane and carbon oxides; (3) treated as in (2) except for the steam temperature which was 1270 DEG C. and the steam : hydrocarbon ratio which was 4.5 : 1 to give a product containing, calculated in terms of total carbon, 35 per cent ethylene, 9 per cent acetylene and 10 per cent propylene.