| 摘要 |
Ethylene is produced from a hydrocarbon feed of a type which on cracking produces primarily ethylene but also yields propylene (e.g. light naphtha, propane or ethane/propane mixtures), by mixing the feed with propylene and steam and thermally cracking the mixture at a temperature of at least 816 DEG C. in a pyrolysis zone with a residence time of not more than 1 second, cooling the effluent to below 538 DEG C., separating ethylene product, and also separating propylene and recycling at least part of it to be mixed with incoming hydrocarbon feed. The amount of propylene mixed with the feed may be up to 25%, e.g. 10-20%, of the total feed (excluding steam). The process gives improved selectivity for ethylene production and also yields useful quantities of benzene. The pyrolysis zone, suitably a tube, may be periodically cleaned of deposits of coke &c. without cooling, by switching off the feed and recycle propylene streams and allowing steam to pass through alone at a temperature of at least 982 DEG C.
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