Stone & Webster Engineering Corp.

Allan R Huntley

Robert L DeRoeck

The invention provides a process for treating a sulfide-containing alkaline aqueous effluent, which includes subjecting it to a wet air oxidation treatment which oxidizes sulfide ions to environmentally acceptable sulfur acid ions, the oxidation being carried out in two or more chambers connected in series, flow of effluent between the chambers being effected at least primarily by gravity such that the pressures in the respective chambers can be maintained at substantially the same value.

Spent caustic system

A process is provided for treating a sulfide-containing alkaline aqueous effluent to improve its environmental acceptability, which comprises: (a) intimately mixing a water-immiscible solvent, such as a pyrolysis gasoline, therewith for a sufficient time to extract polymerizable hydrocarbon compounds and/or other compounds which may cause fouling of downstream plant, (b) allowing the solvent phase and the aqueous phase to separate, (c) removing the solvent phase, and (d) subjecting the separated aqueous phase to an oxidation treatment which oxidizes sulfide ions to environmentally acceptable sulfur acid ions, particularly sulfate ions, e.g. a wet air oxidation process. The invention has been particularly developed for treating spent caustic which has been used to scrub gases produced by cracking for ethylene production. Such effluents have been found to cause fouling of the oxidation plant and the Applicants have found that this is due to polymerizable hydrocarbons. Furthermore they have found that prolonged contact times between a readily available solvent and the effluent can ensure that the fouling problem is cured.

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Northwood, United Kingdom

Allan R Huntley