GB808394A - Improvements in or relating to process for sulfonation of hydrocarbons - Google Patents

Abstract

A two-step process for the complete sulphonation of sulphonatable hydrocarbons diluted with unsulphonatable hydrocarbons comprises introducing into the hydrocarbon mixture, under sulphonatable conditions, an amount of sulphonating agent sufficient to sulphonate 50 to 97 per cent of the sulphonatable hydrocarbons in the hydrocarbon mixture. The mixture is separated into a lower layer comprising sulphonated hydrocarbons and an upper layer comprising unsulphonatable hydrocarbons diluted with unsulphonated sulphonatable hydrocarbons, the two layers are separated and the upper layer subjected to a further sulphonating process which is sufficient to completely sulphonate all the remaining sulphonatable hydrocarbons which are then separated as before. In a preferred method of carrying out the process the diluted sulphonatable hydrocarbons are applied as a film to a heat-exchange surface which is maintained at - 1 DEG to 82 DEG C., sufficient sulphonating agent to sulphonate 50 to 97 per cent of the sulphonatable hydrocarbons is introduced at a point closely in advance of a progressively moving scraper which removes the partially sulphonated film of liquid. The liquid is allowed to separate into two layers and the diluted unsulphonated sulphonatable hydrocarbons forming the upper layer are reapplied as a film and treated as before. The reaction vessel incorporating the heat exchange surface and scraper with inlets for the sulphonating agent is described in Specifications 804,346. Sulphonating agents which may be used are sulphuric acid, chlorosulphonic acid, oleum or sulphur trioxide, the preferred ones being oleum and sulphur trioxide. Sulphur trioxide may be used in the form of a stabilized liquid or, preferably, as a gaseous mixture with an inert gas such as dry air, nitrogen, carbon dioxide or a lower alkane. Any ratio of sulphur trioxide to inert gas may be used but the preferred ratios, when dry air is used, are air:sulphur trioxide 9; 1 to 1:1. Suitable hydrocarbons mentioned are alkylated benzenes, toluenes or xylenes where the alkyl group contains 9 to 18 carbon atoms. Alkaryl hydrocarbons with a C12 side chain, known as dodecylbenzene intermediate and containing on average 57 per cent sulphonatable hydrocarbons, are preferred. Examples are given: (i) sulphonation of dodecyl benzene intermediate with SO3/air mixture at 60 DEG C. in two steps to give a 93 per cent yield of the sodium salt of the resulting sulphonic acid; (iii) as (i) but working on a batch principle instead of continuous; rather more SO3 was needed and a 92.5 per cent yield of sodium salt was obtained; (v) sulphonation with oleum at 54 DEG C. in a batch process using two sulphonating steps.