GB669899A - Improvements in or relating to the sulphonation of alkyl aryl hydrocarbons - Google Patents

Abstract

A process for the sulphonation of hydrocarbons consisting substantially of one or more alkyl-aryl hydrocarbons having in the molecule at least one alkyl group of 6-18 carbon atoms comprises treating the hydrocarbons in the liquid phase with a mixture of sulphur trioxide vapour and an inert gas. The starting material hydrocarbons include those containing an aromatic nucleus such as a benzene or a naphthalene nucleus and substituted by at least one alkyl group containing 6-18 carbon atoms which may have a straight or branched chain or may be a cyclo-alkyl group and the nucleus may be substituted with further alkyl groups. Examples of such starting materials are the various isomeric dodecyl benzenes, dodecyl toluenes, dodecyl xylenes and hexyl naphthalenes and commercial mixtures of these isomers, usually in admixture with minor amounts of compounds having alkyl groups of different sizes. The sulphonates of these mixtures are stated to be detergents. Any non-reacting gas may be used and mentioned are air, carbon dioxide, gaseous sulphur dioxide or nitrogen. The sulphur trioxide/inert gas mixture may be produced, for example by generating sulphur trioxide vapour from liquid sulphur trioxide and diluting it with inert gas or by taking the product from the "contact" process for sulphur trioxide manufacture. The process is conveniently carried out by passing a suitable mixture of gases into the well stirred liquid hydrocarbons. It is sometimes convenient to place a small proportion of already sulphonated material in the reaction mixture to assist the reaction and it is sometimes advantageous to add a small proportion of sulphuric acid or phosphoric acid to the hydrocarbon before sulphonating. Inert liquid diluents such as sulphur dioxide and carbon tetrachloride may be employed in the reaction mixture. When the sulphonated products are to be used as detergents the excess sulphur trioxide can be conveniently neutralized with alkali and the resulting sulphate left in the product. The process may be carried out in either a batch or a continuous manner. The latter may be carried out by passing a stream of hydrocarbon (containing a small amount of sulphuric acid if desired) into a well cooled mixing vessel provided with an efficient stirrer whilst a sulphurtrioxide/air stream is passed into the bottom of the mixing vessel. Waste air is removed from the top of the vessel and the liquid mixture is withdrawn at such a rate as to leave a constant amount therein and is passed to a holding vessel where the liquid is held long enough for the reaction to proceed to completion. In examples I a commercial hydrocarbon, of average molecular weight 265, consisting principally of dodecyl toluenes is placed in a reactor and a sulphur trioxide/air mixtures is stirred in and the sulphonated product is neutralized; II a sulphur trioxide/air mixture is passed into a stirred commercial hydrocarbon of average molecular weight 246, consisting principally of dodecyl benzenes, at elevated temperature and after further heating is neutralized with caustic soda solution; III a process similar to that described in example I is carried out but using two sulphonation steps, the second at a higher temperature than the first. The product is neutralized with caustic soda and bleached with sodium hypochloride.