Process for the manufacture of ester sulfonate pastes of low viscosity

A process for the preparation of an aqueous concentrate of an .alpha.-sulfonated fatty acid alkyl ester comprising the steps of:

• (a) sulfonating an alkyl fatty acid ester with a sulfonating agent to produce an .alpha.-sulfonated fatty acid alkyl ester;
• (b) adding to said .alpha.-sulfonated fatty acid alkyl ester from about 1 to about 10 mole percent of the total moles of said .alpha.-sulfonated fatty acid alkyl ester of at least one compound of the formula ##STR7## wherein in the compound of formula I X and Y are different and are OH or SO.sub.3 M wherein M is selected from the group consisting of hydrogen, an alkali metal ion, an alkaline earth metal ion, or NR.sub.4 wherein R is hydrogen, an alkyl or hydroxy alkaly radical having from 1 to 4 carbon atoms;
• a and c are integers having a value of from 0 to 18;
• b is an integer having a value of from 0 to 2 such that the sum of a+b+c is from 12 to 18;
• Z is an oxyethylene, oxypropylene, or oxybutylene group;
• n is an integer having a value of from 0 to 30;
• and (c) neutralizing said .alpha.-sulfonated fatty acid alkyl ester with an aqueous alkaline solution.