was obtained in a vapor liquid equilibrium still a number of esters of similar structure and molecular weight were investigated and found to be ineffective they are isobutyl butyrate isobutyl isobutyrate hexyl acetate methyl amyl acetate phenyl acetate ethyl phenyl acetate methyl acetoacetate isobornyl acetate diethyl maleate ethyl benzoate methyl heptanoate ethyl heptanoate ethyl valerate dimethyl malonate and 2 ethyl hexyl acetate the usefulness or utility of this invention can be demonstrated by referring to the data presented in tables 1 7 all of the successful agents show that styrene can be separated from ethyl benzene or o xylene by means of azeotropic or extractive distillation in a rectification column and that the ease of separation as measured by relative volatility is considerable without these agents little improvement will occur in a rectification column table 1 shows that ethyl benzene and styrene have a relative volatility of 1 40 and table 2 shows that o xylene and styrene have a relative volatility of only 1 04 the data also show that the most attractive agents will operate at a boil up rate low enough to make this a useful and efficient method of recovering styrene from ethyl benzene or o xylene from any mixture of these compounds the stability of the agents used and the boiling point difference is such that complete recovery and recycle is obtainable by a simple distillation and the amount for make up is small example 1 twenty grams of ethyl benzene ten grams of styrene and thirty grams of ethyl isovalerate were charged to.