Process for inhibiting polymerization of styrene during distillation

Claim 1

The method for inhibiting the polymerization of styrene during separation and recovery thereof from a mixture consisting substantially of ethylbenzene, styrene and styrene tar in a plurality of distillation stages to recover ethylbenzene, styrene and styrene tar, respectively, which comprises introducing into the first of said distillation stages in an amount sufficient to inhibit polymerization of styrene, a solution of a dinitrophenol, said dinitrophenol having no substituents on the benzene ring other than the hydroxy group and the nitro groups, obtained by intimately contacting styrene tar containing such a dinitrophenol inhibitor with an aqueous solution of the hydroxide of an alkali metal or ammonia at a temperature between about 70° and about 95° C. while controlling the pH of the aqueous phase between about 5 and 10, separating the resulting liquid phases, intimately contacting the separated aqueous phase simultaneously with hydrochloric acid and an organic solvent selected from the group consisting of ethylbenzene and ethylbenzene in admixture with sytrene, benzene and toluene while controlling the pH of the aqueous phase below 3 and recovering the organic phase containing substantially all the dinitrophenol dissolved therein from said acid-solvent contacting.

Claim 2

The method for inhibiting the polymerization of styrene during separation and recovery thereof from a mixture consisting substantially of ethylbenzene, styrene and styrene tar in a plurality of distillation stages to recover ethylbenzene, styrene and styrene tar, respectively, which comprises introducing into the first of said distillation stages in an amount sufficient to inhibit polymerization of styrene, a solution of a dinitrophenol, said dinitrophenol having no substituents on the benzene ring other than the hydroxy group and the nitro groups, obtained by intimately contacting styrene tar containing such a dinitrophenol inhibitor with an aqueous solution of the hydroxide of an alkali metal or ammonia at a temperature between about 70° and about 95° C. while controlling the pH of the aqueous phase between about 5 and 10, separating the resulting liquid phases, intimately contacting the separated aqueous phase simultaneously with hydrochloric acid and an organic solvent selected from the group consisting of ethylbenzene and ethylbenzene in admixture with sytrene, benzene and toluene while controlling the pH of the aqueous phase below 3 and recovering the organic phase containing substantially all the dinitrophenol dissolved therein from said acid-solvent contacting.