a process is provided for recovery and re - use of dinitrophenols employed as inhibitors of polymerization in the distillation and purification of styrene . the styrene still residues commonly referred to as tar or tars are treated with an aqueous hydroxide at a controlled ph , the phases are separated , the aqueous phase is treated with an acid and an organic solvent at a controlled ph and the resulting organic phase is recycled to a suitable point in the styrene purification system . the recycled solution is a more effective inhibitor than the dinitrophenol originally employed .