Methods and compositions for inhibiting polystyrene formation during styrene production

Abstract

Methods and compositions are provided for inhibiting the polymerization of a vinyl aromatic monomer, such as styrene monomer, during elevated temperature processing or distillation thereof. The compositions comprise an inhibitor combination of (A) a hydroxylamine and (B) a stable free radical plus a retarder that is either; (C) dinitrobutylphenol or (D) quinone methide. The ratio of (A) to (B) ranges from about 5% (A) to 95% (B) to about 95% (A) to about 5% (B). The compositions are added to the vinyl aromatic monomer in amounts sufficient to prevent polymerization during the distillation process. Typically the inhibitor combination is added to the vinyl aromatic monomer in an amount ranging from about 10 to 150 ppm of the monomer. Retarders are typically added in an amount ranging from 50 to 1500 ppm of the vinyl aromatic monomer.

What is claimed is: 
     
         1 . A method for inhibiting the polymerization of a vinyl aromatic monomer comprising:
 adding to the monomer an effective polymerization inhibitor combination comprising (A) a hydroxylamine; and   (B) stable free radical.   
     
     
         2 . The method of  claim 1 , wherein the ratio of (A) to (B) ranges from about 5% (A) to 95% (B) to about 95% (A) to about 5% (B). 
     
     
         3 . The method of  claim 2 , wherein the hydroxylamine (A) is 2-propanol, 1,1′-(hydroxyimino)bis. 
     
     
         4 . The method of  claim 3 , wherein the stable free radical (B) is 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy. 
     
     
         5 . The method of  claim 1 , wherein the inhibitor combination is added to the vinyl aromatic monomer in an amount ranging from about 10 to about 150 ppm of the vinyl aromatic monomer. 
     
     
         6 . The method of  claim 5 , wherein a retarder is added to the vinyl aromatic monomer in an amount ranging from about 50 to about 1500 ppm of the vinyl aromatic monomer. 
     
     
         7 . The method of  claim 6 , wherein the retarder is (C) dinitrobutylphenol. 
     
     
         8 . The method of  claim 6 , wherein the retarder is (D) quinone methide. 
     
     
         9 . The method of  claim 1 , wherein the vinyl aromatic monomer is selected from the group consisting of styrene, bromostyrene, divinylbenzene and α-methylstyrene. 
     
     
         10 . The method of  claim 1 , wherein temperature of polymerization of the vinyl aromatic monomer ranges from about 75° C. to about 125° C. 
     
     
         11 . The method of  claim 6 , wherein the inhibitor combination and retarder further comprise a liquid carrier including water or a non-polar organic solvent. 
     
     
         12 . The method of  claim 6 , further comprising the step of heating the vinyl aromatic monomer. 
     
     
         13 . The method of  claim 6 , further comprising the step of distilling the vinyl aromatic monomer to remove impurities therefrom.