Processes for recycling polystyrene waste

Abstract

There are provided recycled polystyrene polymers having a melt flow index of less than about 25 g/10 min. There are provided processes for recycling polystyrene waste. The processes can comprise dissolving said polystyrene waste in p-cymene under conditions to obtain a polystyrene/p-cymene mixture, adding the polystyrene/p-cymene mixture to a hydrocarbon polystyrene non-solvent under conditions to obtain precipitated polystyrene and washing the precipitated polystyrene with additional portions of hydrocarbon polystyrene non-solvent under conditions to obtain twice-washed polystyrene. The twice-washed polystyrene can optionally be dried and formed into polystyrene pellets. There is also provided recycled polystyrene obtained from such processes for recycling polystyrene waste.

1 . A process for recycling polystyrene waste, comprising:
 dissolving said polystyrene waste in p-cymene to obtain a polystyrene/p-cymene mixture;   filtering said polystyrene/p-cymene mixture to remove insoluble material;   adding said polystyrene/p-cymene mixture to a first portion of a hydrocarbon polystyrene non-solvent under conditions to obtain precipitated polystyrene and a first portion of hydrocarbon waste solution,   wherein said conditions to obtain said precipitated polystyrene and said first portion of hydrocarbon waste solution comprise adding said polystyrene/p-cymene mixture to said first portion of hydrocarbon polystyrene non-solvent at the boiling point of said hydrocarbon polystyrene non-solvent such that said first portion of hydrocarbon polystyrene non-solvent keeps said polystyrene waste in a malleable paste form and agitating to diffuse said p-cymene from said polystyrene/p-cymene mixture into said hydrocarbon polystyrene non-solvent;   separating said precipitated polystyrene from said first portion of hydrocarbon waste solution;   optionally repeating said dissolving, adding and separating;   washing said precipitated polystyrene with a second portion of hydrocarbon polystyrene non-solvent under conditions to obtain washed polystyrene and a second portion of hydrocarbon waste solution,   wherein said conditions to obtain said washed polystyrene and said second portion of hydrocarbon waste solution comprise adding said second portion of hydrocarbon polystyrene non-solvent to said precipitated polystyrene at the boiling point of said hydrocarbon polystyrene non-solvent such that said second portion of hydrocarbon polystyrene non-solvent keeps said precipitated polystyrene in a malleable paste form and agitating to diffuse said p-cymene from said precipitated polystyrene into said hydrocarbon polystyrene non-solvent;   separating said washed polystyrene from said second portion of hydrocarbon waste solution;   washing said washed polystyrene with a third portion of hydrocarbon polystyrene non-solvent under conditions to obtain twice-washed polystyrene and a third portion of hydrocarbon waste solution,   wherein said conditions to obtain said twice-washed polystyrene and said third portion of hydrocarbon waste solution comprise adding said third portion of hydrocarbon polystyrene non-solvent to said washed polystyrene at the boiling point of said hydrocarbon polystyrene non-solvent such that said third portion of hydrocarbon polystyrene non-solvent keeps said washed polystyrene in a malleable paste form and agitating to diffuse said p-cymene from said washed polystyrene into said hydrocarbon polystyrene non-solvent;   separating said twice-washed polystyrene from said third portion of hydrocarbon waste solution; and   optionally drying said twice-washed polystyrene to obtain dried polystyrene,   wherein said first portion of hydrocarbon polystyrene non-solvent, said second portion of hydrocarbon polystyrene non-solvent and said third portion of hydrocarbon polystyrene non-solvent comprise a hydrocarbon polystyrene non-solvent having a boiling point at 1 atm of pressure of from 98° C. to 110° C.;   wherein said boiling point of said hydrocarbon polystyrene non-solvent is about or above the glass transition temperature of said twice-washed polystyrene; and   wherein said polystyrene waste is post-industrial waste, post-consumer waste or a combination thereof.   
     
     
         2 . The process of  claim 1 , wherein said polystyrene/p-cymene mixture comprises polystyrene in an amount of from 10 wt % to 30 wt %, based on the total weight of said polystyrene/p-cymene mixture. 
     
     
         3 . The process of  claim 1 , wherein said polystyrene/p-cymene mixture comprises insoluble material and said process further comprises filtering said polystyrene/p-cymene mixture to remove said insoluble material prior to adding said polystyrene/p-cymene mixture to said first portion of hydrocarbon polystyrene non-solvent. 
     
     
         4 . The process of  claim 1 , wherein greater than 90 wt % of said p-cymene in said polystyrene/p-cymene mixture diffuses into said hydrocarbon polystyrene non-solvent, based on the total weight of said polystyrene/p-cymene mixture. 
     
     
         5 . The process of  claim 1 , wherein the ratio by volume of said first portion of hydrocarbon polystyrene non-solvent to said polystyrene/p-cymene mixture is from 2:1 to 4:1. 
     
     
         6 . The process of  claim 1 , wherein said washed polystyrene comprises less than 0.3 wt % p-cymene. 
     
     
         7 . The process of  claim 1 , wherein said twice-washed polystyrene comprises less than 0.1 wt % p-cymene. 
     
     
         8 . The process of  claim 1 , wherein said first portion of hydrocarbon polystyrene non-solvent, said second portion of hydrocarbon polystyrene non-solvent and said third portion of hydrocarbon polystyrene non-solvent comprise a hydrocarbon polystyrene non-solvent having a boiling point at 1 atm of pressure of from 105° C. to 110° C. 
     
     
         9 . The process of  claim 1 , wherein said first portion of hydrocarbon polystyrene non-solvent, said second portion of hydrocarbon polystyrene non-solvent and said third portion of hydrocarbon polystyrene non-solvent comprise a C 6 -C 8  alkane or a petroleum distillate. 
     
     
         10 . The process of  claim 1 , wherein said first portion of hydrocarbon polystyrene non-solvent, said second portion of hydrocarbon polystyrene non-solvent and said third portion of hydrocarbon polystyrene non-solvent comprise n-heptane. 
     
     
         11 . The process of  claim 1 , wherein said twice-washed polystyrene is dried to remove remaining hydrocarbon polystyrene non-solvent. 
     
     
         12 . The process of  claim 11 , wherein said twice-washed polystyrene is dried at a temperature of from 115° C. to 125° C. 
     
     
         13 . The process of  claim 1 , wherein said first portion of hydrocarbon polystyrene non-solvent, said second portion of hydrocarbon polystyrene non-solvent and said third portion of hydrocarbon polystyrene non-solvent consist essentially of said hydrocarbon polystyrene non-solvent having a boiling point at 1 atm of pressure of from 98° C. to 110° C. 
     
     
         14 . The process of  claim 1 , wherein said first portion of hydrocarbon polystyrene non-solvent, said second portion of hydrocarbon polystyrene non-solvent and said third portion of hydrocarbon polystyrene non-solvent consist essentially of n-heptane. 
     
     
         15 . The process of  claim 1 , wherein said process further comprises processing said dried polystyrene under conditions to obtain polystyrene pellets, wherein said conditions to obtain said polystyrene pellets comprise extruding said dried polystyrene at a temperature of from 140° C. to 160° C. 
     
     
         16 . The process of  claim 1 , wherein said polystyrene waste comprises expanded polystyrene. 
     
     
         17 . The process of  claim 1 , wherein said polystyrene waste comprises white, expanded polystyrene. 
     
     
         18 . The process of  claim 1 , wherein recycled polystyrene prepared according to said process comprises from 0.05 wt % to 0.3 wt % p-cymene.