Method and system for treating polymer waste comprising heteroatomic polymers

Abstract

The present invention relates to a method for producing a hydrocarbon product from mixed polymer waste, preferably plastic waste and/or post consumer plastic waste, wherein said mixed polymer waste comprises 50-99.5 wt % polyolefins and 0.5-50 wt % polymer comprising heteroatoms, based on the total weight of the mixed polymer waste, comprising: (i) feeding said mixed polymer waste into an extruder, preferably a single screw extruder; (ii) adding chemicals, preferably alkali metal salt and/or alkali earth metal salt, to said mixed polymer waste to degrade said polymer comprising heteroatoms; (iii) removing degradation products derived from said polymer comprising heteroatoms from said hydrocarbon product; and (iv) collecting the hydrocarbon product. The method and system of the present invention may be used as a pre-treatment in recycling mixed polymer waste to produce a hydrocarbon product ideally suited for pyrolysis.

1 . A method for producing a hydrocarbon product from mixed polymer waste, wherein said mixed polymer waste comprises 50-99.5 wt % polyolefins and 0.5-50 wt % polymer comprising heteroatoms, based on the total weight of the mixed polymer waste, comprising:
 (i) feeding said mixed polymer waste into an extruder;   (ii) adding chemicals, to said mixed polymer waste to degrade said polymer comprising heteroatoms;   (iii) removing degradation products derived from said polymer comprising heteroatoms from said hydrocarbon product; and   (iv) collecting the hydrocarbon product.   
     
     
         2 . A method as claimed in  claim 1 , wherein said mixed polymer waste comprises 50-99 wt % polyolefins, based on the total weight of the mixed polymer waste composition. 
     
     
         3 . A method as claimed in  claim 1 , wherein said polyolefins are selected from polyethylene, polypropylene, polystyrene and mixtures thereof. 
     
     
         4 . A method as claimed in  claim 1 , wherein said mixed polymer waste comprises 1-50 wt % polymer comprising heteroatoms, based on the total weight of the mixed polymer waste composition. 
     
     
         5 . A method as claimed in any  claim 1 , wherein said polymer comprising heteroatoms is selected from polyethylene terephthalate (PET), polyamide (PA), polyurethane (PU), biopolymers (e.g. polylactic acid, polyhydroxyalkanoates), cellulose, poly(ethylene-co-vinyl acetate) (EVA), poly(vinyl alcohol-co-ethylene) (EVOH), polycarbonate, poly(acrylonitrile-co-butadiene-co-styrene) (ABS), poly(styrene-co-acrylonitrile) (SAN), polymethylmethacrylate (PMMA) and mixtures thereof. 
     
     
         6 . A method as claimed in  claim 1 , wherein said mixed polymer waste further comprises non-polymeric compounds comprising heteroatoms. 
     
     
         7 . A method as claimed in  claim 1 , wherein said mixed polymer waste is mixed with alkali metal salt, and/oralkali earth metal salt prior to feeding said mixed polymer waste to the extruder. 
     
     
         8 . A method as claimed in  claim 7 , wherein the mixture of alkali metal salt and/or alkali earth metal salt and mixed polymer waste is all fed into the extruder 
     
     
         9 . A method as claimed in  claim 1 , wherein said extruder is at a temperature of at least 300° C. 
     
     
         10 . A method as claimed in  claim 1 , wherein the residence time of said mixed polymer waste in said extruder is 0.1-20 minutes. 
     
     
         11 . A method as claimed in  claim 1 , wherein said polymers comprising heteroatoms and optionally non-polymeric compounds comprising heteroatoms, are simultaneously degraded in said extruder. 
     
     
         12 . A method as claimed in  claim 1 , wherein the degradation products derived from the polymer comprising heteroatoms, and optionally from non-polymeric compounds comprising heteroatoms, are removed in the form of volatiles and via a devolatization outlet of the extruder, the extruder die or a devolatization unit connected to the extruder exit. 
     
     
         13 . A method as claimed in  claim 1 , wherein the degradation products derived from the polymer comprising heteroatoms, and optionally from non-polymeric compounds comprising heteroatoms, are removed in the form of solids and via a melt filter. 
     
     
         14 . A method as claimed in  claim 1 , wherein said hydrocarbon product comprises 0-5 wt % polyethylene terephthalate (PET), based on the total weight of the hydrocarbon product, and/or said hydrocarbon product comprises 0-5 wt % polyamide (PA), based on the total weight of the hydrocarbon product. 
     
     
         15 . A method as claimed in  claim 1 , wherein said polyolefins present in said mixed polymer waste undergo cracking in said extruder, and preferably wherein said hydrocarbon product has:
 a lower weight average molecular weight than said mixed polymer waste;   a lower complex viscosity, Eta (0.5) than said mixed polymer waste;   a lower complex viscosity, Eta (200) than said mixed polymer waste; and/or   a higher MFR2 than said mixed polymer waste.   
     
     
         16 . A method as claimed in  claim 1 , further comprising pyrolysis of said hydrocarbon product. 
     
     
         17 . A system for producing a hydrocarbon product from mixed polymer waste, comprising:
 an extruder for conversion of mixed polymer waste comprising 50-99.5 wt % polyolefins and 0.5-50 wt % polymer comprising heteroatoms into a mixture of hydrocarbon product and degradation products derived from the polymer comprising heteroatoms;   a melt filter for receiving the mixture of hydrocarbon product and degradation products from the extruder and removing solid degradation products from said hydrocarbon product; and   a degassing unit for receiving the hydrocarbon product from the melt filter and removing volatile degradation products from said hydrocarbon product.   
     
     
         18 . A method for recycling mixed polymer waste comprising a pre-treatment to remove polymer comprising heteroatoms, wherein said pre-treatment comprises a method as defined in  claim 1 . 
     
     
         19 . A system for recycling mixed polymer waste, comprising:
 an extruder for conversion of mixed polymer waste comprising 50-99.5 wt % polyolefins and 0.5-50 wt % polymer comprising heteroatoms, and chemicals into a mixture of hydrocarbon product and degradation products derived from the polymer comprising heteroatoms;   a melt filter for receiving the mixture of hydrocarbon product and degradation products from the extruder and removing solid degradation products from said hydrocarbon product;   a degassing unit for receiving the hydrocarbon product from the melt filter and removing volatile degradation products from said hydrocarbon product; and   a pyrolysis unit for receiving the hydrocarbon product from the degassing unit and pyrolysing said the hydrocarbon product.