A process for steam cracking chlorine-containing feedstock

Abstract

A method of processing a plastic and a method of processing pyoil derived from a plastic. A numerical model for a correlation between chlorine content in one or more process streams of a steam cracking unit and a hydrocarbon to steam ratio in a feed stream of the steam cracking unit is constructed. A pyoil and naphtha blend is mixed with steam at a hydrocarbon to steam ratio obtain from the model to produce the feed stream for a steam cracking unit. The feed stream is processed in the steam cracking unit to produce olefins.

1 . A method of processing pyoil, the method comprising:
 mixing a pyoil obtained via pyrolysis of plastics with naphtha to produce a hydrocarbon stream having a chlorine content lower than a chlorine content of the pyoil;   mixing the hydrocarbon stream with steam to form a feed stream; and   steam cracking the feed stream under reaction conditions sufficient to produce olefins.   
     
     
         2 . The method of  claim 1 , wherein the pyoil comprises more than 60 ppm chlorine. 
     
     
         3 . The method of  claim 1 , wherein the hydrocarbon stream comprises 1 to 3 ppm elemental chlorine. 
     
     
         4 . The method of  claim 1 , wherein the feed stream has a chlorine content less than a chlorine content of the hydrocarbon stream. 
     
     
         5 . The method of  claim 1 , wherein the hydrocarbon stream is mixed with steam at a mass ratio greater than 0.35. 
     
     
         6 . The method of  claim 1 , wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof. 
     
     
         7 . The method of  claim 1 , wherein the naphtha and the pyoil are mixed at a mass ratio of up to 167:1, preferably 50:1. 
     
     
         8 . A method of processing plastics, the method comprising:
 (a) processing plastics under pyrolysis conditions sufficient to produce a pyoil comprising hydrocarbons and more than 60 ppm chlorine;   (b) mixing the pyoil with naphtha to produce a hydrocarbon stream comprising 1 to 3 ppm chlorine;   (c) mixing the hydrocarbon stream with steam at a first steam to hydrocarbon ratio to produce a first feed stream;   (d) steam cracking, in a steam cracker, the first feed stream under reaction conditions sufficient to produce an effluent stream comprising olefins, aromatics and steam;   (e) separating the effluent stream in a separation unit to produce one or more product streams comprising an ethylene stream, a propylene stream, a C 4  stream, and a pyrolysis gas stream;   (f) determining chlorine content of one or more process streams produced during steps (d) and (e);   (g) repeating steps (c) to (f) but with a second steam to hydrocarbon ratio in step (c) to obtain data for steam to hydrocarbon ratios and chlorine contents of the one or more process streams;   (h) construct a numerical model for correlation between steam to hydrocarbon ratios and chlorine contents of the one or more process streams;   (i) determining a final steam to hydrocarbon ratio using the numerical model such that the chlorine contents for the one or more process streams are each below 3 ppm; and   (j) operating the steam cracker using the final steam to hydrocarbon ratio to process the hydrocarbon stream.   
     
     
         9 . The method of  claim 8 , wherein the separating at step (e) can include separating effluent stream from the steam cracker to produce a top stream comprising C 1 -C 8  hydrocarbons and steam, a cracked distillate comprising C 9 -C 12  hydrocarbons, and carbon black oil comprising C 12 + hydrocarbons. 
     
     
         10 . The method of  claim 8 , wherein step (e) further comprises:
 quenching the top stream to produce a quench water stream comprising 0.1 to 20 ppm chlorine, a quench effluent stream comprising ethylene, propylene, C 4  hydrocarbons, C 5 + hydrocarbons, and a pygas stream comprising C 5 + hydrocarbons.   
     
     
         11 . The method of  claim 10 , wherein the pygas stream is combined with a compressed liquid fraction of the quench effluent stream to form a combined pyrolysis gas stream. 
     
     
         12 . The method of  claim 11 , wherein the combined pyrolysis gas stream comprises 0.1 to 1 ppm chlorine. 
     
     
         13 . The method of  claim 3 , wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof. 
     
     
         14 . The method of  claim 4 , wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof. 
     
     
         15 . The method of  claim 5 , wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof. 
     
     
         16 . The method of  claim 7 , wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof. 
     
     
         17 . The method of  claim 8 , wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof. 
     
     
         18 . The method of  claim 9 , wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof. 
     
     
         19 . The method of  claim 10 , wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof. 
     
     
         20 . The method of  claim 11 , wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof.