Conversion of waste plastics to petrochemicals

Abstract

Processes and systems for converting waste plastics include feeding a waste plastic to a melt tank, and in the melt tank, heating the waste plastic to form a molten plastic. The molten plastic is withdrawn from the melt tank and fed to a pyrolysis reactor. In the pyrolysis reactor, the molten plastic is heated to a pyrolysis temperature, producing a pyrolysis oil product and a liquid pitch product. The pyrolysis oil is then separated into a pyrolysis gas fraction, a light pyrolysis oil fraction, a medium pyrolysis oil fraction, and a heavy pyrolysis oil fraction.

What is claimed as new and desired to be protected by Letters Patent is: 
     
         1 . A process for converting waste plastics, comprising:
 feeding a waste plastic to a melt tank;   in the melt tank, heating the waste plastic to form a heated molten plastic;   withdrawing the heated molten plastic from the melt tank and feeding the heated molten plastic to a pyrolysis reactor;   in the pyrolysis reactor, heating the heated molten plastic to a pyrolysis temperature, producing a pyrolysis oil product and a liquid pitch product;   separating the pyrolysis oil product into a pyrolysis gas fraction, a light pyrolysis oil fraction, a medium pyrolysis oil fraction, and a heavy pyrolysis oil fraction; and   recycling a diluent comprising the medium pyrolysis oil fraction to the melt tank.   
     
     
         2 . The process of  claim 1 , wherein the waste plastic is provided to the melt tank as a partially or fully melted waste plastic recovered from an extruder, the process further comprising partially or fully melting the waste plastic in the extruder. 
     
     
         3 . The process of  claim 1 , further comprising controlling a temperature in the pyrolysis reactor to limit a temperature of the heated molten plastic to a temperature below that at which char or coke will form. 
     
     
         4 . The process of  claim 1 , further comprising:
 dividing the heated molten plastic into a first portion and a second portion;   mixing the second portion with the waste plastic upstream of the melt tank; and   feeding the first portion to the pyrolysis reactor.   
     
     
         5 . The process of  claim 1 , further comprising, prior to feeding the waste plastic to the melt tank, contacting the waste plastic with nitrogen at a temperature sufficient to remove water from the waste plastic. 
     
     
         6 . The process of  claim 1 , further comprising providing heat to one or both of the melt tank or the pyrolysis reactor directly or indirectly via combustion of the pyrolysis gas fraction. 
     
     
         7 . The process of  claim 1 , further comprising mixing an alkaline reagent with the heated molten plastic, downstream of the melt tank and upstream of the pyrolysis reactor, reacting the alkaline reagent with chlorine contained in the heated molten plastic to form calcium salts, and recovering the calcium salts with the liquid pitch product. 
     
     
         8 . The process of  claim 1 , further comprising withdrawing a vapor stream from the melt tank, and optionally treating the vapor stream to remove any halogens contained therein. 
     
     
         9 . A process for converting waste plastics, comprising:
 feeding a waste plastic to a melt tank;   in the melt tank, heating the waste plastic to form a heated molten plastic;   withdrawing the heated molten plastic from the melt tank and feeding the heated molten plastic to a pyrolysis reactor;   in the pyrolysis reactor, heating the heated molten plastic to a pyrolysis temperature, producing a pyrolysis oil product and a liquid pitch product;   separating the pyrolysis oil product into a pyrolysis gas fraction, a light pyrolysis oil fraction, a medium pyrolysis oil fraction, and a heavy pyrolysis oil fraction; and   recycling a diluent comprising the heavy pyrolysis oil fraction to the melt tank.   
     
     
         10 . The process of  claim 9 , wherein the waste plastic is provided to the melt tank as a partially or fully melted waste plastic recovered from an extruder, the process further comprising partially or fully melting the waste plastic in the extruder. 
     
     
         11 . The process of  claim 9 , further comprising controlling a temperature in the pyrolysis reactor to limit a temperature of the heated molten plastic to a temperature below that at which char or coke will form. 
     
     
         12 . The process of  claim 9 , further comprising:
 dividing the heated molten plastic into a first portion and a second portion;   mixing the second portion with the waste plastic upstream of the melt tank; and   feeding the first portion to the pyrolysis reactor.   
     
     
         13 . The process of  claim 9 , further comprising, prior to feeding the waste plastic to the melt tank, contacting the waste plastic with nitrogen at a temperature sufficient to remove water from the waste plastic. 
     
     
         14 . The process of  claim 9 , further comprising providing heat to one or both of the melt tank or the pyrolysis reactor directly or indirectly via combustion of the pyrolysis gas fraction. 
     
     
         15 . The process of  claim 9 , further comprising mixing an alkaline reagent with the heated molten plastic, downstream of the melt tank and upstream of the pyrolysis reactor, reacting the alkaline reagent with chlorine contained in the heated molten plastic to form calcium salts, and recovering the calcium salts with the liquid pitch product. 
     
     
         16 . The process of  claim 9 , further comprising withdrawing a vapor stream from the melt tank, and optionally treating the vapor stream to remove any halogens contained therein. 
     
     
         17 . A system for pyrolyzing a waste plastic, the system comprising:
 a melt tank having:
 an inlet configured for receiving a feed stream comprising waste plastic from a waste plastic feed system; 
 a heating system configured for heating the waste plastic from a feed temperature to a melt temperature, producing a molten plastic; 
 an outlet configured for outputting the molten plastic; 
   a pyrolysis reactor having:
 an inlet configured to receive the molten plastic; 
 a heating system configured to heat the molten plastic to a pyrolysis temperature; 
 a first outlet for recovering a pyrolysis oil; 
 a second outlet for recovering a pitch product; and 
 a control system configured to control the heating system to limit a temperature of the molten plastic to a temperature for production of the pitch product. 
   
     
     
         18 . The system of  claim 17 , wherein the waste plastic feed system comprises an extruder for partially or melting the waste plastic. 
     
     
         19 . The system of  claim 17 , further comprising a separation system configured to separate the pyrolysis oil into two or more fractions. 
     
     
         20 . The system of  claim 19 , wherein the separation system is configured to separate the pyrolysis oil into a pyrolysis gas fraction, a light pyrolysis oil fraction, a medium pyrolysis oil fraction, and a heavy pyrolysis oil fraction.