Thermal cracking method for producing lower hydrocarbons

Abstract

A method for producing lower hydrocarbons by a thermal cracking reaction from mixed waste plastic (MWP) is disclosed herein. The method includes: a. forming a mixed gas comprising methane and hydrogen, b. combining the mixed gas with the MWP to form a reaction mixture, c. reacting the reaction mixture in a reactor at a pressure of 1 to 40 bars, a temperature of 800° C. to 1200° C. and a residence time of 10 to 300 milliseconds in the reactor, and d. producing a lower hydrocarbon product stream through the outlet of the reactor. The methane/hydrogen mol ratio in the mixed gas is from 0.1 to 5.

1 . A method for producing lower hydrocarbons by a thermal cracking reaction from mixed waste plastic (MWP) comprising:
 a. forming a mixed gas comprising methane and hydrogen;   b. combining the mixed gas with the MWP to form a reaction mixture;   c. reacting the reaction mixture in a reactor at a pressure of 1 to 40 bars, a temperature of 800° C. to 1200° C. and a residence time of 10 to 300 milliseconds in the reactor; and   d. producing a lower hydrocarbon product stream through the outlet of the reactor;   wherein the methane/hydrogen mol ratio in the mixed gas is from 0.1 to 5.   
     
     
         2 . The method according to  claim 1 , wherein the mixed gas comprising methane and hydrogen has a methane/hydrogen mol ratio from 0.5 to 4. 
     
     
         3 . The method of  claim 1 , wherein the temperature of the thermal cracking reaction is from 850° C. to 1100° C. 
     
     
         4 . The method of  claim 1 , wherein the residence time in the reactor is from 50 to 150 milliseconds. 
     
     
         5 . The method of  claim 1 , wherein the initial heat required for the thermal cracking reaction is generated by a heat carrier circulated within the reactor. 
     
     
         6 . The method of  claim 5 , wherein the heat carrier is selected from one or more of oxide and carbonate salts of alkali-earth metals. 
     
     
         7 . The method of  claim 5 , wherein the heat carrier is the mixed gas comprising methane and hydrogen. 
     
     
         8 . The method of  claim 1 , wherein the MWP comprises waste plastics, waste textiles, waste modified cellulose, waste biomass, post-industrial waste streams, intermediate industrial waste streams, or combinations thereof. 
     
     
         9 . The method of  claim 1 , further comprising melting the MWP before feeding it to the reactor. 
     
     
         10 . The method of  claim 1 , wherein the mol ratio of hydrogen to carbon in the reaction mixture is ≥1. 
     
     
         11 . The method of  claim 1 , wherein the lower hydrocarbon product stream comprises from 40% to 50% by weight of a mixture of ethane and propane. 
     
     
         12 . The method of  claim 1 , wherein the lower hydrocarbon product stream comprises from 40% to 50% by weight of a mixture of ethylene and propylene. 
     
     
         13 . The method of  claim 11 , wherein product yields of ethane and propane is at least 3 to 4 times higher than those obtained by thermal cracking of a reaction mixture wherein the mol ratio of hydrogen to carbon in the reaction mixture is <1. 
     
     
         14 . The method of  claim 12 , wherein product yields of ethylene and propylene is at least 40% higher than those obtained by thermal cracking of a reaction mixture wherein the mol ratio of hydrogen to carbon in the reaction mixture is <1. 
     
     
         15 . The method of  claim 1 , wherein the MWP comprises 30 to 99 wt. percent of at least one of high density polyethylene, low density polyethylene, or polypropylene. 
     
     
         16 . The method of  claim 1 , wherein the residence time in the reactor is from 5 to 300 milliseconds. 
     
     
         17 . The method of  claim 1 , wherein the pressure of the thermal cracking reaction is from 5 to 20 bars. 
     
     
         18 . The method of  claim 1 , wherein the reaction mixture is externally heated to temperatures from 800° C. to 1200° C. before feeding it to the reactor. 
     
     
         19 . The method of  claim 1 , wherein the mixed gas comprising methane and hydrogen has a methane/hydrogen mol ratio from 0.2 to 4. 
     
     
         20 . A method for preventing coke clogging when thermally cracking a mixed waste plastic (MWP), the method comprising:
 a. forming a mixed gas comprising methane and hydrogen;   b. combining the mixed gas with the MWP to form a reaction mixture;   c. reacting the reaction mixture in a reactor to produce a lower hydrocarbon product stream; and   d. while reacting the reaction mixture in the reactor, maintaining a methane/hydrogen mol ratio in the mixed gas of no greater than 5.