Systems and methods for the oxidative coupling of methane

Abstract

The present disclosure provides systems and methods for producing olefins via an oxidative coupling of methane (OCM) process. The systems and methods may comprise the use of a staged process comprising at least one non-adiabatic section that is in thermal communication with a heat transfer medium and at least one substantially adiabatic section. The systems and methods may also comprise the use of a diluent stream which may improve methane conversion in an OCM reactor and an ethylene/ethane ratio in a post-bed cracking unit. The methods and systems may further comprise injecting oxygen (O2) and a paraffin into a gas stream containing a radical transfer agent to provide a reaction mixture. The reaction mixture may be held in a vessel for a time period greater than an auto-ignition delay time (AIDT), such that the reaction mixture may ignite to liberate heat and convert to a product mixture comprising olefins.

What is claimed is: 
     
         1 . A method for producing an olefin, the method comprising:
 (a) producing a gas stream comprising methane (CH 4 ), oxygen (O 2 ), and a diluent; and   (b) passing the gas stream over an oxidative coupling of methane (OCM) catalyst at a pressure of at least 2 bar(g) to convert at least some of the CH 4  into hydrocarbon compounds having two or more carbon atoms (C 2+  compounds),   wherein a ratio of diluent molecules to carbon atoms in the gas stream is at least 0.1:1.   
     
     
         2 . The method of  claim 1 , wherein the diluent comprises water (H 2 O). 
     
     
         3 . The method of  claim 1 , wherein the diluent comprises carbon dioxide (CO 2 ). 
     
     
         4 . The method of  claim 1 , wherein the diluent comprises H 2 O and CO 2 . 
     
     
         5 . The method of  claim 1 , wherein the ratio of diluent molecules to carbon atoms in the gas stream is at least 0.5:1. 
     
     
         6 . The method of  claim 1 , wherein the ratio of diluent molecules to carbon atoms in the gas stream is at most 20:1. 
     
     
         7 . The method of  claim 1 , wherein the ratio of diluent molecules to carbon atoms in the gas stream is from 0.1:1 to 5:1. 
     
     
         8 . The method of  claim 1 , wherein the pressure is at least 4 bar(g). 
     
     
         9 . The method of  claim 1 , wherein the pressure is from 2 bar(g) to 10 bar(g). 
     
     
         10 . A method for producing ethylene, the method comprising:
 (a) injecting an oxygen stream comprising oxygen (O 2 ), a methane stream comprising methane (CH 4 ), and a diluent stream comprising water (H 2 O), carbon dioxide (CO 2 ), or both H 2 O and CO 2 , into a reactor containing an oxidative coupling of methane (OCM) catalyst to produce an OCM effluent gas containing a diluent,
 wherein at least one of: 
 (i) at least 20 mol % of the streams injected into the reactor is from the diluent gas stream; 
 (ii) a methane conversion is at least about 10%; or 
 (iii) an outlet temperature of the reactor is at least 800° C., is satisfied; and 
   (b) injecting the OCM effluent gas and an ethane stream containing ethane into a post bed cracking (PBC) unit, wherein the PBC unit converts at least a portion of the ethane in the OCM effluent gas and the ethane stream to ethylene, thereby generating a PBC effluent stream having an ethylene-to-ethane ratio greater than 3:1.   
     
     
         11 . The method of  claim 10 , wherein at least 20 mol % of the gas streams injected into the reactor is from the diluent gas stream and the outlet temperature of the reactor is at least 800° C. 
     
     
         12 . The method of  claim 10 , wherein the reactor containing the OCM catalyst and the PBC unit are contained in a single vessel. 
     
     
         13 . The method of  claim 10 , further comprising mixing the oxygen stream and the diluent stream to produce a diluted oxygen stream, and injecting the diluted oxygen stream into the reactor containing the OCM catalyst. 
     
     
         14 . The method of  claim 13 , wherein the diluted oxygen stream is injected into the reactor containing the OCM catalyst downstream of the methane stream. 
     
     
         15 . The method of  claim 10 , further comprising generating the diluent stream by directing a stream containing H 2 O to a heat exchanger that is in thermal communication with the OCM effluent gas to produce a steam stream and directing at least a portion of the steam stream as a portion of the diluent stream into the reactor containing the OCM catalyst. 
     
     
         16 . The method of  claim 15 , wherein the heat exchanger is integrated with the reactor. 
     
     
         17 . The method of  claim 15 , wherein the reactor containing the OCM catalyst, the heat exchanger, and the PBC unit are contained in a single vessel. 
     
     
         18 . A system for producing ethylene comprising:
 (a) an oxidative coupling of methane (OCM) reactor comprising an OCM catalyst that facilitates an OCM reaction, the OCM reactor configured to receive an oxidant stream comprising oxygen (O 2 ), a methane stream comprising methane (CH 4 ), and a diluent stream comprising water (H 2 O), and to permit at least a portion of the CH 4  and the O 2  to react in the OCM reaction to yield an OCM effluent stream;   (b) a heat exchanger downstream of and in thermal and fluid communication with the OCM reactor, wherein the heat exchanger is configured to receive a stream containing H 2 O and produce a steam stream by exchanging heat with the OCM effluent stream and to direct at least a portion of the steam stream into the OCM reactor as a portion of the diluent stream; and   (c) a post-bed cracking (PBC) unit downstream of and in fluid communication with the heat exchanger, wherein the PBC unit is configured to receive the OCM effluent stream and a stream comprising ethane and to convert at least some ethane to ethylene, thereby generating a PBC effluent stream comprising ethylene.   
     
     
         19 . The system of  claim 18 , further comprising a mixer upstream of and in fluid communication with the OCM reactor, wherein the mixer is configured to receive and mix the oxidant stream and the diluent stream to produce a diluted oxygen stream that is injected into the OCM reactor. 
     
     
         20 . The system of  claim 18 , wherein the OCM reactor, the heat exchanger, and the PBC unit are contained in a single vessel.