Oxidative coupling of methane implementations for olefin production
The present disclosure provides oxidative coupling of methane (OCM) systems for small scale and world scale production of olefins. An OCM system may comprise an OCM subsystem that generates a product stream comprising C 2+ compounds and non-C 2+ impurities from methane and an oxidizing agent. At least one separations subsystem downstream of, and fluidically coupled to, the OCM subsystem can be used to separate the non-C 2+ impurities from the C 2+ compounds. A methanation subsystem downstream and fluidically coupled to the OCM subsystem can be used to react H 2 with CO and/or CO 2 in the non-C 2+ impurities to generate methane, which can be recycled to the OCM subsystem. The OCM system can be integrated in a non-OCM system, such as a natural gas liquids system or an existing ethylene cracker.
1. A method for performing oxidative coupling of methane (OCM), comprising:
(a) in a substantially adiabatic OCM reactor comprising a fixed catalyst bed, reacting oxygen (O 2 ) with methane (CH 4 ) in an OCM process to yield a product stream comprising (i) compounds with two or more carbon atoms (C 2+ compounds), including ethylene (C 2 H 4 ), ethane (C 2 H 6 ), and propylene (C 3 H 6 ), (ii) hydrogen (H 2 ), and (iii) carbon monoxide (CO) or carbon dioxide (CO 2 ), wherein said OCM process liberates heat, and wherein an inlet temperature of said OCM reactor is at most about 600° C.;
(b) directing said product stream from said OCM reactor and C 2 H 6 from an ethane stream external to said OCM reactor into a cracking unit that cracks C 2 H 6 using energy derived from said heat liberated in said OCM process, thereby increasing a concentration of C 2 H 4 and H 2 in said product stream;
(c) directing said product stream from said cracking unit into a compressor that increases a pressure of said product stream using energy derived from said heat liberated in said OCM process;
(d) directing said product stream from said compressor into a separations unit that enriches said C 2 H 4 from said product stream using energy derived from said heat liberated in said OCM process; and
(e) directing H 2 and CO or CO 2 from said product stream from said separations unit into a methanation reactor that reacts said H 2 with said CO or CO 2 from said product stream to form CH 4 .
2. The method of claim 1 , wherein at least a portion of said C 2 H 6 that is cracked in (b) is produced in said OCM reactor.
3. The method of claim 1 , wherein at least portion of said ethane stream is from said separations unit.
4. The method of claim 1 , wherein said product stream comprises CO and CO 2 , and wherein at least a portion of said CO and CO 2 from said product stream is methanated in (e).
5. The method of claim 1 , wherein said separations unit enriches said C 2 H 4 or C 2+ compounds by removing CH 4 , H 2 , CO or CO 2 .
6. The method of claim 1 , wherein said cracking unit is integrated with said OCM reactor.
7. The method of claim 1 , wherein at least a portion of said CH 4 formed in (e) is returned to said OCM reactor.
8. The method of claim 1 , further comprising using a power generation unit in thermal communication with said OCM reactor to convert at least a portion of said heat liberated in said OCM process to power.
9. The method of claim 1 , wherein said product stream comprises C 2 H 6 and H 2 .
10. The method of claim 1 , wherein said methane in (a) and said C 2 H 6 from said ethane stream in (b) are derived from natural gas that is initially directed into said compressor in (c) or said separations unit in (d).
11. The method of claim 1 , wherein said methanation reactor has a methanation catalyst that converts CO and/or CO 2 into CH 4 at a selectivity for formation of CH 4 that is at least about 10-fold greater than a selectivity of said catalyst for formation of coke from said CO and/or CO 2 .
12. The method of claim 1 , wherein said inlet temperature is from about 460 ° C. to 600 ° C.
13. The method of claim 1 , wherein at least a portion of said CH 4 formed in (e) is returned to said OCM reactor through a heat exchanger.