Efficient oxidative coupling of methane processes and systems
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 generating at least one product stream comprising compounds with two or more carbon atoms (C 2+ compounds), comprising:
(a) selecting a plurality of operating conditions to perform a process comprising (i) conducting at least one OCM reaction to generate said C 2+ compounds and one or more alkanes, (ii) generating one or more alkenes, including ethylene (C 2 H 4 ), from at least a subset of said one or more alkanes, and (iii) generating said at least one product stream comprising said C 2+ compounds and said one or more alkenes, wherein said plurality of operating conditions is selected such that said process generates said at least one product stream at a carbon efficiency of at least about 0.50;
(b) conducting said at least one OCM reaction to generate said C 2+ compounds and said one or more alkanes, wherein said C 2+ compounds comprise ethylene (C 2 H 4 ) and said at least one OCM reaction liberates heat, and wherein said at least one OCM reaction is performed using at least a subset of said plurality of operating conditions selected in (a);
(c) generating said one or more alkenes, including said C 2 H 4 , from at least a subset of said one or more alkanes using at least a portion of said heat liberated in said at least one OCM reaction, to increase a concentration of said C 2 H 4 , thereby providing an effluent stream comprising said C 2+ compounds and said one or more alkenes, wherein said one or more alkenes are generated using at least a subset of said plurality of operating conditions selected in (a); and
(d) generating said at least one product stream comprising said C 2+ compounds and said one or more alkenes, wherein said at least one product stream is generated using at least a subset of said plurality of operating conditions selected in (a).
2. The method of claim 1 , wherein said at least one OCM reaction is conducted in an OCM unit, and wherein said one or more alkenes are generated in at least one cracking unit downstream of and in fluidic communication with said OCM unit.
3. The method of claim 2 , wherein (c) further comprises directing at least one additional feed stream external to said OCM unit directly into said at least one cracking unit, wherein said at least one additional feed stream comprises ethane (C 2 H 6 ).
4. The method of claim 2 , wherein said at least one cracking unit is separate from and in thermal communication with said OCM unit.
5. The method of claim 2 , wherein said at least one cracking unit is integrated with said OCM unit.
6. The method of claim 2 , wherein said C 2+ compounds and said one or more alkanes are directed into said at least one cracking unit without passing through a separations unit.
7. The method of claim 2 , wherein said OCM unit is operated substantially adiabatically.
8. The method of claim 2 , wherein said at least one cracking unit is operated substantially adiabatically.
9. The method of claim 2 , wherein at least a portion of said C 2+ compounds and said one or more alkanes are directed into a treatment unit prior to being directed into said at least one cracking unit.
10. The method of claim 2 , wherein said OCM unit comprises a plurality of OCM reactors, each comprising at least one OCM catalyst that facilitates said at least one OCM reaction.
11. The method of claim 2 , wherein each of said at least one cracking unit comprises a plurality of cracking vessels which cracks ethane (C 2 H 6 ) with the aid of said heat liberated in said at least one OCM reaction, thereby increasing said concentration of said ethylene (C 2 H 4 ) in said effluent stream.
12. The method of claim 1 , wherein said one or more alkanes comprise ethane (C 2 H 6 ).
13. The method of claim 1 , further comprising directing said effluent stream into a compressor, which compressor increases a pressure of said effluent stream with the aid of at least a portion of said heat liberated in said at least one OCM reaction.
14. The method of claim 1 , wherein said generating in (d) further comprises directing said effluent stream into a separations unit, wherein said separations unit enriches said C 2 H 4 from said effluent stream by removing hydrogen (H 2 ), carbon monoxide (CO) or carbon dioxide (CO 2 ) from said effluent stream.
15. The method of claim 14 , wherein said separations unit reacts said C 2 H 4 from said effluent stream to yield compounds comprising three or more carbon atoms (C 3+ compounds).
16. The method of claim 14 , wherein said generating in (d) further comprises using a methanation reactor in fluidic communication with said separations unit to react said H 2 with said CO or said CO 2 to form methane (CH 4 ).
17. The method of claim 16 , wherein at least a portion of said CH 4 is returned to said OCM unit.
18. The method of claim 16 , wherein said methanation reactor comprises at least one methanation catalyst that converts CO and/or CO 2 into CH 4 at a selectivity for the formation of CH 4 that is at least about 10-fold greater than a selectivity of the catalyst for formation of coke from the CO and/or CO 2 .
19. The method of claim 16 , wherein at least 90% of energy used to perform (c) through (d) is derived from said heat liberated from said at least one OCM reaction.
20. The method of claim 2 , wherein an inlet temperature of said OCM unit is at most about 600° C.
21. The method of claim 1 , further comprising using a power generation unit in thermal communication with said OCM unit to generate power from at least a portion of said heat liberated in said at least one OCM reaction.
22. The method of claim 1 , further comprising directing (1) said one or more alkanes and (2) said at least said portion of said heat liberated in said at least one OCM reaction to a reactor, and generating said one or more alkenes in (c) in said reactor.
23. The method of claim 22 , wherein said at least one OCM reaction is performed in an OCM reactor, which OCM reactor is upstream of said reactor that generates said one or more alkenes.