Oxidative coupling of methane systems and methods
Systems and methods conducive to the formation of one or more alkene hydrocarbons using a methane source and an oxidant in an oxidative coupling of methane (OCM) reaction are provided. One or more vessels each containing one or more catalyst beds containing one or more catalysts each having similar or differing chemical composition or physical form may be used. The one or more catalyst beds may be operated under a variety of conditions. At least a portion of the catalyst beds may be operated under substantially adiabatic conditions. At least a portion of the catalyst beds may be operated under substantially isothermal conditions.
1. A method for generating hydrocarbons having two or more carbon atoms (C 2+ hydrocarbons), comprising:
(a) providing a methane source and an oxidant source;
(b) directing methane from said methane source and an oxidant from said oxidant source into a reaction unit, wherein said reaction unit comprises a catalyst bed that includes at least one oxidative coupling of methane (OCM) catalyst that facilitates an OCM reaction using said methane and said oxidant, wherein said at least one OCM catalyst is a nanostructured catalyst, and wherein said catalyst bed has an inlet zone that is contacted by a bulk gas mixture formed upon entry of said methane from said methane source and said oxidant from said oxidant source into said reaction unit; and
(c) in said reaction unit, conducting said OCM reaction using said methane and said oxidant to generate said C 2+ hydrocarbons under conditions that are selected to:
a. maintain a thermal profile across said catalyst bed during said OCM reaction, which thermal profile is characterized by (i) a temperature of said inlet zone being less than 550° C., and (ii) a maximum temperature within said catalyst bed being greater than about 800° C.;
b. maintain a pressure within said reaction unit greater than about 15 pounds per square inch gauge (psig); and
c. maintain said OCM reaction within said catalyst bed at a methane conversion of at least about 6% and a C 2+ hydrocarbon selectivity of at least about 40%.
2. The method of claim 1 , wherein said conditions are selected to maintain said OCM reaction within said catalyst bed under substantially adiabatic conditions.
3. The method of claim 1 , wherein said conditions are selected to maintain said OCM reaction at a C 2+ hydrocarbon selectivity of at least about 50%.
4. The method of claim 1 , further comprising maintaining said methane source at a temperature of at least about 400° C. using at least one heat transfer unit thermally coupled to said methane source.
5. The method of claim 1 , further comprising maintaining said oxidant source at a temperature of at least about 400° C. using at least one heat transfer unit thermally coupled to said oxidant source.
6. The method of claim 1 , further comprising maintaining said methane source at a temperature of at most about 600° C. using at least one heat transfer unit thermally coupled to said methane source.
7. The method of claim 1 , wherein said OCM reaction is maintained at a methane conversion of at least about 10%.
8. The method of claim 1 , wherein said reaction unit comprises a plurality of serially coupled vessels, wherein each of said serially coupled vessels includes at least one catalyst bed, and wherein said method further comprises (i) operating said catalyst bed in each of said plurality of serially coupled vessels under substantially adiabatic conditions and (ii) maintaining said OCM reaction at a C 2+ hydrocarbon selectivity of at least 50% within said catalyst bed in each of said plurality of serially coupled vessels.
9. The method of claim 8 , further comprising using a thermal transfer unit located upstream of a given vessel among said plurality of serially coupled vessels to maintain a bulk gas temperature of at most about 700° C. in an inlet zone of said given vessel.
10. The method of claim 8 , further comprising, using at least one thermal adjustment unit fluidly coupled between a first vessel and a second vessel of said plurality of serially coupled vessels, said first vessel being upstream of said second vessel, performing at least one of (i) removing a portion of an OCM product stream comprising said C 2+ hydrocarbons from said first vessel and directing a remainder of said OCM product stream to said second vessel, (ii) directing said methane or said oxidant to said second vessel, and (iii) transferring heat from said OCM product stream to a coolant.
11. The method of claim 1 , further comprising conducting said OCM reaction using said methane and said oxidant to generate said C 2+ hydrocarbons under conditions that are selected to maintain said pressure within said reaction unit greater than about 30 pounds per square inch gauge (psig).
12. The method of claim 1 , further comprising conducting said OCM reaction using said methane and said oxidant to generate said C 2+ hydrocarbons under conditions that are selected to maintain said pressure within said reaction unit greater than about 45 pounds per square inch gauge (psig).
13. The method of claim 1 , further comprising adjusting a proportion between a concentration of said methane and a concentration of said oxidant in said inlet zone to provide a ratio between said methane and said oxidant in said inlet zone such that said oxidant acts as a limiting reagent.
14. The method of claim 1 , further comprising measuring a temperature of said catalyst bed using a temperature sensor positioned within said catalyst bed.
15. The method of claim 1 , wherein said thermal profile across said catalyst bed has a maximum temperature within said catalyst bed of less than about 900° C.
16. The method of claim 2 , wherein said thermal profile is further characterized by a temperature increase across said catalyst bed of greater than about 200° C.
17. The method of claim 1 , wherein said nanostructured catalyst is selected from the group consisting of a metal oxide, a metal hydroxide, a perovskite, a metal oxyhydroxide, a metal oxycarbonate, a metal carbonate, a metal element from any of Groups 1 through 7, a lanthanide, and an actinide.
18. The method of claim 1 , wherein said nanostructured catalyst comprises at least one metal dopant that provides said C 2+ hydrocarbon selectivity of at least about 40%.
19. The method of claim 1 , wherein said methane source has a temperature that is less than about 600° C.
20. The method of claim 1 , wherein said temperature of said inlet zone is less than 500° C.