Continuous process for converting natural gas to liquid hydrocarbons
An improved continuous process for converting methane, natural gas, or other hydrocarbon feedstocks into one or more higher hydrocarbons or olefins by continuously cycling through the steps of alkane halogenation, product formation (carbon-carbon coupling), product separation, and regeneration of halogen is provided. Preferably, the halogen is continually recovered by reacting hydrobromic acid with air or oxygen. The invention provides an efficient route to aromatic compounds, aliphatic compounds, mixtures of aliphatic and aromatic compounds, olefins, gasoline grade materials, and other useful products.
1. A continuous process for converting a hydrocarbon feedstock into one or more higher hydrocarbons, comprising:
(a) forming alkyl halides by reacting molecular halogen with a hydrocarbon feedstock containing methane, under process conditions sufficient to form alkyl halides and hydrogen halide, whereby substantially all of the molecular halogen is consumed;
(b) forming reproportionated alkyl halides by reacting some or all of the alkyl halides with an alkane feed, whereby the fraction of monohalogenated hydrocarbons present is increased;
(c) contacting the reproportionated alkyl halides with a first catalyst under process conditions sufficient to form higher hydrocarbons and additional hydrogen halide;
(d) separating the higher hydrocarbons from the hydrogen halide;
(e) regenerating molecular halogen by contacting the hydrogen halide with a second catalyst in the presence of a source of oxygen, under process conditions sufficient to form molecular halogen and water;
(f) separating the molecular halogen from water to allow reuse of the halogen; and
(g) repeating steps (a) through (f) a desired number of times.
2. A continuous process as recited in claim 1 , further comprising separating monohalogenated alkyl halides from polyhalogenated alkyl halides after steps (a) and/or (b).
3. A continuous process as recited in claim 1 , wherein the hydrocarbon feedstock comprises one or more C 1 - C 4 hydrocarbons.
4. A continuous process as recited in claim 1 , wherein the hydrocarbon feedstock comprises natural gas.
5. A continuous process as recited in claim 1 , wherein the halogen comprises bromine.
6. A continuous process as recited in claim 1 , wherein the halogen comprises chlorine.
7. A continuous process as recited in claim 1 , wherein the alkane feed contains at least 1% by volume of one or more C2-C5 hydrocarbons.
8. A continuous process as recited in claim 1 , wherein the amount of monohalogenated alkyl halide(s) present is increased in the presence of a reproportionation catalyst.
9. A continuous process as recited in claim 1 , wherein the reproportionation catalyst comprises a metal, metal-oxygen material, or metal halide.
10. A continuous process as recited in claim 1 , wherein the first catalyst comprises a zeolite.
11. A continuous process as recited in claim 10 , wherein the zeolite comprises a metal-doped or ion-exchanged zeolite.
12. A continuous process as recited in claim 10 , wherein the zeolite is doped with manganese.
13. A continuous process as recited in claim 1 , wherein the second catalyst comprises at least one material selected from the group consisting of CaO, CeO 2 , Co 3 O 4 , CuO, NiO, MgO, carbides, nitrides, carbons, and clays.
14. A continuous process as recited in claim 1 , wherein the second catalyst comprises CuO or CeO 2 .
15. A continuous process as recited in claim 1 , wherein the second catalyst comprises at least one material selected from the group consisting of halides, oxides, and oxyhalides of Ag, Au, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Ni, Pb, Pd, Pt, Sr, Ta, V, W, Mg, V, or Zn.
16. A continuous process as recited in claim 1 , wherein the hydrogen halide separated from the higher hydrocarbons comprises HBr and aqueous hydrobromic acid, and wherein HBr is separated from aqueous hydrobromic acid using pressure swing distillation or extractive distillation.
17. A continuous process as recited in claim 16 , wherein separation of the HBr from the aqueous hydrobromic acid comprises utilizing extractive distillation with an aqueous solution of CaBr 2 , MgBr 2 , KBr, NaBr, LiBr or mixtures thereof used as an extracting agent.
18. A continuous process as recited in claim 16 , wherein separation of the HBr from the aqueous hydrobromic acid comprises utilizing extractive distillation with sulfuric acid used as an extracting agent.
19. A continuous process as recited in claim 1 , wherein the alkane feed used for reproportionation comprises a hydrocarbon feed gas containing significant quantities of C2-C5 hydrocarbons.
20. A continuous process as recited in claim 1 , wherein the formation of alkyl halides and the formation of reproportionated alkyl halides are carried out in separate reactors.
21. A continuous process for converting a hydrocarbon feedstock into one or more higher hydrocarbons, comprising:
(a) forming alkyl halides by reacting molecular halogen with a hydrocarbon feedstock containing methane in a halogenation reactor, under process conditions sufficient to form alkyl halides and hydrogen halide, whereby substantially all of the molecular halogen is consumed;
(b) separating unreacted methane from the alkyl halides and directing it back into the halogenation reactor;
(c) forming reproportionated alkyl halides by reacting some or all of the alkyl halides with an alkane feed containing at least 1% by volume of C2-C5 hydrocarbons, whereby the fraction of monohalogenated hydrocarbons present is increased;
(d) contacting the reproportionated alkyl halides with a first catalyst under process conditions sufficient to form higher hydrocarbons and additional hydrogen halide;
(e) separating the higher hydrocarbons from the hydrogen halide;
(f) regenerating molecular halogen by contacting the hydrogen halide with a second catalyst in the presence of a source of oxygen, under process conditions sufficient to form molecular halogen and water;
(g) separating the molecular halogen from water to allow reuse of the halogen; and
(h) repeating steps (a) through (g) a desired number of times.
22. A continuous process as recited in claim 21 , wherein formation of alkyl halides and formation of reproportionated alkyl halides are carried out in separate reactors.