Processes and systems for reforming of methane and light hydrocarbons to liquid hydrocarbon fuels
Processes for converting methane and/or other hydrocarbons to synthesis gas (i.e., a gaseous mixture comprising H 2 and CO) are disclosed, in which at least a portion of the hydrocarbon(s) is reacted with CO 2 . At least a second portion of the methane may be reacted with H 2 O (steam), thereby improving overall thermodynamics of the process, in terms of reducing endothermicity (ΔH) and the required energy input, compared to “pure” dry reforming in which no H 2 O is present. Such dry reforming (reaction with CO 2 only) or CO 2 -steam reforming (reaction with both CO 2 and steam) processes are advantageously integrated with Fischer-Tropsch synthesis to yield liquid hydrocarbon fuels. Further integration may involve the use of a downstream finishing stage involving hydroisomerization to remove FT wax. Yet other integration options involve the use of combined CO 2 -steam reforming and FT synthesis stages (optionally with finishing) for producing liquid fuels from gas streams generated in a number of possible processes, including the hydropyrolysis of biomass.
1. A process for producing C 4 + hydrocarbons, the process comprising:
(a) in a reforming stage, contacting a gaseous mixture comprising methane and CO 2 with a reforming catalyst to produce a synthesis gas product; and
(b) converting H 2 and CO in the synthesis gas product to hydrocarbons, including the C 4 + hydrocarbons, provided in a Fischer-Tropsch (FT) product of an FT reactor,
wherein the FT product further comprises unconverted H 2 and CO, in addition to C 1 -C 3 hydrocarbons,
the process further comprising:
(c) without separating the FT product, feeding the FT product, including the C 4 + hydrocarbons, unconverted H 2 and CO, and C 1 -C 3 hydrocarbons, to a finishing reactor to convert normal C 20 + hydrocarbons in a wax fraction of the FT product to C 4 -C 19 hydrocarbons,
wherein no supplemental source of hydrogen is added to the finishing reactor.
2. The process of claim 1 , wherein step (b) is carried out with an FT feed having a substantially same molar H 2 :CO ratio as in the synthesis gas product, produced in step (a).
3. The process of claim 1 , wherein, prior to step (b), water is condensed from the synthesis gas product, produced in step (a).
4. The process of claim 1 , wherein at least about 75% of the normal C 20 + hydrocarbons in the wax fraction of the FT product are converted in the finishing reactor to normal or branched C 4 -C 19 hydrocarbons, provided in a hydroisomerization/hydrocracking product of the finishing reactor.
5. The process of claim 1 , wherein the gaseous mixture further comprises H 2 O and step (a) is carried out in a CO 2 -steam reforming reactor at a temperature from about 677° C. (1250° F.) to about 788° C. (1450° F.), a gauge pressure from about 0 kPa (0 psig) to about 517 kPa (75 psig), and a weight hourly space velocity (WHSV) from about 0.1 hr −1 to about 2.5 hr −1 .
6. The process of claim 4 , wherein the hydroisomerization/hydrocracking product comprises less than about 1 wt-% hydrocarbons that are solid at room temperature.
7. The process of claim 1 , wherein the finishing reactor comprises a dewaxing catalyst having hydroisomerization and/or hydrocracking activity with respect to normal C 20 + hydrocarbons.
8. The process of claim 7 , wherein the dewaxing catalyst comprises a dewaxing active metal deposited on a solid acidic support.
9. The process of claim 8 , wherein the dewaxing active metal is selected from Group 13 or Group 14 of the Periodic Table.
10. The process of claim 9 , wherein the dewaxing active metal is gallium.
11. The process of claim 8 , wherein the acidic support is a zeolitic or non-zeolitic molecular sieve having at least about 15 mmol/gram of acid sites, measured by temperature programmed desorption (TPD) of ammonia.
12. The process of claim 11 , wherein the acidic support is a zeolitic molecular sieve having a silica to alumina molar framework ratio of less than about 50.
13. The process of claim 12 , wherein the zeolitic molecular sieve is ZSM-5.
14. The process of claim 1 , wherein the finishing reactor is at a temperature from about 232° C. (450° F.) to about 399° C. (750° F.).
15. The process of claim 1 , wherein at least a portion of the gaseous mixture comprises a hydrocarbon-containing feedstock component selected from the group consisting of a hydropyrolysis gaseous mixture, natural gas comprising CO 2 , biogas obtained from bacterial digestion of organic waste, a hydrogen-depleted PSA tail gas, or a gaseous effluent from a bacterial fermentation stage.
16. The process of claim 9 , wherein the metal selected from Group 13 or Group 14 of the Periodic Table is present in an amount from about 0.1 wt-% to about 3 wt-%, based on the weight of the dewaxing catalyst.
17. The process of claim 16 , wherein the dewaxing catalyst comprises from about 0.1 wt-% to about 3 wt-% gallium, and the solid acidic support comprises ZSM-5.
18. The process of claim 1 , wherein the finishing reactor is incorporated into the FT reactor.
19. The process of claim 18 , wherein a bed of finishing catalyst is positioned downstream of a bed of FT catalyst, within a single vessel.
20. The process of claim 1 , wherein the FT product is maintained in the vapor phase from an outlet of the FT reactor to an inlet of the finishing reactor.