Gas: heating and illuminating – Processes – Manufacture from methane
Reexamination Certificate
1999-11-03
2003-06-17
Johnson, Jerry D. (Department: 1764)
Gas: heating and illuminating
Processes
Manufacture from methane
C048S198200, C048S198700, C048SDIG005, C422S186220, C422S198000, C422S211000, C422S236000, C422S240000, C095S051000, C096S014000
Reexamination Certificate
active
06579331
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a membrane process and system for the purification of a fuel, e.g., hydrocarbon, gasoline, diesel, methanol, ethanol or natural gas, to hydrogen for fuel cells. The purification process selectively reomves CO
2
from the reformed product thereby enriching the reformed product in H
2
and increasing the H
2
/CO
2
ratio. This invention also relates to a polymer composition suitable for forming a membrane that is useful for separating CO
2
from a CO
2
-containing gas stream in the purification process. The present invention is particularly useful when the process is carried-out on-board a vehicle using a fuel cell for transportation.
BACKGROUND OF THE INVENTION
Reforming of a fuel, e.g., hydrocarbon, gasoline, diesel, methanol, ethanol or natural gas, to hydrogen is generally proceeded with the formation of the synthesis gas of CO and H
2
first. For example, steam reforming of methanol with a NiO/Al
2
O
3
catalyst at 300-400° C. (T. B. Su and M. H. Rei,
J. Chin. Chem. Soc
. (Taipei), 38, 535 (1991)) gives the synthesis gas:
CH
3
OH→CO+2H
2
(1)
Steam reforming of CH
4
with a nickel-based catalyst at 800° C. is:
CH
4
+H
2
O→CO+3H
2
(2)
Partial oxidation of CH
4
is:
CH
4
+½O
2
→CO+2H
2
(3)
Similarly, partial oxidation of other hydrocarbons, e.g., gasoline and diesel, produces the synthesis gas:
C
n
H
2n+2
+{fraction (n/2)}O
2
→n CO+(n+1)H
2
(4)
where n is an integer. In the partial oxidation, the synthesis gas produced does not contain N
2
when O
2
is used. If air is used instead of O
2
, the synthesis gas produced contains N
2
.
The synthesis gas is then sent conventionally to two-stage water gas shifters, in which CO is converted to CO
2
via the water gas shift reaction:
CO+H
2
O→CO
2
+H
2
(5)
Typically, the first-stage shifter operates at higher temperature than the second- stage shift, e.g., 373° C. for the first stage and 225° C. for the second stage. For the water gas shift reaction, CuO/ZnO/Al
2
O
3
catalysts can be used. The product gas from steam reforming of methanol under the optimum conditions at 1 atm and 227° C. with a water rich feed (water/methanol =1.5) contains approximately 66% H
2
, 21% CO
2
, 1% CO, and 12%,H
2
O (J. C. Amphlett, M. J. Evans, R. A. Jones, R. F. Mann, and R. D. Weir,
Can. J. Chem. Eng
., 59, 720 (1981)).
In some reforming cases, such as the steam reforming of methanol with a CuO/ZnO/Al
2
O
3
catalyst, methanol is converted directly and predominantly to CO
2
and H
2
:
This reaction operates at temperatures lower than 260° C. with methanol conversion as high as 90%; however, trace CO appears at temperatures above 300° C. and high methanol conversions of about 90% (C. J. Jiang, D. L. Trimm, and M. S. Wainwright,
Appl. Catal. A
, 93, 245 (1993)).
Japanese Patents 04,321,502 and 04,325,402 claim processes employing H
2
-selective membranes, which selectively pass H
2
and reject other gases, for hydrogen manufacture for fuel cells. However, these processes suffer from a low pressure for the H
2
product gas which is much lower than the pressure for the feed gas. Thus, a compressor is needed to compress the product gas to the pressure of the feed gas. In addition, these processes also usually have other shortcomings, such as low H
2
recovery, large membrane areas, and a high CO
2
concentration in the product gas.
It is an object of the present invention to provide a CO
2
-selective membrane process that selectively passes CO
2
over H
2
and other gases and that is useful for the purification and/or water gas shift reaction of a reformed gas, generated from reforming of a fuel, e.g., hydrocarbon, gasoline, diesel, methanol, ethanol or natural gas, to hydrogen for fuel cells. This CO
2
-selective membrane process can be more advantageous than H
2
-selective membrane processes in terms of H
2
product pressure (to avoid the need of a compressor for the product gas), H
2
recovery, membrane area, and CO
2
concentration. Another object of the present invention is to provide a novel polymer composition that is suitable in formation of a membrane useful for the CO
2
-selective membrane process. Membranes disclosed in U.S. Pat. No. 5,611,843 may also be used for the CO
2
selective membrane process.
SUMMARY OF THE INVENTION
The present invention is a process and system to purify a fuel feedstream so that the feedstream is enriched in H
2
. In general, the process includes the steps of reforming the feedstream, and separating CO
2
with a membrane that selectively removes CO
2
from the feedstream. For most fuel feedstreams, a step of water gas shift reaction is also included in the process. The CO
2
selectively permeable membrane may also be used to perform both steps of enhancing water gas shift reaction and separating CO
2
. The process further comprises the step of methanating the H
2
-enriched feedstream.
If the fuel feedstream is methanol, then a water gas shift reaction step is not necessary. In this embodiment, the CO
2
selectively permeable membrane may be used to perform both steps of reforming and separating.
In a preferred embodiment, the process is carried-out on board a vehicle that uses a fuel cell for transportation.
Another embodiment of the present invention is directed toward a composition comprising a hydrophilic polymer and at least one ammonium halide salt, the ammonium halide salt being present in an amount ranging from about 10 to about 80 wt % based on the total weight of the composition. The composition is suitable in formation of a membrane useful for separating CO
2
from a CO
2
-containing gas, particularly from an on-board reformed gas for the CO
2
-selective membrane process.
The embodiments of the present invention will become apparent upon a reading of the brief description of the drawings and the detailed description of the invention which follow.
REFERENCES:
patent: 3765946 (1973-10-01), Werner et al.
patent: 4117079 (1978-09-01), Bellows
patent: 4238468 (1980-12-01), Bonacci et al.
patent: 4921765 (1990-05-01), Gmeindl et al.
patent: 5611843 (1997-03-01), Ho
patent: 19600954 (1996-07-01), None
patent: 0311903 (1989-04-01), None
patent: 0729196 (1996-08-01), None
ExxonMobil Research and Engineering Company
Hantman Ronald D.
Johnson Jerry D.
Ridley Basia
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