Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Reexamination Certificate
1996-09-24
2001-01-09
Langel, Wayne (Department: 1754)
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
C095S056000, C422S177000
Reexamination Certificate
active
06171574
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to generating hydrogen by catalytic steam reforming of methanol and similar fuels (hereafter referred to as “methanol-like fuels”, embracing methanol and carbon monoxide-containing gases, subject to the hydrogen-generating shift reaction later detailed) and purifying the hydrogen by its permeation through a selective membrane, being particularly directed to advances in linking the generation and permeation processes, utilizing preferably palladium-bearing membranes.
BACKGROUND
The demand for pure hydrogen is rapidly increasing in, for example, the electronics industry and further major growth is anticipated in the emerging market of low temperature fuel cells. Methanol, though more costly than natural gas, has a unique combination of characteristics as “hydrogen source”, including easy transportation, handling, safe and low cost storage. Methanol is thus particularly suited for on-site pure hydrogen generation by catalytic steam reforming. The well known catalytic carbon monoxide shift reaction is, presumably, a step in methanol-like fuel reforming, as later described. In general, carbon monoxide, with or without admixed hydrogen, such as is produced by partial oxidation of carbon (e.g. coal) or of methane, respectively, is a similar hydrogen source; carbon monoxide, as well as methanol itself, being subject to substantially higher conversions at much lower steam reforming temperatures than natural gas and other hydrocarbons; and they lend themselves to simpler energy efficiencies.
The prior art is replete with descriptions of steam reforming of methanol on a copper-bearing catalyst at ca. 150° C.-350° C., as illustrated, for example, in three publications by J. C. Amphlett and associates, entitled “Hydrogen Production by the Catalytic Steam Reforming of Methanol Parts 1, 2 & 3” [The Canadian Journal of Chemical Engineering, 59, 720-727 (1981); 63,, 605-611 (1985); and 66, 950-956 (1988) respectively], and in two publications by R. O. Idem and N. N. Bakhshi, entitled “Production of Hydrogen from Methanol. 1. & 2.” [Ind. Eng. Chem. Res. 33, 2047-2055 and 2056-2065, (1994)], incorporated herein by reference.
Generally, it is understood that methanol is first decomposed to carbon monoxide and hydrogen according to
CH
3
OH=CO+2H
2
(1)
followed by the also well-known carbon monoxide “shift” reaction with steam,
CO+H
2
O=CO
2
+H
2
(2)
resulting in the overall equation
CH
3
OH+H
2
O=CO
2
+3H
2
(3)
Unavoidably, some carbon monoxide remains unreacted. The temperature is maintained between about 150° C. and 350° C. to attain reasonable kinetics and catalyst endurance. Within this range, methanol conversion increases with temperature, but so also does carbon monoxide formation, up to as high as a few percent. As shown, for example, in the R. O. Idem et al publication (page 2061), with the stoichiometric 1:1 methanol/water feed, the carbon monoxide content is between 1.2 and 1.9% (12,000 to 19,000 ppm) at 250° C. with about 74% methanol conversion depending on the particular copper catalyst. Excess steam over the stoichiometric ratio of 1:1 increases the conversion and reduces the carbon monoxide content, but adds to the vaporization heat input. The excess steam effect is illustrated in Table 1 of an article by O. A. Belsey, C. M. Seymour, R. A. J. Dams and S. C. Moore [Electrochemical Engineering and the Environment 92, Hemisphere Publishing Corporation, page 52, 1992] which shows, with a water-to-methanol ratio of about 3.6, a conversion of 94.3% and 800 ppm of carbon monoxide at the low temperatures of 230° C. at the catalyst wall and 183-195° C. across the catalyst bed, and of 99.36% conversion and 4000 ppm of carbon monoxide at the high temperature of 300° C. at the wall and 195-235° C. across the bed. Similarly, copper-based low-temperature shift catalysts, such as described in “Heterogeneous Catalysis in Practice” by C. N. Satterfield, McGraw-Hill, Inc. pages 294-295 (1980), result in similar levels of carbon monoxide. To avoid excessive sintering, the copper-based catalysts should be operated below about 325° C., and preferably below about 300° C.
The prior art is also replete with descriptions of catalytic reactions coupled with selective hydrogen permeation across, among others, palladium alloy membranes. The following discussed citations are believed to be representative of the state-of-the-art in this area.
Reference is made, for example, to “Catalysis with Permselective Inorganic Membranes”, by J. N. Armor, a 25-page Review published by Elsevier Science Publishers B.V. in 1989; to an article entitled “Catalytic Palladium-based Membrane Reactors: A Review,” J. Shu, B. P. A. Grandjean, A. Van Neste and S. Kaliaguine, The Canadian Journal of Chemical Engineering, 69, 1036-1059 (1991); to an article entitled “Catalytic Inorganic-Membrane Reactors: Present Experience and Future Opportunities”, by G. Saracco and V. Specchia, CATAL. REV. - SCI. ENG., 36 (2), 305-384 (1994); and to yet another review entitled “Current hurdles to the success of high-temperature membrane reactors”, by G. Saracco, G. F. Versteeg and W. P. M. Swaaj, J. of Membrane Science, 95, 105-123 (1994), all incorporated herein by reference. The emphasis in the above cited art has been on enhancing hydrogenation and dehydrogenation reactions.
Reference is also made to U.S. Pat. No. 4,810,485 to Marianowski et al., which describes broadly in situ hydrogen production and membrane purification, naming hydrocarbon steam reforming reactions “such as reforming of methane, propane, ethane, methanol, natural gas and refinery gas; water-gas shift reactions; and carbonaceous material gasification reactions, such as gasification of coal, peat and shale” (Col. 2, 1.60-65); and metallic membrane foils, stating that “suitable metals include palladium, nickel, cobalt, iron, ruthenium, rhodium, osmium, iridium, platinum titanium, zirconium, hafnium, vanadium, niobium, tantalum, copper , silver and gold and alloys thereof, particularly palladium, copper nickel and palladium silver alloys.” (Col. 3,1.57-62). The patentees further state that “foils of copper, nickel and mixtures thereof are particularly preferred - - - ”, and speculations are offered limited to high temperatures above 1000° F. or 538° C. and to membrane thicknesses of 0.0001 and 0.001 inch. There is no teaching in this patent or even a hint of the ruinous flux deterioration and the potentially catastrophic carbon monoxide poisoning described more fully hereinafter, which occur at the much lower temperatures with which the present invention is concerned and which have, surprisingly, been solved thereby. Moreover, with the exception of palladium-bearing membranes, the patentees membranes made of other metals are useless for the purposes of the present invention, including their preferred copper and nickel membranes, which are impermeable to hydrogen at the relatively low temperatures of the present invention.
As later more fully explained, the present invention is concerned with linking steam reforming of a methanol-like fuel to pure hydrogen generation by permeation through selective membranes, a concept that differs radically from mere prior art coupling hydrogenation and/or dehydrogenation with such membranes. By way of explanation, as illustrated generically in
FIG. 11
, page 1051 of the J. Shu et al publication, either pressurized hydrogen is permeated from the “upstream” across the membrane into the “downstream”, where it hydrogenates the reactant in the presence or absence of a catalyst; or, in dehydrogenation, hydrogen is extracted upstream from the reactant, also in the presence or absence of a catalyst, and permeated to the downstream side, where it becomes merely an impurity in a sweep gas.
In neither case, however, is pure hydrogen generated downstream, at a usable (i.e. at least atmospheric) pressure, by permeation from its mixture with the much heavier carbon oxides and steam upstream; the
Juda Walter
Krueger Charles W.
Langel Wayne
Rines and Rines
Walter Juda Associates, Inc.
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