HYDROGEN SEPARATION PROCESS

US 2008 350A1

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A method for separating a hydrogen-rich product stream from a feed stream comprising hydrogen and at least one carbon-containing gas, comprising feeding the feed stream, at an inlet pressure greater than atmospheric pressure and a temperature greater than 200° C., to a hydrogen separation membrane system comprising a membrane that is selectively permeable to hydrogen, and producing a hydrogen-rich permeate product stream on the permeate side of the membrane and a carbon dioxide-rich product raffinate stream on the raffinate side of the membrane. A method for separating a hydrogen-rich product stream from a feed stream comprising hydrogen and at least one carbon-containing gas, comprising feeding the feed stream, at an inlet pressure greater than atmospheric pressure and a temperature greater than 200° C., to an integrated water gas shift/hydrogen separation membrane system wherein the hydrogen separation membrane system comprises a membrane that is selectively permeable to hydrogen, and producing a hydrogen-rich permeate product stream on the permeate side of the membrane and a carbon dioxide-rich product raffinate stream on the raffinate side of the membrane. A method for pretreating a membrane, comprising: heating the membrane to a desired operating temperature and desired feed pressure in a flow of inert gas for a sufficient time to cause the membrane to mechanically deform; decreasing the feed pressure to approximately ambient pressure; and optionally, flowing an oxidizing agent across the membrane before, during, or after deformation of the membrane. A method of supporting a hydrogen separation membrane system comprising selecting a hydrogen separation membrane system comprising one or more catalyst outer layers deposited on a hydrogen transport membrane layer and sealing the hydrogen separation membrane system to a porous support.

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Claims

1. A method for separating a hydrogen-rich product stream from a feed stream comprising hydrogen and at least one carbon-containing gas, the method comprising:
feeding the feed stream, at an inlet pressure greater than atmospheric pressure and a temperature greater than 200° C., to a hydrogen separation membrane system comprising a membrane that is selectively permeable to hydrogen, and producing a hydrogen-rich permeate product stream on the permeate side of the membrane and a carbon dioxide-rich product raffinate stream on the raffinate side of the membrane.

Show 49 dependent claims

51. A method for pretreating a membrane, comprising:
(a) heating the membrane to a desired operating temperature and desired feed pressure in a flow of inert gas for a sufficient time to cause the membrane to mechanically deform;
(b) decreasing the feed pressure to approximately ambient pressure; and optionally,
(c) flowing an oxidizing agent across the membrane before, during, or after deformation of the membrane.

Show 9 dependent claims

61. A method of supporting a hydrogen separation membrane system comprising selecting a hydrogen separation membrane system comprising one or more catalyst outer layers deposited on a hydrogen transport membrane layer and sealing the hydrogen separation membrane system to a porous support.

Description

This application claims benefit from provisional application Ser. No. 60/765,524 filed Feb. 6, 2006, which is hereby incorporated herein by reference in its entirety for all purposes as if reproduced in full below.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of DOE Contracts No. DE-FC26-00NT40762, DE-FC26-05NT42469, DE-FG02-04ER83934, DE-FG02-04ER83935, and DE-FG02-05ER84199 awarded by the Department of Energy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates to a method of separating hydrogen from a hydrogen-containing stream using a hydrogen separation membrane system. More particularly, this disclosure relates to a method of separating a stream consisting essentially of hydrogen from impure hydrogen streams at temperatures greater than about 200° C. through the employment of a hydrogen separation membrane system.

2. Background of the Invention

Methods of producing hydrogen and carbon monoxide include steam reforming, gasification, or partial oxidation of natural gas, petroleum, coal, biomass, and municipal waste. Production of hydrogen from these sources is accompanied by production of carbon dioxide, carbon monoxide, and other gases. It is highly desired to separate hydrogen from these side-products and gaseous contaminants.

One currently used well-known and established method to separate H2 from impurities (i.e., other gases) is Pressure Swing Adsorption (PSA). PSA uses multiple beds, usually two or more, of solid adsorbent to separate impure H2 streams into a very pure (99.9%) high pressure product stream and a low pressure tail gas stream containing the impurities and some of the hydrogen. For example, synthesis gas (H2 and CO) may be introduced into one bed wherein everything but the hydrogen is adsorbed onto the adsorbent bed. Ideally, just before complete loading, this adsorbent bed is switched offline and a second adsorbent bed is placed online. The pressure on the loaded bed is subsequently reduced, which liberates the raffinate (in this case largely CO2) at low pressure. A percentage of the inlet hydrogen, typically 10 to 20 percent, is lost in the tail gas. Greater recovery means more CO2 and CO in the H2 product stream.

PSA is currently generally the first choice for steam reforming H2 plants because of its combination of high purity, modest cost, and ease of integration into the hydrogen plant. It is often used for purification of refinery off gases, where it competes with other kinds of membrane systems. One of the major disadvantages of this type system is that it operates at about 38° C. (100° F.). This entails a loss of thermal efficiency because the entire gas stream must be cooled prior to introduction into the pressure swing adsorption beds.

As the earth continues to warm, focus has been placed on effective methods for capturing and sequestering CO2 (a greenhouse gas) which has theoretically been linked to this warming trend. PSA is not advantageous from this standpoint, because the raffinate (i.e. tail gas) is produced at low pressure. Thus, if CO2 is to be captured from the system, large amounts of CO2 must be compressed from nearly atmospheric pressure to greater than 1000 psig. This compression from atmospheric pressure to 1000 psi can consume about 1/7th the total energy of the feed (e.g., coal). The critical pressure needed to liquefy CO2 for convenient transport and sequestration is 73.9 bar (1071 psi). Pressures well in excess of this (greater than 2000 psi) are required, however, to force the CO2 into oil wells or other underground storage sites.

Another disadvantage of PSA is that low raffinate pressure essentially limits the system to a single stage of water gas shift, WGS, which is often used to convert CO to CO2 and to produce additional hydrogen from synthesis gas streams. Limiting a hydrogen separation system to a single stage of WGS decreases the amount of CO conversion as well as the H2 recovery. PSAs are also undesirable compared to filters and membranes, due to mechanical complexity, which leads to higher capital and operating expenditures and, potentially, increased downtime.

Accordingly, an ongoing need exists for a process to separate hydrogen that does not require cooling of the feed stream prior to separation and decreases or eliminates compression requirements of separation products.

BRIEF SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS

Disclosed herein is a method for separating a hydrogen-rich product stream from a feed stream comprising hydrogen and at least one carbon-containing gas, the method comprising: feeding the feed stream, at an inlet pressure greater than atmospheric pressure and a temperature greater than 200° C., to a hydrogen separation membrane system comprising a membrane that is selectively permeable to hydrogen, and producing a hydrogen-rich permeate product stream on the permeate side of the membrane and a carbon dioxide-rich product raffinate stream on the raffinate side of the membrane. The method may be used to produce a hydrogen-rich permeate product stream that is greater than 99% by volume hydrogen. In embodiments, the carbon dioxide-rich raffinate product stream has a pressure greater than 400 psig. Suitable membranes for carrying out the method are also disclosed. In embodiments, the membrane is a composite membrane comprising a hydrogen transport layer. The membrane may further comprise one or more outer catalyst layers. The hydrogen transport layer may be acid etched prior to deposition of the one or more catalyst outer layers thereon. In some embodiments, the membrane is a three layer membrane comprising a hydrogen transport layer, a hydrogen dissociation catalyst outer layer on the raffinate side of the membrane and a hydrogen desorption catalyst outer layer on the permeate side of the membrane. In embodiments, the hydrogen dissociation catalyst outer layer and the hydrogen desorption catalyst outer layer comprise different materials. In embodiments, the hydrogen dissociation catalyst outer layer and the hydrogen desorption catalyst outer layer comprise different thicknesses. In embodiments, the hydrogen dissociation catalyst outer layer and the hydrogen desorption catalyst outer layer comprise different materials and different thicknesses.

In some embodiments, the membrane has a total thickness of from about 50 micrometers to about 1000 micrometers. The one or more catalyst outer layers may have thicknesses of from about 1 nm to 1500 nm. The hydrogen transport layer may comprise a metal selected from the group consisting of V, Nb, Ta, Zr and alloys thereof. Optionally, the hydrogen transport layer may comprise a material selected from the group consisting of cermets and proton conducting ceramics. A suitable hydrogen transport layer comprises about 90% V and about 10% Ni. The at least one outer catalyst layer may comprise a metal selected from the group consisting of Pd and alloys thereof, such as alloys of palladium with a metal selected from the group consisting of Ag, Cu, Au and Pt. In embodiments, the outer catalyst layer retains catalytic activity for feed streams comprising up to 20 ppm S. In embodiments, the membrane has a selectivity to hydrogen of greater than 99%.

The feed stream comprising hydrogen and at least one carbon-containing gas from which a hydrogen-rich product stream is separated via the disclosed method may comprise hydrogen and carbon dioxide and, in some embodiments, the hydrogen recovery is greater than 70% by volume. Alternatively, the hydrogen recovery is greater than 90% by volume. The feed stream will often, of course, comprise other gases, such as carbon monoxide and water (steam). At least one component of the feed stream may be separated out of the feed stream prior to feeding the feed stream to the hydrogen separation membrane system. Components removed from the feed stream prior to introduction to the hydrogen separation membrane system may be selected from surface catalyst poisons and water, for example.

The feed stream may be a water gas shift reaction mixture comprising hydrogen, carbon monoxide and carbon dioxide. The carbon dioxide-rich product raffinate stream may feed into a water gas shift reactor. If desirable, the carbon dioxide-rich product raffinate stream may be recycled to the hydrogen separation membrane system.

In some variations of the method, the hydrogen separation membrane system has a hydrogen flux through the membrane of greater than 20 mL/min/cm2 at standard temperature and pressure. Some embodiments exhibit a hydrogen flux through the membrane of greater than 50 mL/min/cm2 at standard temperature and pressure.

The hydrogen-rich permeate product stream has a hydrogen partial pressure of at least 20 psig, and the carbon dioxide-rich raffinate product stream has a total pressure of at least 200 psig in certain embodiments. The operating temperature of the hydrogen separation system may be in the range from about 200° C. to about 500° C. The operating temperature range may be from about 300° C. to about 400° C.

The membrane system is sometimes operated in the range of from about 300 psig to about 1000 psig and the pressure on the permeate side of the membrane is in the range of from about 0 psig to about 1000 psig. In alternative embodiments, the membrane system is operated in the range of from about 300 psig to about 1000 psig and the pressure on the permeate side of the membrane is in the range of from about 100 psig to about 500 psig. In some embodiments, where the pressure on the permeate side of the membrane is greater than 100 psig, the hydrogen flux through the membrane is greater than 20 mL/min/cm2.

The hydrogen separation membrane system of the present disclosure may not require a permeate side sweep gas. Sometimes, however, especially when the product is to be combusted, an inert permeate side sweep gas is employed.

In embodiments, the method comprises feeding the carbon dioxide-rich product raffinate stream to a second hydrogen separation membrane system comprising a second membrane that is selectively permeable to hydrogen, and producing a second hydrogen-rich permeate product stream on a permeate side of the second membrane and a second carbon dioxide-rich product raffinate stream on a raffinate side of the second membrane. Still further, the second carbon dioxide-rich product raffinate stream may be further processed in a third hydrogen separation membrane system comprising a third membrane that is selectively permeable to hydrogen.

The feed stream comprising hydrogen and at least one carbon-containing gas may be obtained by reacting a carbonaceous feed with an oxidant to produce a first product stream comprising hydrogen and carbon monoxide at a pressure of above 200 psig; and reacting the first product stream with a water-containing stream to produce the feed stream, wherein the feed stream comprises hydrogen, carbon monoxide and carbon dioxide at a temperature of from about 200° C. to about 500° C. The carbonaceous feed may be selected from the group consisting of: natural gas, coal, petroleum coke, biomass and petroleum derived liquid fuel. Also disclosed herein is a method of integrating a water gas shift and hydrogen separation systems wherein a water gas shift reaction used in the production of the feed stream is integrated in a unit whereby reacting the first product stream with a water-containing stream to produce the feed stream and feeding the feed stream, at a pressure above atmospheric pressure, to a hydrogen separation membrane system are carried out in a singular reactor. The method integrating the WGSR and the hydrogen separation may enable conversion of carbon monoxide in the singular reactor of greater than 82%.

Also disclosed herein is a method of supporting a hydrogen separation membrane system comprising selecting a hydrogen separation membrane system comprising one or more catalyst outer layers deposited on a hydrogen transport membrane layer and sealing the hydrogen separation membrane system to a porous support. In embodiments, the composite hydrogen separation membrane system comprises a hydrogen transport layer comprising a metal selected from the group consisting of V, Nb, Ta, Zr and alloys thereof; and at least one catalyst outer layer comprising a metal selected from the group consisting of Pd and alloys thereof. The porous support comprises a material selected from the group consisting of porous metal, porous refractory ceramic, metal mesh screen and combinations thereof. In certain embodiments, the porous support is a tube and the membrane encircles the porous support tube. Alternatively, the porous support is planar. In some embodiments wherein the membrane is supported on a porous support, the hydrogen transport layer has a thickness of less than 100 μm.

Also disclosed herein is a method for pretreating the membrane, the pretreating comprising: heating the membrane to a desired operating temperature and desired feed pressure in a flow of inert gas for a sufficient time to cause the membrane to mechanically deform; decreasing the feed pressure to approximately ambient pressure; and optionally, flowing an oxidizing agent across the membrane before, during, or after deformation of the membrane. The oxidizing agent used may be air.

Further disclosed herein is a method for pretreating a membrane, comprising: heating the membrane to a desired operating temperature and desired feed pressure in a flow of inert gas for a sufficient time to cause the membrane to mechanically deform; decreasing the feed pressure to approximately ambient pressure; and optionally, flowing an oxidizing agent across the membrane before, during, or after deformation of the membrane.

The foregoing has outlined rather broadly the features and technical advantages of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages of the apparatus and method will be described hereinafter that form the subject of the claims of this disclosure. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the apparatus and method as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of the methods of the present disclosure, reference will now be made to the accompanying drawings in which:

FIG. 1 is a schematic of an embodiment of the method of the present disclosure comprising three stages of hydrogen separation with a membrane reactor system.

FIG. 2 is an exemplary process flow diagram according to the present disclosure for producing very pure hydrogen from natural gas.

FIG. 3 is an exemplary process flow diagram for an embodiment of the present disclosure wherein oxygen transport membranes and hydrogen purification membranes are integrated with coal gasifier(s).

FIG. 4 is a flowchart of an embodiment of the pretreatment method of the present disclosure.

FIG. 5 is a schematic showing the role of hydrogen dissociation catalysts on both surfaces of dense hydrogen transport membranes which transport hydrogen in a dissociated form.

FIG. 6 is a schematic of a supported hydrogen separation membrane system of the present disclosure.

FIG. 7 is a plot of flux of hydrogen through a composite hydrogen transport membrane, HTM, as a function of the difference of the square roots of the inlet and outlet partial pressures of H2.

FIG. 8 is a plot of CO conversion and H2 productivity each as a function of the differential pressure across a composite hydrogen transport membrane of an integrated WGS-hydrogen transport membrane reactor.

FIG. 9 is a plot of hydrogen flux through a composite HTM as a function of time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is intended to include non-limiting examples of specific embodiments of the disclosed invention. The term hydrogen transport membrane is used herein to refer to a membrane comprising a hydrogen transport layer and optionally one or more catalyst outer layers as discussed hereinbelow.

Herein disclosed is a method for the separation of hydrogen from a hydrogen-containing stream using a hydrogen separation membrane system, hereinafter HSMS. The method is useful in numerous industrial processes that produce hydrogen in, for example, a mixture of other gases. In embodiments, the hydrogen separation membrane system can be used directly in process systems without the need for additional steps to lower the gas pressure or temperature before the hydrogen separation step. In embodiments, the disclosed method minimizes or eliminates the additional costly and time-consuming step of compressing the hydrogen or other gases which are separated. In embodiments, the method of the present disclosure offers a means for economic sequestration of CO2.

In embodiments, the method for separating hydrogen from a carbonaceous feed gas comprises the use of an integrated water gas shift-hydrogen transport membrane reactor, IWGSMR. In embodiments, the IWGSMR increases hydrogen production, lowers unit hydrogen production costs, and/or reduces the costs associated with CO2 capture and compression when compared with conventional water gas shift and separation processes.

The method disclosed may comprise pretreating hydrogen separation membranes to enable the membranes to withstand higher pressures (for example, higher hydrogen partial pressures) than previously possible.

In specific embodiments, the methods of this disclosure can be employed for separation of hydrogen from various hydrogen-containing gases to produce purified hydrogen (e.g., separated from other gases in the hydrogen source), gas mixtures enriched in hydrogen (e.g., hydrogen in an inert gas), a gas stream from which undesirable hydrogen has been removed, or hydrogen for further reaction. In embodiments, the hydrogen-containing gas from which hydrogen is removed comprises, for example, water-gas shift mixtures, reformed petroleum products, or reformed methane, butane, methanol, ethanol or ammonia.

Hydrogen produced via the herein disclosed method may be used in any fashion as is known in the art. In embodiments, the separated hydrogen is very pure, i.e. greater than 99% by volume hydrogen. In embodiments, the separated hydrogen permeate is greater than 99.9% by volume hydrogen. In embodiments, the separated hydrogen permeate is greater than 99.99% by volume hydrogen. In various embodiments, hydrogen produced by these methods can, for example, be transported to another reactor for reaction to make desired products including methanol and hydrocarbon fuels. Alternatively, hydrogen can be reacted with a hydrogen-reactive gas within the reactor directly after transport. In an embodiment, the reactive gas is oxygen, and the products water and energy.

In an embodiment, a feed stream comprising hydrogen and at least one carbon-containing gas is fed, at a pressure greater than atmospheric pressure, to a hydrogen separation membrane system comprising an inorganic membrane whereby a hydrogen-rich product stream (permeate) and a carbon dioxide-rich product stream (raffinate) are produced. The term permeate is used herein to indicate the hydrogen-rich stream from the hydrogen separation membrane. The term raffinate is used to indicate at least a portion of the stream remaining after separation of at least some of the hydrogen from the hydrogen separation membrane.

In embodiments, the permeate pressure is from 0 psig to 1000 psig. In embodiments, the raffinate pressure is from 0 psig to 1000 psig. In some embodiments the permeate pressure is greater than 50 psig, in others greater than 100 psig, and still others greater than 200 psig. In embodiments, the membrane system is operated at from about 200° C. to about 500° C. In certain embodiments, further described hereinbelow, wherein an inert permeate side sweep stream is used, the permeate pressure may be the same as the feed pressure. In certain embodiments, wherein a permeate side sweep stream is used, the permeate pressure is the same as the raffinate pressure.

The hydrogen separation membrane used in the methods of this disclosure is generally incorporated in a reactor, as known in the art. In embodiments, the methods comprise the use of a hydrogen separation membrane reactor as one stage in a process. Alternatively, the methods can comprise the use of more than one hydrogen separation reactor in series or in parallel in a process. The hydrogen separation membrane and reactors incorporating such membranes described herein can be used in the processes described herein, as well as other processes, as known in the art. Methods of constructing the hydrogen separation membrane system and incorporating the hydrogen separation membrane system into a process are known to one of ordinary skill in the art using the disclosure herein and knowledge available to one of ordinary skill in the art.

In embodiments, the method comprises multiple stages of the hydrogen separation membrane system, HSMS. In one example of a multiple-stage process, one hydrogen separation membrane reactor is used to separate one portion of the hydrogen from a feed stream, a second membrane reactor is placed in series in the process and separates another portion of the hydrogen from a stream, and so on. In the multiple-stage process, each stage can have a different inlet and output pressure. In embodiments, the permeate at each stage is essentially pure H2. Impurities can be present from imperfect seals, piping degassing, and other sources, as known in the art. In an alternative embodiment, raffinate from one hydrogen separation membrane reactor can be recycled back into the same reactor, for a continuous process.

FIG. 1 is a schematic of an embodiment of the method of the present disclosure comprising three stages of hydrogen separation with a membrane reactor system. Feed stream 11 comprising hydrogen and at least one carbon-containing gas (CO and CO2 in FIG. 1) is fed into a first hydrogen separation membrane stage 10. Permeate 12 from hydrogen separation membrane stage 10 consisting essentially of pure hydrogen exits at a pressure of greater than 200 psig, for example. Permeate 12 may comprise, for example, about 50% of the hydrogen in feed stream 11. Raffinate 21 is sent to a second hydrogen separation membrane stage 20, wherein a permeate stream 22 is separated. Permeate stream 22 may have a pressure of, for example, 100 psig and comprise, for example, about 35% of the hydrogen in feed stream 11. Raffinate 31 is sent to third hydrogen separation membrane stage 30 wherein it is separated into raffinate 33 and permeate 32. Permeate 32 may be, for example, at a pressure of about 20 psig and may contain, for example, 15% of the hydrogen in feed stream 11. Different numbers of stages are also envisioned in alternative embodiments.

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