Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Reexamination Certificate
2001-08-22
2004-08-31
Langel, Wayne A. (Department: 1754)
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
C252S373000, C423S650000, C423S651000
Reexamination Certificate
active
06783750
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of producing hydrogen in which oxygen is separated from an oxygen containing feed by an oxygen transport membrane, the oxygen is reacted with a hydrocarbon and steam to produce a synthesis gas, and the hydrogen is separated from the synthesis gas through the use of a hydrogen transport membrane. More particularly, the present invention relates to such a method in which a hydrogen-depleted crude synthesis gas is combusted to heat the oxygen containing feed.
BACKGROUND OF THE INVENTION
Hydrogen is currently used in the synthesis of many different industrial chemicals. It is expected that additional production of hydrogen will be required for fuel cells to be used in transportation and distributed power generation markets. Many of the current and future hydrogen requirements can be most economically met by the use of small-scale hydrogen plants having an output of less than about 4 million standard cubic liters per day. In this regard, the use of fuel cells in the distributed power generation market is projected to grow substantially over the next 10 to 20 years. It is expected that this market will require a large number of such small-scale hydrogen plants.
A well-known method for producing hydrogen is steam methane reforming. Hydrocarbons such as methane are reformed with steam in a steam methane reformer to produce a synthesis gas mixture containing hydrogen and carbon monoxide. In a shift reactor, carbon monoxide and steam are reacted to produce a hydrogen-rich gas containing hydrogen and carbon dioxide. The hydrogen-rich gas can be purified by pressure swing adsorption to recover pure hydrogen. As can be appreciated, the foregoing processes are conducted in large-scale installations that can be capable of producing more than 3 billion standard cubic liters of hydrogen per day.
Reactors have at least been proposed in the prior art in which steam, one or more hydrocarbons, and air are reacted to produce a synthesis gas. Hydrogen is separated from the synthesis gas by a hydrogen transport membrane. An example of such a reactor is disclosed in U.S. Pat. No. 5,741,474. In this patent, hydrogen is produced by reforming hydrocarbons with oxygen or air and steam to produce a crude synthesis gas containing hydrogen, carbon monoxide, water, and carbon dioxide. The hydrogen is recovered from the synthesis gas by use of a hydrogen transport membrane.
U.S. Pat. Nos. 4,810,485 and 5,637,259 also describe membrane reactors that integrate hydrogen generation with hydrogen separation by a membrane. In U.S. Pat. No. 4,810,485 a reactor is disclosed in which a hydrogen containing gas is produced by steam methane reforming or a water gas shift reaction and a hydrogen transport membrane is used to separate hydrogen from the hydrogen containing gas. U.S. Pat. No. 5,637,259 describes a tubular reactor and membrane to produce hydrogen from a synthesis gas produced within the reactor.
Hydrogen transport membranes, that are effective to separate hydrogen from hydrogen containing gases, include membranes made of metals or metal alloys, proton conducting ceramic materials and porous ceramic membranes. All of such membranes function at high temperatures.
In metal-based and porous ceramic membranes, hydrogen permeation is due to the higher hydrogen partial pressure on the retentate side as compared to the permeate side. Several examples of metal-based membranes in the prior art include U.S. Pat. Nos. 3,350,846, 5,215,729, and 5,738,708. The membranes of the foregoing patents are composite membranes in which a layer, formed of Group IVB or VB metals, is sandwiched between two layers of a metal selected from either palladium, platinum or their alloys. In U.S. Pat. No. 5,217,506, a composite membrane is disclosed that contains intermetallic diffusion barriers between two top layers and a central membrane layer to prevent diffusion of top metal layer into the central metal layer. The barrier is made from oxides or sulfides of molybdenum, silicon, tungsten and vanadium. U.S. Pat. No. 5,652,020 describes a hydrogen transport membrane comprised of a palladium layer deposited on porous ceramic support layer. U.S. Pat. No. 5,415,891 describes a porous ceramic membrane modified by either metallic oxide (e.g. aluminum or zirconium oxide) or non-metallic oxide (e.g. silicon oxide).
Proton conducting ceramic materials can be characterized as being either electrically-driven (a pure proton conductor) or pressure driven (a mixed conductor).
Electrically-driven membranes are pure proton conductors that do not have electrical conductivity. Such membranes need an external circuit to drive electrons from an anode surface of the membrane to cathode surface. One of the advantages of an electrically-driven membrane is that there is no need to maintain high pressure because electrical force can be used to transport hydrogen to the permeate zone and to produce pressurized hydrogen directly. A second advantage is the reduced need for a purge gas on the permeate side. Proton conducting ceramics suitable for high-temperature application include perovskite-type oxide based on cerates or zirconates as cited in H. Iwahara, “Hydrogen Pumps Using Proton Conducting Ceramics And Their Applications”, Solid State Ionics 125 (1999), pp 271-278 (1999).
Pressure driven membranes capable of conducting both protons and electrons do not need external circuit and can operate in non-galvanic mode. Examples of mixed conducting, hydrogen transport membranes are disclosed in U.S. Pat. Nos. 6,066,307 and 6,037,514. U. Balachandran et al., “Development of Mixed-Conducting Ceramic Membrane for Hydrogen Separation”, presented at the Sixteenth Annual International Pittsburgh Coal Conference Proceedings, Pittsburgh, Pa., Oct. 11-15, 1999 discloses that electronic conductivity can be increased by mixing metal powder with mixed conductors such as partially substituted perovskite-type oxides such as CaZrO
3
, SrCeO
3
and BaCeO
3
.
Other prior art reactor designs, in addition to the hydrogen transport membrane, incorporate an oxygen transport membrane to produce oxygen for partial oxidation reactions that provide heat for the endothermic steam methane reforming reaction. For instance, in the reactor design shown in U.S. Pat. No. 6,066,307, hydrogen is produced from partial oxidation and steam methane reforming reactions of a hydrocarbon fuel, steam, and oxygen using a reactor containing oxygen transport membranes to produce the oxygen and hydrogen transport membranes to separate hydrogen from a crude synthesis gas. As the hydrogen is removed, the shift conversion reaction results in additional hydrogen generation. An oxygen containing feed, composed of air, is heated by three streams, composed respectively of oxygen-depleted air, hydrogen-depleted crude synthesis gas, and hydrogen returning from the reactor. In a reaction zone of the reactor, oxygen from the heated air permeates through the oxygen transport membrane and reacts with a mixture of a hydrocarbon containing fuel and steam to produce the synthesis gas. Hydrogen from the reaction zone permeates through the hydrogen transport membrane. The oxygen-depleted air, hydrogen-depleted crude synthesis gas, and the hydrogen are cooled to recover thermal energy and thereby heat the incoming feed and in turn help heat the membranes to their operational temperatures.
It is to be noted that oxygen transport membranes function by transporting oxygen ions, formed from oxygen at a surface of the membrane known as the cathode side, to the opposite surface of the membrane, known as the anode side. The oxygen molecule is reconstituted at the anode side and electrons lost from the oxygen ions upon reconstitution of the oxygen are transported to the cathode side for oxygen ionization.
There are membrane materials, referred to as mixed conductors, that can conduct oxygen ions as well as electrons. Various known perovskites are suitable for such purposes. There are also dual phase metal and metallic oxide combinations that can also be used. Examples of mixed
Drnevich Raymond Francis
Gottzmann Christian Friedrich
Shah Minish Mahendra
van Hassel Bart Antonie
Langel Wayne A.
Praxair Technology Inc.
Rosenblum David M.
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