Synthesis gas production by ion transport membranes

Details Synthesis gas production by ion transport membranes Synthesis gas production by ion transport membranes

1999-08-04

2001-04-10

Tran, Hien (Department: 1764)

Gas: heating and illuminating

Processes

Manufacture from methane

C048S127500, C048S198100, C095S045000, C095S054000, C422S239000, C423S245300, C423S418200, C423S651000

Reexamination Certificate

active

06214066

ABSTRACT:

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
Synthesis gas containing hydrogen and carbon oxides is an important feedstock for the production of a wide range of chemical products. Synthesis gas mixtures with the proper ratios of hydrogen to carbon monoxide are reacted catalytically to produce liquid hydrocarbons and oxygenated organic compounds including methanol, acetic acid, dimethyl ether, oxo alcohols, and isocyanates. High purity hydrogen and carbon monoxide are recovered by further processing and separation of synthesis gas. The cost of generating the synthesis gas usually is the largest part of the total cost of these products.
Two major reaction routes are used for synthesis gas production—the steam reforming of light hydrocarbons, primarily natural gas, naphtha, and refinery offgases, and the partial oxidation of carbon-containing feedstocks ranging from natural gas to high molecular weight liquid or solid carbonaceous materials. Autothermal reforming is an alternative process using light hydrocarbon feed which combines features of both partial oxidation and steam reforming in a single reactor. In the various versions of this process, feed gas is partially oxidized in a specially-designed burner and the resulting hot gas passes through a catalyst bed where steam reforming occurs. Newer synthesis gas generation processes include various heat exchange reformers such as gas heated reforming (GHR) developed by ICI, the SMART reformer by KTI, and the CAR reformer by UHDE; the improved Texaco gasification process (TGP) included in their HyTEX™ hydrogen production system; Haldor Topsoe's HERMES process; the Shell gasification process (SGP); Exxon's fluidized bed synthesis gas process; and Kellogg's KRES process.
The state of the art in commercial synthesis gas generation technology is summarized in representative survey articles including “Steam Reforming—Opportunities and Limits of the Technology” by J. Rostrup-Nielsen et al, presented at the NATO ASI Study on Chemical Reactor Technology for Environmentally Safe Reactors and Predictors, Aug. 25-Sep. 5, 1991, Ontario, Canada; “Improve Syngas Production Using Autothermal Reforming” by T. S. Christiansen et al,
Hydrocarbon Processing
, March 1994, pp. 39-46; “Evaluation of Natural Gas Based Synthesis Gas Production Technologies” by T. Sundset et al,
Catalysis Today,
21 (1994), pp. 269-278; “Production of Synthesis Gas by Partial Oxidation of Hydrocarbons” by C. L. Reed et al, presented at the 86
th
National AlChE meeting, Houston, Tex., Apr. 1-5, 1979; “Texaco's HYTEX™ Process for High Pressure Hydrogen Production” by F. Fong, presented at the KTI Symposium, Apr. 27, 1993, Caracas, Venezuela; and “Custom-Made Synthesis Gas Using Texaco's Partial Oxidation Technology” by P. J. Osterrieth et al, presented at the AlChE Spring National Meeting, New Orleans, La., Mar. 9, 1988.
In the commercial partial oxidation processes described above, oxygen is required and is typically supplied at purifies of 95 to 99.9 vol %. Oxygen is obtained by the separation of air using known methods, usually the low-temperature distillation of air for larger volumes and pressure swing adsorption for smaller volumes.
An alternative technology for synthesis gas production is in the early stages of development in which oxygen for the partial oxidation reactions is provided in situ by the separation of air at high temperatures using ceramic, ceramic-metal, or ceramic-ceramic composite membranes which conduct both electronic species and oxygen ions. These membranes are part of a class of membranes known generically as ion transport membranes, and are in a specific class of ion transport membranes which conduct both electronic species and oxygen ions known collectively as mixed conducting membranes. These membranes can be used in combination with appropriate catalysts to produce synthesis gas in a membrane reactor without the need for a separate oxygen production step. The reactor is characterized by one or more reaction zones wherein each zone comprises a mixed conducting membrane which separates the zone into an oxidant side and a reactant side.
An oxygen-containing gas mixture, typically air, is contacted with the oxidant side of the membrane and oxygen gas dissociates to form oxygen ions which diffuse through the membrane material. A reactant gas containing methane and other low molecular weight hydrocarbons, typically natural gas with optional steam addition, flows across the reactant side of the membrane. Oxygen on the reactant side of the membrane reacts with components in the reactant gas to form synthesis gas containing hydrogen and carbon monoxide. A catalyst to promote the transfer of oxygen into the membrane can be applied to the surface of the membrane on the oxidant side. A catalyst to promote the conversion of reactant gas components to synthesis gas may be applied to the surface of the reactant side of the membrane; alternatively, a granular form of the catalyst may be placed adjacent to the membrane surface. Catalysts which promote the conversion of hydrocarbons, steam, and carbon dioxide to synthesis gas are well-known in the art.
Numerous reactors and compositions of mixed conducting membranes suitable for this purpose have been disclosed in the art. Membrane reactors and methods of operating such reactors for the selective oxidation of hydrocarbons are disclosed in related U.S. Pat. Nos. 5,306,411 and 5,591,315. Ceramic membranes with wide ranges of compositions are described which promote the transfer of oxygen from an oxygen-containing gas and reaction of the transferred oxygen with a methane-containing gas to form synthesis gas. Mixed conductors having a single phase perovskite structure are utilized for the membrane material; alternatively multiphase solids are used as dual conductors wherein one phase conducts oxygen ions and another conducts electronic species. A membrane reactor to produce synthesis gas is disclosed which operates at a temperature in the range of 1000 to 1400° C., wherein the reactor may be heated to the desired temperature and the temperature maintained during reaction by external heating and/or exothermic heat from the chemical reactions which occur. In one general embodiment, It is disclosed that the process is conducted at temperatures within the range of 1000 to 1300° C. Experimental results are reported for oxygen flux and synthesis gas production in an isothermal laboratory reactor using a dual-conductor membrane at a constant temperature of 1100° C. Inert diluents such as nitrogen, argon, helium, and other gases may be present in the reactor feed and do not interfere with the desired chemical reactions. Steam if present in the reactor feed is stated to be an inert gas or diluent.
In a paper entitled “Ceramic Membranes for Methane Conversion” presented at the Coal Liquefaction and Gas Conversion Contractors, Review Conference, Sep. 7-8, 1994, Pittsburgh, Pa., U. Balachandran et al describe the fabrication of long tubes of Sr—Co
0.5
—Fe—O
x
membranes and the operation of these tubes for conversion of methane to synthesis gas in laboratory reactors at 850° C.
U.S. Pat. No. 4,793,904 discloses the use of a solid electrolyte membrane with conductive coatings on both sides which are optionally connected by an external circuit. The membrane is used in an electrolytic cell at temperatures in the range of 1050 to 1300° C. to convert methane to synthesis gas at a pressure of about 0.1 to about 100 atmospheres. Experimental results are presented for the conversion of methane to synthesis gas components in a reactor cell with an yttria-stabilized zirconia membrane having platinum electrodes optionally using an external electrical circuit. The reactor cell was operated isothermally at a temperature of 800, 1000, or 1100° C.
Related U.S. Pat. Nos. 5,356,728 and 5,580,497 disclose cross-flow electrochemical reactor cells and the operation of these cells to produce synthesis gas from methane and other light hydrocarbons. Mixed cond

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