Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing inorganic compound
Reexamination Certificate
2000-12-01
2002-08-06
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing inorganic compound
C205S615000, C205S637000
Reexamination Certificate
active
06428678
ABSTRACT:
The present invention relates to a process and an apparatus for producing synthesis gas.
Following the progress made in the development of fuel cells for generating electrical energy, there exists an increased demand for hydrogen-containing fuels for the fuel cell reaction. These fuels may be either hydrogen gas or also a hydrogen-containing compound, e.g. methyl alcohol, which is fed to the fuel cell directly or after passing through a gas reforming process. Especially when using fuel cells for electrically operated motor vehicles it is advantageous when the fuel can be made available directly inside the vehicle. A possible process for producing hydrogen as fuel or as starting product for producing a hydrogen-containing fuel is, for example, the known production of synthesis gas from the substances CO
2
and H
2
O. At present the synthesis gas production takes place by high-pressure electrolysis processes at approx. 1000° C. on large plants.
The principle of such a synthesis gas production is described, for example, in the article “Production of liquid fuels from atmospheric carbon dioxide” by M. Specht and A. Bandi, published in “Themen 94/95” of the Forschungsverbund Sonnenenergie (Solar Enemy Research Institute). According to this publication a tube reactor is used for the synthesis gas production. However, for use in motor vehicles a process is required which permits, in the smallest possible space, a highly efficient yield of synthesis gas.
It is, therefore, the object of the present invention to indicate a process and an apparatus which permits the production of synthesis gas in the smallest possible space, e.g. on board a motor vehicle.
According to the invention this object is addressed by a process for producing synthesis gas by electrolysis, characterised in that the electrolysis is carried out using textile micro-hollow fibers as solid electrolytes, the inside and outside surfaces of which carry the anodes and cathodes respectively, as well as by an apparatus for producing synthesis gas by electrolysis, characterised in that it comprises a multitude of stacked textile micro-hollow fibers as solid electrolytes, the inside and outside surfaces of which carry the anodes and cathodes respectively, wherein the ends of the micro-hollow fibers are bound in a form-stable manner into a frame.
The use of textile micro-hollow fibers as solid electrolytes has the advantage that for the electrolysis reaction only little space is required at a simultaneously large electrode surface. Understood under textile fibers are in general those fibers that can be processed in the manner of textiles. Such fibers have a great length compared to their cross-section as well as sufficient strength and flexibility. Because of the small diameter and the corresponding small wall thicknesses of these fibers, the diffusion through the hollow fibers takes place in an extremely short time compared to the tube reactors of the state of the art. For the use of micro-hollow fibers in the process according to the invention, they must be extremely homogeneous with regard to their dimensions, so as to ensure a uniform reaction pattern. For this reason the fluctuations of wall thickness and outside diameter of the micro-hollow fibers should not be more than each approx. +/−10%, in particular not more than each approx. +/−8%. Particularly preferred are those micro-hollow fibers with which these fluctuations each lie under +/−6%.
The manufacture of such micro-hollow fibers is described, for example, in the EP-A-0 874 788 of the same applicant. The micro-hollow fibers can be made with very small wall thicknesses of approx. 0,01 to 15 &mgr;m and outside diameters from down to 0,5 to 35 &mgr;m. Because of the small dimensions such micro-hollow fibers display textile properties, i.e. they can be bent particularly easily without breaking. By the manufacturing process described in the EP-A-0 874 788 the micro-hollow fibers can be manufactured with extremely accurate dimensions, wherein the fluctuation range of wall thickness and outside diameter is not more than approx. +/−6%. The precision of maintaining the values of the diameter and in particular of the wall thickness ensures a homogeneous reaction pattern over the entire length of the hollow fibers.
Alternatively, it is possible to manufacture the required hollow fibers from flat, smooth or structured, plastic bipolar electrolytic foils, which are rolled into straws or wound into helical or spiral tubes. In this way, in particular hollow fibers with an outside diameter of approx. 0,28 to 10 mm can be produced. When rolling the foils into straws, one proceeds in this connection in the same way as with the process which is known, for example, for making cigarettes. The lengths of the straws or spiral tubes produced in this manner generally lies preferably between approx. 0,03 m and 3,00 m, in which connection for the use of the straws in the process according to the invention for the synthesis gas production a length of approx. 0,03 m to approx. 0,20 m is preferred. It is possible to realise any desired and technically expedient length/diameter ratio. After the forming of the straws or spiral tubes, they are ceramically baked. The electrolytic foils can be extruded together with the electrode material before they are processed further into straws or spiral tubes. To manufacture the electrolytic foils, in this connection in particular the sol-gel process can be used.
By using structured, e.g. pleated, or curved or corrugated electrolytic foils for making the straws or spiral tubes, the surface of the straws or tubes that is available for the reaction can be increased further. Another advantage of the use of structured foils lies in the increased bending strength of the straws and tubes produced therefrom.
As starting materials for the micro-hollow fibers used in the process according to the invention, among others hydrolysable substances, collagens, proteins, urea, gelatine, starches or ceramic materials or the precursors of a ceramic material can be used.
The thermal energy required for the synthesis gas production can be made available, for example, by wetting a zeolite. Also suitable for storing heat are melts of aluminium and tin. Also the use of a catalytic atmospheric burner is conceivable.
To improve the reactivity and to achieve a lower operating temperature, the textile micro-hollow fibers are coated on both sides with a catalyst, preferably an element of the eighth sub-group, wherein platinum is regarded as particularly suitable. With this catalyst an effective synthesis gas reaction can take place already at approx. 85° C. to 180° C. or 500° C. to 730° C. in the case of the high-temperature electrolysis and at a pressure of approx. 0,1 to 3 bar. The pressure vessel must in this case be designed for a pressure up to 12 bar. When using a platinum catalyst, the number of atoms per cluster is preferably increased to 8 to 15. In this way an additional saving of material can be obtained. Furthermore, because of the increased number of atoms in the clusters, the starting time of the catalyst can be shortened and the reactivity of the reactants increased. The catalyst must be porous so that it will not prevent the flow of gas through the micro-hollow fiber membrane. Also suitable as catalysts are the following materials: spinnel (MgAlO), titanium dioxide (in its anatase form), vanadium pentoxide, tungsten trioxide, copper oxide, molybdenum oxide and iron oxide. Heavy as well as light platinum is suitable as catalyst material.
Preferably, the textile micro-hollow fibers are made from an oxide of the titanium group which is stabilised with a rare earth metal. Particularly preferred for the process according to the invention are textile micro-hollow fibers which are made from yttrium-stabilised zirconium oxide. This material is known as electrolyte material and has proved eminently suitable under the temperature conditions required for the electrolysis.
For use in the process according to the invention for the synthesis
Fay Sharpe Fagan Minnich & McKee LLP
Wong Edna
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