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  Method for producing a uniform cross-flow of an electrolyte chamber of an electrolysis cellUSPTO Application #: 20070221496Title: Method for producing a uniform cross-flow of an electrolyte chamber of an electrolysis cell Abstract: The invention relates to a method for producing a uniform flow through an electrolyte space of an electrolysis cell, in which a maximum deviation of less than 1% to 25% from the average flow rate is achieved by suitable design measures. The invention also relates to an electrolysis cell with at least two electrolyte spaces, in each of which at least one electrode is arranged and each of which has an inlet region and an outlet region, the flow cross section being reduced in the inlet and/or outlet region so as to produce an additional pressure reduction (end of abstract) Agent: Oblon, Spivak, Mcclelland, Maier & Neustadt, P.C. - Alexandria, VA, US Inventors: Harald Bohnke, Hermann Putter, Torsten Mattke USPTO Applicaton #: 20070221496 - Class: 204242000 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Apparatus, Electrolytic, Cells The Patent Description & Claims data below is from USPTO Patent Application 20070221496. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to a method for producing a uniform flow through an electrolyte space of an electrolysis cell, and to an electrolysis cell. [0002] Electrolysis is very important in the chemical industry. Examples of fields in which electrolysis is used are the synthesis of chlorine by chloralkali electrolysis or hydrogen chloride electrolysis, electrolytic generation of chromic acid, electrochemical production of sodium dithionite and electrochemical water purification and metal precipitation to obtain pure metals. [0003] For a large number of electrochemical cells, it is desirable to provide an electrode surface whose active surface area is larger than its purely geometrical dimensions. [0004] The most prominent examples of this are to be found in fuel cell technology. In a polymer electrolyte fuel cell, for example, the active electrode face consists of a gas diffusion layer based on carbon black, which is activated by special methods, saturated with ionomers and hydrophobicized in order to offer a much larger reaction area to the gases than would correspond to the dimensions of the gas diffusion layer. [0005] In organic electrochemistry, for example, electrodes made of felt are used in order to increase the active surface area of the electrodes for mediated processes in particular, that is to say for processes in which there are small amounts of an electro-catalytically active redox system in the reaction solution. Similar arrangements are also used in electro-enzymatics. For example, a multi-cathode cell containing cathodes which consist of a plurality of assembled network layers is used for the electrochemical reduction of vat dyes. [0006] The oxidation of sugars to sugar acids is carried out in a special stirred reactor equipped with anode grids. [0007] Cathodes to which a ribbed structure is imparted to increase the throughput are used for the reduction of phthalic acid to dihydrophthalic acid. [0008] The so-called Swiss roll cell has been developed for nickel oxide-catalyzed reactions. Here, the anode and the cathode are spirally wound. [0009] Electrodes whose active surface area is larger than their purely geometrical dimensions are often referred to as three-dimensional electrodes. [0010] Arrangements in which layers of materials with a large surface area are precoated onto an electrode substrate are also known. [0011] Lamellar designs which are formed from strips of metallic glasses, for example, are also known for organic and inorganic electrolysis. [0012] Such three-dimensional electrodes are used in inorganic electrolysis, for example, in order to precipitate traces of metal from effluents. Felted electrodes or electrodes of particle beds, for example, are used for this purpose. [0013] Electrodes in the form of a networked design, for example, may be used for the production of sodium dithionite. [0014] A disadvantage with the electrolysis cells used at present is the fact that the hydrodynamics on the electrode face, that is to say the 2-phase flow of the liquid/gas mixture, are often defined only insufficiently by the design configuration of the overall electrode and of the electrolyte space. In fuel cells, for example, the gas feed is established accurately by the so-called flow field, but the formation of a liquid phase is a phenomenon to be feared since it can critically interfere with the gas supply as well as the potential distribution and the current density distribution. This interference can lead to destruction of the cell. [0015] The design configuration of the overall electrode and of the electrolyte space using the flow field is relatively uncritical in some cases, for example in chloralkali electrolysis according to the membrane method, in which two grid electrodes that evolve gases face each other while being separated by a membrane. The mammoth pump effect, which is created by the gas bubbles being evolved, ensures sufficient equidistribution in the two electrolyte spaces. Neither strong nor defined recirculation of the electrolyte is required. [0016] For electrolysis cells in which a high selectivity with high throughput is a critical quantity, problems occur in electrolysis cells without defined hydrodynamics. In order to avoid dead spaces in which the uncontrolled formation of secondary components can occur, and in order to achieve optimum use of the electrode surface, it is necessary to ensure a maximally uniform distribution of the reaction liquid in the electrolyte space so as to ensure a maximally homogeneous current density distribution. To that end, it is also necessary to control the liquid flows outside the immediate vicinity of the electrode surface. Examples of dead spaces are gas cushions (that is to say static gas bubbles) or regions through which no liquid flows. Such regions occur, for example, owing to vortex formation, backward flows or stagnation at obstacles in the flow path. [0017] When through-flow porous electrodes are used in membrane electrolysis cells, a nonuniform pressure distribution in the anolyte space and the catholyte space can lead to a bypass, through which the electrolyte flows, being formed between the membrane and the porous electrode. This leads to a reduction of the throughput. In the case of through-flow electrodes, the term bypass is here intended to mean a stream which flows past the electrode rather than through it. [0018] From U.S. Pat. No. 4,204,920, in the case of a membrane electrolysis cell, it is known to set up a higher pressure in the anolyte space than in the catholyte space, so that the membrane is pushed away from the anode towards the cathode. [0019] But a narrow dwell time distribution, and therefore a uniform flow through the cross section, which is necessary for uniform conversion in the electrolyte spaces, is not achieved by setting different backpressures for the anolyte space and the catholyte space. [0020] It is an object of the present invention to provide a method which ensures a uniform flow through an electrolyte space of an electrolysis cell and therefore a narrow dwell time distribution. [0021] The object is achieved by a method for producing a uniform flow through an electrolyte space of an electrolysis cell, in which a maximum deviation of less than 1% to 25% from the average flow rate is achieved by suitable design measures. [0022] An electrolysis cell is preferably formed by at least two electrolyte spaces. In this case, at least one electrolyte space is an anolyte space and at least one electrolyte space is a catholyte space. An anolyte space and a catholyte space are respectively adjacent and separated from each other by at least one membrane. [0023] The maximum deviation from the average flow rate is preferably achieved by setting up an additional pressure reduction. This is preferably from 1 to 10 times the pressure difference in the inlet region of the electrolyte space (that is to say the pressure reduction in the inlet region between the feed to the inlet region and the electrode in the electrolyte space, if no additional pressure reduction is applied). The calculation is carried out according to a equation (1): .DELTA. .times. .times. p DV = p dyn + .DELTA. .times. .times. p V ( A + 1 ) 2 - 1 - .DELTA. .times. .times. p E , ( 1 ) when the feed into the inlet region of the electrolyte space is such that the incoming volume flow is distributed approximately uniformly into two sub-flows with opposite principal flow directions in the inlet region. Here, the width of the electrolyte space is the dimension which extends perpendicularly to the principal flow direction in the electrolyte space and perpendicularly to the principal direction of the electric field (gap width). [0024] When the feed is organized in a different way from the type described above, the calculation is carried out according to Equation (2): .DELTA. .times. .times. p DV = p dyn + .DELTA. .times. .times. p V ( A + 1 ) 2 - 1 - .DELTA. .times. .times. p E , ( 2 ) Continue reading... 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