MXPA00002856A - Coated products - Google Patents

Abstract

A product (20, 21, 41, 60) comprised of a three-dimensional network of material is coated with a particulate support. The coating may be applied by an electrophoretic coating procedure to apply a particulate coating on the surface or into the interior portions of such three-dimensional network of material (20, 21, 41, 60). In one embodiment, the particles are a catalyst or a catalyst precursor or a catalyst support to thereby provide a catalyst structure in which catalyst may be supported as a coating in the interior and on the exterior of a three-dimensional network of material (20, 21, 41, 60) having a high void volume. Edge effects may be reduced by control or disruption of field lines during the coating. In addition, larger particles may be electrophoretically coated onto a product (20, 21, 41, 60) by the use of smaller particles which function as a"glue".

Description

COATED PRODUCTS This application claims the priority of the Provisional Patent Application of the U.S.A. Serial number 60 / 059,795 filed on September 23, 1997 and the Provisional Patent Application of the US. Serial number 60 / 097,483 filed August 21, 1998. The invention relates to coated products and their production. More specifically, the invention relates to electrophoretic coating and to the products thus produced. This invention is further related to providing a more uniform coating by the use of an electrophoretic deposition or coating. In a particular aspect, the present invention relates to the production of a three-dimensional network coated with material in which interior and exterior portions of the material are electrophoretically coated. The invention further relates to a coated catalyst structure, wherein the structure is formed from a plurality of layers of fibers that are electrophoretically coated, with a particulate coating that includes a catalyst. There is a wide variety of technologies available to provide coated materials. Such a method involves coating materials when spraying or immersing them. Attempts to employ this technology to coat a three-dimensional network of material generally result in a coated product where a single portion of the interior of the material is coated. Another coating method known in the art is electrophoretic coating. This electrophoretic coating has generally been applied only to dense bodies or surfaces. Furthermore, in electrophoretic coating processes, in many cases, difficulties are encountered in providing a coating wherein the coating thickness at the edges of the material is essentially the same as the coating thickness in other portions of the material. In accordance with one aspect of the present invention, there is provided a process for depositing particles, such as a coating, in a product or support comprising a three dimensional network of material, with the particles that are applied to this product or support by a process of electrophoretic coating. The applicant has found by electrophoretic coating of a porous product or support consisting of a three dimensional network of material, this porous product or support can be effectively coated with a particulate coating with or without coating penetration into the interior of the product or porous support, preferably with penetration and the degree of penetration can be controlled. This three-dimensional network of material is preferably formed of a plurality of fiber layers that are randomly oriented. Still further, it is possible to coat the interior of the porous product to obtain a uniform coating over a defined thickness of the porous product: however, the invention is not limited to achieving this uniform coating; that is, the porous product may have a non-uniform coating over a defined thickness. Although in a preferred embodiment, a porous product is electrophoretically coated to produce a product having particle coating, wherein a defined thickness is uniformly coated (the inner portion of the multi-layer product is coated), the present invention is also applicable to produce a coated product where there is no essential penetration into the interior of the product or where there is a controlled penetration and where the coating is not uniform. The applicant has surprisingly found that contrary to expectations in the art, an electrophoretic coating process can be used to deposit particles inside a product constituted by a three dimensional network of material. Still further, the Applicant has surprisingly found that an electrophoretic coating process can be employed to deposit particles as a uniform coating for a defined thickness of the inner portion of this three-dimensional network. By the use of an electrophoretic coating, a coated porous product is provided which differs from coated porous products which are made by procedures previously employed in the art, such as immersion or spray coating. For example, the use of the technique of the invention provides a more uniform coating, i.e. there is less variation in coating thickness over a defined thickness of the product. In addition, unlike the prior art methods, at intersections of the material forming the three-dimensional network, an excessive accumulation of the coating material that blocks or closes pores can be reduced or eliminated. Furthermore, by a more uniform application of the coating, "blocking" or "closing" of the pores is reduced and / or eliminated. Furthermore, on a defined thickness, by proceeding according to the invention, uncoated or "bare" portions of the material are reduced or eliminated. Thus, according to one aspect of the present invention, a product constituted by a three-dimensional network of materials can be produced in which a defined thickness of the inner portion of the material is uniformly coated with the particles. The defined thickness of the three-dimensional network of material may be a portion of the total thickness or may be the entire thickness of this three-dimensional network. In a preferred embodiment of this aspect of the invention, the coating constituted by particles, forms a porous coating both on the outside and on the inside of the three-dimensional network of material, this coating can be comprised of one, two or more layers of deposited particles. According to another aspect of the present invention, a coated product and process is provided, wherein a non-particle carrier is electrophoretically coated with particles having an average particle size greater than .0005 mm (0.5 miera) where these large particles are coated electrophoretically on the support, in conjunction with smaller particles that have an average particle size of less than 150 nanometers (this is smaller particles can be in the form of a sol or colloid). The applicant has found that an electrophoretic coating of larger particles (particles of an average particle size greater than 0.5 miera) can be applied more effectively if the coating bath employed in this electrophoretic coating process includes particles having an average particle size. less than 150 nanometers in addition to the larger particles. Although the applicant does not intend to be bound by any theoretical reasoning, it is considered that the smaller particles function to bind more effectively the larger particles together and / or the support or product that is coated. In effect, the smaller particles function as a "glue" to improve the adhesion of the larger particles to each other and / or the coated product or support and increase the mobility of the larger particles in the electric field. In a particularly preferred embodiment, the larger particles to be coated on the product or support are already a catalyst support, catalyst precursor, a catalyst or a catalyst or catalyst precursor in a particulate support. The smallest particles may be of the same material as the larger particles or may be of a different material. In many cases, the product is suitable as a catalyst system in which a particulate catalyst (the particulate form of the catalyst coated with the non-particulate support can be a catalyst support for particles coated or impregnated with a catalyst) and it is present as a coating on a non-particulate support, where the particulate catalyst, when held in the non-particulate support, has an average particle size greater than .0005 mm (0.5 miera). In these cases, the Applicant has found that by using an electrophoretic process to coat particles of a catalyst or catalyst precursor or catalyst support (with or without a catalyst or catalyst precursor) on a solid non-particulate support, this catalyst, precursor of catalyst or support has an average particle size greater than 0.5 miera, it is desirable that the electrophoretic coating bath containing these larger particles also include smaller particles (in the form of a sol or colloid) in an amount that provides a coating the larger particles on the non-particulate support, such that the coating of the larger particles adheres effectively to the non-particulate support. The smaller particles may comprise the same material as the larger particles or they may be a different material or materials or may include the material of larger particles plus a different material. As indicated above, it is considered that the smaller particles function as a "glue" that improves the adhesion to the larger particles together and / or the non-particle support. As previously indicated, the average particle size of the smallest particles is generally less than 150 nanometers. In general, the average particle size is at least 2 nanometers. For example, in one embodiment, the average particle size is 20-40 nanometers. The larger particles to be coated on the non-particulate support generally have an average particle size of at least .0005 mm (0.5 miera) eg .001 mm (1.0 miera) at least. In general, the average particle size does not exceed .020 mm (20 microns). In the coating bath, the relative amounts of the larger and smaller particles are chosen to achieve in the final coating, the desired amount of the larger particles and an amount of smaller particles that provide effective adhesion of the coating containing the larger particles to the support that is not particle. In general, based on the total amount of the largest and smallest particles, the amount of the smallest particles employed in the coating bath is 0.1% to 10% by weight.

The aspect of the present invention, wherein the larger particles are coated electrophoretically on a support, is applicable to the electrophoretic coating of porous supports (three-dimensional supports with a thickness where the coating is applied both to the exterior and to the interior of the support). as to the electrophoretic coating of dense or non-porous supports, wherein the coating essentially only applies to the exterior of the support. The product or support to which a particle coating is applied by electrophoretic coating is that which is capable of accepting a load.

The product can be formed from only conductive materials or from a mixture of conductive and non-conductive materials, provided that the total product is capable of accepting a load. As representative examples of conductive materials that can be used alone or in combination to form all or a portion of product constituted of a three-dimensional network of material, metals, carbon as well as electrically conductive polymers and / or ceramics can be mentioned. Representative examples of preferred metals may be mentioned: stainless steel: Fe-Ni or Fe-Cr alloys; Fe-Cr-Al alloys; copper; nickel; brass; etc. The product or support that is coated may be of the type described in US Patents. Nos. 5,304,330; 5,080,962, 5,102,745 or 5,096,663. The three-dimensional network of materials can be one that is made up of fibers or wires, such as wire or fiber mesh, a gauze or metal felt, a filter of metal or paper fibers and the like, or it can be a porous metal compound , for example formed from sintered porous metal powder. The compacted powder and / or fibers define a three dimensional network of material having a thickness. In general, the thickness of the three-dimensional network of material containing the uniform coating is at least .005 mm (5 microns) and generally does not exceed 10 mm. According to a preferred embodiment, the thickness of the net containing the uniform coating is at least 0.50 mm (50 microns) and more preferably at least 0.1 mm (100 microns) and generally does not exceed 2 mm. In general, when the product is a fibrous web of material, the thickness or diameter of the fiber is less than .5 mm (500 microns), preferably less than .1 mm (100 microns), and more preferably less than .030. mm (30 microns). The product that is coated, preferably consists of a plurality of layers of fibers that are randomly oriented in the layers, and according to the invention, the fibers in the interior as well as on the outside of the product are covered with a coating of particles to form a porous coating. Particles that are applied to the three-dimensional network of material as a coating, by an electrophoretic coating process, generally have an average particle size that does not exceed .1 mm (100 microns) and in most cases does not exceed .01 mm (10 microns) In general, the particle size of these particles is at least one nanometer and preferably at least two nanometers. The particles may be colloidal particles or mixtures of colloidal particles and / or mixtures of colloidal particles with one or more particles that are not colloidal particles. The thickness of the formed coating can vary. In general, the thickness is at least 1 miera and in general no greater than .1 mm (100 micras). The particles to be coated on the support can consist of a single material or multiple materials (two, three or more different materials). For example, the material can be a complex of two or more materials, such as an ionic or absorbed complex. The inner portion of the product that is coated according to the invention has a porosity that is sufficient to allow the particles comprising the coating to penetrate or migrate to the three-dimensional network. In this way, the pore size of the three-dimensional material and the particle size of the particles comprising the coating, in effect determines the distance at which the particles penetrate into and line the interior of the three-dimensional network of material and / or the coating thickness In the net. The larger the pore sizes, the greater the coating thickness that can be uniformly coated according to the invention. In general, the average void opening of the product that is coated is at least .01 mm (10 microns) and preferably at least .02 mm (20 microns), preferably the total void volume is 60-90% (per Hundred volume of voids is the ratio of open volume to total volume multiplied by 100). In this way, by coordinating the particle size and the pore size of the product to be coated, it is possible to control the penetration or migration of the coating into the porous product, for example by varying the pore size of the material to be coated. The product or support that is coated can have different pore sizes on its thickness and within the scope of the invention, it is contemplated that the three-dimensional product that is coated has a complete uniform porosity or that its porosity varies and that this product can be a laminated and / or formed of the same or different materials and / or may have multiple layers. The material forming the three-dimensional network to be coated electrophoretically may be coated or uncoated and this three-dimensional network may have particles trapped or contained therein. In general, these particles, if present, have a size from .001 - .3 mm (1-300 microns). The particulate material that is used as the coating may comprise a single material or a mixture of materials and when the mixture is used, the particles may be a composite constituted by smaller particles (a sol) that adhere to larger particles. The selection of the materials and their size as well as the coating conditions are coordinated to ensure that the particles retain a sufficient charge to effect the electrophoretic coating. Thus, in some cases, for example, when coating a support with large particles (for example large particles in the form of a catalyst support or catalyst), the coating mixture may include an appropriate sol, all or a portion of the which adheres to the larger particles, to provide a sufficient charge and / or binding properties, to produce a particulate coating according to the invention. It will be understood that, within the scope of the invention, the particulate material that is applied as a coating, may be particles larger than a sol, these larger particles may be applied as a coating with or without the addition of a sol, preferably with the addition of a sol. In some cases, it may be convenient to treat the product before coating to facilitate the coating and / or improve the adhesion to the coating; for example etching with acid or gas treatment with a gas containing oxygen. In a preferred embodiment, the particles that are applied to the three-dimensional network of porous material can be catalyst particles or a catalyst support and / or a catalyst support containing active catalyst or precursor and / or a catalyst precursor. In this embodiment, the particles preferably form a uniform coating over a defined thickness of the interior of the three-dimensional network of material, with this three-dimensional network of material that is porous (having a void volume) and with the coating of particles in this. material that is also porous. In this way, it is possible to provide a total catalyst structure where there is a high void volume and where the catalyst is uniformly distributed through a defined thickness of the interior of the three-dimensional network. In the case where the particles are in the form of a catalyst precursor, the product, after depositing the particles, is treated to convert the catalyst precursor to an active catalyst. In the case where the particles that are deposited in the three-dimensional network of material is a catalyst support, active catalyst or catalyst precursor, then it can be applied to this support, for example, by spraying, dipping or impregnation. The catalytically active material or a precursor can be multiple. For example, the catalytically active material as representative but non-limiting examples may comprise one or more of the catalytically active metals of the groups VIB, VIIB, VIII, metal oxides or sulfides and mixtures thereof and optionally includes activators such as phosphorus , halogen or boron or these metals, metal oxides or metal sulphides or nitrides of catalytically active metals of Groups VIB, VIIB, VIII and optionally including activators such as phosphorus, halogen or boron and their mixtures deposited in an oxide base of refractory metal such as alumina, silica, silica-alumina, titanium oxide, zirconium oxide, etc., and mixtures thereof, and alumina-silicates such as natural or synthetic zeolites such as zeolite X, zeolite Y, zeolite beta, ZSM- 5, offerita, mordenita, erronita, etc., and their mixtures. Oxides such as alumina, zeolites, zirconium oxide, silica, titanium oxide phases, vanadium oxide phases, transition aluminas, zinc phases, can be deposited directly from suspensions, for example as nano- or micrometer particles or suns the compounds or mixtures of both. Coated particles may include carbon supports, such as carbon black, oxidized carbon supports, sieves and carbon molecules, etc., which are porous or non-porous. The concentration of the solid in the suspensions can vary between 0.01 and 80% by weight. In general, the particles that are applied to the three-dimensional material (catalyst, catalyst support, catalyst precursor) are inorganic particles. When using a coating bath, the coating bath may in some cases include additional agents, such as stabilizers, binders, agents that improve mobility, etc., and in some cases a single material can perform multiple functions in this regard. As representative stabilizing agents, there can be mentioned: a polyacrylic acid type polymer, acrylamides, organic quaternary ammonium compounds, or other special mixtures that are chosen based on the particles to be coated. By choosing the appropriate stabilizing agent / binder, different materials can be co-deposited, which means that they migrate simultaneously to the article to be coated and deposited simultaneously. The deposited quantity is determined by the speed of migration and the concentration of particles in the system. Soles may also act as binders and / or stabilizing agents. The advantage of suns is that they are not pyrolyzed during subsequent heat treatment, which is used in most cases to achieve an adequate bond between the coating and the matrix. For example, to obtain a gamma-alumina coating with very strong connection between the oxide and the metal wire, alumina powder is suspended in an aqueous system and alumina sol is added to obtain, for example, a concentration between 1 and 30 % by weight of alumina in this aqueous system. After the deposition, the article is dried and calcined. The dry and calcined sun is a good binder for alumina. In addition, during the coating process, the sun functions as a stabilizer and gives mobility to the alumina particles. In preparing a catalyst according to the invention, the catalyst can be applied to the support in a variety of ways. In one embodiment, a particulate catalyst support can be applied to the support by electrophoretic coating according to the invention, followed by application of a catalyst solution to the coated product; for example by spraying or impregnation. In another embodiment, unsupported catalyst particles can be applied to a support according to the invention. In a further embodiment, a particulate catalyst support having catalyst or applied catalyst precursor is coated on the support according to the invention. In any of the above processes, the electrophoretic coating can be achieved with or without a binder added to the electrophoretic coating mixture. In a further embodiment, a binder may be applied to the three-dimensional network before or subsequent to coating with a particulate material, with this binder being preferably applied by electrophoretic coating according to the invention. Even in a further embodiment, multiple coatings may be applied to the same product in multiple coating steps, these coatings may be the same or different from each other. In yet another embodiment during the electrophoretic coating, a material may also be applied to the non-particulate support in addition to the particles applied by the electrophoretic coating. These and other modalities should be apparent to those with skill in the specialty from the present teachings. The product constituted by a three-dimensional network of material, has particles applied by a deposition process or electrophoretic coating, this electrophoretic process can be of a type known in the art. It is unexpected that this known deposition or electrophoretic coating process can be effectively applied both to the interior and to the exterior of a product or support constituted by a three-dimensional porous network of material (a product having a thickness) since the particles would be expected to be applied only to the exterior surfaces instead of to the exterior and interior of this three-dimensional network. According to the present invention, the product comprises a three-dimensional network of materials, it is connected to the power supply as a positive or negative pole, depending on the charge of the particles that are to be applied to this product. The particles are used in suspension in a liquid medium suitable for application to the product or support. In this way, the product to which the particles are applied forms one of the poles or electrodes used in the process. The proportion and amount of particles that are applied to the support and therefore the coating thickness can be controlled by regulating the current (which are determined by electrophoretic deposition parameters such as voltage and solids content of the suspension of particles used in the process and additives) and the total time of the coating process. After the coating process, the coated porous body is usually dried and if required, one or more treatment steps can be carried out. More particularly, the article to be coated is immersed in the coating suspension. Parallel to the geometric surface of the article, which is considered laminar type, the electrodes are located. The electrodes may be constituted by a metal, (for example stainless steel). Depending on the surface charge of the suspended particles, the article to be coated is the pole + or - (cathodic or anodic deposition). The deposition process is usually carried out under constant voltage, which depends on the geometry of the whole system (size / distance of the electrodes) and the properties of the suspension. In general, the correlation is given by: I = n2 * Q2 / n * Uv / d I = current n2 = concentration of colloidal particles Q = colloidal particle charge? = viscosity of the colloidal system U = voltage v = volume between the electrodes d = distance of the electrodes After deposition of the coating, the article that has been coated, dries between 0 ° C and 150 ° C.

Subsequently, a second heating step is performed to achieve an adequate bonding of the coating on the substrate and to make the coating itself more stable against abrasion and other influences. The specific heating cycles and conditions depend on the coating. When used alone, the heating cycle forms the appropriate crystallographic phase. A sol-alumina for example can be dried at 110 ° C and subsequently treated at 550 ° C in an inert atmosphere or containing oxygen to form a transition alumina. Thus, in accordance with the present invention, it is possible to apply a uniform coating essentially to the entire material for a defined thickness of the inner portion of the porous three-dimensional network. For example, if this three-dimensional network is constituted by fibers or wires or their mixtures, each of the fibers or wires in the defined thickness can be coated with these particles uniformly. Although, in a preferred embodiment, essentially the entire thickness of the material is coated with the particles, it is within the spirit and scope of the invention to coat less than all of the thickness with these particles. It is also possible within the spirit and scope of the present invention to have various coating thicknesses within the three-dimensional structure. As indicated above, the aspect of the present invention, wherein large particles are coated electrophoretically more efficiently on a support or product for the use of a sol or colloid is applicable to electrophoretic coating of non-porous supports, wherein essentially only the outside is coated as well as the coating of porous supports, where both the interior and exterior are coated. The invention is further made to a catalytic reactor wherein the reactor contains at least one fixed bed of catalyst constituted by a porous three-dimensional product, coated in accordance with the present invention. The coating of the porous three-dimensional product includes an appropriate catalyst. All or a portion of the coating is applied to the product or support by an electrophoretic process as previously described wherein the electrophoretically applied coating is comprised of only catalyst, or combination of catalyst and support or support and in the case where only the Catalyst support is applied by electrophoretic coating, the catalyst is subsequently applied by another process, for example spray coating or immersion or impregnation. The void volume of the electrophoretically coated product is preferably at least 45% and preferably at least 55% and more preferably at least 65%. In general, the void volume does not exceed 95%, and preferably does not exceed 90%. The term "void volume" as used herein is determined by dividing the volume of the electrophoretically coated product that is open (free of catalyst and material forming the mesh) by the total volume of the electrophoretically coated product (openings, mesh material). and coating) and multiplied by 100. The reactor contains at least one catalyst bed, and this catalyst bed can be formed from one or more layers of the electrophoretically coated product according to the invention. In most cases, the catalyst bed is constituted by multiple layers of this electrophoretically coated product. The electrophoretically coated product according to the present invention can be formed in a wide variety of structures and can therefore be used as a packing element for a catalytic reactor. In this way, for example, the mesh can be processed in corrugated packaging elements, wherein each corrugated packing element forms the fixed catalyst bed that constitutes the electrophoretically coated product. The catalyst bed can be formed from a plurality of these corrugated elements, and the elements can be arranged in a wide variety of shapes and structures. According to a further aspect of the present invention, there is provided a catalyst structure constituted by a plurality of layers of fibers (the layers form a three-dimensional network of material), with the fibers randomly oriented in the layers, with the fibers electrophoretically coated with a porous particle coating, wherein the particle coating is applied to the fibers in the form of particles. In this way, when producing the catalyst structure, the particles comprising the catalyst or a catalyst precursor or a catalyst support (the catalyst support may or may not include a catalyst or catalyst precursor) is applied to the fibers during the coating process in the shape of the particles. In accordance with one aspect of the present invention, a process (and resulting product) is provided to produce a catalyst structure consisting of a support structure that is covered with a particle coating comprising a catalyst. The support structure is a porous mesh structure consisting of multiple randomly oriented fiber layers wherein the fibers inside the mesh-like structure and the fibers in the outer portion of the mesh-like structure are covered with the particulate coating . According to the present invention, the particles of the particulate coating are in the form of particles when applied to the fibers. Thus, according to one aspect of the present invention there is provided a support that is not porous particles, constituted by a plurality of layers of fibers, which are preferably randomly oriented, wherein the fibers of the multiple layers are covered. with a particulate coating comprising a catalyst wherein the coating particles are applied to the fibers as particles. The particles that are applied as a coating can be (i) a catalyst support which may or may not include a catalyst or catalyst precursor or (ii) a catalyst or (iii) a catalyst precursor. In the case where the particles are a catalyst support or heated precursor (applied to the fibers during the coating process in the form of particles.) In accordance with one aspect of the present invention, a process (and product) is provided. resulting) to produce a catalytic structure consisting of a support structure that is covered with a coating of particles comprising a catalyst The support structure is a porous mesh-like structure consisting of multiple layers of randomly oriented fibers, wherein the fibers in the Inside the mesh-like structure and the fibers in the outer portion of the mesh-like structure are covered with the particulate coating In accordance with the present invention, the particles of the particulate coating are in the form of particles when applied to the In this way, according to one aspect of the present invention, a support is provided which is not porous particles, constituted by a plurality of layers of fibers, which are preferably randomly oriented, one of the fibers of the multiple layers is covered with a particulate coating comprising a catalyst wherein the coating particles are applied to the fibers as particles. The particles that are applied as a coating can be (i) a catalyst support which may or may not include a catalyst or catalyst precursor or (ii) a catalyst or (iii) a catalyst precursor. In the case where the particles are a catalyst support that does not contain a catalyst, the catalyst can be added to the support particles coated in the fibers. In the case where the particles are or include a catalyst precursor or where the particles are a catalyst support containing a catalyst precursor, the catalyst precursor is converted to a catalyst by procedures known in the art. The fibers used in the catalyst structure can be of the previously described type and the resulting catalyst structure can also have the properties (void volume etc.) as previously described. The support structure employed in this aspect of the invention is constituted by a plurality of randomly oriented fiber layers and therefore is not and is different from woven mesh structures employed in the prior art. In particular, woven mesh structures include a single layer of material. Thus, in accordance with one aspect of the present invention, a three-dimensional catalyst support, or packing, is provided for a catalytic reactor, wherein the support or packing is formed of a three-dimensional reactive porous product having the previously described characteristics. . The use of a gasket coated with catalyst in a reactor, in particular a fixed bed reactor according to the invention, can provide one or more of the following improvements: low formation of by-products (improved selectivity); superior volumetric activity per unit of reactor volume; improved catalyst life, reduction or elimination of countercurrent mixing; lower pressure drop; improved mixing of reagents and / or products such as liquids and / or gases; superior ratio of geometric surface area of the catalyst; improved mass and heat transfer; etc. The catalytic reactor can be used for a wide variety of chemical reactions. As representative examples of these chemical reactions, there may be mentioned hydrogenation reactions, oxidations, dehydrogenation reactions, catalytic or steam reforming, alkylation reactions, hydrotreating, condensation reactions, hydrocracking, etherification reactions, isomerization reactions, selective catalytic reductions. and catalytic removal of volatile organic compounds, etc. In accordance with another aspect of the present invention, there is provided a method for electrophoretically coating a material in a form that reduces the "edge effect" with respect to the coating on the material. The "edge effect" is one in which the reactive material receives a thicker coating twice its edges than in other portions, particularly the central portions.

Although the ability to reduce the "edge effect" as described herein has particular applicability to electrophoretic coating of a three-dimensional material as previously described, the teachings of the present invention in this respect are also applicable to the electrophoretic coating of non-porous materials , where only the surface of the material is coated. In accordance with this aspect of the present invention, the "edge effect" is reduced so that the difference between the coating thickness around the edges of the coated material and other portions of the coated material is minimized; that is, in the same plane, the coating thickness at the edge of the material essentially equals the coating thickness in other portions of the material. According to one embodiment of the present invention to reduce the edge effect, this edge effect is reduced by electrophoretically coating the material in a shape such that the field lines between the electrode comprising a material to be coated and the electrode or electrodes of opposite polarity adjacent to the electrode comprising the material to be coated, are interrupted. The Applicant has found that the edge effect can be minimized by interrupting or changing the field lines between the electrode comprising a material to be coated and the adjacent electrodes of opposite polarity, this reduction of edge effect can be achieved without the use of counter electrode In this way, in accordance with one aspect of the invention, the electrophoretic coating is achieved by a process employing non-uniform or non-uniform field lines. In another embodiment, the edge effect in an electrophoretic coating process is minimized by electrophoretically coating a material in such a way that the cross section of the electrode comprising material to be coated, and the electrode (s) of opposite polarity adjacent to the material to be coated , as well as the cross section of the coating bath between these electrodes are essentially equal to each other. In this way, the outer shape and dimensions of these electrodes and the outer shape and dimensions of the coating bath between these electrodes are essentially equal to each other. The applicant has found that the use of these dimensions reduces the edge effect. According to another embodiment, the distance between the electrode comprising the material to be coated and the electrodes of opposite polarity adjacent to the electrode comprising material to be coated, is chosen to be a value that minimizes the edge effect during this electrophoretic coating. The applicant has found that by reducing the distance between these electrodes, the edge effect can be reduced. In a preferred embodiment, the distances between the electrode comprising material to be coated and the electrodes of opposite polarity adjacent to this electrode, is less than 100 mm and in general not less than 1 mm. In another embodiment, a dielectric material is placed between the electrode comprising the material to be coated and the adjacent polarity electrodes. This dielectric material has an opening and the dielectric constant thereof is different from that of the coating bath suspension. Preferably, the dielectric constant of this dielectric material is at least 10 times greater than the dielectric constant of the suspension in the coating bath. The opening (s) in the dielectric material generally comprise from 10% to 90% of the area of the dielectric material. In particular, the size or area of the opening or plurality of openings is smaller than the size or cross-sectional area of the material to be coated. In a still further embodiment, the electrophoretic coating is carried out in such a way that the electrodes adjacent to the electrode comprising the material to be coated, and having an opposite polarity, are constituted of a polarity of spaced electrodes, each of which is more It is necessary that the electrode (s) that comprise the material to be coated. In this way, in effect, the electrodes having a polarity opposite to that of the electrode comprising the material to be coated, which is adjacent to the material to be coated, each one is constituted by a plurality of pin-type electrodes, anchored or placed in a dielectric material, with the pin electrodes spaced apart. These pin electrodes create an inhomogeneous or interrupted electric field, which improves the uniformity of the electrophoretic coating; that is, they reduce edge effects. It is contemplated within the present invention that a combination of the techniques described above can be employed to reduce the edge effect. In this way, two or more of these techniques can be used to improve the uniformity of the coating. In this aspect, for example when using the technique where the dimensions of the electrodes as well as the bath between electrodes have essentially identical dimensions, the distance between the electrodes is chosen to minimize the distance between the material to be coated and the electrode of opposite polarity adjacent, thus improving the uniformity of the coating. Similarly, in some cases the two prior techniques can be combined with the use of a dielectric material between adjacent electrodes having an appropriate opening. When a dielectric material with appropriate bevels is employed, the uniformity of the coating thickness can be manipulated to provide a wide variety of coating thickness differences. In this way it is possible to control the openings in this dielectric material, so that the central portions of the material to be coated have a coating thickness greater than the edge portions and vice versa.

However, in a preferred embodiment, by appropriately controlling the openings in the dielectric material, it is possible to reduce the edge effect and obtain a uniform coating on the cross-sectional area in a given plane of the material being coated. The drawings illustrate embodiments of the invention, wherein: Figure 1 is a simplified schematic of an electrophoretic coating apparatus; Figure 2 is a simplified schematic of an electrophoretic coating apparatus with means for reducing edge effects; Figure 3 is a simplified schematic of an electrode for reducing edge effect; Figure 4 is a simplified schematic of an electrophoretic coating apparatus for reducing edge effects; and Figure 5 is a simplified schematic of an electrophoretic coating apparatus that includes means for locating the material to be coated. An example for a deposition apparatus is given in Figure 1. The electrodes (1) made of an electrically conductive sheet, for example of stainless steel, are immersed in the colloidal fluid (10), all of which is inserted in a container ( fifteen) . The article to be coated by the colloidal particles is placed between the two electrodes. The geomeof the structure can be varied such that one electrode or more than two electrodes are used. The article to be coated (20) can be placed between two electrodes (1) or opposed to a single electrode or between an assembly of two or more electrodes. In Figure 2 a schematic representation of a coating unit is illustrated, which includes a dielectric material between the electrode comprising the product to be coated and the electrode of opposite polarity. As illustrated in Figure 2, the product electrode is 21, the electrode of opposite polarity is 22, and the dielectric material is 23, which includes a slot opening 24. Although a dielectric material with a slot opening is illustrated, As indicated above, other openings in the dielectric material are possible, within the scope of the present invention. For example, the opening may be a square or rectangular opening or a plurality of openings in the dielectric material. With reference to Figure 3, an electrode is illustrated in which the electrode is constituted by a plurality of separate and distinct electrodes, which are used as an electrode with a polarity opposite to the electrode comprising material to be coated electrophoretically. As illustrated in Figure 3 this electrode is constituted by a plurality of pin-type electrodes 31 in a dielectric material 32. In Figure 4, a schematic representation of an electrophoretic coating design is illustrated, wherein the electrode comprising Coating, the electrodes of opposite polarity and the coating bath between the electrodes, have essentially the same dimension. As illustrated in Figure 4, the electrode comprising material to be coated is designated as 41, and the two electrodes of opposite polarity are designated 42 and 43. As shown, the electrodes 41, 42 and 43 essentially have the same dimensions and the height and width of the tank 44 to contain the electrophoretic coating material 46 is such that the electrophoretic coating material in the tank can be maintained essentially equal to the height of the electrodes. As previously indicated, the techniques for reducing the edge effect of the present invention have particular applicability to the coating of a three-dimensional porous network of material by electrophoretic coating in a form such that in addition to the exterior of the material, at least a portion of the interior of this three-dimensional network is coated. However, these techniques can also be used to coat the surface of non-porous materials. In a preferred but non-limiting embodiment of the invention, electrophoretic coating is effected in such a way that the distance between the sheet and each electrode of opposite polarity is 50 mm. The size of the electrode, the specimen and the cross section of the bathroom is 30 x 30 cm. In this aspect, this structure can be achieved by the use of a support that locates the sheet to be coated at the desired distance from the other electrode. The sheets are fixed in a container box, which is mobile. The container is inserted into coating units and drying units. The mobile container is removed with the electrodes with a design that allows "self-location by gravity" (distance support) of the leaves - mesh. The electrical contacts are guided through the distance supports, so that no external electrical contact is necessary. This makes the process easy to handle, reliable and allows simple atuomatization. With reference to Figure 5, a container or cell 64 is illustrated, constituted by a first wall in the form of an electrode 62, a second wall in the form of an electrode 63 and a non-conductive bottom wall 66. As illustrated in Figure 5, the sheet 60 to be coated is placed in the deposition vessel 64, (Figure 5a); and the sheet 60 is supported "not located" in the deposition cell vessel 64 (Figure 5b). The container 64 is inclined at an angle of 45 ° (Figure 5c) and the sheet 60 falls into the distance supports 61 which include an electrode 67 which is of opposite polarity to both electrodes 62 and 63. The transport of electrical current during the deposition Electrophoretic, is regulated by the transport of charge of colloidal particles and ion transport. The latter is undesired because it is a current transport without any benefit. Because of this, the concentration of ions should be kept to a minimum. The invention will be further described with respect to the following examples; however, the scope of the invention is not limited in this way: Example 1: Configuration and process to electrophoretically incorporate gamma-alumina into and within a sheet of metal felt. The tank contains an alumina sol with particle size in the range of 1 to 60 nm, preferably 10-30 mm. The system is stabilized to establish a sufficiently long storage life by the addition of nitric acid or acetic acid. Aqueous solutions are preferred because these systems are easy to handle. The concentration of solids of alumina in the sol is between 1 and 30% by weight, 5-10% by weight is preferred. Positive electrodes of stainless steel plates are preferred while the negatively charged electrode is the article to be coated, which may consist for example of a metal felt with a thickness of 1 mm made of metal fibers with a thickness of .02 mm (20 microns). ) with 90% void volume and an average void gap of .02 (20 microns). The article to be coated with a size of 10 by 10 cm. For deposition, a current is applied, a voltage between 10 and 20 V and a current between 0.1 and 100 mA per cm 2 of specimen surface, preferably 10-40 mA per cm 2 of surface. After 1-10 minutes of deposition, the specimen is removed from the tank, dried to evaporate water and subsequently sintered (for example at a temperature of 500 ° to 550 ° C for 1 to 3 hours, preferably 500 ° C for 1 hour) to form oxide of gamma alumina which is suitably bonded to the metal surface and has the appropriate active surface between 100 and 300 m2 / g. Depending on the concentration, the current and the deposition time, charges of alumina up to 30% can be incorporated into the metal felt. Example 2: Co-deposition of sol and particles in an electrophoretic process Suspensions of micrometer particles exhibit an electrophoretic mobility and the solid particles migrate to the fiber network of the article to be coated. These micrometer-sized particles having a size of .0005-.01 mm (0.5-10 microns) can be titanium oxide, alumina, zeolite or any other compound. Depending on the nature of the particles, it is possible to improve the connection of the particles on the metallic wire surface by co-deposition of the particles in conjunction with a sol. The sun acts as an adhesive that connects the particles to the fiber surface and to each other. The process begins with a stable suspension of micro particles containing a sol (nano-particles) with a concentration in the range from less than 1% to 20% or even higher. By subjecting the sol / suspension mixture to electrophoretic deposition, it results in a migration of both the nano-particles (ie sol) and the micrometer particles to the fiber network. A co-deposition on the surface of the fibers is carried out. As a result, the micrometer particles are more firmly connected on the metal surface by the sun: after heating at temperatures above 100 ° C, the dry coating begins to solidify and the sun begins to form a crystalline state. The micro-particles are embedded in a porous thin-film coating and thus tightly connected to the metal. The coated products of the present invention can be used for a wide variety of applications, including but not limited to, use as a catalyst, separation membrane, packing (non-catalytic or catalytic) for columns, particularly distillation columns; detectors; separation devices other than membranes; adsorbents for adsorption columns. These and other uses should be apparent to those skilled in the art from the present teachings. Example 3: Coating with Edge Effect Removed A coating deposition cell contains two plaque-type stainless steel electrodes, with the same geometry as the cross section of the bath: 30 cm by 30 cm. The distance of the electrodes from each other is 100 mm.

Water and a sol-alumina binder (40 nm) are mixed: the amount of sol-binder is regulated by the total amount of aluminum oxide (<0.003 mm (<3 microns)) of oxide powder, which in this example it is 10% by weight. The amount of sol-binder is 2% by weight of the amount of solid powder. This mixture is stirred vigorously and 1% by weight (related to the amount of oxide powder) of quaternary amine is added. The pH is then adjusted by adding diluted nitric acid to pH 4-4.5. Finally, the aluminum oxide (<0.003 mm (<3 microns)) powder is added step by step while the suspension is stirred further. After transferring the suspension to the deposition unit, a fiber mesh sheet (30 cm x 30 cm) that has been annealed at 300 ° C for 1 hour is inserted in the midplane between the two electrodes. A potential of 10 V is applied through the electrodes and the fiber mesh. A deposition time of 60 seconds is sufficient to charge the interior of the fiber mesh structure with 25% by weight of oxide powder. After the deposition is made, the mesh is removed from the bath, the adhering drops are blown off by an air blower and dried by a stream of hot air. The final stage is sintering at 500 ° C for 1 hour in the air.

Numerous modifications and variations of the present invention are possible in the light of the foregoing teachings and therefore, within the scope of the appended claims, the invention may be practiced otherwise, not as particularly described.

Claims (21)

1. CLAIMS 1. A process for applying a coating to a product comprising a three-dimensional porous network of material, characterized in that a porous product comprises a three-dimensional network of material, is coated by applying particles to the product by electrophoretic coating in an electrophoretic coating bath, for coating the outer surface of the product and at least a portion of the interior of the product, and further characterized in that the electrophoretic coating bath comprises a liquid and the particles when applied as a coating, because the particles are suspended in the liquid, the particles include at least a portion of the particles and at least a second portion of particles, and in that the first portion of particles has an average particle size of at least .005 mm (0.5 microns) and the second portion of particles has a lower average size at 150 nanometers.
2. 2. The process according to claim 1, further characterized in that the particles that are applied comprise a member selected from the group consisting of an unsupported catalyst, a catalyst support and a supported catalyst.
3. 3. The method according to claim 1, further characterized in that the coating is applied to the interior and penetrates the interior of the product to a depth of at least .005 mm (5 TT? ' HS i.
4. 4. The process according to claim 1, further characterized in that the product that is electrophoretically coated comprises a fibrous network of material.
5. 5. The process according to claim 4, further characterized in that the fibers of the fibrous web of material have a thickness of less than .5 mm (500 microns).
6. 6. The process according to claim 4, further characterized in that the particles that are applied have a particle size of less than 0.1 mm (100 microns).
7. 7. The process according to claim 4, further characterized in that the product that is electrophoretically coated has an average void opening of at least 0.01 mm (10 microns).
8. The method according to claim 1, further characterized in that the three-dimensional network of material forms a structure comprising a plurality of layers of fibers having a particulate coating on the fibers, and that the particles that are applied comprise minus one member selected from the group consisting of a catalyst support, an unsupported catalyst precursor and an unsupported catalyst.
9. The process according to claim 8, further characterized in that the particles comprise a catalyst support that includes a catalyst or catalyst precursor comprising fibers with a diameter or thickness less than .1 mm (100 microns).
10. The method according to claim 8, further characterized in that the three-dimensional network of material forming a structure has a thickness of at least .05 mm (50 microns) and the fibers of the three-dimensional network of material comprise fibers with a diameter or thickness less than .1 mm (100 microns).
11. The method according to claim 1, further characterized in that the three-dimensional network of material comprises a plurality of layers of fibers, because the fibers on the outside are covered with a uniform coating and because at least a portion of the fibers in their interior is covered with a uniform coating.
12. 12. The process according to claim 11, further characterized in that the particles are selected from the group consisting of a catalyst support, a catalyst precursor and a catalyst, and because the three-dimensional network of material has a thickness of at least .05 mm (50 microns).
13. The method according to claim 12, further characterized in that the catalyst support includes a catalyst.
14. 14. The method according to claim 11, further characterized in that the fibers are metal fibers.
15. 15. The process according to claim 12, further characterized in that the fibers have a thickness of less than 0.1 mm (100 microns) and that the three-dimensional network of material has a thickness of at least 0.05 mm (50 microns).
16. 16. The method according to claim 1, further characterized in that the electrophoretically coated product has a gap of at least 45%.
17. The method according to claim 1, further characterized in that the three-dimensional network of material is electrophoretically coated in an electrophoretic coating bath by application of a potential between a first electrode comprising the three-dimensional network of material and a second electrode, and because the electrophoretic coating is effected with electric field lines interrupted between the first and second electrodes, to reduce the difference in thickness between the coating of the edges of the three-dimensional network of material and other portions of the three-dimensional network of material.
18. 18. The method according to claim 17, further characterized in that the first and second electrodes are positioned at a distance from each other that produces non-homogeneous field lines between the first and second electrodes.
19. The method according to claim 17, further characterized in that a dielectric material having an opening is placed between the first and second electrodes during the electrophoretic coating and because the three-dimensional network of material has a dielectric constant that differs from the dielectric constant. of the bathroon.
20. The method according to claim 18, further characterized in that the second electrode is constituted by a plurality of electrodes spaced apart to produce non-homogeneous field lines.
21. 21. The method according to claim 17, further characterized in that the cross section of the first and second electrodes and the portion of the electrophoretic coating bath between the first and second electrodes are essentially equal to each other.