COMPOSITE MEMBRANE FOR CHEMICAL SYNTHESIS

Abstract: This invention is a composite membrane for chemical synthesis, a method of using the composite membrane, and a chemical reactor into which the composite membrane might be incorporated. The composite membrane comprises a multiphase conducting path having both a cation conductive phase and an electron conductive phase. Surfaces of the composite membrane can be supplied with appropriate catalyst layers in order to increase favorability of a given reaction. By placing appropriate composition(s) in contact with each surface of the composite membrane, cations and electrons are conducted from one surface through the composite membrane to the other surface in order to form reaction products without the use of an external electrical circuit. A chemical reactor utilizing this composite membrane may safely react such elements as H2 and O2 to form H2O2 at room temperature without input of external electricity or use of complex electrical equipment or organic solvents.

Description: COMPOSITE MEMBRANE FOR CHEMICAL SYNTHESIS This invention pertains to a composite membrane for chemical synthesis, a method of using the composite membrane, and a chemical reactor into which the composite membrane is incorporated. Most hydrogen peroxide (H2O2) is manufactured by a well known anthraquinone process. See for example Binran, 1 Appl. Chem., Ed. Chem. Soc. 302 (Japan 1986). Among the disadvantages of this process are that it requires the addition of numerous organic solvents, forms many unwanted by-products, and requires various separation steps. In contrast, fuel cells provide a potential means for synthesis by safely reacting H2 and O2 directly in a single reactor without the use of organic solvents. Using a reactor cell design similar to fuel cells provides an environment wherein reactants are separated by an ion exchange membrane. With H2O2 synthesis, for example, it is advantageous to separate the H2 and O2 reactants because mixtures of the reactants may be explosive and constitute a serious safety hazard. Separating the reactants allows relatively high pressures to be used safely, increasing the rate of reaction. Reactor ceils also provide effective environments for the use of catalysts that are optimized for specific reactions. However, fuel and reactor cells typically require complex electrical equipment in order to collect and transport electrons from one side of the cell to the other. This equipment is generally inappropriate for large scale manufacturing operations. Other methods require the input of external electrical energy, the use of corrosion resistant equipment, or a combination thereof. In addition, many reactor cells require relatively high operating temperatures (for example 70°C-90°C) in order to be effective. It would be desirable to have a method and reactor cell that does not require organic solvents, complex electrical equipment, or input of external electricity, but yet relieves the danger of explosion and is effective at room temperature. The invention seeks to eliminate many of the difficulties indicated above. A reactor cell has now been discovered that does not require complex electrical equipment or input of external electricity. The reactor cell also provides a means for effective, room temperature, H2O2 synthesis by safely reacting H2 and O2 directly in a single reactor in the absence of organic solvents. The reactor cell has a composite membrane comprising both electron and cation conducting materials. For purposes of this invention, any reference to "cation" also includes "proton." Thus, a cation conductive material is inherently a proton conductive material. By filling a porous electronic conductor, such as graphite cloth, carbon paper, or porous metal, with a cationically conductive material, such as a polymer of perfiuorinated sulfonic acid (PFSA), the electronic conductor becomes a path to transfer electrons required to activate reactants. In addition, cationically conductive material surfaces can be coated with appropriate catalysts to increase favorability of a given reaction. This reactor cell may be effective in performing many different chemical synthesis reactions such as: H2O2 from l- and O2; H2SO4 from SO2, H2O, and O2 (see Langer et al., "Chemicals With Power," Chemtech 226, 229 (April 1985)); amine dyes from organo-nitro compounds (see Spillman et al., "Why Not Make Chemicals in Fuel Cells?," Chemtech 176, 182 (March 1984)); and phenol from benzene (see Otsuka et al., "Direct Synthesis of Phenol from Benzene during O2-H2 Fuel Cell Reactions," 139 [No. 9] J. Electrochem. Soc. 2381 (1992)). Of these reactions, synthesis of H2O2 is currently felt to be of significant importance and shall be discussed more specifically herein. However, one skilled in the art is capable of adapting the composite membrane system of this invention to other chemical reactions, including electrochemical reactions, and the specific discussion of only H2O2 synthesis is not meant to limit the scope of this invention. Specifically, a first aspect of this invention comprises a multiphase conductive path. The multiphase conductive path comprises an intimate, substantially gas-impervious, multiphase mixture of an electron conducting material with a cation conducting material wherein the electron conductive phase is internally dispersed throughout the cation conductive phase. "Internally dispersed" means that the phases, although independent and substantially continuous, are integrally intermixed such that the electron conductive phase is an interpenetrating network and not exclusively positioned external in relation to the cation conductive phase. The phrase "substantially gas-impervious" means that the mixture serves to prevent all but an insignificant amount of gas to pass through the mixture as a gas (that is, the mixture is non-porous, rather than porous, with respect to relevant gases). In some cases, an insignificant degree of permeability to gases might be acceptable or unavoidable, such as when hydrogen gas is present. The multiphase conductive path differs substantially, however, from "doped" materials known in the art. Typical doped materials have a small amount of a material (dopant) added to a host material such that atoms of the dopant become permanently intermingled with atoms of the host material and form a substantially single phase. In contrast, although the multiphase conductive path of the invention has an electron conductive phase internally dispersed throughout a cation conductive phase, each phase is substantially discrete and identifiable by such routine procedures as electron microscopy, X-ray diffraction analysis, X-ray absorption mapping, and electron diffraction analysis. The cation conductive phase may comprise any material which exhibits both a sufficient cationic conductivity under the method of this invention and an ability to have the electron conductive phase internally dispersed or embedded therein. One skilled in the art is capable of determining effective cation conductive phases for performing this function. A typical cation conductive phase is an ion exchange membrane having negatively charged groups bound within the membrane. A particularly preferable cation conductive phase comprises a polymer of perfluorosulfonic acid (PFSA). For a discussion of some commonly preferred PFSA polymers, and methods of preparing such polymers, see De Vellis et al., U.S. Patent No. 4,846,977, col. 5, lines 1-36. See also Kirk-Othmer, "Perfluorinated-lonomer Membranes," Encyclopedia of Chemical Technology, pp. 591- 98 (1984) and A. Eisenberg and H. Yeager, "Perfluorinated lonomer Membranes", ACS Symposium Series No. 180 (1982). An example of a commercially available PFSA polymer is NAFION™ (E.I. du Pont de Nemours and Company). Additional cation conductive phases may be materials such as sulfonated styrene grafts on a polytetrafluoroethylene backbone (commercially available from RAI Research Corporation as RAIPORE™ membranes) and crosslinked sulfonated copolymers of vinyl compounds (commercially available from Ionics, Inc., as TYPE CR™ membranes). The electron conductive phase of the membrane can be any material which exhibits sufficient electronic conductivity under the conditions of a given reaction such as porous metal or metal screen, carbon paper, graphite cloth, graphite or carbon powder, graphite or carbon fibers, or combinations thereof. The porous metal or metal screens may also be formed from one or more metals or metal compounds. Suitable metals include such metals as silver, gold, rhodium, ruthenium, palladium, nickel, cobalt, and copper. A suitable metal alloy, described by Gosser et al., U.S. Pat. No. 4,832,938 (1989), comprises platinum and palladium. Depending upon the physical structure and density of each phase, a typical multiphase conductive path contains from 1 to 75 percent by volume (v/o) of electron conductive phase and from 25 to 99 v/o cation conductive phase. Materials that have a lower density or form more randomly oriented phases generally must be present in a higher percent by volume to obtain sufficient conductivity for typical reactions. The multiphase conductive path of this invention may be fabricated by combining at least one electron conductive phase with at least one cation conductive phase and shaping the combined phases to form a dense, gas-impervious, multiphase solid membrane, sheet, film, or body. In particular, the multiphase conductive path may be prepared as follows: (a) prepare an intimate mixture of at least one material which is electronically conductive and at least one material that is cationically conductive; (b) form the mixture into a desired shape; and (c) heat the formed mixture to a temperature sufficient to form a dense and solid membrane having electron and cation conductive properties. One skilled in the art will recognize that, depending upon the materials used, pressure may also be beneficially applied in forming the dense and solid membrane. It is important to note that, as is well known in the art, non-thermoplastic, commercially available cation conductive materials may require some pretreatment before forming the multiphase conductive path. For example, before preparing the "intimate mixture" of Step (a), above, NAFION™ may be dissolved into a solution with an appropriate solvent (for example dimethylformarnide (DMF)) as described by Martin et al., "Dissolution of Perfluorinated Ion Containing Polymers," 54 Analytical Chemistry\639 (1982). This solution can then be used to mix with, or impregnate, the electronically conductive material. The solvent is then evaporated, forming the desired multi-conductive path of this invention. Another fabrication technique utilizes extrusion of the materials to form the multi-conductive path. Here, for example, graphite fibers can be mixed with a thermoplastic ion conductive or ion conductive precursor material (for example a polymer of perfluorosulfonyl fluoride (PFSF)) to form a mixture that can be extruded by any well-known extrusion technique to form the multi-conductive path. If an ion conductive precursor material is used to mix with the electron conductive material, it is necessary to convert the precursor material into the ion conductive material. For example, in the case of PFSF, this may typically be done by treating the precursor material with a 22 v/o sodium hydroxide (NaOH)/H2θ solution at 80°C for about 16 hours. The composite membrane for chemical synthesis may further comprise a first layer that includes an oxidizing agent and a second layer that includes a reducing agent. The multiphase conductive path has at least a first surface and second surface. The first and second layers are separately and operatively connected, one layer to each surface. "Operatively connected" means that the first and second layers are positioned such that the multiphase conductive path is capable of conducting both cations and electrons from the first layer to the second layer. Each surface of the multiphase conductive path may or may not be distinguishable from the other surface and may be operatively connected to either of the layers as long as both cations and electrons are conducted from the first layer to the second layer. In H2O2 synthesis, the first layer oxidizes hydrogen to protons and electrons and the second layer, in combination with the protons and electrons produced at the first layer, reduces oxygen to hydrogen peroxide. The first layer may comprise any catalytic material ("agent") that facilitates oxidation and the second layer may comprise any catalytic material ("agent") that facilitates reduction. One skilled in the art is capable of determining effective oxidizing and reducing agents for performing these functions. The agents may be "supported" and, as long as cations and electrons are conducted from the first layer to the second layer through the multiphase conductive path, the layers may be operatively connected by either: discrete layers attached, or adjacent, to the multiphase conductive path; or, a non-discrete layer, mixed directly into the multiphase conductive path. Methods for depositing metallized layers on membranes are well known in the art and a skilled artisan is capable of optimizing these deposition methods to operatively connect the first and second layers to the multiphase conductive path of this invention. Examples of such deposition methods are • disclosed in Nidola et al., U.S. Pat. No. 4,364,803 (1982) and Takenaka et al., U.S. Pat. No. 4,328,086 (1982). Particularly preferable oxidizing and reducing agents include metals and metal containing compounds. Examples of metals and metal containing compounds useful for the first layer in H2O2 synthesis include: platinum, palladium, ruthenium, sodium tungsten bronzes, tungsten carbide, platinized boron carbide, and mixed metal and spinel electrocatalysts. Further examples of potential oxidizing agents are generally discussed in Appleby et al., "Electrocatalysis of Hydrogen," Fuel Cell Handbook 322-35 (Van Nostrand Reinhold 1989). A preferred oxidizing agent in H2O2 synthesis is platinum (Pt). Examples of metals and metal containing compounds useful for the second layer in H2O2 synthesis include: silver, gold, bismuth, palladium, lanthanum, zinc, lanthanides such as gadolinium, niobium-titanium, lanthanum-manganese mixtures, indium-tin oxide mixtures, praeseodymium-indium oxide mixtures, metal phthalocyanines (see for example Cook et al., 137 [No. 6] J. Electrochem. Soc. 2007 (1990)), metal porphyrins (see for example Chan et al., 105 J. Am. Chem. Soc. 3713-14 (1983)), and anthraquinone-based catalysts (see for example Degrand, 169 J. Electoanal. Chem. 259-68 (1984)). Such catalysts may also include mixtures and compounds (such as oxides thereof) containing at least one of the above described catalysts. Preferred reducing agents for H2O2 synthesis include gold (Au), gadolinium (Gd), or compounds thereof . A second aspect of this invention is a method of chemical synthesis. This method comprises, first, placing an electron and cation producing composition in contact with an oxidizing agent to produce at least one electron and at least one cation. For H2O2 synthesis using this invention's composite membrane having the first and second layers, it is necessary that the electron and cation producing composition be a hydrogen containing composition. A preferable hydrogen containing composition is, simply, H2- When the electron and cation producing composition contacts the first layer of the composite membrane, the composition is oxidized. For example, with H2O2 synthesis, when H2 is used as the electron and cation producing composition, the oxidizing agent (for example Pt), upon contact with the H2, promotes oxidation to two protons and two electrons. The method of chemical synthesis comprises, second, conducting at least one electron and at least one cation via a multiphase conductive path to an interface between a reducing agent and a reducible composition. For H2O2 synthesis, using this invention's composite membrane having the first and second layers, at least one electron and at least one cation is conducted from the first layer to the second layer through the multiphase conducting path. Electrons and cations, generated at the first layer and conducted through the multiphase conducting path to the second layer of the composite membrane, are then placed in contact with the reducible composition at an interface between the second layer and the reducible composition. The electron(s) and the cation(s) then react with the reducible composition to form a reaction product such as H2O2. For H2O2 synthesis, the reducible composition must be an oxygen containing composition. A preferred oxygen containing composition comprises air or, simply, O2. It may also be preferable for the oxygen containing composition to further comprise H2O when using this invention's composite membrane having the first and second layers. The H2O helps dilute the H2O2, thereby reducing its potential decomposition. The H2O also helps keep the composite membrane hydrated, thereby allowing good ionic conductivity. For the latter purpose, the hydrogen containing composition, described above, may also further comprise H2O. When the reducible composition is placed in contact with the layer comprising a reducing agent, and at least one electron is provided, the composition is reduced. For example, when O2 is used as the reducible composition, the reducing agent (for example Au) and an electron, upon contact with the O2, promote reduction of the O2 to an anion (O2-). H2O2 may then be formed by contacting two protons (H+) and another electron with the anion (O2-). This method of chemical synthesis may, if desired, be conducted at an elevated temperature. Generally, the temperature should not exceed a temperature at which any one of the materials of the composite membrane significantly decomposes or degrades. This temperature, and the significance of composite membrane degradation, vary according to the composition of the composite membrane. One skilled in the art is capable of determining both appropriate temperatures for conducting various synthesis reactions and whether decomposition is significant. For example, by placing a gaseous H2 feed in contact with a first layer having Pt deposited thereon and placing a gaseous O2 and H2O feed mixture in contact with a second layer having Au deposited thereon, H2O2 synthesis is favorable using a PFSA/graphite-cloth composite membrane at a temperature of from 0°C to 50°C. Preferably, the synthesis is conducted at a temperature from 5°C to 20°C. A temperature in this range not only favors H2O2 synthesis, but is also far below the temperature at which this composite membrane will begin to degrade (about 200°C). In addition, the method of the invention is typically conducted at a pressure of from ambient (taken as about 100 kPa) to 14,000 kPa (about 2030 psi). It is preferred that a pressure differential between each side of the composite membrane does not exceed 415 kPa (about 60 psi). Generally, increased pressure provides an increased mass transfer rate of the reactants. By optimizing the mass transfer rates to suit a particular reaction, a skilled artisan may increase yield of a given reaction product. For H2O2 synthesis, a particularly preferable pressure is from 750 kPa (about 109 psi) to 5,516 kPa (about 800 psi). Finally, it is preferable to remove any reaction products from the second layer of the composite membrane. This isolates desirable reaction products and minimizes undesirable side reactions such as H2O2 decomposition. A third aspect of this invention is a chemical reactor. The chemical reactor comprises the composite membrane having the first and second layers described above, an oxidizing chamber, and a reducing chamber. The composite membrane having the first and second layers is positioned between, and operatively connected to, both the oxidizing chamber and the reducing chamber such that the first layer of the composite membrane faces the oxidizing chamber and the second layer of the composite membrane faces the reducing chamber. "Operatively connected" means that the chambers are positioned such that relevant composition(s) contained therein can be placed in contact with appropriate layers forming an interface between the relevant composition(s) and the appropriate layers. "Chamber" includes any vessel, space, zone, or the like, capable of substantially containing • and facilitating contact between any relevant composition and an appropriate surface of the composite membrane. Thus, an oxidizing chamber provides an effective environment for introducing, containing, and placing the electron and cation producing composition in contact with the first layer of the composite membrane. Similarly, the reducing chamber provides an effective environment for introducing, containing, and placing the reducible composition in contact with the second layer of the composite membrane. In addition, each chamber desirably has at least one opening for supply, removal, or a combination thereof, of relevant composition(s), reaction products, or both. The chemical reactor may further comprise a means for supplying the electron and cation producing composition to the oxidizing chamber and a means for supplying the reducible composition to the reducing chamber. Each of these means may be any conventional system or apparatus that transports relevant compositions from a source of the compositions into the oxidizing or reducing chamber. In its simplest form, each means may be a pump and a conduit or passageway operatively connected to a source of the composition such that the relevant composition is pumped from its source, through the conduit, and into its respective chamber. The chemical reactor may further comprise a similar type of means to recover reaction products, such as H2O2, from the reducing chamber. A typical chemical reactor of this invention functions by oxidizing an electron and cation producing composition, contained in the oxidizing chamber, at an interface between the first layer and the composition, producing at least one electron and at least one cation. The electron(s) and cation(s) are then conducted through the composite membrane to the second layer of the composite membrane where the electrons contact a reducible composition, contained in the reducing chamber, at an interface between the composition and the second layer of the composite membrane, the electron(s) reducing the composition. The reduced composition then reacts with the internally conducted cation(s) to form at least one reaction product. The reaction product(s) may then be recovered from the reducing chamber by conventional means. EXAMPLES EXAMPLE 1 The invention will be further clarified by a consideration of the following examples, which are intended to be purely exemplary of the use of the invention. Alcohol was allowed to evaporate off of 100 milliliters (ml_) of a 5 weight percent (wt%) PFSA/alcohol solution (commercially available from Aldrich Chemical as NAFION™) at room temperature and atmospheric pressure to form a PFSA residue. The PFSA residue was then dissolved in 100 ml. of dimethylformamide (DMF) to form a solution of 5% PFSA/DMF. An amount of 0.085 grams of 1 micron graphite powder (available from Ultra Carbon Corporation, Item No. UCP 1- M) was then formed into a suspension with 6 mL of the PFSA/DMF solution. The suspension was then poured into a 1.5 inch (3.81 cm) diameter aluminum dish and the dish was allowed to sit at room temperature and atmospheric pressure for about 24 hours so that the DMF evaporated. After evaporation of the DMF, an approximately 100 micron thick film of multiphase conductive path containing 20% graphite carbon was removed from the dish. The film had an electronic resistivity of about 0.3 ohms. Oxidizing and reducing catalysts were applied to approximately 6 cm 2 of surface area on separate sides of the film by a direct paint on (DPO) method. For the DPO method, two inks were made, one for each catalyst. Both inks were made by forming suspensions of a catalyst with a propylene carbonate vehicle and a binder. A reducing catalyst ink was made from 40% gold on carbon black (commercially available from E-TEK, Inc.). An oxidizing catalyst ink was made from 20% platinum on carbon black (commercially available from E-TEK, Inc.). The binder consisted of the same 5 wt% PFSA DMF solution as used to form the film and it was added to each of the catalyst inks in an amount such that the weight of the catalyst on carbon black was 2.5 times greater than the weight of PFSA in the PFSA/DMF binder. The reducing catalyst ink was painted onto the film in an amount sufficient to provide a 1.0 mg/cm 2 metal loading and the oxidizing catalyst ink was painted onto the opposite side of the film in an amount sufficient to provide a 0.3 mg/cm 2 metal loading. Each ink was painted one at a time onto the composite membrane while the membrane was on a heated (about 50°C), fritted vacuum table. The table ensured that the membrane remained flat and aided in the evaporation of the propylene carbonate and DMF. Evaporation of the propylene carbonate vehicle and DMF formed a multiphase conductive path composite membrane having an oxidizing agent layer and a reducing agent layer deposited thereon. The composite membrane was then operatively connected into a reactor such that the oxidizing catalyst faced an oxidizing chamber of the reactor and the reducing catalyst faced a reducing chamber of the reactor. Hydrogen gas, which had been humidified with water vapor at 50°C, was contacted with the oxidizing catalyst at a pressure of about 300 kPa (about 44 psi). Oxygen gas was contacted with the reducing catalyst at a pressure of about 350 kPa (about 51 psi). The reactor was maintained within a temperature range of between 0 and 40°C. Each gas was continuously fed to its respective catalyst for a period of 4.25 hours. A reaction product was formed having a concentration of 0.05 wt% hydrogen peroxide. EXAMPLE 2 Two 1.5 inch (38.1 millimeter (mm)) by 1.5 inch pieces of 5 mil (127 micron) thick carbon paper (available from Spectrocarb Corporation) having a density of about 0.35 g/cm 3 were sandwiched around a 3.5 inch (88.9 mm) by 3.5 inch sheet of 3 mil (76.2 micron) thick perfluorosolfonylfluoride (PFSF) to form a carbon paper, PFSF, carbon paper sandwich. The sandwich was then covered on each side with independent non-stick sheets of about 2 mil (50.8 micron) thick KAPTON™ polyimide film (available from 3M Corporation), then hot pressed at 290° C and 1380 kPa for five minutes. Hot pressing the sandwich caused the two carbon papers to touch each other and PFSF extruded through pores in the papers, to form a cohesive sandwiched body. The cohesive sandwiched body was then immersed in a caustic solution of 25 wt% NaOH/^O at a temperature of 80° C for 20 hours. This converted the PFSF to its PFSA-sodium salt form, resulting ' in a multiphase conductive path. The multiphase conductive path was then rinsed with deionized (Dl) water. Oxidizing and reducing catalysts were independently applied to separate sides of the multiphase conductive path by a direct paint on (DPO) method. For the DPO method, two inks were made, one for each catalyst. Both inks were made by forming suspensions of a catalyst with a propylene carbonate vehicle and a binder. The binder consisted of 5 wt% PFSA in a 50 wt% ethanol in water solution and it was added to each of the catalyst inks in an amount such that the weight of the catalyst on carbon black was 2.5 times greater than the weight of PFSA in the PFSA/ethanol/^O binder. The propylene carbonate was added in such an amount that it was 2.5 times the amount of catalyst and carbon, by weight. The reducing catalyst in the reducing catalyst ink was 20% gadolinium oxide on carbon black (weight ratio of Gd to Gd and carbon weight) made from crystalline Gd(Nθ3)3 • 6 H2O (a water soluble salt of gadolinium available from Aldrich Chemical Company). First, crystals of the gadolinium salt (0.72 g salt/g carbon) are dissolved in a minimum amount of water. Second, carbon black (available as VULCAN XC-72R™ carbon black from Cabot Corporation) is added to the salt solution to form a paste, as per a method of incipient wetness as known in the art. Next, the water is removed from the paste by heating the paste gently while grinding in a mortar and pestle. The resulting Gd +3 /carbon powder was then placed into a convection oven and maintained at a temperature of 120 ° C for at least 30 minutes to form the reducing catalyst. The oxidizing catalyst in the oxidizing catalyst ink was made from 20% platinum on carbon black (available from E-TEK, Inc.). The reducing catalyst ink was painted onto a carbon paper part of the composite in an amount sufficient to provide a 0.2 mg/cm 2 metal loading and the oxidizing catalyst ink was painted the carbon paper on the opposite side of the composite in an amount sufficient to provide a 0.3 mg/cm 2 metal loading. Each ink was painted one at a time onto the composite membrane while the membrane was on a heated (about 50°C), fritted vacuum table for at least 30 minutes. The table ensured that the membrane remained flat and aided in the evaporation of the propylene carbonate and ethanol/^O. Evaporation of the propylene carbonate vehicle and ethanol/^O formed a multiphase conductive path composite membrane having an oxidizing agent layer and a reducing agent layer deposited thereon. This multiphase conductive path composite membrane was then placed back into the same hot press, as described previously using the non-stick sheets of about 2 mil (50.8 micron) thick KAPTON™ polyimide film, and hot pressed at 150° C and 1380 kPa for five minutes. The composite membrane was then removed and cooled to room temperature. This cooled composite membrane was then immersed in 1 N H2SO4 for 30 minutes at room temperature to convert the sodium salt form of the PFSA to its proton form. The composite membrane was then re-flattened by putting it back on the heated (about 50°C), fritted vacuum table for at least 30 minutes. The composite membrane was then operatively connected into a parallel-channel, flow-field, fuel cell reactor (available from Fuel Cell Technologies, Inc.) such that the oxidizing catalyst faced an ' oxidizing chamber of the reactor and the reducing catalyst faced a reducing chamber of the reactor. Filling the oxidizing chamber was a TEFLON 'IM /carbon black impregnated carbon cloth diffuser (available from E-TEK, Inc., as ELAT™). Similarly, the reducing chamber was filled with a 3 mil (76.2 micron) thick carbon paper (available from Spectrocarb, Corp.). The inlet pressure of the hydrogen gas which was contacted with the oxidizing catalyst was about 2070 kPa (about 300 psi) and that of the oxygen gas which was contacted with the reducing catalyst was about 1930 kPa (about 280 psi). The oxygen gas was fed to the reducing catalyst as a segmented flow of O2 with Dl water, the water being added to the gas at a rate of 0.05 mlJmin. The reactor was operated at room temperature with continuous gas feed for a period of about 20 minutes. A reaction product was formed and combined with the added water to produce a concentration of 2.08 wt% hydrogen peroxide. EXAMPLE 3 Identical procedures were followed as described above in Examples 2 with the following exception: the inlet pressure of the hydrogen gas which was contacted with the oxidizing catalyst was about 3450 kPa (about 500 psi); the oxygen gas which was contacted with the reducing catalyst was about 3380 kPa (about 490 psi); and the segmented flow of O2 with Dl water was such that the water was added at a rate of 0.20 mL/min. A reaction product was formed and combined with the added water producing a concentration of 0.84 wt% hydrogen peroxide. Therefore, of note in this example is that a 4-fold addition of water to the reactor brought about only a little over a 2-fold decrease in the peroxide concentration. Therefore, one may conclude that the peroxide is being formed from the reaction in an efficient manner. COMPARATIVE EXAMPLE Identical procedures were followed as described above in Examples 2 and 3 with the exception that the composite membrane was externally shorted by electrically connecting the surfaces of each side of the composite membrane external to the composite membrane. Gold current collection plates were placed in electrical contact with each electrically-conductive graphite block which make up the outermost parts of the reaction chambers and wired to each other through a one milli-Ohm shorting bar. Under two separate replications of the above procedures at the pressure and segmented flow conditions of Example 2, H2O2 was produced in amounts of 1.82 wt% and 1.88 wt%, respectively. Under two separate replications of the pressure and segmented flow conditions of Example 3, H2O2 was produced in amounts of 0.79 wt% and 0.65 wt%, respectively. Therefore, of note is that the internally-shorted results of this invention are generally better than the results for the case of a both internally- and externally-shorted reactor of this comparative example, demonstrating an H2O2 yield advantage for using the internally-shorted membrane of this invention, rather than an externally-shorted membrane. Other embodiments of the invention will be apparent to the skilled in the art from a consideration of this specification or practice of the invention disclosed herein. It is intended that the' specification and example -be considered as exemplary only, with the true scope and spirit of the inyention being indicated by the following claims.

Claims: CLAIMS What is claimed is: 1. A composite membrane for chemical synthesis comprising a multiphase conductive path, wherein at least one phase of the path is a cation conductive phase and at least one phase of the path is an electron conductive phase that is dispersed internally throughout the cation conductive phase. 2. The composite membrane of Claim 1 wherein the cation conductive phase comprises a polymer of perfluorosulfonic acid. 3. The composite membrane of Claim 1 wherein the electron conductive phase is selected from the group consisting of porous metals, metal screens, carbon paper, graphite cloth, carbon or graphite fibers, carbon or graphite powders, and any combination thereof. 4. The composite membrane of Claim 1 further comprising: (a) a first layer comprising an oxidizing agent; and (b) a second layer comprising a reducing agent; wherein the multiphase conductive path is positioned between and operatively connected to the first and second layers. 5. The composite membrane of Claim 4 wherein the oxidizing agent comprises Pt. 6.. The composite membrane of Claim 4 wherein the reducing agent is Au, Gd, La, or a compound or mixture thereof. 7. A method for chemical synthesis comprising the following steps: (a) placing an electron and cation producing composition in contact with an oxidizing agent to produce at least one electron and at least one cation; (b) conducting the at least one electron and the at least one cation produced in step (a) via a multiphase conductive path to an interface between a reducing agent and a reducible composition; and (c) reacting the at least one electron and the at least one cation conducted in step (b) with the reducible composition to form a reaction product. 8. The method of Claim 7 wherein the at least one electron is conducted through an electron conductive phase of the multiphase conductive path and the at least one cation is conducted through a cation conductive phase of the multiphase conductive path, the electron conductive phase being dispersed internally throughout the cation conductive phase. 9. The method of Claim 7 wherein the electron and cation producing composition is a hydrogen containing composition. 10. The method of Claim 7 wherein the reducible composition is an oxygen containing composition. 11. The method of Claim 7 wherein the reaction product is hydrogen peroxide. 12. A chemical reactor comprising: (a) a composite membrane as defined in Claim 4; (b) an oxidizing chamber for containing an electron and cation producing composition and placing said composition in contact with the first layer of the composite membrane; and (c) a reducing chamber for containing a reducible composition and placing said composition in contact with the second layer of the composite membrane, wherein the composite membrane is positioned between the oxidizing chamber and the reducing chamber such that the first layer of the composite membrane faces, and is operatively connected to, the oxidizing chamber and the second layer of the composite membrane faces, and is operatively connected to, the reducing chamber.

Inventors: MCINTYRE JAMES A, WEBB STEVEN P, MCINTYRE, JAMES, A., WEBB, STEVEN, P.
Applicants: DOW CHEMICAL CO, MCINTYRE JAMES A, WEBB STEVEN P, MCINTYRE, JAMES, A., THE DOW CHEMICAL COMPANY, WEBB, STEVEN, P.
Application year: 1995
Main classification: B01D69
IPC codes: B01D69, B01J12, B01J35, C01B15