Production of hydrogen peroxide

Abstract: A process for the manufacture of hydrogen peroxide by the reaction of hydrogen and oxygen in an acidic aqueous medium. The process comprises using a catalyst comprising at least one group VIII metal on a hydrophobic support, and contacting the catalyst with hydrogen and oxygen in an acidic aqueous solution at a hydrogen partial pressure from about 0.3kPa to 5MPa and an oxygen partial pressure of 20kPa to 5MPa and at a temperature from the freezing point of the aqueous medium to 60°C.

Description: This invention relates to the production of hydrogen peroxide by the reaction of hydrogen with oxygen using a catalyst comprising at least one group VIII metal. Hydrogen peroxide is a powerful oxidizing agent. It is widely used in bleaching, preparation of chemicals, pollution control, mining and power generation. It is particularly ecologically desirable as a pollution control agent, since it yields only water and/or oxygen upon decomposition. Most commercial production of hydrogen peroxide is by processes based on the electrolysis of sulphuric acid solution, or the autoxidation of isopropyl alcohol and anthraquinones. It has been proposed to conduct direct oxidation of hydrogen and oxygen in an acidic aqueous solution, using a group VIII metal catalyst. Examples of such processes are shown in U.S. Patent No. 4,661,337 of Brill and U.S. Patent No. 4,681,751 of Gosser. However, yields in such a process are very low, unless high pressures are used to increase hydrogen and oxygen solubilities and to reduce transfer limitations. High pressures complicate the process by requiring pressure vessels. Further, the carrying out of the process at high pressures increases the risk of explosion. It is therefore important to develop a process which makes possible the manufacture of hydrogen peroxide at ambient or near ambient temperatures, and at ambient or near ambient pressures. The present invention accomplishes this by making use of group VIII metal catalysts on particular hydrophobic supports. Hydrophobic catalyst supports are already known for other purposes. For example, U.S. Patent No. 4,025,560 of Rolston et al. shows a catalyst for the exchange of hydrogen isotopes between a gas stream and a water stream where the catalyst comprises an inherently hydrophobic material such as cubes of polytetrafluoroethylene (PTFE), polyethylene or the like. European Patent Appln. Publn. No. 0 015 585 of Hitachi Inc. shows catalysts similar to those of Rolston for other types of gas-liquid reactions. An activated carbon catalyst which has been reacted with a monomer which forms hydrophobic polymers, is disclosed for carbon monoxide oxidation in U.S. Patent No. 4,652,537 of Tamura. Hydrophobic catalysts of this sort have not previously been proposed for the production of hydrogen peroxide. They provide the advantage of much higher yields at ambient pressures and temperatures than previous catalysts used for reaction in an acidic solution. While it is not desired to limit the application by reliance on a particular mechanism of the reaction, it is believed that the hydrophobic material allows the hydrogen and oxygen to reach the metal sites directly by gas phase diffusion, thus eliminating mass transfer limitations. The present invention provides a process for the manufacture of hydrogen peroxide which comprises reacting hydrogen and oxygen in an acidic aqueous medium in the presence of a catalyst comprising at least one group VIII metal, wherein the process is carried out at a temperature from the freezing point of the aqueous medium to about 60°C, at a hydrogen partial pressure of from about 0.3 kPa to 5 MPa, and at an oxygen partial pressure of from 20 kPa to 5 MPa, and wherein the catalyst is provided on a hydrophobic support selected from the group consisting of: (i) styrene divinylbenzene copolymers; (ii) polytetrafluoroethylene; (iii) polyethylene, polypropylene, and ethylene-propylene copolymers; (iv) silicalite; (v) silica or fumed silica which has been rendered hydrophobic by treatment with a silane or with fluorine or a fluorinated compound; (vi) fluorinated carbon; (vii) carbon which has been rendered hydrophobic by treatment with a silane or with fluorine or a fluorinated compound; and, (viii) a support that has been rendered hydrophobic by treatment with a tetrafluoroethylene monomer. Thus, in accordance with the invention, hydrogen peroxide may be manufactured by the direct reaction of hydrogen and oxygen in an acidic aqueous solution. The process may comprise supplying a catalyst consisting of at least one group VIII metal on a hydrophobic support of the type described above, and contacting the catalyst with hydrogen and oxygen in the acidic aqueous solution, under the conditions mentioned above. Generally a stoichiometric excess of oxygen over hydrogen will be used, as the oxygen can be supplied as air, which is of course cheaper than hydrogen. The catalyst is deposited on a hydrophobic support. The hydrophobic support preferably has a surface area of at least 50 square meters per gram, and can have a surface area as high as 1,500 square meters per gram. An area of 50 to 1,000 m²/g is preferred. The support may be selected, for example, from the group of inherently hydrophobic plastic materials such as styrene divinylbenzene copolymers ("SDB"), polytetrafluoroethylene ("PTFE"), polyethylene, polypropylene, and ethylene-propylene copolymers, or it may be silicalite (a silica having a highly structured lattice which is described in U.S.P. No. 4,061,724 dated December 6, 1977). Alternatively, the hydrophobic support may, for example, comprise an initially hydrophilic material which has been chemically treated so as to render it hydrophobic. For example, silica, carbon and fumed silica (for example, that produced by Cabot Corp. under the name CAB-O-SIL EH-5) can be rendered hydrophobic by treatment with a silane, fluorine, or a fluorinated compound. Treatment with tetrafluoroethylene monomer can be used to render the support hydrophobic, in the case of those supports which form reasonably strong bonds with tetrafluoroethylene. The support is preferably porous. One convenient way of determining the hydrophobicity of a solid material, and hence its suitability as a support is by measuring its "contact angle" according to Young's Theory. The support material advantageously has a contact angle of at least 30°, although materials with a contact angle of at least 50° are preferred. For best results, a material with a contact angle of at least 90° is preferred. The support material can be present, for example, as discrete particles or granules, or it can be deposited on a second support, for example, a ceramic or a metal screen. For example, the support material can be deposited on conventional screens, plates, ceramic beads, saddles or rings. Preferably, the discrete particles of the hydrophobic support material are attached to the second support by means of a liquid-water-repellant, water vapor permeable, coating of an organic resin or polymer. The coating may be, for example, of polytetrafluoroethylene or a silicone. Suitable silicones for example, are poly-siloxanes, for example, polyalkylsiloxanes. The silicone may include at least one substituent selected from ethyl, propyl, isopropyl and t-butyl groups. The catalyst comprises a Group VIII metal, with Pt, Pd, Ru, Rh and Ir being preferred. Any Group VIII metal, or mixture of such metals, may be used in accordance with the invention. Any one or more of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt may be used. If desired, the catalyst may be Pt or Pd and another metal from Group VIII. The Group VIII metal is deposited on the hydrophobic support material in any suitable manner, for example, by slurrying the support material in a solution of a chloride of the desired Group VIII metal. The process of the present invention can be carried out at temperatures from the freezing point of the aqueous solution to about 60°C. The freezing point will of course vary with the solute concentration and pressure but will usually be below about -15°C. The preferred temperature range is from -10°C to +40°C. Operation at or near ambient temperature (i.e., 10 - 30°C) is particularly preferred, as the apparatus does not then require heating or cooling means. The process of the invention is carried out with a partial pressure of hydrogen from about 0.3 kPa to 5 MPa and a partial pressure of oxygen from about 20 kPa to 5 MPa. Gases which do not react with hydrogen or oxygen, or with each other, can also be present. Conveniently, the oxygen is provided as air, and the reaction is carried out at ambient pressure, which avoids the necessity of using pressure vessels. The invention will be further described with respect to the following example. A hydrophobic carbon powder (Cabot Corp. RC-72 [T.M.]), with a surface area of about 300 m²/g was platinized to 2% by weight Pt by treatment with H₂PtCl₆ in ethanol. It was aligned at 200°C under helium flow and reduced in hydrogen flow at 200°C for one hour. The platinized carbon powder was then slurried in water with a 20% solution of Triton X-100 [T.M.] surfactant (from J.T. Baker Chemical Co.). Polytetrafluoroethylene dispersion (duPont TEFLON 30 [T.M.], which is a 66% dispersion of PTFE in water) was added to the slurry, and the mixture was used to coat 6mm. diameter ceramic rings. The water was removed by gentle heating while rotating the reaction flask. The product was then heated at 150°C in air to remove the surfactant, then heated at 360°C for 15 minutes. The resulting hydrophobic catalyst has a composition by weight of 10% carbon, 3% polytetrafluoroethylene, 0.2% platinum, and the remainder ceramic rings. A one inch diameter trickle bed reactor made of PYREX (T.M.) heat resistant glass was packed with 40 cm³ of hydrophobic catalyst and was operated at 25°C and 1 atmosphere. The feed gas, which was at atmospheric pressure, was air containing 3% by volume hydrogen, based on the volume of the air, and the total flow rate was 6.5 L/h. An aqueous solution containing 1 N H₂SO₄ and 0.03 N HCl was circulated through the reactor and the flow rate was 0.6 L/h. The total volume of the solution was 100 cm³. Both gas and liquid streams were introduced at the top of the column and flowed concurrently downward to avoid flooding in the packed bed. The liquid loop was constructed of PTFE to avoid corrosion and to reduce the likelihood of side reactions which would decompose H₂O₂. The concentration of hydrogen peroxide was determined by titration with KMnO₄, and hydrogen and oxygen in the feed and effluent streams were monitored with a gas chromatograph. Three sets of samples were taken during a 5 hour test period. It was found that after 0.5, 1 and 5 hours of operation, the concentrations of hydrogen peroxide in the liquid was measured to be 0.15%, 0.23% and 0.3%, respectively. Gas chromatography measurements showed that hydrogen was totally consumed in the reactor. A mass balance calculation indicated the selectivity was approaching 100% for the first hour of reaction.

Claims: A process for the manufacture of hydrogen peroxide which comprises reacting hydrogen and oxygen in an acidic aqueous medium in the presence of a catalyst comprising at least one group VIII metal, wherein the process is carried out at a temperature from the freezing point of the aqueous medium to about 60°C, at a hydrogen partial pressure of from about 0.3 kPa to 5 MPa, and at an oxygen partial pressure of from 20 kPa to 5 MPa, and wherein the catalyst is provided on a hydrophobic support selected from the group consisting of: (i) styrene divinylbenzene copolymers; (ii) polytetrafluoroethylene; (iii) polyethylene, polypropylene, and ethylene-propylene copolymers; (iv) silicalite; (v) silica or fumed silica which has been rendered hydrophobic by treatment with a silane or with fluorine or a fluorinated compound; (vi) fluorinated carbon; (vii) carbon which has been rendered hydrophobic by treatment with a silane or with fluorine or a fluorinated compound; and, (viii) a support that has been rendered hydrophobic by treatment with a tetrafluoroethylene monomer. A process as claimed in claim 1, in which the hydrophobic support has a surface area of from 50 to 1,000 m²/g. A process as claimed in claim 1 or claim 2, in which the Group VIII metal is selected from Pt, Pd, Ru, Rh, Ir and mixtures thereof. A process as claimed in any one of claims 1 to 3, in which the temperature is from -10°C to +40°C. A process as claimed in any one of claims 1 to 4, in which the oxygen is supplied as air. A process as claimed in any one of claims 1 to 5, in which the hydrophobic support has a contact angle according to Young's theory of at least 30°. A process as claimed in claim 6, in which the hydrophobic support has a contact angle according to Young's theory of at least 50°. A process as claimed in claim 7, in which the hydrophobic support has a contact angle according to Young's theory of at least 90°.

Inventors: CHUANG KARL T, CHUANG, KARL T.
Applicants: ATOMIC ENERGY OF CANADA LTD, ATOMIC ENERGY OF CANADA LIMITED -ENERGIE ATOMIQUE DU CANADA LIMITEE
Application year: 1989
Main classification: C01B15
IPC codes: B01J35, B01J33, B01J23, B01J32, C01B15