CATALYTIC PROCESS FOR MAKING H2O2 FROM HYDROGEN AND OXYGEN

Abstract: A process for making hydrogen peroxide from hy­ drogen and oxygen at superatmospheric pressures employ­ ing, as catalyst, Pd on adsorbent carbon in a ratio of more than about one-half percent Pd based on the weight of Pd plus C, the reaction being run in an aqueous medium com­ prising substantially no organic component.

Description: CATALYTIC PROCESS FOR MAKING H 202 FROM HYDROGEN AND OXYGEN This invention concerns an improved catalytic process for producing hydrogen peroxide from hydrogen and oxygen. The process improvements described herein permit production of hydrogen peroxide in concentrations greater than heretofore possible. Direct reaction of hydrogen and oxygen catalyzed by Group VIII metals to produce hydrogen peroxide is known. A typical reaction is disclosed in U.S. 4,379,778. The art processes, however, appear to be incapable of producing H202 in concentrations even as high as 13%. For instance, U.S. 4,009,252 discloses a Pd-catalyzed process for making H202 in concentrations as high as 12.8% (7.2 mol %); see Table 4, column 9. That relatively high concentration of H2O2 (relatively high compared to the prior art) is achieved, however, by hydrogen pretreatment of a Pd-on-silica catalyst. U.S. 4,279,883 discloses supported Pd catalysts with carbon, silica, and a number of other materials being described as equivalent for support purposes. U.S. 4,336,238 and U.S. 4,336,239 disclose the use of a palladium on carbon catalyst. However, the medium employed comprises up to 95% by volume of an organic solvent. Moreover, H202 concentrations are quite low, significantly below those described in U.S. 4,009,252 supra. This invention concerns an improved catalytic method for making hydrogen peroxide from hydrogen and oxygen in a reaction medium at superatmospheric pressures, wherein the improvement comprises: (i) employing an aqueous reaction medium having substantially no organic component present, (ii) employing a catalytically effective amount of Pd on adsorbent carbon in the weight ratio of Pd to Pd plus carbon of above about 0.5 percent. By wadsorbentw carbon is meant carbon which adsorbs at least 0.1 mg of palladium per 10 mg of powdered carbon when the carbon is contacted at room temperature for five minutes with a solution prepared from 1 mg of PdC12 per gram of 0.1 N HC1 at a ratio of carbon to palladium solution of 6 mg/g. It is characteristic of the improved process of this invention that the Pd/C catalyst is relatively resistant to loss of Pd from the C in solutions comprising HC1 and hydrogen peroxide. This characteristic is believed to affect the levels of hydrogen peroxide that are obtainable by this process. In that regard, concentrations of the H202 in excess of 13% by weight are regularly achievable without hydrogen pretreatment of the catalyst or the aqueous medium. Good catalyst lifetime is characteristic of the process of this invention. This invention also concerns an improved method for making hydrogen peroxide as described employing not a preformed Pd/C catalyst but one that is made in situ. Process step (ii) wherein the catalyst is made in situ comprises: (ii) employing a catalytically effective amount of Pd on adsorbent carbon catalyst, said catalyst prepared by adding a Pd salt solution and finely divided adsorbent carbon to the reaction vessel or to a vessel interconnected with said reaction vessel, so that the resulting reaction mixture has a weight ratio of Pd to Pd plus C of above about 0.5 percent. The ratio of Pd to Pd plus carbon can vary from pore than about 0.5 normally up to 10 percent, the upper limit being a practical one. Acceptable results are achieved at 2% Pd to Pd plus carbon. The concentration of Pd/C catalyst in the reaction mixture will be about 0.01 to 2 percent, preferably 0.05 to 1 percent by weight of the reactants for best results. Catalyst particles that pass a 325 mesh screen are preferred. Best results are obtained with particles that are smaller than about 5 microns in size. Typically, the process has been run at relative partial pressures of 2 to H2 of about 2 to 1 up to 20 to 1 or higher. Ratios of 20 to 1 and above are preferred to avoid the danger of explosion during continuous process runs. Although ratios of less than 2 to 1 can be employed, such ratios may result in lower H2O2 concentrations. When stated that substantially no organic component is present in the aqueous reaction medium, it is meant that no organic component in excess of about 2% by weight of the reaction medium is present. It is preferred that the source of Pd for in situ catalyst preparation be a solution of a palladium chloride complex in aqueous HC1. When the catalyst is made in situ it is preferred that chloride ion be present in stoichiometric excess over that necessary to supply PdC12. Excess chloride ion should also be present when preformed Pd on C catalyst is used. The reaction mixture will comprise both an acid component and a chloride ion component for good selectivity. The presence of acid helps improve R202 concentrations at low chloride ion concentrations. Acids found to be acceptable for use in the process of this invention include hydrochloric, phosphoric, sulfuric and perchloric. It is believed that other strong protonic acids can also be employed provided they are compatible with the reaction ingredients. It is convenient that HC1 be employed as the source of chloride ion. In addition, other acids can be used to increase the hydrogen ion concentration. For best results, chloride ion and hydrogen ion concentrations in the reaction mixture from 0.01 to 2.0 M are preferably employed, though they need not be identical. The carbon support can be derived from many sources providing that it exhibits the above described palladium-adsorption characteristics. Representative adsorbent carbons include Alfa USP activated charcoal, Strem activated carbon, Supelco Carbosieve B and West States carbon cc-521 G. Some commecially available carbons which are not adsorbent can be converted to adsorbent carbons by methods (described hereafter) designed for that purpose. Typical of carbons which are nonadsorbent. as purchased are MCB wood charcoal, Carbopak C, Graphite-38 and Fisher reagent charcoal. Operable carbons have been obtained from a number of sources including coconut husks, petroleum, coal and vinylidene chloride polymer. Suitable carbons can also be prepared by heating sugars and cellulose in N2 by stages to 9000 to 11000C and then post-treating to generate activity. The most preferred post-treatment includes high temperature treatment in an atmosphere containing water vapor. Other activation procedures such as high temperature (about 10000C) treatment in CO2 or H2 can also be employed. Suitable material was also formed by mild oxidation (4500 in air) of pyrolyzed cellulose. Material formed in this way can be improved by subsequent heating to about 9500C in N2. In many instances the adsorbency of initially poorly adsorbent carbons can be enhanced substantially by such activation procedures. An advantage of the use of a substantially all-aqueous medium is that explosion hazards associated with high hydrogen peroxide concentrations and organic cosolvents are avoided. Another advantage is that there is easier separation of hydrogen peroxide from reaction product in the absence of organics. Other advantages include the lessening of explosive hazards caused by buildup of organic peroxy compounds and elimination of catalyst-fouling caused by decomposition of organic materials. The process can be carried out at OOC to 500C and preferably from about OOC to 16 C. Lower temperatures can be employed so long as liquid freezing is not a problem. Depending on the type and concentration of reaction ingredients, temperatures below -100C are contemplated. Presence of about 15% H202 in the reaction mass will permit operation at -100C without freezing. Preferred pressures for hydrogen peroxide formation are about 400 psig (2.86 MPa) to 2500 psig (17.34 MPa). A pressure range of from about 100 psig to 4000 psig can be used. In semibatch operation, with gases continuously entering and exiting the reactor, peroxide concentrations above about 15% can be achieved at about 400 psig, an inlet O2/H2 ratio of about 1.1, and exit gas O2/H2 ratios of up to about 6 or 7 at the end of the run. Continuous operation of the process of this invention is contemplated at about 1000 psig, about 50 psig H2 partial pressure, about 950 psig O2 partial pressure, about 1 mg of 5% Pd/C per gram of reaction mixture, about 0.05 to 0.1 N HCl, about 0.5M H3PO4, and about -100C to l5C, with vigorous gas-liquid contact. The following Examples illustrate the direct formation of hydrogen peroxide from hydrogen and oxygen. The 1procedure represents the standard test employed to determine carbon adsorbency. With regard to exemplification of this invention, it is noted that experimental results not included herein support the conclusion that the described process very often produces concentrations of H202 in excess of 13%. EXAMPLE 1 A reaction mixture was prepared from 5.0 mg of commercial (Alfa) 5% Pd/C and 1.00 g of aqueous 0.1 N SC1. This was placed in a small heavy walled glass flask containing a Teflono covered magnetic stirring bar and sparged with N2. The flask was closed with a metal flange and Teflons gasket so that a flow of gas could be maintained under pressure. The outside of the flask was cooled with a stream of cold air and the outside wall temperature was monitored with a thermocouple. The flask and gas supply equipment were put into a heavy metal barricade. The apparatus was evacuated to 25 in Hg (0.017 MPa), and then filled to 450 psig (3.20 MPa) with argon for a 15 min pressure test. The pressure was reduced again to 25 in Hg (0.017 MPa) and then H2 was admitted to 100 psig (0.79 MPa) for 5 min (all at room temperature). The pressure was again reduced to 25 in Hg (0.017 MPa) and mixed gas was admitted to a pressure of 391 psig (2.80 MPa) and maintained between that pressure and 381 psig (2.73 MPa) during the experiment. The reaction mixture was stirred for 4.5 hr while gas was allowed to flow slowly from the flask and be replaced by gas from the supply reservoir. The temperature varied between 90 and 11 . The gas supply reservoir and the exit from the reaction flask were both connected to a gas chromatograph analytical system. The reservoir gas compositon was He 5.44, H2 44.2, O2 50.4 mol %. The gas flowing from the flask showed decreasing B2 concentration and increasing O2 during the run (He, 11.4; H2, 23.9; 2 64.8 in last analysis). The weight gain by the reaction mixture during the run was 0.96 g. The H202 content was determined by titration with potassium permanganate solution to be 15.1 weight percent. EXAMPLE 2 The apparatus was the same as that described in Example 1. The reaction mixture was prepared by mixing 3 mg of commercial (Alfa) 5% Pd/C catalyst with 1.00 ml of 0.1 N HC1 (aqueous). The leak check was done with 450 psig (3.20 MPa) of 2- No nydrogen pressure step was employed. The reaction period was 3.9 hr with the temperature between 10 and 5 . The pressure varied between 540 psig (3.82 MPa and 370 psig (2.65 MPa) during the run. The reservoir gas composition was He, 4.8; H2, 41.7; 2' 53.6 mol %. Near the end of the run the exit gas from the flask contained He, 11.1; H2, 14.4; 2' 74.5%. The weight gain during the run was 0.88 g. The H202 content was 18.1 weight percent. EXAMPLE 3 The apparatus for this experiment was a 400 ml autoclave containing a glass liner. The autoclave was mounted on a shaking table in a large metal barricade with facilities for adding and removing gases and monitoring temperature from outside of the barricade. The reaction mixture consisted of a mixture prepared from 10 mg of commercial adsorbent carbon powder (Strem), 10.0 g of 0.1 N HC1 and 1.7 mg of PdC12. The charged autoclave was evacuated to 25 in Hg (0.017 MPa) and then 250 psig (1.83 MPa) of H2 was added. After 15 minutes, O2 was added to bring the pressure up to 750 psig (5.27 MPa). After 4 hours agitation with the autoclave body temperature at 10Q, the weight gain was 2.60 g and the hydrogen peroxide content in the reaction mixture was found to be 8.9 weight percent by titration with potassium permanganate solution. EXAMPLE 4 The apparatus used was the 400 ml shaken autoclave described in Example 3. The reaction mixture was prepared from 10 mg of adsorbent carbon (Strem) which had passed through a 400 mesh sieve (37 pom), 0.85 ing of PdCl2, and 10.0 g of 0.1 N HC1. Oxygen was added to the vessel to 1000 psig (7.00 MPa) and after 10 minutes hydrogen was added to bring the pressure to 1500 psig (10.44 MPa). Agitation was continued for 4 hr with the autoclave body at 120 to 140, The weight gain was 2.74 g and permanganate titration showed the H202 content of the recovered mixture to be 10.7 weight percent. EXAMPLE 5 The apparatus used was the 400 ml shaken autoclave described in Example 3. The reaction mixture was prepared from 10 mg of adsorbent carbon (Strem) of particle size less than 5 m added to 10.0 g of an aqueous solution of 0.85 mg of PdC12 dissolved in 0.1 N RC1. Oxygen was added to 1000 psig (7.00 MPa) and after 10 minutes hydrogen was added to 1500 psig (10.44 MPa). Agitation was continued for 4 hr with the temperature 11 to 130. The weight gain was 5.48 g and the permanganate titration showed that 18.7 weight percent of hydrogen peroxide had been formed. EXAMPLE 6 The apparatus used was the 400 ml shaken autoclave described in Example 3. The reaction mixture was prepared from 20 mg of commercial (Alfa) 5% Pd/C catalyst which had been passed through a 325 mesh (44 um) sieve and 10.0 g of 0.1 N HCl. Hydrogen was added to 300 psig (2.17 MPa) and then oxygen was added to 2500 psig (17.34 MPa). Agitation was continued for 3.3 hr with the autoclave body at 140 to 160. The weight increase was 5.16 g and the H2O2 content of the recovered reaction mixture was 22.8 weight percent. EXAMPLE 7 The apparatus used was the 400 ml shaken autoclave described in Example 3. The reaction mixture was prepared from 15 mg of powdered Alfa 10%Pd/C catalyst and 10.0 g of 0.1 N HC1. Oxygen was added to the vessel to 1000 psig (7.00 MPa) andr after 15 minutes, hydrogen was added to 1500 psig (10.44 MPa). The mixture was shaken for 4 hr with the autoclave body at about 100C. The weight gain was 6.38 g and the R202 content of the recovered reaction mixture was 25.2 weight percent. EXAMPLE 8 The apparatus used was the 400 ml shaken autoclave described in Example 3. The reaction mixture was prepared from 0.50 g of solution containing 1.7 mg of PdCl2/g of solution, 1.0 g of a solution containing 1 mg Tamol dispersing agent (Rohm L Raas SN 6-0224) per g distilled water, 4.0 g of distilled water, 4.5 g of 0.2 N HC1 and 10 mg of Strem carbon particles less than 5um in size. Oxygen was added to the vessel to 1000 psig (7.00 MPa) and after 10 minutes hydrogen was added to 1500 psig (10.44 MPa). The mixture was shaken for 4 hr with the autoclave body at 10 to 120C. The weight gain was 5.33 g and the R202 content of the recovered reaction mixture was 22.9 weight percent. Procedure The following formula was employed to determine whether a particular carbon had the required degree of adsorbency: EMI10.1 <tb> No. <SEP> of <SEP> mg <tb> of <SEP> Pd <SEP> per <SEP> adsorbence <SEP> of <tb> 10 <SEP> mg <SEP> of <SEP> = <SEP> 1- <SEP> carbon-treated <SEP> solution <tb> carbon <SEP> adsorbence <SEP> of <SEP> untreated <tb> <SEP> solution <tb> <SEP> x <SEP> r <SEP> mg <SEP> of <SEP> Pd <SEP> 1 <tb> <SEP> x <SEP> mg <SEP> of <SEP> Pd <tb> <SEP> 10 <SEP> zng <SEP> of <SEP> carbon <tb> <SEP> in <SEP> starting <SEP> solution <tb> The net optical densities of the supernatant PdC12-containing liquids were determined at 450 nm in a 1 cm cell using a Carey 14 spectrometer.

Claims: Claims: 1. A method of making hydrogen peroxide from hydrogen and oxygen in a reaction medium at superatmospheric pressures, characterized in that: (i) the oxygen and hydrogen are reacted in an aqueous reaction medium having sub stantially no organic component present; and (ii) as catalyst, is used a catalytically effective amount of Pd on adsorbent carbon in the weight ratio of Pd to Pd plus carbon of above about 0.5 percent. 2. A method as claimed in Claim 1 wherein the Pd on carbon catalyst is prepared in situ. 3. A method as claimed in Claim 2 wherein the catalyst is prepared in situ by charging a palladium salt solution together with finely divided carbon to the aqueous reaction medium. 4. A method as claimed in any preceding claim wherein the weight ratio of Pd to Pd plus carbon is above about 2 percent. 5. A method as claimed in any preceding claim wherein the reaction medium has a chloride ion concentration between about 0.01 and 2 M and a hydrogen ion concentration between about 0.01 and 2 M. 6. A method of making hydrogen peroxide from hydrogen and oxygen in a 'reaction medium at superatmospheric pressures, characterized in that: (i) an aqueous reaction medium having substantially no organic component present is used; and (ii) A catalytically effective amount of Pd on adsorbent carbon is used as catalyst, said catalyst being prepared in situ by adding a Pd salt solution and finely divided carbon to the H2Q2 reaction vessel or to a vessel interconnected with said reaction vessel, so that the resulting reaction mixture has a ratio of Pd to Pd plus carbon of above about 0.5 percent. 7. A method as claimed in Claim 6 wherein the weight ratio of Pd to Pd plus carbon is above about 2 percent. 8. A method as claimed in Claim 6 or Claim 7 wherein the chloride ion concentration is between about 0.01 and 2 M and the hydrogen ion concentration is between about 0.01 to 2.M.

Inventors: GOSSER, LAWRENCE WAYNE
Applicants: E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1984
Main classification: C01B15
IPC codes: B01J23, C01B15