MXPA97004247A - Catalysts improved for the hydrogenation of aqueous maleic acid to form 1,4-butanod - Google Patents

Abstract

The maleic acid, maleic anhydride or other hydrogenatable precursor is catalytically hygienized to give 1,4-butanediol and tetrahydrofuran. It has been found that high yields of 1,4-butanediol are achieved when the hydrogenation catalyst comprises at least one noble metal of Group VIII of the Periodic Table and at least one of rhenium, tungsten and molybdenum, on a carbon support. , wherein the carbon support has been contacted with an oxidizing agent before the deposition of the metals. This hydrogenation catalyst is prepared by the steps of: (i) oxidizing the carbon support by contacting the carbon support with an oxidizing agent, (ii) impregnating in one or more impregnation steps, comprising contacting the support of carbon with a Group VIII metal agent and at least one metal selected from the group consisting of rhenium, tungsten and molybdenum which are in at least one solution, (iii) after each impregnation step, drying at a temperature less than about 150 ° C the impregnated carbon support for the purpose of removing the solvent, and (iv) heating the impregnated carbon support to a temperature of approximately 100 ° C under reducing conditions

Description

IMPROVED CATALYSTS FOR THE HYDROGENATION OF AQUEOUS MALECTIC ACID TO FORM 1, 4-BUTANODIOL BACKGROUND DB THE INVENTION The invention relates to an improved process for the hydrogenation of maleic acid, maleic anhydride or another hydrogenatable precursor to 1,4-butanediol and tetrahydrofuran. The process is characterized by the use of a catalyst comprising at least one noble metal of Group VIII of Periodic Table and at least one of rhenium, tungsten or molybdenum, on a carbon support, where the carbon support has been put in contact with an oxidizing agent before the deposition of the metals. The process is also characterized by an overall activity superior to the reaction products and / or by higher yields of 1,4-butanediol with minimal formation of gara-butyrolactone by-products.

DESCRIPTION OF THE PRIOR ART It is well known that tetrahydrofuran, gamma-butyrolactone and 1,4-butanediol is obtained by the catalytic hydrogenation of maleic anhydride and related compounds. Tetrahydrofuran is a useful solvent for natural and synthetic resins and is a valuable intermediary in the manufacture of a number of • • • • •: chemical and plastics agents The gamma-butyrolactone is an intermediate for the synthesis of butyric acid compounds, polyvinylpyrrolidone and methionine.The gamma-butyrolactone is a useful solvent for acrylate and styrene polymers and also A useful ingredient in paint removers and textile auxiliaries, l, 4-butanediol (also known as 1,4-butylene glycol) is useful as a solvent, a humectant, an intermediate for plasticizers and pharmaceutical compounds, a crosslinking agent for polyurethane elastomers, a precursor in the manufacture of tetrahydrofuran and used for the manufacture of terephthalate plastic.Hydrogenating catalysts comprising noble metals of Group VIII and at least one metal selected from the group are of particular interest in the present invention. consisting of rhenium, tungsten and molybdenum, on a carbon support, British Patent No. 1,534,232 shows the hydroge Nation of carboxylic acids, lactones or anhydrides using a hydrogenation catalyst consisting of palladium and rowing, on a carbon support. U.S. Patent Nos. 4,550,185 and 4,609,636 show a process for the preparation of tetrahydrofuran and 1,4-butanediol by the hydrogenation of maleic acid, maleic anhydride or another hydrogenatable precursor in the presence of a catalyst comprising palladium and rhenium. , on a carbon support, where palladium and rhenium were present in the form of crystallites having an average palladium crystallite size of about 10 to 25 nm and an average rhenium crystallite size of less than 2.5 nm. The preparation of this catalyst is characterized by the deposition and reduction of the palladium species on the carbon support, followed by the deposition and reduction of the rhenium species on the palladium impregnated carbon support. U.S. Patent No. 4,985,572 teaches a process for the catalytic hydrogenation of a carboxylic acid or an anhydride thereof in the corresponding alcohol and / or carboxylic acid ester, using a catalyst comprising rhenium and a palladium-silver alloy on a carbon support. The preparation of this catalyst is characterized by the simultaneous deposition of palladium and silver on carbon support, followed by a high-temperature (600 ° C) heat treatment to alloy the catalyst. The rhenium is then deposited on the carbon support impregnated with the alloy. The resulting catalyst is subsequently reduced. In general, in the hydrogenation of maleic acid, maleic anhydride and other hydrogenatable precursors the aforementioned catalysts are prone to produce more tetrahydrofuran and gamma-butyrolactone than 1,4-butanediol. An object of this invention is a process and a more active catalyst that will maximize the production of 1,4-butanediol.

SUMMARY OF THE INVENTION Maleic acid, maleic anhydride or other hydrogenatable precursors are catalytically hygienized in 1,4-butanediol and tetrahydrofuran. It has been found that high yields of 1,4-butanediol are achieved when the hydrogenation catalyst comprises at least one noble metal of Group VIII of the Periodic Table and at least one of rhenium, tungsten and molybdenum, wherein the support of carbon has been contacted with an oxidizing agent before the deposition of the metals. This hydrogenation catalyst is prepared by the steps of: (i) oxidizing the carbon support by contacting the carbon support with an oxidizing agent; (ii) impregnating in one or more impregnation steps, comprising contacting the carbon support with a Group VIII metal agent and at least one metal selected from the group consisting of rhenium, tungsten, and molybdenum; (iii) after each impregnation step, dry the impregnated carbon support at a temperature below about 150 ° C, in order to remove the solvent; and (iv) heating the impregnated charcoal support at a temperature of about 100 ° C to 350 ° C under reducing conditions.

DETAILED DESCRIPTION OF THE INVENTION A hydrogenated precursor is catalytically hydrogenated to provide high yields of 1,4-butanediol and minor yields of tetrahydrofuran with minimal gamma-butyrolactone formation.

REAGENTS At least one hydrogenatable precursor is reacted with a gas containing hydrogen in the presence of the catalyst. In the sense in which "hydrogenated precursor" is used herein refers to any carboxylic acid or anhydride thereof, carboxylic acid ester, lactone or mixtures thereof which, when hydrogenated, produce 1,4-butanediol. Representative hydrogenatable precursors include maleic acid, maleic anhydride, fumaric acid, succinic acid, malic acid, dimethyl succinate, gamma-butyrolactone or mixtures thereof. Preferred hydrogenatable precursors are maleic acid, maleic anhydride, butyrolactone range and mixtures thereof. Typically, the hydrogen-containing gas (H2) is commercially pure hydrogen. However, hydrogen-containing gas in addition to hydrogen (H2) may also contain nitrogen (N2), any gaseous hydrocarbon (for example: methane), as well as gaseous carbon oxides (for example: carbon monoxide, carbon dioxide) .

CATALYST The catalyst used in the present invention comprises at least one noble metal of Group VIII of the Periodic Table of Elements and at least one metal selected from the group consisting of rhenium, tungsten and molybdenum supported on a carbon support. The metals of Group VIII are palladium, platinum, rhodium, ruthenium, osmium and iridium. The preferred metals of Group VIII are palladium, platinum, rhodium and ruthenium. The most preferred metal in Group VIII is palladium. The support of this carbon used in this invention refers to carbons having a large surface area and must have a surface area of at least 200 m2 / g and preferably in the range of 500-1500 m / g. The carbon support is generally obtained from commercially available activated carbons, which are commonly derived, either from wood or from coconut shells. The catalyst composition is from about 0.1 to about 20 weight percent of the Group VIII metal, preferably from about 1 to about 10 weight percent of the Group VIII metal, and preferably from about 0.1 to about 20 weight percent. weight of at least one of rhenium, tungsten or molybdenum, preferably from about 1 to about 10 weight percent of at least one of rhenium, tungsten or molybdenum. The weight ratio of Group VIII metal to total rhenium, tungsten and molybdenum is between 10: 1 and 1:10. The composition of the catalyst can also be further modified through the incorporation of one or more additional metals. The preferred additional metals are selected from Group IA, IIA and IB of the Periodic Table. In the present invention, the carbon support is oxidized by contacting the carbon support, prior to deposition of the metals, with an oxidizing agent. The catalyst prepared in this form shows a dramatic improvement in activity and selectivity over catalysts prepared with non-oxidized carbon support.

A number of oxidizing agents such as nitric acid, hydrogen peroxide, sodium hypochlorite, ammonium persulfate, perchloric acid and oxygen can be effective in this process. The liquid phase oxidizing agents at elevated temperatures (between about 60 ° C and-about 100 ° C) are preferred. It has been found that concentrated nitric acid at elevated temperatures is specifically effective for this process. The gas phase oxidizing agents include any gas containing oxygen, for example air. The gaseous oxidizing agents are contacted with the carbon support at temperatures of about 200 ° C or higher, at approximately atmospheric or higher pressures. In preparing the catalysts of the invention, the metals are deposited on the carbon support by impregnation of the carbon support, either in a single impregnation step or in multiple impregnation steps, with a solution, using solutions containing at least a solution of Group VIII. In the sense in which it is used herein, impregnation of the carbon support means that the carbon support is caused to fill, embed, permeate, saturate or magazine. The impregnated carbon support is then dried after each impregnation step. The solution or solutions of the metal-containing compound that are used to impregnate the carbon support may optionally contain complexed agents to help solubilize one or more of the metal compounds. The carrier or carrier solvent is removed by drying after each impregnation step. The drying temperatures are between about 100 ° C and about 150 ° C. The solution or solutions of the metal-containing compounds can impregnate the carbon support by dipping or suspending the support material in the solution or by spraying the solution onto the carbon. The solution containing the Group VIII compound is typically the acidic aqueous medium containing HNO3 and an amount of the Group VIII metal compound, to give a catalyst product with the required amount of the Group VIII metal. The metal compound and Group VIII can be a chloride, nitrate, carbonate, carboxylate, acetate, acetyl acetonate, or amine. The solution or solutions containing the rhenium, tungsten or molybdenum compound is typically an aqueous solution containing an amount of the rhenium, tungsten or molybdenum compound to give a catalyst product with the required amount of at least one of these three metals. When rhenium is used in the catalyst, the rhenium compound is typically perrhenic acid, ammonium perrhenate or an alkali metal perrhenate.

After impregnation of the carbon support with palladium, silver and rhenium, and after drying, the catalyst (i.e. the impregnated carbon support) is activated by heating it under reducing conditions at a temperature of 120 to 700 ° C, preferably of 150 to 300 ° C. The hydrogen or a mixture of hydrogen and nitrogen is contacted with the catalyst and is typically employed for the reduction of the catalyst.

THE PROCESS The typical method for carrying out the process comprises: (a) reacting n-butane or benzene in an oxygen-containing gas in the presence of a mixed vanadium oxide / phosphorus catalyst, to oxidize the vapor phase in the vapor phase; n-butane or benzene in maleic anhydride; (b) collecting the maleic anhydride by rapid cooling with water to produce maleic acid in an aqueous solution at a concentration of about 40 weight percent; (c) reacting the solution obtained in (b) with a gas containing hydrogen in the presence of a hydrogenation catalyst, and (d) recovering and purifying the reaction products by distillation. Preferably, the oxidation step (a) operates at a temperature of about 300 ° C to 600 ° C and at a pressure of about 0.5 to 20 atmospheres (50 to 2000 kPa) and the hydrogenation step (c) is run at a. temperature of about 50 ° C to 350 ° C and at a hydrogen pressure of about 20 to 400 atmospheres, more preferably from 80 to 200 atmospheres, with proportions of hydrogen to hydrogenatable precursor (H / P) of between 5 to 1 and 1000 to 1 and contact times of 0.1 minutes to 20 hours. The liquid phase hydrogenation of this invention can be carried out using conventional apparatus and techniques in a stirred tank reactor or in a fixed bed reactor. The amount of catalyst that is required will vary widely and will depend on a number of factors such as reactor size and reactor design, contact time and the like. The hydrogen is fed continuously, generally in a considerable stoichiometric excess without inert diluent gases. The unreacted hydrogen can be returned to the reactor as a recirculation stream. The solution of the precursor, ie solution of maleic acid, is fed concentrations ranging from diluted solutions to solutions near the maximum level of solubility, typically around 50% by weight. The reaction products, 1,4-butanediol, tetrahydrofuran, gamma-butyrolactone or mixtures thereof are advantageously separated by fractional distillation. The gamma-butyrolactone can also be recycled to the hydrogenation reactor. Using the process of this invention, more specifically using the hydrogenation catalyst described herein, maleic acid is converted virtually in a quantitative manner into a simple reaction. The 1,4-butanediol and tetrahydrofuran yields achieved are about 80 mole percent or more, typically about 90 mole percent or more, with a major portion of the yield being 1,4-butanediol. The formation of unusable by-products is low. The reaction by-products may include n-butanol, n-butyric acid, n-propanol, propionic acid, methane, propane, n-butane, carbon monoxide and carbon dioxide.

SPECIFIC MODALITIES The following modalities should be interpreted simply as illustrative and in no way as limiting the rest of the exhibition.

Example 1: (5% Pd / 5 of Re on oxidized coal) 100 g of the activated carbon of 30 x 70 mesh (ACL40, produced by CECA SA of France and sold in the United States by Atochem North America Inc., successive referred to as "ECSC ACL40") was stirred with an excess of concentrated acid (69-71% HN03) at 80 ° C for about 18 hours. After cooling, the product was recovered by filtration and washed several times with an excess of water, followed by drying in the oven at 120 ° C. 25.00 g of the oxidized carbon were treated with 120 g of an aqueous solution containing 1.90 g of NH4Re04 and 18.12 g of Pd (N03) 2 solution (7.26% Pd). The resulting suspension was evaporated to dryness on a "roto-vac" and dried in the oven at 120 ° C. The product was then reduced in hydrogen at 200 ° C. The temperature rise rate was Io / min with a retention time of 5 hours at 200 ° C. 8.00 g of the reduced catalyst (nominally 5% Pd / 5% Re on carbon) were mixed with 100.0 g of 30% aqueous maleic acid and the mixture was placed in an autoclave. The autoclave was purged three times with 2500 psig H at room temperature, followed by an increase in temperature to 160 ° C at a stir rate of 1000 rpm, while maintaining the pressure at 2500 psig. The reagents were kept under these conditions for 9.5 hours and then allowed to cool to room temperature. The products were analyzed by gas chromatography and showed 100% male conversion in 1,4-butanediol (BDO) with a selectivity of 86.9%, as well as 5.2% trahydrofuran (THF), 2.4% gamma-butyrolactone ( GBL) and 4.6% n-butanol.

Comparative Example A: (5% Pd / 5% Re on carbon - not oxidized) The procedure of Example 1 was repeated using the same activated carbon but without the nitric acid treatment. When this catalyst was tested under conditions identical to those used in Example 1, the selectivity of BDO was simply 0.3% while the selectivities of GBL, THF, and n-butanol were 84.5%, 12.0% and 2.0% respectively.

Example 2; (3% of Pd / 3% of Ag / 6% of Re on oxidized coal) 100 gms. of the CECA ACL40 activated carbon extruded were placed in a 1-liter, 3-necked flask, equipped with a mechanical stirrer, a liquid addition funnel, and a glass inlet to adapt a thermocouple. A 1/8"diameter K-type thermocouple was inserted into the glass inlet and connected to a temperature control box.The temperature control box was in turn connected to a heating mantle within which The flask rested.The mechanical stirrer was turned on at low RPM and about 450 ml of concentrated nitric acid (69-71% HNO3) was added dropwise to the flask for a period of about 2 hours. The addition funnel was removed and replaced with a reflux condenser.The set point of the temperature controller was slowly increased to 80 ° C. The contents of the flask were left under slow stirring at the temperature of 80 ° C. After the treatment with nitric acid, the coal was vigorously washed with distilled water, and then dried overnight at 100 ° C. 50 cc (23.85 gms) of the oxidized carbon was used as the catalyst support. or for this catalyst preparation. An impregnation solution was prepared by placing 11.31 gms. of solution Pd (N03) 2 (7.70% of Pd by weight), 1.34 gms. of AgN03, and 3.37 g s. of HRE0 solution (52.63% Re by weight) in > a 25 ml volumetric flask, together with enough acetonitrile to make the volume of the solution reach 25 ml. The density of the solution was 1,109 gms / cc. 25.39 gms. from the above solution were used to impregnate 50 cc of the oxidized carbon extrudate. After the impregnation of the coal with the metal solution, the coal was placed in a stove at 90 ° C for drying. The loading of metals in this catalyst preparation was 0.016 gm of Pd / cc of support, 0.016 gm of Ag / cc of support and 0.032 gm of Re / cc of support. 20 cc (11.79 gms) of the catalyst preparation of oxidized carbon impregnated with metals and dried were loaded into a Hastelloy C reactor tube (external diameter 0.62"x internal diameter 0.55"). The catalyst was initially reduced to 280 ° C for 5 hrs under a stream of hydrogen flow (at atmospheric pressure). The catalyst was started under the following conditions: System Pressure = 1300 PSIG H2 Feeding Ratio: Maleic Acid = 65: 1 Liquid Composition Feeding = 400 gms. Maleic Acid / Liter Liquid Hourly Space Velocity (LHSV) = 0.38 Reactor Set Point Temperature = 180 ° C Under the above process conditions the following product selectivities were observed: Tetrahydrofuran (THF) = 13.9% Gama-butyrolactone (GBL) = 1.6% Butanediol (BDO) = 46.1% n-Butanol (BuOH) = 30.6% In order to test the inherent activity of the catalyst, the hourly space velocity of the LHSV liquid normally increases and / or the set point temperature of the reactor decreases until a considerable increase in gamma-butyrolactone is observed in the product solution (a saturation of GBL). For this catalyst, a GBL saturation was observed at a set point temperature of 150 ° C and an LHSV = 0.55.

The selectivities of the product observed under these conditions were the following: Tetrahydrofuran (THF) 4.7% Gama-butyrolactone (GBL) 4.2% Butanediol (BDO) 84.8% n-Butanol (BuOH) 3.9% Comparative Example B: (4% Pd / 4% Ag / 8% Re on carbon - non-oxidized) 120 cc (51.8 gms.) Of the CECA activated carbon extruded ACL40 were used as the catalyst support in this preparation of catalysts. An impregnation solution was prepared by placing 27.8 gms. of the solution Pd (N03) 2 (7.70% of Pd by weight), 3.3 gms. of AgN03, and 8.3 gms. of the HRE04 solution (52.6% Re by weight) in a 50 ml volumetric flask with enough acetonitrile to make the volume of the solution reach 25 ml. The density of the solution was 1.1828 gms / cc. 57.2 gms. of the solution were used to impregnate the 120 cc of extruded activated carbon.

After impregnation with the metal solution, the charcoal was placed in an oven at 120 ° C until dry. The filler metals that were used in this catalyst preparation were 0.017 gm of Pd / cc of support, 0.017 gm of Ag / cc of support and 0.035 gm of Re / cc of support. This is the same metal load as that used for the catalyst of Example 2. 20 ce (10.67 Gms) of the preparation of the catalyst impregnated with metals and dry were loaded into a Hastelloy C reactor tube (external diameter 0.62"x internal diameter 0.55"). The catalyst was initially reduced to 280 ° C for 5 hrs under a stream of hydrogen flow (at atmospheric pressure). The catalyst was started under the following conditions: System Pressure = 1300 PSIG H2 Feeding Ratio: Maleficic Acid = 65: 1 Liquid Feeding Composition = 400 gms. of Maleic Acid / liter Liquid Hourly Space Velocity (LHSV) = 0.38 Reactor Set Point Temperature = 180 ° C Under the conditions of previous processes, the following product selectivities were observed: Tetrahydrofuran (THF) = 44.3% Gama-butyrolactone (GBL) = 1.4% Butanediol (BDO) = 30.7% n-Butanol (BuOH) = 18.2% In order to test the inherent activity of the catalyst, the LHSV is normally increased and / or the temperature of the set point of the reactor is lowered until a considerable increase in gamma-butyrolactone is observed in the product solution (saturation of gamma-butyrolactone occurs). For this catalyst, the saturation or outcrop of GBL is observed at a set point temperature of 175 ° C and an LHSV = 0.55.

The product selectivities observed under these conditions were as follows: Tetrahydrofuran (THF) = 41.2% Gama-butyrolactone (GBL) = 12.7% Butanediol (BDO) = 36.0% n-Butanol (BuOH) = 6.4% Example 3: (3% of Pd / 3% of Ag / 6% of Re on oxidized coal) Two batches of 100 gms. of CECA ACL40 activated carbon extrudate were oxidized according to the procedure described in Example 2 above. 350 CE (166.17 gms.) Of the oxidized carbon were used as the catalyst support for this catalyst preparation. An impregnation solution was prepared by placing 112.45 gms. of the solution Pd (N03) 2 (7.70% of Pd by weight), 13.3 gms. of AgN03, and 33.50 gms. of HRE04 (52.63% of Re by weight) in a 250 ml volumetric flask, together with enough acetonitrile to bring the solution to 250 ml. The density of the solution was 1.1006 gms / cc. 177.39 gms. from the previous solution were used to impregnate the 350 cc of extruded activated carbon. After impregnation of the carbon with the metal solution, the coal was placed in an oven at 90 ° C until dry. The metal loading in this catalyst preparation per carbon support ce was 0.016 gm of Pd / cc, 0.016 gm of Ag / cc of support and 0.032 gm of Re / cc. 40 cc (23.36 gms) of the catalyst preparation of oxidized carbon impregnated with metals and dry were loaded into a Hastelloy C reactor tube (external diameter of 0.745"x internal diameter 0.475") and subsequently into a recirculation facility of the reactor. The catalyst is initially reduced to 280 ° C for 5 hrs under a stream of hydrogen flow (at atmospheric pressure). The catalyst was started under the following conditions:System Pressure = 2500 PSIG H2 Feeding Ratio: Maleic Acid = 65: 1 Liquid Feeding Composition = 400 gms. of Maleic Acid / liter Time Spatial Speed of Liquid (LHSV) = 0.55 Temperature of Reactor Set Point = 180 ° C Under the conditions of previous processes the following product selectivities were observed: Tetrahydrofuran (THF) = 8.5% Gamma-butyrolactone (GBL) = 0.2% Butanediol (BDO) = 55.4% n-Butanol (BuOH) = 29.6% In order to test the inherent activity of the catalyst, the LHSV is normally increased and / or the set point temperature of the reactor is lowered until a considerable increase in gamma-butyrolactone is observed in the product solution (a saturation of GBL occurs). In this case, in order to obtain a collateral comparison with the catalyst in Comparative Example C, the setpoint temperature was reduced to 150 ° C and the LHSV was kept at 0.55. The product selectivities observed under those conditions were as follows: Tetrahydrofuran (THF) = 2.1% Gamma-butyrolactone (GBL) = 0.1% Butanediol (BDO) = 90.2% n-Butanol (BuOH) = 6.6% As can be seen in the table above, there was no saturation or significant outgrowth of GBL for this catalyst under this set of conditions. In order to further test the activity of this catalyst, the LHSV was maintained at 0.55 while the set point temperature was reduced to 140 ° C. The product selectivities observed under these conditions were as follows: Tetrahydrofuran (THF) 1.6% Gama-butyrolactone (GBL) 0.3% Butanediol (BDO) 92.8% n-Butanol (BuOH) 4.6% As an additional example of the selectivity and activity of the catalyst, the set point temperature increased again to 150 ° C and the LHSV increased to 0.75. The product selectivities observed under these conditions were as follows: Tetrahydrofuran (THF) 2.4% Gamma-butyrolactone (GBL) 0.2% Butanediol (BDO) 91.1% n-Butanol (BuOH) 5.5% Comparative Example C: (4% of Pd / 4% of Ag / 8% of Re on carbon - not oxidized) 650 ce (276.5 gms.) Of extruded of the activated carbon CECA ACL40 were used as the catalyst support for this catalyst preparation . An impregnation solution was prepared by placing 139.25 gms. of the Pd (N03) 2 solution (7.70% Pd by weight), 16.5 gms. of AgN03, and 41.5 gms. of the HRE04 solution (52.6% of Re by weight) in a 250 ml volumetric flask together with sufficient acetonitrile to bring the solution to 250 ml. The density of the solution was 1.1846 gms / cc. 286.4 gms. of the solution were used to impregnate the 650 cc of extruded activated carbon. After impregnation with the catalyst preparation, it was allowed to stand for 5.75 hours, then it was placed in an oven at 120 ° C for 23 hours until dry. The metal load used in this catalyst preparation per carbon support ce was 0.016 gm of Pd / cc, 0.016 gm of Ag / cc and 0.032 gm of Re / cc. This catalyst had the same metal fillers per volume of catalyst as the catalyst prepared in Example 3. 40 cc (21.02 gms) of the dry-impregnated carbon catalyst preparation, above, was loaded into a Hastelloy reactor tube. C (external diameter 0.7445"x internal diameter 0.475") and subsequently were introduced to the reactor recirculation apparatus. The catalyst was initially reduced to 280 ° C for 5 hrs under a stream of hydrogen flow (at atmospheric pressure). The catalyst was started under the following conditions: System Pressure = 2500 PSIG H2 Feeding Ratio: Maleficic Acid = 65: 1 Liquid Feeding Composition = 400 gms Maleic Acid / liter Liquid Hourly Space Velocity (LHSV) = 0.55 Reactor Set Point Temperature = 180 ° C Under the above process conditions the following product selectivities were observed: Tetrahydrofuran (THF) = 21.9% Gama-butyrolactone (GBL) = 0.3% Butanediol (BDO) = 49.6% n-Butanol (BuOH) = 22.8% In order to test the inherent activity of the catalyst, the LHSV is normally increased and / or the set point of the reactor is decreased until a considerable increase is observed in the gamma-butyrolactone in the product solution (saturation or outcrop of GBL occurs). For this catalyst, the saturation or outcrop of GBL was observed at a set point temperature of 150 ° C and an LHSV = 0.55. The product selectivities observed under these conditions were as follows: Tetrahydrofuran (THF) = 11.2% Gama-butyrolactone (GBL) = 6.9% Butanediol (BDO) = 77.5% n-Butanol (BuOH) = 3.6% Example 4: (5% Pd / 5% Re on oxidized carbon) 100 g activated carbon 30 x 70 mesh (AC40, produced by CECA of France and sold in the United States by Atochem North America Inc.) were shaken with an excess of oxidizing agent (90% HN03, 30% H202 or 35% HNO3 as set forth in Table I) at 80 ° C for about 18 hours. After cooling the product was recovered by filtration and washed several times with an excess of water, followed by drying in the oven at 120 ° C. 25.00 g of the oxidized carbon were treated with 120 g of an aqueous solution containing 1.90 g of? H4 Re0 and 18.12 g of Pd (? 03) 2 solution (7.26% Pd). The resulting suspension was evaporated to dryness on a "roto-vac" and dried in the oven at 120 ° C. The product was then reduced in hydrogen at 200 ° C. The lifting speed was Io / min. with a retention time of 5 hours at 200 ° C. 8.00 g of the reduced catalyst (nominally 5% Pd / 5% Re on carbon) were mixed with 100.0 g of 30% aqueous maleic acid and the mixture was placed in an autoclave. The autoclave was purged three times with H2 at 2500 psig at room temperature, followed by an increase in temperature of up to 160 ° C or 180 ° C, as set forth in Table I, at a stirring speed of 1000 rpm, while that the pressure was maintained at 2500 psig. The reagents were kept under these conditions for the time shown in Table I and then allowed to cool to room temperature. The products were analyzed by gas chromatography and showed 100% male conversion with selectivities of 1,4-butanediol (BDO), trahydrofuran (THF), gamma-butyrolactone (GBL) and n-butanol, as established in the Table I.

Comparative Example D; (5% Pd / 5% Re on carbon - not oxidized) The procedure of Example 4 was repeated using the same activated carbon but without the oxidizing agent treatment. This catalyst was tested under conditions identical to those used in Example 4, and as set forth in Table 1. The results of these tests are set forth in Table I.

TABLE 1 Agent Time T Selectivities Oxidizing example (hr) (° C) BDO THF GBL n-Butanol Common example 9.5 160 59.9 32.6 parativo D 90 ': HNO. 9.5 160 82.3 6.5 6.9 The results of Example 4, when compared to Comparative Example D, show that the invention described herein (ie, using a catalyst wherein the carbon support is contacted with an oxidizing agent as in Example 4, provides superior yields of 1,4-butanediol (BDO) with minimal gamma-butyrolactone formation (GBL).

It should be understood that the subject invention is not limited by the examples set forth above. These have been provided simply to demonstrate the functionality of the invention and the selection of the catalysts, sources of m tal, carbon supports, concentrations, contact times, solids charges, feeds, reaction conditions and products, as the case may be, and can be determined from the overall disclosure provided without departing from the spirit of the invention disclosed and described herein, the scope of the invention includes modifications and variations which fall within the scope of the appended claims.

Claims (13)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1. A process for the production of 1,4-butanediol comprising catalytically hydrogenating a hydrogenatable precursor, in contact with a gas containing hydrogen and a hydrogenation catalyst, comprising at least one noble metal of Group VIII of Periodic Table and at least one of rhenium, tungsten and molybdenum, deposited on a carbon support, wherein the carbon support has been contacted with an oxidizing agent selected from the group consisting of maleic acid, hydrogen peroxide, sodium hypochlorite, ammonium persulfate and perchloric acid, before the deposition of the metals.
2. 2. The process according to claim 1, wherein the hydrogenatable precursor is selected from the group consisting of maleic acid, maleic anhydride, fumaric acid, succinic acid, succinic anhydride, dimethyl succinate, gamma-butyrolactone or mixtures thereof.
3. 3. The process according to claim 2, wherein the hydrogenatable precursor is at least one of maleic acid, succinic acid or gamma-butylactone.
4. 4. The process according to claim 1, wherein the hydrogenation catalyst is prepared by the steps of: (i) oxidizing the carbon support by contacting the carbon support with an oxidizing agent; (ii) impregnating in one or more impregnating steps, comprising contacting the carbon support with a Group VIII metal agent and at least one metal selected from the group consisting of rhenium, tungsten, and molybdenum, which are in at least one solution; (iii) drying the impregnated carbon support in order to remove the solvent after each impregnation step; and (iv) heating the impregnated charcoal support at a temperature of about 100 ° C to 350 ° C, under reducing conditions. The process according to claim 1, wherein the noble metal of Group VIII is selected from the group consisting of palladium, platinum, rhodium and ruthenium. 6. The process according to claim 1, wherein the hydrogenation catalyst comprises palladium and rhenium. The process according to claim 1, wherein the hydrogenation catalyst comprises palladium, rhenium and silver. The process according to claim 4, wherein the metal sources are combined in a single solution and the metals are deposited on the carbon support in a single impregnation step. The process according to claim 1, wherein the hydrogenation catalyst comprises from about 0.1 to about 20 weight percent of the Group VIII metal, and about 0.1 to about 20 weight percent of at least one of rhenium, tungsten or molybdenum. The process according to claim 1, wherein the ratio of hydrogen to hydrogenatable precursor is between 5 to 1 and about 1000 to 1. The process according to claim 1, wherein the pressure of the hydrogen-containing gas is between about 20 to 400 atmospheres. 12. The process according to claim 1, wherein the contact time is between approximately 0.1 minute and 20 hours. 13. A process for the production of tetrahydrofuran and 1,4-butanediol, comprising catalytically hydrogenating a hydrogenatable precursor in contact with a hydrogenation catalyst comprising at least one noble metal of Group VIII of the Periodic Table and at least one of rhenium, tungsten or molybdenum, on an oxidized carbon support, wherein the catalyst is prepared by the steps of: (i) oxidizing the carbon support by contacting the carbon support with an oxidizing agent selected from the group consisting of nitric acid, hydrogen peroxide, sodium hypochlorite, ammonium persulphate and perchloric acid; (ii) impregnating in one or more impregnation steps, comprising contacting the carbon support with an agent of at least one metal of the Group VIII and at least one metal selected from the group consisting of rhenium, tungsten and molybdenum, those metal sources are at least in one solution; (iii) drying the impregnated carbon support in order to remove the solvent after each impregnation step; and (iv) heating the impregnated carbon support at a temperature from about 100 ° C to about 350 ° C under reducing conditions. SUMMARY OF THE INVENTION Maleic acid, maleic anhydride or other hydrogenatable precursor are catalytically iggenated to give 1,4-butanediol and tetrahydrofuran. It has been found that high yields of 1,4-butanediol are achieved when the hydrogenation catalyst comprises at least one noble metal of Group VIII of the Periodic Table and at least one of rhenium, tungsten and molybdenum, on a carbon support. , wherein the carbon support has been contacted with an oxidizing agent before the deposition of the metals. This hydrogenation catalyst is prepared by the steps of: (i) oxidizing the carbon support by contacting the carbon support with an oxidizing agent; (ii) impregnating in one or more impregnation steps, comprising contacting the carbon support with a Group VIII metal agent and at least one metal selected from the group consisting of rhenium, tungsten and molybdenum which are in at least one solution; (iii) after each impregnation step, dry the impregnated carbon support at a temperature of less than about 150 ° C in order to remove the solvent; and (iv) heating the impregnated charcoal support at a temperature of about 100 ° C to 350 ° C under reducing conditions.