FR2991318A1 - PROCESS FOR THE PRODUCTION OF SHORT ALCOHOLS IN THE PRESENCE OF A CATALYST BASED ON TUNGSTEN ALUMINA - Google Patents

Abstract

The present invention relates to a process for converting into an aqueous medium a feedstock comprising at least one polyol of formula C H 2 O with 3 <= n <= 6 in alcohol or mixture of alcohols having a number of carbon atoms less than that of the starting polyol, in which the charge is brought into contact at a temperature of between 180 and 350 ° C. and at a pressure of between 0.5 and 20 MPa with a catalyst. The catalyst comprises at least one metal chosen from groups 7 to 11 of the periodic table of the elements deposited on a support, said support comprising alumina on which tungsten is deposited with a tungsten element content of between 1 and 50% by weight. relative to the total weight of catalyst.

Description

FIELD OF THE INVENTION The present invention relates to a process for the selective transformation of polyols, for example obtained from the treatment of biomass, into an alcohol or mixture of alcohols having a number of carbon atoms lower than that of the starting polyol. . The products obtained are particularly usable as biofuels that can be incorporated into the fuel pool or as chemical intermediates used in the field of chemistry and petrochemistry. Prior art In recent years, rising fossil fuel costs and environmental concerns have stimulated global interest in developing alternatives to petroleum products. In particular, there is a keen interest in the incorporation of renewable products into the fuel and chemical sectors, in addition to or in substitution for products of fossil origin. Indeed, the production of chemicals and fuels from biomass 15 in particular reduces the energy dependence on oil. The conversion of polyols resulting from the transformation of biomass, in particular into hydrocarbon and mono-oxygenated products containing a number of carbon atoms of greater than or equal to 5, is a particularly advantageous route because these products may, for example, be incorporated into the gasoline pool after transformation. The literature is abundant in the field of catalytic conversion of polyols. Thus the mass metal catalysts (Ni Raney, Cu Raney) or supported of the M / SiO 2 type (M = Ru, Rh, Pt, Ir, Co, Cu) allow the transformation of an aqueous solution of polyols (glycerol, erythritol, xylitol or sorbitol) in poly-oxygenated molecules and hydrocarbons containing predominantly less than three carbon atoms such as glycerol, ethylene glycol, and C1-C3 alkanes (Montassier et al., Bulletin of the Chemical Society of France 148-155 , 1989). Huber et al. (Angewandte Chemie-International Edition 43, 1549-1551, 2004) observe the production of a mixture of dihydrogen, CO2 and hydrocarbons by conversion of sorbitol in the aqueous phase by employing a catalyst comprising 4% by weight of Pt on a silica alumina. The hydrocarbons produced have a chemical composition C ~ H2, + 2 with n less than or equal to six.

Patent Application WO2004 / 039918 describes a process for producing C1-C6 alkanes from water-soluble oxygenated hydrocarbons in the presence of a Group 8 catalyst.

Li et al. (ChemSusChem 2010, 3, 1154-1157) studied the conversion of sorbitol in an aqueous medium in the presence of a catalyst comprising 4% by weight of Pt on a silica alumina. Thus, at 245 ° C., at an hourly space velocity of 3 h -1, with an aqueous load containing 5% by weight of sorbitol, they observe, after 36 hours of test, a specific selectivity of C5-C6 alkanes of 34% and a yield of carbon at 10% alkanes (hence a carbon yield of C5-C6 compounds of the order of 3.4%). These same authors also studied the performance of a catalyst having 4% weight of Pt on a support WOX / ZrO2 under the same conditions; they observe a specific selectivity (the specific selectivity for alkane Ci being defined as the ratio of the carbon contained in the alkane Ci to the sum of the carbon contained in the alkanes detected in the gas phase) to C5-C6 alkanes equivalent to that obtained in presence of the catalyst 4% by weight of Pt on a silica alumina, ie of approximately 30% with a carbon yield of alkane of 1.2%. The carbon yield of C5-C6 compounds is thus about 0.4%.

The use of bimetallic catalysts supported on carbonaceous materials is also known. For example, a catalyst containing 5% by weight Pt and 5% by weight Re on a carbon support makes it possible to obtain a mixture of CO2 (corresponding to approximately 30% of the introduced carbon), alkanes and oxygenated compounds (approximately 70% of the carbon). introduced carbon). The carbon ratio between the hydrocarbon products and the oxygenated compounds varies with the operating conditions (Kunkes et al., Science 2008, 332, 417). More recently, it has been described in US 2011/0160482 the implementation of a trimetallic catalyst (Pt-Ru- Sn) on a support zirconia or titanium dioxide for the conversion of oxygenated hydrocarbons to oxygenated products of weight lower molecular weight.

One of the aims of the invention is therefore to provide a process for converting an aqueous feedstock containing at least one polyol which makes it possible to selectively transform the polyols into an alcohol or mixture of alcohols having a carbon number lower than that of the starting polyol. . SUMMARY OF THE INVENTION The present invention therefore relates to a process for converting into an aqueous medium a filler comprising at least one polyol of formula CnH2n + 20 'with 3 sns 6 in alcohol or a mixture of alcohols having a number of carbon lower than that of the starting polyol. According to the invention the charge is brought into contact at a temperature of between 180 and 350 ° C. and at a pressure of between 0.5 and 20 MPa with a catalyst, said catalyst comprising at least one metal chosen from groups 7 to 11. of the periodic table of the elements, and a support, said support comprising alumina on which is deposited tungsten with a tungsten element content of between 1 and 50% by weight relative to the total weight of catalyst.

Surprisingly, it has been found that when a catalyst having the combination of characteristics in the ranges of values mentioned above is used under the operating conditions indicated above, it makes it possible to selectively convert the polyols into an alcohol or mixture of alcohols having a number of carbon atoms lower than that of the starting polyol.

The process according to the invention makes it possible in particular to obtain a specific selectivity of at least 30% C in alcohols having a number of carbon atoms lower than that of the starting polyol. The specific selectivity is defined as the ratio of the carbon contained in the alcohols having a carbon number lower than that of the starting polyol to the sum of the total carbon contained in the gas phase and in the liquid phase. Preferably the support consists of alumina on which tungsten is deposited, with a tungsten element content of between 1 and 50% by weight relative to the total weight of catalyst.

Preferably, the conversion reaction is carried out at a temperature of between 200 and 270 ° C. and at a pressure of between 2 and 8 MPa.

According to a preferred embodiment, the conversion reaction is carried out under a reducing atmosphere or under an inert atmosphere. Advantageously, the conversion reaction is carried out under a dihydrogen atmosphere, the molar ratio dihydrogen / polyol (s) being between 1 and 400 mol / mol.

The content of each metal chosen from groups 7 to 11 of the periodic table of the elements is preferably between 0.01 and 10% by weight relative to the total weight of catalyst.

The tungsten element content is preferably between 1 and 30% by weight relative to the total weight of catalyst. According to a preferred embodiment, the catalyst has undergone a heat treatment step in a reducing atmosphere at a temperature between 100 and 600 ° C before its implementation in the conversion reaction. The catalyst used in the process may be in any form known to those skilled in the art, such as for example in the form of beads, extrudates or pellets.

The process according to the invention is particularly suitable for the conversion of polyols selected from glycerol, erythritol, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, dulcitol, fucitol, iditol, inositol, isomalt, maltitol, lactitol, polyglycitol. Preferably, the polyol is sorbitol, xylitol or mannitol.

Advantageously, the polyol is derived from the treatment of biomass. For example, the polyol can be obtained by transformation of sugar plants, starch plants or by transformation of lignocellulosic biomass such as wood or vegetable waste. DETAILED DESCRIPTION OF THE INVENTION The invention relates to a process for converting into an aqueous medium a filler comprising at least one polyol of formula CnH2,20 'with 3 sns 6 in alcohol or mixture of alcohols having a number of carbon lower than that of the starting polyol. According to the invention the charge is brought into contact at a temperature of between 180 and 350 ° C. and at a pressure of between 0.5 and 20 MPa with a catalyst, said catalyst comprising at least one metal chosen from groups 7 to 11. of the periodic table of the elements and a support, said support comprising alumina on which tungsten is deposited with a tungsten element content of between 1 and 50% by weight relative to the total weight of catalyst. The process according to the present invention makes it possible in particular to obtain an improved selectivity for an alcohol or mixture of alcohols having a number of carbon atoms of less than or equal to 3 and preferably of an alcohol or mixture of alcohols having 2 or 3 atoms. carbon such as ethanol, n-propanol and 2-propanol. Thus, for example, when carrying out the process according to the invention with a feedstock containing a 6-carbon polyol such as sorbitol or mannitol, it is possible to obtain a mixture of different products including in particular carbon dioxide. , 15 of the dihydrogen, poly-oxygenated compounds such as isosorbide, hydrocarbons and mono-oxygen compounds containing a number of carbon atoms of less than or equal to six, with predominantly alcohols having a lower number of carbon atoms to that of the starting polyol, such as propanol (and its isomers) and ethanol. The solution obtained at the end of the conversion contains, for example, methane, ethane, propane, butane, pentane, hexane, cyclopentane and methylcyclopentane as nonlimiting examples of hydrocarbons; hexanol, pentanol, butanol, propanol, ethanol and methanol as non-limiting examples of mono-alcohol compounds; hexanone, pentanone, butanone, propanone, acetone as non-limiting examples of mono-ketones and also carboxylic acids. Polyoxygenated compounds such as diols, diones containing a carbon chain of 1 to 6 carbon atoms can also be obtained. The maximum hydrocarbon chain length of the products obtained depends on that of the starting polyol; for example, six carbon atoms for sorbitol and mannitol, five for xylitol, etc. The process according to the invention makes it possible to obtain high conversions of the polyol and high selectivities in alcohols or mixtures of alcohols containing a polyol. number of carbon atoms lower than that of the starting polyol while minimizing the formation of compounds of the hydrocarbon type and carbon dioxide. The process according to the invention allows the selective conversion of polyols having 5 or 6 carbon atoms to n-propanol, 2-propanol and ethanol.

These conversions and selectivities are obtained in hydrothermal conditions, that is to say in the presence of liquid water and temperature. The reaction atmosphere may be a neutral atmosphere or a reducing atmosphere. The catalytic conversion reaction is preferably carried out continuously in the condensed phase.

The charge The charge contains at least one polyol. The term polyol refers to a compound corresponding to the chemical formula CnH2e.2On with 3 sns 6. The charge may contain one or more polyols chosen from glycerol, erythritol, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, dulcitol, fucitol, iditol, inositol, isomalt, maltitol, lactitol, polyglycitol. Preferably, the feed contains sorbitol (n = 6), mannitol (n = 6) and / or xylitol (n = 5). Most preferably, the filler contains sorbitol. The filler may also contain impurities related, for example, to the process for obtaining polyols, in particular from biomass. For example, the feed may contain monomeric sugars such as glucose or xylose, inorganic or organic compounds. The impurity content is preferably less than 10% by weight of the filler. The feedstock to be treated contains water, the content of which is between 1% and 99% by weight relative to the weight of the filler, preferably between 30% and 99%, more preferably between 40% and 98% by weight. of water relative to the weight of the load. The concentration of polyol (s) in the filler is generally between 1% and 99%, preferably between 1% and 70% by weight, very preferably between 2% and 60% by weight relative to the weight of the filler.

The polyol (s) contained in the feed is (are) preferably of biobased origin. The polyols can thus be produced, for example, by transformation of sugar plants such as sugar beet or sugar cane, by transformation of starchy plants such as wheat, corn, potato, cassava or by transformation of lignocellulosic biomass. The lignocellulosic raw material may consist of wood or vegetable waste. Other non-limiting examples of lignocellulosic biomass material are farm residues (straw, grass, stems, cores, shells, etc.), logging residues (first-thinning products, bark, sawdust, chips, falls ...), logging products, dedicated crops (short-rotation coppice), residues from the agri-food industry (residues from the cotton industry, bamboo, sisal, banana, maize, panicum virgatum, coconut, bagasse ...), household organic waste, waste from wood processing facilities, used timber from construction, paper, recycled or not.

Obtaining polyols from sugar plants or starch plants involves steps of hydrolysis and hydrogenation. On the other hand, obtaining polyols from crude lignocellulosic biomass is more complex and requires several steps, simultaneous or successive, namely: - pretreatment of the lignocellulosic biomass, - hydrolysis of the carbohydrate part (cellulose and hemicellulose) and a hydrogenation of the monomeric sugars obtained after hydrolysis. The lignocellulosic biomass feed can be used in its raw form, i.e., in its entirety, of these three constituents cellulose, hemicellulose and lignin. The raw biomass is generally in the form of fibrous residues or powder. In general, it is crushed or shredded to allow its transport. The biomass is preferably pretreated to increase the reactivity and accessibility of the cellulose within the biomass prior to processing. These pretreatments are of a mechanical, thermochemical, thermomechanical-chemical and / or biochemical nature and cause the decystallinization of the cellulose, the solubilization of hemicellulose and / or lignin or the partial hydrolysis of hemicellulose according to treatment. The lignocellulosic biomass feed may also be pretreated to be in the form of water-soluble oligomers. These pretreatments are of a mechanical, thermochemical, thermomechanical-chemical and / or biochemical nature. They cause decystallinization and solubilization of cellulose in the form of water-soluble oligomers.

The hydrogenation step makes it possible to transform part of the monosaccharides of the biomass into polyol (s). For example, it makes it possible to partially convert hexoses such as glucose into a hydrogenated product such as sorbitol or mannitol, according to the following equation: C6H12O6 + H2 C6H1406 The hydrogenation step is carried out at temperatures of between 40 ° C. and 300 ° C, preferably between 60 ° C and 250 ° C, and at a hydrogen pressure of between 0.5 MPa 10 and 20 MPa, preferably between 1 MPa and 15 MPa. The catalyst The catalyst used in the process according to the invention comprises at least one metal chosen from groups 7 to 11 of the periodic table of the elements. The metal or metals are advantageously deposited on a support. The support consists of alumina on which tungsten is deposited with a tungsten element content of between 1 and 50% by weight relative to the total weight of catalyst. Alumina is prepared according to any technique known to those skilled in the art (Handbook of Porous Solids, Schüth, Wiley-VCH Edition, Volume 3). The alumina of the invention may be in different crystallographic phases, transition alumina (eta, gamma, delta, theta ...) or alpha alumina, pure or mixed. The catalyst of the invention may be prepared according to any of the techniques known to those skilled in the art: dry impregnation (s), excess impregnation (s), ion exchange (s), deposit (s) precursor vapor phase containing tungsten on an Al 2 O 3 aluminum oxide support or an aluminum derivative such as, for example, aluminum oxyhydroxide AlOH or aluminum trioxide Al (OH) 3. A synthetic route may also be a coprecipitation of tungsten and aluminum oxides. The tungsten precursors useful for the deposition of tungsten may be, for example, tungsten oxides, tungsten chlorides, tungsten sulfides, tungsten carbides, tungsten fluorides, tungsten oxychlorides, organic derivatives based on tungsten. of tungsten, the iso- or heteropolyanions containing tungsten. Preferably, the tungsten precursors are selected from tungstic acid, peroxotungstic acid, ammonium metatungstate, or isopolyanions or heteropolyanions based on tungsten. Preferably, the precursors are ammonium metatungstate or tungstic acid. The use of tungstic acid in solution in hydrogen peroxide allows the formation of monomeric tungsten species in solution, and the preparation of WOX Al2O3 materials by ion exchange. After the deposition step of tungsten, the tungsten support can be subjected to a heat treatment. The treatment is for example a calcination at a temperature between 350 and 800 ° C under air flow. At the end of the calcination step, the tungsten is partially or completely oxidized to form the WOX species with x between 0.5 and 5. For example, a method for preparing the tungstated alumina support is to impregnate solution of ammonium metatungstate (NH4) 4H2W12O40 on an alumina support followed by calcination. The tungsten content of the catalyst is between 1 and 50% by weight relative to the weight of the catalyst, preferably between 1% and 30% by weight and preferably between 1 and 20% by weight. The catalysts used in the invention contain, in addition to the tungsten element, at least one metal chosen from groups 7 to 11 of the periodic table (according to the new notation of the periodic table of elements: Handbook of Chemistry and Physics , 76th edition, 1995-1996). Thus, the metal element may be chosen from: Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Re, Au, Ag. Preferably, the element is chosen from Ru, Rh, Pd, Pt, Ni, Cu, Ir, Cu, Re, alone or in admixture. Even more preferably, the metal chosen is platinum. The deposition of said metal selected from Groups 7 to 11 of the Periodic Table generally involves a precursor of the metal. For example, it may be metal organic complexes, metal salts such as metal chlorides, metal nitrates.

The introduction of the metal can be carried out by any technique known to those skilled in the art such as ion exchange, dry impregnation, excess impregnation, vapor phase deposition, etc. The introduction of the metal can be carried out before or after forming the tungsten alumina support. It is also possible to first deposit the metal on the alumina-based support before the deposition of tungsten. The weight content of each introduced metal element is advantageously between 0.01 and 10% by weight, and preferably between 0.05 and 5% by weight relative to the total weight of the catalyst. After introduction of the metal element and tungsten onto the alumina support, the catalyst is generally subjected to a heat treatment step. The heat treatment is advantageously carried out between 250 ° C. and 700 ° C. The heat treatment step may be followed by a temperature reduction treatment. The reducing heat treatment is advantageously carried out at a temperature of between 100 ° C. and 600 ° C. under a flow or atmosphere of dihydrogen. The reduction step can be carried out in situ, that is to say in the reactor where the reaction takes place, before the introduction of the reaction charge. The reduction can also be carried out ex situ. In the preparation of the catalysts according to the invention, the alumina may be in the form of powder or shaped, for example, balls, extrudates, pellets or any other form commonly used. The shaping can be carried out before or after the deposition of tungsten and before or after the introduction of the metal. The catalysts used in the present invention are characterized by the techniques known to those skilled in the art, such as X-ray fluorescence, nitrogen adsorption-desorption and transmission electron microscopy. The catalyst preferably has a surface area of from 5 to 400 m 2 / g and a pore volume of from 0.1 to 2.0 ml / g.

Transformation Process The polyol (s) transformation process according to the invention comprises the reaction in a medium containing water in the presence of a catalyst described above. The polyol conversion process according to the invention is advantageously carried out under a reducing atmosphere or under an inert atmosphere such as dinitrogen or argon. Preferably, the reaction is carried out under a dihydrogen atmosphere. The dihydrogen can be used pure or in mixture. For example, the dihydrogen / polyol molar ratio may be between 1 and 400, preferably between 5 and 300 mol / mol.

The process is carried out at a temperature of between 180 ° C. and 350 ° C., preferably between 200 ° C. and 270 ° C., and at a total pressure of between 0.5 MPa and 20 MPa, preferably between 2 MPa and 8 ° C. MPa. The reaction is carried out continuously, for example in a fixed bed. The hourly mass velocity (mass flow rate of polyol / mass of catalyst) is between 0.01 and 10 h -1, preferably between 0.05 and 2 h -1 .Examples Example 1: Preparation of Catalyst Cl according to the invention: 1 2% -weight Pt / Al 0320 WOY 50 g of Al2O3-WOX powder are prepared by anion exchange by mixing 58 g of boehmite powder γ-AOHOH with tungstic acid in solution (0 25 mol / L) in 150 mL of 30% volume hydrogen peroxide solution The solution obtained is filtered and the collected solid is dried at 110 ° C. for 18 hours The resulting solid is then calcined at a rate of Dry air at the temperature of 600 ° C. for 3 hours The solid powder is then put into the form of extrudates The solid S1 obtained contains 8.6% by weight of tungsten The specific surface area of the solid S 1 is 240 m 2 / g and the pore volume of 0.9 ml / g X-ray diffraction analysis shows the diffraction lines of gamma alumina. Catalyst C1 is prepared by dry impregnation of an aqueous hexachloroplatinic acid solution H2PtC16.xH2O. The aqueous solution is prepared at 25 ° C. by diluting 1.6 g of H.sub.2 PtCl.sub.4 .times .H.sub.2 O in demineralized water to a volume corresponding to the pore volume of the solid S1. This solution is then impregnated with 50 g of the previously prepared solid S1. The solid obtained is then dried at 120 ° C. for 12 h and then calcined under a flow of dry air at a temperature of 550 ° C. for 2 h.

The catalyst C1 obtained contains 1.2% by weight of platinum and 8.5% by weight of tungsten. EXAMPLE 2 Preparation of catalyst C2 (not in accordance with the invention): 1.2% by weight Pt / ZrO2WO 50 g of ZrO2-WOX powder (MEL Chemicals) are extruded with zirconium hydroxide powder (Zr ( OH) 4, MEL Chemicals). The solid obtained is calcined under a flow of dry air at a temperature of 700 ° C. for 3 hours. The solid S2 contains 9.7% by weight of tungsten. The surface area of the solid S 2 is 73 m2 / g and the pore volume 0.2 ml / g. Catalyst C2 is prepared by dry impregnation of solid S 2 with an aqueous solution of hexachloroplatinic acid H 2 PtCl 6 .xH 2 O. An aqueous solution is prepared at 25 ° C. by diluting 1.6 g of H 2 PtCl 4 .xH 2 O in demineralized water to a volume which corresponds to the pore volume of the solid S 2. This solution is then impregnated with 50 g of the previously prepared solid S2. The solid obtained is dried at 120 ° C. for 12 h and then calcined under a dry air flow rate at a temperature of 550 ° C. for 2 hours. The catalyst C2 obtained contains 1.2% by weight of platinum and 9.6% by weight of tungsten. EXAMPLE 3 Preparation of Catalyst C3 (not according to the invention): 1.2% by weight Pt / SiO 2 -Al 2 O 3 50 g of catalyst C 3 are prepared by dry impregnation of a siliceous alumina (30% SiO 2 / 70% Al 2 O 3, Siralox 30, from Sasol) with an aqueous solution of hexachloroplatinic acid H 2 PtCl 4 .xH 2 O. The solid obtained is dried at 120 ° C. for 12 h and then calcined under a flow of dry air at a temperature of 550 ° C. for two hours. The catalyst C3 obtained contains 1.2% by weight of platinum.

EXAMPLE 4 Transformation of a Solution Containing Sorbitol Using the Catalysts Prepared in Examples 1 to 3 This example relates to the conversion of a feed containing 10% by weight of sorbitol in water by catalysts C1, C2 and C3 for the production of short alcohols, in particular ethanol and propanol. The progress of a standard catalytic test is as follows: 4 g of crushed catalyst and sieved to a particle size of 150-355 μm are loaded into the reactor. The catalyst is then dried and reduced under dihydrogen in situ for 2 hours at 450 ° C. After cooling to 50 ° C., degassed water is sent to the reactor. The reactor pressure rises gradually to the set value of 3.8 MPa. The reactor is then heated to the test temperature of 240 ° C. The mass flow rate / catalyst mass ratio is set at 2 h -1 The flow rate of hydrogen is adjusted to have an H 2 / sorbitol molar ratio of 75. When the pressure and temperature conditions are stabilized, the sorbitol charge dissolved in water (10% by weight) is a substitute for pure water and at the outlet of the reactor the products present in the liquid phase and in the gas phase are periodically analyzed.

The products obtained and their mode of analysis At the outlet of the reactor, the products of the reaction are analyzed according to several techniques. The reaction products contained in the gas phase, such as CO, CO 2, dihydrogen, hydrocarbons containing one to six carbon atoms as well as some light oxygen compounds, are analyzed by gas chromatography. The reaction products contained in the liquid phase are analyzed by gas chromatography and by high performance liquid chromatography (HPLC). The products analyzed by these two techniques contain the following families: polyols, monoalcohols: in particular sorbitol, xylitol, glycerol, isosorbide, anhydrosorbitol, hexanol, pentanol, butanol, propanol, isopropanol, ethanol and methanol, hexanediol, pentanediol, butanediol, propylene glycol, ethylene glycol, hexanetriol, butanetriol, pentanetriol, ketones, for example hexanone, hexanedione, pentanone, pentanedione, butanone, propanone, acetone, carboxylic acids and their esters, lactones, such as formic acid, acetic acid, lactic acid, levulinic acid, alkyl levulinates, lactic acid, pentanoic acid, hexanoic acid, 3-hydroxybutyrolactone, 7-butyrolactone, cyclic ethers: for example tetrahydrofuran (THF) , methyltetrahydrofuran (MTHF), dimethyltetrahydrofuran, 5- (hydride) oxymethyl) furfural, acetylfuran, tetrahydropyran, - hydrocarbon compounds such as hexane, pentane, methylcyclopentane, cyclopentane, butane. The sum of the carbon contained in the water-soluble reaction products is determined by the TOC analysis (Total Organic Carbon).

Conversion, selectivity and yield Conversion of sorbitol The conversion of sorbitol at time t is calculated according to the following formula: Sorbitol conversion (t) = (Qm sorbitol load - Qm sorbitol (t)) / Qm sorbitol load With Qm sorbitol charge = flow sorbitol mass input, in g / h Qm sorbitol (t) = mass flow rate of sorbitol output, in g / h The efficiency of a catalyst for the sorbitol transformation reaction is expressed in selectivities and yields of different families of products obtained, in particular hydrocarbons (denoted HC), short alcohols (ethanol / propanol) and CO2. The carbon yield of compound Ci (Rdtc Ci) and the carbon selectivity of compound Ci (Sc Ci Ci) are defined as follows: Rdt, C; = Qc Ci / Qc sorbitol Sc Ci = Rdtc Ci / Sorbitol conversion with: Q (sorbitol) = carbon fraction of sorbitol x Qm (sorbitol) = 0.40 x Qm (sorbitol), in gC / h Oc C = carbon flow compound C; = carbon fraction of the compound Ci x Qm (Ci), in gC / h Qm (sorbitol) = mass flow rate of the sorbitol at the inlet, in g / h Qm (Ci) = mass flow rate of the compound Ci at the exit, in g / h By for example, Qc (n-hexane) = carbon fraction n-hexane x Qm (n-hexane) = 0.84 x Qm (n-hexane), in gC / h Oc (CO2) = carbon fraction CO2 x Qm (CO2) = 0.37 x Qm (CO2), in gC / h The results obtained after 40 hours of test under a reaction charge are grouped in Table 1. It should be noted that at 240 ° C., the transformation of sorbitol is complete so that the yield is equal to the selectivity.

Catalyst Conversion Carbon yields (= carbon selectivities) sorbitol (% C) Hydrocarbon Ethanol Propanol Ethanol + propanol CnH2n + 2 C2H6O C3H8O (C2H6O + C3H8O) n = 1 to 6 Without catalyst 0 0 0 0 0 Pt / AI2O3-WOX 100 8 22 (C1, Example 1, compliant) Pt / ZrO2-WOX 100 11 6 9 (C2, Example 2, non-compliant) Pt / SiO2-Al2O3 100 16 11 15 26 (C3, Example 3, non-compliant) Table 1 : Conversion of a charge containing 10% by weight of sorbitol by catalysts C1, C2 and C3, after 40 hours of test, at 240 ° C., PPH = 2 h -1.

Without catalyst, the sorbitol is not converted and no reaction product is detected. It is found that when the catalyst C3 (1.2% by weight Pt / SiO2-Al2O3, not in accordance with the invention) is used, a total conversion of sorbitol is obtained with a yield (selectivity) of ethanol and propanol products which represents 26% of the carbon introduced. During the conversion, hydrocarbons containing 1 to 6 carbon atoms are also formed with a yield (selectivity) of the order of 16% of the carbon introduced. When the catalyst C2 (1.2% by weight Pt / ZrO2-WOx not in accordance with the invention) is used, a total conversion of sorbitol is also obtained, which is accompanied by the production of ethanol, propanol and hydrocarbons. C1-C6. The yield (selectivity) of ethanol and propanol produced represents 15% of the carbon introduced while the yield (selectivity) of C1-C6 hydrocarbons is 11% of the carbon introduced. Thus, the use of a catalyst containing a zirconia doped with tungsten and platinum does not make it possible to improve the ethanol / propanol selectivity with respect to the Pt / SiO2-Al2O3 reference catalyst. Using the catalyst Cl (1.2 wt% Pt / Al2O3-WOx, in accordance with the invention), the sum (ethanol + propanol) produced represents 43% of the carbon introduced. The use of the Cl catalyst makes it possible to increase by 65% the carbon yield of short alcohols in comparison with the reference catalyst C3 Pt / SiO2-Al2O3. The alcohol selectivity of the process is thus improved with the use of a catalyst containing platinum deposited on a tungsten alumina support.

Thus, these examples demonstrate that the use of heterogeneous catalysts based on tungstated alumina and further comprising at least one metal-state element selected from Groups 7 to 11 of the Periodic Table enables the polyols to be selectively transformed alcohols or mixture of alcohols having a lower number of carbon atoms than that of the starting polyol. 30

Claims (15)

REVENDICATIONS1. A method of converting into a water medium a feedstock comprising at least one polyol of the formula CrsH2rv + 2Ors with 3 ss 6 in alcohol or a mixture of alcohols having a number of carbon atoms lower than that of the starting polyol, wherein the charge is brought into contact at a temperature of between 180 and 350 ° C. and at a pressure of between 0.5 and 20 MPa with a catalyst, said catalyst comprising at least one metal selected from groups 7 to 11 of the periodic table of elements and a support, said support comprising alumina on which is deposited tungsten with a tungsten element content of between 1 and 50% by weight relative to the total weight of catalyst. 2. The process according to claim 1, wherein the conversion reaction is carried out at a temperature between 200 and 270 ° C and at a pressure of between 2 and 8 MPa. 15 3. Method according to one of the preceding claims, wherein the conversion reaction is carried out under a reducing atmosphere or under an inert atmosphere. 4. The process according to claim 3, wherein the conversion reaction is carried out under a dihydrogen atmosphere and wherein the dihydrogen / polyol molar ratio is between 1 and 400 mol / mol. 5. Method according to one of the preceding claims, wherein the content of each metal selected from groups 7 to 11 of the periodic table of the elements is between 0.01 and 10% by weight relative to the total weight of catalyst. 25 6. Method according to one of the preceding claims wherein the tungsten element content is between 1 and 30% by weight relative to the total weight of catalyst. 30 7. The method of claim 6, wherein the content of tungsten element is between 1 and 20% by weight relative to the total weight of catalyst. 8. Process according to one of the preceding claims, in which the alumina is a transition alumina and / or an alpha alumina. 9. The process as claimed in one of the preceding claims, in which the metal chosen from groups 7 to 11 of the periodic table of the elements is selected from Ru, Rh, Pd, Pt, Ni, Cu, Ir, Cu or Re. 10. Process according to one of the preceding claims, in which the catalyst has undergone a heat treatment step under a reducing atmosphere at a temperature of between 100 and 600 ° C. before being used in the conversion reaction. 11. Method according to one of the preceding claims, wherein the catalyst is in the form of beads, extrudates or pellets. 15 12. Method according to one of the preceding claims, wherein the polyol is selected from ethylene glycol, glycerol, erythritol, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, dulcitol, fucitol, iditol, inositol, isomalt, maltitol, lactitol, polyglycitol. 20 The process according to claim 12, wherein the polyol is selected from sorbitol, xylitol and mannitol. 14. Method according to one of the preceding claims, wherein the polyol is derived from the treatment of biomass. 25 15. Method according to one of the preceding claims wherein the alcohol or mixture of alcohols resulting from the conversion comprises a number of carbon atoms less than or equal to 3, preferably equal to 2 or 3 carbon atoms. 30