EP2279160A1

EP2279160A1 - Methanol production process

Info

Publication number: EP2279160A1
Application number: EP09735386A
Authority: EP
Inventors: Shik Chi Edman Tsang; William Owusu Oduru; Daniel James Redman
Original assignee: Oxford University Innovation Ltd
Current assignee: Oxford University Innovation Ltd
Priority date: 2008-04-21
Filing date: 2009-04-21
Publication date: 2011-02-02
Also published as: GB0807255D0; WO2009130452A1

Abstract

The invention provides a process for producing methanol, which process comprises treating a compound which is: a sugar alcohol of formula (I) in which n is 0 or an integer equal to or greater than 1, or a sugar of formula (II) in which m is an integer equal to or greater than 1, with hydrogen in the presence of a hydrogenolysis catalyst comprising a transition metal, and thereby producing said methanol by hydrogenolysis of said compound.

Description

METHANOL PRODUCTION PROCESS

FIELD OF THE INVENTION

The present invention relates to a process for the production of methanol.

BACKGROUND TO THE INVENTION

The decreasing reserves of fossil carbon and environmental problems related to their use have led to a continuously growing interest in the use of renewable energy sources.

Methanol is undoubtedly one of the key chemicals in our present chemical industry with a huge potential as a source of renewable energy and also a building block for the production of other chemicals. Presently, about 90% of the world's methanol production is from the synthesis gas reaction which utilizes fossil fuel as the main raw material. To place methanol in the elite class of green fuel sources, an alternative route for its production needs to be discovered that will not rely on fossil fuel as its feedstock. 3h nature, microorganisms produce methanol from biomass through the fermentation process. However, the process is rather slow and will not support an industrial scale production that will meet the demand for methanol in the world economy. There is therefore an ongoing need to discover an alternative route for the production of methanol which does not rely on a fossil fuel feedstock.

Glycerol, a sugar alcohol, is the major byproduct in the production of biodiesel and also in the production of oleochemicals from vegetable oils. For every 9 kg of vegetable oil processed, 1 kg of glycerol is produced. However, despite the intensive research in the conversion of glycerol to other products, no viable commercial process has yet been identified. The majority of research efforts have focussed on reforming glycerol to synthesis gas, oxidation, dehydration, hydrogenolysis, oligomerization, (i.e. etherification with alkenes to form tertiary ethers as fuel additives) and polymerization to chemical intermediates ('Catalysis for Renewables' edited by G. Centi and R.A. van Santen, Wϊley- VCH, 1^st Edit. Weiriheim, 2007). The catalytic hydrogenolysis of glycerol has been studied, but the main reported products of the reaction between glycerol and hydrogen are propanediols and ethylene glycols. These reactions require a degree of carbon-oxygen bond cleavage and involve the addition of hydrogen under harsh conditions. SUMMARY OF THE INVENTION

The present inventors have found that methanol can be formed selectively by direct catalytic hydrogenolysis of glycerol and other poly-alcohols. Selectivities of from 60 to 100 % have been achieved.

Accordingly, the invention provides a process for producing methanol, which process comprises treating a compound which is: a sugar alcohol of formula (T)

in which n is 0 or an integer equal to or greater than 1 , or a sugar of formula (U)

in which m is an integer equal to or greater than 1 , with hydrogen in the presence of a hydrogenolysis catalyst comprising a transition metal, and thereby producing said methanol by hydrogenolysis of said compound.

This process involves one reaction step. As such it differs from conventional processes which involve two catalytic stages, namely reformation of glycerol to synthesis gas (CCVH₂) followed by the subsequent catalytic conversion of synthesis gas to methanol using existing syn gas-to-methanol technology.

BRIEF DESCRIPTIONS OF THE FIGURES

Fig. 1 is a schematic representation of possible reaction pathways to account for the formation of various products in the catalytic hydrogenolysis of glycerol.

Fig. 2 shows a TEM image of ruthenium nanoparticles synthesised by the polyol process and a histogram of the particle size distribution showing a mean particle diameter of 2.99 nm.

Fig. 3 shows an X-ray diffraction spectra of (a) 10% wt. ruthenium nanoparticles as synthesised loaded on graphite and (b) 5% wt. ruthenium on charcoal (Johnson Matthey). Fig. 4 shows an X-ray diffraction spectrum of palladium nanoparticles as synthesised showing the (111) and (200) diffraction indices. The mean particle diameter estimated from peak broadening using the Scherer's equation is 5.77 nm.

Fig. 5 shows a TEM image of palladium nanoparticles synthesised by the polyol process and a histogram of the particle size distribution showing a mean particle of 3.53 nm.

Fig. 6 shows a TEM image of nickel nanoparticles synthesised by the polyol process and a histogram of the particle size distribution showing a mean particle of 33.83 nm.

Fig. 7 shows FTIR spectra of adsorbed glycerol on the catalysts' surfaces showing; a) the C-H symmetric and asymmetric stretching modes and, b) C-O stretching mode of the primary and secondary alcohols. The shift in wave number is as a result of the substrate- catalyst interaction.

Fig. 8 shows deconvolution of Pd 3d XPS spectra for as-synthesised Pd nanoparticles on different types of support.

Fig. 9 shows the shift in binding energy of 3d5/2 and 3d3/2 spectra for the as- synthesised Pd nanoparticles as they interact with the different supports.

DETAILED DESCRIPTION OF THE INVENTION

In the process of the invention, the sugar alcohol of formula (I) or sugar of formula (H) is treated with hydrogen in the presence of a hydrogenolysis catalyst which comprises a transition metal. The term "hydrogenolysis catalyst", as used herein, means a catalyst which is capable of catalysing a hydrogenolysis reaction.

Typically, the transition metal of the hydrogenolysis catalyst is selected from a Group 6, 7, 8, 9 or 10 transition metal. Thus, the hydrogenolysis catalyst may comprise a Group 6 transition metal (for instance, chromium, molybdenum or tungsten), a Group 7 transition metal (for instance, manganese, technetium or rhenium), a Group 8 transition metal (for instance, iron, ruthenium or osmium), a Group 9 transition metal (for instance, cobalt, rhodium or iridium) or a Group 10 transition metal (for instance nickel, palladium or platinum). Typically, the hydrogenolysis catalyst comprises a transition metal selected from chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium and platinum. More typically, the transition metal is ruthenium, platinum, iron or molybdenum. In another embodiment, the transition metal of the hydrogenolysis catalyst is selected from molybdenum, tungsten, technetium, ruthenium, osmium, rhodium, iridium, nickel, platinum and palladium.

In yet another embodiment, the transition metal of the hydrogenolysis catalyst is selected from molybdenum, tungsten, technetium, ruthenium, osmium, rhodium, iridium, nickel and palladium. More typically, in this embodiment, the hydrogenolysis catalyst comprises a transition metal selected from ruthenium, osmium, rhodium, iridium, nickel and palladium. Even more typically, in this embodiment the transition metal is ruthenium, osmium, iridium, nickel or palladium.

In yet another embodiment, the transition metal of the hydrogenolysis catalyst is selected from osmium, iridium, nickel and palladium. More typically, in this embodiment, the transition metal is nickel or palladium. Even more typically, the transition metal is palladium.

In one embodiment, the oxidation state of the transition metal of the hydrogenolysis catalyst is zero. Thus, for instance, in one embodiment the transition metal of the hydrogenolysis catalyst is selected from nickel (0) and palladium (0). Even more typically, the transition metal is palladium (0).

Ih one embodiment, the hydrogenolysis catalyst comprises two or more transition metals, at least one of which is typically a Group 6, 7, 8, 9 or 10 transition metal. Thus, the catalyst may comprise two or more transition metals, at least one of which is selected from: chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium and platinum. More typically, the catalyst comprises two or more transition metals, at least one of which is ruthenium, platinum, iron or molybdenum. Typically, one of those transition metals is ruthenium.

In one embodiment, the transition metal of the hydrogenolysis catalyst is ruthenium.

In another embodiment, the hydrogenolysis catalyst comprises two or more transition metals, at least one of which is typically molybdenum, tungsten, technetium, ruthenium, osmium, rhodium, iridium, platinum, nickel and palladium. More typically, the catalyst comprises two or more transition metals, at least one of which is molybdenum, tungsten, technetium, ruthenium, osmium, rhodium, iridium, nickel and palladium. Even more typically, the catalyst comprises two or more transition metals, at least one of which is ruthenium, osmium, rhodium, iridium, nickel and palladium. Still more typically, the catalyst comprises two or more transition metals, at least one of which is ruthenium, osmium, indium, nickel or palladium. Typically, one of those transition metals is nickel or palladium. Even more typically, one of those transition metals is palladium.

Usually, the transition metal of the hydrogenolysis catalyst is palladium.

The transition metal may be present in the form of small particles, for instance microparticles or nanoparticles. Thus, the hydrogenolysis catalyst typically comprises small particles, for instance microparticles or nanoparticles, of said transition metal.

By "microparticle" herein is meant a microscopic particle whose size is measured in micrometres (μm). Typically, such particles have a diameter of from 1 μm to 1000 μm. More typically, the microparticle has an average diameter of from 1 μm to 500 μm, for instance from 1 μm to 250 μm. Most typically, the microparticle has an average diameter of from 1 μm to 100 μm.

Typically, the transition metal is present in the form of nanoparticles. Thus, the hydrogenolysis catalyst typically comprises nanoparticles of said transition metal. By "nanoparticles" herein is meant particles whose size is measured in nanometres (nm). Typically, such particles have a diameter of from 0.5 nm to lOOOnm or, for instance, from 1 nm to lOOOnm. Nanoparticles of transition metals can be prepared by wet impregnation, incipient wetness or other conventional catalyst preparative methods, or by the polyol process, as described below for ruthenium (see Example 1), palladium and nickel.

Typically, the transition metal is present in the form of nanoparticles having a mean particle diameter of from 1 to 100 nm. More typically, nanoparticles have a mean particle diameter of from 1 to 50 nm or, for instance, from 1 to 40 nm. m one embodiment, the hydrogenolysis catalyst comprises ruthenium nanoparticles. Typically, the ruthenium nanoparticles have a mean particle diameter of from 0.5 to 50 nm, more typically from 0.5 to 20 nm, even more typically from 0.5 to 10 nm or, for instance, from 1 to 5 nm. In one embodiment, the mean particle diameter of the ruthenium nanoparticles is about 3.5 nm.

In another embodiment, the hydrogenolysis catalyst comprises nanoparticles of ruthenium, osmium, iridium, nickel or palladium. More typically, the hydrogenolysis catalyst comprises nanoparticles of ruthenium, nickel or palladium.

In one embodiment, the hydrogenolysis catalyst comprises palladium nanoparticles. Typically, the palladium nanoparticles have a mean particle diameter of from 0.5 to 50 nm, more typically from 0.5 to 20 nm, even more typically from 0.5 to 10 nm or, for instance, from 1 to 5 run. In one embodiment, the mean particle diameter of the palladium nanoparticles is about 3 nm.

In one embodiment, the hydrogenolysis catalyst comprises nickel nanoparticles. Typically, the nickel nanoparticles have a mean particle diameter of from 0.5 to 100 nm, more typically from 15 to 50 nm, even more typically from 25 to 40 nm. In one embodiment, the mean particle diameter of the nickel nanoparticles is about 34 nm.

The hydrogenolysis catalyst usually further comprises a support material ("support"), on which the transition metal or transition metals are supported. In another embodiment, however, the hydrogenolysis catalyst does not comprise such a support. Thus, the transition metal may be unsupported or supported on a support material. Typically, when the catalyst comprises a support, the transition metal is present in an amount of from 0.5 to 30 weight %, more typically from 0.5 to 25 weight %, based on the total weight of the catalyst including the support. The transition metal may for instance be present in an amount of from 1 to 15 weight %, more typically from 2 to 15 weight % or, for instance from 2 to 13 weight %, based on the total weight of the catalyst including the support. The transition metal maybe present in an amount of from 1 to 10 weight %, or from 2 to 8 weight %, for instance about 5 weight %, based on the total weight of the catalyst including the support. In another embodiment, the transition is present in an amount of from 5 to 15 weight %, or, for instance, from 7 to 13 weight %, based on the total weight of the catalyst including the support.

Nanoparticles of the transition metal on a support can be prepared by wet impregnation, incipient wetness or other conventional catalyst preparative methods, or by the polyol process (as described below for ruthenium, nickel and palladium).

In one embodiment, the hydrogenolysis catalyst comprises a transition metal which is ruthenium, osmium, iridium, nickel or palladium, wherein the transition metal is unsupported or supported on a support material. In another embodiment, the hydrogenolysis catalyst comprises a transition metal which is ruthenium, nickel or palladium, wherein the transition metal is unsupported or supported on a support material.

It has been found that acidic supports, for instance acidified silica-alumina, may be detrimental to the selectivity of the hydrogenolysis reaction for methanol. Thus, although acidic supports can be used in the present invention, it is preferred that a pH-neutral support is employed, for instance, carbon, alumina or silica. Thus, the support is typically pH neutral. The support typically comprises a metal oxide, carbon, silica, a pillar clay or a zeolite. In one embodiment, however, the support comprises a metal oxide, carbon, silica or a pillar clay. Typically, the metal oxide, carbon, silica, pillar clay or zeolite is pH- neutral.

When the support comprises a metal oxide, the metal is typically, titanium, zinc, an alkaline earth metal, a rare earth metal (typically a lanthanide), or a p-block metal. Thus, the metal oxide support may for instance be titania, zinc oxide, gallium oxide, alumina, MgO, ceria or lanthium oxide.

More typically, the support comprises titania, zinc oxide, carbon, silica, gallium oxide, alumina, MgO, ceria, lanthium oxide, a pillar clay or a zeolite. Even more typically, the support comprises titania, zinc oxide, carbon, gallium oxide, alumina or a zeolite. Still more typically, the support comprises titania, zinc oxide, alumina, carbon or gallium oxide, for instance titania, zinc oxide, gallium oxide or alumina. m one embodiment, the support is carbon, silica, titania, alumina, MgO, ceria, lanthium oxide or a pillar clay.

Typically the support is other than a zeolite.

The support typically has a BET surface area of at least 5 m²g^"1, more typically from 5 m²g⁴ to 3000 m²g^"1. More typically, the BET surface area is for instance, at least 8 mV, or from 8 mV to 3000 mY¹.

In one embodiment, the support is carbon. The carbon support typically has a BET surface area of at least 5 more typically from 5 m²g^"! to 3000 m²g^"\ More typically, the BET surface area is for instance, at least 8 m²g^"1, or from 8 m²g^-1 to 3000 m²g^'1.

Usually, when the support is carbon, it is selected from graphite powder (for instance T-44 graphite, which is commercially available), carbon black, activated carbons and any other high surface area carbons, for instance, microporous carbon, glassy carbon, charcoal, coke, carbon nanoparticles or carbon nanotubes. All of these forms of carbon are widely available.

In one embodiment, the transition metal is ruthenium and the support material is carbon, for instance any of the forms of carbon listed above. More typically, the hydrogenolysis catalyst comprises ruthenium nanoparticles on a carbon support. The carbon support is usually graphite powder or charcoal. Typically, the graphite powder (which is usually T-44 graphite) has a surface area of at least 5 m²g^"1, for instance at least 7 m²g^"1 • The ruthenium is usually present in an amount of from 0.5 to 30 weight %, more typically from 0.5 to 25 weight %, based on the total weight of the catalyst including the support. In one embodiment, however, the ruthenium is present in an amount of from 1 to 15 weight %, more typically from 5 to 15 weight %, or, for instance, from 7 to 13 weight %, based on the total weight of the catalyst including the carbon support. Even more typically, the ruthenium is present in an amount of from 8 to 12 weight %, for instance about 10 weight %. Typically, in this embodiment, the support is graphite powder: selectivities for methanol approaching 100 % have been observed using these amounts of ruthenium metal on graphite.

Without wishing to be bound by theory, it is thought that the catalysts employed in the present invention can catayse the cleavage of the C-C bonds in the sugar or sugar alcohol with substantially no C-O bond cleavage. This avoids the production of CO₂, hydrocarbon gases such as methane, and other by-products such as isopropanol and acetaldehyde. The hydrogenolysis reaction can therefore be selective for methanol, m some cases a product of the cleavage of the C-C bonds in the sugar or sugar alcohol is ethylene glycol, which can be converted into methanol subsequently by hydrogenolysis, in the presence of the catalyst employed. The hydrogenolysis reaction can therefore be selective for ethylene glycol and then methanol. As detailed in the Examples, high selectivities towards ethylene glycol and methanol have been achieved.

The selectivity of the hydrogenolysis reaction to a specific product (p), expressed as a percentage, can be calculated as follows:

100 x [moles of carbon present in product p] / [moles of carbon in all products formed]

Thus, the selectivity of the hydrogenolysis reaction for methanol is the molar percentage of carbon present in the methanol product, based on the total moles of carbon in all of the products formed.

In one embodiment, the selectivity of the hydrogenolysis reaction for methanol is at least 5 % (i.e. from 5 to 100 %) or, for instance, at least 8 % (i.e. from 8 to 100 %). More typically, in this embodiment, the selectivity of the hydrogenolysis reaction for methanol is at least 9 %. For instance, the selectivity for methanol may be at least 10 %. Typically, the selectivity is that determined after a reaction time of 15 hours, a reaction temperature of 150 °C, and a reaction pressure of 20 bar hydrogen. Typically, the selectivity is determined using a mass ratio of the compound which is a sugar alcohol of formula (I) or a sugar of formula (D) to the catalyst of 6.26. Typically, the compound is a sugar alcohol of formula (T) which is glycerol.

Typically, the hydrogenolysis catalyst comprises palladium, ruthenium, nickel, indium or osmium. The hydrogenolysis catalyst may be unsupported or may further comprise a support material. The support material maybe as defined hereinbefore. Typically, in this embodiment, the support comprises titania, zinc oxide, carbon (for instance, graphite), gallium oxide, alumina or a zeolite. Typically, however, when the hydrogenolysis catalyst comprises palladium and a support, the support is other than a zeolite.

More typically, the hydrogenolysis catalyst comprises ruthenium supported on titania, ruthenium supported on zinc oxide, ruthenium supported on carbon, ruthenium supported on a zeolite, unsupported nickel (for instance Raney nickel), nickel supported on titania, nickel supported on zinc oxide, nickel supported on carbon, nickel supported on a zeolite, palladium supported on titania, palladium supported on zinc oxide, palladium supported on carbon, palladium supported on gallium oxide, palladium supported on alumina, indium supported on gallium oxide or osmium supported on gallium oxide. In one embodiment, where a support is present, the metal loading of the transition metal on the support is from 1 to 15 weight %, more typically about 5 weight %.

In another embodiment, the selectivity of the hydrogenolysis reaction for methanol is at least 17 % (i.e. from 17 to 100 %) or, for instance, at least 19 % (i.e. from 19 to 100 %). More typically, in this embodiment, the selectivity of the hydrogenolysis reaction for methanol is at least 20 %. For instance, the selectivity for methanol may be at least 22 %, or at least 25 %. Typically, the selectivity is that determined after a reaction time of 15 hours, a reaction temperature of 150 °C, and a reaction pressure of 20 bar hydrogen. Typically, the selectivity is determined using a mass ratio of the compound which is a sugar alcohol of formula (T) or a sugar of formula (D) to the catalyst of 6.26. Typically, the compound is a sugar alcohol of formula (T) which is glycerol.

Typically, the hydrogenolysis catalyst comprises palladium, nickel, iridium or osmium. The hydrogenolysis catalyst may be unsupported or may further comprise a support material. The support material may be as defined herein. Typically, in this embodiment, the support comprises titania, zinc oxide, carbon (for instance, graphite), gallium oxide, alumina or a zeolite. Typically, when the hydrogenolysis catalyst comprises palladium and a support, the support is other than graphite or a zeolite. More typically, the hydrogenolysis catalyst comprises unsupported nickel (for instance Raney nickel), nickel supported on titania, nickel supported on zinc oxide, nickel supported on carbon, nickel supported on a zeolite, palladium supported on titania, palladium supported on zinc oxide, palladium supported on gallium oxide, palladium supported on alumina, iridium supported on gallium oxide or osmium supported on gallium oxide. In one embodiment, where a support is present, the metal loading of the transition metal on the support is from 1 to 15 weight %, more typically about 5 weight %.

In another embodiment, the selectivity of the hydrogenolysis reaction for methanol is at least 29 % (i.e. from 29 to 100 %) or, for instance, at least 30 % (i.e. from 30 to 100 %). More typically, in this embodiment, the selectivity of the hydrogenolysis reaction for methanol is at least 33 %. For instance, the selectivity for methanol may be at least 35 %. Typically, the selectivity is that determined after a reaction time of 15 hours, a reaction temperature of 150 ⁰C, and a reaction pressure of 20 bar hydrogen. Typically, the selectivity is determined using a mass ratio of the compound which is a sugar alcohol of formula (I) or a sugar of formula (TT) to the catalyst of 6.26. Typically, the reactant compound is glycerol.

Typically, the hydrogenolysis catalyst comprises palladium or nickel. More typically, the hydrogenolysis catalyst comprises palladium(O) or nickel(O). The hydrogenolysis catalyst may be unsupported or may further comprise a support material. The support material may be as defined herein. Typically, in this embodiment, the support comprises titania, zinc oxide, carbon (for instance, graphite), gallium oxide, alumina or a zeolite, more typically titania, zinc oxide, gallium oxide or alumina. Typically, when the hydrogenolysis catalyst comprises palladium and a support, the support is other than graphite or a zeolite.

More typically, the hydrogenolysis catalyst comprises nickel supported on zinc oxide, nickel supported on a zeolite, palladium supported on titania, palladium supported on zinc oxide, palladium supported on gallium oxide or palladium supported on alumina. The palladium typically comprises palladium(O). The nickel typically comprises nickel(O). In one embodiment, where a support is present, the metal loading of the transition metal on the support is from 1 to 15 weight %, more typically about 5 weight %.

In another embodiment, the selectivity of the hydrogenolysis reaction for methanol is at least 50 % (i.e. from 50 to 100 %) or, for instance, at least 52 % (i.e. from 52 to 100 %). More typically, in this embodiment, the selectivity of the hydrogenolysis reaction for methanol is at least 55 %. For instance, the selectivity for methanol may be at least 58 %. Typically, the selectivity is that determined after a reaction time of 15 hours, a reaction temperature of 150 °C, and a reaction pressure of 20 bar hydrogen. Typically, the selectivity is determined using a mass ratio of the compound which is a sugar alcohol of formula (I) or a sugar of formula (H) to the catalyst of 6.26. Typically, the reactant compound is glycerol.

Typically, the hydrogenolysis catalyst comprises palladium. The hydrogenolysis catalyst may be unsupported or may further comprise a support material. The support material may be as defined herein. Typically, the hydrogenolysis catalyst comprises palladium supported on titania or palladium supported on zinc oxide. The palladium is typically palladium (0). In one embodiment, where a support is present, the metal loading of the transition metal on the support is from 1 to 15 weight %, more typically about 5 weight %.

In one embodiment, the selectivity of the hydrogenolysis reaction for methanol plus the selectivity of the hydrogenolysis reaction for ethylene glycol (a partial hydrogenolysis product) is at least 20 %. More typically, the selectivity of the hydrogenolysis reaction for methanol plus the selectivity of the hydrogenolysis reaction for ethylene glycol is at least 30 % or, for instance, at least 40 %, at least 50 % or at least 60 %. In this embodiment, the compound which is initially subjected to hydrogenolysis (the sugar or sugar alcohol) is other than ethylene glycol, and is typically glycerol. Typically, the selectivities are those determined after a reaction time of 15 hours, a reaction temperature of 150 ⁰C, and a reaction pressure of 20 bar hydrogen. Typically, the selectivities are determined using a mass ratio of the compound which is a sugar alcohol of formula (I) or a sugar of formula (H) to the catalyst of 6.26.

In one embodiment, the selectivity of the hydrogenolysis reaction for methanol is at least 60 % (i.e. from 60 to 100 %) or, for instance, at least 70 %. More typically, said selectivity is at least 80 %, for instance at least 85 %. In one embodiment, said selectivity for methanol is at least 90 %, for instance at least 95 % or at least 98 %. Ih one embodiment, methanol is substantially the only product of said hydrogenolysis, thus the selectivity for methanol is (approximately) 100 %.

The hydrogenolysis of the sugar alcohol of formula (I) to methanol in accordance with the present invention may be represented as shown in the following reaction scheme: Similarly, the hydrogenolysis of the sugars of formula (H) may be represented as follows:

As the skilled person will appreciate, these reaction schemes apply in the case where the hydrogenolysis reaction is 100 % selective for methanol, where methanol is the exclusive product of hydrogenolysis. At lower selectivities, it is understood that reaction products other than methanol will also be formed.

In the process of the invention, the step of treating the sugar alcohol or sugar with hydrogen is carried out in the presence or absence of a solvent, typically in the presence of a solvent. The solvent, when present, should be an inert solvent. The term "inert solvent", as used herein, means a solvent which does not itself undergo hydrogenolysis, hydrogenation or any other chemical conversion under the reaction conditions of the process of the present invention. Thus, the solvent cannot be an organic compound which would undergo C-C bond cleavage and hydrogenolysis during the present process. Accordingly, the solvent, when present, is typically an inorganic solvent. Usually, the solvent is water.

The hydrogenolysis reaction is typically carried out at relatively mild temperatures and pressures.

In particular, the step of treating the sugar alcohol or sugar with hydrogen is typically performed at a temperature of 200 ⁰C (473 K) or less than 200 ⁰C (473 K), and more typically at a temperature of 180⁰C or less. In one embodiment, the step of treating the sugar alcohol or sugar with hydrogen is carried out at a temperature of from 50 ⁰C to 200 ⁰C, or for instance from 80 ⁰C to 200 ⁰C, or from 100 ⁰C to 200 ⁰C.

In another embodiment, the step of treating the sugar alcohol or sugar with hydrogen is performed at a temperature of 150 ⁰C (423 K) or less than 150⁰C (423 K), and more typically at a temperature of 130 ⁰C or less. In one embodiment, the step of treating the sugar alcohol or sugar with hydrogen is carried out at a temperature of from 50 ⁰C to 150 ⁰C, or for instance from 50 ⁰C to less than 150 ⁰C. In one embodiment, a ruthenium/graphite catalyst is used and the step of treating the sugar alcohol or sugar with hydrogen is carried out at a temperature of from 50 ⁰C to 120⁰C. More typically, this step is carried out at a temperature of from 75 ⁰C to 120⁰C, and even more typically at a temperature of from 85 ⁰C to 115 ⁰C, or from 90 ⁰C to 110 ⁰C. In this embodiment, the reaction temperature is normally about 100 ⁰C.

The hydrogen pressure was found typically to affect the selectivity of the hydrogenolysis reaction for methanol, and was found to affect the conversion of the sugar or sugar alcohol to methanol. Accordingly, the step of treating the sugar or sugar alcohol with hydrogen is usually performed at a hydrogen pressure of at least 1 bar, typically at least 12 bar, more typically at a hydrogen pressure of at least 15 bar, and even more typically at a hydrogen pressure of at least 18 bar. Typically, the hydrogen pressure employed is from 1 bar to 250 bar, more typically from 12 bar to 250 bar, and even more typically from 15 bar to 250 bar, for instance from 18 bar to 250 bar. In one embodiment, the hydrogen pressure employed is about 20 bar.

The process of the invention maybe carried out as continuous process or a batch process. In one embodiment, the process is a continuous process in which hydrogen is cofed in a recycled catalyst bed, either in the presence or absence of a solvent.

In the case of a batch process, the step of treating the sugar or sugar alcohol with hydrogen is usually performed for longer than 5 hours, and more typically for at least 10 hours, in order to ensure that a relatively high percent conversion of the reactant is achieved. Even more typically, the reaction time is at least 15 hours, for instance for about 15 hours or for about 24 hours.

In one embodiment, the sugar alcohol of formula (I), from which methanol may be produced in accordance with the process of the invention, has from 2 to 10 carbon atoms. Thus, typically n is 0 or an integer from 1 to 8. Examples of sugar alcohols of formula (I) include, but are not limited to, the following compounds:

sorbitol mannitol

Ih one embodiment, n is O or an integer of 1 to 6. In this embodiment, the sugar alcohol is selected from ethylene glycol (C2), glycerol (C3), butane-l,2,3,4-tetrol (C4), pentane-1,2,3 ,4,5-pentol (C5), hexane-l,2,3,4,5,6-hexol (C6), heptane-l,2,3,4,5,6,7-heptol (C7), octane-l,2,3,4,5,6,7,8-octol (C8).

More typically, n is 0, 1, 2, 3 or 4. In this embodiment, the sugar alcohol is selected from ethylene glycol (C2), glycerol (C3), butane- 1,2,3,4-tetrol (C4), ρentane-1,2,3,4,5- pentol (C5) and hexane-l,2,3,4,5₅6-hexol (C6).

Even more typically, n is O, 1 or 2 and the sugar alcohol is selected from ethylene glycol (C2), glycerol (C3) and butane-l,2,3,4-tetrol (C4).

Usually, however, n is 1 and the sugar alcohol is glycerol.

In one embodiment, the sugar of formula (E-), from which methanol may be produced in accordance with the process of the invention, has from 3 to 10 carbon atoms. Thus, typically m is an integer from 1 to 8. Examples of sugars of formula (IT) include the following compounds: D-<31ys6nal4e-iyylfi

D-Erytlmose D-Tlreose

D-Kϋosβ D-Araliaose

°V^H <VH

H- -OH HO- -H H- -OH H- -OH H- -OH H- -OH H- -OH H- -OH

CH₂OH CH₂OH D-ALbs« D-AUrose

Typically, m in the compound of formula (JT) is an integer of 1 to 6, more typically an integer of 1 to 4, and even more typically an integer of 1 or 2.

Typically, the compound which is treated with hydrogen in accordance with the process of the present invention is a sugar alcohol of formula (I) as defined above. More typically, the compound is glycerol.

Typically, the methanol produced by the process of the invention is recovered from the reaction mixture. Typically, the reaction mixture comprises the methanol product, the catalyst and, when the reaction is carried out in the presence of a solvent, the solvent. The reaction mixture usually also comprises unreacted starting material, i.e. an unreacted sugar alcohol of formula (I) or an unreacted sugar of formula (H). The reaction mixture may also contain by-products (i.e. reaction products other than methanol) and/or impurities.

Thus, the step of recovering the methanol from the reaction mixture typically involves separation of the methanol from the catalyst, from any unreacted starting material and, when solvent is present, from the solvent. Typically, when a by-product or impurity is present in the reaction mixture, the methanol is also separated from that by-product or impurity.

Accordingly, in one embodiment, the process of the invention further comprises the step of recovering said methanol.

The methanol produced by the process of the invention may be used as a fuel, typically an automotive fuel, or as a building block, reactant or feedstock in the production of other chemicals. The methanol may for instance be used to esterify unwanted free fatty acids present in the production of biodiesel. Thus, the process of the invention can be used to convert the glycerol by-product of a biodiesel production process into methanol, and that methanol can in turn be used to esterify free fatty acids present in the biodiesel production process in order to produce further biodiesel.

Accordingly, in one embodiment, the process of the invention further comprises esterifying a fatty acid with the methanol thus produced. Typically, the fatty acid is from a biodiesel production process and the esterification of the fatty acid with the methanol produces further biodiesel. Typically, in this embodiment, the compound which is converted to methanol in the first place is glycerol, which glycerol is a by-product of the same biodiesel production process.

The present invention is further illustrated in the Examples which follow:

EXAMPLES

Example 1 - Catalytic hydrogenolysis of glycerol to form methanol

Preparation of the catalyst

Ruthenium nanoparticles were synthesised via the polyol process: 0.52 mmol of Tris(acetylacetonato) ruthenium (IE) (Alfa Aesar Ru-70, 24.59%) was dissolved in 6 mL of octyl ether (99% Aldrich), 0.26 mmol of oleic acid (Aldrich, 90%) and 0.26 mmol of oleylamine (70%, Aldrich) was added to the mixture as stabilisers followed by 2 mmol of 1,2-hexadecanediol (Aldrich, 90%) as a reducing agent. The mixture was stirred under nitrogen atmosphere for 30 minutes in a refluxing set-up without heating. The mixture was then heated in to 280⁰C for 40 minutes under nitrogen to form a black sol. The reaction was then cooled to room temperature before turning the nitrogen off. The sol was repeatedly washed with equal portions of ethanol and hexane and centrifuged to precipitate the Ru metal nanoparticles in order to remove the excess stabilisers on the particles. The Ru nanoparticles were dried, weighed and re-dispersed in hexane using an ultrasonic bath at 40⁰C for an hour before wet impregnating on graphite powder T-44 (Johnson Matthey) to form a 10% wt Ru on the graphite powder.

Catalyst testing in a liquid phase batch reactor

The testing experiment was carried out in the liquid phase in a 25 mL stainless steel Parr autoclave with a glass vial fitted tightly to its inner walls. The autoclave, equipped with a magnetic stirrer, pressure gauge and a thermocouple is heated by a jacket regulated by a Parr 4842 microprocessor based temperature controller.

25 mg of catalyst was placed in the autoclave and 5 mL of 5% vol. solution of glycerol (Aldrich, spectrophometric grade >99.5%) in deionised water was added. The autoclave was then flushed with pure hydrogen for a minute to remove any traces of oxygen. The autoclave was then charged with 20.0 bar of hydrogen and heated to a temperature of 100 ⁰C for 24 h. The autoclave was then cooled to 10 ⁰C and the gas phase was sampled and analysed by a gas chromatograph equipped with a BP 10 capillary column and TCD detector. The liquid phase was analyzed by both a Perkin Elmer 200 series HPLC with reversed phase Cl 8 column using 80:20 acetonitrile: water solvent system at a flow rate of 0.5 mL/min with diode array detector at wavelengths 205 and 220 nm for glycerol analysis and also with a GC-FID using a HayeSep R 80-100 mesh packed column for methanol analysis. The results are summarised in Table 1.

Table 1

Reaction conditions are as above: 25 mg of catalyst, 100 ⁰C₅ 20 bar of hydrogen and 24 h reaction time, 5 mL of 5% vol. aqueous solution of glycerol.

As can be seen from Table 1, glycerol can be cracked hydrolytically to methanol as an exclusive product, using ruthenium nanoparticles impregnated on graphite T-44 as the catalyst, under the relatively mild reaction conditions of 100⁰C and 20 bar of hydrogen over a reaction period of 24 hours.

Example 2 - Study of the effect of supports and base promoter

The reaction of Example 1 was repeated using various different materials in place of the 10% Ru / graphite catalyst, to study the effect of supports and base promoter. The results are shown in Table 2.

Table 2

Reaction conditions: 25 mg of catalyst, 5 vol. % glycerol solution, 20 bar hydrogen, 100 ⁰C, 2 hours.

Example 3 - Study of different metals as the catalyst, without support

The reaction of Example 1 was repeated using various different supported and unsupported metals as the catalyst, in place of the 10% Ru / graphite catalyst. The results are shown in Tables 3.1 and 3.2. Reaction conditions: 25 mg of catalyst, 5 vol. % glycerol solution, 20 bar hydrogen, 100 ⁰C, 24 hours (surface areas of metals are not yet obtained). Table 3,1

1,2-pro: 1,2 propane-diol; 1,3-pro: 1,3 propane-diol; EG: ethylene glycol; LA: lactic acid; %Conversion is defined as % mol. Glycerol converted to all products; % Selectivity is defined as % mol of carbon in specific product/total mol. of carbon in all products

Table 3.2

c . - , , ,. ,. ._^ , , -_l ■ -is moles of glycerol converted

Specific catalytic activity ψiolg mm ) = ±-²- — time x mass of metal

_T. j _/o-i_\ moles of glycerol converted per unit time

Turnover number (S ) = ^:L-^≤ ~ moles of metal Example 4 - Study of effect of reaction time, using the 10% Ru / graphite catalyst

The reaction of Example 1 was repeated for various different reaction times. The results are shown in Table 4.

Table 4

Reaction conditions: 25 mg Ru/Graphite catalyst, 5 vol. % glycerol solution, 20 bar of hydrogen, 100 ⁰C, 24 h

Example 5 - Study of effect of reaction temperature, using the 10% Ru / graphite catalyst

The reaction of Example 1 was repeated at various different reaction temperatures. The results are shown in Table 5. For the reaction at 423 K, product selectivities were 23% towards 1,2-propanediol, 52.8% ethylene glycol and 6% hydrocarbon fragments (methane, ethane, etc).

Table 5

Reaction conditions: 25 mg of Ru/Graphite catalyst, 5 vol. % glycerol solution, 20 bar of hydrogen, 2 h. Example 6 - Study of effect of hydrogen pressure, using the 10% Ru / graphite catalyst

The reaction of Example 1 was repeated at various different reaction pressures. The results are shown in Table 6. Selectivity to methanol as the exclusive product was maintained over this pressure range.

Table 6

Reaction conditions: 25 mg of Ru/Graphite catalyst, 5 vol. % glycerol solution, 100 0C, 24 h

NB. The results for the % selectivity of the hydrogenolysis reaction towards methanol observed in Examples 1 to 6 could not be replicated in subsequent experiments. This might be explained by the fact that subsequent experiments (see Example 7 below) employed an improved product analysis technique enabling complete gas / liquid analysis. The complete gas / liquid analyses indicated that gaseous methane and, in some cases, gaseous ethane are typically produced together with methanol. It is therefore possible that the methanol selectivity values in Examples 1 to 6 were overestimated due to incomplete detection of such gaseous by-products during the experiments described in those Examples.

Example 7 - Catalytic hydrogenolysis of glycerol to form methanol using various catalysts

Preparation of nickel, ruthenium and palladium catalysts

Supported nickel, ruthenium, and palladium catalysts were synthesised using a modified version of the polyol process for forming metal nanoparticles, as described above in Example 1 for ruthenium. Once the nickel, ruthenium, or palladium nanoparticles were synthesised using the polyol process, the as-synthesised metal nanoparticles were redispersed in ethanol and placed on different supports using the incipient wetness impregnation method to form a 5 wt. % metal loading on the support. In this way, the following catalysts were synthesized: 5 wt % Ru on TiO₂, 5 wt % Ru on ZnO, 5 wt % Ru on graphite, 5 wt % Ru on zeolite, 5 wt % Ni on TiO₂, 5 wt % Ni on ZnO, 5 wt % Ni on graphite, 5 wt % Ni on zeolite, 5 wt % Pd on TiO₂, 5 wt % Pd on ZnO, 5 wt % Pd on graphite, 5 wt % Pd on Ga₂O₃, and 5 wt % Pd on zeolite. 5 wt % Pd on alumina (Al₂O₃) is a commercially available catalyst and was purchased from Aldrich.

Preparation of 5 wt. % Os/ Ga₂U₃ catalyst

For the preparation of 5 wt. % loading of Os on Ga₂O₃, 58 mg of ammonium hexachloroosmate(IV), (NBU)₂OsCIg, (Aldrich, used without any further purification) was dissolved in 10 mL of deionised water. 442.3 mg OfGa₂O₃ was then added to the solution with vigorous stirring for 1 h to form a slurry mixture. The slurry was then dried at 120 ⁰C, ground in an agate mortar and reduced directly under a stream of hydrogen with a flow rate of 60 mL/min without previous calcination. The reduction temperature was 400 ⁰C for 1 h at a heating rate of 2 °C/min. (Eliche-Quesada, D., Merida-Robles, J. M., Rodriguez- Castellόn, E. and Jimenez-Lopez, A. (2005). Applied Catalysis A: General, 279, 209-221.)

Preparation of 5 wt. % Iridium/ Ga₂θ 3 catalyst

0.4764 g of iridium(πr)chloride (Alfa Aesar 52.42%) is dissolved in 25 mL of deionised water. 4.750 g of Ga₂O₃ (Aldrich) and stirred vigorously for 1 h at 50 ⁰C. The slurry obtained is then dried at 100 ⁰C. The dry powder after grinding in an agate mortar is calcined in air at 600 ⁰C for 1 h. The catalyst is then reduced under a flow of hydrogen (50 mL/min) at 500 ⁰C for 2 h.

Catalyst characterisation

Ru, Pd and Ni nanoparticles synthesised through the modified polyol process exhibited a narrow size distribution though different sizes. The TEM micrographs and the particle size distribution charts in Figures 2 to 4 depict varying particle diameters for the different metal particles. The Pd and Ru particles are within a size range of 1-7 nm with a mean particle diameter of ca. 3.0 and 3.5 nm respectively whilst the Ni particles were much larger in size (mean diameter ca. 33.8 nm). This could be as a result of the different nucleation and growth characteristics of the crystals formed by the different elements.

Catalyst testing

Hydrogenolysis reactions were carried out in a liquid phase batch high pressure reactor system. In a typical experiment, a 100 mL batch autoclave was loaded with 20 niL of glycerol solution with concentration 0.68 mol/L and 200 mg of catalyst (glycerol/catalyst mass ratio of 6.26). The reactor was purged with hydrogen, charged to 20 bar hydrogen pressure and heated to 150 ⁰C for 15 h with constant stirring.

Table 7 gives a summary of the results on activity and product selectivity for the different catalysts tested for the hydrogenolysis of glycerol. Reaction conditions are 150 ⁰C, 20 bar H₂ for 15 h using glycerol to catalyst mass ratio 6.26.

Table 7

Metal Suppor Conv. CH₃O CH₄ C₂H EtOH E.G 1,2- 1,3- IPA 1- L.A t (%) H SeL 6 SeI. SeL PD PD SeL POL SeL

SeI. (%) SeI. (%) (%) SeL SeL (%) SeL (%)

(%) (%) (%) (%) (%)

Rτi TiO₂ 31.33 9.47 74.51 0.10 11.97 3.59 - 0.10 0.25 -

ZnO 30.06 9.20 28.88 3.78 1.94 33.62 15.61 - 3.88 3.69 -

Graphite 27.02 9.96 65.67 0.31 0.52 12.50 10.12 - 0.11 0.84 -

Zeolite 28.15 6.18 79.76 0.29 - 7.38 6.11 0.29 - - -

Ni TiO₂ 30.00 27.49 51.50 10.31 1.29 8.04 0.18 0.98 0.21

ZnO 18.04 37.06 36.96 - 3.13 3.08 12.92 _ 2.62 2.80 1.44

Graphite 24.20 23.35 19.70 - - 0.11 52.28 0.58 0.54 0.48 2.96

Zeolite 23.93 30.38 42.80 - 23.91 1.40 0.33 0.19 0.57 0.43 -

Pd TiO₂ 0.30 52.37 1.72 14.53 9.56 21.82

ZnO 0,58 59.71 1.82 - 4.96 14.46 - 10.54 5.94 2.58

Graphite 1.78 6.32 3.46 0.35 19.00 1.94 36.46 - 32.18 0.32 -

Ga₂O₃ 1.54 33.43 1.28 - 27.77 37.52 - - - -

Zeolite 1.44 0.77 0.02 - 1.62 3.16 2.88 - 82.94 8.61 -

Al₂O₃ 5.56 36.07 1.32 - - - 39.36 - 22.86 2.99 0.39

Ir Ga₂O₃ 1.08 26.89 0.69 1.51 - 54.73 6.17 - 2.71 8.15 -

Os Ga₂O₃ 0.49 23.85 6.79 5.72 0.78 53.88 5.83 - - 6.23 -

5% Pd Al₂Oa is a commercial catalyst purchased ftom Aldrich, 5% Ir on and Os Ga₂O₃ was prepared by wet impregnation method.

Table 8 gives a summary of the activity of a 5% Ru / Charcoal catalyst towards ethylene glycol hydrogenolysis, and its selectivity towards various products.

Table 8

4.93% Ru / Charcoal; (0.68M ethylene glycol in water); catalyst: 200mg, 20 bar

H₂, 2 hours; 195⁰C Temp / ⁰C Conv. / % Selectivity / %

CO CH. CH₃CH₃ Methanol Ethanol

155 4.04 0.11 78.33 5.07 13.88 2.61

195 48.89 0 83.78 5.13 9.73 1.37

It is evident from Table 7 that the ruthenium and nickel based catalysts generally give high conversion as well as high selectivity to methane reflecting the high activity towards hydrogenolysis (breaking all C-C and C-O bonds using hydrogen). The trend of the average yield in methane formation followed the order Ru (17.13%) > Ni (8.28%) > Pd (0.021%). Similarly, Table 8 shows that supported Ru displays high conversions but relatively low selectivity towards methanol using ethylene glycol as the substrate under conditions comparable to those for glycerol. The fact that Ru catalysts produce methane from either glycerol or ethylene glycol has been attributed to excessive C-C and C-O bond cleavage on the metal surface. The relatively low selectivity to methanol observed for most of the supported Ru catalysts suggests a possible further reduction of any intermediary products like methoxyl (CH₃O), formaldehyde (HCHO) and methanol (CH₃OH) to methane under the reaction conditions. Nickel and palladium based catalysts, on the other hand, generally gave a lower activity in glycerol hydrogenolysis (Table 7) but exhibited a lower average methane formation hence a higher selectivity towards the hydrogenolysis products methanol and ethylene glycol. From Table 7 it can be seen that supported Ni catalysts gave more than 30% selectivity to methanol while some Pd catalysts gave over 50% selectivity to methanol under the test conditions. In the case of ethylene glycol hydrogenolysis, the high surface area Raney Ni (no support) gave relatively high selectivity to methanol: see Table 9, which gives a summary of the activity of the Raney Ni catalyst towards hydrogenolysis of ethylene glycol under various temperature conditions and at 20 bar H₂ for 2 h. Table 9

Temperature Study - Raney Ni; Ethylene Glycol (0.68M, the same concentration as glycerol); catalyst: 200mg, 20 bar H2, 2 hours; 195⁰C Temp / ⁰C Conv. / % Selectivity / %

CO CH4 CHsCH₃ Methanol Ethanol

155 8.42 0.57 73.75 0.71 23.01 1.79

175 13.90 0.18 75.49 0.46 22.73 2.01

195 20.98 0.11 78.89 0.59 18.64 1.76

Thus, in terms of hydrogenolysis activity the unmodified metal catalysts follow the order of Ru > Ni > Pd. However, Ru tends to break C-C and C-O with lesser discrimination than Ni and Pd, which appear to be the most selective catalysts. This study gives guidance to obtain high selectivity towards methanol from polyols (sugars and sugar alcohols) such as glycerol by either poisoning the vagarious activity of Ru (through addition of catalyst poisons) or by enhancing the conversion of the selective Pd or Ni catalysts.

FTIR studies of the bond characteristics of chemisorbed glycerol on the catalyst surface

The shift in the vibrational frequency of a molecule as a result of it being adsorbed on the surface of a catalyst gives useful information about bond strengths and therefore, an important lead as to which bond the chemisorption is likely to weaken. Since the C-C bond vibration in infrared spectroscopy has no diagnostic value between 4000 cm^"1 and 650 cm^"1 infrared region, the C-O stretching of the alcohol (primary and secondary) functional group, and the C-H stretching (symmetric and asymmetric) in the glycerol molecule were examined at a resolution of 4 cm^"1. The results as shown in Figure 7 demonstrate a change in bond energy (chemical shift) as a direct consequence of the interaction of the glycerol molecule with the different catalysts surfaces (see Table 10, which gives the vibrational frequency of glycerol adsorbed on different catalysts and the induced change in bond vibration energy as a result of catalyst interaction). Table 10

A careful observation of the wavenumber shifts in the C-O stretching and the C-H stretching vibrational frequency of glycerol (Table 10), shows that the Ru/Graphite induces the biggest shift to lower wavenumber (energy). This implies that of the catalyst systems studied the C-O and C-H bonds of glycerol adsorbed onto Ru/Graphite catalyst are least stable. This evidence is confirmed by the relatively high conversion of the Ru catalyst. The high yield in methane formation (a product of excessive C-O and C-C bond cleavage) further confirms the evidence from FTIR studies. The shift to lower wavenumbers induced by the Ru catalyst can be as a result of the stronger metal-carbon bond strength of Ru (48.5 kcal/mol) compared to Pd (41.6 kcal/mol) for sp³ hybridised carbon atoms, as determined by quantum chemical calculations. ¹⁷ The u(C-O) of both the primary and secondary alcohol of glycerol on Os/ Al₂O₃ (Commercial Johnson Matthey Catalyst) shifts most to higher frequencies (energy). This suggests that the C-O bonds should be most stable in the hydrogenolysis of glycerol involving the use of OsZAl₂O₃ catalyst and hence a lower selectivity towards C-O cleaved products. It is noted from Table 7 that the selectivity towards hydrogenolysis products (methanol and ethylene glycol) are indeed much higher in the case of Pd and Os catalysts. This clearly suggests the ability of these catalysts of cleaving C-C instead of C-O in the hydrogenolysis of glycerol.

XPS studies on the Pd support interaction

Catalyst supports, apart from providing the high surface area on which the metals are dispersed, are also known to exert an electronic effect on the metal thereby affecting its catalytic property. The electronic effect of the different supports on Pd nanoparticles is investigated to determine how it influences selective C-C bond breakage. The deconvoluted spectra in Figure 8 show that the Pd species in the catalysts are present in the zero-valent form (Pd⁰). This shows that surface oxidation of the Pd metal to Pd²⁺ is minimal and also the precursor salt used in the synthesis of the catalyst were successfully reduced during the synthesis step. The results as shown in Figure 9 and tabulated in Table 11 demonstrate clearly the electronic effect of support interaction with the Pd nanoparticle, as evidenced by the shift in binding energy of the Pd 3d5/2 and 3d3/2 XPS spectra as the support differs. Table 11 gives XPS binding energy of Pd 3d as electronically influenced by support and its effect on catalyst performance.

Table 11

Catalyst Binding Energy (eV) Catalytic activity

3d 5/2 3d 3/2 Conv. (%; ) CHOH₃ SeL Other and E.G pdts (%)

SeI. (%)

Pd TiO₂ 332.11 337.41 0.30 66.90 33.10

Pd Ga₂O₃ 332.31 337.41 1.54 61.20 38.80

PdAl₂O₃ 334.11 338.51 5.56 36.07 63.93

(Aldrich)

Pd Zeolite 334.21 339.21 1.44 3.93 96.07

Pd Graphite 335.11 340.51 1.78 8.26 91.74

The general trend shown in Figure 9 and Table 11 is that the n-type semi-conducting oxides (TiO₂, ZnO and Ga₂O₃) give the greatest shifts towards lower binding energies. This can be attributed to the increase in the concentration of electrons on the Pd metal displacing the Fermi level from the valence zone to the conduction zone. On the other hand, the Pd on graphite gives the greatest shift towards higher binding energy because the graphite support channels electrons from the surface of the Pd metal. The binding energy of electrons the Pd 3d orbital for Pd on insulating oxide supports (Al₂O₃ and ZSM-5 zeolite, an aluminosilicate) lie in-between the semi conducting oxides and graphite. The electronic effect of the support on Pd clearly affects their catalytic performance. The relation between binding energy and catalyst performance as shown in Table 11 suggests that the more electron rich the Pd metal surface the less active the catalyst for glycerol hydrogenolysis. In relation to the products formed the Pd on n-type semi-conducting oxide support catalysts lead to a higher selectivity towards C-C bond cleavage as compared with the insulating oxides and graphite support.

Claims

1. A process for producing methanol, which process comprises treating a compound which is: a sugar alcohol of formula (T)

in which n is 0 or an integer equal to or greater than 1 , or a sugar of formula (IT)

in which m is an integer equal to or greater than 1, with hydrogen in the presence of a hydrogenolysis catalyst comprising a transition metal, and thereby producing said methanol by hydrogenolysis of said compound.

2. A process according to claim 1 which further comprises recovering said methanol.

3. A process according to claim 1 or claim 2 wherein the selectivity of said hydrogenolysis for methanol is from 20 to 100 %.

4. A process according to any one of claims 1 to 3 wherein n is 0 or an integer from 1 to 8, and m is an integer from 1 to 8.

5. A process according to any one of the preceding claims wherein said compound which is treated with hydrogen is glycerol.

6. A process according to any one of the preceding claims wherein the transition metal is a Group 6, 7, 8, 9 or 10 transition metal.

7. A process according to any one of the preceding claims wherein the hydrogenolysis catalyst comprises ruthenium, platinum, iron or molybdenum.

8. A process according to any one of claims 1 to 6 wherein the hydrogenolysis catalyst comprises molybdenum, tungsten, technetium, ruthenium, osmium, rhodium, iridium, nickel or palladium.

9. A process according to claim 8 wherein the hydrogenolysis catalyst comprises ruthenium, osmium, iridium, nickel or palladium.

10. A process according to claim 8 or claim 9 wherein the hydrogenolysis catalyst comprises nickel or palladium.

11. A process according to any one of the peceding claims wherein the oxidation state of the transition metal of the hydrogenolysis catalyst is zero.

12. A process according to any one of the preceding claims wherein the hydrogenolysis catalyst comprises nanoparticles of said transition metal.

13. A process according to any one of the preceding claims wherein the hydrogenolysis catalyst comprises said transition metal and a support material, wherein the transition metal is supported on said support material.

14. A process according to claim 13 wherein the transition metal is present in an amount of from 0.5 to 15 weight %, based on the total weight of the catalyst including the support.

15. A process according to claim 13 or 14 wherein the support material comprises a metal oxide, carbon, silica, a pillar clay or a zeolite.

16. A process according to any one of claims 13 to 15 wherein the support material comprises titania, zinc oxide, carbon, silica, gallium oxide, alumina, MgO, ceria, lanthium oxide, a pillar clay or a zeolite.

17. A process according to any one of claims 13 to 16 wherein the support material has a BET surface area that is at least 5 m²g^"1.

18. A process according to any one of claims 13 to 17 wherein the support material is pH neutral.

19. A process according to any one of claims 13 to 18 wherein said support material comprises carbon, which carbon comprises graphite powder, carbon black, activated carbon, microporous carbon, glassy carbon, charcoal, coke, carbon nanoparticles or carbon nanotubes.

20. A process according to any one of claims 13 to 19 wherein the support material comprises titania, zinc oxide, carbon, gallium oxide or alumina.

21. A process according to any one of claims 13 to 20 wherein the transition metal is ruthenium, osmium, iridium, nickel or palladium.

22. A process according to any one of claims 13 to 21 wherein the transition metal is osmium, indium, nickel or palladium..

23. A process according to any one of claims 13 to 22 wherein the transition metal is nickel or palladium.

24. A process according to any one of the preceding claims wherein the hydrogenolysis catalyst comprises ruthenium supported on titania, ruthenium supported on zinc oxide, ruthenium supported on carbon, ruthenium supported on a zeolite, unsupported nickel, nickel supported on titania, nickel supported on zinc oxide, nickel supported on carbon, nickel supported on a zeolite, palladium supported on titania, palladium supported on zinc oxide, palladium supported on carbon, palladium supported on gallium oxide, palladium supported on alumina, indium supported on gallium oxide or osmium supported on gallium oxide.

25. A process according to any one of the preceding claims wherein the hydrogenolysis catalyst comprises unsupported nickel, nickel supported on titania, nickel supported on zinc oxide, nickel supported on carbon, nickel supported on a zeolite, palladium supported on titania, palladium supported on zinc oxide, palladium supported on gallium oxide, palladium supported on alumina, iridium supported on gallium oxide or osmium supported on gallium oxide.

26. A process according to any one of the preceding claims wherein the selectivity of the hydrogenolysis reaction for methanol is at least 30 %.

27. A process according to any one of the preceding claims wherein the hydrogenolysis catalyst comprises nickel supported on zinc oxide, nickel supported on a zeolite, palladium supported on titania, palladium supported on zinc oxide, palladium supported on gallium oxide or palladium supported on alumina.

28. A process according to any one of the preceding claims wherein the selectivity of the hydrogenolysis reaction for methanol is at least 50 %.

29. A process according to any one of the preceding claims wherein the hydrogenolysis catalyst comprises palladium supported on titania or palladium supported on zinc oxide.

30. A process according to any one of the preceding claims wherein the step of treating said compound with hydrogen is carried out in the presence or absence of a solvent.

31. A process according to claim 30 wherein the solvent is water.

32. A process according to any one of the preceding claims wherein the step of treating said compound with hydrogen is carried out at a temperature of from 50 ⁰C to 200 ⁰C.

33. A process according to any one of the preceding claims wherein the step of treating said compound with hydrogen is carried out at a hydrogen pressure of from 1 bar to 250 bar.

34. A process according to any one of the preceding claims which further comprises esterifying a fatty acid with the methanol thus produced and thereby producing biodiesel.