Process for preparing mono propylene glycol (MPG)

Abstract

The invention relates to a process for preparing MPG from an aldohexose. It also relates to the use of a catalytic system to prepare MPG from a monosaccharide.

Description

[0001] Process for preparing mono propylene glycol (MPG)

[0002] Technical Field of the Invention

[0003] The present invention relates to a process for preparing MPG from an aldohexose . It also relates to the use of a catalytic system to prepare MPG from a starting material comprising a monosaccharide .

[0004] Background Art

[0005] Conventional methods for producing MPG involve the use of nonrenewable resources . The inventors have recogni zed the need to provide a method for producing MPG using biobased materials .

[0006] Direct hydrogenolysis of carbohydrates is a promising field o f technology to directly obtain biobased mono ethylene glycol (MEG) and MPG . It is commonly understood that the reaction mechanism involves a retro aldol (RA) reaction step that cleaves the carbohydrate into C2 ( glycolaldehyde ) and C3 fragments ( dihydroxy acetone , glyceraldehyde , pyruvaldehyde ) . The C2 and C3 fragments are then converted to MEG and MPG respectively in the presence of hydrogen and a suitable hydrogenation catalyst usually selected from the transition metals of group 8- 10 of the periodic table .

[0007] To catalyze the RA-step tungstic acid is typically added such as in Example 2 of WO 2019 / 175369 . However, this delivers low MPG yields and low MPG / MEG selectivity from glucose as the starting material .

[0008] It is known that the MPG yields and MPG / MEG selectivities may be influenced by the starting material . However, changing the starting material in industrial processes is complicated as it may introduce di f ferent impurities and may require a new supply chain . Furthermore , changing a biobased starting material i s not always practical due to fluctuations in the availability of the starting materials . On top of this , it is useful to be able to tune the output of these industrial processes to give di f ferent products depending on the demand .

[0009] Technical Problem

[0010] Accordingly, in view of the prior art there is a demand for an improved process for preparing MPG having improved yield and selectivity for MPG . There is also a demand to do so from biobased starting material without changing the starting material . More generally, there is a desire to be able to easily adj ust the output of biorefineries to give di f ferent products depending on the demand .

[0011] Summary of the Invention

[0012] The present invention surprisingly solves the above problem by providing a process for preparing MPG from an aldohexose , and the use of a catalytic system to prepare MPG from a starting material .

[0013] The invention encompasses the following embodiments :

[0014] 1 . A process for preparing mono propylene glycol (MPG) , comprising : introducing a catalytic system, hydrogen and a starting material into a reactor, reacting the starting material with the hydrogen in the presence of the catalytic system to deliver MPG, wherein the starting material comprises an aldohexose ; and wherein the catalytic system comprises : i ) at least one active metal component selected from groups 8 , 9 or 10 of the Periodic Table ; and ii ) one or more selected from molybdic acid, lithium molybdate , sodium molybdate , alkaline earth metal molybdates , ammonium molybdate, molybdenum bronzes, molybdenum trioxide, and alkaline earth metal tungstates.

[0015] 2. The process according to embodiment 1, wherein the at least one active metal component is selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, and mixtures thereof; optionally wherein the at least one active metal component comprises or consists of a Ni-alloy; and / or optionally wherein the at least one active metal component comprises or consists of a heterogeneous Ru catalyst, preferably Ru / C.

[0016] 3. The process according to any of embodiments 1 and 2, wherein the reaction is carried out at a temperature of 120 - 300 °C, preferably 180 - 270 °C, preferably 230 - 270 °C, preferably 250 °C; and / or wherein the pressure in the reaction is 1 - 20 MPa, preferably 3 - 15 MPa; and / or wherein the time that the starting material is reacted with hydrogen is 5 minutes - 3 hours, preferably 30 minutes - 1.5 hours .

[0017] 4. The process according to any of embodiments 1 - 3, wherein the mass ratio of i) calculated as the metal to ii) in the catalytic system is in the range of 0.5 to 25, preferably from 1 to 15; and / or wherein the molar ratio of aldohexose in the starting material to ii) is in the range of 5 - 1000, preferably 10 to 300, preferably 12 to 150; and / or wherein the mass ratio of aldohexose to i) calculated as the metal is 1 - 100, preferably 2 - 10.

[0018] 5. The process according to any of embodiments 1 - 4, further comprising introducing a solvent into the reactor, wherein the solvent preferably comprises water. 6. The process according to any of embodiments 1 - 5, wherein the aldohexose is biobased, and / or wherein the aldohexose comprises or consists of glucose.

[0019] 7. The process according to any of embodiments 1 - 6, wherein the starting material comprises additional carbohydrates, wherein the additional carbohydrates are preferably selected from cellulose, fructose and / or xylose.

[0020] 8. The process according to any of embodiments 1 - 7, wherein the process has a higher selectivity for MPG than ethylene glycol.

[0021] 9. The process according to any of embodiments 1 - 8, wherein the process has an MPG molar yield of at least 20% based on the aldohexose in the starting material.

[0022] 10. Use of a catalytic system to prepare MPG from a starting material , wherein the catalytic system comprises one or more selected from molybdic acid, lithium molybdate, sodium molybdate, alkaline earth metal molybdates, ammonium molybdate, molybdenum bronzes, molybdenum trioxide, and alkaline earth metal tungstates, and wherein the starting material comprises a monosaccharide.

[0023] Where the present description refers to "preferred" features, combinations of these "preferred" features shall also be deemed as disclosed as long as this combination of "preferred" features is technically meaningful.

[0024] Hereinafter, the use of the term "comprising" should be understood as disclosing, as a more restricted embodiment, the term "consisting of" as well, as long as this is technically meaningful . Brief Description of the Figures

[0025] Figure 1 : Graph of molar yields o f MPG and MEG with various catalysts from glucose .

[0026] Figure 2 : Graph of molar yields o f MPG and MEG with various catalysts and starting materials .

[0027] Detailed Description of the Invention

[0028] The present invention relates to a process for preparing mono propylene glycol (MPG) , comprising : introducing a catalytic system, hydrogen and a starting material into a reactor, reacting the starting material with hydrogen in the presence of the catalytic system to deliver MPG, wherein the starting material comprises an aldohexose ; wherein the catalytic system comprises : i ) at least one active metal component selected from groups 8 , 9 or 10 of the Periodic Table ; and ii ) one or more selected from molybdic acid, lithium molybdate , sodium molybdate , alkaline earth metal molybdates , molybdenum bronzes , molybdenum trioxide , and alkaline earth metal tungstates .

[0029] The process of the invention delivers MPG, also called 1 , 2- propanediol . This may be biobased, meaning that it is derived from biological feedstocks . Such biobased, renewably sourced materials can be di f ferentiated from their non-renewable counterparts by their carbon isotope ratios using ASTM International Radioisotope Standard Method D 6866-21 . Biobased means at least about 20 percent or more of the carbon content is derived from biological feedstocks as shown by ASTM D 6866-21 .

[0030] The process of the invention may deliver a product composition comprising or consisting of MPG . The product composition may comprise or consist of a solvent as defined below, MPG, MEG ( also called 1 , 2-ethanediol ) , and 1 , 2-butane diol (BDO, also called butylene glycol ) . The total diol concentration of the product composition may be 0 . 1 - 40 weight-% based on the total weight of the composition . The product composition may also comprise other side products .

[0031] The process of the invention comprises introducing a catalytic system, hydrogen and a starting material into a reactor . This may be achieved by physically placing the catalytic system, hydrogen and starting material in the reactor, or one or more of these components may be produced in the reactor . The catalytic system, hydrogen and a starting material may be introduced into the reactor simultaneously or sequentially . It is preferred that they are introduced sequentially in the order : 1 ) catalytic system, 2 ) hydrogen and 3 ) starting material .

[0032] The catalytic system increases the rate of the reaction of the starting material with hydrogen to deliver MPG without modi fying the overall standard Gibbs energy change in this reaction . The catalytic system is defined at the time of introduction into the reactor . It may change during the reaction .

[0033] The catalytic system of the invention comprises or consists of components i ) and ii ) . Prior to introduction to the reactor, components i ) and ii ) may be part of a single catalytic composition comprising both i ) and ii ) . They are preferably separate components .

[0034] Component i ) of the catalytic system of the invention is at least one active metal component selected from groups 8 , 9 or 10 of the Periodic Table . It catalyses the hydrogenation reaction . Preferably the at least one active metal component is selected from iron, cobalt , nickel , ruthenium, rhodium, palladium, iridium, platinum, and mixtures thereof . The at least one active metal component may be heterogeneous , meaning that it remains solid and does not dissolve during the reaction. The at least one active metal component may comprise or consist of a Ni-alloy, optionally spongy nickel. The Ni-alloy may be a heterogenous Ni-alloy catalyst. The at least one active metal component may be in the form of metal powder catalyst which may be a Ni-alloy. The at least one active metal component may comprise or consist of a heterogeneous Ru catalyst, preferably Ru / C.

[0035] The active metal component of i) of the catalytic system may be supported by a carrier comprising activated carbon, alumina, silica, silicon carbide, zirconia, zinc oxide, titanium dioxide, or a mixture thereof. The active metal component of i) may account for 0.05 - 70 weight-% of the total weight of component i) of the catalytic system.

[0036] Component i) of the catalytic system may be introduced into the reactor in the form of a slurry. The slurry may comprise 1 - 20% w / w, optionally 5 - 15% w / w of component i) of the catalytic system based on the total weight of the slurry. The liquid for the slurry may comprise or consist of the solvent defined below. The liquid for the slurry preferably comprises or consists of water.

[0037] Component ii) of the catalytic system of the invention is one or more selected from molybdic acid (H2M0O4) , lithium molybdate (Li2Mo04) , sodium molybdate (Na2Mo04) , alkaline earth metal molybdates (e.g. BeMo04, MgMo04, CaMo04, SrMo04, BaMo04) , ammonium molybdate ( (NH4)2Mo04 ) , molybdenum bronzes (AXMO03, where A is H or an alkali metal, and x is greater than 0 and equal to or less than 2) , molybdenum trioxide (M0O3) , and alkaline earth metal tungstates (e.g. BeWO4,

[0038] MgWO2, CaWO2, SrWO4, BaWO4) . The hydrates and solvates of each of these compounds are included in the general terms used in the embodiments. For example, processes including the following are included: Mo03*2H20, Li2Mo04*2H20, Na2Mo04*2H20, BeMo04*2H20, MgMo04*2H20, CaMo04*2H20, SrMo04*2H20, BaMo04*2H20, ZnMo04*2H20, AxMo03*2H20 (where A is H or an alkali metal, and x is greater than 0 and equal to or less than 2) , BeWO4*2H2O, MgWO4*2H2O, CaWO4*2H2O, SrWO4*2H2O, BaWO4*2H2O. Processes including the following are also included: (where A is H or an alkali metal, and x is greater than 0 and equal to or less than 2) , BeWO4*H2O, MgWO4*H2O, CaWO4*H2O, SrWO4*H2O, BaWO4*H2O.

[0039] Component ii) catalyzes the RA reaction. The component ii) of the catalytic system of the invention may be homogeneous, meaning that it is in the dissolved state during the reaction .

[0040] Including one or more of these compounds in component ii) of the catalytic system of the invention allows the preparation of MPG having improved yield and selectivity for MPG relative to the known catalysts. They remove the need to change the starting material to achieve these advantages, and instead allow the product to be selected simply by changing the catalyst. Sodium molybdate, lithium molybdate, calcium molybdate, and calcium tungstate are preferred. Sodium molybdate (Na2Mo04and / or Na2Mo04*2H20) is most preferred as it leads to a particularly high yield of MPG.

[0041] The process of the invention may include a step of pretreating the catalytic system before addition of the starting material. The pretreatment may be carried out at a temperature of 120 - 300 °C, preferably 180 - 270 °C, preferably 230 - 270 °C, and preferably 250 °C. The pretreatment may be carried out at a pressure of 1 - 20 MPa, preferably 3 - 15 MPa. The pretreatment may be carried out until the temperature and pressure are constant. It may be carried out for a time in the range of 10 seconds - 30 minutes, and preferably 1 minute - 5 minutes. The pretreatment may be carried out in the presence of hydrogen. Prior to the introduction of hydrogen in the pretreatment step, an inert gas may be used as the atmosphere in the reactor . The inert gas is preferably nitrogen .

[0042] The starting material comprises one or more compounds which react to deliver MPG . It comprises or consists of one or more aldohexoses . An aldohexose is a monosaccharide with six carbon atoms which, in the linear form, has the carbonyl at carbon 1 , forming an aldehyde derivative with structure H-C (=0) - ( CHOH)5- H . The starting material may comprise one or more aldohexoses selected from allose , altrose , glucose , mannose , gulose , idose , galactose and / or talose . It is preferred that the aldohexose comprises or consists of glucose as this is a more abundant biobased feedstock maximising the industrial applicability of the invention . Where the aldohexose consists of glucose , the only aldohexose present in the starting material is glucose . The aldohexose is preferably biobased as defined above .

[0043] The starting material may comprise carbohydrates other than aldohexoses . The carbohydrates may be monosaccharides , disaccharides , oligosaccharides made of three to ten monosaccharide units and / or polysaccharides made of greater than ten monosaccharide units . For reasons of using an abundant biobased feedstock maximising the industrial applicability of the invention, the other carbohydrates preferably comprise or consist of cellulose , fructose and / or xylose . They most preferably comprise or consist of fructose and / or xylose . Including these other carbohydrates in the starting material also allows the preparation of MPG having improved yield and selectivity for MPG relative to the known catalysts .

[0044] Alternatively aldohexoses may be the only carbohydrates contained in the starting materials . The starting material may comprise the aldohexoses in a total amount of 5 - 100% w / w, optionally 25 - 75% w / w, optionally 40 - 50% w / w based on the total weight of the starting material .

[0045] In the process of the invention, a solvent may be introduced into the reactor . The solvent is a liquid in which the aldohexose is soluble at 25 °C and atmospheric pressure . The solvent may comprise or consist of one or more compounds , optionally selected from water , methanol , ethanol , MEG, MPG , BDO , PEG, or Ci-e alcohols . As such, the solvent may be the product composition defined above comprising or consisting of water , MPG, MEG, and optionally BDO . The solvent preferably comprises or consists of water from the perspective of maximising the industrial applicability of the invention . Some or all of the solvent is preferably introduced into the reactor at the same time as the starting material , and preferably the starting material is introduced into the reactor dissolved in some or all of the solvent . Alternatively, the solvent and starting material may be introduced into the reactor separately .

[0046] In the reaction, aldohexoses and optional carbohydrates other than aldohexoses may be present in a total amount of 5 - 100% w / w, optionally 10 - 50% w / w, optionally 15 - 25% w / w based on the total combined weight of the starting material and solvent introduced into the reactor .

[0047] The reactor is a hydrogenation reactor and may be a batch or continuous reactor . The reactor may be one or more continuously stirred tank ( CSTR) reactor . Where there is more than one CSTR, they may be configured as a cascade of CSTRs .

[0048] The reaction may be operated in batch- or fed-batch mode or continuously, and the reactor may be configured to be operated in batch- or fed-batch mode or continuously . In the reaction, the starting material is reacted with hydrogen in the presence of the catalytic system to deliver MPG . This means that the aldohexose comprised in the starting material is contacted with the catalytic system and the hydrogen to allow the reaction of the aldohexose to MPG to take place . When present , the optional additional carbohydrates comprised in the starting material are also contacted with the catalytic system and the hydrogen to allow the reaction of these components to MPG to take place .

[0049] Without wishing to be bound by theory, the aldohexose and optional additional carbohydrates may undergo a RA reaction catalysed by component ( ii ) of the catalytic system . The product of the RA reaction may subsequently be reduced to MPG by hydrogen in a reaction catalysed by component ( i ) of the catalytic system . The process of the invention is a one-step conversion of the starting material to MPG .

[0050] Prior to the introduction of hydrogen, an inert gas may be used as the atmosphere in the reactor . The inert gas is preferably nitrogen . The hydrogen in the reaction may be molecular hydrogen, i . e . H2. The hydrogen may be introduced to create a pressure of 1 - 20 MPa, preferably 3 - 15 MPa ; preferably 10 - 14 MPa .

[0051] The reaction may be initiated by introducing starting material into a reactor containing hydrogen and the catalytic system . The starting material may optionally be introduced dissolved in the solvent .

[0052] The reaction may be carried out at a temperature of 120 - 300 ° C, preferably 180 - 270 ° C, preferably 230 - 270 ° C, preferably 250 ° C .

[0053] The reaction may be carried out at a pressure of 1 - 20 MPa, preferably 3 - 15 MPa ; preferably 10 - 14 MPa . The reaction may be carried out for a time in the range of 5 minutes - 3 hours, preferably 30 minutes - 1.5 hours, most preferably 45 minutes - 1 hour.

[0054] The reaction may be carried out batch-wise, semi-batch-wise, or in a continuous process. In a continuous process, the starting material is a feedstock. The liquid hourly space velocity (LHSV) is a volume of the reactant (comprising the starting material and the hydrogen) per unit volume of catalyst per hour. In the process of the invention in a continuous process the LHSV may be 0.2 hr-1to 2 hr-1.

[0055] The mass ratio of i) to ii) in the catalytic system may be in the range of 0.5 to 25, preferably from 1 to 15 (where i) is calculated based on the mass of the active metal component selected from groups 8, 9 or 10 of the Periodic Table) .

[0056] The molar ratio of aldohexose in the starting material to ii) may be in the range of 5 - 1000 moles, preferably 10 to 300 moles, preferably 12 to 150 moles, more preferably 15 - 50 moles, most preferably 27 - 40 moles. The preferred ranges deliver improved % yields of MPG.

[0057] The mass ratio of aldohexose to i) (calculated based on the mass of the active metal component selected from groups 8, 9 or 10 of the Periodic Table) may be 1 - 100, preferably 2 -

[0058] 10.

[0059] The mass ratio of i) (calculated based on the mass of the active metal component selected from groups 8, 9 or 10 of the Periodic Table) in the reactor based on the total mass of the catalytic system, the starting material and the solvent may be in the range of 0.5 - 10% by mass, preferably 2 - 4% by mass. The mass ratio of ii) in the reactor based on the total mass of the catalytic system, the starting material and the solvent may be in the range of 0.01 - 2% by mass, preferably 0.5 - 1.5% by mass. The mass ratio of the starting material in the reactor based on the total mass of the catalytic system, the starting material and the solvent may be in the range of 5 - 50% by mass , preferably 15 - 25% by mass . The mass ratio of the solvent in the reactor based on the total mass of the catalytic system, the starting material and the solvent may be in the range of 10 - 90% by mass , preferably 60 - 80% by mass .

[0060] The catalytic system comprises several components as discussed above . These components of the catalytic system may be introduced into the reactor together, or they may be introduced separately .

[0061] The starting material may comprise several components as discussed above . These components may be introduced together, or they may be introduced separately . The starting material components may be introduced after the pretreatment of the catalytic system described above .

[0062] The process may have a higher selectivity for MPG than MEG . This MPG / MEG selectivity is the ratio of the molar yield of MPG and molar yield of MEG based on the aldohexose in the starting material . The MPG / MEG selectivity is preferably higher than 1 . 5 , more preferably higher than 2 .

[0063] The process may have an MPG molar yield of at least 20% , preferably at least 30% , more preferably at least 35% based on the aldohexose in the starting material . The calculation of the molar yields is carried out in the following way :

[0064] Index 1 refers to the product (MEG or MPG) , index g refers to starting carbohydrate , w is the mass fraction of the component [ g / g] in the reaction mixture , M the molar mass of the component [ g / mol ] , v is the stochiometric factor in the conversion of the carbohydrate to the product ( e . g . in the case of glucose : vMEG=3 and vMPG=2 , since glucose is C6 so theoretically can give 3 moles of MEG or 2 moles of MPG) .

[0065] The process may have an aldohexose conversion of at least 90% , preferably at least 95% .

[0066] The process of the invention may comprise or consist of the steps speci fied in the claims .

[0067] When the process comprises the steps in the claims , the process may also comprise providing a biological feedstock and subj ecting the feedstock to at least one pretreatment to form a liquid fraction and a fraction comprising solid cellulose particles and subsequently subj ecting the fraction comprising solid cellulose particles to enzymatic hydrolysis to form a lignin fraction and a carbohydrate fraction, wherein the starting material comprises at least part of the carbohydrate fraction .

[0068] The process may also comprise recovering one or both components of the catalytic system .

[0069] The process may also comprise recovering MPG from the composition obtained from the process of the invention .

[0070] The MPG of the invention may be further reacted in downstream processes .

[0071] Component i ) of the catalytic system of the invention may be a heterogenous catalyst and may be recovered by solid / liquid separation and recycled to be reused in the process of the invention . Component ii ) of the catalytic system of the invention may be a homogenous catalyst and may be recovered from the composition comprising of MPG obtained from the process of the invention during the MPG recovery step discussed below . It may subsequently be recycled to be reused in the process of the invention .

[0072] The process of the invention may deliver MPG as a composition comprising of MPG . Recovering MPG from the composition comprising of MPG obtained from the process of the invention may be conducted by a separation technique selected from adsorption, evaporation, distillation, extractive distillation, azeotrope distillation, vacuum distillation, atmospheric distillation, membrane separation, filtration, reactive puri fication or a combination of them .

[0073] The MPG may be recovered by distillation . The distillation may be carried out in at least one distillation column . The distillation may be carried out at a temperature of 50 - 250 ° C, or of 100 - 200 ° C . The distillation may be carried out at a pressure of at least 0 . 1 kPa, or at least 10 kPa, or at least 50 kPa . The pressure may be at most 400 kPa, or at most 200 kPa, or at most 120 kPa . It will be clear to the skilled person to vary the temperature and pressure in relation to each other in order to achieve suitable conditions .

[0074] The MPG obtained from the process of the invention may be used to synthesise polyesters . The MPG may be reacted with a dicarboxylic acid and / or cyclic anhydride to deliver the polyester . The invention may also relate to a process for preparing a polyester, comprising a first step of preparing MPG according to the present invention and a second step of reacting the MPG with a dicarboxylic acid and / or cyclic anhydride to deliver the polyester .

[0075] The MPG obtained from the process of the invention may be used to synthesise polyurethanes . The MPG may be reacted with a diisocyanate to deliver the polyurethane . The invention may also relate to a process for preparing a polyurethane , comprising a first step of preparing MPG according to the present invention and a second step of reacting the MPG with a diisocyanate to deliver the polyurethane .

[0076] The present invention also relates to the use of a catalytic system to prepare MPG from a starting material , wherein the catalytic system comprises one or more selected from molybdic acid, lithium molybdate , sodium molybdate , alkaline earth metal molybdates , ammonium molybdate , molybdenum bronzes , molybdenum trioxide , and alkaline earth metal tungstates , and wherein the starting material comprises at least one monosaccharide .

[0077] The MPG and catalytic system are as defined in detail above . The use also includes all aspects of the invention discussed above . The monosaccharide may be one or more selected from ketoses and aldoses . The ketoses may comprise fructose . The aldoses may comprise one or more aldohexoses (preferably glucose ) as speci fied above and / or xylose . All of the disclosures above concerning aldohexoses and starting material comprising aldohexoses also apply accordingly to monosaccharides and starting material comprising monosaccharides for the present use .

[0078] The use of the catalytic system of the invention delivers improved MPG selectivity, and the MPG yield is also improved .

[0079] The present description also discloses a process for preparing mono propylene glycol (MPG) , comprising : introducing a catalytic system, hydrogen and a starting material into a reactor, reacting the starting material with hydrogen in the presence of the catalytic system to deliver MPG, wherein the starting material comprises at least one monosaccharide ; wherein the catalytic system comprises : i ) at least one active metal component selected from groups 8 , 9 or 10 of the Periodic Table ; and ii ) one or more selected from molybdic acid, lithium molybdate , sodium molybdate , alkaline earth metal molybdates , ammonium molybdate, molybdenum bronzes, molybdenum trioxide, and alkaline earth metal tungstates. The elements of this process apart from the starting material are the same as described above with respect to the process of the invention. The starting material is the same described above in the use of the present invention. This process also delivers improved MPG selectivity and MPG yield.

[0080] Experimental Part

[0081] Examples 1A-1D: Reaction with various W and Mo salts

[0082] To four 50 ml hydrogenation reactors equipped with an overhead stirrer, the catalytic system was added as follows.

[0083] Each reactor was charged with catalytic system component i) , in which the active metal component selected from groups 8, 9 or 10 of the Periodic Table is Ni . The Ni was present on a support and was in the form of a slurry of 1 g catalyst i) in 10 mL deionized water.

[0084] To each reactor was added one of catalytic system component ii) compounds 1A - ID as specified in table 1.

[0085] After purging with nitrogen, the reactors were pressurized with hydrogen (ca. 6 MPa) and the stirring started. The reactors were heated to 250°C, at this temperature the pressure was increased to 12 MPa hydrogen.

[0086] When the conditions were stable, 8.5 g of an aqueous glucose solution (ca. 45% w / w) were added in 15 minutes. The molar ratio of glucose in the starting material to ii) was 33. During this time the pressure in the reactors was maintained at 12 MPa by co-feeding hydrogen gas. After the addition of the glucose solution the reaction mixtures were stirred for another 40 minutes and subsequently allowed to be cooled to room temperature . Afterwards samples were taken, filtered and analyzed by HPLC . The results are shown in table 1 and figure 1. The calculation of the molar yields was carried out in the following way:

[0087] WjMg

[0088] Vi = X 100 MtWgVi

[0089] Index 1 refers to the product (MEG or MPG) , index g refers to starting carbohydrate (in this case glucose) , w is the mass fraction of the component [g / g] in the reaction mixture, M the molar mass of the component [g / mol] , v is the stochiometric factor in the conversion of the carbohydrate to the product. In the case of glucose: vMEG=3; vMPG=2.

[0090] Comparative examples 1E-1I: Reaction with various W and Mo salts

[0091] Comparative examples 1E-1I were carried out in the same manner as examples 1A-1D, except that compounds IE - II as specified in table 1 were used in place of catalytic system component ii) compounds 1A - ID.

[0092] Table 1 Results of Example 1 and Comparative Example 1

[0093] As shown in table 1 and figure 1, using a catalytic system comprising tungstic acid IE, or tungstates in IF - 1H all deliver MEG as the major product. Using a catalytic system comprising potassium molybdate in II gives a low yield of MPG. Surprisingly, in 1A - ID when using a catalytic system comprising Na2Mo04*2H20, Li2Mo04, CaMoCg or CaWCg the selectivity in the hydrogenolysis of glucose is inverted, more MPG than MEG is produced (i.e. the MPG selectivity is improved) , and the MPG yield is also improved. It should also be noted that the conversion of glucose was >99% in the reactions, so the selectivity for MPG is clearly improved with the invention even if the ratio of MPG and MEG is smaller than in II.

[0094] Example 2: Effect of molar ratio of aldohexose to ii)

[0095] Example 2 was carried out in the same manner as example IB using Na2Mo04*2H20 as component ii) of the catalytic system, except that the molar ratio of aldohexose in the starting material to ii) was varied as specified in table 2.

[0096] Table 2 Results of Example 2

[0097] Surprisingly, the relationship between the molar ratio and MPG yield shows that the highest yield is obtained at a molar ratio of glucose to Na2Mo04*2H20 of 34. Example 3 : Effect of carbohydrate in the starting material

[0098] Example 3 was carried out in the same manner as example IB using Na2Mo04* 2H20 as component ii ) of the catalytic system, except that glucose was replaced with fructose or xylose in the starting material . The results are shown in figure 2 .

[0099] Comparative Example 2 : Effect of carbohydrate in the starting material

[0100] Comparative Example 2 was carried out in the same manner as comparative example I F using Na2WO4* 2H2O as component ii ) of the catalytic system, except that glucose was replaced with fructose or xylose in the starting material . The results are shown in figure 2 .

[0101] Surprisingly, as shown in figure 2 using a fructose or xylose starting material , with the catalytic system comprising Na2Mo04* 2H20 instead of Na2WO4* 2H2O the MPG selectivity i s improved, and the MPG yield is also improved .

Claims

Claims1. A process for preparing mono propylene glycol (MPG) , comprising : introducing a catalytic system, hydrogen and a starting material into a reactor, reacting the starting material with the hydrogen in the presence of the catalytic system to deliver MPG, wherein the starting material comprises an aldohexose; and wherein the catalytic system comprises: i) at least one active metal component selected from groups 8, 9 or 10 of the Periodic Table; and ii) one or more selected from molybdic acid, lithium molybdate, sodium molybdate, alkaline earth metal molybdates, ammonium molybdate, molybdenum bronzes, molybdenum trioxide, and alkaline earth metal tungstates.

2. The process according to claim 1, wherein the at least one active metal component is selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, and mixtures thereof; optionally wherein the at least one active metal component comprises or consists of a Ni-alloy; and / or optionally wherein the at least one active metal component comprises or consists of a heterogeneous Ru catalyst, preferably Ru / C.

3. The process according to any of claims 1 and 2, wherein the reaction is carried out at a temperature of 120 - 300 °C, preferably 180 - 270 °C, preferably 230 - 270 °C, preferably 250 °C; and / or wherein the pressure in the reaction is 1 - 20 MPa, preferably 3 - 15 MPa; and / or wherein the time that the starting material is reacted with hydrogen is 5 minutes - 3 hours, preferably 30 minutes - 1.5 hours .

4. The process according to any of claims 1 - 3, wherein the mass ratio of i) calculated as the metal to ii) in the catalytic system is in the range of 0.5 to 25, preferably from 1 to 15; and / or wherein the molar ratio of aldohexose in the starting material to ii) is in the range of 5 - 1000, preferably 10 to 300, preferably 12 to 150; and / or wherein the mass ratio of aldohexose to i) calculated as the metal is 1 - 100, preferably 2 - 10.

5. The process according to any of claims 1 - 4, further comprising introducing a solvent into the reactor, wherein the solvent preferably comprises water.

6. The process according to any of claims 1 - 5, wherein the aldohexose is biobased, and / or wherein the aldohexose comprises or consists of glucose.

7. The process according to any of claims 1 - 6, wherein the starting material comprises additional carbohydrates, wherein the additional carbohydrates are preferably selected from cellulose, fructose and / or xylose.

8. The process according to any of claims 1 - 7, wherein the process has a higher selectivity for MPG than ethylene glycol.

9. The process according to any of claims 1 - 8, wherein the process has an MPG molar yield of at least 20% based on the aldohexose in the starting material.

10. Use of a catalytic system to prepare MPG from a starting material , wherein the catalytic system comprises one or more selected from molybdic acid, lithium molybdate, sodium molybdate, alkaline earth metal molybdates, ammonium molybdate,molybdenum bronzes, molybdenum trioxide, and alkaline earth metal tungstates, and wherein the starting material comprises a monosaccharide.

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