Process for recovering a transition metal oxyacid salt from a mixture

Abstract

A process for recovering a transition metal oxyacid salt at least partially from a mixture is disclosed. The mixture may comprise the transition metal oxyacid salt and organic compounds. The process may comprise subjecting the mixture to a temperature above the melting temperature of the transition metal oxyacid salt, thereby incinerating the organic compounds and obtaining the transition metal oxyacid salt in the form of a melt and optionally of ash; and purifying the transition metal oxyacid salt from the melt and optionally from the ash by recrystallization, thereby recovering the transition metal oxyacid salt at least partially.

Description

[0001] PROCESS FOR RECOVERING A TRANSITION METAL OXYACID SALT

[0002] FROM A MIXTURE

[0003] TECHNICAL FIELD

[0004] The present disclosure relates in general to a process for recovering a transition metal oxyacid salt at least partially from a mixture .

[0005] BACKGROUND

[0006] Transition metal oxyacid salts may be used in processes for manufacturing chemical products from e . g . biomass . They may function as ( co- ) catalysts for e . g . catalyzing retro-aldol reactions converting carbohydrates to chemicals / reaction products from the conversion of biomass .

[0007] Such salts may be soluble in the reaction mixtures , and they may be challenging to recover from the reaction mixtures for reuse .

[0008] SUMMARY

[0009] This Summary is provided to introduce a selection of concepts in a s impli f ied form that are further described below in the Detailed Description . This Summary is not intended to identi fy key features or essential features of the claimed subj ect matter, nor is it intended to be used to limit the scope of the claimed subj ect matter .

[0010] A process for recovering a transition metal oxyacid salt at least partially from a mixture is disclosed . The mixture may comprise the transition metal oxyacid salt and organic compounds . The process may comprise subj ecting the mixture to a temperature above the melting temperature of the transition metal oxyacid salt , thereby incinerating the organic compounds and obtaining the transition metal oxyacid salt in the form of a melt and optionally of ash; and puri fying the transition metal oxyacid salt from the melt and optionally from the ash by recrystalli zation, thereby recovering the transition metal oxyacid salt at least partially .

[0011] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings , which are included to provide a further understanding of the embodiments and constitute a part of this speci fication, illustrate various embodiments . In the drawings :

[0013] Figure 1 illustrates schematically a process for recovering a transition metal oxyacid salt at least partially from a mixture as well as a process for producing diols and / or polyols .

[0014] DETAILED DESCRIPTION

[0015] A process for recovering a transition metal oxyacid salt at least partially from a mixture is disclosed . The mixture may comprise the transition metal oxyacid salt and organic compounds .

[0016] The process may comprise subj ecting the mixture to a temperature above the melting temperature of the transition metal oxyacid salt , thereby incinerating the organic compounds and obtaining the transition metal oxyacid salt in the form of a melt and optionally of ash; and puri fying the transition metal oxyacid salt from the melt and optionally from the ash by recrystalli zation, thereby recovering the transition metal oxyacid salt at least partially .

[0017] The transition metal oxyacid salt may be used as a ( co- ) catalyst for catalyzing e . g . retro-aldol reactions converting carbohydrates , obtained from biomass , to chemicals / reaction products . The transition metal oxyacid salt may be soluble in the reaction product mixture as well as soluble in components of the reaction product mixture. Thus, it may also be dissolved in the mixture. Separating it from the mixture may be relatively cumbersome. Other alternatives, such as aqueous extraction of the transition metal oxyacid salt, could consume significant amounts of water and heat.

[0018] With the process, it is possible to recover and optionally reuse the transition metal oxyacid salt in a relatively convenient manner. The process may be continuous .

[0019] The recrystallization removes impurities such as chlorides, sulfates, carbonates, aluminates and / or other inorganic impurities, which may originate e.g. from the carbohydrates obtained from biomass which are converted into chemicals / reaction products in the reaction. In a process scheme where the transition metal oxyacid salt is reused, the recrystallization may avoid accumulating these impurities in such a process recycle loop.

[0020] The transition metal oxyacid salt may be recovered with a relatively high yield and with high purity. A recovery rate of at least 90 % of the transition metal oxyacid salt may be achieved.

[0021] The recovered (purified) transition metal oxyacid salt may comprise e.g. 400 ppm or less, or preferably 220 ppm or less of chloride (Cl“) ions; 400 ppm or less, or preferably 220 ppm or less of sulphate (SO4-) ions; 200 ppm or less, or preferably 70 ppm or less of aluminate (AlCf) ions; and / or 400 ppm or less, or preferably 120 ppm or less of carbonate (COa-) ions. The amounts of the ions may be understood as parts per million based on the total dry weight of the recovered (purified) transition metal oxyacid salt. The recovered (purified) transition metal oxyacid salt may comprise e.g. 1 - 400 ppm, or preferably 1 - 220 ppm, of chloride ions. The recovered (purified) transition metal oxyacid salt may comprise e.g. 1 - 400 ppm or preferably 1 - 220 ppm of sulphate ions. The recovered (purified) transition metal oxyacid salt may comprise e.g. 1 - 200 ppm, preferably 1 - 70 ppm of aluminate (A1O2“) ions. The recovered (purified) transition metal oxyacid salt may comprise e.g. 1 - 400 ppm, preferably 1 - 120 ppm or less of carbonate (COa-) ions.

[0022] A recycled transition metal oxyacid salt (co- ) catalyst is also disclosed. The recycled transition metal oxyacid salt ( co- ) catalyst may be understood as referring to a recycled transition metal oxyacid salt ( co- ) catalyst composition. Said composition may comprise minor amounts of one or more inorganic impurities, such as chloride ions, sulphate ions, aluminate ions, and / or carbonate ions.

[0023] The recycled transition metal oxyacid salt ( co- ) catalyst may comprise 400 ppm or less, or preferably 220 ppm or less of chloride (Cl“) ions; 400 ppm or less, or preferably 220 ppm or less of sulphate (SO4-) ions; 200 ppm or less, or preferably 70 ppm or less of aluminate (AlCy-) ions; and / or 400 ppm or less, or preferably 120 ppm or less of carbonate (COa-) ions. The amounts of the ions may be understood as parts per million based on the total dry weight of the recycled transition metal oxyacid salt ( co- ) catalyst . The recycled transition metal oxyacid salt ( co- ) catalyst may comprise e.g. 1 - 400 ppm, or preferably 1 - 220 ppm, of chloride ions. The recycled transition metal oxyacid salt ( co- ) catalyst may comprise e.g. 1 - 400 ppm or preferably 1 - 220 ppm of sulphate ions. The recycled transition metal oxyacid salt ( co- ) catalyst may comprise e.g. 1 - 200 ppm, preferably 1 - 70 ppm of aluminate (AlCy-) ions. The recycled transition metal oxyacid salt ( co- ) catalyst may comprise e.g. 1 - 400 ppm, preferably 1 - 120 ppm or less of carbonate (CO3“) ions. The recycled transition metal oxyacid salt ( co- ) catalyst may be obtainable or obtained by the process according to one or more embodiments described in this specification. In other words, it may comprise the recovered (purified) transition metal oxyacid salt .

[0024] Use of the recycled transition metal oxyacid salt ( co- ) catalyst for catalyzing reactions converting carbohydrates to chemicals / reaction products from conversion of biomass, e.g. retro-aldol reactions converting carbohydrates to chemicals / reaction products from conversion of biomass, is also disclosed .

[0025] In the context of this specification, the term "mixture" may be understood as referring to the mixture comprising the transition metal oxyacid salt and the organic compounds, which is subjected to the temperature above the melting temperature of the transition metal oxyacid salt, unless otherwise indicated .

[0026] The mixture may have a viscosity. Typically the viscosity may be high. For example, the viscosity of the mixture may be higher than 50 cP.

[0027] The mixture may be provided at a desired viscosity prior to subjecting the mixture to the temperature above the melting temperature of the transition metal oxyacid salt. Providing the mixture at the desired viscosity may be done e.g. by adjusting its temperature. The desired viscosity may be e.g. 50 cP or lower, preferably 20 cP or lower. The viscosity may be determined as dynamic viscosity at 80 °C or, in some embodiments, at the temperature at which the mixture is provided prior to subjecting it to the temperature above the melting temperature of the transition metal oxyacid salt (e.g. the temperature to which the temperature of the mixture is adjusted) . In other words, the viscosity may be the (dynamic) viscosity of the mixture measured at 80 °C, or the (dynamic) viscosity measured at the temperature at which the mixture is provided prior to subjecting the mixture to the temperature above the melting temperature of the transition metal oxyacid salt (e.g. the temperature to which the temperature of the mixture is adjusted) . When the mixture has the desired viscosity, it may be more easily pumpable e.g. to a furnace in which it is subjected to the temperature above the melting temperature of the transition metal oxyacid salt. Further, the mixture may be sprayed to the furnace through a burner nozzle. At the desired viscosity, the mixture may be well suited for spraying it into small droplets and into the furnace to ensure that it is in good contact with the atmosphere in the furnace for efficient and clean burning. This process may also be referred to as atomization.

[0028] The mixture may, in some embodiments, be preheated to thereby adjust, e.g. to lower, its viscosity .

[0029] The mixture may be obtained e.g. from a process from which the mixture may be obtained at a relatively high temperature, for example from a distillation process. In such embodiments, the temperature of the mixture may be adjusted by cooling.

[0030] The mixture may be provided at the desired viscosity by adjusting the temperature of the mixture to a temperature in the range of 20 - 200 °C, preferably in the range of 50 - 200 °C, more preferably in the range of 70 - 90 °C, even more preferably in the range of 75 - 85 °C.

[0031] The viscosity of the mixture may thus be lowered by adjusting the temperature of the mixture to a temperature in the range of 50 - 200 °C, preferably in the range of 70 - 90 °C, more preferably in the range of 75 - 85 °C. In some embodiments, an additional substance may be added to the mixture, to thereby adjust its viscosity. For example, the mixture may be diluted by adding one or more components capable of adjusting (for example, lowering) the viscosity of the mixture. The one or more components may comprise water, an acid, an alcohol having lower viscosity than the mixture, or any mixture or combination thereof.

[0032] The mixture may comprise the transition metal oxyacid salt in a total amount of e.g. 5 - 25 weight- %, or preferably 8 - 20 weight-%, or more preferably 10 - 15 weight-%, based on the total weight of the mixture .

[0033] The mixture may be subjected to the temperature above the melting temperature of the transition metal oxyacid salt, thereby incinerating the organic compounds and obtaining the transition metal oxyacid salt in the form of a melt and optionally of ash, in a suitable apparatus, such as a furnace and / or combustion chamber. The furnace may be e.g. a salt recovery furnace. The incineration may be done in oxidative conditions, i.e. in the presence of oxygen (e.g. pure oxygen, and / or an oxygen-containing gas, such as air) . The oxidative conditions may ensure that the organic compounds burn cleanly. Typically the organic compounds are incinerated completely, i.e. they all burn yielding mainly carbon dioxide and water .

[0034] Excess heat generated by the furnace may be used to generate steam. Thus the heat generated by the incinerating of the organic compounds may be stored as steam ("green steam", i.e. steam with a reduced carbon footprint as compared e.g. to steam produced by burning fossil fuels) .

[0035] The oxygen containing gas may also comprise or be vent air and / or process off-gases from another unit operation of the process (e.g. a process for producing diols and / or polyols and / or a biomass conversion process) . Thus the furnace may be used to incinerate the vent air and / or process off-gases that may contain organic impurities. Such vent air and / or process off-gases from the another unit operation of the process (e.g. a process for producing diols and / or polyols and / or a biomass conversion process) may be fed to the furnace for incinerating organic impurities contained therein. In this embodiment, there may be no need for a stand alone incinerator for incinerating the organic impurities in the vent air and / or process off-gases. The process off-gases may contain e.g. hydrogen. Thus, in processes in which other unit operations are present, the incineration of the vent air and process off-gases from such other unit operations may be combined with the incineration of the organic compounds of the mixture and the recovering of the transition metal oxyacid salt. It may also reduce emissions from the process, such as a biomass conversion process.

[0036] The transition metal oxyacid salt subjected to the temperature above its melting temperature will then melt. The furnace may e.g. comprise a combustion chamber having a cooling jacket. The melt may travel by gravity along a wall of the combustion chamber to a bottom outlet of the combustion chamber. The melt may be collected at the bottom of the combustion chamber. A portion of the melt may solidify along the wall of the combustion chamber and form a coating, protecting the wall from corrosion.

[0037] The temperature above the melting temperature of the transition metal oxyacid salt, to which the mixture is subjected, may depend on the transition metal oxyacid salt included in the mixture. For example, the melting temperature of sodium molybdate is 687 °C. Therefore, the temperature above the melting temperature of the transition metal oxyacid salt may be a temperature above 687 °C in embodiments in which the transition metal oxyacid salt is sodium molybdate. The melting temperature of sodium tungstate is 698 °C. Therefore, the temperature above the melting temperature of the transition metal oxyacid salt may be a temperature above 698 °C in embodiments in which the transition metal oxyacid salt is sodium tungstate. Dihydrates and other hydrates of sodium molybdate and sodium tungstate tend to lose the crystal water at lower temperatures, and thus the melting points of the (di) hydrates may be considered to be the melting points of corresponding anhydrous forms. In some embodiments, the temperature above the melting temperature of the transition metal oxyacid salt may be e.g. at least 700 °C, or higher. A high temperature may be desirable for environmental reasons, e.g. in order for the organic compounds to burn cleanly. Low temperatures may produce side products, carbon monoxide, soot etc.

[0038] The melt may be collected from the furnace e.g. in a continuous manner. In other embodiments, the melt may be collected in batches.

[0039] The melt may be allowed to cool and solidify to form solidified transition metal oxyacid salt. The melt and / or the solidified transition metal oxyacid salt may be cooled to a temperature in which it is easier to handle, for example to a temperature in the range of 20 - 100 °C. The solidified transition metal oxyacid salt may be crushed. Thus a cooled, solidified and crushed transition metal oxyacid salt may be obtained. Handling such a solidified (and optionally crushed) transition metal oxyacid salt may be safer in subsequent stages, as compared e.g. to dissolving a melt, which may be very hot, directly in water. The solidified (and optionally crushed) transition metal oxyacid salt may be understood as comprising impurities at this stage, for example the inorganic impurities mentioned in this specification. It may be at least partially amorphous.

[0040] The ash may be e.g. fly ash. Such fly ash may be collected from flue gas emitted by the furnace, for example by filtering. In the present process, the fly ash may comprise significant amounts of the transition metal oxyacid salt.

[0041] The melt, or the solidified (and optionally crushed) transition metal oxyacid salt, and optionally the ash may be collected, thereby collecting the transition metal oxyacid salt at least partially. The collected transition metal oxyacid salt in the form of the melt, or the solidified (and optionally crushed) transition metal oxyacid salt, and optionally of the ash may then be subjected to the recrystallization process step.

[0042] In the recrystallization, the melt, or the solidified (and optionally crushed) transition metal oxyacid salt, and optionally the ash may be dissolved in water to obtain a solution comprising the collected transition metal oxyacid salt. It / they may be dissolved in the water in a suitable dissolving system, e.g. in a tank.

[0043] Thus the transition metal oxyacid salt may be purified from the melt and optionally from the ash by recrystallization, thereby recovering the transition metal oxyacid salt in purified form at least partially .

[0044] The solution of the transition metal oxyacid salt may be a nearly saturated solution. Such a nearly saturated solution may comprise e.g. about 40 % of the transition metal oxyacid salt.

[0045] The process may further comprise filtering the solution of the transition metal oxyacid salt prior to the recrystallization. The filtering may remove undissolved solids that could otherwise end up in the purified transition metal oxyacid salt. It may thus improve the purity of the recovered transition metal oxyacid salt. The filtered solution may then be subjected to the recrystallization.

[0046] In the recrystallization, the solution of the transition metal oxyacid salt may be subjected to conditions in which the transition metal oxyacid salt crystallizes, such that impurities mainly remain in the solution.

[0047] The transition metal oxyacid salt may be recrystallized at least partially by evaporative crystallization.

[0048] The transition metal oxyacid salt may be recrystallized at least partially by evaporative crystallization, for example at an operating pressure of at least 0.1 kPaA and / or until a mass ratio of the transition metal oxyacid salt and the water in the solution is in the range of 0.05 - 10:1.

[0049] The transition metal oxyacid salt may be recrystallized at least partially by cooling the solution, i.e. by cooling crystallization. Prior to the cooling, the solution of the transition metal oxyacid salt may be heated.

[0050] The recrystallization may be done at least once. In other words, the transition metal oxyacid salt may be subjected to the recrystallization at least once, or e.g. once.

[0051] The recrystallization may be repeated at least once. In other words, the transition metal oxyacid salt may, in some embodiments, be subjected to the recrystallization at least twice. This may improve its purity.

[0052] The transition metal oxyacid salt may have, i.e. be represented by, the formula RyMxOz, wherein R is Na, K, Li, Rb, Cs, Mg, Ca, Sr, or Ba; y is 1 or 2; M is W or Mo; x is 1; and z is 4; wherein the transition metal oxyacid salt is optionally a hydrate. 0 may be understood as referring to oxygen. The hydrate may have the formula RyMxOz-NH2O, wherein N is 10, 2 or less, and R, y, M, x and z are as above. The transition metal oxyacid salt may be soluble at a temperature in the range of 20 to 90°C in water and in ethylene glycol. In embodiments in which R is Na, K, Li, Rb, or Cs, y may be 2. In embodiments in which R is Mg, Ca, Sr, or Ba, y may be 1.

[0053] The transition metal oxyacid salt may have the formula RyMxOz, wherein R is Na, K, Be, Mg, or Ca; y is 1 or 2; M is W or Mo; x is 1; and z is 4; wherein the transition metal oxyacid salt is optionally a hydrate .

[0054] The transition metal oxyacid salt may have the formula RyMxOz, wherein R is Na, K, Be, Mg, or Ca; y is 1 or 2; M is Mo; x is 1; and z is 4; wherein the transition metal oxyacid salt is optionally a hydrate.

[0055] The transition metal oxyacid salt may have the formula RyMxOz, wherein R is Na, K, or Ca; y is 1 or 2; M is W or Mo; x is 1; and z is 4; wherein the transition metal oxyacid salt is optionally a hydrate.

[0056] The transition metal oxyacid salt may have the formula RyMxOz, wherein R is Na, K, or Ca; y is 1 or 2; M is Mo; x is 1; and z is 4; wherein the transition metal oxyacid salt is optionally a hydrate.

[0057] The transition metal oxyacid salt may be e.g. sodium molybdate or a hydrate thereof, or sodium tungstate or a hydrate thereof.

[0058] The transition metal oxyacid salt may be e.g. sodium molybdate, sodium molybdate dihydrate, sodium tungstate, or sodium tungstate dihydrate.

[0059] Additionally or alternatively, the transition metal oxyacid salt may have the formula R1R2MXOZ, wherein R1and R2are independently selected from Na, K, Li, Rb and Cs; M is W or Mo; x is 1; and z is 4; wherein the transition metal oxyacid salt is optionally a hydrate. The transition metal oxyacid salt may have the formula R1R2MXOZ, wherein R1and R2are independently selected from Na and K; M is W or Mo; x is 1; and z is 4; wherein the transition metal oxyacid salt is optionally a hydrate.

[0060] The transition metal oxyacid salt may have the formula R2R2MXOZ, wherein R1and R2are independently selected from Na and K; M is Mo; x is 1; and z is 4; wherein the transition metal oxyacid salt is optionally a hydrate.

[0061] Additionally or alternatively, transition metal oxyacid salt may have the formula Ry(MxOz)m, wherein R is Al; y is 2; M is W or Mo; x is 1; z is 4; and m is 3; wherein the transition metal oxyacid salt is optionally a hydrate.

[0062] In some embodiments, M in any one of the above formulae is Mo.

[0063] As a skilled person will understand, the transition metal oxyacid salt may be in the form of a hydrate (e.g. a dihydrate or a lower hydrate) , in anhydrous form, or in dissolved form, depending e.g. on the stage of the process in which it is present. For example, in the mixture, it may be in dissolved form. In the ash, it may likely be anhydrous. The purified transition metal oxyacid salt may be e.g. a hydrate (or, if dissolved in water, in dissolved form) .

[0064] The transition metal oxyacid salt may be sodium molybdate or a hydrate thereof. The transition metal oxyacid salt may be sodium molybdate and / or sodium molybdate dihydrate. Sodium molybdate may be well suited as a ( co- ) catalyst in certain reactions. It is also well suited for the present process.

[0065] The mixture may be obtained from various processes, for example processes in which the transition metal oxyacid salt may function as a (co- ) catalyst for e.g. catalyzing retro-aldol reactions, or for processing carbohydrates to oxo chemicals.

[0066] The mixture may be obtained from a process for converting biomass into chemicals / reaction products .

[0067] The mixture may be obtained from a process for converting carbohydrates to chemicals / reaction products. The carbohydrates may comprise e.g. C6 sugars, such as glucose. The carbohydrates may be obtainable or obtained from biomass.

[0068] The mixture may be obtained from a process for producing diols and / or polyols, and the organic compounds comprise at least polyols and degradation products of carbohydrates. In such processes, carbohydrates may be converted to diols and / or polyols. The organic compounds may, at least in some embodiments, also comprise a portion of the diols. Byproducts such as pentane- and butane-diols may also be obtained in such processes; the organic compounds may thus, at least in some embodiments, also comprise pentane diols and / or butane diols. As the transition metal oxyacid salt may be soluble in water and in ethylene glycol, it may be dissolved in the product comprising diols and / or polyols. If the product of the reaction is fractionated e.g. by distillation into at least one light component and a heavy component, the transition metal oxyacid salt may remain in the heavy component. The mixture may thus further comprise heavy polyols (such as compounds having a boiling point above 200 °C under standard conditions, such as sorbitol and glycerol) , humin-like polymers, and other compounds. In some embodiments, the mixture may further comprise sugars.

[0069] The mixture may be obtained from a reaction in which the transition metal oxyacid salt functions as a ( co- ) catalyst . The co-catalyst may be used in a process wherein a carbohydrate fraction is subj ected to a catalytical conversion reaction in which a liquid composition comprising the diols and / or polyols is formed . In other words , the reaction in which the transition metal oxyacid salt functions as a ( co- ) catalyst may be a catalytical conversion reaction in which a liquid composition comprising the diols and / or polyols is formed . The carbohydrate fraction to be used in the catalytical conversion process may be formed for example through a process , wherein a woodbased feedstock, such as wood chips , are firstly pretreated to form a liquid fraction and a fraction comprising solid cellulose particles . The fraction comprising solid cellulose particles may then be subj ected to enzymatic hydrolysis to form a lignin fraction and a carbohydrate fraction, which carbohydrate fraction may then be subj ected to the catalytical conversion reaction to form the liquid composition comprising the diols and / or polyols .

[0070] The wood-based feedstock may be pretreated by at least one of the following : pre-steaming of the wood-based feedstock, subj ecting the wood-based feedstock to an impregnation treatment , and subj ecting the wood-based feedstock to steam explosion . The presteaming of the wood-based feedstock may be carried out with steam having a temperature of 95 - 130 ° C at atmospheric pressure . The impregnation treatment may be carried out with an impregnation liquid selected from water, at least one acid, at least one alkali , at least one alcohol , or any combination or mixture thereof . The pretreatment may comprise subj ecting the wood-based feedstock to steam explosion . In this speci fication, the term " steam explosion" may refer to a process of hemihydrolysis in which the wood-based feedstock is treated in a reactor with steam having a temperature of e . g . 130 - 240 ° C under a pressure of 0.17 - 3.25 MPaG followed by a sudden, explosive decompression of the steam-treated wood-based feedstock that results in the rupture of the fiber structure. The output from the steam explosion may be mixed with a suitable liquid, e.g. water, to form a slurry comprising solid cellulose particles. The fraction comprising solid cellulose particles may be separated from the liquid fraction by a suitable separation method, e.g. by a solid-liquid separation.

[0071] The enzymatic hydrolysis of the fraction comprising solid cellulose particles may be carried out e.g. at a temperature of 30 - 70 °C, or 35 - 65 °C, or 40 - 60 °C, or 45 - 55 °C, or 48 - 53 °C while keeping the pH of the fraction comprising solid cellulose particles e.g. at a pH value of 3.5 - 6.5, or 4.0

[0072] - 6.0, or 4.5 - 5.5, and wherein the enzymatic hydrolysis is allowed to continue for e.g. 20 - 120 h, or 30

[0073] - 90 h, or 40 - 80 h. Enzymatic hydrolysis may result in the formation of a lignin fraction and a carbohydrate fraction. At least one enzyme may be used for carrying out the enzymatic hydrolysis and may be selected from a group consisting of cellulases, hemicellulases, laccases, and lignolytic peroxidases. Cellulases are multi-protein complexes consisting of synergistic enzymes with different specific activities that can be divided into exo- and endocellulases (glucanase) and p-glucosidase (cellobiose) . The enzymes may be either commercially available cellulase mixes or on-site manufactured.

[0074] Also other processes may be used to provide the carbohydrate fraction. Thus, the method as described in the current specification should not be understood to be bound to the above described process for producing the carbohydrate fraction.

[0075] The catalytical conversion reaction of the carbohydrate fraction may comprise subjecting the carbohydrate fraction to catalytical hydrogenolysis. I.e. the carbohydrate fraction may be subjected to catalysts in the presence of hydrogen. A solvent, such as water, may also be present. The catalytical conversion reaction may be carried out in the presence of a catalyst system comprising e.g. a main catalyst and the co-catalyst.

[0076] The main catalyst may comprise an active metal component selected from Group 8, Group 9, or Group 10 of the IUPAC periodic table of elements such as iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, and platinum, or a mixture of at least two of these. As an example may be mentioned that the main catalyst may comprise or consist of a heterogeneous Ni-alloy, such as Raney Nickel. The active metal component of the main catalyst 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 the main catalyst may account for 0.05 - 70 weight- % of the total weight of the catalyst.

[0077] The mixture may be obtained from a process for producing ethylene glycol and propylene glycol, and the organic compounds comprise at least polyols and degradation products of carbohydrates. In such embodiments, the organic compounds may also comprise a portion of the ethylene glycol and the propylene glycol .

[0078] The process may further comprise dissolving the purified transition metal oxyacid salt in water, and optionally diluting it to a predetermined concentration. Thus a solution of the purified transition metal oxyacid salt in water may be recovered. The process may further comprise feeding it back to the reaction.

[0079] Some of the transition metal oxyacid salt is typically lost in the process (regardless of the typically high yield) . Make-up transition metal oxyacid salt, i.e. supplementary transition metal oxyacid salt , may be added to the solution of the transition metal oxyacid salt . In other words , the process may be operated as a loop . Transition metal oxyacid salt lost in the process may be compensated by adding the supplementary transition metal oxyacid salt . The supplementary transition metal oxyacid salt may also be re ferred to as replacement or compensatory transition metal oxyacid salt . For example , it may be added to the dissolving system, i . e . the system in which the melt , or the solidi fied ( and optionally crushed) transition metal oxyacid salt , and optionally the ash are dissolved in water to obtain a solution comprising the collected transition metal oxyacid salt . The supplementary transition metal oxyacid salt is thus then also puri fied in the recrystalli zing process unit .

[0080] A process for producing diols and / or polyols is also disclosed . The process may comprise using a transition metal oxyacid salt as a ( co- ) catalyst in a reaction for producing the diols and / or polyols ; wherein a mixture comprising the transition metal oxyacid salt and organic compounds is withdrawn from the process ; and wherein the process comprises the process for recovering a transition metal oxyacid salt at least partially from the mixture according to one or more embodiments described in this speci fication .

[0081] In other words , the process for producing diols and / or polyols may comprise using a transition metal oxyacid salt as a ( co- ) catalyst in a reaction for producing the diols and / or polyols ; wherein a mixture comprising the transition metal oxyacid salt and organic compounds is withdrawn from the process for producing the diols and / or polyols ; and wherein the process further comprises subj ecting the mixture to a temperature above the melting temperature of the transition metal oxyacid salt , thereby incinerating the organic compounds and obtaining the transition metal oxyacid salt in the form of a melt and optionally of ash; and puri fying the transition metal oxyacid salt from the melt and optionally from the ash by recrystalli zation, thereby recovering the transition metal oxyacid salt at least partially .

[0082] Any features described in this speci fication in the context of the process for recovering the transition metal oxyacid salt at least partially from the mixture may also be understood as being disclosed in the context of the process for producing diols and / or polyols .

[0083] The process may be a process for producing ethylene glycol and propylene glycol , i . e . the diols may comprise or be ethylene glycol and propylene glycol .

[0084] EXAMPLES

[0085] Reference will now be made in detail to various embodiments , an example of which is illustrated in the accompanying drawing .

[0086] The description below discloses some embodiments in such a detail that a person skilled in the art is able to utili ze the embodiments based on the disclosure . Not all steps or features of the embodiments are discussed in detail , as many of the steps or features will be obvious for the person skilled in the art based on this speci fication .

[0087] Figure 1 illustrates schematically a process for recovering a transition metal oxyacid salt at least partially from a mixture 1 as well as a process for producing diols and / or polyols .

[0088] The mixture 1 is obtained from a reaction 2 in which the transition metal oxyacid salt functions as a ( co- ) catalyst . In this exemplary embodiment , the reaction 2 is a catalytic conversion of carbohydrates, but other reactions could be employed instead. A carbohydrate solution 3 is fed into the reaction 2. Further reagents, such as hydrogen 4, may be fed into the reaction. The transition metal oxyacid salt is included in the reaction 2 as the ( co- ) catalyst . Liquid reaction product mixture 5 obtained from the reaction 2 may be subjected to a first separation treatment at 6. In the first separation treatment 6, water and monoalcohols, such as methanol, ethanol, and / or isopropanol, may be separated from the liquid reaction product mixture 5. The dehydrated reaction product mixture 7 obtained from the separation treatment 6 may be subsequently subjected to a second separation treatment 8, in which diols, such as glycols 9 are separated from a heavier fraction, which is considered as the mixture 1. The second separation treatment 8 may comprise or be e.g. a distillation phase, in which lighter products, such as the glycols 9, may be distillated from the heavier fraction considered as the mixture 1. The mixture 1 comprises the transition metal oxyacid salt as well as a heavier fraction from the dehydrated reaction product mixture 7, including e.g. a portion of the glycols present in the dehydrated reaction product mixture 7 and other diols, such as butane-1 , 4-diol ; polyols, such as glycerol, erythritol and / or sorbitol; and various ions, such as chloride ions, sulfate ions, iron ions and / or heavy metal ions.

[0089] The glycols 9 may then proceed to a product workup phase at 10, at which further components contained in the glycol fraction 9, such as monoethylene glycol 11 and monopropylene glycol 12, may be separated from the glycol fraction 9. At the product workup phase 10, the components of the glycol fraction 9 may be separated e.g. by distillation. A further fraction 13 containing e.g. organic components having a lower viscosity than the mixture 1, for example light boil- ing components, may be obtained from the product workup phase 10.

[0090] At adjustment phase 14, the mixture 1 may be adjusted such that it is provided at a desired viscosity. The mixture 1 obtained from the second separation treatment 8, such as distillation, may be cooled at adjustment phase 14 to a desired temperature, for example to a temperature of 80 °C. In other embodiments, the mixture 1 may be preheated to a desired temperature. Additionally or alternatively, an additional substance may be added to the mixture 1, to thereby adjust its viscosity. For example, water may be added to the mixture 1 (not shown for clarity) . As another example, at least a portion of the further fraction 13 may be added to the mixture 1 at or before the adjustment phase 14 to thereby lower its viscosity. After the at least the portion of the further fraction 13 is added to the mixture 1, the temperature of the mixture 1 may be adjusted e.g. by cooling.

[0091] The mixture 1 having a desired viscosity from the adjustment phase 14 may be fed to a furnace 15. The viscosity of the mixture 1 may be suitable for pumping the mixture 1 to the furnace 15 and for atomizing the mixture 1 in a burner nozzle for feeding it to the furnace 15 after the viscosity has been adjusted. In some embodiments, there may not be a need to adjust the viscosity of the mixture 1; instead, it may be directly fed to the furnace 15. Thus the adjustment phase 14 may be omitted.

[0092] The furnace 15 may be e.g. a salt recovery furnace. In the furnace 15, the mixture 1 may be subjected to a temperature above the melting temperature of the transition metal oxyacid salt, thereby incinerating the organic compounds. In other words, the organic compounds are burnt at the temperature above the melting temperature of the transition metal oxyacid salt. At such a temperature, the transition metal oxyacid salt melts, producing a melt 16. The furnace 15 may e.g. comprise a combustion chamber having a cooling jacket (not shown in this schematic illustration) . The melt 16 may run down a wall of the combustion chamber and be collected at the bottom of the combustion chamber. The melt 16 may be collected from the furnace e.g. in a continuous manner. In other embodiments, the melt 16 may be collected in batches. The melt 16 may then be cooled, solidified and crushed to solidified and crushed obtain transition metal oxyacid salt. The melt 16 may be collected e.g. in a water-cooled screw conveyor, which cools the hot melt 16 such that it is solidified. The solidified transition metal oxyacid salt from the melt 16 may then be sent e.g. to a lump breaker, which may crush lumps of the solidified transition metal oxyacid salt 16 to smaller and more easily dissolvable particles.

[0093] A portion of the transition metal oxyacid salt may be collected as ash 17, for example fly ash, from the furnace 15. Such fly ash 17 may be collected from flue gas emitted by the furnace, for example by filtering .

[0094] The transition metal oxyacid salt from the solidified and crushed transition metal oxyacid salt 16 and optionally from the ash 17 may then be purified by recrystallization. The solidified and crushed transition metal oxyacid salt 16 and the ash 17 may be fed to a recrystallizing unit comprising a dissolving system 18 comprising e.g. a tank, in which the solidified and crushed transition metal oxyacid salt 16 and the ash 17 are dissolved in water, thereby obtaining a solution 19 comprising the transition metal oxyacid salt that has been collected from the furnace 15. In the dissolving system 18, the solidified and crushed transition metal oxyacid salt 16 and the ash 17 may be mixed with and dissolve in the water. The dissolving system 18 may also operate as a buffering system between the furnace 15 and a purification stage 20. It may, additionally or alternatively, be possible to add the hot melt 16 directly from the furnace 15 to water in the dissolving system 18, in which the hot melt 16 may cool, solidify and dissolve.

[0095] The solution 19 may be an almost saturated solution, comprising e.g. about 40 % (w / w) of the transition metal oxyacid salt. The recrystallizing unit may further comprise the purification, i.e. recrystallization, stage 20, at which the transition metal oxyacid salt may be recrystallized. The purification stage 20 may comprise e.g. a filter in which the solution 19 comprising the transition metal oxyacid salt may be filtered to remove insoluble matter prior to the recrystallization.

[0096] The transition metal oxyacid salt may be recrystallized at the purification stage 20 at least partially e.g. by evaporative crystallization, for example at an operating pressure of at least 0.1 kPaA and / or until a mass ratio of the transition metal oxyacid salt and the water in the solution 19 is in the range of 0.05 - 10:1. The recrystallized transition metal oxyacid salt may be washed with a solvent comprising water. The washing may be done so that the dissolution of the crystals is minimized. Inorganic impurities 23 may thus be removed at the purification stage 20.

[0097] The recrystallized transition metal oxyacid salt is thus recovered at least partially in purified form 21.

[0098] The recrystallizing unit may further comprise a second purification, i.e. recrystallization, stage (not shown for simplicity) , at which the recrystallization of the transition metal oxyacid salt may be repeated. I f desired, supplementary transition metal oxyacid salt 22 may be added to the dissolving system 18 .

[0099] At the puri fication stage 20 , the puri fied transition metal oxyacid salt 21 may be dissolved in water, optionally diluting it to a predetermined concentration . It may then be fed back to the reaction 2 .

[0100] It is obvious to a person skil led in the art that with the advancement of technology, the basic idea may be implemented in various ways . The embodiments are thus not limited to the examples described above ; instead they may vary within the scope of the claims .

[0101] The embodiments described hereinbefore may be used in any combination with each other . Several of the embodiments may be combined together to form a further embodiment . A process , a product , or a use, disclosed herein, may comprise at least one of the embodiments described hereinbefore . It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments . The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages . It will further be understood that reference to ' an ' item refers to one or more of those items . The term " comprising" or " including" is used in this speci fication to mean including the feature ( s ) or act ( s ) followed thereafter, without excluding the presence of one or more additional features or acts .

Claims

25CLAIMS1. A process for recovering a transition metal oxyacid salt at least partially from a mixture, the mixture comprising the transition metal oxyacid salt and organic compounds, wherein the process comprises subjecting the mixture to a temperature above the melting temperature of the transition metal oxyacid salt, thereby incinerating the organic compounds and obtaining the transition metal oxyacid salt in the form of a melt and optionally of ash; and purifying the transition metal oxyacid salt from the melt and optionally from the ash by recrystallization, thereby recovering the transition metal oxyacid salt at least partially.

2. The process according to claim 1, wherein the transition metal oxyacid salt has the formula RyMxOz, wherein R is Li, Na, K, Rb, Cs, Mg, Ca, Sr, or Ba; y is 1 or 2; M is W or Mo; x is 1; and z is 4; or the formula Ry(MxOz)m, wherein R is Al; y is 2; M is W or Mo; x is 1; z is 4; and m is 3; or the formula R1R2MXOZ, wherein R1and R2are independently selected from Na, K, Li, Rb and Cs; M is W or Mo; x is 1; and z is 4; wherein the transition metal oxyacid salt is optionally a hydrate.

3. The process according to claim 1 or 2, wherein the transition metal oxyacid salt is sodium molybdate and / or a hydrate thereof, or sodium tungstate and / or a hydrate thereof.

4. The process according to any one of claims 1 - 3, wherein the transition metal oxyacid salt is sodium molybdate and / or a hydrate thereof.

5. The process according to any one of claims 1 - 4, wherein the mixture is obtained from a process for producing diols and / or polyols, and the organiccompounds comprise at least polyols and degradation products of carbohydrates.

6. The process according to any one of claims 1 - 5, wherein the mixture is obtained from a reaction in which the transition metal oxyacid salt functions as a ( co- ) catalyst .

7. The process according to claim 6, wherein the method further comprises dissolving the purified transition metal oxyacid salt in water, optionally diluting it to a predetermined concentration, and feeding it back to the reaction.

8. The process according to claim 6 or 7, wherein the melt is allowed to solidify, and the solidified transition metal oxyacid salt and optionally the ash is / are dissolved in water to obtain a solution of the transition metal oxyacid salt for the recrystallization; and wherein supplementary transition metal oxyacid salt is added to the solution of the transition metal oxyacid salt.

9. The process according to any one of claims 1 - 8, wherein the mixture is provided at a desired viscosity, optionally by adjusting its temperature, prior to subjecting the mixture to the temperature above the melting temperature of the transition metal oxyacid salt.

10. The process according to claim 9, wherein the mixture is provided at the desired viscosity by adjusting the temperature of the mixture to a temperature in the range of 50 - 200 °C.

11. The process according to any one of claims 1 - 10, wherein the mixture is subjected to the temperature above the melting temperature of the transition metal oxyacid salt in a furnace.

12. The process according to claim 11, wherein the melt is collected from the furnace in a continuous manner.

13. The process according to any one of claims 1 - 12, wherein the melt is allowed to solidify to obtain a solidified transition metal oxyacid salt, and the solidified transition metal oxyacid salt and optionally the ash is / are dissolved in water to obtain a solution of the transition metal oxyacid salt for the recrystallization, and the process further comprises filtering the solution of the transition metal oxyacid salt prior to the recrystallization.

14. The process according to any one of claims 1 - 13, wherein the transition metal oxyacid salt is recrystallized at least partially by evaporative crystallization, optionally at an operating pressure of at least 0.1 kPaA until the mass ratio of the transition metal oxyacid salt and the water in the solution is in the range of 0.05 - 10:1.

15. The process according to any one of claims 11 - 14, wherein excess heat generated by the furnace is used to generate steam.

16. A process for producing diols and / or polyols, the process comprising using a transition metal oxyacid salt as a ( co- ) catalyst in a reaction for producing the diols and / or polyols; wherein a mixture comprising the transition metal oxyacid salt and organic compounds is withdrawn from the process; and wherein the process comprises the process for recovering a transition metal oxyacid salt at least partially from the mixture as defined in any one of claims 1 - 15.

17. A recycled transition metal oxyacid salt (co-) catalyst, wherein the recycled transition metal oxyacid salt ( co- ) catalyst comprises 400 ppm or less of chloride (Cl“) ions; 400 ppm or less of sulphate (SO4-) ions; 200 ppm or less of aluminate (AlCy-) ions; and / or 400 ppm or less of carbonate (COa-) ions.

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