EA040952B1 - METHOD FOR PRODUCING ETHYLENE GLYCOL - Google Patents

Description

The technical field to which the invention belongs

The invention relates to a method for the production of ethylene glycol.

State of the art

Alkylene glycols, such as ethylene glycol, are mass-produced chemicals that can be used in a variety of applications. They can be used as a monomer in the preparation of polyesters such as poly(ethylene terephthalate), poly(ethylene naphthenate) or poly(ethylene furandicarboxylate), but ethylene glycol can also be used in heat transfer media and antifreeze formulations.

Recently, there has been an increasing effort to produce alkylene glycols from renewable resources such as carbohydrates. By providing alkylene glycols such as ethylene glycol from renewable resources, dependence on fossil fuels is advantageously reduced.

CN 102643165 describes a process for the production of ethylene glycol and 1,2-propylene glycol by continuous hydrocracking of sugars. The method is carried out in a reactor using catalytically active tungsten particles. The liquid stream leaving the reactor is divided into two parts. One part of the liquid stream leaving the reactor is charged to the distillation system, and the other part of the liquid stream leaving the reactor is returned directly to the reactor to dilute the reaction liquid. In the distillation system, polyhydric heavy ends and unreacted saccharide are obtained, which are returned to the reactor for subsequent hydrocracking. Thus, the dissolved components of tungsten in the heavy fractions are recovered and recycled to the reaction.

Also WO 2016/114658 describes a process for producing ethylene glycol from a carbohydrate source. The carbohydrate source is reacted with hydrogen in the presence of a diluent and a catalyst system containing a tungsten compound and at least one hydrogenolysis metal selected from Groups 8, 9, or 10 of the Periodic Table of the Elements. WO 2016/114658 shows that higher polyols such as glycerol, erythritol or sorbitol are generally formed as by-products in the process for producing ethylene glycol from carbohydrates. Optionally, a polyol such as glycerol, xylitol, sorbitol or erythritol may be added to the diluent. They can also be used as butylene glycol scavenger and then recycled to the process. The process can be carried out under continuous operation conditions, where the feed contains at least a diluent (containing alkylene glycol) and a source of carbohydrate; and where such feedstock is passed through a plug flow reactor in the presence of hydrogen as well as in the presence of a catalyst system.

Although higher polyols such as sorbitol can be recycled as described in WO 2016/114658, significant recycling of such higher polyols is undesirable. Under the conditions of the carbohydrate source conversion reactor, higher polyols such as sorbitol cannot be completely converted. As a result, the concentration of such higher polyols will increase, making the process less suitable for continuous operation.

WO 2015028398 describes a process for producing ethylene glycol and 1,2-propylene glycol from a feedstock containing one or more saccharides, wherein the process comprises the steps of: i) feeding the feedstock and hydrogen into a first reactor, where the first reactor is operated with stirring; ii) interaction of the specified source material and hydrogen in the first reactor in the presence of a solvent and a catalyst system; iii) continuously removing the first reactor product stream from the first reactor; iv) feeding at least a portion of the product stream of the first reactor to the second reactor, where the reactor operates essentially in the mode of the displacement flow; and v) further reacting the product stream of the first reactor with hydrogen in the presence of a solvent and optionally a catalyst system in the second reactor. The catalyst system may contain one or more materials selected from transition metals from groups 8, 9 or 10 or their compounds and one or more materials selected from tungsten, molybdenum and their compounds and complexes. In one embodiment, a homogeneous catalyst system is used in the first reactor, which may remain in the product stream of the first reactor and be fed to the second reactor in this stream.

In WO 2015028398 it is desired to obtain complete conversion of the starting material and/or any intermediates and it is desired to reduce the formation of by-products. The reduction in the formation of by-products, however, is not shown in the examples. On the contrary, as shown in the examples of WO 2015028398, although in examples 2 and 3 the formation of the desired product, mono-ethylene glycol, is increased by tens of percent, the formation of the by-product 1,2 butanediol is increased by hundreds of percent. The formation of by-product higher polyols such as glycerol, erythritol or sorbitol has not been determined but may also be expected to increase under the circumstances.

It would be an advance in the art to provide an improved process for making ethylene glycol that avoids the accumulation of higher polyols (also referred to as heavy polyols), such as sorbitol, in the process. Furthermore, it would be an advance in the art if the accumulation of such heavy polyols could be prevented in an economically attractive manner.

The essence of the invention

Such a method was obtained using the method in accordance with this invention. Therefore, the present invention provides a process for the production of ethylene glycol, comprising the steps of:

(i) supplying to the first reactor a source of carbohydrate, solvent, hydrogen, a first heterogeneous catalyst, where the first heterogeneous catalyst contains one or more transition metals from groups 8, 9 and 10 of the Periodic Table of the Elements, and a homogeneous catalyst, where the homogeneous catalyst contains tungsten;

(ii) reacting in a first reactor at a temperature in the range of 170° C. or more to 270° C. or less of at least a portion of the carbohydrate source in the presence of hydrogen, a solvent, a first heterogeneous catalyst, and a homogeneous catalyst;

(iii) removing the first reactor product stream from the first reactor and separating at least one ethylene glycol rich fraction from such first reactor product stream; and one fraction rich in sorbitol containing a concentrated homogeneous catalyst;

(iv) feeding into the second reactor hydrogen and at least a portion of the sorbitol-rich fraction containing the concentrated homogeneous catalyst;

(v) reacting in a second reactor at a temperature of 200° C. or more to 300° C. or less of at least a portion of the sorbitol-rich fraction containing the concentrated homogeneous catalyst, wherein the second heterogeneous catalyst contains one or more transition metals from Groups 8, 9, and 10 Periodic system of elements;

(vi) removing the second reactor product stream from the second reactor.

Step (vi) may further advantageously comprise optionally recycling at least a portion of the second reactor product stream to the first reactor.

As stated in WO 2016114658, higher polyols such as glycerol, erythritol or sorbitol are formed as by-products in the first reactor. These higher polyols have high boiling points (i.e., boiling points above 250°C at atmospheric pressure of 0.1 MPa (megapascals)) and are also referred to here as heavy polyols. A polyol is here understood to mean an organic compound containing a plurality, three or more sufficient, of hydroxyl groups. A particularly interesting by-product heavy polyol is sorbitol.

As explained above, simply recycling such heavy polyols will slowly increase the concentration of heavy polyols in the reactor product stream, making the process less suitable for continuous operation. As shown in WO 2015028398, simply further reacting the reactor product stream from the first reactor to another second reactor does not solve the problem either.

The high solubility of a homogeneous catalyst in heavy polyols also makes it difficult to separate such a homogeneous catalyst from the reactor product stream by settling and/or filtration. Removal of heavy polyols by vacuum distillation was also found to be difficult.

By separating heavy polyols and converting such heavy polyols to lower boiling point products in a separate second reactor, a stream can be obtained containing a homogeneous catalyst dissolved in a mixture containing alkylene glycols, other diols and/or other polyols, which is very suitable for recycling to first reactor. A homogeneous catalyst can also be more easily separated from such a mixture by evaporation, distillation, precipitation and/or filtration.

The inventors have surprisingly found that conversion of heavy polyols becomes possible in the second reactor if a catalyst system with higher concentrations of homogeneous catalyst is used in such second reactor than in the first reactor.

Advantageously, in the process according to the invention, the by-product sorbitol formed in the first reactor can be concentrated in a sorbitol-rich fraction also containing a concentrated homogeneous catalyst. This sorbitol-rich fraction can then advantageously be sent, together with the concentrated homogeneous catalyst, to a second reactor, where the sorbitol can be at least partially converted to low-boiling products.

Brief description of the drawings

The invention is illustrated in the following drawing.

The figure shows an example of a method according to the present invention.

Detailed description of the invention

Stage (i) includes feeding into the first reactor a source of carbohydrate, solvent, hydrogen, a first heterogeneous catalyst, where the first heterogeneous catalyst contains one or more transition metals from groups 8, 9 and 10 of the Periodic system of elements, and a homogeneous catalyst, where the homogeneous catalyst contains tungsten .

By carbohydrate source is meant here any carbohydrate source. The carbohydrate source may be selected from a variety of sources. Preferably, the carbohydrate source contains one or more carbohydrates selected from the group consisting of polysaccharides, oligosaccharides, disaccharides, monosaccharides, and mixtures thereof.

Suitable examples may include preferably renewable carbohydrate sources such as cellulose, hemicellulose, starch, sugars such as sucrose, mannose, arabinose, fructose, glucose, and mixtures thereof. Carbohydrate sources that contain the above carbohydrates may include

- 2 040952 dextrose syrups, maltose syrups, sucrose syrups, glucose syrups, crystalline sucrose, crystalline glucose, wheat starch, corn starch, potato starch, cassava starch and other carbohydrate-containing streams, such as paper pulp streams, wood waste, paper waste, agricultural waste, pulp residues recovered from household waste, paper, cardboard, sugarcane, sugar beets, wheat, rye, oats, corn, rice, potatoes, cassava, other crops, and combinations thereof. These streams may require pre-treatment to extract carbohydrates (eg wet milling in the case of corn) or to remove components that interfere with this process such as major fillers (eg removal of calcium carbonate in paper waste). Thus, natural sources can be used in the process according to the invention, but it can also be used to improve and beneficially recycle waste. Preferably, the carbohydrates in the carbohydrate source are selected from the group consisting of cellulose, hemicellulose, starch, glucose, sucrose, glucose oligomers, and combinations thereof. Since cellulose causes problems not found in other carbohydrate sources, the carbohydrate source is most preferably selected from the group consisting of starch, hemicellulose and hemicellulose sugars, glucose and mixtures thereof. Most preferably, the carbohydrate source contains or consists of glucose, fructose, sucrose, or a combination thereof.

Accordingly, the carbohydrate source may be fed into the first reactor along with at least a portion of the solvent. More preferably, the carbohydrate source is partially or completely dissolved in such a solvent. Preferences for such a solvent are presented below. The solvent may be, for example, an aqueous medium, an organic medium including alkylene glycols, or a mixture containing water, diols and/or other polyols. Many carbohydrates are soluble in water or mixtures containing water, diols and/or other polyols. The carbohydrate source may also be fed to the first reactor in the form of a slurry. Examples of such suspensions include aqueous mixtures of water and hemicellulose, hemicellulose sugars, glucose and/or starch.

This method advantageously allows a very concentrated feed containing a source of carbohydrate to be fed into the first reactor. With the use of such concentrated raw materials, the economy of the process increases. Such feedstock may suitably contain a carbohydrate source and a solvent such as water and/or diols and/or other polyols.

Preferably, the carbohydrate source is fed to the first reactor in a feed stream containing a carbohydrate source and a solvent, where such feed stream contains from 1.0 wt.% (mass percent) or more, preferably 10.0 wt.% or more, and more preferably 20.0 wt.% or more to 90.0 wt.% or less, preferably 70.0 wt.% or less, and more preferably 50.0 wt.% or less, of a carbohydrate source based on total weight of carbohydrate source and solvent. A feed stream containing a source of carbohydrate in the specified concentration range can be easily transported. The feed stream may also consist of only (100% by weight) carbohydrate source. For practical purposes, the carbohydrate source may be supplied to the first reactor by a feed stream containing a carbohydrate source and a solvent, where such a feed stream contains from 2.0 wt.% or more, more preferably 10.0 wt.% or more, to 50.0 wt. .% or less, more preferably 30.0 wt.% or less of the carbohydrate source relative to the total weight of the carbohydrate source and solvent. Most preferably, a feed stream containing or consisting of a source of carbohydrate and a solvent is fed to the first reactor, where such feed stream contains from 20.0 wt.% or more to 50.0 wt.% or less, more preferably 30.0 wt.% or less of the source of carbohydrate relative to the total weight of the source of carbohydrate and solvent. It is believed that such a feed stream containing 20.0% by weight or more of a carbohydrate source may make the process more economically attractive. Such a solvent may contain any of the solvents mentioned below, but preferably water. Most preferably, the carbohydrate source is fed to the first reactor in a feed stream containing the carbohydrate source and water, where such feed stream contains from 2.0 wt.% or more to 30.0 wt.% or less of the carbohydrate source relative to the total weight of the source carbohydrate and water.

Preferably, the carbohydrate source is continuously or intermittently added to the first reactor. Preferably, the carbohydrate source is fed into the first reactor under an inert gas such as nitrogen.

Preferably, a portion of the solvent is fed into at least a portion of the second reactor product stream recycled from step (vi). Such at least a portion of the second reactor product stream preferably contains a homogeneous catalyst dissolved in a solvent. Such a solvent may preferably contain conversion products of heavy polyols, such as alkylene glycols and/or other diols. As explained below, these alkylene glycols and/or other diols can be very suitable solvents.

The solvent may be supplied as part of the feed stream containing the carbohydrate source as described above. It is also possible to supply the solvent to the first reactor separately or independently of the carbohydrate source and/or product stream of the second reactor.

Preferably, a feed stream containing a source of carbohydrate and a solvent is used. The concentration of the carbohydrate source in such a feed stream can be appropriately adjusted

- 3 040952 so as to supply a sufficient amount of solvent to the first reactor.

Water can be a very suitable solvent since most carbohydrates are water soluble. Such water may optionally be mixed with organic solvents, which has a favorable effect on the solubility of any reactants or provides other advantages.

Therefore, the solvent is preferably selected from the group consisting of water and organic solvents such as diols and/or other polyols and mixtures thereof. As appropriate, the solvent may be a mixture of water and optionally one or more of the above organic solvents. Alkanols are the preferred organic solvents. Such alkanols may be monoalkanols such as methanol, ethanol, propanol, butanol, and mixtures thereof. For the process according to the invention, however, such light monoalkanols are less preferred. The alkanol may also be a water-miscible diol or other polyol, such as ethylene glycol, propylene glycol, butylene glycol, glycerol, xylitol, sorbitol or erythritol. A diol is here understood to mean an organic compound containing two hydroxyl groups. Preferably, the solvent contains an alkylene glycol. Examples of preferred alkylene glycols include ethylene glycol, propylene glycol, butylene glycol, and mixtures thereof. The use of alkylene glycol is particularly preferred since diols and/or polyols, including alkylene glycols, have been found to help dissolve the tungsten or tungsten compound in the solvent, thereby contributing to the catalytic activity of the tungsten or tungsten compound. It has also been found that the selectivity of the reaction to alkylene glycols is improved by using an alkylene glycol as a component in the solvent. Without wishing to be bound by any theory, it is believed that tungsten forms complexes with alkylene glycol while conversion to by-products is reduced. Moreover, the use of alkylene glycol as a solvent does not imply the introduction of a foreign reagent into the reaction mixture, which is also an advantage. Preferably, the solvent contains or consists of water, one or more alkylene glycols, one or more alkanols, optionally one or more heavy polyols, or a mixture of two or more of them. Most preferably, the solvent contains a mixture of water, one or more alkylene glycols, and optionally one or more heavy polyols.

Preferably, the solvent is continuously or intermittently added to the first reactor. At the same time, part of the solvent can be continuously or intermittently withdrawn from the first reactor.

The hydrogen may be supplied as substantially pure hydrogen. Alternatively, the hydrogen may be supplied in the form of a mixture of hydrogen and an inert gas. The inert gas may suitably be selected from nitrogen, argon, helium, neon, and mixtures thereof. The volume ratio of hydrogen to inert gas can vary over a wide range. Properly, the volume ratio is not very low, since the reaction proceeds well at a sufficiently high hydrogen partial pressure. Therefore, the volume ratio of hydrogen to inert gas can be from 1:1 to 1:0.01. More preferably, only hydrogen is used as the gas in the process according to the invention.

The total pressure during the reaction includes the vapor pressure of the solvent and reactants at the applied temperature and pressure, in addition to the partial pressure of hydrogen and, if present, the partial pressure of any inert gas. Preferred total pressures are shown below.

Hydrogen may be appropriately supplied through a dip tube, such as a dip tube adjacent to the stirrer, or through a distributor, such as an aerator, to the first reactor. Through such a dip tube or distributor, and optionally through one or more stirring mechanisms, hydrogen can be dissolved in the reaction mixture. Preferably, hydrogen is continuously or intermittently added to the first reactor.

In addition to the source of carbohydrate, solvent and hydrogen, a homogeneous catalyst is fed into the first reactor, where the homogeneous catalyst contains tungsten, and a heterogeneous catalyst, where the heterogeneous catalyst contains one or more transition metals from groups 8, 9 and 10 of the Periodic Table of the Elements.

A homogeneous catalyst and a heterogeneous catalyst together are also referred to as a catalyst system.

A homogeneous catalyst is also referred to herein as a tungsten-containing homogeneous catalyst.

The tungsten may be present as elemental tungsten or as a tungsten compound. Such a tungsten compound can be, for example, tungstic acid or tungstate. Therefore, a homogeneous catalyst may suitably contain one or more tungsten compounds. The tungsten or tungsten compound(s) can be properly dissolved in the reaction mixture. Preferably, tungsten has an oxidation state of at least +2. More preferably, tungsten has an oxidation state of +5 or +6. When dissolved in the reaction mixture, the dissolved tungsten or tungsten compound may form complexes with (other) components of the solvent and/or reaction mixture.

The homogeneous catalyst fed to the first reactor may be fresh homogeneous catalyst or recycled homogeneous catalyst originating from, for example, the product stream of the second reactor. Fresh homogeneous catalyst is also referred to here as straight run homogeneous

- 4 040952 catalyst. Such a straight-run homogeneous catalyst is preferably selected from the group consisting of tungstic acid (H ₂ WO ₄ ) and tungstate compounds such as tungsten salts, for example containing at least one Group 1 or 2 element, such as sodium tungstate (Na ₂ WO ₄ ) or potassium tungstate (K ₂ WO ₄ ) or, for example, containing ammonium tungstate, and combinations of one or more of them.

Recycled homogeneous catalyst may simply be referred to as recycled homogeneous catalyst. Preferably, the homogeneous catalyst fed to the first reactor in step (i) comprises recycled homogeneous catalyst or a combination of straight run homogeneous catalyst and recycled homogeneous catalyst. The homogeneous catalyst fed to the reactor according to the invention may, for example, contain or consist of recycled tungsten particles recovered directly or indirectly (eg by distillation) from the reactor effluent.

Any recycled homogeneous catalyst may contain tungsten as a complex with solvent components in which such homogeneous catalyst may be dissolved. Therefore, the recycled homogeneous catalyst may suitably contain tungsten in the form derived from the precursor tungsten compound, as originally envisaged.

Preferably, the homogeneous catalyst contains a tungsten compound or tungsten derived from a tungsten compound, where such tungsten compound is selected from the group consisting of tungstic acid (H ₂ WO ₄ ), tungsten bronze (present as H _x WO ₃ or M _x WO ₃ , where x is a variable less than 1 (<1) and M is a metal, such as an alkali or alkaline earth metal), ammonium tungstate, ammonium metatungstate, ammonium paratungstate, tungstate compounds containing at least one Group 1 or 2 element, metatungstate compounds containing at least one Group 1 or 2 element, paratungstate compounds containing at least one Group 1 or 2 element, tungsten oxide (WO ₃ ), tungsten heteropoly compounds, and combinations thereof. Tungstic acid (H ₂ WO ₄ ), tungsten bronze (H _x WO ₃ ) and tungstate compounds containing at least one Group 1 or 2 element, such as sodium tungstate (Na ₂ WO ₄ ) or potassium tungstate (K ₂ WO ₄ ) are preferred. Most preferably, the homogeneous catalyst contains a tungsten compound or tungsten derived from a tungsten compound, where such tungsten compound is sodium tungstate and/or tungstic acid and/or tungsten bronze.

It has been found that the catalytic activity of the tungsten or tungsten compound is preferably increased if the tungsten or, properly, the tungsten compound is dissolved. Preferably, the homogeneous catalyst is continuously or intermittently added to the first reactor. Preferably, such continuously or intermittently fed homogeneous catalyst contains tungsten which has an oxidation state of at least +2. Preferably, the homogeneous catalyst is selected from the group consisting of tungstic acid (H2WO4), tungsten bronze (HxWO3), sodium tungstate, dissolved tungstate ion, dissolved metatungstate ion, and dissolved paratungstate ion.

Since tungsten can be present in such a variety of forms, tungsten compounds are also referred to here as tungsten particles. Under the particles of tungsten here understand any compound containing the element tungsten in any form or form or oxidation state.

Preferably, the homogeneous catalyst is dissolved in a solvent. Such a solvent may be any solvent described above. The composition of the solvent may vary during the process. While the reaction is carried out in the first reactor, the solvent may be formed by the reaction mixture itself.

The amount of tungsten fed into the first reactor is preferably such that its concentration in the reactor remains substantially constant. By substantially constant here is meant that the difference between the highest and the lowest amount of tungsten is not more than 10% of the average amount of tungsten in the reactor. Preferably, the process according to the invention is a continuous or semi-continuous process. Preferably, the tungsten compound is continuously or intermittently added to the first reactor. At the same time, a portion of the tungsten compound may be continuously or intermittently withdrawn from the first reactor, as appropriate through the product stream of the first reactor. Although it is possible to add tungsten intermittently, it is preferable to provide continuous addition of tungsten to the first reactor. More preferably, the tungsten compound is added to the reactor as a solution of the tungsten compound in a solvent.

Preferably, the concentration of the tungsten compound in the reaction mixture during the reaction ranges from 0.01 wt.% or more (corresponding to 100 mass parts per million (wt.ppm)) to 1.0 wt.% or less of tungsten (calculated as metallic tungsten) relative to the total weight of the reaction mixture. More preferably, the concentration of the tungsten compound in the reaction mixture during the reaction varies from 0.01 wt.% (corresponding to 100 mass parts per million (wt.ppm)), preferably 0.05 wt.% or more, to 0, 5 wt.% or less tungsten (calculated as metallic tungsten) relative to the total weight of the reaction mixture.

- 5 040952

The first heterogeneous catalyst and the second heterogeneous catalyst each independently contain one or more transition metals from groups 8, 9 and 10 of the Periodic Table of the Elements. As shown in WO 2016/114658, the transition metals can be selected from a wide variety of transition metals. Preferably, one or more transition metals are selected from the group consisting of Cu, Fe, Ni, Co, Pt, Pd, Ru, Rh, Ir, Os, and combinations thereof. More preferably, one or more transition metals are selected from the group consisting of Ni, Pd, Pt, Ru, Rh, Ir, and combinations thereof. Nickel, ruthenium and combinations thereof are most preferred. These metals have been found to give good yields. The transition metal may suitably be present in its metallic form, or as its hydride or oxide, or as another compound. It is also possible for the transition metal to be present in a partially tungsten form. Partially tungsten transition metal is here understood to mean a transition metal which is partially covered by deposited tungsten particles.

The first heterogeneous catalyst, respectively the second heterogeneous catalyst, each independently preferably contains one or more transition metals from groups 8, 9 and 10 of the Periodic Table of the Elements, on a carrier support. The carrier may be selected from a wide range of known carriers. Suitable carriers include activated carbon (also called active carbon), silica, zirconia, alumina, silica-alumina, titanium dioxide, niobium oxide, iron oxide, tin oxide, zinc oxide, silica-zirconia, zeolite aluminosilicates , titanosilicates, magnesium oxide, silicon carbide, clays and combinations thereof. By activated carbon is meant here an amorphous form of carbon with a surface area of at least 800 m ² /g. Such activated carbon properly has a porous structure. The most preferred carriers are activated carbon, silica, silica-alumina and alumina. Even more preferably, the catalyst contains ruthenium and/or nickel as the transition metal and activated carbon as the support. Most preferably, the first heterogeneous catalyst comprises ruthenium and/or nickel on an activated carbon support and/or the second heterogeneous catalyst comprises ruthenium and/or nickel on an activated carbon support. Most preferably, the heterogeneous catalyst contains ruthenium, preferably on an activated carbon support.

As explained in more detail below, the first heterogeneous catalyst and/or the second heterogeneous catalyst, for example, may be present in the form of an emulsion, suspension or fixed bed. Preferably, the first heterogeneous catalyst and/or the second heterogeneous catalyst each independently contains 1.0 wt.% or more to 50.0 wt.% or less of the transition metal, more preferably 2.0 wt.% or more, even more preferably 5 .0 wt.% or more, up to 50.0 wt.% or less, more preferably 20.0 wt.% or less of the transition metal in relation to the total weight of the transition metal and support. If the applied feed stream to the first reactor contains 20.0 wt.% or more of a carbohydrate source relative to the total weight of the carbohydrate source and solvent, it is preferable to use a first heterogeneous catalyst containing from 5.0 wt.% or more, more preferably 10.0 wt.% or more, up to 50.0 wt.% or less, more preferably 20.0 wt.% or less of the transition metal in relation to the total weight of the transition metal and support. It is believed that this higher transition metal loading may advantageously promote the conversion of a feed stream with a higher concentration of carbohydrate source.

It is possible for the first heterogeneous catalyst to contain more than one metal. Suitably, the first heterogeneous catalyst may contain at least one noble metal selected from the group consisting of Pd, Pt, Ru, Rh and Ir, in combination with a transition metal selected from the group of transition metals from groups 8, 9 or 10 of the Periodic element systems. The first heterogeneous catalyst, for example, may contain a combination of metals, such as Ni/Ir, Ni/Pt, Ni/Pd, Ni/Ru, Ru/Ir, Ru/Pt or Ru/Pd.

Moreover, as explained in more detail below, during the reaction, tungsten particles may be deposited on the first heterogeneous catalyst and/or the second heterogeneous catalyst. Therefore, at least a portion of the first heterogeneous catalyst and/or at least a portion of the second heterogeneous catalyst may contain tungsten in addition to one or more transition metal from groups 8, 9 and 10 of the Periodic Table of the Elements.

Preferably, the process according to the invention is a continuous or semi-continuous process. Preferably, the slurry of the first heterogeneous catalyst, for example together with a solvent, is intermittently or continuously added to the first reactor.

During step (ii), at least a portion of the transition metal may be tungsten. Tungsten is here understood to mean that such a transition metal can be coated with deposited tungsten particles. Any partially or fully tungsten heterogeneous catalyst can be partially recovered and recycled. Therefore, the first heterogeneous catalyst fed to the first reactor may or may not contain any tungsten transition metal.

Preferably, such a suspension of the first heterogeneous catalyst contains from 5 wt.% or

- 6 040952 more to 90 wt.% or less, more preferably 70 wt.% or less, most preferably 50 wt.% or less of a heterogeneous catalyst in relation to the total mass of such a suspension. Preferably, such a slurry is a slurry of the heterogeneous catalyst in water and/or an alkylene glycol, for example ethylene glycol and/or propylene glycol and/or butylene glycol and/or a polyol.

The weight ratio of total tungsten particles (calculated based on metal) fed into the first reactor to transition metal (calculated based on metal) fed to the first reactor can vary over a wide range. The mass ratio of the mass of tungsten to the total mass of transition metal, all calculated on the basis of the metal supplied to the first reactor, is preferably 1:3000 or more to 50:1 or less (mass ratio of tungsten metal:transition metal (w/w) ). More preferably, the mass ratio of the mass of tungsten to the total mass of transition metal, all calculated on the basis of the metal supplied to the first reactor, is preferably 1:200 or more to 50:1 or less (mass ratio of tungsten metal:transition metal (wt./ wt.)).

The weight ratio of total tungsten particles (calculated based on metal) present in the first reactor to transition metal (calculated based on metal) present in the first reactor can also vary within a significant range. The mass ratio of the mass of tungsten to the total mass of transition metal, all calculated on the basis of the metal present in the first reactor, preferably ranges from 1:3000 or more to 50:1 or less (mass ratio of transition metal tungsten metal (w/w) ). More preferably, the mass ratio of the mass of tungsten to the total mass of transition metal, all calculated based on the metal present in the first reactor, preferably ranges from 1:200 or more to 50:1 or less (mass ratio of tungsten metal:transition metal (wt. /wt)).

More preferably, the molar ratio of moles of tungsten to total moles of transition metal, all calculated as the metal present in the first reactor, is preferably 1:1 or more to 25:1 or less, more preferably 2:1 or more to 20:1 or less (tungsten metal transition metal (mol/mol)).

The concentration of the tungsten compound, calculated as tungsten metal, based on the weight of the carbohydrate source introduced into the first reactor, is preferably 0.1 wt% or more, more preferably 1 wt% or more to 35 wt% or less , more preferably 0.2 wt.% or more, even more preferably 2 wt.% or more to 25 wt.% or less.

The concentration of the transition metal introduced per hour into the first reactor, based on the mass of the carbohydrate source introduced into the first reactor, preferably ranges from 0.001 wt.% or more, more preferably from 0.01 wt.% or more, even more preferably 0.1 wt% or more, even more preferably 0.2 wt% or more to 2.0 wt% or less, more preferably 1.0 wt% or less.

The first reactor may be any type of reactor suitable for producing ethylene glycol from a carbohydrate source. Preferably, the first reactor is a stirring or mixing reactor. The first reactor, for example, may be a slurry reactor, a fluidized bed reactor, a fluidized bed reactor, a bubbling reactor, an external recirculation loop reactor, or a stirred flow reactor (STR), or another type of mechanically stirred reactor. Most preferably, the first reactor is a stirred flow reactor (STR). The use of a PFP is very advantageous for this process because the PFP provides an excellent means of diluting the final carbohydrate concentration in the PFP while the feed stream may contain a high concentration of carbohydrate. At the same time, the alkylene glycols that are produced by the reaction of the carbohydrate form a medium where tungsten compounds can be dissolved, thereby promoting the catalytic activity of the tungsten catalyst component.

Step (ii) involves reacting in a first reactor at a temperature of 170°C or more to 270°C or less of at least a portion of the carbohydrate source in the presence of hydrogen, a solvent, a first heterogeneous catalyst, and a homogeneous catalyst. Such a reaction properly yields at least ethylene glycol and sorbitol, and optionally one or more other diols and/or other polyols. The residence time in the first reactor may vary. Preferably, the average residence time of the carbohydrate source in the first reactor is at least 1 minute. (Residence time here refers to the average time spent by a material flowing at a volume velocity u through a volume V, as further explained in Modeling of Chemical Kinetics and Reactor Design by A. Kayode Coker, published in 2001 by Butterworth Heinemann). Preferably, the average residence time of the carbohydrate source in the first reactor is 1 minute or more to 6 hours or less, more preferably 3 minutes or more to 2 hours, most preferably 5 minutes or more to 45 minutes or less. If the carbohydrate source reacts quickly, however, the average residence time can also be less than 5 minutes and even less than 3 minutes. If a feed stream to the first reactor is used containing 20.0 wt.% or more of a carbohydrate source, based on the total weight of the carbohydrate source and solvent, the average residence time of the carbohydrate source in the first reactor is preferably 5 minutes or more, more preferably 10 minutes. or more and preferably 2 hours or less, more preferably 45 minutes or less. It is believed that such a long residence time may advantageously promote the conversion of a feed stream with a higher concentration of carbohydrate source.

Preferably, the continuous process is operated at an Hourly Average Feed Rate (HORR), expressed as weight of carbohydrate source per weight of transition metal, expressed as metal, per hour, in the range of 0.01-100 h' ¹ , preferably 0.05-10 h' ¹ . For practical purposes, an HCPS of 0.5-2.0 h ^-1 can be used.

The hydrogen partial pressure during step (ii) is preferably 1.0 megapascal (MPa) or more, preferably 2.0 MPa or more, more preferably 3.0 MPa or more to 16.0 MPa or less, preferably 12.0 MPa or less, more preferably 8.0 MPa or less. Any pressure here is absolute pressure.

The total pressure in step (ii) is suitably at least 1.0 MPa, preferably at least 2.0 MPa, more preferably at least 3.0 MPa. The total pressure in step (ii) is suitably not more than 16.0 MPa, more preferably not more than 10.0 MPa. Preferably, the reactor is pressurized with hydrogen before any feed is added. One skilled in the art will appreciate that the pressure at 20° C. will be lower than the actual pressure at the reaction temperature. The pressure in step (ii), when converted back to 20°C, is preferably equal to a pressure in the range of 0.7 MPa or more to 8.0 MPa or less.

As explained above, the pressure may be provided by hydrogen or a hydrogen-containing gas, optionally in combination with partial pressures of the contents of the reaction mixture. When the reaction mixture is heated, the total pressure during the reaction is properly 1.0-16.0 MPa.

It is preferable to maintain the hydrogen partial pressure at the reaction temperature in step (ii) in the range of 1.0 to 16.0 MPa abs., preferably throughout the entire reaction. Therefore, hydrogen or a hydrogen-containing gas is preferably introduced into the reaction mixture during the reaction as described above.

As indicated above, the pressure may be provided with hydrogen or a hydrogen-containing gas. If a hydrogen-containing gas is used, the hydrogen content of the hydrogen-containing gas is suitably up to 100% by volume. Most preferably, pure hydrogen is used for pressurization. During the reaction, hydrogen is consumed. If the process is a continuous or semi-continuous process, hydrogen is preferably supplied continuously or semi-continuously.

The reaction can be carried out over a wide range of temperatures. In the first reactor, at least a portion of the carbohydrate source is contacted with hydrogen or a temperature of 170°C or more to 270°C or less. More preferably, at least a portion of the carbohydrate source and hydrogen interact at a temperature in the range from 200°C or more to 240°C or less. The first reactor may be brought to a temperature in these ranges prior to the addition of any starting material, and may be maintained at a temperature in this range.

The reaction in step (ii) properly produces a first reactor product stream. This first reactor product stream suitably contains ethylene glycol, sorbitol, and optionally one or more other by-products such as erythritol. The first reactor product stream may suitably contain, for example, ethylene glycol (ethane-1,2-diol) and one or more by-products such as diethylene glycol (2,2'-oxydi(ethane-1-ol)), propylene glycol (propane -1,2-diol), glycerin (propane 1,2,3-triol), butane-1,2-diol, butane-1,3-diol, butane-2,3-diol, butane-1,4-diol , methanol, ethanol, propanol, butanol, sorbitol (hexane-1,2,3,4,5,6-hexol) and/or erythritol (butane-1,2,3,4-tetraol). Glycerin (propane 1,2,3-triol), sorbitol (hexane-1,2,3,4,5,6-hexol) and erythritol (butane-1,2,3,4-tetraol) are high temperature polyols. boiling point (i.e. boiling point over 250°C at atmospheric pressure of 0.1 MPa). As explained above, such polyols having a boiling point above 250° C. at an atmospheric pressure of 0.1 megapascal are also referred to herein as heavy polyols.

Step (iii) comprises removing from the first reactor a first reactor product stream and separating at least one ethylene glycol-rich fraction from such first reactor product stream; and one sorbitol-rich fraction containing a concentrated homogeneous catalyst.

By sorbitol-rich fraction is here meant a fraction of the first reactor product stream containing a higher concentration, for example a higher weight percentage of sorbitol, than the first reactor product stream itself. Such a sorbitol-rich fraction may also be referred to herein as a sorbitol-rich fraction. Preferably, the sorbitol-rich fraction may comprise 5 wt% or more, more preferably 10 wt% or more, even more preferably 20 wt% or more, and most preferably 30 wt% or more to 100 wt% or less of sorbitol. , suitably 90% by weight or less, based on the total weight of the sorbitol-rich fraction.

By ethylene glycol-rich fraction is here meant a fraction of the first reactor product stream containing a higher concentration, eg a higher weight percentage, of ethylene glycol than the first reactor product stream itself. Such an ethylene glycol-rich fraction may also be referred to herein as an ethylene glycol-rich fraction. Preferably, the ethylene glycol-rich fraction may comprise 5 wt.% or more, more preferably 10 wt.% or more, even more preferably 20 wt.% or more, and most preferably 30 wt.% or more to 100 wt. % or less, as appropriate, 90 wt.% or less of ethylene glycol, based on the total weight of the ethylene glycol-rich fraction.

Separation can be carried out by any method known to any person skilled in the art as suitable, including, for example, evaporation and/or distillation.

More preferably, step (iii) comprises separating, for example by distilling, at least a portion of the first reactor product stream into one or more sorbitol-poor fractions and at least one sorbitol-rich fraction. By sorbitol-poor fraction is here meant the fraction of the first reactor product stream containing lower concentrations, eg a lower weight percentage, of sorbitol than the first reactor product stream itself. Such a sorbitol-poor fraction may also be referred to herein as a sorbitol-poor fraction. One or more sorbitol-poor fractions may suitably be fortified with an alkylene glycol, such as ethylene glycol or propylene glycol. As appropriate, step (iii) may therefore include separating, for example, distilling at least a portion of the first reactor product stream into at least one ethylene glycol-rich, sorbitol-poor fraction;

one or more other sorbitol-poor fractions; and one sorbitol-rich fraction containing a concentrated homogeneous catalyst.

The ethylene glycol-rich fraction can be suitably further purified to obtain a purified ethylene glycol product.

Prior to separating, for example in a distillation step, the sorbitol-rich fraction and/or the ethylene glycol-rich fraction, the first reactor product stream is preferably first degassed to remove any residual hydrogen. The degassed first reactor product stream may then be sent to one or more evaporators to separate one or more fractions containing or consisting of one or more C1-C4 monoalkanols and/or water. By C1-C4 monoalkanols is meant here monoalkanols containing from 1 to 4 carbon atoms. Examples of such one or more C1-C4 monoalkanols include methanol, ethanol, propanol and/or butanol.

Preferably, at least a portion of the remaining first reactor product stream (which optionally has already had hydrogen, C ₁ -C ₄ monoalkanols and/or water removed) is then distilled into at least one or more sorbitol-poor, optionally alkylene glycol-enriched fractions; and one sorbitol-rich fraction containing concentrated homogeneous catalyst, sorbitol, and optionally one or more other heavy polyols such as glycerol and/or erythritol.

It is possible to distill only a portion or distill the entire product stream of the first reactor. The alkylene glycol is preferably ethylene glycol, propylene glycol, butanediol, or a mixture of two or more of them.

A sorbitol-rich fraction can be properly obtained by separating a fraction containing compounds boiling at 250° C. or higher under a pressure of 0.1 MPa. Therefore, as appropriate, step (iii) comprises removing from the first reactor a first reactor product stream and separating from such first reactor product stream at least one fraction containing compounds boiling at 250° C. or higher at a pressure of 0.1 MPa, as well as containing a concentrated homogeneous catalyst. Such a fraction containing compounds boiling at a temperature of 250° C. or higher under a pressure of 0.1 MPa may also be referred to herein as a heavy fraction.

As appropriate, step (iii) may comprise separating, for example, distilling at least a portion of the first reactor product stream into a fraction containing compounds boiling below 250° C. at a pressure of 0.1 MPa (also referred to herein as the light fraction) ; and a fraction containing compounds boiling at a temperature of 250°C or higher, under a pressure of 0.1 MPa (also referred to here as a heavy fraction). Such a light fraction may appropriately be an ethylene glycol-rich fraction, while such a heavy fraction may appropriately be a sorbitol-rich fraction. The person skilled in the art will understand that any distillation under reduced pressure or even under vacuum can be carried out to separate the above compounds in order to carry out the separation at a temperature below 250°C.

This sorbitol-rich fraction or heavy fraction preferably contains not only sorbitol but also other heavy polyols such as glycerol and erythritol. Preferably, the fraction contains from 0.5 wt.% or more to 99.5 wt.% or less, more preferably from 1.0 wt.% or more to 60.0 wt.% or less of heavy polyols (i.e. polyols boiling at a temperature equal to or higher than 250°C under a pressure of 0.1 MPa), relative to the total mass of such a fraction. More preferably, the fraction contains from 0.5 wt.% or more to 99.5 wt.% or less, more preferably from 1.0 wt.% or more to 60.0 wt.% or less of sorbitol in relation to the total mass such a faction. Most preferably, the sorbitol-rich fraction contains from 2.0 wt.% or more to 50 wt.% or less of sorbitol, based on the total weight of the sorbitol-rich fraction.

- 9 040952

The sorbitol-rich fraction additionally contains a concentrated homogeneous catalyst. By concentrated homogeneous catalyst is meant here a homogeneous catalyst at a concentration greater than the concentration of homogeneous catalyst in the product stream of the first reactor. Preferably, the concentration of homogeneous catalyst in the sorbitol-rich fraction ranges from 0.5 wt.% or more to 10.0 wt.% or less, more preferably from 0.5 to 5.0 wt.% or less, and most preferably in the range of 1.0 to 5.0 wt.% or less, based on metallic tungsten, in relation to the total mass of the sorbitol-rich fraction. The homogeneous catalyst may be concentrated in the sorbitol-rich fraction by any method known to those skilled in the art as suitable, including evaporation and/or distillation of other compounds in the first reactor product stream.

Sorbitol and/or dissolved homogeneous catalyst cannot be easily distilled. Therefore, the dissolved homogeneous catalyst can be suitably concentrated with sorbitol in the sorbitol-rich fraction by evaporation and/or distillation of other compounds in the first reactor product stream. Preferably, such a sorbitol-rich fraction further comprises a concentrated homogeneous catalyst, sorbitol, and one or more other heavy polyols such as glycerol and/or erythritol. In addition, the sorbitol-rich fraction may contain other compounds.

Step (iv) includes feeding the second reactor hydrogen and at least a portion of the sorbitol-rich fraction containing the concentrated homogeneous catalyst.

The second reactor may be any type of reactor known to be suitable for producing ethylene glycol from a carbohydrate source. The second reactor may, for example, be a fixed bed reactor, a drop flow reactor, a slurry reactor, a fluidized bed reactor, a fluidized bed reactor, a plug flow reactor, a bubbling reactor, a reactor with an external recycle loop, or a stirred flow reactor (SFR). ) or another type of mechanically stirred reactor. Most preferably, the second reactor is a plug flow reactor. The first reactor and the second reactor may be of the same or different reactor type. Preferably, the process according to the invention is carried out in a combination of reactors, where the first reactor is a stirred flow reactor and the second reactor is a plug flow reactor.

When the sorbitol-rich fraction is introduced into the second reactor, the sorbitol-rich fraction becomes part of the reaction mixture in the second reactor and can then be converted as described below.

Only part or all of the sorbitol-rich fraction may be fed to the second reactor.

In addition, a fresh stream of hydrogen is fed into the second reactor. As appropriate, the preferences for feeding such hydrogen are the same as previously described for the first reactor. For example, hydrogen may be supplied as a mixture of hydrogen and an inert gas in the amounts previously described for the first reactor.

If the second reactor is not a fixed bed reactor but a slurry reactor, the second heterogeneous catalyst may be fed separately to such a second reactor as a slurry. Preferences for such a slurry are indicated above for the first heterogeneous catalyst slurry.

Optionally, step (iv) may further comprise supplying additional solvent to the second reactor. Preferences for such additional solvent are as described above for the solvent.

Step (v) comprises reacting in a second reactor at a temperature of 200°C or more to 300°C or less at least a portion of the sorbitol-rich fraction containing the concentrated homogeneous catalyst with hydrogen in the presence of a second heterogeneous catalyst, wherein the second heterogeneous catalyst contains one or more transition metals from groups 8, 9, and 10 of the Periodic Table of the Elements.

The residence time in the second reactor may vary. Preferably, the average residence time of the sorbitol-rich fraction in the second reactor is longer than the average residence time of the carbohydrate source in the first reactor. Preferably, the average residence time of the sorbitol-rich fraction in the second reactor is at least 1 hour. Preferably, the average residence time of the carbohydrate source is 1 to 6 hours, more preferably 1 to 3 hours, most preferably 45 to 90 minutes. It is believed that the conversion of heavy side polyols, such as sorbitol and/or erythritol, benefits from a longer residence time. Preferably, the second reactor is a plug flow reactor operating at an hourly mean feed rate (HORR) expressed as weight of carbohydrate source per weight of transition metal, expressed as metal, per hour, in the range of 0.01-100 h ^-1 , preferably 0, 05-10 h ^-1 .

The preferences for the hydrogen partial pressure used in the second reactor in step (v) are the same as for the hydrogen partial pressure used in the first reactor in step (ii). Also the preference for the total pressure applied in the second reactor is the same as for the first reactor.

The reaction in step (v) is preferably carried out at a temperature in the range of 220°C or more to 260°C or less.

- 10 040952

More preferably, the temperature T2 used during the reaction in the second reactor in step (v) is equal to or higher than the temperature T1 used during the reaction in the first reactor in step (ii).

The second heterogeneous catalyst contains one or more transition metals from groups 8, 9 and 10 of the Periodic Table of the Elements. The second heterogeneous catalyst may be the same or different from the first heterogeneous catalyst. Preferably, however, the composition of the second heterogeneous catalyst is the same as the composition of the first heterogeneous catalyst, and the transition metal and support preferences are the same as for the first heterogeneous catalyst, as described above. Preferably, the second heterogeneous catalyst contains ruthenium and/or nickel as the transition metal and activated carbon as the carrier. That is, most preferably, the heterogeneous catalyst comprises ruthenium and/or nickel on an activated carbon support. Most preferably, the second reactor is a plug flow reactor where the second heterogeneous catalyst is present as a fixed bed.

The homogeneous catalyst in step (v) is the same as the homogeneous catalyst in step (ii). Advantageously, however, the homogeneous catalyst may be present in a higher concentration in step (v) than in step (ii). That is, the concentration of homogeneous catalyst in the reaction mixture in the second reactor in step (v) may properly be higher than the concentration of homogeneous catalyst in the reaction mixture in the first reactor in step (ii).

Preferences for the concentration of homogeneous catalyst are as described above for the sorbitol-rich fraction. Most preferably, the concentration of homogeneous catalyst in the reaction mixture in the second reactor ranges from 0.5 wt.% or more to 5.0 wt.% or less, based on tungsten metal, relative to the total weight of the reaction mixture.

The weight ratio between the total amount of tungsten compound (calculated based on metal) present in the second reactor and transition metal (calculated based on metal) present in the second reactor can vary over a wide range. If the second reactor is an SFP or slurry reactor, the weight ratio between the total amount of tungsten compound (calculated based on metal) present in the second reactor and transition metal (calculated based on metal) present in the second reactor is preferably higher than the weight ratio between the total amount of tungsten compound (calculated based on metal) present in the first reactor and transition metal (calculated based on metal) present in the first reactor. Also, if the second reactor is a SRT or slurry reactor, the molar ratio of moles of tungsten to total moles of transition metal, calculated as metal, is preferably higher in the second reactor than in the first reactor.

If the desired additional solvent can be added to the reaction mixture in the second reactor in step (v), the preference for such additional solvent is the same as indicated above for the first reactor in step (ii). Most preferably, any additional solvent is water.

Advantageously, the second reactor may be operated at less than full sorbitol conversion, preferably at a sorbitol conversion in the range of 50 wt% or more to 90 wt% or less. This advantageously allows a portion of the sorbitol to remain as a solvent for the homogeneous catalyst while optionally recycling at least a portion of the second reactor product stream to the first reactor.

Step (vi) includes removing the second reactor product stream from the second reactor and optionally recycling at least a portion of the second reactor product stream to the first reactor. As indicated above, the product stream of the second reactor may advantageously be used as the stream for adding the dissolved homogeneous catalyst to the first reactor.

Therefore, preferably, the process according to the present invention further comprises recycling at least a portion of the homogeneous catalyst from the second reactor back to the first reactor.

As appropriate, the second reactor product stream may be degassed to remove hydrogen prior to recycling. In addition, it may be desirable to remove at least part of the water and C ₁ -C ₄ monoalkanols (eg methanol, ethanol, propanol and/or butanol) prior to recycling.

A non-limiting example of a method in accordance with this invention is shown in the figure.

In the figure, a hydrogen stream (102), a stream containing a homogeneous catalyst solution (108), a stream containing a first heterogeneous catalyst slurry (106), and a feed stream containing a carbohydrate source (104) are fed into a stirred flow reactor (110). In this example, the stirred flow reactor (STR) acts as the first reactor; the homogeneous catalyst solution (108) suitably contains tungstic acid, sodium hydroxide and/or sodium tungstate in glycerin and water; and the first heterogeneous catalyst (106) suitably contains 5% by weight of ruthenium on active carbon suspended in water. The carbohydrate source (104) properly contains a solution of glucose in water, alkylene glycols and other diols and polyols). In addition, the homogeneous catalyst is recycled from the second reactor via stream (150). This stream (150) properly contains a homogeneous

- 11 040952 catalyst dissolved in other alkylene glycols, other diols and/or other polyols.

In PFP(110), glucose reacts with hydrogen at a temperature of about 220°C in the presence of a homogeneous catalyst and a heterogeneous catalyst. The PFP (110) is maintained at a total pressure of about 6.5 megapascals. Water, alkylene glycols and other diols and/or other polyols act as a solvent. The reaction mixture contains an average concentration of tungsten metal, corresponding to about 0.4 wt.% tungstic acid, relative to the total weight of the reaction mixture. The first reactor product stream (112) is removed from the PFP (110). This exemplary first reactor product stream (112) suitably contains, among others, hydrogen, ethylene glycol, propylene glycol, erythritol, sorbitol, water, methanol, ethanol, propanol and butanol. This first reactor product stream (112) then contains an amount of tungsten metal corresponding to about 0.4% by weight of tungstic acid, based on the total weight of the first reactor product stream (112). In addition to the first reactor product stream, it may or may not contain particles of the first heterogeneous catalyst. If such first heterogeneous catalyst particles are present, these particles can be separated from the first reactor product stream by filtration and recycled to the PFP (110). The hydrogen stream (114) is then removed from the product stream of the first reactor (114) in the degasser (116). From the resulting stream (118), the C1-C4 monoalkanols (such as methanol, ethanol, propanol and butanol) stream (120) and part of the water are removed to the evaporator (122). The resulting stream (124) is then sent to a distiller (126) where the stream (124) is separated into four sorbitol-poor fractions (128a, 128b, 128c and 128d, all containing compounds having a boiling point at 0.1 MPa below 250°C) and a sorbitol-rich fraction (130) containing compounds having a boiling point at 0.1 MPa above 250°C. Tungsten particles such as tungstic acid, tungsten bronze, sodium tungstate or their derivatives remain undissolved in the sorbitol-rich fraction (130). As a result of the distillation of the other components, the concentration of tungsten metal increases, and this sorbitol-rich fraction (130) properly contains an amount of tungsten metal corresponding to about 1.9 wt.% tungstic acid, relative to the total weight of the sorbitol-rich fraction (130).

The sorbitol-rich fraction (130) is sent to a plug flow reactor (132) where it contacts a fresh hydrogen stream (134). In this example, the plug flow reactor (PRE) acts as the second reactor. RIV contains a fixed bed (136) of the second heterogeneous catalyst, consisting of 5 wt.% ruthenium on activated carbon (5 wt.% Ru/AU). In RIV (132), sorbitol reacts with hydrogen at a temperature of about 240°C in the presence of a homogeneous catalyst and a second heterogeneous catalyst to obtain a product stream of the second reactor (138). This second reactor product stream (138) is removed from the RIV (132). The sorbitol itself and other components of the sorbitol-rich fraction act as a solvent. The second reactor product stream suitably contains hydrogen, propane, methanol, tetrahydrofuran, ethanol, propanol, butanol and water in addition to ethylene glycol and propylene glycol. Preferably, RIV does not operate at full conversion, but at a conversion of about 70% by weight of the total sorbitol conversion, allowing about 30% by weight of sorbitol to remain unconverted. In due course, the second product stream (138) is sent to a degasser (142) to remove the hydrogen stream (140). From the resulting stream (144), a stream of C1-C ₄ monoalkanols (such as methanol, ethanol, propanol and butanol) (146) and part of the water are removed in the evaporator (148). The resulting stream (150) is predominantly recycled to the first reactor (110).

The method in accordance with this invention is further illustrated by the following non-limiting example.

Example 1

The method shown in the figure is demonstrated using the ASPEN PLUS computer simulation program version 8.8 (ASPEN is a trademark) in combination with the APV88 PURE32, APV88 AQUEOUS, APV88 SOLIDS, APV88 INORGANIC, NISTV88 NIST-TRC databanks available from ASPEN PLUS 8.8, and additionally combined with VLE data for mixtures of ethylene glycol, propylene glycol and butylene glycol obtained from the Dortmund Data Bank. The concentration of tungsten compounds is taken as the concentration corresponding to 0.4 wt.% tungstic acid in the SMR reactor acting as the first reactor, and the concentration of tungsten compounds corresponding to 1.9 wt.% tungstic acid in the plugging reactor acting as the second reactor. The simulated heterogeneous catalyst is taken as 5 wt% ruthenium on activated carbon suspended in water.

The composition of the hydrogen stream (102) and the feed stream containing the source of carbohydrate (104) fed into the simulated PFP reactor are listed in Table 1. 1A. In addition, the composition of the recycle stream (150) also fed to the simulated PFR reactor is listed. Compositions of the obtained first product stream (112), product stream after removal of H ₂ , part of H2O and C1-C4 monoalkanol (125), 1 sorbitol-poor fraction (128a), 2 sorbitol-poor fraction (128b), 3 sorbitol-poor fraction (128c) 4, the sorbitol-poor fraction (128d), the sorbitol-rich fraction (130) and the second reactor product stream (138) are all listed in Table 1. 1b.

Hydrogen and low boiling components such as C ₁ -C 4 alkanols and part of the water are properly removed from the second reactor product stream (138), leaving a recycle stream (150) which

- 12 040952 are recycled to the first reactor. The composition of the recycle stream (150) is already presented in table. 1A.

All listed quantities in the table. 1A and 1B are given in kilograms per hour (kg/h). The tables use the following abbreviations:

H2: Hydrogen

PROP: C1-C6 alkanes (in the Aspen model used, propane is used as the "standard compound" for all alkanes containing 1-6 carbon atoms)

MEON : Methanol

THF: Tetrahydrofuran

ETOH : Ethanol

PROH-1: 1-Propanol

PROH-2: 2-Propanol (isopropyl alcohol)

BUOH: n-Butanol

H2O : Water

GLYALD : Glycolaldehyde (hydroxyacetaldehyde)

HO ASET: Hydroxyacetone (1-hydroxypropan-2-one)

THF-: Tetrahydrofurfuryl alcohol

ALC

PG: 1,2-Propanediol (propylene glycol)

BG: 1,2-Butanediol

EG: 1,2-Ethandiol (ethylene glycol)

1,3-BG: 1,3-Butanediol

GL : Glycerin (propane-1,2,3-triol)

ET: Meso-erythritol (butane-1,2,3,4-tetraol)

SB: sorbitol (hexane-1,2,3,4,5,6-hexol)

GLU : Dextrose (D-glucose)

DIETHYL : Diethylene glycol (2,2'-oxydi(ethan-1-ol))

PG-13: 1,3-Propanediol

BG-14: 1,4-Butanediol

Table 1A. Composition of feed streams (all in kg/h)

Component Raw Glucose Flow (104) Hydrogen flow (102) Recycled stream(150) H2 0 3212 0 PROP 0 0 0 MEON 0 0 0 THF 0 0 0 this 0 0 0 PROH-1 0 0 0 PROH-2 0 0 0 BUOH 0 0 14 H2O 39470 0 2681 GLUE ALD 0 0 93 HOASET 0 0 0 THF-ALA 0 0 0 PG 0 0 13 BG 0 0 0 EG 0 0 402 1,3-BG 0 0 2 GL 0 0 358 THIS 0 0 10567 Sat 0 0 15022 GLU 92097 0 1

- 13 040952

diethyl 0 0 64242 PG-13 0 0 292 BG-14 0 0 177

Table 1B. Product composition and fraction streams (all in kg/h)

Component First reactor product stream (112) Product stream after removal of H2, part of H2O and C1-C4 monoalkanol (125) 1 sorbitol-poor fraction (128a) 2 fraction poor in sorbitol (128b) 3 fraction poor in sorbitol (128s) 4 sorbitol-poor fraction (128d) Fraction rich in sorbitol (130) Second reactor product flow (kg/h) (138) H2 125 0 0 0 0 0 0 468 PROP 0 0 0 0 0 0 0 1878 MEON 1763 0 0 0 0 0 0 88 THF 0 0 0 0 0 0 0 222 this 1197 0 0 0 0 0 0 44 PROH-1 1042 0 0 0 0 0 0 92 PROH-2 104 0 0 0 0 0 0 23 BUOH 28 0 0 0 0 0 0 237 H2O 279875 59 59 0 0 0 0 3647 GLUE ALD 4349 3792 3790 2 0 0 0 95 HOASET 176 112 112 0 0 0 0 0 THF-ALA 0 0 0 0 0 0 0 0 PG 11038 11012 22 10963 28 0 0 13 BG 1290 1289 0 0 1225 64 0 0 EG 64228 64210 0 13 1244 62700 254 408 1,3-BG 33 33 0 0 0 27 7 2 GL 358 358 0 0 0 0 358 364 this 15466 15466 0 0 0 0 15466 10728 Sat 21893 21893 0 0 0 0 21893 15251 GLU 92 92 0 0 0 0 92 1 diethyl 59753 59753 0 0 0 0 59753 65221 PG-13 318 318 0 0 0 27 291 297 BG-14 208 206 0 0 0 0 206 180

Example 2

A Stirred Flow Reactor (STR), equipped with a mechanical stirrer and having a volume of about 6 ml, is filled with 500 milligrams (mg) of the wetted heterogeneous catalyst (50% by weight moisture). The wetted heterogeneous catalyst contains 250 mg (on a dry basis) of a heterogeneous catalyst containing 5 wt.% ruthenium on activated carbon, where the balance is water. The PRM is then completely filled with water.

Prepare an aqueous solution of raw materials containing about 10 wt.% glucose, about 0.15 wt.% tungstic acid (H ₂ WO ₄ ), about 19 wt.% glycerol and about 0.18 g/l NaOH, combining the components as shown in table. 2A.

The flow of raw materials of an aqueous solution of raw materials from the table. 2A is fed at a flow rate of 0.25 ml/min to a stirred flow reactor (STR) for about 5 hours. The hydrogen feed flow is 100 normalized milliliters per minute (nml/min).

The PRM is stirred at a stirrer speed of 1500 rpm. The reaction temperature is maintained at about 220°C. The hydrogen pressure is maintained at about 80 bar (corresponding to about 8 MPa). The average residence time of the liquid in the reactor is therefore about 24 minutes. On average, the ratio of ruthenium to tungsten calculated from metals is about 3.8, the weight ratio of tungsten (calculated as metal) to glucose is about 0.03, and the weight ratio of ruthenium (calculated as metal) to glucose is about 0. 04. The PFP operates until a steady state is reached. The reaction effluent at this steady state is analyzed and the results are summarized in Table 1. 2B. The glucose conversion was found to be constant above 99 wt% conversion (conversion calculated based on glucose fed to the reactor). Ethylene glycol (EG), propylene glycol (PG), butylene glycol (BG), and sorbitol (SB) concentrations and weight percentages are determined by high performance liquid chromatography (HPLC). Selectivity (wt %) is calculated in terms of ethylene glycol, propylene glycol, butylene glycol and sorbitol as the weight percent in the reactor effluent is divided by the weight percent of glucose introduced into the PFP.

- 14040952

Table 2A. The composition of the aqueous solution of raw materials

Component Mass in grams (g)/microliters (µl) Mass percentage in raw materials (% wt.) Glucose 20 g 10 Water 141.7 g 71 5% wt, tungstic acid (H ₂ WO ₄ ) dissolved in glycerin 6 g 3 Glycerol 32.3 g 16 50% mass, sodium hydroxide (NaOH) dissolved in water 48 µl <1

Table 2B. Conversion and composition of the reactor effluent

Selectivity (in wt %) Mass percentage in the output stream (% wt.) Conversion >99 ethylene glycol 44 4.4% wt. propylene glycol 16 1.6% wt. Butylene glycol 1.6 0.2% wt. Sorbitol 26 2.6% wt.

Then the outgoing RFP stream listed in Table. 2B may be distilled in a distillation compartment containing one or more distillation columns (actually not performed) to produce a single ethylene glycol-rich fraction; and one sorbitol-rich fraction containing a concentrated homogeneous catalyst.

Example 3

To demonstrate the conversion of sorbitol in the second reactor, a feed is prepared that mimics the composition of the sorbitol-containing stream leaving the distillation compartment, such as shown as (126) in the figure.

20.18 g of erythritol, 35.23 g of sorbitol, 11.14 g of glucose, 50.25 g of ethylene glycol and 196.33 g of glycerol are mixed at 120° C. for 1 hour. After dissolving the erythritol, sorbitol, glucose and glycerol in ethylene glycol and while the mixture is still heated, 202.43 g of tungstic acid containing the glycerol solution is added to the mixture. The tungstic acid-containing glycerol solution contains 5 wt. % tungstic acid (H2WO4) and 95 wt. % glycerol, based on the total mass of the glycerol solution (5 wt. and boiling under reflux at 180°C for 3 hours). Then, 2134 µl of an aqueous 50 wt% sodium hydroxide (NaOH) solution was also added to obtain a raw material composition. The composition of raw materials is presented in table. BEHIND.

Table FOR. Composition of raw materials

Component Mass percentage in raw materials (% wt.) erythritol 4 sorbitol 7 glucose 2 ethylene glycol 10 glycerol 75 _{H2WO4 _} 2

The above feedstock is fed into a small scale plug flow reactor. This plug-flow reactor contains a substantially vertical stainless steel tubular reactor 0.98 cm in diameter and 45 cm long, giving a total internal volume of 33.75 ml. The reactor is placed inside an electric furnace, which is kept at operating temperature. The reactor has an isothermal zone 17 cm long, giving an effective reactor volume of 12 ml. The frit is inserted into the reactor to store the catalyst bed in the isothermal zone. Approximately one centimeter of quart wool is placed on the surface of the frit. Then the isothermal zone of the reactor is filled with 16 cm of heterogeneous

-15040952 catalyst containing 5 wt.% ruthenium on carbon extrudates (approximately 5 g). The rest (top) of the reactor is filled with an inert material.

Once the catalyst is loaded into the reactor, the reactor is placed in an oven and the catalyst is reduced to reaction by keeping the catalyst in a stream of nitrogen for 1 hour, then heating the catalyst up to 300°C in a stream of hydrogen (heating at a temperature rate of 5°C/min) and keeping catalyst at 300°C in such a stream of hydrogen for 4 hours Then the catalyst is kept in a stream of nitrogen until the reaction.

The stream is fed into the reactor at a liquid hourly space velocity (LFSV) of 0.75 h ^-1 and subjected to interaction in the isothermal zone of the reactor at a temperature of 220°C, a reactor pressure of 50 bar (corresponding to 5 MPa) and a molar ratio of hydrogen to polyol of 5:1. Both feedstock and hydrogen are introduced through the top of the reactor.

The concentration of tungstic acid in the stream is about 2 wt.% in relation to the total mass of raw materials.

After stabilization of the operating parameters, the experiment is started (t=0). Samples are taken from the reactor effluent at t=0 h, t=2 h, t=4 h, t=21 h, t=23 h, t=25 h and t=28 h.

It was found that the process remains unstable during the first 4 hours and only then becomes stable. Conversion and exit after 4 hours, i.e. at t=21 h, t=23 h, t=25 h and t=28 h are summarized in Table. 3b.

Samples are analyzed by liquid chromatography (LC) and gas chromatography (GC) to determine the conversion of the components present in the feed and the formation of potential products, as summarized in table. 3b.

As shown in Table. 3B, the conversion of the main components in the feedstock is as follows:

glycerin: about 34% by weight;

glucose: about 100% by weight;

sorbitol: about 50% by weight;

erythritol: about 45% by weight.

The ethylene glycol conversion was negative, illustrating that ethylene glycol was indeed formed during the process.

As the results summarized in Table. 3B, the use of a concentrated homogeneous catalyst results in the conversion of the so-called heavy polyols of glycerol, sorbitol and erythritol.

Table 3B. results

The sample taken in sampling time (in hours): Glycerol conversion (% mass) Glucose conversion (% mass) Sorbitol Conversion(wt %) Erythritol conversion (% mass) Ethylene glycol conversion (% mass) ** Yield of 1,2propanediol (propylene glycol) (% wt.) Yield of 1,3propanediol (% wt.) Exit C1-C4 monoalkanol* (% wt.) 21 34.4 100.0 51.3 45.5 -z, o 9.5 0.9 2.5 23 35.8 100.0 52.0 44.6 0.0 9.2 0.6 2.5 25 32.8 100.0 49.7 42.4 -5.0 9.3 1.0 2.8 28 33.0 100.0 50.2 45.2 -z, o 9.1 0.9 2.0

* Combined yield of methanol, ethanol, 2-propanol, 1-propanol and n-butanol.

** Ethylene glycol conversion is negative, illustrating that ethylene glycol is indeed formed during the process.

Example 4

To demonstrate the conversion of sorbitol in the second reactor, a feed is obtained that mimics the composition of the sorbitol-containing stream exiting the distillation compartment, such as described in example 2.

127.02 g of erythritol, 181.83 g of sorbitol, 0.90 g of glucose, 2.88 g of ethylene glycol, 184.76 g of glycerol, 2.42 g of 1,3-propylene glycol and 1.94 g of 1,4-butylene glycol are mixed at 120°C for two hours. Once erythritol, sorbitol, glucose, ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol and glycerol are mixed into a homogeneous mixture, and while the mixture is still heated, 323.04 g of tungstic acid containing the glycerol solution is added to the mixture. The tungstic acid-containing glycerin solution contains 5% by weight of tungstic acid (H2WO4) and 95% by weight of glycerol, based on the total weight of the glycerol solution. (5 wt% H2WO4 in glycerol solution is prepared by mixing 35.25 g of H2WO4 with 666.47 grams of glycerol and refluxing at 180°C for 3 hours). Then, 3414.4 μl of an aqueous 50 wt% sodium hydroxide (NaOH) solution was also added to obtain a raw material composition. The composition of raw materials is presented in table. 4A.

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Table 4A. Composition of raw materials

Component Mass percentage in raw materials (% wt.) ethylene glycol 0.35 Glycerol 59.61 erythritol 15.40 Sorbitol 22.05 Glucose 0.11 1,3-propylene glycol 0.29 1,4-butylene glycol 0.24 Tungstic acid (H2WO4) 1.96

The above feedstock is fed into a small scale plug flow reactor. This plug-flow reactor contains a substantially vertical stainless steel tubular reactor 0.98 cm in diameter and 45 cm long, giving a total internal volume of 33.75 ml. The reactor is placed inside an electric furnace, which is kept at operating temperature. The reactor has an isothermal zone 17 cm long, giving an effective reactor volume of 12 ml. The frit is inserted into the reactor to store the catalyst bed in the isothermal zone. Approximately one centimeter of quart wool is placed on the surface of the frit. Then the isothermal zone of the reactor is filled with 8 cm of a heterogeneous catalyst containing 10 wt.% ruthenium on carbon extrudates (approximately 3.5 g). The rest (top) of the reactor is filled with an inert material.

Once the catalyst is loaded into the reactor, the reactor is placed in an oven and the catalyst is reduced to reaction by keeping the catalyst in a stream of nitrogen for one hour, then heating the catalyst up to 300°C in a stream of hydrogen (heating at a temperature rate of 5°C/min) and by keeping the catalyst at 300° C. in this flow of hydrogen for 4 hours. The catalyst is then kept in a flow of nitrogen until the reaction starts.

The stream is fed into the reactor at a liquid hourly space velocity (LFSV) of 0.5 h ^-1 and subjected to interaction in the isothermal zone of the reactor at a temperature of 240°C, a reactor pressure of 50 bar (corresponding to 5 MPa) and a molar ratio of hydrogen to polyol of 5.7 :1. Both feedstock and hydrogen are introduced through the top of the reactor.

The concentration of tungstic acid in the stream is about 2 wt.% in relation to the total mass of raw materials.

After stabilization of the operating parameters, the experiment is started (t=0). Samples are taken from the reactor effluent at t=0 h, t=2 h, t=3 h, t=20 h, t=21 h, t=23 h, t=26 h, t=43 h, t=45 h, t=47 h, t=49 h, t=51 h, t=68 h, t=70 h, t=72 h, t=75 h, t=91 h, t=93 h, t=95 h, t=97 h and t=98 h.

It was found that at or t=43 h the process becomes stable. The transformation and output at t=43 hours are shown in table. 4B below.

Samples are analyzed by liquid chromatography (LC) and gas chromatography (GC) to determine the conversion of components present in the feed and the formation of potential products, as summarized in table. 4b.

As shown in Table. 4B, the transformation of the main components into raw materials is as follows:

glycerin: about 62-75% by weight;

glucose: about 100% by weight;

sorbitol: about 75-87% by weight;

erythritol: about 68-81% by weight.

Ethylene glycol conversion was negative, illustrating that ethylene glycol is indeed formed during the process.

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Table 4B. Results (Yields indicated as Yields are ________ average % of ingredient in product blend)___________

Sample taken during sampling (in hours): Glycerol conversion (wt. %) Glucose Conversion (% wt.) Sorbitol Conversion (wt %) Erythritol Conversion (% wt.) Ethylene glycol conversion (% mass) ** Yield of 1,2propanediol (propylene glycol) (% wt.) Yield of 1,3propanediol a (% wt.) Exit C1-C4 monoalkanol * (% wt.) 43 75.7 100.0 87.2 81.9 7 12.3 0.7 4.8 45 74.9 100.0 86.4 81.1 6 12.2 0.7 4.7 47 73.2 100.0 85.0 79.5 6 12.0 0.6 4.4 49 72.3 100.0 84.3 78.5 6 12.3 oh oh 4.5 51 71.3 100.0 83.4 77.4 6 I,5 0.6 4.4 68 67.6 100.0 80.3 73.5 6 10.6 0.6 4.3 70 67.4 100.0 80.3 73.5 6 10.8 0.6 4.1 72 65.9 100.0 79.1 72.7 6 10.7 0.6 3.6 75 65.8 100.0 78.7 71.8 6 10.2 0.8 3.7 91 63.8 100.0 76.4 69.5 5 9.7 0.7 3.4 93 63.9 100.0 76.6 69.6 6 9.9 0.7 3.7 95 63.4 100.0 76.1 69.3 6 9.9 0.7 3.2 97 63.9 100.0 76.6 69.6 5 9.8 0.7 3.9 98 62.7 100.0 75.6 68.4 5 9.6 0.7 3.6

* Combined yield of methanol, ethanol, 2-propanol, 1-propanol and n-butanol.

* * Ethylene glycol conversion is negative, illustrating that ethylene glycol is indeed formed during the process.

Example 5

A Stirred Flow Reactor (STR), equipped with a mechanical stirrer and having a volume of about 6 ml, is filled with 500 milligrams (mg) of the wetted heterogeneous catalyst (50% by weight moisture). The wetted heterogeneous catalyst contains 250 mg of a heterogeneous catalyst containing 5 wt.% ruthenium on activated carbon, where the balance is water. The PRM is then completely filled with water. The PRM is then completely filled with water.

Prepare an aqueous feed solution containing glucose, glycerol, water, NaOH and the effluent from the plug flow reactor from Example 4 containing 1.62 wt.% tungsten (calculated as metallic W) by combining the components as shown in table. 5A.

The flow of raw materials of an aqueous solution of raw materials from the table. 5A is fed at a flow rate of 0.25 ml/min to a stirred flow reactor (STR) for about 5 hours.

The hydrogen feed flow is 100 normalized milliliters per minute (nml/min).

The PRM is stirred at a stirrer speed of 1500 rpm. The reaction temperature is maintained at about 220°C. The hydrogen pressure is maintained at about 80 bar (corresponding to about 8 MPa). The average residence time of the liquid in the reactor is therefore about 24 minutes. On average, the ratio of ruthenium to tungsten calculated from metals is about 1.9, the weight ratio of tungsten (calculated as metal) to glucose is about 0.011, and the weight ratio of ruthenium (calculated as metal) to glucose is about 0.020. The PFP operates until a steady state is reached. The reaction effluent at this steady state is analyzed. The conversion of glucose was found to be constant above 99 wt% conversion (conversion calculated based on glucose fed to the reactor). Ethylene glycol (EG), propylene glycol (PG), butylene glycol (BG) and sorbitol (SB) concentrations and weight percentages are determined by high performance liquid chromatography (HPLC). Selectivity (wt%) is calculated in terms of ethylene glycol, propylene glycol, butylene glycol and sorbitol, as the weight percent in the reactor effluent is divided by the weight percent of glucose introduced into the PFP.

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Claims (7)

Table 5A. The composition of the aqueous solution of raw materials Component Weight in grams (g) Glucose 20 Water 138.8 The output stream from example 4, containing 1.62% of the mass. W in polyol blend 13.75 Glycerol 28.89 50% mass, sodium hydroxide (NaOH) dissolved in water 5 drops Table 5B. results Selectivity (in wt %) Mass percentage in the output stream (% wt.) Conversion >99% ethylene glycol 50 4.9 propylene glycol 17 1.7 Butylene glycol 1.1 0.10 Sorbitol AND 1.1 Examples 4 and 5 illustrate that a homogeneous catalyst containing tungsten can advantageously be recycled from the second reactor to the first reactor. CLAIM 1. A method for producing ethylene glycol, including the steps: (i) feeding into the first reactor a source of carbohydrate, solvent, hydrogen, a first heterogeneous catalyst, where the first heterogeneous catalyst contains one or more transition metals from groups 8, 9, and 10 of the Periodic Table of the Elements, and a homogeneous catalyst, where the homogeneous catalyst contains a tungsten compound, selected from the group consisting of tungstic acid (H ₂ WO ₄ ), tungsten bronze present as HxWO3 or MxWO3, where x is a variable less than 1 and M is a metal, ammonium tungstate, ammonium metatungstate, tungstate compounds containing at least one group 1 or 2 element; (ii) reaction in the first reactor at a temperature in the range from 170 to 270°C, at least part of the carbohydrate source in the presence of hydrogen, a solvent, a first heterogeneous catalyst and a homogeneous catalyst; (iii) removing the first reactor product stream from the first reactor and separating at least one ethylene glycol rich fraction from such first reactor product stream; and one fraction rich in sorbitol containing a concentrated homogeneous catalyst; (iv) feeding into the second reactor hydrogen and at least a portion of the sorbitol-rich fraction containing the concentrated homogeneous catalyst; (v) reacting in a second reactor at a temperature of 200 to 300° C. at least a portion of the sorbitol-rich fraction containing the concentrated homogeneous catalyst with hydrogen in the presence of a second heterogeneous catalyst, wherein the second heterogeneous catalyst contains one or more Group 8 transition metals, 9 and 10 of the Periodic Table of the Elements; (vi) removing the second reactor product stream from the second reactor. 2. The method of claim 1 further comprising recycling at least a portion of the second reactor product stream to the first reactor. 3. The process according to claim 1 or 2, further comprising recycling at least a portion of the homogeneous catalyst from the second reactor back to the first reactor. 4. Process according to any one of claims 1 to 3, wherein the first reactor is a stirred tank reactor. 5. Process according to any one of claims 1 to 4, wherein the second reactor is a plug flow reactor. 6. The method according to any one of claims 1 to 5, where in step (i) the carbohydrate source is fed to the first reactor in a feed stream containing a carbohydrate source and water, where such a feed stream contains from 2.0 to 50.0 wt.% carbohydrate source, relative to the total weight of the carbohydrate source and water. 7. The method according to any one of claims 1 to 6, where the first heterogeneous catalyst contains ruthenium and/or ni- -