阅读说明：本技术 用于生产乙二醇的方法 (Process for the production of ethylene glycol ) 是由 P·迪克 J·C·范德沃 G·J·M·格鲁特 J·辛格 B·麦克凯 于 2019-03-14 设计创作，主要内容包括：生产乙二醇的方法,其包含以下步骤：(i)向第一反应器提供碳水化合物源、溶剂、氢气、第一非均相催化剂和均相催化剂,该第一非均相催化剂含有一种或多种元素周期表第8、9或10族的过渡金属,该均相催化剂含有钨；(ii)在第一反应器中,在大于或等于170℃至小于或等于270℃的温度范围内,在氢气、溶剂、第一非均相催化剂和均相催化剂的存在下,使碳水化合物源的至少一部分反应；(iii)从第一反应器移除第一反应器产物流,并从该第一反应器产物流分离至少：-一个乙二醇富级分；和-一个含有浓缩均相催化剂的山梨醇富级分；(iv)向第二反应器提供氢气和含有浓缩均相催化剂的山梨醇富级分的至少一部分；(v)在第二反应器中,在大于或等于200℃至小于或等于300℃的温度范围内,在氢气、第二非均相催化剂的存在下,使含有浓缩均相催化剂的山梨醇富级分的至少一部分反应,该第二非均相催化剂含有一种或多种元素周期表第8、9或10族的过渡金属；(vi)从第二反应器移除第二反应器产物流。(A process for producing ethylene glycol comprising the steps of: (i) providing a carbohydrate source, a solvent, hydrogen, a first heterogeneous catalyst comprising one or more transition metals from groups 8, 9 or 10 of the periodic table of elements, and a homogeneous catalyst comprising tungsten to a first reactor; (ii) reacting at least a portion of the carbohydrate source in the first reactor in the presence of hydrogen, a solvent, a first heterogeneous catalyst, and a homogeneous catalyst at a temperature in the range of greater than or equal to 170 ℃ to less than or equal to 270 ℃; (iii) removing a first reactor product stream from the first reactor and separating from the first reactor product stream at least: -one ethylene glycol rich fraction; and-a sorbitol rich fraction containing concentrated homogeneous catalyst; (iv) providing hydrogen and at least a portion of the sorbitol rich fraction containing the concentrated homogeneous catalyst to a second reactor; (v) reacting at least a portion of the sorbitol rich fraction containing the concentrated homogeneous catalyst in a second reactor at a temperature in the range of greater than or equal to 200 ℃ to less than or equal to 300 ℃ in the presence of hydrogen gas, a second heterogeneous catalyst containing one or more transition metals of groups 8, 9 or 10 of the periodic Table of the elements; (vi) the second reactor product stream is removed from the second reactor.)

1. A process for producing ethylene glycol comprising the steps of:

(i) providing a carbohydrate source, a solvent, hydrogen, a first heterogeneous catalyst comprising one or more transition metals from groups 8, 9 or 10 of the periodic table of elements, and a homogeneous catalyst comprising tungsten to a first reactor;

(ii) reacting at least a portion of the carbohydrate source in the first reactor in the presence of hydrogen, a solvent, a first heterogeneous catalyst, and a homogeneous catalyst at a temperature in the range of greater than or equal to 170 ℃ to less than or equal to 270 ℃;

(iii) removing a first reactor product stream from the first reactor and separating from the first reactor product stream at least:

-one ethylene glycol rich fraction; and

-a sorbitol rich fraction containing concentrated homogeneous catalyst;

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

(v) reacting at least a portion of the sorbitol rich fraction containing the concentrated homogeneous catalyst in a second reactor at a temperature in the range of greater than or equal to 200 ℃ to less than or equal to 300 ℃ in the presence of hydrogen gas, a second heterogeneous catalyst containing one or more transition metals of groups 8, 9 or 10 of the periodic Table of the elements;

(vi) The second reactor product stream is removed 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 method of 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. The process of any one of claims 1 to 3, wherein the first reactor is a continuous stirred tank reactor.

5. The process of any of claims 1 to 4, wherein the second reactor is a plug flow reactor.

6. The process of any one of claims 1 to 5, wherein the carbohydrate source is provided in step (i) to the first reactor by a feed stream comprising the carbohydrate source and water, wherein such feed stream comprises the carbohydrate source in the following ranges based on the total weight of carbohydrate source and water: greater than or equal to 2.0 wt% to less than or equal to 50.0 wt%.

7. A process as claimed in any one of claims 1 to 6 wherein the homogeneous catalyst comprises a tungsten compound or tungsten derived from a tungsten compound, wherein such tungsten compound is sodium tungstate and/or tungstic acid and/or tungsten bronze.

8. The process of any of claims 1 to 7, wherein the first heterogeneous catalyst comprises ruthenium and/or nickel supported on activated carbon, and/or wherein the second heterogeneous catalyst comprises ruthenium and/or nickel supported on activated carbon.

9. The process of any of claims 1 to 8, wherein at least a portion of the first heterogeneous catalyst and/or at least a portion of the second heterogeneous catalyst comprises tungsten in addition to one or more transition metals selected from groups 8, 9 or 10 of the periodic Table of elements.

10. The process of any one of claims 1 to 9, wherein the concentration of homogeneous catalyst in the reaction mixture in the second reactor of step (v) is higher than the concentration of homogeneous catalyst in the reaction mixture in the first reactor of step (ii).

11. The process of any one of claims 1 to 10, wherein the concentration of homogeneous catalyst in the reaction mixture in the first reactor of step (ii) is from greater than or equal to 0.01 wt% to less than or equal to 0.5 wt%, calculated as tungsten metal, based on the total weight of the reaction mixture.

12. The process of any one of claims 1 to 11, wherein one sorbitol rich fraction containing concentrated homogeneous catalyst in step (iii) contains homogeneous catalyst in the following concentration ranges, calculated as tungsten metal, based on the total weight of the sorbitol rich fraction: greater than or equal to 0.5 wt% to less than or equal to 10.0 wt%.

13. The process of any one of claims 1 to 12, wherein the concentration of homogeneous catalyst in the reaction mixture in the second reactor of step (v) is from greater than or equal to 0.5 wt% to less than or equal to 5 wt%, calculated as tungsten metal, based on the total weight of the reaction mixture.

14. The process of any one of claims 1 to 13, wherein the temperature T2 during the reaction in the second reactor in step (v) is greater than or equal to the temperature T1 during the reaction in the first reactor in step (ii).

15. The process of any one of claims 1 to 14, wherein step (iv) further comprises providing additional solvent to the second reactor.

Technical Field

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

Background

Alkylene glycols (e.g., ethylene glycol) are bulk chemicals that can be used in a variety of applications. They can be used as monomers in the preparation of polyesters, such as polyethylene terephthalate, polyethylene naphthenate or polyethylene furandicarboxylate, but ethylene glycol can also be used, for example, in heat transfer media and deicing compositions.

Recently, there has been an increasing effort to produce alkylene glycols from sustainable sources (e.g., carbohydrates). By enabling the production of alkylene glycols (e.g., ethylene glycol) from sustainable resources, reliance on fossil fuel resources is advantageously reduced.

CN102643165 describes a process for the production of ethylene glycol and 1, 2-propanediol, which is achieved by continuous hydrocracking of sugars. The process is carried out in a reactor using a catalytically active tungsten species. The liquid reactor effluent is separated into two portions. One portion of the liquid reactor effluent is sent to the distillation system and another portion of the liquid reactor effluent is sent directly back to the reactor to dilute the reaction liquid. In the distillation system, a polyol heavy fraction and unreacted sugars are obtained, which are sent back to the reactor for further hydrocracking. In this way, the tungsten component dissolved in the heavy fraction is recovered and recycled for the reaction.

WO2016/114658 also describes a process for the preparation of ethylene glycol from a carbohydrate source. The carbohydrate source is reacted with hydrogen in the presence of a diluent and a catalyst system comprising a tungsten compound and at least one hydrogenolysis metal selected from group 8, 9 or 10 of the periodic table of elements. WO2016/114658 shows that higher polyols (e.g. glycerol, erythritol or sorbitol) tend to be produced as by-products in a process for the preparation of ethylene glycol from carbohydrates. A polyol (e.g., glycerol, xylitol, sorbitol, or erythritol) may be added to the diluent. They can also be used as entrainers for butanediol and subsequently recycled to the process. The method may be operated in a continuous mode of operation: wherein the feedstock comprises at least a diluent (comprising an alkylene glycol) and a carbohydrate source; and wherein such feedstock is passed through a plug flow reactor in the presence of hydrogen and in the presence of a catalyst system.

Although higher polyols (e.g. sorbitol) can be recycled as described in WO2016/114658, the recycling of such higher polyols in large quantities is not ideal. Higher polyols (e.g., sorbitol) cannot be completely converted under reactor conditions for conversion of the carbohydrate source. Therefore, the concentration of such higher polyols will build up slowly, making the process less suitable for continuous operation.

WO2015028398 describes a process for the preparation of ethylene glycol and 1, 2-propylene glycol from a starting material comprising one or more saccharides, wherein the process comprises the steps of: i) providing starting materials and hydrogen to a first reactor, the first reactor operating in a mixed manner; ii) reacting the starting material and hydrogen in the presence of a solvent and a catalyst system in a first reactor; iii) continuously removing the first reactor product stream from the first reactor; iv) feeding at least a portion of the first reactor product stream to a second reactor, the reactor operating substantially in plug flow mode; and v) further reacting the first reactor product stream and hydrogen in the presence of a solvent and optionally a catalyst system in a second reactor. The catalyst system may comprise one or more materials selected from group 8, 9 or 10 transition metals or compounds thereof and one or more materials selected from tungsten, molybdenum and compounds and complexes thereof. In one embodiment, a homogeneous catalyst system is used in the first reactor, which may be left in the first reactor product stream and fed to the second reactor in that stream.

WO2015028398 desires to obtain complete conversion of the starting material and/or any intermediates and to reduce the formation of by-products. However, the examples do not show a reduction in the formation of by-products. In contrast, as illustrated by the examples of WO2015028398, while the formation of the desired product monoethylene glycol increased by several tens of percentage points in examples 2 and 3, the formation of the by-product 1, 2-butanediol increased by several hundred percentage points. The formation of higher polyol by-products (e.g., glycerol, erythritol, or sorbitol) was not confirmed, but it is expected that it also increases under these circumstances.

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

Disclosure of Invention

Such a method is obtained according to the method of the invention. Accordingly, the present invention provides a process for the production of ethylene glycol comprising the steps of:

(i) providing a carbohydrate source, a solvent, hydrogen, a first heterogeneous catalyst comprising one or more transition metals from groups 8, 9 or 10 of the periodic table of elements, and a homogeneous catalyst comprising tungsten to a first reactor;

(ii) reacting at least a portion of the carbohydrate source in the first reactor in the presence of hydrogen, a solvent, a first heterogeneous catalyst, and a homogeneous catalyst at a temperature in the range of greater than or equal to 170 ℃ to less than or equal to 270 ℃;

(iii) removing a first reactor product stream from the first reactor and separating from the first reactor product stream at least:

-one ethylene glycol rich fraction; and

-a sorbitol rich fraction containing concentrated homogeneous catalyst;

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

(v) reacting at least a portion of the sorbitol rich fraction containing the concentrated homogeneous catalyst in a second reactor at a temperature in the range of greater than or equal to 200 ℃ to less than or equal to 300 ℃ in the presence of hydrogen gas, a second heterogeneous catalyst containing one or more transition metals of groups 8, 9 or 10 of the periodic Table of the elements;

(vi) the second reactor product stream is removed 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 described in WO2016114658, higher polyols (e.g. glycerol, erythritol or sorbitol) tend to be produced as by-products in the first reactor. These higher polyols have high boiling points (i.e., boiling points above 250 ℃ at 0.1 megapascals atmospheric pressure) and are also referred to herein as "heavy polyols". A polyol is herein understood to be an organic compound comprising a plurality of, suitably three or more, hydroxyl groups. A heavy polyol by-product of particular interest is sorbitol.

As noted above, recycling only such heavy polyols will result in a slow build-up of heavy polyol concentration in the reactor product stream, making the process less suitable for continuous operation. Merely reacting the reactor product stream from the first reactor further in a further second reactor does not solve the problem as described in WO 2015028398.

The high solubility of homogeneous catalysts in heavy polyols further makes it difficult to separate such homogeneous catalysts from the reactor product stream by precipitation and/or filtration. Removal of heavy polyols by vacuum distillation is also considered difficult.

By separating heavy polyols and converting such heavy polyols into lower boiling products in a further second reactor, a stream containing homogeneous catalyst dissolved in a mixture containing alkylene glycol, other diols and/or other polyols can be obtained which is very suitable for recycling to the first reactor. Homogeneous catalysts can also be more simply separated from such mixtures by evaporation, distillation, precipitation and/or filtration.

The inventors have surprisingly found that the conversion of heavy polyols in such second reactors is possible if a catalyst system is used in the second reactor which has a higher concentration of homogeneous catalyst than in the first reactor.

Advantageously, in the process according to the invention, the sorbitol by-product formed in the first reactor can be concentrated to a sorbitol rich fraction, which also contains the concentrated homogeneous catalyst. Such sorbitol rich fraction may then advantageously be fed together with the concentrated homogeneous catalyst to a second reactor where sorbitol may be at least partially converted to lower boiling products.

Drawings

The invention is shown in the following drawings:

figure 1 shows an example of a method according to the invention.

Detailed Description

Step (i) comprises: a carbohydrate source, a solvent, hydrogen, a first heterogeneous catalyst comprising one or more transition metals from groups 8, 9 or 10 of the periodic table of the elements, and a homogeneous catalyst comprising tungsten are provided to the first reactor.

A carbohydrate source in this context is understood to be a source of carbohydrates. The carbohydrate source may be selected from a variety of sources. Preferably, the carbohydrate source comprises one or more carbohydrates selected from the group consisting of: polysaccharides, oligosaccharides, disaccharides, monosaccharides, and mixtures thereof.

Suitable examples may include sources of (preferably sustainable) carbohydrates, such as: cellulose, hemicellulose, starch, sugars (such as sucrose), mannose, arabinose, fructose, glucose and mixtures thereof. Carbohydrate sources containing the above carbohydrates may include: dextrose syrup, maltose syrup, cane syrup, glucose syrup, crystalline sucrose, crystalline glucose, wheat starch, corn starch, potato starch, tapioca starch, and other carbohydrate-containing streams (e.g., pulp streams), wood waste, paper waste, agricultural waste, cellulosic residues recovered from municipal waste, paper, cardboard, sugarcane, sugar beet, wheat, rye, barley, corn, rice, potato, tapioca, other crops, and combinations thereof. These streams may require pre-treatment to extract carbohydrates (e.g. wet milling in the case of corn) or to remove components that interfere with the process, such as alkaline fillers (e.g. to remove calcium carbonate from waste paper). Thus, the process according to the invention can use natural resources, but can also be used for upgrading and efficient reuse of waste streams. Preferably, the carbohydrates in the carbohydrate source are selected from: cellulose, hemicellulose, starch, glucose, sucrose, glucose oligomers, and combinations thereof. Since cellulose has difficulties not present 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.

Suitably, the carbohydrate source may be provided to the first reactor together with at least part of the solvent. More preferably, the carbohydrate source is partially or completely dissolved in the solvent. Preferences for such solvents are provided below. The solvent may be, for example, an aqueous medium, an organic medium including an alkylene glycol, or a mixture containing water, glycol, and/or other polyol. Many carbohydrates are soluble in water or mixtures containing water, glycols and/or other polyols. The carbohydrate source may also be provided to the first reactor in the form of a slurry. Examples of such slurries include aqueous mixtures of water and hemicellulose, hemicellulose sugars, glucose and/or starch.

The present process advantageously allows for providing a very concentrated feed stream containing a carbohydrate source to the first reactor. When such a concentrated feed stream is employed, process economics benefit. Such a feed stream may suitably comprise a carbohydrate source and a solvent, for example water and/or a glycol and/or other polyol.

Preferably, the carbohydrate source is provided to the first reactor by a feed stream comprising the carbohydrate source and the solvent, wherein such feed stream comprises the carbohydrate source in the following ranges based on the total weight of the carbohydrate source and the solvent: greater than or equal to 1.0 wt% (weight percent), preferably greater than or equal to 10.0 wt%, more preferably greater than or equal to 20.0 wt%, to, less than or equal to 90.0 wt%, preferably less than or equal to 70.0 wt%, more preferably less than or equal to 50.0 wt%. Feed streams containing a source of carbohydrate within this concentration range may suitably be readily transportable. The feed stream may also consist of only (100 wt.%) carbohydrate source. For practical purposes, the carbohydrate source may be provided to the first reactor by a feed stream comprising the carbohydrate source and a solvent, wherein such feed stream comprises the carbohydrate source in the following ranges based on the total weight of the carbohydrate source and the solvent: greater than or equal to 2.0 wt%, preferably greater than or equal to 10.0 wt%, to, less than or equal to 50.0 wt%, preferably less than or equal to 30.0 wt%. Most preferably, feed streams containing or consisting of a carbohydrate source and a solvent are provided to the first reactor, wherein such feed streams contain the carbohydrate source in the following ranges based on the total weight of the carbohydrate source and the solvent: greater than or equal to 20.0 wt% to less than or equal to 50.0 wt%, more preferably to less than or equal to 30.0 wt%. It is believed that such feed streams containing greater than or equal to 20.0 wt% of the carbohydrate source may make the process more economically attractive. Such solvents may comprise any of the solvents described below, but are preferably water. Most preferably, the carbohydrate source is provided to the first reactor by a feed stream comprising the carbohydrate source and the solvent, wherein such feed stream comprises the carbohydrate source in the following ranges based on the total weight of the carbohydrate source and the solvent: greater than or equal to 2.0 wt% to less than or equal to 30.0 wt%.

The carbohydrate source is preferably added to the first reactor continuously or periodically. The carbohydrate source is preferably provided to the first reactor under a blanket of inert gas (e.g. nitrogen).

Preferably, part of the solvent is provided by at least part of the second reactor product stream recycled from step (vi). At least a portion of such second reactor product stream preferably comprises a homogeneous catalyst dissolved in a solvent. Such solvents may suitably comprise products of heavy polyol conversion, such as alkylene glycols and/or other glycols. These alkylene glycols and/or other glycols may be very suitable solvents, as described below.

As described above, the solvent may be supplied as part of a feed stream comprising the carbohydrate source. It is also possible to provide the solvent to the first reactor separately or independently from the carbohydrate source and/or the second reactor product stream.

Preferably, a feed stream containing a carbohydrate source and a solvent is used. The concentration of the carbohydrate source in such feed streams may be suitably adjusted to provide sufficient solvent to the first reactor.

Water may be a very suitable solvent, as most carbohydrates are soluble in water. The water may optionally be mixed with an organic solvent, which may have a beneficial effect on the solubility of any of the reactants, or other advantages.

Thus, the solvent is preferably selected from water and organic solvents (e.g. glycols and/or other polyols) and mixtures thereof. Suitably, the solvent may be a mixture of water and optionally one or more of the above organic solvents. The organic solvent is preferably an alkanol. Such alkanols may be monoalcohols, preferably water-miscible monoalcohols such as methanol, ethanol, propanol, butanol and mixtures thereof. However, such light monoalcohols are less preferred for the process according to the invention. The alkanol may also be a water-miscible diol or other polyol, for example: ethylene glycol, propylene glycol, butylene glycol, glycerol, xylitol, sorbitol or erythritol. By a diol is herein understood an organic compound comprising two hydroxyl groups. The solvent preferably comprises an alkylene glycol. Examples of preferred alkylene glycols include ethylene glycol, propylene glycol, butylene glycol, and mixtures thereof. The use of alkylene glycols is particularly advantageous because it has been found that glycols and/or polyols (including alkylene glycols) promote dissolution of tungsten or tungsten compounds in the solvent, thereby promoting the catalytic activity of the tungsten or tungsten compounds. It has also been found that by using an alkylene glycol as a component in the solvent, the selectivity of the reaction to the alkylene glycol is increased. Without wishing to be bound by any theory, it is believed that tungsten forms complexes with alkylene glycols, thus reducing conversion to by-products. Furthermore, the use of an alkylene glycol as solvent does not involve the introduction of extraneous agents into the reaction mixture, which is an advantage. The solvent preferably comprises 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 thereof. Most preferably, the solvent comprises a mixture of water, one or more alkylene glycols and optionally one or more heavy polyols.

The solvent is preferably added to the first reactor continuously or periodically. While a portion of the solvent may be continuously or periodically removed from the first reactor.

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

The total pressure during the reaction comprises the vapor pressure of the solvent and reactants at the applied temperature and pressure, the partial pressure of hydrogen, and if present, the partial pressure of any inert gases. Preference for total pressure is provided below.

The hydrogen may suitably be supplied to the first reactor through a dip tube (e.g. a dip tube near the stirrer) or through a distributor (e.g. a sparger). Through such dip tubes or dispensers, and optionally through one or more stirring mechanisms, hydrogen can be dissolved in the reaction mixture. Hydrogen is preferably added continuously or periodically to the first reactor.

In addition to the carbohydrate source, the solvent and hydrogen, a homogeneous catalyst containing tungsten and a heterogeneous catalyst comprising one or more transition metals of groups 8, 9 or 10 of the periodic table of the elements are provided to the first reactor.

Homogeneous and heterogeneous catalysts together are also referred to herein as catalyst systems.

Homogeneous catalysts are also referred to herein as tungsten-containing homogeneous catalysts.

Tungsten may be present as elemental tungsten or as a tungsten compound. Such tungsten compounds may be, for example, tungstic acid or tungstate. Thus, the homogeneous catalyst may suitably comprise one or more tungsten compounds. Tungsten or a tungsten compound may suitably be dissolved in the reaction mixture. Preferably, the oxidation state of tungsten is at least + 2. More preferably, the oxidation state of tungsten is +5 or + 6. When dissolved in the reaction mixture, the dissolved tungsten or the dissolved tungsten compound may form a complex with the solvent and/or the (other) components of the reaction mixture.

The homogeneous catalyst provided to the first reactor can be the homogeneous catalyst as-prepared or recycled from, for example, the second reactor product stream. The as-prepared homogeneous catalyst is also referred to herein as a "virgin" homogeneous catalyst. Such native homogeneous catalysts are preferably selected from tungstic acid (H) ₂WO₄) With tungstic acids, e.g. tungstatesSubstances, e.g. containing at least one group 1 or 2 element, e.g. sodium tungstate (Na)₂WO₄) Or potassium tungstate (K)₂WO₄) Or for example, ammonium tungstate, as well as mixtures of one or more of the foregoing.

The recycled homogeneous catalyst may simply be referred to as "recycled" homogeneous catalyst. The homogeneous catalyst provided to the first reactor in step (i) preferably comprises a recycled homogeneous catalyst or a combination of a virgin homogeneous catalyst and a recycled homogeneous catalyst. The homogeneous catalyst provided to the reactor in the present invention may, for example, comprise or consist of recycled tungsten species recovered directly or indirectly (e.g., by distillation) from the reactor effluent.

Any recycled homogeneous catalyst may contain tungsten in the form of a complex with components from the solvent in which such homogeneous catalyst may be dissolved. Thus, the circulating homogeneous catalyst may suitably comprise tungsten in a form derived from the precursor tungsten compound initially provided.

The homogeneous catalyst preferably contains a tungsten compound or tungsten derived from a tungsten compound, wherein such tungsten compound is selected from tungstic acid (H)₂WO₄) Tungsten bronze (with H)_xWO₃Or M_xWO₃Wherein x is a variable less than 1: ( <1) And M is a metal such as an alkali metal or an alkaline earth metal), ammonium tungstate, ammonium metatungstate, ammonium paratungstate, a tungstic acid compound containing at least one group 1 or 2 element, a metatungstic acid compound containing at least one group 1 or 2 element, a paratungstic acid compound containing at least one group 1 or 2 element, tungsten oxide (WO)₃) Heteropoly acid compounds of tungsten and combinations thereof. Tungstic acid (H) is preferred₂WO₄) Tungsten bronze (H)_xWO₃) And tungstic acid compounds containing at least one group 1 or 2 element (e.g., sodium tungstate (Na)₂WO₄) Or potassium tungstate (K)₂WO₄)). Most preferably, the homogeneous catalyst comprises a tungsten compound or tungsten derived from a tungsten compound, wherein such tungsten compound is sodium tungstate and/or tungstic acid and/or tungsten bronze.

It has been found that if tungsten or suitably a tungsten compound is dissolved,the catalytic activity of tungsten or tungsten compounds is advantageously increased. The homogeneous catalyst is preferably added continuously or periodically to the first reactor. Preferably, such homogeneous catalysts, which contain tungsten with a titanium oxide of at least +2, are added continuously or periodically. The homogeneous catalyst is preferably selected from tungstic acid (H)₂WO₄) Tungsten bronze (H)_xWO₃) Sodium tungstate, dissolved tungstate ions, dissolved metatungstate ions, and dissolved paratungstate ions.

Since tungsten can exist in such various forms, the tungsten compounds herein are also referred to as tungsten species. Tungsten species in this context is understood to be any compound comprising or consisting of the element tungsten in any form or oxidation state.

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

The amount of tungsten supplied to the first reactor is preferably such that its concentration in the reactor remains substantially constant. Substantially constant in this context is to be understood as meaning that the difference between the highest and the lowest amount of tungsten does not exceed 10% of the average amount of tungsten in the reactor. The process of the present invention is preferably a continuous or semi-continuous process. The tungsten compound is preferably added continuously or periodically to the first reactor. While a portion of the tungsten compound may be continuously or periodically removed from the first reactor, suitably by the first reactor product stream. Although periodic addition of tungsten is feasible, it is preferred to provide a 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: greater than or equal to 0.01 weight percent (corresponding to 100 parts per million by weight (ppmw)) to less than or equal to 1.0 weight percent tungsten (calculated as metallic tungsten). More preferably, the concentration of the tungsten compound in the reaction mixture during the reaction ranges from: greater than or equal to 0.01 wt% (corresponding to 100 parts per million by weight (ppmw)), preferably greater than or equal to 0.05 wt%, to, less than or equal to 0.5 wt% tungsten (calculated as metallic tungsten).

The first heterogeneous catalyst and the second heterogeneous catalyst each independently comprise one or more transition metals of groups 8, 9 or 10 of the periodic table of the elements. The transition metal may be selected from a wide range of transition metals as described in WO 2016/114658. The one or more transition metals are preferably selected from the group consisting of Cu, Fe, Ni, Co, Pt, Pd, Ru, Rh, Ir, Os, and combinations thereof. More preferably, the one or more transition metals are selected from the group consisting of Ni, Pd, Pt, Ru, Rh, Ir, and combinations thereof. Most preferred are nickel, ruthenium, and combinations thereof. These metals have been found to provide good yields. The transition metal may suitably be present in its metallic form or in the form of its hydride or oxide or as other compound. The transition metal may also be present in a partially tungstated form. Partially tungstated transition metal in this context is understood to be a transition metal which is partially covered by deposited tungsten species.

Preferably, the first heterogeneous catalyst and the second heterogeneous catalyst each independently comprise one or more transition metals of groups 8, 9 or 10 of the periodic table of the elements supported on a carrier. The support may be selected from a wide range of known support materials. Suitable supports include activated carbon (also referred to as "activated carbon"), silica, zirconia, alumina, silica-alumina, titania, niobia, iron oxide, tin oxide, zinc oxide, silica-zirconia, zeolitic aluminosilicates, titanosilicates, magnesia, silicon carbide, clays, and combinations thereof. Activated carbon in this context is understood to mean a surface area of at least 800m²Amorphous carbon per gram. Such activated carbon suitably has a porous structure. Most preferred supports are activated carbon, silica-alumina and alumina. More preferably, the catalyst comprises ruthenium and/or nickel as transition metal and comprises activated carbon as support. Most preferably, the first heterogeneous catalyst comprises ruthenium and/or nickel supported on activated carbon and/or the second heterogeneous catalyst comprises ruthenium and/or nickel supported on activated carbon. Most preferably, the heterogeneous catalyst comprises ruthenium, preferably supported On activated carbon.

As described in more detail below, the first heterogeneous catalyst and/or the second heterogeneous catalyst may be present, for example, in the form of an emulsion, a slurry or a fixed bed. The first heterogeneous catalyst and/or the second heterogeneous catalyst each independently comprise a transition metal in the following ranges, based on the total weight of the transition metal and the support: preferably greater than or equal to 1.0 wt% to less than or equal to 50.0 wt%, more preferably greater than or equal to 2.0 wt%, more preferably greater than or equal to 5.0 wt%, to, less than or equal to 50.0 wt%, more preferably less than or equal to 20.0 wt%. If a feed stream to the first reactor containing greater than or equal to 20.0 wt% of the carbohydrate source based on the total weight of the carbohydrate source and solvent is used, a first heterogeneous catalyst comprising a transition metal in the following range is preferably used, based on the total weight of transition metal and support: greater than or equal to 5.0 wt%, more preferably greater than or equal to 10.0 wt%, to less than or equal to 50.0 wt%, more preferably less than or equal to 20.0 wt%. It is believed that such high loadings of transition metal can advantageously aid in the conversion of a feedstream containing a high concentration of carbohydrate source.

The first heterogeneous catalyst may comprise more than one metal. Suitably, the first heterogeneous catalyst may comprise at least one noble metal selected from Pd, Pt, Ru, Rh and Ir and a transition metal selected from groups 8, 9 or 10 of the periodic table of the elements. The first heterogeneous catalyst can comprise, for example, a combination of metals, such as Ni/Ir, Ni/Pt, Ni/Pd, Ni/Ru, Ru/Ir, Ru/Pt, or Ru/Pd.

Furthermore, as described in more detail below, tungsten species may deposit on the first heterogeneous catalyst and/or the second heterogeneous catalyst during the reaction. Thus, at least a part of the first heterogeneous catalyst and/or at least a part of the second heterogeneous catalyst may contain tungsten in addition to one or more transition metals selected from groups 8, 9 or 10 of the periodic table of the elements.

The process of the present invention is preferably a continuous or semi-continuous process. The slurry of the first heterogeneous catalyst is preferably added to the first reactor continuously or periodically, for example together with a solvent.

At least part of the transition metal may be tungstated during step (ii). Tungstated herein is understood to mean that such transition metals are covered by deposited tungsten species. Any partially or fully tungstated heterogeneous catalyst may be partially regenerated and recycled. Thus, the first heterogeneous catalyst provided to the first reactor may or may not comprise any tungstated transition metal.

Preferably, such a slurry of first heterogeneous catalysts comprises heterogeneous catalysts in the following ranges, based on the total weight of such slurry: greater than or equal to 5 wt% to less than or equal to 90 wt%, more preferably less than or equal to 70 wt%, and most preferably less than or equal to 50 wt%. Such slurries are preferably heterogeneous catalyst slurries in water and/or alkylene glycols (e.g. ethylene glycol and/or propylene glycol and/or butylene glycol) and/or polyols.

The weight ratio of the total amount of tungsten species (calculated on a metal basis) provided to the first reactor relative to the transition metal (calculated on a metal basis) provided to the first reactor can vary between wide ranges. The weight ratio of the weight of tungsten relative to the total weight of the transition metal, both calculated on the basis of the metal, when supplied to the first reactor, is preferably greater than or equal to 1:3000 to less than or equal to 50:1 (weight ratio of metallic tungsten to transition metal (weight/weight)). More preferably, the weight ratio of the weight of tungsten relative to the total weight of the transition metal, both calculated on the basis of the metal, when provided to the first reactor, is preferably greater than or equal to 1:200 to less than or equal to 50:1 (weight ratio of metallic tungsten to transition metal (weight/weight)).

The weight ratio of the total amount of tungsten species present in the first reactor (calculated on the basis of the metal) relative to the transition metal species present in the first reactor (calculated on the basis of the metal) may also vary between wide ranges. The weight ratio of the weight of tungsten relative to the total weight of the transition metal, both calculated on the basis of the metal, when present in the first reactor, is preferably greater than or equal to 1:3000 to less than or equal to 50:1 (weight ratio of metallic tungsten to transition metal (weight/weight)). More preferably, the weight ratio of the weight of tungsten relative to the total weight of the transition metal, both calculated on the basis of the metal, when present in the first reactor, is preferably greater than or equal to 1:200 to less than or equal to 50:1 (weight ratio of metallic tungsten to transition metal (weight/weight)).

More preferably, the molar ratio of moles of tungsten relative to the total moles of transition metal, all calculated on the metal basis, when present in the first reactor, is preferably greater than or equal to 1:1 to less than or equal to 25:1, more preferably greater than or equal to 2:1 to less than or equal to 20:1 (metal tungsten: transition metal (moles/mole)).

The concentration of tungsten compounds (calculated as metallic tungsten) based on the weight of the carbohydrate source introduced into the first reactor is in the following range: preferably greater than or equal to 0.1 wt%, more preferably greater than or equal to 1 wt%, to, less than or equal to 35 wt%; more preferably greater than or equal to 0.2 wt%, more preferably greater than or equal to 2 wt%, to less than or equal to 25 wt%.

The concentration of transition metal introduced into the first reactor per hour is preferably in the following range based on the weight of the carbohydrate source introduced into the first reactor per hour: greater than or equal to 0.001 wt%, more preferably greater than or equal to 0.01 wt%, more preferably greater than or equal to 0.1 wt%, more preferably greater than or equal to 0.2 wt%, to, less than or equal to 2.0 wt%, more preferably less than or equal to 1.0 wt%.

The first reactor may be any type of reactor known to be suitable for the production of ethylene glycol from a carbohydrate source. The first reactor is preferably a stirred or mixed reactor. The first reactor may be, for example, a slurry reactor, an ebullated bed reactor, a fluidized bed reactor, a bubble reactor, an external circulation loop reactor, or a Continuous Stirred Tank Reactor (CSTR), or other type of mechanically stirred reactor. The first reactor is most preferably a Continuous Stirred Tank Reactor (CSTR). The use of a CSTR is very advantageous for the present process, since a CSTR provides an excellent means of diluting the final concentration of carbohydrates in the CSTR, whereas the feed stream may contain a high concentration of carbohydrates. While the alkylene glycol produced by the reaction of the carbohydrate provides a medium in which the tungsten compound can dissolve, thereby contributing to the catalytic activity of the tungsten catalyst component.

Step (ii) comprises: reacting at least a portion of the carbohydrate source in the first reactor in the presence of hydrogen, a solvent, a first heterogeneous catalyst, and a homogeneous catalyst at a temperature in the range of greater than or equal to 170 ℃ to less than or equal to 270 ℃. Such reactions suitably produce at least ethylene glycol and sorbitol, and optionally one or more other glycols and/or other polyols. The residence time in the first reactor can vary. Preferably, the average residence time of the carbohydrate source in the first reactor is at least 1 minute (average residence time herein is understood to be the average time it takes for the material to flow through volume "V" at a volume rate "u", as further explained in the handbook of Chemical Kinetics and reactor design, published in 2001 by a. kayode coder, Butterworth Heinemann). The mean residence time of the carbohydrate source in the first reactor is preferably greater than or equal to 1 minute to less than or equal to 6 hours, more preferably greater than or equal to 3 minutes to 2 hours, most preferably greater than or equal to 5 minutes to less than or equal to 45 minutes. However, if the carbohydrate source reacts rapidly, the average residence time may also be shorter than 5 minutes or even shorter than 3 minutes. If a feed stream to the first reactor containing greater than or equal to 20 wt% of the carbohydrate source based on the total weight of the carbohydrate source and solvent is used, the average residence time of the carbohydrate source in the first reactor is preferably greater than or equal to 5 minutes, more preferably greater than or equal to 10 minutes, and preferably less than or equal to 2 hours, more preferably less than or equal to 45 minutes. It is believed that such longer mean residence times may advantageously aid in the conversion of a feedstream containing a high concentration of carbohydrate source.

The continuous process is preferably operated at a Weight Hourly Space Velocity (WHSV), expressed as mass of carbohydrate source per mass of transition metal per hour, calculated as metal, in the following ranges: 0.01 to 100 hours^-1Preferably 0.05 to 10 hours^-1. For practical purposes, it can be used for 0.5 to 2.0 hours^-1WHSVB in between.

The partial pressure of hydrogen applied during step (ii) is preferably in the following range: greater than or equal to 1.0 megapascals (MPa), preferably greater than or equal to 2.0MPa, more preferably greater than or equal to 3.0MPa, to, less than or equal to 16.0MPa, preferably less than or equal to 12.0MPa, more preferably less than or equal to 8.0 MPa. All pressures herein are absolute pressures.

The total pressure applied during step (ii) is suitably at least 1.0MPA, preferably at least 2.0MPA, more preferably at least 3.0 MPA. The total pressure applied during step (ii) is suitably at most 16.0MPA, more preferably at most 10.0 MPA. Preferably, the reactor is pressurized with hydrogen prior to the addition of any starting materials. One skilled in the art will appreciate that the pressure at 20 ℃ will be lower than the actual pressure at the reaction temperature. The pressure applied during step (ii) when switching back to 20 ℃ is preferably equal to a pressure of greater than or equal to 0.7MPA to less than or equal to 8.0 MPA.

As described above, pressure may be applied by hydrogen or a hydrogen-containing gas, optionally in combination with the partial pressure of the contents of the reaction mixture. When heating the reaction mixture, the total pressure during the reaction is suitably in the range of from 1.0MPA to 16.0 MPA.

Preferably, during step (ii), the partial pressure of hydrogen at the reaction temperature is maintained in the range of from 1.0MPA to 16.0MPA (abs), preferably throughout the reaction. Thus, as mentioned above, hydrogen or a hydrogen-containing gas is preferably introduced into the reaction mixture during the reaction.

As described above, the pressure may be applied by hydrogen gas or a hydrogen-containing gas. When a hydrogen-containing gas is used, suitably the hydrogen content of the hydrogen-containing gas is up to 100% by volume. Most preferably, pure hydrogen is used to apply the pressure. Hydrogen is consumed during the reaction. Thus if the process is a continuous or semi-continuous process, it is preferred to provide the hydrogen in a continuous or semi-continuous manner.

The reaction can be carried out at a wide range of temperatures. At least a portion of the carbohydrate source is reacted with hydrogen in the first reactor at a temperature in a range from greater than or equal to 170 ℃ to less than or equal to 270 ℃. More preferably, at least a portion of the carbohydrate source is reacted with hydrogen at a temperature in the range of greater than or equal to 200 ℃ to less than or equal to 240 ℃. The first reactor may be brought to a temperature within these ranges before any starting materials are added, and may be maintained at a temperature within this range.

The reaction in step (ii) suitably results in a first reactor product stream. The first reactor product stream suitably contains ethylene glycol, sorbitol, and optionally one or more other by-products (e.g. erythritol). The first reactor product stream may suitably contain, for example, ethylene glycol (1, 2-ethanediol) and one or more by-products, such as diethylene glycol (2,2' -oxybis (eth-1-ol)), propylene glycol (1, 2-propanediol), glycerol (1,2, 3-propanetriol), 1, 2-butanediol, 1, 3-butanediol, 2, 3-butanediol, 1, 4-butanediol, methanol, ethanol, propanol, butanol, sorbitol (1,2,3,4,5, 6-hexanehexol) and/or erythritol (1,2,3, 4-butanetetraol). Glycerol (1,2, 3-propanetriol), sorbitol (1,2,3,4,5, 6-hexanehexol) and erythritol (1,2,3, 4-butanetetraol) are polyols having a high boiling point, i.e. a boiling point above 250 ℃ at 0.1 MPa atmospheric pressure. As noted above, such polyols having a boiling point above 250 ℃ at an atmospheric pressure of 0.1 megapascals are also referred to herein as "heavy polyols".

Step (iii) comprises: removing a first reactor product stream from the first reactor and separating from the first reactor product stream at least:

-one ethylene glycol rich fraction; and

-a sorbitol rich fraction containing concentrated homogeneous catalyst.

By sorbitol rich fraction is herein understood a fraction of the first reactor product stream comprising a higher concentration (e.g. a higher weight percentage) of sorbitol than the first reactor product stream itself. Such sorbitol rich fractions may also be referred to herein as sorbitol rich fractions. Preferably, the sorbitol rich fraction may comprise sorbitol in the following ranges based on the total weight of the sorbitol rich fraction: greater than or equal to 5 wt%, more preferably greater than or equal to 10 wt%, more preferably greater than or equal to 20 wt%, most preferably greater than or equal to 30 wt%, to, less than or equal to 100 wt%, preferably less than or equal to 90 wt%.

An ethylene glycol-rich fraction is herein understood to be a fraction of the first reactor product stream comprising a higher concentration (e.g. a higher weight percentage) of ethylene glycol than the first reactor product stream itself. Such ethylene glycol rich fractions may also be referred to herein as ethylene glycol rich fractions. Preferably, the ethylene glycol rich fraction may comprise ethylene glycol in the following ranges based on the total weight of the ethylene glycol rich fraction: greater than or equal to 5 wt%, more preferably greater than or equal to 10 wt%, more preferably greater than or equal to 20 wt%, most preferably greater than or equal to 30 wt%, to, less than or equal to 100 wt%, preferably less than or equal to 90 wt%.

The separation may be carried out by any suitable means known to those skilled in the art, including for example evaporation and/or distillation.

More preferably, step (iii) comprises separating (e.g., by distillation) at least a portion of the first reactor product stream into one or more sorbitol-depleted fractions and at least one sorbitol-enriched fraction. By sorbitol depleted fraction is herein understood a fraction of the first reactor product stream comprising a lower concentration (e.g. lower weight percentage) of sorbitol than the first reactor product stream itself. Such sorbitol-poor fractions may also be referred to herein as sorbitol-deficient fractions. One or more sorbitol depleted fractions may suitably be enriched in an alkylene glycol (e.g. ethylene glycol or propylene glycol). Thus, step (iii) may suitably comprise separating (e.g. by distillation) at least a portion of the first reactor product stream into at least:

-one ethylene glycol rich and sorbitol lean fraction;

-one or more further sorbitol depleted fractions; and

-a sorbitol rich fraction containing concentrated homogeneous catalyst.

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

Prior to separating (e.g., in a distillation step) the sorbitol rich fraction and/or the ethylene glycol rich fraction, the first reactor product stream is preferably 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. C1-C4 monoalkanols are to be understood herein as monoalkanols comprising from 1 to 4 carbon atoms. Examples of such one or more C1-C4 monoalcohols include methanol, ethanol, propanol, and/or butanol.

Subsequently, at least a portion of the first reactor product stream residue (from which optional hydrogen, C1-C4 monoalkanol, and/or water has been removed) is preferably distilled into at least:

-one or more sorbitol-depleted and optionally alkylene glycol-rich fractions; and

a sorbitol rich fraction containing concentrated homogeneous catalyst, sorbitol and optionally one or more other heavy polyols (e.g. glycerol and/or erythritol).

Only a portion of the first reactor product stream or all of it may be distilled. The alkylene glycol is preferably ethylene glycol, propylene glycol, butylene glycol or a mixture of two or more thereof.

The sorbitol rich fraction may suitably be obtained by separating a fraction comprising compounds boiling at a temperature higher than or equal to 250 ℃ at a pressure of 0.1 mpa. Thus, step (iii) suitably comprises removing the first reactor product stream from the first reactor and separating from such first reactor product stream at least one fraction containing compounds boiling at a temperature greater than or equal to 250 ℃ at a pressure of 0.1 megapascals and further containing concentrated homogeneous catalyst. Such fractions containing compounds that boil at a temperature greater than or equal to 250 ℃ at a pressure of 0.1 megapascals are also referred to herein as "heavy fractions".

Suitably, step (iii) may comprise separating (e.g. by distillation) at least a portion of the first reactor product stream into: a fraction comprising compounds having a boiling point below 250 ℃ at a pressure of 0.1 mpa (also referred to as "light fraction"); a fraction comprising compounds having a boiling point higher than or equal to 250 ℃ at a pressure of 0.1 megapascal (also referred to as "heavy fraction"). Such light fraction may suitably be an ethylene glycol rich fraction, while such heavy fraction may suitably be a sorbitol rich fraction. It will be appreciated by those skilled in the art that any distillation may actually be carried out at reduced or vacuum pressure in order to isolate the above compounds, such that the separation is carried out at a temperature below 250 ℃.

Preferably, the sorbitol rich or heavy fraction contains not only sorbitol but also other heavy polyols, such as glycerol and erythritol. Preferably, such fractions contain the following ranges of heavy polyols (i.e., polyols that boil at a temperature greater than or equal to 250 ℃ at a pressure of 0.1 megapascals), based on the total weight of the fraction: greater than or equal to 0.5% to less than or equal to 99.5% by weight, more preferably greater than or equal to 1.0% to less than or equal to 60.0% by weight. More preferably, such fractions contain sorbitol in the following ranges based on the total weight of the fraction: greater than or equal to 0.5% to less than or equal to 99.5% by weight, more preferably greater than or equal to 1.0% to less than or equal to 60.0% by weight. Most preferably, the sorbitol rich fraction contains greater than or equal to 2.0 wt% to less than or equal to 50.0 wt% sorbitol, based on the total weight of the sorbitol rich fraction.

The sorbitol rich fraction further contains a concentrated homogeneous catalyst. Concentrated homogeneous catalyst is herein understood to be a homogeneous catalyst having a higher concentration than the concentration of homogeneous catalyst in the first reactor product stream. Preferably, the concentration of the homogeneous catalyst in the sorbitol rich fraction is in the following range based on the total weight of the sorbitol rich fraction: greater than or equal to 0.5 wt.% to less than or equal to 10.0 wt.%, more preferably 0.5 wt.% to less than or equal to 5.0 wt.%, most preferably 1.0 wt.% to less than or equal to 5.0 wt.%, all calculated as tungsten metal. The homogeneous catalyst may be concentrated in the sorbitol rich fraction by any suitable means known to those skilled in the art, including evaporation and/or distillation of other compounds in the first reactor product stream.

Sorbitol and/or dissolved homogeneous catalyst cannot be simply distilled off. Thus, the dissolved homogeneous catalyst can be suitably concentrated together with sorbitol in the sorbitol rich fraction by evaporating and/or distilling off other compounds in the first reactor product stream. Subsequently, such sorbitol rich fraction preferably contains the concentrated homogeneous catalyst, sorbitol and one or more other heavy polyols (e.g. glycerol and/or erythritol). In addition, the sorbitol rich fraction may contain other compounds.

Step (iv) comprises: hydrogen and at least a portion of the sorbitol rich fraction containing the concentrated homogeneous catalyst are provided to a second reactor.

The second reactor may be any type of reactor known to be suitable for the production of ethylene glycol from a carbohydrate source. The second reactor may be, for example, a fixed bed reactor, a trickle flow reactor, a slurry reactor, an ebullating bed reactor, a fluidized bed reactor, a plug flow reactor, a bubble reactor, an external circulation loop reactor, or a Continuous Stirred Tank Reactor (CSTR), or other type of mechanically stirred reactor. Most preferably, the second reactor is a plug flow reactor. The first reactor and the second reactor may be the same or different types of reactors. Preferably, the process according to the invention is carried out in a reactor combination, wherein the first reactor is a continuous stirred tank 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 may subsequently be converted, as described below.

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

Additionally, a fresh hydrogen stream is provided to the second reactor. Suitably, the preference for providing such hydrogen is the same as in the case of the first reactor described above. For example, hydrogen may be supplied as a mixture of hydrogen and an inert gas in the amount as in the case of the above-described first reactor.

When the second reactor is not a fixed bed reactor but a slurry reactor, such second reactor may be separately provided with the second heterogeneous catalyst in the form of a slurry. Such a slurry is preferred as in the case of the first heterogeneous catalyst slurry described above.

Optionally, step (iv) may further comprise providing additional solvent to the second reactor. Preferred of such additional solvents are those mentioned above.

Step (v) comprises: reacting at least a portion of the sorbitol rich fraction containing the concentrated homogeneous catalyst with hydrogen in a second reactor at a temperature in the range of greater than or equal to 200 ℃ to less than or equal to 300 ℃ in the presence of a second heterogeneous catalyst containing one or more transition metals from group 8, 9 or 10 of the periodic Table of the elements.

The residence time in the second reactor can vary. The average residence time of the sorbitol rich fraction in the second reactor is preferably longer than the average residence time of the carbohydrate source in the first reactor. Preferably, the sorbitol rich fraction has an average residence time in the second reactor of at least 1 hour. The mean residence time of the carbohydrate source is preferably from 1 hour to 6 hours, more preferably from 1 hour to 3 hours, most preferably from 45 minutes to 90 minutes. It is believed that longer mean residence times favor the conversion of heavy polyol byproducts (e.g., sorbitol and/or erythritol). Preferably, the second reactor is a plug flow reactor operating at a Weight Hourly Space Velocity (WHSV), expressed as metal per mass of carbohydrate source of transition metal per hour, in the following ranges: 0.01 to 100 hours ^-1Preferably 0.05 to 10 hours^-1。

The hydrogen partial pressure applied in the second reactor during step (v) is preferably the same as in the case of the hydrogen partial pressure applied in the first reactor during step (ii). Likewise, the total pressure applied in the second reactor is preferably the same as in the first reactor.

The reaction in step (v) is preferably carried out at a temperature in the range of from 220 ℃ or higher to 260 ℃ or lower.

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

The second heterogeneous catalyst contains one or more transition metals of groups 8, 9 or 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 similar to the composition of the first heterogeneous catalyst, and the transition metal and support are preferably as described above for the first heterogeneous catalyst. Preferably, the second heterogeneous catalyst contains ruthenium and/or nickel as transition metal and contains activated carbon as support. Most preferably, the heterogeneous catalyst comprises ruthenium and/or nickel supported on activated carbon. Most preferably, the second reactor is a plug flow reactor, wherein the second heterogeneous catalyst is present in the form of a fixed bed.

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

Homogeneous catalyst concentrations are preferred as in the case of the sorbitol rich fraction described above. Most preferably, the concentration of homogeneous catalyst in the reaction mixture in the second reactor is greater than or equal to 0.5 wt% to less than or equal to 5.0 wt%, calculated as tungsten metal, based on the total weight of the reaction mixture.

The weight ratio between the total amount of tungsten compounds present in the second reactor (calculated on the basis of the metal) and the transition metal present in the second reactor (calculated on the basis of the metal) may vary between wide ranges. When the second reactor is a CSTR or a slurry reactor, the weight ratio between the total amount of tungsten compounds present in the second reactor (calculated on the basis of the metal) and the transition metal present in the second reactor (calculated on the basis of the metal) is preferably higher than the weight ratio between the total amount of tungsten compounds present in the first reactor (calculated on the basis of the metal) and the transition metal present in the first reactor (calculated on the basis of the metal). Likewise, when the second reactor is a CSTR or slurry reactor, the molar ratio of moles of tungsten relative to the total moles of transition metal in the second reactor (both calculated on a metal basis) is preferably higher than in the first reactor.

If desired, in the second reactor in step (v), additional solvent may be added to the reaction mixture. Such additional solvent is preferred as in the case of the first reactor of step (ii) described above. Most preferably, any additional solvent is water.

Advantageously, the second reactor can be operated in such a way that there is less than complete conversion of sorbitol, preferably greater than or equal to 50% to less than or equal to 90% by weight conversion of sorbitol. This advantageously allows a portion of the sorbitol to remain as solvent for the homogeneous catalyst when optionally at least a portion of the second reactor product stream is recycled to the first reactor.

Step (vi) comprises: 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 described above, the second reactor product stream may advantageously be used as a stream for adding dissolved homogeneous catalyst to the first reactor.

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

The second reactor product stream may suitably be degassed to remove hydrogen before recycling. Additionally, it may be desirable to remove at least a portion of the water and the C1-C4 monoalkanols (e.g., methanol, ethanol, propanol, and/or butanol) prior to recycling.

One non-limiting example of the process of the present invention is shown in FIG. 1.

In fig. 1, a hydrogen stream (102), a stream comprising a homogeneous catalyst solution (108), a stream comprising a first heterogeneous catalyst slurry (106), and a feed stream comprising a carbohydrate source (104) are provided to a continuous stirred tank reactor (110). In this example, a Continuous Stirred Tank Reactor (CSTR) was used as the first reactor; the homogeneous catalyst solution (108) suitably comprises tungstic acid, sodium hydroxide and/or sodium tungstate in glycerol and water; the first heterogeneous catalyst (106) suitably comprises 5 wt% ruthenium on activated carbon slurried in water. The carbohydrate source (104) suitably comprises a glucose solution in water, alkylene glycols and other glycols and polyols. In addition, the homogeneous catalyst is recycled from the second reactor via stream (150). The stream (150) suitably comprises a homogeneous catalyst dissolved in, for example, alkylene glycol, other glycols and/or polyols.

In the CSTR (110), glucose is reacted with hydrogen at a temperature of about 220 ℃ in the presence of homogeneous and heterogeneous catalysts. The total pressure of the CSTR (110) is maintained at about 6.5 MPa. Water, alkylene glycols and other diols and/or other polyols as solvents. The reaction mixture contained tungsten metal in an average concentration equivalent to about 0.4 wt.% tungstic acid based on the total weight of the reaction mixture. The first reactor product stream (112) is removed from the CSTR (110). The exemplary first reactor product stream (112) suitably contains, for example: hydrogen, ethylene glycol, propylene glycol, erythritol, sorbitol, water, methanol, ethanol, propanol, and butanol. Further, the first reactor product stream (112) comprises tungsten metal in an amount corresponding to about 0.4 wt% tungstic acid, based on the total weight of the first reactor product stream (112). Additionally, the first reactor product stream may or may not contain first heterogeneous catalyst particles. If such first heterogeneous catalyst particles are present, these particles may be separated from the first reactor product stream by filtration and recycled to the CSTR (110). Subsequently, the hydrogen stream (114) is removed from the first reactor product stream (114) in a degassing unit (116). In the evaporation unit (122), a stream (120) of C1-C4 monoalcohols (e.g. methanol, ethanol, propanol and butanol) and part of the water are removed from the resulting stream (118). The resulting stream (124) is then directed to a distillation unit (126) where the stream (124) is separated into four sorbitol-depleted fractions (128a, 128b, 128c and 128d, each containing compounds boiling below 250 ℃ at 0.1 mpa) and a sorbitol-rich fraction (130) containing compounds boiling above 250 ℃ at 0.1 mpa. Tungsten species (e.g., tungstic acid, tungsten bronze, sodium tungstate, or derivatives thereof) remain dissolved in the sorbitol rich fraction (130). As a result of distilling off other components, the tungsten metal concentration increases, and such sorbitol rich fraction (130) suitably contains tungsten metal in an amount equivalent to about 1.9 wt.% tungstic acid, based on the total weight of the sorbitol rich fraction (130).

The sorbitol rich fraction (130) is directed to a plug flow reactor (132) where it is contacted with a fresh hydrogen stream (134). In this example, a Plug Flow Reactor (PFR) was used as the second reactor. The PFR contains a fixed bed (136) of a second heterogeneous catalyst consisting of 5 wt% ruthenium on activated carbon (5 wt% Ru/AC). In the PFR (132), sorbitol is reacted with hydrogen in the presence of a homogeneous catalyst and a second heterogeneous catalyst at a temperature of about 240 ℃ to yield a second reactor product stream (138). A second reactor product stream (138) is removed from the PFR (132). Sorbitol itself and other components of the sorbitol rich fraction act as solvents. The second reactor product stream suitably comprises, in addition to ethylene glycol and propylene glycol, hydrogen, propane, methanol, tetrahydrofuran, ethanol, propanol, butanol and water. Preferably, the PFR is not operated in a fully converted manner, but at a conversion of about 70 wt% of the total amount of sorbitol, so that about 30 wt% of the sorbitol remains unconverted. The second product stream (138) is suitably directed to a degassing unit (142) to remove the hydrogen stream (140). In the evaporation unit (148), a stream (146) of C1-C4 monoalcohols (e.g., methanol, ethanol, propanol, and butanol) and part of the water are removed from the resulting stream (144). The resulting stream (150) can advantageously be recycled to the first reactor (110).

The process according to the invention is further illustrated by the following non-limiting examples.