WO2023186840A1

WO2023186840A1 - Process for preparing ethylene glycol from a carbohydrate source and hydrogen in a continuous way

Info

Publication number: WO2023186840A1
Application number: PCT/EP2023/057891
Authority: WO
Inventors: Faezeh ESMAEILI; Scott Henry RUSSELL; Benjamin Mckay
Original assignee: Avantium Knowledge Centre B.V.
Priority date: 2022-03-29
Filing date: 2023-03-28
Publication date: 2023-10-05

Abstract

A process for producing ethylene glycol from a carbohydrate source by reacting said carbohydrate source with hydrogen in the presence of a catalyst system in a reactor. More specifically, the process uses one or more of ruthenium, palladium or platinum on a carrier as heterogeneous catalyst and wherein the homogeneous catalyst is prepared using tungstic acid, alkali hydroxide and an alkylene glycol, and wherein these catalysts are added to the reactor in multiple doses or added continuously.

Description

PROCESS FOR PREPARING ETHYLENE GLYCOL FROM A CARBOHYDRATE SOURCE AND HYDROGEN IN A CONTINUOUS WAY

Introduction

The present invention relates to a process for producing ethylene glycol from a carbohydrate source by reacting said carbohydrate source with hydrogen in the presence of a catalyst system in a reactor. More specifically, the invention relates to such process in which one or more of ruthenium, palladium or platinum on a carrier as heterogeneous catalyst is used in multiple doses or added continuously, and wherein the homogeneous catalyst is prepared using tungstic acid.

Background of the invention

WO 2016/114661 discloses a continuous process for preparation of ethylene glycol from a carbohydrate source. Said process is carried out in a stirred tank reactor (CSTR) in which a catalyst system is present. Said catalyst system comprises a tungsten compound and at least one hydrogenolysis metal. The hydrogenolysis metal is preferably present in the form of a catalyst supported on a carrier. Such heterogeneous catalyst particles can fairly easily be separated from the effluent stream e.g. by a sieve plate and added back. The tungsten compound on the other hand is generally present dissolved or dispersed in the liquid reaction medium (i.e. present as a homogenous catalyst compound) and not so easily removed from the effluent stream. Hence, the tungsten compound is partly removed as part of the effluent in operating the process in a CSTR. In order to maintain a desired concentration of the tungsten compound, it is thus needed that continuously or periodically the required tungsten compound is added to the reactor (next to carbohydrate source, diluent and hydrogen). This is what is done in the process of WO2016/114661.

WO2019/175365 it is reported that longer run times (e.g. over 7 hours) in the process as in the previous reference may lead to deactivation of the heterogeneous catalyst. It is thought that deactivation may be due to formation of humins on the ruthenium, and/or the formation of tungsten deposits in the ruthenium. This reference provides a way to overcome such, by removing part of the heterogeneous catalyst from the reactor, washing such to regenerate such, and feeding such back to the reactor. Said washing is reported to be carried out with e.g. an alkylene glycol. Apart from a loss in activity for the heterogeneous catalyst like ruthenium on carbon, also the homogeneous (tungsten-based) catalyst frequently used in the type of reactions concerned may suffer from "deactivation". When practicing the processes concerned in a continuous reactor in a continuous way, with a continuous feed of hydrogen, carbohydrate and homogeneous tungsten-based catalyst, and an outlet, the deactivation herein relates to a loss of the homogeneous form of tungsten-based catalyst, which manifests itself as a reduction on the amount of tungsten-compound in the outlet compared to the amount of tungsten fed to the reactor. Processes as in the two references mentioned above in an ideal case, have, when practiced in a continuous way, the same amount of tungsten-compound going into the reactor (as homogeneous tungsten compound) as coming out of the reactor (as homogeneous tungsten- compound). The nature of the solubilized or dissolved tungsten may change, yet the molar amount of tungsten going in (as homogeneous tungsten compound) should be the same as coming out (as homogeneous tungsten compound. This appears not to be the case, in particular when performing long run times, e.g. in excess of 24 hours. In other words, a while after starting the reaction, less homogenized tungsten comes out of the continuous reactor as goes in. Based on the understanding that it is the homogeneous form of the tungsten-based catalyst that is most active, as past research has shown, it is desired that the loss of homogeneous catalyst is low.

The loss in the homogeneous form of tungsten is in particularly noted shortly after the addition of a portion of a heterogeneous hydrogenation catalyst like ruthenium on a carrier, which may occur when adding portions of regenerated heterogeneous hydrogenation catalyst, as is set out in WO2019/175365.

Hence, there is a need for a process for converting a carbohydrate source with hydrogen using a catalyst system, which catalyst system relates both to a heterogeneous hydrogenation catalyst (such as one or combination of ruthenium, palladium, platinum) in combination with a homogeneous catalyst system made from tungstic acid (H₂WO₄), wherein the heterogeneous hydrogenation catalyst is added to the reactor at least at two different moments, or over time, and wherein loss of the homogeneous form of the tungsten-based catalyst (as evidenced by a difference in tungsten-based compound going into the reactor and what comes out of the reactor, both in homogeneous form) is reduced. In particular the loss of homogeneous tungsten based catalyst as evidenced a while (1-5 hours) after addition of a heterogeneous hydrogenation catalyst portion is preferably reduced. Preferably such should be achieved without negatively affecting conversion of carbohydrate source and/or selectivity for ethylene glycol too much, nor increasing selectivity for (less desired) polyols such as erythritol and sorbitol too much. Summary of the invention

It has now been found that the above objective can be achieved, at least in part, by a process for preparing ethylene glycol from a carbohydrate source comprising one or more of glucose, sucrose, fructose, starch, partially hydrolysed starch, hemicelluloses and hemicellulosic sugars by reacting said carbohydrate source with hydrogen in the presence of a catalyst system in a reactor, which reactor has at least one inlet and at least one outlet, wherein said process comprises: a. preparing a carbohydrate feed of the carbohydrate source dissolved in a liquid, b. preparing a first catalyst feed that comprises a tungsten compound, by combining tungstic acid, an alkali hydroxide and a liquid comprising alkylene glycol, to form a homogeneous tungsten-catalyst feed, c. preparing a second catalyst feed that comprises one or more of ruthenium, palladium or platinum on a carrier material, d. heating the reactor to a temperature of between 170° and 270 °C, pressurising the reactor with hydrogen to a pressure of between 1 MPa and 10 MPa, feeding the reactor with hydrogen as well as the carbohydrate feed and the first catalyst feed, and providing to the reactor at least a one dose of the second catalyst feed, e. providing to the reactor further amounts of second catalyst feed, as single dose, in multiple doses, or continuously; wherein the first catalyst feed b. is prepared by combining tungstic acid and an alkali hydroxide in amounts such that the molar ratio alkali hydroxide over tungstic acid (alkali/W) is between 1.0 and 1.7.

Detailed description of the invention

"Continuous process" or "in continuous manner" is herein to be understood as not a batch process. It takes place in a reactor system with at least one feed, and one product stream, and is intended to run in steady state (after start-up). Duration (from start-up to stopping the reaction) is preferably at least 5 times the average residence time of the liquid phase in the reactor system, more preferably at least 10 times the average residence time, most preferably at least 100 times the average residence time.

It was found by the present inventors that a drop in homogeneous tungsten compound in the outlet of the reactor fluid compared to the amount of homogeneous tungsten compound in the inlet, when producing ethylene glycol from carbohydrates in a reactor, can be reduced, without substantial negative consequences in selectivity for ethylene glycol, by increasing the molar ratio alkali hydroxide over tungsten in the feed, when the catalyst feed is prepared using tungstic acid. The fact that this can be achieved is surprising as using an increased amount of hydroxide will raise the pH of the reaction medium, and it is known from several references (e.g. EP 3365317) that for this type of reaction it is important to maintain the pH within a certain range. When the pH is too high (too basic) selectivities or conversion may drop and/or more humins may be formed. This is in said references achieved using an organic acid-based buffer system. The advantage of the presently claimed system is that organic acid-based buffers (e.g. acetic acid / sodium acetate) can be dispensed with, which is an asset, as it is desired to minimise including organic compounds in the reactor, as it increases the risk of side reactions (as the acetic acid may be affected by the hydrogen and catalysts under the reactions conditions to form side products).

In connection to this, to achieve the desired effect, the first catalyst feed b. is prepared by combining tungstic acid and an alkali hydroxide in amounts such that the molar ratio alkali hydroxide over tungstic acid (alkali hydroxide / tungstic acid, or for short alkali/W) is between 1.0 and 1.7.

As mentioned, it was surprisingly found that the amount of homogeneous tungsten-based catalyst in the outlet, when using the presently claimed process, drops less (when compared to what is fed at the inlet) over time than when not according to the present invention. Some drop in this concentration may still occur, as not too much alkali hydroxide can be added, to avoid humin formation or selectivities to deteriorate. Hence, in the now claimed process it is preferred that at 24 hours after the start of the reaction the amount of tungsten dissolved in the liquid part in the outlet of the reaction is at least 50 wt% (calculated as elemental tungsten) of the amount of tungsten fed to the reactor. Preferably, such is at least 60 wt%, more preferably at least 70 wt%.

In the present invention, it is preferred that the concentration of homogeneous tungsten compound in the combined liquid feed (the feed under a. and b. above) is between 0.05 wt% and 5 wt%, preferably between 0.1 and 2 wt%, more preferably between 0.1 and 1 wt%. To this end, the feed under b. is preferably prepared by combining tungstic acid and an alkali hydroxide and a liquid comprising alkylene glycol, wherein the amount of alkylene glycol and tungstic acid is such that the amount of tungstic acid is between 0.1 and 10 wt% on the weight of alkylene glycol, more preferably between 0.2 and 6 wt%, more preferably between 0.4 and 3 wt %. Several alkylene glycols are suitable in this connection, but it is preferred to use alkylene glycols also produced in the present process, as by such there are no extraneous compounds added. In this connection, it is preferred that said alkylene glycol comprises one or more of ethylene glycol, propylene glycol, and mixtures thereof.

Preferred alkali hydroxide compounds in the context of the present invention are sodium hydroxide and potassium hydroxide. Hence, it is preferred that the alkali hydroxide in the process according to the present invention comprises sodium hydroxide and/or potassium hydroxide. The preferred hydroxide in this case is sodium hydroxide (it is cheap and easily available).

The second catalyst feed relates to the heterogenous hydrogenation catalyst, and such comprises one or more of ruthenium, palladium or platinum on a carrier material. Preferably, in the process according to invention, the second catalyst feed is ruthenium on a carrier material. Although it is stated that in the process according to the invention the second catalyst feed that comprises one or more of ruthenium, palladium or platinum on a carrier material is present at the start of the reaction, and is subsequently added in at least one portion later in the reaction, or from a certain moment onwards such is added in a continuous way, it is preferred that also one or more of ruthenium, palladium or platinum on carrier is removed from the reactor. Such removal both allows for a substantially constant concentration of one or more of ruthenium, palladium or platinum on carrier in the reactor (and hence allow a form of process control) and it also allows one or more of ruthenium, palladium or platinum being regenerated and recycled back to the reactor, as fart of the feed prepared under c. Hence, in the present invention it is preferred that continuously or periodically amounts of one or more of ruthenium, palladium or platinum on carrier are removed from the reactor, preferably such that the concentration is substantially constant, wherein substantially constant is herein to be understood as that the difference between the highest and lowest amount of one or more of ruthenium, palladium or platinum is not more than 10% of the highest amount. Such addition and removal of one or more of ruthenium, palladium or platinum on carrier, with regeneration in between, are known from WO2019/175365.

Such regeneration of the heterogeneous hydrogenation catalyst (e.g. one or more of ruthenium, palladium or platinum on carrier) can be carried out in any manner known by a person skilled in the art to remove tungsten species from a catalyst. More preferably, at least a portion of the deposited tungsten species is removed from the spent heterogeneous catalyst by washing of the spent heterogeneous catalyst with a washing liquid. Such washing suitably yields a washed, regenerated, heterogeneous catalyst. The washing liquid preferably comprises or consists of an alkylene glycol, glycerol or other polyol, an alkali metal hydroxide solution or an alkali earth metal hydroxide solution or a combination of any of these. Preferably such washing liquid is chosen from the group consisting of alkylene glycols, a mixture of water and alkylene glycol, glycerol, a mixture of water and glycerol, an alkali metal hydroxide solution or an alkali earth metal hydroxide solution. More preferably the washing liquid is an alkylene glycol or a mixture of alkylene glycol and water. Examples of suitably alkylene glycols are ethylene glycol, propylene glycol and butylene glycol. Most preferably the washing liquid comprises or consists of ethylene glycol, propylene glycol, butylene glycol or a mixture thereof, such as an ethylene glycol/propylene glycol mixture, an ethylene glycol/butylene glycol mixture or an propylene glycol/butylene glycol mixture. The washing liquid preferably contains no, or essentially no, tungsten species. Preferred alkali metal hydroxide solutions include aqueous solutions of sodium hydroxide, potassium hydroxide and combinations thereof. An aqueous solution of sodium hydroxide is most preferred.

The washing can be carried out at a wide range of temperatures. Preferably, the washing of the spent heterogeneous catalyst is carried out at a temperature (herein also referred to as the "washing temperature") in the range from equal to or more than 100 °C, more preferably equal to or more than 150 °C, still more preferably equal to or more than 170 °C, and most preferably equal to or more than 180 °C, to equal to or less than 300 °C, more preferably equal to or less than 250 °C and most preferably equal to or less than 230 °C. The amount of washing liquid applied may vary widely. Preferably the volume of washing liquid applied per weight of catalyst ranges from equal to or more than 2 ml washing liquid per gram of catalyst (2 ml/gram) to equal to or less than 500 ml washing liquid per gram of catalyst (500 ml/gram). More preferably the volume of washing liquid applied per weight of catalyst ranges from equal to or more than lOml/gram to equal to or less than 100 ml/grams.

The one or more of ruthenium, palladium or platinum on carrier can be prepared by conventional method, and also is available as such. The carrier may be selected from a wide range of known carrier materials. Suitable carriers include activated carbon (also referred to as "active 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. By activated carbon is herein understood an amorphous form of carbon with a surface area of at least 800 m2/g. Such activated carbon suitably has a porous structure. Most preferred carriers are activated carbon, silica, silica-alumina and alumina. Even more preferably, the catalyst comprises one or more of ruthenium, palladium or platinum and/or nickel as the transition metal and activated carbon as the carrier. Most preferably the heterogeneous catalyst contains one or more of ruthenium, palladium or platinum and/or nickel supported on activated carbon. Most preferably the heterogeneous catalyst contains one or more of ruthenium, palladium or platinum, preferably supported on activated carbon. Hence, it is preferred that the carrier material for the second catalyst feed comprises one or more of activated carbon, silica, zirconia, alumina, silica-alumina, with activated carbon being preferred . The one or more of ruthenium, palladium or platinum on carrier is preferably added to the reactor in the form of a slurry or suspension in a liquid, as such is easier to dose than a solid. Preferably, the liquid should not introduce extraneous materials into the reaction mixture, and hence, the one or more of ruthenium, palladium or platinum on carrier is preferably provided in a slurry or suspension in an alkylene glycol or polyol. Preferably such a slurry of heterogeneous catalyst comprises in the range from equal to or more than 5 wt. % to equal to or less than 90 wt. %, more preferably equal to or less than 70 wt. %, most preferably equal to or less than 50 wt. % of heterogeneous catalyst, based on the total weight of such slurry. Preferably such a slurry is a slurry of 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.

Hence, the second catalyst feed in c. is prepared by mixing one or more of ruthenium, palladium or platinum on a carrier with a liquid to form a slurry (or dispersion or suspension), preferably the liquid comprises a polyol, more preferably said liquid comprises glycerol, or an alkylene glycol, such as ethylene glycol and/or propylene glycol. The time during which the catalyst is washed (also herein referred to as the "washing time"), can also vary widely. Good results can already be achieved when a washing time of 1 hour is used. Preferably the washing of the spent heterogeneous catalyst is carried out whilst applying washing times in the range from equal to or more than 15 minutes to equal to or less than 16 hours, more preferably in the range from equal to or more than 0.5 hour to equal to or less than 12 hours, and most preferably in the range from equal to or more than 1 hour to equal to or less than 8 hours.

As mentioned, the one or more of ruthenium, palladium or platinum on carrier is present at the start of the reaction, and subsequently, over time, further one or more of ruthenium, palladium or platinum on carrier is added. This can be done by single portions, or by a continuous feed. As mentioned, this is done as the one or more of ruthenium, palladium or platinum gets inactivated over time. Initially, not so much one or more of ruthenium, palladium or platinum will be inactivated, so it may be desired to start adding the one or more of ruthenium, palladium or platinum on carrier only after a certain time after starting the reaction. This means that after an hour or so after starting the reaction one or more of ruthenium, palladium or platinum on carrier will certainly be needed and added, yet the initial period (e.g. hour) after the start of the reaction no one or more of ruthenium, palladium or platinum on carrier is required to be added, as sufficient catalyst is still active. Hence, it may be preferred in the process of the present invention that at least part of the further amounts of second catalyst feed in e. (either portion wise or continuously) are added one hour or later after the start of the reaction. Alternatively, one may start with a low amount of one or more of ruthenium, palladium or platinum on carrier in the reactor, and start adding further portions (or adding one or more of ruthenium, palladium or platinum on carrier continuously) right from the start onwards. Preferably the process according to the invention is a continuous or semi-continuous process. In such a continuous or semi-continuous process a slurry of heterogeneous catalyst, for example together with liquid in which it is dispersed or suspended, can be periodically or continuously added to the reactor.

The weight ratio of the total amount of tungstic acid (calculated on metal basis) provided to the reactor, to the one or more of ruthenium, palladium or platinum (calculated on metal basis) provided to the reactor, may vary between wide ranges. The weight ratio of weight tungsten to the total weight of one or more of ruthenium, palladium or platinum, all calculated on metal basis, as provided to the reactor preferably ranges from equal to or more than 1:3000 to equal to or less than 50:1 (tungsten metal: one or more of ruthenium, palladium or platinum metal weight ratio (wt/wt)). More preferably the weight ratio of weight tungsten to the total weight of one or more of ruthenium, palladium or platinum metal, all calculated on metal basis, as provided to the reactor preferably ranges from equal to or more than 1:200 to equal to or less than 50:1 (tungsten metal: one or more of ruthenium, palladium or platinum metal weight ratio (wt/wt)).

Preferably the process according to the invention is a continuous or semi-continuous process. Preferably the tungstic acid is continuously or periodically added to the reactor. At the same time a portion of the tungsten species inside the reactor may be continuously or periodically withdrawn from the reactor, suitably via the reactor product stream.

The presently claimed process is aimed at conducting the process in a continuous manner, for a duration of at least 24 hours, more preferably at least 48 hours. Hence, in the process according to the present invention it is preferred that the feeding of the reactor with hydrogen, the carbohydrate feed and the first catalyst feed are occurring for at least 24 hours on a continuous basis, preferably for at least 48 hours on a continuous basis. Suitable reactors for conducting such continuous process are known in the art. Most preferably, the process according to the present invention is preferably carried out in a continuously stirred tank reactor with a mechanical stirrer (CSTR).

A continuous reactor for performing the now claimed process will typically be fitted out with one or more inlets for the liquid feed, an inlet for gaseous feed, an inlet for the one or more of ruthenium, palladium or platinum on carrier, at least one outlet for liquid and solid (the latter typically the one or more of ruthenium, palladium or platinum on carrier particles), or separate outlets for liquid and solids. The solid fraction (one or more of ruthenium, palladium or platinum on carrier) can be separated off and regenerated and recycled, as is set out e.g. in WO 2019/175365. The carbohydrate feed may be combined with the first catalyst feed (which comprises a solublised or dissolved tungsten compound, by mixing such with an alkylene glycol and an alkali hydroxide) and then added to the reactor, or they can be added to the reactor as two separate streams. Hence, it may be preferred that the carbohydrate feed of the carbohydrate source dissolved in a liquid prepared under a. and the first catalyst feed that comprises a tungsten compound prepared under b. are first combined prior to adding to the reactor.

By a carbohydrate source comprising one or more of glucose, sucrose, fructose, starch, partially hydrolysed starch, hemicelluloses and hemicellulosic sugars is herein understood a source of said carbohydrates. The carbohydrate source comprising one or more of glucose, sucrose, fructose, starch, partially hydrolysed starch, hemicelluloses and hemicellulosic sugars can be selected from a variety of sources. Preferably, the carbohydrate source comprises one or more carbohydrates chosen from the group consisting of polysaccharides, oligosaccharides, disaccharides, monosaccharides and mixtures thereof. Suitable examples may include, preferably sustainable, sources of carbohydrates 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 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, for example paper pulp streams, wood waste, paper waste, agricultural waste, cellulosic residues recovered from municipal waste, paper, cardboard, sugar cane, sugar beet, wheat, rye, barley, corn, rice, potatoes, cassava, other agricultural crops and combinations thereof. These streams may require pre-treatment to extract the carbohydrates (for example wet milling in the case or corn) or to remove components that interfere with the current process such as basic fillers (for example the removal of calcium carbonate in waste paper). In this way the process according to the invention can use natural sources, but can also be used to upgrade and usefully re-use waste streams. Preferably, the carbohydrates in the carbohydrate source are chosen from the group consisting of cellulose, hemicellulose, starch, glucose, sucrose, glucoseoligomers and combinations thereof. Since cellulose presents difficulties that are absent in other carbohydrate sources, the carbohydrate source is most preferably selected from the group consisting of starch, hemicelluloses and hemicellulosic sugars, glucose and mixtures thereof. Most preferably the carbohydrate source comprises or consists of glucose, fructose, sucrose or a combination thereof. Depending on e.g. price, availability, etcetera easily soluble carbohydrates glucose, sucrose, fructose, starch, partially hydrolysed starch are preferred. In the present invention, the carbohydrate source comprises one or more of glucose, sucrose, fructose, starch, partially hydrolysed starch, hemicelluloses and hemicellulosic sugars. The carbohydrate feed is prepared by dissolving the carbohydrate source in a liquid. For reasons of e.g. cost and solubility, it is preferred that the liquid in which the carbohydrate feed of the carbohydrate source is dissolved comprises water, and preferably is water.

Preferably the carbohydrate source is provided to the reactor by a feed stream containing the carbohydrate source and a solvent, wherein such feed stream preferably contains in the range from equal to or more than 1.0 wt. % (weight percent), preferably equal to or more than 2.0 wt. %, more preferably equal to or more than 5.0 wt. %, even more preferably equal to or more than 10.0 wt. %, and still more preferably equal to or more than 20.0 wt. % of carbohydrate source to equal to or less than 90.0 wt. %, preferably equal to or less than 70.0 wt. % and more preferably equal to or less than 50.0 wt. % of carbohydrate source, based on the total weight of the carbohydrate source and solvent. A feed stream containing carbohydrate source within this concentration range can suitably be easily transported. The feed stream can also consist of only (100 wt. %) carbohydrate source. For practical purposes the carbohydrate source can be provided to the reactor by a feed stream containing the carbohydrate source and a solvent, wherein such feed stream contains in the range from equal to or more than 2.0 wt. %, more preferably equal to or more than 10.0 wt. %, to equal to or less than 50.0 wt. %, more preferably to equal to or less than than 30.0 wt. % of carbohydrate source, based on the total weight of the carbohydrate source and solvent. Most preferably a feed stream containing or consisting of carbohydrate source and solvent is provided to the reactor, wherein such feed stream contains in the range of equal to or more than 20.0 wt. % to equal to or less than 50.0 wt. %, more preferably equal to or less than 30.0 wt. % of carbohydrate source, based on the total weight of the carbohydrate source and solvent. Preferably the carbohydrate source is continuously or periodically added to the reactor. The concentration of tungstic acid, calculated as tungsten metal, based on the weight of carbohydrate source introduced into the reactor, preferably ranges from equal to or more than 0.1 wt. %, more preferably from equal to or more than 1 wt. % to equal to or less than 50 wt. %, more preferably equal to or less than 35 wt. %. Even more preferably the concentration of tungstic acid, calculated as tungsten metal, based on the weight of carbohydrate source introduced into the reactor, preferably ranges from equal to or more than 0.2 wt. %, even more preferably from equal to or more than 2 wt. % to equal to or less than 25 wt. %.

The residence time in the reactor may vary. Preferably the mean residence time of the carbohydrate source in the reactor is at least 1 min. (By mean residence time is herein understood the average time spent by a material flowing at a volumetric rate "u" through a volume "V", as further explained in the handbook "Modeling of Chemical Kinetics and Reactor Design" by A. Kayode Coker, published in 2001 by Butterworth Heinemann). Preferably the mean residence time of the carbohydrate source is in the range from equal to or more than 1 minutes to equal to or less than 6 hours, more preferably from equal to or more than 3 minutes to 2 hours, most preferable in the range from equal to or more than 5 minutes to equal to or less than 45 minutes. If the carbohydrate source reacts quickly, however, the mean residence time may also be shorter than 5 minutes and even shorter than 3 minutes.

Preferably the process is a continuous process. Preferably a continuous process is operated at a weight hourly space velocity (WHSV), expressed as the mass of carbohydrate source per mass of transition metal, expressed as metal, per hour, in the range of 0.01 to 100 hr ^-1, preferably from 0.05 to 10 hr ^-1. For practical purposes a WHSV in the range between 0.5 to 2.0 hr ¹ can be used.

The hydrogen partial pressure applied during step (i) preferably lies in the range from equal to or more than 1.0 Megapascal (MPa), preferably equal to or more than 2.0 MPa, more preferably equal to or more than 3.0 MPa to equal to or less than 16.0 MPa, preferably equal to or less than 12.0 MPa, more preferably equal to or less than 8.0 MPa. All pressures herein are absolute pressures. The total pressure applied during the reaction is suitably at least 1.0 MPa, preferably at least 2.0 MPa, more preferably at least 3.0 MPa. The total pressure applied during the reaction is suitably at most 16.0 MPa, more preferably at most 10.0 MPa. Preferably the reactor is pressurized with hydrogen before addition of any starting material. The person skilled in the art will understand that the pressure at 20°C will be lower than the actual pressure at the reaction temperature. The pressure applied during the reaction when converted back to 20°C, preferably equals a pressure in the range from equal to or more than 0.7 MPa to equal to or less than 8.0 MPa.

If the process is a continuous or semi-continuous process, the hydrogen is preferably supplied in a continuous or semi-continuous manner. In the reactor at least a portion of the carbohydrate source is reacted in the presence of the hydrogen, or with the hydrogen, at a temperature in the range from equal to or more than 170°C to equal to or less than 270°C. More preferably a temperature in the range from equal to or more than 200°C to equal to or less than 250°C is applied. The reactor may be brought to a temperature within these ranges before addition of any starting material and can be maintained at a temperature within the range. As will be understood by the person skilled in the art, to start the reaction to form ethylene glycol in the reactor carbohydrate feed, hydrogen, and both catalysts need to be present at the right temperature and pressure. Hence, in stage d. of the process according to the present invention, the reaction starts to form ethylene glycol.

EXAMPLES

Comparative: sucrose (purity > 99%) as feed carbohydrate in hydrogenolysis with a Na/W molar ratio of 0.75.

Example 1 : sucrose (purity > 99%) as feed carbohydrate in hydrogenolysis with a Na/W molar ratio of 1.35.

Process description

Hydrogenolysis experiments were carried out in a continuously stirred tank reactor. The amount of liquid in the reactor was about 220 ml. The reactor had a total volume of 500 ml (length = 68 mm, internal diameter 101 mm). The liquid level was controlled using a 20 micron filter fixed at the desired liquid volume which also served as the gas outlet. The reactor was stirred using a Parr gas entrainment stirrer for the reactor (manufacturer: Parr Model: N4523-T-SS-FMD1-230-VS.12-2000-BDV-CE/PED), at approximately 1100 RPM.

Trials were done with at 30 minutes residence time (for the combined liquid flow of FEED 1 + FEED 2, see below).

The reactor contained as heterogeneous catalyst ruthenium on activated carbon. The amount of ruthenium on activated carbon was about 5 wt% Ru on AC. The total weight of heterogeneous catalyst on carrier added to the reactor before the experiment began as a pre-fill was about 12.1 g Ru + AC in both example 1 and comparative. The reactor was filled with the pre-fill Ru/AC and water before the reactor was heated (to 230°C) and pressurized. All of the heterogeneous catalyst remained in the reactor during the reaction. Liquid product and effluent gas were collected continuously from the reactor through a 20 micron dead-end filter which is set at the reactor level.

The carbohydrate feed was prepared by dissolving the sucrose in a mixture of water and ethylene glycol at a concentration of about 25 wt% on the final liquid feed composition (for FEED 1 + FEED 2, see below) which further contained about 55 wt% water and 20 wt% ethylene glycol.

The homogeneous catalyst solution was prepared by dissolving sodium hydroxide and H2WO4 in ethylene glycol, to arrive at a concentration H₂WO₄ of 0.44 wt % on the total liquid feed composition (all components except Ru/AC in slurry). For the comparative example , a Na/W molar ratio of 0.75 mol Na: mol W was prepared; in experiment 2, a ratio of 1.35 mol Na: mol W was prepared. Hence, the homogeneous catalyst feed contained the same amount of tungsten for example 1 and comparative, solely the amount of sodium hydroxide was different for these two.

The carbohydrate feed solution (FEED 1) comprising the sugar (41w%) and water and homogeneous catalyst solution (FEED 2) comprising ethylene glycol, H₂WO₄, NaOH and remaining water were dosed to the reactor separately. FEED 1 and 2 are fed to the reactor using HPLC pumps.

A make up heterogeneous catalyst feed (FEED 3) was prepared by suspending the 5% Ru on AC in glycerol at a concentration of 50 g Ru/AC per liter. FEED 3 is fed to the reactor using a high pressure syringe pump (manufacturer: Cetoni, Model: neMESYS 1000N).

The reactor was heated to 230°C and pressurised with hydrogen gas to 65 bar. Hydrogen gas was entered into the reactor at a flow of about 85 NL/h (NL/h = normal litres per hour, normalized to atmospheric conditions) or 1420 Nml/minute.

At the start of the reaction (t = 0 hours) the mixture of carbohydrate feed and homogeneous catalyst feeds were pumped into the reactor at a steady flow to obtain the residence times indicated (flow rates FEED 1: 176 ml/h FEED 2: 255 ml/h). The feeds were stored and added at room temperature.

At time = 6 hours, FEED 3 was started to replace the deactivated heterogenous catalyst activity in the reactor at a flow rate of 7.97 ml/h (continuous stream). The reaction in control experiment was carried out for approximately 48 hours, while example 1 was stopped after 31.5 hours. Note: example 1 also intended to be run for 48 hours but an equipment failure (blockage of syringe pump for dosing Ru/AC) at approximately 28 hours caused the experiment to end early. Through the experiment, samples were taken approximately every hour during the day and evening (7 am until 10 pm), while no samples were possible overnight. Experiments were started at approximately 9 am on the first day. The reactor was kept at 230°C.

Results

The samples obtained were analysed on concentration of polyol (ethylene glycol, propylene glycol, erythritol and sorbitol) using HPLC and from this reaction selectivities were calculated. The results are set out in figures 1A to ID. Samples were additionally analysed for dissolved tungsten metal in the liquid effluent by ICP-MS. These results are set out as raw concentrations of tungsten in the effluent in Figure 2. Conversions, based on sugar, where in excess of 99% for both experiments.

Figure 1A: selectivity of ethylene glycol obtained in the product stream, for Na/W in the feed =0.75 (squares) and Na/W in the feed = 1.35 (circles).

Figure IB: selectivity of sorbitol obtained in the product stream, for Na/W in the feed =0.75 (squares) and Na/W in the feed = 1.35 (circles).

Figure 1C: selectivity of propylene glycol obtained in the product stream, for Na/W in the feed =0.75 (squares) and Na/W in the feed = 1.35 (circles).

Figure ID: selectivity of erythritol obtained in the product stream, for Na/W in the feed =0.75 (squares) and Na/W in the feed = 1.35 (circles).

Figure 2: concentration of tungsten in the effluent, for Na/W in the feed =0.75 (squares) and Na/W in the feed = 1.35 (circles).

Conclusion

Figures 1 and 2 show that increasing the Na/W ratio in the feed to the reactor can prevent the build-up of tungsten in the reactor, without substantially affecting conversion (on carbohydrate) or selectivities.

Claims

1. Process for preparing ethylene glycol from a carbohydrate source comprising one or more of glucose, sucrose, fructose, starch, partially hydrolysed starch, hemicelluloses and hemicellulosic sugars by reacting said carbohydrate source with hydrogen in the presence of a catalyst system in a reactor, which reactor has at least one inlet and at least one outlet, wherein said process comprises: a. preparing a carbohydrate feed of the carbohydrate source dissolved in a liquid, b. preparing a first catalyst feed that comprises a tungsten compound, by combining tungstic acid, an alkali hydroxide and a liquid comprising alkylene glycol, to form a homogeneous tungsten-catalyst feed, c. preparing a second catalyst feed that comprises one or more of ruthenium, palladium or platinum on a carrier material, d. heating the reactor to a temperature of between 170° and 270°C, pressurising the reactor with hydrogen to a pressure of between 1 MPa and 10 MPa, feeding the reactor with hydrogen as well as the carbohydrate feed and the first catalyst feed, and providing to the reactor at least a one dose of the second catalyst feed, e. providing to the reactor further amounts of second catalyst feed, as single dose, in multiple doses, or continuously; wherein the first catalyst feed b. is prepared by combining tungstic acid and an alkali hydroxide in amounts such that the molar ratio alkali hydroxide over tungstic acid (alkali/W) is betweenl.O and 1.7.

2. Process according to claim 1, wherein the first catalyst feed b. is prepared by combining tungstic acid and an alkali hydroxide and a liquid comprising alkylene glycol, wherein the amount of alkylene glycol and tungstic acid is such that the amount of tungstic acid is between 0.1 and 10 wt% on the weight of alkylene glycol, preferably between 0.2 and 6 wt% on the weight of alkylene glycol.

3. Process according to any of the preceding claims, wherein the alkali hydroxide comprises sodium hydroxide and/or potassium hydroxide.

4. Process according to any of the preceding claims, wherein continuously or periodically amounts of one or more of ruthenium, palladium or platinum on carrier is removed from the reactor, preferably such that the concentration is substantially constant, wherein substantially constant is herein to be understood as that the difference between the highest and lowest amount of one or more of ruthenium, palladium or platinum is not more than 10% of the highest amount.

5. Process according to any of the preceding claims wherein the second catalyst feed in c. is prepared by mixing one or more of ruthenium, palladium or platinum on a carrier with a liquid to form a slurry, preferably the liquid comprises a polyol, more preferably said liquid comprises glycerol.

6. Process according to any of the preceding claims, wherein the carrier material for the second catalyst feed comprises one or more of activated carbon, silica, zirconia, alumina, silica-alumina.

7. Process according to one of the preceding claims, wherein the second catalyst feed is ruthenium on a carrier material.

8. Process according to any of the preceding claims, wherein at 24 hours after the start of the reaction the amount of tungsten dissolved in the liquid part of the outlet of the reaction is at least 50 wt% (calculated as elemental tungsten) of the amount of tungsten fed to the reactor.

9. Process according to any of the preceding claims, wherein the feeding of the reactor with hydrogen, the carbohydrate feed and the first catalyst feed are occurring for at least 24 hours on a continuous basis, preferably for at least 48 hours on a continuous basis.

10. Process according to any of the preceding claims, wherein stage d. starts the reaction to form ethylene glycol.

11. Process according to any of the preceding claims, wherein the liquid in which the carbohydrate feed of the carbohydrate source is dissolved comprises water, and preferably is water.

12. Process according to any of the preceding claims, wherein the carbohydrate feed of the carbohydrate source dissolved in a liquid prepared under a. and the first catalyst feed that comprises a tungsten compound prepared under b. are first combined prior to adding to the reactor.