WO2015154258A1

WO2015154258A1 - Selective conversion of saccharide containing feedstock to ethylene glycol

Info

Publication number: WO2015154258A1
Application number: PCT/CN2014/075000
Authority: WO
Inventors: Azlan Shah HUSSAIN; Poh Gaik LAW; Mingyuan Zheng; Jifeng Pang; Zhang Tao
Original assignee: Petroliam Nasional Berhad (Petronas); Dalian Institute Of Chemical Physics (Dicp)
Priority date: 2014-04-09
Filing date: 2014-04-09
Publication date: 2015-10-15
Also published as: CN106573860B; TWI735409B; TW201604178A; CN106573860A

Abstract

Provided is a catalytic process for the preparation ethylene glycol from a saccharide containing feedstock. More specifically, provided is a process for the selective conversion of saccharide to ethylene glycol using a catalyst system under acidic conditions, the process comprising conversion of a feedstock comprising at least one saccharide and comprising the steps of: i) contacting the feedstock comprising at least one saccharide with a catalyst system in the presence of hydrogen and a reaction medium; and ii) obtaining ethylene glycol from the reaction mixture; wherein the catalyst system comprises: a) tungsten, molybdenum, or a combination thereof; and b) one or more transition metals selected from IUPAC Groups8, 9and10, and combinations thereof; and wherein step i) is conducted at a pH of from 2.0 to 6.5.

Description

SELECTIVE CONVERSION OF SACCHARIDE CONTAINING FEEDSTOCK

TO ETHYLENE GLYCOL

The present invention relates to a catalytic process for the preparation ethylene glycol from a saccharide containing feedstock. More specifically, the invention relates to a process for the selective conversion of saccharide to ethylene glycol using a catalyst systemunder acidic conditions.

Ethylene glycol is a useful polyhydric alcohol that is primarily used as a raw material in the manufacture of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) resins. It has also found use in antifreeze, lubricants, plasticizers and surfactants. Historically, ethylene glycol has been prepared from ethylene, typically derived from the petroleum industry, via the ethylene oxideintermediate. With an increasing focus on the use of renewable feedstocks, such as a biomass, several alternative methods have emerged for converting biomass derived saccharides to ethylene glycol.

Biomass, more specifically lignocellulosic biomass, is one of the most abundant raw materials on Earth. It is composed principally of cellulose and hemicellulose carbohydrate polymers and lignin, an aromatic polymer, to which the cellulose and hemicellulose components can be tightly bound. There are generally considered to be three different classes of lignocellulosic biomass: i) virgin biomass; ii) waste biomass; and iii) energy crops. Virgin biomass includes naturally occurring plants and vegetation. Waste biomass corresponds to a low value industrial byproduct, commonly from the agricultural and forestry sectors, examples of which include oil palm frond (OPF), empty fruit bunches (EFB), corn stover, sugarcane bagasse, and straw, as well as saw mill and paper milldiscards. Energy crops are known to afford a high yield of lignocellulosic biomass and serve as raw material for production of second generation biofuel, examples of which include switch grass and elephant grass.

It is known, for instance, from US 2010/0255983that cellulose, a principal component of biomass, may be converted to ethylene glycol through a heterogeneous catalytic reaction under hydrogen atmosphere and hydrothermal conditions. When a bimetallic catalyst of nickel-tungsten carbide on activated carbon was used as the catalyst, together with a pure cellulose starting material, 100% cellulose conversion was achieved and ethylene glycol yield was reported to be as high as 62%. However, as reported in CN102731254, when a similar heterogeneous catalytic reaction was undertaken on corn stalk/sorghum stalk biomass raw material, as opposed to pure cellulose, both conversion and yield of ethylene glycol were significantly reduced. Specifically, only 70% of feedstock conversion was achieved when corn stalk was used and the yield of ethylene glycol was only 18%. Moreover, in this case there was a significant proportion of less preferred polyol formed, namely 1 ,2-propylene glycol. Only by conducting an extensive pretreatment of the cornstalk raw material, including consecutive exposure to steam, strong alkaline conditions and H₂0₂, was a cellulosic material obtained which, when used as the feedstock, resulted in significantly improved feedstock conversion and ethylene glycol yield. Such an extensive pretreatment is time consuming, as well as significantly energy and labour intensive.

US 4,404,41 1 discloses a process for the hydrogenolysis of polyols to ethylene glycol where the use of at least 10 mol % of a strong base in non-aqueous solvent is used for increasing the yield of ethylene glycol. US 4,404,41 1 indicates that the strongly basic process taught therein is likely to be suitable for saccharides which are reduced to polyols in situ.\n that regard, xylitol and sorbitol are indicated as being preferred polyols as they are readily available from cellulose and hemicellulose, derivable from biomass.

There remains a need for an alternative process for the selective preparation of ethylene glycol over other polyols, such as 1 ,2-propylene glycol, from saccharides, particularly where the saccharides are contained in a biomass feedstock which has not undergone any extensive chemical pretreatment.

The present invention is based on the surprising discovery that the yield of ethylene glycol over other polyols, in particular 1 ,2-propylene glycol, in a heterogeneous catalytic conversion of saccharides may be improved where the catalytic reaction is performed at an acidic pH, specifically at a pH of from 2.0 to 6.5.

Thus, in a first aspect, the present invention provides a process for preparing ethylene glycol from a feedstock comprising at least one saccharide comprising the steps of: i) contacting the feedstock comprising at least one saccharide with a catalyst system in the presence of hydrogen and reaction medium; and ii) obtaining ethylene glycol from the reaction mixture; wherein the catalyst system comprises: a) tungsten, molybdenum, or a combination thereof; and

b) one or more transition metals selected from lUPAC Groups 8, 9 and 10, and combinations thereof; and wherein step i) is conducted at a pH of from 2.0 to 6.5, preferably at a pH of from 2.25to 5, more preferably at a pH of from 2.5 to 4, still more preferably a pH of from 2.5 to 3.5, most preferably a pH of from 2.75 to 3.25, for example a pH of 3.0.

"Saccharide" used herein in reference to a component of the feedstock refers to all classes of saccharides, including monosaccharides, disaccharides, oligosaccharides, and polysaccharides, any of which may be edible, inedible, amorphous or crystalline in nature. Examples of monosacharides include, glucose, fructose, galactose, xylose, arabinose and mannose. Examples of polysaccharides include cellulose, hemicellulose, glycogen, starch and chitin.

In a preferred embodiment, the saccharide comprises cellulose, hemicellulose or a combination thereof. More preferably, the saccharide comprises cellulose. The saccharide contained in the feedstock may be amorphous, crystalline, or a combination thereof.

The saccharide used in the present invention may be derived from biomass. "Biomass" used herein refers to all forms of lignocellulosic biomass. Examples of biomass include oil palm biomass, for example oil palm frond (OPF) and empty fruit bunches (EFB), corn stover, sugarcane bagasse, straw, energy crops, for example switch grass and Elephant grass, as well as saw mill and paper milldiscards. Biomass in accordance with the present invention may comprise varying levels of the principal components cellulose, hemicellulose and lignin. In a preferred embodiment, the biomass is oil palm biomass, more preferably empty fruit bunches (EFB). The term "biomass" used herein is intended to cover "raw biomass" or "crude biomass" which has not been subjected to any refinement, or only physical refining such as by shredding/chipping and/or dewatering. A further form of biomass which is also intended to be covered for the purpose of the present invention is "chemically treated biomass" or "pretreated biomass", where raw or crude biomass has undergone some form of treatmenteither to at least partially remove lignin and/or hemicellulose, or to at partially depolymerize any of its polymeric components. Examples of pretreatments include hot water treatment, steam treatment, chemical treatment, biological treatment, catalytic treatment, thermal treatment, hydrolysis, and/or pyrolysis.

It has been surprisingly found that the process of the present invention is particularly useful for preparing ethylene glycol, in good yield and with high selectivity over 1 ,2- propylene glycol, directly from raw or crude biomass which has not undergone any pretreatment. Thus, in one preferred embodiment, the feedstock comprising at least one saccharide is derived from raw or crude biomass which has not undergone any pretreatment. More preferably, the raw or crude biomass which has not undergone any pretreatment is oil palm based biomass, for example empty fruit bunches (EFB).

As described above, step i) of the process of the invention is conducted under acidic conditions, specifically at a pH of from 2.0 to 6.5. It has surprisingly been found that there are multiple advantages for the hydrogenolysis/hydrogenation of a saccharide containing feedstock in operating the reaction at this particular range of pH. High levels of feedstock conversion and yield of ethylene glycol have been found to be achievable with this level of pH. This has the benefit that it eliminates the requirement for intensive pretreatment of the biomass prior to hydrogenolysis/hydrogenation. For example, conversion levels of raw biomass feedstock have been found to be as high as 85 % (residual unconverted material principally comprising lignin and ashes), whilst yields of ethylene glycol from the raw biomass feedstock have been found to exceed 40%. Previously, high feedstock conversion and high yield of ethylene glycol were only associated with processes conducted with a purified cellulose feedstock, such as obtained following consecutive exposure to steam, strong alkaline conditions and H₂0₂, and not with raw biomass feedstocks. Furthermore, conducting the hydrogenolysis/hydrogenation reactions at the above range of pH has also been found to promote the formation of ethylene glycol over other polyols, such as 1 ,2-propylene glycol. For instance, the ratio of ethylene glycol to 1 ,2-propylene glycol has been found to exceed 4:1 in embodiments of the invention. This is particularly advantageous as ethylene glycol is a preferred precursor for several commercial processes, for instance in the preparation of PET, and has wider application than the other polyols which may be prepared from the hydrogenolysis/hydrogenation of biomass derived feedstock.

Preferably, step i) of the process of the invention is conducted in the presence of an organic or inorganic acid. Thus, in an embodiment, step i) of the process of the invention is conducted in the presence of an inorganic acid selected from hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, preferably selected from hydrochloric acid and sulfuric acid. In another embodiment, step i) of the process of the invention is conducted in the presence of an organic acid selected from acetic acid, maleic acid, butyric acid, benzenesulfonic acid, terephthalic acid, benzoic acid, phthalic acid and salicylic acid. Preferably, the organic acid used is benzenesulfonic acid. When present, the organic or inorganic acid may be in an amount of from 0.0001 to 2.0 wt.%, preferably 0.001 to 0.1 wt.%, based on the total weight of the reaction mixture, or in an amount of 1 ppm to 20,000 ppm, preferably 10 ppm to 1000 ppm.

As described hereinbefore, the catalyst system for use in the process of the present invention comprises: a) tungsten, molybdenum, or a combination thereof; and b) one or more transition metals selected from lUPAC Groups 8, 9 and 10, and combinations thereof.

In one embodiment of the invention, component a) of the catalyst system comprises molybdenum in elemental form or in the form of molybedic acid.

In a preferred embodiment, component a) of the catalyst system comprises tungsten in elemental form or in the form of a compound selected from sodium tungstate, tungsten nitride, tungsten carbide, tungsten phosphide, tungsten oxide, tungsten sulfide, tungsten chloride, tungsten hydroxide, tungsten bronze, tungstic acid, tungstate, metatungstic acid, metatungstate (for example, ammonium metatungstate), paratungstic acid, paratungstate, peroxotungstic acid, peroxotungstate, heteropoly tungstic acid or combinations thereof.

In a more preferred embodiment, component a) of the catalyst system comprises tungsten in the form of a compound selected from sodium tungstate, tungsten carbide, tungsten bronze, tungstic acid or a combination thereof. In a yet more preferred embodiment, the catalyst system comprises tungsten in the form of a compound selected from sodium tungstate, tungstic acid or a combination thereof.

In one embodiment of the invention, component b) of the catalyst system comprises a metal selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum or a combination thereof. In a preferred embodiment, component b) of the catalyst system comprises a metal selected from nickel, ruthenium, platinumor a combination thereof. In a more preferred embodiment, component b) of the catalyst system comprises nickel.

The catalyst system utilized in the process of the present invention comprises metallic components a) and b), as described hereinbefore. Without being bound to any particular theory, it is believed that component a) of the catalyst system, comprising tungsten, molybdenum, or a combination thereof, promotes hydrogenolysis of the saccharide contained in the feedstock. Meanwhile, component b), comprising one or more transition metals selected from lUPAC Groups 8, 9 and 10, and combinations thereof, is believed to promote hydrogenation to form polyols. Both components are therefore active in promoting the formation of ethylene glycol directly from a saccharide containing feedstock.

The amount of the catalyst system used in the process of the present invention may range from 0.1 to 10 wt. %, preferably 0.3 to 7 wt.%, based on the weight of feedstock comprising saccharide and the catalytic system measured on the basis of elemental tungsten or molybdenum. The ratio of active metals in catalyst components a) and b) respectively is preferably 1 :100 to 100:1 , more preferably 1 :10 to 10:1 , measured on an elemental basis. Step i) of the process is conducted at a temperature and pressure which is suitable for the catalytic reaction to occur and which avoids thermal decomposition of the saccharide. Preferably, step i) of the process of the invention is conducted at a temperature of at least 150°C, more preferably at a temperature of from 200 to 300°C, for example at a temperature of 245°C. Preferably, step i) of the process of the invention is conducted at a pressure of 1 to 15 MPa, more preferably at a pressure of 1 to 7 MPa, for example at a pressure of 5 MPa.

Step (i) of the process is conducted in the presence of a reaction medium which is compatible with the catalytic reaction and typically comprises water and/or an organic solvent. In one embodiment, the reaction medium comprises a solvent selected from water, methanol, ethanol, propanols, butanols, ethylene glycol, glycerol, or a combination thereof. In a preferred embodiment, the reaction medium comprises anaqueous solvent. Preferably, the amount of reaction medium present is such that the feedstock represents between 1 and 30wt.%, based on the combined weight of reaction medium and feedstock. More preferably, the amount of reaction medium present is such that the feedstock represents between 5 and 15 wt.%, based on the combined weight of reaction medium and feedstock.

In some embodiments of the invention, the feedstock comprising at least one saccharide is derived from pretreated biomass, i.e. biomass which has undergone a pretreatment prior to use. Pretreatment may comprise any of the pretreatments mentioned above, of which the person skilled in the art would be aware.

In one preferred embodiment, the feedstock comprising saccharide is derived from biomass which has undergone a pretreatment comprising treatment of raw or crude biomass with a basic solution at a temperature of from 20°C to 1 10°C, preferably from 30°C to 80°C. Pretreatment can be conducted over a time period suitable for achieving a desired level of depolymerisation and/or removal of lignin and/or hemicellulose, which may be monitored intermittently. Preferably, the pretreatment is conducted over a timescale of from 30 minutes to 48 hours, more preferably over a timescale of from 1 to 24 hours. The ratio of feedstock to basic solution is preferably 1 :10-1 :100.

Preferably, the basic solution comprises alkali or alkaline earth metal hydroxide, such as sodium hydroxide, lithium hydroxide, potassium hydroxide, calcium hydroxide and/or magnesium hydroxide, and/or the basic solution comprises ammonium hydroxide. More preferably the basic solution comprises sodium hydroxide. The basic solution may comprise any suitable amount of alkali or alkaline earth metal hydroxide or ammonium hydroxide for the purpose of treating biomass. Preferably, the basic solution comprises 0.1 to 30 wt.%, more preferably 0.3 to 5 wt.%, of alkali or alkaline earth metal hydroxide or ammonium hydroxide.

The basic solution may comprise any suitable solvent which is known for the purpose of treating biomass, including water, methanol and/or ethanol. Preferably, the basic solution is aqueous. Once pretreatment has been conducted, the pretreated biomass may be washed and dried before being supplied to the acidic hydrogenolysis/hydrogenation reactions according to the present invention. For instance, the pretreated biomass may be washed with water before being dried at elevated temperature. The pretreated biomass may instead be washed with water and converted to an acidic mixture, without any drying step, before being supplied to the acidic hydrogenolysis/hydrogenation reactions according to the present invention. Alternatively, the pretreated biomass, together with the basic solution, may be supplied to the reaction directly, neutralized and converted to an acidic mixture before undergoing hydrogenolysis/hydrogenation in accordance with the process of the invention.

Pretreatment with a basic solution as described above has surprisingly been found to further improve the yield of ethylene glycol from the biomass derived feedstock when followed by the acidic hydrogenolysis/hydrogenation reactions according to the process of the invention. This particular pretreatment of biomass has also been shown to further improve the selectivity of the subsequent hydrogenolysis/hydrogenation reactions for the production of ethylene glycol, rather than alternative polyols. Moreover, the combination of a pretreatment with a basic solution followed by an acidic hydrogenolysis/hydrogenation in accordance with the present invention has been found to be particularly preferable for the selective preparation of ethylene glycol.

In another preferred embodiment, the feedstock comprising saccharide is derived from biomass which has undergone a pretreatment comprising treatment of raw or crude biomass with a hydrogenation catalyst at a temperature of at least 120°Cand at a hydrogen partial pressure of from 1 to 12 MPa. Preferably, the pretreatment with a hydrogenation catalyst is conducted at at least 150 °C, more preferably from 180 to 270 °C. Preferably, the pretreatment with a hydrogenation catalyst is conducted at a hydrogen partial pressure of 3 to 7 MPa.

The hydrogenation catalyst used for the pretreatment may be the same as component b) of the catalyst system described hereinabove, and thus may comprise one or more transition metals selected from lUPAC Groups 8, 9 and 10, and combinations thereof. Preferably, the hydrogenation catalyst for the pretreatment is selected from platinum or palladium. The hydrogenation catalyst may be in unsupported form or, preferably, in supported form. Suitable supports for the hydrogenation catalyst for the pretreatment include carbon, activated carbon, silica, zirconia, alumina, alumina-silica, silicon carbide, zeolites, zirconium oxide, magnesium oxide, zinc oxide, titanium oxide, clays and combinations thereof. Preferably, the support is carbon or activated carbon. Preferably the weight loading of metal active component on catalyst is 0.05 to 50 %, more preferably 1 to 20 %.

Pretreatment can be conducted over a time period suitable for achieving a desired level of depolymerisation and/or removal of lignin and/or hemicellulose, which may be monitored intermittently. Preferably, the pretreatment is conducted over a timescale of from 10 minutes to 48 hours, more preferably over a timescale of from 30 minutes to 4 hours. The mass ratio of catalyst to feedstock is preferably 1 :1 to 1 :100.The hydrogenation pretreatment is conducted in the presence of a reaction medium which is compatible with the catalytic reaction and typically comprises water and/or an organic solvent. The reaction medium may comprise a solvent selected from water, methanol, ethanol, propanols, butanols, ethylene glycol, glycerol, or a combination thereof. In a preferred embodiment, the reaction medium comprises water.

Once pretreatment has been conducted, solid products may be collected by means of vacuum filtration before oven drying and sieving to separate the pretreated feedstock from catalyst. Pretreated feedstock may then be supplied to the acidic hydrogenolysis/hydrogenation reactions according to the present invention.

A hydrogenation pretreatment in the presence of a hydrogenation catalyst as described above has surprisingly been found to further improve the yield of ethylene glycol from the biomass derived feedstock when followed by the acidic hydrogenolysis/hydrogenation reactions according to the process of the invention. This particular pretreatment of biomass has also been shown to further improve the selectivity of the subsequent hydrogenolysis/hydrogenation reactions for the production of ethylene glycol, rather than alternative polyols. Moreover, the combination of a hydrogenation pretreatment with a hydrogenation catalyst followed by an acidic hydrogenolysis/hydrogenation in accordance with the present invention has been found to be particularly preferable for the selective preparation of ethylene glycol.

In accordance with the present invention, contacting step i) of the process typically comprises mixing feedstock, reaction medium and catalyst system in a sealed reaction vessel, adjusting the pH of the reaction mixture if necessary, introducing hydrogen and stirring the resulting mixture using, for example, a mechanical stirrer, an ultrasonic stirrer or an electromagnetic stirrer. Thereafter, the reaction mixture is left for a suitable period of time to allow the catalytic reaction to proceed. An adequate residence time is no less than 5 minutes. In a preferred embodiment, the residence time is from 30 minutes to 3 hours, for example, 2 hours.

The catalyst system utilized in the process of the present invention may be either partially or fully supported or in unsupported form. Thus, component a) and/or b) of the catalyst system may be supported or unsupported. Where a component of the catalyst system is utilized in supported form, it is preferred that component b) of the catalyst system is supported. Suitable supports for use in the present invention include carbon, activated carbon, silica, zirconia, alumina, alumina-silica, silicon carbide, zeolites, zirconium oxide, magnesium oxide, zinc oxide, titanium oxide, clays and combinations thereof. Preferably, the support is selected from silica, titanium oxide and activated carbon.

Any method of which the person skilled in the art is aware for generating supported metallic catalysts may be used for generating a supported catalyst component. For instance, a supported catalyst may be prepared by first dissolving the chosen catalyst component in a suitable solvent, such as water, ethers, alcohols, carboxylic acids, ketones and aldehydes, preferably water or alcohols. The mixture may then be added to the chosen support or, alternatively, the support is immersed in the mixture. An impregnated support may then be recovered using any conventional separation technique, including, for example, decantation and/or filtration. Once recovered, the impregnated support may be dried, preferably by placing the support in an oven at elevated temperature. Alternatively, or additionally, a desiccator may be employed. For the purposes of the present invention, component a) and/or b) may be adsorbed onto the support such that the metal active component of component a) and/or b) is present in an amount of 0.05-50wt.%, based on the weight of the supported catalyst component.

The process according to the present invention may be conducted via a batch or continuous mode of operation. With a batch mode operation, the feedstock reaction medium and catalyst are typically combined in the presence of hydrogen, stirred and allowed to react for a suitable amount of time. An adequate contact time for the catalytic reaction to proceed sufficiently is at least 5 minutes. Following the contacting step, the reaction mixture is removed from the reaction vessel and the constituents separated and product ethylene glycol recovered.

In a continuous mode of operation, a feedstock containing stream is continuously fed into a reaction zone, whilst an ethylene glycol product/effluent stream is continuously being withdrawn. The reaction zone may include separate feed streams for feedstock and hydrogen. The feed stream for the feedstock may also comprise reaction medium, any acidic species necessary for modifying pH of the reaction, as well as components of the catalyst system, or alternatively these may be fed to the reaction zone separately. One or more components of the catalyst system may be immobilized in the reaction zone, for instance, as part of a catalyst bed reactor system.

Thus, where component a) and/or b) of the catalyst system are supported, contacting step (i) may include passing the feedstock and reaction medium through a column packed with the supported catalyst system component(s) (i.e. a packed bed arrangement). Thus, the feedstock comprising at least one saccharide may be passed through a column containing the supported catalyst system component(s). The saccharide will thus undergo catalytic reaction in the presence of the at least partially supported catalyst and hydrogen, following which an effluent stream may be removed from the column comprising ethylene glycol. In addition, or alternatively, a fixed-bed arrangement having a plurality of plates and/or trays may be used.

As well as product ethylene glycol, the reaction mixture removed from the reaction vessel / effluent stream may comprise by-product polyols, such as 1 ,2-propylene glycoland glycerol, other alcohols, aldehydes, unreacted saccharides, phenolic compounds and any acidic species used for modifying the pH of the reaction mixture. Solid components of the reaction mixture, in particular components of the catalyst system may be separated by, for instance, by filtration, centrifugation, hydrocyclone, fractionation, extraction, evaporation, or combinations thereof. In this way, it is possible to isolate components of the catalyst system such that they may be recycled. Thus, in one embodiment, the process of the invention further comprises a step of recycling one or more of the catalyst system components.

Where the saccharide containing feedstock is derived from biomass, ethylene glycol prepared by the process of the invention preferably has a carbon-14 to carbon-12 ratio of at least 0.5 x 10^~13, or, in other words, a carbon-14 to carbon-12 ratio of at least 1 :2x 10¹³. The carbon-14 to carbon-12 ratio may suitably be measured using radiometric dating or accelerator mass spectrometry.

The present invention will now be illustrated by way of the following examples and with reference to the following figures:

FIGURE 1 : Graphical representation of the influence of pH of the catalytic reaction according to the process of the invention on polyol yield (1 wt.% treated EFB loading).

FIGURE 2: Graphical representation of the influence of pH of the catalytic reaction according to the process of the invention on polyol yield (10wt.% treated EFB loading).

FIGURE 3: Graphical representation of the influence of ammonium metatungstate and HCI acid addition on polyol yield (10 wt.% treated EFB loading, 700 ppm HCI).

Examples Preparation of feedstock

Raw biomass, specifically empty fruit bunches (oil palm biomass), was physically refined by milling with a knife mill and sorting with a sieve. The untreated EFB fibres obtained were subsequently dried at 100 °C for 12 hours.

Preparation of ethylene glycol from saccharide containing biomass without chemical pretreatment

Comparative Example 1

50ml deionized water, 0.05g Raney-Nickel and 0.05g sodium tungstate was added to 0.5g of untreated empty fruit bunch (EFB) feedstock in a pressure vessel. Dilute sulfuric acid was added until a reaction mixture was formed having a pH of 7. At ambient temperature, hydrogen was pumped into the stirred (500 rpm) pressure vessel up to a pressure of 2 MPa before the temperature was increased to 245°Cfor a reaction time of 2 hours. Upon completion of the reaction, the temperature was reduced to ambient temperature and hydrogen evacuated through an exhaust system before a sample was withdrawn for analysis by high performance liquid chromatography (HPLC). Polyol yield was then subsequently calculated, the results of which are presented in Table 1 .

Example 1

The process of Comparative Example 1 was repeated, except that 1 wt.% sulfuric acid solution was added until a reaction mixture was formed having a pH of 6.

Example 2

The process of Comparative Example 1 was repeated, except that 1 wt.% sulfuric acid solution was added until a reaction mixture was formed having a pH of 5.

Table 1 : effect of pH on polyol yield

yield, % glycol (1 ,2-PG) EG/1 ,2-PG

yield, %

Comparative

7 27.8 1 1 .2 2.48

Example 1

Example 1 6 30.4 9.2 3.30

Example 2 5 33.4 7.7 4.34

As can be seen from the results in Table 1 , when pH is neutral, the ratio of ethylene glycol to 1 ,2-propylene glycol is 2.48 is obtained. Adjustment to pH 6, using inorganic acid, sees the ratio of ethylene glycol to 1 ,2-propylene glycol increase to 3.30. Meanwhile, adjustment from pH 7 to pH 5, using inorganic acid, sees the ratio of ethylene glycol to 1 ,2-propylene glycol increase even more substantially to4.34.Yields reported in the above table are calculated based on the whole feedstock, of which approximately 15 wt.% is lignin and/or ashes components.

Preparation of ethylene glycol from saccharide containing biomass with alkaline pretreatment

Example 3

1 wt.% sodium hydroxide solution was added to a vessel containing 10g of empty fruit bunch (EFB) feedstock such that the weight ratio of feedstock to sodium hydroxide solution was 1 :10. The vessel was then heated to60 °C and the pretreatment conducted for 12 hours before the pretreated feedstock was isolated. Following completion of the pretreatment, the pretreated EFB was separated by filtration before being washed with water, at a volume ratio of pretreated EFB to water of 1 :10. The washing step was repeated twice.

50ml deionized water, 0.05g Raney-Nickel and 0.05g tungstic acid was added to 0.5g samples of pretreated feedstock in individual pressure vessels, along with varying amounts of hydrochloric acid (0-200 ppm). The catalytic reaction was then performed under the same conditions described in Comparative Example 1 . The results for ethylene glycol and 1 ,2-propylene glycol yield over varying hydrochloric acid concentration according to this example are represented graphically in Figure 1 . Table 2 below is a correspondence table showing the amount of HCI added in this example and the resulting pH of the reaction mixture.

Table 2: effect of pH on polvol yield

Example 4

1 wt.% sodium hydroxide solution was added to a vessel containing 10g of empty fruit bunch (EFB) feedstock such that the weight ratio of feedstock to sodium hydroxide solution was 1 :10. The vessel was then heated to 60 °C and the pretreatment conducted for 12 hours before the pretreated feedstock was isolated.

50ml deionized water, 0.5g Raney-Nickel and 0.5g tungstic acid was added to 5g samples of pretreated feed stock in individual pressure vessels, along with varying amounts of hydrochloric acid (0-1 100 ppm; corresponding to pH values of between 3.0 and 7.0). The catalytic reaction was then performed under the same conditions described in Comparative Example 1 . The results for ethylene glycol and 1 ,2-propylene glycol yield over varying hydrochloric acid concentration according to this example are represented graphically in Figure 2.

Example 5

40ml deionized water, 0.5g Raney-Nickel and700 ppm HCI was added to 4.4 g samples of pretreated feed stock in individual pressure vessels, along with varying amounts of ammonium metatungstate (AMT) (0-1 100 ppm; corresponding to pH values of between 3.0 and 7.0). The catalytic reaction was then performed under the same conditions described in Comparative Example 1 . The results for ethylene glycol and 1 ,2-propylene glycol yield over varying AMT concentration according to this example are represented graphically in Figure 3.

As can be seen in Figures 1 and 2, increasing the amount of HCI in the catalytic reaction, and reducing the pH to approximately 3, reduces the yield of 1 ,2-propylene glycol whilst at the same time increases the yield of preferred ethylene glycol up to a certain point. Meanwhile, Figure 3 illustrates that increasing the concentration of the hydrogenation catalyst (AMT) increases the yield of ethylene glycol whilst also subtly decreasing the yield of 1 ,2-propylene glycol yield when acidic conditions are employed in the catalytic reaction.

The yield of ethylene glycol versus 1 ,2-propylene glycol in Figures 1 to 3 also illustrates a further improvement in conducting a pretreatment of biomass derived feedstock using a basic solution prior to conducting an acidic hydrogenolysis/hydrogenation in accordance with the present invention. This particular combination of process steps has surprisingly been found to maximize the yield of ethylene glycol over other polyols, including 1 ,2-propylene glycol.

Claims

Claims:

1 . A process for preparing ethylene glycol from a feedstock comprising at least one saccharide comprising the steps of: i) contacting the feedstock comprising at least one saccharide with a catalyst system in the presence of hydrogen and a reaction medium; and

ii) obtaining ethylene glycol from the reaction mixture; wherein the catalyst system comprises: a) tungsten, molybdenum, or a combination thereof; and b) one or more transition metals selected from lUPAC Groups 8, 9 and 10, and combinations thereof; and wherein step i) is conducted at a pH of from 2.0 to 6.5.

2. A process according to Claim 1 , wherein step i) is conducted at a pH of from 2.25 to 5.

3. A process according to Claim 1 or Claim 2, wherein step i) is conducted at a pH of 2.5 to 4.

4. A process according to any of Claim 1 or Claim 2, wherein step i) is conducted at a pH of 2.75 to 3.25.

5. A process according to any of Claims 1 to 4, wherein step i) is conducted in the presence of an organic or inorganic acid.

6. A process according to Claim 5, wherein the acid is an inorganic acid selected from hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid.

7. A process according to Claim 6, wherein the acid is hydrochloric acid or sulfuric acid.

8. A process according to Claim 5, wherein the acid is an organic acid selected from acetic acid, maleic acid, butyric acid, benzenesulfonic acid, terephthalic acid, benzoic acid, phthalic acid and salicylic acid.

9. A process according to Claim 8, wherein the acid is benzenesulfonic acid.

10. A process according to any of Claims 5 to 9, wherein the acid is present in an amount of from 0.001 to 0.1 wt.%, based on the total weight of the reaction mixture.

1 1 . A process according to any of Claims 5to 9, wherein the acid is present in an amount of from 10 ppm to 1000 ppm.

12. A process according to any of Claims 1 to 1 1 , wherein the reaction medium comprises a solvent selected from water, methanol, ethanol, propanols, butanols, ethylene glycol and glycerol, or a combination thereof.

13. A process according to any of Claims 1 to 12, wherein the reaction medium comprises an aqueous solvent.

14. A process according to any of Claims 1 to 13, wherein step i) is conducted at a temperature of at least 150°C.

15. A process according to any of Claims 1 to 14, wherein step i) is conducted at a temperature of from 200 to 300°C.

16. A process according to any of Claims 1 to 15, wherein step i) is conducted at a pressure of 0.1 to 15MPa.

17. A process according to any of Claims 1 to 16, wherein step i) is conducted at a pressure of 1 to 7MPa.

18. A process according to any of Claims 1 to 17, wherein the feedstock is present in an amount of 1 to 30wt%, based on the total weight of the reaction mixture.

19. A process according to any of Claims 1 to 18, wherein component a) of the catalyst system comprises tungsten in elemental form or in the form of a compound selected from sodium tungstate, tungsten nitride, tungsten carbide, tungsten phosphide, tungsten oxide, tungsten sulfide, tungsten chloride, tungsten hydroxide, tungsten bronze, tungstic acid, tungstate, metatungstic acid, metatungstate, paratungstic acid, paratungstate, peroxotungstic acid, peroxotungstate, heteropoly tungstic acid.

20. A process according to Claim 19, wherein component a) of the catalyst system comprises tungsten in the form of a compound selected from sodium tungstate, tungsten carbide, tungsten bronze, ammonium metatungstate and tungstic acid.

21 . A process according to Claim 20, wherein the component a) of catalyst system comprises tungsten in the form of a compound selected from sodium tungstate, ammonium metatungstate and tungstic acid.

22. A process according to any of Claims 1 to 21 , wherein component a) of the catalyst system comprises molybdenum in elemental form or in the form of molybedic acid.

23. A process according to any of Claims 1 to 22, wherein component b) of the catalyst system comprises a metal selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium and platinum.

24. A process according to any of Claims 1 to 23, wherein component b) of the catalyst system comprises a metal selected from nickel, ruthenium or platinum.

25. A process according to any of Claims 1 to 24, wherein component b) of the catalyst system comprises nickel.

26. A process according to any of Claims 1 to 25 wherein the feedstock comprises saccharide in the form of monosaccharide, disaccharide, oligosaccharide, and/or polysaccharide.

27. A process according to any of Claims 1 to 26wherein the feedstock comprises saccharide which is amorphous or crystalline.

28. A process according to any of Claims 1 to 27 wherein the saccharide comprises cellulose, hemicellulose or a combination thereof.

29. A process according to any of Claims 1 to 28, wherein the feedstock is derived from biomass.

30. A process according to Claim 29, wherein the biomass is oil palm biomass.

31 . A process according to Claim 30, wherein the oil palm biomass is empty fruit bunches (EFB).

32. A process according to any of Claims 29 to 31 , wherein the biomass is raw or crude biomass which has not undergone any chemical pretreatment prior to use as feedstock.

33. A process according to any of Claims 29 to 31 , wherein the biomass is pretreated biomass which has undergone pretreatment prior to use as feedstock.

34. A process according to Claim 33, wherein the pretreatment comprises treatment of raw or crude biomass with a basic solution at a temperature of from 20°C to 1 10°C.

35. A process according to Claim 34, wherein the temperature is from 30°C to 80°C.

36. A process according to Claim 34 or Claim 35, wherein the pretreatment is conducted over a timescale of from 30 minutes to 48 hours.

37. A process according to Claim 36, wherein the pretreatment is conducted over a timescale of from 1 to 24 hours.

38. A process according to any of Claims 34 to 37, wherein the basic solution comprises 0.1 to 30 wt.% of ammonium hydroxide, an alkali or alkaline earth metal hydroxide.

39. A process according to Claim 38 wherein the basic solution is an aqueous solution of sodium hydroxide.

40. A process according to Claim 33, wherein the pretreatment comprises hydrogenation in the presence of a hydrogenation catalyst comprising one or more transition metals selected from lUPAC Groups 8, 9 and 10, and combinations thereof, at a temperature of at least 120 °C and a hydrogen partial pressure of from 1 to 12 MPa.

41 . A process according to Claim 40, wherein the temperature of the hydrogenation pretreatment is from 180 to 270 °C.

42. A process according to Claim 40 or Claim 41 , wherein the hydrogen partial pressure of the hydrogenation pretreatment is from 3 to 7 MPa.

43. A process according to any of Claims40 to42, wherein the pretreatment is conducted over a timescale of from 30 minutes to 4 hours.

44. A process according to any of Claims 40 to 43, wherein the hydrogenation catalyst used for the pretreatment is supported by a carrier material.

45. A process according to Claim 44, wherein the carrier material is selected from any of carbon, activated carbon, silica, zirconia, alumina, alumina-silica, silicon carbide, zeolites, zirconium oxide, magnesium oxide, zinc oxide, titanium oxide, clays and combinations thereof.

46. A process according to Claim 45, wherein the carrier material is selected from carbon or activated carbon.

47. A process according to any of Claims 44 to 46, wherein the metal active component of the hydrogenation catalyst used for the pretreatment is present in an amount of 1 to 20 wt.%, based on the total weight of the supported catalyst.

48. A process according to any of Claims 29 to 47, wherein the ethylene glycol product obtained has a carbon-14 to carbon-12 ratio of at least 0.5 x 10^"13, that is, a carbon-14 to carbon-12 ratio of at least 1 :2 x 10¹³.

49. A process according to any of Claims 1 to 48, wherein the catalyst system comprising components a) and b) is unsupported.

50. A process according to any of Claims 1 to 49, wherein component a) and/or component b) of the catalyst system is supported by a carrier material.

51 . A process according to Claim 50, wherein the carrier material is selected from any of carbon, activated carbon, silica, zirconia, alumina, alumina-silica, silicon carbide, zeolites, zirconium oxide, magnesium oxide, zinc oxide, titanium oxide, clays and combinations thereof.

52. A process according to Claim 51 , wherein the carrier material is selected from silica, titanium oxide and activated carbon.

53. A process according to any of Claims 50 to 52, wherein the metal active component of component a) and/or component b) is present in an amount of 0.05-50wt.%, based on the total weight of the supported catalyst component.