WO2016034727A1

WO2016034727A1 - Selective extraction and conversion of a cellulosic feedstock to ethylene glycol

Info

Publication number: WO2016034727A1
Application number: PCT/EP2015/070299
Authority: WO
Inventors: Adi Aizat RAZALI; Poh Gaik LAW; Azlan Shah HUSSAIN
Original assignee: Petroliam Nasional Bhd Petronas
Current assignee: Petroliam Nasional Bhd Petronas
Priority date: 2014-09-05
Filing date: 2015-09-04
Publication date: 2016-03-10
Anticipated expiration: 2017-03-05
Also published as: MY182605A

Abstract

The present invention relates to a process for selectively solubilizing and removing lignin and hemi-cellulose components of cellulosic biomass and obtaining a cellulosic feedstock having a higher proportion of cellulose, as compared to the biomass from which it is derived, and having a greater cellulose Crystallinity Index. In particular, the process comprises: i) contacting cellulosic biomass with a deep eutectic solvent (DES) formed from a mixture of a) a choline derivative selected from choline chloride, chlorocholine chloride, choline acetate, acetylcholine chloride or phosphatidyl choline; and b) an alpha-hydroxy carboxylic acid;and ii) obtaining a solid cellulosic feedstock which has a higher proportion of cellulose component, as compared with the cellulosic biomass from step i), wherein the majority of the cellulosic feedstock obtained in step ii) is obtained without regenerating cellulose by precipitation.

Description

Selective extraction and conversion of a cellulosic feedstock to ethylene glycol

The present invention relates to a process for treating cellulosic biomass and subsequently converting to ethylene glycol. More specifically, the invention relates to a process for selectively solubilizing and removing lignin and hemi-cellulose components of cellulosic biomass and obtaining a cellulosic feedstock having a higher proportion of cellulose, as compared to the biomass from which it is derived, and having a greater cellulose Crystallinity Index. The cellulosic feedstock obtained by the process of the invention may subsequently be converted to ethylene glycol by catalytic hydrothermal methods. The present invention incorporates the use of specifically selected DES solvents for the treatment of cellulosic biomass, in combination with specifically selected process conditions for the selective hydrogenolysis/hydrogenation of the cellulosic feedstock obtained from the cellulosic biomass treatment to afford ethylene glycol. 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 oxide intermediate. With an increasing focus on the use of renewable feedstocks, such as a biomass, several alternative methods have emerged for each of the stages in the conversion of biomass 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 mill discards. 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. Methods for converting saccharide-containing materials to ethylene glycol and other polyols include hydrothermal catalytic processes, for example catalytic hydrogenolysis/hydrogenation. For example, US 2010/0255983 discloses a method for converting cellulose, a principal component of biomass, 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%. Such high levels of conversion and ethylene glycol yield are however not readily achievable with cellulose-containing feedstock that has not undergone substantial pretreatment. As reported in CN102731254, when a 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.

According to CN102731254, 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 4,404,411 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 4,404,411 also indicates that the strongly basic process taught therein is likely to be suitable for saccharides which are reduced to polyols in situ. In that regard, xylitol and sorbitol are indicated as being preferred polyols as they are readily available from cellulose and hemicellulose, derivable from biomass.

In contrast, US 2013/0252285 exemplifies the use of [Bmim][Ac] and [Emim][Ac] ionic liquids for pretreating biomass in order to provide hydrolysable sources of hemicellulose and cellulose. In US 2013/0252285, cellulosic biomass is completely dissolved in a composition comprising [Bmim][Ac] or [Emim][Ac], water and a kosmotrophic anion, the latter facilitating separation of precipitated solids, the aqueous phase and the ionic liquid phase. The solubilized cellulosic content of the biomass is said to be subsequently recovered from the reaction medium by addition of an anti-solvent, such as water, which precipitates the cellulosic material from the ionic liquid phase. The extraction of cellulose reported in US 2013/0252285 thus corresponds to a two stage regeneration process necessarily requiring the use of an anti-solvent for selectively precipitating dissolved cellulose. Notably, the object of the method of US 2013/0252285 is to provide cellulosic material which may be subjected to enzymatic hydrolysis, rather than hydrogenolysis reactions using conventional metallic catalyst systems, at high solids loadings, short residence times and low enzyme concentrations. The aim of the pretreatment in US 2013/0252285 is to increase the surface area of the polysachharides and to decrystallize cellulose, specifically for enhancing depolymerisation thereof by enzymatic hydrolysis. Enzymatic hydrolysis is more effective with substrates having lower cellulose crystallinity.

Other ionic solvents having comparable properties, as well as similar industrial applications, to those of ionic liquids are the deep eutectic solvents (DESs). A DES is an ionic solvent formed of a mixture of two components, which mixture forms a eutectic with a melting point significantly lower than that of either of the individual components of the mixture. Typically DESs are based on quaternary ammonium salts, such as choline chloride, with hydrogen bond donors, such as amides and carboxylic acids. These solvents are generally considered to be more water compatible and less toxic than many ionic liquids.

US 2009/0247432 describes the use of DESs as part of a method for solubilizing/removing cellulose, or chemically modified cellulosic polymers, specifically when used in subterranean drilling operations, such as fracturing. In that method, the DES is pumped downhole after fracturing operations to remove cellulosic material used for thickening the fracturing fluid. US 2009/0247432 discloses a number of DES formed from mixtures of (chlor-)choline chloride and various amides and mono- and di- carboxylic acids, including oxalic, malonic and succinic acids. US 2009/0247432 does not disclose the use of the DES for the purpose of selective biomass extraction, nor is there any mention of the modification of the crystallinity of cellulose. WO 2011/155829 discloses a number of DESs based on mixtures of materials of natural origin comprising at least two components. The first component is selected from at least one naturally occurring organic acid or an inorganic compound, such as a salt. The second component is selected from at least one naturally occurring mono- or dimeric sugar, sugar alcohol, amino acid, di- or tri- alkanal or choline derivatives. Extraction of polysaccharides is also generally referred to, although only lentinan, heparin, hyaluronan, alginate, agar, starch and inulin polysaccharides are mentioned specifically. WO 2011/155829 does not mention any form of selective extraction of a particular polysaccharide from a biological product containing multiple polysaccharides.

Zhang, et al, "Green and Inexpensive Choline-Derived Solvents for Cellulose Decrystallization". Chemistry - A European Journal, Vol.18, (2012), pp 1043-1046 discloses a class of choline-derived solvents which are shown to rapidly dissolve and decrystallize microcrystalline cellulose. Specifically, the choline-derived solvents are based on choline, either in the chloride, hydroxide or acetate form, together with a quaternary ammonium chloride salt, such as tributylmethylammonium chloride ([TBMA]CI). Once the microcrystalline cellulose has been solubilized in the choline- derived solvent, amorphous cellulose is regenerated by the addition of an anti-solvent (water), and the amorphous cellulose may be subsequently isolated.

The choline-derived solvents are considered by Zhang et al to represent valuable alternatives to the traditional imidazolium-based ionic liquids used in solubilizing and decrystallizing cellulose, such as those reported in US 2013/0252285. An extraction performed with the choline-derived solvents reported by Zhang et al would thus also correspond to a two stage regeneration process, necessarily requiring the use of an anti- solvent for selective precipitation of dissolved cellulose, as in US 2013/0252285.

The present invention is based on the surprising discovery that a valuable cellulosic feedstock may be obtained following treatment of cellulosic biomass with specifically selected deep eutectic solvents, in particular, those based on a mixture of certain choline derivatives with an alpha-hydroxy carboxylic acid. In particular, use of these specific deep eutectic solvents as part of a selective extraction obviates the use of anti-solvents for isolating the cellulose component of the cellulosic biomass by a precipitation process. Furthermore, cellulosic feedstock obtained from the treatment with the above deep eutectic solvent has been found to give desirable yields of ethylene glycol in subsequent catalytic hydrogenolysis/hydrogenation reactions, as well as desirable selectivity for ethylene glycol over other polyols, such as 1 ,2-propylene glycol. Thus, in a first aspect, the present invention provides a process for preparing a cellulosic feedstock comprising the steps of: i) contacting cellulosic biomass with a deep eutectic solvent (DES) formed from a mixture of a) a choline derivative selected from choline chloride, chlorocholine chloride, choline acetate, acetylcholine chloride or phosphatidyl choline; and b) an alpha-hydroxy carboxylic acid; and ii) obtaining a cellulosic feedstock which has a higher proportion of cellulose component, as compared with the cellulosic biomass from step;

wherein the majority of the cellulosic feedstock obtained in step ii) is obtained without regenerating cellulose by precipitation.

Treatment of cellulosic biomass with a deep eutectic solvent according to the process of the present invention has been found to selectively solubilize and remove amorphous components of cellulosic biomass, such as lignin and hemicellulose, over cellulose. Meanwhile, the cellulosic feedstock obtainable by the process of the present invention has surprisingly been found to exhibit increased cellulose crystallinity compared with its level of crystallinity whilst entrained in untreated biomass.

This is in contrast to known ionic liquid treatments of biomass, such as that disclosed in US 2013/0252285, where the cellulose component of biomass is completely dissolved by [Emim][Ac] and [Bmim][Ac], in addition to the other components of the biomass. This also contrasts with alternative deep eutectic solvents which completely dissolve microcrystalline cellulose. In both cases, in order to isolate the cellulose component, it is necessary to perform a precipitation of dissolved cellulose using an anti-solvent, following which a cellulose material is obtained having a lower crystallinity index, which is preferable for enzymatic hydrolysis. However, it is possible for significant amounts of cellulose to remain in solution and go unrecovered, despite the use of an anti-solvent, making the overall extraction process less efficient. Alternatively, precipitation steps must be repeated several times, making the overall process significantly more labour intensive. Thus, the present invention also provides a process for selectively solubilizing and removing lignin and hemi-cellulose components of a cellulosic biomass comprising the steps of: i) contacting cellulosic biomass with a deep eutectic solvent (DES) formed from a mixture of a) a choline derivative selected from choline chloride, chlorocholine chloride, choline acetate, acetylcholine chloride or phosphatidyl choline; and b) an alpha-hydroxy carboxylic acid; and ii) obtaining a cellulosic feedstock which has a higher proportion of a cellulose component, as compared with the cellulosic biomass from step i); wherein the majority of the cellulosic feedstock obtained in step ii) is obtained without regeneration of cellulose by precipitation. In another aspect, the present invention also provides a use of a deep eutectic solvent formed from a mixture of a) a choline derivative selected from choline chloride, chlorocholine chloride, choline acetate, acetylcholine chloride or phosphatidyl choline; and b) an alpha-hydroxy carboxylic acid for selectively solubilizing and removing lignin and hemi-cellulose components of a cellulosic biomass and/or for increasing the cellulose Crystallinity Index of the cellulose component of cellulosic biomass. In one embodiment, the deep eutectic solvent as described herein is used to increase the cellulose Crystallinity Index value of the cellulose component of cellulosic biomass to a value of 42.5 % or above, as measured using CP/MAS. "Cellulosic 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 mill discards. In a preferred embodiment, the biomass is oil palm biomass, more preferably empty fruit bunches (EFB).

Biomass in accordance with the present invention comprises the three principal components of cellulose, hemicellulose and lignin, at varying levels. As will be appreciated by the skilled person, the biomass may also contain other polysacharides, such as glycogen, starch and chitin. In addition, the biomass may also contain monosacharides, disaccharides and oligosaccharides. Examples of monosacharides include glucose, fructose, galactose, xylose, arabinose and mannose.

The term "biomass" used herein is intended to cover "raw biomass" or "crude biomass" which has not been subjected to any form of refinement, or only physical refining such as by shredding/chipping and/or dewatering.

A further form of biomass includes "chemically treated biomass" or "pretreated biomass", where raw or crude biomass has undergone some form of treatment either to partially remove lignin and/or hemicellulose, or to 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. Whilst this form of biomass may be used in conjunction with the present invention, it will be appreciated that a benefit of the present invention is that it is unnecessary to pretreat biomass prior to use in the process. As such, it is preferred that the biomass used in the present invention is raw or crude biomass, or biomass which has only undergone physical refining.

The term "cellulosic feedstock" used herein refers to the material obtained as a result of the treatment of cellulosic biomass with a deep eutectic solvent according to the invention and which contains a higher proportion of cellulose component than the cellulosic biomass from which it is derived. Preferably, the cellulose contained within the cellulosic feedstock exhibits greater cellulose Crystallinity Index (CI), as compared with its level of crystallinity whilst entrained in untreated biomass.

The term "deep eutectic solvent (DES)" used herein is intended to refer to an ionic solvent formed from a eutectic mixture of two components. The term "deep eutectic solvent (DES)" includes mixtures having both high melting points and compounds having low melting points, e.g. at or below room temperature. Thus, many DESs have melting points below 200°C, particularly below 100°C, around room temperature (15 to 30°C), or even below 0°C. The deep eutectic solvent used with the process of the present invention comprises a mixture of a) a choline derivative selected from choline chloride, chlorocholine chloride, choline acetate, acetylcholine chloride or phosphatidyl choline and b) an alpha-hydroxy carboxylic acid. Preferably, the alpha-hydroxy carboxylic acid component of the deep eutectic solvent is selected from naturally occurring acids, such as glycolic acid, lactic acid, tartaric acid, citric acid, mandelic acid, and malic acid. Synthetic versions of these acids, which may exist in different stereoisomeric forms, may of course also be used in accordance with the present invention, however. More preferably, the alpha-hydroxy carboxylic acid is selected from malic acid and lactic acid. Most preferably, the alpha-hydroxy carboxylic acid is selected from malic acid.

Preferably, the choline derivative of the deep eutectic solvent is selected from choline chloride, chlorocholine chloride, or acetylcholine chloride. Most preferably, the choline derivative is selected from choline chloride.

The specific deep eutectic solvents used in the process of the present invention have been found to be particularly suitable for dissolution, and selective removal, of amorphous components of biomass, such as lignin and hemicellulose. The preferential dissolution of hemicellulose over cellulose is particularly notable in the context of the present invention. As a result, a cellulosic material having a higher proportion of cellulose component than that of the untreated biomass may be obtained following pretreatment with the specific deep eutectic solvents described hereinbefore.

Surprisingly, the cellulosic material obtained by the process of the present invention, has been found to exhibit increased crystallinity, as compared with its crystallinity in the untreated biomass. This is the opposite of what would be expected based on known prior art biomass pretreatments using ionic liquids or alternative deep eutectic solvents. For example, treatment of biomass with [Bmim][Ac] or [Emim][Ac] completely dissolves biomass and the cellulose component, once regenerated, is substantially decrystallized. This has been verified by the present inventors who have found that cellulose Crystallinity Index of biomass treated with [Bmim][Ac] is significantly lower than that of untreated biomass (which findings are reported hereinbelow). Moreover, deep eutectic solvents based on choline and a quaternary ammonium chloride salt, such as tributylmethylammonium chloride ([TBMA]CI) have been shown to solubilize microcrystalline cellulose and form amorphous cellulose once regenerated. The cellulosic feedstock obtained from the process of the invention has also been found to be particularly suitable for converting to ethylene glycol, in good yield and with high selectivity over 1 ,2-propylene glycol, by catalytic hydrogenolysis/hydrogenation methods. The DESs described hereinbefore are readily prepared from commodity chemicals by processes well known to the person of skill in the art. For instance, the skilled person is able to prepare a deep eutectic solvent for use with the present invention by mixing the choline derivative together with the alpha-hydroxy carboxylic acid under heating (for example, at about 80 °C), until a homogeneous, clear liquid has been formed. Alternatively, the choline derivative and alpha-hydroxy carboxylic acid may both be dissolved in water solvent before the water component of the resulting mixture is removed at low temperature (for example, at about 70 °C) using, for instance, a rotary evaporator to leave a eutectic mixture. A suitable molar ratio of the two components which leads to a eutectic mixture may be readily ascertained by the skilled person. For a DES, often the components are present in the mixture in equimolar ratio, although other ratios are known. Generally, however, the molar ratio of the components can be expressed as integers, typically varying from 1 :1 to 4:1 . Illustrative ratios of preferred DESs according to the present invention are provided in Table 1 below. J. Am. Chem. Soc, 2004, 126 (29), pp 9142-9147, also describes the formation of deep eutectic solvents between choline chloride and various carboxylic acids.

Table 1

In step i) of the process of the invention, cellulosic biomass is contacted with the DES. Contacting step i) may be carried out by contacting the cellulosic biomass with the DES in a vessel wherein the resulting mixture is stirred using, for example, a mechanical stirrer, an ultrasonic stirrer, an electromagnetic stirrer or by bubbling an inert gas through the mixture. Step i) may be conducted at ambient temperature up to temperatures lower than which polysachharide decomposition occurs. Step i) is suitably conducted at a temperature of from 25°C to 110°C, preferably from 30°C to 100°C.

Suitably, the mass ratio of cellulosic biomass to deep eutectic solvent in contacting step i) is from 1 :1 to 1 :300, preferably in a mass ratio of from 1 :20 to 1 :100. Mixing of the cellulosic biomass with the deep eutectic solvent as part of contacting step i) may suitably last from from 1 hour to 48 hours, preferably 2 hours to 24 hours, more preferably 6 to 20 hours, and most preferably 10 to 18 hours, for example 16 hours.

If desired, contacting step i) may be conducted in the presence of a co-solvent which is compatible with the deep eutectic solvent and the components of cellulosic biomass. The use of a co-solvent may be appropriate where it is desired to modify the viscosity of the DES; provide a medium to ensure sufficient mixing of components; and/or to enhance dissolution effects of the DES. Suitable co-solvents include, for example, water and/or an organic co-solvent. In one embodiment, the reaction medium comprises a co-solvent selected from water, methanol, ethanol, propanols, butanols, ethylene glycol, glycerol, or a combination thereof. In a preferred embodiment, the reaction medium comprises an aqueous co-solvent.

In one embodiment of the invention, co-solvent is present in an amount of no more than 15 wt% based on the total weight of the reaction mixture. In a further embodiment of the invention, co-solvent is present in an amount no more than 10 wt% based on the total weight of the reaction mixture.

In a further embodiment, contacting step i) is conducted substantially in the absence of a co-solvent (i.e. less than 5 wt%, for example 2 wt% or 1 wt% based on the total weight of the reaction mixture). In yet a further embodiment of the invention, contacting step i) of the process of the invention consists essentially of contacting cellulosic biomass with a deep eutectic solvent as described hereinbefore.

In step ii) of the process of the invention, a cellulosic feedstock is obtained, wherein the majority of the cellulosic feedstock is obtained without regeneration of cellulose by precipitation. Separation of the feedstock from the reaction mixture in step ii) may be carried out by simple filtration methods. The deep eutectic solvents used in conjunction with the present invention may selectively dissolve the amorphous components of the biomass, such as lignin and hemicellulose, and can therefore leave a solid cellulosic material, typically in a fibrous form.

Where reference herein is made to "the majority" of the cellulosic feedstock obtained, it is intended to refer to over 50 wt.% of the total amount of cellulose feedstock obtained. In preferred embodiments, at least 60 wt.% of the total amount of cellulose feedstock obtained is obtained without regeneration of cellulose by precipitation, more preferably at least 70 wt.%, at least 80.wt%, at least 90 wt.% or even at least 95 wt.% of the total amount of cellulose feedstock is obtained without regeneration of cellulose by precipitation. Most preferably, none of the cellulose feedstock is obtained by regeneration of cellulose by precipitation. One of the notable advantages of the present invention is that the particular deep eutectic solvents are able to selectively solubilise hemicellulose and lignin components over cellulose, thus obviating regeneration steps involving precipitation of dissolved cellulose by means of anti-solvents, which are relied upon as part of cellulose extraction processes employed in the prior art.

Nevertheless, the present invention does not preclude the use of an anti-solvent and an anti-solvent may be used in combination with the process of the present invention for any purpose. For instance, in some embodiments, an anti-solvent, preferably water, may be used to wash fibrous cellulose which is obtained from the extraction with the above described deep eutectic solvents in accordance with the invention. In other embodiments, where a solvent is used alongside the deep eutectic solvent as part of the extraction, step ii) of the process may be assisted by the use of an anti-solvent, such as water, acetone, dichloromethane and/or acetonitrile, in order to isolate the cellulosic feedstock product.

Although less preferred, in some alternative embodiments where a co-solvent is employed, gravity separation, for example, in a settling unit, may be used. For example, the cellulosic material may occupy a co-solvent phase which is distinct from the deep eutectic phase which contains the substantial content of lignin and hemicellulose components, and may be separated on this basis. Such phases may also be separated using, for example, a decanter, a hydrocyclone, electrostatic coalescer or a centrifuge. Step i) followed by step ii) may be repeated several times, until a desired level of extraction of the biomass has occurred. Steps i) and ii) may also be carried out together in a centrifugal contact separator, for example, a centrifugal contact separator as described in US 4,959,158, US 5,571 ,070, US 5,591 ,340, US 5,762,800, WO 99/12650, and WO 00/29120. Suitable centrifugal contact separators include those supplied by Costner Industries Nevada, Inc. The deep eutectic solvent and optional co-solvent/biomass mixture may be introduced into an annular mixing zone of the centrifugal contact separator. Preferably, the DES, any optional co-solvent and biomass are introduced as separate feed streams into the annular mixing zone. The deep eutectic solvent any optional co-solvent and biomass are rapidly mixed in the annular mixing zone such that at least a portion of amorphous components of the biomass are extracted into the deep eutectic solvent. The resulting mixture is then passed to a separation zone wherein a centrifugal force is applied to the mixture to produce a clean separation of any optional co-solvent phase, deep eutectic solvent extract phase and solid biomass derivative.

The deep eutectic solvent phase which has been used in the process of the present invention may be recycled after use. For instance, a precipitating solvent (anti-solvent) may be used to precipitate amorphous components of the biomass dissolved, which may then be separated for instance, by filtration. The precipitating solvent may then by separated from the deep eutectic solvent by, for instance, driving off the solvent at reduced pressure. Normal solvents which are immiscible with the deep eutectic solvent may also be used for extracting by-products dissolved in the deep eutectic solvent which may then be phase-separated as described hereinbefore.

Without being bound by any particular theory, it is believed that the greater crystallinity of the cellulose component of the obtained cellulosic feedstock, in combination with the reduced level of amorphous components such as lignin and hemi-cellulose obtained from the process of the invention, has an impact on its subsequent conversion to ethylene glycol. Crystalline cellulose is known to exist in the form of four different crystallographic allomorphs (I through IV), and it is also known that one allomorph may be converted to another by chemical (e.g. ammonia) and/or heat treatment. As the skilled person will be aware, cellulose crystallinity is commonly reported by reference to the Crystallinity Index (CI) parameter. CI measurements made and reported in the context of the present invention were calculated using the known solid state method, nuclear magnetic resonance (¹³C NMR) with cross-polarization and magic angle spinning (CP/MAS). Reference in that regard is also made to the solid state method for CI measurement reported in Park et al., "Biotechnology for Biofuels. Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulose performance", 2010; 3:10.

The cellulosic feedstock obtained from the process of the invention has been found to be particularly suitable for converting to ethylene glycol, in good yield and with high selectivity over 1 ,2-propylene glycol, by catalytic hydrogenolysis/hydrogenation methods.

Thus, in another aspect, the present invention provides a process for preparing ethylene glycol from cellulosic biomass comprising the steps of: i) contacting cellulosic biomass with a deep eutectic solvent formed from a mixture of a) a choline derivative selected from choline chloride, chlorocholine chloride, choline acetate, acetylcholine chloride or phosphatidyl choline; and b) an alpha-hydroxy carboxylic acid; ii) obtaining a cellulosic feedstock which has a higher proportion of cellulose, as compared with the cellulosic biomass from step i), and wherein the majority of the cellulosic feedstock is obtained without regenerating cellulose by precipitation;

iii) performing hydrogenolysis and hydrogenation of the cellulosic feedstock by contacting with a heterogeneous catalyst system in the presence of hydrogen and a reaction medium; and

iv) obtaining ethylene glycol from the reaction mixture.

Features of the method steps i) and ii) of the above further aspect of the invention are as described for steps i) and ii) of the process described hereinbefore. Thus, the deep eutectic solvent used in this further aspect of the invention is as described hereinbefore. Preferred deep eutectic solvents described hereinbefore are also preferred in the context of this further aspect of the invention. As will be appreciated by the person of skill in the art, the heterogenous catalyst system for use with step iii) of the process of the invention will have at least two components which are suitable for catalysing the hydrogenolysis and hydrogenation reactions respectively. Preferably, the heterogeneous catalyst system comprises:

1 ) tungsten, molybdenum, or a combination thereof; and

2) one or more transition metals selected from lUPAC Groups 8, 9 and 10, and combinations thereof. The preferred heterogeneous catalyst system utilized in the process of the present invention comprises metallic components 1 ) and 2). Without being bound by any particular theory, it is believed that component 1 ) of the catalyst system, comprising tungsten, molybdenum, or a combination thereof, promotes hydrogenolysis of saccharides contained in the feedstock. Meanwhile, component 2), 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 from the cellulosic feedstock. In one embodiment, component 1 ) of the preferred heterogeneous catalyst system comprises molybdenum in elemental form or in the form of molybedic acid.

In another embodiment, component 1 ) of the preferred heterogeneous catalyst 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.

More preferably component 1 ) of the heterogeneous catalyst system comprises tungsten in the form of a compound selected from sodium tungstate, tungsten carbide, tungsten bronze, tungstic acid or a combination thereof. Even more preferably, the heterogeneous catalyst system comprises tungsten in the form of a compound selected from sodium tungstate, tungstic acid or a combination thereof. In one embodiment, component 2) of the preferred heterogeneous catalyst system comprises a metal selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum or a combination thereof. Preferably, component 2) of the heterogeneous catalyst system comprises a metal selected from nickel, ruthenium, platinum or a combination thereof. More preferably, component 2) of the catalyst system comprises nickel.

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 cellulosic feedstock and the catalytic system measured on the basis of elemental tungsten or molybdenum. The ratio of active metals in catalyst components 1 ) and 2) respectively is preferably 1 :100 to 100:1 , more preferably 1 : 10 to 10:1 , measured on an elemental basis.

Step iii) 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 cellulosic material. Preferably, step iii) of the process 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 iii) of the process of the invention is conducted at a pressure of 0.1 to 15 MPa, more preferably at a pressure of 1 to 7 MPa, for example at a pressure of 2 MPa.

Step iii) 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 an aqueous solvent. Preferably, the amount of reaction medium present is such that the feedstock represents between 1 and 30 wt.%, 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. The hydrogenolysis/hydrogenation reactions of step iii) of the process are preferably conducted under acidic conditions. In particular, it has been found to be advantageous to conduct the hydrogenolysis/hydrogenation reactions preferably at a pH of from 2.0 to 6.5, preferably at a pH of from 2.25 to 5, more preferably at a pH from 2.5 to 4, most preferably at a pH of from 2.75 to 3.25, for example a pH of 3. Particularly high levels of cellulosic feedstock conversion and yield of ethylene glycol have been found to be achievable with this range of pH.

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.

Step iii) of the process of the above further aspect of the invention is preferably conducted in the presence of an organic or inorganic acid. Thus, in an embodiment, step iii) of the process 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 iii) 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 selected from benzenesulfonic acid. When present, the 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. The cellulosic feedstock obtained in step ii) may be used directly or may be further processed before being reacted in step iii) of the process. Step iii) typically comprises mixing cellulosic feedstock, reaction medium and heterogeneous catalyst system in a sealed reaction vessel, optionally adjusting the pH of the reaction mixture, 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 for step c) of the process is from 30 minutes to 3 hours, for example, 2 hours. The heterogeneous catalyst system utilized in the process of the present invention may be either partially or fully supported or in unsupported form. Thus, for example, component 1 ) and/or 2) of the preferred catalyst system may be supported or unsupported. Where a component of the preferred catalyst system is utilized in supported form, it is preferred that component 2) of the preferred catalyst system is supported. Suitable supports 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 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, one or two of the at least two components of the heterogeneous catalyst system may be adsorbed onto the support such that the active component(s) is present in an amount of 0.05-50wt.%, based on the weight of the supported catalyst component.

Steps iii) and/or v) of the further aspect of the invention may be conducted via a batch or continuous mode of operation. With a batch mode operation, the cellulosic 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 cellulosic 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, optionally any acidic species 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 one or more components of the catalyst system are supported, contacting step iii) may include passing the cellulosic feedstock and reaction medium through a column packed with the supported catalyst system component(s) (i.e. a packed bed arrangement). Thus, the cellulosic feedstock may be passed through a column containing the supported catalyst system component(s). The cellulosic feedstock 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 glycol and 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.

In a further aspect, the present invention also provides a use of a cellulosic feedstock obtained by the process described hereinbefore for preparing ethylene glycol. The present invention will now be illustrated by way of the following examples. EXAMPLES

Preparation of Deep Eutectic Solvents

Deep eutectic solvents based on mixtures of malic acid or lactic acid with choline chloride ((ChCI)(Mal) and (ChCI(Lac) respectively) were chosen for the pretreatment of empty fruit bunches (EFB), a form of oil palm biomass. The DESs were each prepared by adding one of the alpha-hydroxy acids and choline chloride at a molar ratio of 1.2:1 to water solvent. The aqueous mixture was then heated to 60 °C and stirred for approximately 16 hours before the water component of the mixture was removed by slow rotary evaporation (3 kPa) for 3 hours at 70 °C, after which a eutectic mixture was obtained.

Experimental Procedure

EFB biomass was contacted in a reaction vessel with deep eutectic solvent at a temperature and for a time period indicated below. A cellulosic material was subsequently obtained from the reaction mixture. After isolation of the cellulosic material, the Crystallinity Index of the cellulose was measured using nuclear magnetic resonance (¹³C NMR) with "cross polarization and magic angle spinning" (CP/MAS). Following this characterisation, a sample of the cellulosic material was hydrolysed in order to assess its sugar monomer composition. The assessment was made according to the NREL Laboratory Analytical Procedure (LAP) (version 07-08-2011 ) entitled "Determination of Structural Carbohydrates and Lignin in Biomass". As part of that procedure, a sample is hydrolysed in a two-step hydrolysis, whereupon the cellulosic material is converted into its monomeric form, before quantifying with HPLC with refractive index detector.

Example 1

300.74 g (ChCI)(Mal) was added to a vessel containing 15.03 g of empty fruit bunch (EFB) feedstock such that the weight ratio of biomass to deep eutectic solvent was 1 :20. The vessel was then heated to 80 °C and the pretreatment conducted for 16 hours, before the pretreated feedstock was isolated as a fibrous solid by filtration and washed repeatedly with water. A sample of the cellulosic material was then analysed as described above. Results are provided in Table 2 below.

Example 2

482.33 g (ChCI)(Lac) was added to a vessel containing 12.06 g of empty fruit bunch (EFB) feedstock such that the weight ratio of biomass to deep eutectic solvent was 1.40. The vessel was then heated to 80 °C and the pretreatment conducted for 16 hours, before the pretreated feedstock was isolated by filtration and washed repeatedly with water. A sample of the cellulosic material was then analysed as described above. Results are provided in Table 2 below. Comparative Example 1

48.76 g [Bmim][Ac] ionic liquid was added to a vessel containing 1.25 g of empty fruit bunch (EFB) feedstock such that the weight ratio of biomass to ionic liquid was 1 :39. The vessel was then heated 80 °C and the treatment conducted for 16 hours with continuous mixing, before the treated feedstock was isolated. The sample was then mixed with 200 ml of distilled water and heated to 50 °C for one hour. This washing step was repeated three times. A sample of the cellulosic material was then analysed as described above. Results are provided in Table 2 below. Table 2

EFB

Untreated EFB treated with EFB treated with treated with

EFB (ChCI)(Lac) [Bmim][Ac]

(ChCIXMal)

Cellulose

41.41 42.79 42.38 31 .89 Crystallinity Index

Glucose wt.% 35.11 36.07 48.94 29.39

Xylose wt.% 25.13 13.76 7.55 13.15

Arabinose wt.% 1 .54 0.59 0.00 0.52 The results in Table 2 demonstrate the surprising increase in cellulose Crystallinity Index following treatment in accordance with the process of the present invention. Moreover, the compositional analysis illustrates a selective removal of the hemicellulose component of the cellulosic biomass. The principal constituents of hemicellulose are xylose and arabinose (which are not components of cellulose). It is clear that the levels of xylose and arabinose monomers have been significantly reduced thereby demonstrating a significant reduction in the level of hemicellulose in the treated material obtained.

The results of Table 2 also demonstrate the selectivity associated with the use of a deep eutectic solvent in accordance with the present invention in comparison with that of an ionic liquid, ([Bmim][Ac]). Significant loss of glucose upon treatment with [Bmim][Ac] indicates that there is no selectivity for the solubilzation of the amorphous components of the biomass when [Bmim][Ac] is used, in contrast with the deep eutectic solvents used in accordance with the present invention. Furthermore, treatment with [Bmim][Ac] results in substantial decrystallization of the cellulose component of the biomass, illustrated by the significant drop in cellulose Crystallinity Index as compared with the untreated value.

Preparation of ethylene glycol from cellulosic biomass with deep eutectic solvent pretreatment Example 3

In a pressure vessel, 25 ml deionized water, 0.25 g Raney-Nickel, 0.25 g sodium tungstate was added to 2.5g of cellulosic feedstock obtained following treatment of empty fruit bunch (EFB) according to Example 1 and the mixture stirred at 500 rpm. At ambient temperature, hydrogen was pumped into the vessel up to a pressure of 2 MPa, before the temperature was increased to 245°C for 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. A sample was then withdrawn for analysis by high performance liquid chromatography (HPLC). Polyol yields were then subsequently determined, the results of which are provided in Table 3.

Example 4

In a pressure vessel, 25 ml deionized water, 0.25 g Raney-Nickel, 0.25 g sodium tungstate was added to 2.5g of cellulosic feedstock obtained following treatment of empty fruit bunch (EFB) according to Example 2 and the mixture stirred at 500 rpm. At ambient temperature, hydrogen was pumped into the vessel up to a pressure of 2 MPa, before the temperature was increased to 245°C for 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. A sample was then withdrawn for analysis by high performance liquid chromatography (HPLC). Polyol yields were then subsequently determined, the results of which are provided in Table 3.

Preparation of ethylene plycol from cellulosic biomass without deep eutectic solvent pretreatment

Comparative Example 2

50ml deionized water, 0.5g Raney-Nickel, 0.5g sodium tungstate was added to 5g of untreated empty fruit bunch (EFB) feedstock into 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°C for 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 3.

Table 3: Polyol yield and distribution

The yields of ethylene glycol and 1 ,2 propylene glycol for Examples 3 and 4 are calculated on the basis of the deep eutectic solvent treated feedstock, whereas the yields for Comparative Example 2 are based on the untreated EFB feedstock. Table 3 demonstrates that a superior ratio of ethylene glycol to 1 ,2 propylene glycol is obtainable from a feedstock obtained following treatment with a deep eutectic solvent in accordance with the invention, as opposed to an untreated biomass feedstock (6.42/5.05 vs 2.48 respectively).

Effect of pH on polyol yield in feedstock conversion

Comparative Example 3

The process of Comparative Example 2 was repeated, except that 1 wt.% sulfuric acid solution was added until a reaction mixture was formed having a pH of 6. Results are presented in Table 4 below. Comparative Example 4

The process of Comparative Example 2 was repeated, except that 1 wt.% sulfuric acid solution was added until a reaction mixture was formed having a pH of 5. Results are presented in Table 4 below.

Table 4: Effect of pH on polyol yield and distribution

When a neutral pH was used for the hydrolysis/hydrogenation reactions in Comparative Example 1 , the ratio of ethylene glycol to 1 ,2-propylene glycol obtained was 2.48. Adjustment to pH 6, using inorganic acid, sees the ratio of ethylene glycol to 1 ,2- propylene glycol increase to 3.30, as shown in Table 3. Meanwhile, adjustment to pH 5, using inorganic acid, sees the ratio of ethylene glycol to 1 ,2 propylene glycol increase even more substantially to 4.34. The yields reported in Table 4 illustrate the benefit of conducting the hydrolysis/hydrogenation reactions in the conversion to polyol in terms of the ratio of ethylene glycol to 1 ,2 propylene glycol which is obtained. This same trend is also observable in the conversion of a cellulosic feedstock obtained from the deep eutectic solvent treatment in accordance with the invention. Thus, treating biomass first with the deep eutectic solvent in accordance with the invention to obtain a cellulosic feedstock, then converting the cellulosic feedstock by hydrolysis/hydrogenatation with a heterogeneous catalyst as described herein is considered particularly preferable for obtaining a desirable yield of ethylene glycol over 1 ,2 propylene glycol.

Claims

A process for preparing a cellulosic feedstock comprising the steps of:

i) contacting cellulosic biomass with a deep eutectic solvent (DES) formed from a mixture of a) a choline derivative selected from choline chloride, chlorocholine chloride, choline acetate, acetylcholine chloride or phosphatidyl choline; and b) an alpha- hydroxy carboxylic acid; and

ii) obtaining a solid cellulosic feedstock which has a higher proportion of cellulose component, as compared with the cellulosic biomass from step i),

A process according to Claim 1 , wherein the cellulosic biomass and the deep eutectic solvent are contacted in a mass ratio of from 1 :1 to 1 :300.

A process according to Claim 2, wherein the cellulosic biomass and the deep eutectic solvent are contacted in a mass ratio of from 1 :20 to 1 : 100.

A process according to any one of the preceding claims, wherein at least 80 wt.%, preferably at least 90 wt.%, of the total cellulosic feedstock obtained in step ii) is not obtained by regeneration of cellulose by precipitation.

A process according to any one of the preceding claims, wherein none of the cellulosic feedstock obtained in step ii) is obtained by regeneration of cellulose by precipitation.

A process according to any one of the preceding claims, wherein the alpha- hydroxy carboxylic acid component of the deep eutectic solvent is selected from glycolic acid, lactic acid, tartaric acid, citric acid, mandelic acid, and malic acid.

7. A process according any one of the preceding claims, wherein the alpha-hydroxy carboxylic acid component of the deep eutectic solvent is selected from lactic acid and malic acid.

8. A process according any one of the preceding claims, wherein the alpha-hydroxy carboxylic acid component of the deep eutectic solvent is malic acid.

9. A process according to any one of the preceding claims, wherein the choline derivative component of the deep eutectic solvent is selected from choline chloride, chlorocholine chloride, and acetylcholine chloride.

10. A process according to any one of the preceding claims, wherein the choline derivative component of the deep eutectic solvent is choline chloride.

1 1 . A process according to any one of the preceding claims, wherein the cellulosic biomass is oil palm biomass.

12. A process according to Claim 11 , wherein the oil palm biomass is empty fruit bunches (EFB).

13. A process according any one of the preceding claims, wherein the cellulosic biomass is raw or crude biomass which has not undergone any chemical pretreatment prior to contact with the deep eutectic solvent.

14. A process according to any of Claims 1 to 12, wherein the cellulosic biomass is pretreated biomass which has undergone chemical pretreatment prior to being contacted with the deep eutectic solvent.

15. A process according to any one of the preceding claims, further comprising recovering the deep eutectic solvent.

16. A process for preparing ethylene glycol from cellulosic biomass comprising the steps of:

i) contacting cellulosic biomass with a deep eutectic solvent formed from a mixture of a) a choline derivative selected from choline chloride, chlorocholine chloride, choline acetate, acetylcholine chloride or phosphatidyl choline; and b) an alpha-hydroxy carboxylic acid; ii) obtaining a cellulosic feedstock which has a higher proportion of cellulose, as compared with the cellulosic biomass from step i), and wherein the majority of the cellulosic feedstock is obtained without regenerating cellulose by precipitation;

iv) obtaining ethylene glycol from the reaction mixture.

17. A process according to Claim 16, wherein the deep eutectic solvent is as defined in any of Claims 6 to 10.

18. A process according Claim 16 or Claim 17, wherein at least 80 wt.%, preferably at least 90 wt.%, of the total cellulosic feedstock obtained in step ii) is obtained without regeneration of cellulose by precipitation.

19. A process according to any one of Claims 16 to 18, wherein none of the cellulosic feedstock obtained in step ii) is obtained by regeneration of cellulose by precipitation.

20. A process according to any one of Claims 16 to 19 , wherein step iii) is conducted at a pH of from 2.0 to 6.5, more preferably at a pH of from 2.25 to 5, yet more preferably at a pH from 2.5 to 4, most preferably at a pH of from 2.75 to 3.25, for example a pH of 3.

21 . A process according to any one of the preceding claims, wherein step iii) is conducted in the presence of an organic or inorganic acid.

22. A process according to Claim 21 , wherein the acid is an inorganic acid selected from hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid.

23. A process according to Claim 22 wherein the acid is hydrochloric acid or sulfuric acid.

24. A process according to Claim 21 , 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.

25. A process according to Claim 24, wherein the acid is benzenesulfonic acid.

26. A process according to any of Claims 21 to 25, 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.

27. A process according to any of Claims 16 to 26, wherein the heterogeneous catalyst system comprises:

1 ) tungsten, molybdenum, or a combination thereof; and

2) one or more transition metals selected from lUPAC Groups 8, 9 and 10, and combinations thereof.

28. A process according to Claim 27, wherein component 1 ) of the heterogeneous 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.

29. A process according to Claim 28, wherein component 1 ) of the heterogeneous catalyst system comprises tungsten in the form of a compound selected from sodium tungstate, tungsten carbide, tungsten bronze and tungstic acid.

30. A process according to Claim 29, wherein component 1 ) of the heterogeneous catalyst system comprises tungsten in the form of a compound selected from sodium tungstate, ammonium metatungstate and tungstic acid.

31 . A process according to Claim 27, wherein component 1 ) of the catalyst system comprises molybdenum in elemental form or in the form of molybedic acid.

32. A process according to any of Claims 27 to 31 , wherein component 2) of the catalyst system comprises a metal selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium and platinum.

33. A process according to any of Claim 32, wherein component 2) of the catalyst system comprises a metal selected from nickel, ruthenium or platinum.

34. A process according to any of Claim 33, wherein component 2) of the catalyst system comprises nickel.

35. A process according to any of Claims 16 to 34, wherein the reaction medium comprises a solvent selected from water, methanol, ethanol, propanols, butanols, ethylene glycol and glycerol, or a combination thereof.

36. A process according to any of Claims 22 to 35, wherein the reaction medium comprises an aqueous solvent.

37. A process according to any of Claims 16 to 36, wherein step iii) is conducted at a temperature of at least 150°C, preferably at a temperature of from 200 to 270°C.

38. A process according to any of Claims 16 to 37, wherein step iii) is conducted at a pressure of from 0.1 to 15 MPa, preferably at a pressure of from 1 to 7 MPa.

39. A process according to any of Claims 16 to 38, wherein in step iii) the cellulosic feedstock is present in an amount of 1 to 30wt%, based on the total weight of the reaction mixture.

40. A process according to any of Claims 16 to 39, wherein the heterogeneous catalyst system is unsupported.

41 . A process according to any of Claims 16 to 39, wherein component 1 ) and/or component 2) of the catalyst system is supported by a carrier material.

42. A process according to Claim 41 , 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.

43. A process according to Claim 42, wherein the carrier material is selected from carbon or activated carbon.

44. A process according to any one of Claims 41 to 43, wherein the metal active component of component 1 ) and/or component 2) is present in an amount of 0.05-50wt.%, based on the total weight of the supported catalyst component.

45. A use of a deep eutectic solvent formed from a mixture of a) a choline derivative selected from choline chloride, chlorocholine chloride, choline acetate, acetylcholine chloride or phosphatidyl choline; and b) an alpha-hydroxy carboxylic acid for selectively solubilizing and removing lignin and hemicellulose components of cellulosic biomass and/or increasing the cellulose Crystallinity Index of the cellulose component of cellulosic biomass.

46. A use according to Claim 45, wherein the deep eutectic solvent is as defined in any of Claims 6 to 10.