The present invention relates to improvements in and relating to a process for the production of carbohydrate/sugar and lignin products from cellulosic materials, in particular a process involving acid hydrolysis of cellulose. More particularly, it relates to improvements in the recovery of acid used in such a process.

Large scale conversion of cellulose and lignocellulose materials into sugars (carbohydrates) and lignin products has utility in supplementing natural gas or crude oil for the production of fuels and platform chemicals. Downstream processing of sugars may be by catalytic processes, bacterial fermentation or yeast fermentation. In the cases of fermentation, the presence of inhibitory impurities affects the economics and usability of the sugar product. Examples of chemical downstream processes for sugar include production of sugar alcohols by hydrogenation such as xylitol from xylose, production of platform chemicals such as furfural, hydroxymethyl furfural and levulinic acid by dehydration of pentose and hexose sugars. Examples of biological downstream processes include the production of solvents and organic acids by fermentation, production of enzymes for industrial or other usage and biomass production for use as feed or fodder.

Moreover, alcohol, produced by fermenting biomass, is rapidly becoming a major alternative to hydrocarbons such as natural gas and petroleum. While the current focus is on the production of ethanol from plant seed, e.g. maize or sugar cane juice, the magnitude of the demand for alcohol threatens a reduction in the land area devoted to food production and a desirable alternative to plant seed as the starting material is plant material other than seed, e.g. grass, wood, paper, maize husks, straw, etc. In this case the ethanol is produced by first breaking down the cellulose and hemi-cellulose into fermentable sugars.

Cellulose and lignocellulose are generally non-food resources and are considered sustainable resources by many production methods. Sources of cellulose and lignocellulose that may be industrially applicable feedstocks include: wood, forest and agricultural residues and wastes, waste-paper, cotton or cotton waste, municipal waste, papermaking wastes, biomass sludges etc. Typically these feedstocks will contain cellulose, hemicellulose, glucans, lignin, minerals, salts and a range of organic compounds or so-called 'extractives'. Some form of pretreatment process is generally required to separate lignin from cellulose and/or to convert the cellulose and hemicellulose into carbohydrates that can be processed further. These carbohydrates include C5 (pentose) and C6 (hexose) sugars. Pretreatment methods include the use of strong and weak acids, enzymes, thermomechanical processing, supercritical fluids and organic and inorganic solvents. Inorganic acids, such as H ₃ P0 ₄ and H ₂ S0 ₄ , as a result of their high proton activity, can catalyse both decrystallisation of cellulose and the hydrolysis of hemicellulose and cellulose to mono-, di- and oligosaccharides. The acid is itself not consumed by these processes. A certain amount of acid may, however, be consumed by reversible or irreversible reactions such as neutralisation of basic components and esterification.

For large scale production of sugar and lignin products in this way, a major proportion of the acid must be recovered and recycled. Recovery of the acid may be carried out by contacting the hydrolysate with an organic extraction solvent, such as that described in WO 02/02826, the contents of which is incorporated herein by reference. Separation of a slurry of solid lignin and precipitated sugars (referred to herein as the "sugar slurry") yields an acid solution comprising water, extraction solvent, acid and some dissolved sugars. The extraction solvent in the acid solution is then evaporated off under vacuum to be recycled and to leave an aqueous acid and sugar solution which can be further evaporated off to yield a concentrated acid / sugar mixture.

In a process such as that described in WO 02/02826, the fraction containing solid lignin and precipitated sugars which is separated from the hydrolysate during the extraction step (the "sugar slurry") also contains some residual extraction solvent. Typically this fraction is dried under reduced pressure and carefully controlled temperature conditions (ideally no more than 85°C to avoid degradation of the sugars) to remove the remaining solvent. The dried sugar and lignin is then added to water to yield a lignin, sugar, water and residual acid mixture which is then pumped to a second hydrolysis tank. Oligomeric sugars produced by the initial hydrolysis of the cellulosic plant material are then hydrolysed into monomeric sugars in a second hydrolysis step in order to produce a solution of monomeric sugars suitable for further processing.

In WO 02/02826, methyl ethyl ketone (MEK) is proposed for use in the recovery of acid. MEK is water-miscible, with solubility in water of 25%. The use of ketones as extraction solvents is also proposed in WO 2010/038021 and in WO 2010/146331 , the contents of which are incorporated herein by reference. In both of these earlier applications, it is stipulated that the ketones should be water-miscible. An extraction solvent in which the major component is 2-butanone (MEK) is the solvent of choice. Recovery of acid typically involves a final acid concentration step in which water is separated from a mixture of acid, water and any residual solvent. When the solvent is a ketone, this can give rise to problems due to their instability in an acid environment. In the presence of a strong acid, ketones undergo aldol condensation which can eventually lead to the formation of benzene rings. The rate of this reaction increases at high acid concentrations and at high temperature, but can occur even at ambient temperature with as little as 3 wt.% acid. The condensed products have a higher boiling point and are less polar than the parent ketone. At ambient temperature, benzene rings may form solids which give rise to deposits within the reaction system. Methyl ethyl ketone, for example, has a half-life of just 5 days under conditions typically encountered in the acid concentration process. Solid deposits require periodic removal to avoid eventual clogging of the apparatus and a forced shut-down. The need to carry out periodic removal of any deposits, which can only be carried out following a controlled shut-down of the process, impacts on the efficiency and cost of the overall production process.

In an industrial process it is important that the maximum amount of acid is recovered and recycled in the most efficient manner. In this regard, we have now found that the use of a water-immiscible ketone as an extraction solvent for the acid provides a number of advantages over the conventional use of water-miscible ketones, such as methyl ethyl ketone.

In combination with the use of a water-immiscible ketone to recover acid, we have also found that modifications may be made to the drying step conventionally used for the removal of residual extraction solvent prior to the second hydrolysis stage. Such modifications lead to a more efficient and less energy demanding recovery of residual extraction solvent from the sugar slurry. What we have found is that the addition of water to the sugar slurry prior to drying (de-solventising) significantly increases the efficiency of solvent recovery. As will be described herein, the addition of water further leads to the possibility that de-solventising and the second hydrolysis stage may be carried out in the same unit. The methods which are the subject of this invention provide a number of benefits over conventional methods for the production of alcohols from cellulosic materials involving the use of strong acids, for example by achieving acid recovery whilst minimising the formation of undesirable deposits (aldol condensation). Depending on the method used for recovery of the ketone solvent, this can be less energy demanding than methods conventionally used for removal of extraction solvents, e.g. that described in WO 20120/146331. As will be discussed, the water- immiscible ketone solvent may be separated from the acid using simply water.

The addition of water to the sugar slurry prior to de-solventising has the additional advantage that the water-immiscible ketone can be removed as an azeotrope with water; this improves the efficiency of solvent recovery. Wet slurry also has more favourable heat transfer. The ability to remove a greater proportion of extraction solvent than when carrying out a conventional drying step gives rise to a higher purity sugar product. Other benefits include the ease of transportation of the sugar slurry when this is mixed with water - this may be especially important in cases where production of the fermentable sugars, fermentation and distillation steps necessary to produce the final alcohol product are carried out at a separate site.

Generally, the invention thus relates to the use of a water-immiscible ketone as an extraction solvent for the recovery of acid in a process for the production of carbohydrates (with the optional subsequent production of alcohol) from a cellulosic feedstock. It further relates to the production of an aqueous solution of fermentable carbohydrates/sugars and to the production of a carbohydrate/sugar composition, both of which are suitable for further processing to produce a variety of products as herein described.

Thus, viewed from a first aspect, the invention provides a process for the production of a carbohydrate (e.g. sugar) composition from a cellulosic material, said process comprising:

(i) hydrolyzing said cellulosic material with an aqueous acid to produce a hydrolysate;

(ii) extracting acid and water from said hydrolysate with an extraction solvent which comprises a water-immiscible ketone to yield (a) a first aqueous acidic solution containing said extraction solvent and (b) a residue containing carbohydrates (e.g. sugars);

(iii) removing said extraction solvent from said first aqueous acid solution to yield (c) a second aqueous acid solution containing less extraction solvent than said first aqueous acid solution (e.g. containing less than 80 wt.% of said extraction solvent, preferably less than 50 wt.%. more preferably less than 40 wt.%, especially preferably less than 10 wt.%) and (d) extraction solvent for recycling; and

(iv) optionally concentrating said second aqueous acid solution for

recycling.

Unless otherwise specified, the term "sugar" as used herein should generally be understood to be interchangeable with "carbohydrate" and thus encompasses structural carbohydrates, polysaccharides, monomeric sugars, oligomeric or crystalline regions of cellulose, nanocellulose crystal whiskers, and glucans.

Viewed from a second aspect, the invention provides a process for the production of an aqueous solution of fermentable carbohydrates (e.g. sugars) from a cellulosic material, said process comprising:

(i) hydrolyzing said cellulosic material with an aqueous acid to produce a hydrolysate;

(ii) extracting acid and water from said hydrolysate with an extraction solvent which comprises a water-immiscible ketone to yield (a) a first aqueous acidic solution containing said extraction solvent and (b) a residue containing carbohydrates (e.g. sugars) ;

(iii) removing said extraction solvent from said first aqueous acid solution to yield (c) a second aqueous acid solution containing less extraction solvent than said first aqueous acid solution (e.g. containing less than 80 wt.% of said extraction solvent, preferably less than 50 wt.% more preferably less than 40 wt.%, especially preferably less than 10 wt.%) and (d) extraction solvent for recycling;

(iv) optionally concentrating said second aqueous acid solution for

recycling; and

(v) subjecting said residue containing carbohydrates (e.g. sugars) to an oligosaccharide cleavage reaction to yield an aqueous solution of fermentable carbohydrates (e.g. sugars). Fermenting the sugars and distilling alcohol from the resulting fermented mixture allows the process to be extended to produce alcohol.

Thus, viewed from a third aspect, the invention provides a process for producing alcohol, particularly ethanol or butanol, especially ethanol, from a cellulosic material, said process comprising:

(i) hydrolyzing said cellulosic material with an aqueous acid to produce a hydrolysate;

(ii) extracting acid and water from said hydrolysate with an extraction solvent which comprises a water-immiscible ketone to yield (a) a first aqueous acidic solution containing said extraction solvent and (b) a residue containing carbohydrates (e.g. sugars);

(iii) removing said extraction solvent from said first aqueous acid solution to yield (c) a second aqueous acid solution containing less extraction solvent than said first aqueous acid solution (e.g. containing less than 80 wt.% of said extraction solvent, preferably less than 50 wt.% more preferably less than 40 wt.%, especially preferably less than 10 wt.%) and (d) extraction solvent for recycling;

(iv) optionally concentrating said second aqueous acid solution for

recycling;

(v) subjecting said residue containing sugars to an oligosaccharide

cleavage reaction to yield an aqueous solution of fermentable carbohydrates (e.g. sugars); and

(vi) fermenting said fermentable carbohydrates (e.g. sugars) and distilling alcohol (e.g. ethanol or butanol) from the resulting fermented mixture.

The overall production process (e.g. of alcohol or other end products) may, if desired, be performed at a set of production sites, e.g. with production of the fermentable sugars on one site and fermentation and distillation at another.

Equally, the acid hydrolysis, acid removal and solvent extraction removal may be performed at one site with the oligosaccharide cleavage and other downstream steps being performed at another site.

The extraction solvent for use in the processes herein described may comprise any water-immiscible (e.g. water insoluble) ketone which is capable of taking up a mineral acid (especially sulphuric and/or phosphoric acids) and thereby causing the carbohydrates in the hydrolysate to precipitate. By "water-immiscible ketone" is meant a ketone having a solubility in water at ambient temperature (e.g. 25°C) of 2 to 10 wt.%, e.g. 4 to 6 wt.%. A water-immiscible solvent will form a separate phase when mixed with water.

Preferred for use in the invention are those ketones which are capable of forming a heteroazeotrope with water, the heteroazeotrope having a boiling point below that of water.

Typically the solvent will be or will comprise an aliphatic ketone, preferably an aliphatic ketone containing from 5 to 7 carbon atoms, e.g. an aliphatic ketone having 5 carbon atoms. Examples of ketones suitable for use as an extraction solvent in the methods herein described include diethyl ketone (DEK), methyl propyl ketone (MPK), methyl isopropyl ketone (MIPK), cyclohexanone and mesityl oxide, especially diethyl ketone, methyl propyl ketone and methyl isopropyl ketone. Diethyl ketone is particularly preferred; it shows good stability with respect to aldol condensation in a strong acid environment and, even when condensation occurs, the reaction stops almost completely prior to the formation of benzene rings.

The water-immiscible ketone may be used in substantially pure form, for example at a purity level in excess of 80%, more preferably in excess of 90%, e.g. 95% or higher.

Water-immiscible ketones preferably form the majority of the extraction solvent. Preferably, the extraction solvent comprises a total of at least 50 wt.% water- immiscible ketone, especially at least 75 wt.%, more preferably at least 90 wt.%, where the values quoted are for the total water-immiscible ketone content of the extraction solvent (i.e. where more than one water-immiscible ketone is present). Other components of the extraction solvent may be alcohols or small ethers.

Preferably the extraction solvent consists substantially of one or more water- immiscible ketones. In a further preferred embodiment, the extraction solvent comprises (in addition to a water immiscible ketone) an alcohol, preferably a water miscible alcohol, especially a C1 -4 alcohol, preferably methanol, ethanol or propanol, e.g. isopropanol and/or an ether (e.g. diethyl ether). Other suitable alcohols include tertiary butyl alcohol and tertiary amyl alcohol. Preferably the extraction solvent and/or the water-immiscible ketone is substantially free from water, e.g. less than 5 wt.% water, especially less than 1 wt.% water is present. If water is present in mixture with the water-immiscible ketone, the ketone/water mixture is preferably less than 2 wt.% water, especially less than 1 wt.% water. When the extraction solvent comprises components other than water immiscible ketone, e.g. an alcohol, water tolerance is a little higher as alcohols will prevent the formation of a two liquid phase system during extraction, i.e. the water content of the extraction solvent is preferably less than 5 wt.%, e.g. less than 3 wt.%, preferably less than 2 or 1 wt.%.

It is preferred that the extraction solvent for use in the invention will be substantially free from other organic solvents, in particular water-miscible ketones and/or alcohols. For example, the extraction solvent should contain less than 20 wt. %, especially less than 10 wt.%, preferably less than 5 wt.% of other organic solvents. Most preferably the extraction solvent will be substantially free from (e.g. free from) lower ketones, such as C ₃ and C ₄ ketones, especially methyl ethyl ketone.

Following acid extraction, the water-immiscible ketone solvent may be separated from the acid using various different methods. Typically, separation may be effected by: (i) extraction of the ketone from the acid using an organic solvent; (ii) extraction of the acid from the ketone using water; or (iii) distillation of a ketone / water azeotrope and ketone from the acid. In the context of a water-immiscible ketone, each of these methods has a number of distinct advantages when compared to the use of a water-miscible ketone, such as methyl ethyl ketone. These advantages will be discussed herein. Of these separation methods, extraction using water is particularly preferred.

In one embodiment, the ketone extraction solvent may be recovered by contacting the first aqueous acidic solution with an organic solvent having an affinity for the water-immiscible ketone whereby to yield a second aqueous acid solution and a solvent mixture of the extraction solvent and organic solvent. Preferably, the solvent mixture will be separated to yield extraction solvent for recycling. Optionally, a concentrated aqueous acid may be separated from the second aqueous acid solution for recycling. In comparison to the use of a water-miscible ketone, such as methyl ethyl ketone, the water-immiscible ketone which is used in the invention has a higher affinity for the organic solvent thus leading to a more effective removal of ketone and, in turn, lower energy costs associated with downstream acid concentration. Since residual ketone can react with acid during this concentration step, a lower input of ketone into this later stage of the process not only reduces ketone loss, but also minimises the formation of any ketone-ketone aldol condensation products which may interfere with the process.

Suitable for use as the organic solvent are water-immiscible, e.g. water-insoluble, lipophilic solvents. The addition of an organic solvent gives rise to a second aqueous acid solution and a solvent mixture of the extraction solvent and the organic solvent. This solvent mixture may be separated to yield extraction solvent for recycling.

The lipophilic solvent is preferably a halocarbon (e.g. dich!oromethane, chloroform) or a hydrocarbon (e.g. an alkane, alkene, alkyne, or a low-boiling aromatic hydrocarbon such as for example benzene, toluene or xylene), or mixture thereof. The halocarbon or hydrocarbons used will conveniently have a carbon content of up to 12 atoms, e.g. 1 to 10, 1-8 or 1-6 atoms, especially 5 atoms. Especially preferably it is a material that is readily available in liquid or liquefied form, particularly a hydrocarbon or hydrocarbon mixture. Accordingly, the lipophilic solvent is desirably decane, cyclohexane or a cyclohexane mixture, hexane or a hexane mixture, pentane or a pentane mixture, butane or a butane mixture, propane, ethane or a liquefied hydrocarbon gas, e.g. liquefied petroleum gas (LPG) or liquefied natural gas. Liquefied gases may be flashed off from the resulting solvent mixture by depressurisation, however their subsequent recycling requires liquefaction and thus is energy demanding. They moreover require pressurised storage vessels and they require the separation column to be pressure resistant. As a result, the use of lipophilic solvents which are liquid at ambient conditions (e.g. 20°C and 1 atmosphere) is preferred. The use of pentane or pentane mixtures as the lipophilic solvent is preferred.

The boiling points of the ketone extraction solvent and the organic (lipophilic) solvent at 1 atmosphere are preferably separated by at least 20°C, more especially at least 30°C, e.g. at least 50°C so as to facilitate their separation. The extraction solvent will generally have the higher boiling point of the two solvents. For example, where diethyl ketone is used as the extraction solvent and pentane is used as the lipophilic solvent, their boiling points are separated by more than 60°C (boiling point of pentane: 30°C; boiling point of diethyl ketone: 102°C). In a further embodiment, the lipophilic solvent may have the higher boiling point, e.g. decane (boiling point 174°C ) can be used to extract diethyl ketone (boiling point: 102°C).

The organic (lipophilic) solvent will preferably be contacted with the first aqueous acidic solution at a temperature between 0 and 80°C, especially between 10 and 60°C, more particularly between 15 and 50°C, especially 25°C or less. The pressure used will be one sufficient to maintain the lipophilic solvent in liquid form at the contact temperature used and can readily be determined by those skilled in the art.

Contact between the organic (lipophilic) solvent and the water/acid/extraction solvent (first aqueous acidic solution) is preferably effected in a counter-flow separation column with the lipophilic solvent being fed in at the base, the

water/acid/extraction solvent being fed in at the top, the extraction solvent/lipophilic solvent stream being discharged from the top and the water/acid stream being discharged from the base. The separation column is preferably equipped with static or active mixers and/or deflection plates so as to ensure thorough mixing. Due to the efficiency with which the organic solvent is able to remove the ketone, the residual water / acid stream (second aqueous acidic solution) may be recycled to the hydrolysis stage without further purification. Typically, however, this will be further processed whereby to concentrate the acid prior to re-use. Acid

concentration may be achieved by methods known in the art, e.g. by distillation. Following condensation of the vapours distilled off during acid concentration, water and any residual water-immiscible ketone separate. Due to the low water content of the ketone-rich organic phase, this phase can typically be recycled without further purification.

The weight ratio of the in-flowing first aqueous acidic solution containing extraction solvent and the organic (lipophilic) solvent feeds is preferably in the range 7:1 to 1 :1 , especially 5:1 to 2:1 , particularly 4:1 to 3:1 . The feed: lipophilic solvent ratio is optimally about 3:1 , although this varies depending on other cost-related factors. The weight ratio of the discharged streams (extraction solvent/lipophilic solvent stream and water/acid stream) may be similar, e.g. also in the range 7:1 to 1 :1 , especially 5:1 to 2:1 , particularly 4:1 to 3:1 .

The out-flowing extraction solvent/lipophilic solvent stream is preferably separated on a continuous basis, e.g. by temperature increase (e.g. distillation) and/or pressure decrease. Particularly preferably the pressure used is one at which the lipophilic solvent will recondense if cooled using ambient water, e.g. at 4 to 25°C. The resultant extraction solvent stream (typically the bottom product) will generally be sufficiently pure for recycling to the separation column in which hydrolysate and extraction solvent are contacted. The resultant lipophilic solvent stream (the top product) will also generally be sufficiently pure for recycling.

Where the extraction solvent and lipophilic solvent are separated by distillation, the organic solvent (e.g. pentane) may form a heteroazeotrope with water, thus removing water from the extraction solvent during distillation. As higher

hydrocarbons have more water-rich azeotropes, an option for more efficient water- removal in this manner is to use a higher hydrocarbon, e.g. cyclohexane (8.5 wt% water in azeotrope, boiling point of azeotrope: 70 °C) compared to pentane (1.4 wt% water in azeotrope, boiling point of azeotrope: 34 °C).

The lipophilic solvent stream following separation of the extraction solvent can be conveniently stored in a vessel with water off take at the bottom (e.g. for the removal of water from the solvent distillation where water is taken out as an heteroazeotrope of water and lipophilic solvent as described above).

In an alternative embodiment the ketone extraction solvent may be recovered by contacting the first aqueous acidic solution with water. The use of a water- immiscible ketone enables the extraction of acid by water since the ketone does not enter into the resulting water / acid phase to any significant extent. The use of water to separate the ketone from the acid avoids the need for the use of any organic solvent (e.g. pentane) thereby lowering the energy cost associated with this part of the process. Although to some extent this is off-set by the requirement for a higher energy input in any subsequent acid concentration step (due to the higher energy needed for heating and evaporating the water compared to an organic solvent), this is more than off-set by the ability to do away with the need for equipment to carry out distillation of any organic solvent. The water will preferably be contacted with the first aqueous acidic solution at ambient or elevated temperature, e.g. a temperature between 10 and 70 °C, especially between 15 and 50 °C, more particularly between 20 and 30 °C. The pressure used will be one sufficient to maintain the water in liquid form at the contact temperature used.

Contact between the added water and the water/acid/extraction solvent (first aqueous acidic solution) may be carried out in a counter-flow column with the water being fed in at the base and the water/acid/extraction solvent being fed in at the top. The column is preferably equipped with static or active mixers and/or deflection plates so as to ensure thorough mixing. More preferably, a simple mixer-settler system, e.g. two in series in counter-current operation is used. Following mixing in the column, or as part of the settler system, the mixture is allowed to separate, e.g. in a settling tank. Phase separation yields a second aqueous acid solution and extraction solvent. The extraction solvent may be separated and will generally be sufficiently pure for recycling. The second aqueous acid solution may be recycled to the hydrolysis stage without further purification, however typically this will be further concentrated prior to re-use.

Due to the efficiency with which the water is able to effect separation of the acid and ketone, the resulting low concentration of ketone entering into the acid

concentration reduces the potential for acid-catalysed ketone-ketone condensation. The increased water activity also reduces the rate of acid-solvent reactions compared to when a lipophilic solvent is used for extracting the ketone-containing extraction solvent. Acid concentration may be achieved by methods known in the art, e.g. by distillation during which any residual ketone is evaporated off as a water: ketone heteroazeotrope. The organic phase of the condensate can be re-used without further purification. If desired, this may be combined with the organic phase from the water extraction of acid prior to recycling.

The weight ratio of the in-flowing first aqueous acidic solution containing extraction solvent and the water feeds is preferably in the range 49:1 to 6:1 , particularly 19:1 to 9:1 . The first aqueous acidic solution feed : water ratio is optimally about 10:1.

In a yet further embodiment, the water-immiscible ketone solvent may be separated from the acid (i.e. the first aqueous acid solution) by distillation. Distillation may be carried out by conventional methods known in the art. Typically, this will involve heating of the first aqueous acid solution. Whilst heating may be carried out at reduced pressure, for example by applying a vacuum, it is generally preferred that this is carried out at atmospheric pressure. The distillation step may be effected continuously or batch-wise, although continuous distillation is generally preferred. In one aspect, the distillation may be carried out in steps, optionally with the addition of a small amount of water prior to the last step in order to liberate acid-bound ketone.

During the distillation step, extraction solvent is evaporated to yield gaseous extraction solvent. This is subsequently condensed to yield a distillate which will typically be sufficiently pure that this can be recycled. The evaporation step may be performed at ambient or reduced pressure, e.g. at a pressure in the range of 1 to 0.01 bar, preferably 0.5 to 0.03 bar. Suitable temperatures for evaporation may readily be selected dependent on the pressure conditions, but will typically range from 60 to 200 °C, preferably 60 to 180 °C. It is particularly desirable that this step should be performed at about 85 °C. Preferred conditions are under vacuum (e.g. 50-10 mbar) and lower than 90 °C (to preserve the sugars). Higher temperatures may be used, but result in lower sugar yields, albeit with reduced capital cost and electricity cost (due to the requirement of less vacuum). The temperature and pressure combination however will be one at which the extraction solvent is gaseous.

The condensation step is preferably effected at a temperature in the range 10 to 90 °C, e.g. 10 to 60 °C, especially 20 to 40 °C. A particularly suitable temperature is about 30 °C. Suitable pressures can be readily determined. Reduced, ambient or elevated pressures, in the range of 0.5 to 2 bar are generally preferred. The temperature and pressure combination however should be one at which the extraction solvent is liquid. Desirably, the condensation step is performed at ambient pressure using un-cooled water. Preferably, the condensation step is effected at a temperature within 100 °C of that of the extraction step, especially within 65°C, and a pressure within 1 bar of that of the extraction step, especially within 0.5 bar. In one embodiment both the evaporation and condensation steps will be carried out at ambient pressure. Cooling to effect condensation is preferably effected using water from the local environment, e.g. from a river, a lake or the sea. The condensed extraction solvent or "distillate" produced may contain a proportion of water; however the water content will generally not be so high as to prevent carbohydrate (e.g. oligosaccharide) precipitation in the event the distillate is recycled for use in the extraction step. If desired, the recycled extraction solvent may be combined with fresh extraction solvent for re-use in further extraction steps.

Any water present in the distillate can be removed as a polar phase after

condensation of vapours. Furthermore the water present in the organic phase of the distillate, can be removed by evaporating a given amount of the solvents stream, after which water can be removed by azeotropic distillation, similar to a Dean-Stark distillation. In this way, by evaporating 10 % of a water saturated DEK solution, water in the remaining, un-evaporated solution may be reduced from 2 wt% to 0.7 wt%. Water can also be removed by other methods known in the art, e.g. by membranes or zeolites.

The acid used in the process of the invention may be any strong acid, but will generally be an inorganic acid such as phosphoric or sulphuric acid. The use of sulphuric acid is preferred (especially the use of sulphuric acid in the absence of other acids); the use of hydrochloric acid is generally not preferred. The use of a mixture of sulphuric and phosphoric acids, e.g. in a 1 :1 to 4:1 volume ratio, especially about 2:1 volume ratio, is especially preferred. Expressed as a percentage, mixtures comprising up to 50 wt% phosphoric acid, (i.e. up to 50 wt% of the total acid is phosphoric acid), preferably up to 25 wt% (e.g. 5 to 25 wt%), especially preferably up to 10 wt% phosphoric acid (e.g. in combination with sulphuric acid) are preferred.

The acid solution as contacted with the cellulosic starting material preferably corresponds to an acid:water weight ratio of 1 :1 to 4:1 , especially about 3:1 . Acid solutions of the acid strengths conventionally used in strong acid hydrolysis of cellulosic materials may be used. It should be noted that acid and water may be added separately or that the initial acid added may be diluted or concentrated to yield the desired acid:water balance.

A typical acid solution (hydrolyzing solution) used for hydrolysis is 70 % acid (and therefore 30% water). The weight ratio of acid to water in such a solution is thus 2.33 (70/30). This ratio will be slightly less in the extract after acid extraction, typically around 2.2. Increasing the proportion of water in the hydrolyzing solution has been found to increase recovery of the ketone solvent.

Thus, a preferred aspect of the present invention is the use of an aqueous acid solution with an acid/water weight ratio of less than 2.2, e.g. 0.50 to 1 .85, preferably 0.7 to 1.5, especially around 1 (i.e. an acid solution of 50 wt% acid, 50 wt% water) in the processes of the invention.

The acid hydrolysis may be performed in conventional fashion. Typically, hydrolysis, which is exothermic, will be performed on a continuous basis, under cooling, e.g. water cooling, to maintain the hydrolysis mixture at 20 to 55°C (preferably 25 °C or less). The acid solutiomcellulosic material ratio is typically 2:1 to 4:1 by weight and the hydrolysis duration will generally be 0.15 to 4 hours, especially about 1 hour. In this way the cellulose is broken down to produce oligosaccharides which can be precipitated out by the extraction solvent to yield a lignin / sugars slurry.

Contact between hydrolysate and ketone extraction solvent is preferably performed at a temperature of 25 °C or less, particularly 15 °C or less, especially preferably 10 °C or less.

Contact between hydrolysate and ketone extraction solvent is preferably effected in a counter-flow column such that extraction solvent is added from below and removed from above and hydrolysate is added from above and the lignin / sugar slurry is removed from below. Typically, this step of the process may be expected to recover from 90 to 98% of the acid from the hydrolysate. The in-flow of extraction solvent can be adjusted according to need, i.e. based on the amount of acid.

Generally, this will be fed to achieve an acid : ketone ratio in the range 1 :1 to 1 :10 especially 1 :2 to 1 :4 e.g. about 1 :4.

Alternatively, contact between hydrolysate and ketone extraction solvent may be effected in such a way that the extractant (i.e. the first aqueous acid solution) is removed by gravity, i.e. the first aqueous acid solution can be separated from the precipitate, e.g. via filtration or centrifugation. This is useful if the amount of water in the system is so high that a two phase system is formed, in which case the polar phase can be collected together with the ketone extract, instead of leaving a column together with the sugar and lignin. in such cases (i.e. where the amount of water is high) two liquid phases are formed a further aqueous acid solution containing the extraction solvent, water, acid and soluble sugars is produced (as the second phase), in addition to the sugar slurry and the first aqueous acid solution. Extraction solvent may be removed from this second phase, e.g. for recycling, by a variety of methods as discussed above.

Following extraction, the sugar slurry (residue containing sugars, which typically also contains lignin) will generally still contain a proportion of acid due to its association with any water which is present in or attached to the sugars. The slurry may be washed with additional extraction solvent if desired, it may be drained of liquids if desired, or it may be dried in order to aid removal of residual acid. In one embodiment of the invention, residual acid in the raffinate may be washed out using water (a residual acid wash). Contact between the sugar slurry and water will preferably be effected in a counter-current fashion; this tends to minimise the quantity of water which is required. The liquid resulting from the residual acid wash is typically sent to the second extraction, i.e. the extraction which separates the ketone solvent from the acid. This increases acid recycle.

A preferred aspect of the invention is the addition of water to the raffinate (residue containing sugars/sugar slurry). A two phase liquid stream may be extracted (e.g. by pressing the raffinate in a screw press or similar device, or decanting, filtering or centrifuging) containing an organic, water-saturated, top phase (which contains extraction solvent to be reused in the process) and a polar phase containing acid, soluble sugar and water. The top, ketone-containing, phase may be recycled to the extraction solvent reservoir for reuse in the first extraction step. The polar phase is sent to the dryer/desolventiser. By returning the polar phase to the dryer, instead of to the acid extraction by water or the extraction of the ketone solvent by a lipophilic second extractant, this aspect minimises sugar loss, and allows the removal of much of the ketone in the lignin/sugar mix without the need for evaporation

Following acid extraction by the extraction solvent comprising a water immiscible ketone, further acid extraction (i.e. extraction of acid from the first aqueous acid solution) may in some aspects of the invention be performed using water. The amount of water used is typically 0.02 to 0.20, e.g. 0.05 to 0.15 parts water to that of the first aqueous acid solution. In this way a phase separation when mixing the two extracts is achieved, i.e. extracting the acid into the polar phase.

A preferred aspect of the invention relates to the use of a de-solventising step in which residual ketone solvent is removed either prior to or simultaneously with the second hydrolysis step (conversion of oligosaccharides to simple sugars). This step involves the addition of water to the feed stream to the dryer (de-solventiser unit). The amount of water added to the slurry will generally be the minimum required to remove the ketone solvent as an azeotrope with water; the maximum will typically be the amount of water that is required to perform the second hydrolysis of the sugars present in the feed. The amount of water may be determined by those skilled in the art but will generally range from about 2 to 50 wt.%, preferably 5 to 30 wt.%, especially 10 to 20 wt.%. The water will preferably be added at a temperature of 80 °C. Due to the low solubility of water in the ketone, the recovered ketone can be reused directly in extraction solvent.

Temperatures in the de-solventising unit will be sufficient to drive off residual ketone and will generally be in the range from ambient to 120°C, e.g. 60 to 85 °C.

Following condensation of the resulting vapour, any water may readily be separated from the ketone solvent in a phase separator unit. Both phases can readily be recycled.

Where the next step of the process is carried out at another site, the sugars will typically be transported as an aqueous solution. By subjecting the distillation residue to an oligosaccharide cleavage reaction, an aqueous solution of fermentable sugars can be produced. Fermenting said fermentable sugars and distilling alcohol from the resulting fermented mixture allows the process to be extended to produce alcohol.

The oligosaccharide cleavage reaction may be effected enzymatically or alternatively, and preferably, by acid hydrolysis. The residue of acid retained in the unwashed slurry may be adequate for oligosaccharide cleavage to proceed via such a second acid hydrolysis step. Alternatively further acid may be added, for example to bring the acid content of the sugar solution up to about 0.1 to 5 wt%, especially, 0.2 to 4 wt%, preferably 0.5 to 2 wt%, particularly about 4 wt% or about 1 wt%. Addition of excess acid is undesirable as, following a second acid hydrolysis, the resulting hydrolysate must be adjusted to a pH suitable for the microorganisms responsible for fermentation (generally yeasts). This second hydrolysis may be effected under conventional conditions for weak acid hydrolysis of oligosaccharides, e.g. a temperature of 100 to 180 °C, particularly about 120 °C, a pressure of 1 to 10 bar, preferably 2 bar, and a duration of about 0.5 to 4 hours, particularly about 1 to 3 hours, preferably around 2 hours.

The addition of water prior to de-solventising allows for simultaneous de- solventising and second hydrolysis in the same unit. This reduces equipment cost and also total residence time of the raffinate typically has had its water-immiscible ketone content reduced by pressing or centrifugal decanting, either with or without water addition (see above) to reduce the ketone loading. Water may be added to the stream to help pumping and water is added to achieve the appropriate acid concentration (e.g. 4 wt%). The vessel is heated, and the vapour flows thorough a distillation column, packed or with plates, with or without rectification. The top temperature should be that of the boiling point of the ketone-water azeotrope (e.g. 83 °C for DEK), the vapours are condensed. When the top temperature rises to 100 °C (only water remains), the vapour outlet is closed, and the pressure rises up the desired temperature (2 bar, 120 °C). The temperature is held for the desired time (2 hours) then emptied. Some of the heat could optionally be recycled by heating another feed to second hydrolysis.

Before fermentation, the fermentable sugars in aqueous solution are preferably filtered to recover any lignin. This is preferably washed to recover any entrained sugars for fermentation and compressed for use as a fuel, e.g. to provide energy for one or more of the steps in the overall alcohol production process.

The microorganism used in the fermentation step may be any microorganism capable of converting fermentable sugars to alcohol, e.g. brewer's yeast. Preferably however a yeast or yeast mixture is used which can transform the pentoses yielded by hemicellulose hydrolysis as well as the hexoses yielded by cellulose hydrolysis. Such yeasts are available commercially. The use of microorganisms that can transform pentoses to alcohol (e.g. Pichia stipitis, particularly P. stipitis CBS6054), particularly in combination with ones which can transform hexoses to alcohol, is especially preferred. Where fermentation is performed using microorganisms other than brewer's yeast (e.g. C. beijerinckii BA101 ), alcohols other than ethanol, in particular butanol, can be produced and these too can be used as biofuels. The invention covers the production of such other alcohols.

Distillation of alcohol from the fermented sugars may be effected in conventional fashion. The sugars produced using the invention can be fermented or respired by Baker's yeast or other microorganisms to yield many different biologically produced compounds such as glycerol, acetone, organic acids (e.g. butyric acid, lactic acid, acetic acid), hydrogen, methane, biopolymers, single cell protein (SCP), antibiotics and other pharmaceuticals. Specific proteins, enzymes or other compounds could also be extracted from cells grown on the sugars. The sugars moreover may be transformed into desired end products by chemical and physical rather than biological means, e.g. reflux boiling of xylose will yield furfural. The invention thus also covers the production of all such other produced compounds besides alcohols, Thus, processing of the sugar/carbohydrate compositions or aqueous solutions of sugars/carbohydrates produced by the processes described herein to form the above products thus forms a further aspect of the invention. The compositions produced by the processes of the invention also form a further aspect.

Viewed from another aspect, the invention provides apparatus for use in the processes herein described, said apparatus comprising:

a first hydrolysis reactor;

an acid reservoir arranged to supply acid to said first hydrolysis reactor; a first separator arranged to receive hydrolysate from said first hydrolysis reactor and to discharge carbohydrate (e.g. sugar) slurry;

an extraction solvent reservoir arranged to supply an extraction solvent which comprises a water-immiscible ketone solvent to said first separator;

a second separator arranged to receive an extraction solvent/acid/water mixture from said first separator and to discharge extraction solvent and aqueous acid;

optionally an acid re-concentration unit arranged to receive aqueous acid from said second separator; and

optionally, recycling conduits arranged to return extraction solvent to said first separator or an extraction solvent reservoir and/or to return concentrated aqueous acid to said reactor or an acid reservoir.

It is preferred that the apparatus also comprises a recycling conduit to return concentrated aqueous acid to said first hydrolysis reactor or an acid reservoir. In a preferred aspect, the apparatus further comprises an organic solvent reservoir arranged to supply an organic solvent (e.g. a lipophilic solvent as herein described) to said second separator; and optionally a rectifier arranged to receive an extraction solvent / organic solvent mixture from said second separator and to discharge an extraction solvent and, separately, an organic solvent.

In another preferred aspect, the apparatus further comprises a water reservoir arranged to supply water to said second separator, and optionally a phase separation system to receive a water/ketone solvent mixture from said optional acid re-concentration unit and to discharge water and separately an organic solvent.

The apparatus preferably also comprises components for feeding cellulosic material to the reactor. Conveniently, it also comprises components for the downstream handling of the carbohydrate slurry, e.g. further hydrolysis reactors, reservoirs for a base for neutralizing the residual acid, fermentors and distillation units. To allow for continuous operation of the process when individual steps are performed batch- wise, individual units within the apparatus may be duplicated, i.e. with such units being in parallel, so that one may be in operation while the other is being

loaded/unloaded. This is particularly the case for the second acid hydrolysis, the fermentation, the distillation, and the lignin separation steps.

Preferably, the desolventising unit is capable of acting as a second hydrolysis reactor and thus comprises heating and pressurising means and is arranged to discharge a mixture containing fermentable sugars.

Embodiments of the invention will now be described further with reference to accompanying Figures 1 a, 1 b, 2a and 2b which are schematic diagrams of apparatus according to the invention.

Figure 1 a shows an aspect of the invention in which the water-immiscible ketone solvent is separated from the acid via extraction with an organic solvent.

Cellulosic starting material ("feed") is mixed with a strong acid and acid hydrolysis ("1 st hydrolysis") is performed in conventional fashion in a first hydrolysis reactor. The first hydrolysis causes the cellulose of the starting material to be broken down to produce oligosaccharides. The hydrolysate is transferred to a first separator in order to undergo an extraction with an extraction solvent comprising a water immiscible ketone in order to eventually recover acid from the hydrolysate.

Contact between hydrolysate and ketone extraction solvent is then effected ("1 st acid extraction"). The carbohydrates (e.g. oligosaccharides) produced by the first hydrolysis are precipitated out by the extraction solvent to yield a lignin /

carbohydrate slurry ("raffinate" in Figure 1 a) and an aqueous acid solution containing the extraction solvent (first aqueous acid solution, "extract" in Figure 1 a).

Following the first acid extraction, the carbohydrate slurry (residue containing sugars) undergoes desolventisation to remove residual ketone solvent and produce a solids/sugars stream and a mixed stream for further separation. The

desolventisation step involves the addition of water to the feed stream to the dryer (de-solventiser unit). The vapour resulting from the drying step is condensed and water is separated from the ketone solvent in a phase separator unit ("solvent-water separation"). Both phases from the condensate are recycled, i.e. the water- immiscible ketone stream is recycled to the first acid extraction step and the water is recycled to the desolventiser.

The solids/sugars stream, i.e. the residue produced by desolventising undergoes a second hydrolysis to effect the conversion of oligosaccharides to simple sugars. An aqueous solution of fermentable sugars is thus produced and is subjected to a product finishing step.

The product can be solid sugar or a solution. After the second hydrolysis, lignin is typically removed by filtration and water is used to remove residual acid and sugar from the filter cake. Acid can then be removed from the sugar solution by neutralization and gypsum removed by filtration. Sugar may be removed from the filter cake by washing. Preferably, due to high sugar concentration in the second hydrolysis and the use of countercurrent washing, water should go from the product finishing to the water buffer. Gypsum cake washing is performed with pure water from water make-up, and water from the first stage gypsum washing is used for last stage lignin washing.

The sugar composition which results can then be used to form sugar/lignin by- products, e.g. glycerol, acetone, organic acids (e.g. butyric acid, lactic acid, acetic acid), hydrogen, methane, biopolymers, single cell protein (SCP), antibiotics and other pharmaceuticals.

The other product of the first acid extraction, i.e. the first aqueous acid solution is subjected to a second extraction in a second separator in order to remove ketone extraction solvent for recycling. The ketone is separated from the acid using pentane to yield a second aqueous acid solution and a solvent mixture of the extraction solvent and organic solvent. The solvent mixture is separated in a rectifier unit via distillation to yield ketone extraction solvent for recycling to the first extraction and pentane for recycling to the second extraction. The second aqueous acid solution, i.e. the residual water / acid stream produced by the second extraction is further processed in an acid reconcentration unit to concentrate the acid ("acid reconcentration") before being recycled for use in the initial hydrolysis step. The water removed in this step passes via the solvent-water separation step before eventual reuse.

Figure 2a shows an alternative embodiment in which the ketone extraction solvent is recovered by contacting the first aqueous acidic solution with water, i.e. the second acid extraction described in Figure 1 a takes place with addition of water, rather than pentane. Figure 2a therefore shows the extraction of acid by water in the second acid extraction step. The water is supplied via a recycling conduit from the solvent-water separator. The water immiscible ketone solvent forms a separate phase to the acid/water phase and thus can be removed for recycling to the first acid extraction. The resulting acid/water stream ("second aqueous acid solution") proceeds to an acid re-concentration step as outlined in Figure 1 a.

Figures 1 b and 2b show an optional further step in relation to the processes of Figures 1 a and 2a respectively of a residual acid wash. Following the first extraction, the carbohydrate slurry is contacted with water in order to remove residual acid. The residual acid/water stream which results is directed to the second extraction for recovery of acid. The water necessary for this step is sourced from the solvent-water separator.

The invention will now be further described with reference to the following non- limiting examples: Example 1 : Comparison between methyl ethyl ketone, methyl isobutyl ketone and diethyl ketone (formation of aldol-condensation product)

The following experiments were performed to compare the extent of formation of condensation products when using the solvents methyl ethyl ketone, methyl isobutyl ketone and diethyl ketone.

Experimental set-up: 1.89 g water, 4.50 g methyl ethyl ketone and 44.53 g acid mixture (h^SC^HsPC^water 0.5:0.25:0.25 parts wt. basis) was mixed in a 100 mL screw cap bottle. 1 .88 g water, 4.51 g methyl isobutyl ketone and 45.09 g of the same acid mixture was mixed in a 100 mL screw cap bottle. 1.84 g water, 4.47 g diethyl ketone and 46.10 g of the same acid mixture was mixed in a 100 mL screw cap bottle.

The three bottles were placed in a heating cabinet at 75°C for 24 hours. Then the mixture was extracted 5 times with equal amounts of dichioromethane (50 g in total) in order to extract ketone reaction products from the acidic mixture. The extract was then extracted two times with equal amounts of water (2 g in total) in order to remove residual acid. Acid traces were neutralised with Ca(OH) ₂ and then the samples were dried using CaCI ₂ . The dichioromethane extract was then filtered and analyzed on a GC/MS. The concentration of the different condensation products was quantified. The conversion rate was 0.7, 1 .0, and 0.2 mg condensation products/ g solvent / hour for methyl ethyl ketone, methyl isobutyl ketone and diethyl ketone, respectively.

Example 2: Comparison between water-miscible ketone and water-immiscible ketone

The following experiments were carried out to show that the opportunity for acid catalysed ketone condensation is reduced when using a water immiscible ketone instead of a water miscible ketone as the amount of ketone entering into the acid re- concentration step is lower at similar experimental set ups. All examined ketones undergo aldol condensation catalysed by sulfuric acid. The conversion rate is positively correlated with temperature and acid concentration. In the overall process, it is the step of re-concentration of acid which is the one where the conditions for ketone condensation are most favorable. There is thus an incentive for reducing the amount of ketone entering into the acid concentration process.

2a - water extraction

Experiments were set up using mixtures typically found in an acid-catalysed hydrolysis process. Acids, water and ketones were mixed. Additional water was added for use in phase separation where the acid is extracted into the polar phase. Table 1 below shows the experimental set-up for two water immiscible ketones, diethyl ketone (DEK) and methyl-propyl ketone (MPK) and one water miscible ketone, methyl ethyl ketone (MEK). All experiments were set up with similar acid, ketone and water contents, except for the MEK experiment where in order to achieve phase separation a larger amount of water was needed.

The mixtures separate into two phases, and the composition of the different phases is shown below in Table 1 .

Table 1

DEK MPK MEK

H ₂ S0 ₄ (g) 4.34 4.40 4.47

H ₃ P0 ₄ (g) 2.17 2.50 2.29

Experimental

Water (g) 7.34 7.02 15.54

set-up

Ketone (g) 30.25 30.01 30.83

Sum (g) 44.1 1 43.93 53.12

H ₂ S0 ₄ (g) 4.23 3.55 3.83

H ₃ P0 ₄ (g) 2.03 1 .68 1.89

polar phase Water (g) 6.95 5.46 12.97

Ketone (g) 0.70 1 .04 17.52

Sum (g) 13.91 11 .73 36.21 organic H ₂ S0 ₄ (g) 0.1 1 0.85 0.64 phase H3PO4 (g) 0.14 0.82 0.40

Water (g) 0.39 1.56 2.56

Ketone (g) 29.20 28.83 12.76

Sum (g) 29.84 32.05 16.36

The results show that the amount of water needed to provoke a phase separation is much higher when MEK is used compared to the water immiscible ketones (note that the water added in the water immiscible ketone experiments exceeds that required for phase separation; the amount used is that needed for extraction of approximately 90% of the acid from the system into the polar phase). The results also show that the amount of ketone entering into the polar phase is much higher for MEK than for the other experiments.

2b - pentane extraction

Experiments were set up using mixtures typically found in an acid-catalysed hydrolysis process. Acids, water and ketones were mixed. Pentane was added for use in phase separation where the ketone is extracted into the organic phase.

Table 2 below shows the experimental set-up for six experiments with different ketones, two water miscible, acetone and MEK, and three water immiscible, methyl- isopopyl ketone, methyl-propyl ketone and diethyl ketone.

The mixtures separate into two phases, and the composition of the different phases is shown in the following table (Table 2):

Table 2

Acetone MEK MIPK MPK DEK

H ₂ S0 ₄ (g) 4.35 4.48 4.09 4.87 4.50 H3PO ₄ (g) 2.18 2.24 2.05 2.76 2.25 Water (g) 2.77 2.85 2.61 2.55 2.87

Experimental

Ketone (g) 29.84 29.00 27.00 30.04 31 .42 Set-up

Pentane

(g) 10.00 10.86 9.57 12.09 12.34

Sum (g) 49.14 49.43 45.32 52.31 53.38 H ₂ S0 ₄ (g) 4.27 4.46 3.85 4.76 4.42

H ₃ P0 ₄ (g) 2.15 2.23 1.92 2.70 2.21

Water (g) 2.68 2.80 2.42 2.44 2.79

Ketone (g) 13.74 1 1 .06 8.63 10.00 7.23

Pentane

(g) 0.00 0.00 0.00 0.00 0.00

Sum (g) 22.84 20.55 16.82 19.90 16.65

H ₂ S0 ₄ (g) 0.08 0.08 0.08 0.11 0.08

H3PO4 (g) 0.03 0.04 0.05 0.06 0.04

Water (g) 0.09 0.09 0.08 0.11 0.08 organic

Ketone (g) 14.27 17.27 16.72 19.51 24.04 phase

Pentane

(g) 10.00 10.86 9.57 12.09 12.34

Sum (g) 24.46 28.35 26.50 31 .88 36.58

The results show that when using a water immiscible ketone the amount of ketone entering into the water phase, and thus into the acid re-concentration is lower than for the water miscible ketones such as acetone and MEK.

In addition to less formation of condensation products, the reduction in ketones entering into acid re-concentration also means there is less ketone to be evaporated off, giving a lower energy demand for the process.

Example 3: Comparison between water-miscible ketone and water-immiscible ketone (amount of sugar passing into acid concentration step)

After initial hydrolysis /de-crystallization of the feedstock, the acid is extracted by solvent. During this extraction some small molecular weight sugars are also soluble and are extracted together with the acid. The experiments described below show that less sugar is dissolved into this solvent /acid stream when using a water immiscible ketone as an extractant rather than a water miscible ketone (MEK). As sugar that enters the acid/solvent stream ends up in the acid re-concentration step, some of this sugar will be converted to other products such as HMF and will result in a lower yield and precipitation problems. Experimental set-up:

50.02 g of ground (<2 mm) spruce chips having a water content of approximately 10 wt.% was added to 230.55 g of an acid mixture containing 50 wt.% H ₂ S0 ₄ and 25 wt.% H ₃ P0 ₄ in water. The wood chips / acid mixture was stirred for 1 hour at 50°C.

During this time the wood de-crystallised and formed a slurry together with the acid.

This hydrolysate was divided into three parts. In order to extract the acid from the hydrolysate, solvent was added. Either MEK with 5 wt.% water or water saturated

DEK was used as an extractant. During this process, solubilised compounds such as sugars will precipitate and form a solid together with de-crystallised raw material.

The hydrolysate was extracted four times with 1 part solvent to 1 part of hydrolysate per wash. The acid / solvent solution was removed by filtration between each

extraction. The extraction was performed at room temperature.

The filtrates from the four extractions were combined and the solvent was removed from the filtrate by evaporation in a rotavapor. A small amount of water was added to help facilitate the removal of solvent. The solution was concentrated to an acid concentration of approximately 70 wt.%. To the concentrated acid, water was

added to give a final acid concentration of 20 wt.%. The resulting solution was

heated for 3 hours at 80°C during which time samples were taken every hour. This treatment hydrolyses oligomeric sugars either in native form from the feedstock or oligomers produced from monomeric sugar during the acid concentration. After the hydrolysis the solution was neutralised by the addition of Ca(OH) ₂ and subsequently filtered. The neutral solution was analysed for sugar composition by HPLC. The results are given in Table 3.

Table 3

MEK

Hydrolysis Unk. Sum wt.% sugar ii (h) Glucose Xylose Galactose Arabinose Mannose Olig. solvent/acid extrac

0.000 0.235 0.032 0.000 0.030 0.102 0.233 0.632

1 .000 0.315 0.034 0.000 0.039 0.1 19 0.164 0.670

2.000 0.342 0.056 0.000 0.044 0.133 0.152 0.728

3.000 0.373 0.060 0.000 0.040 0.120 0.131 0.723

DEK Unk.

Glucose Xylose Galactose Arabinose Mannose Olig.

0.000 0.055 0.012 0.000 0.007 0.038 0.030 0.142

1 .000 0.056 0.010 0.000 0.000 0.044 0.045 0.155

2.000 0.064 0.01 1 0.000 0.009 0.071 0.035 0.191

3.000 0.064 0.008 0.000 0.005 0.077 0.021 0.175

The results show clearly that more sugars are soluble in the solvent / acid extract when MEK is used as the extractant than DEK. The amount of water in the different solvents may be expected to play an important role in solubility of sugar in the solvent. In this experiment, water-saturated WIK and only 5wt.% water in MEK (11 % saturated) is used since these would typically be used in practice. Had water- saturated MEK been used, the difference in sugar solubility would be expected to be far greater.

Table 3 shows how oligomeric sugar is hydrolysed during the experiment yielding monomeric sugars.

Example 4: Solvent recovery from dryer

The following experiments were carried out to show how water addition to the dryer / de-solventiser helps the recovery of ketone from the sugar lignin stream. These show that the addition of water in the dryer increases solvent extraction and that the use of a water immiscible ketone, when compared to MEK, provides a stream that can be reused directly.

Experimental set-up:

To 1 part spruce wood chips (<2mm) having a water content of 10 wt.% moisture was added 4 parts acid solution (47 wt.% H ₂ S0 ₄ , 23 wt.% H ₃ P0 ₄ , 30 wt.% water). The mixture was stirred for 1 hour at 40°C. The resulting slurry (hydrolysate) was divided into three equal parts. The parts were extracted 4 times with 1 part ketone in order to extract acid from the hydrolysate. The extractions were done by centhfugation and syphoning off the top acid / ketone layer. MEK or DEK was used as single solvent for the three parts. After the extraction the three parts with extracted sugar / lignin solids were further split in two giving a total of six samples. Two of these were extracted using MEK and two with DEK. To one sub-sample from each of the groups was added approximately 0.2 parts water (see Table 4 below). Solvents were evaporated from the samples in a rotavapor at 60°C at 40 mbar pressure. The condensate vapors were collected and analysed for ketone content by GC analysis. To the dry sugar lignin residue was added 10 ml water and 10 ml of pentane in order to extract residual ketone from the solid matrix. The pentane extract was analysed for ketone

Table 4

MEK with DEK wit,

MEK

water water

Sugar/lignin raffinate (g) 10.92 10.13 13.38 12.32

Added water (g) 0 2.14 0 2.69

Condensate organic phase (g) 2.99 3.44 4.23 3.50

Condensate polar phase (g) 0 0 0 0.72

Ketone in organic phase (wt ) 97.14 91.42 97.74 98.98 Ketone in polar phase (wt%) 3.43

Ketone in sugar/lignin solids (wt%) 1.80 0.18 2.27 0.77

As can been seen from the results in the table, the amount of residual ketone is higher in the samples extracted with DEK then the MEK extracted samples. This is the case both for the sample without added water and for the samples with water addition. When water is added a large increase in ketone removal is observed. The residual amount is lowest in the MEK extracts samples.

From the results a water immiscible ketone might seem a poor choice for efficient removal of ketone from the dryer by water addition. The problem with MEK is, however, too high water content in the condensate (9% water, contrasting 1 % for the water immiscible ketones). This high water content will cause problems with water accumulation in the process, and high solubility of sugar into the MEK / acid stream during acid extraction, and thus give a negative impact on yield. The water will thus need to be removed, and it is difficult to remove water from MEK due to relatively low boiling point differences, and the relatively low amount of water in the MEK-water azeotrope makes azeotropic distillation inefficient as a tool for water removal. Water addition is thus not a viable option when using MEK for acid extraction, only when using a water miscible ketone is there a potential for water addition giving a higher solvent recovery in the water immiscible ketone + water addition set-up than for MEK without water addition.

Example 5 - Diochloromethane (PCM) as lipophilic solvent

All examined ketones undergo aldol condensation catalyzed by sulfuric acid. The conversion rate is positively correlated with temperature and acid concentration. The re-concentration of acid is the place in the process where conditions for ketone condensation are most favorable. There is thus an incentive for reducing the amount of ketone entering into the acid concentration process.

Experiments were set up using mixtures typical found in the process. Acids, water and ketones were mixed and Dichloromethane was added for phase separation where the ketone is extracted into the organic phase. The table below shows experimental set up for two experiments with different ketones, MEK and DEK.

The mixtures separates into two phases, and the composition of the different phases is also shown.

Table 5 : Experimental set-up and the mass composition of the two occurring phases is given, r : ratio of mass halocarbon to mass feed (acids, water and ketone), used to establish the two phases as given in the results.

MEK/DCM DEK/DCM

Feed H ₂ S0 ₄ (g) 4.31 4.25

H ₃ P0 ₄ (g) 2.25 2.22

Water (g) 2.76 2.72

Ketone (g) 30.31 30.31

Halocarbon (g) 24.17 10.81 r 0.61 0.27

r needed for phase >0.40 <0.27 sep. <0.54

Organic H ₂ S0 ₄ (g) 1.06 0.90

phase H ₃ P0 ₄ (g) 0.67 0.56

(top) Water (g) 0.63 0.59

Ketone (g) 22.99 22.87

Halocarbon (g) 22.75 9.84

Polar H ₂ S0 ₄ (g) 3.25 3.35

phase H ₃ P0 ₄ (g) 1 .57 1.66

(bottom) Water (g) 2.13 2.13

Ketone (g) 7.32 7.44

Halocarbon (g) 0.95 0.39

We see from the results above that the MEK/pentane system is superior to the MEK/DCM system. Acid concentration in the polar phase in the two cases is similar, but the amount of pentane:feed ratio was only 0.3 compared to an

DCM:feed of 0.61 . We see the same when we compare the DEK/DCM system with DEK/pentane system. Pentane also has a slightly lower boiling point and heat of vaporization.

Example 6 -Trichloromethane (TCM, chloroform) as lipophilic solvent

Experiments were set up using mixtures typical found in the process. Acids, water and ketones were mixed and trichloromethane was added for phase separation where the ketone is extracted into the organic phase. The table below shows experimental set up for two experiments with different ketones, MEK and DEK. The mixtures separates into two phases, and the composition of the different phases is also shown.

MEK/TCM DEK/TCM

Feed H ₂ S0 ₄ (g) 4.34 4.22

H ₃ P0 ₄ (g) 2.26 2.20

Water (g) 2.77 2.70

Ketone (g) 30.84 30.84

Halocarbon (g) 13.85 13.73 r 0.34 0.34 r needed for phase >0.31 <0.34 >0.31

sep.

Organic H ₂ S0 ₄ (wt%) 2.66 1 .13

phase H ₃ P0 ₄ (wt%) 1 .52 0.73

(top) Other (wt%) 95.82 98.14

Polar H ₂ S0 ₄ (wt%) 18.20 25.48

phase H ₃ P0 ₄ (wt%) 8.96 12.48

(bottom) Other (wt%) 72.84 62.04

We see from the results above that although TCM gives a better phase separation results then DCM (more acid in the polar phase) it is still inferior to the use of pentane as a lipophilic solvent. TCM also has a relatively high boiling point.

This experiment shows that we can reduce the amount of acid need for

decrystallization from 3.5 parts acid (as 96 %) : 1 part feed, to 1 .75 parts acid (as 96%):1 part feed, and still have a good yield. In practice this helps reduce the amount of solvent and thus water or pentane needed for acid extraction and solvent recovery. This reduces the amount of energy needed in the process.

313 g spruce wood particles <2 mm, with a moisture content of 8.8 wt%, was mixed with 724 g 75 wt% H ₂ S0 ₄ in water. The mixture was mixed in a stirred reactor with a water jacket, for 1 hour at 50 °C. After this decrystallization, acid was extracted from the slurry by adding 3556 g of extraction solvent in four equal extraction steps. Oligomeric sugars that were dissolved in the acid, precipitate in this solvent. The extraction solvent used was a solvent recycled from similar experiments. The solvent consisted of 99 wt% DEK with traces of sulfuric acid and water (< 1 %). The extraction was performed using a glass sinter filtration set up. The four filtrates containing solvent and extracted acid were pooled.

The extracted filter cake containing lignin and precipitated sugars was added to 192g of recycled water solution containing 98 wt% water and 2 % DEK. After the water addition the filter cake slurry was heated to 70 °C at 60 mbar pressure in order to remove residual solvent as an azeotrope with the added water. 183 g of vapor was removed. After condensation they formed two phases. One upper organic phase of 125 g consisting of water saturated DEK (2 wt% water), and a lower polar phase of 58 g consisting of DEK saturated water (5 wt% DEK). Both the water and organic solvent phase can be reused in subsequent experiments without any further purification.

A subsample was taken from the de-solventized filter cake was to added water in order to bring the sulfuric acid content in the mixture down to 4 wt%. The slurry was then heated to 120 °C for two hours, hydrolyzing the oligomeric sugars into monomeric sugars.

After hydrolysis the lignin was removed by filtration, and the filter cake was washed in order to remove the residual acid and sugar. The lignin was dried and the lignin yield was calculated to 26.35 g/100g dry feed.

The acidic sugar solution was pH adjusted to 4.5 by the addition of Ca(OH) ₂ . The resulting gypsum was removed by filtration. Sugar content was determined in the filtrate and the sugar yield was calculated to 45.23 g /100 g dry feed.

The extract containing DEK and extracted sulfuric acid (3552 g) was added to 0.8 parts water (285 g). This water addition resulted in a two phase system being formed. The upper organic phase (3104g) contained 1 % water and 1 % acid in DEK. This solution can be directly reused for acid extraction in a subsequent experiment. The polar phase contained 40 % sulfuric acid and 5% DEK in water. The polar phase was heated to 95 °C at 16 mbar in order to concentrate the acid solution to 75 wt% and for reuse in a subsequent experiment. 254 g vapor was removed, and after condensation a two phase system was formed. 234 g of DEK saturated water solution and 24 g of water saturated DEK solution. Both the water and organic solvent phase can be reused in subsequent experiments without any further purification.

Example 8 - Extraction of acid using DEK and isopropanol mixture

1 part (dry basis) spruce wood particles <2 mm, with a moisture content of 8.8 wt%, was mixed with 1 .75 parts (100% basis) 75 wt% H ₂ S0 ₄ in water. The mixture was stirred for 1 hour at 50 °C, decrystallizing the wood matrix forming a pumpable

hydrolysate slurry.

A subsample of 50.74 g of the hydrolysate was extracted using 5 equal volumes of DEK with a total mass of 262.83 g DEK, in a filtration set-up. After the extraction of acid by DEK, acid was further extracted from the filter cake by 39.9 g of water in two equal volumes. Residual acid was measured in the filter cake after each extraction.

A subsample of 47.87 g of the hydrolysate was extracted using 5 equal volumes of solvent with a total mass of 262.83 g DEK, in a filtration set-up. The solvent was 20 wt% isopropanol in DEK. . After the extraction of acid by DEK/isopropanol, acid was further extracted from the filter cake by 35.45 g of water in two equal volumes

Residual acid was measured in the filter cake after each extraction.

As seen from the results presented in Figure 3, the addition of 2-propanol greatly increases the acid extraction efficiency. The results also show that a second

extraction using water can increase total acid extraction.

Example 9- exhaustive extraction of DEK from an acid-DEK stream using pentane.

DEK.103.82 g, water, 10.53 g, H ₂ S0 ₄ , 15.82 g, and H ₃ P0 ₄ , 8.23 g were mixed. This feed solution (138.42 g) was extracted by 0.3 parts (by weight) pentane, the

resulting polar phase was extracted again by 0.3 parts pentane. This cross current extraction was performed 8 times. All resulting phases were analyzed and the

results are shown in the following table. The results show that the almost complete extraction of DEK from acid water solution is feasible using pentane as an

extractant.

Organic phase Polar phase

Extraction Feed (g) pentane (g) pentane:feed Acid (g) Water (g) DEK (g) Pentane (g) Acid (g) Water (g) DEK (g) Pentar

1 138..42 41..50 0..30 0..34 0.25 81.96 36.92 23.87 10.28 25.22 O.C

2 58.59 17.53 0.43 0.01 0.01 11.41 15.55 23.36 10.27 14.94 O.C

3 47.8 14.59 0.53 0.00 0.01 4.72 13.92 22.73 10.26 10.17 O.C

4 42.55 12.86 0.62 0.00 0.00 2.78 12.42 22.23 10.26 7.14 O.C

5 39.11 11.83 0.71 0.00 0.00 2.15 11.01 21.67 10.26 5.00 O.C

6 36.49 11.04 0.79 0.00 0.00 1.94 10.01 21.09 10.25 3.42 O.C

7 34.34 10.33 0.86 0.00 0.00 1.28 9.72 20.62 10.25 2.08 O.C

8 32.45 9.74 0.93 0.00 0.00 0.81 9.34 20.12 10.25 0.97 O.C