Field of the invention

The present invention relates to processes for producing sodium lactate, lactic acid or derivatives of lactic acid such as alkyl lactate, lactide and polylactic acid. Background of the invention

Lactic acid (2-hydroxypropanoic acid) and its cyclic dimer lactide (3,6-dimethyl-l,4- dioxan-2,5-dione) are important building blocks for the chemical and pharmaceutical industries. One example of their use is in the manufacture of polylactic acid, the

biodegradability of which makes it an attractive candidate to replace more conventional polymers. A number of processes are known for producing lactic acid, including chemical synthesis and fermentation methods. According to Boudrant et al, Process Biochem 40 (2005) p. 1642, "In 1987, the world production of lactic acid averaged approximately equal proportions being produced by chemical synthesis and fermentation processes". Such chemical syntheses typically employed the hydrocyanation of acetaldehyde. However, chemical processes of this type have long been regarded as inefficient on an industrial scale, and today virtually all large scale production of the lactic acid available commercially is manufactured by fermentation processes, see for example Strategic Analysis of the

Worldwide Market for Biorenewable Chemicals M2F2-39, Frost and Sullivan, 2009. In a typical fermentation process, glucose is fermented by microorganisms to produce either D- or L- lactic acid. Companies such as Cargill and Corbion operate large-scale fermentation processes for the production of optically active lactic acid, and the patent literature is replete with improvements in such processes. Fermentation processes tend to be demanding in respect of the saccharide feedstocks that can be tolerated, often requiring low levels of impurities and/or chemically homogeneous feedstocks, due to the sensitivity of the microorganism species typically employed. However, the effectiveness of fermentation of hemicellulosic feedstocks is limited by the fact that, unlike cellulosic feedstocks, they contain a mixture of pentose and hexose sugars which is typically harder for microorganisms to utilise. Additionally, hemicellulosic feedstocks tend to contain acids, aldehydes, furan derivatives and lignin-derived products which can act to inhibit the effectiveness of fermentation-utilising processes, due to the sensitivity of the species of microorganisms typically employed to those compounds. As a result, hemicelluloses currently represent the largest polysaccharide fraction wasted in most cellulosic ethanol pilot and demonstration plants around the world (Girio et al, Bioresource Technology, 2010, 101 p4775-4800).

There remains a need for improved processes for the production of lactic acid and related products. The present inventors have now identified certain saccharide feedstocks, in particular hemicellulosic streams obtained from processes for producing dissolving pulp, that when subjected to chemical processing conditions involving the use of sodium hydroxide, provide sodium lactate, lactic acid and derivatives of lactic acid in unexpectedly good yield.

Processes for producing metal lactate from saccharides are known, for example WO2012/052703 discloses a process for producing a complex of lactic acid and either ammonia or an amine, comprising reaction of one or more saccharides with barium hydroxide to produce a first reaction mixture comprising barium lactate, and contacting at least part of the first reaction mixture with ammonia or an amine and with carbon dioxide, or with the carbonate and/or bicarbonate salt of ammonia or an amine, to produce a second reaction mixture comprising the complex and barium carbonate. WO2012/052703 recommends the use of cellulose or starch as feedstocks. In particular, it refers to the use of invert sugar, or of glucose obtained from enzymatic hydrolysis of starch contained in biomass feedstocks such as maize, rice or potatoes. There is no mention of the possible use of hemicellulose.

Summary of the invention The present invention provides a process for producing sodium lactate, lactic acid, or a derivative of lactic acid selected from the group consisting of an alkyl lactate, oligomeric lactic acid, lactide, an alkyl lactyllactate, polylactic acid, and a complex of lactic acid and either ammonia or an amine, the process comprising:

(a) providing an aqueous hemicellulosic stream, the hemicellulosic stream having been obtained from a process for producing dissolving pulp, and the hemicellulosic stream containing hemicellulose-derived monosaccharide;

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid. Detailed description of the invention

The three principal components of lignocellulosic biomass are cellulose, lignin and hemicellulose, and they are present in almost all plant cell walls. The cellulosic material obtained from such biomass has a number of important industrial uses, notably in the production of paper from wood pulp. Accordingly, a variety of processes have been developed for treating biomass to separate cellulosic material from other components of lignocellulosic biomass, including the well-known Kraft and sulfite processes. In recent times, demand for wood pulp containing higher cellulose content has been increasing, and processes for producing such forms of wood pulp (known as "dissolving pulp" or "dissolving cellulose") have been developed. Dissolving pulp finds use in the production of products such as rayon, viscose and cellophane. It has now been found that hemicellulosic streams which have been separated from cellulosic solids during the production of dissolving pulp are particularly good feedstocks for the production of sodium lactate, lactic acid and other lactate-derived products. Typically in a process for producing dissolving pulp, an additional "pre-hydrolysis" stage is carried out in which lignocellulosic biomass is treated to remove hemicellulosic material and lignin/lignin-derived products, prior to subjecting the remainder of the cellulosic solids to further pulping conditions, such as Kraft conditions (treatment with an aqueous solution of sodium hydroxide and sodium sulphide at elevated temperature) or sulfite conditions (treatment with aqueous metal sulfite and/or bisulfite at elevated temperature). One set of preferred pre-hydrolysis conditions for producing the hemicellulosic stream used in the process of the invention comprise treating lignocellulosic biomass such as wood chips with an acid (e.g. a mineral acid) in the presence of water at elevated

temperature. For example, in one particularly preferred embodiment lignocellulosic biomass is treated with dilute sulfuric acid (e.g. 0.2-5 % v/v aqueous sulfuric acid, or at a sulfuric acid concentration in water of from 0.05M to 1.5M) at a temperature in the range of from 100 to 250°C, more preferably in the range of from 150 to 250°C. In another embodiment lignocellulosic biomass is treated with concentrated sulfuric acid (e.g. 10-30 % v/v aqueous sulfuric acid, or at a sulfuric acid concentration in water of from 2.0M to 6.0M) at a temperature in the range of from 40 to 100°C. The separated hemicellulosic stream obtained from processes for producing dissolving pulp is typically referred to as "pre-hydrolysate liquor". Treatment of lignocellulosic biomass with water under acidic conditions at high temperature provides hemicellulosic feedstocks which are particularly suitable for the production of lactic acid in high yield, when processed according to the process of the invention. It will of course be understood that other methods of treating biomass, for example using steam or mild caustic treatment, may also be used.

Whereas cellulose is a highly uniform linear polysaccharide (it is a l→4-P-linked polyglucan), the term hemicellulose defines a group of heterogeneous polysaccharides of comparatively low molecular weight, having a degree of polymerisation of from about 40 to about 600 (in many cases the degree of polymerisation is from about 80 to about 200). Most hemicelluloses are branched structures (see for example Ren and Sun, Cereal Straw as a Resource for Sustainable Biomaterials and Biofuels; Chemistry, Extractives, Lignins, Hemicelluloses and Cellulose, 2010, Chapter 4; also Girio et al, Bioresource Technology, 2010, 101 p4775-4800).

Hemicelluloses have been classified into four groups: i) xyloglycans (xylans); ii) mannoglycans (mannans); iii) xyloglucans (XG); and iv) mixed-linkage β-glucans (Ren and Sun, Cereal Straw as a Resource for Sustainable Biomaterials and Biofuels; Chemistry, Extractives, Lignins, Hemicelluloses and Cellulose, 2010, Chapter 4).

Xylans comprise a P(l→4)-D-xylanopyranose backbone, and typically contain carbohydrate groups on the 2- or 3- position of backbone residues. Examples include glucuronoxylans (GX), arabino(glucurono)xylans (AGX), glucurono(arabino)xylans (GAX) and arabinoxylans (AX). Xylans are the most common hemicelluloses, and in particular are abundant in hardwood or annual plants.

Mannans have been categorised in two groups: i) galactomannans, which comprise a β(1→4) linked D-mannopyranose backbone; and ii) glucomannans, which have a backbone comprising D-mannopyranose and D-glucopyranose residues with β(1→4) linkages.

Mannans may have varying degrees of branching, with D-galactopyranose groups on the 6- position of the mannose backbone.

Xyloglucans (XG) comprise a P(l→4)-linked D-glucopyranose backbone with D- xylanopyranose residues at the 6-position of glucopyranose residues. There are two categories of xyloglucans, depending on the nature of the xylanopyranose-containing side- chains. Xyloglucans comprising two xylanopyranose units followed by two

glucanopyranose units are referred to as XXGG, and xyloglucans comprising three xylanopyranose units followed by one glucopyranose unit are referred to as XXXG.

Additional side-chains may also be present.

Mixed linkage β-glucans have a D-glucopyranose backbone with mixed β linkages (1→3, 1→4). In many industrial processes, following treatment of lignocellulosic biomass, a hemicellulosic stream and cellulosic solids are obtained and are separated from one another. The hemicellulosic stream used in the process of the invention contains a greater proportion by weight of hemicellulosic material relative to cellulosic material than the proportion by weight of hemicellulosic material relative to cellulosic material present in the lignocellulosic biomass itself. In other words, the hemicellulosic stream contains a fraction of

lignocellulosic biomass-derived material that is enriched in hemicellulosic material over that present in the lignocellulosic biomass itself. Similarly, the cellulosic solids contain a greater proportion by weight of cellulosic material (i.e. cellulose and/or cellulose-derived

saccharides) relative to hemicellulosic material than the proportion by weight of cellulosic material relative to hemicellulosic material present in the lignocellulosic biomass itself.

Processing of heterogeneous hemicellulosic streams into useful chemical products is more difficult than for cellulosic solids; however the present invention finds a use for such hemicellulosic streams.

In one embodiment at least 60 wt%, or at least 70 wt%, or at least 80 wt%, or at least

90 wt %, or at least 95 wt% of the saccharide material present in the aqueous hemicellulosic stream is hemicellulosic material. In one embodiment less than 20 wt%, or less than 15 wt%, or less than 10 wt%, or less than 5 wt% of the saccharide material present in the aqueous hemicellulosic stream is cellulosic material. In one embodiment the aqueous hemicellulosic stream is free or substantially free of cellulosic material. In one embodiment at least 60 wt% of the lignocellulosic biomass-derived material present in the hemicellulosic stream is hemicellulosic material and less than 20 wt% of the lignocellulosic biomass-derived material present in the hemicellulosic stream is cellulosic material. In one embodiment at least 70 wt% of the lignocellulosic biomass-derived material present in the hemicellulosic stream is hemicellulosic material and less than 15 wt% of the lignocellulosic biomass-derived material present in the hemicellulosic stream is cellulosic material. In one embodiment at least 80 wt% of the lignocellulosic biomass-derived material present in the hemicellulosic stream is hemicellulosic material and less than 10 wt% of the lignocellulosic biomass-derived material present in the hemicellulosic stream is cellulosic material. The analysis of saccharide material may routinely be performed by chromatographic methods (principally HPLC and ion chromatography), as described in standard procedures issued by organisations such as ASTM [D5896-96 (2012)], the National Renewable Energy Laboratory (TP-510-42623) and TAPPI (T-249). The aqueous hemicellulosic stream may contain other components, for example it may include other components of biomass such as lignin or lignin-derived products. Spent chemicals from initial processing of biomass may also be present. The concentration of hemicellulosic material present in the aqueous hemicellulosic stream will be a characteristic of the biomass source and will depend on the conditions used to obtain the aqueous hemicellulosic stream from biomass. In one embodiment at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt%, at least 30 wt%, at least 40 wt% or at least 50 wt% of the aqueous hemicellulosic stream is hemicellulosic material.

The proportions of hemicellulose, cellulose and lignin present in lignocellulosic biomass vary depending on the type of biomass, as do the proportions of different polysaccharides which make up the hemicellulose proportion of the biomass. In one preferred embodiment the biomass from which the hemicellulosic stream is obtained comprises a hardwood, for example an Acer (maple), Populus (aspen), Betula (birch), Fagus (beech), Eucalyptus, Quercus (oak) Populus (poplar) or Liquidambar (sweetgum). In one preferred embodiment the biomass from which the hemicellulosic stream is obtained comprises a softwood, for example an Abies (fir), Larix (larch), Picea (spruce) or Pinus (pine). In one preferred embodiment the biomass from which the hemicellulosic stream is obtained comprises a grass, for example a Panicum (e.g. Panicum virgatum, switch grass), a Sorghum (e.g. sweet sorghum) or a Saccharum (e.g. sugar cane).

The hemicellulosic stream obtained from a process for producing dissolving pulp (e.g. pre-hydrolysate liquor) comprises hemicellulose, hemicellulose-derived oligosaccharides and/or hemicellulose-derived monosaccharides. The proportions of the hemicellulose, hemicellulose-derived oligosaccharides and/or hemicellulose-derived monosaccharides present in the hemicellulosic stream will depend on the conditions used to obtain the hemicellulosic stream from lignocellulosic biomass. Hemicellulosic streams having a higher proportion by weight of hemicellulose-derived monosaccharide relative to the combined proportion by weight of hemicellulose and hemicellulose-derived oligosaccharide will typically result in a higher yield of sodium lactate being obtained in step (b). Accordingly, where the hemicellulosic stream obtained from a process for producing dissolving pulp initially contains a low proportion by weight of hemicellulose-derived monosaccharide relative to the combined proportion by weight of hemicellulose and hemicellulose-derived oligosaccharide, the hemicellulosic stream provided in step (a) has preferably been subjected to hemicellulosic hydrolysis conditions prior to use in the process of the invention. Subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions increases the proportion by weight of hemicellulose-derived monosaccharide present in the hemicellulosic stream relative to the combined proportion by weight of hemicellulose and hemicellulose-derived

oligosaccharide.

Similarly, where the hemicellulosic stream obtained from a process for producing dissolving pulp initially contains no hemicellulose-derived monosaccharide (i.e. all of the saccharides present in the hemicellulosic stream obtained from a process for producing dissolving pulp are hemicellulose and/or hemicellulose-derived oligosaccharide), the hemicellulosic stream provided in step (a) will have been subjected to hemicellulosic hydrolysis conditions prior to use in the process of the invention.

On the other hand, where the hemicellulosic stream obtained from a process for producing dissolving pulp contains a high proportion by weight of hemicellulose-derived monosaccharide relative to the combined proportion by weight of hemicellulose and hemicellulose-derived oligosaccharide, subjecting the hemicellulosic stream to the conditions of step (b) will result in high yields of sodium lactate being obtained without subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions beforehand.

Preferred hemicellulosic hydrolysis conditions comprise contacting the hemicellulosic stream with an acid (e.g. a mineral acid) in the presence of water at elevated temperature. For example, in one particularly preferred embodiment the hemicellulosic stream is treated with dilute sulfuric acid (e.g. 0.2-5 % v/v aqueous sulfuric acid, or at a sulfuric acid concentration in water of from 0.05M to 1.5M) at a temperature in the range of from 100 to 250°C, more preferably in the range of from 150 to 250°C. In another embodiment the hemicellulosic stream is treated with concentrated sulfuric acid (e.g. 10-30 % v/v aqueous sulfuric acid, or at a sulfuric acid concentration in water of from 2.0M to 6.0M) at a temperature in the range of from 40 to 100°C.

In one embodiment, at least 80 wt%, at least 90 wt%, at least 95 wt%, or all or substantially all of the saccharides present in the hemicellulosic stream provided in step (a) are hemicellulose-derived monosaccharides.

In one embodiment, the hemicellulosic stream obtained from a process for producing dissolving pulp provided in step (a) has been subjected to hemicellulosic hydrolysis conditions.

In one embodiment, the process comprises:

(al) obtaining an aqueous hemicellulosic stream produced by a process for producing dissolving pulp, the hemicellulosic stream comprising hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide; (a2) subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions, thereby increasing the proportion by weight of hemicellulose-derived monosaccharide present in the hemicellulosic stream relative to the combined proportion by weight of hemicellulose and hemicellulose-derived oligosaccharide;

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

In one preferred embodiment, the process comprises:

(al) obtaining an aqueous hemicellulosic stream produced by a process for producing dissolving pulp, the hemicellulosic stream comprising hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide, and the process for producing dissolving pulp comprising treating lignocellulosic biomass with an acid in the presence of water at elevated temperature;

(a2) subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions, thereby increasing the proportion by weight of hemicellulose-derived monosaccharide present in the hemicellulosic stream relative to the combined proportion by weight of hemicellulose and hemicellulose-derived oligosaccharide;

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

In one preferred embodiment, the process comprises:

(al) obtaining an aqueous hemicellulosic stream produced by a process for producing dissolving pulp, the hemicellulosic stream comprising hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide;

(a2) contacting the hemicellulosic stream with an acid in the presence of water at elevated temperature, thereby increasing the proportion by weight of hemicellulose-derived monosaccharide present in the hemicellulosic stream relative to the combined proportion by weight of hemicellulose and hemicellulose-derived oligosaccharide; (b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

In one embodiment, the process comprises:

(al) obtaining an aqueous hemicellulosic stream produced by a process for producing dissolving pulp, the hemicellulosic stream comprising hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide;

(a2) where the proportion by weight of saccharide material present in the

hemicellulosic stream that is hemicellulose-derived monosaccharide is less than a pre-defined value (e.g. less than 50 wt%, less than 60 wt%, less than 70 wt%, less than 80 wt%, less than 90 wt%, or less than 95 wt% hemicellulose-derived monosaccharide), subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions until the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value;

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

In one embodiment, the process comprises:

(al) obtaining an aqueous hemicellulosic stream produced by a process for producing dissolving pulp, the hemicellulosic stream comprising hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide, and the process for producing dissolving pulp comprising treating lignocellulosic biomass with an acid in the presence of water at elevated temperature;

(a2) where the proportion by weight of saccharide material present in the

hemicellulosic stream that is hemicellulose-derived monosaccharide is less than a pre-defined value (e.g. less than 10 wt%, less than 20 wt%, less than 30 wt%, less than 40 wt%, less than 50 wt%, less than 60 wt%, less than 70 wt%, less than 80 wt%, less than 90 wt%, or less than 95 wt% hemicellulose-derived monosaccharide), subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions until the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value;

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

In one embodiment, the process comprises:

(al) obtaining an aqueous hemicellulosic stream produced by a process for producing dissolving pulp, the hemicellulosic stream comprising hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide;

(a2) where the proportion by weight of saccharide material present in the

hemicellulosic stream that is hemicellulose-derived monosaccharide is less than a pre-defined value (e.g. less than 10 wt%, less than 20 wt%, less than 30 wt%, less than 40 wt%, less than 50 wt%, less than 60 wt%, less than 70 wt%, less than 80 wt%, less than 90 wt%, or less than 95 wt% hemicellulose-derived monosaccharide), contacting the hemicellulosic stream with an acid in the presence of water at elevated temperature, until the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value;

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

In one embodiment, the process comprises:

(al) obtaining an aqueous hemicellulosic stream produced by a process for producing dissolving pulp, the hemicellulosic stream comprising hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide;

(a2) receiving information concerning the proportion by weight of the saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide; and either, where the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is less than a pre-defined value (e.g. less than 50 wt%, less than 60 wt%, less than 70 wt%, less than 80 wt%, less than 90 wt%, or less than 95 wt% hemicellulose-derived monosaccharide), subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions until the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value, prior to carrying out step (b),

or,

where the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value, not subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions prior to carrying out step (b);

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

The information received concerning the proportion by weight of the hemicellulosic material present in the aqueous hemicellulosic stream that is hemicellulose-derived monosaccharide may for example be information obtained by analysing the aqueous hemicellulosic stream obtained from a process for producing dissolving pulp (e.g. the pre- hydrolysate liquor). Alternatively it may for example be prior knowledge based on analysis of a previous aqueous hemicellulosic stream which was obtained by treating lignocellulosic biomass by the same or similar process steps as those used to obtain the present

hemicellulosic stream from lignocellulosic biomass.

In one embodiment, the process comprises:

(al) obtaining an aqueous hemicellulosic stream produced by a process for producing dissolving pulp, the hemicellulosic stream comprising hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide;

(a2) analysing the hemicellulosic stream and determining the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide; and

either, where the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is less than a pre-defined value (e.g. less than 10 wt%, less than 20 wt%, less than 30 wt%, less than 40 wt%, less than 50 wt%, less than 60 wt%, less than 70 wt%, less than 80 wt%, less than 90 wt%, or less than 95 wt%

hemicellulose-derived monosaccharide), subjecting the hemicellulosic stream to

hemicellulosic hydrolysis conditions until the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value, prior to carrying out step (b),

or,

where the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value, not subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions prior to carrying out step (b);

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

It will be appreciated that initial processing of lignocellulosic biomass to produce dissolving pulp is typically carried out at a location where suitable lignocellulosic biomass is readily available, and that in some instances that location may be remote from the location at which the process of the invention is carried out, for example it may be in a different country. However, in one embodiment the process of the invention includes subjecting lignocellulosic biomass to process conditions suitable for obtaining dissolving pulp, thereby producing the hemicellulosic stream, i.e. the process comprises:

(aa) subjecting lignocellulosic biomass to pre-hydrolysis conditions, thereby producing (i) an aqueous hemicellulosic stream containing hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide, and (ii) cellulosic solids;

(ab) separating the aqueous hemicellulosic stream from the cellulosic solids;

(ac) converting said cellulosic solids into dissolving pulp;

(a2) where the proportion by weight of saccharide material present in the

hemicellulosic stream that is hemicellulose-derived monosaccharide is less than a pre-defined value (e.g. less than 50 wt%, less than 60 wt%, less than 70 wt%, less than 80 wt%, less than 90 wt%, or less than 95 wt% hemicellulose-derived monosaccharide), subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions until the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value;

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

Preferred pre-hydrolysis conditions used in step (aa) comprise contacting

lignocellulosic biomass such as wood chips with an acid (e.g. a mineral acid) in the presence of water at elevated temperature. For example, in one particularly preferred embodiment in step (aa) lignocellulosic biomass is treated with dilute sulfuric acid (e.g. 0.2-5 % v/v aqueous sulfuric acid, or at a sulfuric acid concentration in water of from 0.05M to 1.5M) at a temperature in the range of from 100 to 250°C, more preferably in the range of from 150 to 250°C. In another embodiment in step (aa) lignocellulosic biomass is treated with

concentrated sulfuric acid (e.g. 10-30 % v/v aqueous sulfuric acid, or at a sulfuric acid concentration in water of from 2.0M to 6.0M) at a temperature in the range of from 40 to 100°C.

In step (ab) the hemicellulosic stream may be separated from the cellulosic solids by routine processing, for example by draining the liquid phase, by filtering the product mixture, or by decanting or siphoning off the liquid phase.

In step (ac) the cellulosic solids may be converted into dissolving pulp by known processing steps. For example, the cellulosic solids may be subjected to further pulping conditions as described above, and may in addition be subjected to, for example, treatment by oxygen delignification, bleaching and/or alkali extraction.

In one preferred embodiment the process comprises:

(aa) treating lignocellulosic biomass with an acid in the presence of water at elevated temperature, thereby producing (i) an aqueous hemicellulosic stream containing

hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide, and (ii) cellulosic solids;

(ab) separating the aqueous hemicellulosic stream from the cellulosic solids;

(ac) converting said cellulosic solids into dissolving pulp; (a2) where the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is less than a pre-defined value (e.g. less than 10 wt%, less than 20 wt%, less than 30 wt%, less than 40 wt%, less than 50 wt%, less than 60 wt%, less than 70 wt%, less than 80 wt%, less than 90 wt%, or less than 95 wt% hemicellulose-derived monosaccharide), subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions until the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value;

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

In one preferred embodiment the process comprises:

(aa) subjecting lignocellulosic biomass to pre-hydrolysis conditions, thereby producing (i) an aqueous hemicellulosic stream containing hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide, and (ii) cellulosic solids;

(ab) separating the aqueous hemicellulosic stream from the cellulosic solids;

(ac) converting said cellulosic solids into dissolving pulp;

(a2) where the proportion by weight of saccharide material present in the

hemicellulosic stream that is hemicellulose-derived monosaccharide is less than a pre-defined value (e.g. less than 10 wt%, less than 20 wt%, less than 30 wt%, less than 40 wt%, less than 50 wt%, less than 60 wt%, less than 70 wt%, less than 80 wt%, less than 90 wt%, or less than 95 wt% hemicellulose-derived monosaccharide), contacting the hemicellulosic stream with an acid in the presence of water at elevated temperature, until the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value;

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid. In one embodiment the process comprises:

(aa) subjecting lignocellulosic biomass to pre-hydrolysis conditions, thereby producing (i) an aqueous hemicellulosic stream containing hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide, and (ii) cellulosic solids;

(ab) separating the aqueous hemicellulosic stream from the cellulosic solids;

(ac) converting said cellulosic solids into dissolving pulp;

(a2) receiving information concerning the proportion by weight of the saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide; and

either,

where the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is less than a pre-defined value (e.g. less than 10 wt%, less than 20 wt%, less than 30 wt%, less than 40 wt%, less than 50 wt%, less than 60 wt%, less than 70 wt%, less than 80 wt%, less than 90 wt%, or less than 95 wt%

hemicellulose-derived monosaccharide), subjecting the hemicellulosic stream to

hemicellulosic hydrolysis conditions until the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value, prior to carrying out step (b),

or,

where the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value, not subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions prior to carrying out step (b);

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

In one embodiment the process comprises:

(aa) subjecting lignocellulosic biomass to pre-hydrolysis conditions, thereby producing (i) an aqueous hemicellulosic stream containing hemicellulose, hemicellulose-derived oligosaccharide and/or hemicellulose-derived monosaccharide, and (ii) cellulosic solids;

(ab) separating the aqueous hemicellulosic stream from the cellulosic solids; (ac) converting said cellulosic solids into dissolving pulp;

(a2) analysing the hemicellulosic stream and determining the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide; and

either,

where the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is less than a pre-defined value (e.g. less than 10 wt%, less than 20 wt%, less than 30 wt%, less than 40 wt%, less than 50 wt%, less than 60 wt%, less than 70 wt%, less than 80 wt%, less than 90 wt%, or less than 95 wt%

hemicellulose-derived monosaccharide), subjecting the hemicellulosic stream to

hemicellulosic hydrolysis conditions until the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value, prior to carrying out step (b),

or,

where the proportion by weight of saccharide material present in the hemicellulosic stream that is hemicellulose-derived monosaccharide is equal to or greater than said pre-defined value, not subjecting the hemicellulosic stream to hemicellulosic hydrolysis conditions prior to carrying out step (b);

(b) reacting said hemicellulose-derived monosaccharide with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate;

(c) optionally converting the sodium lactate into lactic acid or said derivative of lactic acid; and

(d) recovering the sodium lactate, lactic acid or said derivative of lactic acid.

The process of the invention may be carried out batchwise, or as a continuous or semi-continuous process. For example, the hemicellulosic stream may be processed as a succession of batches. Similarly, if desired the hemicellulosic stream may be provided as a succession of batches (e.g. in a series of containers shipped from the location where the process for producing dissolving pulp is carried out to the location where the process of the invention is carried out).

In step (b), hemicellulose-derived monosaccharide is reacted with sodium hydroxide in the presence of water at a temperature in the range of from 50 to 140°C to produce sodium lactate. The non-fermentation conditions of step (b) are particularly suitable for use with the monosaccharide-containing feedstocks provided in step (a) (or following steps (al and a2), or following steps (aa), (ab) (ac) and (a2)).

In one embodiment the hemicellulosic stream is combined with another saccharide- containing feedstock prior to reaction with sodium hydroxide. In another embodiment the hemicellulosic feedstock is not combined with another saccharide-containing feedstock prior to reaction with sodium hydroxide.

The reaction between the hemicellulose-derived monosaccharide and sodium hydroxide takes place in the presence of water. It may also take place in the presence of one or more additional organic solvents, for example an oxygenate such as an alcohol, ester, ether, or ketone; and/or in the presence of one or more reactive extractants such as an amine. However, in a preferred embodiment, no additional organic solvent is added to the hemicellulosic stream prior to carrying out step (b). In other words no additional organic solvent is added over that already present in the hemicellulosic stream (for example there may be traces of organic solvents used in earlier processing steps). In one preferred embodiment water is the only solvent used in step (b).

The reaction between hemicellulose-derived monosaccharide and sodium hydroxide is carried out at a temperature in the range of from 50 to 140 °C. More preferably step (b) is carried out at a temperature in the range of from 60 to 120 °C. In one embodiment, hemicellulose-derived monosaccharide is reacted with sodium hydroxide in water at reflux.

Step (b) is typically carried out at ambient pressure, but it may be carried out at higher or lower pressure if desired. Step (b) is typically carried out under ambient atmosphere (i.e. the reaction is typically carried out in the absence of added oxygen). Alternatively step (b) may be carried out under an inert atmosphere (e.g. under N ₂ atmosphere).

In one preferred embodiment, step (b) is carried out batchwise and hemicellulose- derived monosaccharide in water is added to an aqueous solution of sodium hydroxide over a period of time at elevated temperature. For example, a mixture comprising hemicellulose- derived monosaccharide and water may be added over a period of time to a mixture of sodium hydroxide and water that is at elevated temperature, for example at reflux. Preferably the mixture comprising hemicellulose-derived monosaccharide is added to an aqueous solution of sodium hydroxide over a period in the range of from at least 5 minutes to 12 hours, at least 5 minutes to 3 hours, or at least 5 minutes to 1 hour. In one preferred embodiment hemicellulose-derived monosaccharide is reacted with sodium hydroxide over a period in the range of from 15 minutes to 3 hours. In one preferred embodiment hemicellulose-derived monosaccharide is reacted with sodium hydroxide over a period in the range of from 10 minutes to 1 hour.

The ratio of sodium hydroxide to hemicellulose-derived monosaccharide should be sufficient to effect high conversion of hemicellulose-derived monosaccharide to lactate. For example the molar ratio of sodium hydroxide to hemicellulose-derived monosaccharide may be up to 10: 1, preferably in the range of from 1.5 : 1 to 6: 1, more preferably in the range of from 1.5 : 1 to 4 : 1 , still more preferably in the range of from 1.5 : 1 to 2.5 : 1 , yet more preferably 1.5 : 1 to 2.1 : 1.

Typically racemic sodium lactate is produced in step (b).

In step (c) sodium lactate may optionally be converted into lactic acid or a derivative of lactic acid. In one preferred embodiment sodium lactate is reacted with an acid to produce lactic acid. The reaction with acid may be carried out at ambient temperature, although higher or lower temperatures may be used if desired. The acid used is preferably a mineral acid, more preferably hydrochloric acid or sulfuric acid.

In one preferred embodiment sodium lactate is converted into a derivative of lactic acid selected from the group consisting of an alkyl lactate, oligomeric lactic acid, lactide, an alkyl lactyllactate, polylactic acid and a complex of lactic acid and either ammonia or an amine. Processes for the production of such derivatives of lactic acid are known in the art.

In one preferred embodiment the derivative of lactic acid is an alkyl lactate, and in step (c) sodium lactate is reacted with an acid (e.g. a mineral acid such as hydrochloric acid or sulfuric acid) to produce lactic acid, and the lactic acid is reacted with an alkyl alcohol to produce the alkyl lactate. Preferably the alkyl alcohol is a Ci-6 alkyl alcohol, more preferably a Ci-6 alkyl alcohol containing only one hydroxy group (e.g. ethanol, n-propanol, i-propanol, n-butanol, n-pentanol, n-hexanol), more preferably a C3-6 alkyl alcohol containing only one hydroxy group, most preferably the alkyl alcohol is n-butanol. The esterification step may be carried out in the presence of a catalyst, for example an acid catalyst (e.g. a mineral acid, such as hydrochloric acid or sulfuric acid, or an organic acid such as lactic acid, or a solid acid, such as a resin- supported acid or an acidic zeolite), and is suitably carried out at elevated temperature, for example at a temperature in the range of from 50 to 140 °C. Water is typically removed from the reaction mixture during the esterification step, for example by evaporation or distillation. For example a mixture containing water, Ci-6 alkyl alcohol (e.g. n-butanol, or ethanol), lactic acid and optionally a mineral acid (e.g. HC1 or H2SO4) may be heated under reflux with water being removed (e.g. as an azeotropic mixture). Alkyl lactate produced by the process of the invention will typically be racemic (i.e. it contains substantially equal proportions of (S)-lactate and (R)-lactate enantiomers). As a result, except in the case where a resolution step is carried out to separate enantiomers, a mixture of alkyl lactates will normally be obtained (e.g. a mixture of alkyl (R)-lactate and alkyl (S)- lactate).

In one embodiment the derivative of lactic acid is a complex of lactic acid and either ammonia or an amine. Sodium lactate may be converted into complex by, for example, converting the sodium lactate into lactic acid as described above, and reacting the lactic acid with an amine or ammonia to produce the complex.

In one embodiment, the derivative of lactic acid is oligomeric lactic acid. Sodium lactate may be converted into oligomeric lactic acid by, for example, converting the sodium lactate into lactic acid, complex or alkyl lactate as described above, and by heating the lactic acid, complex or alkyl lactate, and removing water, amine or ammonia and/or alcohol.

In one preferred embodiment, the derivative of lactic acid is lactide. Lactide is a cyclic dimer of lactic acid that is itself useful in the production of polylactic acid. Sodium lactate may be converted into lactide by, for example, converting the sodium lactate into oligomeric lactic acid as described above, and the oligomeric lactic acid may be converted into lactide by heating in the presence of a transesterification catalyst. There are three forms of lactide, (S,S)- or L-lactide, (R,R)- or D-lactide, and (R,S)- or meso-lactide. Since the sodium lactate produced in step (b) will typically be racemic (i.e. it contains substantially equal proportions of (S)-lactate and (R)-lactate anions), except in the case where a resolution step is carried out, a mixture of lactides will normally be obtained. (R,S)-lactide may be separated from (S,S)-lactide and (R,R)-lactide by standard separation techniques, for example by distillation, solvent extraction, or crystallisation.

In one preferred embodiment the derivative of lactic acid is alkyl lactyllactate.

Sodium lactate may be converted into alkyl lactyllactate by, for example, converting sodium lactate into lactide as described above, and reacting the lactide with an alkyl alcohol to produce alkyl lactyllactate. Where (R,R)-lactide is reacted, the alkyl lactyllactate will be alkyl (R,R)-lactyllactate. Where (S,S)-lactide is reacted, the alkyl lactyllactate will be alkyl (S,S)-lactyllactate.

In one preferred embodiment the derivative of lactic acid is polylactic acid. Sodium lactate may be converted into polylactic acid by, for example, converting the sodium lactate into lactide, and polymerising the lactide to produce polylactic acid (e.g. by contacting with a catalyst at elevated temperature). Where (R,R)-lactide is polymerised, poly (R)-lactic acid is produced. Where (S,S)-lactide is polymerised, poly (S)-lactic acid is produced. Poly (R)- lactic acid may be combined with poly (S)-lactic acid, for example using melt blending, to produce stereocomplex polylactic acid.

In step (d) the sodium lactate, lactic acid or derivative thereof may be recovered using any suitable means. For example, liquid-liquid extraction, membrane separation, distillation and/or crystallization techniques may be used. In one preferred embodiment, the derivative of lactic acid is an alkyl lactate (e.g. n-butyl lactate, or ethyl lactate), and the alkyl lactate is recovered by distillation. In one preferred embodiment, the derivative of lactic acid is lactide, and the lactide is recovered by distillation and/or crystallisation. In one preferred embodiment, the derivative of lactic acid is an alkyl lactyllactate (e.g. n-butyl lactyllactate), and the alkyl lactyllactate is recovered by distillation.

Additional reagents or routine processing steps may be carried out at any stage of the process, e.g. to add or remove solvent, or to remove unreacted reagents and/or byproducts. By way of example, the hemicellulosic stream will typically contain water and so, if desired, the hemicellulosic stream may be concentrated to remove water (e.g. by distillation, evaporation or membrane separation) prior to carrying out step (b).

The following Example illustrates the invention.

Example 1: Production of lactic acid from hemicellulosic stream

(a) To a 100 mL flask was charged xylan (3.301 g, from beech wood, Sigma-Aldrich, 96.4% purity based on UPLC area) followed by water (50 mL) and concentrated H2SO4 (0.5 mL). The suspension was stirred and heated to reflux for 3 hours, in order to increase the proportion of hemicellulose-derived monosaccharides. The mixture was then cooled to ambient temperature.

(b) The resulting hydrolysate was then added over a period of 60 min to 50% aqueous sodium hydroxide (8.2 mL) at 100-120°C.

(c) The reaction mixture was then cooled to ambient temperature, acidified by the addition of 10 mL of 37% HC1, made up to 1 L with water in a volumetric flask and analysed for lactic acid content by UPLC. The results indicated a yield of 1.10 g lactic acid. Example 2: Processing of a pre-hydrolysate liquor as hemicellulosic stream

Samples of pre-hydrolysate liquor obtained from a commercial dissolving pulp process were analysed for acetic acid and formic acid content (by HPLC) as well as lignin content (by UV spectroscopy) and found to contain the following concentrations: acetic acid, 0.64%w/v; formic acid, 0.07%w/v; and lignin, 0.65%w/v.

The pre-hydrolysate liquor (50mL/51g) was charged to a 250mL flask followed by concentrated sulphuric acid (0.5mL). The suspension was stirred and heated to reflux for 3hrs and cooled to ambient. Analysis by HPLC indicated that the monosaccharide produced was mainly xylose present at a concentration of 0.17M.

The above hydrolysate was then added over a period of 65min to 50% aqueous caustic solution (4.65mL) at 100-120°C. The reaction mixture was then cooled to ambient and acidified with HC1 and made up to 1L in a volumetric flask and analysed for lactic acid by HPLC. The results indicated a yield of 31.3% based on monosaccharide following hydrolysis of the PHL, which equates to generation of 11. lg of lactic acid per litre of PHL.

Example 3: Processing of a pre-hydrolysate liquor as hemicellulosic stream

In this example, pre-hydrolysis of the PHL of Example 2 was carried out using the organic acid already present in the PHL for hydrolysis.

PHL (30mL/30.1g) was charged to a 50mL autoclave. This was stirred and heated to 200°C and maintained at this temperature for 15min. The autoclave was cooled to 25°C. Analysis of the product by HPLC indicated that the monosaccharide produced was mainly xylose present at a concentration of 0.01M. The hydrolysate was then added over a period of 60min to 50% aqueous caustic solution (2.8mL) at 100-120°C. The reaction mixture was then cooled to ambient and acidified with HC1 and made up to 500mL in a volumetric flask and analysed for lactic acid by HPLC. The results indicated a yield of 100% based on monosaccharide following hydrolysis of the PHL, which equates to 1.9g of lactic acid per litre of PHL.

Example 4: Comparison of production of lactic acid from hemicellulosic stream with production from cellulose-derived material

In experiments (i) to (iv), lactic acid was prepared from a hemicellulosic stream produced by acid treatment of xylan under various conditions. In experiments (v) to (viii), lactic acid was prepared from a cellulose-derived material produced by acid treatment of cellulose: Experiment (i): Hydrolysis of xylan at atmospheric pressure

(a) To a 100 mL round bottomed flask equipped with a reflux condenser was charged xylan (3.2930 g, from beech wood, Sigma- Aldrich) followed by demineralised water (50.0 mL) and concentrated H2SO4 (0.5 mL). The suspension was stirred and heated to reflux for 3 hours. The mixture was then cooled to ambient temperature, yielding a hazy, brown coloured solution (52 mL). Analysis by HPLC indicated that the monosaccharide produced was mainly xylose present at a concentration of 3.67% w/v. Also present were glucose (0.06% w/v), arabinose (0.03% w/v), galactose (0.08% w/v) and mannose (0.01% w/v).

(b) 45mL of the resulting hydrolysate was then added over a period of 60 min to 50% aqueous sodium hydroxide (4.3 mL) at 100-120°C.

(c) The reaction mixture was then cooled to ambient temperature, acidified by the addition of 4 mL of 37% HCl to achieve a pH <3, made up to 1 L with demineralised water in a volumetric flask and analysed for lactic acid content by HPLC. The results indicated a yield of 0.88g.

Experiment (ii): Combined hydrolysis and extraction of xylan at atmospheric pressure

(a) To a 100 mL round bottomed flask equipped with a reflux condenser was charged xylan (3.3048 g, from beech wood, Sigma- Aldrich) followed by demineralised water (50.0 mL), concentrated H2SO4 (0.5 mL) and n-butanol (30 mL). The biphasic mixture was stirred and heated to reflux for 3 hours during which most of the suspended solids dissolved. The mixture was then cooled to ambient temperature and the layers separated. The organic phase (32ml) was brown coloured and the lower aqueous phase (51ml) was pale straw coloured and slightly hazy. Analysis of the aqueous layer by HPLC indicated that the monosaccharide produced was mainly xylose present at a concentration of 2.90% w/v. Also present were glucose (0.02%) w/v), arabinose (0.02% w/v), galactose (0.05% w/v) and mannose (0.01% w/v).

(b) 45mL of the resulting hydrolysate was then added over a period of 60 min to 50% aqueous sodium hydroxide (3.9 mL) at 100-120°C.

(c) The reaction mixture was then cooled to ambient temperature, acidified by the addition of 4 mL of 37% HCl to achieve a pH <3, made up to 1 L with demineralised water in a volumetric flask and analysed for lactic acid content by HPLC. The results indicated a yield of 0.70g. Experiment (in): Hydrolysis ofxylan at elevated temperature and pressure

(a) To a 100 mL Parr reactor was charged xylan (1.9845 g, from beech wood, Sigma- Aldrich) followed by demineralised water (30.0 mL) and concentrated H2SO4 (0.3 mL). The reactor was sealed and then heated, with stirring to 135°C / 1.7 bar over 30min. The mixture was then cooled to ambient temperature, yielding a brown coloured solution (32 mL).

Analysis by HPLC indicated that the monosaccharide produced was mainly xylose present at a concentration of 4.51% w/v. Also present were glucose (0.07% w/v), arabinose (0.03% w/v), galactose (0.09% w/v) and mannose (0.01% w/v).

(b) 30mL of the resulting hydrolysate was then added over a period of 60 min to 50% aqueous sodium hydroxide (4.0 mL) at 100-120°C.

(c) The reaction mixture was then cooled to ambient temperature, acidified by the addition of 4 mL of 37% HCl to achieve a pH <3, made up to 1 L with demineralised water in a volumetric flask and analysed for lactic acid content by HPLC. The results indicated a yield of 0.60g.

Experiment (iv): Combined hydrolysis and extraction ofxylan at elevated temperature and pressure

(a) To a 100 mL Parr reactor was charged xylan (1.9895 g, from beech wood, Sigma- Aldrich) followed by demineralised water (30.0 mL), concentrated H2SO4 (0.3 mL) and n- butanol (15 mL). The reactor was sealed and then heated, with stirring to 132°C / 2.3 bar over 30min. The mixture was then cooled to ambient temperature and the layers separated. The organic phase (15ml) was brown coloured and the lower aqueous phase (31.5ml) was pale straw coloured. Analysis of the aqueous layer by HPLC indicated that the

monosaccharide produced was mainly xylose present at a concentration of 3.29% w/v. Also present were glucose (0.05% w/v), arabinose (0.02% w/v) and galactose (0.06% w/v).

(b) 30mL of the resulting hydrolysate was then added over a period of 60 min to 50% aqueous sodium hydroxide (4.0 mL) at 100-120°C.

(c) The reaction mixture was then cooled to ambient temperature, acidified by the addition of 4 mL of 37% HCl to achieve a pH <3, made up to 1 L with demineralised water in a volumetric flask and analysed for lactic acid content by HPLC. The results indicated a yield of 0.49g. Experiment (v): Hydrolysis of cellulose at atmospheric pressure

(a) To a 100 mL round bottomed flask equipped with a reflux condenser was charged cellulose (3.3297 g, acid treated, Sigma-Aldrich) followed by demineralised water (5.0 mL) and concentrated H2SO4 (0.5 mL). The suspension was stirred and heated to reflux for 3 hours. The mixture was then cooled to ambient temperature and filtered, yielding a pale straw coloured filtrate (52 mL). Analysis by HPLC indicated that the monosaccharide glucose was present at a concentration of 0.09% w/v, and xylose at a concentration of 0.02%.

(b) 45mL of the resulting hydrolysate was then added over a period of 60 min to 50% aqueous sodium hydroxide (1.4 mL) at 100-120°C.

(c) The reaction mixture was then cooled to ambient temperature, acidified by the addition of 1 mL of 37% HC1 to achieve a pH <3, made up to 100 mL with demineralised water in a volumetric flask and analysed for lactic acid content by HPLC. The results indicated a yield of 0.029g.

Experiment (vi): Combined hydrolysis and extraction of cellulose at atmospheric pressure (a) To a 100 mL round bottomed flask equipped with a reflux condenser was charged cellulose (3.3216 g, acid treated, Sigma-Aldrich) followed by demineralised water (5.0 mL), concentrated H2SO4 (0.5 mL) and n-butanol (30 mL). The biphasic mixture was stirred and heated to reflux for 3 hours. The mixture was then cooled to ambient temperature, filtered, and the layers separated. The organic phase (28ml) was pale straw coloured and the lower aqueous phase (49ml) was colourless. Analysis of the aqueous layer by HPLC indicated that the monosaccharide glucose was present at a concentration of 0.03% w/v, and xylose at a concentration of 0.01%.

(b) 45mL of the resulting hydrolysate was then added over a period of 60 min to 50% aqueous sodium hydroxide (1.4 mL) at 100-120°C.

(c) The reaction mixture was then cooled to ambient temperature, acidified by the addition of 1 mL of 37% HC1 to achieve a pH <3, made up to 100 mL with demineralised water in a volumetric flask and analysed for lactic acid content by HPLC. The results indicated a yield of 0.014g.

Experiment (vii): Hydrolysis of cellulose at elevated temperature and pressure

(a) To a 100 mL Parr reactor was charged cellulose (1.9869 g, acid treated, Sigma- Aldrich) followed by demineralised water (30.0 mL) and concentrated H2SO4 (0.3 mL). The reactor was sealed and then heated, with stirring to 133°C / 1.5 bar over 30min. The mixture was then cooled to ambient temperature, filtered and washed, yielding a pale straw coloured filtrate (55.5 mL). Analysis by HPLC indicated that the monosaccharide glucose was present at a concentration of 0.06% w/v, and xylose at a concentration of 0.01%.

(b) 40mL of the resulting hydrolysate was then added over a period of 60 min to 50% aqueous sodium hydroxide (1.4 mL) at 100-120°C.

(c) The reaction mixture was then cooled to ambient temperature, acidified by the addition of 1 mL of 37% HC1 to achieve a pH <3, made up to 100 mL with demineralised water in a volumetric flask and analysed for lactic acid content by HPLC. The results indicated a yield of 0.022g.

Experiment (viii): Combined hydrolysis and extraction of cellulose at elevated temperature and pressure

(a) To a 100 mL Parr reactor was charged cellulose (1.9833 g, acid treated, Sigma- Aldrich) followed by demineralised water (30.0 mL), concentrated H2SO4 (0.3 mL) and n- butanol (15 mL). The reactor was sealed and then heated, with stirring to 133°C / 2.5 bar over 30min. The mixture was then cooled to ambient temperature, filtered and washed. The layers were then separated. The organic phase (17 ml) was pale straw coloured and the lower aqueous phase (40 ml) was colourless. Analysis of the aqueous layer by HPLC indicated that the monosaccharide glucose was present at a concentration of 0.06% w/v, and xylose at a concentration of 0.01%.

(b) 40mL of the resulting hydrolysate was then added over a period of 60 min to 50% aqueous sodium hydroxide (1.4 mL) at 100-120°C.

(c) The reaction mixture was then cooled to ambient temperature, acidified by the addition of 1 mL of 37% HC1 to achieve a pH <3, made up to 100 mL with demineralised water in a volumetric flask and analysed for lactic acid content by HPLC. The results indicated a yield of 0.016g.

A comparison of experiments (i) to (iv) with experiments (v) to (viii) shows that the yield of lactic acid was significantly higher when the starting material was a hemicellulosic stream than when it was cellulose-derived material.