WO2015155535A1

WO2015155535A1 - Process for producing lactate

Info

Publication number: WO2015155535A1
Application number: PCT/GB2015/051082
Authority: WO
Inventors: Urvish Rameshchandra PANDYA; Edward Leslie Marshall
Original assignee: Plaxica Limited
Priority date: 2014-04-09
Filing date: 2015-04-09
Publication date: 2015-10-15
Also published as: GB201406368D0

Abstract

A process for producing an alkali metal lactate comprising: a) reacting a stream rich in saccharide with barium hydroxide to produce a first reaction mixture comprising barium lactate; and b) contacting at least a portion of said first reaction mixture with an alkali metal hydroxide to produce a second reaction mixture comprising alkali metal lactate and solid barium hydroxide, wherein the alkali metal is selected from the group consisting of sodium, lithium and potassium.

Description

Process for producing lactate

The invention relates to a process for producing lactate from monosaccharide using barium hydroxide, with direct recovery and reuse of barium hydroxide being possible.

Lactic acid is an important industrial chemical typically prepared from microbial fermentation of carbohydrates. A number of chemical processes for preparing lactic acid from carbohydrates are known. For example, GB 400,413, dating from 1933, describes an improved process for preparing lactic acid or lactates comprising reacting a carbohydrate-containing material with a strong alkali at a temperature of at least 200 °C, preferably at a pressure of at least 20 atmospheres, and recovering the lactic acid so produced by adding sulfuric acid or zinc sulfate to the reaction mixture.

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, biomass is fermented with microorganisms to produce an optically active lactate salt. Companies such as Cargill and Purac operate large-scale fermentation processes for the production of optically active lactic acid, and the patent literature is replete with improvements in such processes.

Recovery of lactic acid from fermentation processes can be challenging and many patent documents relate to lactic acid preparation via fermentation and subsequent lactic acid recovery. For example, US 4,444,881 (Urbas, 1984) describes a process for the recovery of an organic acid (which may be lactic acid) from a fermentation reaction, which comprises converting the acid to its calcium salt, and adding a water-soluble tertiary amine carbonate (which may be prepared by addition of carbon dioxide to a solution or suspension of the tertiary amine in water). US 5,510,526 (Baniel, 1994) claims a process, stated to be an improvement over that of Urbas, for the recovery of lactic acid from a lactate feed solution, comprising the use of an extractant comprising at least one water immiscible trialkylamine having a total of at least 18 carbon atoms in the presence of carbon dioxide at a partial pressure of at least 50 psig (about 3½ atmospheres, 3.4 x 10⁵ Pa). Those processes involve preparation of a complex between the lactate species and an amine.

WO 2012/052703 describes an improved process for the production of a complex of lactic acid and either ammonia or an amine, which does not involve production of lactic acid by fermentation. The process comprises reacting 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. The process of WO2012/052703, which involves preparation of barium salts, has significant advantages over prior art processes. It does, however, have some disadvantages:

specifically, if it is required to recycle the barium, a barium carbonate calcination step is required. Calcination (also referred to as calcining) is a thermal treatment process in absence of air applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. The process of calcination derives its name from its most common application, the decomposition of calcium carbonate (limestone) to calcium oxide (lime) and carbon dioxide. The terms calcination, and calcine (the product of calcination), are typically used regardless of the actual minerals undergoing thermal treatment. Whilst calcination of barium carbonate to barium oxide is feasible, it is not currently widely operated at industrial scale.

We have now found an improved process for the preparation of lactate, which retains the advantages of using barium, but which does not require a barium carbonate calcination step. The present invention provides a technically simple and particularly economic route for regeneration of barium hydroxide, enabling reuse of the barium species. Summary of the invention

The invention provides a process for producing an alkali metal lactate comprising: a) reacting a stream rich in saccharide with barium hydroxide to produce a first reaction mixture comprising barium lactate; and

b) contacting at least a portion of said first reaction mixture with an alkali metal hydroxide to produce a second reaction mixture comprising alkali metal lactate and solid barium hydroxide,

wherein the alkali metal is selected from the group consisting of sodium, lithium and potassium.

Detailed description of the invention

In the process of the invention, a stream rich in saccharide is reacted with barium hydroxide. The saccharide present in said stream may be a mono-, di-, tri-, oligo- or poly-saccharide, with disaccharides and, especially, monosaccharides, being preferred. Preferably, the stream rich in saccharide is a stream rich in monosaccharide. In some preferred embodiments, at least 50 wt % of the saccharides, at least 60 wt% of the saccharides, at least 70 wt % of the saccharides, at least 80 wt % of the saccharides, at least 90 wt % of the saccharides, at least 95 wt % of the saccharides present in said stream rich in saccharides are monosaccharides. Suitable monosaccharides include for example hexose monosaccharides, for example glucose, fructose, psicose, galactose and mannose, and pentose monosaccharides, for example arabinose, xylose, ribose, xylulose and ribulose. In one embodiment, the stream rich in saccharide comprises glucose. In another embodiment, the stream rich in saccharide comprises fructose. In another embodiment, the stream rich in saccharide comprises mannose. In another embodiment, the stream rich in saccharide comprises xylose. Mixtures of saccharides may be present in the stream rich in saccharides. For example, a mixture of two or more

monosaccharides, for example a mixture of glucose and fructose, may be present.

Monosaccharides may be obtained from any known monosaccharide source, for example a higher saccharide such as sucrose, starch, cellulose or hemicellulose. In some embodiments, the stream rich in saccharide may contain a mixture of glucose and fructose (known as invert sugar) obtained from sucrose, for example by enzymatic hydrolysis using a sucrase or invertase, or by heating the disaccharide in the presence of an acidic catalyst such as sulphuric acid, citric acid or ascorbic acid. In some embodiments, the stream rich in saccharide may be glucose obtained by enzymatic hydrolysis (e.g. using an amylase) of starch contained in biomass feedstocks, for example maize, rice or potatoes. In some embodiments, the stream rich in saccharide may contain glucose obtained by hydrolysis of cellulose (e.g. enzymatic hydrolysis using one or more cellulases) contained in biomass feedstocks. In some preferred embodiments the stream rich in saccharide is a hemicellulose hydrolysate stream obtained by subjecting a hemicellulosic feedstock (i.e. a stream comprising hemicellulose and/or hemicellulose-derived oligosaccharides) to hemicellulose hydrolysis conditions. Examples of hemicellulosic feedstocks include black liquor (a byproduct of the Kraft process for production of wood pulp), brown liquor (a byproduct of the sulfite process used for making wood pulp, also known as red liquor, thick liquor and sulfite liquor), and hemicellulosic waste streams produced in processes for producing bioethanol (e.g. processes for producing bioethanol involving fermentation of cellulose hydrolysate). Examples of hemicellulose hydrolysis conditions include treating the hemicellulosic feedstock with acid (e.g. sulphuric acid), contacting with a combination of hemicellulase enzymes (e.g. xylanases and/or mannanases), use of autohydrolysis conditions, use of steam explosion conditions, use of ammonia fibre explosion conditions, or treating with alkali (e.g. sodium hydroxide, barium hydroxide, potassium hydroxide, calcium hydroxide). If barium hydroxide is used as the alkali, this can lead directly to production of barium lactate from the hemicellulosic feedstock.

The stream rich in saccharides may contain components other than saccharides, for example it may include other components of biomass such as lignin or lignin-derived products. Spent chemicals from processing of biomass may, for example, also be present. Water will typically be present. In some embodiments, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt% of the material other than water present in the stream rich in saccharides is saccharide (e.g. monosaccharide).

The reaction between saccharide and barium hydroxide is normally carried out in the presence of water. As discussed above, some sources of saccharide contain water, and such feedstocks may readily be used in the process of the invention. In certain embodiments, the reaction between the saccharide and barium hydroxide may take place in the presence of additional water (i.e. additional to that present in the starting materials). The reaction between the saccharide and barium hydroxide may also, if desired, take place in the presence of one or more organic solvents, for example an oxygenate such as an alcohol, ester, ether, or ketone. However, in a preferred embodiment, the reaction between the saccharide and barium hydroxide does not take place in the presence of an organic solvent (e.g. water may be the only solvent).

Barium hydroxide reacts with saccharide (e.g. monosaccharide) to produce barium lactate. Any form of barium hydroxide may be used, for example anhydrous barium hydroxide, barium hydroxide monohydrate, barium hydroxide octahydrate. Sources of barium hydroxide such as barium oxide may be used in the process of the invention, barium oxide being converted into barium hydroxide in the presence of water. The barium hydroxide generated in situ reacts with the saccharide to produce barium lactate.

The ratio of barium hydroxide to saccharide should be sufficient to effect high conversion of saccharide to barium lactate. For example, when the saccharide comprises glucose, for each mole of glucose there is preferably used at least one mole of barium hydroxide (i.e. the molar ratio of barium hydroxide to saccharide (calculated as monosaccharide) is at least 1 : 1). Excess quantities of barium hydroxide may be used, for example the molar ratio of barium hydroxide to saccharide (calculated as

monosaccharide) may be up to 10: 1. In a preferred embodiment, the molar ratio of barium hydroxide to saccharide (calculated as monosaccharide) is from 1 : 1 to 10: 1, more preferably 1 : 1 to 5 : 1, still more preferably 1 : 1 to 4: 1, especially 1.5 : 1 to 2.5 : 1. The present invention also encompasses molar ratios of barium hydroxide to saccharide (calculated as monosaccharide) that are lower than 1 : 1, although this is not preferred since use of sub-stoichiometric quantities of barium hydroxide will generally lead to lower conversion of saccharide to barium lactate.

The conversion of saccharide to barium lactate may be carried out at ambient temperature, although the reaction is preferably carried out at elevated temperature, for example at a temperature of up to 150 °C. Preferably, saccharide is reacted with barium hydroxide at a temperature of from 50 to 120 °C, more preferably from 70 to 1 10 °C, for example from 75 to 100 °C. In one embodiment, saccharide is reacted with barium hydroxide at 80 °C. In another embodiment, saccharide is reacted with barium hydroxide in water at reflux.

In some preferred embodiments, saccharide (e.g. monosaccharide) in water is added over a period of time to a mixture of barium hydroxide and water that is at elevated temperature, for example at a temperature of from 70 to 1 10 °C. Slow addition of saccharide (e.g. monosaccharide) generally leads to a reduction in the formation of side products during the process of the invention, and leads to an improved conversion of saccharide (e.g. monosaccharide) into barium lactate. Preferably the saccharide (e.g. monosaccharide) in water is added over a period of at least 10 minutes, more preferably at least 30 minutes, still more preferably over at least 1 hour. Preferably the concentration of saccharide in water is less than 4.0M, more preferably in the range of from 0.2 to 2.0 M, most preferably in the range of from 0.5 to 1.5 M.

The reaction of saccharide with barium hydroxide produces a reaction mixture comprising barium lactate. The process typically produces racemic barium lactate.

At least a portion of the first reaction mixture is contacted with an alkali metal hydroxide to produce a second reaction mixture comprising alkali metal lactate and solid barium hydroxide. The alkali metal hydroxide is selected from the group consisting of sodium hydroxide, lithium hydroxide and potassium hydroxide (i.e. the alkali metal is sodium, lithium or potassium). The corresponding alkali metal lactate is produced (i.e. sodium lactate, lithium lactate or potassium lactate). Use of those alkali metal hydroxides in the reaction with barium lactate leads to recovery of solid barium hydroxide in good yield, which may then be recycled to the process if desired. In some preferred

embodiments, the alkali metal is sodium or lithium. In some preferred embodiments, the alkali metal is sodium (i.e. at least a portion of the first reaction mixture is contacted with sodium hydroxide to produce sodium lactate and solid barium hydroxide). In other embodiments, the alkali metal is lithium. In other embodiments, the alkali metal is potassium.

The reaction between barium lactate and alkali metal hydroxide is normally carried out in the presence of water. Depending on the amount of water present during the reaction of barium hydroxide with saccharide, the reaction mixture may be partially concentrated prior to reaction of barium lactate with alkali metal hydroxide. Step b) is preferably carried out at a temperature in the range of from 5 to 150°C, more preferably at a temperature in the range of from 20 to 100°C, still more preferably at elevated temperature, for example a temperature in the range of from 50 to 100°C. In other embodiments, step b) is carried out at ambient temperature.

Preferably, the molar ratio of barium lactate to alkali metal hydroxide is in the range of from 1 :2 to 1 : 10, more preferably of from 1 :2 to 1 :6. The invention also encompasses molar ratios of barium lactate to alkali metal hydroxide that are lower than 1 :2 (e.g. 1 : 1), although this is not preferred, since use of such ratios will generally lead to lower conversion of barium lactate to barium hydroxide.

Following production of alkali metal lactate and barium hydroxide, solid barium hydroxide normally precipitates from the second reaction mixture. Solid barium hydroxide is normally separated from the second reaction mixture, for example by decanting, centrifugation or, preferably, filtration. Where the reaction between alkali metal hydroxide and barium lactate is carried out at elevated temperature, the temperature of the reaction mixture may be reduced (e.g. the reaction mixture may be allowed to cool) prior to filtration. In some embodiments, solid barium hydroxide is produced by precipitation from the second reaction mixture at a temperature in the range of from 5 to 40°C, more preferably from 5 to 20 °C. Depending on the amount of water present during the reaction of barium lactate with alkali metal hydroxide, the reaction mixture may be partially concentrated prior to filtration, to maximise the quantity of solid barium hydroxide obtained, and to minimise the quantity of solid alkali metal salts obtained. The alkali metal lactate produced by the process of the invention is typically racemic.

As discussed above, the present invention provides for regeneration of barium hydroxide, without requiring calcination of barium carbonate. In some embodiments, at least a portion of the barium hydroxide produced in step b) is recycled to the process, facilitating production of further quantities of barium lactate.

In some preferred embodiments, following separation of solid barium hydroxide from the second reaction mixture, at least a portion of the second reaction mixture is contacted 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 third reaction mixture comprising alkali metal carbonate and/or bicarbonate and a complex of lactic acid and either ammonia or an amine. The step of contacting at least a portion of the second reaction mixture with ammonia or an amine and with carbon dioxide, or with the carbonate and/or bicarbonate salt of ammonia or an amine, is typically carried out in the presence of water. In some preferred embodiments, the alkali metal is sodium (i.e. at least a portion of the first reaction mixture is contacted with sodium hydroxide to produce a second reaction mixture comprising sodium lactate and solid barium hydroxide and, following separation of solid barium hydroxide, at least a portion of the second reaction mixture is contacted with an ammonia or an amine and with carbon dioxide, or with the carbonate and/or bicarbonate salt of ammonia or an amine, to produce a third reaction mixture comprising sodium carbonate and/or bicarbonate and a complex of lactic acid and either ammonia or an amine).

Where carbon dioxide is used, it may be added in any suitable form, for example as a solid or, preferably, as a gas.

The amines used include primary, secondary and tertiary amines, of which tertiary amines are preferred. The amines used are preferably alkylamines, most preferably trialkylamines. Examples of suitable trialkylamines include triethylamine,

tripropylamine, tributylamine, tripentylamine and trihexylamine. The amine used may be a single component, or it may be a mixture of amines. Suitably an equivalent amount or an excess of ammonia or amine, based on the alkali metal lactate present, is used. For example, at least one equivalent, up to 10 equivalents, preferably up to 8, more preferably up to 6, still more preferably up to 4, especially 2 equivalents, of ammonia or amine, may be used.

In some embodiments, ammonia or an amine that is at least partially water soluble is used to produce complex. Amines that are at least partially water soluble permit the use of carbon dioxide at low or atmospheric reaction pressures (e.g. by bubbling a slight overpressure of carbon dioxide gas from a pressurised cylinder or other carbon dioxide source into a reaction mixture that is substantially at atmospheric pressure). Accordingly, in some embodiments, a portion of the second reaction mixture is contacted with ammonia or an amine that is at least partially water soluble, and in the presence of carbon dioxide at a pressure of not more than 250 kPa gauge. As defined herein, an amine that is at least partially water soluble has a solubility in water of at least 1 g per litre at 25 °C. Preferably, the amine is an alkylamine that has less than 12 carbon atoms. In one embodiment, the amine has less than 10 carbon atoms. In another embodiment, the amine has less than 9 carbon atoms. Examples of suitable amines include t-butylamine, octylamine, diethylamine, diisopropylamine and triethylamine. In some embodiments, the amine is triethylamine. In other embodiments, ammonia is used.

Where ammonia or an amine that is at least partially soluble in water is used, solid alkali metal carbonate and/or bicarbonate is typically produced by precipitation from the third reaction mixture. The solid alkali metal carbonate/bicarbonate is typically separated from the third reaction mixture, for example by decanting, centrifugation or, preferably, filtration. Water miscible solvents, for example a water miscible alkyl alcohol (e.g. methanol, ethanol, n-propanol, isopropanol), a water miscible ketone (e.g. acetone) or a water miscible ether (e.g. THF, dioxane) may be added to encourage precipitation of alkali metal carbonate/bicarbonate from solution (e.g. sodium carbonate and/or bicarbonate). In some preferred embodiments, the third reaction mixture comprises water and a water miscible alkyl alcohol (e.g. ethanol). In some preferred embodiments, the alkali metal carbonate and/or bicarbonate is sodium carbonate and/or bicarbonate, and the third reaction mixture comprises water and ethanol. Depending on the amount of water present during the production of complex, the reaction mixture may be partially concentrated prior to filtration.

Alternatively, if the complex is to be extracted from the third reaction mixture, it will usually be necessary to add a suitable organic solvent to form a biphasic mixture. Examples of solvents suitable for use with conditions employing the use of ammonia or an amine that is at least partially water soluble are described in US 4,444,881 (Urbas, 1984).

In some embodiments, at least a portion of the second reaction mixture is contacted with an amine that is immiscible with water. Such amines generally have a total of at least 12 carbon atoms. In one embodiment, the amine has at least 18 carbon atoms. In another embodiment the amine has at least 24 carbon atoms. The amine that is immiscible with water preferably has up to 42 carbon atoms, for example the amine may have from 12 to 42 carbon atoms, from 18 to 42 carbon atoms, or from 24 to 42 carbon atoms. Examples of such amines include trihexylamine, triheptylamine, trioctylamine (e.g. tri-(n-octyl) amine, triisooctylamine, tri-(2-ethylhexyl)amine), tridecylamine, tridodecylamine and Alamine 336™. Where at least a portion of the second reaction mixture is contacted with a water-immiscible amine is used, high pressures of carbon dioxide are normally used, e.g. at least 300 kPa gauge, to ensure that good conversion of alkali metal lactate into complex and alkali metal carbonate/bicarbonate is achieved. Where high pressures of carbon dioxide are used, a pressure vessel will typically be used. Preferably the carbon dioxide in the reaction vessel is maintained at a partial pressure of at least 500 kPa gauge and most preferably from 1,000 to 2,000 kPa gauge. In such embodiments, an alcohol/water/hydrocarbon/ water-immiscible amine mixture may typically be employed. As an alternative, if hydrocarbon co-solvents are avoided, production of complex may be carried out using a water-immiscible amine and lower pressures of carbon dioxide (e.g. up to 250 kPa gauge). In such embodiments, an alcohol/water/amine mixture is typically employed.

Where an amine that is immiscible with water is used, separation of complex from alkali metal carbonate/bicarbonate may be achieved by partitioning of the complex into the amine phase of a biphasic water-amine mixture. In order to aid the extraction of the complex into the amine-rich phase, one or more organic solvents may also be added. Examples of suitable solvents are described in US 5,510,526 (Baniel, 1994).

As an alternative to contacting the second reaction mixture containing alkali metal lactate with an amine and carbon dioxide, the second reaction mixture may instead be contacted with the carbonate or bicarbonate salt of ammonia or an amine. For example, an alkylammonium carbonate or bicarbonate such as triethylammonium bicarbonate, or ammonium carbonate, may be added to the first reaction mixture. The carbonate or bicarbonate salt of ammonia or the amine may be added neat, or alternatively the carbonate or bicarbonate salt of ammonia or the amine may be added as a solution.

Suitable solvents include water and aqueous/organic mixtures, for example water/amine mixtures.

The carbonate or bicarbonate salt of ammonia or an amine may, for example, be prepared from ammonia or an amine and carbon dioxide. For example, it may be produced from the addition of carbon dioxide to a solution of ammonia or an amine in water. The resulting solution containing the carbonate or bicarbonate salt of ammonia or the amine may then be contacted with the second reaction mixture comprising alkali metal lactate.

The product formed by contacting the second reaction mixture comprising alkali metal lactate with ammonia or an amine and with carbon dioxide is referred to herein as a complex. In such a complex, both ion pair and hydrogen bond interactions may occur between the lactic acid and ammonia or the amine. The precise form of the complex will depend on the environment in which it is found. The complex may be regarded as a partly ionised liquid or, alternatively, as a simple salt between the acid and ammonia or the amine, existing in equilibrium with free acid and ammonia or amine. For example, in the case of tri(n-octyl)amine, tri(n-octyl)ammonium lactate may be produced. Since the barium lactate and alkali metal lactate produced by the process is typically racemic, the complex will typically be racemic also.

In some embodiments, where alkali metal carbonate and/or bicarbonate is produced (for example following contacting of at least a portion of the second reaction mixture with ammonia or an amine that is at least partially water soluble and with carbon dioxide, and following filtration to separate solid alkali metal carbonate and/or bicarbonate) at least a portion of the alkali metal carbonate and/or bicarbonate may be reacted with an alkaline earth metal hydroxide to produce alkali metal hydroxide and solid alkaline earth metal carbonate. The alkaline earth metal is selected from the group consisting of calcium and magnesium (i.e. the alkaline earth metal hydroxide is calcium hydroxide or magnesium hydroxide, and the corresponding alkaline earth metal carbonate is produced - calcium carbonate or magnesium carbonate). Use of those alkaline earth metal hydroxides in the reaction with the alkali metal carbonate and/or bicarbonate leads to regeneration of alkali metal hydroxide and recovery of solid alkaline earth metal carbonate in good yield. The alkali metal hydroxide may then be recycled to the process if desired. In some preferred embodiments, the alkaline earth metal is calcium (i.e. the alkaline earth metal hydroxide is calcium hydroxide, and the alkaline earth metal carbonate is calcium carbonate). In other embodiments, the alkaline earth metal is magnesium. In some preferred

embodiments, the alkali metal is sodium and the alkaline earth metal is calcium (i.e. at least a portion of the first reaction mixture is contacted with sodium hydroxide to produce a second reaction mixture comprising sodium lactate and solid barium hydroxide and, following separation of solid barium hydroxide, at least a portion of the second reaction mixture is contacted with an ammonia or an amine and with carbon dioxide, or with the carbonate and/or bicarbonate salt of ammonia or an amine, to produce a third reaction mixture comprising solid sodium carbonate and/or bicarbonate and a complex of lactic acid and either ammonia or an amine and, following separation of solid sodium carbonate and/or bicarbonate, at least a portion of the sodium carbonate and/or bicarbonate is reacted with calcium hydroxide to produce sodium hydroxide and calcium carbonate). The reaction between alkali metal carbonate/bicarbonate and alkaline earth metal hydroxide is normally carried out in the presence of water.

The reaction between alkali metal carbonate/bicarbonate and alkaline earth metal hydroxide may be carried out at room temperature, although the reaction is preferably carried out at elevated temperature, for example at a temperature of up to 150 °C. More preferably, the reaction is carried out at a temperature of from 5 to 100 °C, still more preferably from 5 to 90°C. In some embodiments, the reaction is carried out at reflux.

Preferably, the molar ratio of the combined amount of alkali metal carbonate and/or bicarbonate to alkaline earth metal hydroxide is in the range of from 0.8: 1 to 1.5: 1, more preferably from 1 : 1 to 1.2: 1.

Following production of alkaline earth metal carbonate and alkali metal hydroxide, solid alkaline earth metal carbonate normally precipitates from the reaction mixture. The solid alkaline earth metal carbonate is typically separated from the alkali earth metal hydroxide, for example by decanting, centrifugation or, preferably, filtration. In some embodiments the reaction mixture containing alkaline earth metal carbonate and alkali metal hydroxide is filtered at elevated temperature (e.g. at a temperature of at least 40 °C, at least 50 °C, at least 60 °C or at least 70 °C). Depending on the amount of water present during the reaction of alkali metal carbonate/bicarbonate with alkaline earth metal hydroxide, the reaction mixture may be partially concentrated to maximise the quantity of solid alkaline earth metal salt obtained, and to minimise the quantity of solid alkali metal salts obtained.

In some embodiments, at least a portion of the alkali metal hydroxide produced by reacting alkali metal carbonate and/or bicarbonate with alkaline earth metal hydroxide is recycled to the process, facilitating production of further quantities of alkali metal lactate from barium lactate.

The alkaline earth metal carbonate produced by the process may optionally be recycled. For example, where the alkaline earth metal carbonate is calcium carbonate, the calcium carbonate may be converted to calcium oxide by calcination. As discussed above, calcination is a thermal treatment process in the absence of air applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. Unlike barium carbonate calcination technology, industrial scale processes for calcination of calcium carbonate to calcium oxide are well-established, and are commonly operated in chemical plants. The calcination process normally takes place at temperatures below the melting point of the product materials. Calcination may be carried out in furnaces or reactors (sometimes referred to as kilns or calciners) of various designs including shaft furnaces, rotary kilns, multiple hearth furnaces, and fluidized bed reactors. The calcium oxide produced may be converted to calcium hydroxide in the presence of water (e.g. by reacting with water). In some embodiments, at least a portion of the calcium hydroxide is recycled to the process.

The alkali metal lactate or complex produced may be converted into further useful downstream products by routine methods. Accordingly, the invention also provides a process for the production of lactic acid, alkyl lactate, oligomeric lactic acid, lactide, alkyl lactyllactate or polylactic acid, which comprises producing alkali metal lactate or producing complex according to the invention; and converting at least a portion of the alkali metal lactate or the complex into lactic acid, alkyl lactate, oligomeric lactic acid, lactide, alkyl lactyllactate or poly-lactic acid. Unless a resolution step is carried out, the downstream products will typically be racemic also.

For example, lactic acid may be produced by reacting alkali metal lactate with an acid, such as hydrochloric acid or sulphuric acid. Alternatively, where complex is produced by contacting at least a portion of the second reaction mixture with ammonia or an amine that is at least partially water soluble and where solid barium carbonate is separated from complex by filtration, lactic acid may be obtained by heating the complex (e.g. by distilling off amine and/or water and/or optional co-solvent). As a further example, following separation of an amine-rich phase containing complex from the alkali metal carbonate and/or bicarbonate, lactic acid may be obtained from the amine-rich phase by distillation.

Alkali metal lactate may also be converted into alkyl lactate. For example, alkali metal lactate may be converted into complex as described above, and the complex may then be converted into alkyl lactate, for example by heating the complex to remove ammonia or amine, and further heating in the presence of an alkyl alcohol (e.g. ethanol, n-propanol, isopropanol, n-butanol) to produce the alkyl lactate. As discussed above, the alkali metal lactate and complex produced by the process of the invention will typically be racemic. 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).

Alkali metal lactate may also be converted into oligomeric lactic acid, for example by converting the alkali metal lactate into lactic acid or alkyl lactate as described above, and by heating the lactic acid or alkyl lactate, and removing water and/or alcohol. Complex may also be converted into oligomeric lactic acid, for example by heating the complex and removing water and amine or ammonia.

Alkali metal lactate and/or complex may also be converted into lactide, a cyclic dimer of lactic acid that is itself useful in the production of polylactic acid. For example, alkali metal lactate and/or complex may be converted 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. As discussed above, the alkali metal lactate and/or complex produced by the processes described above will typically be racemic. As a result, 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.

Alkali metal lactate and/or complex may be converted into alkyl lactyllactate, for example by conversion into lactide, 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.

Alkali metal lactate and/or complex may also be converted into polylactic acid, for example by conversion 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.

The following examples illustrate the invention.

Example 1 - Production of alkali metal (sodium) lactate from monosaccharide with regeneration of barium hydroxide A 100 mL flask was charged with barium hydroxide octahydrate (2.0 molar equivalents with reference to the sugar used) and the solid was heated to 100 ± 2 °C to form a solution. A solution of monosaccharide (0.4 M, 50 mL, 1.0 molar equivalents) was then added over a period of 20 minutes with stirring, whilst maintaining the temperature at approximately 100 °C. After the addition was complete the reaction was allowed to cool to ambient temperature. Barium lactate content was determined by liquid chromatography analysis, following acidification of samples taken from the reaction mixture.

Sodium hydroxide (2.0 - 6.0 molar equivalents) was then added to the reaction mixture. The reaction mixture was then cooled to 5 - 10 °C for two hours. The resulting precipitate was separated by filtration, washed with cold water (50 mL) and dried at 50 °C for 18 hours. Barium recovery (%) was calculated from the dry mass of the solid and the filtrate was analysed for residual barium content by flame photometry.

In addition, a 25 mg sample of solid was added to 2 mL water, the pH was tested and found to be 14. Furthermore, a 1 g sample of the solid was made up to 100 mL in a volumetric flask containing 1 mL hydrochloric acid. A clear solution resulted. Analysis of the solution by HPLC indicated no detectable levels of lactic acid in the solid sample.

Subsequently, a 100 mL flask was charged with a 3.45 g portion of the recovered solid material from experiment #1 above and was used in a fructose conversion experiment analogous to that described above (but with quantities of the other reagents/solvent being based on the solid material being anhydrous barium hydroxide, and with the concentration of the fructose solution being 0.2 M). A lactic acid selectivity of 65.8% was determined by HPLC analysis, which is within the range expected for conversion of fructose to barium lactate using barium hydroxide, indicating that the barium hydroxide produced was suitable to be recycled to a process of this nature. Example 2 - Production of sodium carbonate and complex from sodium lactate

To 50 mL sodium lactate solution, triethylamine (50 mL) and IPA (50 mL) were added at ambient temperature. The mixture was stirred at 400 rpm and C0₂ (g) was bubbled through the reaction mixture at ambient temperature for 3 hours. The resulting Na₂CC"3 precipitate was filtered and dried at 50 °C for 18 hours. The weight of dry Na₂C03 was 5.3 g (66.3% recovery).

Example 3 - Production of sodium carbonate and complex from sodium lactate

A 20 ml aqueous solution containing sodium lactate (4.7 g, 42 mmols) and sodium hydroxide (1.6 g, 40 mmols) was stirred at room temperature for 60 minutes with a mixture of n-butanol : trioctylamine pre-saturated with water (2: 1 ratio by volume, 80 mL combined volume of alcohol and amine, 100 mL total reaction mixture volume) whilst bubbling C0₂ (g) through the mixture at a rate of 65 mL/min. A precipitate of sodium carbonate gradually formed and, once the C0₂ flow was terminated, the precipitate was filtered off under vacuum. The filtrate then separated on standing into a more dense aqueous layer (less than 10 mL) and a less dense organic phase. The concentration of lactic acid remaining in the aqueous layer was determined by acidification and analysis by liquid chromatography. Extraction efficiency into the organic layer was 77.1%.

Example 4 - Production of sodium carbonate and complex from sodium lactate

50 mL of an aqueous solution of sodium lactate (2 M, 100 mmoles) and sodium hydroxide (2 M, 100 mmoles) was added to ethanol (50 mL) and stirred at room temperature. Ammonium carbonate (10.57 g, 110 mmoles) was added resulting in a fine, white precipitate. The precipitate was filtered off under vacuum and dried in an oven at 50 °C overnight to yield a mass of dry solid equivalent to a 95.5% recovery of sodium carbonate. Analysis of the solid indicated the presence of 3 % of lactate (assumed to be sodium lactate). Example 5 - Production of sodium hydroxide from sodium carbonate

To a mixture of sodium carbonate (10 g), barium carbonate (1.0 g) and calcium hydroxide (7.68 g) was added water (40 mL). The resulting suspension was stirred and heated in an oil bath set to 100 °C (pot temperature 85 - 90 °C) for five hours. The reaction mass was filtered hot and washed with hot water (2 x 40 mL). The resulting solid was dried in oven at 50 °C for 18 hours and weighed (10.98 g). The filtrate was titrated for sodium hydroxide (5.25 %) and sodium carbonate (not detected) content which corresponds to a causticisation efficiency of 83.5%.

Example 6 - Production of alkali metal (lithium, potassium) lactate from

monosaccharide with regeneration of barium hydroxide To a 100 mL flask was charged barium hydroxide octahydrate (2.0 molar equivalents based on the sugar used). The solid was heated to 100 ±2 °C (to form a solution). A solution of sugar (0.4M, 50 mL, 1 equivalent) was then added to the hot Ba(OH)₂ over a period of 20 minutes. After the addition was complete the reaction was allowed to cool to ambient temperature and alkali metal hydroxide (6.0 equivalents with reference to the sugar used) was added. The reaction mixture was then cooled to 5 - 10 °C for 2 hours. The Ba(OH)₂ precipitate was filtered, washed with cold water (50 mL) and dried at 50 °C for 18 hours. The filtrate was analysed for residual barium content by flame photometry.

Example 7 - Production of lithium carbonate and complex from lithium lactate

To the lithium lactate filtrate obtained in Example 4, experiment #2, above, was added ammonium carbonate (3 molar equivalents). A suspension formed, the mixture was stirred for 40 minutes at ambient temperature and filtered. The solid obtained was washed with water (50 mL) and dried at 50 °C for 18 hours to afford 1.98g of solid.

EtOH / THF was added to the filtrate following removal of the solid. A further quantity of solid material was obtained.

Example 8 - Production of lithium carbonate and complex from lithium lactate

50 mL of an aqueous solution containing lithium lactate (0.52 M, 26 mmoles) and lithium hydroxide (1 M, 50 mmoles) was stirred at room temperature. Ammonium carbonate (4.02 g, 41.8 mmoles) was added which dissolved fully. Ethanol (50 mL) was added resulting in the immediate formation of a fine, white precipitate. The precipitate was filtered off under vacuum and dried in an oven at 50 °C overnight to yield a mass of dry solid equivalent to a 85.8% recovery of lithium carbonate. Analysis of the solid indicated the presence of 4.8 % of lactate, assumed to be lithium lactate.

Example 9 - Production of potassium carbonate and complex from potassium lactate

To the potassium lactate filtrate obtained in Example 4, experiment #1, above, was added triethylamine (20 mL) and THF (30 mL). Carbon dioxide gas was bubbled through the mixture for 2 hours with stirring. The resulting suspension was filtered and the solid was dried at 50°C overnight to afford 1.01 g solid which effervesced on treatment with hydrochloric acid (assumed to be potassium carbonate).

Claims

1. A process for producing an alkali metal lactate comprising:

a) reacting a stream rich in saccharide with barium hydroxide to produce a first reaction mixture comprising barium lactate; and

2. A process as claimed in claim 1, wherein at least a portion of the barium hydroxide in the second reaction mixture is recycled to the process.

3. A process as claimed in any preceding claim, wherein the wherein the stream rich in saccharide is a stream rich in monosaccharide.

4. A process as claimed in any preceding claim, wherein the molar ratio of barium hydroxide to saccharide, calculated as monosaccharide, is in the range of from 1 : 1 to 5: 1.

5. A process as claimed in any preceding claim, wherein saccharide is reacted with barium hydroxide at a temperature in the range of from 70 to 110°C.

6. A process as claimed in any preceding claim, wherein the alkali metal is sodium.

7. A process as claimed in any preceding claim, wherein the molar ratio of barium lactate to metal hydroxide is in the range of from 1 : 1 to 1 : 10.

8. A process as claimed in any preceding claim, wherein solid barium hydroxide is produced by precipitation from the second reaction mixture at a temperature in the range of from 5 to 40°C.

9. A process as claimed in any preceding claim, wherein solid barium hydroxide is separated from the second reaction mixture by filtration.

10. A process as claimed in any preceding claim, wherein, following separation of solid barium hydroxide from the second reaction mixture, at least a portion of the second reaction mixture is contacted 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 third reaction mixture comprising alkali metal carbonate and/or bicarbonate and a complex of lactic acid and either ammonia or an amine.

11. A process as claimed in claim 10, wherein the alkali metal is sodium.

12. A process as claimed in claim 10 or claim 11, wherein at least a portion of the second reaction mixture is contacted with ammonia or an amine that is at least partially water soluble.

13. A process as claimed in claim 12, wherein the carbon dioxide pressure is not more than 250 kPa gauge.

14. A process as claimed in claim 12 or claim 13, wherein solid alkali metal carbonate and/or bicarbonate is produced by precipitation from the third reaction mixture.

15. A process as claimed in claim 14, wherein the third reaction mixture comprises water and a water-miscible alkyl alcohol.

16. A process as claimed in claim 14 or claim 15, wherein solid alkali metal carbonate and/or bicarbonate is separated from the third reaction mixture by filtration.

17. A process as claimed in claim 16,wherein at least a portion of the alkali metal carbonate and/or bicarbonate is reacted with an alkaline earth metal hydroxide to produce alkali metal hydroxide and alkaline earth metal carbonate, and wherein the alkaline earth metal is selected from the group consisting of calcium and magnesium.

18. A process as claimed in claim 17, wherein the alkaline earth metal is calcium.

19. A process as claimed in claim 18, wherein the alkali metal is sodium.

20. A process as claimed in any one of claims 17 to 19, wherein at least a portion of the alkali metal carbonate and/or bicarbonate is reacted with alkaline earth metal hydroxide at a temperature in the range of from 5 to 90 °C.

21. A process as claimed in any one of claims 17 to 20, wherein at least a portion of the alkali metal hydroxide produced by reacting alkali metal carbonate and/or bicarbonate with alkaline earth metal hydroxide is recycled to the process.

22. A process for the production of lactic acid, alkyl lactate, oligomeric lactic acid, lactide alkyl lactyllactate or poly-lactic acid, which comprises producing alkali metal lactate as defined in any one of claims 1 to 9 or producing complex as defined in any one of claims 8 to 19; and converting at least a portion of the alkali metal lactate or the complex into lactic acid, alkyl lactate, oligomeric lactic acid, lactide, alkyl lactyllactate or polylactic acid.