WO2015092425A1

WO2015092425A1 - Manufacture of lactic acid

Info

Publication number: WO2015092425A1
Application number: PCT/GB2014/053784
Authority: WO
Inventors: Kris WADROP
Original assignee: Krew Environmental Limited
Priority date: 2013-12-20
Filing date: 2014-12-19
Publication date: 2015-06-25
Also published as: GB201322785D0

Abstract

The present invention relates to a novel method for the production of substantially racemic lactic acid, and derivatives thereof. More particularly, the invention relates to a novel method for the production of substantially racemic lactic acid, and derivatives thereof, by the fermentation of biomass material. In particular, the biomass material may comprise solids and may be derived from municipal and/or commercial sources of organic waste. The fermentation reaction preferably takes place in a membrane bioreactor. The present invention also relates to the enantiomeric separation of substantially racemic lactic acid, and derivatives thereof.

Description

Manufacture of Lactic Acid

Field of the Invention

The present invention relates to a novel method for the production of substantially racemic lactic acid, and derivatives thereof.

More particularly, the invention relates to a novel method for the production of substantially racemic lactic acid, and derivatives thereof, by the fermentation of biomass material. In particular, the biomass material may comprise solids and may be derived from municipal and/or commercial sources of organic waste. The fermentation reaction preferably takes place in a membrane bioreactor.

The present invention also relates to the enantiomeric separation of substantially racemic lactic acid, and derivatives thereof.

Substantially racemic lactic acid shall include a mixture that has equal amounts D- and L- enantiomers, as well as mixtures which approach equal amounts of D- and L- enantiomers, but may generally comprise mixtures in which there is an enantiomeric excess of one of the D- or L- enantiomers.

Background to the Invention

Lactic acid is an important building block for the chemical and pharmaceutical industries, for example, in the manufacture polylactic acid (PLA).

In 2011 the global production capacity of bioplastics was 1.2 million mt, this compares with overall global plastic production of 280 million mt (2010). However demand for bioplastics is growing and is facilitated by the increasing availability of sophisticated bioplastic materials and products in the market.

One of the most significant commercially available bioplastics is polylactic acid (PLA). Polylactic acid is useful in replacing conventional polymers, such as polyethylene terephthalate (PET), for example in the fabrication of food and beverage containers. PLA is of particular interest because polylactic acid can be recycled by depolymerisation back to the monomer facilitating repeated recycling and re-use.

l Lactic acid is chiral and can form two stereo isomers L- and D- (also referred to as S- and R). To date the PLA market has developed through polymerisation of the L- isomer to poly-L-lactic acid (referred to as PLLA). However, PLLA has a number of inherent flaws, including thermal instability above 60°C, primarily due to its amorphous structure. Temperature instabilities in PLLA can be overcome by blending small quantities (up to 10% w/w) of poly-D-lactic acid (PDLA) into the PLLA, the resultant polymer forms a more crystalline structure which exhibits significantly enhanced thermal properties. This enhanced blended polymer is called PDLLA. This approach requires greater quantities of PDLA, and consequently pure D-lactic acid, than are currently manufactured, since conventional fermentation technologies principally generate L-lactic acid with little D-lactic acid being formed.

As already mentioned, lactic acid is chiral and can exist as the L-enantiomer, S-lactic acid; and the D-enantiomer, R-lactic acid. Lactic acid also forms a cyclic dimer, lactide (3,6- dimethyl-1 ,4-dioxan-2,5-dione). Lactide is also chiral and exists in twoenantiomeric forms, S,S-lactide and R, R-lactide. A third diastereomeric form also exists, R,S-lactide, which is sometimes also referred to as meso-lactide.

Polylactic acid is typically prepared in two steps in which lactic acid is first dehydrated to produce lactide and then the lactide is polymerised under carefully controlled conditions to ensure that long polymer chains are produced in preference to shorter oligomers. Since, as explained above, the most readily available source of lactic acid is L-lactic acid, the lactide employed commercially to date has been S,S- lactide and the polymer produced poly-L-lactic acid (PLLA) (also known as poly-S- lactic acid).

Lactic acid is typically made by the microbial fermentation of monosaccharides derived from crops such as maize and other natural products. Conventional fermentation technologies have specifically been developed to principally generate L- lactic acid with little D-lactic acid being formed.

Conventional lactic acid production processes require the input of substantially, pure carbohydrate containing feedstocks, such as corn syrup. Such feedstocks are necessarily free of solids. The conversion of less pure feedstocks to lactic acid cannot be achieved using existing lactic acid production processes. In particular, feedstocks which comprise solid material, such as municipal solid waste (MSW), cannot be used in conventional processes. One reason for this is that pH control of the conventional processes involves the addition of calcium carbonate. This base reacts with the lactic acid formed in the fermentation to form a base addition salt (typically calcium lactate) as a solid. By this means the lactic acid is recovered from the fermentation vessel. If solid materials derived from the impure feedstock are also present, these are recovered along with the calcium lactate, causing contamination, reduction of yields and additionalpurification steps, thus lowering the practicality and efficiency of the process.

Furthermore it is difficult to remove solid material from a waste stream as any conventional means of removing solids from the waste stream would also remove substantial amounts of the carbohydrates which are intended to be converted into lactic acid, substantially reducing the carbon efficiency of the process.

A further issue with low purity feedstocks, is that they will frequently have partially

decomposed during the time in which the solid waste is stored at the source (e.g. for MSW in a domestic waste bin), transported, sorted, and transferred to the lactic acid production plant. This partial decomposition would generate large amounts of byproducts including a range of carboxylic acids which are difficult to separate from the carbohydrate content of the feedstock using conventional means. These impurities can include either enantiomer of lactic acid which is undesirable when high enantiopurity lactic acid is desired as an end product.

One of the industry leaders (Purac) has developed a genetically engineered microbial system that produces high purity D-lactic acid in fermentation. This has led to a product range that is referred to as poly-DL-lactide (PDLLA), with increased thermal stability (up to 180°C), enabling PLA to compete with thermally stable plastics, such as PET

(polyethylene terephthalate). However, high volume production of D-lactic acid, using genetically modified microorganisms, is challenging due to stability of the organism and the ability to retain enantiomeric purity.

An increased demand for PDLA and D-lactic acid could be met by preparing racemic lactic acid and subsequently separating the enantiomers.

Plaxica Limited has developed and demonstrated a technology that can separate the D-LA and L-LA. This is generally disclosed in Plaxica's International patent application No. WO 2013/01 1298. If successful, this technology gives rise to a significant demand for racemic lactic acid. But current technology provides only a non-biological route to racemic lactic acid, using a metal catalyzed synthetic method and /or aqueous strong base.

By developing a fermentation process able to produce a substantially racemic lactic acid, or a mixture of the D- and L- enantiomers of lactic acid, it will enable the PLA industry to produce high volumes of PDLLA by, for example, biologically retrofitting existing L-LA production units and applying the aformentioned Plaxica technology, to produce two optically pure streams, one D-lactic acid and the other L-lactic acid, which can then be polymerised and blended to form PDLLA.

An objective of certain embodiments of the present invention is to provide a

microbiological method of manufacturing substantially racemic lactic acid from biomass material. The lactic acid can then be separated to provide two pure enantiomers, D- and L- lactic acid. Thus, the D- and L- lactic acid enantiomers can be polymerised and blended to form complex crystalline structures which offer new opportunities for the bioplastics industry to challenge historical petro-plastic markets in higher temperature applications.

A further object of the present invention is to provide a method for the conversion of lignocellulosic waste biomass material, e.g. Municipal Solid Waste, to commercially useful chemical products, specifically lactic acid and more specifically substantially racemic lactic acid, i.e. a mixed stream of L- and D- lactic acid isomers as defined herein.

Summary of the Invention

Thus in a first aspect of the invention is provided a process for the manufacture of substantially racemic lactic acid, or a derivative thereof, said process comprising:

fermenting a slurry of biomass material comprising solids in a membrane bioreactor using at least one microbial strain that converts carbohydrates into substantially racemic lactic acid; and recovering the substantially racemic lactic acid, or a derivative thereof, from or downstream from the membrane.

A membrane bioreactor is an apparatus that allows the fermentation medium to be in contact with a microfiltration or ultrafiltration membrane. The term membrane bioreactor as used in this specification is not intended to be limited to any particular product. It is intended to mean any apparatus that comprises: a vessel or combination of vessels (and optionally conduits) which are suitable for conducting a fermentation process and which are in fluid communication with the membrane; and the membrane.

The inventors have found that lactic acid can be produced from waste materials.

Surprisingly, the fermentation can be successful even with low purity feedstocks, including those comprising solids. The presence of impurities such as proteins, fats, oils, ashes and other solids are tolerated. The obtained lactic acid can be recovered from the fermentation vessel as it passes through the membrane of the bioreactor, preventing the contamination with solids. The membrane serves a number of purposes. It concentrates the solid portions of the waste allowing them to be recovered efficiently, provides a reasonably pure product stream and maintains the population of microbes in the bioreactor. Suitable micro- and ultrafiltration membranes are commercially available and well-known to the person skilled in the art.

It may be that a base is added to the fermentation step to control the pH of the fermentation broth. The base will typically be selected from those that produce lactate salts with high aqueous solubility. Examples include bases which form alkali metal salts, such as sodium salts, of lactic acid and bases which form ammonium salts of lactic acid. Examples include hydroxide, carbonate and bicarbonate salts of alkali ion and ammonium. Specific examples include, potassium hydroxide, sodium hydroxide, ammonium hydroxide, potassium carbonate, sodium carbonate and sodium bicarbonate. The base will typically be added during the course of the fermentation. Thus it may be added portionwise or continuously. The base may be added at a predetermined rate or it may be added in response to changes in the fermentation broth pH..

Thus, according the present invention may provide a process for the manufacture of substantially racemic lactic acid, or a derivative thereof, said process comprising the fermentation of biomass material using one or more of a microbial strain which selectively produces a substantially racemic lactic acid, or a derivative thereof.

It will be understood that the term derivative, in respect of lactic acid shall include, inter alia, the cyclic dimer of lactic acid, e.g. lactide; the acyclic dimer, e.g.

lactyllactic acid; and esters of lactic acid and/ or lactyllactic acid. Thus, according to one aspect the invention the fermentation of biomass material is used in the manufacture of lactic acid, or an ester thereof.

The term ester used herein will be understood by the person skilled in the art, and shall include, but shall not be limited to aliphatic esters, i.e. an ester formed with an aliphatic alcohol, such as, /^'-propyl, n-propyl, n-butyl, methyl, ethyl etc.

The feedstock used in the process could be a mixture of commercial and public

biodegradable waste (Municipal Solid Waste (MSW)) from a range of sources or agricultural by-products such as wheat/rice straw, corn cobs/stover and bagasse. The feedstock will be pretreated and conditioned on site using a range of technologies to produce a stream containing fermentable substrate (carbohydrates) and nutrients to support microbial growth. The fermentation media will be sterilized prior to inoculation with lactic acid producing microorganisms. Typically the sterilization will occur coincidentally during the thermal hydrolysis process:

(C6H10O5)n + nH20 » nCnH1206

Starch/cellulose Glucose

C12H22011 + H20 ► C6H1206 + C6H1206

Sucrose Glucose Fructose

(C5H804)n + nH20 — * nC5H10O5

Hemicellulose Xylose

The sterile media is fed to the fermentation section of the process plant. In parallel with feed preparation the seed culture (innoculum) will be prepared. This is the growth of the appropriate bacterium culture from the initial working stock through various stages of growth to generate a culture population sufficient in size to sustain the industrial fermentation process.

The substrate is fed to the fermentation unit in a controlled manner to maximise utilization of the hydraulic volume in the fermentation unit. Once in the fermentors the available sugars are converted to lactic acid: C6H1206 + H20 — C3H603

Lactic acid

As the system is designed to be a homolactic fermentation there will be very little off-gas from the fermentation.

As the feedstock stream is a derived from waste and by-product biomass it contains solids (typically between 2-6% w/w) which are insoluble in the substrate and soluble carbohydrates that are typically in the range 6-10%, with a specific target of 8%.

The fermentation system is a combination of residence time in a conventional anaerobic fermentation vessel working in series with a membrane bioreactor system e.g. Koch

Membrane Systems HFK Spiral Wound ultrafiltration systems or similar.

Figure 1 is a block diagram showing one possible way of performing the process of the present invention.

The fermentation system works under chemostatic conditions with the carbon source being the rate limiting component in the system. PH is controlled using a suitable alkali that produce soluble lactate salts (no precipitation is desired) that will pass through the membrane.

Solids enter the fermentation system in the substrate, typically at concentrations between 2- 8% w/w, more typically 4%. As material is recirculated around the filter the solids

concentration in the system is increased to circa 30% w/w. Solids are allowed to settle in the fermenter and are removed from the system using augurs, or similar devices capable of transporting dense slurries.

Following removal of the solids (circa 30% dry weight) from the fermentation system they are pressed to further deliquor them, typically to a dry weight circa 60%.

The fermentation liquor that passes through the filtration membrane is effectively solid free. This solution will typically be around 8% lactic acid salts plus the salts of other carboxylic acids that were in the system. At some part of the process the lactic acid must be

concentrated to reduce the energy demands in the equipment, by concentrating this stream it effectively reducing the size of the downstream process equipment. The mixed carboxylic acid stream (lactic + others) can be concentrated through conventional multi-effect evaporation (application of heat and vacuum that reuses heat within the system a number of times to minimise the overall energy footprint - known Art). Typically the stream will leave the evaporators between 60-80% w/w carboxylic acid salts.

The carboxylic acids are regenerated by reacting the salt stream with a mineral acid, typically in a system pH <2. Acids that could be used include sulphuric, nitric and hydrochloric.

Following regeneration of the lactic acid the stream can be purified in a number of ways:

1. Esterification of the crude, acidified stream:

a. A stoichiometric excess (to the carboxylic acid groups present) of alcohol is added to the system (most probably ethanol, n-/iso-propanol or n-butanol);

b. The system will be catalyzed by the residual acid present from the salt metathesis; c. Using a combination of temperature (100-250C) and pressure (0.05-0.5 bara) the system can be esterified (would target 100-150C at circa 0.1-0.2 bara);

i. Initially the excess water in the system is boiled off using the alcohol to form an azeotrope with the water and remove it from the system;

ii. The alcohol then acts as the mobilizing solvent for the system;

iii. The alcohol and carboxylic acids then react to form alkyl esters;

iv. The esters are then distilled in a fractionating system to separate the various components. The operating conditions of the system are dictated by the alcohol used earlier in the process however the column would operate in the range 75-150C at a pressure <0.1 bara.

d. The lactate ester can be sold directly into the solvent market as-is, or the lactic acid can be regenerated through a reactive hydrolysis column:

1. The lactate ester is introduced into the middle of a distillation column that is being fed steam at a lower entry point than the ester;

ii. The ester hydrolyses in the presence of high concentrations of water at elevated temperature (circa 150-200C);

iii. The water is removed from the system as an azeotrope with the alcohol;

iv. The lactic acid falls to the bottom of the column where it is recovered;

2. Additional salt metathesis prior to esterification and fractional distillation: a. Due to the other soluble impurities that may have passed through the filter membrane it may be necessary to purify the carboxylic acid stream

i. Once the carboxylic acids have been regenerated in the system introduce calcium carbonate, or similar calcium compound that will react with the carboxylic acids and form insoluble calcium carboxylates;

ii. Recover the solid precipitate through a suitable filtration mechanism;

iii. Re-suspend the solid calcium salts in a clean acidic system with pH<2 (using a mineral acid such as sulphuric acid - resultant salt needs to be insoluble);

iv. Filter out the resultant solids leaving a mildly acidic stream of carboxylic acids;

v. If, due to the presence of soluble proteins, the evaporators foul significantly during the earlier evaporation process, the evaporation stage could be moved to this point in the process; b. Add a stoichiometric excess (to the carboxylic acid groups present) of alcohol is added to the system (most probably ethanol, n-/iso-propanol or n-butanol);

c. The system will be catalyzed by the residual acid present from the salt metathesis; d. Using a combination of temperature (100-2500) and pressure (0.05-0.5 bara) the system can be esterified (would target 100-1500 at circa 0.1-0.2 bara);

ii. The alcohol then acts as the mobilizing solvent for the system;

iii. The alcohol and carboxylic acids then react to form alkyl esters;

iv. The esters are then distilled in a fractionating system to separate the various components. The operating conditions of the system are dictated by the alcohol used earlier in the process however the column would operate in the range 75-1500 at a pressure <0.1 bara. e. The lactate ester can be sold directly into the solvent market as-is, or the lactic acid can be regenerated through a reactive hydrolysis column:

i. The lactate ester is introduced into the middle of a distillation column that is being fed steam at a lower entry point than the ester;

ii. The ester hydrolyses in the presence of high concentrations of water at elevated temperature (circa 150-2000);

iii. The water is removed from the system as an azeotrope with the alcohol;

iv. The lactic acid falls to the bottom of the column where it is recovered; The resultant stillage and other liquid streams taken from the process are sent directly to an anaerobic digestion (AD) plant. Any remaining unfermented sugars and available biomass is digested to form biogas. The biogas is used as a fuel at the site co-generation facility

(combined heat and power). The aqueous discharge from the AD process is sent to the waste water treatment plant (WWTP) for further processing prior to recycling the water. The biomass sludge from the AD plant is harvested and removed from site as a biocompost.

To maximise energy efficiency various streams within the process interchange energy to minimise the external heat requirements.

The entire plant is designed to minimise the potential of a bacterial infection as the fermenters run under controlled environments. The plant is operated using the philosophy of exclusion from the fermenters and sterilisation of the media, effectively controlling all potential sources of microbial infection to the fermentation vessel.

As the anaerobic fermenters are vessels with significant hydraulic capacity (>200 m3) they are effectively engineered to low-pressure storage tank engineering standards. To ensure the vessels are economic to construct they are carbon steel vessels lined with a polymer ensuring a smooth internal coating resistant to both fermentation conditions and cleaning media.

To reduce the potential of an infection and resulting decreases in productivity the plant is equipped with a Clean-ln-Place (CIP) system. Due to the limited mechanical and structural integrity of the fermenters preventing thermal sterilization a comprehensive CIP system will be employed using appropriate bactericides to ensure mono-culture conditions can be maintained within the process environment. Whilst the operating plant is not ordinarily deemed sterile it is should be maintained and operated at high levels of hygiene, approaching or meeting food industry standards.

Most preferably, the product of the fermentation is substantially racemic lactic acid and/or a salt thereof. Typically, the substantially racemic lactic acid or salt thereof is comprised in a mixture with other products and in particular with other carboxylic acids and/or salts thereof (e.g. succinic acid, acetic acid, citric acid, fumaric acid, pyruvic acid, n-butyric acid) and other organic species (e.g. alcohols, carbohydrates etc). These organic species may have been originally present in the feedstock, they may have been generated within the feedstock by random degradation of the carbohydrates within the feedstock during storage and transport of the material or they may have been generated as a byproduct of the presently described fermentation process.

According to a further aspect of the invention the microbial strain may comprise one or more of a Streptococcus; Bacillus; Lactobacillus; Pseudomonas; Pediococcus;

Weissella; Sporolactobacillus; and Caldicellulosiruptor strain; and combinations thereof.

Strains were investigated based upon attributes as follows:

Caldicellulosiruptor bescii was selected for its thermophillic properties.

Lactobacillus pentosus and Pediococcus pentosaceus were selected based upon literature suggesting they utilise 5-carbon sugars.

Sporolactobacillus cellulosolvens was selected due to evidence that it is a cellulolytic strain and could be used, potentially, to degrade cellulosic substrates into sugars in the earlier stages of a waste treatment process, followed by the utilisation of sugars at a later stage.

In a preferred aspect of the invention the microbial strain comprises one or more of a Lactobacillus or a Pediococcus strain and combinations thereof. In a particular aspect of the invention, the microbial strain is not a strain of Lactobacillus Acidophilus.

The microbial strain may be a Lactobacillus, The strain may preferably be selected from the group L. plantarum, L. reuteri, L. sakei, L. pentosus, L. fermentum, L. helveticus, L. brevis and L. buchneri, and combinations thereof. The strain may be L. plantarum. The strain may be L. reuteri. The strain may be L. sakei. The strain may be L. pentosus. The strain may be L. fermentum. The strain may be L. helveticus. The strain may be L. brevis.Jhe strain may be L. buchneri.

The microbial strain may be a Pediococcus strain. The strain may be P. pentosaceus. It is within the scope of the present invention to use combinations of any of the aforementioned microbial strains. The microbial strains hereinbefore described, e.g. the Lactobacillus or a Pediococcus strains are commercially available from national cultures collections, such as, DSMZ, Braunschweig, Germany (http://www.dsmz.de); NCIMB, Aberdeen, UK (http://www.ncimb.com); etc. The ratio of L-enantiomer to D-enantiomer produced in the fermentation may vary depending on, inter alia, the microbial strain used. However, it is desirable to achieve substantially racemic lactic acid, although it will be understood by the person skilled in the art that, for example, non-racemic mixtures of L-enantiomer and D-enantiomers of lactic acid will be suitable. The term "substantially racemic" lactic acid will be understood by the person skilled in the art. Since "racemic" or "racemic mixture" means a mixture that has equal amounts D- and L- enantiomers of a chiral molecule, the term "substantially racemic" shall be construed as meaning a mixture which approaches equal amounts of D- and L- enantiomers, but may generally comprise mixtures in which there is an enantiomeric excess of one of the D- or L- enantiomers. Thus, the ratio of D-lactic acid, or a derivative thereof, to L-lactic acid, or a derivative thereof, produced by the fermentation of the present invention is preferably 1 : 1 , i.e. truly racemic, however, the ratio of D- to L- may be from about 25:75 to about 75:25 (e.g. from about 70:30 to 30:70or from about 60:40 to about 40:60) D- to L- lactic acid or a derivative thereof. Most preferably, the ratio of D- to L- is from about 45:55 to about 55:45.

Where lactic acid is described as substantially enantiomerically pure L-lactic acid it means that the majority of the lactic acid is the L-enantiomer. Thus it may be that greater than 80% is L-lactic acid or greater than 90% is L-lactic acid or greater than about 95% is L-lactic acid or even greater than about 98% is L-lactic acid. Likewise, where lactic acid is described as substantially enantiomerically pure D-lactic acid it means that the majority of the lactic acid is the D-enantiomer. Thus it may be that greater than 80% is D-lactic acid or greater than 90% is D-lactic acid or greater than about 95% is D-lactic acid or even greater than about 98% is D-lactic acid. Thus, the microbial strain preferably produces at least 30% w/w of L-lactic acid, or a derivative thereof, the remainder being substantially D-lactic acid, or a derivative thereof; preferably at least 35% w/w of L-lactic acid; or at least 40% w/w L- lactic acid; or at least 45% w/w L- lactic acid; or at least 50% w/w L- lactic acid; or at least 55% w/w L- lactic acid; or at least 60% w/w L- lactic acid, or a derivative thereof; the remainder substantially being D-lactic acid, or a derivative thereof. Most preferably, the microbial strain produces about 50% w/w of L-lactic acid, or a derivative thereof, the remainder being substantially D-lactic acid, or a derivative thereof.

It will be understood by the person skilled in the art that the yield of the substantially racemic lactic acid, or a derivative thereof, may vary depending upon, inter alia, the microbial strain used, but may be at least 50% w/w based on the weight of carbohydrate material used in the formation; preferably at least 55% w/w; or at least 60% w/w; or at least 65% w/w; or at least 70% w/w; or at least 75% w/w; or at least 80% w/w; or at least 85% w/w; or at least 90% w/w; or at least 95% w/w. Furthermore, the yield may vary depending upon, inter alia, whether the fermentation is homolactic-fermentation or heterolactic-fermentation. In homolactic-fermentation one molecule of glucose (or other carbohydrate) is converted to two molecules of lactic acid. Thus, homolactic- fermentation, which metabolises carbohydrates via the glycolytic pathway, generally provides a high yield, e.g. >85% w/w, due to lactic acid being the only/dominant product. Heterolactic-fermentation employs two metabolic pathways and typically produces carbon dioxide and ethanol, in addition to lactic acid. Thus, heterolactic-fermentation generally provides a lower yield, e.g. from about 60% to about >80% w/w. Preferably the fermentation is homolactic fermentation.

The biomass material may comprise a variety of materials. Preferably it contains solids. The solids will typically be insoluble in water. Thus, for example, the biomass material may comprise conventionally used food plant biomass, such as maize, etc. Alternatively, the biomass material may comprise a non-food plant biomass, such as the so l i d non- edible parts of food crops, e.g. the non-edible parts of rice and oats, including corn cobs, corn stover, rice straw, wheat straw, etc. The biomass may comprise other waste materials, e. g. paper and/or cardboard. It will be understood by the person skilled in the art that any combination of the aforementioned biomass source materials may suitably be used.

However, a particular advantage of the present invention is that the biomass material may comprise solids, examples of such biomass material comprising solids include lignocellusic waste biomass material, such as, municipal and/or commercial waste sources. Thus, the present invention may use Municipal Solid Waste (MSW), e.g. MSW derived sugars as a feedstock for the fermentation process. It is within the scope of the present invention that the MSW, or the sugars derived therefrom, may optionally be combined with other plant biomasses, e.g. those that do not comprise solids. The sugars comprised in the MSW or derived from the MSW will generally include C5 or C6 sugars, such as, pentoses, xylans (C5); and hexoses, e.g. glucose, etc. (C6); including their hemiacetals; and combinations thereof. Thus, according to a further aspect of the invention there is provided a process as hereinbefore described which comprises the fermentation of one or more C5 or C6 sugars using a microbial strain which selectively produces a substantially racemic lactic acid, or a derivative thereof. When the feedstock for the lactic acid fermentation is prepared from MSW, the MSW may be pre-treated prior to fermentation, for example, by subjecting the MSW to one or more of: size reduction, homogenisation, thermal hydrolysis and enzymatic hydrolysis, or a combination thereof.

When the pre-treatment comprises thermal hydrolysis, such thermal hydrolysis of MSW may be carried out at temperatures of from about 130°C to about 230°C; or from about 140°C to about 220°C; or from about 150°C to about 210°C; or from about 160°C to about 200°C; or from about 170°C to about 190°C; e.g. about 180°C.

In addition, the aforementioned thermal hydrolysis of the MSW may be carried out in the presence of a base, such as potassium hydroxide, ammonia or ammonium hydroxide, which is usually added to the wet biomass waste material. In a preferred aspect of the invention the thermal hydrolysis is carried out in the presence of ammonia or ammonium hydroxide. On a large scale this may optionally involve the use of ammonia in an aqueous medium.

In addition, the aforementioned thermal hydrolysis of the MSW may be carried out in the presence of an acid, such as sulphuric acid or hydrochloric acid, which is usually added to the wet biomass waste material. In a preferred aspect of the invention the thermal hydrolysis is carried out in the presence of sulphuric acid.

The solids content of the biomass (e.g. MSW) may vary in composition and comprise from about 10 to about 50% w/w solids; or from about 15 to about 45% w/w; or from about 15 to about 40% w/w; or from about 20 to about 35% w/w; usually from about 25 to about 30% w/w solids. It may be that the w/w values provided above are for the content of the biomass which is dry solids.

The lactic acid fermentation may optionally include a sterilisation step, e.g. at elevated temperature, prior to inoculation with the fermentation microbial strain, e.g. one or more of a Lactobacillus or a Pediococcus strain as hereinbefore described. However, it is within the scope of the present invention for the sterilisation step to be omitted, for example, when a process of thermal hydrolysis of biomass material is employed, sterilisation will effectively happen during the thermal hydrolysis. When the pre-treatment comprises enzymatic hydrolysis of the MSW this may be carried using commercially available technical enzymes, for example, available from Novozymes. Alternatively, the enzymatic hydrolysis of the biomass may optionally be conducted in parallel with fermentation using, for example, Chrysosporium lucknowense eukaryotic host production organism, such as C1 available commercially from Dyadic I nc. In a yet further alternative, the parallel enzymatic hydrolysis/fermentation may comprise simultaneous saccharification and fermentation of the biomass to lactic acid. Such simultaneous saccharification and fermentation may comprise the use of thermophile enzymes, which operate at from about 45°C to about 120°C, e.g. about 50°C, or mesophile enzymes, which operate at from about 20°C to about 45°C.The fermentation of the biomass material, including the MSW or sugars derived from MSW, may be carried out at ambient temperature or at elevated temperature. Thus, the fermentation may be carried out a t a temperature of from about 25°C to about 120°C; or from about 25°C to about 100°C; or from about 25°C to about 75°C; or from about 25°C to about 50°C; or from about 28°C to about 42°C; or from about 30°C to about 40°C; or from about 30°C to about 37°C.

The duration of the fermentation will depend upon, inter alia, the nature of the biomass material, the temperature used, the scale of the fermentation; the amount of inoculate present etc. Such parameters would be understood by the person skilled in the art.

Thus, the method for producing substantially racemic lactic acid according to the present invention may comprise bringing the above lactic acid microbial strain, e.g. the Lactobacillus or a Pediococcus strain, into contact with a biomass material (e.g. one containing solids), such as MSW or an MSW derived material, in the presence or the absence of sterilisation and thus performing lactic fermentation.

It may be that a base is added to the membrane bioreactor to maintain the pH of the fermentation broth within a desired range. The base will typically be selected from those that produce lactate salts with high aqueous solubility. Examples include bases which form alkali metal salts, such as sodium salts, of lactic acid and bases which form ammonium salts of lactic acid. Examples include hydroxide, carbonate and bicarbonate salts of alkali ion and ammonium. Specific examples include, potassium hydroxide, sodium hydroxide, ammonium hydroxide, potassium carbonate, sodium carbonate and sodium bicarbonate. The base will typically be added during the course of the fermentation. Thus it may be added portionwise or continuously. The base may be added at a predetermined rate or it may be added in response to changes in the pH. The pH conditions of the fermentation b r o t h may vary depending upon, inter alia, the microbial strain, etc. For example, the pH may be from about from pH 4 to about pH 11 ; from about pH 4.5 to about pH 9, e.g. less than about pH 6. Generally, the

fermentation will start at less than about pH 6 finish at about pH 4.5. The rate of addition and the addition profile of the base to the fermentation medium will depend on the desired pH. The desired pH may itself depend on the microbe or combination of microbes used.

Preferably, the fermentation is chemostatic with respect to carbon. Thus, the feedstock is added to the fermentation broth and the product mixture is drained from the fermentation broth at rates such that the rate of addition of carbon atoms into the membrane bioreactor is the same as the rate at which carbon atoms (in the form of lactic acid and any impurities) are passing through the membrane. Chemostatic addition helps to minimize the amount of carbohydrates which pass out of the reactor with the lactic acid and therefore increases the carbon efficiency of the process. Where the fermentation is chemostatic with respect to carbon, the fermentation is preferably homolactic fermentation. The rate of removal of carbon is easier to monitor in a homolactic fermentation process.

With the method for producing substantially racemic lactic acid according to the present invention, the prepared lactic acid fermentation microbes, e.g. the Lactobacillus or a

Pediococcus strain, may, for example, be inoculated in a medium, such as MRS media, which typically contains (w/v): 1.0% peptone; 0.8% egg extract; 0.4% yeast extract; 2.0% glucose; 0.5% sodium acetate trihydrate; 0.1 % polysorbate 80 (Tween 80); 0.2% dipotassium hydrogen phosphate; 0.2% trammonium citrate; 0.02% magnesium sulfate heptahydrate; and 0.005% manganese sulfate tetrahydrate.

The substantially racemic lactic acid may be obtained from the reaction in the form of the base addition salts. It may be obtained in the form of the free acids. Typically, however, it will be obtained as a mixture of the two. The product stream will also contain a range of other carboxylic acids (e.g. succinic acid, acetic acid, citric acid, fumaric acid, pyruvic acid, n-butyric acid) and/or salts thereof and other organic species (e.g. alcohols, carbohydrates).

The process may comprise treating the product stream comprising the lactic acid with an acid to form an acidified product mixture comprising substantially racemic lactic acid. Exemplary acids include hydrochloric acid and sulfuric acid. This causes any base addition salts (of lactic acids and/or of impurity carboxylic acids) to be converted into the free carboxylic acids. The process may comprise treating the acidified product mixture with a base to form a solid comprising the salt of lactic acid; and recovering the solid. The base will typically be selected from those that produce lactate salts with low aqueous solubility. Examples include bases which form alkali earth metal lactate salts, such as calcium salts, of lactic acid and bases which form ammonium salts of lactic acid. Specific examples include calcium carbonate. The solid will typically contain only the salts of lactic acid and any other carboxylic acids present and will not contain significant amounts of other organic impurities formed in the fermentation reaction (e.g. alcohols, carbohydrates etc.). The process may therefore comprise recovering the solid and separating it from the liquid components of the mixture. The step of separating the solid may be achieved by filtration. The process will typically also comprise reacidifying the solid to provide substantially racemic lactic acid optionally in the form of a mixture with at least one other carboxylic acid selected from succinic acid, acetic acid, citric acid, fumaric acid, pyruvic acid and n-butyric acid. Exemplary acids include hydrochloric acid and sulfuric acid.

The process may comprise esterifying the carboxylic acid mixture to obtain a mixture of esters. The esters may be formed from an alcohol, e.g. a C C₄ aliphatic alcohol. Exemplary alcohols include methanol, ethanol, isopropanol, n-propanol, iso-butanol, n-butanol, t-butanol. The esterification step may be conducted on the acidified product mixture. The ester mixture may then be subjected to fractional distillation to separate the component esters of the carboxylic acid providing . One product of the fractional distillation will be the ester of the substantially racemic lactic acid. Other products are likely to include the esters of succinic acid, acetic acid, citric acid, fumaric acid, pyruvic acid and n-butyric acid. Any one or more of the separated esters may then be subjected to ester hydrolysis to obtain the corresponding acid, i.e. substantially racemic lactic acid and optionally at least one of succinic acid, acetic acid, citric acid, fumaric acid, pyruvic acid, n-butyric acid.

The process may further comprise separating the enantiomers of lactic acid to obtain L-lactic acid and/or D-lactic acid in substantially enantiopure form.

The invention also provides, a process of making poly-L-lactic acid and/or poly-D-lactic acid, the process comprising:

obtaining L-lactic acid and/or D-lactic acid according to the processes of the invention; and polymerising the L-lactic acid and/or D-lactic acid to obtain poly-L-lactic acid and/or poly-D- lactic acid. The invention also provides, a process of making PDLLA, the process comprising: obtaining poly-L-lactic acid and poly-D-lactic acid according to the processes of the invention; and

mixing the poly-L-lactic acid and poly-D-lactic acid to obtain PDDLA.

The invention also provides, a process of making PDLLA, the process comprising:

obtaining poly-L-lactic acid or poly-D-lactic acid according to the processes of the invention; and

mixing the poly-L-lactic acid or poly-D-lactic acid with poly-D-lactic acid or poly-L-lactic acid respectively to obtain PDDLA.

The invention also provides, a product comprising PDA, PLA or PDLLA obtained according to the processes of the invention.

The lactic acid fermentation microbes, e.g. the Lactobacillus or a Pediococcus strain, may be inoculated at from about 0.1g to about 1g, or more, of wet cells per 1 kg of biomass material.

After fermentation the substantially racemic lactic acid can be used directly with or without a further purification step. Typically however the lactic acid will be purified using the methods described above before being subjected to enantiomer separation.

As hereinbefore described, the fermentation of substantially racemic lactic acid is especially advantageous in that, inter alia, the substantially racemic lactic acid obtained may be separated into D- and L- enantiomers of lactic acid using methods known in the art, such as that developed by Plaxica Limited. Thus, the substantially racemic lactic acid

manufactured by the method of the present invention may be used in the manufacture of large volumes of poly-DL-lactide (PDLLA), for example, by biologically retrofitting an existing L-lactic acid production unit and applying aforementioned Plaxica technology, to produce two substantially optically pure streams of lactic acid enantiomers (D- and L- lactic acid), which can then be polymerised and blended to form PDLLA. Plaxica's technology for the separation of substantially racemic lactic acid into D- and L- enantiomers of lactic acid is generally described in International patent application No. WO 2013/01 1298, incorporated herein by reference.

Generally the Plaxica process comprises the production of an aliphatic ester of lactic acid and/or an aliphatic ester of lactyllactic acid. More particularly, Plaxica provide a process for treating a mixture of R,R- and S,S- lactide which comprises contacting the mixture of R, R- and S,S- lactide with an aliphatic alcohol (such as, ethanol, n-propanol, /^'-propanol, n- butanol, s-butanol, /-butanol or 2-ethylhexanol) and an enzyme (usually an esterase) to produce a mixture comprising aliphatic ester of lactic acid corresponding to one lactide enantiomer and the aliphatic ester of lactyllactic acid corresponding to the other lactide enantiomer.

The Plaxica process further includes the separation of the mixture comprising aliphatic ester of lactic acid corresponding to one lactide enantiomer and the aliphatic ester of lactyllactic acid corresponding to the other lactide enantiomer from the enzyme, and then separating the enantiomers by fractional distillation. A fixed enzyme bed may be used which may negate the need for recycling of the enzyme.

Therefore, according to a further aspect of the invention there is provided a process for the separation of D-lactic acid, or a derivative thereof, and L-lactic acid, or a derivative thereof, said method comprising the steps of:

(a) manufacturing substantially racemic lactic acid, or a derivative thereof, by the fermentation of biomass material using one or more of a microbial strain which selectively produces a substantially racemic lactic acid, or a derivative thereof;

(b) isolating/ purifying the substantially racemic lactic acid from the fermentation broth;

(c) contacting the substantially racemic lactic acid, or a derivative thereof, with an alcohol and an enzyme to produce a mixture comprising an ester of lactic acid

corresponding to one lactic acid enantiomer, or a derivative thereof; and an ester of lactyllactic acid corresponding to the other lactic acid enantiomer, or a derivative thereof;

(d) separating the mixture comprising the ester of lactic acid corresponding

to one lactic acid enantiomer and the ester of lactyllactic acid corresponding to the other lactic acid enantiomer from the enzyme; and (e) optionally, separating the ester of lactic acid from the ester of lactyllactic acid by fractional distillation.

In one aspect the aforementioned separation process comprises formation of D-lactic acid ester and L- lactyllactic acid ester.

In another aspect the separation process comprises formation of L-lactic acid ester and D- lactyllactic acid ester.

In another aspect of the present invention, the ester of lactic acid and the ester of lactyllactic acid are separated by fractional distillation.

According to another aspect of the invention there is provided a process for producing D-lactic acid comprising:

(a) manufacturing substantially racemic lactic acid by the fermentation of biomass material using one or more of a microbial strain which selectively produces a substantially racemic lactic acid;

(b) isolating/purifying the substantially racemic lactic acid from the fermentation broth;

(c) forming a derivative of the racemic lactic acid such that derivative of the D-lactic acid is separatable from the derivative of the L-lactic acid;

(d) optionally, separating the derivative of D-lactic acid from the derivative of L-lactic acid by fractional distillation; and

(e) reacting the derivative of lactic acid to produce D-lactic acid.

Therefore, according to a preferred embodiment of this aspect of the invention, there is provided a process for producing D-lactic acid comprising:

(c) contacting the substantially racemic lactic acid, or a derivative thereof, with an alcohol and an enzyme to produce a mixture comprising an ester of lactic acid corresponding to one lactic acid enantiomer, or a derivative thereof; and an ester of lactyllactic acid corresponding to the other lactic acid enantiomer, or a derivative thereof; (d) separating the mixture comprising the ester of lactic acid corresponding to one lactic acid enantiomer and the ester of lactyllactic acid corresponding to the other lactic acid enantiomer from the enzyme, optionally recycling the enzyme to the process;

(e) optionally, separating the ester of lactic acid from the ester of lactyllactic acid by fractional distillation; and

(f) either hydrolysing the ester of lactic acid to produce D-lactic acid or, hydrolysing the ester of lactyllactic acid to produce D-lactic acid.

In one aspect the aforementioned process for producing D-lactic acid comprises hydrolysing the ester of lactic acid to produce D-lactic acid.

In another aspect the separation process for producing D-lactic acid comprises hydrolysing the ester of lactyllactic acid to produce D-lactic acid.

According to another aspect of the invention there is provided a process for producing L-lactic acid comprising:

(c) forming a derivative of the racemic lactic acid such that derivative of the L-lactic acid is separatable from the derivative of the D-lactic acid;

(d) optionally, separating the derivative of L-lactic acid from the derivative of D-lactic acid by fractional distillation; and

(e) reacting the derivative of lactic acid to produce L-lactic acid.

Therefore, according to a preferred embodiment of this aspect of the invention, there is provided a process for producing L-lactic acid comprising:

(c) contacting the substantially racemic lactic acid, or a derivative thereof, with an alcohol and an enzyme to produce a mixture comprising an ester of lactic acid corresponding to one lactic acid enantiomer, or a derivative thereof; and an ester of lactyllactic acid corresponding to the other lactic acid enantiomer, or a derivative thereof; (d) separating the mixture comprising the ester of lactic acid corresponding to one lactic acid enantiomer and the ester of lactyllactic acid corresponding to the other lactic acid enantiomer from the enzyme, and optionally recycling the enzyme to the process;

(f) either hydrolysing the ester of lactic acid to produce L-lactic acid or, hydrolysing the ester of lactyllactic acid to produce L-lactic acid.

In one aspect the aforementioned process for producing L-lactic acid comprises hydrolysing the ester of lactic acid to produce L-lactic acid.

In another aspect the separation process for producing L-lactic acid comprises hydrolysing the ester of lactyllactic acid to produce L-lactic acid.

According to a further aspect of the invention there is provided substantially racemic lactic acid, substantially racemic lactide or substantially racemic lactyllactic acid, or an ester thereof, prepared by a process as hereinbefore described.

The invention further provides D-lactic acid, D-lactide or D-lactyllactic acid, or an ester thereof, prepared by a process as hereinbefore described.

The invention further provides L-lactic acid, L-lactide or L- lactyllactic acid, or an ester thereof, prepared by a process as hereinbefore described.

The invention will now be described by way of example only.

Example 1

Bacterial cultures were purchased from the following suppliers:

DSMZ - Leibniz I nstitute DSMZ-German Collection of Microorganisms and Cell Cultures Culture Growth & Maintenance

Bacterial cultures were supplied as freeze dried cell pellets and resuscitated according to the suppliers instructions on MRS broth (DE MAN, ROGOSA, SHARPE, Oxoid cat no. CM0359). Stock bacterial cultures were grown on 5 ml MRS broth (in 25 ml sterile universal tube) at 30°C in a static incubator. Cultures were maintained by sub- culturing 10 % inoculum every 4 days into fresh broth. Regular Gram staining and microscopic investigation was performed to ensure integrity of cultures was preserved.

Lactic Acid Fermentation on Complex Growth Media

Nine bacterial species were grown on MRS broth for 72 hours at 30°C with static incubation. Each bacterial species was sub-inoculated into fresh 5 ml MRS broth, in triplicate, to a final optical density (600 nm) of 0.5. An un-inoculated 5 ml sample of MRS broth was prepared as a sterile control. The 27 bacterial cultures and sterile control were sealed in an anaerobic jar (Becton Dickinson & co, GasPak™ 150 system) with three GasPak™ EZ C02 Container System Sachets to create a 5 % C02 atmosphere. Cultures were incubated at 30°C in a static incubator for 72 hours. Following incubation, cultures were filter sterilised to remove cell debris using 0.2μΜ sterile syringe filters into sterile containers and stored at 4°C until chemical analysis was undertaken. Results of Chiral Analysis are shown in Table I.

Chiral Analysis for Laboratory Fermentation of Biomass

TABLE I

The experiment enables the strains to be classified in terms of their ability to produce D- and L- lactic acid isomers at racemic concentration. Four strains, L plantarum, L sakei, L. pentosus and L. helveticus were classified as having a high potential to produce racemic lactic acid. All four strains converted more than 85% of the starting glucose into lactic acid, and synthesised near racemic ratios of the D- and L- lactic acid. The best performing strain was L helveticus with a yield 87.3% and racemic ratio of 46% L-lactic acid to D-lactic acid.

A further five strains, L. reuteri, L. fermentum, P. pentosacaseus, L. brevis and L. buchneri, were classified as having a medium potential to synthesise the racemic lactic acid mixture. Whilst all five synthesised closer to racemic ratios than three of the strains identified as having a high potential, their final yields of lactic acid were found to be lower at between 50- 70% of the starting glucose.

Generally, the HPLC data allowed an insight into the metabolic potential of the strains to produce either of the D- and L- isomers of lactic acid. All strains had the capacity to synthesise both isomers and, under certain growth conditions, a number of them produced either racemic or near racemic mixtures of the isomers. However, it is important at this stage not to eliminate any of the strains as being incapable of producing a racemic mixture of lactic acid since the fermentation conditions have not been manipulated and investigated fully. Further study using the principles described here would allow a more in-depth analysis of the metabolic requirements of each strain relative to the synthesis of the two isomers. pH Data Following Culture on MRS Broth:

A regression analysis was conducted on the end point pH and lactic acid concentrations (mg/ml) for the bacterial cultures incubated in a C0₂ atmosphere to determine if there was a positive correlation between the two parameters. The analysis revealed a strong correlation (R² = 0.96) with a low final pH linked to a high lactic acid concentration.

Bacterial Viable Counts Following Culture on Waste Hydrolysate:

Bacterial colony forming units (CFU) per ml of waste hyrolysate were calculated at the end point of the fermentation. Almost 5 days post-inoculation, the viable bacterial counts in the waste were up to one to two orders of magnitude lower (10⁶ or 10⁷) than those growing in the nutrient rich MRS broth. There was a general trend of the viable cell counts decreasing marginally as the dilution of the waste increased from 1 in 5 to 1 in 10. Notwithstanding, these data suggested that the waste has sufficient nutrient availability at the tested dilutions to support Lactobacillus growth over a period of days. HPLC Data Following Culture on Waste Hydrolysate:

Cell-free broth from the bacterial cultures incubated in a C0₂ atmosphere were subject to HPLC analysis to determine the concentration of D- and L- lactic acid isomers.

The yield of lactic acid for four bacterial strains (L. helveticus, L sakei, L. planetarium and L. pentosus) grown on the undiluted waste hydrolysate was approximately 60-75% of the output obtained from growth on the nutrient rich MRS medium. Lactic acid concentrations achieved after fermentation of the waste hydrolysate were calculated per ml of waste in the starting fermentation and revealed that the yield of lactic acid per ml of waste increased as the waste dilution increased. When extrapolated, these trends suggested that there was enough sugar in the waste to give a theoretical yield of 25 mg lactic acid per ml on the undiluted waste.

Data suggested that the fermentation of sugars in the undiluted waste was not as efficient as on the diluted waste. This could be due to several factors such as a lack of optimal microbial growth or metabolism due to a limited availability of specific essential nutrients, or inhibition by product build up or lowered pH.

The bacterial strains used in the invention have been documented as utilising different fermentative pathways for the conversion of sugars to lactic acid. The published classification of each of the bacterial species used are either obligate or facultative and homo-fermentative or hetero-fermentative organisms. The homo-fermentative species metabolise sugars via the Embden-Meyerhof pathway with lactic acid the dominant product but are not reported to ferment pentose sugars via this route. Obligate hetero-fermentative organisms metabolise sugars (hexose and pentose) via the phosphoketolase-dependant pathway. Facultative hetero-fermentative strains can utilize both pathways and are susceptible to glucose repression. However, there does not appear to be an obvious pattern to link either isomeric ratio or lactic acid yield to the fermentative pathway of the organism. It is hypothesised that the hetero- fermentative organisms may produce a lower yield of lactic acid when grown on the MRS agar, which predominantly contains glucose as the carbon source. Such organisms typically produce a mixture of lactic acid, ethanol and carbon dioxide during fermentation.

Claims

1. A process for the manufacture of substantially racemic lactic acid, or a derivative

thereof, said process comprising:

fermenting a slurry of biomass material comprising solids in a membrane bioreactor using at least one microbial strain that converts carbohydrates into substantially racemic lactic acid; and

recovering the substantially racemic lactic acid, or a derivative thereof, from or downstream from the membrane.

2. A process of claim 1 , wherein a base is added to the membrane bioreactor during the course of the fermentation.

3. A process of claim 2, wherein the base is selected from sodium hydroxide and

ammonium hydroxide.

4. A process of any preceding claim, wherein the fermentation is chemostatic with respect to carbon.

5. A process of any preceding claim, wherein the microbial strain causes a homolactic

fermentation.

6. A process of any preceding claim, wherein the microbial strain is a Lactobacillus strain.

7. A process of any preceding claim, wherein the biomass material is municipal solid waste.

8. A process of any preceding wherein the municipal solid waste is pre-treated prior to fermentation, the pre-treatment of municipal and/or commercial waste comprising one or more of size reduction, homogenisation, thermal hydrolysis and enzymatic hydrolysis, or a combination thereof.

9. A process according to claim 7 wherein the pre-treatment comprises thermal hydrolysis, preferably at a temperature from about 130 °C to about 230 °C.

10. A process according to claim 8 wherein the thermal hydrolysis is carried out in the

presence of a base or an acid.

1 1. A process according to any preceding claim, the process further comprising

treating the product stream comprising the lactic acid with an acid to form an acidified product mixture comprising substantially racemic lactic acid;

treating the acidified product mixture with a base to form a solid comprising the salt of lactic acid;

recovering the solid; and reacidifying the solid to provide substantially racemic lactic acid optionally in the form of a mixture with at least one other carboxylic acid selected from succinic acid, acetic acid, citric acid, fumaric acid, pyruvic acid and n-butyric acid.

12. A process according to claim 11 , wherein the substantially racemic lactic acid is in the form of a mixture with at least one other carboxylic acid, the process further comprising: esterifying the carboxylic acid mixture to obtain a mixture of esters; and

subjecting the mixture of esters to fractional distillation to obtain the ester of the lactic acid in a substantially racemic form and optionally the ester of the at least one other acid.

13. A process according to claim 12, further comprising hydrolysing the ester of the lactic acid in a substantially racemic form to obtain substantially racemic lactic acid

14. A process according to claim 12, further comprising hydrolysing the ester(s) of the at least one other carboxylic acid to form at least one other carboxylic acid selected from succinic acid, acetic acid, citric acid, fumaric acid, pyruvic acid and n-butyric acid.

15. A process of any one of claims 1 to 10 and claim 13, further comprising separating the enantiomers of lactic acid to obtain L-lactic acid and/or D-lactic acid in substantially enantiopure form.

16. A process of making poly-L-lactic acid and/or poly-D-lactic acid, the process comprising: obtaining L-lactic acid and/or D-lactic acid according to the process of claim 14; and polymerising the L-lactic acid and/or D-lactic acid to obtain poly-L-lactic acid and/or poly-D-lactic acid.

17. A process of making PDLLA, the process comprising:

obtaining poly-L-lactic acid and poly-D-lactic acid according to the process of claim 15; and

mixing the poly-L-lactic acid and poly-D-lactic acid to obtain PDDLA.

18. A process of making PDLLA, the process comprising:

obtaining poly-L-lactic acid or poly-D-lactic acid according to the process of claim 15; and

19. A product comprising PDA, PLA or PDLLA obtained according to any one of claims 16 to 18.