Enantiomeric enrichment of L-lactic acid or salts thereof

Abstract

The present invention relates to a process for the enantiomeric enrichment of lactic acid or salts thereof obtained from waste recovery.

Description

Technical Field

[0001] The present invention relates to a process for enriching the enantiomeric purity of lactic acid originating from recycled waste. Background Art

[0002] Polylactic acid is an alternative to petroleum-derived plastics. As a result, its use in the manufacture of products such as food packaging, disposables, and fibers in the textile and hygiene industries continues to grow. In addition, polylactic acid is a biodegradable polymer and is therefore used in various biomedical applications, including the production of sutures, bone fixation screws, and drug delivery devices.

[0003] Polylactic acid is polymerized from lactic acid monomers. Lactic acid has chiral carbon atoms and therefore exists in two enantiomeric forms, namely D-lactic acid and L-lactic acid. In order to produce polylactic acid suitable for industrial applications, the D-lactic acid or L-lactic acid entering the production process must be highly purified to meet the specifications required for polymerization and must contain a major (~98% or more) one lactic acid enantiomer to produce PLLA (from L-lactic acid) or PDLA (from D-lactic acid).

[0004] In recent years, lactic acid fermentation has attracted increasing attention due to the ability of certain bacteria to produce an independent lactic acid enantiomer (L or D). Traditional fermentation methods are usually based on anaerobic fermentation of carbohydrate sources (such as starch and sugar from corn or sugarcane) by lactic acid-producing microorganisms, which produce lactic acid as the main metabolic end product of carbohydrate fermentation. In the production of polylactic acid, the lactic acid produced during the fermentation process is separated from the fermentation broth and purified by various methods, and then the purified lactic acid is polymerized. Any endogenous D-lactic acid that may be present in the fermentation broth needs to be removed in order to produce optically pure polylactic acid. WO2017 / 122197, which is transferred to the applicant of the present invention, discloses dual-acting bacteria that utilize lactic acid (LA), which are genetically modified to secrete polysaccharide degrading enzymes such as cellulases, hemicellulases and amylases, which can be used to treat organic waste, both eliminating lactic acid present in the waste and degrading complex polysaccharides. WO2020 / 208635, assigned to the applicant of the present invention, discloses a system and method for treating organic waste (particularly mixed food waste) using D-lactate oxidase, which can eliminate D-lactic acid present in the organic waste.

[0005] PLA waste can be recycled by landfill, composting, anaerobic digestion (production of biogas), incineration or chemical hydrolysis to lactic acid monomer or lactide. One of the common forms of PLA on the market is the copolymer PDLLA (poly (DL-) lactic acid), which consists mainly of PLLA (made from L-lactic acid) and a small amount of PDLA (made from D-lactic acid). A large part of the PLA plastics available on the market contains a small amount of PDLA, which releases D-lactic acid when hydrolyzed. The hydrolyzed material may also contain an unknown amount of D-lactic acid formed by racemization during the hydrolysis.

[0006] Both D-lactic acid and L-lactic acid entering the new polylactic acid production process usually require an optical purity of more than 98%. Therefore, the use of lactic acid from a fermentation process or polylactic acid hydrolysis should solve the problem of isomer separation, which is expensive and usually involves liquid or solid enantiomer selection membranes or high performance liquid chromatography (HPLC).

[0007] Research has been conducted on the hydrolysis of polylactic acid using alkaline materials such as sodium hydroxide (Cam, Hyon and Ikada (1995), Biomaterials, 16 (11): 833-43); Chauliac (2013) "Development of a thermochemical process for hydrolysis of polylactic acid polymers to L-lactic acid and its purification using an engineered microbe" Ph.D. thesis, University of Florida, UMINumber: 3583516; and Karlsson (2013) Polymer Degradation and Stability, 98(1):73-78.

[0008] Siparsky, Voorhees and Miao (1998) Journal of environmental polymer degradation, 6(1):31-41 reported the hydrolysis of polylactic acid (PLA) and polycaprolactone (PCL) in aqueous acetonitrile.

[0009] Xu, Crawford and Gorman (2011) Macromolecules, 44(12):4777-4782 reported the effects of temperature and pH on the degradation of poly(lactic acid) brushes.

[0010] Elsawy et al. (2017) Renewable and Sustainable Energy Reviews, 79: 1346-1352, reviewed the hydrolytic degradation of polylactic acid (PLA) and its composites.

[0011] Motoyama et al. (2007) Polymer Degradation and Stability, 92(7):1350-1358 reported the effect of MgO catalyst on the depolymerization of poly-L-lactic acid to L,L-lactide.

[0012] WO 2015 / 112098 discloses a method for preparing lactide from a plastic having polylactic acid (PLA-based plastic), the method comprising preparing a PLA-based plastic, accelerating the decomposition of polylactic acid in the plastic by alcoholysis or hydrolysis to provide low molecular weight polylactic acid, and thermally decomposing the low molecular weight polylactic acid to provide lactide. In addition, the method also comprises minimizing the size of the PLA-based plastic after the preparation step, and purifying lactide after thermal decomposition of the low molecular weight polylactic acid.

[0013] US7,985,778 discloses a method for decomposing and recovering a synthetic resin having an ester bond in a composition structure by performing a hydrolysis treatment and then performing a separation collection treatment. In the hydrolysis treatment, an article containing the synthetic resin to be decomposed and recovered is exposed to a water vapor atmosphere filled under a saturated water vapor pressure at a treatment temperature equal to or lower than the melting point of the synthetic resin. The synthetic resin in the article to be treated is hydrolyzed by the generated water vapor at the treatment temperature to produce a decomposition product, which is then polymerized into a synthetic resin containing an ester bond. The separation collection treatment is a treatment in which the decomposition product produced by the hydrolysis treatment is separated into a liquid component and a solid component to be collected separately.

[0014] US8,614,338 discloses a method for stereospecific chemical recovery of a polymer mixture based on polylactic acid PLA in order to reform one of its monomers or its derivatives. The method comprises suspending the polymer mixture in a lactate capable of dissolving the PLA fraction, followed by first separating the lactate, PLA and other dissolved impurities, and secondly separating the mixture of other polymers and insoluble impurities. Then, a catalytic depolymerization reaction is carried out on the solution containing the PLA thus obtained by transesterification to form oligoesters. Then, the depolymerization reaction by transesterification is stopped at a given moment, and the residual lactate is separated. Then, the oligoester thus obtained is subjected to a cyclization reaction to produce lactide, which will eventually be stereospecifically purified to obtain a purified lactide fraction also having a meso-lactide content of 0.1% to 40%.

[0015] US Pat. No. 8,431,683 and US Pat. No. 8,481,675 disclose a process for recovering polymer blends necessarily containing PLA, which process comprises grinding, compacting, dissolving in a solvent for PLA, removing undissolved contaminating polymers, alcoholysis depolymerization and purification steps.

[0016] US8,895,778 discloses the depolymerization of polyesters such as post-consumer polylactic acid. Ultrasound-induced implosion can be used to promote depolymerization. Post-consumer PLA is exposed to methanol as a suspension medium in the presence of organic or ionic salts of alkali metals such as potassium carbonate and sodium hydroxide as depolymerization catalysts to provide high-quality lactic acid monomers in high yields.

[0017] US2018 / 0051156 discloses a method for enhancing / accelerating the depolymerization of polymers (such as those containing hydrolyzable bonds), which generally involves contacting the polymer containing hydrolyzable bonds with a solvent and an alcohol to give a polymer mixture in which the polymer is substantially dissolved, wherein the contact is carried out at a temperature equal to or lower than the boiling point of the polymer mixture. The depolymerized polymer (including, for example, monomers and / or oligomers) obtained can be separated therefrom. Such methods can be carried out under relatively mild temperature and pressure conditions. In some embodiments, the polymer is poly (lactic acid).

[0018] WO 2021 / 165964, assigned to the applicant of the present invention, discloses industrial fermentation for producing lactic acid from organic waste combined with chemical recovery of polylactic acid to obtain lactic acid in high yield.

[0019] WO 2022 / 157768, assigned to the applicant of the present invention, discloses a method for crystallizing high-purity magnesium L-lactate from decomposed organic waste.

[0020] WO 2023 / 012791, assigned to the applicant of the present invention, discloses a method for producing magnesium L-lactate having high enantiomeric purity and a low content of non-lactate impurities, and a method for enriching the enantiomeric purity of a regenerated lactate containing an enantiomeric mixture of L- and D-lactate.

[0021] There remains an unmet need for an economical and reliable process for producing enantiomerically pure L-lactic acid / lactate from decomposition wastes. Summary of the invention

[0022] The present invention provides a method for enriching the enantiomeric purity of lactic acid, such as lactic acid obtained from lactic acid fermentation of organic waste and / or chemical recovery of PLA waste. The present invention also provides a method for obtaining L-lactate with enriched enantiomeric purity.

[0023] The present invention is based in part on the unexpected discovery that the enantiomeric purity of L-lactic acid can be increased by selectively precipitating L-lactate from a mixture of enantiomers containing D-lactic acid and L-lactic acid. Thus, the present invention enables the recycling of wastes from a variety of sources, including wastes containing endogenous D-lactic acid monomers, while not requiring the use of D-lactic acid-utilizing bacteria or enzymes to eliminate the D-lactic acid. The present invention advantageously produces L-lactate having an enantiomeric purity in excess of 98%, which can be used in the commercial production of PLA without the need for additional isomer separation processing.

[0024] The present invention discloses for the first time a method for selectively precipitating L-lactate from a mixture of D-lactic acid and L-lactic acid enantiomers derived from organic waste. The selective precipitation results in the enrichment of L-lactic acid / lactate monomers for subsequent use.

[0025] According to a first aspect, the present invention provides a method for enriching L-lactic acid enantiomers or salts thereof, the method comprising the following steps:

[0026] (a) obtaining a decomposed organic waste comprising an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 g / L to about 1,100 g / L, wherein the enantiomeric mixture comprises 10% or less of D-lactic acid;

[0027] (b) contacting the enantiomeric mixture with a basic substance comprising a divalent cation in an amount of about 50 equivalent % to about 120 equivalent % based on the number of carboxyl groups present in the enantiomeric mixture; and

[0028] (c) precipitating L-lactate with the divalent cation to obtain L-lactate having an enriched enantiomeric purity compared to the initial enantiomeric mixture, wherein steps (b) and / or (c) are carried out at a temperature in the range of about 40°C to about 100°C, including each value in the specified range.

[0029] According to another aspect, the present invention provides a method for producing enantiomerically enriched L-lactate, the method comprising the steps of:

[0030] (a) obtaining a decomposed organic waste comprising an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 g / L to about 1,100 g / L, wherein the enantiomeric mixture comprises 10% or less of D-lactic acid;

[0031] (b) contacting the enantiomeric mixture with a basic substance comprising a divalent cation in an amount of about 50 equivalent % to about 120 equivalent % based on the number of carboxyl groups present in the enantiomeric mixture; and

[0032] (c) precipitating L-lactate with the divalent cation to obtain L-lactate having an enriched enantiomeric purity compared to the initial enantiomeric mixture, wherein steps (b) and / or (c) are carried out at a temperature in the range of about 40°C to about 100°C, including each value in the specified range.

[0033] In some embodiments, the enantiomeric mixture comprises 9% or less D-lactic acid. In other embodiments, the enantiomeric mixture comprises 8% or less D-lactic acid. In other embodiments, the enantiomeric mixture comprises 7% or less D-lactic acid. In other embodiments, the enantiomeric mixture comprises 6% or less D-lactic acid. In other embodiments, the enantiomeric mixture comprises 5% or less D-lactic acid. In various embodiments, the enantiomeric mixture comprises 4% or less D-lactic acid. In specific embodiments, the enantiomeric mixture comprises 3% or less D-lactic acid. In certain embodiments, the enantiomeric mixture comprises 3% or more D-lactic acid. In some embodiments, the enantiomeric mixture comprises 4% or more D-lactic acid. In exemplary embodiments, the enantiomeric mixture comprises 5% or more D-lactic acid.

[0034] In other embodiments, steps (b) and / or (c) are performed at a temperature in the range of about 45°C to about 100°C, including each value in the specified range. In other embodiments, steps (b) and / or (c) are performed at a temperature in the range of about 50°C to about 100°C, including each value in the specified range.

[0035] According to another aspect, the present invention provides a method for enriching L-lactic acid enantiomers or salts thereof, the method comprising the steps of:

[0036] (a) obtaining a decomposed organic waste comprising an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 g / L to about 1,100 g / L, wherein the enantiomeric mixture comprises 6% or less of D-lactic acid;

[0037] (b) contacting the enantiomeric mixture with a basic substance comprising a divalent cation; and

[0038] (c) precipitating L-lactate with the divalent cation to obtain L-lactate having an enriched enantiomeric purity compared to the initial enantiomeric mixture, wherein steps (b) and / or (c) are carried out at a temperature in the range of about 50° C. to about 100° C., including each value in the specified range.

[0039] According to another aspect, the present invention provides a method for producing enantiomerically enriched L-lactate, the method comprising the steps of:

[0040] (a) obtaining a decomposed organic waste comprising an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 g / L to about 1,100 g / L, wherein the enantiomeric mixture comprises 6% or less of D-lactic acid;

[0041] (b) contacting the enantiomeric mixture with a basic substance comprising a divalent cation; and

[0042] (c) precipitating L-lactate with the divalent cation to obtain L-lactate having an enriched enantiomeric purity compared to the initial enantiomeric mixture, wherein steps (b) and / or (c) are performed at a temperature in the range of about 50°C to about 100°C, including each value in the specified range.

[0043] In various embodiments, the methods disclosed herein provide an enrichment of 1% or more of an L-lactic acid enantiomer or a salt thereof. In another embodiment, the method provides an enrichment of 5% or more of an L-lactic acid enantiomer or a salt thereof. In another embodiment, the method provides an enrichment of 10% or more of an L-lactic acid enantiomer or a salt thereof. In a specific embodiment, the method provides an enrichment of up to 10% of an L-lactic acid enantiomer or a salt thereof. In other embodiments, the method provides a reduction of 10% or more of a D-lactic acid enantiomer or a salt thereof. In other embodiments, the method provides a reduction of 20% or more of a D-lactic acid enantiomer or a salt thereof. In another embodiment, the method provides a reduction of 30% or more of a D-lactic acid enantiomer or a salt thereof. In certain embodiments, the method provides a reduction of 40% or more of a D-lactic acid enantiomer or a salt thereof. In another embodiment, the method provides a reduction of 50% or more of a D-lactic acid enantiomer or a salt thereof. In further embodiments, the method provides a 60% or more reduction of a D-lactic acid enantiomer or a salt thereof. In an exemplary embodiment, the method provides a 70% or more reduction of a D-lactic acid enantiomer or a salt thereof. In a specific embodiment, the method provides an 80% or more reduction of a D-lactic acid enantiomer or a salt thereof. In some embodiments, the method provides a 90% or more reduction of a D-lactic acid enantiomer or a salt thereof. In a specific embodiment, the method provides a reduction of up to 95% of a D-lactic acid enantiomer or a salt thereof.

[0044] In one embodiment, the decomposed organic waste comprises lactic acid derived from a low pH lactic acid fermentation process.

[0045] In certain embodiments, the organic waste comprises a carbohydrate source. In other embodiments, the organic waste is selected from food waste, municipal food waste, residential food waste, agricultural waste, industrial food waste from food and beverage processing facilities, commercial food waste (from hospitals, restaurants, shopping centers, airports, etc.), and mixtures or combinations thereof. Each possibility represents a separate embodiment.

[0046] In a further embodiment, the decomposed organic waste is pre-treated prior to step (a). In a particular embodiment, the pre-treatment comprises removing non-lactic acid containing impurities.

[0047] In other embodiments, the low pH lactic acid fermentation process is conducted at a pH of about 2 to about 5.5, including every value within the specified range.

[0048] In one embodiment, the decomposed organic waste comprises lactic acid derived from the decomposition of polylactic acid in an acidic medium.

[0049] In certain embodiments, the decomposition of polylactic acid in an acidic medium comprises hydrolysis of polylactic acid in the presence of an acid selected from hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid, and combinations thereof. Each possibility represents a separate embodiment.

[0050] In further embodiments, the decomposed organic waste comprises lactic acid byproducts derived from industrial production of polylactic acid. In other embodiments, the decomposed organic waste comprises lactic acid byproducts derived from industrial purification of lactic acid. In other embodiments, the decomposed organic waste comprises lactic acid obtained by hydrolyzing lactide byproducts of industrial production of polylactic acid.

[0051] In some embodiments, the alkaline material comprising divalent cations comprises hydroxide. In another embodiment, the alkaline material comprising divalent cations is selected from magnesium hydroxide, calcium hydroxide and mixtures thereof. Each possibility represents a separate embodiment. In one embodiment, the alkaline material comprising divalent cations is magnesium hydroxide. In a further embodiment, the alkaline material comprising divalent cations comprises carbonate or bicarbonate. Each possibility represents a separate embodiment. In a further embodiment, the alkaline material comprising divalent cations is selected from magnesium bicarbonate, magnesium carbonate, calcium bicarbonate, calcium carbonate and mixtures thereof. Each possibility represents a separate embodiment.

[0052] In certain embodiments, the alkaline material is added in solid form. In an optional embodiment, the alkaline material is added as an aqueous solution or suspension. In a further embodiment, the alkaline material is added stepwise. In other embodiments, the alkaline material is added as an aqueous solution having a concentration of about 50 g / L to about 500 g / L, including each value within the specified range.

[0053] In various embodiments, steps (b) and / or (c) are carried out at a temperature in the range of about 55°C to about 100°C, including each value in the specified range. In an exemplary embodiment, steps (b) and / or (c) are carried out at a temperature in the range of about 60°C to about 100°C, including each value in the specified range. In a specific embodiment, steps (b) and / or (c) are carried out at a temperature in the range of about 70°C to about 100°C, including each value in the specified range. In another embodiment, steps (b) and / or (c) are carried out at a temperature in the range of about 80°C to about 100°C, including each value in the specified range.

[0054] In further embodiments, steps (b) and / or (c) are performed at a pressure of about 100 mbar to about 1,000 mbar, including each value within the specified range. In other embodiments, steps (b) and / or (c) are performed at a mixing speed of about 200 revolutions per minute to about 1,000 revolutions per minute (RPM), including each value within the specified range.

[0055] In some embodiments, the precipitation of L-lactate in step (c) is carried out over a period ranging from 10 minutes to 1 day, including each value in the specified range. In other embodiments, the precipitation of L-lactate in step (c) is carried out over a period ranging from 1 hour to 1 day, including each value in the specified range.

[0056] In further embodiments, the precipitation of L-lactate in step (c) is carried out at a pH range of about 3 to about 10, including each value in the specified range. In specific embodiments, the precipitation of L-lactate in step (c) is carried out at a pH range of about 4 to about 9, including each value in the specified range. In some embodiments, the precipitation of L-lactate in step (c) is carried out at a pH range of about 5 to about 8, including each value in the specified range. In further embodiments, the precipitation of L-lactate in step (c) is carried out at a pH range of about 6 to about 7, including each value in the specified range.

[0057] In other embodiments, the obtained L-lactate is separated by filtration or centrifugation. In a further embodiment, the obtained L-lactate is subjected to subsequent purification. In other embodiments, subsequent purification comprises at least one of crystallization, recrystallization, distribution, silica gel chromatography, preparative HPLC and combinations thereof. Each possibility represents a separate embodiment.

[0058] In certain embodiments, subsequent purification includes washing the obtained L-lactate, for example, using purified water. In other embodiments, subsequent purification includes dissolving and recrystallizing the obtained L-lactate.

[0059] In one embodiment, the resulting L-lactate contains less than 6% D-lactate. In another embodiment, the resulting L-lactate contains less than 5% D-lactate. In another embodiment, the resulting L-lactate contains less than 4% D-lactate. In another embodiment, the resulting L-lactate contains less than 3% D-lactate. In another embodiment, the resulting L-lactate contains less than 2% D-lactate. In another embodiment, the resulting L-lactate contains less than 1.5% D-lactate. In a specific embodiment, the resulting L-lactate contains less than 1% D-lactate.

[0060] In a further embodiment, the resulting L-lactate salt is a crystalline L-lactate salt.

[0061] In other embodiments, the resulting L-lactic acid salt is acidified by at least one of hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid and combinations thereof to form L-lactic acid. Each possibility represents a separate embodiment. In a specific embodiment, the L-lactic acid is used for subsequent polylactic acid formation.

[0062] Other objects, features and advantages of the present invention will become apparent from the following description, examples and accompanying drawings. DETAILED DESCRIPTION

[0063] The present invention provides a method for the enantiomeric enrichment of L-lactic acid or its salt in a mixture of enantiomers of D-lactic acid and L-lactic acid derived from a recovery process. Surprisingly, neutralization of the lactic acid mixture with an alkaline base comprising a divalent cation results in the selective precipitation of L-lactate, thereby providing L-lactic acid / lactate enrichment. The high purity L-lactate can be further used to produce new lactic acid-based products.

[0064] According to some aspects and embodiments, a method for enriching L-lactic acid enantiomers or salts thereof is provided, the method comprising obtaining a solution comprising an enantiomeric mixture of D-lactic acid and L-lactic acid; contacting the enantiomeric mixture with an alkaline substance comprising a divalent cation; and precipitating L-lactate with the divalent cation, thereby obtaining L-lactate having enriched enantiomeric purity.

[0065] According to other aspects and embodiments, a method for producing L-lactate with enriched enantiomeric purity is provided, the method comprising obtaining a solution comprising an enantiomeric mixture of D-lactic acid and L-lactic acid; contacting the enantiomeric mixture with an alkaline substance comprising divalent cations; and precipitating L-lactate with the divalent cations, thereby obtaining L-lactate with enriched enantiomeric purity.

[0066] In certain aspects and embodiments, the solution comprising the enantiomeric mixture of D-lactic acid and L-lactic acid is derived from decomposed organic waste.

[0067] As used herein, the term "lactic acid" refers to a hydroxycarboxylic acid having the chemical formula CH3CH(OH)CO2H. The term lactic acid or lactate (unprotonated lactic acid) may refer to the stereoisomers of lactic acid: L-lactic acid / L-lactate, D-lactic acid / D-lactate, or a combination thereof.

[0068] For most industrial applications, high purity L-lactic acid monomers are required to produce polylactic acid (PLA) with suitable properties. Therefore, the method of the present invention is particularly directed to the production of L-lactates with enriched enantiomeric purity, which can be converted into L-lactic acid suitable for repeated use without eliminating D-lactic acid / D-lactate monomers.

[0069] An advantage of the method of the present invention is enantiomeric enrichment, which is particularly beneficial for the reuse of lactic acid. Enantiomeric enrichment is at least 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or even more of the initial L-lactic acid content. Each possibility represents a separate embodiment. For example, for an initial enantiomeric mixture containing 90% L-lactic acid and 10% D-lactic acid, 10% enrichment produces a lactate containing 99% L-lactate and 1% D-lactate. The content of D-lactic acid is reduced to at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or even 100% of the initial D-lactic acid content by the method disclosed herein within the scope of the present invention. Each possibility represents a separate embodiment. For example, for an initial enantiomeric mixture containing 90% L-lactic acid and 10% D-lactic acid, a 50% reduction in the D-enantiomer content produces a lactate containing 95% L-lactate and 5% D-lactate. According to the principles of the present invention, the resulting L-lactate precipitate contains less than 6% D-lactate, less than 5% D-lactate, less than 4% D-lactate, less than 3% D-lactate, less than 2% D-lactate, less than 1.5% D-lactate, or less than 1% D-lactate. Each possibility represents a separate embodiment.

[0070] According to the principle of the present invention, the enantiomeric mixture of D-lactic acid and L-lactic acid is derived from decomposed organic waste. For example, the enantiomeric mixture of D-lactic acid and L-lactic acid can be obtained from the hydrolysis of polylactic acid in the presence of acid. In another example, the enantiomeric mixture of D-lactic acid and L-lactic acid can be a by-product of polylactic acid industrial production or lactic acid industrial purification. The source of the lactic acid containing the mixture of other D-enantiomers and L-enantiomers can be a by-product of lactide hydrolysis in polylactic acid industrial production. The enantiomeric mixture of D-lactic acid and L-lactic acid derived from organic wastes carrying out lactic acid fermentation at low pH is within the scope of the present invention.

[0071] Organic waste within the scope of the present invention includes, but is not limited to, waste obtained from various sources, including food and beverage waste, such as urban food waste, residential food waste, agricultural waste, industrial food waste from food processing facilities, commercial food waste (from hospitals, restaurants, shopping centers, airports, etc.), and mixtures or combinations thereof. Each possibility represents a separate embodiment. In addition, organic waste can also come from residues such as animal and human excrement, vegetable and fruit residues, plants, cooked food, protein residues, slaughter waste, and combinations thereof. Each possibility represents a separate embodiment. Industrial organic food and beverage waste may include factory waste, such as by-products, factory waste (e.g., expired products, defective products), market returns, or scraps of inedible food parts (e.g., skins, fats, shells, and peels). Each possibility represents a separate embodiment. Commercial organic food and beverage waste may include waste from shopping centers, restaurants, supermarkets, etc. Each possibility represents a separate embodiment.

[0072] According to certain aspects and embodiments, organic waste includes monosaccharides or disaccharides obtained as byproducts of sugar production from beet sugar or cane sugar, such as, but not limited to, fructose, molasses or high fructose corn syrup (HFCS) production. According to other aspects and embodiments, organic waste includes starch and starch derivatives, such as refined glucose syrup derived from starch hydrolysis, which can be corn starch, tapioca starch, wheat starch, potato starch, etc. Each possibility represents a separate embodiment. Organic waste can also be derived from byproducts of wine or beer production, such as, but not limited to, yeast autolysates and hydrolysates, and plant protein hydrolysates, animal protein hydrolysates, and soluble byproducts from soaking wheat or corn. Paper sludge hydrolysates obtained by hydrolyzing paper sludge by cellulolytic enzymes, as well as dairy byproducts produced in the production of dairy beverages such as cheese production and milk-based beverages (including, for example, lactose-free beverages).

[0073] According to various aspects and embodiments, the organic waste of decomposition comprises the fermentation liquor obtained from the fermentation method of carbohydrate source.When using heterogeneous raw materials, the organic waste of decomposition or fermentation liquor generally comprise insoluble impurities based on organic matter, such as but not limited to microorganism (such as including lactic acid producing microorganisms such as yeast, bacteria and fungi), fat and oil, lipid, aggregated protein, bone fragments, hair, precipitated salt, cell fragments, fiber (such as fruit and / or vegetable peel) and residual untreated waste (such as food shell, seed, food insoluble particles and debris etc.).Each possibility represents a separate embodiment.The non-limiting examples of insoluble impurities based on inorganic matter include plastics, glass, residues from food packaging, sand and combinations thereof.Each possibility represents a separate embodiment.

[0074] Although not required, the decomposed organic waste may be further pretreated prior to use in the methods of the present invention. Suitable pretreatments include, but are not limited to, filtration, ultrafiltration, nanofiltration, reverse osmosis (RO) filtration, solvent extraction, exclusion extraction, salt precipitation, crystallization, distillation, evaporation, electrodialysis, and various types of chromatography (such as adsorption or ion exchange). Each possibility represents a separate embodiment.

[0075] According to the principles of the present invention, fermentation is carried out at low pH. An endogenous decrease in pH occurs due to the formation of L-lactic acid. Therefore, in the absence of a neutralizing base, the pH range of the fermentation is from about 2 to about 5.5, including each value within the specified range.

[0076] Typically, fermentation at low pH can be performed by acid-tolerant (AT) yeast strains, including but not limited to those belonging to a genus selected from Saccharomyces, Candida, Schizosaccharomyces, Torulaspora, Kluyveromyces, Zygosaccharomyces, and Dekkera. Each possibility represents a separate embodiment.

[0077] In other aspects and embodiments, the decomposed organic waste is derived from the acidic hydrolysis of polylactic acid waste. The acidic hydrolysis can be carried out in the presence of an acid, such as hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid and combinations thereof. Each possibility represents a separate embodiment. The hydrolysis can be carried out at a temperature in the range of about 30°C to about 120°C, including each value in the specified range. For example, the hydrolysis can be carried out at a temperature of about 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C. Each possibility represents a separate embodiment. The hydrolysis can be carried out at atmospheric pressure or at a reduced or elevated pressure, for example in the range of about 100mbar to about 1,500mbar, including each value therebetween. Optionally, a catalyst can be added to promote the hydrolysis.

[0078] Decomposed waste can contain different concentrations of D-enantiomer and L-enantiomer.Usually, the concentration of D-lactic acid and L-lactic acid is in the range of about 100g / L to about 1,100g / L, including each value in the specified range.Exemplary concentrations of D-lactic acid and L-lactic acid include but are not limited to about 100g / L, 150g / L, 200g / L, 250g / L, 300g / L, 350g / L, 400g / L, 450g / L, 500g / L, 550g / L, 600g / L, 650g / L, 700g / L, 750g / L, 800g / L, 850g / L, 900g / L, 950g / L, 1,000g / L, 1,050g / L or 1,100g / L.Every possibility represents a separate embodiment. The ratio of lactic acid enantiomers in the decomposed waste can vary depending on the endogenous content of D-lactic acid and the formation of racemic lactic acid that occurs in fermentation or decomposition. Decomposed organic wastes containing 10% or less endogenous D-lactic acid, such as 9%, 8%, 7%, 6%, 5%, 4%, 3% or less are within the scope of the present invention. Each possibility represents a separate embodiment. Typically, the ratio of D-monomer to L-monomer includes, but is not limited to, 1:99, 2:98, 3:97, 4:96, 5:95, 6:94, 7:93, 8:92, 9:91 or 10:90. Each possibility represents a separate embodiment. According to some embodiments, the decomposed organic waste contains endogenous D-lactic acid of at least 3%, such as 4%, 5%, 6%, 7%, 8%, 9% and up to 10% D-lactic acid. Each possibility represents a separate embodiment.

[0079] If the decomposed organic waste contains unhydrolyzed PLA waste particles or impurities without lactic acid, they can be separated from the decomposed organic waste, for example, by solid-liquid separation techniques such as filtration or decantation. Each possibility represents a separate embodiment.

[0080] According to the principles of the present invention, an alkaline substance containing a divalent ion is then added to cause an L-lactate precipitation with an enriched enantiomeric purity. Suitable alkaline substances include, but are not limited to, hydroxides, carbonates and bicarbonates containing divalent cations (such as, but not limited to, magnesium, calcium or a mixture thereof). Each possibility represents a separate embodiment. Exemplary alkalis include, but are not limited to, magnesium hydroxide, calcium hydroxide, magnesium bicarbonate, magnesium carbonate, calcium bicarbonate, calcium carbonate or a mixture and combination thereof. Each possibility represents a separate embodiment. It is currently preferred to add magnesium hydroxide to provide a precipitation of L-lactate magnesium with an enriched enantiomeric purity. The alkaline substance can be added in solid form or as an aqueous solution or suspension. Each possibility represents a separate embodiment. When added as an aqueous solution, the aqueous solution typically contains an alkaline substance in a concentration range of about 50 g / L to about 500 g / L, including each value within a specified range. Typical concentration includes but is not limited to 50g / L, 60g / L, 70g / L, 80g / L, 90g / L, 100g / L, 125g / L, 150g / L, 175g / L, 200g / L, 225g / L, 250g / L, 275g / L, 300g / L, 325g / L, 350g / L, 375g / L, 400g / L, 425g / L, 450g / L, 475g / L or 500g / L.Every kind of possibility represents independent embodiment.In some embodiments, alkaline material is progressively added while stirring.It is envisioned that alkaline material can be progressively added to avoid the excessive heating that exothermic reaction causes.

[0081] In the whole process of adding alkaline material and the mixing speed during precipitation comprises stirring with about 200RPM to about 1,000RPM, including each value in the specified range. Typical mixing speed includes but is not limited to 200RPM, 250RPM, 300RPM, 350RPM, 400RPM, 450RPM, 500RPM, 550RPM, 600RPM, 650RPM, 700RPM, 750RPM, 800RPM, 850RPM, 900RPM, 950RPM or 1,000RPM. Every kind of possibility represents independent embodiment.

[0082] In some aspects and embodiments, alkaline material is added with stoichiometric amount. In other aspects and embodiments, alkaline material is added with excess. In other aspects and embodiments, alkaline material is added with insufficient amount. According to the principles of the present invention, alkaline material is added with about 50 equivalents to about 120 equivalents based on the number of carboxyl groups present in the enantiomeric mixture. The typical amount of alkaline material based on the number of carboxyl groups present in the enantiomeric mixture includes but is not limited to 50 equivalents, 55 equivalents, 60 equivalents, 65 equivalents, 70 equivalents, 75 equivalents, 80 equivalents, 85 equivalents, 90 equivalents, 95 equivalents, 100 equivalents, 105 equivalents, 110 equivalents, 115 equivalents or 120 equivalents. Each possibility represents a separate embodiment. As will be appreciated by those skilled in the art, any amount less than 100 equivalent % refers to a deficiency of alkaline material compared to lactic acid, based on the number of carboxyl groups present in the enantiomeric mixture, while any amount greater than 100 equivalent % refers to an excess of alkaline material compared to lactic acid, based on the number of carboxyl groups present in the enantiomeric mixture. Thus, the pH at which precipitation occurs is typically in the range of about 3 to about 10, such as about 4 to about 9, about 5 to about 8, or about 6 to about 7, including each value within the specified range. Each possibility represents a separate embodiment.

[0083] In some aspects and embodiments, precipitation occurs after adding alkaline substances.Alternatively, precipitation can occur at any time after adding alkaline substances, for example, any duration between about 10 minutes to about 1 day, including each value in a specified range.In various aspects and embodiments, precipitation occurs by forming an initial precipitate and making the initial precipitate mature in a certain period of time.In other aspects and embodiments, precipitation occurs in two steps, first forming an initial precipitate and separating from a mother liquor, then forming a second precipitate from the mother liquor and making it mature.Usually, precipitation occurs in the time period ranging from about 1 hour to about 24 hours, for example, in 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours or 24 hours process.Every possibility represents a separate embodiment.

[0084] Adding alkaline substances and precipitating L-lactate at elevated temperatures is within the scope of the present invention. As used herein, the term "elevated temperatures" refers to temperatures above room temperature. Suitable temperatures include temperatures of 40°C or higher. For example, in the step of adding alkaline substances and precipitating L-lactate with enriched enantiomeric purity, the temperature is in the range of 40°C to 100°C, 45°C to 100°C, 50°C to 100°C, 60°C to 100°C, 70°C to 100°C or 80°C to 100°C, including each value in the specified range. Each possibility represents a separate embodiment. Typically, a temperature in the range of 40°C to 100°C is used, for example, about 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C can be used. Each possibility represents a separate embodiment.

[0085] As will be appreciated by those skilled in the art, the duration of precipitation depends on the temperature at which precipitation occurs. Thus, in some embodiments, the step of precipitating L-lactate is performed at a temperature of about 40°C for a duration of about 18 hours to about 22 hours, including each value within the specified range. In other embodiments, the step of precipitating L-lactate is performed at a temperature of about 50°C for a duration of about 5 hours to about 10 hours, including each value within the specified range. In other embodiments, the step of precipitating L-lactate is performed at a temperature of about 90°C for a duration of about 2 hours to about 5 hours, including each value within the specified range.

[0086] The addition of alkaline substances and the precipitation of L-lactate can be carried out under various pressures. For example, the pressure of the step of adding alkaline substances and / or precipitating L-lactate with the enantiomeric purity of enrichment is in the range of about 100 mbar to about 1,000 mbar, including each value in the specified range. Exemplary pressures include but are not limited to about 100 mbar, 200 mbar, 300 mbar, 400 mbar, 500 mbar, 600 mbar, 700 mbar, 800 mbar, 900 mbar or 1,000 mbar. Each possibility represents a separate embodiment.

[0087] Typically, the method of the present invention produces a lactate with the divalent cation as the final product. However, in order to obtain polylactic acid, the lactate may be acidified using, for example, hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, sulfuric acid and mixtures or combinations thereof for subsequent polymerization. Each possibility represents a separate embodiment.

[0088] The L-lactate thus obtained can be further subjected to a downstream purification process. It was surprisingly found that a simple purification that improves the enantiomeric purity of the L-lactate is to wash the precipitate, for example using purified water. Additional purification steps, such as crystallization, recrystallization, distribution, silica gel chromatography, preparative HPLC and combinations thereof, are within the scope of the present invention. Each possibility represents a separate embodiment.

[0089] Purification methods may include extraction, electrodialysis, adsorption, ion exchange, crystallization, and combinations of these methods. Several methods have been reviewed, for example, in Ghaffar et al. (2014) Journal of Radiation Research and Applied Sciences, 7(2):222-229; and López-Garzón et al. (2014) Biotechnol Adv., 32(5):873-904. Alternatively, the recovery of lactic acid into lactide in a single step may also be used (Dusselier et al. (2015) Science, 349(6243):78-80).

[0090] Specific downstream purification methods for purifying enantiomerically enriched lactate by crystallization are described in WO 2020 / 110108 and WO 2022 / 157768, assigned to the applicant of the present invention.

[0091] The resulting lactate precipitate can be separated from the remaining liquid by microfiltration or nanofiltration. The remaining liquid can be concentrated and then subjected to at least one additional precipitation. After the precipitate is separated from the liquid, the enriched L-lactate can be washed and purified with an aqueous solution or an organic solvent such as ethanol.

[0092] Although the process disclosed herein is primarily contemplated for enriching the L-lactic acid / lactate enantiomer from a mixture of enantiomers comprising D-lactic acid and L-lactic acid derived from decomposed organic waste, the present invention also contemplates enrichment of the D-enantiomer.

[0093] Therefore, according to certain aspects and embodiments, the present invention provides a method for enriching D-lactic acid enantiomers or salts thereof or producing enantiomerically enriched D-lactate, the method comprising the following steps:

[0094] (a) obtaining a decomposed organic waste comprising a mixture of enantiomers of D-lactic acid and L-lactic acid;

[0095] (b) contacting the enantiomeric mixture with a basic substance comprising a divalent cation; and

[0096] (c) precipitating D-lactate with the divalent cation, thereby obtaining D-lactate with enriched enantiomeric purity.

[0097] As used herein and in the appended claims, the term "about" means ± 10%.

[0098] As used herein and in the appended claims, a reference not containing a specific number includes a plural reference unless the context clearly dictates otherwise. Thus, for example, "an alkaline substance" includes a plurality of such substances unless the context clearly dictates otherwise. It should be noted that the term "and" or the term "or" is generally used in its sense including "and / or" unless the context clearly dictates otherwise.

[0099] The following examples are provided to more fully illustrate certain embodiments of the present invention. However, they should never be construed as limiting the broad scope of the present invention. Without departing from the scope of the present invention, those skilled in the art can easily design various changes and modifications of the principles disclosed herein.

[0100] Example

[0101] Example 1

[0102] Decomposed organic waste from low pH fermentation

[0103] Acid-resistant (AT) yeast strains of Saccharomyces cerevisiae are used to carry out lactic acid fermentation on a carbohydrate source in a suitable culture medium to obtain a lactic acid concentration of at least 100 g / L. HPLC is used to measure the % of lactic acid concentration and D-lactic acid respectively. Magnesium hydroxide is then added to the fermented liquid to precipitate the L-lactate magnesium with an enriched enantiomeric purity. The precipitated solid is then filtered off and washed with water to obtain a crude product MgLa2 · 2H2O. Optionally, the crude product magnesium lactate is dissolved in water and then recrystallized.

[0104] Example 2

[0105] Decomposed organic waste from acid hydrolysis of PLA

[0106] PLA from cafeteria waste was cut into small pieces and immersed in a 0.01% w / w H2SO4 solution with a pH of ~2.5. The mixture was heated to 90°C to promote PLA degradation for a duration of 1-2 days. Optionally, a catalyst was added. A pH meter was used to monitor the pH decrease caused by the formation of PLA oligomers and monomers with carboxylic acid end groups. At the end of the reaction, a P3 sintered glass funnel (cutoff 16-40 μm) was used to filter out the residual PLA and solid impurities. The lactic acid concentration and the % of D-lactic acid in the filtered solution were measured separately using HPLC. Magnesium hydroxide was added to the filtered solution to precipitate L-magnesium lactate with enriched enantiomeric purity. The crude magnesium lactate was further purified by subsequent recrystallization.

[0107] Example 3

[0108] Enantiomeric enrichment of LA by precipitation using magnesium hydroxide

[0109] A mixture containing L-lactic acid and D-lactic acid at a D:L ratio of 4:96 and a concentration of about 45% was placed in a chemical reactor preheated to 50°C and stirred at 300RPM. 0.5 molar equivalents of an aqueous slurry of magnesium hydroxide (15% w / w) was added dropwise over 0.5h. The reaction was stirred at 50°C overnight, during which time magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (cutoff 16-40 μm), washed with 1 weight equivalent of water, and dried at 70°C.

[0110] The total LA / lactate concentration and the concentration % of D-LA / lactate in the total LA / lactate were measured using HPLC, respectively. Due to the precipitation of magnesium lactate, the overall LA / lactate concentration in the solution decreased from 43% to 7%, however the concentration % of D-LA / lactate in the total LA / lactate in the solution showed an increase from 5.8% to 7.8%. The increase in the concentration % of D-lactic acid / lactate in the solution indicated that the precipitation of magnesium L-lactate had an enantiomeric purity enriched in the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 1 below.

[0111] Table 1.

[0112]

[0113] Example 4

[0114] Enantiomeric enrichment of LA by precipitation with magnesium hydroxide at 90 °C

[0115] A mixture containing L-lactic acid and D-lactic acid with a D:L ratio of 6:94 and a concentration of about 45% was placed in a chemical reactor preheated to 90°C and stirred at 300RPM. 0.5 molar equivalent of magnesium hydroxide aqueous slurry (15% w / w) was added dropwise over 12 min. The reaction was stirred at 90°C overnight, during which time magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (cut-off 16-40 μm), washed with 1 weight equivalent of water, and dried at 70°C.

[0116] The total LA / lactate concentration and the concentration % of D-LA / lactate in the total LA / lactate were measured using HPLC, respectively. Due to the precipitation of magnesium lactate, the overall LA / lactate concentration in the solution decreased from 45% to 13%, however the concentration % of D-LA / lactate in the total LA / lactate in the solution showed an increase from 5.7% to 10.5%. The increase in the concentration % of D-LA / lactic acid in the solution indicates that the precipitation of magnesium L-lactate has an enantiomeric purity that is enriched in the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 2 below.

[0117] Table 2.

[0118]

[0119] Example 5

[0120] Enantiomeric enrichment of LA by precipitation with magnesium hydroxide at different temperatures

[0121] A mixture containing L-lactic acid and D-lactic acid with a D:L ratio of 6:94 and a concentration of about 45% was placed in a chemical reactor preheated to 40°C and stirred at 300RPM. 0.5 molar equivalent of magnesium hydroxide aqueous slurry (15% w / w) was added dropwise over 26 min. Due to the exothermic nature of the reaction during the addition of alkali, the temperature rose to 45°C. The reaction was cooled to 40°C and stirred at 40°C overnight, during which time magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (cut-off 16-40 μm), washed with 1 weight equivalent of water, and dried at 70°C.

[0122] HPLC was used to measure the total LA / lactate concentration and the concentration % of D-LA / lactate in the total LA / lactate, respectively. Due to the precipitation of magnesium lactate, the overall LA / lactate concentration in the solution decreased from 45% to 9%, however the concentration % of D-LA / lactate in the total LA / lactate in the solution showed an increase from 5.7% to 7.7%. The increase in the concentration % of D-LA / lactic acid in the solution indicates that the precipitation of magnesium L-lactate has an enantiomeric purity that is enriched in the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 3 below.

[0123] Table 3.

[0124]

[0125] The process was repeated at temperatures of 50°C and 90°C and the % reduction of the D-enantiomer was determined. The results show that at elevated temperatures, enantiomeric enrichment is increased while providing a shorter precipitation duration. The results are summarized in Table 4 below.

[0126] Table 4.

[0127]

[0128]

[0129] Example 6

[0130] Enantiomeric enrichment of LA by precipitation with magnesium carbonate at 50 °C

[0131] A mixture containing L-lactic acid and D-lactic acid with a D:L ratio of 6:94 and a concentration of about 45% was placed in a chemical reactor preheated to 50°C and stirred at 300RPM. 1 molar equivalent of a slurry of magnesium carbonate (33% w / w) was added dropwise over 10 minutes. During the addition, visible carbon dioxide gas was produced, indicating that the reaction was ongoing. The reaction was stirred at 50°C overnight, during which time magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (cutoff 16-40μm), washed with 1 weight equivalent of water, and dried at 70°C.

[0132] HPLC was used to measure the total LA / lactate concentration and the concentration % of D-LA / lactate in the total LA / lactate, respectively. Due to the precipitation of magnesium lactate, the overall LA / lactate concentration in the solution decreased from 45% to 15%, however, the concentration % of D-LA / lactate in the total LA / lactate in the solution showed an increase from 5.7% to 6.8%. The increase in the concentration % of D-LA / lactate in the solution indicated that the precipitation of magnesium L-lactate had an enantiomeric purity enriched in the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 5 below.

[0133] Table 5.

[0134]

[0135] Example 7

[0136] Enantiomeric enrichment of LA by precipitation from a mixture of enantiomers containing 9.0% D-lactic acid

[0137] A mixture containing L-lactic acid and D-lactic acid at a D:L ratio of 9:91 and a concentration of about 45% was placed in a chemical reactor preheated to 70°C and stirred at 300RPM. 0.5 molar equivalent of magnesium hydroxide aqueous slurry (15% w / w) was added dropwise over 13min. The reaction was stirred at 70°C overnight, during which time magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (cutoff 16-40 μm), washed with 1 weight equivalent of water, and dried at 70°C.

[0138] The total LA / lactate concentration and the concentration % of D-LA / lactate in the total LA / lactate were measured using HPLC, respectively. Due to the precipitation of magnesium lactate, the overall LA / lactate concentration in the solution decreased from 45% to 9%, however the concentration % of D-LA / lactate in the total LA / lactate in the solution showed an increase from 9% to 9.3%. The increase in the concentration % of D-LA / lactic acid in the solution indicates that the precipitation of magnesium L-lactate has an enantiomeric purity that is enriched in the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 6 below.

[0139] Table 6.

[0140]

[0141] Example 8

[0142] Enantiomeric enrichment of LA by precipitation with a single addition of magnesium hydroxide to 80% conversion

[0143] A mixture containing L-lactic acid and D-lactic acid at a D:L ratio of 3:97 and a concentration of about 35% was placed in a chemical reactor preheated to 40°C and stirred at 300RPM. 0.4 molar equivalents of magnesium hydroxide powder were added in a single portion. Due to the exothermic nature of the reaction, the temperature rose sharply to 70°C within 2 minutes and then gradually cooled to 50°C. The reaction was stirred at 50°C overnight, during which time magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (cutoff 16-40μm), washed with 1 weight equivalent of water, and dried at 70°C.

[0144] The total LA / lactate concentration and the concentration % of D-LA / lactate in the total LA / lactate were measured using HPLC, respectively. Due to the precipitation of magnesium lactate, the overall LA / lactate concentration in the solution decreased from 35% to 16%, however the concentration % of D-LA / lactate in the total LA / lactate in the solution showed an increase from 2.6% to 3.7%. The increase in the concentration % of D-LA / lactic acid in the solution indicates that the precipitation of magnesium L-lactate has an enantiomeric purity that is enriched in the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 7 below.

[0145] Table 7.

[0146]

[0147] Example 9

[0148] Enantiomeric enrichment of LA by precipitation using magnesium hydroxide to 90% conversion

[0149] A mixture containing L-lactic acid and D-lactic acid with a D:L ratio of 5:95 and a concentration of about 45% was placed in a chemical reactor preheated to 70°C and stirred at 300RPM. 0.45 molar equivalents of an aqueous slurry of magnesium hydroxide (15% w / w) were added dropwise over 16 min. The reaction was stirred at 70°C for 5 hours, during which time magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (cutoff 16-40 μm), washed with 1 weight equivalent of water, and dried at 70°C.

[0150] HPLC was used to measure the total LA / lactate concentration and the concentration % of D-LA / lactate in the total LA / lactate, respectively. Due to the precipitation of magnesium lactate, the overall LA / lactate concentration in the solution decreased from 45% to 11%, however the concentration % of D-LA / lactate in the total LA / lactate in the solution showed an increase from 5.6% to 8.7%. The increase in the concentration % of D-LA / lactic acid in the solution indicates that the precipitation of magnesium L-lactate has an enantiomeric purity that is enriched in the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 8 below.

[0151] Table 8.

[0152]

[0153] Example 10

[0154] Enrichment of LA enantiomers by precipitation with calcium hydroxide

[0155] A mixture containing L-lactic acid and D-lactic acid with a D:L ratio of 5:95 and a concentration of about 45% was placed in a chemical reactor preheated to 70°C and stirred at 300RPM. Over 18 minutes, 0.5 molar equivalents of calcium hydroxide aqueous slurry (15% w / w) were added dropwise. The reactants were stirred at 70°C overnight, but no precipitation occurred during this period. After the temperature was reduced to 50°C, calcium lactate precipitated immediately and the solution solidified completely. The solid was centrifuged at 12,000g for 5 minutes to extract the mother liquor, and then centrifuged and washed with 1 weight equivalent of water. The product was dried at 70°C.

[0156] The total LA / lactate concentration and the concentration % of D-LA / lactate in the total LA / lactate were measured using HPLC, respectively. Due to the precipitation of calcium lactate, the overall LA / lactate concentration in the mother liquor decreased from 45% to 10%, however the concentration % of D-LA / lactate in the total LA / lactate in the mother liquor showed an increase from 5.0% to 7.7%. The increase in the concentration % of D-LA / lactate in the mother liquor indicates that the precipitation of magnesium L-lactate has an enantiomeric purity that is enriched in the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 9 below.

[0157] Table 9.

[0158]

[0159] Embodiment 11

[0160] Enantiomeric enrichment of LA by precipitation with 10% excess magnesium hydroxide

[0161] A mixture containing L-lactic acid and D-lactic acid with a D:L ratio of 5:95 and a concentration of about 45% was placed in a chemical reactor preheated to 70°C and stirred at 300RPM. Over 15 minutes, 0.55 molar equivalents of an aqueous slurry of magnesium hydroxide (15% w / w) were added dropwise. The reaction was stirred at 70°C for 5 hours, during which time magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (cutoff 16-40 μm), washed with 1 weight equivalent of water, and dried at 70°C.

[0162] The total LA / lactate concentration and the % concentration of D-LA / lactate in the total LA / lactate were measured using HPLC, respectively. Due to the precipitation of magnesium lactate, the overall LA / lactate concentration in the solution decreased from 45% to 8%, however the % concentration of D-LA / lactate in the total LA / lactate in the solution showed an increase from 5.4% to 9.6%. The increase in the % concentration of D-LA / lactic acid in the solution indicates that the precipitation of magnesium L-lactate has an enantiomeric purity that is enriched in the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 10 below.

[0163] Table 10.

[0164]

[0165] The results show that although the addition of 10% excess magnesium hydroxide has little effect on the purity of magnesium lactate, it significantly improves the enantiomeric purity of the L-enantiomer in the product.

[0166] Comparative Example 1

[0167] Enantiomeric reduction of LA by precipitation with magnesium hydroxide at 30 °C

[0168] A mixture containing L-lactic acid and D-lactic acid at a D:L ratio of 6:94 and a concentration of about 45% was placed in a chemical reactor preheated to 30°C and stirred at 300RPM. To avoid overheating, 0.5 molar equivalents of an aqueous slurry of magnesium hydroxide (15% w / w) was added dropwise over 1.25 hours. The reaction was stirred at 30°C overnight, during which time magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (cutoff 16-40 μm), washed with 1 weight equivalent of water, and dried at 70°C.

[0169] HPLC was used to measure the total LA / lactate concentration and the concentration % of D-LA / lactate in the total LA / lactate, respectively. The overall LA / lactate concentration in the solution and the concentration % of D-LA / lactate in the total LA / lactate showed a decrease from 45% to 14% and from 5.7% to 3.7%, respectively. The decrease in the concentration % of D-LA / lactate in the solution indicated that the precipitation of magnesium L-lactate had a reduced enantiomeric purity of the L-enantiomer compared to the initial L-lactic acid content. The decrease in the enantiomeric purity of the L-enantiomer was further aggravated by washing with 1 weight equivalent of water. The results are summarized in Table 11 below.

[0170] Table 11.

[0171]

[0172] Therefore, the addition of magnesium hydroxide to a mixture of L-lactic acid and D-lactic acid at a temperature of 30°C does not provide enantiomeric enrichment of the L-enantiomer.

[0173] Comparative Example 2

[0174] LA enantiomer reduction by precipitation from a mixture of enantiomers containing 10.4% D-lactic acid

[0175] A mixture of L-lactic acid and D-lactic acid at a concentration of 45% containing 10.4% of the D-enantiomer was placed in a chemical reactor preheated to 70°C and stirred at 300RPM. Over 14 minutes, 0.5 molar equivalents of an aqueous slurry of magnesium hydroxide (15% w / w) were added dropwise. The reaction was stirred at 70°C for 5 hours, during which time magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (cutoff 16-40 μm), washed with 1 weight equivalent of water, and dried at 70°C.

[0176] The total LA / lactate concentration and the concentration % of D-LA / lactate in the total LA / lactate were measured using HPLC, respectively. The overall LA / lactate concentration in the solution and the concentration % of D-LA / lactate in the total LA / lactate showed a decrease from 45% to 11% and from 10.4% to 9.0%, respectively. The decrease in the concentration % of D-LA / lactate in the solution was comparable to the decrease in the total LA / lactate concentration, indicating that the enantiomeric purity of the L-enantiomer in the obtained precipitate did not change. The ratio of the D-enantiomer to the L-enantiomer was increased by washing with 1 weight equivalent of water, indicating that the enantiomeric purity of the L-enantiomer in the precipitate was reduced. The results are summarized in Table 12 below.

[0177] Table 12.

[0178]

[0179] Therefore, it can be expected that enantiomeric enrichment of the L-enantiomer is not achievable when using an initial mixture containing more than 10% D-lactic acid.

[0180] The above description of the specific embodiments will fully reveal the overall nature of the present invention, so that others can easily modify and / or adjust such specific embodiments for various applications by applying current knowledge without undue experimentation, and without departing from the overall concept, and therefore, such adjustments and modifications should be understood to be within the meaning and scope of the equivalents of the disclosed embodiments. It should be understood that the phrases or terms used herein are for the purpose of description rather than limitation. Without departing from the present invention, the means, materials and steps for carrying out the various functions disclosed may take various alternative forms.

Claims

1. A method for enriching L-lactic acid enantiomers or salts thereof, the method comprising the following steps: (a) obtaining a decomposed organic waste comprising an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 g / L to about 1,100 g / L, wherein the enantiomeric mixture comprises 10% or less of D-lactic acid; (b) contacting the enantiomeric mixture with a basic substance comprising divalent cations in an amount of about 50 equivalent % to about 120 equivalent % based on the number of carboxyl groups present in the enantiomeric mixture; and (c) precipitating L-lactate with said divalent cation, thereby obtaining L-lactate having an enriched enantiomeric purity compared to the initial enantiomeric mixture, wherein steps (b) and / or (c) are performed at a temperature in the range of about 40°C to about 100°C.

2. The method according to claim 1, comprising an enrichment of 5% or more of the L-lactic acid enantiomer or its salt.

3. The process according to claim 1, comprising an enrichment of up to 10% of the L-lactic acid enantiomer or its salt.

4. The method according to any one of claims 1 to 3, wherein the decomposed organic waste comprises lactic acid derived from a low pH lactic acid fermentation process.

5. The method according to any one of claims 1 to 3, wherein the decomposed organic waste comprises lactic acid originating from the decomposition of polylactic acid in an acidic medium.

6. The method according to any one of claims 1 to 3, wherein the decomposed organic waste comprises lactic acid byproduct derived from industrial production of polylactic acid, or wherein the decomposed organic waste comprises lactic acid byproduct derived from industrial purification of lactic acid, or wherein the decomposed organic waste comprises lactic acid obtained by hydrolyzing a lactide byproduct of industrial production of polylactic acid.

7. The method according to any one of claims 1 to 6, wherein the alkaline substance comprises a hydroxide selected from magnesium hydroxide, calcium hydroxide and mixtures thereof.

8. The method according to any one of claims 1 to 6, wherein the alkaline substance comprises a carbonate or bicarbonate selected from magnesium bicarbonate, magnesium carbonate, calcium bicarbonate, calcium carbonate and mixtures thereof.

9. The method according to any one of claims 1 to 8, wherein the alkaline substance is added in solid form.

10. The method according to any one of claims 1 to 8, wherein the alkaline substance is added as an aqueous solution or suspension.

11. The method of claim 10, wherein the alkaline substance is added as an aqueous solution having a concentration of about 50 g / L to about 500 g / L.

12. The method of any one of claims 1 to 11, wherein steps (b) and / or (c) are performed at a pressure of about 100 mbar to about 1,000 mbar, or wherein steps (b) and / or (c) are performed at a mixing speed of about 200 revolutions per minute to about 1,000 revolutions per minute (RPM).

13. The process according to any one of claims 1 to 12, wherein the obtained L-lactate is separated by filtration or centrifugation.

14. The process according to any one of claims 1 to 13, wherein the obtained L-lactate is subsequently purified.

15. The method of claim 14, wherein the subsequent purification comprises at least one of crystallization, recrystallization, partitioning, silica gel chromatography, and preparative HPLC, or wherein the subsequent purification comprises washing the obtained L-lactate with purified water.

16. The process according to any one of claims 1 to 15, wherein the resulting L-lactate contains less than 6% D-lactate.

17. The method according to any one of claims 1 to 16, wherein the obtained L-lactic acid salt is acidified by at least one of hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, sulfuric acid and combinations thereof to form L-lactic acid and used for subsequent polylactic acid formation.

18. A method for enriching L-lactic acid enantiomers or salts thereof, the method comprising the following steps: (a) obtaining a decomposed organic waste comprising an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 g / L to about 1,100 g / L, wherein the enantiomeric mixture comprises 6% or less of D-lactic acid; (b) contacting the enantiomeric mixture with a basic substance comprising a divalent cation; and (c) precipitating L-lactate with said divalent cation, thereby obtaining L-lactate having an enriched enantiomeric purity compared to the initial enantiomeric mixture, wherein steps (b) and / or (c) are carried out at a temperature in the range of about 50°C to about 100°C.

19. The method according to claim 18, comprising an enrichment of 5% or more of the L-lactic acid enantiomer or its salt.

20. The process according to claim 18, comprising enrichment of up to 10% of the L-lactic acid enantiomer or its salt.

21. The method of any one of claims 18 to 20, wherein the decomposed organic waste comprises lactic acid derived from a low pH lactic acid fermentation process.

22. The method according to any one of claims 18 to 20, wherein the decomposed organic waste comprises lactic acid derived from the decomposition of polylactic acid in an acidic medium.

23. The method of any one of claims 18 to 20, wherein the decomposed organic waste comprises lactic acid byproduct derived from industrial production of polylactic acid, or wherein the decomposed organic waste comprises lactic acid byproduct derived from industrial purification of lactic acid, or wherein the decomposed organic waste comprises lactic acid obtained by hydrolyzing a lactide byproduct of industrial production of polylactic acid.

24. The method of any one of claims 18 to 23, wherein the alkaline material comprises a hydroxide selected from magnesium hydroxide, calcium hydroxide, and mixtures thereof.

25. The method according to any one of claims 18 to 23, wherein the alkaline material comprises a carbonate or bicarbonate selected from magnesium bicarbonate, magnesium carbonate, calcium bicarbonate, calcium carbonate and mixtures thereof.

26. The method according to any one of claims 18 to 25, wherein the alkaline substance is added in solid form.

27. The method according to any one of claims 18 to 25, wherein the alkaline substance is added as an aqueous solution or suspension.

28. The method of claim 27, wherein the alkaline substance is added as an aqueous solution having a concentration of about 50 g / L to about 500 g / L.

29. The method of any one of claims 18 to 28, wherein steps (b) and / or (c) are performed at a pressure of about 100 mbar to about 1,000 mbar, or wherein steps (b) and / or (c) are performed at a mixing speed of about 200 revolutions per minute to about 1,000 revolutions per minute (RPM).

30. The process according to any one of claims 18 to 29, wherein the obtained L-lactate is isolated by filtration or centrifugation.

31. The process according to any one of claims 18 to 30, wherein the obtained L-lactate is subsequently purified.

32. The method of claim 31, wherein the subsequent purification comprises at least one of crystallization, recrystallization, partitioning, silica gel chromatography, and preparative HPLC, or wherein the subsequent purification comprises washing the resulting L-lactate with purified water.

33. A process according to any one of claims 18 to 32, wherein the resulting L-lactate contains less than 3% D-lactate.

34. The method according to any one of claims 18 to 33, wherein the obtained L-lactic acid salt is acidified by at least one of hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, sulfuric acid and combinations thereof to form L-lactic acid and used for subsequent polylactic acid formation.

35. A method for producing enantiomerically enriched L-lactate, the method comprising the steps of: (a) obtaining a decomposed organic waste comprising an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 g / L to about 1,100 g / L, wherein the enantiomeric mixture comprises 10% or less of D-lactic acid; (b) contacting the enantiomeric mixture with a basic substance comprising divalent cations in an amount of about 50 equivalent % to about 120 equivalent % based on the number of carboxyl groups present in the enantiomeric mixture; and (c) precipitating L-lactate with said divalent cation, thereby obtaining L-lactate having an enriched enantiomeric purity compared to the initial enantiomeric mixture, wherein steps (b) and / or (c) are performed at a temperature in the range of about 40°C to about 100°C.

36. The method of claim 35, wherein the L-lactate is enantiomerically enriched by 5% or more.

37. The method of claim 35, wherein the L-lactate is enantiomerically enriched by up to 10%.

38. A method according to any one of claims 35 to 37, wherein the decomposed organic waste comprises lactic acid derived from a low pH lactic acid fermentation process.

39. The method of any one of claims 35 to 37, wherein the decomposed organic waste comprises lactic acid derived from the decomposition of polylactic acid in an acidic medium.

40. The method of any one of claims 35 to 37, wherein the decomposed organic waste comprises lactic acid byproduct derived from industrial production of polylactic acid, or wherein the decomposed organic waste comprises lactic acid byproduct derived from industrial purification of lactic acid, or wherein the decomposed organic waste comprises lactic acid obtained by hydrolyzing a lactide byproduct of industrial production of polylactic acid.

41. The method of any one of claims 35 to 40, wherein the alkaline material comprises a hydroxide selected from magnesium hydroxide, calcium hydroxide, and mixtures thereof.

42. The method of any one of claims 35 to 40, wherein the alkaline material comprises a carbonate or bicarbonate selected from magnesium bicarbonate, magnesium carbonate, calcium bicarbonate, calcium carbonate, and mixtures thereof.

43. The method according to any one of claims 35 to 42, wherein the alkaline substance is added in solid form.

44. The method according to any one of claims 35 to 42, wherein the alkaline substance is added as an aqueous solution or suspension.

45. The method of claim 44, wherein the alkaline substance is added as an aqueous solution having a concentration of about 50 g / L to about 500 g / L.

46. ​​The method of any one of claims 35 to 45, wherein steps (b) and / or (c) are performed at a pressure of about 100 mbar to about 1,000 mbar, or wherein steps (b) and / or (c) are performed at a mixing speed of about 200 revolutions per minute to about 1,000 revolutions per minute (RPM).

47. The method according to any one of claims 35 to 46, wherein the obtained L-lactate is isolated by filtration or centrifugation.

48. The process according to any one of claims 35 to 47, wherein the obtained L-lactate is subsequently purified.

49. The method of claim 48, wherein the subsequent purification comprises at least one of crystallization, recrystallization, partitioning, silica gel chromatography, and preparative HPLC, or wherein the subsequent purification comprises washing the resulting L-lactate with purified water.

50. The process of any one of claims 35 to 49, wherein the resulting L-lactate contains less than 6% D-lactate.

51. The method of any one of claims 35 to 50, wherein the resulting L-lactic acid salt is acidified by at least one of hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, sulfuric acid, and combinations thereof to form L-lactic acid and used for subsequent polylactic acid formation.

52. A method for producing enantiomerically enriched L-lactate, the method comprising the steps of: (a) obtaining a decomposed organic waste comprising an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 g / L to about 1,100 g / L, wherein the enantiomeric mixture comprises 6% or less of D-lactic acid; (b) contacting the enantiomeric mixture with a basic substance comprising a divalent cation; and (c) precipitating L-lactate with said divalent cation, thereby obtaining L-lactate having an enriched enantiomeric purity compared to the initial enantiomeric mixture, wherein steps (b) and / or (c) are carried out at a temperature in the range of about 50°C to about 100°C.

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