Enantiomeric enrichment of L-lactic acid or its salts

Abstract

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

Description

Technical Field

[0001] The present invention relates to a process for increasing the enantiomeric purity of lactic acid derived from recycled waste.

Background Art

[0002] Polylactic acid constitutes an alternative to petroleum-derived plastics. Thus, its use in the manufacture of products such as food packaging, disposable articles, and fibers in the textile and hygiene product industries has been on the rise. Furthermore, polylactic acid is a biodegradable polymer and is thus used in various biomedical applications including the production of sutures, bone fixation screws, and devices for drug delivery.

[0003] Polylactic acid is formed by the polymerization of lactic acid monomers. Since lactic acid has a chiral carbon atom, it exists in two enantiomeric forms, D- and L-lactic acid. In order to produce polylactic acid suitable for industrial use, the D- or L-lactic acid entering the production process must be highly purified to meet the specifications required for polymerization and must mainly (more than about 98%) contain one lactic acid enantiomer in order to produce either PLLA (from L-lactic acid) or PDLA (from D-lactic acid).

[0004] In recent years, lactic acid fermentation has attracted attention because certain bacteria have the ability to produce only one of the individual lactic acid enantiomers (L or D). Conventional fermentation processes typically rely on the anaerobic fermentation of carbohydrate sources (e.g., starch and sugars from corn or sugarcane) by lactic acid-producing microorganisms that produce lactic acid as the main metabolic end product of carbohydrate fermentation. To produce polylactic acid, the lactic acid generated during fermentation is separated from the fermentation broth, purified by various processes, and then the purified lactic acid is subjected to polymerization. To produce optically pure polylactic acid, it is necessary to remove any endogenous D-lactic acid that may be present in the fermentation broth. International Publication No. WO 2017 / 122197, assigned to the applicant of the present invention, discloses dual-action lactic-acid (LA)-utilizing bacteria that are genetically modified to secrete polysaccharide-degrading enzymes such as cellulase, hemicellulase, and amylase, which are useful for treating organic waste to eliminate lactic acid present in the waste and decompose complex polysaccharides. International Publication No. WO 2020 / 208635, assigned to the applicant of the present invention, discloses a system and method for treating organic waste, particularly mixed food waste, using D-lactic acid oxidase to eliminate D-lactic acid present in the organic waste.

[0005] Polylactic acid waste can be recycled by returning it to lactic acid monomers or lactide by landfill, composting, anaerobic digestion (biogas production), incineration, or chemical hydrolysis. One of the common forms of commercially available polylactic acid is the copolymer PDLLA (poly(D-L-)lactic acid), which is mainly composed of PLLA (made from L-lactic acid) and trace amounts of PDLA (made from D-lactic acid). A significant portion of the polylactic acid plastics present in the market contains small amounts of PDLA that release D-lactic acid when hydrolyzed. The hydrolyzed material may also contain an unknown amount of D-lactic acid formed by racemization during hydrolysis.

[0006] For both D-lactic acid and L-lactic acid entering the new polylactic acid production process, an optical purity typically exceeding about 98% is required. Therefore, by using lactic acid from the fermentation process or the hydrolysis of polylactic acid, it should be possible to address the problem of isomer separation, which can be expensive, typically involving liquid or solid enantioselective membranes or high-performance liquid chromatography (HPLC).

[0007] The hydrolysis of polylactic acid using alkaline substances such as sodium hydroxide has been studied (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, UMI Number: 3583516; Wadso 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 on the hydrolysis of polylactic acid (PLA) and polycaprolactone (PCL) in aqueous acetonitrile solutions.

[0009] Xu, Crawford and Gorman (2011) Macromolecules, 44(12):4777-4782 reported on 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 reviews the hydrolysis of polylactic acid (PLA) and its composites.

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

[0012] International Publication No. 2015 / 112098 discloses a process for producing lactide from a plastic having polylactic acid (PLA-based plastic), the process including preparing a PLA-based plastic, promoting the decomposition of polylactic acid in the plastic by alcoholysis or hydrolysis to provide a low molecular weight polylactic acid, and thermally decomposing the low molecular weight polylactic acid to provide lactide. Further, this process further includes minimizing the size of the PLA-based plastic after the preparation step and purifying lactide after the thermal decomposition of the low molecular weight polylactic acid.

[0013] U.S. Patent No. 7,985,778 discloses a method for decomposing and regenerating a synthetic resin having an ester bond in its composition structure by performing a hydrolysis treatment and then a separation and recovery treatment. In the hydrolysis treatment, an article containing the synthetic resin to be decomposed and regenerated is exposed to a steam atmosphere filled under a saturated steam pressure at a treatment temperature below the melting point of the synthetic resin. The synthetic resin in the article to be treated is hydrolyzed by the steam generated at the treatment temperature to generate decomposition products and then polymerized to the synthetic resin containing an ester bond. The separation and recovery treatment is a treatment for separating the decomposition products generated by the hydrolysis treatment into a liquid component and a solid component and recovering them individually.

[0014] U.S. Patent No. 8,614,338 discloses a method for the stereospecific chemical recycling of a mixture of polymers based on polylactic acid (PLA) in order to reform one of its monomers or its derivatives. This method involves suspending the polymer mixture in a lactate ester capable of dissolving the PLA fraction, then first separating the lactate ester, PLA, and other dissolved impurities, and then separating the mixture of other polymers and insoluble impurities. Next, the solution containing the thus-obtained PLA is subjected to a transesterification-catalyzed depolymerization reaction to form oligoesters. Then, the transesterification-catalyzed depolymerization reaction is stopped at a given point in time, and the residual lactate ester is separated. The oligoesters thus obtained then undergo a cyclization reaction to produce lactide, which is finally stereospecifically purified such that a fraction of purified lactide having a meso-lactide content of 0.1% to 40% is obtained.

[0015] U.S. Patent Nos. 8,431,683 and 8,481,675 disclose a process for recycling a polymer blend necessarily containing PLA, the process including grinding, compression, dissolution of PLA in a solvent, removal of undissolved contaminating polymers, alcoholysis depolymerization reaction, and purification steps.

[0016] U.S. Patent No. 8,895,778 discloses the depolymerization of polyesters such as used polylactic acid. Ultrasonic-induced cavitation can be used to promote the depolymerization. The used PLA was exposed to methanol as a suspension medium in the presence of an organic or ionic salt of an alkali metal such as potassium carbonate and sodium hydroxide as a depolymerization catalyst in order to provide high-quality lactic acid monomer in high yield.

[0017] U.S. Patent Application Publication No. 2018 / 0051156 discloses a method for enhancing / accelerating the depolymerization of a polymer (e.g., one containing hydrolyzable bonds), generally including contacting a polymer containing hydrolyzable bonds with a solvent and an alcohol to obtain a polymer mixture in which the polymer is substantially dissolved, and the contacting is carried out at a temperature below the boiling point of the polymer mixture. The obtained depolymerized polymer can be separated therefrom (e.g., including monomers and / or oligomers). Such a method can be carried out under relatively mild temperature and pressure conditions. In some embodiments, the polymer is poly(lactic acid).

[0018] International Publication No. 2021 / 165964 assigned to the applicant of the present invention discloses an industrial fermentation for producing lactic acid from organic waste in combination with chemical recycling of polylactic acid to obtain lactic acid in high yield.

[0019] International Publication No. 2022 / 157768 assigned to the applicant of the present invention discloses a process for crystallizing high-purity magnesium L-lactate from decomposed organic waste.

[0020] International Publication No. 2023 / 012791 assigned to the applicant of the present invention discloses a process for producing high enantiomeric purity magnesium L-lactate and a small amount of non-lactate impurities and enhancing the enantiomeric purity of recycled lactate containing an enantiomeric mixture of L- and D-lactates.

[0021] There is an unmet need for an economical and reliable process for producing enantiomerically pure L-lactic acid / lactate from decomposed waste. SUMMARY OF THE INVENTION

[0022] The present invention provides a process for enhancing the enantiomeric purity of lactic acid obtained, for example, from lactic acid fermentation in the chemical recycling of organic waste and / or PLA waste. The present invention further provides a process for obtaining L-lactate with enhanced enantiomeric purity.

[0023] The present invention is based in part on the unexpected finding that the enantiomeric purity of L-lactate can be increased by selectively precipitating L-lactate from an enantiomeric mixture containing D- and L-lactic acid. Thus, the present invention enables the recycling of waste from various sources, including waste containing endogenous D-lactic acid monomers, while avoiding the need for D-lactic acid-utilizing bacteria or enzymes to eliminate D-lactic acid. Advantageously, in the present invention, L-lactate is produced with an enantiomeric purity of more than 98%, which can be used for the commercial production of PLA without additional treatment for separating the isomers.

[0024] The selective precipitation of L-lactate from an enantiomeric mixture of D-lactic acid and L-lactic acid of organic waste origin is disclosed herein for the first time. As a result of the selective precipitation, the L-lactic acid / lactate monomer for subsequent use is concentrated.

[0025] According to a first aspect, the present invention is a process for concentrating an L-lactic acid enantiomer or a salt thereof, comprising: (a) obtaining a decomposed organic waste containing an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 to about 1,100 g / L, the enantiomeric mixture containing 10% or less of D-lactic acid; (b) contacting the enantiomeric mixture with an alkaline substance containing a divalent cation in an amount of about 50 to about 120 equivalent% based on the number of carboxyl groups present in the enantiomeric mixture; (c) precipitating L-lactate with the divalent cation, thereby obtaining L-lactate with increased enantiomeric purity compared to the initial enantiomeric mixture; and providing a process wherein step (b) and / or (c) is carried out at a temperature in the range of about 40°C to about 100°C (including each value within the specified range).

[0026] According to another aspect, the present invention is a process for producing an enantiomerically enriched L-lactate, comprising: (a) A step of obtaining a decomposed organic waste containing an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 to about 1,100 g / L, the step in which the enantiomeric mixture contains 10% or less of D-lactic acid, and (b) A step of contacting the enantiomeric mixture with an alkaline substance containing a divalent cation in an amount of about 50 to about 120 equivalent% based on the number of carboxyl groups present in the enantiomeric mixture, and (c) A step of precipitating L-lactate with the divalent cation, thereby obtaining an L-lactate with enhanced enantiomeric purity compared to the initial enantiomeric mixture, and comprising, providing a process in which step (b) and / or (c) is carried out at a temperature in the range of about 40°C to about 100°C (including each value within the specified range).

[0027] In some embodiments, the enantiomeric mixture contains 9% or less of D-lactic acid. In other embodiments, the enantiomeric mixture contains 8% or less of D-lactic acid. In still other embodiments, the enantiomeric mixture contains 7% or less of D-lactic acid. In additional embodiments, the enantiomeric mixture contains 6% or less of D-lactic acid. In further embodiments, the enantiomeric mixture contains 5% or less of D-lactic acid. In various embodiments, the enantiomeric mixture contains 4% or less of D-lactic acid. In a specific embodiment, the enantiomeric mixture contains 3% or less of D-lactic acid. In a particular embodiment, the enantiomeric mixture contains 3% or more of D-lactic acid. In some embodiments, the enantiomeric mixture contains 4% or more of D-lactic acid. In an exemplary embodiment, the enantiomeric mixture contains 5% or more of D-lactic acid.

[0028] In additional embodiments, step (b) and / or (c) is carried out at a temperature in the range of about 45°C to about 100°C (including each value within the specified range). In other embodiments, step (b) and / or (c) is carried out at a temperature in the range of about 50°C to about 100°C (including each value within the specified range).

[0029] According to another aspect, the present invention is a process for concentrating an L-lactic acid enantiomer or a salt thereof, (a) A step of obtaining a decomposed organic waste containing an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 to about 1,100 g / L, wherein the enantiomeric mixture contains 6% or less of D-lactic acid, and (b) A step of contacting the enantiomeric mixture with an alkaline substance containing a divalent cation, and (c) A step of precipitating L-lactate with the divalent cation, thereby obtaining an L-lactate with enhanced enantiomeric purity compared to the initial enantiomeric mixture, and including, providing a process in which step (b) and / or (c) is carried out at a temperature in the range of about 50°C to about 100°C (including each value within the specified range).

[0030] According to an additional aspect, the present invention is a process for producing an enantiomerically enriched L-lactate, (a) A step of obtaining a decomposed organic waste containing an enantiomeric mixture of D-lactic acid and L-lactic acid at a concentration of about 100 to about 1,100 g / L, wherein the enantiomeric mixture contains 6% or less of D-lactic acid, and (b) A step of contacting the enantiomeric mixture with an alkaline substance containing a divalent cation, and (c) A step of precipitating L-lactate with the divalent cation, thereby obtaining an L-lactate with enhanced enantiomeric purity compared to the initial enantiomeric mixture, and including, providing a process in which step (b) and / or (c) is carried out at a temperature in the range of about 50°C to about 100°C (including each value within the specified range).

[0031] In various embodiments, the processes disclosed herein concentrate the L-lactic acid enantiomer or a salt thereof by 1% or more. In another embodiment, the process concentrates the L-lactic acid enantiomer or a salt thereof by 5% or more. In yet another embodiment, the process concentrates the L-lactic acid enantiomer or a salt thereof by 10% or more. In a specific embodiment, the process concentrates the L-lactic acid enantiomer or a salt thereof by up to 10%. In other embodiments, the process reduces the D-lactic acid enantiomer or a salt thereof by 10% or more. In still other embodiments, the process reduces the D-lactic acid enantiomer or a salt thereof by 20% or more. In additional embodiments, the process reduces the D-lactic acid enantiomer or a salt thereof by 30% or more. In certain embodiments, the process reduces the D-lactic acid enantiomer or a salt thereof by 40% or more. In additional embodiments, the process reduces the D-lactic acid, enantiomer or a salt thereof by 50% or more. In further embodiments, the process reduces the D-lactic acid enantiomer or a salt thereof by 60% or more. In an exemplary embodiment, the process reduces the D-lactic acid enantiomer or a salt thereof by 70% or more. In a specific embodiment, the process reduces the D-lactic acid enantiomer or a salt thereof by 80% or more. In some embodiments, the process reduces the D-lactic acid enantiomer or a salt thereof by 90% or more. In a designated embodiment, the process reduces the D-lactic acid enantiomer or a salt thereof by up to 95%.

[0032] In one embodiment, the decomposed organic waste contains lactic acid derived from a low pH lactic acid fermentation process.

[0033] In certain embodiments, the organic waste contains 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.

[0034] In a further embodiment, the decomposed organic waste is pretreated before step (a). In a specific embodiment, the pretreatment includes removal of non-lactic acid-containing impurities.

[0035] In an additional embodiment, the low pH lactic acid fermentation process is carried out at a pH of about 2 to about 5.5 (including each value within the specified range).

[0036] In one embodiment, the decomposed organic waste contains lactic acid derived from the decomposition of polylactic acid in an acidic medium.

[0037] In a particular embodiment, the decomposition of polylactic acid in an acidic medium includes the hydrolysis of polylactic acid in the presence of an acid selected from the group consisting of hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid, and combinations thereof. Each possibility represents a separate embodiment.

[0038] In a further embodiment, the decomposed organic waste contains lactic acid by-products derived from the industrial production of polylactic acid. In other embodiments, the decomposed organic waste contains lactic acid by-products derived from the industrial purification of lactic acid. In still other embodiments, the decomposed organic waste contains lactic acid obtained from hydrolyzing lactide by-products from the industrial production of polylactic acid.

[0039] In some embodiments, the alkaline substance containing divalent cations contains hydroxides. In another embodiment, the alkaline substance containing divalent cations is selected from the group consisting of magnesium hydroxide, calcium hydroxide, and mixtures thereof. Each possibility represents a separate embodiment. In one embodiment, the alkaline substance containing divalent cations is magnesium hydroxide. In a further embodiment, the alkaline substance containing divalent cations contains carbonates or bicarbonates. Each possibility represents a separate embodiment. In a further embodiment, the alkaline substance containing divalent cations is selected from the group consisting of magnesium bicarbonate, magnesium carbonate, calcium bicarbonate, calcium carbonate, and mixtures thereof. Each possibility represents a separate embodiment.

[0040] In certain embodiments, the alkaline substance is added in solid form. In alternative embodiments, the alkaline substance is added as an aqueous solution or suspension. In further embodiments, the alkaline substance is added gradually. In other embodiments, the alkaline substance is added as an aqueous solution at a concentration of about 50 to about 500 g / L (including each value within the specified range).

[0041] 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 within the specified range). In exemplary embodiments, 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 within the specified range). In specific embodiments, 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 within the specified range). In yet additional embodiments, 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 within the specified range).

[0042] In further embodiments, steps (b) and / or (c) are carried out at a pressure of about 100 to about 1,000 mbar (including each value within the specified range). In other embodiments, steps (b) and / or (c) are carried out at a mixing rate of about 200 to about 1,000 revolutions per minute (RPM) (including each value within the specified range).

[0043] In some embodiments, the precipitation of L-lactate in step (c) is carried out for a period in the range of 10 minutes to 1 day (including each value within the specified range). In additional embodiments, the precipitation of L-lactate in step (c) is carried out for a period in the range of 1 hour to 1 day (including each value within the specified range).

[0044] In a further embodiment, the precipitation of L-lactate in step (c) is carried out in a pH range of about 3 to about 10 (including each value within the specified range). In a specified embodiment, the precipitation of L-lactate in step (c) is carried out in a pH range of about 4 to about 9 (including each value within the specified range). In some embodiments, the precipitation of L-lactate in step (c) is carried out in a pH range of about 5 to about 8 (including each value within the specified range). In a further embodiment, the precipitation of L-lactate in step (c) is carried out in a pH range of about 6 to about 7 (including each value within the specified range).

[0045] 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, the subsequent purification includes at least one of crystallization, recrystallization, partitioning, silica gel chromatography, preparative HPLC, and combinations thereof. Each possibility represents a separate embodiment.

[0046] In a specific embodiment, the subsequent purification includes washing the obtained L-lactate, for example, using purified water. In other embodiments, the subsequent purification includes dissolving and recrystallizing the obtained L-lactate.

[0047] In one embodiment, the obtained L-lactate contains less than 6% D-lactate. In another embodiment, the obtained L-lactate contains less than 5% D-lactate. In another embodiment, the obtained L-lactate contains less than 4% D-lactate. In another embodiment, the obtained L-lactate contains less than 3% D-lactate. In another embodiment, the obtained L-lactate contains less than 2% D-lactate. In another embodiment, the obtained L-lactate contains less than 1.5% D-lactate. In a specified embodiment, the obtained L-lactate contains less than 1% D-lactate.

[0048] In a further embodiment, the obtained L-lactate is crystalline L-lactate.

[0049] In other embodiments, the obtained L-lactate is acidified with 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.

[0050] Other objects, features, and advantages of the present invention will become apparent from the following description, examples, and drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0051] The present invention provides a process for enantioconcentrating L-lactic acid or its salt from an enantiomeric mixture of D-lactic acid and L-lactic acid derived from a recycling procedure. Surprisingly, when the lactic acid mixture is neutralized with an alkaline base containing a divalent cation, L-lactate selectively precipitates, thereby concentrating the L-lactic acid / lactate. The high-purity L-lactate can be further used to produce novel lactate-based products.

[0052] According to some aspects and embodiments, a process for concentrating an L-lactic acid enantiomer or its salt, comprising obtaining a solution comprising an enantiomeric mixture of D-lactic acid and L-lactic acid, contacting the enantiomeric mixture with an alkaline substance containing a divalent cation, and precipitating L-lactate with the divalent cation, thereby obtaining an L-lactate with increased enantiopurity, is provided.

[0053] According to other aspects and embodiments, a process for producing an L-lactate with increased enantiopurity, comprising obtaining a solution comprising an enantiomeric mixture of D-lactic acid and L-lactic acid, contacting the enantiomeric mixture with an alkaline substance containing a divalent cation, and precipitating L-lactate with the divalent cation, thereby obtaining an L-lactate with increased enantiopurity, is provided.

[0054] In certain aspects and embodiments, the solution containing the enantiomeric mixture of D-lactic acid and L-lactic acid is derived from decomposed organic waste.

[0055] 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 (deprotonated lactic acid) can refer to stereoisomers of lactic acid: L-lactic acid / L-lactate, D-lactic acid / D-lactate, or combinations thereof.

[0056] For most industrial applications, high-purity L-lactic acid monomers are required to produce polylactic acid (PLA) with suitable properties. Thus, the process of the present invention relates particularly to the production of L-lactate with enhanced enantiomeric purity that can be converted to L-lactic acid suitable for reuse without the need to specifically exclude D-lactic acid / lactate monomers.

[0057] One advantage obtained from the process of the present invention is enantiomeric enrichment, which is particularly beneficial for the reuse of lactic acid. The enantiomeric enrichment is at least 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or 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, a lactate containing 99% L-lactate and 1% D-lactate is obtained by 10% enrichment. A reduction in the content of at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or even 100% of D-lactic acid in the initial D-lactic acid content by the process disclosed herein is 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 lactate containing 95% L-lactate and 5% D-lactate is obtained by a 50% reduction in the content of the D-enantiomer. The L-lactate precipitate obtained according to the principle of the present invention 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.

[0058] According to the principle of the present invention, an enantiomeric mixture of D-lactic acid and L-lactic acid is derived from decomposed organic waste. For example, an enantiomeric mixture of D-lactic acid and L-lactic acid can be obtained from the hydrolysis of polylactic acid in the presence of an acid. In another example, an enantiomeric mixture of D-lactic acid and L-lactic acid may be a by-product of the industrial production of polylactic acid or the industrial purification of lactic acid. An additional source of lactic acid containing a mixture of the D-enantiomer and the L-enantiomer can result as a by-product of the hydrolysis of lactide from the industrial production of polylactic acid. An enantiomeric mixture of D-lactic acid and L-lactic acid derived from organic waste subjected to lactic acid fermentation at low pH is within the scope of the present invention.

[0059] Examples of organic waste within the scope of the present invention include waste obtained from various sources including food and beverage waste, such as municipal food waste, household 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, but are not limited thereto. Each possibility represents a separate embodiment. The organic waste may further originate from animal and human excrement, vegetable and fruit residues, plants, cooked food, protein residues, slaughter waste, and residues extending to combinations thereof. Each possibility represents a separate embodiment. Industrial organic food and beverage waste can include factory waste such as by-products, factory rejects (e.g., expired products, defective products), market returns or inedible food parts (e.g., skin, fat, bread crusts, and peel) trimmings. Each possibility represents a separate embodiment. Commercial organic food and beverage waste can include waste from shopping malls, restaurants, supermarkets, etc. Each possibility represents a separate embodiment.

[0060] According to certain aspects and embodiments, the organic waste includes monosaccharides or disaccharides obtained as by-products of sugar production from beet sugar or sucrose, such as, but not limited to, the production of fructose, molasses, or high fructose corn syrup (HFCS). According to other aspects and embodiments, the organic waste includes starch and starch derivatives, such as purified glucose syrup originating from the hydrolysis of starch, and the starch may be corn starch, tapioca starch, wheat starch, potato starch, etc. Each possibility represents a separate embodiment. The organic waste may further be derived from by-products of wine or beer production, such as, but not limited to, yeast autolysates and hydrolysates, as well as plant protein hydrolysates, animal protein hydrolysates, and soluble by-products from steeped wheat or corn. It is also possible to use paper sludge hydrolysates obtained by hydrolyzing paper sludge with cellulolytic enzymes, as well as dairy by-products generated during the production of cheese and during the production of dairy beverages such as lactose-free beverages.

[0061] According to various aspects and embodiments, the digested organic waste includes fermentation broth obtained from the fermentation process of a carbohydrate source. When using heterogeneous feedstocks, the digested organic waste or fermentation broth typically contains insoluble organic-based impurities such as, but not limited to, microorganisms (e.g., lactic acid-producing microorganisms including, for example, yeast, bacteria, and fungi), fats and oils, lipids, aggregated proteins, bone fragments, hair, precipitated salts, cell debris, fibers (e.g., skins of fruits and / or vegetables), and residual untreated waste (e.g., food husks, seeds, food insoluble particles and fragments, etc.). Each possibility represents a separate embodiment. Non-limiting examples of insoluble inorganic-based impurities include plastics, glass, residues from food packaging, sand, and combinations thereof. Each possibility represents a separate embodiment.

[0062] Although not necessary, the decomposed organic waste may be further pretreated before using the process of the present invention. Suitable pretreatments include, but are not limited to, filtration, ultrafiltration, nanofiltration, reverse osmosis (RO) filtration, solvent extraction, repulsive extraction, salt precipitation, crystallization, distillation, evaporation, electrodialysis, and various types of chromatography (such as adsorption or ion exchange). Each possibility represents a separate embodiment.

[0063] According to the principle of the present invention, fermentation is carried out at a low pH. The formation of L-lactic acid causes an endogenous decrease in pH. Therefore, in the absence of a neutralizing base, the pH of the fermentation is in the range of about 2 to about 5.5 (including each value within the specified range).

[0064] Typically, fermentation at a low pH can be carried out by acid-tolerant (AT) yeast strains belonging to, but not limited to, the genera selected from Saccharomyces, Candida, Schizosaccharomyces, Torulaspora, Kluyveromyces, Zygosaccharomyces, and Dekkera. Each possibility represents a separate embodiment.

[0065] In other aspects and embodiments, the decomposed organic waste is derived from the acid hydrolysis of polylactic acid waste. The acid 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 within 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 under reduced pressure or high pressure, for example in the range of about 100 mbar to about 1500 mbar (including each value therebetween). Optionally, a catalyst may be added to accelerate the hydrolysis.

[0066] The decomposed waste may contain D- and L-enantiomers at various concentrations. Typically, the concentrations of D- and L-lactic acid are in the range of about 100 to about 1100 g / L (including each value within the specified range). Exemplary concentrations of D- and L-lactic acid include, but are not limited to, about 100 g / L, 150 g / L, 200 g / L, 250 g / L, 300 g / L, 350 g / L, 400 g / L, 450 g / L, 500 g / L, 550 g / L, 600 g / L, 650 g / L, 700 g / L, 750 g / L, 800 g / L, 850 g / L, 900 g / L, 950 g / L, 1,000 g / L, 1,050 g / L, or 1,100 g / L. Each possibility represents a separate embodiment. The lactic acid enantiomer ratio in the decomposed waste can vary depending on the endogenous content of D-lactic acid and the racemic lactic acid formation that occurs during fermentation or decomposition. Decomposed organic waste containing endogenous D-lactic acid in an amount of 10% or less, such as 9%, 8%, 7%, 6%, 5%, 4%, 3%, or less, is within the scope of the present invention. Each possibility represents a separate embodiment. Typically, the ratio of D-monomer to L-monomer is, 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 in an amount of at least 3%, such as 4%, 5%, 6%, 7%, 8%, 9%, and up to 10% of D-lactic acid. Each possibility represents a separate embodiment.

[0067] If the decomposed organic waste contains particles of unhydrolyzed PLA waste or non-lactic acid-containing impurities, they can be separated from the decomposed organic waste by solid-liquid separation techniques such as filtration or decantation, for example. Each possibility represents a separate embodiment.

[0068] According to the principles of the present invention, an alkaline substance containing divalent ions is then added to induce precipitation of L-lactate with increased enantiomeric purity. Suitable alkaline substances include, but are not limited to, hydroxides, carbonates, and bicarbonates containing divalent cations such as magnesium, calcium, or mixtures thereof. Each possibility represents a separate embodiment. Exemplary bases include, but are not limited to, magnesium hydroxide, calcium hydroxide, magnesium bicarbonate, magnesium carbonate, calcium bicarbonate, calcium carbonate, or mixtures and combinations thereof. Each possibility represents a separate embodiment. It is currently preferred to add magnesium hydroxide to obtain a precipitate of magnesium L-lactate with increased 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, typically the aqueous solution contains the alkaline substance at a concentration in the range of about 50 to about 500 g / L (including each value within the specified range). Typical concentrations include 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 125 g / L, 150 g / L, 175 g / L, 200 g / L, 225 g / L, 250 g / L, 275 g / L, 300 g / L, 325 g / L, 350 g / L, 375 g / L, 400 g / L, 425 g / L, 450 g / L, 475 g / L, or 500 g / L, but are not limited thereto. Each possibility represents a separate embodiment. In some embodiments, the alkaline substance is added gradually with mixing. The stepwise addition of the alkaline substance can be performed to avoid excessive heating caused by the exothermic reaction.

[0069] Throughout the addition of the alkaline substance and during precipitation, the mixing speed includes stirring at about 200 to about 1,000 RPM (including each value within the specified range). Typical mixing speeds include, but are not limited to, 200 RPM, 250 RPM, 300 RPM, 350 RPM, 400 RPM, 450 RPM, 500 RPM, 550 RPM, 600 RPM, 650 RPM, 700 RPM, 750 RPM, 800 RPM, 850 RPM, 900 RPM, 950 RPM, or 1,000 RPM. Each possibility represents a separate embodiment.

[0070] In some aspects and embodiments, the alkaline substance is added in a stoichiometric amount. In other aspects and embodiments, the alkaline substance is added in excess. In still other aspects and embodiments, the alkaline substance is added in a deficient amount. According to the principles of the present invention, the alkaline substance is added in an amount of about 50 to about 120 equivalent % based on the number of carboxyl groups present in the enantiomeric mixture. Typical amounts of the alkaline substance include, but are not limited to, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, or 120% equivalent based on the number of carboxyl groups present in the enantiomeric mixture. Each possibility represents a separate embodiment. As will be understood by those skilled in the art, any amount less than 100 equivalent % based on the number of carboxyl groups present in the enantiomeric mixture refers to a deficient amount of the alkaline substance compared to lactic acid, and any amount greater than 100 equivalent % based on the number of carboxyl groups present in the enantiomeric mixture refers to an excess amount of the alkaline substance compared to lactic acid. Thus, the pH at which precipitation occurs is typically in the range of about 3 to about 10, for example, 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.

[0071] In some embodiments and implementations, precipitation occurs upon addition of an alkaline substance. Alternatively, precipitation may occur at any point after addition of the alkaline substance, for example, within any period from about 10 minutes to about 1 day (including each value within the specified range). In various embodiments and implementations, precipitation occurs by forming an initial precipitate and maturing the initial precipitate over a specific period. In other embodiments and implementations, precipitation occurs in two stages, first forming an initial precipitate, separating it from the mother liquor, and then forming and maturing a second precipitate from the mother liquor. Typically, precipitation occurs over a period in the range of about 1 hour to about 24 hours, for example, 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. Each possibility represents a separate embodiment.

[0072] Addition of an alkaline substance and precipitation of L-lactate at elevated temperature are within the scope of the present invention. As used herein, the term "elevated temperature" refers to a temperature higher than room temperature. Suitable temperatures include temperatures of 40°C or higher. For example, the temperature in the step of adding an alkaline substance and the step of precipitating L-lactate with enhanced enantiomeric purity 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 within the specified range). Each possibility represents a separate embodiment. Typically, a temperature in the range of 40°C to 100°C is utilized, 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.

[0073] As will be understood 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 carried out at a temperature of about 40 °C for a duration of about 18 to about 22 hours (including each value within the specified range). In other embodiments, the step of precipitating L-lactate is carried out at a temperature of about 50 °C for a duration of about 5 to about 10 hours (including each value within the specified range). In still other embodiments, the step of precipitating L-lactate is carried out at a temperature of about 90 °C for a duration of about 2 to about 5 hours (including each value within the specified range).

[0074] The addition of the alkaline substance and the precipitation of L-lactate can be carried out at various pressures. For example, the pressure in the step of adding the alkaline substance and / or the step of precipitating L-lactate with enhanced enantiomeric purity is in the range of about 100 to about 1,000 mbar (including each value within the specified range). Exemplary pressures include, but are not limited to, about 100, 200, 300, 400, 500, 600, 700, 800, 900, or 1,000 mbar. Each possibility represents a separate embodiment.

[0075] Typically, in the process of the present invention, a lactate having the divalent cation is produced as the final product. However, in order to obtain polylactic acid, the lactate may be acidified for subsequent polymerization using, for example, hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, sulfuric acid, and mixtures or combinations thereof. Each possibility represents a separate embodiment.

[0076] The L-lactate thus obtained may be further subjected to a downstream purification process. Surprisingly, it has also been found that one simple purification that improves the enantiomeric purity of L-lactate is, for example, washing the precipitate with purified water. Additional purification steps, such as crystallization, recrystallization, partitioning, silica gel chromatography, preparative HPLC, and combinations thereof, are within the scope of the present invention. Each possibility represents a separate embodiment.

[0077] The purification process may include extraction, electrodialysis, adsorption, ion exchange, crystallization, and combinations of these methods. For example, several methods are outlined in Ghaffar et al. (2014) Journal of Radiation Research and Applied Sciences, 7(2):222-229; and Lopez-Garzon et al. (2014) Biotechnol Adv., 32(5):873-904. Alternatively, the recovery of lactic acid and its conversion to lactide in a single step may be used (Dusselier et al. (2015) Science, 349(6243):78-80).

[0078] Specific downstream purification processes for purifying enantiomerically enriched lactate via crystallization are described in International Publication No. WO 2020 / 110108 and International Publication No. WO 2022 / 157768, which are assigned to the applicant of the present invention.

[0079] The resulting lactate precipitate can be separated from the remaining liquid by microfiltration or nanofiltration. The remaining liquid may be subjected to concentration, followed by at least one additional precipitation. After separating the precipitate from the liquid, the concentrated L-lactate may be washed and purified with an aqueous solution or an organic solvent such as ethanol.

[0080] The processes disclosed herein are primarily intended to concentrate the L-lactic acid / lactate enantiomer from an enantiomeric mixture containing D- and L-lactic acid derived from decomposed organic waste, although the concentration of the D-enantiomer is also contemplated by the present invention.

[0081] Thus, according to certain aspects and embodiments, the present invention is a process for concentrating a D-lactic acid enantiomer or a salt thereof, or for producing an enantiomerically enriched D-lactate, comprising: (a) obtaining a decomposed organic waste containing an enantiomeric mixture of D-lactic acid and L-lactic acid; (b) contacting the enantiomeric mixture with an alkaline substance containing a divalent cation; (c) precipitating D-lactate with the divalent cation, thereby obtaining D-lactate with enhanced enantiomeric purity; A process comprising is provided.

[0082] As used herein and in the appended claims, the term "about" refers to ±10%.

[0083] As used herein and in the appended claims, the singular forms "a", "an", and "the" encompass plural references unless the context clearly dictates otherwise. Thus, for example, reference to "an alkaline substance" includes plural such substances unless the context clearly dictates otherwise. It should be noted that the terms "and" or "or" are generally employed in the sense of "and / or" unless the context clearly dictates otherwise.

[0084] The following examples are presented to more fully illustrate specific embodiments of the invention. However, they should in no way be construed as limiting the broad scope of the invention. Those skilled in the art can readily devise many variations and modifications of the principles disclosed herein without departing from the scope of the invention.

Examples

[0085] Example 1 Decomposed organic waste from low pH fermentation To obtain lactic acid at a concentration of at least 100 g / L, lactic acid fermentation of a carbohydrate source is carried out using an acid-tolerant (AT) yeast strain of Saccharomyces cerevisiae in a suitable medium. The lactic acid concentration and the % of D-lactic acid are measured separately using HPLC. Then, magnesium hydroxide is added to the broth to precipitate magnesium L-lactate with enhanced enantiomeric purity. The precipitated solid is then filtered off and washed with water to typically obtain crude MgLa2·2H2O. Optionally, the crude magnesium lactate is dissolved in water and then recrystallized.

[0086] Example 2 Organic waste decomposed from the acid hydrolysis of PLA The PLA from cafeteria waste is shredded into small pieces and immersed in a 0.01% w / w H2SO4 solution having a pH of about 2.5. The mixture is heated to 90 °C to promote PLA decomposition over a duration of 1 - 2 days. Optionally, a catalyst is added. The decrease in pH due to the formation of PLA oligomers and monomers with carboxylic acid end groups is monitored using a pH meter. At the end of the reaction, residual PLA and solid impurities are filtered off using a P3 sintered glass funnel (16 - 40 μm cut-off). The lactic acid concentration and the % of D-lactic acid in the filtered solution are measured separately using HPLC. Magnesium hydroxide is added to the filtered solution to precipitate magnesium L-lactate with enhanced enantiopurity. The crude magnesium lactate is further purified by subsequent recrystallization.

[0087] Example 3 LA Enantiomer Enrichment by Precipitation with Magnesium Hydroxide A mixture containing L- and D-lactic acid with a D:L ratio of about 4:96 and a concentration of about 45% was placed in a chemical reactor preheated to 50 °C and stirred at 300 RPM. A 0.5 molar equivalent of magnesium hydroxide slurry (15% w / w) in water was added dropwise over 0.5 hours. The reaction mixture was stirred at 50 °C overnight, during which magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (16 - 40 μm cut-off), washed with 1 weight equivalent of water, and dried at 70 °C.

[0088] Both the total LA / lactate concentration and the % D-LA / lactate of the total LA / lactate concentration were measured separately using HPLC. The total LA / lactate concentration in the solution decreased from 43% to 7% due to the precipitation of magnesium lactate, while the % D-LA / lactate of the total LA / lactate concentration in the solution showed an increase from 5.8% to 7.8%. This increase in the % D-LA / lactate concentration in the solution indicates the precipitation of magnesium L-lactate with enhanced enantiopurity of the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 1 below.

[0089]

Table 1

[0090] Example 4 LA Enantiomer Concentration by Precipitation with Magnesium Hydroxide at 90 °C A mixture containing L - and D - lactic acid with an approximate D:L ratio of 6:94 and a concentration of approximately 45% was placed into a pre - heated chemical reactor at 90 °C and stirred at 300 RPM. A 0.5 molar equivalent of magnesium hydroxide slurry (15% w / w) in water was added dropwise over 12 hours. The reaction mixture was stirred at 90 °C overnight, during which magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (16 - 40 μm cut - off), washed with 1 weight equivalent of water, and dried at 70 °C.

[0091] Both the total LA / lactate concentration and the % D - LA / lactate of the total LA / lactate concentration were measured separately using HPLC. The total LA / lactate concentration in the solution decreased from 45% to 13% due to the precipitation of magnesium lactate, while the % D - LA / lactate of the total LA / lactate concentration in the solution showed an increase from 5.7% to 10.5%. This increase in the % D - LA / lactate concentration in the solution indicates the precipitation of L - magnesium lactate with enhanced enantiopurity of the L - enantiomer compared to the initial L - lactic acid content. The results are summarized in Table 2 below.

[0092]

Table 2

[0093] Example 5 LA Enantiomer Concentration by Precipitation with Magnesium Hydroxide at Different Temperatures A mixture containing L- and D-lactic acids with a D:L ratio of about 6:94 and a concentration of about 45% was placed in a chemical reactor preheated to 40 °C and stirred at 300 RPM. A 0.5 molar equivalent of magnesium hydroxide slurry (15% w / w) in water was added dropwise over 26 minutes. Due to the exothermic nature of the reaction during base addition, the temperature rose to 45 °C. The reaction mixture was cooled to 40 °C and stirred overnight at 40 °C, during which magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (16 - 40 μm cut-off), washed with 1 weight equivalent of water, and dried at 70 °C.

[0094] Both the total LA / lactate concentration and the % D-LA / lactate of the total LA / lactate concentration were measured separately using HPLC. The total LA / lactate concentration in the solution decreased from 45% to 9% due to the precipitation of magnesium lactate, while the % D-LA / lactate of the total LA / lactate concentration in the solution showed an increase from 5.7% to 7.7%. This increase in the % D-LA / lactate concentration in the solution indicates the precipitation of magnesium L-lactate with enhanced enantiopurity of the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 3 below.

[0095]

Table 3

[0096] This procedure was repeated at temperatures of 50 °C and 90 °C to determine the % decrease in the D-enantiomer. The results show that enantiomeric enrichment is enhanced at higher temperatures, which also allows for a shorter precipitation time. The results are summarized in Table 4 below.

[0097]

Table 4

[0098] Example 6 LA Enantiomeric Enrichment by Precipitation with Magnesium Carbonate at 50 °C A mixture containing L- and D-lactic acid at a D:L ratio of about 6:94 and a concentration of about 45% was placed in a preheated chemical reactor at 50 °C and stirred at 300 RPM. A slurry of 1 molar equivalent of magnesium carbonate in water (33% w / w) was added dropwise over 10 minutes. During the addition, the evolution of CO2 gas indicating the progress of the reaction was observed. The reaction mixture was stirred at 50 °C overnight, during which magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (16 - 40 μm cut-off), washed with 1 weight equivalent of water, and dried at 70 °C.

[0099] Both the total LA / lactate concentration and the % D-LA / lactate of the total LA / lactate concentration were measured separately using HPLC. The total LA / lactate concentration in the solution decreased from 45% to 15% due to the precipitation of magnesium lactate, while the % D-LA / lactate of the total LA / lactate concentration in the solution showed an increase from 5.7% to 6.8%. This increase in the % D-LA / lactate concentration in the solution indicates the precipitation of L-magnesium lactate with enhanced enantiopurity of the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 5 below.

[0100]

Table 5

[0101] Example 7 LA Enantiomer Enrichment by Precipitation from an Enantiomeric Mixture Containing 9.0% D-Lactic Acid A mixture containing L- and D-lactic acid at a D:L ratio of about 9:91 and a concentration of about 45% was placed in a preheated chemical reactor at 70 °C and stirred at 300 RPM. A slurry of 0.5 molar equivalent of magnesium hydroxide in water (15% w / w) was added dropwise over 13 minutes. The reaction mixture was stirred at 70 °C overnight, during which magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (16 - 40 μm cut-off), washed with 1 weight equivalent of water, and dried at 70 °C.

[0102] Both the total LA / lactate concentration and the %D-LA / lactate of the total LA / lactate concentration were measured separately using HPLC. The total LA / lactate concentration in the solution decreased from 45% to 9% due to the precipitation of magnesium lactate, while the %D-LA / lactate of the total LA / lactate concentration in the solution showed an increase from 9% to 9.3%. This increase in the %D-LA / lactate concentration in the solution indicates the precipitation of magnesium L-lactate with enhanced enantiomeric purity of the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 6 below.

[0103]

Table 6

[0104] Example 8 LA Enantiomer Concentration by Adding Magnesium Hydroxide Once to Precipitate up to 80% Conversion A mixture containing L- and D-lactic acid at a D:L ratio of approximately 3:97 and a concentration of approximately 35% was placed in a preheated chemical reactor at 40°C and stirred at 300 RPM. 0.4 molar equivalent of magnesium hydroxide powder was added all at once. Due to the exothermic nature of the reaction, the temperature rapidly rose to 70°C over 2 minutes and then gradually decreased to 50°C. The reaction mixture was stirred at 50°C overnight, during which magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (16 - 40 μm cut-off), washed with 1 weight equivalent of water, and dried at 70°C.

[0105] Both the total LA / lactate concentration and the %D-LA / lactate of the total LA / lactate concentration were measured separately using HPLC. The total LA / lactate concentration in the solution decreased from 35% to 16% due to the precipitation of magnesium lactate, while the %D-LA / lactate of the total LA / lactate concentration in the solution showed an increase from 2.6% to 3.7%. This increase in the %D-LA / lactate concentration in the solution indicates the precipitation of magnesium L-lactate with enhanced enantiomeric purity of the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 7 below.

[0106]

Table 7

[0107] Example 9 LA Enantiomer Concentration by Precipitation with Magnesium Hydroxide up to 90% Conversion A mixture containing L- and D-lactic acids at a D:L ratio of approximately 5:95 and a concentration of approximately 45% was placed in a chemical reactor preheated to 70 °C and stirred at 300 RPM. A 0.45 molar equivalent slurry of magnesium hydroxide in water (15% w / w) was added dropwise over 16 minutes. The reaction mixture was stirred at 70 °C for 5 hours, during which magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (16 - 40 μm cut-off), washed with 1 weight equivalent of water, and dried at 70 °C.

[0108] Both the total LA / lactate concentration and the % D-LA / lactate of the total LA / lactate concentration were measured separately using HPLC. The total LA / lactate concentration in the solution decreased from 45% to 11% due to the precipitation of magnesium lactate, while the % D-LA / lactate of the total LA / lactate concentration in the solution showed an increase from 5.6% to 8.7%. This increase in the % D-LA / lactate concentration in the solution indicates the precipitation of L-magnesium lactate with enhanced enantiopurity of the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 8 below.

[0109]

Table 8

[0110] Example 10 LA Enantiomer Concentration by Precipitation with Calcium Hydroxide A mixture containing L- and D-lactic acids at a D:L ratio of about 5:95 and a concentration of about 45% was placed in a preheated chemical reactor at 70 °C and stirred at 300 RPM. A 0.5 molar equivalent slurry of calcium hydroxide (15% w / w) in water was added dropwise over 18 minutes. The reaction mixture was stirred at 70 °C overnight, during which no precipitation occurred. After the temperature was lowered to 50 °C, calcium lactate precipitated immediately and the solution completely solidified. The solid was centrifuged at 12,000 g for 5 minutes to extract the mother liquor, and then washed with 1 weight equivalent of water by centrifugation. The product was dried at 70 °C.

[0111] Both the total LA / lactate concentration and the % D-LA / lactate of the total LA / lactate concentration were measured separately using HPLC. The total LA / lactate concentration in the mother liquor decreased from 45% to 10% due to the precipitation of calcium lactate, while the % D-LA / lactate of the total LA / lactate concentration in the mother liquor showed an increase from 5.0% to 7.7%. This increase in the % D-LA / lactate concentration in the mother liquor indicates the precipitation of calcium L-lactate with enhanced enantiopurity of the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 9 below.

[0112]

Table 9

[0113] Example 11 LA Enantiomer Concentration by Precipitation with 10% Excess Magnesium Hydroxide A mixture containing L- and D-lactic acids at a D:L ratio of about 5:95 and a concentration of about 45% was placed in a preheated chemical reactor at 70 °C and stirred at 300 RPM. A 0.55 molar equivalent slurry of magnesium hydroxide (15% w / w) in water was added dropwise over 15 minutes. The reaction mixture was stirred at 70 °C for 5 hours, during which magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (16 - 40 μm cut-off), washed with 1 weight equivalent of water, and dried at 70 °C.

[0114] Both the total LA / lactate concentration and the % D-LA / lactate of the total LA / lactate concentration were measured separately using HPLC. The total LA / lactate concentration in the solution decreased from 45% to 8% due to the precipitation of magnesium lactate, while the % D-LA / lactate of the total LA / lactate concentration in the solution showed an increase from 5.4% to 9.6%. This increase in the % D-LA / lactate concentration in the solution indicates the precipitation of magnesium L-lactate with enhanced enantiopurity of the L-enantiomer compared to the initial L-lactic acid content. The results are summarized in Table 10 below.

[0115]

Table 10

[0116] The results indicate that the addition of 10% excess magnesium hydroxide had little effect on the purity of magnesium lactate, but significantly enhanced the enantiopurity of the L-enantiomer in the product.

[0117] Comparative Example 1 LA Enantiomer Reduction by Precipitation with Magnesium Hydroxide at 30 °C A mixture containing L- and D-lactic acid at a D:L ratio of approximately 6:94 and a concentration of approximately 45% was placed in a preheated chemical reactor at 30 °C and stirred at 300 RPM. To avoid overheating, a 0.5 molar equivalent slurry of magnesium hydroxide in water (15% w / w) was added dropwise over 1.25 hours. The reaction mixture was stirred overnight at 30 °C, during which time magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (16 - 40 μm cut-off), washed with 1 weight equivalent of water, and dried at 70 °C.

[0118] The total LA / lactate concentration and the % D-LA / lactate of the total LA / lactate concentration were measured separately using HPLC. Both the total LA / lactate concentration in the solution and the % D-LA / lactate of the total LA / lactate concentration showed a decrease from 45% to 14% and from 5.7% to 3.7%, respectively. This decrease in the % D-LA / lactate concentration in the solution indicates the precipitation of magnesium lactate with a decrease in the 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 enhanced by washing with 1 weight equivalent of water. The results are summarized in Table 11 below.

[0119]

Table 11

[0120] Therefore, adding magnesium hydroxide to a mixture of L- and D-lactic acid at a temperature of 30 °C does not result in enantiomeric enrichment of the L-enantiomer.

[0121] Comparative Example 2 LA Enantiomer Reduction by Precipitation from an Enantiomeric Mixture Containing 10.4% D-Lactic Acid A mixture containing L- and D-lactic acid with 10.4% D-enantiomer at a concentration of approximately 45% was placed in a preheated chemical reactor at 70 °C and stirred at 300 RPM. A 0.5 molar equivalent magnesium hydroxide slurry (15% w / w) in water was added dropwise over 14 minutes. The reaction mixture was stirred and left at 70 °C for 5 hours, during which magnesium lactate precipitated. The precipitate was filtered off using a P3 sintered glass funnel (16 - 40 μm cut-off), washed with 1 weight equivalent of water, and dried at 70 °C.

[0122] The total LA / lactate concentration and the %D-LA / lactate of the total LA / lactate concentration were measured separately using HPLC. Both the total LA / lactate concentration in the solution and the %D-LA / lactate of the total LA / lactate concentration showed a decrease from 45% to 11% and from 10.4% to 9.0%, respectively. The decrease in the %D-LA / lactate concentration in the solution was equivalent to the decrease in the total LA / lactate concentration, indicating that no change in the enantiomeric purity of the L-enantiomer in the precipitate was achieved. Washing with 1 weight equivalent of water increased the ratio of the D-enantiomer to the L-enantiomer, indicating a decrease in the enantiomeric purity of the L-enantiomer in the precipitate. The results are summarized in Table 12 below.

[0123]

Table 12

[0124] Therefore, it is considered that enantiomeric enrichment of the L-enantiomer cannot be achieved when an initial mixture containing more than 10% D-lactic acid is used.

[0125] The foregoing description of the specific embodiments fully reveals the general nature of the invention, so that others can, by applying current knowledge, make various uses of such specific embodiments without undue experimentation and without departing from the general concept, and thus such adaptations and modifications should be understood to be within the meaning and scope of the equivalents of the embodiments of this disclosure and are so intended. It should be understood that the expressions or terms used herein are for the purpose of description and not for the purpose of limitation. Means, materials, and steps for carrying out various functions of this disclosure can take various alternative forms without departing from the invention.

Claims

1. A process for concentrating L-lactic acid enantiomers or salts thereof, or for producing enantioconcentrated L-lactic acid salts, (a) A step to obtain decomposed organic waste containing an enantiomixture of D-lactic acid and L-lactic acid at a concentration of approximately 100 to approximately 1,100 g / L, wherein the enantiomixture contains 10% or less D-lactic acid; (b) A step of contacting the enantiomixture with an alkaline substance containing a divalent cation in an amount of about 50 to about 120 equivalents based on the number of carboxyl groups present in the enantiomixture, (c) A step of precipitating the L-lactate with the divalent cation, thereby obtaining an L-lactate with higher enantiopurity compared to the initial enantio mixture, Includes, Step (b) and / or (c) are performed at a temperature in the range of approximately 40°C to approximately 100°C. process.

2. This includes concentrating L-lactic acid enantiomer or a salt thereof to 5% or more; or This includes concentrating L-lactic acid enantiomer or a salt thereof to a maximum of 10%; The process according to claim 1.

3. The decomposed organic waste contains lactic acid derived from a low-pH lactic acid fermentation process; or The decomposed organic waste contains lactic acid derived from the decomposition of polylactic acid in an acidic medium; or The decomposed organic waste contains lactic acid by-products derived from the industrial production of polylactic acid, or the decomposed organic waste contains lactic acid by-products derived from the industrial refining of lactic acid, or the decomposed organic waste contains lactic acid obtained from the hydrolysis of lactide by-products from the industrial production of polylactic acid; The process according to claim 1.

4. The alkaline substance includes a hydroxide selected from the group consisting of magnesium hydroxide, calcium hydroxide, and mixtures thereof; or The alkaline substance includes a carbonate or bicarbonate selected from the group consisting of magnesium bicarbonate, magnesium carbonate, calcium bicarbonate, calcium carbonate, and mixtures thereof; The process according to claim 1.

5. The alkaline substance is added in solid form; or The alkaline substance is added as an aqueous solution or suspension, preferably as an aqueous solution with a concentration of about 50 to about 500 g / L; The process according to claim 1.

6. The process according to claim 1, wherein step (b) and / or step (c) are carried out at a pressure of about 100 to about 1,000 mbar, or step (b) and / or step (c) are carried out at a mixing rate of about 200 to about 1,000 revolutions per minute (RPM).

7. The resulting L-lactate is separated by filtration or centrifugation; or The obtained L-lactate is subjected to subsequent purification, preferably comprising at least one of crystallization, recrystallization, partitioning, silica gel chromatography, and preparative HPLC, or comprising washing the obtained L-lactate with purified water; The process according to claim 1.

8. The obtained L-lactate contains less than 6% D-lactate; and / or The resulting L-lactate is acidified with at least one of hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, sulfuric acid, or a combination thereof to form L-lactic acid, which is then used for subsequent polylactic acid formation; The process according to any one of claims 1 to 7.

9. A process for concentrating L-lactic acid enantiomers or salts thereof, or for producing enantioconcentrated L-lactic acid salts, (a) A step to obtain decomposed organic waste containing an enantiomixture of D-lactic acid and L-lactic acid at a concentration of approximately 100 to approximately 1,100 g / L, wherein the enantiomixture contains 6% or less D-lactic acid; (b) A step of contacting the enantio mixture with an alkaline substance containing a divalent cation, (c) A step of precipitating the L-lactate with the divalent cation, thereby obtaining an L-lactate with higher enantiopurity compared to the initial enantio mixture, Includes, Step (b) and / or (c) are performed at a temperature in the range of approximately 50°C to approximately 100°C. process.

10. This includes concentrating L-lactic acid enantiomer or a salt thereof to 5% or more; or This includes concentrating L-lactic acid enantiomer or a salt thereof to a maximum of 10%; The process according to claim 9.

11. The decomposed organic waste contains lactic acid derived from a low-pH lactic acid fermentation process; or The decomposed organic waste contains lactic acid derived from the decomposition of polylactic acid in an acidic medium; or The decomposed organic waste contains lactic acid by-products derived from the industrial production of polylactic acid, or the decomposed organic waste contains lactic acid by-products derived from the industrial refining of lactic acid, or the decomposed organic waste contains lactic acid obtained from the hydrolysis of lactide by-products from the industrial production of polylactic acid; The process according to claim 9.

12. The alkaline substance includes a hydroxide selected from the group consisting of magnesium hydroxide, calcium hydroxide, and mixtures thereof; or The alkaline substance includes a carbonate or bicarbonate selected from the group consisting of magnesium bicarbonate, magnesium carbonate, calcium bicarbonate, calcium carbonate, and mixtures thereof; The process according to claim 9.

13. The alkaline substance is added in solid form; or The alkaline substance is added as an aqueous solution or suspension, preferably as an aqueous solution with a concentration of about 50 to about 500 g / L; The process according to claim 9.

14. The process according to claim 9, wherein step (b) and / or step (c) are carried out at a pressure of about 100 to about 1,000 mbar, or step (b) and / or step (c) are carried out at a mixing rate of about 200 to about 1,000 revolutions per minute (RPM).

15. The resulting L-lactate is separated by filtration or centrifugation; or The obtained L-lactate is subjected to subsequent purification, preferably comprising at least one of crystallization, recrystallization, partitioning, silica gel chromatography, and preparative HPLC, or comprising washing the obtained L-lactate with purified water; The process according to claim 9.

16. The obtained L-lactate contains less than 3% D-lactate; and / or The resulting L-lactate is acidified with at least one of hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, sulfuric acid, or a combination thereof to form L-lactic acid, which is then used for subsequent polylactic acid formation; The process according to any one of claims 9 to 15.