A method for separating and extracting lactic acid

Abstract

The present invention relates to the field of extraction and purification of biological fermentation monomers and discloses a method for separating and extracting lactic acid. The method comprises: subjecting a first solution to an extraction treatment using an extraction system containing a complexing extractant to obtain an aqueous solution and an organic solution, wherein the extraction treatment extracts at least a portion of the lactic acid in the first solution into the organic solution; the first solution comprises lactic acid fermentation broth and / or lactic acid fermentation treatment broth, and the complexing extractant comprises an organic amine compound.

Description

Technical Field

[0001] The present invention relates to the field of extraction and purification of biological fermentation monomers, and in particular to a method for separating and extracting lactic acid. Background Art

[0002] Lactic acid is the raw material for the production of biodegradable polylactic acid (PLA). With the growing demand for biodegradable polymers, the industry currently relies heavily on biological methods for lactic acid production. These methods use starch, glucose, biomass, and other raw materials, inoculated with mold or lactic acid bacteria, and fermented to produce a fermentation broth containing lactic acid or lactate. The lactic acid is then separated and isolated. Lactic acid fermentation broth is a highly complex system, containing not only lactic acid but also a large amount of bacterial cells, proteins, residual sugars, pigments, inorganic salts, by-product organic acids, and other metabolites. This makes the extraction and purification of lactic acid in this field challenging.

[0003] Currently, the main methods for isolating and extracting lactic acid from fermentation broths include calcium salt crystallization, esterification and hydrolysis, extraction, molecular distillation, membrane separation, adsorption, and in-situ separation techniques coupled with fermentation. In lactic acid extraction, the pH of the fermentation broth is typically adjusted with calcium salts, resulting in the lactic acid being present as calcium lactate. This is then followed by acid hydrolysis with sulfuric acid for extraction. However, there are currently no systematic reports on the direct isolation of lactic acid from biowaste fermentation broths using extraction methods. Summary of the Invention

[0004] The first object of the present invention is to provide a method for separating and extracting lactic acid, which comprises: subjecting a first solution to an extraction treatment using an extraction system containing a complexing extractant to obtain an aqueous solution and an organic solution, wherein the extraction treatment causes at least a portion of the lactic acid in the first solution to be extracted into the organic solution; the first solution comprises lactic acid fermentation broth and / or lactic acid fermentation treatment broth, and the complexing extractant comprises an organic amine compound.

[0005] In the present invention, the lactic acid fermentation treated liquid is obtained by centrifuging and filtering the lactic acid fermentation liquid to remove impurities such as bacterial cells; or by adjusting the pH of the lactic acid fermentation liquid to 6-10.5 and then centrifuging and filtering to remove impurities such as bacterial cells. The lactic acid fermentation liquid and / or the lactic acid fermentation treated liquid of the present invention may also be concentrated before extracting lactic acid, and those skilled in the art may choose the method according to actual needs.

[0006] In some embodiments of the present invention, the first solution contains lactic acid, metal ions, pigments, proteins, sugars and water.

[0007] In some embodiments of the present invention, the concentration of metal ions in the first solution is below 5 wt %, further below 4 wt %, and further below 3 wt %.

[0008] In some embodiments of the present invention, the concentration of lactic acid in the first solution is below 50 wt %, further below 30 wt %, and further below 15 wt %.

[0009] In some embodiments of the present invention, the pH value of the first solution is below 10, further 1-5, further 1-4; for example, 1.0, 1.5, 2.1, 2.6, 3.0, 3.5, 4.0, etc.

[0010] The present invention has a wide range of selection for the metal ions. Preferably, the metal ions include but are not limited to one or more of calcium ions, magnesium ions and iron ions.

[0011] In some specific embodiments of the present invention, the carbon source in the fermentation medium used in the first solution is derived from the hydrolyzate of agricultural and forestry waste, and the agricultural and forestry waste includes but is not limited to at least one of straw (corn straw, wheat straw, rice straw, rapeseed stalks, barley straw, oat straw, sorghum straw, etc.), rice husks, cork, hardwood, branches and livestock manure.

[0012] In some specific embodiments of the present invention, the carbon source in the fermentation medium used in the first solution includes hexose, and the hexose includes at least one of glucose, fructose, galactose, and mannose.

[0013] In some embodiments of the present invention, the molar ratio of the complexing extractant to the lactic acid in the first solution is (0.5-40):1, further (1-40):1, further (1.5-40):1, further (3-40):1, further (3-20):1, further (5-20):1.

[0014] In some embodiments of the present invention, preferably, the volume ratio of the extraction system to the first solution is (0.4-50):1, further (0.5-40):1, further (0.8-20):1, further (1-10):1.

[0015] In some embodiments of the present invention, preferably, the organic amine compound is selected from at least one of primary amine compounds, secondary amine compounds, tertiary amine trialkyl compounds and quaternary ammonium salt compounds.

[0016] In a specific embodiment of the present invention, the general formula of the primary amine compound is RR′CHNH2, wherein R+R′=C 16 -C 22 In the present invention, R and R' represent a hydrocarbon group or an alkyl group with a certain number of carbon atoms, and R+R'=C 16 -C 22It means that the total number of carbon atoms contained in R and R' is 16 to 22. The primary amine compounds of the present invention include, but are not limited to, secondary carbon primary amine (N1923) and the like.

[0017] In a specific embodiment of the present invention, the general formula of the secondary amine compound is (R2CH)2NH, wherein R=C6-C8. In the present invention, R=C6-C8 represents a hydrocarbon group or alkyl group with 6-8 carbon atoms. The secondary amine compound of the present invention includes, but is not limited to, N7201 secondary amine (structural formula (R2CH)2NH, R=C 7-9 wait).

[0018] In a specific embodiment of the present invention, the general formula of the tertiary amine trialkyl compound is R3N, wherein R is C m H 2m+1 , m is 8, 9 or 10. The tertiary amine trialkyl compound of the present invention includes, but is not limited to, trioctylamine (TOA), tri(octyl-decyl)alkyl tertiary amine (commonly known as 7301 extractant, N235), and the like.

[0019] In a specific embodiment of the present invention, the general formula of the quaternary ammonium salt compound is R3N + CH3Cl - , where R=C8H 17 -C 10 H 21 .

[0020] In some embodiments of the present invention, the extraction system further comprises a diluent, wherein the diluent is selected from at least one of ether compounds, ester compounds, linear, branched or cyclic alcohol compounds, phosphorus oxide compounds, alkyl halides, aromatic compounds and alkanes. Further, the diluent comprises a phosphorus oxide compound and at least one selected from ether compounds, ester compounds, linear, branched or cyclic alcohol compounds, alkyl halides, aromatic compounds and alkanes. In the present invention, when the diluent comprises a phosphorus oxide compound, the mass ratio of the complexing extractant to the phosphorus oxide compound is 1:(0-20), further 1:(0.5-15), further 1:(1-10).

[0021] According to some specific embodiments of the present invention, the ether compound is preferably an ether compound with 4-10 carbon atoms, for example including but not limited to isopropyl ether, ethyl ether, n-butyl ether, etc.

[0022] According to some specific embodiments of the present invention, the ester compound is preferably an ester compound with 2-10 carbon atoms, for example including but not limited to ethyl acetate and / or butyl acetate.

[0023] According to some specific embodiments of the present invention, the linear, branched or cyclic alcohol compound is preferably a linear, branched or cyclic alcohol compound containing at least four carbon atoms, for example, including but not limited to one or more of n-octanol, isooctyl alcohol, n-heptanol, cyclohexanol, isobutanol and decanol.

[0024] According to a preferred embodiment of the present invention, the general formula of the phosphorus oxide compound is XYP(O)OH; wherein X and Y are each independently an alkoxy group or an alkyl group having a straight chain or branched structure with 2-10 carbon atoms; preferably an alkoxy group or an alkyl group having a straight chain or branched structure with 5-10 carbon atoms; further, the phosphorus oxide compound is selected from at least one of 2-ethylhexyl mono-2-ethylhexyl phosphate, dimethylheptyl methyl phosphate and di(2-ethylhexyl)phosphoric acid.

[0025] According to some specific embodiments of the present invention, the haloalkane is preferably a haloalkane with 1-3 carbon atoms, and the haloalkane with 1-3 carbon atoms may be a chloroalkane and / or a bromoalkane, or may be a monohaloalkane, a dihaloalkane, a trihaloalkane, or a tetrahaloalkane, for example, including but not limited to carbon tetrachloride, chloroform, dichloromethane, 1,2-dichloroethane, etc.

[0026] According to some specific embodiments of the present invention, the aromatic compounds include but are not limited to benzene, toluene, ethylbenzene, chlorobenzene, xylene, etc.

[0027] According to some specific embodiments of the present invention, the alkane is preferably a linear or cyclic alkane compound containing five carbon atoms and a mixture thereof, for example including but not limited to one or more of n-octanol, isooctyl alcohol, n-heptanol, cyclohexanol, isobutanol and decanol.

[0028] In some embodiments of the present invention, preferably, the absolute value of the difference between the pH value of the aqueous solution and the pH value of the first solution, ΔpH, is 0-5, further 0-3, further 0.4-2; for example, 0.5, 1, 1.2, 1.4, 1.8, etc. The higher the absolute value of ΔpH, the more lactic acid is extracted.

[0029] In some embodiments of the present invention, preferably, the pH value of the first solution is less than or equal to the pH value of the aqueous solution.

[0030] The present invention has no particular limitation on the temperature of the extraction treatment. Preferably, the temperature of the extraction treatment is 10-95°C, further 20-60°C, further 20-40°C, for example, 10°C, 22°C, 25°C, 28°C, 30°C, 32°C, 35°C, 38°C, 50°C, 60°C, 70°C, 80°C, 90°C, etc.

[0031] In some embodiments of the present invention, preferably, the total number of extraction stages of the extraction process is 1-24, preferably 1-15, and the extraction adopts a multi-stage countercurrent or multi-stage cross-current extraction method. In the present invention, a concentration step can be performed between any two extraction stages.

[0032] The present invention does not particularly limit the manner in which the extraction system is brought into contact with the first solution for extraction treatment, and conventional methods in the art can be used. For example, when the extraction system contains a complexing extractant, the complexing extractant is mixed with the first solution to achieve contact between the first solution and the complexing extractant, thereby extracting lactic acid; when the extraction system contains both a complexing extractant and a diluent, the complexing extractant is first mixed with the diluent and then mixed with the first solution to achieve contact between the first solution, the complexing extractant and the diluent, thereby extracting lactic acid.

[0033] The present invention does not particularly limit the extraction equipment used in the extraction process, and conventional extraction equipment in the field can be used, such as but not limited to centrifugal extraction, mixing and settling tanks, vibrating screen plate towers, turntable towers, packed towers, high gravity rotating beds and other equipment.

[0034] In some embodiments of the present invention, the method further comprises: stripping the organic solution with a stripping agent to obtain a lactic acid solution; the stripping agent comprises an aqueous phase system, and the concentration of the alkaline substance in the aqueous phase system is 0-8 mol / L. Further, the concentration of the alkaline substance in the aqueous phase system can be 0-0.01 mol / L, 0.01-0.05 mol / L, 0.05-5 mol / L, 5-8 mol / L, 0.01-8 mol / L, 0.05-5 mol / L, 0.1-5 mol / L, etc., and specifically can be 0 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2.5 mol / L, 3 mol / L, 4 mol / L, etc. In the present invention, depending on the selection of the stripping agent, the lactic acid solution can be a lactic acid aqueous solution or a lactate aqueous solution.

[0035] The present invention has a wide range of choices for the alkaline substance, including but not limited to ammonia water, sodium hydroxide, potassium hydroxide, calcium hydroxide, calcium oxide and combinations thereof.

[0036] In the present invention, when an aqueous phase system is used to back-extract the organic solution, the method of adding the aqueous phase system is not particularly limited. The aqueous phase system can be added all at once or in batches. Alternatively, aqueous phase systems containing different alkaline substances can be added separately, or aqueous phase systems containing different alkaline substances can be mixed first and then added all at once. Furthermore, when back-extraction is performed using an aqueous phase system, a single-stage extraction or two or more-stage extractions are preferably used, and a concentration step can be performed between any two back-extraction stages.

[0037] In some embodiments of the present invention, preferably, the volume ratio of the stripping agent to the organic solution is (0.1-100):1, further (0.2-50):1, and further (0.2-30):1.

[0038] In some embodiments of the present invention, preferably, the number of extraction stages of the back extraction is 1 to 24, more preferably 1 to 15. The back extraction of the present invention can be performed in a multi-stage countercurrent manner.

[0039] In some embodiments of the present invention, preferably, the back extraction temperature is 10-120°C, further 20-100°C, further 20-95°C, and further 25-30°C.

[0040] A second object of the present invention is to provide a method for preparing a lactic acid product, comprising: obtaining a lactic acid solution using the method described above, and purifying the lactic acid solution to obtain the lactic acid product. As described above, the lactic acid solution may be an aqueous lactic acid solution or an aqueous lactate solution. In the case of an aqueous lactate solution, the lactic acid solution is first acidified to obtain the aqueous lactic acid solution, and then purified to obtain the lactic acid product.

[0041] In a specific embodiment of the present invention, the purification method comprises: subjecting the lactic acid solution to a first concentration step, decolorization with activated carbon, further concentration and dehydration, and molecular distillation to obtain a lactic acid product, wherein the first concentration step results in a lactic acid concentration of 15-40 wt%.

[0042] In another specific embodiment of the present invention, the purification method comprises: concentrating the lactic acid solution, decolorizing with activated carbon, purifying with a resin, purifying with a nanofiltration membrane, and concentrating and dehydrating to obtain a lactic acid product.

[0043] In another specific embodiment of the present invention, the purification method comprises: concentrating, dehydrating, and subjecting the lactic acid solution to multi-stage molecular distillation to obtain a lactic acid product, wherein the number of stages of molecular distillation is 2 or more.

[0044] The third object of the present invention is to provide a lactic acid product, wherein the chemical purity of the lactic acid product is greater than 98wt%, further greater than 98.5wt%, and / or the content of reducing sugars in the lactic acid product is less than 200ppm; the lactic acid product is prepared by the method as described above.

[0045] In some embodiments of the present invention, the chemical purity of the lactic acid product is above 99 wt%.

[0046] In some embodiments of the present invention, the content of reducing sugars in the lactic acid product is less than 100 ppm, further less than 30 ppm.

[0047] In some embodiments of the present invention, the content of residual metal ions in the lactic acid product is less than 100 ppm, further less than 50 ppm, and further less than 10 ppm, wherein the metal ions include but are not limited to one or more of calcium ions, magnesium ions, and iron ions.

[0048] In some embodiments of the present invention, the total content of residual extractant and diluent in the lactic acid product is less than 100 ppm, further less than 50 ppm, further less than 10 ppm.

[0049] Through the above technical solution, the present invention efficiently extracts lactic acid from lactic acid fermentation broth and / or lactic acid fermentation treated broth through an extraction process, improving stripping efficiency and reducing the proportion of pigment entering the oil phase, thereby reducing the difficulty of subsequent purification. Furthermore, the extraction method can be operated continuously, offering advantages such as large processing capacity, strong selectivity, low cost, high yield, and recyclable extractant. Furthermore, the extracted lactic acid is dissociated and recovered through the stripping process, thereby separating the entire lactic acid system from metal ions, resulting in a relatively pure lactic acid aqueous solution, which is then purified to obtain a high-purity, high-yield lactic acid product. DETAILED DESCRIPTION

[0050] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, all raw materials used can be obtained from commercial channels; the physical properties of each raw material or the performance parameters of the product are measured using conventional methods in the art.

[0051] Chromaticity ratio = (pigment content in the aqueous solution / pigment content in the first solution) * 100%. The aqueous solution and the first solution are characterized using an ultraviolet-visible light spectrophotometer. The pigment therein has absorption at a wavelength of 400 nm, and the pigment content is proportional to the absorbance value of the solution. Therefore, chromaticity ratio = (absorbance of the aqueous solution / absorbance of the first solution) * 100%.

[0052] Preparation of the first solution

[0053] The first solution was prepared by referring to the method disclosed in CN11294117A, specifically comprising:

[0054] Pretreated solid granular corn straw with a solid content of 30 (w / w)% was placed in a fermentation tank as a raw material, cellulase with a protein content of 5 mg / g straw (dry basis) was added, and pre-saccharification was carried out at 48° C. and 200 rpm for 6.5 h. After the pre-saccharification, a seed solution of Pediococcus acidilactici was inoculated into the fermentation tank at a rate of 5% (v / v), and nutrient salts (10 g / L peptone, 10 g / L yeast extract, 2 g / L diammonium hydrogen citrate, and 0.25 g / L manganese sulfate monohydrate) were added. During the fermentation process, calcium carbonate was used as a neutralizer to adjust and maintain the pH value of the fermentation liquid at 5.4. The fermentation was carried out at 42° C. and 200 rpm for 96 h, and then the fermentation liquid was separated from the corn straw residue by filtration. The pH value of the fermentation liquid was adjusted to 2.01 with sulfuric acid to obtain a first solution for standby use, wherein the concentration of lactic acid in the first solution was 9 wt%, and the concentration of calcium ions was 2 wt%.

[0055] Example 1

[0056] A first solution (lactic acid concentration of 9 wt %, calcium ion concentration of 2 wt %, pH of 2.01) was placed in a separatory funnel, and trioctylamine (TOA), n-heptanol, and C12 alkane were added such that the volume ratio of the total amount of the trioctylamine (TOA), n-heptanol, and C12 alkane to the first solution was 1:1, and the molar ratio of trioctylamine (TOA) to lactic acid in the first solution was 1:1. The solution was subjected to four-stage countercurrent extraction at 25° C. to obtain an aqueous solution (pH of 2.9) and an organic solution. The extraction process extracted lactic acid in the first solution into the organic solution, with a lactic acid extraction rate of 99.3% and a chromaticity ratio of 27.5%.

[0057] The organic solution was subjected to four-stage countercurrent stripping at 30° C. using an aqueous phase system containing sodium hydroxide, wherein the concentration of sodium hydroxide in the aqueous phase system was 1.5 mol / L and the volume ratio of the aqueous phase system containing sodium hydroxide to the organic solution was 1:1, to obtain a lactate aqueous solution. The stripping yield of lactic acid was 59%.

[0058] Example 2

[0059] A first solution (lactic acid concentration of 9 wt %, calcium ion concentration of 2 wt %, pH of 2.01) was placed in a separatory funnel, and trioctylamine (TOA), n-heptanol, and cyclohexane were added such that the volume ratio of the total amount of the trioctylamine (TOA), n-heptanol, and cyclohexane to the first solution was 1:1, and the molar ratio of trioctylamine (TOA) to lactic acid in the first solution was 1:1. The solution was subjected to four-stage countercurrent extraction at 25° C. to obtain an aqueous solution (pH of 2.9) and an organic solution. The extraction process extracted lactic acid in the first solution into the organic solution, with a lactic acid extraction efficiency of 99.4% and a chromaticity ratio of 29%.

[0060] The organic solution was subjected to four-stage countercurrent stripping at 30° C. using an aqueous phase system containing sodium hydroxide, wherein the concentration of sodium hydroxide in the aqueous phase system was 1.5 mol / L and the volume ratio of the aqueous phase system containing sodium hydroxide to the organic solution was 1:1, to obtain a lactate aqueous solution. The stripping yield of lactic acid was 63%.

[0061] Example 3

[0062] A first solution (lactic acid concentration of 9 wt %, calcium ion concentration of 2 wt %, pH of 2.01) was placed in a separatory funnel, and trioctylamine (TOA), P204, and C12 alkane were added such that the volume ratio of the total amount of trioctylamine (TOA), P204, and C12 alkane to the first solution was 2:1, and the molar ratio of trioctylamine (TOA) to lactic acid in the first solution was 1.2:1. The solution was subjected to six-stage countercurrent extraction at 25° C. to obtain an aqueous solution (pH of 3.3) and an organic solution. The extraction process extracted lactic acid in the first solution into the organic solution, with a lactic acid extraction rate of 99.6% and a chromaticity ratio of 60%.

[0063] The organic solution was subjected to four-stage countercurrent stripping at 30° C. using an aqueous phase system containing sodium hydroxide, wherein the concentration of sodium hydroxide in the aqueous phase system was 1.5 mol / L, and the volume ratio of the aqueous phase system containing sodium hydroxide to the organic solution was 1:1, to obtain a lactate aqueous solution. The stripping yield of lactic acid was 81.5%.

[0064] Example 4

[0065] A first solution (lactic acid concentration of 9 wt %, calcium ion concentration of 2 wt %, pH 2.01) was placed in a separatory funnel, and trioctylamine, P204, and C12 alkane were added such that the volume ratio of the total amount of trioctylamine, P204, and C12 alkane to the first solution was 2:1, and the molar ratio of trioctylamine (TOA) to lactic acid in the first solution was 1.2:1. The solution was subjected to four-stage countercurrent extraction at 25° C. to obtain an aqueous solution (pH 3.0) and an organic solution. The extraction process extracted lactic acid in the first solution into the organic solution, with a lactic acid extraction rate of 99.4% and a chromaticity ratio of 50%.

[0066] The organic solution was subjected to six-stage countercurrent stripping at 30° C. using an aqueous phase system containing sodium hydroxide, wherein the concentration of sodium hydroxide in the aqueous phase system was 1.5 mol / L and the volume ratio of the aqueous phase system containing sodium hydroxide to the organic solution was 1:1, to obtain a lactate aqueous solution. The stripping yield of lactic acid was 88%.

[0067] Example 5

[0068] A first solution (lactic acid concentration of 9 wt %, calcium ion concentration of 2 wt %, pH 2.01) was placed in a separatory funnel, and trioctylamine (TOA), P204, and C12 alkane were added such that the volume ratio of the total amount of the trioctylamine (TOA), P204, and C12 alkane to the first solution was 1:1, and the molar ratio of trioctylamine (TOA) to lactic acid in the first solution was 1.4:1. The solution was subjected to four-stage countercurrent extraction at 25° C. to obtain an aqueous solution (pH 3.4) and an organic solution. The extraction process extracted lactic acid from the first solution into the organic solution, with a lactic acid extraction rate of 99.6% and a chromaticity ratio of 58%.

[0069] The organic solution was subjected to four-stage countercurrent stripping at 30° C. using an aqueous phase system containing sodium hydroxide, wherein the concentration of sodium hydroxide in the aqueous phase system was 1.5 mol / L, and the volume ratio of the aqueous phase system containing sodium hydroxide to the organic solution was 1:1, to obtain a lactate aqueous solution. The stripping yield of lactic acid was 76%.

[0070] Example 6

[0071] A first solution (lactic acid concentration of 9 wt %, calcium ion concentration of 2 wt %, pH 2.01) was placed in a separatory funnel, and trioctylamine (TOA), P204, and C12 alkane were added such that the volume ratio of the total amount of the trioctylamine (TOA), P204, and C12 alkane to the first solution was 1:1, and the molar ratio of trioctylamine (TOA) to lactic acid in the first solution was 1.2:1. The solution was subjected to four-stage countercurrent extraction at 25° C. to obtain an aqueous solution (pH 3.0) and an organic solution. The extraction process extracted lactic acid from the first solution into the organic solution, with a lactic acid extraction rate of 99.5% and a chromaticity ratio of 59%.

[0072] The organic solution was subjected to four-stage countercurrent stripping at 30° C. using an aqueous phase system containing sodium hydroxide, wherein the concentration of sodium hydroxide in the aqueous phase system was 1.5 mol / L, and the volume ratio of the aqueous phase system containing sodium hydroxide to the organic solution was 1:1, to obtain a lactate aqueous solution. The stripping yield of lactic acid was 80%.

[0073] Example 7

[0074] A first solution (lactic acid concentration of 9 wt %, calcium ion concentration of 2 wt %, pH 2.01) was placed in a separatory funnel, 2.76 g of trioctylamine (TOA) and 2.52 g of P204 were added, and then a C12 alkane was added so that the volume ratio of the total amount of the trioctylamine (TOA), P204, and C12 alkane to the first solution was 1:1, and the molar ratio of trioctylamine (TOA) to lactic acid in the first solution was 1.2:1. The solution was subjected to four-stage countercurrent extraction at 25° C. to obtain an aqueous solution (pH 3.3) and an organic solution. The above extraction treatment resulted in the lactic acid in the first solution being extracted into the organic solution, with a lactic acid extraction rate of 99.8% and a chromaticity ratio of 63%.

[0075] The organic solution was subjected to four-stage countercurrent stripping at 30° C. using a pure aqueous phase system, with a volume ratio of the aqueous phase system to the organic solution being 1:1, to obtain a lactic acid aqueous solution. The stripping rate of lactic acid was 85%.

[0076] Example 8

[0077] The first solution (lactic acid concentration of 9wt%, calcium ion concentration of 2wt%, pH value of 2.01) was placed in a separatory funnel, 2.3g of trioctylamine (TOA) and 2.52g of P204 were added, and then a C12 alkane was added so that the volume ratio of the extraction system to the first solution was 1:1, and the molar ratio of trioctylamine (TOA) to lactic acid in the first solution was 1:1. The solution was subjected to four-stage countercurrent extraction at 25°C to obtain an aqueous solution (pH value of 3.6) and an organic solution. The above extraction treatment resulted in the lactic acid in the first solution being extracted into the organic solution, with a lactic acid extraction rate of 99.2% and a chromaticity ratio of 65%.

[0078] The organic solution was subjected to four-stage countercurrent stripping at 30° C. using a pure aqueous phase system, with a volume ratio of the aqueous phase system to the organic solution being 1:1, to obtain a lactic acid aqueous solution. The stripping rate of lactic acid was 94.5%.

[0079] Example 9

[0080] A first solution (lactic acid concentration of 9 wt %, calcium ion concentration of 2 wt %, pH 2.01) was placed in a separatory funnel, and trioctylamine (TOA) was added such that the volume ratio of the trioctylamine (TOA) to the first solution was 1:1, and the molar ratio of the trioctylamine (TOA) to the lactic acid in the first solution was 1:1. The solution was subjected to four-stage countercurrent extraction at 25° C. to obtain an aqueous solution (pH 3.1) and an organic solution. The extraction process resulted in the lactic acid in the first solution being extracted into the organic solution, with a lactic acid extraction efficiency of 78% and a chromaticity ratio of 38%.

[0081] The organic solution was subjected to four-stage countercurrent stripping at 30° C. using an aqueous phase system containing sodium hydroxide, wherein the concentration of sodium hydroxide in the aqueous phase system was 1.5 mol / L, and the volume ratio of the aqueous phase system containing sodium hydroxide to the organic solution was 1:1, to obtain a lactate aqueous solution. The stripping yield of lactic acid was 52%.

[0082] Preparation of lactic acid products

[0083] The lactate aqueous solution obtained in the above embodiment is first subjected to acidification treatment to obtain a lactic acid aqueous solution, and then concentrated, decolorized with activated carbon, purified with a resin, purified with a nanofiltration membrane, and concentrated and dehydrated to obtain a lactic acid product; or the lactic acid aqueous solution is directly concentrated, decolorized with activated carbon, purified with a resin, purified with a nanofiltration membrane, and concentrated and dehydrated to obtain a lactic acid product.

[0084] The chemical purity of the obtained lactic acid product is determined to be greater than 99 wt%, the content of residual metal ions is 3-5 ppm, the content of reducing sugar is ≤30 ppm, and the total content of residual extractant and diluent is ≤10 ppm.

[0085] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for separating and extracting lactic acid, characterized in that: The method comprises: subjecting a first solution to an extraction treatment using an extraction system containing a complexing extractant to obtain an aqueous solution and an organic solution, wherein the extraction treatment extracts at least a portion of the lactic acid in the first solution into the organic solution; the first solution comprises a lactic acid fermentation broth and / or a lactic acid fermentation treatment broth; the complexing extractant comprises an organic amine compound and a diluent, wherein the organic amine compound is selected from tertiary amine trialkyl compounds; The general formula of the tertiary amine trialkyl compound is R3N, wherein R is C m H 2m+1 , m is 8, 9 or 10; The diluent is selected from phosphorus oxide compounds of the general formula XYP(O)OH and linear or cyclic alkane compounds and mixtures thereof, wherein X and Y are each independently an alkoxy group or an alkyl group having a linear or branched structure with 2 to 10 carbon atoms, and the linear or cyclic alkane compounds and mixtures thereof are selected from one, two or more of kerosene, n-pentane, n-hexane, cyclohexane, n-dodecane and n-tridecane; The volume ratio of the extraction system to the first solution is (0.8-1):

1.

2. The method according to claim 1, characterized in that The first solution contains lactic acid, metal ions, pigments, proteins, sugars and water; wherein the concentration of metal ions in the first solution is below 5 wt%; and / or, The concentration of lactic acid in the first solution is below 50 wt %; and / or, The pH value of the first solution is below 10; and / or The metal ions are selected from at least one of calcium ions, magnesium ions and iron ions.

3. The method according to claim 1, characterized in that The concentration of metal ions in the first solution is below 4 wt%; and / or, The concentration of lactic acid in the first solution is below 30 wt %; and / or, The pH value of the first solution is 1-5.

4. The method according to claim 1, wherein The concentration of metal ions in the first solution is below 3 wt %; and / or, The concentration of lactic acid in the first solution is below 15 wt %; and / or, The pH value of the first solution is 1-4.

5. The method according to claim 1, wherein The carbon source in the fermentation medium used in the first solution is derived from the hydrolyzate of agricultural and forestry waste, wherein the agricultural and forestry waste includes at least one of straw, rice husk, cork, hardwood, tree branches and livestock manure; and / or, The carbon source in the fermentation medium used in the first solution includes hexose, and the hexose includes at least one of glucose, fructose, galactose, and mannose.

6. The method according to claim 1, characterized in that The molar ratio of the complexing extractant to the lactic acid in the first solution is (0.5-40):

1.

7. The method according to claim 1, characterized in that The molar ratio of the complexing extractant to the lactic acid in the first solution is (1-40):

1.

8. The method according to claim 1, characterized in that The molar ratio of the complexing extractant to the lactic acid in the first solution is (1.5-40):

1.

9. The method according to claim 1, characterized in that The molar ratio of the complexing extractant to the lactic acid in the first solution is (3-40):

1.

10. The method according to claim 1, characterized in that The molar ratio of the complexing extractant to the lactic acid in the first solution is (3-20):

1.

11. The method according to claim 1, wherein The molar ratio of the complexing extractant to the lactic acid in the first solution is (5-20):

1.

12. The method according to claim 1, characterized in that The tertiary amine trialkyl compound is trioctylamine and / or tri(octyl-decyl)alkyl tertiary amine.

13. The method according to claim 1, wherein In the phosphorus-oxygen compound of the general formula XYP(O)OH, X and Y are each independently an alkoxy group or an alkyl group having a linear or branched structure and 5 to 10 carbon atoms.

14. The method according to claim 1, wherein The phosphorus-oxygen compound is selected from at least one of 2-ethylhexyl monophosphate, dimethylheptyl methylphosphate and di(2-ethylhexyl)phosphoric acid.

15. The method according to claim 1, wherein The absolute value of the difference ΔpH between the pH value of the aqueous solution and the pH value of the first solution is 0-5; and / or, The pH value of the first solution is less than or equal to the pH value of the aqueous solution; and / or, The temperature of the extraction treatment is 10-95°C; and / or, The total number of extraction stages of the extraction process is 1-24, and the extraction adopts a multi-stage countercurrent or multi-stage crosscurrent extraction method.

16. The method according to claim 1, wherein The absolute value of the difference ΔpH between the pH value of the aqueous solution and the pH value of the first solution is 0-3; and / or, The extraction temperature is 20-60°C; and / or, The total number of extraction stages in the extraction process is 1-15.

17. The method according to claim 1, wherein The absolute value of the difference ΔpH between the pH value of the aqueous solution and the pH value of the first solution is 0.4-2; and / or, The temperature of the extraction treatment is 20-40°C.

18. The method according to claim 1, wherein The method further comprises: using a stripping agent to strip the organic solution to obtain a lactic acid solution; the stripping agent comprises an aqueous phase system, and the concentration of the alkaline substance in the aqueous phase system is 0-8 mol / L.

19. The method according to claim 18, characterized in that The volume ratio of the stripping agent to the organic solution is (0.1-100):1; and / or, The number of extraction stages of the back extraction is 1-24; and / or, The stripping temperature is 10-120°C.

20. The method according to claim 19, characterized in that The volume ratio of the stripping agent to the organic solution is (0.2-50):1; and / or, The number of extraction stages of the back extraction is 1-15; and / or, The stripping temperature is 20-100°C.

21. The method according to claim 19, wherein The volume ratio of the stripping agent to the organic solution is (0.2-30):1; and / or, The stripping temperature is 20-95°C.

22. A method for preparing a lactic acid product, characterized in that: The method comprises: obtaining a lactic acid solution by the method according to any one of claims 18 to 21, and then directly purifying the lactic acid solution to obtain a lactic acid product, or first acidifying the lactic acid solution and then purifying it to obtain a lactic acid product.

23. The method according to claim 22, characterized in that The purification method comprises: subjecting the lactic acid solution to a first concentration step, decolorization with activated carbon, further concentration and dehydration, and molecular distillation to obtain a lactic acid product, wherein the first concentration step results in a lactic acid concentration of 15-40 wt %; or The lactic acid solution is concentrated, decolorized with activated carbon, purified with resin, purified with nanofiltration membrane, and concentrated and dehydrated to obtain a lactic acid product; or The lactic acid solution is concentrated, dehydrated, and subjected to multi-stage molecular distillation to obtain a lactic acid product, wherein the number of stages of the molecular distillation is 2 or above.

24. The method according to claim 22, characterized in that The chemical purity of the lactic acid product is above 98 wt %, and / or the content of reducing sugar in the lactic acid product is below 200 ppm.

25. The method according to claim 22, wherein The chemical purity of the lactic acid product is above 98.5 wt%.

26. The method according to claim 22, characterized in that The chemical purity of the lactic acid product is above 99 wt%; and / or, The content of reducing sugar in the lactic acid product is below 100 ppm.

27. The method according to any one of claims 24 to 26, characterized in that The content of residual metal ions in the lactic acid product is less than 100 ppm; and / or, The content of reducing sugars in the lactic acid product is below 30 ppm; and / or, The total content of residual extractant and diluent in the lactic acid product is less than 100 ppm.

28. The method according to claim 27, characterized in that The content of residual metal ions in the lactic acid product is less than 50 ppm; and / or, The total content of residual extractant and diluent in the lactic acid product is less than 50 ppm.

29. The method according to claim 27, characterized in that The content of residual metal ions in the lactic acid product is less than 10 ppm; and / or, The total content of residual extractant and diluent in the lactic acid product is less than 10 ppm.