CN1289459C - Method for Purifying Organic Acids - Google Patents

Abstract

A process for purifying an aqueous feed stream (10) containing a product organic acid and a strong contaminant, such as another organic acid, is disclosed. The molar concentration of the organic acid in the feed stream (10) is at least 20 times greater than the molar concentration of the strong contaminant. The feed stream (10) is contacted with an immiscible basic extractant (18) which has a greater affinity for the contaminants and which complexes with the contaminants and a portion of the organic acid. The complexed extractant is separated from the aqueous stream (10) to produce a first effluent stream (20) containing product organic acid. The complexed extractant is contacted with a displacing acid, the extractant having a greater affinity for the displacing acid than for the contaminant. Thus, a second effluent stream (28) and a third effluent stream (30) containing organic acids are produced.

Description

Method for Purifying Organic Acids

Background technique

The present invention generally relates to methods of producing organic acids such as lactic acid.

Lactic acid has various commercial uses, for example in food production, medicine, plastics, textiles and as a starting material in various chemical processes. It is also used in the production of polylactic acid, a biodegradable plastic.

Although organic acids can be prepared by chemical synthesis, they are generally less expensive to produce by fermentation. It is well known that lactic acid can be produced by fermentation using microorganisms such as Lactobacillus delbrueckii. The broth resulting from fermentation contains unfermented sugars, carbohydrates, amino acids, proteins and salts, as well as organic acids such as lactic acid. Typically, organic acids are recovered from the fermentation broth and further purified before use. Purified organic acids recovered from fermentation broths will contain small amounts of impurities such as strong acids or certain unknown compounds. Some impurities may cause undesired color, or may interfere with downstream processing of organic acids. For example, commercially available lactic acid generally contains minor amounts of impurities such as pyruvic acid, acetic acid, and oxalic acid. Even if these impurities are present in relatively small amounts, they can still have a negative impact on polymers produced from lactic acid. For example when lactic acid is polymerized to produce polylactic acid (PLA), the presence of even small amounts of pyruvate can cause the polymer to have an undesirable yellow color. However, further purification of lactic acid, which in the first case contained only a small fraction of pyruvate, was difficult.

Accordingly, there is a need for improved methods for the production and recovery of relatively pure organic acids, particularly lactic acid.

Summary of the invention

One aspect of the invention is a method of purifying an aqueous feed stream containing a desired product organic acid and at least one potent contaminant. In certain embodiments, the aqueous feedstock stream may include or be derived from a fermentation broth (any acid mentioned herein, whether a desired product or a contaminant, is understood to mean that some or all of the acid may exist in the form of salts). The molar concentration of product organic acids in the feed stream may be at least 10 times greater than the concentration of strong pollutants, more preferably the ratio of molar concentrations of product organic acids to strong pollutants is at least 20. In certain embodiments, the molar concentration ratio of product organic acids to strong pollutants is at least 90, in certain embodiments at least 500, and in certain other embodiments at least 1000 . The aqueous feed stream is contacted with a first immiscible basic extractant having a selectivity for strong contaminants over product organic acids greater than 3. The selectivity - to be further defined below - is preferably greater than 15, more preferably greater than about 25, most preferably greater than about 100. Preferably, the selectivity is greater than the ratio of product organic acids to strong contaminants in the feedstock.

The step of contacting the aqueous feed stream with the first immiscible basic extractant is preferably carried out at or near equilibrium and utilizes a sufficient amount of the first immiscible basic extractant (such as a solid amine ion exchanger or a liquid amine extractant) to remove most of the strong pollutants. In certain embodiments, the first immiscible basic extractant has previously been used to treat a solution containing the product organic acid and at least one weak contaminant (eg, it was recycled).

As a result, most of the strong contaminants and less than about 33% by weight of the product organic acids complexed with the first immiscible basic extractant. "Majority" here refers to more than 50% by weight of a substance, which in this case refers to a strong pollutant present. That is, more than 50% by weight of the strong contaminants in the feedstock are complexed with the extractant. The complexed first immiscible basic extractant is separated from the aqueous stream to produce a first effluent stream containing product organic acids in a greater ratio to strong contaminants than the aqueous feed stream. The complexed first immiscible basic extractant is contacted with a displacement acid. The first immiscible basic extractant has a greater affinity for the displacing acid relative to the strong pollutant or product organic acid, so, over time, the product organic acid and strong pollutant are removed from the complexed first Displaced in an immiscible alkaline extractant. This results in a second effluent stream containing the majority of the product organic acids (ie, more than about 50% by weight of the solids dissolved or suspended in the stream are product organic acids) and a third effluent stream containing the majority of the strong pollutants.

Preferably, the combined amount of product organic acid in the first effluent stream and the second effluent stream is at least about 90% by weight of the product organic acid in the feed stream. More preferably, at least about 98% by weight of the product organic acids in these streams are recovered.

In various embodiments of the method, the strong contaminants include organic acids having a pK _al value lower than the pK _al value of the product organic acid. If the desired product organic acid is lactic acid, the strong contaminant preferably has a pK _al value of less than about 3.46. In some specific embodiments of the present invention involving solid ion exchange resins as the basic extractant, the strong contaminants are selected from the group consisting of pyruvic acid, oxalic acid, citraconic acid, citric acid, and mixtures thereof.

In other embodiments, strong contaminants may be weaker acids (eg, higher pK _al ) than the desired organic acid product, but may have stronger hydrophobic and/or hydrogen bonding properties than the product. Strong contaminants, relative to the organic acid of interest, can be selectively removed by an immiscible alkaline extractant containing a solvent or solvent mixture, such as 1M trilaurylamine and 1M dodecanol diluted with dodecane amine mixture of agents.

When the immiscible basic extractant contains a solvent mixture, the organic acid of interest preferably has some degree of hydrophobicity or strong hydrogen bonding properties, and the strong contaminants must be (1) have a similar Hydrogen bonding and/or hydrophobic properties, and a lower pK _al than the acid of interest (acidic low pK _al species), or (2) sufficiently strong hydrogen bonding and/or hydrophobic properties so that despite strong contamination The compound has a higher relative pK _al , which can still be removed.

Therefore, solid ion exchange resins can be used as extractants to remove strong pollutants if they have a lower pK _al than the organic acid product. For example, if the organic acid to be recovered is lactic acid, strong contaminants that can be removed by the process of the present invention involving ion exchange resins include HCl, _{H2SO4 ,} pyruvate and oxalate, among others. However, acetic acid and butyric acid do not have significantly lower pK _al than lactic acid, so they are not easily removed by ion exchange resins. However, strong contaminants with low pK _al or high hydrophobicity/hydrogen bonding properties relative to the organic acid product can be removed by using an extractant, which is a solvent or solvent mixture. For example pyruvic acid, _H2SO4 and butyric acid can be removed from an aqueous feed stream containing lactic acid by using the amine solvent extractant _of the present invention. While the first immiscible basic extractant can take a variety of forms, it is preferably a weakly basic ion exchange resin. Preferably, the weak ion exchange resins contain tertiary amine moieties. One advantage of various embodiments of the method is the ability to further purify streams that already contain very low percentages of impurities. For example, in one embodiment, the molar concentration of the product organic acid, such as lactic acid, in the feed stream is at least 20 times greater than the molar concentration of strong contaminants in the feed stream with a selectivity greater than about 25. In another embodiment, the molar concentration of the product organic acid, such as lactic acid, in the feed stream is at least 300 times greater than the molar concentration of strong contaminants in the feed stream with a selectivity greater than about 500.

In one embodiment of the process, the feed stream, the first effluent stream and the second effluent stream further contain weak contaminants. For example, when the product organic acid is lactic acid, weak contaminants can be organic acids with a _pKal greater than about 4.26, such as propionic acid, butyric acid, malonic acid, acetic acid, acrylic acid, succinic acid, or mixtures thereof. For acids with multiple acid groups such as succinic acid, only the ionized first group is relevant for _pKal . For acids with only one acid group, _pKal is equivalent to pKa. In this case, the method further comprises the steps of combining the first effluent stream and the second effluent stream to form a mixed product organic acid stream, and then extracting the combined product organic acid stream with the second immiscible base agent contact. Most of the product organic acid is complexed with the second immiscible basic extractant. Preferably, at least 90% by weight of the product acid is complexed, more preferably at least 95%. The complexed second immiscible basic extractant can then be separated from the stream to produce a fourth effluent stream containing most of the weak contaminants present in the combined product organic acid stream. Preferably, the second immiscible basic extractant contains a weakly or strongly basic ion exchange resin.

Optionally, embodiments of the method may further comprise contacting the fourth effluent stream with a third immiscible basic extractant that has a greater impact on the product organic acid relative to weak contaminants. With greater affinity, therefore, most of the product organic acid present in the fourth effluent stream is complexed with the third immiscible basic extractant. The complexed third immiscible basic extractant can then be separated from the stream to produce a fifth effluent stream containing most of the weak contaminants present in the mixed product organic acid stream. Then, the complexed second immiscible basic extractant and the complexed third immiscible basic extractant can be contacted with one or more displacement acids, thereby in one or more additional effluent streams from which Displacement product organic acid.

In another variation of the process, the third effluent stream is contacted with additional immiscible basic extractant having a greater affinity for strong contaminants relative to the product organic acid. As a result, most of the strong contaminants present in the third effluent stream are complexed with the additional immiscible basic extractant. The complexed additional immiscible basic extractant is separated from the residue stream to produce an additional effluent stream containing the majority of the product organic acid present in the third effluent stream.

A particularly preferred embodiment of the invention is a method for purifying lactic acid. This embodiment involves providing an aqueous feedstream comprising lactic acid (defined herein to include any salts thereof) and at least one strong contaminating acid having a _pKal of less than about 3.46. The molar concentration of lactic acid in the feed stream is at least 20 times greater than the molar concentration of the strong pollutant acid. The aqueous feed stream is contacted with a first basic ion exchanger which has a greater affinity for strong polluting acids relative to lactic acid, and thus most of the strong polluting acids and part of the lactic acid complexed with the first basic ion exchanger. The complexed first ion exchanger is separated from the aqueous stream to produce a first effluent stream which contains lactic acid in a greater ratio to strong contaminating acids than the aqueous feed stream. The complexed first basic ion exchanger is contacted with a displacing acid, such as HCl, H ₂ SO ₄ or H ₃ PO ₄ , for which the first basic ion exchanger has an greater affinity. Lactic acid and strongly polluting acids are displaced from the complexed first basic ion exchanger over time, resulting in a second effluent stream containing mostly lactic acid and a third effluent stream containing mostly strongly polluting acids.

In some embodiments of the method, the strong polluting acid is selected from the group consisting of pyruvic acid, oxalic acid, citraconic acid, citric acid, and mixtures thereof. In certain embodiments of the method, the molar concentration of lactic acid in the feed stream is at least 100 times greater than the molar concentration of strong contaminant acids in the feed stream, and the selectivity is greater than about 250. In certain embodiments, the ratio is at least 300 and the selectivity is greater than about 500.

Preferably, the affinity of the first basic ion exchanger for the displacement acid is at least 10 times greater than its affinity for pyruvate.

Preferably, the ratio of lactic acid to strong pollutants in both the first effluent stream and the second effluent stream is greater than 300. More preferably, they all have a ratio of moles of lactic acid to moles of strong pollutants greater than about 1000. In some embodiments of the process, at least 90% by weight, more preferably 98% by weight, of the lactic acid in the feed stream is recovered in the first effluent stream and the second effluent stream.

In a specific embodiment of the process, the aqueous feedstream contains no more than about 0.15 moles of cations selected from the group consisting of Ca, Mg, Na, Fe, Zn, Zr, and Li, per mole of lactic acid; per mole of lactic acid, which contains not more than about 0.05 moles of anions selected from the group consisting of Cl, _SO4 , _PO4 , and _NO3 ; per mole of lactic acid, which contains not more than about 0.03 moles of strong acid contaminants, said Strong acid contaminants selected from the group consisting of pyruvic, oxalic, citraconic, and citric acids; containing no more than about 0.02 moles of weak acid contaminants selected from the group consisting of propionic, butyric, malonic, per mole of lactic acid and succinic acid.

Another aspect of the present invention is a process for the purification of lactic acid which involves providing an aqueous fermentation process comprising lactic acid (herein defined as including any salts thereof) and pyruvate (also defined herein as including any salts thereof). broth. In the aqueous fermentation broth, the molar concentration of lactic acid is at least 20 times greater than the molar concentration of pyruvate. Cells are removed from the broth to form an aqueous feedstock stream. Cells can be removed using any method known in the art (eg, centrifugation or filtration, among others). The aqueous feed stream is contacted with a medium for complexing pyruvate, which has a greater affinity for pyruvate relative to lactic acid, whereby most of the pyruvate and part of the lactic acid form complexes with it . The complex is separated from the aqueous stream to produce a first effluent stream containing lactic acid in a greater ratio of lactic acid to pyruvic acid than the aqueous feed stream. The complex is contacted with a medium for displacing lactic acid and pyruvic acid therefrom, thereby producing a second effluent stream comprising a majority of lactic acid and a third effluent stream comprising a majority of pyruvic acid.

In certain embodiments, the first immiscible basic extractant is a solid basic extractant, and the aqueous feed stream is contacted with the first immiscible basic extractant in a packed bed. Preferably, in embodiments involving packed beds, the ratio between the molar concentration of product organic acids and the molar concentration of strong pollutants in the second effluent stream is within about 10% selectivity.

In other embodiments, the first immiscible basic extractant is a liquid basic extractant, and the aqueous feed stream is contacted with the first immiscible basic extractant in a multi-step process. Preferably, the ratio of product organic acids to strong contaminants is within about 10% selectivity.

Additionally, in certain embodiments the aqueous feedstream contains multiple potent contaminants, and at least one of the potent contaminants is a displacement acid.

Certain embodiments relate to a process involving an aqueous feed stream containing a desired product organic acid, at least one strong and weak contaminant. The first effluent stream also contains weak contaminants, and the first effluent stream is subjected to at least one extraction or rectification (by methods known in the art) to produce at least two fractions, and the purified product organic acid fraction, which contains From about 90% to 99.5% by weight of the product organic acid present in the feed stream, and the weak contaminant fraction, which contains the product organic acid and the weak contaminant. The ratio of the molar concentration of product organic acids to the molar concentration of weak pollutants in the weak pollutant fraction is smaller than the ratio of the molar concentration of product organic acids to the molar concentration of weak pollutants in the feed stream. contacting the weakly contaminated fraction with a third immiscible basic extractant having a selectivity of greater than about 3 for product organic acids, most of which are and less than about 33% of the weak contaminants are complexed with the third immiscible alkaline extractant. The complexed third immiscible basic extractant is separated from the aqueous stream to produce an effluent stream containing weak contaminants. The effluent stream containing weak pollutants will have a greater ratio of weak pollutants to product organic acids than the aqueous feed stream. The complexed third immiscible basic extractant is contacted with the displacement acid, the third immiscible basic extractant having a greater affinity for the displacement acid relative to the product organic acid or weak contaminant. The displacement acid is present in sufficient amount to displace the product organic acids and weak contaminants from the complexed third immiscible basic extractant over a period of time, resulting in a weak contaminant discharge containing most of the weak contaminants stream and the product organic acid stream containing the majority of the product organic acid. Preferably, the purified product organic acid fraction contains from about 95% to 99.5% by weight of the product organic acid present in the feed stream.

Certain embodiments relate to a method of purifying an organic acid comprising providing an aqueous feed stream comprising a product organic acid and at least one potent contaminant. The molar concentration of the product organic acid is at least 20 times greater than the molar concentration of the strong pollutant. The aqueous feed stream is contacted with a first immiscible basic extractant having a selectivity for strong contaminants of greater than about 3 relative to product organic acids. Most of the strong contaminants and less than about 33 wt% of the product organic acids are complexed with the first immiscible basic extractant. The complexed first immiscible basic extractant is separated from the aqueous stream to produce a first effluent stream containing product organic acids in a greater ratio to strong contaminants than the aqueous feed stream. The complexed first immiscible basic extractant is treated with at least one of: (1) changing temperature, (2) changing solvent concentration, or (3) changing displacer concentration. This treatment results in the displacement of product organic acids and strong contaminants from the complexed first immiscible basic extractant over a period of time, resulting in a second effluent stream containing most of the product organic acids and containing most of the strong A third effluent stream of pollutants. Changing the solvent concentration can be accomplished using methods known in the art, such as evaporating the solvent present in the aqueous feed stream. In addition, selective release of the desired product or impurity from the complexed first immiscible basic extractant can be achieved through the combined application of temperature changes, solvent changes, and/or displacement of acid or base concentrations. A displacer may be a displacer acid or a displacer base as described above. A base such as NaOH can be used as a displacer, and the displaced material can be treated by methods known in the art to recover the desired product organic acid.

Partial lactic acid purification methods may involve fermentation from aqueous lactic acid raw materials that have been pretreated to make them suitable as raw materials for primary solvent extraction. Such fermentative pretreatment from an aqueous lactic acid feedstock may include careful separation of solids by filtration and, optionally, dissolved macromolecular species by membrane filtration. Further, cations can be removed with cation exchangers, and anions can be removed with conventional solid anion exchangers or the same amine-based extractants (such as amines, enhancers, and diluents) used for lactic acid main extraction. When used in limited quantities relative to the decationized feedstock, it selectively extracts stronger mineral acids than lactic acid. The latter step is often referred to as pre-extraction. It has now been found that overall lactic acid recovery is effective, as in the present invention, by performing a pre-extraction using as the extractant a composition specific for this purpose and different from that suitable for the main extraction. Thus, preferred embodiments include two sequential solvent extraction steps (eg, pre-extraction and main extraction), each applying an amine-based extractant specific to its function. The lean extractant used in the pre-extraction stage has significantly lower amine concentration and lower enhancer/amine molar ratio than the rich extractant used in the main extraction stage.

The initial aqueous lactic acid feedstock and an extractant selected specifically for this stage (lean extractant) are added in the pre-extraction stage. Mineral and organic acids that are extracted preferentially over lactic acid are injected into the aqueous stream while lactic acid is maintained in a second aqueous stream (eg, the first effluent stream) that enters the main extraction stage. The main extraction stage uses a specialized extractant (rich extractant) that is very different from the lean extractant. Pure lactic acid is obtained in the aqueous stream after stripping from the main extraction stage, while impurities are injected into the side stream.

The method structure of two solvent extraction steps, each with its own unique solvent composition, has the added advantage of providing the option of using non-solvent assisted separation methods for further purification. Thus when used with lactic acid containing streams which are small compared to the main flow and generally also contain lower amounts of impurities, rectification or simulated moving bed chromatography, which are commonly used in such cases, become feasible . The secondary stream, typically the internal recycle stream, can be diverted in whole or in part to a secondary separation process, and in a secondary polymer stream to remove impurities and recover lactic acid.

Certain embodiments of the invention relate to a method of purifying lactic acid. An aqueous feed stream containing free lactic acid and at least one contaminant is contacted with a lean liquid extractant with which most of the contaminants are complexed in the pre-extraction stage. For example, the aqueous feedstock stream can be a fermentation broth. The lean liquid extractant contains less than about 0.75 moles of amine per kilogram of lean liquid extractant; about 0-0.5 moles of enhancer per mole of amine; and diluent. The complexed lean liquid extractant is separated from the aqueous feed stream in a pretreatment stage to produce a first effluent stream containing free lactic acid in a greater ratio of free lactic acid to contaminants than the uncomplexed aqueous feed stream. The first effluent stream is then contacted with the rich liquid extractant in the main extraction stage, and most of the free lactic acid in the first effluent stream is complexed with the rich liquid extractant. Rich liquid extractants contain the same amines, enhancers, and diluents as lean liquid extractants, however, rich liquid extractants contain more moles of amine per kilogram of rich liquid extractant in the main extraction stage than The moles of amine per kg of lean extractant were higher in the pretreatment stage, and the ratio of moles of enhancer to moles of amine was higher in the rich extractant than in the lean extractant. The loading is such that the ratio of the moles of free lactic acid in the first effluent stream to the moles of amine in the rich liquid extractant is less than about 1.1. The process optionally further comprises stripping the complex comprising lactic acid and the liquid-rich extractant with water, thereby producing an aqueous product lactic acid stream.

Brief description of the drawings

Figure 1 is a process flow diagram of one embodiment of the present invention.

FIG. 2 is a process flow diagram of another embodiment of the present invention, which includes practicable steps in addition to the steps shown in FIG. 1 .

FIG. 3 is a process flow diagram of another embodiment of the present invention, which includes practicable steps in addition to the steps shown in FIG. 1 .

Figure 4 is a process flow diagram of one embodiment of the present invention.

Description of Descriptive Embodiments

The method of the present invention can be used to recover and purify various organic acids. The method is especially suitable for the recovery and purification of mono-, di- or tricarboxylic acids having 2 to 8 carbon atoms. Preferably, the organic acid is a hydroxy organic acid (or a mixture of two or more such acids). The hydroxyorganic acid can be an alpha, beta, delta, gamma or epsilon hydroxy acid. The organic acid is most preferably lactic acid.

The method of the present invention allows the recovery of purified organic acids from fermentation broths. However, the method is also suitable for purifying organic acids from other sources, such as commercial lactic acid. "88% lactic acid" and "commercial lactic acid" refer to generally commercially available lactic acid, which is actually monomeric lactic acid, linear dimerized lactic acid or lactoyl lactic acid, short-chain lactic acid oligomers, water, a small amount of cyclic dimerized Mixture of lactic acid or lactide and minor impurities. When commercial lactic acid is diluted with a large amount of water, dimers and oligomers are slowly hydrolyzed or converted into monomeric lactic acid. When the concentrated lactic acid is diluted with water to a concentration of 50 wt%, the initially present dimers and oligomers will be gradually hydrolyzed into a mainly monomeric lactic acid but still containing about 3-4 wt% dimer lactic acid and traces of more A mixture of higher oligomers.

Figure 1 shows an embodiment of a process for recovering lactic acid from a fermentation broth. Seed medium 10 is fed to fermentor 12 containing fermentation medium. Fermentation produces an aqueous broth containing the desired organic acid, in this case lactic acid. [Any mention of organic acids in this patent, including in the claims, should be understood that some or all of the acids can exist in the form of salts. In short, any reference to an acid herein includes either form (free acid or salt) or a mixture of both. ] The broth also contains one or more strong contaminants, in this case pyruvate, as well as unfermented sugars and other impurities. In some embodiments of the invention, the ratio between the molar concentration of the desired product acid (eg, lactic acid) and the molar concentration of a strong impurity (eg, pyruvate) is greater than about 300. In certain embodiments, the ratio between the molar concentration of the desired product acid (eg, lactic acid) and the molar concentration of a strong impurity (eg, pyruvate) is greater than about 500, and in certain embodiments, it is greater than 1000.

As used herein, "strong contaminant" refers to a chemical species, such as an organic acid, for which the selected immiscible alkaline extractant has at least a 3-fold greater selectivity or affinity for the product of interest sex.

For embodiments of the invention where solid immiscible basic extractants containing anion exchange resins are used, strong contaminants to be removed from the organic acid aqueous feed stream may have a higher concentration than the organic acid to be recovered from the feed stream. Low _pKal value.

For embodiments of the invention wherein a liquid immiscible alkaline extractant containing a solvent is involved, strong contaminants are either (a) having a lower pK _al value than the organic acid to be recovered from the feed stream, or (b ) strong contaminants have similar or higher pK _al values than the organic acid of interest, but are more hydrophobic or have more hydrogen-bonding groups or both.

For example in the case of solid ion exchange extractants, oxalic acid (pK _a =1.27) and pyruvic acid (pK _a =2.48) are strong contaminants in lactic acid (pK _a =3.86) solutions. Examples of other strong contaminants that may be present in the lactic acid feed stream include citraconic acid, citric acid, and other organic acids with pK _al values less than about 3.46. Weak contaminants that cannot be removed by solid ion exchange extractants may include non-acidic species such as glucose and weak acids such as acetic acid, succinic acid, and butyric acid.

For liquid amine-based extractants used to recover lactic acid from solution at 20-30°C, strong contaminants may include strong acids as described above as well as hydrophobic weak acids. Examples of hydrophobic weak acids that can be removed by liquid immiscible extractants are n-butyric acid, isobutyric acid, and cyclic weak aromatic acids such as benzoic acid, among others.

In some embodiments of the method, the feedstock may contain one or more potent contaminants of unknown chemical composition. For example, some commercially available lactic acid contains contaminants of unknown chemical composition that have an apparent pK _al value of less than about 3.46. Using the present invention, feed streams containing such lactic acid can be purified to lower concentrations of some unknown contaminants. Broth 14 is drawn from fermenter 12 . Cells in the broth may be separated, such as by filtration or centrifugation, and removed as waste stream 16 . Optionally, the broth can be further purified by removing strong anions and/or cations. Strong anions such as chloride, sulfate, phosphate and nitrate can be selectively removed with high selectivity from neutral or acidic pH streams containing organic acids. Strong cations that can be removed include Ca, Mg, K, Na, Fe, Zn, Zr, and Li cations. For example, the fermentation broth can be contacted sequentially with a cation exchanger, such as a strongly acidic cation exchanger, an anion exchanger, such as a weakly basic anion exchanger.

The broth 14 is then contacted in step 18 with a first immiscible alkaline extractant. Preferably, this is done using countercurrent. Among the many options, mixer-settlers can be used. The extractant is "immiscible" because it does not mix with the broth, but the extractant may or may not be a liquid. For example the extractant may contain an amine compound which has the ability to complex with one or more organic acids present. In particular, this first extractant should have a greater affinity for a strong contaminant (pyruvate) than for the desired product (lactic acid). As used herein, "affinity" refers to the tendency to complex with other species, such as lactic acid or pyruvic acid, under existing process conditions, including the specific combination of acids, solvents and other ingredients present. Equal affinity means that when contacted with a solution of 50% lactic acid and 50% pyruvic acid, the extractant will complex with equal amounts of both acids. Since the ratio of lactic acid to pyruvic acid in the feed solution of the present invention is generally high, the affinity of the extractant for the contaminant (pyruvic acid) should be much greater than its affinity for lactic acid. Preferably, the extractant has an affinity for pyruvate that is at least 20 times greater than its affinity for lactic acid.

Amine liquid extractants may include primary, secondary or tertiary amines. In certain embodiments, the amine is an alkylamine having a total number of carbon atoms of about 4-36. Specific examples include n-butylamine, tri-n-butylamine, octylamine, tri-n-octylamine, didecylamine, dodecylamine, and tris(dodecylamine) (also known as trilaurylamine), among others. The amine should be immiscible with the aqueous feedstock solution so that two phases can form. The liquid extractants of the present invention may also optionally include diluents and/and enhancers. Diluents can be used as a component of an alkaline immiscible extractant to reduce its viscosity, or to increase the selectivity of the extractant to other undesired species, among other reasons. Suitable diluents include, for example, pure or mixed aromatic or aliphatic hydrocarbons such as xylene, toluene, decane, dodecane, kerosene and mixtures thereof. "Enhancer" refers to a chemical substance that enhances the performance of an alkaline immiscible extractant. Enhancers can enhance alkaline immiscible extractants: strong contaminant complexes or immiscible extractants: organic acid complexes and/or help dissolve complexes. Examples of suitable enhancers include polar materials selected from alcohols, including alkanols and diols, ketones, diketones, fatty acids, chlorides, and other materials known in the art.

Preferably, the amine liquid extractant used in the present invention contains three components forming a single homogeneous phase: amine, enhancer and diluent. In a preferred embodiment, the amine may be an aliphatic secondary or preferably tertiary amine having at least about 20 carbon atoms to ensure water insolubility; the diluent may be a neutral liquid such as a hydrocarbon for the extraction agent and The liquid organic phase formed under the actual process conditions provides the viscosity; the enhancer can be an organic compound, which is polar but neutral in nature so that it does not interfere with the acid-base reaction, which is very useful for extracting acids with amine extractants important. Preferably, the enhancer is an alkanol such as octanol; an ester such as butyl acetate; or a ketone that reacts with an amine to increase its base strength.

Alternatively, the first basic extractant may comprise a basic ion exchange resin. As previously stated, the ion exchange resin should have a greater affinity for strong contaminants than it does for the desired product. Suitable ion exchange resins include pyrimidine, imidazole and tertiary amine resins, among others. A particular example is Ionac A365 (Sybron Chemicals, Birmingham, New Jersey). Strongly and weakly basic ion exchangers can also be used. Preferably, the amount of first extractant used in the process is sufficient to produce a total complexation capacity greater than that theoretically required to complex all pyruvate or other strong contaminants present. In this way, the fraction of pyruvic acid that is complexed is maximized, although part of the lactic acid is also complexed.

The first alkaline extractant, which has a greater affinity for pyruvate relative to lactic acid, forms a complex with most of the pyruvate present in the broth. Due to the relatively large concentration of lactic acid in the broth, the extractant also forms partial complexes with lactic acid, although its affinity for lactic acid is lower. Thus, with most of the pyruvate removed, a first effluent stream 20 is produced in which the ratio of lactic acid to pyruvate is higher than in the original broth 14 .

Then, by an acid displacement step 24, the first basic extractant can be separated from most of the complexed pyruvate and lactic acid. Stream 26, containing an aqueous solution of _a displacing acid such _as HCl, _H3PO4 , oxalic acid, _H2SO4 or Tris Fluoroacetic acid. Preferably, the displacing acid has a pK _a of about -2 to 1.8. Displacement acids may also be present in mixtures with other organic acids and substances, such as mixtures _of HCl, _H2SO4 , oxalic acid, and acetic acid. Preferably, the concentration of the displacement acid _is about 1-40%, more preferably 2-5% for _H2SO4 , more preferably 20-30% for mixtures containing different acids. In the case of mixtures of different acids, only acids with a pK _a of -2 to 1.8 in this mixture are used as displacing acids.

Since the extractant (ie ion exchanger) has a greater affinity for the displacing acid than it does for lactic acid or pyruvic acid, the latter two acids are displaced from the complexing sites. Since the extractant has a lower affinity for lactic acid than it does for the other two acids, lactic acid tends to be displaced first and is removed as a second effluent stream 28 rich in lactic acid. The lactic acid-enriched stream can optionally be mixed with the first effluent stream 20 to form a mixed lactic acid product stream. Preferably, the stream contains at least about 98% by weight of lactic acid present in the feedstock and contains less than about 20 ppm, more preferably less than about 10 ppm, and most preferably less than about 2 ppm of both pyruvic and oxalic acids.

After most of the lactate has been replaced, pyruvate begins to be replaced in large quantities. A third effluent stream 30 rich in pyruvate is thus produced, which can optionally be purified for use in processes requiring this particular acid.

The resulting stream 32 contains the first extractant, which is now complexed with the displacement acid. This stream 32 is subjected to an alkaline regeneration step 34 during which a stream 36 containing a base such as 5% aqueous NaOH is contacted with the complexed first extractant. The base displaces the displacing acid from the extractant to produce a regenerated first extractant stream 38 which can be recycled 42 to be used in step 18 . This operation also produces stream 40 containing regenerated acid, which can optionally be recycled to stream 26 for use.

Other methods of regenerating the first extractant may also be used.

Figure 2 shows an alternative downstream processing step that is suitable when the process raw material contains both weak and strong contaminants.

The term "weak contaminant" as used herein in relation to embodiments of the invention involving solid amine extractants refers to compounds having a greater pK _al value than the organic acid to be recovered.

The term "weak contaminant" as used in the context of liquid amine mixtures refers to a compound that has a greater _pKal value than the organic acid being recovered and is generally neither highly hydrophobic nor prone to association with the liquid The various components of the amine mixture form strong hydrogen bonds.

For example, for solid-based amines, acetic acid with a pK _al value of 4.76 can be a weak contaminant in feed streams containing lactic acid. Examples of other mild contaminants commonly present in lactic acid feedstock streams, especially those obtained from fermentation broths, include propionic acid, butyric acid, acetic acid, malonic acid, succinic acid, and other organic acids with pK _al values greater than about 4.26 .

For example, for a liquid extractant that is a mixture containing immiscible amines, acetic acid with a pK _al value of 4.76 can be a weak contaminant in a feedstream containing lactic acid. In this case, however, butyric acid is not a weak contaminant due to its hydrophobicity relative to lactic acid in typical solvents.

In FIG. 2 , first effluent stream 20 and second effluent stream 28 are combined to form combined lactic acid product stream 50 . The combined product stream is then contacted in step 52 with a second immiscible basic extractant. The second immiscible basic extractant can be, for example, a weakly basic ion exchange resin such as Amberlite IR 35 containing tertiary amine moieties. Preferably the second extractant has a greater affinity for lactic acid than it does for acetic acid. In addition, the extractant should be present in an amount sufficient to complex substantially all of the lactic acid present in the stream. Thus, the second extractant primarily forms complexes with lactic acid and, to a much lesser extent, acetic acid. The complex is separated from the residual liquid as part of stream 56 to exit fourth effluent stream 54 .

The fourth effluent stream 54 is contacted with a third immiscible basic extractant, preferably a basic ion exchange resin. Suitable resins include Amberlite IR 35. Preferably this third extractant has a greater affinity for lactic acid than it does for pyruvate. Thus, most of the lactic acid in the fourth effluent stream complexes with the ion exchanger, and the complexes are removed in stream 70. A fifth effluent stream 68 enriched in weak pollutants is produced.

Streams 56 and 70 contain complexes of the second and third extractants primarily with lactic acid. Lactic acid can thus be recovered by contacting these complexes with displacement acid streams 58 and 72 . Since the second and third extractants have a greater affinity for displacing acid relative to lactic acid, lactic acid is displaced into additional discharge streams 62 and 76 from which it can be recovered. Streams 62 and 76 preferably contain greater than about 90% by weight of the lactic acid present in mixed stream 50, more preferably at least about 95%.

Streams 64 and 78 contain ion exchanger complexed with a displacement acid, which can then be regenerated by contact with a base (not shown in Figure 2), and can then be recycled for further use in the process.

FIG. 3 shows another set of optional steps in addition to the steps shown in FIG. 1 . This variation of the method is especially useful when the ratio of lactic acid to pyruvic acid in the starting material (molar lactic acid: molar pyruvic acid) is greater than about 300. In this variation of the process, the pyruvate-enriched third effluent stream 30 is contacted in step 80 with additional immiscible basic extractant. The extractant has a greater affinity for pyruvate relative to lactic acid and is preferably an ion exchange resin such as Amberlite IR-35. Thus, the extractant complexes primarily with pyruvate and these complexes are removed in stream 84. An additional lactic acid-rich effluent stream 82 is produced from which lactic acid can be recovered.

The stream 84 containing the complex of the ion exchanger mainly with pyruvic acid is then contacted in step 86 with a stream 85 containing the displacement acid, such as 4% HCl in water. The extractant has a greater affinity for the displacing acid than it does for pyruvate, so the latter is displaced out as the former complexes with the extractant. Pyruvate is removed in effluent stream 88 while stream 90 containing the displacing acid complex is passed to regeneration step 92 during which the complex is treated with base stream 94 . The result is a regenerated resin stream 98 which can be recycled in the process, and a discharge stream 96 containing the displacing acid which can also be recycled.

Embodiments of the process described above achieve high selectivity and are therefore very effective in removing contaminants from organic acid solutions or suspensions, even if the organic acid solutions or suspensions are initially relatively pure. This ability to selectively remove impurities present in low concentrations is a major advantage of various embodiments of the present invention. "Selectivity" as used herein refers to the concentration of the desired product acids, contaminants, solvents, and other components that come into contact with the extractant under process conditions, which can exist in multiple liquid phases. When the apparent or effective selectivity of the extractant. Selectivity (S) is often slightly less than theoretical selectivity due to contact constraints and other reasons. The theoretical selectivity can be expressed as the following formula:

The amount mentioned in the formula can be any quantitative measurement, such as gas chromatography peak or HPLC peak area, mole, gram and others. Selectivity should be greater than about 1, preferably much greater than 1. Preferably, the selectivity is at least about 10 when the desired product is lactic acid. Preferably, the selectivity is at least 80% of theoretical selectivity. More preferably, the selectivity is at least about 90% to 95% of theoretical selectivity, most preferably at least about 99% of theoretical selectivity.

Preferably, the ratio of the molar concentration of organic acid to the molar concentration of strong pollutants in the feed stream is at least about equal to the selectivity to strong pollutants. If the feed stream contains lactic acid, it is preferred that the ratio of M lactic acid to M pyruvic acid (a strong contaminant) be greater than about 18. In some embodiments of the method, the ratio of organic acids to strong pollutants (M organic acids:M strong pollutants) is greater than the selectivity (S) for strong pollutants and less than the square of the selectivity ( ^S2 ) . While in other embodiments of the process, this ratio is even greater than ^S2 in the feedstock.

Certain embodiments of the invention relate to methods of purifying lactic acid. The method includes providing an aqueous feed stream 100 comprising free lactic acid and at least one contaminant. In certain embodiments, at least one contaminant is selected from the group consisting of maleic acid, malonic acid, fumaric acid, oxalic acid, citric acid, citraconic acid, pyruvic acid, 2-ketobutyric acid, 2-hydroxybutyric acid , acetic acid, 2-hydroxy-3-methylbutanoic acid, 4-hydroxy-phenylpyruvate, phenylpyruvate, 4-hydroxy-phenyllactic acid, phenyllactic acid, and mixtures thereof. Aqueous feed stream 100 can be any stream known in the art. Aqueous feedstock stream 100 may be a fermentation broth or the fluid obtained by partially purifying the broth by methods known in the art. Contaminants of aqueous feed stream 100 include acids with a _pKal less than about 3.46 (eg, the _pKa of lactic acid). In certain embodiments, the contaminants may be selected from pyruvic acid, oxalic acid, citraconic acid, citric acid, and mixtures thereof.

Aqueous feed stream 100 can be prepared by a second method comprising providing an aqueous stream feed comprising lactic acid, at least one contaminant, and solids, and filtering the aqueous feed stream to remove a majority (e.g., greater than about 50%) of the solids . In certain embodiments, the aqueous stream feedstock may contain dissolved molecules (such as fermentation media, proteins, carbohydrates, vitamins, lipophilic pigment precursors or organic acids, among others), and the second method involves treating the filtered aqueous The feed stream is subjected to membrane filtration, which removes most of the dissolved molecules. The aqueous feed stream may contain cations such as Ca, Na, K, Mg, Fe, Zn, Zr, and Li, among others, and a second method of preparing the aqueous feed stream 100 may include combining the filtered aqueous feed stream with a cation exchanger Contact, thereby removing most of the cations. At 102 (pre-extraction stage), aqueous feed stream 100 is contacted with lean liquid extractant 104 . The lean liquid extractant 104 can be regenerated by methods known in the art and recycled in subsequent processes.

The lean liquid extractant 104 contains less than about 0.75 moles of amine per kilogram of lean liquid extractant; about 0-0.5 moles of enhancer per mole of amine; and a diluent. The amines may be, for example, secondary or tertiary aliphatic amines. Preferably, the amines have a total of 20-36 carbon atoms, but may include amine extractants having higher carbon atoms known in the art. In certain embodiments, the lean liquid extractant includes a tertiary amine containing about 0.2-0.5 moles of amine per kilogram of lean liquid extractant. Enhancers may be those known in the art that interact with the amine extractant to increase its basicity. The enhancer may be selected from known enhancers such as alkanols, diols, esters, diesters, ketones and diketones. Preferably, the enhancer is a C ₃ -C ₁₂ primary monohydroxy alcohol. In certain embodiments, lean liquid extractant 104 contains about 0.1-0.25 moles of enhancer per mole of amine. The diluent may be selected from aromatic and aliphatic hydrocarbons. Preferably, the diluent is selected from dodecane, decane, xylene, toluene, kerosene and mixtures thereof. The contact 102 between the aqueous feed stream 100 and the lean liquid extractant 104 results in the complexation of most of the contaminants with the lean liquid extractant.

The complexed lean liquid extractant is separated from the aqueous feed stream and produces a first effluent stream 106 containing free lactic acid in a greater ratio of free lactic acid to contaminants than in the uncomplexed aqueous feed stream 100 . The complexed lean liquid extractant is regenerated by methods known in the art. In certain embodiments, a portion of the lactic acid may be complexed with the lean liquid extractant, and the lactic acid may be recycled 126 when the extractant is regenerated, eg, after secondary separation operation 118 .

The first effluent stream 106 is contacted 108 with a rich liquid extractant 110 (main extraction stage) with which most of the free lactic acid in the first effluent stream 106 is complexed. Rich liquid extractant 110 can be regenerated using methods known in the art. As with the extraction 102 with a lean extractant, the extraction 108 with a rich extractant can have an internal recycle stream 116 that undergoes an auxiliary separation 124 where the removed impurities 122 become part of a waste stream 120 . Components not complexed with the rich liquid extractant 110 are rejected in waste stream 114 . The rich liquid extractant 110 contains the same amines, enhancers and diluents as in the lean liquid extractant 104, but the rich liquid extractant 110 contains more moles of amine per kilogram than the lean liquid extractant 104. The number of moles is greater and the ratio of moles of enhancer to moles of amine is higher in the rich liquid extractant 110 than in the lean liquid extractant.

The loading of the first effluent stream 106 to the rich liquid extractant 110 is such that the ratio of the moles of free lactic acid in the first effluent stream 106 to the moles of amine in the rich liquid extractant 110 is less than about 1.1, more preferably less than about 0.95.

The process may further include stripping 108 the complex comprising lactic acid and the liquid-rich extractant with water to produce an aqueous product lactic acid stream 112 . The stripping is preferably carried out at a temperature which is about 20°C or less higher than the temperature of the step of contacting the rich liquid extractant and the first effluent stream. More preferably, the stripping is preferably performed at a temperature that is about 15°C or less higher than the temperature during the step of contacting the rich liquid extractant and the first effluent stream. It has now been found that performing the extraction and back extraction at approximately the same temperature or at temperatures that are not significantly different significantly increases the purity level of lactic acid obtained by solvent extraction methods. This purity benefit is well achieved using amine-based extractants that fall within the defined composition range and are applied within the defined lactic acid loading level.

The process described in Figure 4 with two main extractions 102 and 108 has the advantage of providing the option to perform solvent-free operation on smaller side streams 126 and 116 on larger streams such as 100, 102, Applications on 106, 108 and 112 may not be valid. Thus, 118 and 124 could be rectification or simulated moving bed (SMB) operations, among others. Such side streams 126 and 116 typically contain a narrower range of impurities than the larger streams 100, 102, 106, 108, and 112. Such small streams such as 126 and 116 may be internal recycle streams, some or all of which are diverted to auxiliary separations (eg, rectification, chromatography, and others). Impurities from this secondary separation may be vented to 128 and 122 and may become part of the main waste stream 120 of the present invention.

Figures 1-4 describe some specific combinations of applicable steps, but those skilled in the art will recognize that there are many ways to practice the invention. For example the process can be carried out in a batchwise, continuous or semi-continuous manner.

Some embodiments of the invention can be further understood from the following examples.

Example 1. Selectivity of resin IRA-35 for pyruvate relative to excess lactic acid.

Table 1 raw material solution balance fluid resin K _d selectivity Concentrationmol/L Pyruvate 0.005 0.001 0.024 26.9115 14.69 lactic acid 0.503 0.386 0.706 1.832 Lactic acid dimer 0.006 0.003 0.019 6.715 3.67

A 3 ml aqueous stock solution containing lactic acid and pyruvic acid as described in Table 1 was prepared. The feedstocks were 45.3 g/L lactic acid and 440 mg/L pyruvate, which represent a typical fermentation broth stream. In a single-step batch equilibrium experiment, it was contacted with weakly basic anion resin IRA-35 at 20 °C. A selectivity of 14.69 for pyruvate over lactic acid was observed. In this single-step batch experiment, a total of 81.8% of pyruvate was transferred from solution to the ion exchange resin, while only 23.4% of lactate was transferred.

Example 2. Purification of a lactic acid feed stream containing traces of pyruvate and oxalate by continuous flow using a packed column (multistage) contactor.

Three stock solutions were prepared to simulate fermentation broths containing lactic acid. The first stock solution (FS1) was prepared as follows: 272.7 g of 88% L-lactic acid (Pfansteihl), 2.572 g of 95% pyruvic acid (Aldrich), 20.868 g of 10% w/v oxalic acid (LabChem, Inc. ) and deionized water to a volume of 4 liters. Similarly, a second stock solution (FS2) was prepared as follows: 270.4 g of 88% L-lactic acid, 2.424 g of 95% pyruvic acid, 20.756 g of 10% w/v oxalic acid and sufficient deionized water were mixed to form 4 liter volume of solution. A third stock solution (FS3) was prepared as follows: 272.7 g of 88% L-lactic acid, 2.4 g of 95% pyruvic acid, 20.7 g of 10% w/v oxalic acid and sufficient deionized water were mixed to form a volume of 4 liters The solution.

A 40 ml column was packed with Ionac A-365 weakly basic anion exchange resin (Sybron Chemicals, Inc.), a basic immiscible extractant. Ionac A-365 has a porous polyacrylate gel bead structure containing divinylbenzene acrylate with polyamine functionality. The resin packed in the column was washed with several bed volumes of deionized water. The packed column was decapped and placed on a ring stand for upflow of feedstock.

An Eldex B-100-S-4 stainless steel reciprocating pump was used to regulate the rate of entry of water, feed solution, and process fluids into the column. The feedstock solution, water and treatment fluid are passed through the column at a temperature of about 19°C to 21°C. Four liters each of lactic acid feedstocks FS1 and FS2, and 2.5 liters FS3, respectively, were pumped sequentially through the column over a period of 52 hours. The solutions were fed sequentially to the bottom of the column and the eluate was collected at the top of the column. Fractions of the eluate from the stock solution were collected in the following order: 6 x 30ml, 2 x 120ml, 29 x 240ml, 1 x 40ml, 8 x 240ml and 9 x 30ml. Treat the column with an acidic solution and then a basic solution, thereby also collecting 4 x 40ml acidic eluent fractions, 2 x 40ml deionized water wash fractions, 4 x 40ml caustic (e.g. basic) eluent fractions and 2 x Wash fractions with 40 deionized water.

Selected eluate fractions were analyzed undiluted sequentially by HPLC. 100 μl of eluate fractions were injected at a flow rate of 1.4 ml per minute in each HPLC run. All analyzes were performed at room temperature between 19°C and 21°C. The mobile phase contained 10% acetonitrile and _0.085 % _H3PO4 in deionized water. The HPLC column was a Jordi organic acid column 300 mm long and 7.8 mm in diameter. Compounds eluted from the HPLC column were detected using UV detection equipment (210 nm). Determine the pH of some eluate fractions.

After collection of the above fractions, two 30 ml samples were collected at approximately half the flow rate used for the previous fractions to determine if there were any kinetic limitations. Based on the data below, there is clearly no kinetic effect.

After the feed stream has flowed through, the column is regenerated. The column was washed with 2 bed volumes of deionized water, 4 bed volumes of 1N HCl, followed by 2 bed volumes of deionized water. Then, wash with 4 bed volumes of 1N NaOH, and then wash with 2 bed volumes of deionized water. The flow of the raw material solution and the regeneration of the column can be described by the following chemical formula:

Raw material processing: R ₃ N → R ₃ N: lactic acid → R ₃ N: pyruvic acid- _{R 3} N: oxalic acid

regeneration (1):

regeneration (2):

Multiple new peaks appeared in the acid and base eluate fractions followed by the water wash. Some of these peaks may be due to the reaction between pyruvic acid and oxalic acid in the resin phase.

Initially the resin exists in the form of R ₃ N. After the feed solution is fed to the column, the immiscible basic extractant complexes any acid present in the feed stream. As more feedstock solution is fed to the column, lactic acid complexed with the immiscible alkaline extractant is displaced by pyruvic acid. As more feed solution is fed to the column, pyruvic acid complexed with the immiscible basic extractant is displaced by oxalic acid. HPLC trace analysis of an eluate sample collected at the end of the feed solution stream on the column showed that oxalic acid was still almost completely absorbed by the immiscible basic extractant at the end of the run. Breakthrough of pyruvate (displacement of pyruvate from the immiscible alkaline extractant) may occur when pyruvate in the eluate sample reaches 5% of the g/L concentration in the feedstock. From the HPLC data, this occurred at 192 bed volumes.

Additional data collected from the run is summarized in the table below.

Table 2

HPLC trace sample peak area of raw material solution FS1 FS2 FS3 oxalic acid 1614 1576 1614 Pyruvate 1462 1251 1292 lactic acid 9503 7921 8285 Lactic acid dimer 3240 3544 3693 Lactic acid trimer 685 911 866

table 3

Relative pK _a values of the acids involved acid pK _a HCL -2 oxalic acid 1.27 Pyruvate 2.48 formic acid 3.75 lactic acid 3.86 Acetic acid 4.76

Table 4

Comparison of eluent sample to its starting material FS1 Eluent fraction (FS1 after column run) oxalic acid 512 0 Pyruvate 639 2 lactic acid 44199 47288 Lactic acid dimer 15070 14179 Lactic acid trimer 3188 2676

The pyruvate area corresponds to a pyruvate content of about 2 ppm or 0.002 g/L in the effluent.

Several impurities of unknown chemical composition appearing in HPLC trace analysis of feed solution and eluate fractions, possibly resin impurities from residual monomers from resin production and impurities present in chemicals used to prepare feed solutions .

table 5

Bed loading at breakthrough point based on theoretical bed capacity of 3.5meq/ml substance method mmol/ml resin oxalic acid from analytics data 1.09 Pyruvate from analytics data 1.27 Lactic acid, lactic acid dimer and lactic acid trimer from theoretical bed capacity 1.14

Example 3. Batch treatment of overhead from azeotropic distillation of lactic acid.

The fermentation broth containing lactic acid is pre-purified by azeotropic distillation and other steps. The product contained 19 ppm pyruvate and 260.9 g/L lactic acid. In a simple intermittent equilibrium absorption, 4.5 ml of this material was treated with about 1.2 ml of weakly basic anion exchange resin Sybron Ionac A-365 in the hydroxyl form. About 38% of the lactic acid was removed. It is evident that about 90% of the pyruvate was removed, leaving less than 2 ppm pyruvate in the product. The selectivity for pyruvate over lactate was estimated to be 14.73.

It was also observed that an unknown acid "strong impurity" was removed by 99% with a selectivity of about 54 in this particular HPLC chromatographic protocol at an elution time of 7.27 minutes by this treatment.

In the table below, the chromatographic response factor for the unknown peak at 210 nm was estimated based on the refractive index data (not shown), which shows that the response factor for the species is 4 times greater than that for pyruvate.

Table 6 Concentrationmol/L raw material solution balance fluid resin k selectivity % removal rate Peak 7.27 12.57×10 ^-4 0.13×10 ^-4 52.47×10 ^-4 401.21 176.51 99% Pyruvate 0.22×10 ^-4 0.02×10 ^-4 0.73×10 ^-4 33.49 14.73 90% lactic acid 2899.92×10 ^-4 1805.11×10 ^-4 4102.98×10 ^-4 2.27 38% Lactic acid dimer 91.26×10 ^-4 0.55×10 ^-4 178.90×10 ^-4 4.11 1.81 52%

Example 4. Continuous processing of overheads from the azeotropic rectification of lactic acid.

The fermentation broth containing lactic acid is pre-purified by azeotropic distillation and other steps.

The product contained no detectable levels of pyruvate, 743 g/L lactic acid and an unknown peak at 0.22 g/L estimated at 7.27 minutes.

In continuous column contact mode, 10.0 ml of this material was treated with about 2.4 ml of weakly basic anion exchange resin Sybron Ionac A-365 in the hydroxyl form.

About 15% of the lactic acid was removed. Clearly, 98% of the unknown strong impurity was removed, resulting in a lactic acid product with less than 4 ppm of this strong impurity.

This example illustrates the effectiveness of the invention for the removal of strong impurities of unknown exact nature.

Example 5. Continuous processing of low pH fermentation broth.

Two low pH lactic acid fermentation broths (approximately 5.5 liters each) were prepared and mixed. The low pH broth was treated with SAC (strongly acidic cation exchange) resin (>0.1 mole resin/mole lactic acid) and WBA (weak base anion exchange) resin (~0.03 mole resin/mole lactic acid). Fill the SAC resin in two 37mm×450mm columns, each 480ml, operate successively and fill the WBA resin in two 15mm×300mm columns, each 53ml.

After processing, the product was found to have a very low pyruvate content, lower than that found in the lactic acid samples supplied by ADM and Pfanstiehl.

Table 7

All concentrations are expressed in ppm except lactic acid which is expressed in g/l acid Impurities raw material discharge 1 discharge 2 exclusion 3 discharge 4 lactic acid product 60.76g/l 40.28g/l 62.64g/l 63.16g/l 62.92g/l Pyruvate powerful 270 <20 <20 <20 <20 HCL powerful 117 <20 <20 <20 <20 _{H2SO4 _} powerful 125 <20 <20 <20 <20 H ₃ PO ₄ powerful 690 <20 <20 <20 <20 malic acid weak 32 19 39 26 twenty three Acetic acid weak 15 <10 12 14 15 Succinic acid weak 48 <20 41 33 30

As can be seen from the data in the table, both inorganic and organic acids can be strong impurities and can be effectively removed despite the high lactic acid content. Use a flow rate of 1.4BV/hour for SAC and 6BV/hour for WBA.

Example 6. Continuous processing of 11 liters of fermentation broth

The resin used in Example 5 was regenerated and the treatment repeated with a new batch of fermentation material. A typical effluent fraction collected on the run contained 62.8 g/L lactic acid and 12.4 ppm pyruvate.

Example 7. Continuous processing of 11 liters of fermentation broth

The resin used in Example 6 was regenerated and the treatment repeated with a fresh batch of fermentation material. Two fractions were collected. After ion exchange treatment, the fractions were concentrated by evaporation to about 28% w/w lactic acid. Before evaporation, the concentrations are shown in Table 8.

Table 8 Concentration g/L raw material distillate Pyruvate 0.145 0.005 lactic acid 62.000 62.000 Malic acid peak 9.00 0.130 0.030

It can be seen that the pyruvate content decreased from 145 mg/L to 0.5 mg/L. A dramatic nearly 300-fold decrease in pyruvate content was achieved with only a small loss of lactic acid.

The anion resin was regenerated and 0.64% of the total feed mass of lactic acid and pyruvate was found to be adsorbed to the ion exchange resin. In this case _{, the strong acids H2SO4 and H3PO4 are present} in the feedstock and also act as displacement acids _.

The resin can be regenerated with additional displacing acid and selectively displaces additional lactic acid over pyruvate.

The anion exchange resin was regenerated and the ratio of M lactic acid to M pyruvic acid in the resin was found to be 19.34. This is thought to be due to the selectivity limit of the resin. This load cannot be exceeded.

Example 8. Comparison of liquid immiscible amine and solid amine ion exchangers for a series of strong impurities

Prepare an acid mixture solution of 52.78 g/L lactic acid and 0.2-0.3 g/L of various acid impurities listed in the table.

An 8 ml aliquot of the acid mixture was equilibrated with 1.0 ml of Sybron Ionac A-365 weak base anion resin and its selectivity was determined relative to lactic acid.

Each 5 ml aliquot of the acid mixture was equilibrated with 5 ml of extractant Y consisting of 1.0 moles of trilaurylamine and 1.0 moles of dodecanol with dodecane as the diluent.

Table 9 substance Ionac A-365 selectivity for impurities relative to lactic acid Selectivity of extractant Y for impurities relative to lactic acid Pyruvate 20.99 L-malic acid 198.8 3.32 formic acid 4.01 3.06 Acetic acid 0.169 0.42 propionic acid 0.101 1.42 n-butyric acid 0.100 5.74 Isobutyric acid 0.072 6.53

Example 9. Selective removal of strong impurities by U38 strongly basic anion resin after displacement acid displacement

Amberlite IRA-93 strong base anion resin was prepared in a 62ml column and regenerated to the hydroxide form. Resins are used to treat excess concentrated lactic acid fermentation broth that has been previously treated with cationic and weakly basic anionic resins.

_The resin was replaced with 1N _H2SO4 . 5 fractions were collected. The first two fractions obtained contained significant amounts of weak impurities, acetic and formic acids and lactic acid. The latter fractions contain large amounts of pyruvate and some lactic acid.

Example 10. Estimation of the Effect of Different Pyruvate Contents in Feedstock on Removal and Replacement Efficiencies

The ratio of the moles of lactic acid to the moles of pyruvic acid in the raw material solution is 117:1. After treatment with an amine-immiscible basic extractant, the product has an equivalent ratio of 486:1. Thus, lactic acid has been purified by the selective removal of pyruvate. The extractant contained 5.6 mole % lactic acid present in the starting material, which reduced the yield.

Typically, more steps or longer extraction sequences do not significantly improve the situation. This is because the starting material already has a very low level of pyruvate impurity and the amine has only a limited 18-fold selectivity for pyruvate relative to lactic acid.

The value of the partition coefficient of each species into the amine phase is assumed to be constant. This is reasonable since the concentration does not change appreciably during extraction. It is also reasonable to assume that the partition coefficients for each species are independent, since the amine is only a small loading in this case. At low loads, amine extractant complexes can be dominated by 1:1 complex formation of pyruvate and amine. The energies and partitions of these complexes are roughly related to the pK _a of the acid. The amines used here may not be highly reinforcing. For example, assume that the _Kd for pyruvate into the amine phase is the ratio between the moles/liter of pyruvate in the acidic free amine phase and the moles/liter of pyruvate in the acidic free water phase. The partition coefficient of pyruvate was assumed to be 5.0 and that of lactic acid was 0.278, resulting in a selectivity of 18.0.

Table 10

Effect of Pyruvate Stock Concentration Using the Same Lactic Acid Concentration (0.66M) Initial pyruvate concentration in feedstock 1000 500 300 100 ppm volume of immiscible alkaline extractant required 10.66 10.57 10.53 10.49 Lift Treated bed volume 93.84 94.64 94.96 95.29 Lift Lactic acid loss during extraction 3.9% 4.7% 5.1% 5.4% The ratio of M pyruvic acid to M lactic acid Y pyruvic acid on the ion exchange bed 30.5% 15.4% 9.2% 3.1%

Due to the multiple steps in the ion exchange, the effective pyruvate content in the effluent after the second bed volume is very low. In practice, a pyruvate content of 2 ppm was observed. Assuming an 18:1 bed selectivity to pyruvate relative to lactic acid, in all cases where the ion-loaded fraction Y _pyruvate on the bed is greater than about 100/18 = 5.56% w/w, almost Thoroughly separate lactic acid from pyruvate. If the loading is less than this value, then additional ion exchange treatment will be required for this effluent. The above example is for the case of total desorption of all species on the ion exchanger without fractional distillation of the effluent, which is ideal.

Example 11. Repeating the estimation of Example 10 but changing the lactic acid concentration

Table 11 has the influence of changing lactic acid concentration in the raw material of identical pyruvate concentration Initial pyruvate concentration in feedstock 500 500 500 ppm volume of immiscible alkaline extractant required 10.57 12.79 15.96 Lift Treated bed volume 94.64 78.19 62.64 Lift Lactic acid loss during extraction 4.74% 4.88% 5.02% Y pyruvate 15.4% 12.7% 10.2% Initial lactic acid concentration in raw material 0.66 0.80 1.00 mol/L

For a given pyruvate content, the fractionation load of lactic acid on the bed decreases as the lactic acid concentration increases. This makes it more difficult to obtain separate lactic and pyruvate fractions.

The above descriptions of specific embodiments of the invention are not exhaustive of the various possible embodiments of the invention. Those skilled in the art will recognize that changes may be made to the particular embodiments described which will fall within the scope of the invention.

Claims (20)

1. the method for a purified lactic acid comprises:

A kind of water-containing material logistics that contains free lactic acid and at least a pollutent is provided;

The water-containing material logistics is contacted with lean solution body extraction agent, in the described lean solution body extraction agent, with respect to every kilogram of lean solution body extraction agent, it contains less than about 0.75 mole of amine, with respect to every mole of amine, it contains the 0-0.5 mole toughener of having an appointment, and contains thinner, thus most of pollutent and the complexing of lean solution body extraction agent;

The lean solution body extraction agent of complexing is separated with the water-containing material logistics, discharge logistics thereby produce first, it contains free lactic acid, and the ratio of free lactic acid and pollutent bigger than in the water-containing material logistics that does not contact; With

Discharging logistics with first contacts with the liquid-rich extraction agent, thereby make the first most of free lactic acid and the complexing of liquid-rich extraction agent of discharging in the logistics, wherein the liquid-rich extraction agent contain with lean solution body extraction agent in identical amine, toughener and thinner, and in the liquid-rich extraction agent, the molar weight of the amine that contains with respect to every kilogram of liquid-rich extraction agent is bigger than the molar weight of amine in every kilogram of lean solution body extraction agent, and the ratio of toughener molar weight and amine molar weight higher than in the lean solution body extraction agent in the liquid-rich extraction agent, and lifting capacity should make first to discharge the ratio of logistics middle reaches molar weight of amine in the molar weight of lactic acid and liquid-rich extraction agent less than about 1.1, wherein said toughener is for strengthening the chemical substance of alkaline unmixing extraction agent performance, for being selected from alcohol, ketone, diketone, lipid acid and muriatic polar material, wherein said alcohol is selected from alkanol and glycol.

2. the process of claim 1 wherein that pollutent is pK _aAcid less than about 3.46.

3. the method for claim 2, wherein pollutent is selected from pyruvic acid, oxalic acid, toxilic acid, propanedioic acid, fumaric acid, 2-alpha-ketobutyric acid, 2-hydroxybutyric acid, acetate, 2-hydroxy-3-methyl butyric acid, 4-hydroxyl-phenylpyruvic acid, phenylpyruvic acid, 4-hydroxyl-phenyl-lactic acid, phenyl-lactic acid, citraconic acid, citric acid and their mixture.

4. the process of claim 1 wherein that amine is the second month in a season or tert-aliphatic amine.

5. the method for claim 4, wherein amine contains 20-36 carbon atom.

6. the process of claim 1 wherein that lean solution body extraction agent contains tertiary amine, and with respect to every kilogram of lean solution body extraction agent, it contains the described amine of 0.2-0.5 mole of having an appointment.

7. the process of claim 1 wherein that with respect to every mole of amine lean solution body extraction agent contains the 0.1-0.25 mole toughener of having an appointment.

8. the process of claim 1 wherein that lifting capacity should make first to discharge ratio between the mole number of logistics middle reaches amine in the mole number of lactic acid and liquid-rich extraction agent less than about 0.95.

9. the process of claim 1 wherein that toughener is selected from alkanol, ester, diester, glycol, ketone and diketone.

10. the process of claim 1 wherein that toughener is C ₃-C ₁₂The monohydroxy primary alkanol.

11. the process of claim 1 wherein that the water-containing material logistics is a fermenting broth.

12. the process of claim 1 wherein that thinner is selected from aromatic hydrocarbon and aliphatic hydrocrbon.

13. the process of claim 1 wherein that thinner is selected from dodecane, decane, dimethylbenzene, toluene, kerosene and their mixture.

14. the method for claim 1, it comprises that further water strips to the complex compound that contains lactic acid and liquid-rich extraction agent, thereby produces the logistics of aqueous product lactic acid.

15. the method for claim 14 is wherein stripped and is carried out under following temperature: high more about below 20 ℃ than the temperature that liquid-rich extraction agent and first is discharged in the logistics contact procedure.

16. the method for claim 15 is wherein stripped and is carried out under following temperature: high more about below 15 ℃ than the temperature that liquid-rich extraction agent and first is discharged in the logistics contact procedure.

17. the process of claim 1 wherein that the water-containing material logistics prepares with second method, it comprises that providing a kind of contains lactic acid, at least a pollutent and the logistics of solid water-containing material, and filters described water-containing material logistics to remove most of solid.

18. the method for claim 17, wherein the water-containing material logistics further contains the dissolved molecule, and second method further comprises membrane filtration is carried out in the water-containing material logistics after filtering, thereby removes most of dissolved molecule.

19. the method for claim 17, wherein the water-containing material logistics further contains positively charged ion, and second method further comprises the water-containing material logistics after filtering is contacted with cationite, thereby removes most of positively charged ion.

20. the method for claim 17, wherein the water-containing material logistics is a fermenting broth.

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