Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/42—Separation; Purification; Stabilisation; Use of additives
  • C07C51/48—Separation; Purification; Stabilisation; Use of additives by liquid-liquid treatment

Definitions

• organic acids can be prepared by chemical synthesis, production by fermentation is generally less expensive. It is well known to produce lactic acid by fermentation using microorganisms such as Lactobacillus delbrueckii.
• the broth that results from fermentation contains unfermented sugars, carbohydrates, amino acids, proteins, and salts, as well as organic acids, such as lactic acid.
• the organic acid is recovered from the fermentation broth and undergoes further purification before it is used.
• Purified organic acids recovered from fermentation broths can comprise small amounts of impurities, such as strong acids or certain unknown compounds. Some of these impurities can cause an undesirable color or can interfere with downstream processing of the organic acid.
• One aspect of the present invention is a process for purifying an aqueous feed stream that comprises a desired product organic acid and at least one strong contaminant.
• the aqueous feed stream can comprise a fermentation broth or can be obtained from a fermentation broth.
• an acid is referenced herein, either as the desired product or as a contaminant, it should be understood that some or all of the acid may be present in the form of salts.
• the molar concentration of the product organic acid in the feed stream can be at least 10 times greater than the molar concentration of the strong contaminant, and more preferably the ratio of the molar concentration of the product organic acid to the strong contaminant is at least 20.
• the ratio of the molar concentration of the product organic acid to the strong contaminant is at least 90, in certain embodiments it is at least 500, and in certain other embodiments it is at least 1000.
• the aqueous feed stream is contacted with a first immiscible basic extractant that has a selectivity, under the existing process conditions (including the combination of acids, solvents, etc., that are present) for the strong contaminant relative to the product organic acid that is greater than 3.
• the selectivity which is further defined below, is preferably greater than 15, more preferably greater than about 25, most preferably greater than about 100.
• the selectivity is greater than the ratio of product organic acid to strong contaminant in the feed.
• One particularly preferred embodiment of the invention is a process for purifying lactic acid.
• the embodiment involves providing an aqueous feed stream comprising lactic acid (defined herein to include any salts thereof) and at least one strong contaminant acid having a pK al 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 contaminant acid.
• the aqueous feed stream is contacted with a first basic ion exchanger that has a greater affinity for the strong contaminant acid than for lactic acid, such that the majority of the strong contaminant acid and some lactic acid become complexed with the first basic ion exchanger.
• the aqueous feed stream comprises 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; no more than about 0.05 moles of anions selected from the group consisting of Cl, SO , PO 4 , and NO 3 , per mole of lactic acid; nor more than about 0.03 mole of strong acid contaminants selected from the group consisting of pyruvic acid, oxalic acid, citraconic acid, and citric acid, per mole of lactic acid; and no more than about 0.02 mole of weak acid contaminants selected from the group consisting of propionic acid, butyric acid, malonic acid, and succinic acid, per mole of lactic acid.
• the aqueous feed stream is contacted with means for complexing pyruvic acid, and the means has a greater affinity for pyruvic acid than for lactic acid, so that the majority of the pyruvic acid and some lactic acid form complexes therewith.
• the complexes are separated from the aqueous stream, thereby producing a first effluent stream that comprises lactic acid and that has a greater ratio of lactic acid to pyruvic acid than the aqueous feed stream did.
• the complexes are contacted with means for displacing lactic acid and pyruvic acid therefrom, thereby producing a second effluent stream that comprises a major amount of lactic acid and a third effluent stream that comprises a major amount of pyruvic acid.
• the ratio of molar concentration of product organic acid to molar concentration of weak contaminant in the weak contaminant fraction is less than the ratio of molar concentration of product organic acid to molar concentration of weak contaminant in the feed stream.
• the weak contaminant fraction is contacted with a third immiscible basic extractant that has a selectivity for the product organic acid relative to the weak contaminant that is greater than about 3, and the majority of the product organic acid and less than about 33 wt% of the weak contaminant become complexed with the third immiscible basic extractant.
• the complexed third immiscible basic extractant is separated from the aqueous stream, to produce an effluent stream that comprises weak contaminant.
• displacing agent can be either a displacing acid as discussed above, or a displacing base.
• a base such as NaOH, can be used as a displacing agent, and the displaced material can then be treated using methods known in the art to recovered the desired product organic acid.
• the lean extractant used in the pre-extraction stage is of a markedly lower concentration of amine and lower molar enhancer/amine ratio than the rich extractant used in the main extraction stage.
• the pre-extraction stage is fed a primary aqueous lactic acid feed and the extractant
• lean extractant that has specifically been selected for this stage.
• Mineral acids as well as organic acids that extract preferentially to lactic acid are rejected in an aqueous stream while the lactic acid stays in a second aqueous stream (e.g., first effluent stream) that feeds the main extraction stage.
• the main extraction stage operates with a dedicated extractant (rich extractant) which differs greatly from the lean extractant. Pure lactic acid is obtained in an aqueous stream from the main extraction stage, after back-extraction, while impurities are rejected in a side stream.
• Complexed lean liquid extractant is separated from the aqueous feed stream in the pre-extraction stage, and a first effluent stream is produced that comprises free lactic acid, and that has a greater ratio of free lactic acid to contaminant than the uncomplexed aqueous feed stream.
• the first effluent stream is then contacted with a rich liquid extractant in a main extraction stage, and a majority of the free lactic acid in the first effluent stream is complexed with the rich liquid extractant.
• the rich liquid extractant comprises the same amine, enhancer, and diluent as in the lean liquid extractant, however the rich liquid extractant comprises more moles of the amine per kg of the rich liquid extractant in the main extraction stage than the moles of amine present per kg in the lean liquid extractant in the pre-extraction stage, and the rich liquid extractant comprises a higher ratio of moles of the enhancer to moles of the amine than in the lean liquid extractant.
• the loading is such that the ratio of moles of free lactic acid in the first effluent stream to moles of amine in the rich liquid extractant is less than about 1.1.
• the process can optionally further comprise back-extracting the complex comprising lactic acid and the rich liquid extractant with water, to produce an aqueous product lactic acid stream.
• Figure 2 is a process flow diagram of another embodiment of the present invention, comprising steps that can be performed in addition to those shown in Figure 1.
• Figure 3 is a process flow diagram of yet another embodiment of the present invention, comprising steps that can be performed in addition to those shown in Figure 1.
• the process of the present invention can recover purified organic acid from a fermentation broth.
• the process is also suitable for use in purifying organic acids from other sources, such as lactic acid of commerce.
• "88% lactic acid” and "lactic acid of commerce” refer to a typical commercially available lactic acid, which is actually a mixture of monomeric lactic acid, linear dimer lactic acid or lactoyl lactic acid, short chain lactic aci ⁇ oligomers, water, a small quantity of cyclic dimer lactic acid or lactide, and small amounts of impurities.
• the dimers and oligomers slowly hydrolyze or convert to the monomeric form of lactic acid.
• the broth 14 is then contacted with a first immiscible basic extractant in step 18.
• a first immiscible basic extractant in step 18.
• this is done using counter-current flow.
• a mixer-settler apparatus can be used, among other possibilities.
• This extractant is "immiscible" in that it does not mix with the broth, but the extractant may or may not be liquid.
• the extractant can comprise an amine compound that has the ability to form complexes with one or more of the organic acids present.
• this first extractant should have an affinity for the strong contaminant (pyruvic acid) that is greater than its affinity for the desired product (lactic acid).
• the first basic extractant can then be separated from most of the pyruvic and lactic acid in the complex by an acid displacement step 24.
• a stream 26 comprising an aqueous solution of a displacing acid, such as HC1, H PO 4 , oxalic acid, H 2 SO or trifluoroacetic acid, is contacted with the first extractant, which at this point is still complexed with pyruvic and lactic acid.
• a displacing acid has a pK a of about -2 to 1.8.
• the displacing acid can also be present in a mixture with other organic acids and species, such as a mixture of HC1, H 2 SO , lactic acid and acetic acid.
• the first effluent stream 20 and the second effluent stream 28 are combined to form a 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 weak base ion exchange resin, such as Amberlite IR35, comprising a tertiary amine moiety.
• This second extractant preferably has a greater affinity for lactic acid than for acetic acid.
• the amount of this extractant present should be more than sufficient to complex with essentially all of the lactic acid present in the steam. Therefore, the second extractant forms complexes primarily with lactic acid, and to a much smaller degree with acetic acid.
• the complexes are separated from the remaining liquid as part of stream 56, thus leaving a fourth effluent stream 54.
• the second and third extractants have greater ⁇ affinity for the displacing acid than for. lactic acid, the latter is displaced into additional effluent streams 62 and 76, from which it can be recovered.
• These streams 62 and 76 preferably comprise more than about 90% by weight of the lactic acid that was present in the combined stream 50, more preferably at least about 95%.
• the back-extraction is preferably carried out at a temperature that is less than about 20 degrees Celsius warmer than the step of contacting the rich liquid extractant and the first effluent stream. More preferably the back-extraction is carried out at a temperature that is less than about 15 degrees Celsius warmer than the step of contacting the rich liquid extractant and the first effluent stream. It has been found that purity levels of lactic acid obtained by solvent extraction processes can be increased significantly by performing extraction and back- extraction processes at approximately the same temperatures or at temperatures that do not differ materially. This beneficial effect on purity is best expressed with amine based extractants that fall within defined composition limits and that are used within defined levels of loading of lactic acid.
• Eluent fractions from the feed solutions were collected in the following order 6 X 30 ml, 2 X 120 ml, 29 X 240 ml, 1 X 40 ml, 8 X 240 ml, and 9 X 30 ml.
• the column was subsequently treated with an acidic solution and a basic solution, and thus 4 X 40 ml acidic eluent fractions, 2 X 40 ml deionized water wash fractions, 4 X 40 ml caustic (e.g. basic) eluent fractions, and 2 X 40 ml deionized water wash fractions were collected, as well.
• Select eluent fractions were subsequently analyzed, undiluted, by HPLC.
• the pyruvic acid area corresponds to a level of about 2 ppm or 0.002 gram liter of pyruvic acid in the effluent.
• This example teaches the effectiveness of the current invention for removing strong impurities whose exact identity is unknown.
• Two low pH lactic acid fermentation broths were prepared (each was about 5.5 liters in volume) and combined.
• the low pH broth was treated with SAC (strongly acid cation exchange) resin (>0.1 moles of resin mole lactic acid) and WBA (weakly basic anion exchange) resin (-0.03 moles resin/mole lactic acid).
• SAC strongly acid cation exchange
• WBA weakly basic anion exchange
• the anion resin was regenerated and it was found that 0.64% of the total feed mass of lactic acid had been adsorbed on the ion exchange resin with the pyruvic acid.
• the strong acids H 2 SO and H 3 PO 4 are present in the feed and also act as displacing acids
• Additional displacing acids can be used to regenerate the resin and selectively displace the additional lactic acid in preference to the pyruvic acid.
• Example 8 Comparison of Liquid Immiscible Amine and Solid Amine Ion Exchanger for Sequence of Strong Impurities.
• a acid mixture solution was prepared with 52.78 g/L lactic acid 0.2 to 0.3 g/L each the acid impurities listed in the table.
• Amberlite IRA-93 strong base anion resin was prepared in a 62 ml column and regenerated to give the hydroxide form. The resin was used to treat an excess of concentrated lactic acid fermentation broth that had previously already been treated with a cation and weak base anion resin.
• the Kd for pyruvic acid into the amine phase was the ratio of pyruvic acid mole/liter of acid free amine phase to pyruvic acid mole/liter of acid free water phase.
• the distribution coefficient for pyruvic acid was assumed to be 5.0 and that for lactic acid to be 0.278, giving a selectivity of 18.0.
• Table 10 Effect of feed concentration of pyruvic acid when the same lactic acid concentration (0.66 M) is used.
• Example 11 The Calculations of Example 10 are Repeated, But the Lactic Acid
• Table 11 Effect of varying concentration of lactic acid concentration in feeds having the same pyruvic acid concentration.

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• 2002
  • 2002-12-11 CN CN02826698.6A patent/CN1289459C/zh not_active Expired - Fee Related
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