A kind of L-lactic acid purification method

Abstract

The invention belongs to the technical field of L-lactic acid production, and specifically discloses a method for purifying and refining L-lactic acid. In the method for purifying and refining L-lactic acid provided by the present invention, by separating and removing the thalline in the fermentation liquid, the thallus slag is obtained as a feed material; after acidolysis and filtration, the clear liquid is decolorized by activated carbon and enters the first ion exchange column to exchange cations and anions to obtain The first ion exchange liquid, the first ion exchange liquid is filtered by nanofiltration membrane and then pre-concentrated, and then the secondary ion exchange liquid is obtained after cation and anion exchange in turn; the second ion exchange liquid is decolorized by activated carbon decolorization column, and then concentrated to obtain L ‑Lactic acid concentrate with a lactic acid content of 80‑90%; the lactic acid concentrate is then purified by short-path distillation to obtain high-purity food-grade lactic acid or to produce polylactic acid. The L-lactic acid purification method provided by the present invention improves the quality of the finished product of L-lactic acid, and the finally obtained L-lactic acid has good quality and high yield, and especially meets the quality requirements of L-lactic acid used as a PLA raw material.

Description

technical field [0001] The invention relates to the technical field of L-lactic acid production, in particular to a method for purifying and refining L-lactic acid. Background technique [0002] L-lactic acid is an organic acid obtained by using glucose or sucrose as raw material, fermented by microorganisms, and then purified from the fermentation broth. The molecular formula of L-lactic acid is C 3 h 6 o 3 , L-lactic acid is a colorless, clear viscous liquid, and its aqueous solution is acidic. L-lactic acid can be freely mixed with water, ethanol or ether, and insoluble in chloroform. Because of its left-handed characteristics, it has good biological compatibility, can be compatible with mammals, can directly participate in human metabolism, without any side effects, and is widely used in food, medicine, cosmetics, tobacco and other industries. L-lactic acid can also be used to produce biodegradable plastic polylactic acid and green solvents L-methyl lactate, L-ethyl...

AI Technical Summary

Problems solved by technology

[0008] First, milk of lime, namely Ca(OH) 2 Adjust the pH value of the solution to 10-11 and heat it to 80-95°C. Under alkaline and high temperature conditions, the residual sugar and protein in the fermentation broth are prone to Maillard reactions, which further deepens the pigment of the fermentation broth and gives Subsequent refining and decolorization brings burden and increases production cost; the pH of the fermentation liquid is adjusted to 10-11, making the cell residue alkaline, and the cell residue obtained by this treatment process cannot be used as feed, but can only be used as compound fertilizer organic matter, which reduces the added value of the cell slag

[0009] Second, attach figure 1 In the process shown, the acidolysis solution contains saturated CaSO 4 , generally Ca 2+ The content is 700-1400mg / L, SO 4 2- content of 1500-2200mg / L; after the acidolysis solution is separated from the positive column, the sulfuric acid content in the acidolysis solution reaches 1.5%-2.2% (w / v), and the concentration of sulfuric acid is very high. The selection and service life of the membrane have a great impact, which increases the difficulty of membrane selection and investment and operating costs

The pigment of crude L-lactic acid filtered by nanofiltration membrane is still relatively high (average chromaticity 600-1200Hazen), the load of carbon column decolorization is very large, the consumption of water and liquid caustic is high, and the production of alkaline wastewater is large. Dealing with high pressure

[0010] Third, with figure 2 The process method shown, directly decolorizes with powdered activated carbon, the consumption of activated carbon is large (60-80kg of lactic acid consumption per ton of finished product), and the production environment is poor, and the cost of waste carbon is high according to solid waste treatment

Due to the residue of impurities, the pigment in the acid concentration process will be further deepened. As a result, only low-end food-grade L-lactic acid can be produced, and the quality and yield of high-quality L-lactic acid obtained after short-path distillation are also affected. Very large, not even up to the quality standard of heat-resistant grade L-lactic acid

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