Method for purifying and refining L-lactic acid

Abstract

The invention belongs to the technical field of L-lactic acid production, and particularly discloses a method for purifying and refining L-lactic acid. The method for purifying and refining L-lactic acid comprises the following steps: removing thalli in a fermentation liquor through separation to obtain thallus residues which can be used as a feed raw material; decolorizing an acidolysis filteredclear liquid by using activated carbon, feeding the decolorized acidolysis filtered clear liquid into a first ion exchange column, carrying out cation and anion exchange to obtain a primary ion exchange liquid, filtering the primary ion exchange liquid by using a nanofiltration membrane, carrying out pre-concentration, and sequentially carrying out cation and anion exchange to obtain a secondary ion exchange liquid; decolorizing the secondary ion exchange solution by adopting an activated carbon decolorizing column, and then concentrating to obtain a lactic acid concentrate with the L-lactic acid content of 80-90%; and carrying out short-path distillation and purification on the lactic acid concentrate to obtain high-purity food-grade lactic acid or produce polylactic acid. According to the L-lactic acid purification and refining method provided by the invention, the finished product quality of the L-lactic acid is improved, and the finally obtained L-lactic acid is good in quality andhigh in yield and particularly meets the quality requirement of the L-lactic acid serving 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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