Preparation of polylactic acid by two-step method：
Preparation of lactic acid from： ⒈ We use regenerated resources corn, potato as raw material, using microbial fermentation method to prepare optically pure L-lactic acid or D-lactate.
Furthermore, L-lactic acid can be absorbed completely by human body without any toxicity and side effects.
Production of L-lactic acid, so we use domestic and foreign general Megan Mildew NAF-032.
Preparation of Rhizopus spores by ⑴;
The ⑵ spores were prepared with rhizopus spores into the spore-milk suspension of rice root.
The seed of Rhizopus ⑶ was immobilized on the immobilized medium by fixing the spore milk suspension of Rhizopus oryzae.
The immobilized Rhizopus ⑷ seeds were inoculated into the fermentation medium for immobilized fermentation.
In this method, the high-yielding Megan strains were cultivated and immobilized to the cotton carrier to obtain the immobilized Rhizopus seed. In the suitable fermentation conditions for immobilized fermentation, potato starch conversion rate is high, fermentation products of high biomass, l-lactic acid yield, low cost, simple steps, easy to control and so on.
Acidification treatment and purification separation of ⒉ lactate ⑴ fermentation process produces a kind of lactic acid salts, because the ph value of fermentation is close to neutral. It is necessary to convert certain lactic acid salts into lactic acid, by adding sulfuric acid directly into the lactate solution, lactic acid can be prepared, and calcium sulfate is hydrated for the crystallized by-product. can be removed by filtration, of course, calcium sulfate dihydrate can be used as a ground-filling gypsum, for example, as a dry wall, cement and agricultural materials. Gypsum is a low value salt produced during the production process, but this is a cost-effective method because the cost of calcium hydroxide and sulfuric acid is low, and gypsum can also be used for other industrial purposes. Other methods that combine the two processes of alkaline and acidification have been tried, such as using ammonia to regulate ph and acidification with sulfuric acid, so that ammonium sulfate is used as a by-product and ammonium sulfate can be used as fertilizer.
Because ammonium salt is higher than calcium hydroxide, and the high value of the by-product ammonium sulfate just compensates for this gap, and ammonium sulfate is soluble in water relative to calcium salts, which is conducive to separation.
⑵ cell Removal The choice of cell removal methods depends mainly on the microorganisms used in the production. Megan is 210-2500μm, the diameter is 5-18μm, because small cells can be removed by flocculation.
Adding chitosan as flocculant in fermentation broth, regulating ph 6.8, heat preservation, stirring and nourishing flocculation, after the flocculation is finished, the 1.5h is removed and the supernatant is removed to the centrifuge tube, and the solid precipitate is separated by centrifuge at 4000r/min rotational speed.
Separation of residual sugar, residual media and fermented by-products from ⑶ This project adopts solvent extraction method.
After solvent extraction, the lactic acid solution after activated carbon, cation exchange resin, anion exchange resin can obtain the yellowish ion product.