WO2022141739A1 - 一种以钙盐法生产乳酸的发酵液为原料生产α-半水硫酸钙晶须并同步回收乳酸单体的方法 - Google Patents

一种以钙盐法生产乳酸的发酵液为原料生产α-半水硫酸钙晶须并同步回收乳酸单体的方法 Download PDF

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WO2022141739A1
WO2022141739A1 PCT/CN2021/074953 CN2021074953W WO2022141739A1 WO 2022141739 A1 WO2022141739 A1 WO 2022141739A1 CN 2021074953 W CN2021074953 W CN 2021074953W WO 2022141739 A1 WO2022141739 A1 WO 2022141739A1
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lactic acid
calcium sulfate
sulfate hemihydrate
calcium
fermentation
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French (fr)
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王正祥
牛丹丹
田康明
路福平
申春莉
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天津科技大学
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Priority to ZA2021/10950A priority patent/ZA202110950B/en
Publication of WO2022141739A1 publication Critical patent/WO2022141739A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/46—Sulfates
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/02—Preparation of carboxylic acids or their salts, halides or anhydrides from salts of carboxylic acids
    • 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
    • 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
    • C07C51/47—Separation; Purification; Stabilisation; Use of additives by solid-liquid treatment; by chemisorption
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P7/00—Preparation of oxygen-containing organic compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/10—Particle morphology extending in one dimension, e.g. needle-like

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  • the invention belongs to the fields of fermentation engineering and chemical engineering, and particularly relates to the direct conversion of calcium lactate fermentation liquid into ⁇ -calcium sulfate hemihydrate crystal whiskers and free lactic acid under the action of sulfuric acid during lactic acid fermentation production.
  • Lactic acid is an important three-carbon organic acid with two optical configurations, L-form and D-form, namely: L-lactic acid and D-lactic acid.
  • L-lactic acid and D-lactic acid are monomer raw materials for the synthesis of polylactic acid and are important components of biodegradable materials.
  • L-lactic acid and D-lactic acid are also used as raw materials for the synthesis of various esters (such as methyl lactate, ethyl lactate, propyl lactate, butyl lactate) and lactate, and L-lactic acid is also widely used as an acidulant It is used in the production of food, beverages, condiments, alcohol, feed and other products, and D-lactic acid is also used in synthetic raw materials such as flavors and fragrances, herbicides, and drugs.
  • the production method of lactic acid is mainly carried out by microbial fermentation, among which the calcium salt method is the most important method for producing lactic acid by fermentation. That is: through fermentation, the metabolically adapted carbon source (such as glucose, glycerol, xylose, lactose, sucrose, fructose) of microbial strains is D-lactic acid or L-lactic acid (Tian, et.al, Biotechnology Bioengineering, 2016, 113: 181-188.; Niu, et. al, Microbial Cell Factories, 13: 78-88.; Chen, et. al, Green Chemistry, 16: 342-350.; Zhou, et al.
  • the metabolically adapted carbon source such as glucose, glycerol, xylose, lactose, sucrose, fructose
  • Sulfuric acid which converts calcium lactate to free lactic acid and produces calcium sulfate that is insoluble in water, precipitates out of solution in the form of amorphous dihydrate.
  • the fermentation broth containing free lactic acid is then purified by a series of procedures such as separation and purification to produce lactic acid products, and the formed water-insoluble calcium sulfate is a by-product of lactic acid fermentation (Zhang Peng et al., ZL200810049644.4) , through separation, drying and other processes, used to produce calcium sulfate dihydrate, namely gypsum.
  • the further conversion of gypsum into other products with better physical and chemical properties is an important way to solve the large-scale production of lactic acid by the calcium salt method, which can solve the problem of by-product generation of calcium sulfate dihydrate (gypsum) while ensuring the large-scale industrial production of lactic acid.
  • raw gypsum is calcined and ground to obtain ⁇ -type hemihydrate gypsum (CaSO4 ⁇ 0.5H2O), namely gypsum of construction, also known as plaster of paris and plaster.
  • Raising the calcination temperature to 190°C can obtain model gypsum with higher fineness and whiteness than building gypsum; increasing the calcination temperature to 400°C to 500°C or higher than 800°C can convert raw gypsum into floor gypsum.
  • ⁇ -Calcium sulfate hemihydrate whiskers have high strength, high modulus, high toughness, high insulation, wear resistance, high temperature resistance, acid and alkali resistance, corrosion resistance, good infrared reflectivity, easy surface treatment, easy to polymer It has many excellent physical and chemical properties such as composite, non-toxic, etc., integrating the advantages of reinforcing fibers and ultra-fine inorganic fillers, so it has high application value (Li Ming, Fine and Special Chemicals, 2016, 24(6) :47-50), can be used in resins, plastics, rubber, coatings, paints, paper, asphalt, friction and sealing materials as reinforcing and toughening agents or functional fillers (He Hang et al., Applied Chemical Industry, 2014: 1671-1674 ; Li Maogang, et al., Bulletin of Silicate, 2017, 36: 1590-1593, 1598; Li Jundai, Journal of East China Jiaotong University, 2013, 30(6): 72-77; Fu Lingjie,
  • the reported method that gypsum is converted into ⁇ -calcium sulfate hemihydrate whisker mainly includes the following methods:
  • Autoclave method crush the natural calcium sulfate dihydrate into 20-50mm blocks, and put them into the autoclave with a metal frame or a trolley.
  • the autoclave method is divided into two types: vertical and horizontal. Pass in steam condensed water or hot flue gas to heat the material to 50 ⁇ 70°C, discharge the condensed water or hot flue gas, close the autoclave, then pass in saturated steam, heat up to 120 ⁇ 160°C and keep the pressure, after 5 ⁇ 8h
  • the autoclaved dehydration and transcrystallization are transformed into ⁇ -calcium sulfate hemihydrate whiskers, which are then removed from the autoclave or dried in the autoclave.
  • the production cycle of the vertical autoclave is about 16-18h, and the production cycle of the horizontal autoclave is about 30-40h (Geng Qingyu et al., Journal of Artificial Crystallography, 2016, 45: 1892-1897, 1905; Yang Lin et al., Architecture Chinese Journal of Materials, 2014, 17: 147-152; Wang Hongyu et al., ZL201610547294.9; Nai Xueying et al., ZL201610547294.9).
  • This method is a traditional process, the process is relatively simple, but the production cycle is long and the production cost is high ⁇ 30MPa or so.
  • the ⁇ -calcium sulfate hemihydrate produced by this method has stable product quality and high compressive strength, which can reach 40-80MPa (Donna et al., Inorganic Salt Industry, 2020, 52(4): 88-92; Wu Feng et al., Progress in Chemical Industry , 2018, 37: 1536-1543; Huang Xu et al, Silicate Bulletin, 2019, 38: 2021-2027; Zhang Zirui et al, Ningxia Engineering Technology, 2019, 18: 40-43, 49; Wang Yubin et al, Journal of Chemical Engineering in Colleges and Universities , 2018, 32: 1444-1449; Liang Xianhong et al., Mineral Conservation and Utilization, 2017(06): 87-92, 96; Wu M, WO 2015/085133 A1).
  • this method has complex process, many production equipment, large investment, small production capacity, low production efficiency, high production cost, and cannot be directly integrated into the lactic acid fermentation production process.
  • Atmospheric pressure salt solution method mix the ground calcium sulfate dihydrate with the salt solution added with the crystallizer, add it to the reaction vessel and boil it under normal pressure conditions, so that the calcium sulfate dihydrate is converted into ⁇ - Calcium sulfate hemihydrate whiskers. Then it is dehydrated, washed and dried to obtain ⁇ -calcium sulfate hemihydrate whiskers.
  • This method does not require a pressure vessel and can reduce equipment investment (Wang Aiwen et al., Nonmetallic Minerals, 2020, 43(4): 84-87; Zhang Huiyong, Chemical Minerals and Processing, 2020, 49(1): 50-54; Fu Wen Jian et al, Journal of East China University of Science and Technology (Natural Science Edition), 2019, 45(2): 266-274; Hu Junyao et al, Inorganic Salt Industry, 2018, 50(6): 47-50; Wang Xin et al, Inorganic Salt Industry, 2017, 49(11):54-58).
  • the process conditions are strict, the reaction time is long, and the product strength is not high. At present, it is still in the laboratory test stage, and no examples of industrial production have yet been seen.
  • Atmospheric pressure glycerin method add industrial by-product calcium sulfate dihydrate into 45% to 75% glycerol solution, add a certain amount of crystal form regulator, maintain at 90°C for 30min, filter, wash and dry to obtain ⁇ type Calcium sulfate hemihydrate whiskers.
  • the method does not require a high-pressure environment, the action conditions are mild, and the product purity is high.
  • the prepared ⁇ -type calcium sulfate hemihydrate whiskers have low length and low hardness (Guan Qingjun et al., Mineral Protection and Utilization, 2019, 39(4): 1-8). Currently in the laboratory test stage, no production examples have been seen.
  • the methods for preparing the above-mentioned ⁇ -calcium sulfate hemihydrate whiskers all use calcium sulfate dihydrate as the starting material, and most of the production processes need to be carried out at a temperature higher than 120 ° C, and some methods also need to add different compounds. Not only increases the manufacturing cost, but also increases the generation of by-products. It can be seen that the existing production technology of calcium sulfate hemihydrate whiskers cannot directly prepare lactic acid monomers from the lactic acid fermentation broth of the calcium salt method and simultaneously prepare ⁇ -calcium sulfate hemihydrate whiskers. In addition, too high reaction temperature and the addition of crystallizing agent will significantly affect the recovery of lactic acid monomer.
  • the lactic acid release process in the calcium lactate generated in the production of lactic acid by the calcium salt method is based on the formation of calcium sulfate by-products, and the synchronization of the formation of lactic acid release and the preparation of ⁇ -calcium sulfate hemihydrate whiskers has not been realized. It is necessary to further process the calcium sulfate "solid waste" in the subsequent production, which not only increases the production cost, but also makes the production process not green enough.
  • the purpose of this invention is to directly release the free lactic acid in the calcium lactate fermentation liquid in the production of lactic acid by the calcium salt method, and the replaced calcium sulfate is directly generated in the ⁇ -calcium sulfate hemihydrate whisker mode, and realizes that the lactic acid monomer and ⁇ - Simultaneous production of calcium sulfate hemihydrate whiskers.
  • the technical scheme provided by the present invention comprises the following steps:
  • a method for producing ⁇ -calcium sulfate hemihydrate crystal whiskers and synchronously reclaiming lactic acid monomers by using the fermentation broth of calcium salt method to produce lactic acid as raw material comprising the following steps:
  • Step 1 After the lactic acid fermentation is completed, the temperature of the fermentation broth is raised to 50°C to 102°C on the spot or in the post-extraction reactor; further, the temperature of the fermentation broth is raised to not lower than 50°C but not higher than 102°C, and further not lower than 55°C but not higher than 102°C, not lower than 60°C but not higher than 102°C, not lower than 65°C but not higher than 102°C, not lower than 70°C but not higher than 102°C, not lower than 75°C but not higher than 102°C, not lower than 80°C but not higher than 102°C, not lower than 85°C but not higher than 102°C;
  • Step 2 Turn on the stirring, add 2-12 mol/L sulfuric acid under the above-mentioned temperature, and maintain the reaction for 1 min-10 h; further, the reaction is stirred at 5-80 r/min and the temperature is maintained, and the total amount of sulfuric acid added is controlled at the ratio of lactic acid and sulfuric acid.
  • the molar ratio is 1:0.499 ⁇ 1:0.501, the time limit for adding the total sulfuric acid is controlled at 1min ⁇ 2h/ton fermentation broth, and the reaction is maintained for 1min ⁇ 10h after all the sulfuric acid is added;
  • Step 3 After the reaction in step 2 is completed, the reaction solution is subjected to solid-liquid separation by filtration, the collected solid part is the ⁇ -calcium sulfate hemihydrate whisker, and the collected liquid part is the free lactic acid solution containing lactic acid monomer; further, the described The solid-liquid separation is carried out by a belt filter device with a pore size of 5.0 ⁇ m to 50 ⁇ m;
  • Step 4-1 After washing and drying the obtained ⁇ -calcium sulfate hemihydrate whiskers, the obtained ⁇ -calcium sulfate hemihydrate whiskers are finished products; Washed with water ethanol, and then dried by steam flash at 101°C ⁇ 160°C, it is the finished product of ⁇ -calcium sulfate hemihydrate;
  • Step 4-2 The obtained free lactic acid liquid is filtered, concentrated, etc., is the crude lactic acid product, which can be used for subsequent purification such as nanofiltration, decolorization, separation, etc., to obtain high-purity lactic acid monomer; further, the obtained free lactic acid.
  • the liquid is filtered through a plate frame with a pore diameter of 0.8 ⁇ m to 10 ⁇ m to remove impurities, and then evaporated and concentrated to a lactic acid content of 20 wt % to 60 wt %, which is a crude lactic acid product.
  • the recovery rate of lactic acid monomer reaches more than 99.5%
  • the recovery rate of calcium sulfate and the formation rate of ⁇ -calcium sulfate hemihydrate whisker reaches more than 98%.
  • the method can convert the calcium salt method lactic acid liquid into free lactic acid liquid and ⁇ -calcium sulfate hemihydrate crystal whisker in one step, realize the simultaneous production of lactic acid monomer and ⁇ -calcium sulfate hemihydrate crystal whisker, and the recovery rate of lactic acid monomer reaches more than 99.5% , the calcium sulfate recovery rate and the ⁇ -calcium sulfate hemihydrate whisker generation rate reach more than 98%, which can on the one hand intensify the lactic acid production process and reduce the input of lactic acid production, on the other hand, can completely solve the problem in the existing industrial production system. Formation of calcium sulfate waste.
  • the present invention can also significantly improve the economic efficiency and environmental benefits of lactic acid fermentation production and significantly reduce the overall cost of lactic acid production.
  • the present invention can also be applied to the generation of other organic acids such as citric acid, malic acid, succinic acid and the like.
  • the present invention converts and treats the lactic acid in calcium lactate with sulfuric acid, it is found that as long as a certain temperature is given, the subsequent separation and purification of the lactic acid is not affected, and the addition speed of the sulfuric acid is controlled, the amorphous dihydrate sulfuric acid can be generated in this process.
  • Calcium which is converted into ⁇ -calcium sulfate hemihydrate whiskers.
  • the key points of the process are the temperature and the addition rate of sulfuric acid. The temperature should not be too high as in the existing literature. If the temperature exceeds 105 °C, the loss of lactic acid will be relatively large, and lactic acid is the main product. Crystallizer, because that will increase the cost of lactic acid separation and purification.
  • Fig. 1 is lactic acid production process route: (a) former production technique; (b) technique of the present invention;
  • Figure 2 is a topography (100X) of the whiskers of ⁇ -calcium sulfate hemihydrate.
  • the fermentation broth for producing lactic acid by the calcium salt method is used as the raw material. After the lactic acid fermentation is completed, the fermentation broth is heated to 50° C. to 102° C., 2 to 12 mol/L sulfuric acid is added, and the reaction is maintained for 1 min to 10 hours.
  • the collected solid part is the ⁇ -calcium sulfate hemihydrate whisker
  • the collected liquid part is the free lactic acid liquid containing lactic acid monomer
  • the obtained ⁇ -calcium sulfate hemihydrate whisker is washed and dried, which is the ⁇ -
  • the finished product of calcium sulfate hemihydrate whiskers, and the obtained free lactic acid liquid is filtered, concentrated, etc., is the crude product of lactic acid, which can be used for subsequent purification such as nanofiltration, decolorization, isolation, etc., to obtain high-purity lactic acid monomer ( Figure 1).
  • the main experimental method adopted in the present invention is as follows:
  • the preparation of the calcium salt method lactic acid fermentation liquid is carried out according to the method of the previous invention authorized patent (Wang Zhengxiang et al., ZL201580000781.7), and the fermentation strain is CGMCC 11059 or CGMCC11060, wherein the strain CGMCC 11059 is used for the fermentation production of D-lactic acid, and the strain CGMCC11060 is used for the fermentation production of L-lactic acid (Wang Zhengxiang et al., ZL201580000781.7).
  • glucose was added to the fermentation basic medium to a final concentration of 10-50g/L, and the culture was carried out at 30-37°C, pH 5.5-7.5, ventilation 0.1-2.0vvm, and stirring at 100-1000r/min.
  • the culture time is 5-15h, and the bacterial volume reaches 10-50 OD; the ventilation is turned off, the stirring speed is reduced to 0-300r/min, the fermentation temperature is increased to 37°C-50°C, and the final concentration of 16%-25% glucose is added Solution, the flow rate is controlled at 3g/(L h) ⁇ 25g/(L h), 5% ⁇ 35% calcium hydroxide is added in synchronous flow, and the fermentation pH is controlled between 5.0 ⁇ 8.0.
  • the fermentation broth is heated to 50 °C ⁇ 102 °C, the stirring is turned on, and 2 ⁇ 12mol/L sulfuric acid is added under the maintenance of the above-mentioned temperature, and the total amount of sulfuric acid is controlled in the mol ratio of lactic acid and sulfuric acid to be 1:0.499 ⁇ 1:0.501, The speed of adding the total amount of sulfuric acid is controlled at 1min ⁇ 2h/ton of fermentation broth, and the reaction is maintained for 1min ⁇ 10h.
  • the solid-liquid separation of the reaction solution is carried out by filtration, and a belt filter device with a pore size of 5.0 ⁇ m to 50 ⁇ m is used for carrying out.
  • the collected solid part is the ⁇ -calcium sulfate hemihydrate whisker, and the collected liquid part is the one containing lactic acid monomer free lactic acid.
  • the obtained ⁇ -calcium sulfate hemihydrate crystal whisker is washed and dried, washed with hot water or absolute ethanol, and then dried by steam flash at 101°C to 160°C, which is the finished product of ⁇ -calcium sulfate hemihydrate crystal whisker.
  • the appearance and morphology of the whiskers were observed and recorded under an optical microscope.
  • the length and diameter of 40 whiskers were measured and their aspect ratios were calculated. All data are the average of the results of 3 parallel experiments.
  • the yield of ⁇ -calcium sulfate hemihydrate whiskers can be expressed as the ratio of the actual value of the whiskers to the theoretical value.
  • the actual value is the mass of the finished ⁇ -calcium sulfate hemihydrate whisker.
  • the theoretical value is the weight of the ⁇ -calcium sulfate hemihydrate whiskers obtained by calculating the number of moles of sulfuric acid added during acidification.
  • the number of moles of sulfuric acid is equal to the number of moles of ⁇ -calcium sulfate hemihydrate whiskers, and the product of the number of moles of sulfuric acid and the relative molecular mass of ⁇ -calcium sulfate hemihydrate whiskers is the theoretical value of the whiskers, in %.
  • Determination of D-lactic acid, L-lactic acid, pyruvic acid, formic acid, acetic acid and succinic acid using HPLC, the chromatographic detection conditions are: the chromatographic column is HPX-87H organic acid analysis column, the column temperature is 65 °C, and the detection wavelength is 210 nm, the mobile phase is a sulfuric acid solution with a concentration of 5 mmol/L, the flow rate is 0.8 mL/min, and the injection volume is 10 ⁇ L. All data are the average of the results of 3 parallel experiments. The content of lactic acid monomer is measured in g/L, and the chemical purity of lactic acid is measured by the percentage (%) of lactic acid monomer in all organic acids. The sugar-to-acid conversion rate of lactic acid is calculated as the percentage (%) of the total lactic acid production mass to the total glucose consumption.
  • the chromatographic detection conditions were as follows: the chromatographic column was an Astec CLC-L optical purity analysis column, the column temperature was 25 °C, the detection wavelength was 254 nm, and the mobile phase was a copper sulfate solution with a concentration of 5 mmol/L. , the flow rate was 1 mL/min, and the injection volume was 10 ⁇ L. All data are the average of the results of 3 parallel experiments.
  • the optical purity of the lactic acid monomer is calculated as the mass percentage (%) of L-lactic acid or D-lactic acid in the total lactic acid.
  • Example 1 Preparation of lactic acid fermentation broth
  • the glycerol tube frozen storage of D-lactic acid producing strain CGMCC 11059 or L-lactic acid producing strain CGMCC 11060 was inoculated into 50 mL of LB liquid medium, and cultivated at 37 ° C, 200 r/min shaker for 12 h, as first-class seeds liquid.
  • the first-grade seed solution was inoculated into 150 mL of M9 liquid medium with glucose as carbon source, the initial sugar concentration was 0.5%, and cultured at 37°C and 200 r/min shaker for 10 h as the second-grade seed solution.
  • the secondary seed liquid was inoculated in the fermenter containing M9 liquid medium according to the inoculation amount of the initial OD value of 0.3, the initial volume of the 50L fermenter after inoculation was 25L, and the initial invert syrup addition was 3%, and the lactic acid monomer was started. Fermentation production.
  • the initial fermentation temperature was controlled at 37°C, and the pH was maintained at 6.5 with ammonia water. During the growth of the cells, the ventilation was adjusted to 1.5vvm, and the stirring speed was 1000r/min.
  • the lactic acid fermentation liquid obtained in above-mentioned embodiment 1 is heated to 88 °C in the reactor and maintains this temperature, 5mol/L sulfuric acid solution is added under 20r/min stirring, and the total amount of sulfuric acid is controlled at the mol ratio of lactic acid and sulfuric acid to be 1.
  • the time limit for adding all the sulfuric acid solution is controlled to be 1h/ton fermentation broth; after all the sulfuric acid solution is added, the reaction is maintained for 15min;
  • the collected solid part is the ⁇ -calcium sulfate hemihydrate whisker, and the obtained ⁇ -calcium sulfate hemihydrate whisker is the finished product of ⁇ -calcium sulfate hemihydrate after washing with absolute ethanol and steam flash drying at 120°C;
  • the collected liquid part is the free lactic acid liquid containing lactic acid monomers, which is filtered through a 6 ⁇ m pore size plate and frame to remove impurities and then evaporated and concentrated to a lactic acid content of 20wt% to 60wt%, which is the crude lactic acid product.
  • the formation rate of ⁇ -calcium sulfate hemihydrate whiskers reaches more than 98% (Table 2), the calcium sulfate whiskers are ⁇ -type, and the aspect ratio of the whiskers is 13.2-130.2, and 80% of the whiskers are The aspect ratio of the whiskers was 54.3 to 85.0 (Table 3), and the recovery rate of lactic acid monomer was 99.5% or more (Table 4).

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Abstract

一种以钙盐法生产乳酸的发酵液为原料生产α-半水硫酸钙晶须并同步回收乳酸单体的方法。包括如下步骤：1)乳酸发酵结束后，将发酵液升温；2)打开搅拌，加入硫酸反应；3)反应结束后，过滤收集固体部分即为α-半水硫酸钙晶须，收集液体部分即为含乳酸单体的游离乳酸液；4)获得的α-半水硫酸钙晶须再经过洗涤干燥后即为α-半水硫酸钙晶须成品，获得的游离乳酸液经过过滤、浓缩，即为乳酸粗成品，经过精制，获得高纯度乳酸单体。本发明可替代现有钙盐法乳酸生产中的乳酸高效分离和硫酸钙副产物的高附加值转化，显著降低乳酸精制成本和废弃物的形成，有利于乳酸生产质量提升和后提取工艺技术简化。

Description

一种以钙盐法生产乳酸的发酵液为原料生产α-半水硫酸钙晶须并同步回收乳酸单体的方法 技术领域
本发明属发酵工程和化学工程领域，具体涉及乳酸发酵生产时乳酸钙发酵液在硫酸的作用下直接转变为α-半水硫酸钙晶须和游离乳酸。
背景技术
乳酸是重要的三碳有机酸，具有L-型和D-型两种光学构型，即：L-乳酸和D-乳酸。L-乳酸和D-乳酸都是聚乳酸合成的单体原料，是生物可降解材料的重要组成部分。此外，L-乳酸和D-乳酸还用于多种酯类(如乳酸甲酯、乳酸乙酯、乳酸丙酯、乳酸丁酯)和乳酸盐合成的原料，L-乳酸还作为酸化剂广泛应用于食品、饮料、调味品、酒类、饲料等产品的生产中，D-乳酸还应用于香精香料、除草剂、药物等合成的原料。
乳酸的生产方式主要通过微生物发酵进行，其中钙盐法是发酵法生产乳酸的最主要方法。即：通过发酵，微生物菌种代谢适应的碳源(如葡萄糖、甘油、木糖、乳糖、蔗糖、果糖)为D-乳酸或L-乳酸(Tian,et.al,Biotechnology Bioengineering,2016,113:181-188.；Niu,et.al,Microbial Cell Factories,13:78-88.；Chen,et.al,Green Chemistry,16:342-350.；Zhou,et al.Metabolic Engineering,14:560-568；Chen,et.al,Biotechnol Adv,31:1200-1223,2013；田康明等，生物工程学报,29:111-114,2013；田康明等，生物工程学报,29:1-10,2013；王正祥等，ZL201580000781.7)，在发酵过程中加入氢氧化钙或碳酸钙等维系生产pH的同时，将生产出的乳酸转化为乳酸钙，所形成的乳酸钙在发酵结束后再通过加入硫酸，将乳酸钙转换为游离乳酸并生成不溶于水的硫酸钙，以无定形二水形式从溶液中析出。含有游离乳酸的发酵液再经过一系列的分离纯化等工序进行乳酸的精制，生产出乳酸产品，所形成的不溶于水的硫酸钙为乳酸发酵生产的副产物(张鹏等,ZL200810049644.4)，通过分离、干燥等工序，用于生产二水硫酸钙，即生石膏。
在乳酸的钙盐法发酵生产过程中，二水硫酸钙(生石膏)的生成量较大，质量与乳酸产品量相当。由于二水硫酸钙(生石膏)的物化属性一般，目前多数应用于食品级石膏的制作、低端水泥添加剂、饲料添加剂等，应用价值不高，甚至 成为“固废”，对规模化乳酸生产极为不利(张凡凡等,无机盐工业,2017,49(8)：10-13)。
将生石膏进一步转化为物化性能更好的其他产品，是解决钙盐法乳酸规模化生产的重要途径，可以在保证乳酸规模化工业生产的同时，解决二水硫酸钙(生石膏)副产物生成问题。
现有技术中，将生石膏经过煅烧、磨细，可得β型半水石膏(CaSO4·0.5H2O)，即建筑石膏，又称熟石膏、灰泥。将煅烧温度提高到190℃，可得模型石膏，其细度和白度均比建筑石膏高；将煅烧温度提高到400℃～500℃或高于800℃下，可将生石膏转变为地板石膏，其凝结、硬化较慢，但硬化后强度、耐磨性和耐水性均较普通建筑石膏为好(张立乾等，绿色环保建材,2020，(02)：14-15，18)。但是上述转化生石膏为β型半水石膏或污水石膏的物理煅烧方案，不适合在乳酸发酵生产时的硫酸钙副产物的加工目的，主要原因在于乳酸发酵生产过程中生成的二水硫酸钙的绝对量相对而言是比较少的，上述产品的附加值不高，投资-收益受限。
近年来，不少研究部分建立起了全新的方法，可以将生石膏转化为α-半水硫酸钙晶须(杨儒等,ZL201910466020.0；史培阳等,ZL201910373883.3；王宏宇等,ZL201610547294.9；周华锋等,硅酸盐通报,2017,36:2090-2094；崔益顺,化工矿物与加工,2017,46(3):13-16)。α-半水硫酸钙晶须具有高强度、高模量、高韧性、高绝缘性、耐磨耗、耐高温、耐酸碱、抗腐蚀、红外线反射性良好、易于表面处理、易与聚合物复合、无毒等诸多优良的理化性能等，集增强纤维和超细无机填料二者的优势于一体，因而具有很高的应用价值(李明,精细与专用化学品,2016,24(6):47-50)，可用于树脂、塑料、橡胶、涂料、油漆、造纸、沥青、摩擦和密封材料中作补强增韧剂或功能型填料(何航等,应用化工,2014:1671-1674；李茂刚等，硅酸盐通报,2017,36:1590-1593，1598；李军代,华东交通大学学报，2013,30(6):72-77；付凌杰等，四川理工学院学报(自然科学版),2013,26(5):7-10；吕鹏飞等,化工进展,2013,32:842-847，890；王泽红等,矿冶,2005(2):38-41)；也可以直接用作过滤材料、保温材料、耐火隔热材料、红外线反射材料和包覆电线的高绝缘材料等(黄明杰等，耐火与石灰,2014,39(3):19-20，23；黄明杰等,现代涂料与涂装,2013,16(11):18-19，26)。
已报道的将生石膏转化为α-半水硫酸钙晶须的方法，主要包括如下方法：
(1)蒸压法：将天然二水硫酸钙破碎成20～50mm的块状料，用金属框或小车放入蒸压釜中，蒸压法分立式和卧式两种。通入蒸汽冷凝水或热烟气加热物料到50～70℃，排出冷凝水或热烟气，封闭蒸压釜，然后通入饱和蒸气，升温到120～160℃并保持压力，经过5～8h的蒸压脱水转晶，转变成为α-半水硫酸钙晶须，然后移出蒸压釜干燥或在蒸压釜内干燥。立式蒸压釜的生产周期约为16～18h，卧式蒸压釜的生产周期约为30～40h(耿庆钰等,人工晶体学报,2016,45:1892-1897，1905；杨林等，建筑材料学报,2014,17:147-152；王宏宇等，ZL201610547294.9；乃学瑛等,ZL201610547294.9)。该方法是传统工艺，工艺较简单，但生产周期长，生产成本较高由于块状原料受热不均匀，脱水、转晶、干燥不均匀，导致产品质量波动大产品强度较低，一般强度在20～30MPa左右。
(2)水热法：将天然二水硫酸钙磨成细粉加入到含有转晶促进剂的水溶液中制成一般固含量不超过30％的悬浮液，将悬浮液加入立式蒸压釜中，不断搅拌悬浮液，同时加温悬浮液，水分蒸发形成蒸汽，产生压力，形成蒸压条件，釜内达到120～180℃的蒸压条件下，经过0.5～8h左右反应后，完成脱水、转晶过程然后排气降压，再经过离心脱水、洗涤、干燥、粉磨得到成品。经过破碎磨细后,与水混合制备成料浆，并加入一些能够促使结晶转化的外加剂或称为转晶剂，然后将料浆加入带有蒸汽夹套的蒸压反应釜内，一面进行搅拌，一面在夹套内通入蒸汽进行加热，二水石膏转变成为结晶良好的α-半水硫酸钙晶须。然后排汽降压，放出料浆进行脱水、洗涤、干燥和磨细，制得α型高强石膏粉。该方法生产的α-半水硫酸钙，产品质量稳定，抗压强度高，可以达到40～80MPa(唐娜等，无机盐工业,2020,52(4):88-92；吴峰等,化工进展,2018,37:1536-1543；黄旭等，硅酸盐通报,2019,38:2021-2027；张紫瑞等，宁夏工程技术,2019,18:40-43，49；王宇斌等,高校化学工程学报,2018,32:1444-1449；梁现红等,矿产保护与利用,2017(06):87-92，96；Wu M,WO 2015/085133 A1)。但此方法工艺复杂，生产设备多，投资大生产能力较小，生产效率较低，生产成本高，无法直接融入乳酸发酵生产工艺中。
(3)常压盐溶液法：将磨细后的二水硫酸钙与加有转晶剂的盐溶液混合，加入到反应容器内在常压条件下进行煮沸，使二水硫酸钙转变成为α-半水硫酸钙晶须。然后经脱水，洗涤和干燥，制得α-半水硫酸钙晶须。该方法不需要压力容器，可以减少设备投资(王艾文等,非金属矿,2020,43(4):84-87；张慧勇,化工 矿物与加工,2020,49(1):50-54；付文健 等,华东理工大学学报(自然科学版),2019,45(2):266-274；胡俊要等,无机盐工业,2018,50(6):47-50；王鑫等,无机盐工业,2017,49(11):54-58)。但是工艺条件严格，反应时间较长，产品强度不高。目前还处于实验室试验阶段，还未见到工业化生产的实例。
(4)常压甘油法：将工业副产物二水硫酸钙加入45％～75％的甘油溶液中，添加一定量的晶型调节剂，90℃维持30min，过滤、洗涤、干燥，获得α型半水硫酸钙晶须。该方法不需要高压环境，作用条件温和，产品纯度高。但是，制备的α型半水硫酸钙晶须长度低，硬度小(管青军等,矿产保护与利用,2019,39(4):1-8)。目前处于实验室试验阶段，未见生产实例。
上述α-半水硫酸钙晶须制备的方法，皆以二水硫酸钙为起始原料，生产过程绝大多数皆需要在温度高于120℃以上进行，部分方法还需要另外添加不同的化合物，不仅增加制造成本，也增加副产物的生成。可见，现有α-半水硫酸钙晶须的生产技术无法直接从钙盐法的乳酸发酵液制备乳酸单体的同时制备α-半水硫酸钙晶须。另外，过高的反应温度和转晶剂的添加会显著影响乳酸单体的回收。
技术问题
至今为止，将钙盐法生产乳酸工艺中所生成的乳酸钙中的乳酸释放过程，都以形成硫酸钙副产物为基础，未能实现形成乳酸释放与α-半水硫酸钙晶须制备的同步进行，需要在后续生产中进一步处理硫酸钙“固废”，既增加生产成本也使生产过程不够绿色环保。可见，实现乳酸单体与α-半水硫酸钙晶须同步生产，一方面可以集约化乳酸生产工艺并降低乳酸生产投入，另一方面则可以彻底解决现有工业生产体系中硫酸钙废弃物的形成。由此，可显著提升乳酸发酵生产的经济效率和环境效益并显著降低乳酸生产综合成本，对推动乳酸发酵产业技术进步和聚乳酸产业链的健康发展具有重要意义。
技术解决方案
本发明的目的是将钙盐法发酵乳酸生产中乳酸钙发酵液直接在释放游离乳酸的同时，所置换出的硫酸钙直接以α-半水硫酸钙晶须方式生成，实现乳酸单体与α-半水硫酸钙晶须的同步生产。
为了实现上述目的，本发明提供的技术方案，包括以下步骤：
一种以钙盐法生产乳酸的发酵液为原料生产α-半水硫酸钙晶须并同步回收乳酸单体的方法，包括以下步骤：
步骤1：乳酸发酵结束后，就地或将发酵液移入后提取反应釜中升温至50℃～102℃；进一步，发酵液的温度提高到不低于50℃但不高于102℃，进一步不低于55℃但不高于102℃，不低于60℃但不高于102℃，不低于65℃但不高于102℃，不低于70℃但不高于102℃，不低于75℃但不高于102℃，不低于80℃但不高于102℃，不低于85℃但不高于102℃；
步骤2：打开搅拌，维持上述温度下加入2～12mol/L硫酸，维持反应1min～10h；进一步，反应在5～80r/min搅拌和温度维持下，加入的硫酸总量控制在乳酸与硫酸的摩尔比为1：0.499～1：0.501，总量硫酸加入时限控制在1min～2h/吨发酵液，全部硫酸加入后维持反应1min～10h；
步骤3：步骤2反应结束后，反应液通过过滤进行固液分离，收集固体部分即为α-半水硫酸钙晶须，收集液体部分即为含乳酸单体的游离乳酸液；进一步，所描述的固液分离采用孔径5.0μm～50μm的带式过滤装置进行；
步骤4-1：获得的α-半水硫酸钙晶须经过洗涤干燥后，即为α-半水硫酸钙晶须成品；进一步，所描述的α-半水硫酸钙晶须经过热水或无水乙醇洗涤，再通过101℃～160℃蒸汽闪蒸干燥，即为α-半水硫酸钙晶须成品；
步骤4-2：获得的游离乳酸液经过过滤、浓缩等，即为乳酸粗成品，可用于后续如纳滤、脱色、离交等精制，获得高纯度乳酸单体；进一步，所获得的游离乳酸液经过过滤孔径0.8μm～10μm板框过滤除杂后蒸发浓缩到乳酸含量20wt％～60wt％，即为乳酸粗成品。
根据所述的方法，乳酸单体回收率达到99.5％以上，硫酸钙回收率和α-半水硫酸钙晶须生成率达到98％以上。
有益效果
本发明能够将钙盐法乳酸液一步转化为游离乳酸液和α-半水硫酸钙晶须，实现乳酸单体与α-半水硫酸钙晶须同步生产，乳酸单体回收率达到99.5％以上，硫酸钙回收率和α-半水硫酸钙晶须生成率达到98％以上，由此可一方面集约化乳酸生产工艺并降低乳酸生产投入，另一方面则可以彻底解决现有工业生产体系中硫酸钙废弃物的形成。由此也可以显著提升乳酸发酵生产的经济效率和环境效益并 显著降低乳酸生产综合成本。本发明经过简单修改后，还可应用于其它有机酸如柠檬酸、苹果酸、丁二酸等的生成。
本发明在用硫酸转换处理乳酸钙中的乳酸时，发现只要给予一定温度，并且不影响乳酸后续分离精制，且控制硫酸的添加速度，就可以在这一过程中将原本生成无定形二水硫酸钙，转变为生成α-半水硫酸钙晶须。工艺的关键点是温度和硫酸添加速度，其中温度又不可以像已有文献那样过高，超过105℃，乳酸的损耗就比较大，乳酸才是主产品；也不可以添加任何转晶剂或促晶剂，因为那样会增加乳酸分离精制的成本。
附图说明
图1为乳酸生产工艺路线：(a)原生产工艺；(b)本发明工艺；
图2为α-半水硫酸钙晶须形貌图(100X)。
本发明的实施方式
为了使本专利的目的、技术方案及优点更加清楚明白，以下结合具体实施例，对本专利进行进一步详细说明。应当理解，此处所描述的具体实施例仅用以解释本专利，并不用于限定本发明。
本发明以钙盐法生产乳酸的发酵液为原料，在乳酸发酵结束后，将发酵液升温至50℃～102℃，加入2～12mol/L硫酸并维持反应1min～10h，然后通过过滤进行固液分离，收集固体部分即为α-半水硫酸钙晶须，收集液体部分即为含乳酸单体的游离乳酸液，获得的α-半水硫酸钙晶须经过洗涤干燥后，即为α-半水硫酸钙晶须成品，获得的游离乳酸液经过过滤、浓缩等，即为乳酸粗成品，可用于后续如纳滤、脱色、离交等精制，获得高纯度乳酸单体(图1)。
本发明采用的主要实验方法如下：
1、钙盐法乳酸发酵液的制备
钙盐法乳酸发酵液的制备按照前期发明授权专利(王正祥等，ZL201580000781.7)方法进行，发酵菌种为CGMCC 11059或CGMCC11060，其中菌种CGMCC 11059用于D-乳酸的发酵生产，菌种CGMCC11060用于L-乳酸的发酵生产(王正祥等，ZL201580000781.7)。在发酵起始阶段，向发酵基本培养基中加入葡萄糖至终浓度10～50g/L，培养在30℃～37℃、pH 5.5～7.5、通风0.1～2.0vvm、100～1000r/min搅拌下进行；培养时间5～15h，菌体量达到10～50 OD；关闭通风，降低搅拌速度到0～300r/min，提高发酵温度到37℃～50℃，补加终浓度16％～25％的葡萄糖溶液，流加速度控制在3g/(L h)～25g/(L h)，同步流加5％～35％氢氧化钙，控制发酵pH在5.0～8.0之间。
2、发酵液酸化与硫酸钙α-型晶须的制备
发酵结束后，将发酵液升温至50℃～102℃，打开搅拌，维持上述温度下加入2～12mol/L硫酸，硫酸总量控制在乳酸与硫酸的摩尔比为1：0.499～1：0.501，总量硫酸加完的速度控制在1min～2h/吨发酵液，维持反应1min～10h。
3、乳酸液和α-半水硫酸钙晶须的分离
反应结束后，反应液通过过滤进行固液分离，采用孔径5.0μm～50μm的带式过滤装置进行，收集固体部分即为α-半水硫酸钙晶须，收集液体部分即为含乳酸单体的游离乳酸液。
4、α-半水硫酸钙晶须的精制
获得的α-半水硫酸钙晶须经过洗涤干燥后，用热水或无水乙醇洗涤，再通过101℃～160℃蒸汽闪蒸干燥，即为α-半水硫酸钙晶须成品。
5、α-半水硫酸钙晶须形态分析
在光学显微镜下观察并记录晶须的外观形态。测量40个晶须的长度及直径，并计算其长径比。所有数据均为3次平行试验结果的平均值。
6、α-半水硫酸钙晶须收得率
α-半水硫酸钙晶须收得率可以表示为晶须实际值与理论值的比值。实际值为α-半水硫酸钙晶须成品的质量。理论值是根据酸化时加入硫酸的摩尔数计算获得的α-半水硫酸钙晶须的重量。硫酸的摩尔数与α-半水硫酸钙晶须的摩尔数相等，硫酸的摩尔数与α-半水硫酸钙晶须相对分子质量的乘积即为晶须的理论值，以％计。
7、乳酸含量、质量与收得率
D-乳酸、L-乳酸、丙酮酸、甲酸、乙酸和丁二酸含量测定：采用HPLC进行，色谱检测条件为：色谱柱为HPX-87H有机酸分析柱，柱温为65℃，检测波长为210nm，流动相为5mmol/L浓度的硫酸溶液，流速为0.8mL/min，进样量为10μL。所有数据均为3次平行试验结果的平均值。乳酸单体的含量用g/L计，乳酸的化学纯度以乳酸单体占全部有机酸的百分比(％)计。乳酸的糖酸转化率以总乳酸生成质量占葡萄糖总消耗的百分比(％)计。
乳酸单体光学纯度测定：采用HPLC进行，色谱检测条件为：色谱柱为Astec CLC-L光学纯度分析柱，柱温为25℃，检测波长为254nm，流动相为5mmol/L浓度的硫酸铜溶液，流速为1mL/min，进样量为10μL。所有数据均为3次平行试验结果的平均值。乳酸单体的光学纯度以L-乳酸或D-乳酸占总乳酸的质量百分比(％)计。
乳酸钙浓度计算：上述游离乳酸含量按照摩尔比换算为乳酸钙含量，即1摩尔乳酸钙由2摩尔游离乳酸与钙盐结合形成。
实施例1：乳酸发酵液的制备
将D-乳酸生产菌种CGMCC 11059或L-乳酸生产菌种CGMCC 11060的甘油管冻藏物，接种于50mL的LB液体培养基中，37℃、200r/min摇床培养12h，作为一级种子液。将一级种子液接种于150mL以葡萄糖为碳源的M9液体培养基中，起始糖浓度均为0.5％，37℃、200r/min摇床培养10h，作为二级种子液。将二级种子液按照起始OD值0.3的接种量接种于含有M9液体培养基的发酵罐中，接种后50L发酵罐初始体积为25L，初始转化糖浆添加量为3％，开始乳酸单体的发酵生产。发酵起始温度控制为37℃，用氨水维持pH 6.5，菌体生长过程中通过调节通气量为1.5vvm，搅拌转速为1000r/min，当菌体浓度达到OD60030后，关闭通风，发酵温度控制在40℃，搅拌转速调为200r/min，流加25％氢氧化钙悬浊液维持pH在7.0，补加总量6.0kg葡萄糖，残余糖浓度低于0.5g/L后即发酵结束。关键发酵结果汇总于表1。
表1乳酸单体发酵液制备及其主要参数
Figure PCTCN2021074953-appb-000001
Figure PCTCN2021074953-appb-000002
实施例2：α-半水硫酸钙晶须的制备
上述实施例1获得的乳酸发酵液，在反应釜中将其加热至88℃并维持此温度，20r/min搅拌下加入5mol/L硫酸溶液，硫酸总量控制在乳酸与硫酸的摩尔比为1:0.5，全部硫酸溶液的加入时限控制在为1h/吨发酵液；全部硫酸溶液加完后，维持反应15min；反应结束后，反应液的固液分离采用孔径8.0μm的带式过滤装置进行，收集固体部分即为α-半水硫酸钙晶须，获得的α-半水硫酸钙晶须经过无水乙醇洗涤和120℃蒸汽闪蒸干燥后，即为α-半水硫酸钙晶须成品；收集液体部分即为含乳酸单体的游离乳酸液，经过过滤孔径6μm板框过滤除杂后蒸发浓缩到乳酸含量20wt％～60wt％，即为乳酸粗成品，经过离子交换、活性炭脱色、超滤等精制工艺，即可获得高纯度乳酸单体。根据所述的方法，α-半水硫酸钙晶须生成率达到98％以上(表2)，硫酸钙晶须为α-型，晶须的长径比为13.2～130.2，并且其中80％的晶须的长径比为54.3～85.0(表3)，乳酸单体回收率达到99.5％以上(表4)。
表2α-半水硫酸钙晶须生成率
批次 晶须生成率(％)
第1批 98.62
第2批 98.14
第3批 99.33
第4批 99.51
第5批 98.92
第6批 99.36
表3α-半水硫酸钙晶须的长径比
批次 晶须长径比范围 80％的晶须长径比范围
第1批 22.1-124.3 60.2-80.6
第2批 13.2-122.4 59.7-85.0
第3批 20.3-128.4 55.6-83.5
第4批 30.4-129.6 54.3-82.6
第5批 14.8-130.2 59.3-80.7
第6批 16.7-127.8 57.8-79.5
表4乳酸单体的回收率
批次 乳酸单体回收率(％)
第1批 99.64
第2批 99.58
第3批 99.63
第4批 99.59
第5批 99.70
第6批 99.82
以上所述仅为本发明的较佳实施例，凡依本发明申请专利范围所做的均等变化与修饰，皆应属本发明的涵盖范围。

Claims (9)

  1. 一种以钙盐法生产乳酸的发酵液为原料生产α-半水硫酸钙晶须并同步回收乳酸单体的方法，其特征在于，包括以下步骤：
    步骤1：乳酸发酵结束后，将发酵液升温；
    步骤2：打开搅拌，维持上述温度下加入硫酸，进行反应；
    步骤3：反应结束后，反应液通过过滤进行固液分离，收集固体部分即为α-半水硫酸钙晶须，收集液体部分即为含乳酸单体的游离乳酸液；
    步骤4-1：获得的α-半水硫酸钙晶须经过洗涤干燥后，即为α-半水硫酸钙晶须成品；
    步骤4-2：获得的游离乳酸液经过过滤、浓缩，即为乳酸粗成品，经过精制，获得高纯度乳酸单体。
  2. 根据权利要求1所述的方法，其特征在于，步骤1乳酸发酵结束后就地升温或移入后提取反应釜中进行升温。
  3. 根据权利要求1所述的方法，其特征在于，步骤1发酵液的升温温度为50℃～102℃。
  4. 根据权利要求3所述的方法，其特征在于，步骤1发酵液的升温温度为85℃～102℃。
  5. 根据权利要求1所述的方法，其特征在于，步骤2的反应在5～80r/min搅拌速度下维持。
  6. 根据权利要求1所述的方法，其特征在于，步骤2中加入硫酸的浓度为2mol/L～12mol/L，硫酸总量控制在乳酸与硫酸的摩尔比为1：0.499～1：0.501，总量硫酸加入时限控制在1min～2h/吨发酵液，全部硫酸加入后维持反应1min～10h。
  7. 根据权利要求书1所述的方法，其特征在于，步骤3的固液分离采用孔径5.0μm～50μm的带式过滤装置进行。
  8. 根据权利要求书1所述的方法，其特征在于，步骤4-1的α-半水硫酸钙晶须经过热水或无水乙醇洗涤，再通过101℃～160℃蒸汽闪蒸干燥，即为α-半水硫酸钙晶须成品。
  9. 根据权利要求书1所述的方法，其特征在于，步骤4-2的获得的游离乳酸液经过过滤孔径0.8μm～10μm板框过滤除杂后蒸发浓缩到乳酸含量20wt％～60wt％，即为乳酸粗成品。
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