Production process method of polymer-grade lactic acid

Abstract

The invention belongs to the technical field of L-lactic acid production, and particularly relates to a production process method of polymer-grade lactic acid, which comprises the following steps: neutralizing lactic acid fermentation liquor with a neutralizer, filtering out thalli, sterilizing to obtain calcium lactate, performing acidolysis with sulfuric acid to obtain lactic acid and calcium sulfate, filtering to obtain lactic acid clear liquor, and drying to obtain the polymer-grade lactic acid. And carrying out decoloration, ion exchange, nanofiltration membrane filtration and molecular rectification to obtain the polymer-grade lactic acid. The physical and chemical indexes of the product meet the requirements of polymer-grade L-lactic acid, the preparation of high-purity and high-quality lactic acid is realized, the heat transfer efficiency is high, the retention time is short, and the method has the advantages of low energy consumption, cost reduction, easiness in operation, large-scale realization and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of L-lactic acid production, in particular to a production process method of polymerization-grade lactic acid. Background Art

[0002] The lactic acid produced by the traditional fermentation method needs to be recovered and refined by the calcium lactate method, the production process is long, the process is complicated, a large amount of inorganic salts are present in the obtained lactic acid, which cannot meet the requirements of polymer-grade lactic acid, and due to the inhibitory effect of lactic acid on microorganisms, the increase of substrate concentration is limited, which affects the fermentation rate. Polymer-grade lactic acid is a new concept proposed in recent years, mainly referring to the lactic acid monomer used to process polylactic acid, and its optical purity requirements are very high or extremely high. In particular, D-lactic acid has a large gap in the diversity of fermentation strains and the fermentation level, and the optical purity is difficult to reach the production polymer-grade lactic acid standard, which is far from meeting the needs of the PLA industrial market. In order to solve the above problems, those skilled in the art are in urgent need of developing a production process method for polymer-grade lactic acid. Meet existing market demand and performance requirements. Summary of the invention

[0003] In view of the above problems, the present invention aims to provide a production process method of polymerization-grade lactic acid and its application.

[0004] A production process for polymer-grade lactic acid comprises the following steps: after the lactic acid fermentation liquid is neutralized with a neutralizer, the bacteria are filtered out and then sterilized to obtain calcium lactate, which is then hydrolyzed with sulfuric acid to obtain lactic acid and calcium sulfate, which is then filtered to obtain a lactic acid clear liquid, and then decolorized, ion exchanged, nanofiltration membrane filtered, and molecular distilled to obtain polymer-grade lactic acid.

[0005] Furthermore, the neutralizing agent is calcium carbonate.

[0006] Furthermore, the process conditions of the nanofiltration membrane filtration are pH 2-3, pressure 2-3 MPa, and temperature 25-30°C.

[0007] Furthermore, the molecular distillation is divided into two stages of molecular distillation: the first stage molecular distillation: distillation temperature 63-65°C, scraping speed 120-150r / min, feed rate 45-60L / h, preheating temperature 50-60°C, distillation pressure 1-7kPa, distillation time 45-50s; the second stage molecular distillation: distillation temperature 63-65°C, scraping speed 120-150r / min, feed rate 45-60L / h, preheating temperature 50-60°C, distillation pressure 1-7kPa, distillation time 45-50s.

[0008] Furthermore, the decolorization is performed by activated carbon column decolorization, the feeding method is low in and high out, the residence time is 3 to 5 hours, and the chromaticity after flowing out of the carbon column is ≤30hazen.

[0009] Furthermore, the ion exchange is carried out through 001×7 cation exchange and 201×7 anion exchange columns, and after the ion exchange, the calcium ion concentration in the L-lactic acid is ≤2ppm, the iron ion concentration is ≤1ppm, the sulfate ion concentration is ≤1ppm, and the chloride ion concentration is ≤1ppm.

[0010] Wipped film evaporator Wipped film evaporator is a new type of high-efficiency evaporator that uses a rotating scraper to force film formation and high-speed flow, has high heat transfer efficiency, short residence time, and can perform falling film evaporation under vacuum conditions.

[0011] Beneficial effects of the present invention: This paper starts with calcium salt lactic acid fermentation broth. After the lactic acid fermentation broth is neutralized with a neutralizer, the bacteria are filtered out and sterilized to obtain calcium lactate, which is then hydrolyzed with sulfuric acid to obtain lactic acid and calcium sulfate. After filtration, lactic acid clear liquid is obtained, and then decolorization, ion exchange, nanofiltration membrane filtration, and molecular distillation are performed to obtain polymerization-grade lactic acid. The physical and chemical indicators of the product meet the requirements of polymerization-grade L-lactic acid, and the preparation of high-purity and high-quality lactic acid is achieved. It has high heat transfer efficiency and short residence time, and has the advantages of low energy consumption, reduced costs, easy operation, and large-scale realization. DETAILED DESCRIPTION

[0012] The present invention is described below with specific examples, but is not intended to be limiting of the present invention. Example 1

[0013] Raw materials and equipment: Glatt Biochemical lactic acid fermentation broth, Junye Process Machinery 850 scraped film evaporator; A production process of polymer-grade lactic acid comprises the following steps: neutralizing lactic acid fermentation liquid with a neutralizing agent, filtering out bacterial cells and sterilizing to obtain calcium lactate, acidolyzing with sulfuric acid to obtain lactic acid and calcium sulfate, filtering to obtain lactic acid clear liquid, and then decolorizing, ion exchanging, nanofiltration membrane filtration, and molecular distillation to obtain polymer-grade lactic acid; the process conditions of DK8040C30 nanofiltration membrane filtration are pH 2, pressure 2MPa, and temperature 25°C, and the molecular distillation is divided into two stages of molecular distillation: the first stage of molecular distillation: distillation temperature 63°C, scraping speed 120r / min, feed rate 45L / h, preheating temperature 50°C, distillation pressure 1kP a. Distillation time 45s; wherein the secondary molecular distillation: distillation temperature 63°C, scraping speed 120r / min, feed rate 45L / h, preheating temperature 50°C, distillation pressure 1kPa, distillation time 45s, the decolorization is activated carbon column decolorization, the feed mode is low in and high out, the residence time is 3h, the chromaticity after flowing out of the carbon column is ≤30hazen, the ion exchange is exchanged and separated by 001×7 cation and 201×7 anion exchange columns, and the calcium ion concentration in L-lactic acid after ion exchange is ≤2ppm, the iron ion concentration is ≤1ppm, the sulfate ion concentration is ≤1ppm, and the chloride ion concentration is ≤1ppm. Example 2

[0014] Raw materials and equipment: Glatt Biochemical lactic acid fermentation broth, Junye Process Machinery 850 scraped film evaporator.

[0015] A production process of polymer-grade lactic acid comprises the following steps: neutralizing lactic acid fermentation liquid with a neutralizing agent, filtering out bacterial cells and sterilizing to obtain calcium lactate, acidolyzing with sulfuric acid to obtain lactic acid and calcium sulfate, filtering to obtain lactic acid clear liquid, and then decolorizing, ion exchanging, nanofiltration membrane filtration, and molecular distillation to obtain polymer-grade lactic acid; the process conditions of DK8040C30 nanofiltration membrane filtration are pH 3, pressure 3MPa, and temperature 30°C, and the molecular distillation is divided into two stages of molecular distillation: the first stage of molecular distillation: distillation temperature 65°C, film scraping speed 150r / min, feed rate 60L / h, preheating temperature 60°C, distillation pressure 7k Pa, distillation time 50s; wherein the secondary molecular distillation: distillation temperature 65°C, scraping speed 150r / min, feed rate 60L / h, preheating temperature 60°C, distillation pressure 7kPa, distillation time 50s, decolorization is activated carbon column decolorization, the feed method is low in and high out, the residence time is 5h, the chromaticity after flowing out of the carbon column is ≤30hazen, the ion exchange is exchanged and separated by 001×7 cation and 201×7 anion exchange columns, and after ion exchange, the calcium ion concentration in L-lactic acid is ≤2ppm, the iron ion concentration is ≤1ppm, the sulfate ion concentration is ≤1ppm, and the chloride ion concentration is ≤1ppm.

[0016] The L-lactic acid obtained in Examples 1 and 2 was subjected to performance testing, and the test results are shown in Table 1.

[0017] Table 1 L-lactic acid performance test results of Examples 1 to 2

[0018] Note: The determination of lactic acid content shall be in accordance with the method specified in A.3 of Appendix A of GB1886.173-2016. Optical purity determination: Reagents and materials: Grade 1 water specified in GB / T6682; Instruments and equipment: High performance liquid chromatograph. Reference chromatographic conditions (1) Chromatographic column: SUMICHIRALOA-5000 (4.6Φ×150mm). (2) Mobile phase: 0.002mol / L copper sulfate solution. (3) Detection wavelength: 254nm. (4) Column temperature: 35℃; (5) Flow rate: 0.5ml / min. (6) Injection volume: 10μL. (7) Separation requirement: Separation between type D and type L ≥1.0. ① Weigh 1.0g of sample into a 250mL beaker containing zeolite, add 35mL of 1mol / LNaOH solution and 40mL of water. ②Put a watch glass on the beaker, boil it on the electric stove for 10 minutes, and add water to 60mL after it is completely cooled. ③Weigh 0.8-1.5g of saponified liquid, add 10mL of water and mix well, adjust the pH value to neutral 7 with 0.36N dilute sulfuric acid, filter the sample with a 0.22um filter into the injection bottle, analyze and obtain the peak area of ​​D-lactic acid and L-lactic acid in the sample (D-lactic acid retention time 23min, L-lactic acid retention time 18.5min), and quantify by area normalization method. Result calculation X1=A L / (A L +A D )×100%, where the optical purity of L-lactic acid is X1; where: X1—is the optical purity of L-lactic acid; A L —peak area value of L-lactic acid in the sample; A D —Peak area value of D-lactic acid in the sample. The determination of ignition residue shall be in accordance with the method specified in A.5 of Appendix A of GB1886.173-2016. The determination of chloride (in terms of Cl) shall be in accordance with the method specified in A.6 of Appendix A of GB1886.173-2016. The determination of sulfate (in terms of SO4) shall be in accordance with the method specified in A.7 of Appendix A of GB1886.173-2016. The determination of iron salt (in terms of Fe) shall be in accordance with the method specified in A.8 of Appendix A of GB1886.173-2016. The determination of heavy metals (in terms of Pb) shall be in accordance with the method specified in GB5009.75 or GB5009.12. The determination of mercury shall be in accordance with the atomic fluorescence analysis method of GB5009.17-2014; the determination of arsenic shall be in accordance with the flame atomic absorption spectrometry of GB5009.76. The determination of chromaticity shall be in accordance with GB / T605-2006.

Claims

1. A production process for polymer-grade lactic acid, characterized in that: The lactic acid fermentation broth is neutralized with a neutralizer, the bacteria are filtered out and then sterilized to obtain calcium lactate, which is then hydrolyzed with sulfuric acid to obtain lactic acid and calcium sulfate, which is then filtered to obtain lactic acid serum, which is then decolorized, ion exchanged, filtered through a nanofiltration membrane, and molecularly distilled to obtain polymerization-grade lactic acid.

2. The production process of polymer-grade lactic acid according to claim 1, characterized in that: The neutralizing agent is calcium carbonate.

3. The production process of polymer-grade lactic acid according to claim 1, characterized in that: The process conditions of the nanofiltration membrane filtration are pH 2-3, pressure 2-3 MPa, and temperature 25-30°C.

4. The production process of polymer-grade lactic acid according to claim 1, characterized in that: The molecular distillation is divided into two stages of molecular distillation: the first stage molecular distillation: distillation temperature 63-65°C, scraping speed 120-150r / min, feed rate 45-60L / h, preheating temperature 50-60°C, distillation pressure 1-7kPa, distillation time 45-50s; the second stage molecular distillation: distillation temperature 63-65°C, scraping speed 120-150r / min, feed rate 45-60L / h, preheating temperature 50-60°C, distillation pressure 1-7kPa, distillation time 45-50s.

5. The production process of polymer-grade lactic acid according to claim 1, characterized in that: The decolorization is performed by using an activated carbon column, the feeding method is low-in and high-out, the residence time is 3 to 5 hours, and the chromaticity after flowing out of the carbon column is ≤30 hazen.

6. The production process of polymer-grade lactic acid according to claim 1, characterized in that: The ion exchange is carried out by exchange separation through 001×7 cation exchange columns and 201×7 anion exchange columns. After the ion exchange, the calcium ion concentration in the L-lactic acid is ≤2ppm, the iron ion concentration is ≤1ppm, the sulfate ion concentration is ≤1ppm, and the chloride ion concentration is ≤1ppm.

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