CN109180914B - Method for producing poly-L-lactic acid by using L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation - Google Patents
Method for producing poly-L-lactic acid by using L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation Download PDFInfo
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Abstract
The invention discloses a method for producing poly-L-lactic acid by utilizing L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation, which comprises the following steps: (1) preparing L-lactic acid oligomer by using L-lactic acid; (2) adding an L-lactic acid oligomer and a melt polycondensation catalyst into a melt polycondensation reaction kettle, and carrying out melt polycondensation to prepare low molecular weight poly-L-lactic acid, wherein the addition amount of the melt polycondensation catalyst is 0.1-1% of the mass amount of the L-lactic acid oligomer; (3) adding low molecular weight poly-L-lactic acid into a solid phase polycondensation reaction kettle, and carrying out solid phase polycondensation to prepare high molecular weight poly-L-lactic acid. The invention takes the cheap and easily obtained L-lactic acid monomer in the actual industrial production as the raw material, deserves the L-lactic acid oligomer with narrower molecular weight distribution, has mild reaction condition, easy control and high L-lactic acid oligomer yield, and is suitable for industrial production; and the poly-L-lactic acid is prepared by using L-lactic acid oligomer through melt polycondensation and solid phase polycondensation, so that the cost is greatly reduced, and the product competitiveness is improved.
Description
Technical Field
The invention relates to the technical field of lactic acid deep processing. And more particularly, to a method for producing poly-L-lactic acid using L-lactic acid through oligomerization, melt polycondensation, and solid phase polycondensation.
Background
The polylactic acid is a polymer with excellent performance, biocompatibility and biodegradability, and is mainly used for degradable packaging materials and medical materials such as drug microsphere carriers, anti-adhesion films, biological catheters, orthopedic fixtures, orthopedic surgery devices, artificial bones and the like.
In the process of preparing polylactic acid by monomer lactic acid, firstly, the monomer lactic acid generates lactic acid oligomer, and then the lactic acid oligomer is directly condensed to prepare the polylactic acid; or preparing lactide from lactic acid oligomer and then carrying out ring-opening polymerization on the lactide to generate polylactic acid. In the prior art, the cost for preparing the polylactic acid by adopting the former method is higher, so that the profit of enterprises is greatly reduced. In the latter method for preparing polylactic acid, since the cost of directly obtaining lactide with high purity from a lactic acid monomer is high, for example, in the method for preparing a lactic acid oligomer disclosed in chinese patent document CN1498237A, a mixture of linear and cyclic lactic acid oligomers can be selectively prepared by using lactide as a raw material. The disadvantages of this method are: (1) lactide is used as a raw material, but in industrial production, lactic acid monomers are used as the most cheap raw material, and the cost for preparing the lactic acid oligomer mixture from the lactide is high; (2) the used solvents such as tetrahydrofuran are toxic and are not suitable for industrial application.
Disclosure of Invention
The invention aims to provide a method for producing poly-L-lactic acid by using L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation, so that the cost is reduced, and the enterprise profit is improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
the method for producing poly-L-lactic acid by utilizing L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation comprises the following steps:
(1) preparing L-lactic acid oligomer by using L-lactic acid;
(2) adding an L-lactic acid oligomer and a melt polycondensation catalyst into a melt polycondensation reaction kettle, and carrying out melt polycondensation to prepare low molecular weight poly-L-lactic acid, wherein the addition amount of the melt polycondensation catalyst is 0.1-1% of the mass amount of the L-lactic acid oligomer;
(3) adding low molecular weight poly-L-lactic acid into a solid phase polycondensation reaction kettle, and carrying out solid phase polycondensation to prepare high molecular weight poly-L-lactic acid.
According to the method for producing poly-L-lactic acid by utilizing L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation, the melt polycondensation catalyst is prepared by uniformly mixing the component A and the component B according to the mass ratio of 1: 2-5;
the preparation method of the component A comprises the following steps: adding diacetyl tartaric acid monoglyceride and diglyceride into 50-60 deg.C water at a mass ratio of diacetyl tartaric acid monoglyceride and water of 1-5:100, stirring for 5-30 min, and adding Mn (H)2P04)2，Mn(H2P04)2Stirring the mixture and water at a mass ratio of 5-10:100 at 50-60 ℃ for 2-3 hours, heating to 80-100 ℃, and evaporating to dryness to obtain a component A;
the preparation method of the component B comprises the following steps: adding N- [ N- (3, 3-dimethylbutyl) -L-alpha-aspartyl ] -L-phenylalanine-1-methyl ester into water at the temperature of 20-30 ℃, wherein the mass ratio of the N- [ N- (3, 3-dimethylbutyl) -L-alpha-aspartyl ] -L-phenylalanine-1-methyl ester to the water is 5-12:1000, and stirring for 5-30 minutes; adding disodium stannous citrate with the mass ratio of 10-15:1000 to water, and stirring for 5-10 minutes; heating to 80-100 deg.C, and evaporating to obtain component B.
The method for producing poly-L-lactic acid by utilizing L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation has the reaction pressure of 500-2000Pa for melt polycondensation, the reaction time of 4-50h, the reaction temperature of 150-200 ℃ and the stirring speed of 30-100 rmp.
In the method for producing poly-L-lactic acid by utilizing L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation, low molecular weight poly-L-lactic acid is pre-crystallized in the solid phase polycondensation, the pre-crystallization temperature is 90-120 ℃, and the pre-crystallization time is 1-5 hours; the reaction temperature of the pre-crystallized low molecular weight poly-L-lactic acid is 140-180 ℃ and the reaction time is 5-30 h.
In the method for producing poly-L-lactic acid by using L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation, in the step (1), the method for preparing L-lactic acid oligomer by using L-lactic acid is as follows:
(1-1) preparation of raw materials: 40-60 wt% of L-lactic acid solution, the optical purity of the L-lactic acid is more than or equal to 99.5%;
(1-2) dehydrating and oligomerizing to obtain the L-lactic acid oligomer.
In the method for producing poly-L-lactic acid by utilizing L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation, in the step (1-2), ethyl pyruvate is added into the L-lactic acid solution, and the volume ratio of the ethyl pyruvate to the L-lactic acid solution is 0.5-1: 1; simultaneously adding cobalt oxide and di-cysteine methyl ester vanadyl as catalysts into the mixed solution, and stirring; the usage amount of the cobalt oxide is 0.02-0.04 percent of the mass of the L-lactic acid, and the usage amount of the di-cysteine methyl ester vanadyl is 0.04-0.08 percent of the mass of the L-lactic acid; the reaction time is 3-6 h, and the reaction temperature is 5-30 ℃.
The method for producing poly-L-lactic acid by using L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation, wherein in the step (1-2):
initial reaction: the mass ratio of the added cobalt oxide to the added di-cysteine methyl ester vanadyl is 1:1.5, and the addition amount of the cobalt oxide in the initial reaction is 1/2 of the total addition amount of the cobalt oxide; the reaction temperature is kept between 5 and 10 ℃ from the initial reaction to the time when one half of the reaction time is passed;
when the reaction time is one-half elapsed: adding all the residual di-cysteine methyl ester vanadyl into a reaction kettle; the reaction temperature is kept between 15 and 20 ℃ from one half of the reaction time to three quarters of the reaction time;
three quarters of the time elapsed: adding the rest cobalt oxide into the reaction kettle; the reaction temperature is kept between 25 and 30 ℃ from the end of the reaction to the end of the reaction after three quarters of the reaction time.
In the method for producing poly-L-lactic acid by using L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation, in the step (1-2), the preparation method of di-cysteine methyl ester vanadyl comprises the following steps: mixing and stirring cysteine methyl ester and vanadyl sulfate in boric acid solution at room temperature, and reacting for 3-5h to obtain purple solid; the amount ratio of the cysteine methyl ester to the vanadyl sulfate substance is 5:1, and the concentration of the cysteine methyl ester in the boric acid solution is 0.1-5 mol/L.
In the method for producing poly-L-lactic acid by using L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation, in the step (1-2), after the reaction is finished, filtering, standing for layering, separating out an organic phase, and washing the organic phase with water; and (3) carrying out vacuum distillation on the organic phase after washing by water to remove the solvent, thus obtaining a white solid, namely the L-lactic acid oligomer.
The invention has the following beneficial effects:
the L-lactic acid monomer which is cheap and easy to obtain in the actual industrial production is taken as a raw material, so that the L-lactic acid oligomer with narrow molecular weight distribution is worth, the reaction condition is mild and easy to control, the yield of the L-lactic acid oligomer is high, and the method is suitable for industrial production; and the poly-L-lactic acid is prepared by using L-lactic acid oligomer through melt polycondensation and solid phase polycondensation, so that the cost is greatly reduced, and the product competitiveness is improved.
Drawings
FIG. 1 influence of different catalyst addition amounts on the molecular weight of polylactic acid in melt polycondensation;
FIG. 2 influence of reaction time on the molecular weight of polylactic acid synthesized by melt polycondensation;
FIG. 3 effect of reaction temperature on polylactic acid molecular weight and yield;
FIG. 4 effect of agitation speed on product molecular weight;
FIG. 5 influence of the precrystallization time on the molecular weight of a solid phase polycondensation product;
FIG. 6 influence of the pre-crystallization temperature on the molecular weight of the solid phase polycondensation product;
FIG. 7 influence of reaction temperature on molecular weight of solid phase polycondensation product;
FIG. 8 influence of reaction time on molecular weight of solid phase polycondensation product.
Detailed Description
In order to more clearly illustrate the invention, the invention is further described below with reference to preferred embodiments and the accompanying drawings. Similar parts in the figures are denoted by the same reference numerals. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
The first part is the research on the technological conditions of producing poly-L-lactic acid by melt polycondensation and solid phase polycondensation of L-lactic acid oligomer
1 melt polycondensation-solid phase polycondensation for producing high molecular weight poly-L-lactic acid
1.1 melt polycondensation Process technical Studies
1.1.1 Effect of catalyst dosage on the molecular weight of Poly-L-lactic acid produced during melt polycondensation
The melt polycondensation of L-lactic acid oligomer to produce poly L-lactic acid is a slow reversible reaction without a catalyst and without a reduced pressure, and the catalyst allows the reaction system to proceed toward poly L-lactic acid, thereby suppressing the production of lactide.
The catalyst used in the embodiment is prepared by uniformly mixing the component A and the component B according to the mass ratio of 1: 2; the preparation method of the component A comprises the following steps: adding diacetyl tartaric acid monoglyceride and diglyceride into water at 60 deg.C, the mass ratio of diacetyl tartaric acid monoglyceride and water is 2:100, stirring for 20 min, and adding Mn (H)2P04)2，Mn(H2P04)2Stirring the mixture and water at the mass ratio of 5:100 and the temperature of 50-60 ℃ for 3 hours, then heating to 80 ℃ and evaporating to dryness to obtain a component A; the preparation method of the component B comprises the following steps: mixing N- [ N- (3, 3-dimethylbutyl) -L-alpha-aspartyl]Adding (E) -L-phenylalanine-1-methyl ester into water at 20 deg.C, and adding N- [ N- (3, 3-dimethylbutyl) -L-alpha-aspartyl]The mass ratio of the L-phenylalanine-1-methyl ester to the water is 5:1000, and stirring is carried out for 10 minutes; then adding disodium stannous citrate and lemonStirring for 5 minutes, wherein the mass ratio of the stannous acid disodium to the water is 15: 1000; heating to 90 deg.C, and evaporating to obtain component B.
Under otherwise identical conditions, the effect of different catalyst addition amounts on the molecular weight (weight average molecular weight Mw) of the melt polycondensation of L-lactic acid oligomers to poly-L-lactic acid was experimentally optimized, and the results are shown in FIG. 1.
As can be seen from FIG. 1, the weight average molecular weight of poly L-lactic acid in the melt polycondensation process increases and then decreases with the increase of the amount of catalyst, the degradation rate of poly L-lactic acid in the reaction system is greater than the generation rate of poly L-lactic acid due to the excessive amount of catalyst, the side reaction is promoted, when the amount of catalyst accounts for more than 0.35% of the mass fraction of oligomeric L-lactic acid, the molecular weight of poly L-lactic acid increases gently, and when the amount of catalyst accounts for more than 0.5% of the mass fraction of oligomeric L-lactic acid, the molecular weight of poly L-lactic acid begins to decrease. Comprehensively considering the production benefit, the optimal dosage is selected when the catalyst dosage accounts for 0.35 percent of the mass fraction of the L-lactic acid oligomer.
1.1.2 Effect of vacuum degree on polymerization
Since the polycondensation reaction of the L-lactic acid oligomer is a thermodynamic equilibrium process, methods such as pressure reduction are required to move the reaction in the polymerization direction. In the melt polycondensation process, the control of the reaction pressure is a decisive factor influencing the molecular weight growth of the polymer and the generation amount of the byproduct lactide, and the optimal control of the reaction pressure can move the equilibrium towards the positive reaction direction and prevent the generation of excessive lactide. The influence of the reaction pressure on the yield of poly-L-lactic acid in the melt polycondensation was examined and the results are shown in Table 1.
TABLE 1 influence of reaction pressure on the yield of poly-L-lactic acid
As can be seen from Table 1, the yield of poly L-lactic acid obtained by melt polycondensation is the greatest and the overall efficiency is the highest at a reaction pressure of 1600Pa, and the optimum parameter is selected at a reaction pressure of 1600 Pa.
1.1.3 Effect of reaction time on the molecular weight of Poly-L-lactic acid produced by melt polycondensation
The effect of reaction time on the molecular weight of poly-L-lactic acid produced by melt polycondensation was examined under otherwise identical conditions, and the results are shown in FIG. 2.
As is clear from FIG. 2, the molecular weight of poly L-lactic acid gradually increased with the increase of the reaction time from 0 to 20 hours, and the rate of increase was decreased after 8 hours. And after 20h, the reaction time is continuously increased, the viscosity of the reaction system is increased, the discharge of small molecular water is difficult, the degradation rate is higher than the synthesis rate of the poly-L-lactic acid, the reaction moves towards the lactide direction, and the molecular weight of the poly-L-lactic acid is reduced. Comprehensively checking the production efficiency, and selecting the reaction time of 8h, 10h and 12h to carry out orthogonal test.
1.1.4 Effect of reaction temperature on molecular weight and yield of Poly-L-lactic acid produced by melt polycondensation
The effect of reaction time on the molecular weight and yield of poly-L-lactic acid produced by melt polycondensation was examined under otherwise identical conditions, and the results are shown in FIG. 3.
As can be seen from FIG. 3, when the temperature is lower than 190 ℃, the molecular weight of the poly L-lactic acid product increases with the increase of the temperature, and when the temperature is higher than 190 ℃, the rate of depolymerization of the poly L-lactic acid into lactide and hydrolysis reaction is accelerated due to the overhigh temperature, resulting in slow decrease of the molecular weight of the poly L-lactic acid. When the temperature is more than 180 ℃, the yield of the poly-L-lactic acid is rapidly reduced. The production efficiency is integrated, and the reaction temperature is 170 ℃, 180 ℃ and 190 ℃ for orthogonal test.
1.1.5 Effect of the stirring speed on the molecular weight of Poly-L-lactic acid produced by melt polycondensation
The effect of the stirring speed on the molecular weight of poly-L-lactic acid produced by the melt polycondensation reaction was examined under the same conditions of reaction time, pressure, temperature, etc., and the results are shown in FIG. 4.
As is clear from FIG. 4, when the stirring speed is less than 60rpm, the molecular weight of poly-L-lactic acid increases with the increase of the rotation speed in the same reaction time, and the stirring makes the temperature of each part in the reactor uniform, thereby accelerating the reaction. When the stirring speed is more than 60rpm, the stirring speed is too high, resulting in a decrease in the molecular weight of poly-L-lactic acid. And (3) synthesizing the production efficiency, and selecting three speeds of 50rpm, 60rpm and 70rpm to perform an orthogonal test.
1.1.6 Combined design of melt polycondensation Process indices
The catalyst addition and the reaction pressure are used as melt polycondensation control constants, the reaction time, the reaction temperature and the stirring speed are used as independent variables, and the molecular weight MW of the product poly-L-lactic acid is used as a dependent variable for analysis.
Test results and significance test thereof:
in the experiment, three main factors influencing the melt polycondensation process are determined, three levels of the three factors are determined through a large number of experiments, 3 levels of the three factors are designed according to the center combination design principle of Box-Behnken, as shown in a table 2, and the experimental results are shown in a table 3.
TABLE 2 three-factor three-level table
TABLE 3 Box-Behnken test results
The Design expert statistical software is used for carrying out regression fitting on the table 3 test data through stepwise regression and carrying out variance analysis on the model, and the influence of each influencing factor on the molecular weight of the product poly-L-lactic acid is not a simple linear relation. Determining the optimal point of the three factors according to a response surface diagram and contour line analysis, selecting the starting point in the model range, optimizing by using a rapid rise method according to the model, and finally determining that the maximum poly-L-lactic acid molecular weight is 3.9 multiplied by 10 when the temperature is A10h, B180 ℃ and C60rpm4。
In order to test the reliability of the design result of the Box-Behnken experiment, the optimized proportioning experiment is adopted for 10 times, and the average value of the molecular weight of the extracted poly-L-lactic acid is finally measured to be 3.8 multiplied by 104Relative error, compared to theoretical predictionLess than 2.5%. Therefore, the technological parameters of reaction time, reaction temperature and stirring speed obtained by Box-Behnken test design are accurate and reliable, have practical value and are the optimal technological parameters.
An optimized process for producing poly-L-lactic acid by melt polycondensation is obtained through the experiments: namely, the adding amount of the catalyst accounts for 0.35 percent of the mass of the lactic acid, the reaction pressure is 1600Pa, the reaction time is 10h, the reaction temperature is 180 ℃, and the stirring speed is 60 rpm.
1.2 solid phase polycondensation Process technical study
Because the molecular weight of the poly-L-lactic acid generated by melt polycondensation is relatively low, the poly-L-lactic acid with higher molecular weight can be prepared by adding a solid phase polycondensation process on the basis of melt polycondensation. Because the conventional solid phase polycondensation reaction time is longer, the invention adopts a pre-crystallization method to shorten the molecular weight distribution of the melt polycondensation product, thereby improving the production efficiency.
1.2.1 Effect of Pre-crystallization time on molecular weight of solid phase polycondensation product
The effect of different pre-crystallization times on the molecular weight of the final product poly-L-lactic acid was tested under the same solid phase polycondensation and other conditions, and the results are shown in FIG. 5.
As can be seen from FIG. 5, with the increase of the pre-crystallization time, the molecular weight of poly L-lactic acid, which is a solid phase polycondensation product, gradually increases under the same conditions, and when the pre-crystallization time is longer than 2 hours, the molecular increase is slow, which indicates that the degree of crystallization of the melt polycondensation product tends to be perfect, and the pre-crystallization time 2 hours is selected as the optimum parameter in view of the production efficiency.
1.2.2 Effect of Pre-crystallization temperature on prepolymer molecular weight
The effect of the precrystallisation temperature on the molecular weight of poly-L-lactic acid formed by the solid phase polycondensation was examined under otherwise identical conditions and the results are shown in FIG. 6.
As can be seen from FIG. 6, in the range of 90 to 120 ℃, the molecular weight of poly L-lactic acid, which is a solid phase polycondensation product, tends to increase with the increase of the pre-crystallization temperature, and the increase of the temperature promotes the growth of crystals, thereby facilitating the progress of the polycondensation reaction. When the temperature is more than 105 ℃, the molecular weight of poly-L-lactic acid is less increased because reactants are bonded into a mass in this temperature range, which is not favorable for increasing the molecular weight, and this is also the reason for the long time of conventional solid phase polycondensation. Therefore, the optimum pre-crystallization temperature is selected to be 105 ℃ in consideration of the production efficiency.
1.2.3 Effect of reaction temperature on molecular weight of solid phase polycondensation product
The prepolymer after pre-crystallization is quickly raised to a proper temperature, and the molecular weight growth trend of the product poly-L-lactic acid can be kept, so that the solid phase polycondensation time is reduced. The effect of different reaction temperatures on the molecular weight of the solid phase polycondensation product was examined and the results are shown in FIG. 7.
As can be seen from fig. 7, the reason why the product poly L-lactic acid increases and then decreases with the increase of the reaction temperature is that the reactivity of the terminal group segment increases with the increase of the reaction temperature, which is advantageous for the solid phase reaction, but too high a temperature causes degradation reaction of poly L-lactic acid and fusion bonding of particles, which results in a decrease in the molecular weight of poly L-lactic acid. In combination, 155 ℃ is selected as the optimal reaction temperature for solid phase polycondensation.
1.2.4 Effect of reaction time on molecular weight of solid phase polycondensation product
The effect of the reaction temperature on the molecular weight of the solid phase polycondensation product poly L-lactic acid was examined under the same conditions at a reaction temperature of 155 ℃ and the results are shown in FIG. 8.
As is clear from FIG. 8, the molecular weight of poly L-lactic acid gradually increased with the increase of the reaction time, and when the reaction time exceeded 15 hours, the thermal degradation reaction of poly L-lactic acid started to rise, and the molecular weight increased slowly. Considering the reaction time of 15h, the molecular weight of the obtained product can meet the application requirements, and selecting the solid phase polycondensation reaction time of 15h as the optimal process parameter by combining the production efficiency.
2 Poly L-lactic acid Synthesis Main control parameters
As can be seen from the pilot plant experiments for selecting and optimizing various process indexes, the main control parameters of the synthesis of poly-L-lactic acid are shown in Table 4.
Table 4 summary of major process control parameters
Results for pilot plant products
TABLE 5 continuous run results of pilot plant test
From the pilot test results of 10 batches of continuous operation, the important indexes of the product poly-L-lactic acid, such as molecular weight, melting point, thermal decomposition point, crystallinity, and the like, are stable and the quality is reliable. The trial production practice proves that the technology has the characteristics of high yield, good quality, low cost and the like, and completely has the conditions of industrial tests.
4 comparing the pilot test result with the similar advanced technology at home and abroad
The project breaks through the technical bottlenecks of poor thermal stability, low isotacticity and crystallinity and the like of the poly-L-lactic acid, and improves the overall technical level of the poly-L-lactic acid in China. The main technical indexes are compared with the advanced technical indexes at home and abroad and are shown in the table 6.
TABLE 6 comparison of project technology products with advanced technology at home and abroad
Note: the product technology of the national and foreign countries is the product technology of the national Nature Works and the product technology of a certain company.
5. Cost analysis
Based on the completed pilot test, we analyzed the production cost of the key technology of the new biodegradable polymer material, and see table 7:
TABLE 7 direct material consumption cost accounting (calculated according to 1 ton of poly-L-lactic acid product)
| Serial number | Product and Material names | Unit consumption | Univalent (yuan) | Cost (Yuan) |
| 1 | 90% common L-lactic acid (/ T) | 1.53 | 6090 | 9317.70 |
| 2 | Catalyst (/ kg) | 5.94 | 91.8 | 545.29 |
| 3 | Steam (/ T) | 3.2 | 130 | 416.00 |
| 4 | Water (/ T) | 6 | 4 | 24.00 |
| 5 | Electric (/ KWh) | 650 | 0.5 | 325.00 |
| 6 | Package (I) | 470.00 | ||
| Total up to | 11097.99 |
Compared with the market polymerization-grade L-lactic acid, the cost of material consumption of each ton of raw material can be reduced by 3100 yuan.
The project industrialization expects the production scale of 1 ten thousand tons of poly L-lactic acid every year, 17500 ten thousand yuan of sales income (the market price of the current like products is 19000 yuan-25000 yuan/ton) can be newly increased every year, and 4148 ten thousand yuan of profit is newly added. The produced poly-L-lactic acid product can meet the domestic market demand and can be exported to a plurality of countries and regions in the world, and the product is expected to occupy more than 40% of the domestic market share and more than 8% of the world market share.
Second part of the research on the preparation of L-lactic acid oligomers Using L-lactic acid monomers
Example 1
A method for producing poly-L-lactic acid by utilizing L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation comprises the following steps:
(1) preparing raw materials: the optical purity of the L-lactic acid produced by the applicant is greater than or equal to 99.5% in a 45 wt% L-lactic acid solution;
(2) dehydrating and oligomerizing to obtain L-lactic acid oligomer;
adding ethyl pyruvate into the L-lactic acid solution, and stirring to obtain a mixed solution, wherein the volume ratio of the ethyl pyruvate to the L-lactic acid solution is 1: 1;
simultaneously, cobalt oxide and di-cysteine methyl ester vanadyl are added into the mixed solution as catalysts according to the following steps:
initial reaction (0 h): the mass ratio of the added cobalt oxide to the added di-cysteine methyl ester vanadyl is 1:1.5, and the addition amount of the cobalt oxide in the initial reaction is 1/2 of the total addition amount of the cobalt oxide; the reaction temperature was kept at 5 ℃ from the initial reaction to the time when one-half of the reaction time elapsed; stirring;
when the reaction time is one half (2 h): adding all the residual di-cysteine methyl ester vanadyl into a reaction kettle; the reaction temperature is kept at 15 ℃ from one half of the reaction time to three quarters of the reaction time; stirring;
three quarters of the reaction time had elapsed (3 h): adding the rest cobalt oxide into the reaction kettle; the reaction temperature is kept at 25 ℃ from three quarters of the reaction time to the end of the reaction; and (4) stirring.
The usage amount of the cobalt oxide is 0.02 percent of the mass of the L-lactic acid, and the usage amount of the di-cysteine methyl ester vanadyl is 0.04 percent of the mass of the L-lactic acid; the preparation method of di-cysteine methyl ester vanadyl comprises the following steps: mixing and stirring cysteine methyl ester and vanadyl sulfate in boric acid solution at room temperature, and reacting for 3-5h to obtain purple solid; the quantity ratio of the cysteine methyl ester to the vanadyl sulfate substance is 5:1, and the concentration of the cysteine methyl ester in the boric acid solution is 2 mol/L.
After the reaction is finished, filtering, standing for layering, separating out an organic phase, and washing the organic phase with water; and (3) carrying out vacuum distillation on the organic phase after washing with water to remove the solvent, thus obtaining a white solid, and carrying out fast atom bombardment mass spectrum and nuclear magnetic detection on the obtained white solid, wherein the white solid is the L-lactic acid oligomer of the 6-19 polymer, and the yield of the L-lactic acid oligomer is 95%.
Example 2
A method for producing poly-L-lactic acid by utilizing L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation comprises the following steps:
(1) preparing raw materials: the optical purity of the L-lactic acid produced by the applicant is greater than or equal to 99.5% in a 60 wt% L-lactic acid solution;
(2) dehydrating and oligomerizing to obtain L-lactic acid oligomer;
adding ethyl pyruvate into the L-lactic acid solution, and stirring to obtain a mixed solution, wherein the volume ratio of the ethyl pyruvate to the L-lactic acid solution is 1: 1; adding cobalt oxide and di-cysteine methyl ester vanadyl as catalysts into the mixed solution; the using amount of the cobalt oxide is 0.04 percent of the mass of the L-lactic acid, the using amount of the di-cysteine methyl ester vanadyl is 0.08 percent of the mass of the L-lactic acid, and the mixture is stirred and reacted for 3 hours at room temperature; the preparation method of di-cysteine methyl ester vanadyl comprises the following steps: mixing and stirring cysteine methyl ester and vanadyl sulfate in boric acid solution at room temperature, and reacting for 3-5h to obtain purple solid; the quantity ratio of the cysteine methyl ester to the vanadyl sulfate substance is 5:1, and the concentration of the cysteine methyl ester in the boric acid solution is 0.5 mol/L.
After the reaction is finished, filtering, standing for layering, separating out an organic phase, and washing the organic phase with water; carrying out vacuum distillation on the organic phase after washing with water to remove the solvent, thus obtaining a white solid, and carrying out fast atom bombardment mass spectrum and nuclear magnetic detection on the obtained white solid, wherein the white solid contains L-lactic acid oligomer of 6-19 polymers and L-lactic acid oligomer of 30-50 polymers; the yield of L-lactic acid oligomer was 82%.
Example 3
A method for producing poly-L-lactic acid by utilizing L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation comprises the following steps:
(1) preparing raw materials: the optical purity of the L-lactic acid produced by the applicant is greater than or equal to 99.5% in a 50 wt% L-lactic acid solution;
(2) dehydrating and oligomerizing to obtain L-lactic acid oligomer;
adding ethyl pyruvate into the L-lactic acid solution, and stirring to obtain a mixed solution, wherein the volume ratio of the ethyl pyruvate to the L-lactic acid solution is 1: 1;
simultaneously, cobalt oxide and di-cysteine methyl ester vanadyl are added into the mixed solution as catalysts according to the following steps:
initial reaction (0 h): the mass ratio of the added cobalt oxide to the added di-cysteine methyl ester vanadyl is 1:1.5, and the addition amount of the cobalt oxide in the initial reaction is 1/2 of the total addition amount of the cobalt oxide; the reaction temperature was kept at 10 ℃ from the initial reaction to the time when one-half of the reaction time elapsed; stirring;
when the reaction time was one-half (3 h): adding the rest cobalt oxide into the reaction kettle; the reaction temperature is kept at 15 ℃ from one half of the reaction time to three quarters of the reaction time; stirring;
three quarters of the reaction time had elapsed (4.5 h): adding all the residual di-cysteine methyl ester vanadyl into a reaction kettle; the reaction temperature is kept at 30 ℃ from three quarters of the reaction time to the end of the reaction; and (4) stirring.
The usage amount of the cobalt oxide is 0.03 percent of the mass of the L-lactic acid, and the usage amount of the di-cysteine methyl ester vanadyl is 0.06 percent of the mass of the L-lactic acid; the preparation method of di-cysteine methyl ester vanadyl comprises the following steps: mixing and stirring cysteine methyl ester and vanadyl sulfate in boric acid solution at room temperature, and reacting for 3-5h to obtain purple solid; the quantity ratio of the cysteine methyl ester to the vanadyl sulfate substance is 5:1, and the concentration of the cysteine methyl ester in the boric acid solution is 1 mol/L.
After the reaction is finished, filtering, standing for layering, separating out an organic phase, and washing the organic phase with water; and (3) carrying out vacuum distillation on the organic phase after washing with water to remove the solvent, thus obtaining a white solid, and carrying out fast atom bombardment mass spectrum and nuclear magnetic detection on the obtained white solid, wherein the white solid is the L-lactic acid oligomer of the 6-40 polymer, and the yield of the L-lactic acid oligomer is 90%.
It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it will be obvious to those skilled in the art that other variations or modifications may be made on the basis of the above description, and all embodiments may not be exhaustive, and all obvious variations or modifications may be included within the scope of the present invention.
Claims (6)
1. The method for producing poly-L-lactic acid by utilizing L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation is characterized by comprising the following steps:
(1) preparing L-lactic acid oligomer by using L-lactic acid;
in the step (1), the method for preparing L-lactic acid oligomer using L-lactic acid is as follows:
(1-1) preparation of raw materials: 40-60 wt% of L-lactic acid solution, the optical purity of the L-lactic acid is more than or equal to 99.5%;
(1-2) performing dehydration oligomerization to obtain an L-lactic acid oligomer;
adding ethyl pyruvate into the L-lactic acid solution, wherein the volume ratio of the ethyl pyruvate to the L-lactic acid solution is 0.5-1: 1; simultaneously adding cobalt oxide and di-cysteine methyl ester vanadyl as catalysts into the mixed solution, and stirring; the usage amount of the cobalt oxide is 0.02-0.04 percent of the mass of the L-lactic acid, and the usage amount of the di-cysteine methyl ester vanadyl is 0.04-0.08 percent of the mass of the L-lactic acid; the reaction time is 3-6 h, and the reaction temperature is 5-30 ℃;
(2) adding an L-lactic acid oligomer and a melt polycondensation catalyst into a melt polycondensation reaction kettle, and carrying out melt polycondensation to prepare low molecular weight poly-L-lactic acid, wherein the addition amount of the melt polycondensation catalyst is 0.1-1% of the mass amount of the L-lactic acid oligomer; the melt polycondensation catalyst is prepared by uniformly mixing a component A and a component B according to the mass ratio of 1: 2-5;
the preparation method of the component A comprises the following steps: adding diacetyl tartaric acid monoglyceride and diglyceride into 50-60 deg.C water at a mass ratio of diacetyl tartaric acid monoglyceride and water of 1-5:100, stirring for 5-30 min, and adding Mn (H)2PO4 )2，Mn(H2PO4 )2Stirring the mixture and water at a mass ratio of 5-10:100 at 50-60 ℃ for 2-3 hours, heating to 80-100 ℃, and evaporating to dryness to obtain a component A;
the preparation method of the component B comprises the following steps: adding N- [ N- (3, 3-dimethylbutyl) -L-alpha-aspartyl ] -L-phenylalanine-1-methyl ester into water at the temperature of 20-30 ℃, wherein the mass ratio of the N- [ N- (3, 3-dimethylbutyl) -L-alpha-aspartyl ] -L-phenylalanine-1-methyl ester to the water is 5-12:1000, and stirring for 5-30 minutes; adding disodium stannous citrate with the mass ratio of 10-15:1000 to water, and stirring for 5-10 minutes; heating to 80-100 deg.C, and evaporating to obtain component B;
(3) adding low molecular weight poly-L-lactic acid into a solid phase polycondensation reaction kettle, and carrying out solid phase polycondensation to prepare high molecular weight poly-L-lactic acid.
2. The method for producing poly-L-lactic acid by oligomerization, melt polycondensation and solid-phase polycondensation using L-lactic acid as claimed in claim 1, wherein the reaction pressure of the melt polycondensation is 500-2000Pa, the reaction time is 4-50h, the reaction temperature is 150-200 ℃, and the stirring speed is 30-100 rmp.
3. The method for producing poly-L-lactic acid by using L-lactic acid through oligomerization, melt polycondensation and solid-phase polycondensation according to claim 1, wherein the low molecular weight poly-L-lactic acid is first pre-crystallized in the solid-phase polycondensation at a pre-crystallization temperature of 90 to 120 ℃ for 1 to 5 hours; the reaction temperature of the pre-crystallized low molecular weight poly-L-lactic acid is 140-180 ℃ and the reaction time is 5-30 h.
4. The method for producing poly-L-lactic acid by oligomerization, melt polycondensation and solid-phase polycondensation using L-lactic acid according to claim 1, wherein in step (1-2):
initial reaction: the mass ratio of the added cobalt oxide to the added di-cysteine methyl ester vanadyl is 1:1.5, and the addition amount of the cobalt oxide in the initial reaction is 1/2 of the total addition amount of the cobalt oxide; the reaction temperature is kept between 5 and 10 ℃ from the initial reaction to the time when one half of the reaction time is passed;
when the reaction time is one-half elapsed: adding all the residual di-cysteine methyl ester vanadyl into a reaction kettle; the reaction temperature is kept between 15 and 20 ℃ from one half of the reaction time to three quarters of the reaction time;
three quarters of the time elapsed: adding the rest cobalt oxide into the reaction kettle; the reaction temperature is kept between 25 and 30 ℃ from the end of the reaction to the end of the reaction after three quarters of the reaction time.
5. The method for producing poly-L-lactic acid by using L-lactic acid through oligomerization, melt polycondensation and solid phase polycondensation according to claim 4, wherein in the step (1-2), the di-cysteine methyl ester vanadyl is prepared by: mixing and stirring cysteine methyl ester and vanadyl sulfate in boric acid solution at room temperature, and reacting for 3-5h to obtain purple solid; the amount ratio of the cysteine methyl ester to the vanadyl sulfate substance is 5:1, and the concentration of the cysteine methyl ester in the boric acid solution is 0.1-5 mol/L.
6. The method for producing poly-L-lactic acid by using L-lactic acid through oligomerization, melt polycondensation and solid-phase polycondensation according to claim 5, wherein in the step (1-2), after the reaction is completed, the mixture is filtered, allowed to stand for layering, the organic phase is separated, and the organic phase is washed with water; and (3) carrying out vacuum distillation on the organic phase after washing by water to remove the solvent, thus obtaining a white solid, namely the L-lactic acid oligomer.
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| CN1295264C (en) * | 2004-07-15 | 2007-01-17 | 合肥工业大学 | Method for preparing high molecular weight poly-L-lactic acid by melt polycondensation-solid phase polymerization |
| CN1951902A (en) * | 2005-10-21 | 2007-04-25 | 江苏九鼎集团有限公司 | Preparation process of lactic acid oligomer |
| CN102040730B (en) * | 2009-10-13 | 2012-05-30 | 中国石油化工股份有限公司 | Melt/solid state polycondensation preparation method for polylactic acid |
| CN103254411A (en) * | 2013-06-07 | 2013-08-21 | 北京理工大学 | Method for preparing high-molecular-weight polylactic acid through direct polycondensation and chain extension |
| KR101711096B1 (en) * | 2014-11-27 | 2017-02-28 | 한국화학연구원 | Method for preparing stereo multi-block polylactic acid using pelletized prepolymer |
| CN107118200B (en) * | 2016-02-24 | 2020-02-28 | 香港纺织及成衣研发中心有限公司 | Method for catalytically synthesizing lactide by using lactic acid |
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