JP4048764B2 - Method for producing lactide using fermented lactic acid as raw material and method for producing polylactic acid - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a method for producing lactide using fermented lactic acid as a raw material, a method for producing polylactic acid, a method for producing lactide from ammonium lactate obtained by lactic acid fermentation, and a method for producing polylactic acid.The
[0002]
Lactic acid includes L-lactic acid, D-lactic acid, and a mixture of L-lactic acid and D-lactic acid. Lactide is a cyclic dimer of lactic acid and is particularly useful as a raw material for producing polylactic acid. Polylactic acid is a polymer mainly composed of lactic acid, and includes not only homopolymers but also copolymers with other monomers. Polylactic acid is useful as a biodegradable plastic made from biomass.
[0003]
[Prior art]
Conventionally, polylactic acid has been produced by direct dehydration condensation from lactic acid, dealcoholization condensation from lactic acid ester, or ring-opening polymerization of lactide.
[0004]
As for the production of polylactic acid from lactic acid esters, for example, US Pat. No. 2,534,255 discloses a process for producing hydroxypolyesters from hydroxycarboxylic acid esters in the presence of an esterification catalyst.
[0005]
JP-A-7-173264 discloses a method for producing polylactic acid having a weight average molecular weight of 15,000 or more by condensing lactic acid esters. Synthesis of lactide from the polymer is not described. It takes a lot of time to make polylactic acid having a weight average molecular weight of 15,000 or more.
[0006]
Japanese Patent No. 3024907 discloses polycondensation of lactic acid ester while removing alcohol produced in a batch reactor, and further polycondensation of the resulting oligomer while removing alcohol produced in a screw type extruder. And a method for producing polylactic acid is disclosed. Synthesis of lactide from the polymer is not described.
[0007]
JP-A-10-36366 discloses a method of synthesizing a lactic acid ester from synthetic lactic acid (DL-lactic acid), de-alcoholizing it to synthesize a lactic acid oligomer, and then synthesizing lactide.
[0008]
In JP-A-11-209370, a lactic acid ester is dealcoholized in the presence of a monobutyltin compound to obtain a composition containing polylactic acid or polylactic acid and lactide, and then the composition is added in the presence of a monobutyltin compound. A method for producing lactide by heating at a temperature is disclosed.
[0009]
In addition, it has been known for a long time that ammonium lactate is directly esterified with alcohol (INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 44, NO.9, 2189-2191, Sept. 1957).
[0010]
In JP-A-6-31886, butanol or pentanol is added to ammonium lactate produced by fermentation, a mineral acid is added in the later stage of the reaction to further advance the reaction, and ammonia is recovered and lactate is recovered. A method is disclosed.
[0011]
Japanese Patent No. 2830896 discloses a method of producing lactic acid from an oligomer having a high degree of polymerization by synthesizing lactic acid oligomer having a high degree of polymerization while oligomerizing lactic acid as a raw material and refluxing the oligomer. ing. There is no disclosure of a method of polycondensation using lactic acid ester while refluxing monomers and oligomers.
[0012]
[Problems to be solved by the invention]
Thus, lactic acid oligomers from fermented lactic acid are used as raw materials to synthesize lactic acid oligomers, and lactide is produced by depolymerization of lactic acid oligomers, and lactic acid oligomers from fermented lactic acid are used as raw materials to synthesize lactic acid oligomers. There is no known method for producing lactide by depolymerization of an oligomer and producing polylactic acid from this lactide.
[0013]
In addition, in the synthesis of lactic acid esters from lactic acid fermentation, it is not known that lactic acid and ethanol are produced by hetero type lactic acid fermentation while neutralizing with ammonia, and this lactic acid is esterified. Heterolactic acid bacteria produce lactic acid and ethanol from glucose, and produce lactic acid and acetic acid from xylose.
[0014]
Conventionally, lactic acid is produced by fermenting hexose (glucose) and sucrose (composed of glucose and fructose) with lactic acid, neutralizing with calcium carbonate, concentrating, precipitating calcium lactate, and releasing it with sulfuric acid. The crude lactic acid was further converted into an ester with methanol or ethanol, and after distillation, the ester was hydrolyzed to obtain lactic acid. This method has a problem that a large amount of calcium sulfate is produced as a by-product.
[0015]
Therefore, a method of neutralizing with ammonia water or ammonia during lactic acid fermentation to obtain ammonium lactate, distilling it into a lactate ester with alcohol, recovering ammonia, and hydrolyzing the lactate ester has been developed.
[0016]
Traditionally, there has been no consistent process for producing polylactic acid from biomass. By completing a consistent process, the cost of producing polylactic acid can be reduced. That is, conventionally, since the production of lactic acid and the production of polylactic acid were considered separately, there were many useless processes. Specifically, the useless process is a process of hydrolyzing a lactic acid ester into lactic acid. Moreover, by synthesizing polylactic acid from lactic acid ester, the corrosion resistance of the reactor is relaxed, which can greatly contribute to capital investment. Lactic acid is corrosive, and in particular when it exceeds 140 ° C., a reactor or piping made of titanium, tantalum, or glass lining is required for concentration or synthesis of lactide. However, when lactate is used, it is not necessary to use a corrosion-resistant material for the reactor, and the cost of the equipment can be greatly reduced.
[0017]
In particular, the use of woody biomass is currently a global problem. In Japan, there are problems with waste disposal such as waste paper, building waste, thinned wood, and rice straw. Overseas, there is a trend of using wood as a raw material for fermentation, which is not directly human food.
[0018]
Woody biomass contains cellulose and hemicellulose, and methods for saccharifying this biomass include the sulfuric acid method, the high-pressure hydrothermal method, and the enzymatic method. Saccharides obtained by saccharification are hexose and pentose. The hexose is mainly glucose, and the pentose is mainly xylose.
[0019]
One mole of glucose becomes 2 moles of lactic acid by homo-type lactic acid fermentation, and there is no waste of carbon. In addition, some lactic acid bacteria produce 5 mol of lactic acid from 3 mol of xylose. Also, 1 mol of glucose becomes 1 mol of lactic acid and 1 mol of ethanol by hetero-type lactic acid fermentation (in this case, 1 mol of carbon dioxide gas is generated). That is, glucose is a very suitable raw material for synthesizing lactic acid esters.
[0020]
On the other hand, according to hetero-type lactic acid fermentation, 1 mol of lactic acid and 1 mol of acetic acid are produced from 1 mol of xylose. Therefore, in the present invention, heterolactic fermentation is carried out while neutralizing with ammonia, and the produced alcohol (ethanol) ester of lactic acid and acetic acid is synthesized and taken out from the fermentation broth as acetate ester and lactate ester.
[0021]
When ethyl lactate is produced by reacting ammonium lactate and ethanol, there is a problem that the yield is low and the reaction is slow because the boiling point of ethanol at normal pressure is as low as 78 ° C.
[0022]
When a lactate ester is produced by reacting a hydrophobic alcohol such as butanol with ammonium lactate, the yield is as low as about 50% even if water is removed by a separator.
[0023]
  An object of the present invention is to provide a method for consistently producing lactide from ammonium lactate obtained by lactic acid fermentation and a method for consistently producing polylactic acid from ammonium lactate obtained by lactic acid fermentation.The
[0024]
[Means for Solving the Problems]
  The present inventionIncludes the following inventions.
[1] (1) Culturing a microorganism that conducts heterolactic fermentation in a medium containing hexasaccharides while controlling the pH with ammonia to produce ammonium lactate and ethanol,
  Ammonium lactate and alcohol are reacted to synthesize lactate ester and to recover ammonia,
  (2) The above lactic acid ester is polycondensed in the presence of a catalyst other than monobutyltin to synthesize polylactic acid (lactic acid prepolymer) having a weight average molecular weight of less than 15,000,
  (3) A method for producing lactide, wherein the polylactic acid is depolymerized to produce lactideLaw.
[0025]
[2] (1) Culturing a microorganism that conducts heterolactic fermentation in a medium containing hexasaccharides while controlling the pH with ammonia to produce ammonium lactate and ethanol,
  Ammonium lactate is reacted with an alcohol other than a C 4 or 5 alcohol to synthesize a lactate ester and recover ammonia.
  (2) The lactic acid ester is polycondensed in the presence of a catalyst other than monobutyltin to synthesize polylactic acid (lactic acid prepolymer) having a weight average molecular weight of less than 15,000,
  (3) A method for producing lactide, wherein the polylactic acid is depolymerized to produce lactide.
[0028]
in frontIn step (1), the aqueous ammonium lactate solution obtained by lactic acid fermentation and water and alcohol having 4 or more carbon atoms separated into two layers are reacted in a reactor while refluxing,
  At least a part of the condensed water and alcohol is stored in a separator, at least a part of the lower layer water stored in the separator is discharged, fresh water is added to the separator, and at least a part of the upper layer alcohol is added. Return to the reactor and repeat this series of operations.
  Synthesize lactic acid ester and recover ammoniaMay be.
[0029]
in frontIn the step (1), an aqueous solution of ammonium lactate obtained by lactic acid fermentation and water and an alcohol having 4 or more carbon atoms separated into two layers are reacted in a reactor while being refluxed, and a part or all of the alcohol is successively added. Is distilled, and new alcohol is added to the reactor to synthesize lactate and recover ammonia.May be.
[0030]
[3]  In the step (2), the lactic acid ester is polycondensed to obtain a lactic acid prepolymer, and the resulting alcohol is recovered.[1] or [2]A method for producing lactide according to claim 1.
[0031]
[4] (1) Culturing a microorganism that performs heterolactic fermentation in a medium containing pentose while controlling the pH with ammonia to produce ammonium lactate and ammonium acetate,
  Ammonium lactate and ammonium acetate are reacted with ethanol to synthesize ethyl lactate and ethyl acetate, and ammonia is recovered.
  Ethyl acetate is removed by distillation,
  (2) The polylactic acid (ethyl lactate) is polycondensed in the presence of a catalyst other than monobutyltin to obtain polylactic acid (lactic acid prepolymer) having a weight average molecular weight of less than 15,000, and the resulting ethanol is recovered,
  (3) A method for producing lactide, wherein the polylactic acid is depolymerized to produce lactide.
[0032]
[5] (1) Culturing a microorganism that performs heterolactic fermentation in a medium containing pentose and hexose while controlling the pH with ammonia to produce ammonium lactate, ethanol, and ammonium acetate,
  Ammonium lactate and ammonium acetate are reacted with ethanol to synthesize ethyl lactate and ethyl acetate, and ammonia is recovered.
  Ethyl acetate is removed by distillation,
  (2) The polylactic acid (ethyl lactate) is polycondensed in the presence of a catalyst other than monobutyltin to obtain polylactic acid (lactic acid prepolymer) having a weight average molecular weight of less than 15,000, and the resulting ethanol is recovered,
  (3) A method for producing lactide, wherein the polylactic acid is depolymerized to produce lactide.
[0033]
[6] The process (2) The method for producing lactide according to any one of [1] to [5], wherein polycondensation is performed while refluxing polylactic acid (lactic acid prepolymer) which is a lactic acid ester and / or a polycondensate thereof.
[0034]
[7] Step (2) The method for producing lactide according to any one of the above [1] to [6], wherein in the step of polycondensing the lactic acid ester, the temperature of the reactor is successively increased.
[0038]
[8] The method according to any one of [1] to [7]A method for producing polylactic acid, in which lactide obtained by the lactide production method is subjected to ring-opening polymerization to obtain polylactic acidLaw.
[0039]
  Said process (1) In this case, ammonium lactate obtained by lactic acid fermentation and ethanol may be reacted under pressure.
[0040]
  Said process (1) In the reaction, ammonium lactate obtained by lactic acid fermentation and ethanol are reacted, and after completion of the reaction, ethanol and ethyl lactate are distilled off,
  Add ethanol to the remaining ammonium lactate solution, or add ethanol and ammonium lactate obtained by lactic acid fermentation to the remaining ammonium lactate solution, and react again with ammonium lactate and ethanol. May be repeated to synthesize ethyl lactate and recover ammonia.
[0043]
In the case of producing an ester by reacting ammonium lactate with ethanol, for example, a method in which 5 to 20 times mole of ethanol is added to ammonium lactate and the equilibrium is inclined toward the ester side can be considered.
[0044]
Furthermore, after distilling off ethanol and the produced ethyl lactate, the recovery rate of ethyl lactate can be increased by reacting the unreacted ammonium lactate remaining in the reactor with a new lactic acid fermentation broth and ethanol. it can.
[0045]
In this reaction, since the boiling point of ethanol is as low as 78 ° C., the reaction rate can be increased by increasing the vapor pressure of ethanol by applying pressure to increase the reaction temperature. Also in this case, the desorbed ammonia is taken out from the system through the pressure control valve. As a method of pressurization, a method of increasing by the vapor pressure of ethanol itself or a method of pressurizing with an inert gas such as nitrogen is preferable.
[0046]
In the method of reacting ammonium lactate and butanol while refluxing, when water is saturated in water separated from the reactor after being vaporized from the reactor, the ammonia accumulates in the upper butanol and the reaction slows down. . That is, the lower layer water in the separator is considered to play a role of extracting ammonia present in the upper butanol to the water side and reducing the amount of ammonia present in the butanol returning to the reactor. Therefore, by replacing the lower layer water accumulated in the separator with new water, the ammonia in the upper butanol is extracted into this new water, and the butanol having a reduced ammonia content is returned to the reactor. The reaction proceeds further.
[0047]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an outline of the steps of the lactide production method or polylactic acid production method of the present invention. FIG. 2 is a diagram showing an outline of the steps of the method for producing lactide or the method for producing polylactic acid according to the present invention in the case of performing hexa-monosaccharide heterolactic fermentation. FIG. 3 is a diagram schematically showing the steps of the lactide production method or polylactic acid production method of the present invention when pentose heterolactic fermentation is performed.
[0048]
(1) Esterification / deammonia process of fermented lactic acid
In the lactide production method or polylactic acid production method of the present invention, fermented lactic acid is used. Lactic acid has optical isomers of L-lactic acid and D-lactic acid, but in the present invention, an ammonium salt or a mixture of either isomer may be used. The ratio of L-lactide / meso-lactide / D-lactide in the obtained lactide is determined according to the L / D ratio of the ammonium salt used, and the L-lactic acid unit / D-lactic acid in the polylactic acid obtained is also determined. Unit ratios are determined. Polylactic acid containing only L-lactic acid units or D-lactic acid units is crystallized to obtain a high melting point.
[0049]
Hexasaccharides such as glucose are converted from 1 mol of glucose to 1 mol of lactic acid and 1 mol of ethanol by heterolactic fermentation, and 1 mol of carbon dioxide gas is generated. Heterolactic fermentation is carried out while neutralizing with ammonia, and the produced ammonium lactate is esterified with alcohol (ethanol) to give lactate ester (ethyl). Ammonia generated during esterification is recovered. Unreacted alcohol (ethanol) is distilled off, and lactic acid ester (ethyl) is purified.
[0050]
Pentasaccharides such as xylose produce 1 mol of lactic acid and 1 mol of acetic acid from 1 mol of xylose by heterolactic fermentation. Heterolactic fermentation is carried out while neutralizing with ammonia to produce ammonium lactate and ammonium acetate. Ammonium lactate and ammonium acetate are esterified with ethanol to give ethyl lactate and ethyl acetate. Ammonia generated during esterification is recovered. Unreacted ethanol is distilled off, and ethyl lactate is purified by distillation, and ethyl acetate is removed and recovered. Ethyl acetate is useful as a solvent.
[0051]
Woody biomass contains cellulose and hemicellulose, and hexasaccharide and pentose can be obtained by saccharification. As described above, normally, saccharified wood is mixed with hexose such as glucose and pentose such as xylose. This may be purified by chromatographic separation or the like, and heterolactic fermentation may be performed as described above using hexose or pentose as a starting material. Alternatively, it is even better if it can be used as it is as a mixture of hexose and pentose.
[0052]
Therefore, heterolactic fermentation may be performed on a mixture containing hexa- and pentoses. Heterolactic fermentation is carried out while neutralizing with ammonia, ammonium lactate and ethanol are produced from hexose, and ammonium lactate and ammonium acetate are produced from pentose. Ammonium lactate and ammonium acetate are esterified with ethanol (additionally if ethanol obtained by fermentation is not enough) to obtain ethyl lactate and ethyl acetate. Ammonia generated during esterification is recovered. Unreacted ethanol is distilled off, and ethyl lactate is purified by distillation, and ethyl acetate is removed and recovered.
[0053]
In any of the above cases, when esterifying ammonium lactate, it is preferable to add 1 to 3 moles of alcohol to ammonium lactate. In particular, in the case of esterification using ethanol, it is also preferable to raise the reaction temperature by applying pressure. The reaction rate can be increased by increasing the reaction temperature. Furthermore, you may add strong acid, such as 0.1-3 times mole water and a catalytic amount of sulfuric acid with respect to ammonium lactate.
[0054]
Examples of microorganisms performing homo-type lactic acid fermentation include a part of Lactobacillus, Streptococcus, Rhizopus, Bacillus and the like. Examples of microorganisms that perform hetero-type lactic acid fermentation include a part of the genus Leuconostoc and Lactobacillus. L-lactic acid, D-lactic acid, and racemic DL-lactic acid can be obtained depending on the microorganism strain to be used. Therefore, the strain may be selected according to the intended use of polylactic acid.
[0055]
In this method, a lactic acid fermentation broth neutralized with aqueous ammonia may be used as a raw material as it is, or pretreated by a conventionally known method such as microorganism removal by centrifugation, activated carbon treatment, solvent extraction, electrodialysis, membrane filtration, etc. May be performed.
[0056]
(2) Polycondensation / dealcoholation process of lactic acid ester
The obtained lactic acid ester is heated to 130 to 220 ° C. and subjected to polycondensation under a reduced pressure of from normal pressure to about 5 mmHg, and a lactic acid oligomer having a weight average molecular weight of less than 15,000, preferably a weight average molecular weight of about 1000 to 3500. (Lactic acid prepolymer). The monomer and the lactic acid oligomer produced by the polycondensation are refluxed, and the alcohol (ethanol) is removed and recovered from the reaction system.
[0057]
In polycondensation, it is also preferable to gradually raise the temperature in stages. For example, the first stage is preferably 135 ± 3 ° C., the second stage is 150 ± 3 ° C., and the third stage is 160 ± 3 ° C. (Example 2). The polycondensation step may be further performed in multiple stages, or the temperature may be gradually gradually increased. For example, the first stage 135 ± 3 ° C., the second stage 150 ± 3 ° C., the third stage 160 ± 3 ° C., the fourth stage 180 ± 3 ° C., and the fifth stage 200 ± 3 ° C. Preferred (Example 3). It is also preferable to increase the reaction temperature by applying pressure. Further, a polymerization catalyst may be added. Under such conditions, a lactic acid oligomer having a weight average molecular weight of about 1000 to 3500 is obtained, the difference in boiling point from lactide is increased, and separation is facilitated.
[0058]
(3) Depolymerization and intramolecular esterification process of lactic acid oligomer
The obtained lactic acid oligomer is depolymerized and intramolecular esterified (cyclic dimerization) to produce lactide. Depolymerization is generated by heating the lactic acid oligomer to a temperature equal to or higher than the melting temperature of the lactic acid oligomer to be treated in the presence of a depolymerization catalyst other than monobutyltin, and reducing the pressure to a pressure equal to or lower than the vapor pressure of lactide at the above temperature. By distilling off the lactide. Usually, it is preferable to set it as 190-200 degreeC under the reduced pressure of 5-50 mmHg. By using a high vacuum apparatus, the yield of lactide is improved.
[0059]
As the polymerization catalyst or depolymerization catalyst, a catalyst comprising at least one metal or metal compound selected from the group consisting of groups IA, IIA, IIB, IVA, IVB, VA, and VIIA is used. be able to.
[0060]
Examples of those belonging to Group IA include alkali metal hydroxides (for example, sodium hydroxide, potassium hydroxide, lithium hydroxide), alkali metal and weak acid salts (for example, sodium lactate, sodium acetate, sodium carbonate). Sodium octylate, sodium stearate, potassium lactate, potassium acetate, potassium carbonate, potassium octylate, etc.), alkali metal alkoxides (eg sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, etc.) Can be mentioned.
[0061]
Examples of those belonging to Group IIA include calcium salts of organic acids (for example, calcium acetate).
[0062]
Examples of those belonging to Group IIB include zinc salts of organic acids (for example, zinc acetate).
[0063]
Examples of those belonging to the group IVA include organotin-based catalysts other than monobutyltin (for example, tin lactate, tin tartrate, tin dicaprylate, tin dilaurate, tin dipalmitate, tin distearate, tin dioleate, α -Tin naphthoate, tin β-naphthoate, tin octylate, etc.), and powdered tin.
[0064]
Examples of those belonging to Group IVB include titanium compounds such as tetrapropyl titanate and zirconium compounds such as zirconium isopropoxide.
[0065]
Examples of those belonging to Group VA include antimony compounds such as antimony trioxide.
[0066]
Examples of those belonging to the VIIA group include manganese salts of organic acids (such as manganese acetate).
[0067]
All of these are conventionally known polylactic acid polymerization catalysts, and among these, a catalyst comprising tin or a tin compound is particularly preferred from the viewpoint of activity.
[0068]
In the present invention, the catalyst is 10 of the lactic acid oligomer to be treated.^-FourIt is preferably used in an amount of -1.0% by weight. A more preferred amount is 0.001 to 0.01% by weight.
[0069]
(4) Ring opening polymerization process of lactide
The obtained lactide can be subjected to ring-opening polymerization by a known method to produce polylactic acid or a polylactic acid copolymer. For example, lactide is polymerized at 160 to 180 ° C. in the presence of a tin octylate catalyst. A high molecular weight polylactic acid having a weight average molecular weight of about 100,000 to 1,000,000 (GPC, converted to polystyrene) is obtained.
[0070]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples.
[Example 1]
(1) Esterification / deammonia process
A flask with a volume of 1000 ml equipped with a stirrer, a condenser, and a thermometer was charged with 472 g of an aqueous L-ammonium lactate solution (68%) and 500 g of ethanol, and the temperature of the reaction solution was kept at 90 to 100 ° C. Reflux for 3 hours and esterify. Ammonium generated at this time and not collected by the cooling pipe was collected in a washing bottle containing ice water provided at the tip of the cooling pipe. The recovery rate of ammonia was 98%.
[0071]
(2) Unreacted ethanol removal process
The temperature of the reaction solution obtained in (1) was kept at 80 ° C., and 360 g of unreacted ethanol was distilled off (collected). Subsequently, the reaction liquid temperature was raised to 120 ° C., and 150 g of water in the reaction liquid was distilled off.
[0072]
(3) Ethyl lactate purification process
The reaction solution obtained in (2) was decompressed to 50 mmHg, kept at a liquid temperature of 70 to 100 ° C., and simply distilled to obtain 351 g of purified L-ethyl lactate (yield 99.2%).
[0073]
(4) Ethyl lactate polycondensation process
Charge 236 g of purified L-ethyl lactate obtained in (3) and 1.18 g of tin octylate into a 500 ml flask equipped with a stirrer, cooling tube, thermometer and nitrogen introduction tube, keeping the liquid temperature at 160 ° C. The pressure under a nitrogen stream was gradually reduced from normal pressure to 200 mmHg over 5 hours, and 91 g of ethanol produced by polycondensation of L-ethyl lactate was distilled off. The polycondensate obtained by GPC had a weight average molecular weight of 3000.
[0074]
(5) Lactide production process
The reaction liquid obtained in (4) was maintained at a pressure of 5 mmHg and a liquid temperature of 200 ° C., and distilled to obtain 142.95 g of LL-lactide as the main fraction (yield 99.3%, purity 99.8%). .
[0075]
(6) Polymerization process
10 g of lactide obtained in (5) and 0.25 g of tin octylate were charged into a screw test tube, purged with nitrogen, sealed, and polymerized at 180 ° C. for 20 minutes. The obtained polylactic acid had a weight average molecular weight of 250,000 (GPC, polystyrene conversion).
[0076]
[Example 2]
(1) The esterification / deammonification step, (2) the unreacted ethanol removal step, and (3) the ethyl lactate purification step were carried out in the same manner as in Example 1.
[0077]
(4) Ethyl lactate polycondensation process
236 g of the purified L-ethyl lactate obtained in (3) was charged into a 500 ml flask equipped with a stirrer, a reflux tube and a thermometer, and the liquid temperature was raised stepwise from 135 ° C to 160 ° C. The pressure was gradually reduced from the pressure to 5 mmHg over 3 hours. During this period, the L-lactic acid oligomer produced by the polycondensation of L-ethyl lactate and L-ethyl lactate is refluxed into the flask, and the cooling water temperature of the reflux pipe is set to 10 in steps to take out the generated ethanol out of the system. The temperature was raised from 0 ° C to 60 ° C. 91 g of ethanol generated at this time was collected in a cold trap provided at the tip of the reflux tube. The polycondensate obtained by GPC had a weight average molecular weight of 2800.
[0078]
(5) Lactide production process
To the reaction solution (L-lactic acid oligomer) obtained in (4), 1.2 g of tin octylate was added, maintained at a pressure of 5 mmHg and a liquid temperature of 200 ° C., distilled, and 142.95 g of LL-lactide as the main fraction ( Yield 99.3%, purity 99.8%).
[0079]
(6) Polymerization process
10 g of lactide obtained in (5) and 0.25 g of tin octylate were charged into a screw test tube, purged with nitrogen, sealed, and polymerized at 180 ° C. for 20 minutes. The obtained polylactic acid had a weight average molecular weight of 250,000 (GPC, polystyrene conversion).
[0080]
[Example 3]
(1) The esterification / deammonification step, (2) the unreacted ethanol removal step, and (3) the ethyl lactate purification step were carried out in the same manner as in Example 1.
[0081]
(4) Ethyl lactate polycondensation process
236 g of the purified L-ethyl lactate (optical purity 99.7%) obtained in (3) was charged into a 500 ml flask equipped with a stirrer, a reflux tube and a thermometer, and the liquid temperature was changed from 135 ° C. to 220 ° C. at normal pressure. The L-lactic acid oligomer produced by the polycondensation of L-ethyl lactate and L-ethyl lactate was refluxed into the flask during this period, and a reflux tube was used to take out the generated ethanol out of the system. The cooling water temperature was set to 85 ° C.
Next, the pressure was gradually reduced from normal pressure to 5 mmHg over 3 hours. During this period, the L-lactic acid oligomer produced by the polycondensation of L-ethyl lactate is refluxed into the flask, and the temperature of the cooling water in the reflux tube is gradually increased from 10 ° C. to 60 ° C. in order to take out the generated ethanol out of the system. Raised. 91 g of ethanol generated at this time was collected in a cold trap provided at the tip of the reflux tube. The polycondensate obtained by GPC had a weight average molecular weight of 2800.
A part of this polycondensate was sampled and hydrolyzed with sodium hydroxide. The optical purity of L-lactic acid of lactic acid obtained by hydrolysis was 99.5%, and no decrease in optical purity was observed in the polycondensation step.
[0082]
(5) Lactide production process
To the reaction solution (L-lactic acid oligomer) obtained in (4), 1.2 g of tin octylate was added, maintained at a pressure of 5 mmHg and a liquid temperature of 200 ° C., distilled, and 142.95 g of LL-lactide as the main fraction ( Yield 99.3%, purity 99.8%).
[0083]
(6) Polymerization process
10 g of lactide obtained in (5) and 0.25 g of tin octylate were charged into a screw test tube, purged with nitrogen, sealed, and polymerized at 180 ° C. for 20 minutes. The obtained polylactic acid had a weight average molecular weight of 250,000 (GPC, polystyrene conversion).
[0084]
[Example 4]
5 L of a medium containing 500 g of glucose, 100 g of yeast extract and 100 g of polypeptone was sterilized by an autoclave, and Streptococcus faecalis was inoculated. The culture was performed at 37 ° C., and the pH was controlled to 7.0 with 6N ammonia water. The culture was completed in about 15 hours, the culture solution was concentrated, 1000 g of ethanol was added, and the temperature was maintained at 90 to 100 ° C. to reflux ethanol for 3 hours. Ammonium generated at this time and not collected by the cooling pipe was collected in a washing bottle containing ice water provided at the tip of the cooling pipe. The recovery rate of ammonia was 98%. The obtained reaction liquid was kept at 80 ° C., and 750 g of unreacted ethanol was distilled off (collected). Subsequently, the reaction solution was raised to 120 ° C., and 120 g of water in the reaction solution was distilled off.
[0085]
The obtained reaction liquid was decompressed to 50 mmHg, the liquid temperature was kept at 70 to 100 ° C., and simple distillation was performed to obtain 650 g of purified L-ethyl lactate.
[0086]
650 g of the obtained purified L-ethyl lactate and 3.3 g of tin octylate were charged into a 1000 ml flask equipped with a stirrer, a cooling tube, a thermometer, and a nitrogen introduction tube, and the liquid temperature was kept at 160 ° C. The pressure was gradually reduced from normal pressure to 200 mmHg over 5 hours, and 250 g of ethanol produced by polycondensation of L-ethyl lactate was distilled off. The polycondensate obtained by GPC had a weight average molecular weight of 3200.
[0087]
The obtained reaction liquid was maintained at a pressure of 5 mmHg and a liquid temperature of 200 ° C., and distilled to obtain 393 g of LL-lactide as a main fraction.
[0088]
10 g of the obtained LL-lactide and 0.25 g of tin octylate were charged into a screw test tube, purged with nitrogen, sealed, and polymerized at 180 ° C. for 20 minutes. The obtained polylactic acid had a weight average molecular weight of 200,000 (GPC, polystyrene conversion).
[0089]
[Example 5]
4 L of a medium containing 400 g of xylose derived from wood, 80 g of yeast extract, and 80 g of polypeptone was sterilized by an autoclave, and the genus Leuconostoc was inoculated. The culture was performed at 37 ° C., and the pH was controlled to 7.0 with 6N ammonia water. The culture was completed in about 25 hours, the culture solution was concentrated, 500 g of ethanol was added, and the temperature was maintained at 90 to 100 ° C. to reflux ethanol for 3 hours. Ammonium generated at this time and not collected by the cooling pipe was collected in a washing bottle containing ice water provided at the tip of the cooling pipe. The recovery rate of ammonia was 98%. The obtained reaction liquid was kept at 80 ° C., and 250 g of unreacted ethanol was distilled off. Subsequently, the reaction solution was raised to 120 ° C., and 75 g of water in the reaction solution was distilled off.
[0090]
The obtained reaction liquid was depressurized to 50 mmHg, kept at a liquid temperature of 70 to 100 ° C., and simply distilled to obtain 310 g of purified L-ethyl lactate and 230 g of ethyl acetate.
[0091]
The obtained purified L-ethyl lactate 310 g and tin octylate 1.5 g were charged into a 1000 ml flask equipped with a stirrer, a condenser, a thermometer, and a nitrogen inlet, and the liquid temperature was kept at 160 ° C. under a nitrogen stream. The pressure was gradually reduced from normal pressure to 200 mmHg over 5 hours, and 120 g of ethanol produced by polycondensation of L-ethyl lactate was distilled off. (120 g of new ethanol was obtained.) When measured by GPC, the polycondensate obtained had a weight average molecular weight of 2900.
[0092]
The obtained reaction liquid was distilled at a pressure of 4 mmHg and a liquid temperature of 210 ° C. to obtain 283 g of LL-lactide as a main fraction.
[0093]
10 g of the obtained LL-lactide and 0.25 g of tin octylate were charged into a screw test tube, purged with nitrogen, sealed, and polymerized at 180 ° C. for 20 minutes. The obtained polylactic acid had a weight average molecular weight of 190,000 (GPC, polystyrene conversion).
[0094]
[Example 6]
4 L of a medium containing 50 g of xylose derived from wood, 350 g of glucose, 80 g of yeast extract and 80 g of polypeptone was sterilized by an autoclave, and the genus Leuconostoc was inoculated. The culture was performed at 37 ° C., and the pH was controlled to 7.0 with 6N ammonia water. The culture was completed in about 30 hours, the culture solution was concentrated, 400 g of ethanol was added, the temperature was maintained at 90 to 100 ° C., and ethanol was refluxed for 3 hours. Ammonium generated at this time and not collected by the cooling pipe was collected in a washing bottle containing ice water provided at the tip of the cooling pipe. The recovery rate of ammonia was 97%. The obtained reaction liquid was kept at 80 ° C., and 426 g of unreacted ethanol was distilled off. Subsequently, the reaction solution was raised to 120 ° C., and 60 g of water in the reaction solution was distilled off.
[0095]
The obtained reaction liquid was decompressed to 50 mmHg, kept at a liquid temperature of 70 to 100 ° C., and simply distilled to obtain 260 g of purified L-ethyl lactate, 20 g of ethyl acetate, and 426 g of ethanol.
[0096]
260 g of the obtained purified L-ethyl lactate and 1.3 g of tin octylate were charged into a 1000 ml flask equipped with a stirrer, a condenser, a thermometer, and a nitrogen inlet, and the liquid temperature was kept at 160 ° C. under a nitrogen stream. The pressure was gradually reduced from normal pressure to 200 mmHg over 5 hours, and 100 g of ethanol produced by polycondensation of L-ethyl lactate was distilled off. The polycondensate obtained by GPC had a weight average molecular weight of 2500.
[0097]
The obtained reaction liquid was kept at a pressure of 5 mmHg and a liquid temperature of 200 ° C., and distilled to obtain 314 g of LL-lactide as a main fraction.
[0098]
10 g of the obtained LL-lactide and 0.25 g of tin octylate were charged into a screw test tube, purged with nitrogen, sealed, and polymerized at 180 ° C. for 20 minutes. The obtained polylactic acid had a weight average molecular weight of 220,000 (GPC, polystyrene conversion).
[0099]
  The present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. Further, all modifications belonging to the equivalent scope of the claims are within the scope of the present invention.
  [Example 1], [Example 2], [Example 3], and [Example 4] are reference examples.
[0100]
【The invention's effect】
  According to the present invention, a method for consistently producing lactide from ammonium lactate obtained by lactic acid fermentation and a method for consistently producing polylactic acid from ammonium lactate obtained by lactic acid fermentation are provided.The
[0101]
In this method, since ammonium lactate from fermented lactic acid is esterified as it is, an operation for converting lactate into a free form of lactic acid as in the conventional method is unnecessary. Therefore, the steps in lactide production and polylactic acid production are reduced, and lactide and polylactic acid can be produced at a lower cost.
[0102]
Further, since neutral ammonium lactate is used as a raw material in this method, acid-resistant ones such as titanium and glass are no longer required for the reaction vessel and various pipes. Therefore, since the lactic acid-free body is used as a raw material, investment in manufacturing equipment is small and economical compared to the conventional method which requires a corrosion-resistant reaction vessel and various pipes.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of the steps of a lactide production method or a polylactic acid production method of the present invention.
FIG. 2 is a diagram showing an outline of the steps of the method for producing lactide or the method for producing polylactic acid according to the present invention in the case of performing a hexasaccharide heterolactic fermentation.
FIG. 3 is a diagram showing an outline of the steps of the lactide production method or polylactic acid production method of the present invention when pentose heterolactic fermentation is performed.

Claims (8)

(1) A microorganism that performs heterolactic fermentation in a medium containing hexamonosaccharide is cultured while controlling the pH with ammonia to produce ammonium lactate and ethanol,
Ammonium lactate and alcohol are reacted to synthesize lactate ester and to recover ammonia,
(2) The above lactic acid ester is polycondensed in the presence of a catalyst other than monobutyltin to synthesize polylactic acid (lactic acid prepolymer) having a weight average molecular weight of less than 15,000,
(3) A method for producing lactide, wherein the polylactic acid is depolymerized to produce lactide. (1) Culturing a microorganism that conducts heterolactic fermentation in a medium containing hexasaccharides while controlling the pH with ammonia to produce ammonium lactate and ethanol,
Ammonium lactate is reacted with an alcohol other than a C 4 or 5 alcohol to synthesize a lactate ester and recover ammonia.
(2) The lactic acid ester is polycondensed in the presence of a catalyst other than monobutyltin to synthesize polylactic acid (lactic acid prepolymer) having a weight average molecular weight of less than 15,000,
(3) A method for producing lactide, wherein the polylactic acid is depolymerized to produce lactide. The method for producing lactide according to claim 1 or 2 , wherein, in the step (2), a lactic acid ester is polycondensed to obtain a lactic acid prepolymer, and the resulting alcohol is recovered. (1) Culturing a microorganism that performs heterolactic fermentation in a medium containing pentose while controlling the pH with ammonia to produce ammonium lactate and ammonium acetate,
Ammonium lactate and ammonium acetate are reacted with ethanol to synthesize ethyl lactate and ethyl acetate, and ammonia is recovered.
Ethyl acetate is removed by distillation,
(2) The polylactic acid (ethyl lactate) is polycondensed in the presence of a catalyst other than monobutyltin to obtain polylactic acid (lactic acid prepolymer) having a weight average molecular weight of less than 15,000, and the resulting ethanol is recovered,
(3) A method for producing lactide, wherein the polylactic acid is depolymerized to produce lactide. (1) Culturing a microorganism that performs heterolactic fermentation in a medium containing pentose and hexose while controlling the pH with ammonia to produce ammonium lactate, ethanol, and ammonium acetate,
Ammonium lactate and ammonium acetate are reacted with ethanol to synthesize ethyl lactate and ethyl acetate, and ammonia is recovered.
Ethyl acetate is removed by distillation,
(2) The polylactic acid (ethyl lactate) is polycondensed in the presence of a catalyst other than monobutyltin to obtain polylactic acid (lactic acid prepolymer) having a weight average molecular weight of less than 15,000, and the resulting ethanol is recovered,
(3) A method for producing lactide, wherein the polylactic acid is depolymerized to produce lactide. The lactide according to any one of claims 1 to 5 , wherein in the step (2), polycondensation is carried out while refluxing a lactic acid ester and / or polylactic acid (lactic acid prepolymer) which is a polycondensate thereof. Manufacturing method. The method for producing lactide according to any one of claims 1 to 6 , wherein in the step (2), in the step of polycondensing the lactic acid ester, the temperature of the reactor is sequentially increased. The manufacturing method of polylactic acid which ring-opening-polymerizes the lactide obtained by the manufacturing method of the lactide of any one of Claims 1-7 , and obtains polylactic acid.

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