This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2011-0027122, filed on Mar. 25, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.
(a) Technical Field
The present invention relates to a method for manufacturing lactide in high yield from
(b) Background Art
The amazing industrialization since the 20th century appears to be largely based on fossil fuel resources, particularly petroleum. With the rapid industrial development and population growth, the petroleum consumption has been increased continuously as well. Petroleum is an unrenewable resource with limited amount of reserves expected to be exhausted soon. Recently, the carbon dioxide generated by the consumption of fossil fuel has been claimed as one of the main causes of global warming, and researches are striving to improve fuel efficiency for reducing carbon dioxide emission and to reduce dependence on petroleum.
Polymers derived from plants, i.e., biomass polymers, can be prepared by a chemical or biological process from renewable plant resources such as corn, bean, sugar cane, wood, etc. Their value lies in solving the environmental problem through carbon dioxide reduction rather than in biodegradability. Of the biomass polymers, polylactic acid is a carbon neutral, environment-friendly, thermoplastic, linear aliphatic polyester, derived from corn starch or potato starch through fermentation or prepared by polymerizing sugar monomers obtained from saccharification of plant-derived cellulose followed by fermentation.
Despite the various advantages of polylactic acid, however, it seems not suitable for use in automobile parts, because of low impact resistance, low heat deflection temperature, etc., as compared to the petroleum-based chemical polymers. Especially, the low impact strength due to its brittleness delimits its application in automobile parts.
For this reason, industrial application of the polylactic acid resin is restricted because of inferior physical properties when compared to the general-use polymer materials. In particular, for use in automobile engine and chassis parts requiring high heat resistance and impact resistance, improvement of physical properties is essential. As a strategy to solve this problem, the technique of preparing a stereocomplex resin by blending the optical isomers of polylactic acid is often used.
To prepare the stereocomplex resin, techniques for preparing
Since lactic acid has one asymmetric carbon atom, it exists as two forms of enantiomers. Meanwhile, since lactide has two asymmetric carbon atoms, there are three stereoisomers, which are
Catalysts presented for this reaction include: tin powder, tin halide or tin carboxylate (European Patent Publication Nos. 261,572 and 275,581); tin alkoxide (Great Britain U.S. Pat. No. 1,007,347); and zinc or tin (European Patent Publication No. 264,926 and U.S. Pat. No. 4,797,468).
A process of producing lactide by heating an alkali or alkaline earth metal salt of 2-halopropionic acid in a non-aqueous solvent is described in U.S. Pat. No. 4,727,163, and a process of preparing 1,4-dioxan-2-one and 5-substituted-1,4-dioxan-2-one by contacting carbon monoxide (CO) with formaldehyde, a 1,2-glycol and a catalytic amount of hydrogen fluoride (HF) is described in U.S. Pat. No. 4,070,375.
In U.S. Pat. No. 4,727,163, a block copolymer of a thermally stable polyether core with an α-hydroxy acid (or its ester) is thermally degraded under vacuum conditions to form a cyclic ester. In U.S. Pat. No. 4,835,293, a prepolymer of α-hydroxy acid (or its ester) on a thermally stable core is cracked at or above atmospheric pressure, and cyclic ester vapors formed from the reaction mixture are exited. However, it has not been proved whether the methods disclosed in the above patents are economical and provide good yield. In addition, the related processes are complicated.
The present invention relates to a process for preparing cyclic lactide by polymerizing liquid lactic acid into low-molecular-weight polylactic acid and degrading it by depolymerization to induce back-biting in the low-molecular-weight polylactic acid chain. In particular, the present invention provides a process allowing a precise control of degree of polymerization during preparation of liquid lactic acid into low-molecular-weight polylactic acid and depolymerization characteristics during depolymerization, production of lactide from liquid lactic, acid conversion of linear lactic acid dimer and trimer vapor to lactide through catalytic reaction in the presence of alumina.
In one general aspect, the present invention provides a method for manufacturing
In another general aspect, the present invention provides a method for manufacturing
The above and other aspects and features of the present invention will be described infra.
The above and other objects, features and advantages of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated in the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the invention, and wherein:
Hereinafter, reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.
The present invention provides a method for manufacturing
For illustration of the present invention, the structure of lactic acid is defined as follows:
L1A: lactic acid, lactic acid monomer, or 2-hydroxypropionic acid;
LD: lactide, or 3,6-dimethyl-1,4-dioxan-2,5-dione (cyclic);
L2A: lactoyllactic acid, or linear lactic acid dimer;
L3A: lactoyllactoyllactic acid, or linear lactic acid trimer; and
LnA: linear n-oligomer of lactic acid.
The degree of polymerization (DP) of polylactic acid is defined as the number n of lactic acid units covalently linked in the lactic acid polymer.
In step (a) of converting liquid
The liquid
More specifically, the liquid
In step (b) of converting the
The one or more catalyst(s) selected from the group consisting of tin powder, tin halide, tin carboxylate and tin alkoxide may be present in an amount of 0.01-0.5 wt % based on the
In step (c) of passing the gas stream through a catalyst layer comprising alumina, silica or an alumina-silica mixture, the gas stream is passed through a catalyst layer comprising alumina, silica or an alumina-silica mixture to convert
The gas stream may pass through the catalyst layer being aided by a carrier gas included therein. Specifically, the carrier gas may comprise nitrogen.
More specifically, the catalyst layer comprising alumina, silica or an alumina-silica mixture may comprise 30 wt % or more of alumina, and the catalyst particle size diameter may be 2-6 mm.
In step (d) of separating
The residue with the
The examples and experiments will now be described. The following examples and experiments are for illustrative purposes only and not intended to limit the scope of this invention.
Rice bran and crushed rice, byproducts resulting form rice polishing, were grinded into fine powder and mixed with water at a volume ratio of 1:2 to prepare a rice slurry. Then, pH was adjusted to 6.0 using calcium chloride (CaCl2, available from Tokuyama Co., Japan). Then, after adding α-amylase (20,000 U/cc, available from Wuxi Jieneng Bioengineering, China) as hydrolase to the rice slurry with a dosage of 14 U/g rice byproduct, the mixture was kept at 95° C. for 60 minutes to prepare a first mixture solution, which was then cooled to 60° C. After adding calcium carbonate to the first mixture solution to lower pH to 4.5, amyloglucosidase (available from Wuxi Jieneng Bioengineering, China) was added with a dosage of 110 U/g rice byproduct. The mixture was allowed to react at 60° C. for 30 hours to prepare a second mixture solution. Then, after heating the second mixture solution to 100° C., it was kept at the temperature for 10 minutes in order to deactivate the enzymes. After cooling the second mixture solution to normal temperature, a saccharification solution and a solid sludge residue were separated finally through centrifugation. High-performance liquid chromatography (HPLC) analysis of the separated saccharification solution revealed a sugar concentration of 100 g/L.
Sporolactobacillus inulinus (ATCC1553) was cultured at 40-45° C. for 24-36 hours in a culture medium containing 10.0 g of pancreatic digest of gelatin, 8.0 g of beef extract, 20.0 g of dextrose, 2.0 g of dipotassium phosphate, 1.0 g of Polysorbate 80, 5.0 g of sodium acetate, 2.0 g of ammonium citrate, 0.2 g of magnesium sulfate, and 0.05 g of manganese sulfate in an aqueous solution (1 L).
After adding Sporolactobacillus inulinus to the saccharification solution, fermentation was carried out in a fermentation reactor at 37° C. and pH 6.5 for 72 hours. Then, after removing inorganic matter from the resulting product by filtration, the remaining salt of lactic acid (sodium lactate) was recovered as pure lactic acid by water-splitting electrodialysis and then concentrated. Thus prepared liquid
The liquid
The
Lactide was prepared in the same manner as in Example 2, except for using 0.2 wt % of stannous octoate catalyst.
Lactide was prepared in the same manner as in Example 2, except for not using the stannous octoate catalyst and not using the alumina layer.
Lactide was prepared in the same manner as in Example 2, except for not using the stannous octoate catalyst.
Lactide was prepared in the same manner as in Example 2, except for not using the alumina catalyst layer.
As seen from Table 1, use of the stannous octoate catalyst and the alumina catalyst resulted in production of
The
The method of the present invention is advantageous in that
Furthermore, the absolute configuration of the liquid lactic acid used as the starting material is maintained in the lactide product, unreacted aqueous lactic acid can be recycled, and few byproducts are produced.
The lactide prepared by the method of the present invention can be used as a source material for
The present invention has been described in detail with reference to specific embodiments thereof. However, it will be appreciated by those skilled in the art that various changes and modifications may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Number | Date | Country | Kind |
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10-2011-0027122 | Mar 2011 | KR | national |