Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-12-19
2003-05-27
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
Reexamination Certificate
active
06569989
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing lactide and a process for producing polylactic acid from fermented lactic acid employed as a starting material, and to a process for producing lactide and a process for producing polylactic acid from ammonium lactate obtained by lactic fermentation. Also, the present invention relates to a process for producing lactate ester from ammonium lactate obtained by lactic fermentation.
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 the lactic acid, and lactide is particularly useful as a starting material for producing polylactic acid. The polylactic acid is a polymer in which the lactic acid is contained as a major constitutional monomer, and the polylactic acid includes not only a homopolymer of the lactic acid but also a copolymer of the lactic acid with other monomers. The polylactic acid is useful as a biodegradable plastic derived from biomass employed as a starting material.
2. Description of the Related Art
Traditionally, the production of polylactic acid has been performed by a dehydration condensation directly from lactic acid, a dealcohol condensation from lactate ester, or a ring-opening polymerization of lactide.
With regard to the production of polylactic acid from lactate ester, for example, the specification of U.S. Pat. No. 2,534,255 discloses a method producing hydroxy polyester from hydroxycarboxylate ester in the presence of a catalyst for esterification.
Japanese Laid-open Patent Publication No. H07-173264 (1995) discloses a method condensing lactate ester to produce polylactic acid with a weight-average molecular weight of 15,000 or above. There is no description in which lactide is synthesized from said polymerized product. It is necessary to consume great time for producing the polylactic acid with a weight-average molecular weight of 15,000 or above.
Japanese Patent Publication (B2) No. 3024907 discloses a process polycondensing lactate ester in a batch type reactor while removing generated alcohol, and further polycondensing the obtained oligomer in a screw type extruding machine while removing generated alcohol so as to produce polylactic acid from the lactate ester. There is no description in which lactide is synthesized from said polymerized product.
Japanese Laid-open Patent Publication No. H10-36366 (1998) discloses a process synthesizing lactate ester from synthesized lactic acid (DL-lactic acid), dealcoholizing the lactate ester to synthesize a lactic acid oligomer, and subsequently synthesizing lactide.
Japanese Laid-open Patent Publication No. H11-209370 (1999) discloses a process for producing lactide, which comprises dealcoholizing lactate ester in the presence of a monobutyltin compound to produce a composition containing polylactic acid or a composition containing polylactic acid and lactide, and then heating the composition in the presence of a monobutyltin compound.
Besides, it has been previously known that ammonium lactate is directly esterified with alcohol (in INDUSTRIAL AND ENGINEERING CHEMISTRY, VOL.44, NO.9, 2189-2191, September 1957).
Japanese Laid-open Patent Publication No. H06-311886 (1994) discloses a process adding butanol or pentanol to ammonium lactate generated by fermentation, and adding mineral acid thereto at the later stage of the reaction to proceed reaction further, thereby recovering lactate ester with recovering ammonia.
Furthermore, Japanese Patent Publication (B2) No. 2830896 discloses a process synthesizing an oligomer from lactic acid used as a starting material, refluxing the oligomer to synthesize an oligomer with higher degree of polymerization, and producing lactide from the oligomer with higher degree of polymerization. There is no disclosure of a process in which polycondensation is conducted employing lactate ester while refluxing a monomer of the lactate ester and an oligomer thereof.
SUMMARY OF THE INVENTION
Thus, a process which comprises synthesizing a lactic acid oligomer in which lactate ester derived from fermented lactic acid is employed as a starting material, and depolymerizing the lactic acid oligomer to produce lactide, and a process which comprises synthesizing a lactic acid oligomer in which lactate ester derived from fermented lactic acid is employed as a starting material, depolymerizing the lactic acid oligomer to produce lactide, and producing polylactic acid from the lactide, have never been known.
Further, in a synthesis of lactate ester from lactic fermentation, producing lactic acid and ethanol by means of hetero-type lactic fermentation while neutralizing with ammonia, and esterifying this lactic acid, have never been known. Hetero-lactic acid bacteria produce lactic acid and ethanol from glucose, and produce lactic acid and acetic acid from xylose.
Hitherto, in producing lactic acid, lactic acid was obtained by steps of performing lactic fermentation of hexose (glucose) or sucrose (consisting of glucose and fructose); neutralizing with calcium carbonate; concentrating to allow calcium lactate to precipitate; liberating with sulfuric acid to produce crude lactic acid; further converting into ester with methanol or ethanol; and distilling the ester followed by hydrolyzing the ester to produce lactic acid. According to this process, there were problems in which significant amounts of calcium sulfate were generated as a byproduct.
Accordingly, a process which comprises neutralizing with ammonia water or ammonia during lactic fermentation to obtain ammonium lactate, converting ammonium lactate into ester with alcohol followed by distilling, recovering ammonia, and hydrolyzing lactate ester, is developed.
Hitherto, there was no consistent process for producing polylactic acid from biomass. By completing the consistent process, cost for producing polylactic acid can be reduced. Namely, there were lots of useless steps conducted, because the production of polylactic acid was formerly considered to be separated from the production of lactic acid. Concretely, the useless step means a step of hydrolyzing lactate ester to produce lactic acid. Besides, by synthesizing polylactic acid from lactate ester, corrosive resistance required for a reactor can be mitigated, and significant contribution in a capital investment can be achieved. Because lactic acid has corrosive properties, especially in the case of concentrating or synthesizing lactide at a temperature exceeding 140° C., it has been necessary to use a reactor and a tube made of titanium or tantalum, or a reactor and a tube with glass lining. However, in the case of using lactate ester, it is not necessary to use a material with corrosive resistance for a reactor, thereby achieving drastic cost reduction in equipments of facilities.
In particular, there is a worldwide subject of how to utilize wood type biomass at present. In Japan, there is a subject of how to treat wastes such as old papers, construction waste materials, lumbers from thinning, rice straws and the others. In overseas, there is a stream to use wood materials as a starting material for fermentation because wood materials cannot be directly used as foodstuffs for people.
The wood type biomass includes cellulose and hemicellulose. As a method for saccharification of cellulose and hemicellulose, a sulfuric acid method, a high-pressure hot water method, and an enzyme method are in a stage of practical use. Sugar obtained by saccharification is hexose and pentose. The hexose is mainly glucose, and the pentose is mainly xylose.
By homo-type lactic fermentation, 1 mol of glucose is converted to 2 mols of lactic acid, which does not waste carbon atoms. Further, among the lactic acid bacteria, there are strains capable of producing 5 mols of lactic acid from 3 mol of xylose. Furthermore, by hetero-type lactic fermentation, 1 mol of glucose is converted to 1 mol of lactic acid and 1 mol of ethanol (in this case, 1 mol of carbon dioxide gas is generated). Namely, glucose is a particularly suitable
Ito Masahiro
Ohara Hitomi
Sawa Seiji
Hampton-Hightower P.
Rader & Fishman & Grauer, PLLC
Toyota Jidosha & Kabushiki Kaisha
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