Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2002-02-27
2004-07-13
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S302000, C528S308000, C528S308600, C528S307000, C525S437000, C525S444000, C524S785000
Reexamination Certificate
active
06762276
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to a process of hydrogenating a polyester oligomer containing terephthalic acid residues wherein terephthalic acid residues are converted to residues of 1,4-cyclohexanedicarboxylic acid. This invention also pertains to a process for the preparation of polyesters containing 1,4-cyclohexane-dicarboxylic acid residues by first hydrogenating a polyester oligomer containing terephthalic acid residues and then reacting the resulting oligomer with one or more polyester-forming reactants to produce a higher molecular weight polyester.
BACKGROUND OF THE INVENTION
Copolyesters comprising terephthalic acid and ethylene glycol residues and residues of one or more saturated dicarboxylic acids comprise a growing market of specialty polyesters. The incorporation of a saturated comonomer such as 1,4-cyclo-hexanedicarboxylic acid (CHDA) into the polyethylene terephthalate (PET) framework can impart desirable properties, e.g., slower crystallization rates, to the resulting polyester. Copolyesters normally are prepared by reaction of a purified dicarboxylic acid such as CHDA and diols under polymerizing conditions. Coployesters derived from CHDA or a diester therof are significantly more expensive due to the cost of the CHDA monomer. For example, 1,4-CHDA normally is prepared commercially from terephthalic acid (TPA) by the ruthenium-catalyzed hydrogenation of the disodium salt of TPA, followed by neutralization and separation of the resulting CHDA from aqueous sodium salts. The present invention provides a process for the production of copolyesters containing CHDA residues by the hydrogenation of polyester oligomers containing TPA residues.
Hydrogenation processes of involving terephthalic acid esters derived from poly(ethylene terephthalate) are known. U.S. Pat. No. 3,501,420 discloses the depolymerization of waste poly(ethylene terephthalate) in an alcohol to give a solution of terephthalic acid esters. The resulting solution is hydrogenated to remove color bodies. In this process, poly(ethylene terephthalate) is converted to primarily monomeric esters before contact with hydrogen. The decolorized solution of TPA esters may be used to prepare high-quality poly(ethylene terephthalate).
U.S. Pat. No. 3,487,100 discloses that bis-hydroxyethyl terephthalate (BHET) prepared from crude TPA and ethylene glycol may be decolorized by treatment with hydrogen in the presence of a hydrogenation catalyst. The BHET is dissolved in water and filtered to remove oligomeric species (which are insoluble in water). The filtered solution is treated with hydrogen at a temperature range of 50-100C. Although the hydrogenation treatment reduces fluorenone impurities, the BHET must be in solution and the product must be crystallized from solution before further use. Another disadvantage is that polyester oligomers cannot be processed by this method. Japanese Kokai JP 50-142537 discloses a process to produce cyclo-hexanedimethanol (CHDM) by the depolymerization and hydrogenation of waste poly(ethylene terephthalate). In this process, waste PET is depolymerized with a 7-fold excess of ethylene glycol in the presence of hydrogen and a hydrogenation catalyst to convert poly(ethylene terephthalate) into a solution of ethylene glycol esters of cyclohexanedicarboxylic acid. The product of this step is separated from the catalyst and treated again with hydrogen at high pressure in the presence of a second hydrogenation catalyst. The object of the second step is to convert the esters of cyclohexanedicarboxylic acid into a solution of CHDM.
SUMMARY OF THE INVENTION
We have developed a process whereby a polyester oligomer, i.e., a low molecular weight polyester, comprising residues of TPA and one or more diols may be hydrogenated under certain conditions to convert at least 1 mole percent of the TPA residues to CHDA residues. Accordingly, one embodiment of the present invention is a process wherein a polyester oligomer comprising terephthalic acid residues is contacted with hydrogen in the presence of a supported or suspended hydrogenation catalyst under a hydrogen pressure of at least about 60 bars gauge (barg; about 870 pounds per square inch gauge—psig) and a temperature of about 180 to 280° C. whereby at least 1 mole percent of the terephthalic acid residues are converted to 1,4-cyclohexanedicarboxylic acid residues. A second embodiment of the present invention is a process comprising the steps of:
(1) contacting a polyester oligomer comprising terephthalic acid residues with hydrogen in the presence of a supported or suspended hydrogenation catalyst under a hydrogen pressure of at least about 60 barg and a temperature of about 180 to 280° C. to convert at least 1 mole percent of the terephthalic acid residues to 1,4-cyclohexanedicarboxylic acid residues; and
(2) reacting the oligomer product of step (1) with one or more polyester-forming reactants in the presence of a polymerization catalyst and under polymerization conditions of pressure and temperature to produce a polyester comprising 1,4-cyclohexanedicarboxylic acid residues.
The present invention offers a more economical means for preparing copolyesters containing TPA and CHDA residues. The resulting oligomer comprised of comonomers may be polymerized by conventional means to produce copolyesters of saturated and unsaturated monomers. The polyesters which may be obtained in accordance with the present invention have a variety of uses such as adhesives, food packaging and coating compositions.
DETAILED DESCRIPTION OF THE INVENTION
The oligomer used in the invention typically is produced by esterifying terephthalic acid, or a diester thereof such as dimethyl terephthalate, with one or more diols such as ethylene glycol, diethylene glycol, 1,3-butanediol, 1,4-cyclo-hexanedimethanol, and the like. The product of the esterification reaction is an oligomer mixture having a degree of polymerization (DP) of about 2 to 20. The oligomer preferably has a DP of about 2 to 10, most preferably about 3 to 5, wherein DP is defined as the number average molecular weight of the oligomer divided by the molecular weight of the repeat unit. The oligomers which may be employed in the present invention also may be characterized by the general formula:
HO-[Diol]
x
-[-TPA-Diol-]
y
-H
wherein Diol is a divalent residue of a diol or glycol component such as ethylene glycol, diethylene glycol, 1,2- and 1,3 propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and the like, TPA is the divalent residue of terephthalic acid, x is 0 or 1, and y has an average value of about 2 to 20. The oligomer starting material of our novel process is insoluble in water and thus is distinguished from BHET that is hydrogenated as described in U.S. Pat. No. 3,487,100.
The oligomer may be preared using crude terephthalic acid, purified terephthalic acid, or a polyester-forming derivative such as dimethyl terephthalate. Crude terephthalic acid (CTA), prepared by the autoxidation of para-xylene, typically contains 4-carboxybenzaldehyde (CBA) as the major impurity and minor but significant amount of colored impurities. The colored impurities have been identified as a mixture of mainly dicarboxyfluorenone isomers (with lesser amounts of mono- and tri-carboxyfluorenones) and dicarboxybenzil. These highly-colored carboxyfluorenone compounds may be hydrogenated to colorless carboxyfluorene compounds. Other compounds such as dicarboxybenzophenone and dicarboxybiphenyl have been identified in low concentrations. Although essentially any grade of CTA can be used in the preparation of the oligomers employed as the starting material for the process of the present invention, the CTA used typically contains less than about 4000 ppm of CBA, preferably less than 700 ppm CBA, and most preferably from about 50 to 250 ppm CBA.
CTA typically is reacted with at least one diol at a temperature between about 200 and about 280° C. to produce an oligomer which may be hydrogenated in accordance with the present inventio
Gustafson Bruce LeRoy
Lin Robert
Sumner, Jr. Charles Edwan
Acquah Samuel A.
Eastman Chemical Company
Graves Bernie
Owen Steven A.
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