Transesterification process using yttrium and samarium compound catalystis

This application claims the priority benefit of provisional application No. 06/126,557, filed Mar. 26, 1999.

This invention relates to processes for making bis(3-hydroxypropyl) dicarboxylate monomer such as bis(3-hydroxypropyl) terephthalate and bis(3-hydroxypropyl) naphthalenedicarboxylate monomers from C 1 -C 4 dialkyl esters of terephthalic acid or naphthalene dicarboxylic acid and 1,3-propanediol in the presence of a yttrium or samarium compound transesterification catalyst.

Preparation of polyester resins by transesterification of a C 1 -C 4 dialkyl ester of terephthalic acid and a diol or of a C 1 -C 4 dialkyl ester of naphthalene dicarboxylic acid acid and a diol, followed by polycondensation is well known in the art.

Generally, the C 1 -C 4 dialkyl ester of terephthalic acid or naphthalene dicarboxylic acid and the diol are reacted in the presence of a transesterification catalyst at elevated temperature and atmospheric pressure to form a monomer and a C 1 -C 4 alkanol corresponding to the C 1 -C 4 alkanol components of the dialkyl ester. The C 1 -C 4 alkanol is removed as it is formed during the reaction. Oligomers having a degree of polymerization of about 4 or less can also be formed. The monomer and any oligomer can then be polymerized at higher temperatures under reduced pressure in the presence of a polycondensation catalyst to form the desired polyester resin. These reactions can be carried out in batch or continuous processes.

Transesterification catalysts known in the art include titanium, manganese, lanthanum and zinc compounds. For example, U.S. Pat. No. 3,671,379 to Evans et al., discloses a process for producing poly(trimethylene terephthalate) using a titanium catalyst compound in both the transesterification and the polycondensation reactions. Cerium and lead acetylacetonate catalysts for the transesterification of dimethyl terephthalate with ethylene glycol are disclosed by Carlson et al. in U.S. Pat. No. 3,532,671. Lanthanum compounds, such as lanthanum acetate, are disclosed by Cavanaugh et al in U.S. Pat. No. 2,820,023 to be effective transestrification catalysts for the preparation of bis(2-hydroxyethyl) terephthalate from dimethyl terephthalate (DMT) and ethylene glycol.

New process improvements which increase transesterification rates resulting in increased throughput and reduced cost of production of bis(3-hydroxypropyl) carboxylate monomer such as bis(3-hydroxypropyl) terephthalate monomer and bis(3-hydroxypropyl) naphthalene dicarboxylate monomer are of significant interest to the chemical industry.

The present invention is an improved process for making bis(3-hydroxypropyl) dicarboxylate monomer, comprising contacting a C 1 -C 4 dialkyl ester of dicarboxcylic acid with 1,3-propanediol in the presence of a catalytic amount of at least one transesterification catalyst selected from the group consisting of compounds of yttrium and samarium at a temperature from about 150° C. to about 245° C.

FIG. 1 is a plot depicting the amount of methanol collected versus time for Example 1 and Example 2 illustrating the invention and Comparative Example A.

FIG. 2 is a plot showing the amount of methanol collected versus time for Example 3 illustrating the invention and Comparative Example A.

This invention is a transesterification process for making bis(3-hydroxypropyl) dicarboxylate monomer such as bis(3-hydroxypropyl) terephthalate monomer and bis(3-hydroxypropyl) naphthalenedicarboxylate monomer. A C 1 -C 4 dialkyl ester of the corresponding dicarboxylic acid is contacted or combined with 1,3-propanediol in the presence of a yttrium or samarium compound transesterification catalyst. Preferably such catalyst is selected from the group consisting of a yttrium or samarium beta-diketonate, a yttrium or samarium beta-ketoester, a yttrium or samarium beta-diester and mixtures thereof. The process is conducted at a temperature from about 150° C. to about 245° C., preferably with a mole ratio of 1,3-propanediol to the dialkyl ester of about 1.1:1 to about 2.2:1.

The C 1 -C 4 dialkyl esters of dicarboxylic acids which are suitable as reactants in the process of the current invention include dimethyl terephthalate, diethyl terephthalate, di-n-propyl terephthalate, di-isoproyl terephthalate, di-n-butyl terephthalate, di-isobutyl terephthalate, di-t-butyl terephthalate, dimethyl-2,6-naphthalene dicarboxylate, diethyl-2,6-naphthalene dicarboxylate, di-n-propyl-2,6-naphthalene dicarboxylate, di-isopropyl-2,6-naphthalene dicarboxylate, di-n-butyl naphthalene dicarboxylate, di-isobutyl naphthalene dicarboxylate and di-t-butyl naphthalene dicarboxylate. These C 1 -C 4 dialkyl esters of the dicarboxylic acid are diesters that are the reaction product of the dicarboxylic acid and an alkanol containing 1-4 carbons. Preferably, the dialkyl ester is dimethyl terephthalate (DMT) or dimethyl-2,6-naphthalene dicarboxylate (DMN).

Minor amounts of one or more other diols (other than 1,3-propanediol), such as in an amount less than about 10 mole percent based on the total diol (including the 1,3-propanediol and the other diols), and/or minor amounts of one or more other C 1 -C 4 dialkyl esters of a dicarboxylic acid (other than terephthalic acid or naphthalene dicarboxylic acid), such as in an amount less than about 10 mole percent based on the total C 1 -C 4 dialkyl ester of dicarboxylic acid (including the C 1 -C 4 dialkyl ester of dicarboxylic acid and the other C 1 -C 4 dialkyl esters of dicarboxylic acid), can be added before or during the transesterification reaction, followed by a polycondensation reaction to form copolymers. For instance, the diol (other than 1,3-propanediol) can be ethylene glycol, 1,4-butanediol, or mixtures thereof. The dicarboxylic acid or diacid (other than terephthalic acid or naphthalene dicarboxylic acid) can be isophthalic acid, adipic acid, or mixtures thereof. The other diols and dicarboxcylic acids and the amounts thereof, if used, are used in amounts which do not interfere with the transesterification reaction, and if such other diols or dicarboxcylic acids are used, the transesterification result is simply a mixture of the bis dicarboxylate monomers.

The yttrium (Y) compounds useful as transesterification catalysts in the present invention include yttrium beta-diketonate compounds, yttrium beta-ketoester compounds, such as yttrium tris(methylacetoacetate), yttrium beta-diester compounds, such as yttrium tris(dialkylmalonate), and mixtures thereof. The yttrium beta-diketonate compounds useful as transesterification catalysts in the present invention include yttrium tris(acetylacetonate) (also known as Y(acac)3) and yttrium tris(2,2,6,6-tetramethyl-3,5-heptanedionate) (also known as yttrium t-butylacetylacetonate or Y(t-Bu-acac)3). Other yttrium beta-diketonate compounds useful as transesterification catalysts in the present invention include tris(t-butylhydroxymethylene-d,l-camphorato) yttrium, yttrium tris(2,2,6-trimethyloctan-3,5-dionate), yttrium tris(hexafluoroacetylacetonate). The preferred yttrium beta-diketonate compounds are yttrium tris(acetylacetonate) and yttrium tris(2,2,6,6-tetramethyl-3,5-heptanedionate).

The samarium (Sm) compounds useful as transesterification catalysts in the present invention include samarium beta-diketonate compounds, samarium beta-ketoester compounds, such as samarium tris(methylacetoacetate), samarium beta-diester compounds, such as samarium tris(dialkylmalonate), and mixtures thereof. The samarium beta-diketonate compounds useful as transesterification catalysts in the present invention include samarium tris(acetylacetonate) (also known as Sm(acac)3) and samarium tris(2,2,6,6-tetramethyl-3,5-heptanedionate) (also known as samarium t-butylacetylacetonate or Sm(t-Bu-acac)3). Other samarium beta-diketonate compounds useful as transesterification catalysts in the present invention include tris(t-butylhydroxymethylene-d,l-camphorato) samarium, samarium tris(2,2,6-trimethyloctan-3,5-dionate), samarium tris(hexafluoroacetylacetonate). The preferred samarium beta-diketonate compounds are samarium tris(acetylacetonate) and samarium tris(2,2,6,6-tetramethyl-3,5-heptanedionate).

The yttrium and samarium compound catalysts are added to the transesterification reaction in concentrations sufficient to cause catalytic activity such as in concentrations corresponding to about 10 ppm to about 550 ppm, preferably to about 35 ppm to about 320 ppm of elemental yttrium or samarium based on C 1 -C 4 dialkyl ester added to the reaction. The term “ppm” is used herein to mean parts per million and is equal to micrograms per gram. When dimethyl terephthalate is the dialkyl ester used in the reaction, the yttrium and samarium compound catalysts are preferably added in concentrations corresponding to about 50 ppm to about 300 ppm of elemental yttrium or samarium based on dimethyl terephthalate. The catalyst can be added directly to the contacted or combined reactants, or added as a solution in 1,3-propanediol.

The transesterification process of the current invention can be conducted by reacting the C 1 -C 4 dialkyl ester of the dicarboxylic acid with the 1,3-propanediol in the presence of the yttrium or samarium compound catalysts at about atmospheric pressure and at a temperature from about 155° C. to about 245° C., preferably about 180° C. to about 240° C. with a mole ratio of 1,3-propanediol to the C 1 -C 4 dialkyl ester of about 1.1:1 to about 2.2:1, preferably about 1.4:1 to about 2.0:1. Residence times of reactants and resulting product in a reaction vessel in which the transesterification reaction occurs are generally from about 0.5 hours to about 4 hours.

Preferably, the reaction vessel is purged with an inert gas, such as nitrogen, before heating. Further, the liquid mixture in the reaction vessel can be stirred. The process can be performed in batch or continuous process.

In the transesterification process, the C 1 -C 4 dialkyl ester of the carboxylic acid reacts with 1,3-propanediol to form the bis(3-hydroxypropyl) ester derivative of the dicarboxylic acid. Depending on the relative concentration of reactants and process conditions, the reaction can also produce oligomers having a degree of polymerization of about 4 or less.

The C 1 -C 4 dialkyl esters of dicarboxylic acids suitable for use in this invention react with 1,3-propanediol to form bis(3-hydroxypropyl) esters and a monohydric alcohol. The monohydric alcohol is a C 1 -C 4 alkanol corresponding to the C 1 -C 4 alkanol components of the dialkyl ester. Thus, the monohydric alcohol, or the C 1 -C 4 alkanol, is methanol, ethanol, propanol, or butanol. For example, 1,3-propanediol is reacted with dimethyl terephthalate in the presence of a yttrium or samarium compound transesterificatin catalyst to form bis(3-hydroxypropyl) terephthalate and methanol.

Other typically undesired byproducts can be formed including allyl alcohol, acrolein and acrylic acid which can be minimized or eliminated by a proper selection of the relative concentration of reactants and process conditions.

The C 1 -C 4 alkanol can be removed by distillation as it is formed during the reaction. This separates bis(3-hydroxypropyl) terephthalate or bis(3-hydroxypropyl) naphthalene dicarboxylate and any oligomers thereof from a product of the reaction. The bis(3-hydroxypropyl) monomer can be polymerized to form poly(trimethylene terephthalate) or poly(trimethylene naphthalate) which have a number of end uses including but not limited to carpeting, hosiery, fishing line, films, and paper making press fabrics.

High quality poly(trimethylene terephthalate) or poly(trimethylene naphthalate) can be made from bis(3-hydroxypropyl) dicarboxylate monomers and oligomers thereof using polycondensation methods known in the art. For example, after transesterification, the temperature can be raised to be in the range of about 240° C. to about 290° C. and the pressure can be reduced to below about 1 mm of mercury absolute pressure in the presence of a suitable catalyst, such as titanium or antimony compounds, to polymerize the monomer and oligomers thereof with removal of excess 1,3-propanediol.

As illustrated in Examples 1-3 versus Comparative Example A, yttrium and samarium beta-diketonate compounds, such as yttrium tris(acetylacetonate) and samarium tris(acetylacetonate), have been found to provide faster transesterification rates than Tyzor® TPT (organic titanate) available from E. I. du Pont de Nemours and Company, Wilmington, Del., for the reaction of 1,3-propanediol with dimethyl terephthalate. Improved rates increases throughput and reduce the cost of production of poly(trimethylene terephthalate) monomer. Alternatively, less catalyst (mole basis) can be used compared to Tyzor® TPT.