This invention relates to synergistic combinations of titanium containing catalysts and catalyst enhancers of carboxylic acid or oxalic acid or their Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba and ammonium salts that are useful for manufacturing polyesters. The synergistic combination of the titanium containing catalysts with a catalyst enhancer such as an oxalic acid, an oxalic acid salt or a carboxylic acid or a carboxylic acid salt provides fast reactions with improved properties such as reduced acetaldehyde content and good color properties for the resulting polyester at substantially reduced catalyst levels.

Polycondensation reactions that produce polyesters require an extremely long period of time that is significantly reduced by a suitable catalyst. Various types of catalysts are used to shorten the reaction time. For example, antimony trioxide antimony triacetate and antimony trisglycoxide are generally used as polycondensation catalysts.

Titanyl oxalate compounds have been suggested as catalysts for polycondensation reactions to produce polyesters. However, titanyl oxalate catalysts when used as polycondensation catalysts for polyesters have caused color problems in the resulting polyester.

Polyesters are obtained by esterification, ester interchange or polycondensation of dibasic acids such as terephthalic acid and isophthalic acid or esters thereof, functional derivatives of acid chlorides and glycols such as ethylene glycol and tetramethylene glycol or oxides thereof and functional derivatives of carbonic acid derivatives. In this case, a single polyester is obtained when one dibasic acid component and glycol component are used. Mixed copolyesters can be obtained when at least two or more types of dibasic acid component and glycol component are mixed, esterified or subjected to ester interchange and then subjected to polycondensation. When a single polyester or two or more initial polycondensates of a mixed copolyester are subjected to polycondensation, an ordered polyester is obtained. In this invention, the term polyester is a general designation for these three types.

Prior literature has disclosed titanyl oxalate compounds for use as polycondensation catalysts for polyesters. The titanyl oxalate compounds disclosed include potassium titanyl oxalate, ammonium titanyl oxalate, lithium titanyl oxalate, sodium titanyl oxalate, calcium titanyl oxalate, strontium titanyl oxalate, barium titanyl oxalate, zinc titanyl oxalate and lead titanyl titanate. However, based upon the examples in such literature references, only potassium and ammonium titanyl oxalate have actually been used to catalyze the polyester forming reaction. See for example Japanese Patent Publication 42-13030, published on Jul. 25, 1967. European Patent application EP 0699700 A2 published Mar. 6, 1996 assigned to Hoechst and entitled “Process for production of Thermostable, Color-neutral, Antimony-Free Polyester and Products Manufactured From It” discloses the use as polycondensation catalyst, however only potassium titanyl oxalate and titanium isopropylate were used for such a catalyst, and, while improved color and antimony free polyester are disclosed, cobalt or optical brighteners were also employed. Other patents have disclosed potassium titanyl oxalate as a polycondensation catalyst for making polyester such as U.S. Pat. No. 4,245,086, inventor Keiichi Uno et al., Japanese Patent JP 06128464, Inventor Ishida, M. et al. U.S. Pat. No. 3,951,886, entitled “Process of Producing Polyester Resin” of Hideo, M. et al, at column 3, line 59 to column 4, line 10, contains a disclosure of titanyl oxalate catalysts for polyesters including a listing of many types of titanyl oxalate catalyst. However, only potassium titanyl oxalate and ammonium titanyl oxalate were used in the examples and lithium titanyl oxalate was not even listed among their preferred titanyl oxalate catalysts.

Titanium based catalysts have shown very high polycondensation activity, however; the resulted polyesters are yellowish color which will limit their applications. Therefore, prior art activity has been directed towards the development of modified titanium catalysts. Titanium compounds are not a good sole catalyst. Ti requires a cocatalysts or modifiers/promoters to form composite catalyst. Titanium compounds in the general formula of Ti(OR)₄, Ti^(III)Ti^(IV) _yO_(3+4y)/2, RO[Ti(OR)₂O]_nR have been widely claimed by others. Cocatalysts or modifiers/promoters, such as antimony compounds, tin compounds, zirconium compounds, silicon compounds, cobalt compound, aluminum compounds, alkali metal compounds, rare earth metal compounds, magnesium compounds, germanium compounds, zinc compounds, lanthanide series compounds, phosphorus compounds, halides, sulfur containing compounds, ammonia hydroxide, and amines, have been claimed together with Ti compounds.

U.S. Pat. No. 6,166, 170, E.I. du Pont de Nemours and Company, issued on Dec. 26, 2000 discloses a catalyst composition of a titanium compound, a complexing agent, and an aqueous solution of hypophosphorous acid or a salt. The titanium compound has a general formula, Ti(OR)₄, combined with a zirconium compound, Zr(OR)₄. The complex agents are hydroxycarboxylic acids, alkanolamines, aminocarboxylic acids and their combinations of two or more.

U.S. Pat. No. 6,066,714, E.I. du Pont de Nemours and Company, issued on May 23, 2000, discloses an organic titanium compound, a phosphorus compound, an amine, and a solvent as a catalyst. The organic compound is Ti(OR)₄. The phosphorus compound is either (RO)_x(PO)(OH)_3−x or (RO)_y(P₂O₃)(OH)_4−y. The amine is a tertiary amine. Aluminum, cobalt, antimony compounds and their combination were claimed as cocatalysts.

U.S. Pat. No. 6,034,203, E.I. du Pont de Nemours and Company, issued on Mar. 7, 2000, discloses a catalytic process that can be used in oligomerization, polymerization, or depolymerization. The catalyst has the formula of M_xTi^(III)Ti^(IV) _yO_(x+3+4y)/2, where M is an alkali metal, such as Li; x and y are numbers greater than or equal to zero wherein if x equals zero, y is a number less than ½.

U.S. Pat. No. 5,981,690, E.I. du Pont de Nemours and Company, issued on Nov. 9, 1999. This patent shows a catalyst solution containing an organic titanate ligand, organic silicates and/or zirconates, and phosphorus compounds. Titanium has a formula of Ti(OR)₄; silicon and zirconium compounds can be organic ortho silicate and zirconate; phosphorus compound can be an organic phosphonic or phosphinic acid. The solvent used was ethylene glycol. The catalyst was claimed to be used in fabrication of PET, PEI, PPT, PBT, and etc.

U.S. Pat. No. 5,866, 710, Tioxide Specialties Limited, issued on Feb. 2, 1999 (EP 0 812 818 Al, published on Dec. 17, 1999). A process of preparing an ester is disclosed in the presence of a catalyst and a base, the product from orthoesters and condensed orthoesters of zirconium and titanium. The orthoesters have the formula of M(OR)₄; the condensed orthoesters, RO[M(OR)₂O]R; where M is either zirconium or titanium. This compound can be illustrated as the following,

M(OR)₄, if n=1

(RO)₃MOM(OR)₃, if n=2

(RO)₃MOM(OR)₂OM(OR)₃, if n=3,

and etc.

The base can be selected sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate, magnesium hydroxide and ammonia.

WO 00/71252 Al, ACMA Limited, published on Nov. 30, 2000. An esterification catalyst composition was disclosed. The catalyst contains 1) hydrolysis product of orthoesters and condensed orthoesters of titanium, zirconium or aluminum; 2) an alcohol containing at least two hydroxyl groups; 3) an organophosphorus compound containing at least one P—OH group and a base; 4) a compound of germanium, antimony or tin.

WO 99/28033 Al, Tioxide Specialties, published on Jun. 10, 1999. An esterification catalyst composition was disclosed. The catalyst contains 1) hydrolysis product of orthoesters and condensed orthoesters of titanium, zirconium or aluminum; 2) an alcohol containing at least two hydroxyl groups; 3) an organophosphorus compound containing at least one P-OH group and a base.

WO 97/47675 Al, Imperial Chemical Industries PLC, published on Dec. 18, 1997 also EP 0906356 jointly with E. I. Du Pont De Nemours & Company Inc. A catalyst is disclosed that is obtained by reacting an alkyl titanate or alkyl zirconate, an alcohol, a 2-hydroxy carboxylic acid and a base. A cobalt (II) salt, a phosphorus compound, and a sodium compound were claimed as catalyst components.

U.S. Pat. No. 5,874,517, Hoechst Celanese Corporation, issued on Feb. 23, 1999. An improved low acetaldehyde process was disclosed. The process utilized mixed Ti and Sb catalysts, however; potassium titanyl oxalate was suggested as a sole catalyst (col. 6, lines 21 and 22). Potassium titanyl oxalate as a polycondensation catalyst was claimed in claims 15 to 20.

U.S. Pat. No. 5,902,873, General Electric Company, issued on May 11, 1999; (EP 0 909 774 Al, published on Apr. 21, 1999. A catalyst composition for the preparation of a polyester on copolyester is disclosed. The catalyst was composed of 1) a titanium or zirconium based compound, general formula, Ti(OR)₄ or Zr(OR)₄, the titanium compounds were water-stable; 2) a lanthanide series compound, such as lanthanum, samarium, europium, erbium, terbium, and cerium; 3) a hafnium based compound; 4) a phosphate-forming compound, such as alkali metal phosphates, alkali metal phosphates, alkali hypophosphates, and alkali metal polyphosphates. The combination of the above components was claimed. In particular, titanium oxide acetylacetonate was claimed (in claim 3, col. 13, lines 52 and 53).

U.S. Pat. No. 6,133,404, National Institute of Technology and Quality, issued on Oct. 17, 2000. A polyester and formation process is disclosed in the presence of a composite catalyst that consists of a titanium compound, a zinc compound, an antimony compound, and a phosphorous compound. This catalyst improved the rate of polyester production and properties of the polymers, in particular, biodegradability of the polymer. The titanium compound has the following general formula,

Ti(OR)₄,

(RO)₄TiHP(O)(OR′)₂

ROTi[OM(O)R″]₃,

where M is selected from carbon atom, phosphorous atom, sulfur atom, and their mixtures.

The zinc compound can be zinc oxide, zinc acetate, zinc chloride, zinc hydroxide and their mixtures. An antimony compound can be selected from antimony chloride, antimony acetate, antimony oxide and their mixtures. A phosphorous compound can be one of the following, Phosphoric acid compounds, phosphite compounds, phosphonic acid compounds, phosphinic acid compound, and their mixtures.

U.S. Pat. No. 5,714,570, Korea Institute of Science and Technology, issued on Feb. 3, 1998. A method for the preparation of polyester by use of a composite catalyst was revealed. The composite catalyst consists of a compound of Sb, a compound of Ti, and a compound of Sn. A compound of Ti has a general formula of (R₁O)₄TiHP(O)(OR₂)₂, and Tin compound, (R₃)₂SnX, where X is selected from sulfur, oxygen, halogen, and a compound containing an ether, a thio or an ester bond. In particular, potassium titanium oxyoxalate was claimed as shown in claim 9 (col. 10, lines 52 and 53) other metals (such as germanium, zinc, manganese, alkali, and alkali earth) compounds were also claimed. It was disclosed that antioxidant, such as a hindered phenol, was used in the process.

U.S. Pat. No. 6,143,837, Sinco Ricerche, S.P.A, issued on Nov. 7, 2000. A process of preparation of polyester resin utilizing Ti compound catalyst was disclosed. The activity of Ti catalysts was shown to be four time higher than S21 catalyst. The titanium compounds can be selected from the group consisting of alkoxides of titanium, acetyl acetonates of titanium, dioxide of titanium, and titanium phosphites. Silica mixed with Ti was used in their examples (but not claimed). A cobalt compound was suggested to be used as a colorants.

The present invention is based upon the discovery of a synergistic combination of a titanium containing catalyst and a catalyst enhancer. This invention provides a novel catalytic mixture comprising a titanium containing catalyst of the formula X_mTiO(C₂O₄)₂(H₂O)_n, where X is selected from the group consisting of H, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, and ammonium, m=1 or 2; and a catalyst enhancer comprising oxalic acid or carboxylic acid containing 1 to 26 carbon atoms or their corresponding Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, or ammonium salt. Also provided is a novel enhanced catalyst mixture comprising a titanium compound of the formula X_mTiY_o with X selected from the group consisting of: H, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba and ammonium, m=1 or 2, Y is a ligand of the formula C_aH_bO_c, a=0 to 30, b=0 to 60, and c=1 to 10; o=2, 3, 4, and a catalyst enhancer of an oxalic acid or its corresponding Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba or ammonium salt. An improved three component enhanced catalyst mixture can be obtained by the addition of second catalyst to either of the above enhanced catalyst mixtures, the second catalyst being a compound containing antimony or germanium. Also provided are enhanced antimony containing catalysts comprising the mixture of an antimony containing catalyst and an enhancer of an oxalic acid or its corresponding Li, Na, K, Rb Cs, Be, Mg, Ca, Sr, Ba or ammonium salt.

This invention also provides an improved process of producing polyester by the polycondensation of polyester forming reactants in the presence of a catalytically effective amount of a polycondensation catalyst, wherein the improvement comprises utilizing, as the polycondensation catalyst, the synergistic combination of a titanium containing catalyst and the catalyst enhancer described in the preceding paragraph. A novel polyester is also provided containing the synergistic combination of a titanium containing catalyst and the catalyst enhancer described in the preceding paragraph. The improved process produces an improved polyester having lower acetaldehyde numbers and good color. The titanium containing catalyst and catalyst enhancer composition can be used as a polycondensation catalyst in combination with other catalysts to achieve synergistic catalytic activity.

The production of polyester by polycondensation of polyester forming reactants is well known to those skilled in the polyester art. A conventional catalyst for the reaction is antimony oxide. The present invention is based upon the discovery of a synergistic relationship between titanium containing catalysts and carboxylic or oxalate catalyst enhancers. The catalyst and catalyst enhancer is surprisingly superior in catalyst performance for polycondensation reactions by providing good catalyst activity at reduced catalyst loadings and superior brightness in the resulting polyester.

Reactants for forming polyesters via a polycondensation reaction are well known to those skilled in the art and disclosed in patents such as U.S. Pat. No. 5,198,530, inventor Kyber, M., et al., U.S. Pat. No. 4,238,593, inventor B. Duh, U.S. Pat. No. 4,356,299, inventor Cholod et al, and U.S. Pat. No. 3,907,754, inventor Tershasy et al, which disclosures are incorporated herein by reference. The art is also described in “Comprehensive Polymer Science, Ed. G. C. Eastmond, et al, Pergamon Press, Oxford 1989, vol. 5, pp. 275-315, and by R. E. Wilfong, J. Polym. Science, 54(1961), pp. 385-410. A particularly important commercial specie of polyester so produced is polyethylene terephthalate (PET).

In addition to catalyzing polycondensation reactions, the synergistic catalyst combinations of the present invention are effective for catalyzing esterification and transesterification reactions when used in catalytically effective amounts with reactants known to participate in esterification or transesterification reactions. A catalytically effective amount is suitable.

An improved three component enhanced catalyst composition can be obtained by the addition of second catalyst to enhanced catalyst composition defined above, the second catalyst being a compound containing antimony or germanium.

TITANIUM OXALATE CATALYSTS:

Examples of titanium oxalate catalysts of the formula X_mTiO(C₂O₄)₂(H₂O)_n, where each X is independently selected from the group consisting of H, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba and ammonium, m=1 or 2 are well known. Titanyl oxalates comprise compounds of the formula: X_mTiO(C₂O₄)₂(H₂O)_n, where X is selected from the group consisting of: H, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr and Ba, m=1 or 2. Titanyl oxalates include metallic titanyl oxalates of the formula M₂TiO(C₂O₄)₂(H₂O)_n wherein each M is independently selected from potassium, lithium, sodium and cesium such as lithium or potassium titanyl oxalate and nonmetallic titanyl oxalates such as ammonium titanyl oxalate. The titanyl oxalate may be anhydrous (n=0) or contain some water of hydration, i.e. n representing the amount of water of hydration. Preferred are H, Li, Na, K, Ca, Cs and ammonium.

CARBOXYLIC ACID OR SALT:

Examples of a catalyst enhancer for the titanium oxalate catalysts are a carboxylic acid containing 1 to 26 carbon atoms or its corresponding carboxylic acid salt having an anion selected from the group consisting of Li, Na, K, Rb Cs, Be, Mg, Ca, Sr, Ba and ammonium. As used herein, “carboxylic acid” includes dicarboxylic acid. Examples of such carboxylic acids or salts are well known and include sodium acetate, sodium propionate, sodium citrate, sodium butyrate, sodium formate, sodium fumarate, malonic acid, potassium acetate, potassium benzoate, succinic acid, glutaric acid, adipic acid, maleic acid. Preferred are potassium acetate, potassium benzoate.

Titanium Containing Catalysts:

Examples of titanium containing compounds of the formula X_mTiY_o with X selected from the group consisting of: H, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba and ammonium, m=0, 1, or 2, Y is a ligand of the formula C_aH_bO_c, a=0 to 30, b=O to 60, and c=1 to 10; o=2, 3, 4, include: acetylacetonate (a=5, b=7, and c=2); i-propoxide (a=3, b=7, and c=l); butoxide (a=4, b=9, and c=1); bis(2,2,6,6,-tetramethy-3,5-heptanedionato), i.e. a=11, b=19, and c=2. Preferred are acetylacetonate, i-propoxide, bis(2,2,6,6,-tetramethy-3,5-heptanedionato).

Oxalic Acid or Salt:

Examples of a catalyst enhancer for said titanium containing compounds are oxalic acids or its corresponding Li, Na, K, Rb Cs, Be, Mg, Ca, Sr, Ba, or ammonium oxalic acid. Preferred are H, Li, Na, K, Ca, Cs, and ammonium.

Antimony Containing Catalysts:

Examples of antimony containing catalysts that can be added to the synergistic combination of enhanced titanium oxalate or titanium containing catalysts defined above are Sb₂O₃, Sb(CH₃COO)₃, and Sb₂(OCH₂CH₂O)₃.

Germanium Containing Catalysts:

Examples of germanium containing catalysts that can be added to the synergistic combination of enhanced titanium oxalate or titanium containing catalysts defined above are GeO₂, Ge(OC₂H₅)₄, Ge[OCH(CH₃)₂]₄, Ge(OCH₃)₄. Preferred is GeO₂.

Enhanceable Antimony Containing Catalysts:

Examples of antimony containing catalysts that can be enhanced with a carboxylic acid or salt or an oxalic acid or salt are Sb₂O₃, Sb(CH₃COO)₃, Sb₂(OCH₂CH₂O)₃.

Cocatalyst:

Cocatalysts that function in combination with the titanium containing catalyst and the enhancer include antimony triacetate, Sb(CH₃COO)₃, antimony glycoxide, Sb₂(OCH₂CH₂O)₃, antimony oxide. (Sb₂O₃).

An effective amount for enhancing the catalytic activity of titanyl oxalate catalysts or a titanium containing catalyst is at least about 0.1 part of enhancer per part of titanyl oxalate catalyst. Preferred is from about 0.1 part to about 100 parts enhancer per part of catalyst based upon the total weight of titanium in the catalyst.

When used in combination with an enhancer, a catalytically effective amount of titanium containing catalyst should be added to the polyester forming reactants, generally at least 0.1 part based upon the weight of titanium. Preferred is from about 1 part to about 40 parts per million of catalyst based on the weight titanium in the catalyst and the weight of the of polyester forming reactants.

When used in combination with an enhancer, a catalytically effective amount of an antimony containing catalyst should be added to the polyester forming reactants. Preferred is from about 1 part to about 240 parts per million of catalyst based on the weight antimony in the catalyst and the weight of the of polyester forming reactants. For enhancing an antimony containing catalyst, an effective amount for of an enhancer for the catalytic activity of an antimony containing catalyst is at least about 0.1 part of enhancer per part of antimony containing catalyst based the weight of antimony in said antimony containing catalyst. Preferred is from about 0.1 part to about 80 parts enhancer per part of catalyst based upon the total weight of titanium in the catalyst.

The preferred amount of a antimony or germanium containing catalyst for use in combination with the enhanced titanium oxalate or titanium containing catalyst described above is from about 0.1 parts to about 80 parts based upon the weight of titanium. Preferred is from 1 to 40 parts of antimony or germanium containing catalyst.

The catalyst and enhancer mixtures of the present invention are used to make polyester typically by first dissolving them in a solvent that is compatible with polyester forming reactants, or preferable in one of the reactants itself, such as ethylene glycol.

The synergistic performance of the catalyst enhancer in combination with one or more catalysts for a polycondensation reaction for the production of PET resin is shown by the following examples.