Titanate compounds as catalysts in processes for producing polyesters

Abstract

The invention relates to a method for producing polyesters in polycondensation reactions catalyzed by aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, zinc titanate compounds or mixtures of these titanate compounds. The invention also relates to a composition comprising an aluminum titanate compound, a barium titanate compound, a calcium titanate compound, a zinc titanate compound or a mixture of these titanate compounds as a catalyst for the production of polyesters in polycondensation reactions. Furthermore, the invention relates to the use of an aluminum titanate compound, a barium titanate compound, a calcium titanate compound, a zinc titanate compound or a mixture of these titanate compounds as a heterogeneous polycondensation catalyst. The aluminum titanate compound, the barium titanate compound, the calcium titanate compound, the zinc titanate compound or a mixture of these titanate compounds is a non-amorphous mixed oxide of aluminum oxide (and / or barium oxide, and / or calcium oxide, and / or zinc oxide) and titanium oxide. These titanate compounds have been found to be excellent heterogeneous catalysts in polycondensation reactions for the production of polyesters, such as polyethylene terephthalate.

Description

Technical Field

[0001] This invention generally relates to a method for producing polyesters in a polycondensation reaction catalyzed by one or more titanate compounds selected from aluminum titanate compounds (AlTi), barium titanate compounds (BaTi), calcium titanate compounds (CaTi), and zinc titanate compounds (ZnTi). The invention also relates to compositions comprising one or more titanate compounds as catalysts for the production of polyesters in a polycondensation reaction. Furthermore, the invention relates to the use of one or more titanate compounds as heterogeneous polycondensation catalysts. Background Technology

[0002] Polyesters, such as polyethylene terephthalate (PET), polypropylene terephthalate (PTT), polyethylene furanate (PEF), and polybutylene terephthalate (PBT), are an important class of industrial polymers. They are widely used in thermoplastic fibers, films, and molding applications.

[0003] Several key reactions occur in the manufacture of high molecular weight acyclic polyesters such as polyethylene terephthalate (PET), polyethylene furanate (PEF), polybutylene terephthalate (PBT), polypropylene terephthalate (PTT), and polyethylene naphthalate (PEN).

[0004] The primary reaction is esterification. In this reaction, polybasic acids and polyols are esterified into monomers suitable for the subsequent polycondensation reaction. During esterification, undesirable byproducts such as 1,3-dioxolane, 2-methyl-1,3-dioxolane, 1,4-dioxane, and vinyl alcohol can be formed. The latter tautomerizes to acetaldehyde.

[0005] The second major reaction is polycondensation. This reaction is important for the molecular weight increase of polyesters. Polycondensation can involve two phases: a molten phase and a solid-state phase (SSP).

[0006] Polycondensation reactions are typically catalyzed by a catalyst. However, esterification reactions can also be catalyzed by a catalyst, preferably the same catalyst used for polycondensation reactions.

[0007] Antimony(III) compounds are commonly used as catalysts for both esterification and polycondensation reactions. However, antimony-based catalysts are facing increasing environmental pressure and regulatory control, particularly in food contact and fiber applications. Antimony-based catalysts can also cause gray discoloration. Tin compounds can also be used in esterification and polycondensation reactions, but they have similar toxicity and regulatory issues as antimony.

[0008] Titanium-based catalysts (alone or in combination with other compounds) for the preparation of polyesters have been described in U.S. Patent Nos. 4,482,700, 4,131,601, 5,302,690, 5,744,571, 5,905,136, and WO 97 / 45470. U.S. Patent Publication 2005 / 0009687 describes the use of titanium alkoxide catalysts, particularly for the polymerization of cyclic esters. Some concerns exist that if titanium catalysts are used in esterification and polycondensation reactions, they tend to hydrolyze upon contact with water, forming diol-insoluble oligomers that lose their catalytic activity, as described in US 2005 / 0215425. Esters and polyesters produced using some titanium compounds as catalysts may also suffer from yellowing, as described in US 4,131,601 and 4,482,700.

[0009] To address these issues, numerous studies have been conducted on using titanium compounds as catalysts in polyester polycondensation reactions, replacing antimony compounds.

[0010] Document CN102391490A discloses a method for preparing a titanium-based polyester catalyst modified with tributyl phosphate supported on activated carbon. A black powder with a low specific surface area is obtained by dissolving isopropyl titanate, tributyl phosphate, aluminum chloride, and activated carbon in an organic solvent (such as ethylene glycol) and then adding water. The molar ratio of aluminum chloride to titanate is 1:19. The catalyst improves the catalytic performance of the final product and reduces the yellowing effect.

[0011] Patent application CN103289069A discloses an aluminum-titanium composite catalyst for polyester polycondensation, designed to replace existing antimony-based catalysts used in the polyester industry. The catalyst is prepared by adding dissolved tetrabutyl titanate to a sodium aluminate solution. The resulting white powder has a molar ratio of titanium to aluminum of 1:2 to 20:1 and is free of heavy metal compounds.

[0012] The preparation and uses of the hydrolysis products of titanium halides are described in document US2002193555(A1). The synthesized titanium hydroxides are stabilized by adding alkaline components (ammonia, magnesium oxide).

[0013] There is a need for catalyst systems for the synthesis of polyesters, particularly PET and its copolyesters, which have increased catalytic activity, have little or no effect on the properties of the polyester, and reduce or eliminate the yellow color of the polyester, thus alleviating concerns about toxicity.

[0014] Therefore, the object of the present invention is to provide a polycondensation catalyst for the manufacture of polyesters that, compared with the antimony-based catalyst systems used in the past, should have similar activity and produce similar color properties of polyesters, but with reduced toxicity and regulatory concerns.

[0015] Another object of the present invention is to provide a catalyst that results in lower formation of byproducts (such as acetaldehyde) during the processing of polyesters (particularly PET) compared to conventionally used titanium alkoxide catalyst systems. An example of byproduct formation is the formation of acetaldehyde, which is formed during resin production and regenerated during processing.

[0016] Another object of the present invention is to provide a catalyst that allows antimony to be substituted in polyester polycondensation reactions without negatively impacting the production process and / or the properties of the final product.

[0017] Another object of the present invention is to provide a catalyst for polyester polycondensation reactions that produces similar reaction rates (molten and solid phases) compared to conventional antimony-based catalysts.

[0018] Another object of the present invention is to provide a method for producing polyester comprising a catalyst that allows for the substitution of at least a portion of antimony in the polyester polycondensation catalyst composition without negatively impacting the production process and the properties of the final product, or with minimal negative impact. Detailed Implementation

[0019] The above-mentioned objectives are achieved by the present invention, namely by providing a composition for polyester polycondensation reaction, the composition comprising: one or more catalysts, wherein at least one of the catalysts is a titanate compound or a mixture of titanate compounds; and at least one polyacid and at least one polyol; wherein the titanate compound or the mixture of titanate compounds is in crystalline form.

[0020] Titanate compounds are selected from aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, and zinc titanate compounds. Mixtures of titanate compounds are selected from:

[0021] - A mixture of aluminum titanate compounds and barium titanate compounds.

[0022] - A mixture of aluminum titanate compounds and calcium titanate compounds.

[0023] - A mixture of aluminum titanate compounds and zinc titanate compounds.

[0024] - A mixture of barium titanate compounds and calcium titanate compounds.

[0025] - A mixture of barium titanate compounds and zinc titanate compounds.

[0026] - A mixture of calcium titanate compounds and zinc titanate compounds.

[0027] - A mixture of aluminum titanate compounds, barium titanate compounds, and calcium titanate compounds.

[0028] - A mixture of aluminum titanate compounds, barium titanate compounds, and zinc titanate compounds.

[0029] - A mixture of barium titanate compounds, calcium titanate compounds, and zinc titanate compounds, and

[0030] - A mixture of aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, and zinc titanate compounds.

[0031] In general, the compositions according to the invention can be used to produce polyesters. In a typical method of producing polyesters, at least one polyacid and at least one polyol are esterified to produce monomers (also known as prepolymers), which are then polycondensed to form polyesters.

[0032] Suitable polybasic acids include terephthalic acid, isophthalic acid, cyclohexanedicarboxylic acid, and naphthalenedicarboxylic acid; and long-chain branched acids such as trimesinic acid, trimellitic acid, and their anhydrides. Terephthalic acid is the preferred polybasic acid.

[0033] Suitable polyols include ethylene glycol, cyclohexanediol, 1,3-propanediol, 2,2-dimethylpropanediol, 1,4-butanediol, and isosorbide; aromatic polyols such as resorcinol and hydroquinone; and long-chain branched polyols such as trimethylolpropane, glycerol, and pentaerythritol. Ethylene glycol is a preferred polyol.

[0034] Currently, compared to conventional titanium compounds, the advantage of using aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, and / or zinc titanate compounds is that conventional titanium compounds are very sensitive to water because they undergo hydrolysis, producing non-catalytically active titanium compounds. Furthermore, water is generated as an unavoidable major product of esterification and polycondensation reactions. Advantageously, the aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, and / or zinc titanate compounds according to the invention are insensitive to water. Therefore, the claimed catalyst composition can further contain water without the risk of deactivation or other negative effects of water on the aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, and / or zinc titanate compounds. This further yields the benefit that the aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, and / or zinc titanate compounds can be directly added to the reaction composition at the start of the polyester polycondensation process.

[0035] For the aluminum titanate, barium titanate, calcium titanate, and / or zinc titanate compounds used according to the present invention, the crucial characteristic is that the compound is in crystalline form. "In crystalline form" here means that the aluminum titanate, barium titanate, calcium titanate, and / or zinc titanate compounds are not amorphous but have at least a polycrystalline or subcrystalline structure. A polycrystalline or subcrystalline structure is typically characterized by multiple microcrystals held together by layers of the compound's amorphous solid material.

[0036] The inventors have discovered that aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, and / or zinc titanate compounds exhibit better catalytic performance when used in crystalline form rather than in amorphous form.

[0037] The superior catalytic properties of crystalline aluminum titanate, barium titanate, calcium titanate, or zinc titanate appear to be due to the fact that titanium has only one free coordination site in the crystalline structure of these compounds. When no titanium atom has a free coordination site in the compound, it cannot catalyze condensation reactions at all. However, it is believed that aluminum titanate, barium titanate, calcium titanate, and / or zinc titanate compounds with more than one free coordination site at the titanium atom (e.g., in the case of amorphous forms of aluminum titanate, barium titanate, calcium titanate, and / or zinc titanate) allow side reactions, leading to undesirable byproducts.

[0038] According to the present invention, the amount of the crystalline aluminum titanate compound, barium titanate compound, calcium titanate compound, or zinc titanate compound in the preferred composition is greater than 10% by weight based on the total amount of one or more catalysts. More preferably, the amount of the crystalline aluminum titanate compound, barium titanate compound, calcium titanate compound, or zinc titanate compound is greater than 50% by weight based on the total amount of one or more catalysts. Most preferably, the amount of the crystalline aluminum titanate compound, barium titanate compound, calcium titanate compound, or zinc titanate compound is greater than 80% by weight, or even 100% by weight based on the total amount of one or more catalysts. In the case of a mixture of two, three, or four of the mentioned titanate compounds, the amounts given above in weight percent apply to mixtures of two, three, or four titanate compounds.

[0039] According to the present invention, the amount of titanium in the form of crystalline aluminum titanate compound, barium titanate, calcium titanate compound and / or zinc titanate compound in the preferred composition is 1 ppm to 100 ppm by weight, preferably 4 ppm to 50 ppm by weight, and more preferably 8 ppm to 30 ppm by weight, based on the total weight of at least one polyacid and at least one polyol in the composition, or based on the polyester formed by polyester polycondensation reaction.

[0040] The aluminum titanate compound, barium titanate compound, calcium titanate compound, and / or zinc titanate compound may be in pure crystalline form but do not need to be in pure crystalline form. Typically, the aluminum titanate compound, barium titanate compound, calcium titanate compound, and / or zinc titanate compound are in polycrystalline or subcrystalline form. Preferably, the aluminum titanate compound, barium titanate compound, calcium titanate compound, and / or zinc titanate compound used according to the present invention have a crystallinity of at least 90% by weight, preferably at least 95% by weight, and more preferably at least 98% by weight.

[0041] The aluminum titanate compound, barium titanate compound, calcium titanate compound, and / or zinc titanate compound used as catalysts in the compositions according to the invention may be free of any rare earth elements. Furthermore, the aluminum titanate compound, barium titanate compound, calcium titanate compound, and / or zinc titanate compound may be free of organic groups.

[0042] This also applies to optional other catalysts that may be present in the compositions according to the invention. Therefore, catalysts containing rare earth elements may be excluded from one or more catalysts in the composition, and / or catalysts containing organic groups (e.g., organometallic catalysts) may be excluded from one or more catalysts in the composition.

[0043] According to the invention, it is also preferred that the composition used for the polyester polycondensation reaction is free of antimony compounds, especially free of antimony-containing catalysts, or contains only a small amount of antimony compounds, i.e. less than 200 ppm, and preferably less than 100 ppm.

[0044] The aluminum titanate, barium titanate, calcium titanate, and / or zinc titanate compounds present in the compositions according to the invention are characterized in that they are mixed oxides comprising aluminum oxide and / or barium oxide and / or calcium oxide and / or zinc oxide together with titanium dioxide. Optionally, water of crystallization may be present in the mixed oxides. In a preferred alternative, the aluminum titanate, barium titanate, or calcium titanate compounds according to the invention are composed of aluminum atoms, titanium atoms, and oxygen atoms, or of barium atoms, titanium atoms, and oxygen atoms, or of calcium atoms, titanium atoms, and oxygen atoms, or of zinc atoms, titanium atoms, and oxygen atoms. Optionally, water of crystallization may additionally be present. However, typically, the aluminum titanate, barium titanate, calcium titanate, and / or zinc titanate compounds present in the compositions according to the invention are characterized in that they do not contain water of crystallization. Preferably, the aluminum titanate, barium titanate, calcium titanate, and / or zinc titanate compounds present in the compositions according to the invention are mixed oxides composed of aluminum oxide and titanium dioxide, or composed of aluminum atoms, titanium atoms, and oxygen atoms.

[0045] Aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, and / or zinc titanate compounds can be prepared via at least two different routes: 1.) a dry route, which involves mixing crystalline oxides or carbonates of aluminum, barium, calcium, or zinc with titanium oxides, and 2.) a wet chemical route, which involves reacting soluble aluminum, barium, calcium, or zinc compounds with soluble titanium compounds in a solvent.

[0046] According to the dry route, aluminum titanate compounds are prepared by mixing crystalline Al₂O₃ (e.g., corundum) and crystalline TiO₂ (e.g., rutile), or a mixture of crystalline Al₂O₃ (e.g., corundum) and crystalline TiO₂ (e.g., rutile), followed by sintering the mixture. Optionally, and in order to have a smaller average primary particle size of the crystalline oxides prior to sintering, the crystalline Al₂O₃ and / or crystalline TiO₂ may be milled before the mixing step or before the sintering step. Milling may also be performed before both steps.

[0047] Preferably, the mixture used for sintering comprises crystalline Al2O3 and crystalline TiO2 in a molar ratio of 1:1 or is composed of crystalline Al2O3 and crystalline TiO2 in a molar ratio of 1:1.

[0048] Barium titanate compounds can be prepared via a dry route by mixing crystalline BaCO3 and crystalline TiO2 (e.g., rutile) or a mixture of crystalline BaCO3 and crystalline TiO2 (e.g., rutile), followed by sintering the mixture (see, for example, J. Mat. Sci. Technol. (2007), pp. 655-658). Optionally, and in order to have a smaller average primary particle size of the crystalline segregates prior to sintering, the crystalline BaCO3 and / or crystalline TiO2 may be milled before the mixing step or before the sintering step. Milling may also be performed before both steps.

[0049] Preferably, the mixture used for sintering comprises crystalline BaCO3 and crystalline TiO2 in a molar ratio of 1:1 or is composed of crystalline BaCO3 and crystalline TiO2 in a molar ratio of 1:1.

[0050] Calcium titanate compounds can be prepared via a dry route by mixing crystalline CaCO3 and crystalline TiO2 (e.g., rutile) or a mixture of crystalline CaCO3 and crystalline TiO2 (e.g., rutile), followed by sintering the mixture (see, for example, Mat. Res. Bulletin (2003), 38(7), pp. 1203-1213). Optionally, and in order to have a smaller average primary particle size of the crystalline oxides prior to sintering, crystalline Al2O3 and / or crystalline TiO2 may be milled before the mixing step or before the sintering step. Milling may also be performed before both steps.

[0051] Preferably, the mixture used for sintering comprises crystalline CaCO3 and crystalline TiO2 in a molar ratio of 1:1 or is composed of crystalline CaCO3 and crystalline TiO2 in a molar ratio of 1:1.

[0052] Zinc titanate compounds can be prepared via a dry route by mixing crystalline ZnO and crystalline TiO2 (e.g., rutile) or a mixture of crystalline ZnO and crystalline TiO2 (e.g., rutile), followed by sintering the mixture (see, for example, Ceramics International (2004), 30(8), pp. 2183-2189).

[0053] After the mixing step, or after one or more optional grinding steps, the mixture is sintered to obtain the aluminum titanate compound, barium titanate compound, calcium titanate compound, or zinc titanate compound used according to the invention.

[0054] After sintering, the aluminum titanate compound, barium titanate compound, calcium titanate compound, or zinc titanate compound used in this invention preferably has an average primary particle size in the range of 100 nm to 500 μm, more preferably 300 nm to 100 μm, more preferably 400 nm to 50 μm, and most preferably 500 nm to 2000 nm. To obtain the desired average primary particle size of the crystalline oxide, according to this invention, the sintered aluminum titanate compound, barium titanate compound, calcium titanate compound, or zinc titanate compound can be ground before use.

[0055] The average primary particle size (μm range) of aluminum titanate, barium titanate, calcium titanate, or zinc titanate compounds obtained via the dry path was determined by transmitted light optical microscopy. For this purpose, a VHX-1000 digital microscope system from Keyence with a VH-Z250R zoom lens was used. A 2.5% suspension of the solid to be examined in ethylene glycol was placed on a microscope slide and covered with a coverslip.

[0056] The average primary particle size (nm range) was determined by dynamic light scattering (DLS) using a Litesizer 100 from Anton Paar GmbH. The solid to be tested was measured in a 0.1% suspension in ethylene glycol in a cuvette.

[0057] The total amount of one or more catalysts contained in the compositions of the present invention may be from 0.1 ppm to 400 ppm, preferably from 1 ppm to 200 ppm, more preferably from 2 ppm to 120 ppm, based on the weight of at least one polyacid and at least one polyol.

[0058] According to the wet chemical pathway, aluminum titanate compounds are prepared by a wet chemical method, which includes the following steps: reacting an aluminum compound with a titanium compound in a solvent, precipitating the reaction product, calcining the precipitated reaction product, and obtaining the aluminum titanate compound.

[0059] Aluminum compounds used in wet chemical pathways can be aluminum alkoxides, aluminum acetate, aluminum nitrate, or aluminum citrate. Titanium compounds can be titanium alkoxides, titanium acetate, titanium halides, or titanium citrate. The aluminum and titanium compounds are reacted using a sol-gel method. HG Riella et al. describe an exemplary synthesis of aluminum titanate compounds in powder form using a sol-gel technique in Trans. Tech. Publ. 416 (2003) 519-524.

[0060] Barium acetate can be used as the barium compound for the wet chemical route. Titanium isopropoxide can be used as the titanium compound. The barium and titanium compounds are reacted using a sol-gel method. An exemplary synthesis of barium titanate compounds using the sol-gel technique is described in J. Mat. Chem (1992), 2, pp. 591-94.

[0061] Calcium acetate can be used as the calcium compound for the wet chemical route. Titanium isopropoxide can be used as the titanium compound. The calcium and titanium compounds are reacted using a sol-gel method. An exemplary synthesis of calcium titanate compounds using the sol-gel technique is described in Chem. Mat. (1994), 6, pp. 58-62.

[0062] Zinc acetate can be used as the zinc compound for the wet chemical route. Titanium butylate can be used as the titanium compound. The zinc compound and the titanium compound are reacted using a sol-gel method. An exemplary synthesis of zinc titanate compounds using the sol-gel technique is described in J. of CrystalGrowth (2002), 243(2), pp. 319-326.

[0063] After calcining the above-mentioned precipitated reaction product and obtaining aluminum titanate, barium titanate, calcium titanate or zinc titanate compound by wet chemical method, the aluminum titanate, barium titanate, calcium titanate or zinc titanate compound may have an average primary particle size of less than 100 nm, preferably less than 50 nm and most preferably less than 25 nm.

[0064] The average primary particle size of aluminum titanate, barium titanate, calcium titanate, or zinc titanate compounds obtained via a wet chemical route was determined by the following method: A colloidal dispersion of AlTi prepared by a known method (or a colloidal dispersion of any other titanate compound described above, such as BaTi, CaTi, ZnTi, or any mixture of two, three, or four of AlTi, BaTi, CaTi, and ZnTi) was diluted (e.g., to 0.025 wt%), and a drop of solution was placed on a 3 mm Cu grid coated with a 200-mesh carbon film. Another drop of the colloidal dispersion was placed on a 3 mm Au grid coated with a porous carbon film. The grid was placed on a sheet of paper that had absorbed the liquid flowing through the perforated membrane, and the sample was air-dried and then stored in a Parafilm-sealed plastic container for electron microscopy analysis. SEM analysis was performed at 300 kV and a magnification of 40,000× in randomly selected areas. The sample distribution of the electron micrographs was determined using suitable software such as ImageJ. Size distribution was measured at 1 nm intervals. The Gaussian distribution is represented by the solid line in the figure. The above method follows the procedure described in C. Shin et al., 2019, ECS J. Solid State Sci. Technol. 8, pp. 3195-3200.

[0065] Examples of titanate compounds prepared according to the present invention and / or used according to the present invention are Al2TiO5 as an aluminum titanate compound, BaTiO3 as a barium titanate compound, CaTiO3 as a calcium titanate compound, and ZnTiO3, Zn2TiO4 or Zn2Ti3O8 as zinc titanate compounds.

[0066] This invention also relates to a method for producing polyester, thereby using one or more catalysts. The method of this invention includes the following steps:

[0067] A reaction mixture is provided, the reaction mixture comprising at least one polyacid and at least one polyol;

[0068] Optionally, in the presence of one or more catalysts, at least one polyacid and at least one polyol in the reaction mixture are esterified to produce a monomer;

[0069] In the presence of one or more catalysts, monomers in a reaction mixture are polymerized by polycondensation to form polyesters;

[0070] At least one of the catalysts is an aluminum titanate compound containing aluminum, titanium, and oxygen atoms; or a barium titanate compound containing barium, titanium, and oxygen atoms; or a calcium titanate compound containing calcium, titanium, and oxygen atoms; or a zinc titanate compound containing zinc, titanium, and oxygen atoms; or a mixture of two, three, or four of the titanate compounds containing titanium and oxygen atoms along with their respective aluminum, barium, calcium, and / or zinc atoms; and

[0071] The mixture of aluminum titanate compounds or barium titanate compounds, calcium titanate compounds or zinc titanate compounds or titanate compounds is in crystalline form.

[0072] For other details and / or preferred options of the method of the present invention, particularly concerning one or more catalysts, at least one polyacid and at least one polyol, monomers, aluminum titanate compounds, barium titanate compounds, calcium titanate compounds or zinc titanate compounds or mixtures of these titanate compounds and their preparation methods, reference is made to the above description of the compositions of the present invention, which, with necessary modifications, can be applied to the method of producing polyester of the present invention. Other details and / or preferred options are as follows.

[0073] Typically, an aluminum titanate compound, a barium titanate compound, a calcium titanate compound, or a zinc titanate compound, or a mixture of these titanate compounds, is added to the reaction compound in an amount such that titanium is present at 1 ppm to 100 ppm, preferably 5 ppm to 50 ppm, most preferably 10 ppm to 30 ppm, based on the weight of the sum of at least one polyacid and at least one polyol in the composition, or based on the resulting polyester.

[0074] According to the invention, it is recommended that more than 10% by weight of one or more catalysts used in the polycondensation step and optionally in the esterification step be crystalline aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, zinc titanate compounds, or mixtures of these titanate compounds. Preferably, more than 30% by weight, and more preferably more than 50% by weight, of one or more catalysts used in the polycondensation step and optionally in the esterification step are crystalline aluminum titanate compounds. However, most preferably, more than 80% by weight, or even 100% by weight, of one or more catalysts used in the polycondensation step and optionally in the esterification step are crystalline aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, zinc titanate compounds, or mixtures of these titanate compounds.

[0075] As mentioned above, the aluminum titanate compound, barium titanate compound, calcium titanate compound, zinc titanate compound, or mixture of these titanate compounds used in the esterification step and / or in the polycondensation step may be free of rare earth elements and / or free of organic groups.

[0076] This also applies to other optional catalysts that can be used in the method according to the invention. Therefore, catalysts containing rare earth elements can be excluded from one or more catalysts used in the esterification step and / or the polycondensation step, and / or catalysts containing organic groups can be excluded from one or more catalysts used in the esterification step and / or the polycondensation step.

[0077] Furthermore, antimony compounds may be used in amounts of less than 200 ppm, and preferably less than 100 ppm, during the esterification step and / or the polycondensation step. Most preferably, antimony compounds are not used in the method for producing polyester according to the present invention.

[0078] The preferred polyester formed in the method according to the invention is polyethylene terephthalate.

[0079] In an advantageous variant of the method of the present invention, the method further includes the step of adding recycled polyethylene terephthalate before or during the esterification step and / or before or during the polycondensation step, in an amount of 10% to 100% by weight, preferably 30% to 100% by weight, more preferably 50% to 100% by weight, and most preferably 80% to 100% by weight, based on the total amount of at least one polyacid and at least one polyol provided, or based on the resulting polyester.

[0080] Aluminum titanate compound, barium titanate compound, calcium titanate compound, zinc titanate compound, or mixtures of these titanate compounds may be used in both the molten and solid phases of the polycondensation reaction at a concentration of 1 to 250 ppm by weight, preferably 1 to 100 ppm and most preferably 5 to 75 ppm, based on the total amount of at least one polyacid and at least one polyol provided, or based on the polyester ultimately formed.

[0081] Furthermore, the aluminum titanate compound, barium titanate compound, calcium titanate compound, zinc titanate compound, or mixtures of these titanate compounds used in the catalyst composition according to the invention exhibit good resistance to hydrolysis. This allows the catalyst to be used as an esterification catalyst and to catalyze esterification reactions. The aluminum titanate compound, barium titanate compound, calcium titanate compound, zinc titanate compound, or mixtures of these titanate compounds according to the invention can be in powder form. The powder of aluminum titanate, barium titanate, calcium titanate, zinc titanate, or mixtures of these titanate compounds can be added to a polyacid and a polyol (the suspension of these is also referred to herein as a "paste"), followed by an esterification reaction. The catalyst-containing suspension can also be added directly to the esterification reaction or directly to the polycondensation reaction. The catalyst operates at the same temperature and pressure as antimony catalysts typically described in the prior art.

[0082] Aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, zinc titanate compounds, or mixtures of these titanate compounds are also insoluble in water and insoluble in most organic solvents. Solvents in the context of this invention can be polar or nonpolar liquid organic molecules having a carbon-based structure and a boiling point below 250°C, which can be used to dissolve reactants, such as polybasic acids or polyols, or even antimony compounds. Organic solvents can be straight-chain, branched, or cyclic alkanols; straight-chain, branched, or cyclic alkanes; straight-chain, branched, or cyclic alkenes; straight-chain, branched, or cyclic ethers; straight-chain, branched, or cyclic esters; and molecules having aromatic ring structures, such as benzene, toluene, and xylene; and combinations thereof.

[0083] According to the present invention, the above compositions or one or more catalysts used in the above methods comprise aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, zinc titanate compounds, or mixtures of these titanate compounds, and may include one or more other catalysts, which may be homogeneous catalysts. The homogeneous catalyst used for polycondensation and / or esterification reactions may be, for example, germanium-containing compounds, titanium-containing compounds such as titanium alkoxides other than the aforementioned aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, zinc titanate compounds, or mixtures of these titanate compounds, or antimony (III) compounds such as antimony oxide, antimony acetate, or antimony glycolate. The use of antimony (III) compounds in catalytic polycondensation reactions increases selectivity and reaction rate. For example, the content of undesirable degradation products (such as acetaldehyde) in processed polyesters is also lower compared to conventional titanium alkoxides or other homogeneous catalysts.

[0084] Furthermore, the reaction rates of the two reaction steps of polycondensation (molten phase and SSP) depend not only on temperature but also on the diffusion of volatile reaction products (such as ethylene glycol or acetaldehyde).

[0085] The aluminum titanate compound, barium titanate compound, calcium titanate compound, or mixture of these titanate compounds used as catalysts in this invention can be used in the form of a fixed-bed catalyst or in the form of a catalyst powder. When the catalyst is in powder form, it can be added directly to the catalyst composition followed by an esterification reaction. Advantageously, by suspending the catalyst powder before adding it to a reaction component containing at least one polyacid and at least one polyol, re-agglomeration of fine particles can be avoided. Additional antimony catalyst can be dissolved in a suitable polyol such as ethylene glycol. The antimony-containing catalyst solution can be added directly to a paste, which is then added to the esterification or polycondensation step.

[0086] Additional antimony(III) catalyst may be present in an amount of 50 to 350 ppm by weight, preferably 150 to 300 ppm by weight, and most preferably 200 to 300 ppm by weight, based on elemental antimony in the final polymer.

[0087] Using the catalyst described above, the final products of polyester manufacturing (especially PET manufacturing) can be further processed to provide PET bottles. PET bottles are manufactured by stretch blow molding preforms made of PET. The term "preform" as used herein refers to an injection-molded article to be stretch blow molded into a bottle, and the preferred material for manufacturing the preform and the bottle is PET.

[0088] The crystallization behavior of PET produced using the catalyst composition according to the invention is similar to that of PET catalyzed by conventional antimony(III) catalysts. In products catalyzed by antimony, elemental antimony nanoparticles act as crystallization nuclei and induce crystallization within the PET. In PET products catalyzed by a catalyst composition comprising aluminum titanate, barium titanate, calcium titanate, zinc titanate, or mixtures of these titanate compounds, the multiphase catalyst itself acts as the crystallization nuclei.

[0089] The final product of a catalytic polycondensation reaction using a catalyst comprising at least an aluminum titanate compound, a barium titanate compound, a calcium titanate compound, a zinc titanate compound, or a mixture of these titanate compounds can be a food-grade polyester. Specifically, food-grade PET is provided using up to 100% by weight of recycled PET as a raw material. Advantageously, using recycled PET reduces the need for virgin PET, thereby contributing to a closed loop in the circular economy. Preferably, the food-grade PET comprises 1% to 100% by weight, more preferably 10% to 100% by weight, and most preferably 25% to 100% by weight of recycled polyethylene terephthalate as a raw material to manufacture the final PET, wherein a catalyst comprising the aluminum titanate compound, barium titanate compound, calcium titanate compound, zinc titanate compound, or a mixture of these titanate compounds of the present invention is used.

[0090] The final product of the catalytic polycondensation reaction, PET, may contain up to 25% by weight, preferably up to 50% by weight, and most preferably up to 100% by weight of recycled PET for use in beverage bottle production or in thermoforming applications such as film packaging.

[0091] The amount of aluminum titanate compound, barium titanate compound, calcium titanate compound, zinc titanate compound, or mixtures of these titanate compounds is calculated based on the amount of elemental titanium required to catalyze the reaction. For example, 57 ppm of aluminum titanate compound as a catalyst corresponds to 15 ppm of elemental titanium (73 ppm of barium titanate compound corresponds to 15 ppm of elemental titanium; 43 ppm of calcium titanate compound corresponds to 15 ppm of elemental titanium; 51 ppm of zinc titanate compound corresponds to 15 ppm of elemental titanium). In a preferred embodiment, one or more catalysts used in the catalyst composition consist only of the aluminum titanate compound, barium titanate compound, calcium titanate compound, zinc titanate compound, or mixtures of these titanate compounds of the present invention, and the catalyst contains a total amount of 1 to 100 ppm, more preferably 5 ppm to 50 ppm, and most preferably 10 ppm to 20 ppm of elemental titanium, based on the weight of at least one polyacid and at least one polyol, or based on the resulting polyester.

[0092] While polymerization catalysts increase the polymerization rate of monomers, these catalysts will begin to degrade polyesters (e.g., PET), thus adversely affecting the polymer's thermal stability. Thermally stable polyesters are those that retain low acetaldehyde content, low discoloration, and high molecular weight after subsequent heat treatment or processing. Acetaldehyde formation is an undesirable consequence of degradation, particularly in the food and beverage industry, as it can adversely affect the taste of bottled products, even when present in very small amounts. Furthermore, polymer degradation typically causes discoloration or yellowing of the polymer, which is undesirable in most applications. Therefore, high amounts and high activity of catalysts should be avoided as much as possible.

[0093] The catalyst composition may further comprise less than 5 ppm of a phosphorus-containing catalyst deactivator, based on the weight of phosphorus. In this case, when a phosphorus-containing catalyst deactivator is present, the deactivator is not added directly to the catalyst suspension.

[0094] Any stabilizer that deactivates the polymerization catalyst (thus preventing polyester degradation and discoloration) is suitable as a deactivator. Typically, heat stabilizers do not react with the polymer and have low residual moisture content.

[0095] The aluminum titanate compound, barium titanate compound, calcium titanate compound, zinc titanate compound, or mixture of these titanate compounds used as catalysts can be employed using the same solvents, temperatures, and general conditions as antimony-containing catalysts. Compared to homogeneous catalysts containing titanium, such as titanium alkoxides, the titanium-containing heterogeneous catalysts according to the invention exhibit lower side-reaction reactivity and therefore do not require catalyst deactivators. Therefore, in a preferred embodiment of the invention, the catalyst composition for polyester polycondensation reactions is free of catalyst deactivators.

[0096] The polyester obtained by the method according to the invention can have a content higher than 0.7 dL·g -1 High molecular weight acyclic polyesters with inherent viscosity (molecular weight higher than 10,000 g·mol⁻¹) -1 Preferably, the concentration is higher than 20,000 g·mol⁻¹ -1 Polyesters such as polyethylene terephthalate (PET), polyethylene furanate (PEF), polybutylene terephthalate (PBT), polypropylene terephthalate (PTT), and polyethylene naphthalate (PEN). Preferably, the polyester is PET.

[0097] Typically, the esterification step can be carried out without any catalyst (autocatalysis), but typically a metal compound is added to catalyze the esterification reaction. The esterification step can be carried out at temperatures above 200°C, more preferably 240°C to 300°C, and pressures from 1 to 10 bar.

[0098] The second step in producing high molecular weight acyclic polyesters (such as PET) is the polycondensation step. Polycondensation is crucial for increasing the molecular weight of the polyester. The polycondensation reaction can involve two phases: a molten phase and a solid-state phase (SSP). Typically, the molten phase of the polycondensation step is carried out at a temperature of 240°C to 300°C and a decreasing pressure of 4 to 0.1 mbar. Typically, the SSP of the polycondensation step is carried out at a temperature of 190°C to 230°C and can be carried out under a nitrogen flow or at a decreasing pressure of 3 to 0.1 mbar.

[0099] The catalyst of the present invention, comprising an aluminum titanate compound, a barium titanate compound, a calcium titanate compound, a zinc titanate compound, or a mixture of these titanate compounds, may be added to the molten phase of the polycondensation step. The amount of titanium added as an aluminum titanate compound, a barium titanate compound, a calcium titanate compound, and / or a zinc titanate compound to the polyester polycondensation reaction is 1 ppm to 100 ppm, preferably 5 ppm to 50 ppm, based on the weight of at least one polyacid and at least one polyol, or based on the weight of the polyester.

[0100] In a preferred embodiment, the aluminum titanate compound, barium titanate compound, calcium titanate compound, zinc titanate compound, or mixture of these titanate compounds added according to the method of the present invention may be in powder form, preferably in the form of nanoparticles with a primary particle size of less than 75 nm, more preferably less than 50 nm, and most preferably less than 25 nm. The particle size was evaluated by SEM (scanning electron microscopy) image analysis as described above. A catalyst may be added as a catalyst composition comprising an aluminum titanate compound (or a barium titanate compound, or a calcium titanate compound, or a zinc titanate compound, or a mixture of these titanate compounds) and at least one polyacid and at least one polyol, followed by an esterification reaction.

[0101] In some embodiments, the catalyst comprises an aluminum titanate compound (or a barium titanate compound, or a calcium titanate compound, or a mixture of these titanate compounds) and an antimony (III)-containing compound, both components being added directly to the paste followed by an esterification reaction. Alternatively, the antimony catalyst can be dissolved in a suitable polyol such as ethylene glycol. The antimony-containing catalyst solution can then be added to the paste and catalyze an esterification or polycondensation reaction.

[0102] Advantageously, by adding aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, zinc titanate compounds, or mixtures of these titanate compounds instead of conventional titanium alkoxides such as tetrabutyl titanate, the acetaldehyde regeneration rate during processing is lower or equal to that of methods containing only antimony catalysts, even in the absence of deactivating agents such as phosphoric acid or potassium acetate.

[0103] The product obtained by the method according to the invention can be further processed to provide the PET bottles described above. In a preferred embodiment, the product obtained by the method of producing polyester can be a food-grade polyester.

[0104] Specifically, the method according to the invention may further include the addition of recycled polyethylene terephthalate (PET). Preferably, 10% to 100% by weight of recycled PET, based on the weight of the final polyester product, may be added to the method according to the invention. More preferably, about 25% to 100% of the final PET, based on the weight of the final polyester product, may be replaced by recycled PET. The final product of the method according to the invention may contain up to 100% recycled PET and may be suitable for use in beverage bottle production or thermoforming applications (such as film packaging).

[0105] The total amount of catalyst added to the polyester polycondensation reaction can be from 1 ppm to 400 ppm, preferably from 5 ppm to 200 ppm, and most preferably from 1 ppm to 100 ppm, based on the weight of at least one polyacid and at least one polyol, or based on the weight of the final polyester.

[0106] According to some embodiments of the present invention, the catalyst deactivator described above can be added to the method for producing polyester. Preferably, the catalyst deactivator is added to the polycondensation reaction.

[0107] The method described above can be used to increase the polycondensation rate in the molten phase of the polycondensation reaction.

[0108] The present invention also relates to the use of aluminum titanate compounds, barium titanate compounds, calcium titanate compounds, zinc titanate compounds, or mixtures of these titanate compounds in crystalline form as heterogeneous catalysts in polyester polycondensation reactions.

[0109] The use of aluminum titanate, barium titanate, calcium titanate, zinc titanate, or mixtures of these titanate compounds as catalysts in polycondensation reactions produces a final product that causes relatively low yellowing in the final product compared to the use of conventional titanium catalysts (such as titanium alkoxides), and thus results in manageable discoloration of the final product.

[0110] Example

[0111] PET is produced using conventional antimony(III)-based catalysts or, according to the invention, crystalline titanium-based catalysts via the following process:

[0112] 242 g of monoethylene glycol (MEG), 0.02 g of an aqueous solution (25%) of tetramethylammonium hydroxide (TMAH, used to inhibit the formation of diethylene glycol), 250 ppm antimony (added as 0.6543 g of antimony glycol) or 10, 15, or 20 ppm titanium (added as 38, 57, and 76 ppm crystalline aluminum titanate (AlTi), 73 ppm crystalline barium titanate (BaTi), 43 ppm crystalline calcium titanate (CaTi), and 51 ppm crystalline zinc titanate (ZnTi), respectively), or crystalline magnesium titanate (MgTiO3) were fed into a glass beaker for mixing the raw materials before feeding them into the reactor. Purified terephthalic acid and isophthalic acid (PTA and IPA: 500 g) were added to the glass beaker with stirring. The MEG / PTA paste was then stirred and fed into the reactor. Apply a full vacuum to the reactor, and then purge the reactor with nitrogen to remove trace amounts of oxygen. Repeat this procedure three times.

[0113] Esterification

[0114] The reactor temperature and pressure setpoints for esterification are approximately 300°C and 4 bar (absolute values). The condensed ethylene glycol (EG) and water (at the top of the reactor) are collected in a bottle. During the esterification time, the product temperature is increased to approximately 260°C. The esterification run (E1) lasts approximately 120 minutes.

[0115] After esterification (E1), the pressure was reduced to 1.0 bar (absolute). After further stirring of the reaction mixture at 1 bar (absolute) for 7.5 minutes (E2), approximately 75% of the reaction mixture was withdrawn from the reactor.

[0116] Melt phase polycondensation

[0117] The polycondensation process was initiated by reducing the stirrer speed to 30 rpm and applying a vacuum of 40 mbar for 1.5 minutes. After this, a full vacuum was applied.

[0118] During polycondensation, the product temperature increases to 270°C. Polycondensation is completed with a fixed power consumption of the electric stirrer.

[0119] Solid-state polycondensation (SSP)

[0120] The SSP reactor used for the Büchi product is a fixed-bed reactor from Roth. This reactor has a batch capacity of 22 g. The temperature is maintained at 210°C via a heating jacket. The preheated nitrogen stream used has a dew point better than -30°C and flows through the reactor from bottom to top across the entire granular bed at a rate of 15 l / h.

[0121] Example 1:

[0122] The reaction rate constants k for melt-phase polycondensation and SSP polycondensation were determined for the following: PET catalyzed with conventional antimony(III) (comparative example), PET catalyzed with magnesium titanate MgTiO3 (as another comparative example), and PET catalyzed according to the present invention with 10, 15, and 20 ppm titanium (Ti, added as 38, 57, and 76 ppm AlTi, 73 ppm BaTi, 43 ppm CaTi, and 51 ppm ZnTi, respectively), based on the weight of the final polymer. The results are shown in Table 1.

[0123] Table 1

[0124]

[0125] The results show that, under molten phase reaction conditions, a very small amount of Ti is sufficient to achieve similar or even higher polycondensation rates. Compared to antimony-catalyzed PET, the polycondensation rate of Ti-catalyzed PET in SSP is slightly lower.

[0126] Example 2:

[0127] Color values ​​L*, a*, and b* are averages of values ​​measured on polyester granules, sheets, or other articles thereof that have been injection-molded or extruded. These values ​​are determined using the CIE (International Commission on Illumination) L*a*b* color system, where L* represents the lightness coordinate, a* represents the red / green coordinate, and b* represents the yellow / blue coordinate.

[0128] Color measurements were performed using a CM-3700A (Konica Minolta) spectrophotometer with SPECTRA Magic software and by applying the following particle measurement parameters:

[0129] Spectral range: 380 to 720 nm

[0130] Principle: Diffuse reflection, d / 8°; SEC, UV 0%

[0131] Cuvette: Height: 50 mm, Width: 35 mm, Depth: 20 mm

[0132] Measurement point: Ø 25mm

[0133] Light source: Daylight D65 / 10

[0134] Reference: Black and white calibration

[0135] The samples were measured in granular form. The cuvettes were cleaned and filled to at least 85% of their maximum volume. The samples were measured four times, with a fresh sample granule required for each measurement. The average of all four measurements and the CIELab L*a*b* values ​​were calculated using SPECTRA MAGIC software. The results are shown in Table 2.

[0136] Table 2

[0137]

[0138] The results showed that AlTi, BaTi, CaTi, and ZnTi, as well as conventional antimony catalysts, all induced a yellowing effect in the final polymer (b* values ​​greater than 0). Advantageously, by using AlTi as a catalyst instead of conventional titanium alkoxides in the polycondensation reaction (results not shown), the yellowing of the final product was comparable to that of antimony-catalyzed PET. Using BaTi, CaTi, or ZnTi as catalysts in the polycondensation reaction resulted in slightly higher yellowing of the final product than that of antimony-catalyzed PET.

[0139] Example 3:

[0140] The acetaldehyde (AA) content of processed PET was determined using the following method:

[0141] First, the sample material was ground in a centrifugal mill using a RETSCH Co. (ZM200) with a 1 mm sieve in the presence of liquid nitrogen. Approximately 0.1 g to 0.3 g of the ground material was placed in a 22 ml sample vial and sealed with a PTFE seal. The vial was heated at a controlled temperature of 150 °C for 90 min in a headspace oven (Perkin Elmer TurboMatrix-40 headspace autosampler) and subsequently analyzed with an external standard by gas chromatography (Perkin Elmer XL GC AutoSystem). Calibration curves were prepared by completely evaporating aqueous solutions of different AAs.

[0142] The headspace autosampler conditions for acetaldehyde determination are as follows:

[0143] Oven temperature: 150℃

[0144] Needle temperature: 160℃

[0145] Delivery pipeline temperature: 170℃

[0146] Retention time: 90 minutes

[0147] Gas chromatography conditions: Column: 1.8 m × 1 / 8, stainless steel

[0148] Packing material: Porapack Q, 80 / 100 mesh

[0149] Carrier gas: Nitrogen, 30 ml / min

[0150] Fuel gas: hydrogen

[0151] Air: Synthetic air

[0152] Column temperature: 140℃

[0153] Detector temperature: 220℃

[0154] Table 3 shows the results of the acetaldehyde (AA) content measurement.

[0155] Table 3

[0156]

[0157] Surprisingly, the acetaldehyde values ​​after processing AlTi, BaTi, or CaTi-catalyzed PET were comparable to those of standard products catalyzed with antimony. Importantly, this effect was achieved without the addition of phosphorus compounds (stabilizers), which are typically mandatory for titanium catalysis. The conventional deactivation mechanism of titanium-based polycondensation catalysts is the formation of Ti-O-Ti bonds. This can be prevented by fixing them within the lattice of the inorganic structure of AlTi, BaTi, or CaTi.

[0158] In summary, AlTi, BaTi, or CaTi were found to be excellent heterogeneous catalysts for PET polycondensation. Manageable discoloration, lower or equal acetaldehyde regeneration rates during processing, increased or similar polycondensation rates (molten phase), and only slightly lower polycondensation rates (SSP) compared to antimony compounds were observed. This confirms that AlTi, BaTi, or CaTi can replace conventional antimony catalysts in polyester polycondensation without negatively impacting the production process and the properties of the final product.

Claims

1. A composition for use in polyester polycondensation reactions, comprising: One or more catalysts, wherein at least one of the catalysts is a titanate compound selected from aluminum titanate, barium titanate, calcium titanate, and zinc titanate compounds, or a mixture of two, three, or four of the titanate compounds, wherein the aluminum titanate compound comprises aluminum, titanium, and oxygen atoms, the barium titanate compound comprises barium, titanium, and oxygen atoms, the calcium titanate compound comprises calcium, titanium, and oxygen atoms, the zinc titanate compound comprises zinc, titanium, and oxygen atoms, and wherein, in the case of a mixture of two, three, or four of the titanate compounds, the mixture comprises titanium atoms and oxygen atoms together with respective aluminum, barium, calcium, and / or zinc atoms; and At least one polyacid and at least one polyol; The titanate compound or mixture of titanate compounds therein is in crystalline form.

2. The composition according to claim 1, wherein the amount of titanium in the composition in the form of the crystalline titanate compound or a mixture of the titanate compounds is 1 ppm to 100 ppm by weight, preferably 4 ppm to 50 ppm by weight, and more preferably 8 ppm to 30 ppm by weight, based on the total weight of the sum of the at least one polyacid and / or the at least one polyol in the composition, or based on the polyester formed by the polyester polycondensation reaction.

3. The composition according to any one of the preceding claims, wherein the titanate compound or mixture of the titanate compounds is free of rare earth elements, and / or wherein the titanate compound or mixture of the titanate compounds is free of organic groups.

4. The composition according to any one of the preceding claims, wherein a catalyst containing a rare earth element is excluded from the one or more catalysts of the composition, and / or a catalyst containing an organic group is excluded from the one or more catalysts of the composition.

5. The composition according to any one of the preceding claims, wherein the composition comprises less than 200 ppm of an antimony compound, preferably less than 100 ppm of an antimony compound, and most preferably wherein the composition does not contain an antimony compound.

6. The composition according to any one of the preceding claims, in, a) The aluminum titanate compound is a mixed oxide comprising aluminum oxide, titanium dioxide, and optionally water of crystallization; or b) The aluminum titanate compound consists of aluminum atoms, titanium atoms, oxygen atoms, and optionally water of crystallization; or Wherein, a) the barium titanate compound is a mixed oxide comprising barium oxide, titanium dioxide, and optionally water of crystallization; or b) the barium titanate compound consists of barium atoms, titanium atoms, oxygen atoms, and optionally water of crystallization; or Wherein, a) the calcium titanate compound is a mixed oxide comprising calcium oxide, titanium dioxide, and optionally water of crystallization; or b) the calcium titanate compound consists of calcium atoms, titanium atoms, oxygen atoms, and optionally water of crystallization; or Wherein, a) the zinc titanate compound is a mixed oxide comprising zinc oxide, titanium dioxide, and optionally water of crystallization; or b) the zinc titanate compound consists of zinc atoms, titanium atoms, oxygen atoms, and optionally water of crystallization; or Wherein, a) the mixture of titanate compounds is a mixture of two, three or four of the mixed oxides, optionally together with water of crystallization; or b) the mixture of titanate compounds consists of titanium atoms and oxygen atoms together with their respective aluminum, barium, calcium and / or zinc atoms, optionally together with water of crystallization.

7. The composition according to any one of the preceding claims, The aluminum titanate compound is prepared by sintering a mixture comprising crystalline Al2O3 and crystalline TiO2 or a mixture of crystalline Al2O3 and crystalline TiO2; or The barium titanate compound is prepared by sintering a mixture comprising crystalline BaCO3 and crystalline TiO2 or a mixture of crystalline BaCO3 and crystalline TiO2; or The calcium titanate compound is prepared by sintering a mixture comprising crystalline CaCO3 and crystalline TiO2 or a mixture thereof; or The zinc titanate compound is prepared by sintering a mixture comprising crystalline ZnO and crystalline TiO2 or a mixture thereof; or The mixture of titanate compounds is prepared by sintering a mixture comprising or consisting of crystalline TiO2 and two, three, or four of the following: crystalline Al2O3, crystalline BaCO3, crystalline CaCO3, and crystalline ZnO; Preferably, the aluminum titanate compound, the barium titanate compound, the calcium titanate compound, the zinc titanate compound, or the mixture of titanate compounds has an average primary particle size in the range of 100 nm to 500 μm, preferably 300 nm to 100 μm, more preferably 400 nm to 50 μm, and most preferably 500 nm to 2000 nm as defined in the specification.

8. The composition according to any one of the preceding claims, The aluminum titanate compound is prepared by a wet chemical method, which includes the following steps: The aluminum compound and the titanium compound are reacted in a solvent, the reaction product is precipitated, and the precipitated reaction product is calcined. Preferably, the aluminum titanate compound has an average primary particle size of less than 100 nm, preferably less than 50 nm, and most preferably less than 25 nm as defined in the specification; or The barium titanate compound is prepared by a wet chemical method comprising the following steps: reacting a barium compound with a titanium compound in a solvent, precipitating the reaction product, and calcining the precipitated reaction product. Preferably, the barium titanate compound has an average primary particle size of less than 100 nm, preferably less than 50 nm, and most preferably less than 25 nm as defined in the specification; or The calcium titanate compound is prepared by a wet chemical method comprising the following steps: reacting a calcium compound with a titanium compound in a solvent, precipitating the reaction product, and calcining the precipitated reaction product. Preferably, the calcium titanate compound has an average primary particle size of less than 100 nm, preferably less than 50 nm, and most preferably less than 25 nm as defined in the specification. The zinc titanate compound is prepared by a wet chemical method comprising the following steps: reacting a zinc compound with a titanium compound in a solvent, precipitating the reaction product, and calcining the precipitated reaction product. Preferably, the zinc titanate compound has an average primary particle size of less than 100 nm, preferably less than 50 nm, and most preferably less than 25 nm as defined in the specification.

9. The composition according to any one of the preceding claims, wherein the at least one polyacid is terephthalic acid and the at least one polyol is ethylene glycol.

10. A method for producing polyester, thereby using one or more catalysts, said method comprising the steps of: A reaction mixture is provided, the reaction mixture comprising at least one polyacid and at least one polyol; Optionally, in the presence of one or more catalysts, the at least one polyacid and the at least one polyol in the reaction mixture are esterified to produce a monomer; The monomers in the reaction mixture are polymerized by polycondensation in the presence of one or more catalysts to form a polyester; At least one of the catalysts is an aluminum titanate compound containing aluminum, titanium, and oxygen atoms; or At least one of the catalysts is a barium titanate compound containing barium, titanium, and oxygen atoms; or At least one of the catalysts is a calcium titanate compound containing calcium, titanium, and oxygen atoms; or At least one of the catalysts is a zinc titanate compound containing zinc, titanium, and oxygen atoms; or At least one of the catalysts is a mixture of two, three, or four of the titanate compounds, the mixture comprising titanium and oxygen atoms along with respective aluminum, barium, calcium, and / or zinc atoms, and The titanate compound or mixture of titanate compounds therein is in crystalline form.

11. The method of claim 10, wherein the method further comprises the following step: Before or during the esterification step and / or before or during the polycondensation step, recycled polyethylene terephthalate is added in an amount of 10% to 100% by weight based on the total amount of at least one polyacid and at least one polyol provided.

12. Use of a crystalline titanate compound as a heterogeneous catalyst in a polyester polycondensation reaction, wherein the titanate compound is selected from aluminum titanate, barium titanate, calcium titanate, zinc titanate, or wherein the titanate compound is a mixture of two, three, or four of the titanate compounds.

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