Titanium containing catalyst and process for the production of polyester

0001The invention relates to a titanium-containing catalyst for polyester production with high catalytic activity which is not impaired by the water formed during the esterification. Furthermore, the invention relates to a process for the production of thermally stable, color-perfect polyesters with the lowest possible ether content by esterification or transesterification and subsequent polycondensation in the presence of this titanium-containing catalyst.

0002The preparation of polyesters is generally carried out so that a diol with a dicarboxylic acid or a lower dicarboxylic acid ester, for. B. dimethyl ester is implemented. First, the corresponding dicarboxylic acid diester is formed, which is polycondensed in one or more stages at increasing temperatures under reduced pressure, with the diol and water being released. Both reaction steps require catalysts or are at least accelerated by them. Suitable catalysts for the esterification are mainly titanium compounds, for the transesterification compounds of Mn, Co and Zn, for the polycondensation compounds of Sb, Ti, Pb, Ge, Zn and Sn, the compounds generally being oxides, alcoholates, acetates or carboxylates be considered. The catalyst metal amounts are usually between 20 and 500 ppm, based on the polyester.

0003Of these catalysts, titanium compounds are the most effective and versatile because they can be used both in esterification or transesterification and in polycondensation and are completely non-toxic. Only with polyethylene terephthalate (PET) is it necessary to use cocatalysts to avoid discolouration. Titanium is mainly used in the form of its alcoholates, and the use of titanium salts has also been described. However, it is known from the titanium alcoholates which are used particularly frequently that they are hydrolyzed in the esterification phase by the water formed there and are thus catalytically inactivated, so that a catalyst make-up for the polycondensation and generally high amounts of catalyst are necessary.

0004About the catalytic activity of TiO₂ there are no clear statements, but it is generally assumed that it is largely catalytically inactive. TiO₂ is used in addition to the usual catalysts in large quantities in PET fiber production as a matting agent and as a white pigment, mostly in the anatase form. The usual concentrations are 0.1 - 3% TiO₂/ PET. In U.S. Patent 2,906,737, TiO₂ in the rutile form as an esterification and polycondensation catalyst in amounts of 0.01 - 5% TiO₂ used. However, the esterification times of more than 7 hours mentioned there are out of the question. In US Pat. No. 3,056,817, a titanium dioxide gel obtained from neutralization precipitation from approximately 5% TiO₂ and 95% water in the esterification phase in amounts of 0.01-10% by weight, based on dicarboxylic acid. However, the catalytic effect of titanium dioxides produced in this way is very low with polyethylene terephthalate. In US Pat. No. 3,463,742, freshly precipitated titanium dioxide hydrate is freed from unbound water and used as a slurry in butanol (with 2-20% Ti) for the transesterification and polycondensation of polyesters, the butanol later being present as an impurity in the reaction vapors to be recycled is. A disadvantage in both cases is the need to have to freshly produce the catalysts immediately before their use, that is, to have to set up a catalyst system in addition to the polyester system.

0005The use of various titanium salts, including lithium or sodium titanate, is described in US Pat. No. 3,965,071. Since otherwise polyesters with strong discolorations and very high diethylene glycol content are formed, the titanium catalyst must be completely deactivated after the esterification by adding phosphorus compounds, and the polycondensation must be continued in the presence of other catalysts, such as antimony compounds or very expensive germanium compounds.

0006In U.S. Patent 4,365,054 alkali titanates of the formula (Me₂O) (TiO₂)_n, where n = 0.05-25, described in polyester production both as an esterification catalyst and as a polycondensation catalyst. The highest catalytic activity is achieved at n = 3-5, but the ether content of the polyester is also relatively high here, for example 1.33% by weight for lithium titanate and 2.15% by weight for sodium titanate. The titanates are obtained by melting alkali carbonate and TiO together₂. Information about the crystallite size or the particle size is missing.

0007The object of the present invention is therefore to improve the known titanium-containing catalysts in such a way that the disadvantages described above do not occur or at least to a lesser extent. The task also includes polyester production using these improved catalysts.

0008This object is achieved according to the invention by a catalyst and a method according to the details of the claims. This catalyst consists of a finely dispersed, surface-rich, hydrated TiO obtained by hydrolysis₂ the composition         y TiO₂ · Z H₂O<dl id="dl0001" compact="compact"><dt>in which</dt><dd>y = 1 z = 0.01-2, preferably 0.15-1.0</dd></dl> or from a finely dispersed, surface-rich titanate of the composition         (Me_nO)_x · (TiO₂)_y · (H₂O)_e.g. in which<dl id="dl0002" compact="compact"><dt>Me =</dt><dd>Li, Na, K, Rb, Cs, Mg, Ca, Sr or Ba, preferably Na or K</dd><dt>n =</dt><dd>1 for Me = alkaline earth and</dd><dt>n =</dt><dd>2nd for Me = alkali</dd><dt>x =</dt><dd>0.0001 to 6, preferably 0.001 to 0.5, particularly preferably 0.02 to 0.04</dd><dt>y =</dt><dd>1</dd><dt>z =</dt><dd>0.01 to 2, preferably 0.3 to 0.7</dd></dl> and where A surface area has a crystallite size of vorzugsweise 100 nm, preferably <10 nm, corresponding to a specific surface area of> 10 m²/ g, preferably> 100 m²/ g, and finely dispersed means a particle / aggregate size of <10 µm, preferably ≦ 1 µm. Rich surface areas can also mean that the catalysts are X-ray amorphous, ie that the crystallite size is below the X-ray diffraction limit. In the following, this catalyst is generally referred to as a titanium catalyst.

0009In the production of polyesters or copolyesters by esterification of at least one diol with at least one dicarboxylic acid or by transesterification of the diols with the dicarboxylic acid dialkyl esters and subsequent single or multi-stage polycondensation, the esterification or transesterification takes place in the presence of an amount of this titanium catalyst corresponding to 0-1000 ppm, preferably 10-1000 ppm, particularly preferably 20-300 ppm titanium, based on dicarboxylic acid, and the subsequent polycondensation in the presence of a total amount of this titanium catalyst, corresponding to 20-1000 ppm, preferably 30-500 ppm, particularly preferably 40-400 ppm titanium, based on dicarboxylic acid, with the polycondensation mixture 10 being added immediately before, during or after the polycondensation - 200 ppm, preferably 20 - 100 ppm phosphorus, based on dicarboxylic acid, can be added in the form of a phosphorus-oxygen compound.

0010The diols on which the polyester is based are alkanediols or cycloalkanediols having 2 to 12 carbon atoms, in particular ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol or mixtures thereof, and the dicarboxylic acids aryldicarboxylic acids or cycloalkyldicarboxylic acids, such as terephthalic acid , Isophthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 1,4-cyclohexanedicarboxylic acid or mixtures thereof. Terephthalic acid is preferred as the main component.

0011The polyester is produced under customary temperature and pressure conditions and using conventional reactors. In addition to the titanium catalyst according to the invention, conventional additives such as chain branching agents, matting agents, dyes, etc. can be added to the reaction mixture.

0012Surprisingly, the present titanium catalyst, with the same to higher catalytic activity, led to polyethylene terephthalate with a lower ether content than that of US Pat. No. 4,365,054 and a significantly reduced COOH end group concentration, both properties which are important for the thermal stability and processability of the polyester. The titanium catalyst is added at the start of the esterification or transesterification, a further amount of catalyst, corresponding to 10-250 ppm, preferably 30-100 ppm titanium, based on dicarboxylic acid, being able to be added at the beginning of the polycondensation, but need not be added. In the case of polyesters, such as polyethylene terephthalate, the esterification of which also takes place without a catalyst, the entire amount can also be added immediately before or at the start of the polycondensation. No other, other catalysts are required.

0013The addition of a phosphorus-oxygen compound, such as phosphoric acid, esters of phosphoric acid or of phosphorous acid, phosphonates or phosphonites, takes place at any time after the esterification has ended. This addition has only a negligible, minor influence on the catalytic activity of the titanium catalyst, but has a positive effect on the oxidative and thermo-oxidative stability and the color of the polyester.

0014The improved catalytic effect of the catalyst according to the invention compared to the prior art described at the outset, with significantly reduced side reactions, is likely primarily due to its extremely finely dispersed and surface-rich structure. However, the water content and the addition of a phosphorus compound during polyester production also have a certain importance. It does not matter whether the titanium catalyst is added to the reactants as a fine powder or as a suspension in the diol on which the polyester is based. The titanium catalyst suspension can, in particular after a long storage, before use by means of a mill, e.g. B. a pearl mill, be finely dispersed again.

0015Titanium compounds with this chemical composition are known per se. What is new and unexpected is their excellent catalytic effect in polyester synthesis. This is probably due to the unique crystallite structure of the present titanium catalyst, which in turn is due to the hydrolysis of TiO (SO₄) can only be attributed to water. The hydrolysis of other titanium compounds with water or alkaline solution leads to titanium compounds which can have a similar chemical composition, but which have a different crystallite structure and are therefore unsuitable or less suitable as a polyester catalyst.

0016These titanium compounds, which are outstandingly suitable as catalysts in polyester synthesis, are produced by hydrolysis, preferably thermal hydrolysis of titanyl sulfate (TiOSO₄) and then either depending on the desired alkali or alkaline earth content<ul id="ul0001" list-style="none"><li>a) removing excess acid by washing or neutralizing and washing, and optionally drying or</li><li>b) reaction at room temperature or at elevated temperature to boiling temperature with alkali or alkaline earth metal hydroxide, washing and optionally drying or</li><li>c) reaction at room temperature or at elevated temperature to boiling temperature with alkali metal or alkaline earth metal hydroxide, washing, partial reaction with mineral acid or carboxylic acid, preferably sulfuric acid, washing again and optionally drying.</li></ul>

0017For example, catalytically active hydrated TiO₂ with extremely low Na content through thermal hydrolysis of a titanyl sulfate solution (corresponding to 200 g TiO₂/ l) with water at 105 ° C, subsequent washing up to a residual sulfuric acid content of 7%, adjusting the suspension to a TiO₂-High content of 330 g / l and neutralization of the suspension with 50% sodium hydroxide solution with stirring to constant pH, washing up to a conductivity of the suspension &lt;300 µS / cm and final drying.

0018Catalytically active sodium titanate with a high Na content arises, for example, when the suspension obtained by hydrolysis, as described above, with a residual sulfuric acid content of 7% in a volume ratio of 250 parts of suspension with 320 g of TiO₂/ l is mixed with 200 parts of 50% sodium hydroxide solution and 200 parts of water, the mixture is heated to boiling and kept at the boil for 2 h, and the sodium titanate formed is washed in a wash water to a residual NaOH content of &lt;3 g / l and is dried.

0019Catalytically active sodium titanate with an intermediate Na content is formed, for example, if the titanate described above with a high Na content is adjusted to a pH of 3 with 30% sulfuric acid before drying at a solids content of 10% and after a standing time is adjusted again from 30 min to pH 3. The acid-treated suspension is washed up to a conductivity of &lt;1000 µS / cm in the filtrate and then dried.

0020The shelf life of these titanium catalysts is excellent, with the catalytic effect in polyester synthesis being independent of the storage time.

0021The intrinsic viscosities given in the examples below were determined on a solution of 0.5 g polyester in 100 ml of a mixture of phenol and 1,2-dichlorobenzene (3: 2 parts by weight) at 25 ° C. The diethylene glycol content was determined by gas chromatography in the transesterification mixture of 1 g polyester with 30 ml obtained in the bomb tube at 200 ° C.

0022Methanol and 50 mg / l zinc acetate determined. The COOH end group concentration was determined by photometric titration with 0.05 N ethanolic potassium hydroxide solution against bromothymol blue of a solution of the polyester in a mixture of o-cresol and chloroform (70:30 parts by weight).

Examples 1 to 5:

0023The esterification of terephthalic acid (TPA) and the transesterification of dimethyl terephthalate (DMT) with various diols was carried out in a manner known per se at normal pressure, in example 1a without catalyst, in example 4a for comparison with titanium tetrabutylate as catalyst and in the other examples in the presence of different Amounts of a sodium titanate powder according to the invention with approx. 2% by weight sodium and approx. 6% by weight water, a particle size of approx. 2nd µm and a specific surface of approx. 300 m²/G. The results are summarized in Table 1.

0024While the esterification of TPA with ethylene glycol, which also takes place without a catalyst, is not significantly influenced by the presence of 210 ppm of the titanium catalyst (Example 1a / 1b), the esterification with 1,3-propanediol, 1, which in any case requires a catalyst, 4-butanediol or 1,4-cyclohexanedimethanol and the transesterification of DMT are already accelerated excellently by small amounts of the titanium catalyst according to the invention. In comparison with a conventional catalyst, namely titanium tetrabutylate, the same degree of conversion is achieved with the same amount of Ti / TPA after a residence time that is about 20% shorter (Example 4a / 4b).

Examples 6 to 15

0025In order to show the influence of the titanium catalyst according to the invention on the polycondensation, terephthalic acid / ethylene glycol esterification product ground under liquid nitrogen and prepared without a catalyst was converted with a degree of conversion of about 98% and a diethylene glycol content (DEG) of about 1.0% by weight. % went out. 42.5 parts by weight of this product were melted under nitrogen blanketing, together with a titanium catalyst according to the invention, corresponding to 105 ppm titanium / TPA, or comparative example 6 with an antimony triacetate catalyst. As soon as the product had melted, with the exception of Examples 6 and 13-15, triphenyl phosphate, corresponding to 76 ppm phosphorus / TPA, was added and the precondensation was initiated at about 270 ° C. and gradually reduced pressure (200 and 50 mbar). After a residence time of 60-70 min, the pressure was reduced to &lt;1 mbar and polycondensed at 275-285 ° C. for 180 min. The results are summarized in Table 2.

0026As can be seen, the catalytic action of the catalysts of Examples 7-9 and 12 is clearly superior to that of the antimony catalyst usually used: with the same residence time, the titanium catalysts according to the invention lead to a substantially higher intrinsic viscosity with polyethylene terephthalate, with otherwise the same quality. A comparison of Examples 12 and 13 shows that the added phosphorus compound reduces the intrinsic viscosity of the polyester with the same residence time, but at the same time ensures the desired neutral white color of the polyester and a reduction in the COOH end group concentration and the diethylene glycol content. In the catalysts of Examples 10 and 11, a somewhat smaller amount of phosphorus stabilizer should be used, in order to better develop the catalytic effect.

Example 16:

0027299 Parts by weight of terephthalic acid are esterified with 191.8 parts by weight of 1,3-propanediol in the presence of the sodium titanate powder used in Examples 1-5 (corresponding to 150 ppm Ti / TPA) at 230 ° C. under normal pressure. After the esterification, the same catalyst is replenished in an amount corresponding to 130 ppm Ti / TPA, and a precondensation is carried out at 240-260 ° C. under gradually reduced pressure (200 and 100 mbar). After a dwell time of 60-80 minutes, polycondensation is carried out at 265 ° C. under a pressure of &lt;1 mbar for 120 minutes. Towards the end of the polycondensation, 10 ppm P / TPA are added as triphenyl phosphate. The polypropylene terephthalate obtained in this way has an intrinsic viscosity of 0.801 dl / g and a COOH end group concentration of 23 meq / kg, the neutral white color of which is clearly superior to that of polypropylene terephthalate produced using conventional catalysts.

Example 17:

0028249.2 parts by weight of terephthalic acid and 259.6 parts by weight of 1,4-cyclohexane dimethanol are esterified at about 220 ° C. in the presence of the sodium titanate powder used in Examples 1-5. The amount of catalyst corresponds to 47 ppm Ti / TPA. After the esterification, the same catalyst is replenished in an amount corresponding to 140 ppm Ti / TPA and precondensed at about 220 ° C. under reduced pressure (100 mbar) for 60 min. The subsequent polycondensation is carried out at 300 ° C. under a pressure of &lt;1 mbar in 75 min. Towards the end of the polycondensation, 10 ppm P / TPA are added as triphenyl phosphate. The poly (cyclohexanedimethylene) terephthalate thus obtained has an intrinsic viscosity of 0.546 dl / g and a COOH end group concentration of 46 meq / kg.

Example 18:

0029291.3 parts by weight of dimethyl terephthalate are transesterified with 270.4 parts by weight of 1,4-butanediol at 220 ° C. The sodium titanate powder used in Examples 1-5 is used as catalyst in an amount which corresponds to 78 ppm Ti / TPA. After the transesterification, the same amount of catalyst is replenished and precondensed at 235 ° C. under gradually reduced pressure (100 and 50 mbar) for 110 min. The polycondensation is carried out at 250 ° C. under a pressure of &lt;1 mbar in 75 min. Towards the end of the polycondensation, 10 ppm P / TPA are added as triphenyl phosphate. The polybutylene terephthalate thus obtained has an intrinsic viscosity of 0.903 dl / g and a COOH end group concentration of 20 meq / kg.<tables id="tabl0001" num="0001"><img file="EP0736560A2_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0736560A2_D0002.tif" /></tables>