POLYCONDENSATION CATALYZERS FOR THE SYNTHESIS OF POLYETHYLENE TEREPHTALATE

Abstract: The subject is a class of catalyzers to be used in the stage of polycondensation of the synthesis of poly(ethylene terephtalate), consisting of metal and non-metal derivatives in composition with sulfonic acids mixed with titanium compounds so that the final polymer contains a sulfur quantity of 5-60 ppm and a quantity of metals between 2 and 100 ppm.

Description: Polycor.άer.sation catalyzers for the synthesis of polyethylene te¬ rephtalate This invention concerns a class of catalyzers to be used in the stage of polycondensation during the synthesis of poly(ethylene terephtalate). Polvi ethvlene terephtalate) (PET) is a thermoplastic polyester used in the production of textile fibers, containers and films for food use. supports for magnetic tapes and photographic fiims. It is industrially compounded through a multi stage synthesis of ethyiene glycol and terephtalic acid or dimethyl terephtalate. in the presence of the proper catalyzers. PET is synthetized in two stages. Dunns the first stage (scheme 1), dimethyl terephtalate (DMT) reacts in the presence of alchoolysis catalyzers in order to give an oligomeric mixture the main component of which is bi-(hydroxyethyi)terephtaiate (BHET). Due to improvements in the purification of terephtalic acid and because it costs less than DMT, in recently perfectioned processes, terephtalic acid instead of ester is used as raw material. In such case the reaction of the first stage (scheme 2) is an esteriπcation ( the result also in this case is BHET) BHET obtained in either of the ways explained is transformed in poly(ethylene terephtalate) scnεme 1 H3COOC-C6H4-COOCH3 - 2 HOCH2CH20H H0CH2CH2OOC-C6H4-COOCHCH2CH2OH - 2 CH30H scheme 2 HOOH-C6H4-COOH i- 2 HOCH2CH20H HOCH2CH200C-C6H4-COOCH2CH20H - 2 H20 scheme 3 n HOCH2CH200C-C6H4-COOCH2CH20H ► n HOCH2CH2OH + -(OCH2CH2OOC-C6H4-CO) n- The optimum characteristics of a polycondensation catalyzer are hign activity, - absence of secondary reactions which could give formations, for example of acetaldehyde or unwanted coloured generations in the final material atoxicity. particularly for the food applications of PET Patent literature describes a huge vaπety of inorganic, organic and organometal compounds that are efficient in catalyzing the polycondensation reaction Since the 10 discovery of PET catalvzers consisting of antimomum compounds are descπbed, especially oxide, acetate, alcoholates It is known, however, that in orαer to obtam sufficiently fast reaction kinetics it is fundamental to use such compounds in quantities so that at the end of the reaction PET contains 200-3 OOppm of metal Which is undesirable for polymer applications to food containers 15 Titanium compounds have a very high activity, though they cause the formation of a yellow colouring in the final mateπal due to the formation of acethaldheyde and of degradation products (J M Besnoin and K Y Choi, J Macromol Sc , Rev Macromol Chem Phys , C29, 55 (1989)) Mixtures of titanium compounds with other metallic deπvatives. such as cobalt, manganese and magnesium nickel. 0 zmc lanthanum, stannum and others are descπbed Germanium compounds represent another considerable class of polycondensation catalvzers The weat ness of germanium compounds consists in the incredibly hign cost and a higher tox city than antimomum Combinations of titanium and germanium are reported in several patents .Another metal that gives deπvatives provided with catalytic activity is stannum, though they have a quite reduced activity, and they also cause the polymer's dark-yellow colouring. The protonic acids have a moderate catalytic activity, and cause the di- and trimerization of ethylene glycol, which remains in the chain of the final polymer 5 drastically lowering its fusion temperature until making it completely amorphous, and reducing its thermic and hydrolytic stability. The compounds described are sulfuric acid and acids, esters, anhydrides, amides and sulfonic amides. None of these systems presents the above described characteristics in the same time (high activity, atoxicity and absence of secondary reactions). 10 We have by now suφrisingly overcome these problems carrying out the polycondensation in the polyethylene terephtalate synthesis through a catalyzer which is formed by a mixture of derivatives of: metallic and non metallic elements, titanium, sulfonic acid. According to this, the puφose of this invention is a composition able to catalyze 15 the polycondensation of bi(2-hydroxyetil) terephtalate or its homologous oligomers, constituted by the derivatives of elements belonging to the following groups : IIA, HIA. IV A, VA, IE, UIB, VB. VB. VIB. VIII. The composition is also characterized by the fact that it contains: - a sulfonic acid in its general formula 20 RS03H in quantity so that sulphur in the final polymer is between 5 and 60 ppm. R stands for an organic radical that can be linear or ramified alkylic. saturated annuiar or aromatic containing up to 20 carbon atoms; - a titatium derivative in such quantity so that the residuum of titanium in the final -5 poiymer is between 1 and 6 ppm: being the elements belonging to the groups IIA, IHA. IV A, VA, HB. IIIB, IVB, VTB, VHB, Nπi in quantitity so that the element in the final polymer is between 0 and 94 ppm. According to the standard procedure, in the first stage (scheme 1), dymethyi terephtalate (DMT) reacts in atmospheric pressure and a temperature of about 160-190°C with residuum of ethviene giycol (2-2.2: 1 in moles) at the presence of aicohoiysis catalyzers in order to give an oligomeric mixture the main constituent of which is bi(2-hydoxyetil) terephtalate (BHET) .As residual product of the reaction methanol is released. The most commonly used catalyzers for the aicohoiysis stage are magnesium, cobalt, manganese, zinc and calcium acetates and titatium alcoholates Terephtalic acid instead of ester can be used as raw material. In such case the reaction of the first stage (scheme 2) is an esterification (the product is also in this case BHET), and water is the residual product distilled, the reaction occurs in mild pressure and with temperatures some tens of degrees higher than in the case of the reaction of DMT Usually no catalyzer is used in such case. BHET obtained through either of the two ways described is tranformed (scheme 3) in poly(ethyiene terephtalate) with temperatures of 260-290°C and pressures below a millibar in the presence of stabilizers and polycondensation catalyzers object of the invention. During the reaction ethviene giycol is removed by distillation The stabilizers (phosphoric acid, trimethyl phosphate, triphenyl phosphate, or the correspondent phosphites) have the puφosε of deactivating the first stage catalyzer ( when used) and preventing unwanted secondary reactions from taking place The quantity of RS03H compound to be used has to provide a polyester containing sulphur expressed as elementary sulphur between 5 and 60ppm, preferably below 50 ppm. Sulfonic acids examples useful in order to put the invention into effect are benzenesulfonic acid, p-toluenesuifonic acid, - naphtalenesulfonic acid, ethanesulfonic acid, propanesulfonic acid, cyclohexanesulfonic acid. Aromatic sulfonic acids are preferred, such as benzenesulfonic acid, p- toluenesulfonic acid, naphtalenesulfonic acids or sulfonic acids derivatives such as anhydrides. 10 Titamum derivatives can be different compounds as long as they are soluble. Carboxylates and alcoholates are preferred. Metallic and non -metallic derivatives to be used together with the compound of RS03H formula and with titanium derivatives can be salts, oxides or metallo- organic derivatives of elements belonging to groups IIA, IHA, IV A. VA. KB, 15 IILB, IVB,VB, VIB. VIIB, Vπi. In this invention are paπiculariy preferred elements such as magnesium, zirconium, manganese, cobalt, zinc, germanium, stannum, antimonium, more specifically germanium and antimomum. Such elements can be used especially in their oxides, carboxylates (paricuiarly acetates), aicoholates (paπiculariy glycolates, methylates, ethylates. isopropyiates or 20 butylates) or sulfonates (especially benzenesuifonates, toluenesulfona.es. naphtalenesulfonates). The quantity of metallic or non-metallic derivative has to provide a polyester with a content of total sum of metal or non-metai and titanium between 2 and lOOppm. A paπiculariy preferred combination is constituted by a titanium derivative and an antimonium derivative, in quantity between i and 6 ppm -- for the first and between 50 and 94 for the second. Otherwise the combination of a titamum and germanium derivative can be used, in the same quantities described for the previous combination, or the the titanium derivative in quantity of 2-6ppm. Catalytic system so conceived have the following characteristics. a) They have high activity. In fact they have to provide PET with intrinsic viscosity of 0.5-0.7dl/g in reaction times not over 4 hours. b) They don't originate widespread secondary reactions, as shown by the final polymer colour and by the levels of diethyleneglycol and of acetaldehyde. c) They contribute to the presence of heavy metals in quantities that are below lOOppm (staπing from terephtalic acid instead of dimethyl ester are the only present metal.) d) They have a contained cost. The polymer obtained with these catalytic systems is characterized by the following parameters. 1. Conversion reaction time diagram. The conversion is expressed through the pressure values of the oleopneumatic circuit of the agitator operating constantly at 100 revolutions per minute. The final temperature of the polymerization is mantained stationary in all the tests at preset value: the geometry and the filling level of the reactor are costant. The conversion is related to the torsional moment of the agitator and therefore to the spindle viscosity and to the polymer molecular weight. 2 Intrinsic viscosity (IV) is measured out of polymer solutions in phenol- tetrachloroethane 60 20 in weight at 30°C by an automatic viscometer Shotte- Gerate 3 The metal content is defined in terms of metal or sulphur ppm in the final polymer, depending on the quantities of catalyzers weighed and introduced in the reaction mixture. 4 Diethylene giycol (DEG) and triethyiene giycol (TEG). It consists of the weight pecentage of DEG (or TEG) contained in the the polymer and it is determined by the gas chromatographic analysis of the hydrolysis products of PET acording to Allen B J 's method in .Anal. Chem. vol 49, pg 741. 1977 5 Acetaldehvde dropout. The polymer is milled in liquid nitrogen and it is processed at 150°C for 20 minutes Acetaldehvde, released because of permanence in the poivmer at 280°C for 5 minutes, is measured through thermic desorotion combined with gas chromatographic analysis by head space Picture 1 for examples 1-5 and picture 2 for comparative examples S-l l and 13, are the diagrams that show the conversion related to the polycondensation time. The following examples are reported for a better comprehension and not for a limit to the invention. Example 1 In a 40 1 steel reactor are introduced, in inert atmosphere, 19 4Kg (100 moles) of dimethyl terephtalate , 13.64 Kg (220 moles) of ethviene giycol and 100 ml of a glycolic solution containing 0.70 g of tetrahydrate manganese acetate. 3 06 g of tetrahydrate magnesium acetate, 1.25 g dihydrate zinc acetate. 2 84 g of tetrahydrate cobalt acetate and 1.64 sodium benzoate The reaction mixture is taken up to 1 S0°C and is mantained at such temperatute for about 4 hours until complete methanol distillation, after which the temperature has gone up to 225°C and l Og of dimethyl phosphate in glycolic solution has been added and the polycondensation catalyzer made of 0 46 g of tetraisopropy ate titamum (Ti 4 ppm), 3 68 g of monohydrate p-toluensulfonic acid (S 32ppm) . The pression is gradually reduced to 0 6 torr and temperature is increased to 285°C. mantaining these conditions for 4 hours; during all this time the excess of ethviene giycol has been removed After bringing the equipment back to atmospheric pressure with N2. the polymer is extruded and pelletted A colourless polymer with the characteristics listed in table 1 is obtained. Examples 2-5 A polymer is prepared using methodologies and reactives as in example 1, though using the catalyzers as follows example 2 0 69 g of tetraisoproplylate titamum (Ti 6ppm ι, 5.52 g of monohydrate p-toluensulfonic acid (S 48ppm), example 3 0 69 g of tetraisopropyiate titanium (Ti 6 ppm), 5.52 g of monohydrate p-toiuensulfonic acid (S 48 ppm), 1 84 g of antimonium trioxide (Sb 80 ppm) , example 4 0 46 tetraisopropyiate .titanium (Ti 4 ppm), 3 68 g monohydrate p- toluensulfo ic acid (S32 ppm), 1 84 g of antimonium trioxide (Sb 80 ppm), example 5 0 23 g tetraisopropyiate titanium (Ti 2 ppm), 1 S4 g of monohydrate p- toluensufonic acid (S 16 ppm), 1 84 g of antimonium trioxide (Sb 80 ppm) In all cases a colourless polymer is obtained, whose characteristics are listed in table 1 Examples 6-" ( comparative) The examples have been effected as in example 1 though using the following polycondensation catalyzers ex 6 7 36 g Sb trioxide (Sb320ppm) ex " 3 68 g Sb " (Sb 160ppm) In both cases the extruded polymer has a grey colour and with high levels of metal and acetaldehvde (consisting respectively of 70 and 62 micrograms per gram) The other characteristics are listed in table 1. Examples 8-9 (comparative) The examples have been carried out as in example 1 though using the following polycondensation catalyzers. es.S 2.76 g Sb trioxide (Sb 120 ppm) es 9 1.84 g " " (Sb SO ppm) In both cases the catalyzer activity is non satisfactory, in the case of example 9 a very fluid polymer is obtained which is also very difficult to extrude. The characteristics are listed in table 1. Examples 10-1 1 (comparative) The examples have been carried out as in example 1 though using the following polycondensation catalyzers. es.10: 2.31 g Ti tetraisopropyiate (Ti 20ppm) es. l l : 0.69 g " " (Ti 6ppm) It is clear from the diagram that in both cases the polymer is degraded due to collateral reactions and the material ends up having a yellow colouring. The other characteristics are listed in table 1. Example 12 (comparative) The example has been carried out as in example 1 though with 36 8 g of p- toiuensufonic acid (S 320ppm) as catalyzer. During the polymerization the reactor's pipelines have repeatedly clogged due to the oϋsomeric sublimination from the reaction mass. The polymer, as table 1 shows, contains high quantites of di- and tri- ethylene giycol. which cause a drastic upsetting of the characteristics such as the absence of the melting point and the reducement of transition to glass temperature below 50°C. - Examples 13-14 (comparative) The examples have been carried out as in example 1. though using the following polycondensation catalyzers. es. 13. 1 84 g Sb trioxide (S 80 ppm). 0.69 Ti tetraisopropyiate (Ti 6 ppm) es. 14: 0.92 g Ti tetraisopropyiate (Ti 8 ppm), 7.36 g p-toluensulfomc acid (S 64 10 ppm) The polymers, once extruded, have a slight yellow colouring and. in the case of example 14 it contains high quantities of diethylene giycol and triethyiene giycol. In the case of example 13 the polymer shows a moderate acetaldehvde release, the characteristics are shown in table 1. 15 Example 15 (comparative) The example has been carried out as in example 1, though with 5.52 g of monohydrate p-toluensulfonic acid (S 48 ppm), 1.84 g of antimonium trioxide (Sb 80 ppm). As table 1 shows, the quantity of DEG is high. 0 TABLE 1 Example Sb Ti S Vi DEG CH3CHO (ppm) (dlg) (% weight) microg/g 1 4 32 _ 053 148 42 6 48 056 205 X 80 6 48 062 220 Λ 4 80 4 062 150 41 5 80 16 060 074 14 6 320 067 070 "0 7 160 066 074 62 8 120 0.50 051 47 9 80 030 nd 46 10 20 059 179 20 11 6 050 154 25 12 320 n.d 166(a) nd 13 80 6 058 090 7S 14 8 64 055 413(b) 40 15 80 48 0.61 441 30 (a) TEG 61% (b) TEG 034% n d not determined

Claims: Claims 1- Composition suitable to catalyze the polycondensation of bi(2-hydroxyetil) terephtalate or its homologous oligomers, consisting of derivatives of elements belonging to groups IIA, IIIA, IV A, VA, IIB, IIIB, IYB. VB, VTB. NUB, VIII and characterized by the fact that it contains: - a sulfonic acid in the general formula RS03H in such quantity so that sulphur in the final polymer is between 5 and 60 ppm. where R represents an organic akyiic linear or ramified radical, cyclic saturated or aromatic containing up to 20 carbon atoms; -a titanium deπvative in such quantity so that the titanium residue in the final polymer is between 1 and 6 ppm; being the derivatives of elements belonging to groups HA, III A. IV A. VA, DB, HLB, IVB. VTJB, VIIB, Viπ in such quantity so that the element in the final polymer is between 0 and 94 ppm. 2- The composition according to claim 1 is characterized by the fact that sulfonic acid is in such quantity so that sulphur in the final polymer is between 5 and 50 ppm. 3- The composition according to claim 1 is characterized by the fact that the sulfonic acid is an aromatic sulfonic acid. 4-The composition according claim 3 is characterized by the fact that the sulfonic acid is p-toiuensulfonic acid. 5 The composition according to claim 3 is characterized by the fact that the sulfonic acid is benzenesulfonic acid. 6- The composition according to claim 3 is characterized by the fact that the sulfonic acid is naphtalenesulfonic acid. 7- The composition according to claim 1 is characterized by the fact that the titanium derivative is a carboxylate. 8- The composition according to claim 1 is characterized by the fact that the titanium derivative is a alcoholate. 9- The composition according claim 1 is characterized by the fact that the element included in the composition is antimonium. 10- The composition according to claim 1 is characterized by the fact that the element included in the composition is germanium.

Inventors: PELOSINI LUIGI, PO' RICCARDO, PELOSINI, LUIGI, PO', RICCARDO
Applicants: ENICHEM SPA, INCA INTERNATIONAL SPA, PELOSINI LUIGI, RICCARDO, ENICHEM S.P.A., INCA INTERNATIONAL S.P.A., PELOSINI, LUIGI, PO', RICCARDO
Application year: 1995
Main classification: C08G63
IPC codes: C08F4, C08G63