MXPA97003991A - Improved procedure for the production of polyes resins - Google Patents

Abstract

The present invention relates to a process for the production of aromatic polyester resins by polycondensation in the solid state of resins with intrinsic viscosity comprised between 0.1 and 0.45 dl / g, in which the proportion by weight between the flow rate at each hour of the inert gas fed to the reactor and the hourly flow rate of the fed polymer is comprised between 0.1 and 0

Description

IMPROVED PROCEDURE FOR THE PRODUCTION OF POLYESTER RESINS DESCRIPTIVE MEMORY r, The present invention relates to an improved process for polycondensation in the solid state of polyester esines. Aromatic polyester resins, particularly three of them, polyethylene terephthalate (PET), copolymers of terephthalic acid with a lower proportion of isophthalic acid, and terephthalate of [> In addition, they find wide application in the fields of fibers as well as films and as material for molding. 1 ri Whereas for the fibers and films the intrinsic viscosity of the resin is generally understood • "ntt 0.6-D. In the case of the molding route, higher values are needed which are difficult to obtain directly by means of polycondensation in the state ? f) fund do. The intrinsic viscosity is brought to desired values (generally greater than 0.75 dl / g) by means of pol condensation in the solid state of the resin (SSP) operating at temperatures generally comprised between 190 ° and 23p ° C. The elimination of polycondensation reaction products is an essential requirement for the deaeration of the same reaction. Several reactions occur during the polycondensation. The main reaction leading to the increase in molecular weight of the PFT is the imining of the long LCO! .

PET - COO - CH: - CH - OH - HO - CH2 - CH2 - OCO - PET I 1 PET - COO - CH: - CH2 - OOC - PET + HO - CH2 - CH2 - OH Other reactions lead to the esterifi cation of the terminal carboxylic groups and the formation of acetal e do. As already indicated, the byproducts of the polycondensation reaction are eliminated by passing a flow of gas downstream or upstream, leaving the polymer feed from the start of the cooling stage. The pol condensation reaction is generally carried out in a longitudinal fluidized bed reactor, where the polymer enters from above and exits from below and a flow of meta gas is passed over the polymer. Procedures such as this are known, for example, from the patent US-R-4 064 112, in which the granular polymer crystallizes at a density suficiently? high to reach at least 1,390 g / crn3 operating in forced motion glass heated to a temperature between 220 ° and 250 ° C and then carrying out the polycondensation reaction in a fluid bed reactor operating at equal or lower temperatures than those used in the crystallization stage. In the crystallisation stage, the operation is carried out at temperatures between 230 ° and 245 ° C to obtain the same temperature values at a density of 1,403 - 1,415 g / cm3 and at a temperature between 230 ° and 245 ° C in the polycondensation stage to obtain an optimum reaction rate combined with a low degree of degradation of the polymer. An inert gas, preferably nitrogen, is used to remove the by-products formed during the pol condensation stage. The gas is recirculated after purification of its by-products. When the water content in the recirculated gas is too high, the hydrolytic cleavage reactions of the polymer increase considerably; When the glycol content exceeds a limit value, the reaction rate decreases signi icantly. High values of oxygen and acetaldehyde determine the discoloration in the formed article; high values of acetal deludo are not allowed in the articles destined for the alimentary sector. To limit1 the costs of purification of the gas to be recirculated and the energy costs of maintaining the gas flow, the ratio R between the mass flow to each hour by weight of the gas and the flow per hour per hour per weight of the polymer that leaves the reactor, it is maintained on a scale of 0.7: 1 to 1: 1, referring to 1.1 2: 1. Using values lower than 0.7 (0.5 and, .3 in the examples) and operating under the conditions reported in the Patent US-A-4 064 112 (crystallization temperature of 235 ° C and polycondensation temperature of 230 ° W), the intrinsic viscosity of the polymer does not increase significantly. In addition, there is an increase in the temperature difference across the reactor section using proportions less than 0.7. US Pat. No. 4,171,558 describes a crystallization / polycondensation process in the sol-sol state, in which the granular polymer is crystallized in an apparatus with forced circulation equipment operating at temperatures between 180 ° and 235 ° C. ° C until a degree of crystallinity is obtained corresponding to a density of at least 1385 g / cm3 and is subsequently fed to the forced polycondensation reactor in which the polymer is heated at higher temperatures than those used in the stage of crystallization. In the polycondensation reactor, the nitrogen is circulated upstream with the polymer feed, with a flow ratio by weight between 0.7 and 3.5 k and N2 / t-g PET. In a prior patent application by the applicant, it had been found that it was possible to operate with ratios R less than 0.6 and efficiently remove the byproducts of the SSP reaction, thereby achieving high reaction kinetics.

The polyester resin subjected to SSP had VT values not lower than 0.6 dl / g. Operating with start-up VI to reach the same VI final, the generation of organic reaction byproducts is much higher and, thus, the concentration of glycol and other organic products in the flow of inert gas is higher for the same proportion R of gas / solid used. Figure 1 shows the variation in concentration (in kg of kg and kg kg of nitrogen) in relation to the ratio R of gas / solid (kg of nitrogen / l <g of PFT) for two different cases: a) polycondensation in the solid state starting from VI = 0.2 with white VI = 0.8 dl / g; b) polycondensation in the solid state starting from VI = 0.6 with white VT = 0.8dl / g. It has now been found that, even using proportions R between 0.1 and 0.6, it is surprisingly possible to efficiently remove the polycondensation reaction byproducts, thereby obtaining high reaction kinetics even when the polyester resin to be subjected to polycondensation in the state solid has a relatively low intrinsic viscosity comprised from 0.1 to 0.45 dl / g. The use of these low proportions allows high energy savings in the gas blowing operation. The proportion R to be used is preferably comprised between 0.2 and 0.5. In the process of the invention, the polycondensation reaction is carried out at a temperature comprised between 180 and 250 ° C, preferably between 210 ° and 35 ° C. The degree of crystallinity of the polymer undergoing the SSP reaction is generally between 40 and 50% by weight. The precursor is generally in the form of spheroidal or lenticular particles obtained, for example, by allowing the polymer to pass through a perforated head and collecting the obtained polymer droplets in a water bath. The flow of inert gas leaving the SSP reactor undergoes purification procedures that lead to the elimination of the impurities of the organic products present in it. The operation is carried out according to the procedure described in the patent UO-fl-95 02 446, the description of which is incorporated herein by reference. The average residence times in the SSP reactor are sufficiently long to obtain an increase in the intrinsic viscosity of the polymer of at least 0.3 dl / g; in general, they are between 15 and 40 hours. The increase in kinetics of the intrinsic viscosity can be markedly improved if the polymer is mixed in the molten state, in a state prior to crystallization, with a functional pol i compound containing two or more groups, capable of reacting through the reaction of addition with the OH and COOH end groups of the polyester. Examples of these compounds are pyromelic anhydride and generally the aromatic or aliphatic acid and r-carboxylic acid dianhydpides. These compounds are used in an amount generally comprised between 0.01 and 2% by weight of the polymer. The pyroclastic anhydride is the preferred compound.

The use of these compounds is described in EP-B-422 282, US-P-5 243 020, US-FL-5 334 669 and US-A-5 338 808, the disclosure of which is incorporated herein by reference. The polyester resins used in the process of the invention comprise the condensation products of C2-C12 diols, such as, for example, glycol ethanol, Uutilin glycol, 1,4-cyclohexanedirine diol with aromatic dicarboxylic acids, such as terephthalic acid, 2,6 naphthalenedicarboxylic acid or reactive derivatives thereof, t or the lower alkyl esters, for example, dimethyl terephthalate. Polyethylene terephthalate and polybutylene terephthalate are the preferred resins. Part of the whole units may be replaced by units derived from other dicarboxylic acids such as softalic acid and naphthalene dicarboxylic acid in amounts ranging from 0.5 to 20% by weight. The following examples are given to illustrate, but not to limit, the invention. The intrinsic viscosity reported in the text and in the examples is measured in a solution of 0.5 g of polymer in 100 ml of a solution 60/40 by weight of phenol and t-trichloroethane at 5 5 ° C according to ASTM 4603 patent -86.

EXAMPLE 1 PET in granular form with VI-0.20dl / g, previously crystallized at a crystallinity value of 40%, had been fed, after having been heated to 215 ° C, in a fluid bed reactor for polycondensation in the state solid with a mass flow of kg / h. The reactor was fed overhead with nitrogen with a loop flow at every hour sufficient to obtain a ratio by weight (R) between the gas and the fed polymer of 0.4. I1"*) The polymer is heated to a temperature of 215 ° C with a long residence time to allow an increase of Q." 5 dl / g. of the intrinsic viscosity. The final VT of the polymer was 0.75 dl / g. The residence time was '30 hours. 0 EXAMPLE 2 Test according to example i, with the difference that the temperature of the polymer fed and maintained in the reactor was? 25 ° C. The VI of the polymer after 30 hours of residence time was 0. 88 dl / g.

EXAMPLE 3 Test according to example 1, with the difference that COPET containing 2% isophthalic acid was fed. An IV was obtained = 0.78 dl / g with a residence time of 30 hours.

EXAMPLE 4 Test according to example 1, with the difference that polyfill terephthalate with VI = 0.18 dl / g, heated at a temperature of 203 ° C, was fed and kept in the pol condensation reactor at the same temperature obtaining a VI-D.96 dl / g with a residence time of 30 hours.

COMPARATIVE EXAMPLE Example 1 repeats, with the difference that the ratio R was 0.05. After a residence time of 30 hours, the final VT was 0.40 di / g.

Claims (10)

NOVELTY OF THE INVENTION CLAIMS

1. - Continuous process for polycondensation in the solid state of aromatic polyester reams with intrinsic viscosity (VI) between 0.10 and 0.45 dl / g, in which the resin is fed from above the mobile bed reactor and released from below, and an inert gas is circulated upstream and downstream of the ream and the reactor temperature is maintained between 180 ° C and 250 ° C with average residence times of the res to sufficiently long to obtain an increase of at least 0.3 dl / g in the intrinsic viscosity of the polymer, characterized in that the proprion R between the hourly mass flow of the gas and the polymer leaving the reactor is between 0.1 and 0.6.

2. Method according to claim 1, wherein the VI of the polymer is between 0.15 and 0.30 dl / g.

3. Method according to claims 1 and 2, wherein the ratio R is between 0.2 and 0.5.

4. Method according to claims 1, 2 or 3, wherein the temperature of the reactor is between 210 ° C and 235 ° C, 5.- Procedure in accordance with claims 1,2,3 or 4, in where the inert gas is nitrogen. 6. Method according to claim 5, wherein the nitrogen is circulated downstream with the polymer. 7. Process according to any of the preceding claims, wherein the polyester resin is selected from the group consisting of polyethylene terephthalate, copolyethylene terephthalate containing from 20% units deriving from isophthalic acid and polybutylene terephthalate. 8. Method according to any of the preceding claims, wherein the nitrogen is recirculated in the reactor after being purified of organic impurities until reaching impurity values lower than 10 pprn expressed as co or methane equivalents. 9. Method according to any of the preceding claims, in which a tetracarboxylic acid dianhydride in amount from 0.01 to 1% by weight is added to the polycondensate reaction in the solid state. 10. Method according to claim 9, wherein the dianhydride is the irimo dianhydride! Italian