Title of Invention

"PROCESS OF INCREASING THE MOLECULAR WEIGHT OF POLYMER GRANULES"

Abstract

A PROCESS OF INCREASING THE MOLECULAR WEIGHT OF POTYNER GRANUTES WHIC COME FROM A POLYONDNSTION PKLAQNT ARE AT LEAST PARTRY CRYSTELIZED,AND IN A POSTCONDEBNSATION ARE BROUGHT IN DIRECT CORTC WITH A NITROGEN-CONTALNING TRETMENT GAS,WHERE IN THE POLYMER GRANULE IS INCRESSE T175 to 250 0c as acomnopared top tEMPERATURY OF THE PLOYMER GRUNDULES COMING FROM THE PLOLYCOPNDENSATION PLNT HARCTERIZED ONTAINING EXHAUST GAS FRO THE POLYONDENSATION VLNYONING ECJJSIDY HSD GTP, YJRPOLYVONFRNDSYION PLSNF ID SFMXED TO THE TREATMENT GA IN A VOLUME RATIO 0F 1:1: TO100

Full Text

Process of Increasing the Molecular Weight of Polymer Granules This invention relates to a process of increasing the molecular weight of polymer granules which come from a polycondensation plant, are at least partly crystallized, and in a postcondensation are brought in direct contact with a nitrogen-containing treatment gas, where in the postcondensation the temperature of the polymer granules is increased to 175 to 250°C as compared to the temperature of the granules coming from the polycondensation plant. As polymer, there can be used polyesters such as polyethylene terephthalate (PETB), polybutylene terephthalate (PBTP), polypropylene terephthalate (PTTP) or mixed polymeres such as polyamides (PA). These polymers in pure or doped form are preferably used for producing packaging materials such as for instance films and bottles or e.g. for producing highly viscous yarns or fibers. The polycondensation of all kinds of monomers and the increase of the molecular weight by postcondensation is known. Details are described for instance in EP 0 685 502 B1, in Rompp "Chemie-Lexikon", 10th edition, page 1316, and in Houben-Weyl, "Methoden der Organischen Chemie", 4th edition, vol. E20, part 1, "Festphasen-Polykondensation (Nachreaktion in fester Phase)" (solid-phase polycondensation - secondary reaction in solid phase). Polycondensation plants are described in Ullmanns Encyklopädie der technischen Chemie, 4th edition, vol. 19, pp. 117 - 119. It is the object underlying the invention to further improve the above-mentioned process and thereby find an inexpensive solution. In accordance with the invention this is achieved in that nitrogen-containing exhaust gas from the polycondensation plant is admixed to the treatment gas in a volume ratio of 1:1 to 1:1000, before it is introduced into the postcondensation. Due to the postcondensation, the chain length of the molecules is usually increased by at least 20 % and preferably by at least 50 %. As a result, polyester granules are produced, for example, which can preferably be used for instance for bottles or films. With the chain length of the molecules the viscosity (intrinsic viscosity) of the polymer is also increased in a manner known per se. By using nitrogen-containing exhaust gas from the polycondensation plant, the addition of fresh nitrogen from outside, in order to compensate leakages, can be reduced or be omitted completely. The nitrogen-containing exhaust gas from the polycondensation plant can also contain hydrocarbons, and advantageously it is then first of all charged into a cleaning stage together with recirculated treatment gas, in which cleaning stage hydrocarbons are removed by oxidation. The treatment gas which is then introduced into the postcondensation is virtually free from O2 and is dried expediently, before it enters the postcondensation. In the postcondensation, the treatment gas effects a levelling of the temperature and the removal of the byproducts formed by chemical reactions. Expediently, the degree of crystallization of the polymer granules should be increased before the postcondensation, e.g. in fluidized-bed crystallizers. Since the treatment gas is passed through a cleaning stage before it enters the postcondensation, the nitrogen supplied to the gas circuit for compensating losses need not be of high purity. It is enough to add fresh gas rich in nitrogen with an N2 content of 80 to 99 vol-% to the treatment gas. This means a remarkable saving of costs also at this point. Embodiments of the process will be explained with reference to the drawing which shows a flow diagram of the process. To a polycondensation plant (1) known per se, starting chemicals, i.e. chiefly alcohols and acids in the case of the production of polyester, are supplied through line (2), and inert gas rich in nitrogen is supplied through line (3). As product, polymer granules are obtained, which via line (4) are supplied to a first crystallization stage (5). A first exhaust gas comes from line (6), it is rich in O2, poor in hydrocarbons, and not suited for the further utilization in the process. A second exhaust gas poor in O2 is withdrawn via line (7). This second exhaust gas consists of N2 for about 70 to 99 vol-%, it is relatively poor in O2 and contains less than 10 vol-% O2; in addition, the second exhaust gas can also contain hydrocarbons, e.g. 1 to 50 vol-% hydrocarbons . To avoid agglutinations, the polymer granules coming from line (4) are crystallized in two stages, and in the first stage (5), e.g. in the fluidized bed, they are fluidized by means of fluidizing gas rich in nitrogen from line (8) and are brought to an elevated temperature. The temperature in the fluidized bed lies in the range from 100 to 250°C and preferably is at least 150°C. The polymer granules are then passed through line (9) to the second crystallization stage (10), which for instance constitutes a paddle mixer, where the granules are heated indirectly. The two-stage crystallization, mostly with an increase in temperature in each stage, already effects an increase in the degree of crystallization, but not a sufficient increase in the molecular weight of the polymer. For the further increase of the molecular weight and hence the viscosity, the postcondensation reactor (12) is provided, to which the granules are supplied through line (11). Dry treatment gas virtually free from O2, whose main component is nitrogen, is supplied to the reactor (12) through line (13a). The treatment gas is passed upwards through the fixed bed disposed in the reactor, the temperature being levelled and reaction products being withdrawn. The dwell times of the granules in the reactor (12) usually lie in the range from 8 to 22 hours. Polymer granules with an increased molecular weight are withdrawn from the reactor (12) via line (14) and are expediently supplied to a cooling and dedusting not represented here. Used treatment gas is withdrawn from the postcondensation reactor (12) via line (15) and mixed with the gases of lines (5a) and (7). Via line (16), the gas mixture formed is passed through a cyclone (17) for dedusting purposes, and dedusted gas is sucked off through line (18) by means of the blowers (19) and (21a) and distributed over lines (20) and (21). Via the heater (22) and line (8), the gas of line (20) flows back to the first crystallization stage (5). After a fine cleaning, the gas stream of line (21) is recirculated as treatment gas to the reactor (12). First of all, fresh gas rich in nitrogen is added to the gas of line (21) through line (23), in order to compensate gas losses. A first heating is effected in the indirect heat exchanger (24), and the gas is then supplied through line (25) to an electric heater (26), so that in line (25a) the desired inlet tempera- ture for the oxidation reactor (27) is reached. The oxidation reactor (27) includes for instance a fixed bed of a granular oxidation catalyst (for instance on the basis of platinum or palladium), in order to remove hydrocarbons by oxidation. If necessary, oxygen is supplied for instance in the form of air through line (28). The gas leaving the reactor (27) via line (29) has an elevated temperature, which can be close to 400°C. The gas dissipates part of its sensible heat in the heat exchanger (24) and then flows through line (30) to another heat exchanger (31), before it is supplied through line (32) to a drying (33). The drying may operate for instance by adsorption in a manner known per se. The dried gas flows through line (13) to the heat exchanger (31) and via line (13a) flows into the reactor (12) as treatment gas. This treatment gas preferably has a carbon monoxide content of 10 to 500 mg/Nm3. Example: In a conventional polycondensation plant (1), polyethylene terephthalate (PETP) is produced from terephthalic acid, isophthalic acid and ethylene glycol, which polyethylene terephthalate is treated further as shown in the drawing. The change of the polycondensation state of the PETP granules is shown in Table I: A fluidized-bed crystallizer (5) is operated at 160°C and a paddle crystallizer (10) is operated at 205°C, the dwell time in the fluidized-bed crystallizer is 15 minutes and in the paddle crystallizer 60 minutes. In the reactor (12), the granules are provided in a fixed bed. At a temperature of 205°C, the dwell time is 11 hours. Furthermore, there is used an electric heater (26) and an absorption drying (33) by means of a molecular sieve. 7532 kg/h PETP granules of 60°C are supplied to the fluidized-bed crystallizer (5), and air is supplied through line (28). Gas. flow rates (kg/h) and temperatures (°C) are shown in Table II: Gas compositions are indicated in Table III (in kg/h), wherein OC = organic components. WE CLAIM 1. A process of increasing the molecular weight of poymer grandee which come from a polycondensestion plant, are at least partly crystalized, and in a protocondensation are brought in direct contect with a nitrogen- conteaining treatmen gas, where in the postcondensation the temperature of the polymer granules is increased 175to 250oC as compared to the tempertatuer of the granules coming from the polycondensation plant, characterized in that nitrogen-containing method gas from the polycondensation plant is a method to the teatment gas bin a volume ratio of 1:1 to 1:1000, before it is introduced into the poolecondensation 2. The process as claimed in claim 1 wherein the nitrogen-containing about gas from the poolecondensation plant contains hydrocarbons and together with the tratment gas is passed through a cleaning stage for the oxidathe rimoval of hydrocarbons before it is introduced into the postcondensation 3 the process as claimed in claim 1 or 2, wherein fesh gas gas rich in nitrogen with an N2 content of 90 to 99 vol% is added to the treatment gas. 4. The process as claimed in dclaim 1 or any of the proceding claims, wherein the cleaning stage for the adative removal of hydrocarbons includes an oxidation catalyst. 5. The process as claimed in calim 1 or any of the proceding claims, wherein from nitrgen-containing about gas from the polycondensation plant, treatment gas from the postcondensation, and from gas withdrawn from the orycitalimation a gas misure is produced, which is at least partly used as treatment gas. A process of increasing the molecular weighy of polymer granules which come from a polycondensation plant, are at least partly crystalized, and in a poolcondensations are broughy in direct contact with a nitrogen-containing treatment gfas, where in the postcondesation the temperature of the polymer granrles coming from the polycondensation plant, characterized in that nitrogen- containing aboout gas from the polycondensation plant is admined to the treatment gfas in a volume rtario of 1:1 to 1:1000, before it is intoduced into the poolcondensation.

Documents:

162-kolnp-2003-granted-abstract.pdf

162-kolnp-2003-granted-claims.pdf

162-kolnp-2003-granted-correspondence.pdf

162-kolnp-2003-granted-description (complete).pdf

162-kolnp-2003-granted-drawings.pdf

162-kolnp-2003-granted-examination report.pdf

162-kolnp-2003-granted-form 1.pdf

162-kolnp-2003-granted-form 18.pdf

162-kolnp-2003-granted-form 2.pdf

162-kolnp-2003-granted-form 26.pdf

162-kolnp-2003-granted-form 3.pdf

162-kolnp-2003-granted-form 5.pdf

162-kolnp-2003-granted-letter patent.pdf

162-kolnp-2003-granted-priority document.pdf

162-kolnp-2003-granted-reply to examination report.pdf

162-kolnp-2003-granted-specification.pdf

162-kolnp-2003-granted-translated copy of priority document.pdf