DD220839A1 - CLEANING REACTION BOILERS AND SUBSEQUENT DEVICES FOR POLYALKYLENEEPHTHALATE MANUFACTURE - Google Patents

Abstract

The invention relates to a process for purifying reaction vessels and subsequent devices for polyalkylene terephthalate production. The aim and the object is to dissolve the deposits of thermally and thermally oxidatively damaged polyalkylene terephthalate in a short time with a low solvent use on the inner walls of reaction vessels and subsequent devices and thereby increase the purity of the melt in the production of polyalkylene terephthalate. According to the invention, the solvent is used effectively in the state of the condensing vapor phase. The vaporous solvent is introduced into the reaction vessel where it condenses on the inner wall releasing the polyalkylene terephthalate deposits. The low-boiling steam-soluble fission products are removed from the top of the system, while the condensate is again subjected to evaporation outside the reaction vessel and returned to the purification process in a continuous cycle. To accelerate the condensation effect, the reactor wall can be cooled from the outside with a gaseous or liquid heat carrier.

Description

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Title of the invention -, '

Purification of reaction vessels and subsequent devices for polyalkylene terephthalate production

Field of application of the invention;

The invention relates to a process for the purification of reaction vessels, pipelines and the associated devices for the production of polyalkylene terephthalates.

C harakteristik of the known technical ^solutions,

Continuous deposition of damaged polyester on the inside wall of the unwashed parts of reactor vessels and in pipelines poses a major problem for the melt's purity. By chipping off these solid deposits due to tempera ture. and pressure surges or when purging these parts with ungehydrated product reach the polyalkylene terephthalate melt contaminating degradation products in the manufacturing process. This results in quality deterioration of the final product.

To eliminate the unwanted deposits, various mechanical and chemical cleaning methods have been developed. One of the oldest is the manual cleaning by repelling or scrapping the polymeric residues. However, this process requires long downtimes,) often leads to damage to the reactor surface and is only partially practicable in pipelines. Other methods propose various solvents and additives to remove polymeric materials. As a solvent z. For example, triethanolamine (US Pat. No. 3,740,267), N-methyldiisopropanolamine or W-ethyldiethanolamine (GB Pat. No. 1,323,886), tetrahydrofuran / water in one

Ratio of 95: 5 parts (JP - OS 7678 794) and others used. They all have the disadvantage that no satisfactory cleaning effect is achieved. Further processes use glycols and glycol mixtures with or without additives for the removal of polymeric residues (JP-PS 79 050 615, JP - ES 80 012 162, JP - PS 80 016 017, JP-PS 80 013 755, JP - PS 74 018 195, JP - PS 74 026 241, JP - PS 74 011 636, JP ~ PS 74 121 894, JP - PS 76 050 911, JP - PS 76 050 308, JP - 'PS 76 016 396). The disadvantages of these methods are based on the large amount of solvent required in order to rinse the damaged polymer layers directly with solvent. This procedure also does not guarantee a sufficient cleaning effect despite long exposure times.

Object of the invention

The aim is to achieve within a short time with a small amount of solvent an improved cleaning effect on reaction vessels and subsequent devices. This is intended to increase the purity of the melt in the production of polyalkylene terephthalates.

Explanation of the essence of the invention

Pie object of the invention is to quickly and effectively detach the deposits of damaged polyalkylene terephthalate from the inner walls of the reaction kettle, piping and associated devices.

According to the invention, this is achieved when the solvent is used in the state of the condensing vapor phase. For this purpose, ethylene glycol and / or oligoethylene glycol is heated to a temperature in the vicinity of the boiling point and ^[ the steam in the reaction vessel to be cleaned or

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directed into adjacent devices. The vapor condenses on the inner wall and causes a dissolution of the thermally and thermooxidatively damaged and deposited polyalkylene terephthalate. The solvent condensate is continuously, leached from the Reaktionskesael or · the pipeline removed, transferred outside the reactor again in the vapor phase, and recycled in the cycle in the purification process. To accelerate Löaungmittelkondensation the .. '' reactor wall can be cooled from the outside with a gaseous or liquid heat transfer medium. The low-boiling vaporous cleavage products are removed overhead from the system. Due to the continuous circulation mode, a high cleaning effect is achieved within a short time.

Ausführungabeispiel

Triäthylengiykol was converted in a heat exchanger at a temperature of 280 - 285 ⁰ C in the vapor state and introduced into the reaction vessel to be cleaned. By constantly blowing the reactor wall with air, an additional cooling of the inner wall was achieved, which in turn caused a faster condensation of the solvent vapor. Was about ¹ / 10th, of the reactor volume with condensate which was supplemented with polymer filled, that the set level border amount of condensate was continuously pumped out again transferred in the heat exchanger in the vapor state and is introduced in circulation into the reaction vessel. The volatile decomposition products were removed from the system via a degassing line with upstream reflux condenser. The cleaning process was carried out for 5 hours. ^l 'advantages of this method consisted in a small amount of solvent consumed and a high cleaning effect was achieved in a short time. The proportion of melt-contaminating particles could be reduced to 30 % .

Claims (2)

1> Purification of reaction vessels and subsequent preparation for polyalkylene terephthalate production using ethylene glycol and / or oligoethylene glycol as solvent, characterized in that the solvent in the vapor state is passed into the reaction cell to be cleaned and the subsequent gate directions, then, by condensing the solvent vapor on the inner wall, dissolving the solid deposits of the thermally and thermo-oxidatively damaged polyalkylene terephthalate, and removing the low-boiling gaseous cleavage products overhead from the process while removing the condensed polymer-enriched solvent from the system subjected to evaporation and recirculated to the cleaning process in a continuous cycle 2. Method, characterized in that the solvent vapor can be cooled from the outside by means of a gaseous or liquid heat carrier.