Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Patent
1995-08-10
1997-06-03
Acquah, Samuel A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
528272, 5283086, 528503, 203 18, 203 73, 203 75, 203 82, C08F 600
Patent
active
056355904
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the treatment of contaminated ethylene glycol which results during a polycondensation process for the production of polyester, wherein the contaminated ethylene glycol is subjected to preliminary distillation for separation of water and the low-boiling fractions, then as a distillation residue is subjected to secondary distillation and the ethylene glycol resulting as a distillate is condensed.
During the polycondensation process for the production of polyester contaminated ethylene glycol results. So for instance a ethylene glycol/water mixtures is formed in the esterification stage, during the esterification of terephthalic acid with ethylene glycol, forming polyester. This ethylene glycol/water mixture is fed to a preliminary distillation column, in order to eliminate water and other low-boiling fractions by distillation over the top of the preliminary distillation column and to condense them in a subsequently arranged condenser. For the treatment of the contaminated ethylene glycol and consequently the recovery of the same ethylene glycol, the bottom product, respectively the distillation residue which consists of ethylene glycol, diethylene glycol and other secondary products, have to be directed to an off-line distillation apparatus, which consequently is not a part of the polycondensation installation. Such an off-line distillation apparatus is expensive from the point of view of plant technology, requires in addition considerable investments and is also disadvantageous from the point of view of space and service personnel requirements. In addition thereto the contaminated ethylene glycol resulting during the polycondensation stage from the cycles of the spray condensers and vacuum pumps, as well as when the polycondensation apparatus is started and closed down, has also to be fed to the off-line distillation apparatus, and as a consequence has to be decontaminated in the course of an interrupted treatment process. The known treatment of contaminated ethylene glycol is unsatisfactory as a whole, from the point of view of process technology as well as plant engineering.
It is the object of the invention to indicate a treatment process of the above-described type, according to which the contaminated ethylene glycol resulting during a polycondensation process can be perfectly decontaminated in a rational, functionally safe and technologically simple way.
The invention solves this problem in the case of a generic process due to the fact that during the polycondensation process the contaminated ethylene glycol is continuously predistilled, then subjected to secondary distillation as a distillation residue, preferably under vacuum, then condensed and again fed to the polycondensation process, respectively its consumers, as decontaminated ethylene glycol. According to the teaching of the invention an in-line vacuum distillation of the entire contaminated ethylene glycol resulting from the polycondensation process takes place. Indeed the ethylene glycol recovery is integrated into the polycondensation process, namely by combining distillation process and treatment tasks. This way an external ethylene glycol recovery becomes superfluous. The ethylene glycol treatment of the invention leads to a particularly good cleansing, so that the decontaminated ethylene glycol is particularly suitable for use in polycondensation installations for producing high-quality polyester products, such as granulate for the production of microfibers, foils, films and bottles. In fact the quality of fresh glycol is reached. In this connection it is particularly important that the secondary distillation take place in vacuum, so that the usually high thermal oxidative load of the glycol is eliminated and an optimal product quality is achieved, namely the quality of fresh glycol. This way savings of fresh glycol are generated.
Further steps which are essential to the invention are mentioned in the following. So for instance the invention provides that the ethylene glycol/water mixture resulting
REFERENCES:
patent: 3878055 (1975-04-01), Cox et al.
patent: 4110316 (1978-08-01), Edging et al.
Geier Rudolf
Rink Jurgen
Stemmer Klaus
Acquah Samuel A.
Dubno Herbert
John Brown Deutsche Engineering GmbH
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