JPH08245449A - Method of post-treating residue containing dihydroxy compound - Google Patents

Abstract

PURPOSE: To provide a method for post-treating a residue containing a dihydroxy compound obtained by a polyester production in a reaction of dicarboxylic acid, its ester or its ester-forming derivative with a dihydroxy compound.

CONSTITUTION: This method for post-treating a residue containing dihydroxy compound is provided by adding a liquid residue containing dihydroxy compound in a process (b), discharging the bottom product essentially in a state of a liquid from a column and then treating it to regenerate the dihydroxy compound, and comprises (a) a first process of performing an ester interchange of a diester of a dicarboxylic acid with an alkanol by an excessive molar dihydroxy compound, (b) a process of transferring a vapor containing the alkanol obtained by the reaction (a) and mainly formed by the ester interchange, the excessive dihydroxy compound, an oligomer and polymeric reaction products into a column wherein the alkanol is separated at its head and the other products are separated as a bottom product, and (c) process of treating the bottom products further for regenerating the dihydroxy compound.

COPYRIGHT: (C)1996,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is a) obtained in the first step by the transesterification of a diester of a dicarboxylic acid and an alkanol with an excess molar amount of a dihydroxy compound, and b) obtained by the reaction of a), and mainly The vapor containing the alkanol formed in transesterification, excess dihydroxy compound and oligomer and polymer reaction products is transferred to a column in which the alkanol is separated from the top and the other products are separated from the bottom product. And c) the bottom product is then further treated to regenerate the dihydroxy compound, such as is obtained in the manufacture of a polyester by reaction of a dicarboxylic acid or its ester or ester forming derivative with a dihydroxy compound. It relates to a method of working up the residue containing the compound.

[0002]

BACKGROUND OF THE INVENTION Polyesters, especially polyalkylene terephthalates, are for the most part prepared by transesterification / polycondensation processes in which transesterification is carried out in the first step and the actual polycondensation is achieved in at least one other step. Manufactured (Chemiefasern / Textilindustrie 40 (1992), 1058-1062
And Ullmann's Enzyklopaedie der technischen Chem
ie, 4th Edition, Volume 19, pp. 61-88).

This process is briefly described using the production of polybutylene terephthalate from dimethyl terephthalate and 1,4-butanediol as an example.

In the first reaction space, dimethyl terephthalate is used in an excess molar amount, preferably 5 to 60 mol%, especially 10 to 10.
It is transesterified with 45 mol% of 1,4-butanediol and the transesterified compound is actually polycondensed in another stage. The vapor obtained by the transesterification is transferred to a column, in which, in addition to the overhead product consisting of low boiling point methanol and an excess of 1,4-butanediol, a bottom product having a small amount of oligomer, polymer and dimethyl terephthalate is produced. The thing is obtained.

Furthermore, the components obtained in the actual polycondensation and consisting mainly of 1,4-butanediol, oligomers and polymers and dimethyl terephthalate can be passed through this column.

In addition, an esterification or transesterification catalyst such as 0.05 to 0.1 kg of tetrabutyl orthotitanate per 250 kg of bottom product is used at the bottom of this column to remove unconverted dimethyl terephthalate. can do.

For environmental reasons, it is desirable to further treat this bottom product to regenerate the 1,4-butanediol present in significant amounts. However, the bottom products obtained in the known manner have a high viscosity or are solids (depending on the composition) and therefore continuous removal from the column is virtually unsatisfactory as it cannot be transported. Since this is possible, problems often arise with this methanol column, with the adverse effect of the process.
Furthermore, the work-up of this residue again gives rise to solids as bottom product, its incineration becomes more difficult and expensive to transport.

Washing the column by section to wash away the resulting residue is also a disadvantage of the continuous process.

[0009]

The object of the present invention is to post-treat the steam in a methanol column in the manner described above (again, as it is pointed out here, is that of the production of polyesters). It is usually used for, not only for the production of polybutylene terephthalate)
The bottom product obtained can therefore be removed from the column more quickly and transferred for regeneration of the dihydroxy compound.

[0010]

Surprisingly, this problem is
The liquid residue containing the dihydroxy compound is added in step b) of the claimed method, the bottom product is discharged from the column in substantially liquid form and then treated to regenerate the dihydroxy compound. It turns out to be resolved if you do.

As a result of the addition of this dihydroxy compound-containing residue, the bottom product in the column in step b) of the process remains liquid and transportable and is therefore easy from a processing engineering point of view. The process can be transferred to another column in which the dihydroxy compound is obtained from the top and the bottom product, which is also liquid or transportable, is obtained at the bottom, The bottom product can be fed to the incineration process in a simple manner.

Thus, in general, a substantial simplification of the treatment of the residue containing the dihydroxy compound is achieved, which results in considerable savings.

The novel process is detailed below, again using the production of polybutylene terephthalate as an example; however, it is again emphasized that it is also suitable for the production of other polyesters known to the person skilled in the art. Keep it.

First, dimethyl terephthalate and 1,
4-butanediol (the latter one is 5 to 60 mol%,
Preferably in excess of 10-45 mol%), 150-22
At 0 ° C., 0.7-1.5 bar, 30-90 minutes, preferably 40-70 minutes, are reacted with each other to carry out the transesterification and the methanol formed is converted into excess butanediol and a small amount of oligomer. And, together with the polymer compound and the residual amount of dimethyl terephthalate, are vapor-transferred to a column in which the dihydroxy compound is obtained, for example as obtained in the distillation of 1,4-butanediol or 1,6-hexanediol. Liquid balance is introduced at the same time. The composition of the balance does not in itself suffer any individual limitations, provided that it is in liquid form,
And there are no compounds that interfere with the separation in the column. This is generally the case for the abovementioned residues obtained from the distillation of butanediol and hexanediol.

The addition is advantageously carried out in the middle or in the lower part of the column, the addition amount generally being from 0.05 to 5 kg / kg of vapor transferred to the column, preferably 0.
It is 1 to 0.3 kg.

In the column of step b) of the novel process, low boiling methanol is separated from the top and the added residue containing the dihydroxy compound is discharged from the column together with the usual bottom products. The products that can be discharged are:
Evacuation was not possible in the case of a wax or paste or solid consistency of the bottom product as obtained by customary methods, since it can be transported in liquid form or at least transported by adding said residue. It can be carried out in an easy way from the point of view of processing engineering and especially continuously.

This considerable simplification of the processing of this residue is
Results in significantly lower costs.

Another decisive advantage of the novel process is that the bottom product obtained in the work-up in the column in step b) for the purpose of regenerating butanediol is likewise liquid and transportable. It is still possible, and therefore, to be further fed to the incineration process in a way that is easy from a processing engineering point of view. This again results in simplification and cost savings compared to conventional methods.

Thus, the addition of the residue containing the dihydroxy compound in step b) of the transesterification / polycondensation process makes it possible, for example, to considerably increase the amount of material to be finally incinerated. Result in cost benefits. The residue added according to the invention is eventually added anyway in the incineration step, which is also advantageous according to the new process, so that there is no additional cost which reduces the cost benefit.

In principle, the residue added is used only in the column of step b) and in the downstream work-up column as a transfer medium for the bottom product, which otherwise cannot be conveyed anymore. , And said residue does not itself interfere with the separation process or reaction.

[0021]

EXAMPLES Dimethyl terephthalate 99 in a stirred vessel
2 kg / h, 1,4-butanediol 640 kg / h and tetrabutyl orthotitanate 1 kg as catalyst
/ H reacted at 195 ° C. and 1 bar for an average residence time of 45 minutes. The vapor liberated in the reaction is continuously transferred to the column, and in the middle of the column, the liquid residue obtained in the distillation of 1,4-butanediol (1,4-butanediol as a main component, 2 -Methyl-1,5-pentanediol, 1,6-hexanediol, 2-methyl-
80 kg / h (containing 1,6-hexanediol and 1,2,5-pentanetriol) were added.

Methanol was continuously discharged at the top of the column and the liquid bottom product was discharged at the bottom of the column. The bottom product was separated into butanediol and transportable bottom product in another column, and the latter was fed via line to the incineration process.

The column for separating the methanol can be operated without problems and the residue can be discharged without problems via lines; if the residue is not added, as in the new process, The bottom product had a wax-to-paste consistency and could not be discharged quickly via line.

Claims (1)

[Claims] 1. a) In the first step, a diester of a dicarboxylic acid and an alkanol is transesterified with an excess molar amount of a dihydroxy compound, b) obtained by the reaction according to a), and mainly formed by transesterification. The vapor containing the alkanol, excess dihydroxy compound and oligomer and polymer reaction product is transferred to a column in which the alkanol is separated from the top and the other product is separated as the bottom product, and c ) Then the bottom product is further processed to regenerate the dihydroxy compound, containing the dihydroxy compound and the residue obtained in the production of the polyester by the reaction of the dicarboxylic acid or its ester or ester forming derivative with the dihydroxy compound. In the post-treatment method, the liquid residue containing the dihydroxy compound was Containing a dihydroxy compound, characterized in that it is added in step b) of the process and the bottom product is discharged from the column in substantially liquid form and then treated for the regeneration of the dihydroxy compound. Residual post-treatment method.