KR100322955B1 - How to Treat Residues Containing Dihydroxy Compounds - Google Patents

Abstract

The present invention,

(a) transesterifying a diester of dicarboxylic acid and alkanol with a molar excess of dihydroxy compound;

(b) vapor containing the alkanol obtained in the reaction according to step (a), predominantly produced in the transesterification reaction, excess dihydroxy compound and oligomer and polymer reaction product to the column, Separating via top and separating the remaining product as the bottom product; And

(c) a dihydride obtained in the preparation of a polyester by the reaction of a dicarboxylic acid or an ester or ester-producing derivative thereof with a dihydroxy compound, further comprising the step of further treating the bottom product to recover the dihydroxy compound. A process for the treatment of residues containing hydroxy compounds, wherein in step (b) of the process a liquid residue containing dihydroxy compounds is added and the bottom product is actually discharged in liquid form from the column and then further treated. To recover the dihydroxy compound.

Description

How to Treat Residues Containing Dihydroxy Compounds

The present invention relates to a process for treating residues containing dihydroxy compounds obtained in the preparation of polyesters by reaction of dicarboxylic acids, their esters or ester-forming derivatives with dihydroxy compounds,

(a) in the first step, a diester of dicarboxylic acid and alkanol is transesterified with a molar excess of dihydroxy compound;

(b) The vapor obtained in the reaction according to step (a), containing mainly alkanols formed in the transesterification reaction, excess dihydroxy compounds, and oligomer and polymer reaction products are transferred to a column, so as to top the alkanols. Separating via, separating the remaining product as the base product;

(c) a further process of the base product to recover the dihydroxy compound.

Polyesters, in particular polyalkylene terephthalates, are mainly produced by transesterification / polycondensation processes, transesterification reactions are carried out in a first stage, and actual polycondensation reactions are carried out in one or more further steps. Textilindustrie 40 (1992), 1058-1062, and Ullmann's Enzyklopaedie der technischen Chemie, 4th Edition, Volume 19, pages 61-88].

The method will be briefly illustrated using a method of preparing terephthalic acid polybutylene from dimethyl terephthalate and 1,4-butaldiol as an example.

In the first reaction stage, terephthalic acid dimethyl undergoes a transesterification reaction with 1,4-butanediol in molar excess, preferably 5 to 60 mol%, in particular 10 to 45 mol%, and the transesterified compound is actually condensed in a further step Cause a sum reaction. The vapor obtained in the transesterification reaction is transferred to a column to obtain a top product consisting of low boiling methanol and a base product containing a small amount of oligomer, polymer and terephthalic acid dimethyl in addition to excess 1,4-butanediol.

In addition, the components obtained in the actual polycondensation reaction and composed mainly of 1,4-butanediol, oligomers, polymers and dimethyl terephthalate can be introduced into the column.

In addition, 0.05 to 0.1 kg of esterification or transesterification catalyst, such as tetrabutyl ortho titanate, per 250 kg of base product can be used at the base of the column to separate off unconverted terephthalate dimethyl.

For economic reasons, it is suitable to further treat the base product to recover 1,4-butanediol present in significant amounts. However, problems often adversely affect the process in the methanol column because the base product obtained by known methods has a high viscosity or solids (depending on the composition) and cannot be transported and continuous recovery from the column is not possible. Occurs. In addition, the treatment of the residue once again produces a solid as the base product, the incineration of which is also complicated and expensive to transport.

Partial washing of the column to wash off the residue obtained is also a disadvantage of the continuous process.

The object of the present invention is to provide a method for the vaporization of methanol in a methanol column by the process described above (which, as pointed out here again, can generally be used for the preparation of polyesters as well as for the preparation of terephthalate polybutylene). It is to improve the treatment so that the resulting base product can be more easily separated from the column and transported for the recovery of the dihydroxy compound.

Surprisingly, we recover the dihydroxy compound after the liquid residue containing the dihydroxy compound is added in step (b) of the process according to the invention and the base product is withdrawn from the column in substantially liquid form. It has been found that the object is achieved when treated to.

As a result of the addition of the residue containing the dihydroxy compound, in step (b) of the process, the base product in the column can be held and transported as a liquid, thus transferring to an additional column in a simple manner from the point of view of process engineering. The dihydroxy compound is obtained via the top, again liquid and transportable base product is obtained at the base which can also be fed to the incineration step in a simple manner.

In general, substantial simplicity of treatment of residues containing dihydroxy compounds is achieved, resulting in significant savings.

The new process is again illustrated below using terephthalic acid polybutylene production as an example again; It is again emphasized that this method is also suitable for the production of other polyesters known to those skilled in the art.

Firstly, terephthalic acid dimethyl and an excess of 1,4-butanediol in an amount of 5 to 60 mol%, preferably 10 to 45 mol%, are 150 to 150 bar at 0.7 to 1.5 bar for 30 to 90 minutes, preferably 40 to 70 minutes. Reacting with each other at 220 ° C. to produce a transesterification reaction, the resulting methanol together with excess butanediol and a small amount of oligomer and polymer compound and residual amount of dimethyl terephthalate, for example of 1,4-butanediol or 1,6-hexanediol The liquid residue containing the dihydroxy compound, obtained in the distillation, is fed with the steam to a column which is introduced simultaneously. The composition of the residue itself is not subject to any particular limitation, provided that it must be in liquid form and no compound exists that prevents separation in the kelum. This is generally the case for the residues described above obtained from the distillation of butanediol and hexanediol.

The addition is preferably carried out in the middle or bottom of the column, with the amount added being generally from 0.05 to 5 kg, preferably from 0.1 to 0.3 kg per kg of steam conveyed to the column.

In the column in step (b) of the novel process, the low boiling methanol is separated via the top and the dihydroxy compound containing residue added is withdrawn from the column along with the general base product. Since the product to be discharged can be in liquid form or at least transported due to the addition of the described residues, the discharge can be carried out in a simple manner by process engineering, and in particular continuously, which is obtained by conventional methods, This is not possible with base products of waxy, pasty or solid hardness.

Simplification of this residue treatment significantly reduces costs.

Another decisive advantage of the novel process is that in step (b) the base product obtained in the treatment in the column can be held and transported as a liquid with the aid of the recovery of butanediol, which is recovered in a simple manner from the point of view of process engineering. It can be supplied to the incineration stage. This also leads to simplicity and cost reduction compared to conventional methods.

As such, the addition of the residue containing the dihydroxy compound in step (b) of the transesterification / polycondensation process, for example, results in significant cost savings without significantly increasing the amount of the component to be finally incinerated. The residue added according to the invention is in any case added to the incineration step (which is also finally useful according to the invention). There is no additional cost to increase the cost.

In theory, the residue added is used only as a conveying medium for the base product which can no longer be transported, both in the column and in the downstream treatment column, in step (b), the permeate itself being a separation process or Does not interfere with the reaction

Example

In a stirred kettle, 992 kg / h dimethyl terephthalate, 640 kg / h 1,4-butanediol and 1 kg / h tetrabutyl ortho titanate as catalyst were reacted at 195 ° C. and 1 bar with an average residence time of 45 minutes. . The vapor liberated in the reaction is continuously conveyed to the column and 80 kg / h of liquid residue (1,4-butanediol, 2-methyl-1,5) obtained in the distillation of 1,4-butanediol in the middle of the column -Pentanediol, 1,6-hexanediol, 2-methyl-1,6-hexanediol and 1,2,5-pentanetriol are contained as main components).

Methanol was withdrawn continuously at the top of the column and liquid base product was withdrawn from the base of the column. The base product was separated into butanediol and transportable base product in an additional column, and the transportable base product was fed to the incineration means via a pipeline.

The column for separating methanol can be operated without problems and the residue can be sold through the pipeline without problems; Without the addition of residues, as in the novel process, the base product has a wax to paste-like hardness and cannot be easily discharged through the pipeline.

Claims (1)

As a method for treating a residue containing a dihydroxy compound, which is obtained in the preparation of a polyester by the reaction of a dicarboxylic acid, an ester or an ester forming derivative thereof with a dihydroxy compound, (a) in the first step, a diester of dicarboxylic acid and alkanol is transesterified with a molar excess of dihydroxy compound; (b) The vapor obtained in the reaction according to step (a), containing mainly the alkanol formed in the transesterification reaction, the excess dihydroxy compound, and the oligomer and polymer reaction products are transferred to a column, so that the alkanol is Via gas separation and the remaining product as the base product; (c) further treating the base product to recover the dihydroxy compound, wherein the liquid residue containing the dihydroxy compound is added in step (b) and the base product is withdrawn from the column in liquid form. Treatment to recover the dihydroxy compound.