Title of Invention

A PROCESS FOR WORKING UP A RESIDUE FRACTION RESULTING FROM RAW ESTER DISTILLATION IN A DMT PROCESS

Abstract (57) Abstract: The present invention relates to a process for working up a residue fraction resulting from raw ester distillation in a DMT process, comprising: admixing the residue fraction with liquid or gaseous methanol, or both to give a reaction mixture; feeding the reaction mixture to a reactor, whereat, prior to entry into the reactor, said reaction mixture is at a temperature of from 230° to 265°C; and methanolysing the reaction mixture in the reactor, wherein a bottom portion of the reactor is maintained at a temperature of from 230° to 265°C. PRICE: THIRTY RUPEES
Full Text



The invention relates to a process for wcrKing up
a residue fraction resulting from raw ester distillation in e DMT process.


a heavy metal catalyst (DE-C 20 10 137) at a temperature of from about 140 to 180'C and a pressure of from about 4 to 8 bar abs. in the liquid phase. The oxidation stage results in a reaction mixture which contains predominant¬ly monomethyl terephthalate (MMT), p-toluic acid (p-TA) and terephthalic acid (TA) dissolved or suspended in p-TE and is esterifled with methanol at a temperature of from about 250 to 280'C at a pressure of from 20 to 25 bar abs. The raw ester obtained is separated by distillation into a p-TE fraction, a raw DMT fraction and a high-boiling, catalytic-containing residue fraction. The p-TE fraction is recirculated to the oxidation and the raw DMT fraction is converted via subsequent purification steps into the desired product quality.
The residue fraction originating from the raw distillation is generally further treated in a methanoly-sis. Figure 1 shows the flow diagram of a single-stage otethanolysis. In the reaction distillation column (1.1), the said residues (1>2) and superheated methanol vapour (1.3) are continuously introduced in countercurrent at atmospheric pressure. The bottom of the column is addi¬tionally heated by means of a heat-transfer oil (1.4). The methanolysis is carried out at a temperature of from 265 to 280"C. Part of the residues are converted into materials which can be reutilized in the process. Acids present in the residue fraction are esterifled in the methanolysis, part of the high-boiling organic compounds are dissociated and organic products of value already present are separated from undesired organic compounds which can no longer be utilized. The valuable or useful materials thus obtained go together with excess methanol via the top of the column to the dephlegmator (1.5) and cure subsequently recirculated to the process, i.e. to the oxidation (1.6). The bottom residue formed in the methanolysis is generally conveyed to catalyst recovery (1.7). It is found in practice that carbon deposits and blockages occur in the reaction column during methanolysis, resulting in more frequent and unplanned stoppages of the unit.
EP-B 0 464 046 discloses a two-stage methanolysis for working up the residue from the raw ester distilla-

tion. The first methanolysis stage here essentially comprises a reactor with upstream heat exchanger and circulation system, a distillation column is arranged downstream of the top of the reactor. In contrast to the first stage, the second methanolysis stage comprises a reaction distillation column. In both stages, additional methanol in vapour form is fed into the respective residue circuit upstream of heat exchangers, i.e. before entry into the respective methanolysis reactors. The operating temperatures for both methanolysis stages are given as more than 265'C; this applies particularly to the second methanolysis stage. Furthermore, each methano¬lysis stage is operated as a circuit and only partial streams are replaced, with the throughput amounts of the residue fraction to be worked up naturally being compara¬tively small. In addition, the two-stage methanolysis requires a high investment and high maintenance cost for operation of the plant.
It is therefore an object of the invention to provide a process which makes it possible to work up the residue fraction formed in the raw ester distillation very economically and, in particular, to reduce carbon deposits in the reactors and pipe systems of the methano¬lysis.
It has now surprisingly been found that carbon deposits can be substantially reduced in a methanolysis procedure characterized by the addition of liquid and/or gaseous methanol to the raw ester distillate, a tempera¬ture of the mixture before entry into the methanolysis reactor between 230 and 265'C and a temperature in the bottom of the reactor of between 230 and 265'C. In particular, in the present process, the reactor bottoms are not subjected to a throughput-reducing circulation procedure, by means of which the capacitor of the methan¬olysis stage is able to be significantly Increased.
The present invention accordingly provides a process for working up a residue fraction by methano¬lysis, the residue fraction originating from the raw ester distillation of the DMT production process, which is characterized in that liquid and/or gaseous methanol is fed into the residue fraction, the mixture before

entry into the methanolysis reactor has a temperature of between 230 and 265.., preferably from 245 to 255'C, and the temperature in the bottom of the reactor is likewise between 230 and 265°C, preferably from 245 to 255°C. The methanolysis is advantageously carried out at a pressure of from I to 40 bar abs., preferably at a pressure of from 1 to 3 bar abs.
Accordingly, the present invention provides a process for working up a residue fraction resulting from raw ester distillation in a DMT process, comprising: admixing the residue fraction with liquid or gaseous methanol, or both to give a reaction mixture; feeding the reaction mixture to a reactor, wherein, prior to entry into the reactor, said reaction mixture is at a temperature of from 230" to 265°C; and methanolysing the reaction mixture in the reactor, wherein a bottom portion of the reactor is maintained at a temperature of from 230° to 265°C.

Figure 2 shows a flow diagram of a preferred embodiment of the process of the invention, where the nethanolysis is carried out, in particular, in a single stage and the residue fraction from the raw ester distillation (2.1.1) is preferably worked up in a reaction distillation column (2.2). Advantageously, the residue fraction admixed with methanol (2.1.2) is here conducted via a heat exchanger (2.3) before entry into the methanolysis reactor. The heat exchanger can be operated electrically and/or by means of high-pressure steam and/or by means of a preheated heat-transfer oil, for example MARLOTHERKR. In the process of the invention, the bottom of the reactor (2.4) can also be heated electrically and/or by means of high-pressure steam and/or by means of a preheated heat-transfer oil. Advantageously, as described above, the residue fraction pretreated with methanol is reacted in the methanolysis reactor with further addition of methanol (2.5). Here too, the methanol can be fed in in liquid and/or vapour form. According to the process of the invention, the reaction is carried out under particularly gentle and comparatively mild conditions. The useful products obtainable in the reaction are advantageously recirculated via a dephlegmator (2.6) to the processed, i.e. to the oxidation stage (2.7). In the process of the invention, the proportion of useful product in the bottom of the reaction column could be reduced to about 3.5% compared with about 8.5% according to the prior art. In the process of the invention, part of the reactor bottoms can be bled off and fed to a process for catalyst recovery (2.8); the fill level in the bottom of the reactor should here be kept essentially constant. The fill level can, for example, also be regulated by means of the feed amount of the residue from the raw ester

iistillation. Part amounts can be taken from the bottom of the reactor continuously or dlscontinuously. Catalyst recovery is carried out, for example, by extraction (c£. EP-B 0 053 241).
By means of the gentle procedure in the process of the invention, the time of operation of the nethanolysis was able to be increased, which represents a further economic advantage. It was particularly surprising that the process of the invention enabled the yield over the entire DMT process to be Increased by about 0.5%, even without circulation of the reactor bottoms: this is an additional improvement in the economics of the process.
Legends for Figure 1;
Flow diagram of a methanolysis for working up a residue
from the raw ester distillation in the preparation of DMT
1.1 Reaction distillation column
1.2 Feed of the residue from the raw ester distillation
1.3 Gaseous methanol feed
1.4 Heating of the bottom of the reaction column
1.5 Dephlegmator
1.6 Recirculation of the useful product to the process
1.7 Substream of the bottom residue to catalyst recovery
Legends for Figure 2;
Flow diagram of a methanolysis of the invention for working up a residue from the raw ester distillation in the preparation of DMT
2.1 Feed of the residue (2.1.1) from the raw ester distillation, to which methanol (2.1.2) has been added
2.2 Reaction distillation column
2.3 Heat exchanger
2.4 Heating of the bottom of the reaction column
2.5 Methanol feed
2.6 Dephlegmator
2.7 Recirculation of the useful products to the process
2.8 Substream of the bottom residue to catalyst recovery


WE CLAIM:
A process for working up a residue fraction resulting from raw ester distillation in a DMT process, comprising: admixing the residue fraction with liquid or gaseous methanol, or both to give a reaction mixture; feeding the reaction mixture to a reactor, wherein, prior to entry into the reactor, said reaction mixture is at a temperature of from 230° to 265°C; and methanolysing the reaction mixture in the reactor, wherein a bottom portion of the reactor is maintained at a temperature of from 230" to 265°C.
The process as claimed in claim 1, wherein the mixture before entry into the methanolysis reactor has a temperature of from 245 to 255°C.
The process as claimed in claim 1 or 2, wherein the temperature in the bottom of the reactor is from 245 to 255°C.
The process as claimed in any one of the preceding claims, wherein the methanolysis is carried out at a pressure of from 1 to 40 bar abs.
The process as claimed in claim 4, wherein the methanolysis is carried out at a pressure of from 1 to 3 bar abs.
The process as claimed in any one of the preceding claims, wherein the residue fraction admixed with methanol is conducted via a heat exchanger before entry into the methanolysis reactor.
The process as claimed in any one of the preceding claims, wherein the heat exchanger is operated electrically and/or by means of high-pressure steam and/or by means of preheated heat-transfer oil.

The process as claimed in any one of the preceding claims, wherein the bottom of the reactor is heated electrically and/or by means of high-pressure steam and/or by means of preheated heat-transfer oil.
The process as claimed in any one of the preceding claims, wherein the residue fraction pretreated with methanol is reacted in the methanolysis reactor with further feeding in of methanol.
The process as claimed in any one of the preceding claims, wherein the residue fraction is worked up in a reaction distillation column.
The process as claimed in any one of the preceding claims, wherein the reactor bottoms are not subjected to a circulation procedure.
The process as claimed in any one of the preceding claims, wherein part of the reactor bottoms is bled off and fed to a process for catalyst recovery.
The process as claimed in any one of the preceding claims, wherein the methanolysis is carried out in a single stage.
The process as claimed in any one of the preceding claims, wherein useful materials obtainable therein are recirculated to the process.
A process for working up a residue fraction resulting from raw ester distillation in a DMT process substantially as herein described with reference to the accompanying drawings.


Documents:

806-mas-96 claims.pdf

806-mas-96 drawings.pdf

806-mas-96 abstract.pdf

806-mas-96 correspondence others.pdf

806-mas-96 correspondence po.pdf

806-mas-96 description (complete).pdf

806-mas-96 form-1.pdf

806-mas-96 form-26.pdf

806-mas-96 form-4.pdf

806-mas-96 form-6.pdf

806-mas-96 others.pdf

806-mas-96 petition.pdf


Patent Number 193907
Indian Patent Application Number 806/MAS/1996
PG Journal Number 30/2009
Publication Date 24-Jul-2009
Grant Date
Date of Filing 14-May-1996
Name of Patentee DEGUSSA AG
Applicant Address BENNIGSENPLATZ 1, D-40474 DUSSELDORF
Inventors:
# Inventor's Name Inventor's Address
1 RALF THIEL ROBERT-KOCH-STR, 20, D-53589 NIEDERKASSEL
2 REINHARD AUSCHNER MAX-ERNST-STR, 15, D-53844 TROISDORF
PCT International Classification Number C07C69/82
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA