MXPA96003493A - Procedure for treating waste from the distillation of ester raw in the elaboration of dimethyltereththalate (d - Google Patents

Abstract

The present invention relates to a process for the transformation of a residual fraction by methanolysis, in which the fraction of the residue comes from the distillation of the crude ester of the DMT processing process, characterized in that the residual fraction is added liquid methanol and / or of steam, the mixture before entering the methanolysis reactor has a temperature between 230 and 265 ° C and the temperature inside the reactor sump is also between 230 and 265

Description

PROCEDURE FOR TEATING RESIDUES FROM THE DISTILLATION OF ESTER RAW IN J? BT.ABORATION OF DIMETHYLTERETHTHALATE (DMT? The invention relates to a process for treating a residual fraction by methanolysis in which the residual fraction comes from the distillation of crude ester from the manufacturing process of DMT. Dimethylterephthalate (DMT) is produced on a large scale at a global level in many facilities. DMT is an important starting compound for the manufacture of psylesters. The fields of application of the polyesters for fibers and films, among others for photographic films and magnetic tapes or polyethylene terephthalate bottles, to present only a few examples, have been known for a long time. The current process for DMT, called "Witten" basically contains the following procedural steps (cf. European Patent EP-PS 0464 046, German Report DE-OS 40 26 733): Oxidation of para-Xylol (pX) and acid methyl ester para-Toluyl (p-TE) with purification of residual gas mounted at a later point. Esterification of the reaction products from oxidation with methanol.

Separation of the so-called crude ester obtained in a) a fraction that is recirculated upon oxidation, b) a fraction of crude DMT with more than 99% by weight of DMT and c) a residual boiling fraction more difficult including its subsequent treatment or transformation. Purification of the crude DMT fraction, for example, by washing, recrystallization and pure distillation. It is also possible to obtain terephthalic acid from DMT-rich fractions by controlled hydrolysis. The oxidation of a mixture of para-Xylol (pX) and methyl ester of para-Toluyl acid (p-TE, or pT-ester) is generally carried out with oxygen from the air in the presence of a heavy metal catalyst ( German DE-PS 20 10 137) at a temperature of the order of 140 to 180 ° C and under an absolute pressure of about 4 to 8 bars in the liquid phase. A reaction mixture containing mainly monomethylterephthalate results from the oxidation phase (MMT), p-toluyl acid (p-TA) and terephthalic acid (TA), in dissolved or suspended condition in p-TE, and which is esterified with methanol at a temperature of approximately 250 to 280 ° C and under a pressure absolute from 20 to 25 bars. The crude ester obtained is distilled off in a p-TE fraction, a crude DMT fraction and a high-boiling residue fraction containing catalyst. The fraction of p-TE is recirculated upon oxidation and the crude DMT fraction through the following purification steps is transformed into the desired product quality. The residual fraction coming from the distillation of the crude ester is generally treated at a later time, in a methanolysis. Figure 1 shows the flow diagram of a single-step methanolysis. In the reactive distillation column (1.1), the mentioned residues (1.2) and the superheated methanol vapor (1.3) are continuously introduced, without back-pressure. The column sump is additionally heated through a heat carrier oil (1.4). The methanolysis is operated at a temperature between 265 and 280 ° C. In this case, a large part of the waste is transformed into substances that can be reused for the process. The acids present in the residual fraction are subsequently esterified in the methanolysis, a part of the organic compounds of high melting point dissociates and the organic useful products already present are separated from those organic compounds, unwanted and no longer usable. The valuable or useful substances thus obtained arrive together with the excess of methanol through the head of the column in the dephlegator (1.5) and are then recirculated to the process, that is to say to the oxidation (1.6). The sink residue that occurs during methanolysis it is generally fed to the catalyst recovery (1.7). The practice shows that in methanolysis there are coking and congestion in the reaction column and the consequence is more frequent unscheduled equipment interruptions. EP-PS 0 464 046 discloses methanolysis, coking and congestion in the reaction column and consequently more frequent and unscheduled interruptions of the equipment. From EP-PS 0 464 046 a two-step methanolysis for the treatment is known, of the residue from the distillation of the crude ester. The first step of methanolysis here essentially consists of a reactor with its previous heat exchanger and recirculation system, and behind the reactor, a distillation column has been mounted on the head side. The second stage of the methanolysis contains, in contrast to the first, a reaction distillation column. In both stages, the methanol is further fed in the form of steam and before the heat exchanger, ie before entering the corresponding methanolysis reactors, to reach the corresponding circulation stream for the waste. The operating temperatures are indicated for both steps of methanolysis with levels of more than 265 ° C, and this applies specifically to the second step of methanolysis. Each step of methanolysis is operated additionally in a circuit system and only partial streams are substituted, while the flow rates are of course comparatively low in relation to the residual fraction subject to transformation. It can also be said that two-step methanolysis requires a costly investment and high maintenance costs to operate the equipment. Therefore, it has been the task of the present invention to provide a process that makes it possible to transform in the most economically possible way the residual fraction produced during the distillation of the crude ester and in particular reduce the coking in the reactors and in the conduction systems of the methanolysis. It has now surprisingly been found that with a methanolysis process characterized by the addition of liquid methanol and / or in the form of steam to the raw ester distillate material, by a mixing temperature before entering the methanolysis reactor of 230 a 265 ° C and for a temperature in the reactor sump from 230 to 265 ° C, coking has been reduced to a maximum. In particular, the reactor sump is not subjected, in this process, to any circuit method that reduces the flow rate by which the capacity of the methanolysis step has been clearly increased. The object of the present invention is therefore a process for transforming a residual fraction by methanolysis, wherein the residual fraction comes from the distillation of the crude ester of the DMT processing process which is characterized in that the residual fraction is fed to the methanol in liquid form and / or steam, because the mixture before entering the methanolysis reactor has a temperature between 230 and 265 ° C, preferably between 245 and 255 ° C and the temperature in the reactor sump is also between 230 and 265 ° C , preferably between 245 and 255 ° C. The methanolysis is effectively operated at an absolute pressure of 1 to 40 bar, preferably at an absolute pressure of 1 to 3 bar. Figure 2 shows a flow diagram of a preferred embodiment of the process according to the invention in which the methanolysis is operated particularly in a single step and the residual fraction from the distillation of the crude ester (2.1.1) is preferably treated in a reaction distillation column (2.2) the residual fraction mixed with methanol (2.1.2) is effectively conducted here before entering the methanolysis reactor, through a heat exchanger (2.3). The heat exchanger can be operated electrically and / or with high-voltage steam and / or with some heat-carrier oil, preheated, for example, MARLOTHERM®. The reactor sump (2.4) can also be heated in the process according to the invention either electrically and / or with high-voltage steam and / or with a pre-heated heat-carrier oil. The residual fraction previously treated with methanol is reacted, as indicated above, in the reactor for the methanolysis under additional feed of methanol (2.5), whereby the methanol can also be fed in liquid and / or vapor form. The reaction is carried out according to the process according to the invention under extremely clean conditions and under comparatively mild conditions. Suitably the useful products thus obtained are recirculated first through a deflector (2.6) and then to the process, that is, to the oxidation stage (2.7). The portion of the product useful in the sump of the reaction column could be reduced in the method according to the invention to a level of the order of 3.5%, compared to about 8.5% corresponding to the current state of the art. In the process according to the invention, a portion of the reactor sump can be selectively extracted and this material fed to a process for recovering catalyst (2.8), in which case the degree of filling of the reactor sump must be maintained to a high degree. it can be regulated, for example, also by the amount introduced of the residue from the distillation of crude ester. The extraction of partial quantities from the reactor sump can be carried out continuously or intermittently. The recovery of the catalyst is carried out, for example, by extraction (cf. EP-PS 0 053 241).

By the efficient process in the process according to the invention it has been possible to lengthen the effective time of the methanolysis, which constitutes another economic advantage. Particularly surprising that by the method according to the invention the yield in the entire DMT process could be increased by approximately 0.5%, even without a system in circuit, all in relation to the reactor sump. This constitutes a complementary improvement in the economy of the process. Legend Regarding Figure 1: Flow diagram of a methanolysis to operate a residue from the distillation of the crude ester in the manufacture of DMT. 1.1 Reaction distillation column 1.2 Feeding the residue from the distillation of the crude ester. 1.3 Feeding methanol in the form of vapor. 1.4 Heating the sump of the reaction column. 1. 5 Dephlegator. 1.6 Return of the products useful to the process. 1.7 Partial current of the sump residue for catalyst recovery. Legend referring to Figure 2: Flow diagram of a methanolysis according to the invention to produce a residue from the distillation of the crude ester in the production of DMT. 2.1 Feeding the waste (2.1.1) from the distillation of the crude ester, to which methanol has been added (2.1.2). 2.2 Reaction distillation column. 2.3 Heat exchanger. 2.4 Heating the sump of the reaction column. 2. 5 Methanol feed. 2.6 Dephlegator. 2.7 Return of the products useful to the process. 2.8 Partial current of the sump residue to recover catalyst.

Claims (3)

1. NOVELTY OF THE INVENTION Having described the foregoing invention, the content of the following CLAIMS is claimed as property; 1. The process for the transformation of a residual fraction by methanolysis, in which the fraction of the residue comes from the distillation of the crude ester of the DMT processing process, characterized in that the residual fraction is added liquid methanol and / or in the form of steam , the mixture before entering the methanolysis reactor has a temperature between 230 and 265 ° C and the temperature inside the reactor sump is also between 230 and 265 ° C. 2. The process according to claim 1, characterized in that the mixture before entering the methanolysis reactor has a temperature between 245 and 255 ° C. 3. The process according to claim 1 or 2, characterized in that the temperature in the sump of the reactor is from 245 to 255 ° C. 4. The process according to any of the preceding claims, characterized in that the methanolysis is carried out at an absolute temperature between 1 and 40 bars 5. The process according to claim 4, characterized in that the methanolysis is carried out at an absolute pressure of 1 to 3 bar.
2. The process according to any of the preceding claims, characterized in that the residual fraction mixed with methanol is conducted through a heat exchanger before being introduced into the methanolysis reactor. The method according to any of the preceding claims, characterized in that the heat exchanger is operated electrically and / or with high pressure steam and / or with preheated heat carrier oil. The method according to any of the preceding claims, characterized in that the reactor sump is heated electrically and / or with high pressure steam and / or with a preheated heat carrier oil. The process according to any of the preceding claims, characterized in that the residual fraction pretreated with methanol is reacted in the methanolysis reactor under additional methanol feed. The process according to any of the preceding claims, characterized in that the residual fraction is transformed into a reaction distillation column. The method according to any of the preceding claims, characterized in that the reactor sump is not subjected to any circuit procedure. The method according to any of the preceding claims, characterized in that it is selectively extracted
3. 3. a portion of the reactor sump and is fed to a process for recovering catalyst. The process according to any of the preceding claims, characterized in that the methanolysis is operated in a single step. The method according to any of the preceding claims, characterized in that the useful substances that can be obtained are returned to the process. SUMMARY: PROCEDURE FOR DEALING WITH WASTE FROM THE DISTILLATION OF RAW ESTER IN ELABORATION OF DIMETHYLTERETHTHALATE (DM-H The present invention relates to a process for treating a residual fraction by methanolysis, in which the residual fraction comes from the distillation of crude ester in the DMT process, which is characterized in that the residual fraction is methanol in liquid form. and / or in the form of steam, because the mixture before entering the methanolysis reactor has a temperature between 230 and 265 ° C and because the temperature in the reactor sump is also between 230 and 265 ° C. - 2 - In compliance with article 47 of the Industrial Property / I declare in the name of the applicant / and under protest to tell the truth, that the method described here is the best known by her to carry out the invention contained herein. IN FAITH WHEREOVER, I sign the present in Mexico City / D.F., today on the nineteenth day of the month of August one thousand nine hundred and ninety six HÜLS AKTIENGESELLSCHAFT.