MXPA97003082A

MXPA97003082A - Procedure for the separation of ester in the process of

Info

Publication number: MXPA97003082A
Application number: MXPA/A/1997/003082A
Authority: MX
Inventors: Lenz Udo; Detlef Dahl Hans
Original assignee: HÜLS Aktiengesellschaft
Priority date: 1996-05-07
Filing date: 1997-04-28
Publication date: 1998-07-03

Abstract

The present invention relates to a process for the separation of crude so-called ester, which is basically obtained by the catalyzed oxidation of para-xylene (pX) and methyl-ester of para-toluyl acid (p-TE), and the subsequent esterification of the products of reaction from oxidation with methanol in the manufacture of dimethylterephthalate (DMT), in a fraction rich in p-TE, a fraction of crude DMT and a fraction of difficult boiling residue, the separation of the crude ester being carried out in a separating unit containing a separating column, or a distillation column with a preliminary column, or a distillation column with a subsequent column. The invention also relates to a process for the manufacture of dimethylterephthalate (DMT), the separation of the crude ester being carried out in a separating unit which is equipped with a separating wall column, a distillation column with a preliminary column, or a distillation column with a posteri column

Description

PROCEDURE FOR THE SEPARATION OF THE RAW STEREO IN THE DMT PROCESS The present invention relates to a process for the separation of the so-called crude ester, which is obtained basically by the catalyzed oxidation of para-xylene (PX) i And para-toluyl acid methyl ester (p-TE) and the subsequent esterification of the reaction products from oxidation with methanol in the preparation of dimethylterephthalate (DMT), in a fraction rich in p-TE, as a fraction of crude DMT, and a fraction of difficult boiling residue, and also concerns the related process for the preparation of dimethylterephthalate (DMT). It is known that the current process of ITT to obtain DMT basically comprises the steps: oxidation of para-xylene (pX) and of methyl ester of para-toluyl acid (p-TE), as a rule with a residual gas purification assembled after, esterification of the reaction products from oxidation with methanol, separation of the so-called crude ester obtained (Raw DMT) in a fraction rich in p-TE, which is usually returned to oxidation, a fraction of crude DMT, which generally contains more than 85% by weight of DMT, and a fraction of boiling residue difficult, optionally its subsequent treatment, by means of a methanolysis or thermolysis placed at a later point, as well as the subsequent recovery of the catalyst, purification of the crude DMT fraction, for example, by washing, recrystallization and pure distillation, ("Terephthalsauredimethylester", Ullman, Volume 22, 4th edition, page 529-533; European Report EP 0 464 046 Bl and German Report DE-OS 4026733). It is also possible to elaborate from the DMT, that is to say from fractions particularly rich in DMT, or DMT of maximum degree of purity, the terephthalic acid of corresponding quality, through a controlled hydrolysis. Oxidation of a para-xylene mixture (pX) and para-toluyl acid methyl ester (p-TE, or pT-ester) is generally carried out with the oxygen in 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 a pressure of about 4 to 8 bars, absolute, in the liquid phase. From the oxidation stage, a reaction mixture results, which mainly contains monomethylterephthalate (MMT), p-toluyl acid (p-TA) and terephthalic acid (TA), in dissolved or suspended condition in p-TE, and it is esterified with methanol at a temperature of the order of 250 to 280 ° C, and a pressure of 20 to 25 bar, absolute. In a separation unit, which in the following is also called distillation of the crude ester, the crude ester obtained is now separated, by distillation, into a fraction of p-TE, a crude DMT fraction and a residue fraction of difficult boiling, which contains catalyst. The p-TE fraction is returned to oxidation, and the crude DMT fraction through the subsequent purification steps is transformed into the desired quality. The fraction of residue coming from the distillation of the crude ester can be subjected to methanolysis or thermolysis, and the useful products thus obtained are returned to the process. In the ITT procedure to obtain DMT, they are used for the execution of the distillation of the crude ester, usually the system of cooling chambers, compare Figure 1, as well as the system of 2 columns, compare Figure 2. It is also knows a system of 3 columns (German Report DE-9S 30 11 858). However, in these systems it is a disadvantage that in addition to the fraction rich in p-TE, the fraction of raw DMT must also be operated on the head, whereby a greater energy consumption is created. Likewise, clear quantities of undesired byproducts are formed in the systems mentioned above, favored by the long residence times in the column sumps, and these by-products notably reduce the yields of production. further, it can be said that the system of abrupt cooling chambers or of 2 or 3 columns is at the same time an important economic factor for the structuring, operation and maintenance of equipment to produce DMT. Therefore, it has been the task of the present invention to provide a process for the separation of the crude ester in the DMT process which makes it possible to lower the energy consumption in the process, and thus also increase the economy to a greater extent. The problem is solved according to the invention, according to the data contained in the claims of this patent. It has now been found that in the DMT process substantial amounts of energy can be saved when the separation of the crude ester is carried out in a separating unit containing a distillation column with separating wall, briefly also called column with separating wall, or a distillation column carrying a preliminary column, or a distillation column with a subsequent column. In its essence are already known the systems of columns with distillers columns, which carry a separating wall, as well as the columns with their auxiliary columns attached, and has also described its general operating mode in the following: ECN 2-8 October from 1995, page 26, "BASF distils energy savings"; Chem. Eng. Res. Des. (1993) 71 (3), page 307, "The control of dividing wall column"; US 2,471,134; Chem. Eng. Res. Des. Part A: Trans IChemE, September 1993, page 639-644, "Heat transfer across the wall of dividing wall"; Chem. Eng. Res. Des., Part A: Trans IChemE, March 1992, page 118-132, "The design and optimization of fully ther ally coupled distillation columns". The particular inherent advantage of the present method results, among other things, from the fact that the raw DMT fraction can be diverted in a lateral line, and that it no longer needs to be operated on the head. Thus, and in comparison with known processes intended for the distillation of the crude ester, considerable energy savings can be achieved with a raw DMT quality otherwise unchanged. In addition, a reduction of the residence time of the useful product in the hot column sump, which can be achieved under comparatively effective conditions of obtaining the product, decreases the formation so harmful to the yields of undesired by-products. The object of the present invention is, therefore, a process for separating the so-called crude ether, which is obtained mainly by the catalyzed oxidation of para-xylene (pX) and para-tolulyl methyl ester (p-TE) with the subsequent esterification of the reaction products from oxidation with methanol in the manufacture of dimethylterephthalate (DMT), in a fraction rich in p-TE, a fraction of crude DMT, and a difficult boiling residue fraction, which is characterized because separation of the crude ester is carried out in a separating unit having a separating wall column, or a distillation column with a preliminary column, or a distillation column with a subsequent column. In the process according to the present invention, the separation of the crude ester is carried out, generally at a temperature in a range of 100 to 280 ° C, preferably between 130 and 260 ° C, and under pressures in the range of 50. to 500 absolute millibars. In order to achieve a particularly suitable separating action in the separating units according to the invention, together with a minimum increase of the pressure in the whole system, it is possible to incorporate the so-called structural packaging, in a preferential way, either in the separating wall column , or also in the distillation column with previous column, or posterior column, and / or also in the preliminary column itself or in the subsequent column. Preferably, the separation of the crude ester in a column system is carried out in the method according to the invention and those separating units that are effectively equipped with a distiller column with a preliminary or subsequent column attached must also be incorporated here. Figure 3 represents the block diagram of a preferred embodiment of a separating unit according to the invention, intended for the separation of the crude ester in the DMT processing process, this system having been realized as a column with separating wall and side discharge. Effectively, in the first instance, the raw ester is added to the separating wall column laterally of said wall. At the head of the separating wall column, the fraction of p-TE that boils more easily with DMT can be removed to return to oxidation. Effectively, the separating wall present in the separating wall column prevents the hard-boiling components of the residual fraction, as well as heavy metal catalyst, from reaching the raw DMT fraction. The raw DMT fraction leaves the separating wall column as a rule through a side drain that is preferably mounted at the height of the separating wall. In the sump of the separating wall column, the waste fraction which is difficult to boil is generally discharged. By suitable or pre-assembling an auxiliary column, also called preliminary column or posterior column, with respect to a distillation column, it can also be avoided according to the present invention, that during the separation of the crude ester the aforementioned components previously, the residual fraction is reaching the interior of the raw DMT fraction; compare for that purpose, Figures 4 and 5. Figure 4 shows block diagram of another preferred embodiment of a separating unit according to the invention, which serves to separate the crude ester in the DMT process, this system being realized as a distiller column with side discharge for the raw DMT fraction, and with its preliminary column attached. Effectively feed the raw ester first to the preliminary column, from one side. From Figure 5, one can see the block diagram of another preferred embodiment of a separating unit, according to the present invention intended to separate the crude ester in the DMT processing process, this system being realized as a distiller column with its back column attached, including side discharge for the raw DMT fraction. Generally, the fraction of crude DMT that occurs in the separation of the crude ester, preferably to obtain dimethylterephthalate with a high degree of purity, such as DMT of maximum purity, as well as terephthalic acid (TA) of corresponding quality, is still being treated. , such as for example PTA, or PTA-p, which can be obtained efficiently by hydrolysis of the corresponding quality of DMT. For the further treatment of the crude DMT fraction, it is possible to proceed in the manner already described at the beginning. The object of the present invention is therefore also a process for producing dimethylterephthalate (DMT) which essentially covers the following steps: oxidation of para-xylene (pX) and para-toluyl methyl ester (p-TE), esterification of the reaction products from oxidation with methanol, separation of the so-called crude ester, obtained, in a fraction rich in p-TE, a fraction of crude DMT, and a fraction of difficult boiling residue, purification of the fraction of raw DMT, at least according to any of claims 1 to 6, which is characterized in that the separation of the crude ester is carried out in a separating unit which is equipped with a column with separating wall, or a distillation column with a preliminary column, or a distiller column that carries a posterior column. The advantage of the method according to the present invention is also that the investment for the separation units according to the invention is generally much lower than the cost for comparable traditional systems. Legend Regarding Figure 1 Figure 1 shows a block diagram of a crude ester distillation in the DMT process, which is identified as a quench chamber system: Substance currents -1 Crude ester from the esterification 2 Fraction of residue containing catalyst, high boiling point, for further treatment. 3 Return of the p-TE fraction to oxidation 4 Raw DMT for further purification Components of the equipment - 5 Abrupt cooling chamber 6 Crude ester distillation column Legend Regarding Fissure 2 Figure 2 shows a block diagram of the crude ester distillation within the DMT process, which is identified as a two-column system: Substance currents -1 Crude ester from esterification 2 Return of the p-TE fraction to oxidation 3 Fraction of crude DMT for further purification 4 Fraction of residue containing catalyst, high boiling point for further treatment. Equipment Components - 5 P-TE distillation column 6 Distiller column for raw DMT Legend Regarding Fissure 3 Figure 3 shows the block diagram of a preferred embodiment of a separating unit according to the invention, for the crude ester in the DMT processing process, which is realized as a distiller column with wall separator and with side discharge. Substance currents - 1 Crude ester from esterification 2 High boiling residue fraction, containing catalyst, for further treatment. 3 Lateral discharge of the crude DMT fraction for further purification. 4 Return of the p-TE fraction to oxidation Components of the equipment - 5 Distillation column with side wall Legend referring to the Framing 4 Figure 4 shows the block diagram of a preferred embodiment of a separating unit according to FIG. invention for the crude ester in the DMT process, which is carried out as a distiller column with its lateral discharge, and the preliminary column attached: Substance streams - 1 Crude ester from esterification 2 High boiling residue fraction, containing catalyst, for further treatment. 3 Lateral discharge of the crude DMT fraction for further purification. 4 Return of the p-TE fraction to oxidation Components of the equipment -5 Crude ester distiller column 6 Preliminary column Legend Regarding Figure 5 Figure 5 shows the block diagram of a preferred embodiment of a separating unit according to the invention for the crude ester in the DMT processing process, which is realized as a distiller column and subsequent column attached and with its lateral discharge: Substance currents -1 Crude ester from esterification High boiling residue fraction, containing catalyst, for further treatment. Lateral discharge of the crude DMT fraction for further purification. Return of the p-TE fraction to oxidation. Components of the Team - 5 Distillation column for crude ester 6 Rear Column Legend of Abbreviations: P-X para-xylene p-TA para-toluyl acid p-TE para-toluyl acid methylester (pT-ester) BME benzoic acid methyl ester HM-BME methyl ester of hydroxymethylbenzoic acid MM-BME methoxymethylbenzoic acid methylester DMT dimethylterephthalate DMT-raw crude ester (stream of crude DMT ester after esterification). DMT-crude: fraction of dimethylterephthalate after distillation of the crude ester. DMT of max. purity: dimethylterephthalate with the highest degree of purity (intermediate or DMT end product) with a high degree of purity.

DMO dimethylortophthalic acid DMI dimethyl isophthalic acid DMP dimethylphthalate = isomeric mixture of DMT, DMO and DMI. MMT monomethylterephthalate (terephthalic acid monomethyl ester). TA terephthalic acid MTA terephthalic acid of medium purity PTA terephthalic acid of high degree of purity PTA-p terephthalic acid of very high grade, ie of maximum degree of purity (content in MMT and p-TA of total less than 50 parts per million by weight). TAS Tereftalaldehyde acid (4-CBA) TAE methyl ester of terephtaldehyde acid

Claims

0. Z.5048 NOVELTY OF THE INVENTION Having described the foregoing invention, property contained in the following is claimed as property CLAIMS;

1. Procedure for the separation of the so-called crude ester that is obtained, which is obtained basically through the catalyzed oxidation of para-xylene (pX), and para-toluyl acid methyl ester (p-TE) with the subsequent esterification of the products of reaction obtained in oxidation with methanol in the manufacture of dimethylterephthalate (DMT), in a fraction rich in p-TE, a fraction of crude DMT, and a difficult boiling fraction, characterized in that the separation of the crude ester is carried out in a separating unit containing a column with a separating wall, or a distillation column with a preliminary column, or a distiller column with a subsequent column.

2. The process according to claim 1, characterized in that the separation of the crude ester is carried out at a temperature in the range of 100 to 200 ° C and with absolute pressures in the range of 50 to 500 mbar.

3. The process according to claim 1 or 2, characterized in that the column with separating wall, as well as in the distillation column with preliminary column or posterior column and / or in the preliminary column itself or in the rear column itself, structural packaging are incorporated.

4. The process according to at least one of claims 1 to 3, characterized in that the fraction rich in p-TE is returned to the oxidation.

5. The process according to at least one of claims 1 to 4, characterized in that the fraction of the boiling residue which is difficult is fed to a methanolysis or thermolysis, as well as to an operating unit intended for catalyst recovery.

6. The process according to at least one of claims 1 to 5, characterized in that the fraction of crude DMT is treated with dimethyl terephthalate with a higher degree of purity and / or with terephthalic acid.

7. The process for the preparation of dimethylterephthalate (DMT), which basically comprises the following steps: oxidation of para-xylene (pX) and methyl ester of para-toluyl acid (p-TE), esterification of the reaction products from the oxidation with methanol, separation of the so-called crude ester obtained in a fraction rich in p-TE, a fraction of crude DMT, and a fraction of difficult boiling residue, purification of the crude DMT fraction, at least according to any of claims 1 to 6, characterized in that separation of the crude ester is carried out in a separating unit which is equipped with a column with a separating wall, or a distillation column with a preliminary column or a distillation column with a subsequent column.