DE1916201B1 - Process for the production of pure trimellitic anhydride - Google Patents

Description

Trimellitic anhydride wins as an intermediate product, which should contain 0.02 percent by weight nitrogen, is therefore an urgent problem for paint raw materials, plasticizers and synthetic resins.
increasingly important. According to the invention, this problem is solved by pressure oxidation of the crude trimellitic acid anhy-pseudocumene either with nitric acid or with 5 drid in a first stage at a pressure of maximum oxygen in acetic acid solution in the presence of 20 torr and one Temperature of a maximum of 250 ° C oxidation catalysts produced and after meh- 2 to 20 weight percent as a preliminary fraction and then reren process, for example by treatment with in a second stage at a maximum of 20 Torr, the pure or without acetic anhydride at increased tem- trimellitic anhydride to a residue of temperature, converted into trimellitic anhydride, a maximum of 12 percent by weight as the main fraction. The anhydride is distilled from the by oxidation with. It has been found that the trimellitic acid obtained from oxy-nitric acid still contains small amounts of nitrogen compounds derived from nitric acid and which cause yellow-containing impurities in the trimellitic acid anhycolouring of the product. drids partly in the residue in the distillation

To reduce the content of nitroverbin- 15 remain, but sometimes also more volatile than tri

It is known from U.S. Patent 2,998,431 are mellitic anhydride. Therefore, in

known, the crude product at temperatures between the first stage a preliminary fraction of 2 to 20 Ge

300 and 400 ° C to treat with vanadium pentoxide separated by weight, which the easier than

and then volatile nitrogen-containing at 265 ° C under a pressure of trimellitic anhydride

Distill 7 torr. The relatively high contains 20 compounds. After separating this slightly

Treatment temperature during a treatment of volatile compounds is a pure trimellitic

Time of 2 to 60 minutes causes a significant acid anhydride to distill over the above

Decomposition of the anhydride and conditionally meets poor purity requirements. At the inven-

Yield. From British patent specification 907 926 proper working method, the main run is practically

it is known that pseudocumene is initially catalytically free of nitrogen-containing impurities,

table air oxidation in acetic acid solution before the residue of the distillation

oxidize and then the oxidation with nitric acid a maximum of 12 percent by weight is again rich in

to continue to trimellitic acid. After the nitrogen compounds and colored dark, however

thermal conversion of the acid into the anhydride practically free of trimellitic anhydride. He follows

if this is done by vacuum distillation at a maximum of 30, on the other hand, distillation at bubble temperatures is

5 Torr and at temperatures from 230 to 260 ° C of half 250 ° C, e.g. at 258 ° C, both the

the residue separated, being a main run and nitrogen content of the main run as well despite the

a higher distillation temperature darkened by nitro compounds represents the absolute amount

run incurred. This procedure has the disadvantage of residue. The increase in residue

that the low volatility contained in the anhydride is due to the higher temperatures

Nitro bodies at bubble temperatures above 250 ° C constant formation of the semi-volatile intermolecular

decompose in more volatile nitro compounds to recycle the dianhydrides.

the trimellitic anhydride is used in the distillation. The preliminary and main distillation is carried out with the aid slide. In addition, the formation of the dianhydride leads to a vacuum column, the one for the separation above 250 ° C to the fact that the amount of residue 40 of the lower and higher boiling impurities increases. Finally, the column cross-section will have a sufficient separating effect. For separation unnecessarily large at pressures below 5 Torr. The flow becomes a higher return ratio German patent specification 1 097 427, the distillation is worked as in the distillation of the main fraction, from those obtained by naphthalene oxidation with air. In general, the more volatile ones are separated Phthalic anhydride known in two stages, with 45 impurities in the first stage by one in the first stage at about 20 to 200 Torr and less rectification column, which with a Rückais 225 ° C the preliminary fraction and then operated at a 200 ° C ratio between 50: 1 and 5: 1, Preferably the reflux ratio is at the bubble temperature not exceeding the bubble temperature fraction are distilled over. The pre-distillation between 30: 1 and 10: 1. At the head office from being distilled by oxidation with nitric acid to separate the pure product posed trimellitic anhydride occurring problems a reflux ratio between 20: 1 and 1: 1, such as difficult separability of nitro- preferably chosen between 5: 1 and 2: 1. The tem connections, The formation of the intermolecular anhyperature must not exceed 250 ° C in either of the two stages and decarboxylation, allow transfer to proceed, hence too much thermal beandes for phthalic anhydride known process 55 and the associated formation of the not to trimellitic anhydride. Finally, intermolecular trimellitic anhydride or a it is known from US Pat. No. 2,971,011 to avoid decarboxylation. The pressure is allowed Accordingly, xylene dissolved crude trimellitic anhydride does not and cannot exceed 20 Torr Repeated treatment to clean with activated charcoal. preferably slightly higher in the first stage than in that This process is through the multiple filtration 60 second stage.

stages and the crystallization of the trimellitic acid- According to the preferred embodiment of the invention

anhydrides from the solution relatively expensive. dung is provided that the flow under

The recovery of pure trimellitic anhydride at a pressure of 5 to 15 Torr, corresponding to one

from the temperature of 220 to 240 ° C obtained by oxidation with nitric acid, and the main course

Crude product, which is distilled by the further processing 65 under a pressure of 3 to 10 Torr.

Industry-specific purity requirements are met, it is expedient to distill in the first

wherein the purified product is at least 99.0 Ge level 3 to 5 percent by weight of the crude product over,

weight percent trimellitic anhydride and at most

3 4

running ratio in the first stage, is to be selected so, return ratio with decrease of a lead

■ that the more volatile impurities are processed. The resulting lead

especially the nitrogenous compounds are discarded; the rest becomes the first again are separated, but on the other hand as little as possible of a distillation stage is fed.

Trimellitic anhydride gets into the flow. A 5 For purification of the crude Tfimellite preliminary fraction by distillation Acid anhydrides will be packed columns or vaginal columns from 3 to 5 percent by weight used all of the more volatile impurity columns with special packings. at included. In the continuous process, the heating takes place

According to a further preferred embodiment, preferably by falling film evaporator, however

the invention separates part of the residue io also the heating by forced circulation or Na-

possible in an amount of 1 to 10 percent by weight of the raw turbo evaporator.

Product before it enters the first stage. An embodiment of the plant for carrying out this separation of a part of the residue of the continuous reivor according to the invention before the two-stage distillation improves the purity of the cleaning process for crude trimellitic anhydride end product and the formation of ab-15 is described below with reference to the drawing. Separations on the evaporators of the distillation The crude trimellitic anhydride obtained in the bottom of the unit is reduced by the oxidation of pseudocumene with aqueous stages and in particular an excessively strong nitric acid and subsequent dehydration thermal load on the product in the sump of the device is the second distillation stage and thus the formation of ^ continuously a thin film evaporator 1 added larger amounts of intermolecular trimellite 20, in which it is evaporated to 95 ⁰ J _0. Avoided the thin acid anhydride. Appropriately, the film evaporator works under a pressure of the separation of the residue from the raw approximately 8 to 15 Torr and at a temperature of product by evaporation from a thin layer. about 240 ^° C. During the relatively nitrogenous addition, which is drawn off, for example, by thermal pre-rich residue at 2, the treatment of crude trimellitic acid obtained tri- 25 trimellitic anhydride vapors in the condenser 3 is condensed into a thin-film or mellitic anhydride. The liquid falling film evaporator freed from the residue is fed in and 90 to 90 to crude product is then fed into the middle region of the 99 percent by weight, preferably 93 to 97 percent by weight, pre-distillation column 4. The Füllkörperprozent vaporized This evaporation takes place at column 4 is in rectifying section and stripping section up to 250 ⁰ C, preferably 225-245 ° C, and 30 divided; the bottom of the column is heated by a vacuum of a maximum of 20 Torr, preferably a heating circuit with falling film evaporator 5. The 3 to 10 torr. The pre-distillation column lighter than trimellitic anhydride is kept under a pressure of 8 torr by a vacuum volatile impurities and part of the system; the less volatile constituents accompany the bottom temperature is about 240 ^° C. From the heating steam trimellitic anhydride, the vaporous circuit 6 of the column 4 is fed the product freed from more easily or volatile impurities after condensation in the first distillation stage. The residue, which is initially relatively nitrogen-rich in the pre-evaporation via line 7 at the bottom of the main loin, is fed to distillation column 8. Those at the head of the generally discarded. To separate off the residue in column 4, lower-boiling water condensing components, some of the customary thin-layer or falling-flow components are used as reflux in the co-evaporators. . lonne 4 and returned to the other part as

The two-fore-runnings following the residue separation are drawn off, collected and from time to time

stage distillation can be carried out in batches in a distillation to recover the trimellite contained therein

tion column or continuously worked up by distillation in two successive acid anhydrides. The swamp

the switched columns are carried out. At 45 of the packed column 8 is also by a

the continuous distillation is heated after the heating circuit 9 with falling film evaporator 10, from

Trimellitic acid anhydride obtained with residue separation continuously or periodically at 11 residue

drid the middle area of the first distillation is withdrawn. This residue is just like

column fed. At the top of this column, the residue withdrawn at 2 and the forerunner become

the first run is continuously withdrawn, and from the 50 recovery of the trimellitl contained therein

The evaporator circuit of this column is worked up by the acid anhydride. Overhead of the main

The tristillation column 8 freed from the volatile impurities becomes the pure one under reflux

mellitic anhydride is continuously distilled off into the sump trimellitic anhydride,

pumped into a second column in which the pure. -I ₁

Trimellitic anhydride is distilled off overhead. 55 B e 1 s ρ 1 e 1 1

From the evaporator circuit of the second column, raw trimellitic anhydride is used as the feedstock

a residue withdrawn, the higher-boiling stick used, which is obtained by oxidation of pseudocumene

contains compounds. If part of the back with 8 ° / _o aqueous solution of nitric acid under pressure at

Manufactured article prior to entry into the two-stage distillation 180 ⁰ C and subsequent dehydration

tion was separated, falls in the sump of the second 60 and has the following specification:

Column a correspondingly lower residue *,. «, -, · 4 _. ' ".,. ,, · ·,

Amount of. ^{In order to obtain the 9} ^ percent by weight trimellitic anhydride in the forerunner of the first distillation

tion stage and the residue of the second distillation 0.3 percent by weight nitrogen,

trimellitic anhydride contained in the tion stage nor Saurezanl 853,

To partially recover, this first run can 65 100 parts by weight of the raw trimellitic anhydride

and the residue is combined and placed in a separate drids every hour of a distillation column that

Distillation column below a maximum of 20 Torr and one filled with a wire mesh packing is fed,

maximum bottom temperature of 250 ° C at high The column is 1.8 m high and has a diameter

5 6

of 0.06 m. The bottom of the column is placed from the outside of the column, the condenser is the forerun heated to 235 ° C. The column operates under a cooled to 170 ° C. The specification of this faction Pressure of 9 torr at the head and with a return is:

^Rat ! I ^tn i 7Γ ³⁰ I ¹ - ^ £ ° f _f ^d l ^{r Kolon1} ^ ^are 47.2 percent by weight of trimellitic anhydride,

hourly 4 parts by weight flow at a temperature of 5 0.71 percent by weight nitrogen,

door of 224 C removed. This forerun is expressed in acid number 802
on a condenser attached to the column

Chilled 170 ° C. To remove the main fraction, the return

The specification of the lead is as follows: run ratio set to 3: 1. Total will be

_{cr a} _. , ",. "., - ■ IJ-J ίο 87 parts by weight of main run distilled off; the swamp

56.8 percent by weight Trrmelhthsaureanhydnd, _{temperature is} 39 ° C and the temperature

0.6 percent by weight of nitrogen, _{deg vapor} , measured at the top of the column, 227 ° C.

baurezani 816. _{The pure product has the} following specification:

From the bottom of this distillation column, "" "_. , ",. "., ..,,.,

96 parts by weight deducted per hour. This 15 99.3 percent by weight of trimolithic anhydride,

Bottom product still contains those higher than trimellite °. ' ⁰¹⁵ percent by weight nitrogen,

Acid anhydride boiling impurities, including building number ö74.

borrowed part of the coloring nitro compounds, and in the bottom of the column 9 parts by weight remain for further purification of a second distillation of a dark, viscous residue, the
column, which is 1.6 m high and a diameter of 20 _. "., ..,,.,
of 0.08 m has been supplied. The column is made with a ⁶ ^ weight percent trimellitic anhydride,
Wire mesh packing is filled and operates under a 1.02 weight percent nitrogen containing and
Pressure of 6 Torr, measured at the top of the column, ^eme acid number of 704 has.
with a reflux ratio of 2: 1. 88 parts by weight of the pure product present in the crude product are released every hour at temperatures of 25 substances in the form of gaseous N compounds in the sump of 240 ° C and over-fertilize at the top of 228 ° C, which distilled by decomposition during the distillation. This main run has the following specification: arise.

99.49 percent by weight of trimellitic anhydride, Example 3

0.012 weight percent nitrogen, ₃₀

Acid number 875. _Robes trimellitic anhydride is used,

Per hour are obtained by oxidation of pseudocumene with 8 ° / _o from the bottom of the column strength

8 parts by weight of a dark, viscous residue of aqueous nitric acid under pressure at 180 ° C and

withdrawn, the subsequent dehydration was made

73.7 percent by weight trimellitic anhydride, ³ S and has the following specifications:

Contains 0.98 percent by weight nitrogen and 95 ^ percent by weight trimellitic anhydride,

has an acid number of 706. 0.3 percent by weight nitrogen,

Part of the nitrogen present in the crude product, acid number 853.

escapes in the form of gaseous nitrogen compounds 40 100 parts by weight of the crude trimellitic anhydride

Chemicals that are produced during the distillation by decomposition drids every hour of a distillation column that

develop. "is filled with a wire mesh packing.

Example 2 The column is 1.8 m high and has a diameter

of 0.06 m. The bottom of the column is from the outside

Crude trimellitic anhydride 45 is heated to 258 ° C. as the starting material. The column works under one

used, which by oxidation of pseudocumene pressure of 18 Torr at the head and with a return

7 ° / ₀ aqueous nitric acid under pressure at ratio of 30: 1st Be at the head of the column

2CO ⁰ C and subsequent thermal dehydration hourly 4 parts by weight forerun at one temperature

was established and the following specification of 251 ° C was accepted. This lead is in

had: 50 on a condenser attached to the column

94.3 percent by weight trimellitic anhydride, 2%. _£ ?? 5i. . "■, * ■ *,

0.33 weight percent nitrogen, ^the specification of the flow is as follows:

Acid number 851. 53 ^ percent by weight trimellitic anhydride,

The entire purification by distillation is carried out in a 55 ° ' ⁸ percent by weight nitrogen,

Distillation column carried out. 100 parts by weight number of units / 98.

of the crude trimellitic anhydride will be taken from the bottom of this distillation column

Distillation still, the content of which is 301, given. 96 parts by weight deducted per hour. This The rectification takes place in the attached distilla- bottoms product still contains the higher than trimellite-

tion column instead. The column is packed with wireframe acid anhydride boiling impurities, including mesh packing filled and has a height of 2.4 m borrowed part of the coloring nitro compounds, and with a diameter of 0.10 m. a second distillation unit is used for further cleaning

During the purification by distillation, the column, which is 1.6 m high and has a diameter, works System under a pressure of 6 Torr, measured at 0.08 m, fed. The column is with a

Head of the column. 4 parts by weight of lead 65 wire mesh packing are filled and works under one removed, the temperatures are at a pressure of 18 Torr, measured at the top of the column, Bottom 230 to 238 ° C and at the top 210 to 226 ° C. with a reflux ratio of 2: 1. 86 Weight-That Return ratio is 35: 1. In a part pure product are hourly at temperatures

distilled over in the bottom of 258 ° C and at the top of 255 ° C. This main run has the following specification:

98.92 percent by weight trimellitic anhydride,
0.05 percent by weight nitrogen,

Acid number 872.

From the bottom of the column 10 parts by weight of a dark, viscous residue per hour deducted that

Contains 76.4 percent by weight trimellitic anhydride, 0.80 percent by weight nitrogen and
has an acid number of 712.

Part of the nitrogen present in the raw product escapes in the form of gaseous nitrogen compounds, caused by decomposition during distillation.

The invention is not restricted to the embodiment described in these examples. A trimellitic anhydride the same or higher degree of purity can also be achieved by stepwise distillation with prior separation of a residue in the Thin film evaporator or obtained by another procedure falling under the following claims will.

Claims (7)

Patent claims: 1. A process for obtaining pure trimellitic anhydride from the crude product obtained in the oxidation of 1,2,4-trialkylbenzene with nitric acid and subsequent dehydration by distillation under reduced pressure, characterized in that in a first stage at a pressure of not more than 20 torr and a maximum temperature of 25O ⁰ C for 2 to 20 weight percent as the flow and then to a residue of a maximum of 12 percent by weight is distilled in a second stage at a maximum of 20 Torr, the trimellitic anhydride as the main fraction. 2. The method according to claim 1, characterized in that the forerun in the first stage under a pressure of 5 to 15 torr and the main barrel under a pressure of 3 to 10 torr distilled over. 3. The method according to claim 1 or 2, characterized in that in the first stage 3 to 5 percent by weight of the crude product distilled over. 4. The method according to any one of claims 1 to 3, characterized in that part of the Residue in an amount of 1 to 10 percent by weight of the crude product before its entry separates into the first stage. 5. The method according to claim 4, characterized in that that the separation of the residue from the crude product by evaporation makes from a thin layer. 6. The method according to any one of claims 1 to 5, characterized in that the two-stage Performs batch distillation in a distillation column. 7. The method according to any one of claims 1 to 5, characterized in that the two-stage The distillation is carried out continuously in two successive distillation columns. 1 sheet of drawings 009 540/396