DE1618787A1 - Production of aromatic acids and aromatic acid anhydrides - Google Patents

Description

DR-ING. BY KREISLER DR.-ING. SCHONWALD DR.-ING. TH. MEYER DR. FUES

COLOGNE 1, DEiCHMANNHAUS

Cologne, May 18, 1967 AvK / Ax / hvk

Princeton Chemical Research Inc.,

P.O. Box 652, Princeton, New Jersey, 08540 (V.8t.A.)

"Production of aromatic acids and aromatic acid anhydrides"

The invention relates to the production of aromatic acids and acid anhydrides, in particular to a measure to improve the yield of the desired product in the production of aromatic acids and acid anhydrides by oxidation of substituted aromatic compounds.

For the production of aromatic carboxylic acids and anhydrides many processes are known which are based on the principle of the oxidation of alkyl-substituted aromatic compounds, such as xylene, toluene or durol, with air or oxygen or on the similar oxidation of aromatics with condensed rings, such as naphthalene. Lots of these Processes are now being carried out on an industrial scale for the large-scale manufacture of these products. Hence would be an increase in the product yield and / or an improvement in the purity of the product obtained is desirable.

For example, oxidation of 1,2,4- and 1,2,4,5-alkyl-substituted benzenes is known to produce mellitic acid, Trimellitic acid or pyromellitic dianhydride produced. Recent improvements to this process relate in particular to the catalysts used for these procedures are used. For example, according to

BATH ORIGINAL

the procedure of the German patent .., .... (patent application 37 325 IVb / 12 o) the applicant a job vanadate catalyst

used, and the German patent ... (patent application

J3 / V12.O corresponding to U.S. Patent Application 545 561 dated • 17 «4.1966) of the applicant is on further improvements of the catalyst system for this process, describing a number of improved catalyst combinations will.

In the known processes for the production of ellitic anhydrides or acids by oxidation of alkyl-substituted aromatics, products are generally obtained which have to be purified before they are used for the intended purpose, for example in the plastics industry. One of the proposed inclination methods, which has proven to be very useful, is described in the US Patent Application 510 386 of 29e11 _# 1965, which is a continuation-in-part application of the USA patent application 421.080 of December 24, 1964 in accordance with the German Patent application P 38 413 IVb / 12 ο is the applicant. In this process, the oxidation reduced product leaves the oxidation reactor in the gas phase and is subjected to a quenching to a still relatively high temperature, solid or liquid particles of the desired product being separated from the grass in relatively impure form. The impure product is with a suitable porous material, a filter cloth or the like. can be, filtered out of the gas stream, while the residual gas passes through the filter medium. The impure product is expediently treated with a gas, such as air, nitrogen or the like, which can also flow through the filter medium, where the desired solid or liquid product is cleaned raw.

The invention is to an improved method of manufacture of oxygen-containing products through oxidation of alkyl-substituted aromatics, namely a · novel Measure® to improve the yield in such a case

10980972tÖ1

BAD ORlGiNAL

Procedure »in particular the improvement of the recoverable Yield of mellitic acids or mellitic anhydrides their production directed by oxidation of tri- or tetraalkyl-substituted benzenes.

The invention accordingly relates to the oxidation of alkyl-substituted aromatic organic compounds with a clay oxygen-containing gas with the formation of one in the vapor phase present Proauktstrom and deposition of the desired Product from this product stream according to a process which is characterized in that at least part of the Residual gas is returned to the oxidation reaction to increase the recoverable yield of the desired product

This process is described in more detail below with the aid of a specific example. Darol (1,2,4,5-tetramethylbenzene) is treated with an oxygen-containing gas a suitable catalyst is oxidized at elevated temperature, a vaporous product stream containing the oxygen-containing product being formed. This that Product-containing stream is passed through the Filter medium quenched in a suitable manner, the desired oxygen-containing product being deposited on the filter and a residual gas passing through the filter medium. As mentioned earlier, this can be secluded Product purified by treatment with a suitable one while it is still on the filter medium In this case, the treatment gas flows out of the separated product contains removed impurities, also through the filter medium. The gases flowing through the filter become irrespective of whether they Residual gases used in addition to cleaning Ieβ product Containing gases or not, appropriately divided, with part being blown off and part being returned to the oxidation reactor la cycle · The amount of dee In oxygen-containing gas introduced into the oxidation reactor is dimensioned so that it is a complement, i.e.

109609/2101: BAD ORIGINAL

the amount of oxygen it contains, taking into account the freshly quoted durol and that contained in the cycle gas fbrstufe of the oxidation product is necessary to to carry out the OxyS & tion reaction properly

It has surprisingly been found that when an oxidation process is carried out in the manner according to the invention not only achieved very large savings through the circulation of the oxidizing part of the residual gas and this reduces the outlay on equipment for fresh oxidizing agent, but rather the yield actually obtained of liellitic acid and mellitic anhydride without loss Product quality is greatly improved.

It is unknown whether the residual gas circulated according to the invention is the desired product, precursors of the desired Product or any combination of the two, or even a mixture of either or both of these materials with other components which contribute in any way to the fact that higher recoverable yields of the desired Product in the process', so that it is impossible to explain the mechanism by which the recoverable product yield is increased by applying the invention.

In the following examples, the quantities given are based on weight, unless otherwise stated.

Examples 1-4

Durol and air are used in the following quantities introduced into a reaction zone and at elevated temperatures in the presence of a plague bed catalyst based on Niobium vanadate reacted at 440 ° C. As a product comes out of the Reactor from a gas which is fed to a filter operating at the temperatures mentioned, in which the gas flow is partially quenched and the desired product pyromellitic dianhydride is deposited, whereupon it is called a pestilent substance

BAD ORJGiNAL

109809/2101

is obtained from the filter. "The light exiting the filter residual gas either completely or partially blown off. The amount of residual gas circulated is given below. The product recovery is specified below for each example, based on amount of product yield _s in percent of theoretical and the product purity.

Example Durol air circulation filter product extraction game use supply ^ emp. Out% clean no. kg / hour kg / hour kg / hour ⁰ C booty means

kg / hour % _

1 80 4000 0 135 37 46 99.6 2 80 4000 0 163 27 34 99.9 3 80 728 3160 135 52 65 99.6 * 4 80 728 3160 163 49 61 99.9 Example 5

The experiment according to Example 3 is repeated, but is Oxygen is introduced into the oxidation reaction instead of air and a different amount of circulation is applied.

With Durol Qp feed use drove No. kg / hour kg / hour

Circuit filter

temp.
kg / hour ⁰ C

Product recovery% pure yield is kg / hour. %

168

2832

135

56 70 99.5

The above values clearly show the improvement achieved by the procedure according to the invention. the The improvement achieved here, however, is not due to the specific process parameters of the preceding examples limited

As organic reactants, it is expedient to use alkyl-substituted benzenes with at least 3 alkyl substituents, for example ₀ tetramethyl ₉ trimethyl, trimethylisopropyl, tetrabutyl and the like. As an oxidizing agent, acidic

109 * 09 / 210-1 "

f AD ORiQINAL

{613787

Substance is used which can be supplied in the form of pure oxygen, air, oxygen-enriched air, oxygen diluted with inert gases, and the like. The catalyst used is a tanadate which contains a second metal component, eg mol) ₃ silver, molybdenum, chromium, tungsten and manganese and is expediently used in the form of a fixed bed or a fluidized bed. The reactor temperature is maintained at about zweokmäflig 370-593 ⁰ C, preferably between 427 and 45O ⁰ C »The eye feed gases containing the oxygen and the organic material to oxidizing and a gaseous diluent. The organic reactant conveniently constitutes about 0.1-1.5 moles, preferably 0.25-0.5 moles of the feed gas.

As already mentioned, in this process the cooling during product recovery is carried out in combination with a filtration, whereby the gas is separated from other components. «Practically every filtration method can be used for the purposes of the invention, provided that the filter medium has such a pore size that the residual gas is allowed through and the precipitated product is retained. Suitably, a filter cloth is used as a filter, but other materials are suitable, üb filters are a deterrent to a still relatively high temperature "It is preferably maintained at about 100-275 ⁰ C at 1œ7 ~ 163 ° C. The pressure during the filtration is not very important. You can work at normal pressure, negative pressure or positive pressure.

The increase in product yield is roughly proportional to the proportion of the residual gas exiting the filter, the is returned to the Cfeydationsreaktor. With a small one Amount of the circulating residual gas, a slight increase in the product yield is achieved while at lonely? large amount of the residual gas circulated, the increase in the yield of product obtained is greater Preferred catfish are about 50-95 according to the invention

104809/2101

of the residual gas is circulated ₉ while the gas is being blown off.

The method is preferably carried out in that, according to asm Äiafskrea, the reaction participant ³ required for an ergonomic process is withdrawn and the residual gas is withdrawn

Preferred Eeaktioast @ iliielm © r hei this is Purolj and as a product wiri vorssugsweis ©

BATH ORIGINAL 109809/2101

Claims (1)

Claims 1.) Process for the production of aromatic. Carboxylic acids and acid anhydrides by oxidation of alkyl-substituted ones aromatic compounds with an oxygen-containing oas to form one present in the vapor phase Product stream and separation of the desired product from this product stream characterized in that at least part of the residual gas is used in the oxidation reaction to increase the recoverable yield of the desired product is returned 2.) The method according to claim I ₁ characterized «that the separation of the desired product from the product stream is carried out by filtration« wherein the desired oxygen-containing product is deposited on the filter and a best gas passes through the filter medium and part of the residual gas in the Oxydatlonsreaktor is returned in the cycle 5.) The method according to claim 1 and 2, characterized in that at 107 to 163 ⁰ C is held. that the filter is at about 100 to 275 ° C, preferably 4.) Method according to claim 1 to 3, characterized in that that as alkyl-substituted aromatic compounds alkyl-substituted benzenes with at least 3 alkyl substituents be used. 5.) The method according to claim 4, characterized in that the alkyl-substituted benzene, durene is used. 6.) Method according to claim 1 to 5, characterized in that that air or oxygen are used as the oxygen-containing gas. 109809m 01,., ^BAD original 7.) Process according to claim 1 to 6, characterized in that 50 to 95 % of the residual gas are returned to the oxidation reactor in the circuit. BAD ORSQiNAL