DE1274569B - Process for the production of phthalic anhydride - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

German KL:

Number:
File number:
Registration date:
Display day:

C07c

BOIj
F25b

12O-14

12 g-11/32

12a-7

P 12 74 569.6-42 (C 29068)

2nd February 1963

August 8, 1968

The invention relates to a process for the preparation of phthalic anhydride by catalytic oxidation of o-xylene with molecular oxygen in the vapor phase at elevated temperature on a fixed vanadium pentoxide catalyst, which is characterized in that a mixture of evaporated o-xylene is used and molecular oxygen with a contact time of about 0.001 to 0.05 seconds passes over the catalyst, the reaction zone of which is kept at a constant temperature essentially at 590 to 815 ° C, especially 650 to 760 ° C by the oxidation mixture at a rate of at least 3.3 to ll ° C / sec-10 ³ by means of a fixedly arranged within the catalyst layer cooling element or with the aid of two successive heat exchangers, the first of which at a temperature of about 455 to 595 ° C and the second at a temperature is kept from about 205 to 430 ° C, cooled and the reaction mixture according to customary _a o methods is working.

The production of phthalic anhydride by oxidation of o-xylene in the vapor phase is known. So far, the reaction has been best carried out at a temperature of about 565 ° C. It is true that the use of higher reaction temperatures would be due to the increased reaction rates has been of great benefit, however, efforts to increase production by applying to increase higher temperatures, unsuccessful, since then a correspondingly lower reaction selectivity, resulted in lower yields and significantly increased operational hazards. When the catalyst Aging, there was a further difficulty that the zone with the highest bed temperature, i. H. the so-called "hot zone", migrated slightly downstream in the catalyst layer. If you have this Allowed migration, there were lower reaction selectivities and consequent losses in yield, and even fires and serious industrial accidents could occur.

Surprisingly, it has now been found that when carrying out the process according to the invention the expected decrease in the reaction selectivity and the yield does not occur, the change the hot catalyst zone remains within acceptable limits and that as a result of migration possible fire and explosion hazards do not occur.

When carrying out the process according to the invention, a reaction vessel is used with a static bed which is made with a vanadium process for the production of
Phthalic anhydride

Applicant:

California Research Corporation,

San Francisco, Calif. (V. St. A.)

Representative:

Dr. W. Beil, A. Hoeppener

and Dr. H. J. Wolff, lawyers,

6230 Frankfurt-Höchst, Adelonstr. 58

Named as inventor:

Calvin Schwartz Smith, El Serrito, Calif .;

Mack F. Hughes, Albany, Calif. (V. St. A.)

Claimed priority:
V. St. ν. America 5 February 1962
(171 251, 171180)

pentoxide catalyst for vapor phase oxidation, preferably on a carrier, is charged. Vaporized o-xylene and a gas containing molecular oxygen, preferably air, are introduced individually or mixed into a catalyst layer, the first part of which as a preheating zone of a Heater with a temperature of about 425 to 595 ° C is surrounded. The temperature of the gas mixture is markedly increased as it moves through the bed in the reaction zone, e.g. B. depending on the heating device by 55 to 220 ° C and more, and is then 590 to 815 ° C. After 0.001 up to 0.05 seconds residence time in the reaction zone and practically when leaving the reaction zone the gas flow is exposed to the action of a coolant in such a way that the production flow by at least 3.3 to 11 ° C / sec-10-3 is cooled. The cooling is preferably carried out until the temperature of the gas stream falls below about 480 ° C., however is decreased above about 205 ° C. Then you can use the phthalic anhydride in the usual way Win wisely.

The required cooling speed and the correct onset of cooling can be determined by two achieve almost equivalent arrangements, namely a fixed arrangement within the catalyst layer

809 589/477

3 4

One cooling element or two consecutive ones, ie about 3.9 ° C / sec · 10 ~ ³ and higher. In the upper heat exchanger. These cooling devices are temperature zone, e.g. B. above 705 ° C, cooling with preferably immobile catalyst layer, rates of at least 4.4 ° C / sec · 10 ^-3 after the start of operation and settling and even higher are recommended. As long as the specified reaction zone is arranged in such a way that it adheres to the correct reaction zone times, the action product when leaving the reaction zone is also subject to shorter cooling rates for the cooling in the required manner. That within the extraction zone in question. The cooling rate of the catalyst layer fixed cooling elements can be up to 11 ° C / sec x 10 ~ ^a , but is placed about 25 to 50 cm downstream. No noticeable advantage can be achieved by these higher cooling speeds and the cooling liquid flowing through the cooling element, and mechanical difficulties can arise when determining the cooling speed of the product Reaction zone. To achieve.

Establishing the reaction zone can be a ge In general, satisfactory results in control of the feed compositions can be obtained when the air-o-xylene substitution is used make. So show the temperature mixture a weight ratio of 16: 1 to 35: 1 profile of the catalyst layer, lower yields and higher. With air-o-xylene ratios and the reaction data indicate that the process is below about 16: 1 and especially at ratios If it proceeds satisfactorily, a slight change below about 14: 1 can decrease the catalyst layer noticeability in the feed and in the flow rate 20 borrowed from. At a ratio of 14: 1, the can be made to increase the catalyst shelf life of the reaction zone z. B. about 1 day while they and the cooling device to match each other at higher air-o-xylene ratios, e.g. B. 17: 1 men that the process at the desired temperatures and more, be about 1 year. Air-o-xylene temperatures from 590 to 815 ° C to the desired ratios above 20: 1 can be used, but at Results. When using two at a time, the air-o-xylene ratio increases significantly other subsequent heat exchangers, e.g. B. Tempe- beyond this number, the procedure due to the temperature baths, these baths must always have essentially reduced process performance connect. The temperature of the first societal. By using an oxygen-attached heat exchanger is between 455 and 595 ° C, enriched gases or pure oxygen and the temperature of the second heat exchanger 30 can vary the results somewhat, in general lies between 205 and 430 ° C. However, since these heating elements correspond to the weight ratios of elements are firmly arranged, one can determine the position of the oxygen to o-xylene that of air and o-xylene, hot reaction zone due to lesser regulations The xylene used should be of a fairly high level

in feed rate and bath cleanliness as most hydrocarbon temperatures change. 35 impurities and especially aliphatic carbon

In the process according to the invention, the term “process” is used to denote hydrogen impurities Reaction zone that catalyst section are oxidized under internal conditions; this is benerhalb the layer in which the local temperature releases considerable heat energy and the temperature significantly complicates the immediately preceding control. It is true that o-xylene has a clean layer temperature and the temperature exceeds the generally about 90% useful for the process, the closing catalyst bed. The re-but becomes an o-xylene with a purity of about Action zone is therefore a zone with a high temperature - 95% and more preferred. One o-xylene charge Temperature gradient and fst in the process according to the invention with a purity of 99% is dangerous for the invention the catalyst section is particularly advantageous within the moderate process, dormant embankment, in which the reaction tem- 45 When carrying out the process at Tempeperatur 590 to 815 ° C. Response times above about 675 ° C will be the best results the transit times of the feed stream nise then achieved when it is used when using through the reaction zone, and the cooling rate fresh catalyst at the beginning during a condensation are the temperature changes of the relatively short conditioning time for a action stream operates in the recovery zone of the 50 temperature in the range of 590 to 650 ° C, verters immediately after the reaction zone. The conditioning time serves the purpose of the catalyst

In general, in the reaction zone can be converted into a form in which it is heat-resistant temperatures of 590 to 815 ° C., in particular of dig. A fresh catalyst that is essentially used at 650 to 760 ° C. In the case of the low V ₂ O ₅ configuration, it melts easily and leads to relatively long temperatures can ultimately lead to the formation of a somewhat inferior reaction zone times and, accordingly, to the formation of a catalyst, if the conditioning time is omitted, lower cooling rates in the win are sufficient , the catalyst must be adhered to during some tension zone. In the case of a higher number of hours in the lower temperature range at the reaction temperature, higher cooling speeds are required, but it is advantageous if it is 1 day and shorter times are advantageous. At a 60 long is conditioned.

Reaction zone temperature in the range of 590. In the preferred embodiment, there is

up to 625 ° C are therefore residence times of 0.05 Se reaction layer essentially consisting of a kenden and cooling rates of 3.3 ° C / vanadium pentoxide catalyst on a support. The see · 10 ~ ³ recommended. If the layer immediately following the reaction zone is increased, the process temperature is increased, e.g. B. up to about 650 to 65 can, however, be filled with the inert catalyst support or 705 ° C. according to the invention, and faster cooling speeds required high cooling speeds

10

enable opportunities. Similarly and in particular When carrying out the process at a temperature above about 650 ° C, it is often advantageous in the front part of the reaction layer a short section of an inert filler, e.g. B. the Carrier material to be arranged through which the reaction stream is preheated.

The following examples serve to illustrate the process according to the invention.

example 1

In an evaporator was o-xylene (95% purity) in an amount of 80.4 g / h. (0.759 mol per hour), after which the gaseous xylene produced in this way was ^{mixed with air at 93 ° C 1} S, which in an amount of 0.022 cbm / min. (0.926 moles per minute) at normal temperature and pressure. The weight ratio of air to o-xylene in the gaseous mixture was therefore 20: 1. The hot gaseous mixture was then passed downwards through a catalyst layer of vanadium pentoxide (about 15 parts of vanadium pentoxide to 85 parts of silicon carbide), which had a diameter of 1.8 cm and was passed through a heat exchanger with a constant temperature of 504 ° C was surrounded. About 50 cm from the upper end of the catalyst layer was a cooling device, which consisted of two coaxial tubes with a length of about 40 cm. The other tube, which was closed at one end, had a diameter of about 0.63 cm, while the diameter of the inner tube was about 0.315 cm. The total length of the catalyst layer was about 90 cm. The cooling device was arranged so that the reaction tube and the cooling element had a common center. Cooling was achieved by passing gases or liquids upward through the inner cooling tube and through the ring formed by the two cooling tubes. The temperatures were measured in the usual manner at various points throughout the reaction layer, and the reaction conditions in the reaction vessel were regulated as desired by regulating the aforementioned surrounding heat exchanger and using the cooling element. In this way, a reaction temperature zone of 593 to 635 ° C, a contact time of about 0.01 second, and a cooling rate of about 4.05 ° C / sec x 10 ^{-3 were} maintained immediately following the hot zone. The conversion of o-xylene was complete and the obtained yield was 99% by weight based on the fed o-xylene.

Carrying out the process at temperatures below 590 ° C gives little or no benefit, while at temperatures above 590 ° C and as the temperature rises, significant improvements in yield and product selectivity as a result of higher reaction temperatures and the use of the described cooling element were achieved. Similarly, when the cooling element was used at reaction zone temperatures above about 590 ° C, no significantly more beneficial effects were found when the cooling rates were below about 3.3 ° C / sec · 10 ^-3 . At cooling rates of 3.3 ° C and more per second · 10 ^-3 , significant improvements in yield and product selectivity were achieved. Similarly, these data showed that significantly longer or shorter residence times than those described above lead to lower yields of phthalic anhydride or conversion of o-xylene.

Example 3

In a 91 ■ 2.2 cm large vertical laboratory converter, which was charged with a catalyst for vapor phase oxidation (about 15 percent by weight Vanadium pentoxide on silicon carbide), o-xylene was converted into phthalic anhydride. The converter was equipped with a first heat exchanger in order to get into the upper 50 cm of the Catalyst layer maintaining a first temperature zone, and having a second heat exchanger, to maintain a second temperature zone in the lower part. The loading was was introduced into the top of the reaction vessel, and the reaction product was withdrawn from the bottom.

The converter was operated: (I) in the usual manner with a single, by heat exchange obtained temperature zone and (II) according to the process according to the invention, whereby on the a second temperature zone was maintained as follows:

Conditions of the operation

First temperature zone ( ⁰ C) 504

Second temperature zone ( ⁰ C) 427

Reaction zone ( ⁰ C) 593-635

Weight ratio of air to o-xylene (1) .. 20
Residence time in reaction zone (seconds) 0.01 time in stream (hours) 96

Results

Example 2

55

Example 1 was repeated in a comparative experiment, but here the cooling element was not put into operation. It has been found that the normal cooling amount in a normal operation of the system about 2.78 ° C / sec x ^10-3. The conversion of o-xylene was complete, but the yield was only 86 weight percent based on the o-xylene feed.

The above examples and many replicates which were used to investigate the effect of the response variables demonstrated that by using the cooling element at Raw phthalic anhydride ..

By-product (in the form of
Maleic anhydride)

Product selectivity ratio

yield

(Weight percent,

based on

inserted

o-xylene)

ι Ι π

86

11

7.8

98

11
8.9

Under condition I, ie without using a second temperature zone, the average cooling rate in the lower part of the reaction vessel is about 2.8 ° C / sec · 10 ^-3 .

Under Conditions II, the average speed was about 3.3 ° C / sec x 10 ~ ^s .

The above data lead directly to the stated and expected yields of crude phthalic anhydride under industrial production conditions in the range of 100 to 115 percent by weight with the corresponding product selectivity ratios of about 9.6 to 10.5.

Claims (1)

Claim: Process for the production of phthalic anhydride by the catalytic oxidation of o-xylene with molecular oxygen in the vapor phase at an elevated temperature at one fixed vanadium pentoxide catalyst, characterized in that one Mixture of evaporated o-xylene and molecular oxygen with a contact time of about 0.001 to 0.05 seconds passes over the catalyst, the reaction zone of which is kept at a constant temperature essentially at 590 to 815 ° C, especially 650 to 760 ° C, that one the oxidation mixture at a rate of at least 3.3 to 11 ° C / sec · ΙΟ " ³ with the help of a fixed cooling element within the catalyst layer or with the help of two successive heat exchangers, the first of which at a temperature of about 455 to 595 ° C and the second is kept at a temperature of about 205 to 430 ° C., cools and the reaction mixture is worked up by customary methods.