CS239764B1 - Naphthalene based raw material for the production of phthalic anhydride - Google Patents

Abstract

The naphthalene-based raw material for the production of phthalic anhydride by selective catalytic oxidation, especially on a vanadium catalyst, consists of a naphthalene fraction with a solidification temperature range of 70 to 78 °C. This naphthalene fraction contains 80 to 96% by weight of naphthalene, 1 to 15% by weight of heavier fractions, especially methylnaphthalenes, 1 to 5% by weight of lighter fractions, especially alkylbenzenes and hydrogenated naphthalene derivatives, and up to 0.2% by weight of phenols.

Description

The invention relates to a naphthalene-based feedstock for the production of phthalic anhydride by selective catalytic oxidation, in particular on a vanadium catalyst.

In industrial practice, o-xylene or naphthalene is used to produce phthalic anhydride by catalytic oxidation. Up to now, the use of naphthalene for this production uses only raw materials with a content of more than 97% of active ingredient, most often technical naphthalene with a pour point of at least 78.9 ° C and a content of naphthalene of over 97.5% by weight.

Technical naphthalene is most often obtained from coal tar fractionation by de-phenolization and four-stage physical refining of the naphthalene fraction. Due to limited resources and increasing demand, naphthalene is becoming a scarce feedstock, therefore, the increasing selectivity of the oxidation reaction in phthalic anhydride production is increasingly urgent, but the current state of the art does not fully meet this requirement.

Indeed, the actual course of the catalytic oxidation of naphthalene consists in the fact that the starting materials in the gas phase, i.e. naphthalene and oxygen, are transported by convection and diffusion to the outer surface of the catalyst particle from the main gas stream entering the reactor and diffuse pores towards its inner surface.

Here they are chemsorbed on active centers and react together to form adsorbed products. These products desorb from the inner surface of the catalyst and diffuse the pores back to the surface of the particle from where they are conveyed to the main stream of gaseous reaction products by diffusion and convection.

The selectivity of the naphthalene to phthalic anhydride oxidation is therefore influenced by the concentration ratios of the individual reactants in the reaction mixture at the active centers of the catalyst in addition to the properties of the catalyst used.

As a result, about 83% of the naphthalene contained in the feedstock is converted to phthalic anhydride with the present gas-phase catalytic oxidation of technical naphthalene on a fixed bed vanadium catalyst.

The remaining 17% of naphthalene is transferred to other reaction products. These are mild oxidation products such as naphthoquinones, but mainly deeper oxidation products such as maleic anhydride, benzoic acid and acrylic acid, but in particular carbon oxides.

all of these by-products are ballast substances from which the phthalic anhydride produced must be isolated. Insufficiently high selectivity of naphthalene oxidation to phthalic anhydride in the prior art, where technical naphthalene is used as a raw material, therefore increases the raw material costs of phthalic anhydride production as well as its energy consumption.

These drawbacks can be largely alleviated by the use of the raw material for the production of phthalic anhydride according to the invention. Its essence is that the feedstock is a naphthalene fraction having a pour point of 70 to 78 ° C, preferably a pour point of 75 ° C.

The naphthalene fraction comprises 80 to 96% by weight, preferably 90% by weight of naphthalene, 1 to 15% by weight, preferably 6.5% by weight of heavier naphthalenes, especially methylnaphthalenes, 1 to 5% by weight, preferably 3.5% by weight % of lighter naphthalene, in particular alkylbenzenes and hydrogenated naphthalene derivatives, and up to 0.2% by weight, preferably up to 0.1% by weight, of phenols.

The advantage resulting from the use of the raw material for the production of phthalic anhydride according to the invention is an increase in the yield of phthalic anhydride by about 5% while reducing the energy consumption of the production. Indeed, it has been found that the presence of substances such as methylnaphthalenes and higher alkylbenzenes in the naphthalene fraction, used as feedstocks for selective catalytic oxidation to phthalic anhydride, is not only an obstacle but also positively affects naphthalene conversion and increases phthalic anhydride yield from The naphthalene contained in the mixture is not deeply oxidized, resulting in the formation of by-products of the oxidation of naphthalene to carbon dioxide. These components are primarily subject to these components, protecting naphthalene from deep oxidation and helping to maintain kinetic equilibrium of ongoing reactions to convert naphthalene to phthalic anhydride. .

In addition to this desirable increase in selectivity of the oxidation reaction, further savings of naphthalene arise, since the loss of naphthalene caused by its leakage during the four-stage physical refining of the naphthalene fraction to technical naphthalene is eliminated.

The preparation of the raw material according to the invention is significantly more advantageous not only in terms of energy, but above all by substantially increasing the efficiency of the isolation of naphthalene from coal tar in the form of this raw material.

The particular composition of the raw material for the production of phthalic anhydride according to the invention and the comparison with the prior art, including the consequences for the production of phthalic anhydride, are evident from the following examples.

Example 1

As a raw material for selective catalytic oxidation on a vanadium catalyst, 100 g of a naphthalene fraction of the following properties were used:

Freezing point Naphthalene content

Content of lighter naphthalene / styrene, mesitylene, hydrindene, indene, tetralin, decalin, pyridine and homologs / Content of heavier naphthalene / especially methylnaphthalenes and thionaphthene / Phenol content

Following oxidation, stabilization and distillation, the following properties were found:

Pour point Color - primary

- after thermal exposure 1,4-naphthoquinone content Maleic anhydride content ° C

90.0% by weight

3.5% by weight

6.5% w / w 0.1% w / w 90.9 g of anhydride fta131.1 ° C 30 ° Hazena 90 ° Hazena

0.0005% by weight 0.01% by weight

The molar yield of phthalic anhydride, based on the naphthalene content of the original naphthalene fraction, was 87.4%.

Example 2

100 g of the naphthalene fraction of Example 1 was subjected to physical refining to give 88.4 g of technical naphthalene having the following properties:

Freezing point 78.9 ° C

Naphthalene content 97.6% by weight

This amount of technical naphthalene was used for selective catalytic oxidation on a vanadium catalyst under the same conditions as in Example 1. After oxidation, stabilization and distillation, a total of 85.1 g of phthalic anhydride having the same properties as in Example 1 was obtained.

The molar yield of phthalic anhydride, based on the naphthalene content of the original naphthalene fraction, was 81.8%.

Example 3

As a raw material for selective catalytic oxidation on a vanadium catalyst, 100 g of a naphthalene fraction of the following properties were used:

Freezing temperature 70 ° C Naphthalene content 80% by weight Content of lighter naphthalene 5% by weight Content of heavier naphthalene 15 t by weight Phenol content 0.15% by weight

After oxidation, stabilization and distillation, 79.2 g of phthalic anhydride was obtained with the following properties:

Freezing point 131.0 ° C

Color - primary 40 ° Hazena

- after 100 ° Hazen heat exposure

Content of 1,4-naphthoquinone 0.0008% by weight

Content of maleic anhydride 0.01% by weight

The molar yield of phthalic anhydride, based on the naphthalene content of the original naphthalene fraction, was 85.6%.

Example 4

100 g of the naphthalene fraction of Example 3 was processed to technical naphthalene by physical refining. A total of 79.3 g of technical naphthalene with a pour point of 77.3 ° C was obtained. and with a naphthalene content of 97,6% by weight.

This amount was oxidized by the method of Example 3. A total of 74.4 g of phthalic anhydride having the properties of Example 3 was obtained after stabilization and distillation. The molar yield of phthalic anhydride, based on the naphthalene content of the original naphthalene fraction, was 80.4%. .

Claims (1)

SUBJECT OF THE INVENTION Naphthalene-based feedstock for the production of phthalic anhydride by selective catalytic oxidation, in particular on a vanadium catalyst, characterized in that it consists of a naphthalene fraction having a pour point of 70 to 78 ° C and containing 80 to 96% by weight of naphthalene, 1 to 15% by weight % of heavier naphthalenes, in particular methylnaphthalenes, 1 to 5% by weight of lighter naphthalene, in particular benzene alkyl homologues and hydrogenated naphthalene derivatives, and up to 0.2% by weight of phenols.