CS216601B1 - Method of separation of phtalanhydride from the wapour-gas mixtures - Google Patents

Abstract

The invention presents a new, continuous method of isolating phthalic anhydride from -gas mixtures formed by the catalytic by air oxidation of naphthalene or o-xylene, containing 0.2 to 2% by volume of phthalic anhydride and other impurities such as maleic anhydride, naphthoquinone and the like concurrently with the cooling of the steam-gas mixture at 50 to 100 ° C gas permeable walls of the crystallizer air evenly distributed throughout his perimeter platform with temperature falling from 100 to 200 ° C to a temperature of 20 to 80 ° C punching speeds from 5.5 to 0.5 cm / s at the point of entry of said mixture into the crystallizer to a speed of 0.5 to 0.02 cm / s at the exit point of the mixture from the crystallizer. The invention is particularly useful in the invention phthalic anhydride production.

Description

The invention relates to a process for the separation of phthalic anhydride from steam-gas mixtures formed by oxidation of naphthalene or o-xylene with air.

Phthalic anhydride is very often produced by catalytic oxidation of naphthalene or o-xylene with air. The naphthalene vapor-gas mixture contains vapors of substances condensable under standard conditions according to the oxidation conditions: 0.2 to 2 vol% phthalic anhydride vapor, 0.005 to 0.05 vol% maleic anhydride vapor, 0.006 to 0.05 vol%. vapors of 1.4 naphthoquinone, 0.005 to 0.04 vol% of tarry substances, 1 to 10 vol% of water vapor, and non-condensing gases under standard conditions such as carbon dioxide, nitrogen, oxygen. The vapor-gas mixture resulting from the oxidation of o-xylene contains 0.2 to 4% v / v of phthalic anhydride,

0.02 to 0.6% v / v maleic anhydride, 0.01 to 0.1% v / v benzoic acid,

0.01 to 0.15 vol% of citraconanhydride vapor, 1 to 10 vol% of water vapor, as well as oxygen, nitrogen and carbon dioxide. The vapor concentration of phthalic anhydride is relatively low in both cases, which causes difficulties in separating the solid phthalic anhydride.

For the separation of phthalic anhydride from the gas-vapor mixtures, they are described in the literature and are protected by a number of patents in which the mixture is cooled to a suitable temperature chosen to condense virtually free vapors of phthalic anhydride with a minimum proportion of condensable impurities. After separation of the solid product, the main proportion of the vapors of the admixtures with non-condensing gases leaves. Condensation is often carried out on chilled surfaces, usually tubular, from which the condensate is usually periodically melted.

This process is protected by a large number of patents, e.g., DOS No. 2,442,420, U.S. Patent No. 3,819,333, DOS No. 2,312,088, DOS No. 2,254,400, British Patent No. 1,235,360, U.S. Patent No. 2,925,367 No. 3,705,617 et seq., Differing either in design or process conditions.

Further, a group of patents protecting the process of separating phthalic anhydride from the vapor-gas mixtures in the fluidized bed on phthalic anhydride granules of different sizes and at different temperatures, e.g. 315 429, DOS No. 2 243 689 protects the continuous process,

U.S. Patent No. 2,817,416 discloses a granule temperature of initially 52 ° C and a gaseous mixture of 132-538 ° C until the temperature gradient is equalized, then the charge is recooled. The disadvantages of this process are the difficulty of fractionating the product to obtain new granules for the continuous process, the sticking of the granules in the case of phthalic anhydride and the undesirable condensation also on the walls of the apparatus. As the product reduces the rate of heat transfer through the wall, cooling the mixture and recovering the sublimation heat of the phthalic anhydride vapors is done with a cooler fluidizing gas or the granules are circulated and cooled outside the desublimation equipment, which complicates the process considerably.

Another group of patents protects the process of separating phthalic anhydride by cooling the steam-gas mixtures by evaporating the injected water. For example, the French patent δ. 1 209 169, according to which phthalic anhydride, produced by catalytic oxidation of hydrocarbons in air at 350 ° C, is obtained from the mixture by cooling it by injecting water in a set of capacitors,

216 601 í

according to DOS δ. In U.S. Pat. No. 2,416,457, the phthalic anhydride obtained by oxidation of the o-xylan is isolated from the reaction mixture from a liquid distillation residue which is cooled with injected water and passed into a vessel of water where granules of product are formed. According to U.S. Pat. No. 2,071,329, the hot steam-gas reaction mixture comes into direct contact with an excess of water in which the phthalic anhydride is hydrated to phthalic acid and the phthalic acid is then separated from the solution or suspension, which must then dehydrate to the phthalic anhydride. British Patent No. 944,232 protects a process for isolating phthalic anhydride from steam-gas mixtures into which water is injected at the inlet of the cyclone separator. The mixture is cooled by evaporation of water, whereby solid phthalic anhydride is precipitated and simultaneously separated from the non-condensable gases in a separator. The separsee process is carried out at a temperature of 80 to 100 ° C to prevent condensation of the maleic anhydride formed as a by-product. The product container walls are maintained at a temperature of 130 to 160 ° C. The patent does not disclose data on the efficiency of separation of phthalic anhydride from mixtures, product moisture or separation efficiency from impurities. For a short contact time of the mixture with the aqueous dispersion in the cyclone capacitors, the product is expected to contain either too much water or a low separation efficiency.

According to German Patent No. 857 052, phthalic anhydride is separated from the steam-gas mixtures by cooling only with an amount of water which is sufficient to evaporate during the process so that a substantially dry product is obtained. The temperature of the outlet gases is between 70 and 85 ° C. The walls of the condensers are heated to a temperature a few degrees higher than the cooled steam-gas mixture to prevent deposition of the product.

The present invention provides a new, continuous process for the isolation of phthalic anhydride from steam-gas mixtures formed by catalytic oxidation of naphthalene or o-xylene with air. The mixture resulting from the naphthalene oxidation typically contains 0.2 to 2 vol% phthalene hydride vapor, 0.005 to 0.05 vol% maleic anhydride vapor, 0.006 to 0.05 vol% vapor of 1,4 naphthoquinone, 0.005 to 0.04 vol. % of tarry substances, 1 to 10% by volume of water vapor and a mixture of gases not condensable under standard conditions (nitrogen, oxygen, carbon dioxide).

The mixture formed by the catalytic oxidation of o-xylene typically contains 0.2 to 4% v / v phthalic anhydride, 0.02 to 0.6% v / v maleic anhydride, 0.01 to 0.1% v / v benzoic acid, 0.01 up to 0.15 vol% of citraconanhydride vapor, 1 to 10 vol% of water vapor as well as nitrogen, oxygen and carbon dioxide. The vapor-gas mixtures are cooled in exchanger to about 150 to 200 ° C after exiting the reactor and continuously fed to the crystallizers where they are cooled and partially condensed by evaporation of the finely dispersed water dispersed in the mixtures.

SUMMARY OF THE INVENTION The present invention is directed to a process wherein air is supplied to the gas-vapor mixtures cooled to 50 DEG-100 DEG C. through the gas-permeable walls of the crystallisers uniformly distributed over its entire peripheral surface, decreasing gradually from 100 DEG to 200 DEG C. and at a rate of 5.5 to 0.5 cm / sec in place

216 6 01 of the inlet of said mixtures into the crystallizer at a temperature of 20 to 80 ° C and at a speed of 0.5 to 0.02 cm / s at the exit point of the mixtures and crystallize only in the volume of peroxygen mixtures obtained by oxidation of naphthalene. 07 to 0.22 wt. Phthalic anhydride containing 0.3 to 1.2% by weight of phthalic anhydride is isolated and crystallized in a volume of steam-gas mixtures obtained by oxidation of o-xylene. % and a moisture content of 0.0 to 0.1 wt. The walls of the crystallizer remain free of solid deposits. The product is continuously separated from the non-condensed portions of the aforementioned mixtures by filtration or in a cyclone, purged with dry or warm air to remove residual wet gas mixtures and transported in a conventional manner from the apparatus, for example by a screw conveyor. The temperature of the residues of the steam-gas mixtures exiting the apparatus is controlled by the concentration of condensable impurities in the feed mixtures with a permissible moisture content and is in the range of 50 to 100 ° C.

The phthalic anhydride produced by the oxidation of naphthalene and separated by the process of the present invention achieves a purity of greater than 99.8% and the phthalic anhydride produced by the oxidation of o-xylene achieves a purity of greater than 98.8% in a single separation stage.

The velocity of the air supplied through the gas-permeable walls depends on the temperature, concentration and velocity of the vapor-gas mixtures.

The gas-permeable walls of the crystallizer are made of a densely woven glass, polyester or other plastic fabric. The air permeability is a maximum of 60 m ^ per 1 m ^{2 of} wall at a minimum pressure difference of 133 Fa.

The use of this method is explained by the following examples.

Example 1

Crude phthalic anhydride, containing 0.5 wt. % maleic anhydride and 0.5 wt. % 1.4 naphthoquinone, was sublimed at a rate of 1.6 kg / h in a fluidized bed sublimator with an inert 5 bed fluidized with 50 m of hot air per hour. The resulting 170 ° C vapor-gas mixture was filtered by a metal filter * to trap entrained mechanical impurities and was then fed to the crystallizer simultaneously with 2.8 L of finely dispersed water per hour from a nozzle located in the head of the crystallizer. Through the gas-permeable walls of the crystallizer b1 air is introduced into the mixture with a temperature gradually reduced from 150 ° C and a speed of 5.5 cm / s at the point of entry of the vapor-gas mixture into the crystallizer at 30 ° C and a speed of 0.06 cm / s. The solid product was separated from the non-condensed portion of the steam-gas mixture in a filter with a densely woven filter cloth. The product was collected in a well to which 1.5 m ^ / h of air was fed at 70 ° C to remove residual wet mixture. The temperature of the vapor-gas mixture exiting the filter was 70 ° C. After about 4 hours, the product residue was removed from the filter cloth by tapping. There was no solid deposit on the walls of the crystallizer. For

216 601 hours of operation yielded 6.18 kg of product, i.e. 96.5 wt. % of the dosed amount, i.e. 99.2 wt. % of the theoretically recoverable quantity. The product contained 0.011 wt. % maleic anhydride and 0.200 wt. % 1.4 naphthoquinone, 0.04 wt. % moisture. Its purity was 99.79% regardless of humidity. (Flow rates are given in m @ 2 at 20 ° C and atmospheric pressure.)

Example 2

Crude phthalic anhydride containing 1 wt. % maleic anhydride and 1 wt. % 1,4 naphthoquinone under otherwise identical conditions. The resulting steam-gas mixture was cooled in a crystallizer of 2.3 L of finely divided water per hour and its temperature at the outlet of the filter was 90 ° C. The air velocity through the gas permeable walls of the crystallizer at the point of inlet of the mixture was 0.5 cm / s and its temperature was 180 ° C and at the point of the outlet of the mixture it was 0.2 cm / s and the temperature was 50 ° C.

No deposition was observed on the crystallizer walls after 8 hours of experiment. After 4 h 5.6 kg of product, i.e. 87.5 wt. % of the dosed amount, i.e. 98 wt. % of the theoretically recoverable quantity. The product contained 0.0030 wt. % maleic anhydride and 0.66 wt. % 1.4 naphthoquinone. Its purity was 99.93%.

Example 3

Crude phthalic anhydride containing 10 wt. % maleic anhydride and 2 wt. % benzoic acid at a rate of 3.2 kg / h at 180 ° C under otherwise the same conditions as in Example 1. The resulting steam-gas mixture was cooled in a 3.3 L finely dispersed water crystallizer and its temperature at the outlet of the filter. was 100 ° C. The air velocity through the gas-permeable walls of the crystallizer at the inlet of the mixture was 3 cm / s, its temperature was 170 ° C, and at the exit point of the mixture from the crystallizer, it was 0.1 cm / s and the temperature was 30 ° C. After 4 hours of experiment, no solid deposit was observed on the crystallizer walls. 4.9 kg of product, i.e. 76.6 wt. % of the feed quantity, i.e. 97.7 wt. % of theoretically obtainable phthalic anhydride. (About 10% of the uncondensed phthalic anhydride and about 12% of the impurities leave in vapors.) The product contained 0.2 wt. % maleic anhydride and 0.1 wt. % benzoic acid.

Example 4

Crude phthalic anhydride containing 2 wt. % maleic anhydride and 0.5 wt. The resulting steam-gas mixture was cooled in a crystallizer of 3.8 l of finely dispersed water and the temperature of the mixture at the outlet of the filter was 60 ° C. Air velocity through the gas permeable walls of the crystallizer at the inlet point was 4 cm / s and its temperature was 160 ° C, at the outlet point the air velocity was 0.3 cm / s and its temperature

216 601 ° C. The walls of the crystallizer were free of solid deposit after 4 h of experiment. After 2 h it was obtained

6.16 kg of product, i.e. 96.3 wt. % of the feed amount of crude phthalic anhydride, i.e. 98.5 wt. % of the theoretically recoverable quantity. The product contained 0.3 wt. % maleic anhydride and 0.2 wt. % benzoic acid.

Claims (1)

OBJECT OF THE INVENTION Process for separating phthalic anhydride from air-gaseous naphthalene oxidation mixtures containing 0 * 2 to 2% v / v phthalic anhydride, 0.005 to 0.05% v / v maleic anhydride, 0.006 to 0.05% v / v 1,4 naphthoquinone 0.005 to 0.04 vol% tars, 1 to 10 vol% water vapor, and non-condensable gases such as carbon dioxide, oxygen, nitrogen, in which phthalic anhydride containing 0.07 to 0.22 wt. % and moisture 0.0 to 0.1 wt. % or of steam-gas mixtures resulting from the oxidation of o-xylene by air containing from 0.2 to 4% v / v phthalic anhydride, 0.02 to 0.6% v / v maleic anhydride, 0.01 to 0.1% v / v benzoic acid, 0.01 to 0.15 vol% citraconarihydride vapor, 1 to 10 vol% water pores, further nitrogen, oxygen and carbon dioxide, in which phthalic anhydride containing 0.3 to 1.2 wt. % and a moisture content of 0.0 to 0.1 wt. % after reducing the temperature of the vapor-gas mixtures in the exchanger to 150 to 200 ° C and cooling them in the crystallizer by evaporating finely dispersed water dispersed in said mixtures, characterized in that simultaneously with the cooling of the vapor-gas mixtures to 50 to 100 ° C They supply air through the crystalline walls of the crystallizer uniformly distributed over its entire peripheral surface with a temperature decreasing to 100 to 200 ° C and a speed of 5.5 to 0.5 cm / s at the point of entry of said mixtures into the crystallizer at 20 to 80 ° C and a speed of 0 5 to 0.02 cm / sec at the exit point of the mixture, and the phthalic anhydride crystallizes only in the volume of the vapor-gaseous mixtures and then separates from the non-condensed portions of said mixtures in a filter or cyclone.