SU1625875A1 - Method for producing phthalic anhydride - Google Patents

Abstract

The invention relates to heterocyclic compounds, in particular to the preparation of phthalic anhydride. Tsech - simplification of the process, ensuring o + saro- and explosion safety and reducing the amount of oi of the local gases Obtaining is carried out by vapor-phase catalytic oxidation of o-xylene, release of phthalic anhydride of potent gases by aosorcine o-xylene and purification of waste 1 nitrogen, After absorption (containing o-nsnol and the products of its catalytic oMir.jiniiin,), 50-402 of the reaction gases are returned to the oxide: n stage, adding air or oxygen to them until the oxygen concentration in the reaction gases is 10.5 - 11% by volume , and the remaining amount of waste gases are sent to the discharge. (ABOUT

Description

The invention relates to organic chemistry, in particular, to a method for producing phthalic anhydride by the vapor-phase catalytic oxidation of o-xylene with atmospheric oxygen.

The purpose of the invention is to simplify the technology, ensure the fire and air safety of the process and reduce the amount of waste gases.

H p and me R 1 (comparative). An o-xylene-air mixture with an o-xylene concentration of 8U g / nm and oxygen of 21 vol.% is subjected to vapor-phase catalytic oxidation and reaction gases are obtained that contain 80 g / nm phthalic anhydride, 5 g / their maleic anhydride and 60 g / nm of water vapor at an oxygen concentration of 13 vol.%. The reaction gases of the composition are fed into an adiabatic column, irrigated at 30 ° C with o-xylene. With

In this case, o-xylene absorbs ttalivyp and maleic anhydride from the reaction gases, and gases that contain at least 35-60 g / o of o-xylene with an oxygen concentration of 13 vol. Thus, all the reaction patterns are: before the reactor 80 g / nm o-xylene and 21 oP oxygen, after the reactor VO g / nm5 phthalic anhydride and 13 vol. oxygen, and after the absorption column 55-60 t-. nm of o-xylene and 13 vol. /, oxygen - fire and explosive, as the composition of gases with oxygen and o-xylene is higher than the lower explosive limit of these mixtures (the lower explosiveness limit of mixtures o-xylene is 47 g / nm, and phthalic anhydride - air 60-6i g / nm, at the temperature of the reaction gases). O-Xylene was recovered from waste gases

00

ate

in the second absorption stage with a high boiling solvent. Thereafter, the waste gases are directed to a discharge.

II p m m e r 2. A mixture consisting of 150 l / h of air and 150 l / h of nitrogen (concentration of oxygen in the mixture 10.5–11%) and containing 60 g / m 3 of mixture o-xylene. Reaction

post-reactor gases contain 63.8 g / nm phthalic anhydride, 2.6 g / nm maleic anhydride and 1.1 g / nm o-toluene aldehyde with

oxygen concentration of 4.8-5 vol.%. Phthalide is absent. Phthalic anhydride is extracted from contact gases ab

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oxidation, adding to it 45% (135 l / h) of air, while the oxygen concentration in the mixture is again set at J0.8–11.0% by volume. In this case, the content of phthalic anhydride in the reaction gases is also kept constant ( 84.9 g / nm), i.e. The yield of phthalic anhydride is 76 mol.%, which also corresponds to the selectivity of the oxidation process without recirculation. Phthalide is absent.

Example4. Under the conditions of Example 2, a mixture consisting of 15E l / h of air and 153 l / h of nitrogen (oxygen concentration 10.5% by volume) and containing 100 g / nm of o-xylene is supplied for oxidation. Pe10

15

the sorption of o-xylene in the packed column at 150 ° C in the lower part and 50 ° C in the upper part. Phthalic anhydride - raw 20 is withdrawn from the lower part of the absorber. The gases coming from the upper part of the absorber are cooled to 25 ° C and a mixture is obtained containing 60 g / nm-o-xylene, 4.8-5.0% by volume of oxygen and the indicated gases in accordance with the procedure of Example 2. The post-reactor gas gases contain 106.1 g / nm phthalic anhydride and 4.4 g / nm maleic anhydride at an oxygen concentration of not more than 0.5-0.7%. Phthalide is absent, and o-toluic aldehyde 1.8 g / nm. Phthalic anhydride is recovered from the reaction products. Of the exhaust gases, 70% (210 l / h) is recycled to the oxidation stage, adding 30% (9U l / h) of air to them, while the oxygen concentration in the mixture is again set at 10.5-11 vol. % With such an organization of the process, the content of phthalic anhydride in the reaction gases is kept constant (63.8 g / nm), i.e. The yield of phthalic 35 anhydride is 76 mol.%, which corresponds to the selectivity of the oxidation process without recirculation. Phthalide in the reaction gases is practically absent ,, 40

Example 3. A mixture consisting of 150 L / h of air and 150 L / h of azo Example 5 is fed to the oxidation conditions of Example 2. In terms of example

ta (concentration 0 10.5-11.0%) and containing 80 g / nm of o-xylene. 40% of the gases after the reactor contain (120 l / h) of the gas mixture and to it is added 84, 9 g / Nm3 of phthalic anhydride, 180 l / h (60%) of air, while

3.5 g / nm3 of maleic anhydride and the o-xylene gas concentration in gas mixture, 46 g / nm 3 of o-toluyl aldehyde at an oxygen concentration of 2.5–3%,% hd Phthalide is absent. Phthalic anhydride is separated from the reaction gases according to the method of Example 2. The gases leaving the upper part of the absorber are cooled with water to 35-36 ° C and a mixture is obtained,

containing 80 g / nm of o-xylene, 2.5 - 3, 90% of 3.0% of oxygen and the specified side (276 l / h) gas mixture and its pre-products are sent for recycling. Of the flue gases, 55% (166 g / h) is recycled to the stage

 - «--- - f« «l v U 1., IF.

80 g / nm, the oxygen concentration rises to 17%, i.e. the gas mixture becomes flammable and explosive. The yield of phthalic anhydride is maintained at the level of Example 3.

Example 6. Under the conditions of the example

Bavl 2.6-2.7 l / h of oxygen. Under these conditions, the gas enters the reactor.

The gases after the reactor contain 106.1 g / nm of phthalic anhydride and 4.4 g / nm of maleic anhydride with an oxygen concentration of not more than 0.5-0.7%. Phthalide is absent, and o-toluic aldehyde 1.8 g / nm. Phthalic anhydride is separated from the reaction, leaving the upper part of the absorber is cooled with water to 40 ° C to obtain a mixture containing 100 g / nm of o-xylene, 0.5-0.7% by volume of oxygen and the indicated by-products. Of the waste gases, 50% (150 L / h) is recycled to the oxidation step, adding 50% (150 L / h) of air to them, while the oxygen concentration in the mixture is set at 11% by volume. With such an organization of the process, the content of phthalic anhydride does not change and is maintained at the level of 106.1 - 106.3 g / nm, i.e. the output of phthalic anhydride does not change and corresponds to the output without recirculation of the gas stream. Phthalide is absent.

Example5. In terms of example

 40% (120 l / h) of the gas mixture is directed to the recirculation and the concentration of o-xylene in the gas mixture 3 is added to it; 90% (276 l / h) of the gas mixture is sent to the recirculation and - to - - - f «« l v U 1., IF.

80 g / nm, the oxygen concentration rises to 17%, i.e. the gas mixture becomes flammable and explosive. The yield of phthalic anhydride is maintained at the level of Example 3.

Example 6. Under the conditions of the example

 3, 90% (276 L / h) of the gas mixture is sent for recycling and 2.6-2.7 L / h of oxygen is added to it. Under these conditions, the gas enters the reactor.

a mixture with an o-xylene concentration of 80 g / nm and an oxygen concentration of 11% by volume. The reaction gases after the reactor contain 86.2 g / mne of phthalic anhydride (77% yield), 3.3 - 3.4 g / mne of small anhydride in the practical absence of aldehydes and phthalide.

Thus, the implementation of the process according to the proposed method allows to simplify the technology by eliminating the need to use high-boiling solvent, reduce the amount of waste gases by returning part of them to the process, as well as ensure the fire and explosion-proof process.

Claims (1)

Invention Formula The method of producing phthalic anhydride by vapor-phase catalytic oxidation of o-xylene, release of phthalic anhydride from contact gases by absorption by o-xylene and purification of waste gases, in order to simplify the process, ensuring fire and explosion safety and reducing the amount of exhaust gases, 50-90% of the reaction gases after absorption containing o-xylene and products of its catalytic oxidation, return to the oxidation stage, adding air or oxygen to them to the oxygen concentration in the reaction gases 10.5-11% by volume, and the remaining off-gases are directed to | reset.