阅读说明：本技术 均四甲苯液相连续富氧精密氧化合成均苯四甲酸二酐的方法 (Method for synthesizing pyromellitic dianhydride by liquid-phase continuous oxygen-enriched precise oxidation of durene ) 是由 曹正国 李江华 王福 任伟 荆晓平 于 2021-08-17 设计创作，主要内容包括：本发明公开了有机化工合成技术领域内的一种均四甲苯液相连续富氧精密氧化合成均苯四甲酸二酐的方法,先进行配料进料,将均四甲苯、醋酸和钴锰锌溴催化剂按照质量百分比5～20%：79.97～94.99%：0.01～0.05%混合完全,混合液与富氧气体连续打入微通道反应器进行氧化反应；催化反应生成均苯四甲酸,生成的富含均苯四甲酸反应液连续出料；然后结晶离心,去除醋酸、水和催化剂,得到的滤饼即为精均苯四甲酸；最后脱水成酐得到均苯四甲酸二酐。该方法具有高速混合、高效传热、反应物停留时间短、转化率高、省去重结晶或升华提纯工艺、便于操控,具有氧化反应能耗小、安全系数高、反应产物纯度高,无放大效应的特点。(The invention discloses a method for synthesizing pyromellitic dianhydride by liquid-phase continuous oxygen-enriched precise oxidation of durene in the technical field of organic chemical synthesis, which comprises the following steps of firstly, preparing and feeding durene, acetic acid and a cobalt-manganese-zinc-bromine catalyst according to the mass percentage of 5-20%: 79.97-94.99%: 0.01-0.05% of the mixture is completely mixed, and the mixed solution and the oxygen-enriched gas are continuously pumped into a micro-channel reactor for oxidation reaction; catalyzing and reacting to generate pyromellitic acid, and continuously discharging the generated pyromellitic acid-rich reaction liquid; then crystallizing and centrifuging, removing acetic acid, water and catalyst, and obtaining a filter cake, namely the refined pyromellitic acid; finally, dehydration is carried out to obtain the pyromellitic dianhydride. The method has the characteristics of high-speed mixing, high-efficiency heat transfer, short reactant retention time, high conversion rate, convenience in operation and control, low energy consumption of oxidation reaction, high safety coefficient, high purity of reaction products and no amplification effect, and a recrystallization or sublimation purification process is omitted.)

1. A method for synthesizing pyromellitic dianhydride by liquid-phase continuous oxygen-enriched precise oxidation of durene is characterized by sequentially comprising the following steps:

(1) material preparation and feeding: durene, acetic acid and a cobalt-manganese-zinc-bromine catalyst are added according to the mass percentage of 5-20%: 79.97-94.99%: 0.01-0.05% of the mixture is completely mixed, and the mixed solution and the oxygen-enriched gas are continuously pumped into a micro-channel reactor for oxidation reaction;

(2) precision oxidation: keeping the oxidation temperature in the microchannel reactor at 180-260 ℃, keeping the pressure in the reactor at 1.2-1.8MPa, carrying out catalytic reaction on durene and oxygen-rich gas to generate durene tetracarboxylic acid, and continuously discharging the generated durene tetracarboxylic acid-rich reaction liquid;

(3) and (3) crystallizing and centrifuging: cooling the pyromellitic acid reaction liquid to 25 ℃ for crystallization, separating in a centrifuge, removing acetic acid, water and a catalyst to obtain a filter cake, namely refined pyromellitic acid;

(4) dehydration to anhydride: the refined pyromellitic acid is sent into an anhydride forming kettle at 245 +/-2 ℃ and the vacuum degree of 0.095MPa for dehydration to obtain the pyromellitic dianhydride.

2. The method for synthesizing the pyromellitic dianhydride by the liquid-phase continuous oxygen-rich precision oxidation of the durene according to claim 1, is characterized in that: the oxygen-enriched gas is a nitrogen-oxygen mixed gas with the oxygen volume content of 21-50%.

3. The method for synthesizing the pyromellitic dianhydride by the liquid-phase continuous oxygen-rich precision oxidation of the durene according to claim 1, is characterized in that: the inner diameter of the micro-channel reactor is 0.6-20 mu m.

4. The method for synthesizing pyromellitic dianhydride by liquid-phase continuous oxygen-rich precision oxidation of durene according to claim 3, is characterized in that: the inner diameter of the micro-channel reactor is 10 mu m.

5. The method for synthesizing the pyromellitic dianhydride by the liquid-phase continuous oxygen-rich precision oxidation of the durene according to claim 1, is characterized in that: the cobalt-manganese-zinc-bromine catalyst is a mixture of cobalt acetate, manganese acetate, zinc acetate and tetrabromoethane.

6. The method for synthesizing pyromellitic dianhydride by liquid-phase continuous oxygen-enriched precision oxidation of durene according to any one of claims 1 to 5, characterized in that: the molar ratio of cobalt, manganese, zinc and bromine in the cobalt-manganese-zinc-bromine catalyst is 1:1:0.5: 0.5.

Technical Field

The invention relates to the technical field of organic chemical synthesis, in particular to a method for synthesizing pyromellitic dianhydride by liquid-phase oxidation of durene.

Background

Durene, also known as durene, is an important organic chemical raw material. The pyromellitic acid is mainly used for producing pyromellitic acid, and then the pyromellitic acid dianhydride is obtained by dehydration. Pyromellitic dianhydride is an important raw material for producing polyimide polymer, and polyimide is a novel synthetic material with high temperature resistance, low temperature resistance, radiation resistance and impact pressure resistance, excellent electrical property and mechanical property, and has important application which cannot be replaced by other engineering plastics in aerospace and electromechanical industries. With the continuous expansion of the market consumption of polyimide, durene is used as a main raw material for synthesizing the polyimide, and the demand is increased day by day.

The production line of pyromellitic dianhydride is divided into two types, one type is that the pyromellitic dianhydride is heated and melted, mixed with hot air after being gasified, and enters a fixed bed tubular reactor filled with a V-Ti-O catalyst and with the reaction temperature of 430-445 ℃ to generate pyromellitic anhydride and byproducts, and comprises a gasification section, an oxidation section, a trapping section, a hydrolysis section, a dehydration or sublimation refining section, a concentration section, a dehydration drying section and a recrystallization or sublimation section to generate pyromellitic acid or pyromellitic dianhydride; the other is liquid-phase oxidation of durene to synthesize reaction liquid rich in durene tetracarboxylic acid, which is then distilled, crystallized, centrifugally separated, dewatered to anhydride, recrystallized or sublimated to obtain the durene tetracarboxylic dianhydride.

Pyromellitic acid and its derivatives have industrially important applications. Pyromellitic acid is used as the main synthetic monomer of polyimide which is a high-temperature resistant insulating material, is widely applied to the fields of aerospace, aviation, electromechanics, electronics and the like, and is also an important curing agent for epoxy resin and polyester resin and an auxiliary agent for powder coating. The ortho carboxyl activity of sodium pyromellitate can generate chelate with polyvalent metal ion to be used as assistant of detergent. Pyromellitic acid ester is a good low-fluidity plasticizer and is also a PVC heat stabilizer. Phthalocyanine made from pyromellitic acid derivatives can be used as pigment, oxidation catalyst, and high-performance lubricant.

The microchannel reactor is essentially a continuous flow pipeline reactor, the microchannel is manufactured by using a precision machining process, and because the microchannel has a small size, compared with a conventional tubular reactor, the microchannel reactor has very large specific surface area and volume ratio, the microchannel reactor has extremely high mixing efficiency, extremely high heat transfer capacity and extremely narrow residence time distribution. Since the micro-reaction technology started to rise in the middle of the 90 s of the 20 th century, the micro-reaction technology is rapidly developed due to unique characteristics and advantages and becomes a common research hotspot in scientific research institutions and business industries; not only obtains a plurality of remarkable scientific research achievements, but also obtains more and more applications in the synthesis of medicines, pesticides, special materials, fine chemical products and intermediates.

Chinese patent CN111960939A discloses a method for producing pyromellitic acid, which comprises mixing and vaporizing durene serving as a raw material and air, and introducing the mixture into a microchannel reactor coated with a catalyst coating for reaction; cooling, crystallizing and centrifuging the reacted gas, distilling the centrifuged mother liquor at normal pressure, and adding the centrifuged solid and the distilled residual liquid into a hydrolysis kettle for hydrolysis; and finally, filtering the hydrolysate, and carrying out sectional cooling crystallization, centrifugation and vacuum drying on the filtrate to obtain the target product pyromellitic acid.

The existing gas phase or liquid phase oxidation process has the following defects:

1) the reaction temperature is higher, and the reaction energy consumption is high;

2) the reaction conversion rate is not high, and a plurality of byproducts are generated;

3) the process route is long, and the product is difficult to separate and purify.

Disclosure of Invention

The invention aims to provide a method for synthesizing pyromellitic dianhydride by liquid-phase continuous oxygen-enriched precise oxidation of durene, which has high conversion rate and easy purification of products.

The purpose of the invention is realized as follows: a method for synthesizing pyromellitic dianhydride by liquid-phase continuous oxygen-enriched precise oxidation of durene sequentially comprises the following steps:

(1) material preparation and feeding: durene, acetic acid and a cobalt-manganese-zinc-bromine catalyst are added according to the mass percentage of 5-20%: 79.97-94.99%: 0.01-0.05% of the mixture is completely mixed, and the mixed solution and the oxygen-enriched gas are continuously pumped into a micro-channel reactor for oxidation reaction;

(2) precision oxidation: keeping the oxidation temperature in the microchannel reactor at 180-260 ℃, keeping the pressure in the reactor at 1.2-1.8MPa, carrying out catalytic reaction on durene and oxygen-rich gas to generate durene tetracarboxylic acid, and continuously discharging the generated durene tetracarboxylic acid-rich reaction liquid;

(3) and (3) crystallizing and centrifuging: cooling the pyromellitic acid reaction liquid to 25 ℃ for crystallization, separating in a centrifuge, removing acetic acid, water and a catalyst to obtain a filter cake, namely refined pyromellitic acid;

(4) dehydration to anhydride: the refined pyromellitic acid is sent into an anhydride forming kettle at 245 +/-2 ℃ and the vacuum degree of 0.095MPa for dehydration to obtain the pyromellitic dianhydride.

The further improvement is that the oxygen-enriched gas is a nitrogen-oxygen mixed gas with the oxygen volume content of 21-50%. The nitrogen plays a role in protection, and the oxygen plays a role in efficient oxidation. The inner diameter of the micro-channel reactor is 0.6-20 mu m. Preferably the inner diameter is 10 μm. On one hand, the micro-channel reactor has extremely large specific surface area due to the internal microstructure thereof, which can reach hundreds of times or even thousands of times of the specific surface area of the stirring kettle. On the other hand, the microchannel reactor has excellent heat transfer and mass transfer capacity, can realize instant uniform mixing and efficient heat transfer of materials, and can greatly accelerate the reaction process. The selection of the inner diameter of the microchannel not only can maintain the high-efficiency reaction of the microchannel reactor, but also can allow partial precipitates in the reaction to pass through, and is not easy to cause the blockage of the microchannel.

The further improvement of the invention is that the cobalt-manganese-zinc-bromine catalyst is a mixture of cobalt acetate, manganese acetate, zinc acetate and tetrabromoethane. The preferred scheme is that the molar ratio of cobalt, manganese, zinc and bromine in the cobalt-manganese-zinc-bromine catalyst is 1:1:0.5: 0.5. The scheme is obtained by screening, and has a high-efficiency catalysis effect.

Compared with the prior art, the invention has the following beneficial effects: compared with the existing gas phase or liquid phase oxidation reaction, the method has the characteristics of high-speed mixing, high-efficiency heat transfer, short reactant retention time, high conversion rate, no need of recrystallization or sublimation purification process, convenience in operation and control, low energy consumption of the oxidation reaction, high safety coefficient, high purity of reaction products and no amplification effect.

Detailed Description

The invention is further illustrated by the following examples, but the scope of the invention as claimed includes, but is not limited to, the scope of the examples.

Example 1:

continuously pumping mixed liquid of durene, acetic acid and cobalt-manganese-zinc bromide catalyst (mass ratio is 5: 94.99: 0.01) into a microchannel reactor, and continuously introducing air into a microchannel device while feeding the liquid, wherein the inner diameter of a microchannel of the microchannel reactor is 10 mu m.

The cobalt-manganese-zinc-bromine catalyst is a mixture of cobalt acetate, manganese acetate, zinc acetate and tetrabromoethane, wherein the molar ratio of cobalt to manganese to zinc to bromine is 1:1:0.5: 0.5.

Keeping the temperature in the microchannel reactor at 180 ℃, the pressure in the reactor at 1.2MPa, carrying out catalytic reaction on durene and oxygen to generate pyromellitic acid, and continuously discharging the generated pyromellitic acid-rich reaction liquid, wherein the content of the pyromellitic acid in the reaction liquid is 98.5 percent.

Cooling the pyromellitic acid reaction liquid to 25 ℃ for crystallization, separating in a centrifuge, removing acetic acid, water and catalyst to obtain a filter cake, namely the refined pyromellitic acid. Finally, the refined pyromellitic acid is sent into an anhydride forming kettle at 245 ℃ and the vacuum degree of 0.095MPa for dehydration to obtain pyromellitic dianhydride with the purity of 99.3 percent.

Example 2:

continuously pumping mixed liquid of durene, acetic acid and cobalt manganese zinc bromide catalyst (mass ratio is 17: 82.98: 0.02) into a microchannel reactor, continuously introducing oxygen-enriched gas into a microchannel device while feeding the liquid, wherein the oxygen content is 30%, and the inner diameter of a microchannel of the microchannel reactor is 10 mu m.

The cobalt-manganese-zinc-bromine catalyst is a mixture of cobalt acetate, manganese acetate, zinc acetate and tetrabromoethane, wherein the molar ratio of cobalt to manganese to zinc to bromine is 1:1:0.5: 0.5.

Keeping the temperature in the microchannel reactor at 260 ℃, the pressure in the reactor at 1.8MPa, carrying out catalytic reaction on durene and oxygen to generate pyromellitic acid, and continuously discharging the generated pyromellitic acid-rich reaction liquid, wherein the content of the pyromellitic acid in the reaction liquid is 98.6 percent.

Cooling the pyromellitic acid reaction liquid to 25 ℃ for crystallization, separating in a centrifuge, removing acetic acid, water and catalyst to obtain a filter cake, namely the refined pyromellitic acid. Finally, the mixture is sent into an anhydride forming kettle at 245 ℃ and dehydrated under the vacuum degree of 0.095MPa to obtain pyromellitic dianhydride with the purity of 99.4 percent.

Example 3:

continuously pumping mixed liquid of durene, acetic acid and cobalt manganese zinc bromide catalyst (mass ratio is 10: 89.95: 0.05) into a microchannel reactor, continuously introducing oxygen-enriched gas into a microchannel device while feeding the liquid, wherein the oxygen content is 50%, and the inner diameter of a microchannel of the microchannel reactor is 20 mu m.

The cobalt-manganese-zinc-bromine catalyst is a mixture of cobalt acetate, manganese acetate, zinc acetate and tetrabromoethane, wherein the molar ratio of cobalt to manganese to zinc to bromine is 1:1:0.5: 0.5.

The temperature in the microchannel reactor is kept at 220 ℃, the pressure in the reactor is 1.4MPa, durene and oxygen react catalytically to generate pyromellitic acid, the generated reaction liquid rich in the pyromellitic acid is discharged continuously, and the content of the pyromellitic acid in the reaction liquid is 98.8 percent.

Cooling the pyromellitic acid reaction liquid to 25 ℃ for crystallization, separating in a centrifuge, removing acetic acid, water and catalyst to obtain a filter cake, namely the refined pyromellitic acid. Finally, the mixture is sent into an anhydride forming kettle at 245 +/-2 ℃ and the vacuum degree of 0.095MPa for dehydration to obtain the pyromellitic dianhydride with the purity of 99.8 percent.

Example 4:

continuously pumping mixed liquid of durene, acetic acid and cobalt manganese zinc bromide catalyst (mass ratio is 20: 79.97: 0.05) into a microchannel reactor, and continuously introducing oxygen-enriched gas into a microchannel device while feeding the liquid, wherein the oxygen content is 45%.

The cobalt-manganese-zinc-bromine catalyst is a mixture of cobalt acetate, manganese acetate, zinc acetate and tetrabromoethane, wherein the molar ratio of cobalt to manganese to zinc to bromine is 1:1:0.5: 0.5.

Keeping the temperature in the microchannel reactor at 240 ℃, the pressure in the reactor at 1.6MPa, carrying out catalytic reaction on durene and oxygen to generate pyromellitic acid, and continuously discharging the generated pyromellitic acid-rich reaction liquid, wherein the content of the pyromellitic acid in the reaction liquid is 98.7 percent.

Cooling the pyromellitic acid reaction liquid to 25 ℃ for crystallization, separating in a centrifuge, removing acetic acid, water and catalyst to obtain a filter cake, namely the refined pyromellitic acid. Finally, the mixture is sent into an anhydride forming kettle at 245 +/-2 ℃ and the vacuum degree of 0.095MPa for dehydration to obtain the pyromellitic dianhydride with the purity of 99.6 percent.

Example 5:

continuously pumping mixed liquid of durene, acetic acid and cobalt manganese zinc bromide catalyst (mass ratio is 15: 84.95: 0.05) into a microchannel reactor, continuously introducing oxygen-enriched gas into a microchannel device while feeding the liquid, wherein the oxygen content is 40%, and the inner diameter of a microchannel of the microchannel reactor is 0.6 mu m.

The cobalt-manganese-zinc-bromine catalyst is a mixture of cobalt acetate, manganese acetate, zinc acetate and tetrabromoethane, wherein the molar ratio of cobalt to manganese to zinc to bromine is 1:1:0.5: 0.5.

Keeping the temperature in the microchannel reactor at 200 ℃, the pressure in the reactor at 1.7MPa, carrying out catalytic reaction on durene and oxygen to generate pyromellitic acid, and continuously discharging the generated pyromellitic acid-rich reaction liquid, wherein the content of the pyromellitic acid in the reaction liquid is 98.4 percent.

Cooling the pyromellitic acid reaction liquid to 25 ℃ for crystallization, separating in a centrifuge, removing acetic acid, water and catalyst to obtain a filter cake, namely the refined pyromellitic acid. Finally, the mixture is sent into an anhydride forming kettle at 245 ℃ and dehydrated under the vacuum degree of 0.095MPa to obtain the pyromellitic dianhydride with the purity of 99.2 percent.

Comparative example

On the basis of example 1, the following comparative examples 1 to 16 were obtained, with the other parameters being kept constant and with the contents of the components in the catalyst being varied only, the results being shown in the following table:

it can be seen that when the molar ratio of the cobalt, manganese, zinc and bromine is 1:1:0.5:0.5, the pyromellitic acid content in the reaction solution is the highest, and the final yield is also the highest.

The present invention is not limited to the above-mentioned embodiments, and based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some technical features without creative efforts according to the disclosed technical contents, and these substitutions and modifications are all within the protection scope of the present invention.