Method for continuously preparing 2-ethyl anthraquinone

Abstract

The invention belongs to the technical field of organic compound preparation, and particularly relates to a method for continuously preparing 2-ethyl anthraquinone. The preparation method comprises the following steps: S1, loading an MOF / phosphotungstic acid composite catalyst on the inner wall of a reaction tube of a continuous reactor for later use; s2, taking phthalic anhydride and ethylbenzene as raw materials, and performing Friedel-Crafts acylation, acidolysis and purification to prepare 2-(4-ethylbenzoyl) benzoic acid; s3, in the continuous reactor, under the action of the MOF / phosphotungstic acid composite catalyst, 2-(4-ethylbenzoyl) benzoic acid is subjected to dehydration and ring closing, and 2-ethyl anthraquinone is prepared. By combining the photosensitive ligand, MOF and phosphotungstic acid, the catalytic reaction efficiency and selectivity of 2-ethyl anthraquinone are improved; by optimizing the preparation process of the 2-ethyl anthraquinone, the operation is simplified, the generation of waste acid is reduced, and green and clean, high yield, good production safety and continuous production in the synthesis process of the 2-ethyl anthraquinone are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of organic compound preparation, and particularly relates to a method for continuously preparing 2-ethylanthraquinone. Background Art

[0002] In industrial production, 2-ethylanthraquinone is a fine chemical product. It is widely used in the synthesis process of hydrogen peroxide and as an intermediate in the synthesis of some medicines, pesticides and dyes. It also has important applications in the fields of photosensitization and photocatalysis.

[0003] The most common method for synthesizing 2-ethylanthraquinone is to use 2-(4'-ethylbenzoyl)benzoic acid as a raw material and subject it to dehydration and ring closure under the catalysis of a strong acid (concentrated sulfuric acid or fuming sulfuric acid) to obtain 2-ethylanthraquinone. For example, Chinese Patent CN1177954A discloses a method for synthesizing 2-ethylanthraquinone. The method comprises reacting ethylbenzene and phthalic anhydride in a mixture of HF and BF3 to obtain a 2-(4'-ethylbenzoyl)benzoic acid complex. After removing the volatile HF and BF3 from the complex, solid 2-(4'-ethylbenzoyl)benzoic acid is obtained. The solid 2-(4'-ethylbenzoyl)benzoic acid is then introduced into concentrated sulfuric acid or fuming sulfuric acid for cyclization to obtain a reaction mixture. The reaction mixture is then subjected to the steps of dilution with water for precipitation, purification with an alkaline aqueous solution, precipitation, and melt sublimation to obtain 2-ethylanthraquinone of suitable purity. This patent uses highly volatile and corrosive reagents such as hydrofluoric acid, boron trifluoride, concentrated sulfuric acid, and fuming sulfuric acid. In industrial production, this will lead to high post-processing costs, equipment corrosion, and complex operations.

[0004] At the same time, the current industrial synthesis of 2-ethylanthraquinone mostly adopts a two-step method, that is, first preparing 2-(4-ethylbenzoyl)benzoic acid, followed by drying, granulation, dehydration and cyclization with concentrated sulfuric acid or fuming sulfuric acid, hydrolysis, extraction, and desolventization to obtain 2-ethylanthraquinone. This process has the characteristics of cumbersome and complex processing, high labor intensity, low product yield, generation of large amounts of acidic wastewater, and environmental unfriendliness.

[0005] In recent years, in order to reduce the use of concentrated sulfuric acid or fuming sulfuric acid, technicians have conducted extensive research on new catalysts such as solid acid catalysts, but the results have been unsatisfactory. Although solid acid catalysts have made good progress in the pilot stage, problems such as catalyst stability, repeatability and cost have made them still a long way from industrialization.

[0006] Others, such as using modified Hβ molecular sieve as a catalyst, catalyze the direct Friedel-Crafts acylation and dehydration ring closure reaction of ethylbenzene and phthalic anhydride to synthesize 2-ethylanthraquinone in one step. For example, Chinese patent CN104803837A discloses a method for preparing 2-ethylanthraquinone, wherein phthalic anhydride and ethylbenzene are added to a kettle reactor, stirred and mixed to obtain a reactant, and then a catalyst, namely, an alkali-desiliconized modified Hβ molecular sieve, is added to the kettle reactor to react to obtain a solid-liquid mixture, and the solid catalyst is separated after cooling to obtain 2-ethylanthraquinone. The main problem of this patent is that the yield of 2-ethylanthraquinone is unstable and low, and the production cost is high. Summary of the Invention

[0007] The object of the present invention is to provide a method for continuously preparing 2-ethylanthraquinone, so as to achieve green and clean, high yield, good production safety and continuous production in the synthesis process of 2-ethylanthraquinone.

[0008] To achieve the above object, the technical solution adopted by the present invention is: The method for continuously preparing 2-ethylanthraquinone according to the present invention comprises the following steps: S1, loading a MOF / phosphotungstic acid composite catalyst on the inner wall of a reaction tube of a continuous reactor for later use; S2, using phthalic anhydride and ethylbenzene as raw materials, through Friedel-Crafts acylation, acidolysis and purification to prepare 2-(4-ethylbenzoyl)benzoic acid; In S3, in a continuous reactor, 2-(4-ethylbenzoyl)benzoic acid undergoes dehydration and cyclization under the action of a MOF / phosphotungstic acid composite catalyst to produce 2-ethylanthraquinone.

[0009] in: In step S1, the loading process is as follows: (1) The reaction tube of the continuous reactor is sequentially treated with nitric acid aqueous solution and pre-loaded with a pre-load solution and then used for standby; (2) Dissolve phosphotungstic acid in organic solvent A, add a surface stabilizer, and disperse by ultrasonication to obtain phosphotungstic acid colloid; add phosphotungstic acid colloid, zinc nitrate hexahydrate, and a photosensitizing ligand into organic solvent B and mix well to obtain a precursor solution for use; (3) coating the inner wall of the reaction tube of the continuous reactor with alumina sol, followed by drying and calcining; (4) After calcination, the precursor solution is coated on the inner wall of the reaction tube of the continuous reactor, and the loading process is completed after drying and coating reaction.

[0010] In the step (1), the continuous reactor adopts a tubular reactor, the preload solution is prepared by mixing 3-aminopropyltriethoxysilane and ethanol aqueous solution in a mass ratio of 1:(8-12), the concentration of the ethanol aqueous solution is 40-50wt%; the concentration of the nitric acid aqueous solution is 4.5-9.5wt%, the pickling time is 18-35min, and the preload treatment time is 30-45min.

[0011] In the step (2), the organic solvent A is methanol, the surface stabilizer is polyvinyl pyrrolidone; the ratio of phosphotungstic acid, the surface stabilizer and the organic solvent A is 400:(230-280):(4000-5000), wherein the phosphotungstic acid and the surface stabilizer are measured in g, and the organic solvent A is measured in mL; the ultrasonic dispersion power is 180-230 W, and the ultrasonic dispersion temperature is 20-30 ° C.

[0012] In the step (2), the photosensitivity ligand is 4,4'-(anthracene-9,10-diyl)dibenzoic acid, and the organic solvent B is N,N-dimethylformamide; the ratio of phosphotungstic acid, zinc nitrate hexahydrate, photosensitivity ligand and organic solvent B is 400:(360-420):(180-250):(2500-3000), wherein phosphotungstic acid, zinc nitrate hexahydrate and photosensitivity ligand are measured in g, and organic solvent B is measured in mL.

[0013] In the step (3), the calcination temperature is 450-550°C and the calcination time is 3.5-5h.

[0014] In the step (4), the coating reaction temperature is 85-105°C, and the coating reaction time is 6-8.5h.

[0015] In step S2, the solvent for Friedel-Crafts acylation is chlorobenzene, the catalyst is anhydrous aluminum chloride, and the molar ratio of phthalic anhydride, ethylbenzene, anhydrous aluminum chloride and chlorobenzene is 1:(1-1.09):(2.2-2.6):(5-6).

[0016] In step S2, the Friedel-Crafts acylation temperature is 0-30°C, the pressure is -0.1-0 MPa, and the reaction time is 1-3 hours. A 4 wt% aqueous hydrochloric acid solution is used for acid hydrolysis at a temperature of 55-70°C and a time of 35-45 minutes. The purification step includes toluene extraction and vacuum distillation. Preferably, the reaction temperature is 10-30°C, the reaction pressure is -0.09-0 MPa, and the reaction time is 1-2.5 hours.

[0017] In step S3, when the MOF / phosphotungstic acid composite catalyst acts, the ultraviolet light intensity is 500~1000μW / cm 2 .

[0018] In step S3, the reaction temperature of the dehydration ring is 180-210° C., the reaction pressure is 0.3-0.5 MPa, and the residence time is 35-50 min.

[0019] The beneficial effects of the present invention are as follows: (1) The photosensitivity ligand (i.e., 4,4'-(anthracene-9,10-diyl)dibenzoic acid) provides a π-conjugated anthracene ring structure, which transitions under ultraviolet light to generate free electrons (e - ) and holes (h + ), without phosphotungstic acid, the free electrons and holes will recombine quickly and cannot effectively activate the substrate; W in phosphotungstic acid 5+ / W 6+ The redox couple can capture conduction band electrons, and the free electrons tend to be transferred directionally to phosphotungstic acid through the MOF conjugated structure, thereby avoiding the ineffective recombination of free electrons and holes.

[0020] The holes retained in the photosensitive ligand can activate 2-(4-ethylbenzoyl)benzoic acid through electron transfer. The carbonyl oxygen of 2-(4-ethylbenzoyl)benzoic acid combines with the hole, enhancing the positive charge of the carbonyl carbon, significantly improving the electrophilic activity and making it easier to dehydrate and cyclize. Therefore, through the synergistic effect of electron transfer, phosphotungstic acid avoids the ineffective recombination of free electrons and holes, prompting the holes to effectively activate the intermediate 2-(4-ethylbenzoyl)benzoic acid.

[0021] (2) On the other hand, when no electrons are accepted, the anionic structure of HPW is [PW 12 O 40 ] 3- , whose protons (H + ) is tightly bound to oxygen atoms. When HPW receives free electrons to form W 5+ After that, W 5+ The electron donating ability is stronger than W 6+ , the electron cloud density of the WO bond increases, the electronegativity of the O atom combined with the proton increases, the proton is more easily dissociated, and the carboxyl group of the intermediate 2-(4-ethylbenzoyl)benzoic acid is protonated, accelerating the dehydration to generate an acyl cation.

[0022] (3) The MOF framework encapsulates phosphotungstic acid, and the photosensitive ligand in the MOF is kept close to the phosphotungstic acid through the pore confinement effect. When the photosensitive ligand activates the intermediate 2-(4-ethylbenzoyl)benzoic acid, the intermediate can quickly diffuse through the MOF pore to the vicinity of the acid site of the phosphotungstic acid. At the same time, the anthracene ring of the photosensitive ligand and the benzene ring of the intermediate have a π-π stacking effect, which can anchor the intermediate to the phosphotungstic acid, improve the utilization rate of the acid site, and avoid the decrease in catalytic efficiency caused by the disordered diffusion of the intermediate.

[0023] The Zn-O bond in MOF and the conjugated π bond of the anthracene ring form a continuous electron transfer network, allowing the free electrons of the photosensitive ligand to be efficiently transferred to phosphotungstic acid; the anthracene ring of the photosensitive ligand can combine with the benzene ring of 2-(4-ethylbenzoyl)benzoic acid through π-π stacking, ensuring that dehydration cyclization occurs.

[0024] (4) In the preparation process of the present invention, during the synthesis stage of 2-(4-ethylbenzoyl)benzoic acid, the reaction is carried out under negative pressure conditions, and a high conversion rate of the reaction is achieved at low temperature, which shortens the reaction time and reduces energy consumption. During the continuous reaction operation, 2-(4-ethylbenzoyl)benzoic acid does not need to be dried, granulated, or dissolved in sulfuric acid. It only needs to increase the temperature compensation to keep it in liquid state, which further simplifies the process steps. 2-(4-ethylbenzoyl)benzoic acid is dehydrated and closed to generate 2-ethylanthraquinone under the catalysis of MOF / phosphotungstic acid composite catalyst, avoiding the use of fuming sulfuric acid, reducing the generation of waste acid and environmental pollution. A tubular reactor is used for the reaction, and the reactor temperature, pressure, reaction time, waste acid concentration and solvent extraction are controlled to separate and purify the product, thereby reducing the occurrence of side reactions. During the entire continuous reaction process, most of the organic phase can be recycled, which can significantly reduce pollution emissions, and the yield of 2-ethylanthraquinone is maintained at above 91%. DETAILED DESCRIPTION

[0025] The present invention is described and illustrated in detail below with reference to the embodiments.

[0026] Example 1 A preload solution was prepared by mixing 3-aminopropyltriethoxysilane and 40wt% ethanol aqueous solution in a mass ratio of 1:8. The reaction tubes in the tubular reactor were sequentially immersed in 7wt% dilute nitric acid for 25 minutes, then immersed in the preload solution for 35 minutes and dried for later use. 400g of phosphotungstic acid was dissolved in 4800mL of methanol and mixed thoroughly. 250g of polyvinylpyrrolidone was added and ultrasonically dispersed at 205W and 25°C to obtain a phosphotungstic acid colloid. The phosphotungstic acid colloid, 380g of zinc nitrate hexahydrate, and 210g of 4,4'-(anthracene-9,10-diyl)dibenzoic acid were added to 2750mL of N,N-dimethylformamide and mixed thoroughly to obtain a precursor solution for later use.

[0027] A 15wt% alumina sol was coated on the inner surface of the reaction tube, dried and calcined at 500°C for 4 hours, and then cooled to room temperature. The precursor solution was coated on the inner surface of the reaction tube to form a uniform liquid film on the inner wall of the tube. The solution was dried and coated again, and the cycle was repeated 5 times. The tube was then reacted at 95°C for 6 hours for MOF coating to obtain a MOF / phosphotungstic acid composite catalyst and a catalyst-loaded reaction tube, wherein the MOF / phosphotungstic acid composite catalyst grew on the inner surface of the reaction tube.

[0028] 5.5 mol of chlorobenzene, 2.4 mol of anhydrous aluminum chloride and 1 mol of phthalic anhydride are placed in a reactor, and stirring is started. Then, 1.05 mol of ethylbenzene is added, and the temperature is controlled at 15°C, the pressure is -0.05 MPa, and the reaction time is 2 hours. After the reaction, a reaction liquid is obtained. The reaction liquid is slowly added to 5.5 kg of a 4 wt% hydrochloric acid aqueous solution, and the acidolysis temperature is controlled at 60°C and the acidolysis time is 40 minutes. After the acidolysis is completed, the mixture is allowed to stand and separate to obtain an aqueous phase and an organic phase. The aqueous phase can be re-concentrated to recover aluminum trichloride for recycling, and the organic phase is washed with water and subjected to reduced pressure distillation to remove the chlorobenzene solvent to obtain 2-(4-ethylbenzoyl)benzoic acid.

[0029] The MOF / phosphotungstic acid composite catalyst-loaded reaction tube was placed in a tubular reactor, and ultraviolet light was set. 2-(4-ethylbenzoyl)benzoic acid was preheated to 195°C and pumped into the tubular reactor through a horizontal flow pump. The mass ratio of 2-(4-ethylbenzoyl)benzoic acid to MOF / phosphotungstic acid composite catalyst was 1:1. The reaction temperature was controlled at 195°C, the reaction pressure was 0.4 MPa, the residence time was 50 min, and the ultraviolet light intensity was 500 μW / cm 2 , then toluene was added for extraction, and after separation, the toluene extract phase was collected and distilled under reduced pressure to obtain 2-ethylanthraquinone. The yield was calculated to be 91.21%.

[0030] Example 2 A preload solution was prepared by mixing 3-aminopropyltriethoxysilane and 50wt% ethanol aqueous solution in a mass ratio of 1:9. The reaction tubes in the tubular reactor were sequentially immersed in 4.5wt% dilute nitric acid for 35 minutes, then immersed in the preload solution for 40 minutes and dried for later use. 400g of phosphotungstic acid was dissolved in 5000mL of methanol and mixed thoroughly. 280g of polyvinylpyrrolidone was added and ultrasonically dispersed at 180W and 20°C to obtain a phosphotungstic acid colloid. The phosphotungstic acid colloid, 420g of zinc nitrate hexahydrate, and 250g of 4,4'-(anthracene-9,10-diyl)dibenzoic acid were added to 3000mL of N,N-dimethylformamide and mixed thoroughly to obtain a precursor solution for later use.

[0031] A 15wt% alumina sol was coated on the inner surface of the reaction tube, dried and calcined at 520°C for 4 hours, and then cooled to room temperature. The precursor solution was coated on the inner surface of the reaction tube to form a uniform liquid film on the inner wall of the tube. The solution was dried and coated again, and the cycle was repeated 5 times. The tube was then reacted at 85°C for 8.5 hours for MOF coating to obtain a MOF / phosphotungstic acid composite catalyst and a catalyst-loaded reaction tube, wherein the MOF / phosphotungstic acid composite catalyst grew on the inner surface of the reaction tube.

[0032] 6 mol of chlorobenzene, 2.6 mol of anhydrous aluminum chloride and 1 mol of phthalic anhydride are placed in a reactor, and stirring is started. Subsequently, 1.09 mol of ethylbenzene is added, and the temperature is controlled at 0°C, the pressure is -0.1 MPa, and the reaction time is 2.5 hours. After the reaction is completed, a reaction liquid is obtained. The reaction liquid is slowly added to 5.5 kg of a 4 wt% hydrochloric acid aqueous solution, and the acidolysis temperature is controlled at 55°C and the acidolysis time is 45 minutes. After the acidolysis is completed, the mixture is allowed to stand and separate to obtain an aqueous phase and an organic phase. The aqueous phase can be re-concentrated to recover aluminum trichloride for recycling, and the organic phase is washed with water and subjected to reduced pressure distillation to remove the chlorobenzene solvent to obtain 2-(4-ethylbenzoyl)benzoic acid.

[0033] The MOF / phosphotungstic acid composite catalyst-loaded reaction tube was placed in a tubular reactor, and ultraviolet light was set. 2-(4-ethylbenzoyl)benzoic acid was preheated to 200°C and pumped into the tubular reactor through a horizontal flow pump. The mass ratio of 2-(4-ethylbenzoyl)benzoic acid to MOF / phosphotungstic acid composite catalyst was 1:0.5. The reaction temperature was controlled at 200°C, the reaction pressure was 0.45 MPa, the residence time was 45 min, and the ultraviolet light intensity was 600 μW / cm 2 , then toluene was added for extraction, and after layering, the toluene extract phase was collected and distilled under reduced pressure to obtain 2-ethylanthraquinone. The yield was calculated to be 93.72%.

[0034] Example 3 A preload solution was prepared by mixing 3-aminopropyltriethoxysilane and 42wt% ethanol aqueous solution in a mass ratio of 1:10. The reaction tubes in the tubular reactor were sequentially immersed in 9.5wt% dilute nitric acid for 20 minutes, then immersed in the preload solution for 45 minutes and dried for later use. 400g of phosphotungstic acid was dissolved in 4000mL of methanol and mixed thoroughly. 230g of polyvinylpyrrolidone was added and ultrasonically dispersed at 230W and 30°C to obtain a phosphotungstic acid colloid. The phosphotungstic acid colloid, 360g of zinc nitrate hexahydrate, and 200g of 4,4'-(anthracene-9,10-diyl)dibenzoic acid were added to 2500mL of N,N-dimethylformamide and mixed thoroughly to obtain a precursor solution for later use.

[0035] A 15wt% alumina sol was coated on the inner surface of the reaction tube, dried and calcined at 480°C for 4.5 hours, then cooled to room temperature, and a precursor solution was coated on the inner surface of the reaction tube to form a uniform liquid film on the inner wall of the tube. The solution was dried and coated again, and the cycle was repeated 5 times. The tube was then reacted at 105°C for 7 hours for MOF coating to obtain a MOF / phosphotungstic acid composite catalyst and a catalyst-loaded reaction tube, wherein the MOF / phosphotungstic acid composite catalyst grew on the inner surface of the reaction tube.

[0036] 5 mol of chlorobenzene, 2.2 mol of anhydrous aluminum chloride and 1 mol of phthalic anhydride are placed in a reactor, and stirring is started. Then, 1 mol of ethylbenzene is added, and the temperature is controlled at 30°C, the pressure is 0 MPa, and the reaction time is 1 hour. After the reaction, a reaction liquid is obtained. The reaction liquid is slowly added to 5.5 kg of a 4 wt% hydrochloric acid aqueous solution, and the acidolysis temperature is controlled at 65°C and the acidolysis time is 38 minutes. After the acidolysis is completed, the mixture is allowed to stand and separate to obtain an aqueous phase and an organic phase. The aqueous phase can be re-concentrated to recover aluminum trichloride for recycling, and the organic phase is washed with water and subjected to reduced pressure distillation to remove the chlorobenzene solvent to obtain 2-(4-ethylbenzoyl)benzoic acid.

[0037] The MOF / phosphotungstic acid composite catalyst-loaded reaction tube was placed in a tubular reactor, and ultraviolet light was set. 2-(4-ethylbenzoyl)benzoic acid was preheated to 180°C and pumped into the tubular reactor via a horizontal flow pump. The mass ratio of 2-(4-ethylbenzoyl)benzoic acid to MOF / phosphotungstic acid composite catalyst was 1:1.5. The reaction temperature was controlled at 180°C, the reaction pressure was 0.3 MPa, the residence time was 40 min, and the ultraviolet light intensity was 800 μW / cm 2 , then toluene was added for extraction, and after separation, the toluene extract phase was collected and distilled under reduced pressure to obtain 2-ethylanthraquinone. The yield was calculated to be 93.50%.

[0038] Example 4 A preload solution was prepared by mixing 3-aminopropyltriethoxysilane and 45wt% ethanol aqueous solution in a mass ratio of 1:12. The reaction tubes in the tubular reactor were sequentially immersed in 5.5wt% dilute nitric acid for 30 minutes, then immersed in the preload solution for 30 minutes and dried for later use. 400g of phosphotungstic acid was dissolved in 4500mL of methanol and mixed thoroughly. 243.5g of polyvinylpyrrolidone was added and ultrasonically dispersed at 185W and 28°C to obtain a phosphotungstic acid colloid. The phosphotungstic acid colloid, 373g of zinc nitrate hexahydrate, and 180g of 4,4'-(anthracene-9,10-diyl)dibenzoic acid were added to 2600mL of N,N-dimethylformamide and mixed thoroughly to obtain a precursor solution for later use.

[0039] A 15wt% alumina sol was coated on the inner surface of the reaction tube, dried and calcined at 550°C for 3.5 hours, then cooled to room temperature, and a precursor solution was coated on the inner surface of the reaction tube to form a uniform liquid film on the inner wall of the tube. The solution was dried and coated again, and the cycle was repeated 5 times. The tube was then reacted at 90°C for 8.5 hours for MOF coating to obtain a MOF / phosphotungstic acid composite catalyst and a catalyst-loaded reaction tube, wherein the MOF / phosphotungstic acid composite catalyst grew on the inner surface of the reaction tube.

[0040] 5.2 mol of chlorobenzene, 2.3 mol of anhydrous aluminum chloride and 1 mol of phthalic anhydride are placed in a reactor, and stirring is started. Then, 1.01 mol of ethylbenzene is added, and the temperature is controlled at 5°C, the pressure is -0.06 MPa, and the reaction time is 3 hours. After the reaction, a reaction liquid is obtained. The reaction liquid is slowly added to 5.5 kg of a 4 wt% hydrochloric acid aqueous solution, and the acidolysis temperature is controlled at 62°C and the acidolysis time is 35 minutes. After the acidolysis is completed, the mixture is allowed to stand and separate to obtain an aqueous phase and an organic phase. The aqueous phase can be re-concentrated to recover aluminum trichloride for recycling, and the organic phase is washed with water and subjected to reduced pressure distillation to remove the chlorobenzene solvent to obtain 2-(4-ethylbenzoyl)benzoic acid.

[0041] The MOF / phosphotungstic acid composite catalyst-loaded reaction tube was placed in a tubular reactor, and ultraviolet light was set. 2-(4-ethylbenzoyl)benzoic acid was preheated to 185°C and pumped into the tubular reactor via a horizontal flow pump. The mass ratio of 2-(4-ethylbenzoyl)benzoic acid to MOF / phosphotungstic acid composite catalyst was 1:0.8. The reaction temperature was controlled at 185°C, the reaction pressure was 0.5 MPa, the residence time was 35 min, and the ultraviolet light intensity was 1000 μW / cm 2 , then toluene was added for extraction, and after separation, the toluene extract phase was collected and distilled under reduced pressure to obtain 2-ethylanthraquinone. The yield was calculated to be 92.86%.

[0042] Example 5 A preload solution was prepared by mixing 3-aminopropyltriethoxysilane and 45wt% ethanol aqueous solution in a mass ratio of 1:9. The reaction tubes in the tubular reactor were then acid-washed in 9.0wt% dilute nitric acid for 18 minutes, then immersed in the preload solution for 38 minutes and dried for later use. 400g of phosphotungstic acid was dissolved in 4500mL of methanol and mixed thoroughly. 273g of polyvinylpyrrolidone was added and ultrasonically dispersed at 220W and 22°C to obtain a phosphotungstic acid colloid. The phosphotungstic acid colloid, 408g of zinc nitrate hexahydrate, and 240g of 4,4'-(anthracene-9,10-diyl)dibenzoic acid were added to 2900mL of N,N-dimethylformamide and mixed thoroughly to obtain a precursor solution for later use.

[0043] A 15wt% alumina sol was coated on the inner surface of the reaction tube, dried and calcined at 450°C for 5 hours, and then cooled to room temperature. The precursor solution was coated on the inner surface of the reaction tube to form a uniform liquid film on the inner wall of the tube. The solution was dried and coated again, and the cycle was repeated 5 times. The tube was then reacted at 98°C for 8 hours for MOF coating to obtain a MOF / phosphotungstic acid composite catalyst and a catalyst-loaded reaction tube, wherein the MOF / phosphotungstic acid composite catalyst grew on the inner surface of the reaction tube.

[0044] 5.8 mol of chlorobenzene, 2.5 mol of anhydrous aluminum chloride and 1 mol of phthalic anhydride are placed in a reactor, and stirring is started. Then, 1.08 mol of ethylbenzene is added, and the temperature is controlled at 25°C, the pressure is -0.08 MPa, and the reaction time is 1.5 hours. After the reaction, a reaction liquid is obtained. The reaction liquid is slowly added to 5.5 kg of a 4 wt% hydrochloric acid aqueous solution, and the acidolysis temperature is controlled at 70°C and the acidolysis time is 43 minutes. After the acidolysis is completed, the mixture is allowed to stand and separate to obtain an aqueous phase and an organic phase. The aqueous phase can be re-concentrated to recover aluminum trichloride for recycling, and the organic phase is washed with water and subjected to reduced pressure distillation to remove the chlorobenzene solvent to obtain 2-(4-ethylbenzoyl)benzoic acid.

[0045] The MOF / phosphotungstic acid composite catalyst-loaded reaction tube was placed in a tubular reactor, and ultraviolet light was set. 2-(4-ethylbenzoyl)benzoic acid was preheated to 210°C and pumped into the tubular reactor via a horizontal flow pump. The mass ratio of 2-(4-ethylbenzoyl)benzoic acid to MOF / phosphotungstic acid composite catalyst was 1:1.25. The reaction temperature was controlled at 210°C, the reaction pressure was 0.35 MPa, the residence time was 40 min, and the ultraviolet light intensity was 700 μW / cm 2 , then toluene was added for extraction, and after layering, the toluene extract phase was collected and distilled under reduced pressure to obtain 2-ethylanthraquinone. The yield was calculated to be 91.63%.

[0046] Comparative Example 1 The photosensitivity ligand was replaced by terephthalic acid, and the remaining steps and raw materials were the same as those in Example 1 to obtain 2-ethylanthraquinone. The yield was calculated to be 77.84%.

[0047] Comparative Example 2 Without adding the photosensitivity ligand, the remaining operation steps and the raw materials used were the same as those in Example 1 to obtain 2-ethylanthraquinone. The yield was calculated to be 74.25%.

[0048] Comparative Example 3 The MOF / phosphotungstic acid composite catalyst was replaced with phosphotungstic acid, and the remaining steps and raw materials were the same as those in Example 1 to obtain 2-ethylanthraquinone. The yield was calculated to be 73.69%.

[0049] Comparative Example 4 Without synthesizing phosphotungstic acid colloid, MOF was synthesized using zinc nitrate hexahydrate and 4,4'-(anthracene-9,10-diyl)dibenzoic acid as raw materials, and then mixed with phosphotungstic acid, i.e., no coating was performed. The remaining operation steps and raw materials used were the same as those in Example 1 to obtain 2-ethylanthraquinone. The calculated yield was 62.57%.

[0050] Comparative Example 5 The MOF / phosphotungstic acid composite catalyst was replaced with concentrated sulfuric acid (polytetrafluoroethylene engineering plastic was used for the tubular reactor). The remaining steps and raw materials were the same as those in Example 1 to obtain 2-ethylanthraquinone. The calculated yield was 71.48%.

Claims

1. A method for continuously preparing 2-ethylanthraquinone, characterized in that: The following steps are involved: S1, loading a MOF / phosphotungstic acid composite catalyst on the inner wall of a reaction tube of a continuous reactor for later use; S2, using phthalic anhydride and ethylbenzene as raw materials, through Friedel-Crafts acylation, acidolysis and purification to prepare 2-(4-ethylbenzoyl)benzoic acid; In S3, in a continuous reactor, 2-(4-ethylbenzoyl)benzoic acid undergoes dehydration and cyclization under the action of a MOF / phosphotungstic acid composite catalyst to produce 2-ethylanthraquinone.

2. The method for continuously preparing 2-ethylanthraquinone according to claim 1, characterized in that: In step S1, the loading process is as follows: (1) The reaction tube of the continuous reactor is sequentially treated with nitric acid aqueous solution and pre-loaded with a pre-load solution and then used for standby; (2) Dissolve phosphotungstic acid in organic solvent A, add a surface stabilizer, and disperse by ultrasonication to obtain phosphotungstic acid colloid; add phosphotungstic acid colloid, zinc nitrate hexahydrate, and a photosensitizing ligand into organic solvent B and mix well to obtain a precursor solution for use; (3) coating the inner wall of the reaction tube of the continuous reactor with alumina sol, followed by drying and calcining; (4) After calcination, the precursor solution is coated on the inner wall of the reaction tube of the continuous reactor, and the loading process is completed after drying and coating reaction.

3. The method for continuously preparing 2-ethylanthraquinone according to claim 2, characterized in that: In step (1), the continuous reactor adopts a tubular reactor, the preload solution is prepared by 3-aminopropyltriethoxysilane and ethanol aqueous solution in a mass ratio of 1: (8~12), the concentration of ethanol aqueous solution is 40~50wt%; the concentration of nitric acid aqueous solution is 4.5~9.5wt%, the pickling time is 18~35min, and the preload treatment time is 30~45min.

4. The method for continuously preparing 2-ethylanthraquinone according to claim 2, characterized in that: In step (2), the organic solvent A is methanol, and the surface stabilizer is polyvinyl pyrrolidone; the ratio of phosphotungstic acid, the surface stabilizer, and the organic solvent A is 400:(230-280):(4000-5000), wherein the phosphotungstic acid and the surface stabilizer are measured in g, and the organic solvent A is measured in mL; the ultrasonic dispersion power is 180-230 W, and the ultrasonic dispersion temperature is 20-30° C.

5. The method for continuously preparing 2-ethylanthraquinone according to claim 2, characterized in that: In step (2), the photosensitivity ligand is 4,4'-(anthracene-9,10-diyl)dibenzoic acid, and the organic solvent B is N,N-dimethylformamide; the ratio of phosphotungstic acid, zinc nitrate hexahydrate, photosensitivity ligand and organic solvent B is 400:(360~420):(180~250):(2500~3000), wherein phosphotungstic acid, zinc nitrate hexahydrate and photosensitivity ligand are measured in g, and organic solvent B is measured in mL.

6. The method for continuously preparing 2-ethylanthraquinone according to claim 2, characterized in that: In step (3), the calcination temperature is 450-550° C., and the calcination time is 3.5-5 h.

7. The method for continuously preparing 2-ethylanthraquinone according to claim 2, characterized in that: In step (4), the coating reaction temperature is 85-105°C, and the coating reaction time is 6-8.5h.

8. The method for continuously preparing 2-ethylanthraquinone according to claim 1, characterized in that: In step S2, the solvent for Friedel-Crafts acylation is chlorobenzene, the catalyst is anhydrous aluminum chloride, and the molar ratio of phthalic anhydride, ethylbenzene, anhydrous aluminum chloride and chlorobenzene is 1:(1-1.09):(2.2-2.6):(5-6).

9. The method for continuously preparing 2-ethylanthraquinone according to claim 1, characterized in that: In step S2, the Friedel-Crafts acylation temperature is 0-30° C., the pressure is -0.1-0 MPa, and the time is 1-3 h; a 4 wt % hydrochloric acid aqueous solution is used for acid hydrolysis, the acid hydrolysis temperature is 55-70° C., and the acid hydrolysis time is 35-45 min.

10. The method for continuously preparing 2-ethylanthraquinone according to claim 1, characterized in that: In step S3, when the MOF / phosphotungstic acid composite catalyst acts, the ultraviolet light intensity is 500~1000μW / cm 2 .

11. The method for continuously preparing 2-ethylanthraquinone according to claim 1, characterized in that: In step S3, the reaction temperature of the dehydration ring is 180-210° C., the reaction pressure is 0.3-0.5 MPa, and the residence time is 35-50 min.