Process for the continuous production of 2-ethylanthraquinone

Abstract

The application belongs to the technical field of organic compound preparation, and particularly relates to a method for continuously preparing 2-ethylanthraquinone. The preparation method 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 standby; S2, using phthalic anhydride and ethylbenzene as raw materials, performing a Friedel-Crafts acylation, acidolysis and purification to prepare 2-(4-ethylbenzoyl)benzoic acid; and S3, in the continuous reactor, 2-(4-ethylbenzoyl)benzoic acid is subjected to dehydration and ring closure under the action of the MOF / phosphotungstic acid composite catalyst to prepare 2-ethylanthraquinone. The application combines a photosensitive ligand, a MOF and phosphotungstic acid to improve the catalytic reaction efficiency and selectivity of 2-ethylanthraquinone. Through optimization of the preparation process of 2-ethylanthraquinone, the operation is simplified, waste acid generation is reduced, and green cleaning, high yield, good production safety and continuous production are realized in the synthesis process of 2-ethylanthraquinone.

Description

TECHNICAL FIELD

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

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

[0003] The most common synthesis method of 2-ethylanthraquinone is to use 2-(4'-ethylbenzoyl) benzoic acid as a raw material, and to prepare 2-ethylanthraquinone by dehydration and ring closure under the catalysis of strong acid (concentrated sulfuric acid or oleum). For example, Chinese patent CN1177954A discloses a method for synthesizing 2-ethylanthraquinone. The method is that ethylbenzene and phthalic anhydride are reacted in a mixed solution of HF and BF3 to obtain a 2-(4'-ethylbenzoyl) benzoic acid complex. After removing the volatile HF and BF3 in the complex, solid 2-(4'-ethylbenzoyl) benzoic acid is obtained. The solid 2-(4'-ethylbenzoyl) benzoic acid is introduced into concentrated sulfuric acid or oleum for cyclization to obtain a reaction mixture. The reaction mixture is subjected to the steps of dilution with water, purification with an alkaline aqueous solution, precipitation and melting sublimation to obtain 2-ethylanthraquinone with appropriate purity. In the patent, hydrofluoric acid, boron trifluoride, concentrated sulfuric acid and oleum are used, which are reagents with strong volatility and strong corrosion. In industrial production, this will cause problems such as high post-treatment cost, equipment corrosion and complex operation.

[0004] At present, two-step method is mostly used in the industrial synthesis of 2-ethylanthraquinone, that is, 2-(4-ethylbenzoyl) benzoic acid is first prepared, and then 2-ethylanthraquinone is obtained through the processes of drying, granulation, dehydration and cyclization with concentrated sulfuric acid or oleum, hydrolysis, extraction, desolventization and the like. This process has the characteristics of complex and tedious treatment process, high labor intensity, low product yield, generation of a large amount of acidic wastewater and environmental unfriendliness.

[0005] In recent years, in order to reduce the use of concentrated sulfuric acid or oleum, researchers have carried out a lot of research on new catalysts such as solid acid catalysts, but the results are not satisfactory. Although good progress has been made in the small test stage of solid acid catalysts, the problems of catalyst stability, repeatability and cost make it still have a long way to go to industrialization.

[0006] Other, for example, with modified Hbeta molecular sieve as catalyst, catalytic ethylbenzene and phthalic anhydride direct Friedel-Crafts acylation and dehydration ring closing reaction, one-step synthesis of 2-ethyl anthraquinone. For example, Chinese patent CN104803837A discloses a method for preparing 2-ethyl anthraquinone, the method is to add phthalic anhydride and ethylbenzene into the kettle reactor, stir the mixture evenly to obtain the reactant, then add the catalyst, namely the Hbeta molecular sieve modified by alkali desilication, into the kettle reactor, and the reaction obtains a solid-liquid mixture. After cooling, the solid catalyst is separated to obtain 2-ethyl anthraquinone. The main problem of this patent is that the yield of 2-ethyl anthraquinone is unstable and low, and the production cost is high. SUMMARY

[0007] The purpose of the present application is to provide a method for continuously preparing 2-ethyl anthraquinone, so as to realize green cleaning, high yield, good production safety and continuous production in the synthesis process of 2-ethyl anthraquinone.

[0008] To achieve the above purpose, the technical scheme adopted by the present application is:

[0009] The method for continuously preparing 2-ethyl anthraquinone according to the present application comprises the following steps:

[0010] S1, loading MOF / phosphotungstic acid composite catalyst on the inner wall of the reaction tube of the continuous reactor for standby;

[0011] S2, using phthalic anhydride and ethylbenzene as raw materials, preparing 2-(4-ethylbenzoyl)benzoic acid through Friedel-Crafts acylation, acidolysis and purification;

[0012] S3, in the continuous reactor, 2-(4-ethylbenzoyl)benzoic acid is dehydrated and ring-closed under the action of the MOF / phosphotungstic acid composite catalyst to prepare 2-ethyl anthraquinone.

[0013] Among them:

[0014] In the step S1, the loading process is as follows:

[0015] (1) the reaction tube of the continuous reactor is sequentially subjected to acid washing with aqueous nitric acid and preloading with a preloading solution, and then is standby;

[0016] (2) phosphotungstic acid is dissolved in an organic solvent A, a surface stabilizer is added, and ultrasonic dispersion is carried out to prepare a phosphotungstic acid colloid; the phosphotungstic acid colloid, zinc nitrate hexahydrate and a photosensitive ligand are added into an organic solvent B and uniformly mixed to obtain a precursor solution for standby;

[0017] (3) alumina sol is coated on the inner wall of the reaction tube of the continuous reactor, and then is dried and calcined;

[0018] (4) After calcination is completed, a precursor solution is coated on the inner wall of the reaction tube of the continuous reactor, dried, and subjected to a coating reaction to complete the loading process.

[0019] In step (1), the continuous reactor is a tubular reactor, the pre-loading solution is prepared by mixing 3-aminopropyltriethoxysilane and an ethanol aqueous solution at a mass ratio of 1:(8-12), the concentration of the ethanol aqueous solution is 40-50 wt%, the concentration of the nitric acid aqueous solution is 4.5-9.5 wt%, the pickling time is 18-35 min, and the pre-loading treatment time is 30-45 min.

[0020] In step (2), the organic solvent A is methanol, the surface stabilizer is polyvinylpyrrolidone, 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 grams, and the organic solvent A is measured in milliliters, the ultrasonic dispersion power is 180-230 W, and the ultrasonic dispersion temperature is 20-30℃.

[0021] In step (2), the photosensitive 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, the photosensitive ligand, and the organic solvent B is 400:(360-420):(180-250):(2500-3000), wherein the phosphotungstic acid, the zinc nitrate hexahydrate, and the photosensitive ligand are measured in grams, and the organic solvent B is measured in milliliters.

[0022] In step (3), the calcination temperature is 450-550℃, and the calcination time is 3.5-5 h.

[0023] In step (4), the coating reaction temperature is 85-105℃, and the coating reaction time is 6-8.5 h.

[0024] In step S2, the solvent for the 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).

[0025] In step S2, the Friedel-Crafts acylation temperature is 0-30℃, the pressure is -0.1-0 MPa, and the time is 1-3 h; the acidolysis is performed using 4 wt% hydrochloric acid aqueous solution, the acidolysis temperature is 55-70℃, the acidolysis time is 35-45 min; and the purification step includes toluene extraction and reduced pressure distillation. Preferably, the reaction temperature is 10-30℃, the reaction pressure is -0.09-0 MPa, and the reaction time is 1-2.5 h.

[0026] The UV light intensity in the step S3 is 500-1000 μW / cm 2 .

[0027] The reaction temperature in the step S3 is 180-210℃, the reaction pressure is 0.3-0.5 MPa, and the residence time is 35-50 min.

[0028] The present application has the following advantages:

[0029] (1) The photosensitive ligand (i.e. 4,4'-(anthracene-9,10-diyl) dibenzoic acid) provides a π conjugated anthracene ring structure, which jumps under UV light to generate free electrons (e - ) and holes (h + ). Without phosphotungstic acid, the free electrons and holes will quickly recombine, and the substrate cannot be effectively activated; the W 5+ / W 6+ redox pair of phosphotungstic acid can capture the conduction band electrons, and the free electrons have a tendency to be transferred to phosphotungstic acid through the MOF conjugated structure, thereby avoiding the ineffective recombination of free electrons and holes.

[0030] The remaining holes in the photosensitive ligand can be activated through electron transfer, thereby activating 2-(4-ethylbenzoyl) benzoic acid, and the carbonyl oxygen of 2-(4-ethylbenzoyl) benzoic acid combines with the hole to enhance the electrophilicity of the carbonyl carbon, significantly improve the electrophilic activity, and more easily undergo dehydration and cyclization. Therefore, through the synergistic effect of electron transfer, phosphotungstic acid avoids the ineffective recombination of free electrons and holes, and effectively activates the intermediate 2-(4-ethylbenzoyl) benzoic acid.

[0031] (2) On the other hand, when not receiving electrons, the anion structure of HPW is [PW 12 O 40 ] 3- , and the proton (H + ) is tightly combined with the oxygen atom. When HPW receives a free electron to form W 5+ , the electron-donating ability of W 5+ is stronger than that of W 6+ , the electron cloud density of the W-O bond is increased, the negative charge of the O atom combined with the proton is increased, and the proton is more easily dissociated, thereby promoting the protonation of the carboxyl group of the intermediate 2-(4-ethylbenzoyl) benzoic acid and accelerating the dehydration to generate an acyl cation.

[0032] (3) The MOF framework coats phosphotungstic acid, and the photosensitive ligand in the MOF keeps close to the phosphotungstic acid through the channel confinement effect. When the photosensitive ligand activates the intermediate 2-(4-ethylbenzoyl)benzoic acid, the intermediate can quickly diffuse to the vicinity of the acid site of the phosphotungstic acid through the MOF channel. At the same time, the π-π stacking effect between the anthracene ring of the photosensitive ligand and the benzene ring of the intermediate can anchor the intermediate on the phosphotungstic acid, improve the utilization rate of the acid site, and avoid the decline of the catalytic efficiency caused by the disordered diffusion of the intermediate.

[0033] The continuous electron transfer network formed by the Zn-O bond in the MOF and the conjugated π bond of the anthracene ring enables the free electrons of the photosensitive ligand to be efficiently transferred to the phosphotungstic acid; and the anthracene ring of the photosensitive ligand can be combined with the benzene ring of 2-(4-ethylbenzoyl)benzoic acid through π-π stacking, ensuring the occurrence of dehydration and cyclization.

[0034] (4) In the preparation process of the application, the reaction in the synthesis stage of 2-(4-ethylbenzoyl)benzoic acid is carried out under negative pressure conditions, high conversion rate is realized at low temperature, reaction time is shortened, and energy consumption is reduced. In the continuous reaction operation process, 2-(4-ethylbenzoyl)benzoic acid does not need to be dried, granulated, and dissolved in sulfuric acid, etc. It only needs to be kept in liquid state by increasing the temperature compensation, which further simplifies the process steps. 2-(4-ethylbenzoyl)benzoic acid is catalyzed by the MOF / phosphotungstic acid composite catalyst to generate 2-ethylanthraquinone through dehydration and ring closure, avoiding the use of fuming sulfuric acid and reducing the generation of waste acid and environmental pollution. The reaction is carried out in a tubular reactor, and the reactor temperature, pressure, reaction time, waste acid concentration and solvent extraction method are used to separate and purify the product, reducing the occurrence of side reactions. In the whole continuous reaction process, most of the organic phase can be recycled, which can significantly reduce the pollution discharge amount, and the yield of 2-ethylanthraquinone is maintained above 91%. DETAILED DESCRIPTION

[0035] The application will be specifically described and explained below in conjunction with examples.

[0036] Example 1

[0037] A pre-loaded solution was prepared by mixing 3-aminopropyltriethoxysilane with 40wt% ethanol aqueous solution at a mass ratio of 1:8; the reaction tube in the tubular reactor was immersed in 7wt% dilute nitric acid for acid washing for 25min, then immersed in the pre-loaded solution for pre-loading for 35min and dried for standby. 400g of phosphotungstic acid was dissolved in 4800mL of methanol and mixed uniformly, and 250g of polyvinylpyrrolidone was added and ultrasonically dispersed at 205W and 25℃ 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 uniformly to obtain a precursor solution for standby.

[0038] A 15wt% alumina sol was coated on the inner surface of the reaction tube, dried and calcined at 500°C for 4h, then cooled to room temperature, the precursor solution was coated on the inner surface of the reaction tube, the solution formed a uniform liquid film on the inner wall of the tube, dried, recoated, and cycled 5 times, then reacted at 95°C for 6h to perform MOF coating to obtain a MOF / phosphotungstic acid composite catalyst and a catalyst-loaded reaction tube, wherein the MOF / phosphotungstic acid composite catalyst was grown on the inner surface of the reaction tube.

[0039] 5.5 mol of chlorobenzene, 2.4 mol of anhydrous aluminum chloride, and 1 mol of phthalic anhydride were placed in a reaction kettle, stirring was started, then 1.05 mol of ethylbenzene was added, the temperature was controlled at 15°C, the pressure was -0.05 MPa, and the reaction time was 2h; after the reaction was completed, a reaction liquid was obtained; the reaction liquid was slowly added to 5.5 kg of a 4wt% hydrochloric acid aqueous solution, the acidolysis temperature was controlled at 60°C, and the acidolysis time was 40 min; after the acidolysis was completed, the liquid was allowed to stand and separate into an aqueous phase and an organic phase; the aqueous phase could be concentrated and recycled to recover aluminum chloride, and the organic phase was washed with water and subjected to reduced pressure distillation to remove the chlorobenzene solvent, thereby obtaining 2-(4-ethylbenzoyl)benzoic acid.

[0040] The MOF / phosphotungstic acid composite catalyst-loaded reaction tube was loaded into a tubular reactor, ultraviolet light was set, 2-(4-ethylbenzoyl)benzoic acid was preheated to 195°C and pumped into the tubular reactor by a laminar 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 500μW / cm 2 , then toluene was added for extraction, after the layers were separated, the toluene extraction phase was collected and subjected to reduced pressure distillation, thereby obtaining 2-ethylanthraquinone, and the yield was calculated to be 91.21%.

[0041] Example 2

[0042] A pre-loading solution was prepared by mixing 3-aminopropyltriethoxysilane with a 50wt% ethanol aqueous solution at a mass ratio of 1:9; the reaction tube in the tubular reactor was sequentially immersed in 4.5wt% dilute nitric acid for acid washing for 35 min, then immersed in the pre-loading solution for pre-loading for 40 min and dried for standby use. 400g of phosphotungstic acid was dissolved in 5000mL of methanol and mixed uniformly, 280g of polyvinylpyrrolidone was added, and ultrasonic dispersion was performed 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 uniformly to obtain a precursor solution for standby use.

[0043] A 15wt% alumina sol was coated on the inner surface of the reaction tube, dried and calcined at 520°C for 4h, then cooled to room temperature, the precursor solution was coated on the inner surface of the reaction tube, the solution formed a uniform liquid film on the inner wall of the tube, dried, recoated, and cycled 5 times, then reacted at 85°C for 8.5h to perform MOF coating to obtain a MOF / phosphotungstic acid composite catalyst and a catalyst-loaded reaction tube, wherein the MOF / phosphotungstic acid composite catalyst was grown on the inner surface of the reaction tube.

[0044] 6 mol of chlorobenzene, 2.6 mol of anhydrous aluminum chloride and 1 mol of phthalic anhydride were placed in a reaction kettle, stirring was started, then 1.09 mol of ethylbenzene was added, the temperature was controlled at 0°C, the pressure was -0.1 MPa, and the reaction time was 2.5h; after the reaction was completed, a reaction liquid was obtained; the reaction liquid was slowly added to 5.5 kg of 4wt% hydrochloric acid aqueous solution, the acidolysis temperature was controlled at 55°C, and the acidolysis time was 45 min; after the acidolysis was completed, it was allowed to stand and separate into water and organic phases; the water phase could be concentrated and recycled to recover aluminum chloride, and the organic phase was washed with water and distilled under reduced pressure to remove chlorobenzene solvent to obtain 2-(4-ethylbenzoyl)benzoic acid.

[0045] The MOF / phosphotungstic acid composite catalyst-loaded reaction tube was loaded into a tubular reactor, UV light was set, 2-(4-ethylbenzoyl)benzoic acid was preheated to 200°C and pumped into the tubular reactor by a laminar 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 UV light intensity was 600μW / cm 2 , then toluene was added for extraction, after separation, the toluene extraction phase was collected and distilled under reduced pressure to obtain 2-ethylanthraquinone, and the yield was calculated to be 93.72%.

[0046] Example 3

[0047] 3-aminopropyltriethoxysilane was mixed with 42wt% ethanol aqueous solution at a mass ratio of 1:10 to prepare a pre-loading solution for standby; the reaction tube in the tubular reactor was sequentially immersed in 9.5wt% dilute nitric acid for acid washing for 20 min, then immersed in the pre-loading solution for pre-loading for 45 min and dried for standby. 400g of phosphotungstic acid was dissolved in 4000mL of methanol and mixed uniformly, 230g of polyvinylpyrrolidone was added, and ultrasonic dispersion was performed 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 uniformly to obtain a precursor solution for standby.

[0048] A 15wt% alumina sol was coated on the inner surface of the reaction tube, dried and calcined at 480°C for 4.5h, then cooled to room temperature, and 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, dried, recoated, and cycled 5 times, then reacted at 105°C for 7h to perform MOF coating to obtain a MOF / phosphotungstic acid composite catalyst and a catalyst-loaded reaction tube, wherein the MOF / phosphotungstic acid composite catalyst was grown on the inner surface of the reaction tube.

[0049] 5 mol of chlorobenzene, 2.2 mol of anhydrous aluminum chloride, and 1 mol of phthalic anhydride were placed in a reaction kettle, stirring was started, then 1 mol of ethylbenzene was added, the temperature was controlled at 30°C, the pressure was 0 MPa, and the reaction time was 1 h; after the reaction was completed, a reaction liquid was obtained; the reaction liquid was slowly added to 5.5 kg of a 4wt% hydrochloric acid aqueous solution, the acidolysis temperature was controlled at 65°C, and the acidolysis time was 38 min; after the acidolysis was completed, the mixture was allowed to stand and separate into an aqueous phase and an organic phase; the aqueous phase could be concentrated and recycled to recover aluminum chloride, and the organic phase was washed with water and subjected to reduced-pressure distillation to remove the chlorobenzene solvent, thereby obtaining 2-(4-ethylbenzoyl)benzoic acid.

[0050] The MOF / phosphotungstic acid composite catalyst-loaded reaction tube was loaded into a tubular reactor, UV light was set, 2-(4-ethylbenzoyl)benzoic acid was preheated to 180°C and pumped into the tubular reactor by a laminar 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 UV light intensity was 800μW / cm 2 , then toluene was added for extraction, after the layers were separated, the toluene extraction phase was collected and subjected to reduced-pressure distillation, thereby obtaining 2-ethylanthraquinone, and the yield was calculated to be 93.50%.

[0051] Example 4

[0052] A pre-loading solution was prepared by mixing 3-aminopropyltriethoxysilane with a 45wt% ethanol aqueous solution at a mass ratio of 1:12; the reaction tube in the tubular reactor was sequentially immersed in 5.5wt% dilute nitric acid for acid washing for 30 min, then immersed in the pre-loading solution for pre-loading for 30 min and dried for standby use. 400g of phosphotungstic acid was dissolved in 4500mL of methanol and mixed uniformly, 243.5g of polyvinylpyrrolidone was added, and ultrasonic dispersion was performed 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 uniformly to obtain a precursor solution for standby use.

[0053] A 15wt% alumina sol was coated on the inner surface of the reaction tube, dried and calcined at 550°C for 3.5h, then cooled to room temperature, the precursor solution was coated on the inner surface of the reaction tube, the solution formed a uniform liquid film on the inner wall of the tube, dried, recoated, and cycled 5 times, then reacted at 90°C for 8.5h to perform MOF coating to obtain a MOF / phosphotungstic acid composite catalyst and a catalyst-loaded reaction tube, wherein the MOF / phosphotungstic acid composite catalyst was grown on the inner surface of the reaction tube.

[0054] 5.2 mol of chlorobenzene, 2.3 mol of anhydrous aluminum chloride, and 1 mol of phthalic anhydride were placed in a reaction kettle, stirring was started, then 1.01 mol of ethylbenzene was added, the temperature was controlled at 5°C, the pressure was -0.06 MPa, and the reaction time was 3h; after the reaction was completed, a reaction liquid was obtained; the reaction liquid was slowly added to 5.5 kg of a 4wt% hydrochloric acid aqueous solution, the acidolysis temperature was controlled at 62°C, and the acidolysis time was 35 min; after the acidolysis was completed, the mixture was allowed to stand and separate into an aqueous phase and an organic phase; the aqueous phase could be concentrated and recycled to recover aluminum chloride, and the organic phase was washed with water and subjected to reduced-pressure distillation to remove the chlorobenzene solvent, thereby obtaining 2-(4-ethylbenzoyl)benzoic acid.

[0055] The MOF / phosphotungstic acid composite catalyst-loaded reaction tube was loaded into a tubular reactor, ultraviolet light was set, 2-(4-ethylbenzoyl)benzoic acid was preheated to 185°C and pumped into the tubular reactor by a laminar 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, after the layers were separated, the toluene extraction phase was collected and subjected to reduced-pressure distillation, thereby obtaining 2-ethylanthraquinone, and the yield was calculated to be 92.86%.

[0056] Example 5

[0057] A 45wt% ethanol aqueous solution was prepared by mixing 3-aminopropyltriethoxysilane and 45wt% ethanol aqueous solution at a mass ratio of 1:9; the reaction tube in the tubular reactor was sequentially immersed in 9.0wt% dilute nitric acid for acid washing for 18 min, then immersed in the preloading solution for preloading for 38 min and dried for standby use. 400 g of phosphotungstic acid was dissolved in 4500 mL of methanol and mixed uniformly, 273 g of polyvinylpyrrolidone was added, and ultrasonic dispersion was performed at 220 W and 22°C to obtain a phosphotungstic acid colloid; the phosphotungstic acid colloid, 408 g of zinc nitrate hexahydrate, and 240 g of 4,4'-(anthracene-9,10-diyl)dibenzoic acid were added to 2900 mL of N,N-dimethylformamide and mixed uniformly to obtain a precursor solution for standby use.

[0058] A 15wt% alumina sol was coated on the inner surface of the reaction tube, dried and calcined at 450°C for 5h, then cooled to room temperature, the precursor solution was coated on the inner surface of the reaction tube, the solution formed a uniform liquid film on the inner wall of the tube, dried, recoated, and cycled 5 times, then reacted at 98°C for 8h to perform MOF coating to obtain a MOF / phosphotungstic acid composite catalyst and a catalyst-loaded reaction tube, wherein the MOF / phosphotungstic acid composite catalyst was grown on the inner surface of the reaction tube.

[0059] 5.8 mol of chlorobenzene, 2.5 mol of anhydrous aluminum chloride and 1 mol of phthalic anhydride were placed in a reaction kettle, stirring was started, then 1.08 mol of ethylbenzene was added, the temperature was controlled at 25°C, the pressure was -0.08 MPa, and the reaction time was 1.5h; after the reaction was completed, a reaction liquid was obtained; the reaction liquid was slowly added to 5.5 kg of a 4wt% hydrochloric acid aqueous solution, the acidolysis temperature was controlled at 70°C, and the acidolysis time was 43 min; after the acidolysis was completed, the liquid was allowed to stand and separate into an aqueous phase and an organic phase; the aqueous phase could be concentrated and recycled to recover aluminum chloride, and the organic phase was washed with water and subjected to reduced pressure distillation to remove the chlorobenzene solvent to obtain 2-(4-ethylbenzoyl)benzoic acid.

[0060] The MOF / phosphotungstic acid composite catalyst-loaded reaction tube was loaded into a tubular reactor, UV light was set, 2-(4-ethylbenzoyl)benzoic acid was preheated to 210°C and pumped into the tubular reactor by a laminar 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 UV light intensity was 700μW / cm 2 , then toluene was added for extraction, after the layers were separated, the toluene extraction phase was collected and subjected to reduced pressure distillation to obtain 2-ethylanthraquinone, and the yield was calculated to be 91.63%.

[0061] Comparative Example 1

[0062] The photosensitive ligand was replaced with terephthalic acid, and the remaining operation steps and raw materials used were the same as in Example 1 to obtain 2-ethylanthraquinone, and the yield was calculated to be 77.84%.

[0063] Comparative Example 2

[0064] No photosensitive ligand was added, and the remaining operation steps and raw materials used were the same as in Example 1 to obtain 2-ethylanthraquinone, and the yield was calculated to be 74.25%.

[0065] Comparative Example 3

[0066] The MOF / phosphotungstic acid composite catalyst was replaced with phosphotungstic acid, and the remaining operation steps and raw materials used were the same as in Example 1 to obtain 2-ethylanthraquinone, and the yield was calculated to be 73.69%.

[0067] Comparative Example 4

[0068] Without synthesizing phosphotungstic acid colloid, MOF was synthesized with zinc nitrate hexahydrate and 4,4'-(anthracene-9,10-diyl)dibenzoic acid as raw materials, and then blended with phosphotungstic acid, that is, without coating, and the remaining operation steps and raw materials were the same as in Example 1 to obtain 2-ethylanthraquinone, and the calculated yield was 62.57%.

[0069] Comparative Example 5

[0070] The MOF / phosphotungstic acid composite catalyst was replaced with concentrated sulfuric acid (polytetrafluoroethylene engineering plastic was used for the tubular reactor), and the remaining operation steps and raw materials were the same as in Example 1 to obtain 2-ethylanthraquinone, and the calculated yield was 71.48%.

Claims

1. A process for the continuous production of 2-ethylanthraquinone, characterized in that, Comprise the following steps: S1, load MOF / phosphotungstic acid composite catalyst on the inner wall of the reaction tube of the continuous reactor for standby; S2, with phthalic anhydride and ethylbenzene as raw materials, through Friedel-Crafts acylation, acidolysis and purification, 2-(4-ethylbenzoyl) benzoic acid is prepared; S3, in a continuous reactor, 2-(4-ethylbenzoyl)benzoic acid is dehydrated and cyclized to prepare 2-ethylanthraquinone under the action of a MOF / phosphotungstic acid composite catalyst; when the MOF / phosphotungstic acid composite catalyst acts, the ultraviolet light intensity is 500-1000 μW / cm 2 ; the reaction temperature for dehydrating and cyclizing is 180-210 ℃, the reaction pressure is 0.3-0.5 MPa, and the residence time is 35-50 min; In step S1, the loading process is as follows: (1) the reaction tube of the continuous reactor is sequentially treated by nitric acid aqueous solution pickling and preloading solution preloading, and then is standby; (2) phosphotungstic acid is dissolved in organic solvent A, a surface stabilizer is added, and ultrasonic dispersion is carried out to prepare phosphotungstic acid colloid; the phosphotungstic acid colloid, zinc nitrate hexahydrate and photosensitive ligand are added into organic solvent B and uniformly mixed to obtain a precursor solution for standby; wherein the photosensitive ligand is 4,4'-(anthracene-9,10-diyl)benzoic acid; Wherein the organic solvent A is methanol, and the surface stabilizer is polyvinylpyrrolidone; the ratio of phosphotungstic acid, surface stabilizer and organic solvent A is 400:(230-280):(4000-5000), wherein the phosphotungstic acid and the surface stabilizer are counted in grams, and the organic solvent A is counted in milliliters; the organic solvent B is N,N-dimethylformamide; the ratio of phosphotungstic acid, zinc nitrate hexahydrate, photosensitive ligand and organic solvent B is 400:(360-420):(180-250):(2500-3000), wherein the phosphotungstic acid, zinc nitrate hexahydrate and photosensitive ligand are counted in grams, and the organic solvent B is counted in milliliters; (3) coating alumina sol on the inner wall of the reaction tube of the continuous reactor, and then drying and calcining; (4) after calcination, coating the precursor solution on the inner wall of the reaction tube of the continuous reactor, and then drying and coating reaction to complete the loading process.

2. The process for the continuous production of 2-ethylanthraquinone according to claim 1, characterized in that, In step (1), the continuous reactor adopts a tubular reactor, the preloading solution is prepared by mixing 3-aminopropyltriethoxysilane and ethanol aqueous solution at a mass ratio of 1:(8-12), and 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 preloading treatment time is 30-45min.

3. The process for the continuous production of 2-ethylanthraquinone according to claim 1, characterized in that, In step (2), the ultrasonic dispersion power is 180-230W, and the ultrasonic dispersion temperature is 20-30℃.

4. The process for the continuous production of 2-ethylanthraquinone according to claim 1, characterized in that, In step (3), the calcination temperature is 450-550℃, and the calcination time is 3.5-5h.

5. The process for the continuous production of 2-ethylanthraquinone according to claim 1, characterized in that, In step (4), the coating reaction temperature is 85-105℃, and the coating reaction time is 6-8.5h.

6. The process for the continuous production of 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).

7. The process for the continuous production of 2-ethylanthraquinone according to claim 1, characterized in that, In step S2, the Friedel-Crafts acylation temperature is 0-30℃, the pressure is-0.1-0MPa, and the time is 1-3h; 4wt% hydrochloric acid aqueous solution is used for acidolysis, the acidolysis temperature is 55-70℃, and the acidolysis time is 35-45min.