A recyclable covalent organic framework supported heteropoly acid catalyst, a preparation method thereof and application of the catalyst to catalytic oxidative desulfurization

Abstract

This invention discloses a recyclable covalent organic framework supported heteropolyacid catalyst, its preparation method, and its application in catalytic oxidative desulfurization. The preparation method of the recyclable covalent organic framework supported heteropolyacid catalyst is as follows: phosphomolybdic acid, phosphotungstic acid, or molybdenum vanadate is mixed with 1,3,5-tris(4-aminophenyl)benzene and 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, and 1,4-dioxane, mesitylene, and acetic acid are added. The mixture is ultrasonicated at room temperature for 5-10 min, degassed under vacuum with nitrogen, and then sealed and heated at 100-120°C for 1-3 days. After natural cooling, it is washed with acetone and dried under vacuum to obtain a COFs-supported heteropolyacid salt catalyst. This invention increases the specific surface area of ​​the heteropolyacid, increases the number of active sites involved in catalytic activity, significantly improves the catalytic oxidative desulfurization efficiency, and provides mild desulfurization conditions, easy operation, low energy consumption, high efficiency, economy, and environmental friendliness. It is also easy to recover, recyclable, and has low operating costs.

Description

Technical Field

[0001] This invention relates to a recyclable covalent organic framework supported heteropolyacid catalyst, its preparation method, and its catalytic oxidation desulfurization application, belonging to the cross-technical fields of environmental protection technology and deep processing of oil and chemical products. Background Technology

[0002] In recent years, with the continuous development of the economy and society, sulfur compounds in fuel oil release sulfur oxides (SOx) after combustion, which is a major cause of air pollution. To address this situation, various regions and countries around the world have implemented strict regulations to limit sulfur in fuel oil. Continuously reducing the sulfur content in fuel oil and achieving "zero" sulfur content is an inevitable trend for the future development of the fuel oil industry. The production of ultra-low sulfur fuel oil is an important task for the refining industry and is also of great significance for achieving sustainable development. Currently, fuel hydrodesulfurization (HDS) is considered the most commonly used desulfurization method in industry. However, the hydrogenolysis of sulfides requires high temperatures (300~400℃) and high pressures (4~8 MPa), placing high demands on equipment and limiting the removal of aromatic sulfides. Therefore, many non-hydrodesulfurization methods have been developed and applied to the removal of aromatic sulfides.

[0003] Oxidative desulfurization is a mild reaction system and a promising desulfurization technology. Its principle involves oxidizing sulfur-containing compounds such as thiophene sulfur in fuel oil into corresponding sulfoxides or sulfones. Because the oxidation products have higher polarity, they can be extracted using polar solvents, thus achieving desulfurization. Oxidative desulfurization is further divided into organic oxidant desulfurization systems, inorganic oxidant desulfurization systems, photocatalytic oxidative desulfurization systems, and plasma oxidative desulfurization systems.

[0004] Oxidative desulfurization technology involves various oxidants. Due to the low corrosiveness of hydrogen peroxide and the fact that its byproducts are oxygen and water, which have no adverse environmental impact, hydrogen peroxide is the dominant oxidant in oxidative desulfurization technology. However, because hydrogen peroxide is insoluble in the oil phase, gasoline cannot fully contact the oxidant during the reaction, slowing down the reaction rate and resulting in unsatisfactory desulfurization effects. This also increases the amount of oxidant required. Phase transfer catalysts are used to enhance the reaction of two reactants in two immiscible solvents (liquid-liquid two-phase systems or solid-liquid two-phase systems), allowing the reaction to proceed in two mutually soluble systems. During the reaction, the actual reactants transfer from one phase to the other under the action of the catalyst, allowing the reactants to combine with the substrate, thus ensuring a smooth and efficient reaction.

[0005] Heteropolyacids, as a novel class of catalytic materials, have relatively small surface areas and are prone to aggregation during reactions, thus hindering their catalytic activity. Supported heteropolyacid catalysts, however, can overcome these drawbacks and have attracted widespread attention from researchers in the field of catalysis. Different supported catalysts are suitable for different reaction types. For heteropolyacid supported catalysts used for deep desulfurization, there are problems such as the catalyst being easily soluble in ionic liquid phases, making recovery difficult or even toxic, and high cost. Furthermore, the desulfurization rate needs further improvement. For example, the patent application with application number 201810972636.0 requires a modified molecular sieve as a support, involving multiple steps, which is cumbersome, costly, and requires 3 hours of reaction time to complete. Moreover, the desulfurization rate still falls short of the increasingly demanding requirements of practical applications. Summary of the Invention

[0006] This invention provides a recyclable covalent organic framework supported heteropolyacid catalyst, its preparation method, and its application in catalytic oxidation desulfurization. The catalyst of this invention has mild desulfurization conditions, high efficiency, and simple operation, and can effectively remove sulfides from oil products.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a recyclable covalent organic framework supported heteropolyacid catalyst includes the following steps: mixing phosphomolybdic acid, phosphotungstic acid, or molybdenum vanadate with 1,3,5-tris(4-aminophenyl)benzene and 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, adding 1,4-dioxane, mesitylene, and acetic acid, sonicating at room temperature for 5-10 min, degassing under vacuum with nitrogen, then sealing the resulting mixture, heating at 100-120°C for 1-3 days, naturally cooling, washing with acetone, and drying under vacuum to obtain a COFs supported heteropolyacid catalyst.

[0008] The above method combines a covalent organic framework with phosphomolybdic acid, which increases the specific surface area of ​​the heteropolyacid, thereby increasing the number of active sites involved in catalytic activity, improving desulfurization efficiency, and under mild conditions.

[0009] Vacuum nitrogen degassing, also known as nitrogen protection degassing, allows the reaction to take place in a nitrogen atmosphere.

[0010] To further improve the catalytic effect, the molar ratio of 1,3,5-tris(4-aminophenyl)benzene to 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine is 1:(0.8~1.2). The molar ratio of phosphomolybdic acid, phosphotungstic acid, or molybdic vanadate to 1,3,5-tris(4-aminophenyl)benzene is (8~12):1.

[0011] To improve reaction efficiency, the volume ratio of 1,4-dioxane to mesitylene is 1:(0.05~0.1).

[0012] To further improve catalytic performance, the mass ratio of phosphomolybdic acid, phosphotungstic acid, or molybdenum vanadate to acetic acid is 1:(1000~1600).

[0013] To better ensure catalytic effect, vacuum drying is performed at a temperature of 80~100℃ for 4-6 hours.

[0014] The recyclable covalent organic framework supported heteropolyacid catalyst prepared by the above method can be used for catalytic oxidative desulfurization. Furthermore, the reaction conditions are mild, the efficiency is high, and the catalyst is easily recoverable.

[0015] This application utilizes the principle of combining catalytic oxidation and extraction separation to remove sulfur-containing compounds from oil products. The extraction separation directly refers to existing mature technologies.

[0016] As one specific implementation scheme, the steps of catalytic oxidation desulfurization are as follows: (1) Take the oil to be desulfurized and the ionic liquid and premix them to obtain mixed solution A; (2) Under normal temperature and pressure conditions, a recyclable covalent organic framework supported heteropolyacid catalyst and H2O2 aqueous solution are added to the mixed solution A prepared in step (1) to carry out the reaction, thereby achieving deep desulfurization of the oil product to be tested.

[0017] In order to improve the desulfurization effect, in step (1) above, the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate, and the volume ratio of the ionic liquid to the volume of the oil to be desulfurized is 1: (90~110).

[0018] In order to balance catalytic effect and efficiency, in step (2), the mass of the recyclable covalent organic framework supported heteropolyacid catalyst is 0.2%-1.5% of the mass of the oil to be tested in mixed solution A; the amount of H2O2 is calculated as follows: the number of moles of H2O2 is determined by the number of moles of sulfur (S) in the oil to be desulfurized, and the O / S molar ratio is (2-6):1.

[0019] In step (2) above, the reaction temperature is 30~50℃; the reaction time is 15~40min. The conditions are mild, the efficiency is high, and the desulfurization effect is good.

[0020] To improve material utilization, after desulfurization, the covalent organic framework supported heteropolyacid catalyst in the reactants is recovered through sedimentation, filtration, and drying, with a recovery rate exceeding 99.9%, and then recycled. After 22 cycles, the reduction in catalytic efficiency is less than 1%.

[0021] This application considers 99.999% or more as 100% or as close to 100%.

[0022] Any techniques not mentioned in this invention are based on existing technologies.

[0023] This invention relates to a recyclable covalent organic framework supported heteropolyacid catalyst, which encapsulates phosphomolybdic acid, phosphotungstic acid, or molybdenum vanadate on a covalent organic framework. This increases the specific surface area of ​​the heteropolyacid, expands the active sites involved in catalytic activity, significantly improves the efficiency of catalytic oxidation desulfurization, and provides mild desulfurization conditions, easy operation, low energy consumption, high efficiency, economy, and environmental friendliness. It is also easy to recover, recyclable, and inexpensive to use. Attached Figure Description

[0024] Figure 1 Scanning electron microscope image of the recyclable covalent organic framework supported heteropolyacid catalyst prepared in Example 1; Figure 2 Scanning electron microscope image of the recyclable covalent organic framework supported heteropolyacid catalyst prepared in Example 2; Figure 3 Scanning electron microscope image of the recyclable covalent organic framework supported heteropolyacid catalyst prepared in Example 3; Figure 4 Infrared spectra of the covalent organic framework supported heteropolyacid catalysts prepared in Examples 1, 2, and 3 (HPMo corresponds to Example 1, HPW corresponds to Example 2, and HMoV corresponds to Example 3). Figure 5 This is a graph showing the desulfurization efficiency over time in Example 4. Figure 6 The graph shows the desulfurization rate of the covalent organic framework supported heteropolyacid catalyst prepared in Example 3 as a function of temperature. Figure 7 This is a graph showing the results of recycling the recyclable covalent organic framework supported heteropolyacid catalyst in Example 4; Figure 8 This is a graph showing the desulfurization efficiency versus time for Comparative Example 1. Detailed Implementation

[0025] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0026] Unless otherwise specified, all experiments were conducted at room temperature, which in each case ranged from 15 to 25°C.

[0027] Example 1

[0028] Preparation of phosphomolybdic acid-recyclable covalent organic framework supported heteropolyacid catalysts: 0.2 g of phosphomolybdic acid, 17.6 mg of 1,3,5-tris(4-aminophenyl)benzene, and 19.65 mg of 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine were mixed, and 2 ml of 1,4-dioxane, 0.15 ml of mesitylene, and 6 M (mol) of acetic acid were added. The mixture was then sonicated for 10 min and degassed three times under vacuum and nitrogen. The mixture was then sealed and heated at 100 °C for one day, allowed to cool naturally, washed with acetone, and then dried under vacuum at 100 °C for 4 h to obtain the COFs-supported heteropolyacid salt catalyst. Scanning electron microscopy (SEM) images are shown below. Figure 1 As shown, by Figure 1 It can be seen that the obtained catalyst is a material with loose pores; the Fourier transform infrared spectrum is as follows. Figure 4 As shown, by Figure 4 It can be seen that 1060cm -1 960cm -1 and 786cm -1 The left and right sides show the characteristic peaks of the Keggin structure of heteropolyacids, indicating that a phosphomolybdic acid-recyclable covalent organic framework supported heteropolyacid catalyst has been successfully prepared.

[0029] Example 2

[0030] Preparation of phosphotungstic acid-recyclable covalent organic framework supported heteropolyacid catalysts: 0.2 g of phosphotungstic acid, 17.6 mg of 1,3,5-tris(4-aminophenyl)benzene, and 19.65 mg of 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine were mixed, and 2 ml of 1,4-dioxane, 0.15 ml of mesitylene, and 6 M acetic acid were added. The mixture was then sonicated for 10 min and degassed three times under vacuum and nitrogen. The mixture was then sealed and heated at 100 °C for one day, allowed to cool naturally, washed with acetone, and then dried under vacuum at 100 °C for 4 h to obtain the COFs-supported heteropolyacid salt catalyst. Scanning electron microscopy (SEM) images are shown below. Figure 2 As shown, by Figure 2 It can be seen that the obtained catalyst is a bulk material; the Fourier transform infrared spectrum is as follows. Figure 4 As shown, by Figure 4 It can be seen that 1060cm -1 960cm -1 and 786cm -1 The left and right sides show the characteristic peaks of the Keggin structure of heteropolyacids, indicating that a phosphotungstic acid-recyclable covalent organic framework supported heteropolyacid catalyst has been successfully prepared.

[0031] Example 3

[0032] Preparation of molybdenum vanadate-based recyclable covalent organic framework supported heteropolyacid catalysts: 0.2 g of molybdenum vanadate, 17.6 mg of 1,3,5-tris(4-aminophenyl)benzene, and 19.65 mg of 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine were mixed, and 2 ml of 1,4-dioxane, 0.15 ml of mesitylene, and 6 M acetic acid were added. The mixture was then sonicated for 10 min and degassed three times under vacuum and nitrogen. The mixture was then sealed and heated at 100 °C for one day, allowed to cool naturally, washed with acetone, and then dried under vacuum at 100 °C for 4 h to obtain the COFs-supported heteropolyacid salt catalyst. Scanning electron microscopy (SEM) images are shown below. Figure 3 As shown, by Figure 3 It can be seen that the obtained catalyst is composed of stacked layered structures; the Fourier transform infrared spectrum is as follows. Figure 4 As shown, by Figure 4 It can be seen that 1060cm -1 960cm -1 and 786cm -1 The left and right sides show the characteristic peaks of the Keggin structure of heteropolyacids, indicating that a molybdenum-vanadate-recyclable covalent organic framework supported heteropolyacid catalyst has been successfully prepared.

[0033] Example 4

[0034] Using dibenzothiophene (DBT), a difficult-to-remove compound in hydrodesulfurization, as a representative, DBT was dissolved in 100 mL of 92# gasoline to prepare a simulated system with a sulfur content of 500 ppm. 1 mL of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate was added and stirred. The amount of H2O2 added was calculated based on an O / S (molar ratio) of 5. The amount of phosphomolybdic acid-covalent organic framework-supported heteropolyacid prepared in Example 1 was calculated based on 1% of the mass of 92# gasoline. H2O2 (30% by mass) and the phosphomolybdic acid-covalent organic framework-supported heteropolyacid were added to the above simulated system. Figure 5 As shown, after reacting at 30℃ for 22 minutes, the conversion rate (desulfurization rate) of DBT in 92# gasoline reached nearly 100%. Figure 5 In the figure, b represents the removal effect of phosphomolybdic acid-covalent organic framework supported heteropolyacid on DBT (prepared in Example 1, 92# gasoline), a represents the removal effect of molybdic vanadic acid-covalent organic framework supported heteropolyacid on DBT (prepared in Example 3) (95# gasoline), and c represents the removal effect of molybdic vanadic acid-covalent organic framework supported heteropolyacid on 4,6-DMDBT (4,6-dimethyldibenzothiophene) (prepared in Example 3) (95# gasoline).

[0035] The covalent organic framework supported heteropolyacid catalyst in the above materials was recovered by sedimentation, filtration and drying, with recovery rates all above 99.9%.

[0036] Example 5

[0037] Using dibenzothiophene (DBT), a difficult-to-remove compound in hydrodesulfurization, as a representative, DBT was dissolved in 100 mL of 95# gasoline to prepare a simulated system with a sulfur content of 500 ppm. 1 mL of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate was added and stirred. The amount of H2O2 added was calculated based on an O / S (molar ratio) of 5. The amount of molybdenum vanadate-recyclable covalent organic framework supported heteropolyacid catalyst added in Example 3 was calculated based on 1% of the mass of 95# gasoline. H2O2 (30% by mass) and the molybdenum vanadate-recyclable covalent organic framework supported heteropolyacid catalyst were added to the above simulated system. After reacting at 30°C for 22 min, as shown... Figure 5 As shown, the conversion rate of DBT in 95# gasoline reaches nearly 100%.

[0038] The molybdenum vanadate-recyclable covalent organic framework supported heteropolyacid catalyst in the above material was recovered through sedimentation, filtration, and drying, with a recovery rate of over 99.9%. Figure 7 As shown, after 22 cycles, the catalytic efficiency decreased by 0.31%.

[0039] Example 6

[0040] Using 4,6-dimethyldibenzothiophene (4,6-DMDBT), which is difficult to remove in hydrodesulfurization, as a representative compound, 4,6-DMDBT was dissolved in 100 mL of 95# gasoline to prepare a simulated system with a sulfur content of 500 ppm. 1 mL of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate was added and stirred. The amount of H2O2 added was calculated based on an O / S (molar ratio) of 5. The amount of molybdenum vanadate-recyclable covalent organic framework supported heteropolyacid catalyst added in Example 3 was calculated based on 1% of the mass of 95# gasoline. H2O2 (mass concentration 30%) and the molybdenum vanadate-recyclable covalent organic framework supported heteropolyacid catalyst were added to the above simulated system. Figure 5 As shown, after reacting at 30℃ for about 22 minutes, the conversion rate of 4,6-DMDBT in 95# gasoline reached over 99.8%.

[0041] Example 7

[0042] Using dibenzothiophene (DBT), a difficult-to-remove compound in hydrodesulfurization, as a representative, DBT was dissolved in 100 mL of 92# gasoline to prepare a simulated system with a sulfur content of 500 ppm. 1 mL of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate was added and stirred. The amount of H2O2 added was calculated based on an O / S (molar ratio) of 5. The amount of the molybdenum-vanadate-covalent organic framework supported heteropolyacid prepared in Example 3 was calculated based on 1% of the mass of 92# gasoline. H2O2 (30% by mass) and the phosphomolybdate-covalent organic framework supported heteropolyacid were added to the above simulated system. Figure 6 As shown, the desulfurization rate after 22 minutes of reaction at 50℃ is not much different from that at 30℃ and 40℃. The conversion rate (desulfurization rate) of DBT in 92# gasoline will reach 100%. As the temperature increases, the desulfurization rate continues to increase, but the difference is small. Therefore, considering the overall economic cost, 30℃ is the most suitable temperature.

[0043] Comparative Example 1

[0044] Using dibenzothiophene (DBT), a difficult-to-remove compound in hydrodesulfurization, as a representative example, DBT was dissolved in 100 mL of 92# gasoline to prepare a simulated system with a sulfur content of 500 ppm. 1 mL of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate was added and stirred. The amount of H2O2 added was calculated based on an O / S (molar ratio) of 5. H2O2 (30% by mass) was then added to the simulated system. Figure 8 As shown, after reacting at 30℃ for about 60 minutes, the conversion rate of DBT in 92# gasoline is only about 38%.

Claims

1. The use of a recyclable covalent organic framework supported heteropolyacid catalyst, characterized in that: A method for preparing a recyclable covalent organic framework supported heteropolyacid catalyst includes the following steps: phosphomolybdic acid, phosphotungstic acid, or molybdenum vanadate is mixed with 1,3,5-tris(4-aminophenyl)benzene and 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, 1,4-dioxane, mesitylene, and acetic acid are added, the mixture is sonicated at room temperature for 5-10 min, degassed under vacuum with nitrogen, then the resulting mixture is sealed and heated at 100-120°C for 1 day, naturally cooled, washed with acetone, and dried under vacuum to obtain a recyclable covalent organic framework supported heteropolyacid catalyst; Recyclable covalent organic framework supported heteropolyacid catalysts are used for catalytic oxidative desulfurization.

2. The use of the recyclable covalent organic framework supported heteropolyacid catalyst as described in claim 1, characterized in that: The molar ratio of 1,3,5-tris(4-aminophenyl)benzene and 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine is 1:(0.8~1.2).

3. The use of the recyclable covalent organic framework supported heteropolyacid catalyst as described in claim 1 or 2, characterized in that: The molar ratio of phosphomolybdic acid, phosphotungstic acid or molybdenum vanadate to 1,3,5-tris(4-aminophenyl)benzene is (8~12):

1.

4. The use of the recyclable covalent organic framework supported heteropolyacid catalyst as described in claim 1 or 2, characterized in that: The volume ratio of 1,4-dioxane to mesitylene is 1:(0.05~0.1); the vacuum drying temperature is 80~100℃ and the time is 4-6h.

5. The use of the recyclable covalent organic framework supported heteropolyacid catalyst as described in claim 1, characterized in that: The steps of catalytic oxidation desulfurization are as follows: (1) Take the oil to be desulfurized and the ionic liquid and premix them to obtain mixed solution A; (2) Under normal temperature and pressure conditions, a recyclable covalent organic framework supported heteropolyacid catalyst and H2O2 aqueous solution are added to the mixed solution A prepared in step (1) to carry out the reaction, thereby achieving deep desulfurization of the oil product to be tested.

6. The use of the recyclable covalent organic framework supported heteropolyacid catalyst as described in claim 5, characterized in that, In step (1), the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate, and the volume ratio of the ionic liquid to the oil to be desulfurized is 1: (90~110).

7. The use of the recyclable covalent organic framework supported heteropolyacid catalyst as described in claim 5 or 6, characterized in that, In step (2), the mass of the recyclable covalent organic framework supported heteropolyacid catalyst is 0.2-1.5% of the mass of mixed solution A; the amount of H2O2 is calculated as follows: the number of moles of H2O2 is determined by the number of moles of sulfur S in the oil to be desulfurized, and the O / S molar ratio is (2-6):1; the reaction temperature is 30~50℃; and the reaction time is 15~40min.

8. The use of the recyclable covalent organic framework supported heteropolyacid catalyst as described in claim 5 or 6, characterized in that, It also includes step 3) recovering the covalent organic framework supported heteropolyacid catalyst in the reactants through sedimentation, filtration and drying, with a recovery rate of over 99.9%, and recycling.

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