Preparation method and application of tungsten tin phosphate solid acid catalyst

Abstract

The invention belongs to the field of catalysts, and particularly relates to a tin tungsten phosphate solid acid catalyst, and the tin tungsten phosphate solid acid catalyst is used for catalyzing the reaction of 2, 5-dimethylfuran and ethanol to prepare p-xylene. The tin tungsten phosphate solid acid catalyst is synthesized by ammonium metatungstate, tin tetrachloride, polyether P123 and phosphoric acid through a one-pot hydrothermal method, and the catalyst can catalyze 2, 5-dimethylfuran to react with ethanol to prepare p-xylene by optimizing the tungsten-tin ratio, the temperature, the reaction time and the like. According to the catalyst disclosed by the invention, the route of preparing p-xylene by using ethanol as an alkene donor instead of a conventional fossil-sourced ethylene is realized, a relatively high yield is obtained, and a new thought and a new method are provided for green production of p-xylene.

Description

Technical Field

[0001] The invention relates to the field of catalysts, and in particular to a preparation method of a tungsten tin phosphate solid acid catalyst and application thereof. Background Art

[0002] Aromatic compounds play a vital role in the chemical industry. They are key raw materials for the synthesis of pesticides, medicines, flavors, additives, polymers, materials, dyes and many other products. Among the many aromatic compounds, p-xylene (pX) is extremely important and is one of the most basic raw materials in the chemical industry. In today's chemical industry, the production of aromatic compounds mainly depends on petroleum resources, and only a small part is produced through other methods such as coal tar and synthesis gas. However, due to the serious global warming and environmental pollution problems caused by petroleum, as well as the goal of achieving carbon neutrality, the use of renewable carbon resources to replace petroleum has received full attention in recent decades.

[0003] As the only renewable carbon source, biomass has received extensive attention in the field of p-xylene synthesis. The reaction pathway for the preparation of pX from biomass platform molecules is basically based on the Diels-Alder cycloaddition reaction. The raw material is mainly 2,5-dimethylfuran (DMF) from cellulose, and the olefin donor (dienophile) is mostly ethylene, thanks to the high selectivity of the cycloaddition reaction between the dimethyl symmetric structure of DMF and ethylene.

[0004] A large number of literatures have reported on this route [Wu C, Wu T, Li J, et al. Highlyefficient catalytic conversion of biomass-derived 2,5-dimethylfuran intorenewable p-xylene over zirconium phosphate catalysts[J]. Applied Catalysis A: General, 2023, 663: 119323.; Feng X, Cui Z, Ji K, et al. Ultra-selective p-xyleneproduction through cycloaddition and dehydration of 2,5-dimethylfuran andethylene over tin phosphate[J].Applied Catalysis B:Environmental,2019,259:118108.;ZHAO R,ZHAO Z,LI S,et al.Excellent Performances of Dealuminated H-Beta Zeolites from Organotemplate-Free Synthesis in Conversion of Biomass-derived 2,5-Dimethylfuran to Renewable p-Xylene[J].ChemSusChem,2018,11(21):3803-3811.;Zhao Y,Wang KZ,Sun ZH,et al.Niobium grafted mesoporous silica forthe production of biorenewable p-xylene from concentrated 2,5-dimethylfuran[J].Green Chemistry,2022,24(10):4095-4107. A method for the co-production of bio-based p-xylene and toluene: CN118459305A; A mixing method for preparing bio-based toluene and p-xylene based on low-cost lignocellulosic biomass: CN118184480A], the yield of pX synthesized by the reaction of DMF and ethylene can reach more than 90%.

[0005] However, ethylene mainly comes from fossil fuels, and the use of ethylene as a dienophile is accompanied by pollution and the depletion of petrochemical resources. Ethanol dehydration can produce ethylene, which mainly comes from renewable biomass resources. If it can be used as an olefin donor together with DMF to achieve the full biomass source of raw materials, it is more in line with the country's dual carbon strategy [Wu Yuke, Luo Lin, Li Zheng, Lin Lu, Zeng Xianhai. Research progress on the preparation of p-xylene from biomass platform molecules [J]. Chemistry and Industry of Forest Products, 2024, 44(5): 125-133.]. At present, the research on ethanol as an olefin donor is relatively limited [Zhao R, Li S, Bi L, et al. Enhancement of p-xylene selectivity in the reaction between 2,5-dimethylfuran and ethanol over an ammonium fluoride-modified ZSM-5zeolite[J]. Catalysis Science&Technology, 2022, 12(7): 2248-56.; Zhao R, Wu L, Sun X, et al. Renewable p-xylene synthesis via biomass-derived 2,5-dimethylfuran and ethanol by phosphorous modified H-Beta zeolite[J]. Microporous and Mesoporous Materials, 2022, 334. A catalyst for producing p-xylene and its preparation method and application: CN114950539A; A preparation method of a catalyst for catalyzing the production of p-xylene from 2,5-dimethylfuran and ethanol: CN113634278A], facing the problems of severe DMF hydrolysis and low yield. Summary of the invention

[0006] In order to solve the problems existing in the above-mentioned prior art, the present invention prepares a tungsten tin phosphate solid acid catalyst, and applies it to catalyze the reaction of 2,5-dimethylfuran and ethanol to prepare p-xylene. The tungsten tin phosphate solid acid catalyst is synthesized by a one-pot hydrothermal method of ammonium metatungstate, tin tetrachloride, polyether P123 and phosphoric acid. Ammonium metatungstate and tin tetrachloride are metal W sources and Sn sources respectively, phosphoric acid is a P source, and the three react to form tungsten tin phosphate. Polyether P123 is a template agent, which is used to assist in forming a catalyst nanosheet structure and controlling the pore size. By optimizing the tungsten tin ratio, temperature, reaction time, etc., the catalyst can catalyze the reaction of 2,5-dimethylfuran and ethanol to prepare p-xylene. The catalyst of the present invention realizes the use of ethanol as an olefin donor to replace the conventional fossil source ethylene to prepare p-xylene, and obtains a higher yield, providing a new idea and method for the green production of p-xylene.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing a tungsten tin phosphate solid acid catalyst comprises the following steps:

[0009] (1) Dissolve polyether P123 and phosphoric acid in water, add tin tetrachloride pentahydrate and ammonium metatungstate hydrate H 42 N 10 O 42 W 12 Dissolve in water, add polyether P123 and phosphoric acid aqueous solution, hydrothermally treat to obtain solid precipitate, wash and dry;

[0010] (2) calcining the dried product obtained in step (1) to obtain a tungsten tin phosphate solid acid catalyst.

[0011] The metal ratio and the amount of phosphoric acid will change the acidity of the catalyst. Adding too much or the ratio being out of balance will make the acidity unsuitable for the reaction and reduce the yield. Therefore, as a preference, in the step (1), the addition ratio of ammonium metatungstate hydrate, tin tetrachloride pentahydrate, polyether P123, and phosphoric acid is 0-6g: 0-7g: 0-6g: 0.5-10g; the preferred ratio is 0-3g: 0-4g: 0-4g: 1-6g.

[0012] Preferably, in step (1), polyether P123 and phosphoric acid are dissolved in 10-50 mL of water; tin tetrachloride pentahydrate and ammonium metatungstate hydrate H 42 N 10 O 42 W 12 Dissolve in 5-30 mL of water.

[0013] Preferably, in step (1), the hydrothermal treatment is carried out at 80-200°C for 24-96h, preferably at 150°C for 48h, under which the reaction effect is the best.

[0014] Preferably, in step (1), the polyether P123 and the aqueous solution of phosphoric acid are added dropwise under rapid stirring for 1-12 hours.

[0015] Preferably, in step (1), the hydrothermal treatment is carried out in an autoclave containing a polytetrafluoroethylene liner.

[0016] Preferably, in step (1), the solid precipitate is obtained by centrifugation, the solid precipitate is washed with water and ethanol, and the solid precipitate is dried in a vacuum drying oven overnight.

[0017] Experiments have found that different process parameters will change the acidity and structure of the catalyst. Therefore, as a preference, in step (2), the calcination is carried out in a muffle furnace at 500-700°C in air for 2-12 hours, preferably increasing the temperature to 600°C at 1°C / min and keeping the temperature for 6 hours.

[0018] Preferably, in step (2), the tungsten tin phosphate solid acid catalyst is Sn x W y PO, x and y represent the molar ratio of Sn and W, x:y=0.1:0.9, 0.3:0.7, 0.5:0.5, 0.7:0.3, 0.9:0.1.

[0019] The present invention also provides an application of the above-mentioned tungsten tin phosphate solid acid catalyst in the preparation of p-xylene by the reaction of 2,5-dimethylfuran and ethanol, comprising the following steps:

[0020] A solid acid catalyst of tungsten tin phosphate, 2,5-dimethylfuran and ethanol are added into a high-pressure resistant reaction kettle, and a catalytic reaction is carried out under a nitrogen atmosphere to obtain p-xylene.

[0021] Preferably, the reactor is sealed and filled with 0.1-1 MPa nitrogen.

[0022] Preferably, the reaction is carried out at 300-800 rpm and 200-400° C. under magnetic stirring for 6-24 hours to obtain p-xylene.

[0023] Preferably, the addition ratio of tungsten tin phosphate solid acid catalyst, 2,5-dimethylfuran and ethanol is 0.02-0.4g: 1mmol: 10ml. Experiments have found that the best effect is achieved when the ratio of catalyst, raw material and solvent is within this range, otherwise the yield will decrease.

[0024] Compared with the prior art, the present invention has the following advantages and effects:

[0025] Phosphates of tungsten and tin were used as catalysts, and the catalytic performance was regulated by adjusting the ratio of the two metals; a higher pX yield (67.7%) was achieved in the reaction of DMF and ethanol; the hydrolysis of DMF was inhibited, and the reaction was carried out in the case where the solvent was entirely ethanol, without using other solvents. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Sn in Example 1 0.3 W 0.7 Thermogravimetric analysis of PO precursor.

[0027] Figure 2 Sn in Example 1 x W y XRD pattern of PO.

[0028] Figure 3 Sn in Example 1 x W y PO's N 2 Adsorption-desorption curves.

[0029] Figure 4 Sn in Example 1 0.3 W 0.7 Transmission electron microscopy (TEM) image of PO.

[0030] Figure 5 Sn in Example 1 x W y Ammonia temperature-programmed desorption test of PO (NH 3 -TPD) spectrum. DETAILED DESCRIPTION

[0031] In order to more clearly explain the purpose, technical solutions and advantages of the present application, the following will be described in detail with reference to the accompanying drawings and specific embodiments. The accompanying drawings show only exemplary embodiments of the present application and do not limit its implementation. The present application can be implemented in various forms, and its design concept and core technology are not limited by the embodiments shown in the accompanying drawings. The purpose of providing these embodiments is to make it easier for technicians to understand the principles, structures and functions of the present application, so as to better grasp and apply its technical solutions. The terms used in this specification are only used to describe specific embodiments and do not constitute a limitation on the present application.

[0032] Embodiment 1:

[0033] A tungsten tin phosphate solid acid catalyst is prepared by the following method:

[0034] (1) Take 2g of polyether P123 and 2.3g of phosphoric acid and dissolve them in 20mL of water. Dissolve 2.1g of tin tetrachloride pentahydrate and 3.57g of ammonium metatungstate hydrate in 10mL of water, and add dropwise to the prepared phosphoric acid solution under rapid stirring conditions; after stirring for 3h, transfer to an autoclave containing polytetrafluoroethylene lining and hydrothermally treat at 150°C for 48h. After taking out, use a centrifuge to centrifuge to obtain a solid precipitate; wash the solid precipitate with water and ethanol, and then put it in a vacuum drying oven to dry overnight;

[0035] (2) The dried solid product obtained in step (1) was placed in a muffle furnace and heated to 600° C. at a rate of 1° C. / min and kept warm for 6 h to obtain a tungsten tin phosphate solid acid catalyst Sn 0.3 W 0.7 P.O.

[0036] While keeping the total metal content at 20 mmol, the metal ratio was changed and Sn was prepared using the same method. x W y PO (x, y represent the molar ratio of Sn to W, x:y = 0.1:0.9, 0.5:0.5, 0.7:0.3, 0.9:0.1). The added amounts of tin tetrachloride pentahydrate are 0.7g, 3.54g, 4.91g, 6.31g, respectively, and the added amounts of ammonium metatungstate hydrate are 4.59g, 2.55g, 1.53g, 0.51g, respectively.

[0037] Thermogravimetric analysis was performed on the catalyst precursor prepared in step (1) of Example 1. Figure 1 The precursor continued to lose weight at 30°C to 400°C, mainly because the template added during the preparation of the catalyst decomposed at high temperature. As the template decomposed, a porous structure gradually appeared in the catalyst. The main reason for the weight loss at 500°C to 750°C was that the catalyst collapsed and decomposed at high temperature. This calcination stage destroyed the catalyst morphology and made it lose its active structure.

[0038] The Sn prepared in Example 1 x W y The PO catalyst was subjected to X-ray diffraction (XRD) analysis, such as Figure 2 As the proportion of W increases, the figures in the XRD pattern become more obvious and the morphology becomes clearer. The characteristic peaks of 2θ=23.1°, 23.8°, 33.5°, 41.5° and 54.8° can also be compared with W. 12 PO 38.5 (PDF#41-0369) Correspondingly, it is shown that as the proportion of W increases, the crystallinity of the catalyst increases. 0.3 W 0.7 PO not only has obvious W 12 PO 38.5Characteristic peaks, and SnP 2 O 7 (PDF#29-1252) The characteristic peaks correspond to each other, indicating that tungsten phosphate oxide and tin phosphate oxide are stably present in the catalyst. 0.5 W 0.5 PO, Sn 0.7 W 0.3 PO, Sn 0.9 W 0.1 The peak of PO catalyst is fuzzy, which indicates that the crystallinity of these three tin tungsten phosphate oxide catalysts is very low and they are mainly amorphous.

[0039] The Sn prepared in Example 1 x W y PO catalyst was subjected to physical adsorption analysis, such as Figure 3 As shown in the figure, there is a mesoporous structure in the catalyst. With the increase of W addition, the specific surface area of ​​the catalyst generally decreases, while the pore size increases.

[0040] The Sn prepared in Example 1 0.3 W 0.7 The PO catalyst was observed by transmission electron microscopy (TEM). Figure 4 As shown. 0.3 W 0.7 PO is an irregular nanosheet structure stacked layer by layer. Figure 4 In b, it can be observed that there are gaps between the nanosheet structures. The existence of the gaps makes the catalyst less likely to be deactivated by carbon deposition. Further increasing the TEM magnification, Figure 4 In Figures c and d, it can be clearly seen that the catalyst has irregular mesopores and macropores distributed on the surface of the nanosheets. The presence of nanosheet layered structures and pores can promote mass transfer between the catalyst and the reactants, thereby improving the catalytic activity and having a certain resistance to carbon deposition.

[0041] The Sn prepared in Example 1 x W y PO catalyst was tested for ammonia temperature-programmed desorption (NH 3 -TPD), such as Figure 5 As shown. Except Sn 0.9 W 0.1 Except for PO, other catalysts have obvious medium-strength acid sites and strong acid sites. As the content of W gradually increases, the strong acid peak becomes more obvious, indicating that the strong acid sites are mainly provided by W, and the medium-strength acid sites are mainly provided by Sn. 0.9 W 0.1 PO lacks strong acidic sites and is not sufficient to provide sufficient acidic catalytic dehydration reaction, resulting in difficulty in ethanol dehydration and difficulty in catalyzing the reaction to produce pX.

[0042] Embodiment 2-6:

[0043] The catalyst prepared in Example 1 is used to react 2,5-dimethylfuran with ethanol to prepare p-xylene, and the steps are as follows:

[0044] 0.2 g of catalyst, 1 mmol of DMF, and 10 ml of ethanol were added to a high-pressure reactor, and the reactor was sealed and filled with 0.1 MPa of nitrogen. The reaction was carried out at 300°C with magnetic stirring at 600 rpm for 9 h, and then cooled to room temperature. The reaction solution was filtered with a 0.45 μm organic filter head and analyzed by gas chromatography (GC) and the product was identified by gas chromatography-mass spectrometry (GC-MS). The catalytic efficiency of different catalysts is shown in Table 1. Examples 2-6 show that Sn 0.3 W 0.7 The pX yield was the highest under the action of PO catalyst.

[0045] Table 1. Different Sn x W y Catalytic efficiency of PO catalyst

[0046] Example catalyst MF conversion rate / % pX selectivity / % pX yield / % 2 <![CDATA[Sn 0.9 IN 0.1 AFTER]]> 42.3 58.9 24.9 3 <![CDATA[Sn 0.7 IN 0.3 AFTER]]> 44.6 52.0 23.2 4 <![CDATA[Sn 0.5 IN 0.5 AFTER]]> 54.1 53.2 28.8 5 <![CDATA[Sn 0.3 IN 0.7 AFTER]]> 60.8 53.3 32.4 6 <![CDATA[Sn 0.1 IN 0.9 AFTER]]> 65.2 43.9 28.6

[0047] Embodiment 7-15:

[0048] The catalyst Sn used in Example 5 was used 0.3 W 0.7 PO was used as the catalyst for subsequent research. Reaction conditions: DMF 1mmol, catalyst 0.2g, ethanol 10ml. The catalytic efficiency under different catalytic conditions is shown in Table 2.

[0049] Table 2. Catalytic efficiency under different catalytic conditions

[0050]

[0051]

[0052] When the temperature is increased from 240℃ to 300℃, the DMF conversion rate is significantly increased to 94.2%, and the pX yield is 61.2% at this time, which indicates that the reaction of DMF and ethanol to prepare pX requires higher temperature conditions. High temperature can accelerate the reaction rate, but after the temperature is higher than 300℃, further increasing the reaction temperature does not significantly improve the DMF conversion rate, some polymer humus increases significantly, and the pX yield also decreases. Considering the DMF conversion rate and pX yield comprehensively, 300℃ can be selected as the optimal reaction temperature. Prolonging the reaction time can significantly improve the DMF conversion rate and pX yield. When the reaction time is extended from 3h to 24h, the DMF conversion rate is increased to 99.4%, and the pX yield can reach 67.7%.

[0053] Finally, we need to emphasize that the embodiments provided here are only part of the embodiments of this application, not all of them. Based on this application, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of this application.

Claims

1. A method for preparing a tungsten tin phosphate solid acid catalyst, characterized in that: The steps include: (1) Dissolve polyether P123 and phosphoric acid in water, add tin tetrachloride pentahydrate and ammonium metatungstate hydrate H 42 N 10 O 42 W 12 Dissolve in water, add polyether P123 and phosphoric acid aqueous solution, hydrothermally treat to obtain solid precipitate, wash and dry; (2) calcining the dried product obtained in step (1) to obtain a tungsten tin phosphate solid acid catalyst.

2. The method according to claim 1, characterized in that: In the step (1), the addition ratio of ammonium metatungstate hydrate, tin tetrachloride pentahydrate, polyether P123 and phosphoric acid is 0-6g: 0-7g: 0-6g: 0.5-10g; the preferred ratio is 0-3g: 0-4g: 0-4g: 1-6g.

3. The method according to claim 1, characterized in that In the step (1), the hydrothermal treatment is carried out at 80-200° C. for 24-96 hours, preferably at 150° C. for 48 hours.

4. The method according to claim 1, characterized in that: In the step (1), the polyether P123 and the aqueous solution of phosphoric acid are added dropwise under rapid stirring conditions for 1-12 hours.

5. The method according to claim 1, characterized in that In the step (2), the calcination is carried out in a muffle furnace at 500-700° C. in air for 2-12 h, preferably the temperature is increased to 600° C. at a rate of 1° C. / min and kept at this temperature for 6 h.

6. The method according to claim 1, characterized in that In the step (2), the tungsten tin phosphate solid acid catalyst is Sn x W y PO, x, y represent the molar ratio of Sn to W, where x:y = 0.1:0.9, 0.3:0.7, 0.5:0.5, 0.7:0.3, 0.9:0.

1.

7. Use of a tungsten tin phosphate solid acid catalyst prepared by the method of any one of claims 1 to 6, characterized in that: It is applied to the reaction of 2,5-dimethylfuran and ethanol to prepare p-xylene.

8. Use of the tungsten tin phosphate solid acid catalyst according to claim 7, adding the tungsten tin phosphate solid acid catalyst, 2,5-dimethylfuran and ethanol into a high-pressure resistant reactor, and catalyzing the reaction under a nitrogen atmosphere to obtain p-xylene.

9. The use of the tungsten tin phosphate solid acid catalyst according to claim 8, characterized in that: After sealing the reactor, fill it with 0.1-1 MPa nitrogen, and react for 6-24 hours at 200-400° C. with magnetic stirring at 300-800 rpm to obtain p-xylene.

10. The use of the tungsten tin phosphate solid acid catalyst according to claim 8, characterized in that: The addition ratio of tungsten tin phosphate solid acid catalyst, 2,5-dimethylfuran and ethanol is 0.02-0.4g:1mmol:10ml.

Images