Alkali metal modified molecular sieve catalyst with high cycle stability and application thereof in catalytic synthesis of para-xylene
By modifying the Beta molecular sieve catalyst with alkali metals to reduce acid strength and suppress side reactions, the problem of catalyst coking was solved, achieving high catalytic activity and stability, suitable for the synthesis of PX from 2,5-DMF.
Patent Information
- Application Number
- CN202411733127.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-29
- Publication Date
- 2025-12-26
- Estimated Expiration
- 2044-11-29
AI Technical Summary
Existing Beta molecular sieve catalysts are highly acidic in the synthesis of PX from 2,5-DMF, which easily leads to catalyst coking and deactivation, poor stability, and frequent regeneration.
Alkali metal modified molecular sieve catalysts were prepared by dissolving and calcining Beta molecular sieves with alkali metal salts. This reduced acid strength, inhibited the hydrolysis of 2,5-DMF and the polymerization of 2,5-hexanedione, and improved catalyst stability.
It significantly reduces the catalyst deactivation rate, improves the catalyst's cycle stability and selectivity, and extends its service life.
Smart Images
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Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of synthetic paraxylene, and particularly relates to a base metal modified molecular sieve catalyst with high cycle stability and application of the base metal modified molecular sieve catalyst in catalytic synthesis of paraxylene. BACKGROUND
[0002] Paraxylene (PX) is a very important chemical raw material, and its main use is to produce terephthalic acid (TA) and terephthalate polymer monomer products. Most of the paraxylene produced in industry depends on petroleum resources, and is prepared through reforming, aromatic extraction, disproportionation, isomerization and adsorption separation processes. With the rapid development of China's economy, the demand for paraxylene is increasing year by year, but China is short of petroleum resources, and the traditional route of producing paraxylene from petroleum resources is facing challenges.
[0003] Biomass is an important carrier of solar energy storage and conversion, and is a renewable organic carbon resource with abundant reserves. Furan compounds, as a kind of diene and dienophile, undergo Diels-Alder cycloaddition reaction, which is a common synthetic method for preparing cyclic compounds. One of the best ways to synthesize PX is to perform Diels-Alder cycloaddition reaction of 2,5-DMF derived from biomass and AA, and then to perform dehydration and decarboxylation. This reaction has the advantages of mild reaction conditions, simple operation and obvious advantages, and shows a strong industrial application prospect.
[0004] This reaction route requires B acid and L acid sites. Among commonly used catalysts, Beta molecular sieve has a good application prospect due to its ordered and stable framework structure, high specific surface area, good shape selectivity and rich B and L acid sites. However, Beta molecular sieve has strong acidity, and the strong acid sites are easy to catalyze the hydrolysis of 2,5-DMF and the further polymerization of 2,5-hexanedione during the reaction, thereby causing the catalyst to be easily carbonized and deactivated, and the catalyst needs to be frequently regenerated. Therefore, it is urgent to develop a molecular sieve catalyst with high activity, high selectivity and anti-coking properties for application in the reaction of 2,5-DMF synthesizing PX. SUMMARY
[0005] In view of the problems of strong acidity, easy carbonization and poor stability of the molecular sieve catalyst, a preparation method of a base metal modified molecular sieve catalyst with high cycle stability is provided. The prepared molecular sieve catalyst has high catalytic activity and selectivity, high cycle stability, excellent regeneration performance and can be used repeatedly for a long time.
[0006] To solve the above technical problems, the technical scheme adopted by the application is as follows:
[0007] The alkali metal salt is dissolved in deionized water to obtain an alkali metal salt solution, the molecular sieve is added to the alkali metal salt solution of step (1) and stirred and mixed, and then dried, and the dried product is calcined in a muffle furnace to obtain an alkali metal modified Beta molecular sieve catalyst.
[0008] Further, the alkali metal is one of sodium, potassium, magnesium and calcium.
[0009] Further, the loading mass of the alkali metal oxide in the alkali metal modified Beta molecular sieve catalyst is 0.25% to 10%.
[0010] Further, the molecular sieve is H-Beta.
[0011] Further, the calcination in the muffle furnace refers to calcination at 500 to 600 DEG C for 2 to 4 hours.
[0012] Further, the catalyst dosage is 2.5% to 3.0% of the total mass of the reactant raw materials.
[0013] The application of the alkali metal modified molecular sieve catalyst in catalyzing the reaction of 2,5-dimethylfuran (2,5-DMF) and acrylic acid (AA) to synthesize dimethylbenzene (PX) is specific to:
[0014] 2,5-DMF and AA are mixed in a solvent to obtain a mixed solution, the mixed solution is transferred to a magnetic stirring kettle, the alkali metal modified molecular sieve is added, high-purity nitrogen is used to replace the reaction gas, the reaction pressure is normal pressure, the reaction temperature is 160 to 190 DEG C, and the reaction time is 10 to 15 hours; after the reaction is completed, the reaction kettle is placed in an ice water bath for cooling, and the product dimethylbenzene is collected.
[0015] The dosage of the alkali metal modified molecular sieve is:
[0016] As preferred, the prepared 1% Na2O / H-Beta molecular sieve is applied to the reaction of 2,5-DMF and AA to synthesize PX, under the conditions that the reaction temperature is 190 DEG C, the reaction time is 15 hours, and the initial reaction pressure is normal pressure, 97.7% of the conversion rate of 2,5-DMF and 99.7% of the PX selectivity can be obtained.
[0017] After the above technical solution is adopted, the application has the following beneficial effects:
[0018] After the above technical solution is adopted, the application has the following beneficial effects:The catalyst acid strength is reduced after the nano-type Beta molecular sieve is modified by a small amount of alkali metal, the 2,5-DMF hydrolysis and the further polymerization reaction of 2,5-hexanedione are effectively inhibited, the catalyst carbon deposition is reduced, and the catalyst stability is improved. In the cycle stability test, compared with the unmodified molecular sieve, the alkali metal modified molecular sieve catalyst activity deactivation rate is significantly reduced. BRIEF DESCRIPTION OF DRAWINGS
[0019] Figure 1 is the XRD pattern of the Beta molecular sieve prepared in Example 1, Example 4, Example 6, Example 7 and Example 8; Figure 1 It can be seen from the figure that the diffraction peaks appearing at about 7.8, 22.5, 25.4, 27.0, 28.8, 29.7 and 43.7 in 2θ all belong to the characteristic diffraction peaks of the Beta molecular sieve, indicating that the modification of alkali metal does not affect the crystal structure of the Beta molecular sieve. DETAILED DESCRIPTION
[0020] The present application will be further illustrated in the following examples, but it should be understood that these examples are only for illustrative purposes and should not be interpreted as a limitation on the implementation of the present application.
[0021] In the present application, the alkali metal modified Beta molecular sieve is prepared by impregnation method. By adjusting the addition amount of different metal precursors during preparation, different modified Beta molecular sieves can be obtained. The specific implementation is as follows:
[0022] Example 1
[0023] First, sodium hydroxide and sodium aluminate are dissolved in deionized water, then added to tetraethylammonium hydroxide (TEAOH, 25wt% aqueous solution) solution, stirred uniformly, then slowly added hydrophilic silica, stirred for 5.5h under water bath at 35℃, to obtain a precursor, the molar ratio of the precursor is controlled as: SiO2: 0.025Al2O3: 0.05Na2O: 12H2O: 0.3TEAOH; the precursor is transferred to the inner liner of the crystallization kettle with polytetrafluoroethylene liner, and is placed in an oven at 150℃ for 2 days for crystallization, and the precursor in the hydrothermal reaction kettle is centrifuged, washed and dried to obtain a white powder without template removal agent. The obtained white powder is calcined in a muffle furnace at 550℃ for 6h, then ion exchanged with 1.0mol·L -1 of NH4Cl aqueous solution for 3 times, then dried, calcined in a muffle furnace at 550℃ for 4h to obtain H-Beta.
[0024] Example 2
[0025] First 0.0412 g NaNO3was dissolved in 20 g deionized water, H-Beta zeolite 6 g was added, stirred at room temperature for 1 h, then evaporated to dryness in an oil bath at 70 °C, followed by further drying in an oven at 110 °C for 2 h, the dried solid powder was calcined in a muffle furnace at 550 °C for 3 h, at this time 0.25% Na2O / H-Beta was obtained.
[0026] Example 3
[0027] First 0.0823 g NaNO3was dissolved in 20 g deionized water, H-Beta zeolite 6 g was added, stirred at room temperature for 1 h, then evaporated to dryness in an oil bath at 70 °C, followed by further drying in an oven at 110 °C for 2 h, the dried solid powder was calcined in a muffle furnace at 550 °C for 3 h, at this time 0.5% Na2O / H-Beta was obtained.
[0028] Example 4
[0029] First 0.1645 g NaNO3was dissolved in 20 g deionized water, H-Beta zeolite was added, stirred at room temperature for 1 h, then evaporated to dryness in an oil bath at 70 °C, followed by further drying in an oven at 110 °C for 2 h, the dried solid powder was calcined in a muffle furnace at 550 °C for 3 h, at this time 1% Na2O / H-Beta was obtained.
[0030] Example 5
[0031] First 0.4113 g NaNO3was dissolved in 20 g deionized water, H-Beta zeolite 6 g was added, stirred at room temperature for 1 h, then evaporated to dryness in an oil bath at 70 °C, followed by further drying in an oven at 110 °C for 2 h, the dried solid powder was calcined in a muffle furnace at 550 °C for 3 h, at this time 2.5% Na2O / H-Beta was obtained.
[0032] Example 6
[0033] First 0.1288 g KNO3was dissolved in 20 g deionized water, H-Beta zeolite 6 g was added, stirred at room temperature for 1 h, then evaporated to dryness in an oil bath at 70 °C, followed by further drying in an oven at 110 °C for 2 h, the dried solid powder was calcined in a muffle furnace at 550 °C for 3 h, at this time 1% K2O / H-Beta was obtained.
[0034] Example 7
[0035] First 0.2208 g Mg(NO3)2was dissolved in 20 g deionized water, H-Beta zeolite 6 g was added, stirred at room temperature for 1 h, then evaporated to dryness in an oil bath at 70 °C, followed by further drying in an oven at 110 °C for 2 h, the dried solid powder was calcined in a muffle furnace at 550 °C for 3 h, at this time 1% MgO / H-Beta was obtained.
[0036] Example 8
[0037] First, 0.1758 g Ca(NO3)2 was dissolved in 20 g deionized water, 6 g H-Beta molecular sieve was added, stirred at room temperature for 1 h, then evaporated to dryness in an oil bath at 70 °C, followed by further drying in an oven at 110 °C for 2 h, and the dried solid powder was calcined in a muffle furnace at 550 °C for 3 h, at which time 1% CaO / H-Beta was obtained.
[0038] The catalysts obtained in Examples 1-8 above were applied in the reaction of 2,5-DMF and AA to synthesize PX, and the specific application was as follows:
[0039] Example 9
[0040] 2,5-DMF and AA were mixed in a molar ratio of 1:2, the concentration of 2,5-DMF was 0.5 mol·L -1 , the concentration of AA was 1.0 mol·L -1 , the solvent was n-heptane, and the total reaction liquid volume was 30 mL. The mixture was transferred to a magnetic stirring kettle, 2.8% (0.1 g) of H-Beta corresponding to the total mass of the reactants was added, and the kettle was replaced with high-purity nitrogen gas for 3 times. The reaction temperature was 190 °C, the initial pressure was atmospheric pressure, and the reaction time was 15 h; after the reaction was completed, the reaction kettle was placed in an ice water bath for cooling. The main product was PX and the by-products 2,5-hexanedione and 2,5-dimethylbenzoic acid.
[0041] Example 10
[0042] 2,5-DMF and AA were mixed and added to n-heptane, the concentration of 2,5-DMF was 0.5 mol·L -1 , the concentration of AA was 1.0 mol·L -1 , and the total reaction liquid volume was 30 mL. The mixture was transferred to a magnetic stirring kettle, 0.25% Na2O / H-Beta corresponding to 2.8% of the total mass of the reactants was added, and the kettle was replaced with high-purity nitrogen gas for 3 times. The reaction temperature was 190 °C, the initial pressure was atmospheric pressure, and the reaction time was 15 h; after the reaction was completed, the reaction kettle was placed in an ice water bath for cooling. The main product was PX and the by-products 2,5-hexanedione and 2,5-dimethylbenzoic acid.
[0043] Example 11
[0044] Compared with Example 10, the difference was that 0.25% Na2O / H-Beta was replaced by 0.5% Na2O / H-Beta, and the other operations were the same as in Example 10.
[0045] Example 12
[0046] The difference compared with Example 10 is that 0.25% Na2O / H-Beta is replaced by 1% Na2O / H-Beta, and other operations are the same as those in Example 10.
[0047] Example 13
[0048] The difference compared with Example 10 is that 0.25% Na2O / H-Beta is replaced by 2.5% Na2O / H-Beta, and other operations are the same as those in Example 10.
[0049] Example 14
[0050] The difference compared with Example 10 is that 0.25% Na2O / H-Beta is replaced by 1% K2O / H-Beta, and other operations are the same as those in Example 10.
[0051] Example 15
[0052] The difference compared with Example 10 is that 0.25% Na2O / H-Beta is replaced by 1% MgO / H-Beta, and other operations are the same as those in Example 10.
[0053] Example 16
[0054] The difference compared with Example 10 is that 0.25% Na2O / H-Beta is replaced by 1% CaO / H-Beta, and other operations are the same as those in Example 10.
[0055] The catalytic activities of the catalysts obtained in Examples 1 to 8 are compared, and the comparison is shown in Table 1 below:
[0056] Table 1 Comparison of catalytic activities of catalysts obtained in Examples 1 to 8
[0057] Examples Catalyst 2,5-DMF conversion (%) PX selectivity (%) Example 9 H-Beta 99.0 98.0 Example 10 0.25% Na2O / H-Beta 98.5 98.4 Example 11 0.5% Na2O / H-Beta 98.1 98.5 Example 12 1% Na2O / H-Beta 97.7 99.7 Example 13 2.5% Na2O / H-Beta 92.6 98.5 Example 14 1% K2O / H-Beta 97.4 99.2 Example 15 1% MgO / H-Beta 96.3 98.1 Example 16 1% CaO / H-Beta 94.5 97.1
[0058] As can be seen from Table 1, the catalytic activity of the modified Beta molecular sieve changes, the most effective modification metal precursor is NaNO3, and when the Na2O loading amount is 1%, the catalytic activity is the best; when the Na2O loading amount is 2.5%, the catalytic activity decreases. This may be because too much Na2O loading amount leads to too weak B acid strength on the outer surface of the molecular sieve, and the total reaction rate is greatly reduced. By comparing Example 9 and Example 12, under the same reaction conditions, by changing the B acid strength of the Beta molecular sieve, the occurrence of side reactions can be inhibited, and then the PX selectivity is improved.
[0059] Example 17
[0060] The H-Beta catalyst obtained after the reaction of Example 9 was recovered by centrifugation, washed with anhydrous ethanol for 2 times, dried at 60°C overnight, and the dried molecular sieve was subjected to a cycle stability test, and the reaction was cycled for 4 times. The reaction conditions of each cycle were the same as those of Example 9. The results are shown in Table 2.
[0061] Table 2 2,5-DMF conversion and PX selectivity under the cycle use conditions of H-Beta
[0062]
[0063]
[0064] Example 18
[0065] The 1% Na2O / H-Beta catalyst obtained after the reaction of Example 12 was recovered by centrifugation, washed with anhydrous ethanol for 2 times, dried at 60°C overnight, and the dried 1% Na2O / H-Beta molecular sieve catalyst was subjected to a cycle stability test, and the reaction was cycled for 4 times. The reaction conditions of each cycle were the same as those of Example 12. The results are shown in Table 3.
[0066] Table 3 2,5-DMF conversion and PX selectivity under the cycle use conditions of 1% Na2O / H-Beta
[0067] Cycle number 2,5-DMF conversion (%) PX selectivity (%) 1 95.4 98.5 2 92.1 97.1 3 90.5 95.1 4 87.3 92.6
[0068] Example 19
[0069] The 1% K2O / H-Beta catalyst obtained after the reaction of Example 14 was recovered by centrifugation, washed with anhydrous ethanol for 2 times, dried at 60°C overnight, and the dried 1% K2O / H-Beta molecular sieve catalyst was subjected to a cycle stability test, and the reaction was cycled for 4 times. The reaction conditions of each cycle were the same as those of Example 14. The results are shown in Table 4.
[0070] Table 4 2,5-DMF conversion and PX selectivity under the cycle use conditions of 1% K2O / H-Beta
[0071] Cycle number 2,5-DMF conversion (%) PX selectivity (%) 1 95.0 98.5 2 92.2 97.0 3 90.7 95.3 4 87.1 93.4
[0072] As can be seen from Tables 3 and 4, the alkali metal modified Beta molecular sieve prepared by the method of the present application has excellent cycle stability, and when used in the synthesis of PX from 2,5-DMF and AA, the 2,5-DMF conversion and PX selectivity of Examples 18 and 19 are significantly better than those of Example 17 after four cycles.
[0073] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.
Claims
1. Use of a metal-modified molecular sieve catalyst having high cycle stability, characterized in that: Application of metal-modified molecular sieve catalyst in catalyzing reaction of 2,5-dimethylfuran and acrylic acid to synthesize dimethylbenzene; The metal salt is dissolved in deionized water to obtain a metal salt solution, the molecular sieve is added into the metal salt solution, and stirred and mixed, and then dried, and the dried product is calcined in a muffle furnace to obtain the metal-modified molecular sieve catalyst. The metal is one of sodium, potassium, magnesium and calcium; and the molecular sieve is H-Beta molecular sieve.
2. Use according to claim 1, characterized in that: The metal salt is any one of NaNO3, KNO3, Mg(NO3)2 or Ca(NO3)2.
3. Use according to claim 1, characterized in that: The loading mass of the metal oxide in the metal-modified molecular sieve catalyst is 0.25% to 10% of the mass of the molecular sieve.
4. Use according to claim 3, characterized in that: The loading mass of the metal oxide in the metal-modified molecular sieve catalyst is 0.25% to 2.5% of the mass of the molecular sieve.
5. The use according to claim 1, characterized in that: The calcination in the muffle furnace is calcination at 500 to 600°C for 2 to 4 hours.
6. Use according to claim 1, characterized in that: The metal-modified molecular sieve catalyst is 1% Na2O / H-Beta; 1% means that the mass percentage of Na2O in H-Beta.