Alkali metal modified molecular sieve catalyst with high cycle stability and application thereof in catalytic synthesis of p-xylene

Abstract

The invention belongs to the technical field of p-xylene synthesis, and particularly relates to an alkali metal modified molecular sieve catalyst with high cycle stability and application thereof in catalytic synthesis of p-xylene. Aiming at the problems of strong acidity, easy carbon deposition, poor stability and the like of a molecular sieve catalyst, an alkali metal modified molecular sieve is adopted, specifically, alkali metal salt is dissolved in deionized water to obtain an alkali metal salt solution, the molecular sieve is added into the alkali metal salt solution, stirring and mixing are performed, then drying is performed, and a dried product is roasted in a muffle furnace to obtain the catalyst. The alkali metal modified molecular sieve catalyst is obtained. And the prepared molecular sieve catalyst shows relatively high catalytic activity and selectivity, high cycle stability and excellent regeneration performance, and can be repeatedly used for a long time.

Description

Technical Field

[0001] The invention belongs to the technical field of synthesizing p-xylene, and specifically relates to an alkali metal modified molecular sieve catalyst with high cycle stability and application of the catalyst in catalyzing the synthesis of p-xylene. Background Art

[0002] Paraxylene (PX) is a very important chemical raw material, and its main use is to produce polymer monomer products such as terephthalic acid (TA) and terephthalate esters. Most of the industrial production of paraxylene depends on petroleum resources, and is produced through reforming, aromatic extraction, disproportionation, isomerization and adsorption separation processes. With the rapid development of my country's economy, the demand for paraxylene has increased year by year. However, my country's petroleum resources are in short supply, and the traditional route of producing paraxylene from petroleum resources faces challenges.

[0003] Biomass is an important carrier for the storage and conversion of solar energy, a renewable organic carbon resource, and has abundant reserves. Furan compounds, as a diene and dienophile, undergo Diels-Alder cycloaddition reaction, which is a common synthetic method for preparing cyclic compounds. Among them, the Diels-Alder cycloaddition reaction of 2,5-DMF derived from biomass with AA, followed by dehydration and decarboxylation is one of the best ways to synthesize PX. The reaction conditions are relatively mild, the operation is simple, the advantages are obvious, and it shows a strong prospect for industrial application.

[0004] This reaction route requires both B acid and L acid sites. Among the commonly used catalysts, Beta molecular sieves have good application prospects due to their ordered and stable skeleton structure, high specific surface area, good shape selectivity, and abundant B and L acid sites. However, Beta molecular sieves are highly acidic. During the reaction, the strong acid sites easily catalyze the hydrolysis of 2,5-DMF and the further polymerization of 2,5-hexanedione, which leads to the catalyst being easily deactivated by carbon deposition, and the catalyst needs to be regenerated frequently. Therefore, it is urgent to develop a molecular sieve catalyst that is resistant to carbon deposition while maintaining high activity and high selectivity for use in the reaction of 2,5-DMF to synthesize PX. Summary of the invention

[0005] In view of the problems of strong acidity, easy carbon deposition and poor stability of molecular sieve catalysts, a method for preparing an alkali metal modified molecular sieve catalyst with high cycle stability is provided. The prepared molecular sieve catalyst exhibits high catalytic activity and selectivity as well as high cycle stability, excellent regeneration performance and can be reused for a long time.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[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 in step (1), 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] Furthermore, the alkali metal is one of sodium, potassium, magnesium and calcium. Furthermore, the alkali metal salt is any one of NaNO3, KNO3, Mg(NO3)2 or Ca(NO3)2. Preferably, the alkali metal is sodium.

[0009] Furthermore, the loading mass of alkali metal oxide in the alkali metal modified Beta molecular sieve catalyst is 0.25% to 10%.

[0010] Furthermore, the molecular sieve is H-Beta. Preferably, the molar ratio of the molecular sieve precursor is: SiO2: 0.025Al2O3: 0.05Na2O: 12-16H2O: 0.3TEAOH.

[0011] Furthermore, calcining in a muffle furnace refers to calcining at 500-600° C. for 2-4 hours.

[0012] Furthermore, the amount of catalyst used is 2.5-3.0% of the total mass of the reactant raw materials.

[0013] Application of alkali metal modified molecular sieve catalyst in catalyzing the reaction of 2,5-dimethylfuran and acrylic acid to synthesize xylene, specifically:

[0014] 2,5-DMF and AA are added to a solvent and mixed to obtain a mixed solution, the mixed solution is transferred to a magnetic stirring kettle, an alkali metal modified molecular sieve is added, and the reaction gas is replaced with high-purity nitrogen. The reaction pressure is normal pressure, the reaction temperature is 160-190°C, and the reaction time is 10-15h. After the reaction is completed, the reactor is placed in an ice water bath to cool and the product paraxylene is collected.

[0015] The dosage of alkali metal modified molecular sieve is:

[0016] As a preferred embodiment, the prepared 1% Na2O / H-Beta molecular sieve is applied to the reaction of synthesizing PX from 2,5-DMF and AA, and a 2,5-DMF conversion rate of 97.7% and a PX selectivity of 99.7% can be obtained under the conditions of a reaction temperature of 190°C, a reaction time of 15h, and an initial reaction pressure of normal pressure.

[0017] After adopting the above technical solution, the beneficial effects achieved by the present invention are:

[0018] After the nano-type Beta molecular sieve is modified by a small amount of alkali metal, the acid strength of the catalyst is reduced, the hydrolysis of 2,5-DMF and the further polymerization reaction of 2,5-hexanedione are effectively inhibited, the formation of catalyst carbon deposits is reduced, and the catalyst stability is improved. In the test of cyclic stability, the activity deactivation rate of the alkali metal modified molecular sieve catalyst is significantly reduced compared with the unmodified molecular sieve. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the XRD diagram of the Beta molecular sieves prepared in Example 1, Example 4, Example 6, Example 7 and Example 8; Figure 1 It can be seen that the diffraction peaks appearing at around 2θ equal to 7.8, 22.5, 25.4, 27.0, 28.8, 29.7 and 43.7 are all attributed to the characteristic diffraction peaks of Beta molecular sieve, indicating that the alkali metal modification does not affect the crystal structure of Beta molecular sieve. DETAILED DESCRIPTION

[0020] The present invention will be further described with reference to the following examples, but it should be understood that these examples are only for illustration and should not be construed as limitations of the present invention.

[0021] In the present invention, an alkali metal-modified Beta molecular sieve is prepared by an impregnation method. Different modified Beta molecular sieves can be obtained by adjusting the amount of different metal precursors added during the preparation process. The specific embodiments are as follows:

[0022] Example 1

[0023] First, sodium hydroxide and sodium aluminate were dissolved in deionized water, and then added to tetraethylammonium hydroxide (TEAOH, 25wt% aqueous solution) solution, stirred evenly, and then hydrophilic silica was slowly added, and stirred in a water bath at 35°C for 5.5h to obtain a precursor, and the molar ratio of the precursor was controlled to be: SiO2: 0.025Al2O3: 0.05Na2O: 12H2O: 0.3TEAOH; the precursor was transferred to the lining of a crystallization reactor with a polytetrafluoroethylene lining, and crystallized in an oven at 150°C for 2 days. The precursor in the hydrothermal reactor was centrifuged, washed, and dried to obtain a white powder without template removal. The obtained white powder was calcined at 550°C in a muffle furnace for 6h, and then subjected to 1.0mol·L -1 The product was ion exchanged with NH4Cl aqueous solution three times, then dried and calcined in a muffle furnace at 550°C for 4 h to obtain H-Beta.

[0024] Example 2

[0025] First, 0.0412 g of NaNO3 was dissolved in 20 g of deionized water, and 6 g of H-Beta molecular sieve was added. The mixture was stirred at room temperature for 1 h, and then evaporated in an oil bath at 70 °C. Subsequently, the mixture was further dried 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 to obtain 0.25% Na2O / H-Beta.

[0026] Example 3

[0027] First, 0.0823 g of NaNO3 was dissolved in 20 g of deionized water, and 6 g of H-Beta molecular sieve was added. The mixture was stirred at room temperature for 1 h, and then evaporated in an oil bath at 70 °C. Subsequently, the mixture was further dried 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 to obtain 0.5% Na2O / H-Beta.

[0028] Example 4

[0029] First, 0.1645 g NaNO3 was dissolved in 20 g deionized water, H-Beta molecular sieve was added, and the mixture was stirred at room temperature for 1 h. Then, the mixture was evaporated in an oil bath at 70°C, and then further dried 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 to obtain 1% Na2O / H-Beta.

[0030] Example 5

[0031] First, dissolve 0.4113g NaNO3 in 20g deionized water, add 6g H-Beta molecular sieve, stir at room temperature for 1h, then evaporate to dryness in a 70℃ oil bath, and then further dry in an oven at 110℃ for 2h. Take the dried solid powder and calcine it at 550℃ in a muffle furnace for 3h to obtain 2.5% Na2O / H-Beta.

[0032] Example 6

[0033] First, dissolve 0.1288g KNO3 in 20g deionized water, add 6g H-Beta molecular sieve, stir at room temperature for 1h, then evaporate to dryness in a 70℃ oil bath, and then further dry in an oven at 110℃ for 2h. Take the dried solid powder and calcine it at 550℃ in a muffle furnace for 3h to obtain 1% K2O / H-Beta.

[0034] Example 7

[0035] First, dissolve 0.2208g Mg(NO3)2 in 20g deionized water, add 6g H-Beta molecular sieve, stir at room temperature for 1h, then evaporate to dryness in a 70℃ oil bath, and then further dry in an oven at 110℃ for 2h. Take the dried solid powder and calcine it at 550℃ in a muffle furnace for 3h to obtain 1% MgO / H-Beta.

[0036] Example 8

[0037] First, dissolve 0.1758g Ca(NO3)2 in 20g deionized water, add 6g H-Beta molecular sieve, stir at room temperature for 1h, then evaporate to dryness in a 70℃ oil bath, and then further dry in an oven at 110℃ for 2h. Take the dried solid powder and calcine it at 550℃ in a muffle furnace for 3h to obtain 1% CaO / H-Beta.

[0038] The catalyst obtained in the above Examples 1 to 8 is applied to the reaction of synthesizing PX from 2,5-DMF and AA, and the specific application is as follows:

[0039] Example 9

[0040] 2,5-DMF and AA were mixed in a molar ratio of 1:2, and the concentration of 2,5-DMF was 0.5 mol·L -1 , AA concentration is 1.0 mol·L -1 , the solvent is n-heptane, the total reaction liquid volume is 30mL, the mixed solution is transferred to a magnetic stirring kettle, H-Beta equivalent to 2.8% (0.1g) of the total mass of the reactants is added, and the gas in the kettle is replaced three times with high-purity nitrogen. The reaction temperature is 190°C, the initial pressure is normal pressure, and the reaction time is 15h; after the reaction is completed, the reactor is placed in an ice water bath to cool. The main products are PX and by-products 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0041] Example 10

[0042] 2,5-DMF and AA were mixed and added into n-heptane. The concentration of 2,5-DMF was 0.5 mol·L -1 , AA concentration is 1.0 mol·L -1 , the total reaction liquid volume is 30mL, the mixed liquid is transferred to a magnetic stirring kettle, 0.25% Na2O / H-Beta equivalent to 2.8% of the total mass of the reactants is added, and the gas in the kettle is replaced three times with high-purity nitrogen. The reaction temperature is 190°C, the initial pressure is normal pressure, and the reaction time is 15h; after the reaction is completed, the reactor is placed in an ice water bath for cooling. The main products are PX and by-products 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0043] Embodiment 11

[0044] Compared with Example 10, the difference is that 0.25% Na2O / H-Beta is replaced by 0.5% Na2O / H-Beta, and the other operations are the same as Example 10.

[0045] Example 12

[0046] Compared with Example 10, the difference is that 0.25% Na2O / H-Beta is replaced by 1% Na2O / H-Beta, and the other operations are the same as Example 10.

[0047] Embodiment 13

[0048] Compared with Example 10, the difference is that 0.25% Na2O / H-Beta is replaced by 2.5% Na2O / H-Beta, and the other operations are the same as Example 10.

[0049] Embodiment 14

[0050] Compared with Example 10, the difference is that 0.25% Na2O / H-Beta is replaced by 1% K2O / H-Beta, and the other operations are the same as Example 10.

[0051] Embodiment 15

[0052] Compared with Example 10, the difference is that 0.25% Na2O / H-Beta is replaced by 1% MgO / H-Beta, and the other operations are the same as Example 10.

[0053] Example 16

[0054] Compared with Example 10, the difference is that 0.25% Na2O / H-Beta is replaced by 1% CaO / H-Beta, and the other operations are the same as Example 10.

[0055] The catalytic activities of the catalysts obtained in Examples 1 to 8 above are compared, as shown in Table 1 below:

[0056] Table 1 Comparison of catalytic activity of catalysts obtained in Examples 1 to 8

[0057] Example catalyst 2,5-DMF conversion rate (%) PX selectivity (%) Example 9 H-Beta 99.0 98.0 Example 10 <![CDATA[0.25%Na2O / H-Beta]]> 98.5 98.4 Embodiment 11 <![CDATA[0.5%Na2O / H-Beta]]> 98.1 98.5 Example 12 <![CDATA[1%Na2O / H-Beta]]> 97.7 99.7 Embodiment 13 <![CDATA[2.5%Na2O / H-Beta]]> 92.6 98.5 Embodiment 14 <![CDATA[1%K2O / H-Beta]]> 97.4 99.2 Embodiment 15 1%MgO / H-Beta 96.3 98.1 Example 16 1%CaO / H-Beta 94.5 97.1

[0058] It can be seen from Table 1 that the catalytic activity of Beta molecular sieve changes after modification. The most effective modified metal precursor is NaNO3. When the Na2O loading is 1%, the catalytic activity is the best; when the Na2O loading is 2.5%, the catalytic activity decreases. This may be due to excessive Na2O loading, resulting in too weak B acid strength on the outer surface of the molecular sieve, and a significant reduction in the overall reaction rate. 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 suppressed, thereby improving PX selectivity.

[0059] Embodiment 17

[0060] The H-Beta catalyst obtained after the reaction in Example 9 was recovered by centrifugation, washed twice with anhydrous ethanol, and dried overnight at 60° C. The molecular sieve obtained by drying was subjected to a cyclic stability test, and the reaction was repeated 4 times in total. The reaction conditions for each cycle were the same as those in Example 9. The results are shown in Table 2.

[0061] Table 2 2,5-DMF conversion and PX selectivity under H-Beta cycle conditions

[0062]

[0063]

[0064] Embodiment 18

[0065] The 1% Na2O / H-Beta catalyst obtained after the reaction in Example 12 was recovered by centrifugation, washed twice with anhydrous ethanol, and dried overnight at 60°C. The molecular sieve obtained by drying was subjected to a cyclic stability test, and the reaction was repeated 4 times in total. The reaction conditions for each cycle were the same as those in Example 12. The results are shown in Table 3.

[0066] Table 3 2,5-DMF conversion and PX selectivity under 1% Na2O / H-Beta circulation conditions

[0067] Cycle times 2,5-DMF conversion rate (%) PX selectivity (%) 1 95.4 98.5 2 92.1 97.1 3 90.5 95.1 4 87.3 92.6

[0068] Embodiment 19

[0069] The 1% K2O / H-Beta catalyst obtained after the reaction in Example 14 was recovered by centrifugation, washed twice with anhydrous ethanol, and dried overnight at 60°C. The 1% K2O / H-Beta molecular sieve catalyst obtained by drying was subjected to a cyclic stability test, and the reaction was repeated 4 times in total. The reaction conditions for each cycle were the same as those in Example 14. The results are shown in Table 4.

[0070] Table 4 2,5-DMF conversion and PX selectivity under 1% K2O / H-Beta cycle conditions

[0071] Cycle times 2,5-DMF conversion rate (%) PX selectivity (%) 1 95.0 98.5 2 92.2 97.0 3 90.7 95.3 4 87.1 93.4

[0072] It can be seen from Tables 3 and 4 that the alkali metal modified Beta molecular sieve prepared by the method of the present invention has excellent cyclic stability. When used in the reaction of synthesizing PX from 2,5-DMF and AA, after four cycles of reaction, the 2,5-DMF conversion rate and PX selectivity of Examples 18 and 19 are significantly better than those of Example 17.

[0073] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An alkali metal modified molecular sieve catalyst with high cycle stability, characterized in that: Dissolving an alkali metal salt in deionized water to obtain an alkali metal salt solution, adding a molecular sieve to the alkali metal salt solution, stirring and mixing, and then drying, and calcining the dried product in a muffle furnace to obtain an alkali metal modified molecular sieve catalyst; Alkali metal is one of sodium, potassium, magnesium and calcium.

2. The alkali metal modified molecular sieve catalyst with high cycle stability according to claim 1, characterized in that: The alkali metal salt is any one of NaNO3, KNO3, Mg(NO3)2 or Ca(NO3)2.

3. The alkali metal modified molecular sieve catalyst with high cycle stability according to claim 1, characterized in that: The loading mass of the alkali metal oxide in the alkali metal modified molecular sieve catalyst is 0.25% to 10% of the molecular sieve mass.

4. The alkali metal modified molecular sieve catalyst with high cycle stability according to claim 3, characterized in that: The loading mass of the alkali metal oxide in the alkali metal modified molecular sieve catalyst is 0.25% to 2.5% of the molecular sieve mass.

5. The alkali metal modified molecular sieve catalyst with high cycle stability according to claim 1, characterized in that: The molecular sieve is H-Beta molecular sieve.

6. The alkali metal modified molecular sieve catalyst with high cycle stability according to claim 1, characterized in that: Calcination in a muffle furnace is at 500-600°C for 2-4 hours.

7. The alkali metal modified molecular sieve catalyst with high cycle stability according to claim 1, characterized in that: The alkali metal modified molecular sieve catalyst is 1% Na2O / H-Beta; 1% refers to the mass percentage of Na2O in H-Beta.

8. Use of the alkali metal modified molecular sieve catalyst with high cycle stability according to any one of claims 1 to 7, characterized in that: Application of alkali metal modified molecular sieve catalyst in catalyzing the reaction of 2,5-dimethylfuran and acrylic acid to synthesize xylene.

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