Method for synthesizing 2,5-dimethyl-2,4-hexadiene by using isobutyraldehyde catalyzed by phosphoric acid-modified Zn / HZSM-5

Abstract

The present invention relates to the field of catalyst technology, and in particular to a method for synthesizing 2,5-dimethyl-2,4-hexadiene from isobutyraldehyde catalyzed by phosphoric acid-modified Zn / HZSM-5, with isobutylene (IB) / isobutyraldehyde (IBA) as reactants, and a Prince condensation reaction is carried out under the conditions of a phosphoric acid-modified Zn-loaded HZSM-5 molecular sieve catalyst to obtain the obtained product. The invention has the advantages that the process is simple, the energy consumption is low, the safety is high, the cost is low, the pollution is small, and large-scale production is possible; the prepared product 2,5-dimethyl-2,4-hexadiene content can reach 60%, which meets the requirements of industrial products; the reaction specificity is strong, there are no other by-products except water, the catalyst is easy to separate, can be reused, and is environmentally friendly and energy-saving.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a method for synthesizing 2,5-dimethyl-2,4-hexadiene by catalyzing isobutyraldehyde with phosphoric acid-modified Zn / HZSM-5. Background Art

[0002] 2,5-dimethyl-2,4-hexadiene is an important chemical raw material, an important intermediate for the synthesis of chrysanthemum esters, and also an important organic intermediate for the preparation of pesticides, medicines and various organic syntheses. There are many methods for preparing 2,5-dimethyl-2,4-hexadiene in the prior art, such as the one-step synthesis of 2,5-dimethyl-2,4-hexadiene reaction catalyst and application disclosed in the Chinese patent document (application number CN96115489.6), in which the dehydration and isomerization reactions of 2,5-dimethyl-2,5-hexanediol are carried out simultaneously under the action of alkali-treated zeolite molecular sieve or zeolite molecular sieve catalyst with appropriate amount of Fe and Cu added, so as to prepare 2,5-dimethyl-2,4-hexadiene in one step. Using the above-mentioned catalytic system, the reaction is carried out under normal pressure and 180-250°C. Although a higher selectivity can be obtained, the main production method of 2,5-dimethyl-2,5-hexanediol is currently to generate it by using the acetylene acetone method, and then 2,5-dimethyl-2,5-hexanediol is dehydrated and isomerized to generate 2,5-dimethyl-2,4-hexadiene. However, this process is complicated, has many by-products, is highly corrosive to equipment, and pollutes the environment. This experiment uses a reaction system with isobutylene and isobutyraldehyde as raw materials. The system has a simple process, is non-corrosive to equipment, and has little environmental pollution, and is increasingly receiving attention.

[0003] Another example is a process for synthesizing 2,5-dimethyl-2,4-hexadiene disclosed in a Chinese patent document (application number CN95112007.7), where the isobutylene / isobutyraldehyde (weight ratio) is 1:6, the reaction temperature is 200-350°C, the pressure is 0.5-5Mpa, and a variety of Fe, Al and Cu inorganic salts, solid acids such as Al2O3, ZrO2 and TiO2, or zeolite molecular sieves are added as additives. The system process is simple, but nitrogen or inert gas needs to be flushed in during the implementation process to stabilize the pressure, and the yield of 2,5-dimethyl-2,4-hexadiene is not particularly high. It is increasingly valued by people. At present, the reaction is mainly based on niobic acid as the main catalyst, but the catalyst needs to be carried out under high pressure, and the catalyst is easily deactivated by carbon deposition at high temperature and cannot be regenerated. Due to the rapid development of agriculture in my country and the continuous increase in the use of pesticides, it is more conducive to industrial application to find a catalyst with a higher yield and good anti-carbon deposition performance. Summary of the invention

[0004] In view of the shortcomings and disadvantages of the prior art, the present invention provides a method for synthesizing 2,5-dimethyl-2,4-hexadiene from isobutylaldehyde catalyzed by phosphoric acid-modified Zn / HZSM-5, which has the characteristics of low raw material price (especially phosphoric acid-modified Zn / HZSM-5 molecular sieve), high conversion rate, and good economic and industrial value. The phosphoric acid-modified Zn / HZSM-5 molecular sieve acts on the HZSM-5 molecular sieve through the synergistic effect between P-Zn, coordinating Lewis and The acid site ratio is more favorable for the preparation of 2,5-dimethyl-2,4-hexadiene by the Prince condensation reaction.

[0005] In order to achieve the purpose of the present invention, the technical scheme adopted is: a method for synthesizing 2,5-dimethyl-2,4-hexadiene by catalyzing isobutyraldehyde with phosphoric acid-modified Zn / HZSM-5, comprising the following steps:

[0006] In a fixed bed reactor, isobutylene and isobutylaldehyde are used as raw materials, and phosphoric acid-modified Zn / HZSM-5 molecular sieve is used to catalyze the Prince reaction to synthesize 2,5-dimethyl-2,4-hexadiene. The reaction temperature is 240-350°C and the reaction pressure is atmospheric pressure.

[0007] The ratio of isobutylene to isobutyraldehyde is 4:1-2:1, and the mass ratio of phosphoric acid-modified Zn / HZSM-5 molecular sieve catalyst to isobutyraldehyde is 1:1-1:30.

[0008] The phosphoric acid-modified Zn / HZSM-5 molecular sieve is prepared by the following method: Zn is loaded on the HZSM-5 molecular sieve, and then the phosphoric acid solution is loaded on the Zn-loaded HZSM-5 molecular sieve by an equal volume impregnation method, and the impurities are removed by drying and calcining to obtain the phosphoric acid-modified Zn / HZSM-5 molecular sieve, wherein the applicable range of the Si / Al molar ratio in the HZSM-5 molecular sieve is 30-50, and the applicable range of the mass concentration of the phosphoric acid solution is 0.01-0.1 mol / L.

[0009] The catalyst carrier HZSM-5 is an effective heterogeneous catalyst. HZSM-5 has strong acidity. The acid site is the active site of the condensation reaction of isobutylene and isobutyraldehyde. The Prins condensation reaction tends to be a medium-strong acid center. The synergistic effect between P and Zn can effectively regulate the acid site. When phosphoric acid modifies the HZSM-5 catalyst, the octahedral coordinated aluminum interacts with phosphate to form aluminum phosphate. However, after the introduction of P, the tetrahedral framework of aluminum species in the HZSM-5 framework is detached. The introduction of P content enhances the distribution of Zn species and also reduces acid sites and generate more Zn-Lewis acid sites.

[0010] Furthermore, the specific preparation method steps of HZSM-5 molecular sieve are as follows:

[0011] (1) Add H2SO4 dropwise to Na2SiO3·9H2O, NaAlO2 and tetrapropylammonium bromide (C 12 H 28 BrN) solution to make solution A; n(Na2SiO3·9H2O): n(NaAlO2): n(C 12 H 28 BrN)=300:1:60~600:1:60.

[0012] (2) Stirring the solution A in step (1) to form a gel, crystallizing and calcining to obtain Na-ZSM-5; the crystallization conditions are crystallization in an autoclave at 100-250° C. for 2-3 days. The calcination conditions are calcining in air at 100-250° C. for 5-10 hours.

[0013] (3) Repeating ion exchange of the sample in step (2) with NH4NO3 solution to obtain NH4ZSM-5, and calcining to obtain molecular sieve HZSM-5; the calcination conditions are calcining at 450-600°C in air for 2-5h.

[0014] Furthermore, the method of loading Zn on HZSM-5 is as follows: HZSM-5 molecular sieve is dispersed in a zinc fluorosilicate solution, filtered, dried, and calcined to obtain Zn / HZSM-5; the drying conditions are drying at 100-300°C for 8-10 hours, the calcination conditions are calcining at 450-600°C for 2-5 hours, and the concentration range of the zinc fluorosilicate solution is 0.01-0.05 mol / L.

[0015] Furthermore, ultrasonic vibration is used for 2 hours during the process of impregnating phosphoric acid with equal volume; and / or the drying condition is drying at 70-180° C. in a vacuum drying oven for 8-10 hours; and / or the calcination condition is calcining in a vacuum at 450-600° C. for 2-5 hours.

[0016] (4) The Zn / HZSM-5 molecular sieve modified by H3PO4 is denoted as xP-Zn / HZSM-5 (x is the concentration of H3PO4 solution).

[0017] Beneficial effects:

[0018] (1) The catalyst carrier HZSM-5 is highly acidic, has a unique pore structure and controllable acidity. Molecular sieve catalysts have a large specific surface area, strong reaction specificity, are easy to separate, and can be reused. HZSM-5 molecular sieves exhibit higher activity and shape selection effects than other molecular sieve catalysts.

[0019] (2) HZSM-5 has strong acidity, which may cause coking. The introduction of P and Zn can significantly reduce the acidity of HZSM-5 and improve its Acid ratio. Phosphorus can further expand the pore size of zeolite, reduce the formation of coke, and have better durability in long-term operation. The Prins condensation reaction tends to be of medium-strong acid centers. After phosphoric acid modification, the molecular sieve crystal particles maintain good integrity, the medium-strength acid site acid content is the highest, and the catalytic activity is high. Zn effectively improves the activity of HZSM-5, and the synergistic modification of Zn and P makes HZSM-5 more resistant to coke. The synergistic effect of zinc and phosphorus is of great significance for the development of highly selective and stable methanol to aromatics catalysts.

[0020] (3) The catalyst of the present invention has no requirements on equipment and does not require a strong acid or strong base environment. Separation is very simple and is more conducive to chemical production. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with embodiments, but is not limited thereto.

[0022] Example 1

[0023] Preparation of catalyst: First, weigh 32g Na2SiO3·9H2O, 0.016g NaAlO2 and 3.4g tetrapropylammonium bromide into a beaker, and slowly add H2SO4 aqueous solution. Stir at room temperature for 6h to form a gel, transfer to an autoclave and crystallize at 180℃ for 2 days. The obtained sample was calcined in air at 180℃ for 6h to remove the organic template. Na-ZSM-5 was repeatedly ion-exchanged with 5wt% NH4NO3 solution to activate the sample to obtain its ammonium NH4ZSM-5, and then calcined at 550℃ for 3h to obtain HZSM-5 catalyst. Take 10g HZSM-5 and disperse it in 150ml solution with a concentration of 0.05mol / L zinc fluorosilicate (ZnSiF6·6H2O), then mix at 90℃ for 12h, filter, wash, dry at 100℃ for 10h, and finally calcine at 550℃ for 5h to obtain Zn / HZSM-5. Zn / HZSM-5 was impregnated with 2wt% H3PO4 solution in equal volumes, and then ultrasonically vibrated for 2h. The obtained catalyst was dried in a vacuum oven at 70°C for 12h and calcined at 550°C for 5h. It is recorded as 3P-Zn / HZSM-5.

[0024] Weigh 0.5 g of the catalyst, 4 g of isobutylaldehyde, and supply gaseous isobutylene at a constant flow rate of 10 ml / min in a fixed-bed reactor at atmospheric pressure with a space velocity of 3 h -1 The reaction temperature was raised from room temperature to 260°C at a rate of 5°C / min, and the reaction product was taken out for analysis by gas chromatography after 2 hours of reaction.

[0025] Example 2

[0026] 3wt% H3PO4 is used to replace 2wt% H3PO4 in Example 1, and the other steps are the same as Example 1.

[0027] Example 3

[0028] 1 wt % H 3 PO 4 is used to replace 2 wt % H 3 PO 4 in Example 1, and the other steps are the same as Example 1.

[0029] Example 4

[0030] The catalyst was dried in a vacuum oven at 70°C for 12 h and calcined at 550°C for 5 h after ultrasonic oscillation for 2 h. This was replaced by drying in a vacuum oven at 70°C for 12 h and calcining at 550°C for 3 h. The other steps were the same as in Example 1.

[0031] Example 5

[0032] The airspeed is 3h -1 The reaction temperature was increased from room temperature to 260°C at a rate of 5°C / min and the space velocity was 5h -1 , the reaction temperature was raised from room temperature to 260°C at a rate of 5°C / min, and the other steps were the same as in Example 1.

[0033] Comparative Example 1 (Compared with Example 1, the difference is that the calcination temperature of 550°C in the Zn loading step is replaced by 400°C)

[0034] Take 10g HZSM-5 and disperse it in 150ml solution with a concentration of 0.05mol / L zinc fluorosilicate (ZnSiF6·6H2O), then mix it at 90℃ for 12h, filter, wash, dry at 100℃ for 10h, and finally calcine at 550℃ for 5h to obtain Zn / HZSM-5. Zn / HZSM-5 is impregnated with an equal volume of 2wt% H3PO4 solution, and the obtained catalyst is dried at 70℃ for 12h in a vacuum drying oven and calcined at 400℃ for 5h. It is recorded as 2P-Zn / HZSM-5.

[0035] The other steps are the same as in Example 1.

[0036] Comparative Example 2 (Compared with Example 1, the difference is that the phosphoric acid concentration is adjusted to 4 wt%)

[0037] Take 10g HZSM-5 and disperse it in 150ml solution with a concentration of 0.05mol / L zinc fluorosilicate (ZnSiF6·6H2O), then mix it at 90℃ for 12h, filter, wash, dry at 100℃ for 10h, and finally calcine at 550℃ for 5h to obtain Zn / HZSM-5. Zn / HZSM-5 is impregnated with an equal volume of 4wt% H3PO4 solution, and the obtained catalyst is dried at 70℃ for 12h in a vacuum drying oven and calcined at 550℃ for 5h. It is recorded as 4P-Zn / HZSM-5.

[0038] The other steps are the same as in Example 1.

[0039] Comparative Example 3 (Compared with Example 1, the difference is that the calcination time in the Zn loading step is replaced by 3 hours from 5 hours)

[0040] Take 10g HZSM-5 and disperse it in 150ml solution with a concentration of 0.05mol / L zinc fluorosilicate (ZnSiF6·6H2O), then mix it at 90℃ for 12h, filter and wash it, dry it at 100℃ for 10h, and finally calcine it at 550℃ for 3h to obtain Zn / HZSM-5.

[0041] The other steps are the same as in Example 1.

[0042] Comparative Example 4

[0043] Weigh 0.7 g of the catalyst, 4 g of isobutylaldehyde, and supply gaseous isobutylene at a constant flow rate of 10 ml / min in a fixed-bed reactor at atmospheric pressure with a space velocity of 3 h -1 The reaction temperature was raised from room temperature to 260°C at a rate of 5°C / min. After reacting at 260°C for 2 hours, the reaction product was taken out and analyzed by gas chromatography.

[0044] The other steps are the same as in Example 1.

[0045] Comparative Example 5 (Compared with Example 1, no phosphoric acid modification was performed)

[0046] Preparation of catalyst: First, weigh 32g Na2SiO3·9H2O, 0.016g NaAlO2 and 3.4g tetrapropylammonium bromide into a beaker, and slowly add H2SO4 aqueous solution. Stir at room temperature for 6h to form a gel, transfer to an autoclave and crystallize at 180℃ for 2 days. The obtained sample was calcined in air at 180℃ for 6h to remove the organic template. Na-ZSM-5 was repeatedly ion-exchanged with 5wt% NH4NO3 solution to activate the sample to obtain its ammonium NH4ZSM-5, and then calcined at 550℃ for 3h to obtain HZSM-5 catalyst. Take 10g HZSM-5 and disperse it in 150ml solution with a concentration of 0.05mol / L zinc fluorosilicate (ZnSiF6·6H2O), then mix at 90℃ for 12h, filter, wash, dry at 100℃ for 10h, and finally calcine at 550℃ for 5h to obtain Zn / HZSM-5.

[0047] Weigh 0.5g Zn / HZSM-5, 4g isobutylaldehyde, and supply gaseous isobutylene at a constant flow rate of 10ml / min in a fixed-bed reactor at atmospheric pressure with a space velocity of 3h -1 , the reaction temperature was raised from room temperature to 260°C at a rate of 5°C / min, and finally the reaction product was taken out and analyzed by gas chromatography.

[0048] Comparative Example 6 (Compared with Example 1, no Zn loading was performed)

[0049] Preparation of catalyst: First, weigh 32g Na2SiO3·9H2O, 0.016g NaAlO2 and 3.4g tetrapropylammonium bromide into a beaker, and slowly add H2SO4 aqueous solution. Stir at room temperature for 6h to form a gel, transfer to an autoclave and crystallize at 180℃ for 2 days. The obtained sample was calcined in air at 180℃ for 6h to remove the organic template. Na-ZSM-5 was repeatedly ion-exchanged with 5wt% NH4NO3 solution to activate the sample to obtain its ammonium NH4ZSM-5, which was then calcined at 550℃ for 3h to obtain HZSM-5 catalyst. HZSM-5 was impregnated with an equal volume of 3wt% H3PO4 solution, and then ultrasonically oscillated for 2h. The obtained catalyst was dried at 70℃ for 12h in a vacuum drying oven and calcined at 550℃ for 5h. It was recorded as 3P / HZSM-5.

[0050] Weigh 0.5g P / HZSM-5, 4g isobutylaldehyde, and supply gaseous isobutylene at a constant flow rate of 10ml / min in a fixed-bed reactor at atmospheric pressure with a space velocity of 3h -1 , the reaction temperature was raised from room temperature to 260°C at a rate of 5°C / min, and finally the reaction product was taken out and analyzed by gas chromatography.

[0051] Table 1 Comparison of product performance under different process conditions in the embodiments and comparative examples

[0052]

[0053]

[0054] Table 1 shows that the phosphoric acid-modified Zn-loaded HZSM-5 molecular sieve catalyst of the method has a high reaction activity for the hydrodeoxygenation performance of the raw materials, the solid product is easy to separate when the catalyst is used, and it does not corrode the equipment. It is an environmentally friendly green catalyst.

[0055] It should be understood that those skilled in the art can make improvements and changes based on the above description, and these improvements and changes should all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for synthesizing 2,5-dimethyl-2,4-hexadiene by catalyzing isobutyraldehyde with phosphoric acid-modified Zn / HZSM-5, characterized in that: The steps include: In a fixed bed reactor, isobutylene and isobutylaldehyde are used as raw materials, and phosphoric acid-modified Zn / HZSM-5 molecular sieve is used to catalyze the Prins reaction to synthesize 2,5-dimethyl-2,4-hexadiene. The reaction temperature is 240~350℃ and the reaction pressure is atmospheric pressure. The ratio of isobutylene to isobutyraldehyde is 4:1~2:1, and the mass ratio of phosphoric acid-modified Zn / HZSM-5 molecular sieve catalyst to isobutyraldehyde is 1:8; The phosphoric acid-modified Zn / HZSM-5 molecular sieve is prepared by the following method: Zn is loaded on the HZSM-5 molecular sieve, and then the phosphoric acid solution is used for equal volume impregnation method to load the phosphoric acid on the Zn-loaded HZSM-5 molecular sieve, and the impurities are removed by drying and calcining to obtain the phosphoric acid-modified Zn / HZSM-5 molecular sieve, the applicable range of Si / Al molar ratio in the HZSM-5 molecular sieve is 30-50, and the applicable range of mass concentration of the phosphoric acid solution is 1wt%, 2wt% or 3wt%; The calcination conditions were calcination at 550°C for 5 h.

2. The method for synthesizing 2,5-dimethyl-2,4-hexadiene by using isobutyraldehyde catalyzed by phosphoric acid-modified Zn / HZSM-5 according to claim 1, characterized in that: The preparation method of HZSM-5 molecular sieve comprises the following steps: (1) Add H2SO4 dropwise to Na2SiO3·9H2O, NaAlO2 and tetrapropylammonium bromide C 12 H 28 BrN solution, make solution A; n (Na2SiO3 · 9H2O): n (NaAlO2): n (C 12 H 28 BrN)=300:1:60~600:1:60; (2) stirring the solution A in step (1) to form a gel, crystallizing and calcining to obtain Na-ZSM-5; The crystallization conditions are crystallization at 100-250°C in an autoclave for 2-3 days, and the calcination conditions are calcination in air at 100-250°C for 5-10 hours; (3) Repeatedly ion exchange the sample in step (2) with NH4NO3 solution to obtain NH4ZSM-5, and calcining to obtain molecular sieve HZSM-5; the calcination conditions are calcining at 450-600°C in air for 2-5h.

3. The method for synthesizing 2,5-dimethyl-2,4-hexadiene by using isobutyraldehyde catalyzed by phosphoric acid-modified Zn / HZSM-5 according to claim 1, characterized in that: The method for loading Zn on HZSM-5 is as follows: HZSM-5 molecular sieve is dispersed in a zinc fluorosilicate solution, and Zn / HZSM-5 is obtained by filtering, drying, and calcining; the drying conditions are drying at 100-300°C for 8-10 hours, and the concentration range of the zinc fluorosilicate solution is 0.01-0.05 mol / L.

4. The method for synthesizing 2,5-dimethyl-2,4-hexadiene by using isobutyraldehyde catalyzed by phosphoric acid-modified Zn / HZSM-5 according to claim 1, characterized in that: During the process of impregnating equal volume of phosphoric acid, ultrasonic vibration is used for 2 hours; and or, the drying condition is drying at 70-180° C. in a vacuum drying oven for 8-10 hours.

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