CN111847477A - A kind of preparation method and application of HZSM-5/HMS composite molecular sieve - Google Patents

Abstract

The invention discloses a method for synthesizing an HZSM-5/HMS composite molecular sieve and application thereof, wherein the method comprises the following steps: step S1: mixing dodecylamine, absolute ethyl alcohol and water to obtain mixed feed liquid A; step S2: dropping a mixed solution of a silicon source and absolute ethyl alcohol into the mixed feed liquid A and violently stirring to obtain a mixed feed liquid B; step S3: after the dropwise addition is finished, adding an HZSM-5 molecular sieve into the mixed material liquid B, and then stirring and crystallizing to obtain a glue liquid C; step S4: and standing and aging the obtained glue solution C at normal temperature, centrifugally washing until the pH is neutral, drying and roasting to obtain the glue solution C. Compared with the traditional molecular sieve, the composite molecular sieve HZSM-5/HMS not only has the acid catalysis and shape-selective effects of HZSM-5, but also has larger specific surface area, higher hydrothermal stability and superior mass transfer diffusion characteristics of HMS, and has a promoting effect on the oxidation reaction of alcohol compared with a single molecular sieve catalyst.

Description

A kind of preparation method and application of HZSM-5/HMS composite molecular sieve

technical field

The invention relates to the field of alcohol oxidation, in particular to a preparation method and application of a HZSM-5/HMS composite molecular sieve.

Background technique

HZSM-5 is a commonly used mesoporous zeolite molecular sieve. Due to its unique pore structure and active centers, it has good hydrothermal properties and shape selection, and has a wide range of applications in adsorption, catalysis and other fields. The presence of Al element in the 5 structure can provide a certain acidity, so it is conducive to the catalytic oxidation reaction. Hexagonal mesoporous molecular sieve HMS is a three-dimensional cross-arranged wormhole structure, which has the excellent characteristics of large specific surface area, thick pore wall, high thermal stability and excellent diffusion performance. Diffusion into the molecular sieve channels.

However, the small pore size of HZSM-5 limits the diffusion of reactants and product molecules, and it is easy to deposit carbon during the reaction process, which will not only cause catalyst deactivation and catalytic performance decline, but also lead to catalyst acidity, specific surface area, pore volume, The active sites, etc. are significantly reduced, and the catalyst life cycle is greatly shortened. As a pure silicon molecular sieve, HMS is not ideal for alcohol oxidation due to its low acidity. Therefore, there is an urgent need for a composite molecular sieve that can not only maintain the excellent surface acidity distribution and shape selection of HZSM-5, but also possess the large specific surface area, high hydrothermal stability and mass transfer and diffusion characteristics of HMS.

SUMMARY OF THE INVENTION

In view of the defects and deficiencies in the prior art, the present invention provides a preparation method of HZSM-5/HMS composite molecular sieve, and the preparation method comprises:

Step S1: mixing dodecylamine, dehydrated alcohol and water to obtain mixed feed solution A;

Step S2: adding the mixture of silicon source and absolute ethanol dropwise to the mixed material liquid A and vigorously stirring to obtain the mixed material liquid B;

Step S3: after the dropwise addition is completed, add HZSM-5 molecular sieve to the mixed material liquid B, stir and crystallize to obtain a glue liquid C;

Step S4: the obtained glue solution C is obtained by standing at room temperature for aging, centrifugal washing to neutral pH, drying and roasting.

The present invention also has the following technical features:

Optionally, the molar ratio of dodecylamine, anhydrous ethanol and water in the mixed material liquid A is 1:(0.13-0.15):(12.7-12.9).

Optionally, the silicon source is a silicate or a silane compound.

Optionally, in step S2, the mixture of silicon source and absolute ethanol is added dropwise to the mixed material liquid A and vigorously stirred to obtain the mixed material liquid B, which specifically includes: the dropping rate is 0.6 mL/min, and the stirring time is 20~ 60min.

Optionally, the temperature of the stirring crystallization in step S3 is controlled to be 40-50° C., and the stirring time is controlled to be 4-5 h.

Optionally, in the step S4, the standing time is 6-18h, the drying temperature is 60-100°C, the drying time is 8-9h, the roasting temperature is 600-700°C, and the roasting time is 5-7h.

The invention also discloses a HZSM-5/HMS composite molecular sieve obtained according to the above preparation method.

The invention also discloses an application of the above-mentioned HZSM-5/HMS composite molecular sieve for the oxidation of isooctanol.

Specifically, in the oxidation process of isooctanol, the HZSM-5/HMS composite molecular sieve is used as a catalyst and the dosage is 0.3-0.7g, the dosage of isooctanol is 10-20ml, the reaction time is 6-12h, and the iso-octanol is 6-12h. The ratio of octanol volume flow to oxygen volume flow rate was 3/5mL/(mL/min).

Compared with the prior art, the present invention has the following beneficial technical effects:

(1) the present invention adopts the roasting treatment, on the one hand, the template agent of the composite molecular sieve can be removed, and on the other hand, the interaction between the molecular sieve and the metal can be enhanced, so as to avoid the template agent from the molecular sieve carrier and enter the reactant in the reaction process, affecting the catalyst. stability.

(2) The method of the present invention adopts dimethylamine as a template agent to directly synthesize HZSM-5/HMS composite molecular sieve products, the preparation process is easy to control, the raw materials are cheap, suitable for large-scale industrial production, and has high industrial utilization value.

(3) The HZSM-5/HMS composite molecular sieve prepared by the present invention is used for the oxidation catalysis process of isooctanol, and has the advantages of high efficiency, environmental protection and high selectivity.

The specific content of the present invention will be further explained in detail below in conjunction with the embodiments.

Description of drawings

Fig. 1 is the XRD pattern of the HZSM-5/HMS composite molecular sieve synthesized by the embodiment of the present invention 2;

Fig. 2 is the NH3-TPD spectrum of the molecular sieves synthesized by Examples 1-3 and Comparative Examples 1-2 of the present invention;

3 is the FT-IR spectrum of the molecular sieves synthesized in Examples 4-6 and Comparative Examples 1-2 of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deductions or substitutions can be made, which should be regarded as belonging to the protection scope of the present invention.

In the specific embodiment of the present invention, the IRAffinity～1S WL infrared spectrometer of Shimadzu Corporation of Japan is used for characterization; the scanning analysis is performed by SmartLab SE type XRD instrument produced by Rigaku Corporation of Japan; NOVA 2200e automatic specific surface analyzer was used for determination and analysis; the product was quantitatively analyzed by GC900A chromatograph produced by Shanghai Kechuang Company, and the acid site on the surface of the material was analyzed by using TP of Tianjin Xianquan Industry and Trade Development Co., Ltd. ～5080 type ammonia gas TPD analyzer was used for detection and analysis. HZSM-5 was purchased from the catalyst factory of Nankai University.

Example 1

A preparation method of HZSM-5/HMS composite molecular sieve, comprising:

(1) 15ml of absolute ethanol and 25ml of distilled water were fully mixed, and then 1.7265g of dodecylamine was added to obtain mixed material liquid A; wherein dodecylamine was used as a template agent.

(2) adding the mixed solution consisting of 8ml tetraethyl silicate and 5ml absolute ethanol dropwise to the mixed solution A at a speed of 0.6mL/min and vigorously stirring for 20～60min to obtain the mixed solution B;

(3) After the dropwise addition, add 0.07477g SiO ₂ /Al ₂ O ₃ to the mixed feed liquid B with HZSM-5 molecular sieve of 52, control the temperature to be 45° C., and perform stirring and crystallization with magnetic stirring for 4h to obtain glue liquid C. ;

(4) The obtained glue solution C was left standing for 12 hours at room temperature, washed by centrifugation for 6 times until the pH was 6-8, dried at 80 °C for 8 hours, and then roasted at 600 °C for 6 hours in a muffle furnace to remove the template agent to obtain HZSM-5/HMS composite molecular sieve.

Performance analysis experiment:

The prepared HZSM-5/HMS composite molecular sieve was subjected to BET specific surface area analysis, and the results showed that the prepared HZSM-5/HMS composite molecular sieve had a specific surface area of 895 m ² /g.

Add 0.5～1.0g of the prepared HZSM-5/HMS composite molecular sieve and 15～30ml isooctanol into a 100ml three-necked flask respectively, connect the three-necked flask to a 300mm serpentine condenser, set the reaction pressure to normal pressure, and heat in an oil bath. When the temperature of the reactant was 120 °C, the temperature was kept constant, high-purity oxygen was introduced at a rate of 25 mL/min, the reaction was continued for 8 h, and then the oxygen was cut off and heating was stopped. The catalyst was removed from the obtained product through a syringe filter, and the supernatant was taken with a micro-injector and added to chromatography for component detection. Wherein isooctanol is a reactant, and isooctanoic acid is a product, the selectivity of isooctanoic acid is calculated according to the following formula (1), and the value with the highest selectivity in the whole reaction process is taken as the selectivity of isooctanoic acid in this embodiment. The results showed that the conversion rate of isooctanol was 18.5%, and the selectivity of isooctanoic acid was 33.9%.

Selectivity %=content of target product isooctanoic acid/content of converted isooctanol×100% Formula (1)

Example 2

This example provides a HZSM-5/HMS composite molecular sieve. The difference from Example 1 is that in this example, the amount of HZSM-5 with SiO ₂ /Al ₂ O ₃ of 52 is 0.2243 g, and other preparation steps The dosage of the medicine is the same as that of Example 1.

Performance analysis experiment:

The BET specific surface area analysis of the prepared HZSM-5/HMS composite molecular sieve showed that the prepared HZSM-5/HMS composite molecular sieve had a specific surface area of 882 m ² /g. The HZSM-5/HMS composite molecular sieve was used for isooctanol oxidation to prepare isooctanoic acid. The results showed that the conversion rate of isooctanol was 26%, and the selectivity of isooctanoic acid was 39%.

Example 3

This example provides a HZSM-5/HMS composite molecular sieve. The difference from Example 1 is that in this example, the amount of HZSM-5 with SiO ₂ /Al ₂ O ₃ of 52 is 0.3738 g, and other preparation steps The dosage of the medicine is the same as that of Example 1.

Performance analysis experiment:

The BET specific surface area analysis of the prepared HZSM-5/HMS composite molecular sieve shows that the prepared HZSM-5/HMS composite molecular sieve has a specific surface area of 831 m ² /g. The HZSM-5/HMS composite molecular sieve was used to oxidize isooctanol to prepare isooctanoic acid. The results showed that the conversion rate of isooctanol was 17.3%, and the selectivity of isooctanoic acid was 32%.

Example 4

This example provides a HZSM-5/HMS composite molecular sieve. The difference from Example 1 is that HZSM-5 with SiO ₂ /Al ₂ O ₃ of 27 is used in this example and the addition amount is 0.2 g. Other preparations The steps and the dosage of the medicine are the same as in Example 1.

Performance analysis experiment:

The BET specific surface area analysis of the prepared HZSM-5/HMS composite molecular sieve shows that the prepared HZSM-5/HMS composite molecular sieve has a specific surface area of 840 m ² /g. The HZSM-5/HMS composite molecular sieve was used to oxidize isooctanol to prepare isooctanoic acid. The results showed that the conversion rate of isooctanol was 15.3%, and the selectivity of isooctanoic acid was 32.3%.

Example 5

This example provides a HZSM-5/HMS composite molecular sieve. The difference from Example 1 is that in this example, the amount of HZSM-5 with SiO ₂ /Al ₂ O ₃ of 52 is 0.2 g, and other preparations The steps and the dosage of the medicine are the same as in Example 1.

Performance analysis experiment:

The BET specific surface area analysis of the prepared HZSM-5/HMS composite molecular sieve shows that the prepared HZSM-5/HMS composite molecular sieve has a specific surface area of 865 m ² /g. The HZSM-5/HMS composite molecular sieve was used for isooctanol oxidation to prepare isooctanoic acid. The results showed that the conversion rate of isooctanol was 24.3%, and the selectivity of isooctanoic acid was 35.6%.

Example 6

This example provides a HZSM-5/HMS composite molecular sieve. The difference from Example 1 is that in this example, the amount of HZSM-5 with SiO ₂ /Al ₂ O ₃ of 85 is 0.2 g, and other preparations The steps and the dosage of the medicine are the same as in Example 1.

Performance analysis experiment:

The BET specific surface area analysis of the prepared HZSM-5/HMS composite molecular sieve shows that the prepared HZSM-5/HMS composite molecular sieve has a specific surface area of 879 m ² /g. The HZSM-5/HMS composite molecular sieve was used for isooctanol oxidation to prepare isooctanoic acid. The results showed that the conversion rate of isooctanol was 10.2%, and the selectivity of isooctanoic acid was 31.7%.

Comparative Example 1

This comparative example provides a kind of HMS molecular sieve. In this comparative example, HZSM-5 is not added, and other preparation steps and drug dosage are the same as those of Example 1.

Performance analysis experiment:

The BET specific surface area analysis of the prepared HMS molecular sieve showed that the specific surface area of the prepared HMS molecular sieve was 900 m ² /g. The HMS molecular sieve was used to prepare isooctanoic acid by oxidation of isooctanol. The results showed that the conversion rate of isooctanol was 2.3%, and the selectivity of isooctanoic acid was 31.3%.

Comparative Example 2

In this comparative example, a directly purchased HMS molecular sieve was used, and the BET specific surface area analysis of the HZSM-5 molecular sieve was carried out. The results showed that the specific surface area of the obtained HZSM-5 molecular sieve was 215 m ² /g.

Performance analysis experiment:

The HZSM-5 molecular sieve was used for isooctanol oxidation to prepare isooctanoic acid, the conversion rate of isooctanol was 5.5%, and the selectivity of isooctanoic acid was 16.3%.

Analysis of results:

According to the above performance test results, it can be determined that the HZSM-5/HMS composite molecular sieve of the present invention takes 0.5-1.0 g of isooctanol, adds 15-30 ml isooctanol, introduces oxygen into the reactant, and reacts at 120 ° C for 8 hours. Caprylic acid has high selectivity, that is, the HZSM-5/HMS composite molecular sieve of the present invention can effectively improve the selectivity of isooctanol compared with the traditional zeolite catalyst when the corresponding amount is added.

The HZSM-5/HMS composite molecular sieve prepared by the experimental example 2 of the present invention takes 0.5g and adds 15ml isooctanol, and oxygen is introduced into the reactant. When the reaction is carried out at 120 ° C for 8h, the isooctanol has the highest conversion rate, and the iso-octanol has the highest conversion rate. Caprylic acid has the highest selectivity. That is, when a certain amount of the HZSM-5/HMS composite molecular sieve of the present invention is added in the isooctanol oxidation reaction, the selectivity of the product isooctanoic acid can be significantly improved compared with the traditional zeolite catalyst.

Figure 2 shows the NH3-TPD curves of Examples 1 to 3 and Comparative Examples 1 to 2. It can be seen from Figure 2 that Examples 1 to 3 exist in the range of 150°C to 300°C and 300°C to 500°C. Weak and strong acid centers. The acid centers of the HZSM-5/HMS composite molecular sieves prepared in Examples 1 to 3 are all larger than those of the HMS prepared in Comparative Example 1, but smaller than the HZSM-5(52) molecular sieve prepared in Comparative Example 2. With the increase of the amount of HZSM-5(52) composite silicon prepared in Comparative Example 2, the weak acid and strong acid centers of the HZSM-5/HMS composite molecular sieve both moved to high temperature, indicating that the weak acid and strong acid content of the HZSM-5/HMS composite molecular sieve Increase, the addition of HZSM-5 (52) can help to improve the acidity of the composite. Combined with specific surface area and average pore size, the prepared HZSM-5/HMS composite molecular sieve showed high activity for the catalytic reaction of isooctanol.

3 is the FT-IR spectra of Examples 4-6 and Comparative Examples 1-2. It can be seen from Fig. 3 that the absorption peak near 3738 cm ^-1 is attributed to the stretching vibration of the Si-OH group at the end of the molecular sieve and the adsorbed water molecules, and the absorption peak near 1604 cm ^-1 is attributed to the adsorption on the molecular sieve sample. on the OH bending vibration peak of water. In addition, all samples have absorption peaks at 435cm ^-1 , 804cm ^-1 , and 1046cm ^-1 , which are caused by the Si-O bending vibration peak in the silicon-oxygen tetrahedron, the asymmetry of the Si-O-Si bond and the Symmetric stretching vibration peaks. It is worth noting that Comparative Example 2 has a characteristic absorption peak of MFI zeolite at 534 cm ^-1 , which is due to the five- and six-membered ring tetrahedral vibration peaks of TOT (T=Si or Al) in HZSM-5 zeolite produced by the existence. In contrast, there is a small diffraction peak at 968 cm ^-1 in Comparative Example 1, which is attributed to the absorption vibration of Si-OH on the surface of the mesoporous molecular sieve HMS. Since both Comparative Example 1 and Comparative Example 2 have their special characteristic absorption peaks, and in Examples 4 to 6, the above-mentioned series of characteristic absorption peaks appeared, indicating that HZSM-5 microporous molecular sieve and HMS mesoporous molecular sieve were successfully compounded , consistent with the characterization results in Figure 1.

Claims (10)

1. A preparation method of HZSM-5/HMS composite molecular sieve is characterized by comprising the following steps:

Step S1: mixing dodecylamine, absolute ethyl alcohol and water to obtain mixed feed liquid A;

step S2: dropwise adding a mixed solution of a silicon source and absolute ethyl alcohol into the mixed feed liquid A and violently stirring to obtain a mixed feed liquid B;

step S3: after the dropwise addition is finished, adding an HZSM-5 molecular sieve into the mixed material liquid B, and then stirring and crystallizing to obtain a glue liquid C;

step S4: and standing and aging the obtained glue solution C at normal temperature, centrifugally washing until the pH is neutral, drying and roasting to obtain the glue solution C.

2. The method for preparing HZSM-5/HMS composite molecular sieve of claim 1, wherein the molar ratio of dodecylamine, absolute ethanol and water in the mixed feed liquid a is 1: (0.13-0.15): (12.7-12.9).

3. The method for preparing HZSM-5/HMS composite molecular sieve of claim 1, wherein the molar ratio of the silicon source to the absolute ethyl alcohol in the mixture of the silicon source and the absolute ethyl alcohol in step S2 is 1 (0.53-0.55).

4. The HZSM-5/HMS composite molecular sieve of claim 1, wherein the silicon source is a silicate ester or a silane compound.

5. The method for preparing HZSM-5/HMS composite molecular sieve of claim 1, wherein step S2 includes dropping a mixture of a silicon source and absolute ethyl alcohol into the mixed material liquid a and vigorously stirring to obtain a mixed material liquid B, which includes: the dropping speed is 0.6mL/min, and the stirring time is 20-60 min.

6. The HZSM-5/HMS composite molecular sieve of claim 1, wherein the temperature of the stirring crystallization in step S3 is controlled to be 40-50 ℃, and the stirring time is controlled to be 4-5 h.

7. The preparation method of the HZSM-5/HMS composite molecular sieve of claim 1, wherein in the step S4, the standing time is 6-18 hours, the drying temperature is 60-100 ℃, the drying time is 8-9 hours, the roasting temperature is 600-700 ℃, and the roasting time is 5-7 hours.

8. An HZSM-5/HMS composite molecular sieve obtained by the method of any one of claims 1 to 7.

9. Use of the HZSM-5/HMS composite molecular sieve as claimed in claim 8 for the oxidation of isooctyl alcohol.

10. The use according to claim 9, wherein the HZSM-5/HMS composite molecular sieve is used as a catalyst in the oxidation of isooctanol and is added in an amount of 0.3 to 0.7g, the amount of isooctanol is 10 to 20mL, the reaction time is 6 to 12 hours, and the ratio of the volume flow rate of isooctanol to the volume flow rate of oxygen is 3/5 mL/(mL/min).

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