CN105498845B - A kind of supercritical CO2The CsPW/Zr-MCM-41 catalyst prepared in environment and its application - Google Patents

Abstract

The invention discloses a CsPW/ _Zr ‑MCM‑41 catalyst prepared in a supercritical _CO2 environment. cesium polyacid salt. Using the catalyst, the conversion rate of glycerin reaches 65.2-100%, and the selectivity of acrolein reaches 56.8-85.4%. The present invention also discloses the application of the aforementioned CsPW/Zr-MCM-41 catalyst in the selective dehydration of glycerol to prepare acrolein. Compared with the prior art, the catalyst heteropolyacid cesium salt prepared by the method of the invention has a high degree of dispersion on the carrier, strong interaction with the carrier, the catalyst has high hydrothermal stability, and the acidity is not easily lost. At the same time, compared with the existing products, the product obtained by the method of the invention has a high conversion rate of glycerin and acrolein selectivity, and a long service life.

Description

A CsPW/Zr-MCM-41 catalyst prepared in a supercritical CO2 environment and its application

technical field

The invention belongs to the field of chemical synthesis, and in particular relates to a CsPW/Zr-MCM-41 catalyst prepared in a supercritical _CO2 environment and an application thereof.

Background technique

As the world's oil resources become increasingly tense, biodiesel, which can be used as an alternative energy source, is widely favored. Accompanied by its increasing production, a large amount of by-product glycerol has led to a surplus in the market. Glycerol is an important biorenewable resource, which is currently widely used in the fields of medicine, food, tobacco and cosmetics. Therefore, research on converting glycerol into high value-added products has become a hotspot.

Acrolein is an important organic synthesis intermediate, mainly used in pharmaceutical synthesis, paper making, paint, oil field, organic synthesis industry and other fields. The most important use of acrolein is the synthesis of methionine, an animal feed additive, and the preparation of 1,3-propanediol; in addition, it is also used in the preparation of flavors, glutaraldehyde, etc. At present, the main method of industrial production of acrolein is the oxidation of propylene. However, the propylene oxidation method uses petroleum as the initial raw material, which not only does not meet the requirements of low-carbon economy, but also has the problem of competing with other chemical products for raw materials. The glycerin dehydration method to produce acrolein is based on renewable resources, the process is simple, and it has strong competitive advantages and industrial application prospects. Therefore, it has attracted more and more attention from academia and industry.

Watanabe M et al. investigated _the influence of glycerin concentration, reaction pressure, temperature and _H2SO4 concentration on the performance of glycerin dehydration reaction under the condition _{of hot} pressurized water. The temperature is favorable for the formation of acrolein. Under the optimal conditions: at 400°C and 34.5MPa, the conversion rate reaches 90%, and the selectivity reaches 80%, indicating that acidic conditions promote the reaction of glycerol dehydration to acrolein. However, the liquid acid-catalyzed reaction has disadvantages such as harsh reaction conditions, corrosion of equipment, easy degradation of the product, and inability to separate the liquid acid from the reaction system.

Patent US2558520 discloses the patent of using diatomite-loaded H ₃ PO ₄ to catalyze the gas-phase or liquid-phase dehydration of glycerin, and the selectivity of acrolein reaches 72%. But the catalyst deactivates rapidly.

The patents US5426249 and US1034803C reported that the dehydration of glycerin by phosphoric acid catalysts supported by alumina, HZSM-5, HY, etc., when the selectivity of acrolein was about 71%, the conversion rate of glycerol was only 19%. It may be that at high temperature, glycerol polymerized on the surface of the catalyst to cover the active sites of the catalyst, resulting in a low conversion rate of glycerol.

Chinese patent document CN201019026084.5 proposes a method for preparing acrolein in a fixed-bed micro-reaction device by loading alumina, diatomite, activated carbon, rutile titanium dioxide, and kaolin with heteropolyacid. Aldehyde selectivity is 49.0-90.5%. However, the catalyst is easily deactivated, and the carbon deposition in the short reaction time seriously leads to the short life of the catalyst.

Patent document CN201210128727.9 reports the use of alkali metal salts (potassium salts, rubidium salts, cesium salts) catalysts of heteropolyacids, and reactive distillation technology to catalyze the liquid phase dehydration of glycerin to produce acrolein, and the conversion rate of glycerin is up to 100%. The yield of acrolein is 58.9-78.2%, and the yields of by-products hydroxyacetone and acetic acid are both lower than 10%. Although this type of catalyst can obtain higher conversion rate of glycerol and yield of acrolein at the initial stage of the reaction, the catalyst is prone to carbon deposition and deactivation, poor stability and short catalyst life.

In the patent documents reported above, although greener and environment-friendly solid acid catalysts are used, the corrosion to equipment is reduced to a certain extent, and a higher conversion rate of glycerin and acrolein yield can be obtained in a short period of time, but the catalyst The surface is prone to serious carbon deposition, and the catalyst deactivation rate is fast. How to more effectively suppress carbon deposition, prolong catalyst life, and at the same time ensure high glycerin conversion and acrolein selectivity is the basis for industrial production.

Supercritical fluid technology has developed rapidly in recent years. Supercritical fluid refers to a special fluid above the critical temperature and critical pressure. The properties of supercritical fluid are between gas and liquid, and it has a viscosity and diffusion similar to gas. coefficient, so that the supercritical fluid has good flow, mass transfer, heat transfer and other properties; it also has a dissolving ability and heat transfer coefficient similar to that of a liquid, and the dissolving ability of a supercritical fluid for a solid is 10 to 100 times higher than that of a gas; Critical fluid has good miscibility with gas; supercritical fluid has very low surface tension, which makes it have excellent surface wetting performance and permeability. Because supercritical fluid has the characteristics of high diffusivity, strong solubility, excellent surface wettability, and continuously adjustable physical and chemical properties, it has become a potential good medium in the fields of extraction and separation, various chemical reactions, and material preparation. a broad application prospect. The use of supercritical fluid, especially supercritical CO ₂ technology to prepare supported catalytic materials has become a hot spot in the research and preparation of new materials at home and abroad.

In the process of producing acrolein with glycerol as raw material in this patent, Zr-MCM-41 is used as a carrier and supercritical _CO2 impregnation technology is used to synthesize a supported heteropolyacid cesium salt catalyst. The heteropolyacid cesium salt has a high degree of dispersion on the surface of the carrier. It has a strong interaction with the carrier and has good hydrothermal stability. The glycerol aqueous solution is pumped into the fixed-bed reactor through a micropump, and a certain space velocity is controlled. The conversion rate of glycerin and the selectivity of acrolein are effectively improved, the generation of carbon deposition is suppressed, and the catalyst life is long.

Contents of the invention

The technical problem to be solved in the present invention is to provide a kind of supercritical CO The CsPW/Zr-MCM-41 catalyst prepared in the _environment , to solve the low glycerol conversion and acrolein selectivity and the service life of the catalyst in the prior art shorter question.

The technical problem to be solved by the present invention is to provide the preparation method of the above-mentioned catalyst.

The final technical problem to be solved by the present invention is to provide the application of the above catalyst in the selective dehydration of glycerin to prepare acrolein.

In order to solve the problems of the technologies described above, the technical scheme adopted in the present invention is as follows:

A kind of supercritical CO in _the environment prepares the method for CsPW/Zr-MCM-41 catalyst, it comprises the steps:

(1) Dissolve the cesium source and heteropolyacid in deionized water, mix well to obtain an aqueous solution of heteropolyacid cesium salt; immerse the Zr-MCM-41 carrier in the aqueous solution of heteropolyacid cesium salt, and stir to obtain a uniform slurry shape;

(2) Warm up the homogeneous slurry obtained in step (2) to a supercritical temperature in a _closed reaction vessel and pump CO into the reaction vessel with a high-pressure syringe pump to make the vessel reach a certain pressure for supercritical Treatment; after the supercritical treatment is completed, the temperature is lowered, the pressure is released, and the product is collected;

(3) The product obtained in step (3) is subjected to centrifugation, and the solid part of the lower layer is taken to dry, and after roasting, the heteropolyacid cesium salt/Zr-MCM-41 catalyst is obtained.

In step (1), the cesium source is cesium carbonate or cesium nitrate, preferably cesium carbonate; the heteropolyacid is phosphotungstic acid, silicotungstic acid, phosphomolybdic acid or silicomolybdic acid.

In step (1), the molar ratio of cesium to heteropolyacid in the cesium source is 0.5-3:1, preferably 2.5:1.

In step (1), the amount of water used is based on the ability to completely dissolve the cesium source, heteropolyacid and Zr-MCM-41 carrier.

In step (1), the Zr-MCM-41 carrier can be purchased from the market, or can be prepared by the following method:

Mix the zirconium source and the silicon source to obtain the mixed system I for later use; dissolve the template agent in water and mix it evenly with the ammonia solution to obtain the mixed system II for later use; add the mixed system I dropwise to the mixed system II under constant stirring, and set aside at room temperature After stirring at low temperature for 2-5 hours, crystallize at 80-100°C for 40-50 hours, filter after cooling, wash the solid part, dry and roast to obtain Zr-MCM-41 carrier.

in,

The zirconium source is preferably zirconium n-propoxide;

The silicon source is preferably ethyl orthosilicate;

The template agent is cetyltrimethylammonium bromide, cetyltrimethylammonium chloride or cetyltriethylammonium bromide, and the ammonia solution is 28wt% ammonia aqueous solution;

The molar ratio of zirconium in the zirconium source, silicon in the silicon source, template agent and ammonia in the ammonia solution is 0.05-0.2:1:0.3-0.4:8;

The molar ratio of the template agent and the water used to dissolve the template agent is 1:150-200;

The ammonia solution is preferably a 28% by weight ammonia solution in water.

In the preparation method of the above-mentioned Zr-MCM-41 carrier, the washing method is to rinse the solid part with deionized water for 3 to 5 times; the drying method is to dry at 80 to 110 ° C for 8 to 12 hours, preferably 12 hours; the roasting method is to 400 to 600 ° C Lower roasting for 3 to 6 hours, preferably 6 hours.

In step (2), the method of supercritical treatment is 30-150° C., 7-16Mpa for 1-6 hours.

In step (3), the centrifugation condition is to centrifuge at 3000-8000 rpm for 5-20 minutes.

In step (3), the drying method is at 80-120°C for 3-6 hours, preferably 3 hours; the roasting method is at 300-500°C for 2-5 hours, preferably 3 hours.

In step (3), in the obtained heteropolyacid cesium salt/Zr-MCM-41 catalyst, the heteropolyacid cesium salt loading is 10～60wt% (loading refers to heteropolyacid cesium salt and heteropolyacid cesium salt/Zr-MCM-41 catalyst weight ratio).

The CsPW/Zr-MCM-41 catalyst prepared by any one of the above preparation methods is also within the protection scope of the present invention.

The application of the above-mentioned CsPW/Zr-MCM-41 catalyst in the selective dehydration of glycerol to prepare acrolein is also within the protection scope of the present invention.

Beneficial effect:

Compared with the prior art, the present invention has the following advantages:

In the choice of raw material glycerin, either industrially pure glycerin or crude glycerin prepared from biodiesel can be selected, and the source of raw materials is wide; the catalyst heteropolyacid cesium salt prepared by supercritical impregnation method has high dispersion, and Zr-MCM- The 41 carrier has a strong force, and the cesium heteropolyacid brine has high thermal stability, and the acidity is not easy to lose; the conversion rate of glycerin and the selectivity of acrolein are high, and the service life is long.

Detailed ways

The present invention can be better understood from the following examples. However, those skilled in the art can easily understand that the content described in the embodiments is only for illustrating the present invention, and should not and will not limit the present invention described in the claims.

Example 1

Synthesis of Zr-MCM-41 (Si/Zr=5) carrier: 9.1ml of zirconium n-propoxide and 22.8ml of ethyl orthosilicate were mixed and stirred to obtain mixed system I for later use; 12.2g of hexadecyltrimethyl Dissolve ammonium chloride in 100ml of deionized water, and then mix with 110ml of 28wt% ammonia solution to obtain mixed system II for later use; add mixed system I dropwise to mixed system II under constant stirring, and stir at room temperature for 2 hours at 500r/min After the gel is formed, transfer the mixed system to a polytetrafluoroethylene-lined hydrothermal synthesis kettle, place it in an oven at 80°C for 40 hours, and then cool it to room temperature; filter the mixed solution in the reaction kettle , the solid part was washed with deionized water for 3 times, and then the solid was dried in a drying oven at 80 °C for 10 h; the dried solid was placed in a muffle furnace at 450 °C for 3 h to prepare Zr-MCM-41 ( Si/Zr=5) carrier.

Synthesis of 20wt% cesium phosphotungstic acid salt/Zr-MCM-41 (Si/Zr=5): in the reactor, 0.043gCs ₂ CO ₃ and 0.302g phosphotungstic acid were dissolved in 20ml of deionized water, and then 1.5 Immerse the gZr-MCM-41 (Si/Zr=5) carrier in the aforementioned solution, stir evenly to obtain a homogeneous slurry, use a temperature program to raise the reaction kettle to 80°C, and then use a high-pressure syringe pump to fill CO ₂ gas, Make the pressure in the kettle reach 8MPa, and maintain the supercritical condition for 2 hours; after the supercritical treatment, cool down, release the pressure, unload the kettle, collect the sample and centrifuge at 3000r/min for 5min, take the solid part of the lower layer, and dry it in an oven at 80°C for 3h. After calcining at 300° C. for 3 hours in a muffle furnace, a 20 wt % cesium phosphotungstate/Zr-MCM-41 (Si/Zr=5) catalyst was obtained.

Catalyst performance evaluation uses a fixed bed reactor, with 10wt% glycerol aqueous solution as raw material, 20wt% cesium phosphotungstate/Zr-MCM-41 catalyst dosage is 0.5g, reaction temperature is 280°C, mass space velocity is 0.5h ^-1 Under the following conditions, after 2 hours of reaction, the conversion rate of glycerol was 87.2%, and the selectivity of acrolein was 70.5%; after 10 hours of reaction, the conversion rate of glycerin was 84.0%, and the selectivity of acrolein was 68.4%.

Example 2

Synthesis of Zr-MCM-41 (Si/Zr=7) carrier: 6.5ml of zirconium n-propoxide and 22.8ml of ethyl orthosilicate were mixed and stirred to obtain mixed system I for later use; 12.2g of hexadecyltriethyl Dissolve ammonium bromide in 110ml of deionized water, and then mix with 110ml of 28wt% ammonia solution to obtain mixed system II for later use; add mixed system I dropwise to mixed system II under constant stirring, and stir at room temperature for 3 hours at 500r/min After the gel was formed, the mixed system was transferred to a polytetrafluoroethylene-lined hydrothermal synthesis kettle, and placed in an oven at 100°C for 45 hours, then cooled to room temperature; the mixed solution in the reaction kettle was filtered , the solid part was washed 4 times with deionized water, and then the solid was dried in a drying oven at 100 °C for 12 h; the dried solid was placed in a muffle furnace at 500 °C for 4 h to prepare Zr-MCM-41 ( Si/Zr=7) carrier.

Synthesis of 30wt% cesium silicotungstic acid salt/Zr-MCM-41 (Si/Zr=7): Dissolve 0.049g cesium nitrate and 0.347g silicotungstic acid in 30ml of deionized water in the reactor, and then add 1gZr- Immerse the MCM-41 (Si/Zr=7) carrier in the aforementioned solution, stir evenly to obtain a uniform slurry, use a temperature program to raise the reaction kettle to 100°C, and then use a high-pressure syringe pump to fill _CO2 gas to make the kettle The internal pressure reached 8MPa, and the supercritical condition was maintained for 4 hours; after the supercritical treatment, the temperature was lowered, the pressure was released, and the sample was collected by unloading the kettle, centrifuged at 5000r/min for 10min, and the solid part of the lower layer was removed, dried in an oven at 100°C for 4h, After calcination at 350°C for 4 hours in a Furnace, a 30wt% cesium silicotungstate/Zr-MCM-41 (Si/Zr=7) catalyst was obtained.

Catalyst performance evaluation uses a fixed bed reactor, with 20wt% glycerol aqueous solution as raw material, 30wt% cesium silicotungstate/Zr-MCM-41 catalyst dosage is 0.5g, reaction temperature is 300°C, mass space velocity is 1.0h ^-1 Under the following conditions, after 2 hours of reaction, the conversion rate of glycerol was 85.2%, and the selectivity of acrolein was 63.5%; after 10 hours of reaction, the conversion rate of glycerin was 82.8%, and the selectivity of acrolein was 61.6%.

Example 3

Synthesis of Zr-MCM-41 (Si/Zr=10) carrier: 4.5ml of zirconium n-propoxide and 22.8ml of ethyl orthosilicate were mixed and stirred to obtain mixed system I for later use; then 12.2g of hexadecyl trimethyl Ammonium bromide was dissolved in 100ml of deionized water, and then mixed with 110ml of 28wt% ammonia solution to obtain the mixed system II for later use; under constant stirring, the mixed system I was added dropwise to the mixed system II, at room temperature 500r/min After stirring for 4 hours until the gel was formed, the mixed system was transferred to a polytetrafluoroethylene-lined hydrothermal synthesis kettle, and placed in an oven at 80°C for 50 hours, then cooled to room temperature; the mixed solution in the reaction kettle After filtering, the solid part was washed with deionized water for 5 times, and then the solid was dried in a drying oven at 100 °C for 10 h; the dried solid was roasted in a muffle furnace at 550 °C for 5 h to obtain Zr-MCM- 41 (Si/Zr=10) support.

Synthesis of 30wt% cesium phosphomolybdate salt/Zr-MCM-41 (Si/Zr=10): in the reactor, 0.081gCs ₂ CO ₃ and 0.364g phosphomolybdic acid were dissolved in 40ml of deionized water, then 1gZr - Immerse the MCM-41 (Si/Zr=10) carrier in the aforementioned solution, stir evenly to obtain a uniform slurry, use a temperature program to raise the reaction kettle to 100°C, and then use a high-pressure syringe pump to fill CO ₂ gas, so that The pressure in the kettle reached 12MPa, and the supercritical condition was maintained for 4 hours; after the supercritical treatment, the temperature was lowered, the pressure was released, and the kettle was unloaded, and the sample was collected and centrifuged at 8000r/min for 15min, and the solid part of the lower layer was taken out, dried in an oven at 120°C for 5 hours, and dried in an oven for 5 hours. After calcining at 400° C. for 5 h in a muffle furnace, a 30 wt % cesium phosphomolybdate salt/Zr-MCM-41 (Si/Zr=10) catalyst was obtained.

Catalyst performance evaluation uses a fixed bed reactor, with 10wt% glycerin aqueous solution as raw material, 30wt% cesium phosphomolybdate salt/Zr-MCM-41 catalyst dosage is 0.5g, reaction temperature is 340°C, mass space velocity is 0.6h ^-1 Under the following conditions, after 2 hours of reaction, the conversion rate of glycerin was 65.2%, and the selectivity of acrolein was 58.5%; after 10 hours of reaction, the conversion rate of glycerin was 60.8%, and the selectivity of acrolein was 56.8%.

Example 4

Synthesis of Zr-MCM-41 (Si/Zr=15) carrier: 3.0ml of zirconium n-propoxide and 22.8ml of ethyl orthosilicate were mixed and stirred to obtain mixed system I for later use; 12.2g of hexadecyltrimethyl Dissolve ammonium bromide in 110ml of deionized water, and then mix it with 110ml of 28wt% ammonia solution to obtain the mixed system II for later use; add the mixed system I dropwise to the mixed system II under constant stirring, and stir at room temperature at 500r/min After 2 hours until the gel was formed, the mixed system was transferred to a polytetrafluoroethylene-lined hydrothermal synthesis kettle, and placed in an oven at 100°C for 50 hours, then cooled to room temperature; Filter, wash the solid part with deionized water for 4 times, then place the solid in a drying oven at 80°C for 12 hours; place the dried solid in a muffle furnace at 600°C for 6 hours to prepare Zr-MCM-41 (Si/Zr=15) support.

Synthesis of 50wt% cesium phosphotungstic acid salt/Zr-MCM-41 (Si/Zr=15): 0.114gCs ₂ CO ₃ and 0.806g phosphotungstic acid were dissolved in 40ml of deionized water in the reactor, and then 1gZr - Immerse the MCM-41 (Si/Zr=15) carrier in the aforementioned solution, stir evenly to obtain a homogeneous slurry, use a temperature program to raise the reaction kettle to 80°C, and then use a high-pressure syringe pump to fill in CO ₂ gas to make The pressure in the kettle reached 10MPa, and the supercritical condition was maintained for 4 hours; after the supercritical treatment, the temperature was lowered, the pressure was released, and the sample was collected by unloading the kettle, centrifuged at 8000r/min for 10min, and the solid part of the lower layer was taken out, dried in an oven at 110°C for 3 hours, and After calcining at 300° C. for 3 hours in a muffle furnace, a 50 wt % cesium phosphotungstate/Zr-MCM-41 (Si/Zr=15) catalyst was obtained.

Catalyst performance evaluation uses a fixed bed reactor, with 20wt% glycerol aqueous solution as raw material, 50wt% cesium phosphotungstate/Zr-MCM-41 catalyst dosage is 0.5g, reaction temperature is 320°C, mass space velocity is 0.4h ^-1 Under the following conditions, after 2 hours of reaction, the conversion of glycerin was 100%, and the selectivity of acrolein was 85.4%; after 10 hours of reaction, the conversion of glycerin was 96.8%, and the selectivity of acrolein was 80.0%.

According to the catalyst preparation method reported in patent CN201210480141.9: vacuum impregnation method. We use their methods to prepare catalysts and compare the methods involved in this patent. Dissolve 0.114g of Cs ₂ CO ₃ in 40ml of deionized water, add 1g of Zr-MCM-41 (Si/Zr=15) carrier we synthesized into the aqueous solution, stir and vacuum impregnate at room temperature, the carrier Zr -MCM-41 was treated at vacuum degree -0.1MPa for 1 hour, then added Cs ₂ CO ₃ solution and impregnated at normal pressure for 24 hours, then dried at 110°C for 10 hours for later use; then dissolved 0.806g of phosphotungstic acid in 30ml of deionized water, stirred Finally, use vacuum impregnation method at room temperature, treat the above-mentioned loaded catalyst carrier at a vacuum degree of -0.1MPa for 1 hour, then add phosphotungstic acid solution and impregnate it at normal pressure for 24 hours, filter, wash, and dry at 110°C 10h, then calcined at 300°C for 3h to prepare cesium phosphotungstate supported catalyst. According to the same reaction conditions as in Example 4, its activity in the reaction of glycerol dehydration to acrolein was evaluated. After 2 hours of reaction, the conversion rate of glycerin was 96.4%, and the selectivity of acrolein was 80.2%. After 10 hours of reaction, the conversion rate of glycerin was 70.1%, and the selectivity of acrolein was 72.8%.

The activity of the catalyst prepared in this patent is higher than that of the catalyst prepared according to CN201210480141.9 patent, and the stability is high. After comparative analysis of characterization results, the cesium salt of the heteropolyacid on the catalyst prepared by the patent method has a high degree of dispersion on the Zr-MCM-41 carrier, strong interaction with the carrier, and the catalyst has high hydrothermal stability.

Example 5

Synthesis of Zr-MCM-41 (Si/Zr=20) carrier: 2.3ml of zirconium n-propoxide and 22.8ml of ethyl orthosilicate were mixed and stirred to obtain mixed system I for later use; 12.2g of hexadecyltriethyl Ammonium bromide and 100ml of deionized water were mixed with 110ml of 28wt% ammonia solution to obtain the mixed system II for later use; under constant stirring, the mixed system I was added dropwise to the mixed system II, and stirred at room temperature at 500r/min for 5h to After the gel was formed, the mixed system was transferred to a polytetrafluoroethylene-lined hydrothermal synthesis kettle, and placed in an oven at 80°C for 50 hours, then cooled to room temperature; the mixed solution in the reaction kettle was filtered, The solid part was washed 3 times with deionized water, and then the solid was dried in a drying oven at 110 °C for 12 h; the dried solid was baked in a muffle furnace at 500 °C for 6 h to obtain Zr-MCM-41 (Si /Zr=20) carrier.

Synthesis of 40wt% cesium phosphotungstic acid salt/Zr-MCM-41 (Si/Zr=20): 0.076gCs ₂ CO ₃ and 0.537g phosphotungstic acid were dissolved in 30ml of deionized water in the reactor, and then 1gZr - Immerse the MCM-41 (Si/Zr=20) carrier in the aforementioned solution, stir evenly to obtain a homogeneous slurry, use a temperature program to raise the reaction kettle to 120°C, and then use a high-pressure syringe pump to fill in CO ₂ gas to make The pressure in the kettle reached 14MPa, and the supercritical condition was maintained for 6 hours; after the supercritical treatment, the temperature was lowered, the pressure was released, and the samples were collected by unloading the kettle, centrifuged at 5000r/min for 15min, and the solid part of the lower layer was removed, dried in an oven at 100°C for 3 hours, and After calcining at 450° C. for 3 hours in a muffle furnace, a 40 wt % cesium phosphotungstate/Zr-MCM-41 (Si/Zr=20) catalyst was obtained.

Catalyst performance evaluation adopts fixed bed reactor, with 20wt% glycerol aqueous solution as raw material, catalyst dosage is 0.5g, reaction temperature is 340 ℃, mass space velocity is 1.5h ^-1 under, catalyst performance evaluation adopts fixed bed reactor, with 10wt% % glycerol aqueous solution as raw material, 40wt% cesium phosphotungstate salt/Zr-MCM-41 catalyst dosage is 0.5g, reaction temperature is 320°C, mass space velocity is 0.8h ^-1 , after reaction for 2h, glycerin conversion rate is 98.4% , the selectivity of acrolein was 82.6%; after 10 hours of reaction, the conversion rate of glycerol was 93.8%, and the selectivity of acrolein was 77.2%.

Claims (8)

1. Supercritical CO₂A method for preparing a cesium heteropolyacid salt/Zr-MCM-41 catalyst in an environment, comprising the steps of:

(1) dissolving a cesium source and heteropoly acid in water, and uniformly mixing to obtain a heteropoly acid cesium salt water solution; soaking the Zr-MCM-41 carrier in aqueous solution of cesium heteropoly acid salt, and stirring to obtain uniform slurry;

(2) heating the uniform slurry obtained in the step (1) in a closed reaction container and pumping CO into the reaction container₂Gas to perform supercritical processing(ii) a After the supercritical treatment is finished, cooling, decompressing and collecting a product;

(3) centrifugally separating the product obtained in the step (2), taking a lower-layer solid part, drying and roasting to obtain the cesium heteropoly acid salt/Zr-MCM-41 catalyst;

in the step (1), the Zr-MCM-41 carrier is prepared by the following method:

mixing a zirconium source and a silicon source to obtain a mixed system I for later use, dissolving a template agent in water, and uniformly mixing the template agent with an ammonia water solution to obtain a mixed system II for later use; dropwise adding the mixed system I into the mixed system II under continuous stirring, stirring at room temperature for 2-5 h, crystallizing at 80-100 ℃ for 40-50 h, cooling, filtering, washing the solid part, drying, and roasting to obtain a Zr-MCM-41 carrier;

in the step (2), the supercritical treatment method is carried out at 30-150 ℃ and under 7-16 Mpa for 1-6 h.

2. The method according to claim 1, wherein in step (1), the cesium source is cesium carbonate or cesium nitrate, and the heteropolyacid is phosphotungstic acid, silicotungstic acid, phosphomolybdic acid or silicomolybdic acid.

3. The preparation method according to claim 1, wherein in the step (1), the molar ratio of cesium to heteropoly acid in the cesium source is 0.5 to 3: 1.

4. the method according to claim 1, wherein the centrifugation in the step (3) is carried out under a condition of 3000 to 8000 rpm for 5 to 20 minutes.

5. The preparation method according to claim 1, wherein in the step (3), the drying method is drying at 80-120 ℃ for 3-6 h; the roasting method is roasting for 2-5 hours at 300-500 ℃.

6. The preparation method according to claim 1, wherein in the step (3), the cesium heteropolyacid salt/Zr-MCM-41 catalyst is loaded in an amount of 10-60 wt%.

7. The cesium heteropolyacid salt/Zr-MCM-41 catalyst prepared by the method of any one of claims 1-6.

8. Use of the cesium heteropolyacid salt/Zr-MCM-41 catalyst of claim 7 in the selective dehydration of glycerol to acrolein.