CN102274722A - V2O3 for preparing anhydrous formaldehyde by directly dehydrogenizing methanol as well as supported V2O3 catalyst and preparation method thereof - Google Patents

Abstract

The invention discloses a novel V ₂ O ₃ and a supported V ₂ O ₃ catalyst for preparing anhydrous formaldehyde by direct dehydrogenation of methanol and a preparation method thereof. The V ₂ O ₃ catalyst is a solvothermal method, using an organic reducing agent to reduce the raw material V ₂ O ₅ powder to a low-valence vanadium-containing compound, after washing and drying, and finally heat treatment for a certain period of time under vacuum or inert atmosphere get. The preparation of supported V ₂ O ₃ catalyst is to impregnate a certain amount of V ₂ O ₃ into the aqueous solution of soluble metal salt for a period of time by impregnation method on the basis of the above synthesis of V ₂ O ₃ , then dry it in vacuum, and then Carry out calcination under vacuum condition or inert atmosphere to decompose the metal salt to produce simple metal, so that the metal is supported on V ₂ O ₃ to obtain a supported catalyst. The prepared methanol has high catalyst activity and good selectivity for direct dehydrogenation of methanol to produce anhydrous formaldehyde. Under normal pressure and at a lower temperature (350 ^o C), the conversion rate of methanol exceeds 99%, the selectivity of formaldehyde is as high as 90%, and the stability of the catalyst is high, the preparation method is simple, the cost is low, and it is suitable for industrial production. need.

Description

V₂O₃ and Supported V₂O₃ Catalysts for Direct Methanol Dehydrogenation to Anhydrous Formaldehyde and its preparation method

technical field

The invention belongs to the technical field of catalysis. The catalysts are _V2O3 and supported _V2O3 catalysts (transition metals and noble metals), and are used for the preparation of novel catalysts for _the direct _{dehydrogenation} of methanol to produce anhydrous formaldehyde.

Background technique

In recent years, with the rise of synthesizing high-quality engineering plastics and medicines such as urotropine, the demand for anhydrous formaldehyde in industrial production is increasing. In addition to being used alone, anhydrous formaldehyde is mainly used as a raw material for the production of other chemical products, such as urea-formaldehyde resin, phenolic resin, melamine-formaldehyde resin, polyoxymethylene, pyridine and its compounds. In addition, anhydrous formaldehyde is also widely used in the synthesis of polymer materials, new drug intermediates, high-grade fragrances, dyes, etc.

At present, the method of industrially preparing formaldehyde mainly adopts the iron-molybdenum method or the silver method to obtain formaldehyde through the air oxidation of methanol. The formaldehyde obtained by this method contains a large amount of water. In the process of separating and purifying formaldehyde, an azeotropic system is formed due to the negative deviation of formaldehyde aqueous solution relative to the ideal solution, which increases the difficulty of purifying formaldehyde by vacuum distillation or solvent azeotropy. Therefore, in the process of preparing anhydrous formaldehyde by this process, not only need to invest huge equipment and operating costs to cause high costs, but also the process is cumbersome and the dehydration effect is not good. Considering the economic benefit and technological process, if anhydrous formaldehyde can be produced directly from methanol, it will generate huge profits and greatly simplify the technological route. The production of anhydrous formaldehyde by the direct dehydrogenation of methanol is a very promising process with significant economic benefits. Compared with the methanol air oxidation method, this process has many advantages: no water is generated in the product, which greatly reduces the equipment investment and operating costs for rectifying formaldehyde aqueous solution; the by-product hydrogen has high purity, and hydrogen is easily separated from formaldehyde; There will be no problem of formic acid corrosion equipment generated by the oxidation of methanol. Therefore, this is an economical and environmentally friendly new process, which will become the development trend of anhydrous formaldehyde preparation in the future.

Among the commonly used catalysts for the direct dehydrogenation of methanol to anhydrous formaldehyde, sodium carbonate catalysts, supported silver catalysts, molecular sieve catalysts, etc. These catalysts have low activity and require high reaction temperatures, usually above 600 ^o C, to obtain considerable yields. However, their selectivity and stability are low and the catalysts are expensive, which limits their application. industrial applications. Therefore, the development of new and efficient catalysts can significantly reduce the reaction temperature under the premise of ensuring a high anhydrous formaldehyde yield and stability, and the cost of the catalyst is low, which will undoubtedly play a huge role in the industrialization of anhydrous formaldehyde. effect. The V ₂ O ₃ ^and the supported V ₂ O ₃ catalyst for producing anhydrous formaldehyde by the direct dehydrogenation of methanol proposed by the present invention have very high activity and selectivity. The conversion rate of methanol is more than 99%, and the selectivity of formaldehyde is as high as 90%. This catalyst is the most active among the catalysts related to the direct dehydrogenation of methanol to produce anhydrous formaldehyde reported in the literature. Moreover, the catalyst has high stability, simple preparation method and low cost, and is suitable for industrial application of preparing anhydrous formaldehyde from methanol.

Contents of the invention

The invention proposes a novel V ₂ O ₃ and a supported V ₂ O ₃ catalyst for producing anhydrous formaldehyde through direct dehydrogenation of methanol and a preparation method thereof. The preparation method of the catalyst is simple, the cost is low, the anhydrous formaldehyde yield is very high under normal pressure and relatively low temperature, and the catalyst is suitable for large-scale industrial application.

The V ₂ O ₃ and supported V ₂ O ₃ catalysts proposed by the present invention for the direct dehydrogenation of methanol to anhydrous formaldehyde, V ₂ O ₃ can be directly used as the active component of the catalyst, and can also be used as a carrier for transition metal loads of precious metals. V ₂ O ₃ is obtained by reducing V ₂ O ₅ to low-valence vanadium species with an organic reducing agent, followed by heat treatment. The supported V ₂ O ₃ catalyst uses the prepared V ₂ O ₃ as a carrier, and the metal is supported by the impregnation method. The amount of loaded metal can be realized by adjusting the concentration of the impregnating solution. The catalyst is V ₂ O ₃ and Type V ₂ O ₃ catalyst.

The present invention proposes the preparation method of V ₂ O ₃ and supported V ₂ O ₃ catalyst, V ₂ O ₃ is prepared by solvothermal method, and V ₂ O ₃ supported catalyst is impregnated with carrier V ₂ O ₃ in a certain concentration In the soluble metal salt aqueous solution, the catalyst is obtained by standing, drying, calcining and other steps. It mainly includes the preparation of V ₂ O ₃ and the preparation of supported V ₂ O ₃ catalyst. The following is the specific catalyst preparation process and related restrictions:

Preparation of V ₂ O ₃ catalyst:

(1) Disperse an appropriate amount of V ₂ O ₅ powder in an organic reducing agent, and stir at room temperature for a certain period of time to form a uniform suspension. Stirring time should be more than 0.5h, control m(V ₂ O ₅ )/g:V(organic reducing agent)/ml=1:100～1:140.

(2) Transfer the suspension in step (1) into the reactor, the filling degree is generally about 80%, and put it in an oven at a certain temperature for a period of time. The separated solid is washed with ethanol and water, and dried under vacuum or at a certain temperature under an inert atmosphere. The reaction temperature is generally 120-300 ^o C, and the reaction time is generally 6-150 hours. The drying temperature is generally about 80-120 ^o C.

(3) The powder dried in step (2) is calcined at a certain temperature for a period of time under vacuum or an inert atmosphere to obtain a sample. The calcination temperature is generally above 400 ^o C, and the calcination time is above 5 hours.

In the above method for preparing V ₂ O ₃ , the V ₂ O ₅ powder should be dispersed in the organic reducing agent under vigorous stirring. Optional organic reducing agents include methanol, ethanol, ethylene glycol, and formaldehyde solutions. Stirring can adopt electromagnetic stirring or mechanical stirring. The inert gas is generally argon, helium, nitrogen, etc. or their mixtures. Vacuum drying generally uses a vacuum drying oven, and calcination under vacuum or an inert atmosphere usually uses a program temperature-controlled tube furnace connected to vacuum or gas.

Preparation of supported V ₂ O ₃ catalyst:

(1) Prepare an aqueous solution of a certain concentration of noble metal salt or transition metal salt, then immerse an appropriate amount of prepared V ₂ O ₃ into the solution, and let it stand for 8 to 24 hours.

(2) Dry the impregnated mixture in a vacuum oven or a tube furnace under an inert atmosphere at 80-120 ^o C, and program the temperature under vacuum or an inert atmosphere to control the temperature above 400 ^o C and calcine for more than 5 hours, or according to different Properly increasing the calcination temperature and calcination time of the decomposition temperature of the metal salt can obtain a V ₂ O ₃ supported metal catalyst.

In the above method for preparing metal-loaded V ₂ O ₃ catalysts, the soluble metal precursors used in the impregnation process can be nitrates, acetates, and chlorides of noble metals or transition metals, and the loading is generally 0.5% to 0.5%. 20%. The inert gas is generally argon, helium, nitrogen, etc. or a mixture thereof.

Description of drawings

Fig. 1 is a flow chart of the preparation of V ₂ O ₃ catalyst.

Fig. 2 is a flow chart of the preparation of the supported V ₂ O ₃ catalyst.

Fig. 3 is the XRD spectrum of the prepared V ₂ O ₃ sample.

Fig. 4 is a diagram of methanol conversion rate in the reaction of V ₂ O ₃ catalyzed direct dehydrogenation of methanol to produce anhydrous formaldehyde.

Fig. 5 is a formaldehyde selectivity diagram of the direct dehydrogenation of methanol catalyzed by V ₂ O ₃ to produce anhydrous formaldehyde.

Fig. 6 is a stability test diagram of the prepared V ₂ O ₃ sample for direct dehydrogenation of methanol to produce anhydrous formaldehyde.

Fig. 7 is the XRD pattern of the prepared V ₂ O ₃ sample before and after the stability test of direct dehydrogenation of methanol to produce anhydrous formaldehyde.

Fig. 8 is a SEM image of the prepared V ₂ O ₃ sample.

Fig. 9 is the TEM image and the corresponding SAED image of the prepared V ₂ O ₃ sample.

Detailed ways

Example 1: As shown in Figure 1, according to the ratio of m(V ₂ O ₅ )/g:V(ethylene glycol)/ml=1:100, disperse V ₂ O ₅ powder in ethylene glycol under vigorous stirring alcohol. Stirred at room temperature for 1 h to obtain an orange-yellow suspension. The suspension was transferred into a polyethylene-lined reactor to a filling degree of about 80%. The reaction kettle was placed in an oven at 200 ^o C for 2 days, and then cooled to room temperature naturally. Separate the blue solid at the bottom of the reaction kettle and wash it with ethanol and water. The washing can be performed by suction filtration or centrifugation. During the washing process, it can be observed that the solid gradually changes from blue to gray-black, and the washed solid is dried in a vacuum oven at 100 ^o C for 12 hours. The dried powder was calcined at 400 ^o C for 5 h in a temperature-programmed tube furnace under an argon atmosphere. The spectrogram of the X-ray diffraction analysis of the sample obtained by calcination is shown in Figure 3, indicating that the sample is pure vanadium trioxide (PDF#71-0342). According to the Scherrer formula, the average particle diameter calculated according to the (104) diffraction peak is 14nm. Fig. 8 SEM shows the microscopic morphology of the V ₂ O ₃ sample, and it can be seen that the sample has a rectangular block shape and a rough surface. Figure 9 shows the transmission electron microscope image and the corresponding selected area electron diffraction image of the sample. Each polycrystalline diffraction ring can be attributed to vanadium trioxide in the R-centered hexagonal phase, indicating that the rectangular sample is assembled from multiple small crystal grains made.

To prepare the supported Cu/V ₂ O ₃ catalyst, follow the steps shown in Figure 2, prepare a 1 mol/L copper nitrate aqueous solution according to the required loading amount, immerse the prepared V ₂ O ₃ in the aqueous solution, and let it stand for 12 hours. After the static mixture was dried in a vacuum oven at 100 ^o C, it was placed in a temperature-programmed tube furnace under an argon atmosphere and calcined at 400 ^o C for 5 hours to obtain a Cu/V ₂ O ₃ catalyst with a loading capacity of 0.5%. . The preparation method of the V ₂ O ₃ catalyst loaded with other metals can refer to the preparation steps of the supported copper catalyst. The concentration of the metal salt can be adjusted according to the loading amount, and the loading amount is generally 0.5% to 20%.

Example 2: According to the quantity ratio of m(V ₂ O ₅ )/g:V(ethylene glycol)/ml=1:120, V ₂ O ₅ powder was dispersed in ethylene glycol under vigorous stirring. At room temperature, stirred for 0.5h to obtain an orange-yellow suspension. The suspension was transferred into a polyethylene-lined reactor to a filling degree of about 80%. The reactor was placed in an oven at 200 ^o C for 2 days, and then cooled to room temperature naturally. Separate the blue solid that sinks to the bottom, wash it with ethanol and water, and wash it by suction filtration or centrifugation. During the washing process, it can be observed that the solid gradually changes from blue to gray-black, and the washed solid is dried in a vacuum oven at 90 ^o C for 12 hours. The dried powder was calcined at 400 ^o C for 5 h in a temperature-programmed tube furnace under an argon atmosphere. The X-ray diffraction analysis of the sample obtained by calcination showed that the sample was pure vanadium trioxide (PDF#71-0342). According to the Scherrer formula, the average particle diameter calculated according to the (104) diffraction peak is about 14nm. The scanning electron microscope and transmission electron microscope of the sample are similar to the results in Figure 8 and Figure 9, and the microscopic morphology of the sample is also a rectangular block assembled from multiple small crystal grains.

To prepare the supported V ₂ O ₃ catalyst, prepare a 2 mol/L copper acetate aqueous solution according to the required loading amount, immerse the prepared V ₂ O ₃ in the aqueous solution, and let it stand for 15 hours. After the static mixture was dried in a vacuum oven at 90 ^o C, it was placed in a temperature-programmed tube furnace under an argon atmosphere and calcined at 400 ^o C for 5 hours to obtain a Cu/V ₂ O ₃ catalyst with a loading capacity of 1%. . The preparation method of the V ₂ O ₃ catalyst loaded with other metals can refer to the preparation steps of the supported copper catalyst. The concentration of the metal salt can be adjusted according to the loading amount, and the loading amount is generally 0.5% to 20%.

Example 3: Adjust m(V ₂ O ₅ )/g: V(methanol)/ml=1:140, the concentration of copper acetate aqueous solution is 4mol/L, the drying temperature is 120 ^o C, the calcination time is 8h, and the rest The conditions are the same as example 2. X-ray diffraction analysis of the sample indicated that the sample was pure vanadium trioxide (PDF #71-0342). According to the Scherrer formula, the average particle diameter calculated according to the (104) diffraction peak is about 14nm. The scanning electron microscope and transmission electron microscope of the prepared V ₂ O ₃ sample are similar to the results in Figure 8 and Figure 9, and the microscopic appearance of the sample is also a rectangular block assembled from multiple small crystal grains. A Cu/V ₂ O ₃ catalyst with a copper content of 2% can be obtained by loading. The preparation method of the V ₂ O ₃ catalyst loaded with other metals can refer to the preparation steps of the supported copper catalyst. The concentration of the metal salt can be adjusted according to the loading amount, and the loading amount is generally 0.5% to 20%.

Example 4: Adjust m(V ₂ O ₅ )/g: V(methanol)/ml=1:140, the concentration of copper nitrate aqueous solution is 6mol/L, the drying temperature is 120 ^o C, the calcination time is 8h, and the rest The conditions are the same as example 1. X-ray diffraction analysis of the sample indicated that the sample was pure vanadium trioxide (PDF #71-0342). According to the Scherrer formula, the average particle diameter calculated according to the (104) diffraction peak is about 14nm. The scanning electron microscope and transmission electron microscope of the prepared V ₂ O ₃ sample are similar to the results in Figure 8 and Figure 9, and the microscopic appearance of the sample is also a rectangular block assembled from multiple small crystal grains. A Cu/V ₂ O ₃ catalyst with a copper content of 5% can be obtained by loading. The preparation method of the V ₂ O ₃ catalyst loaded with other metals can refer to the preparation steps of the supported copper catalyst. The concentration of the metal salt can be adjusted according to the loading amount, and the loading amount is generally 0.5% to 20%.

The activity of the catalyst prepared by the present invention can adopt following method to test:

A fixed-bed quartz tube reactor was used to detect the composition of the reaction mixture gas by gas chromatography. Methanol vapor (vaporization temperature 0-30 ^o C) was brought into the reactor to contact with the catalyst through an inert carrier gas, the reaction temperature was 300-400 ^o C, and the amount of catalyst was 0.1 g. The contents of methanol and formaldehyde in the reacted gas and H ₂ , CO and CO ₂ in the tail gas were respectively determined by gas chromatography.

The reactor is a quartz tube with an inner diameter of 4.0 mm. The new V ₂ O ₃ or supported V ₂ O ₃ catalyst is fixed on the constant temperature section of the quartz tube with deactivated quartz wool, and the temperature of the catalyst bed is measured by a nickel-silicon-nickel-silicon thermocouple , a thermocouple was placed at the center of the catalyst bed to measure the temperature.

Adjust the temperature of the external electric furnace used to heat the reactor to bring the catalyst bed to the desired temperature. The reaction temperature is 200-600 ^o C, and the height of the catalyst bed is 5-30 mm. The flow rate of the carrier gas is controlled at 10-30 sccm (sccm: under standard conditions, ml/min), the pressure is controlled at 0.1-0.5Mpa, and the particle size of the catalyst used is 50-70 mesh.

Test the activity of the V ₂ O ₃ catalyst prepared in Example 1 for the direct dehydrogenation of methanol to produce anhydrous formaldehyde, wherein Figure 4 is the conversion rate of methanol, and Figure 5 is the selectivity of the catalyst to formaldehyde. It can be seen from the conversion rate graph of methanol that the conversion rate of methanol shows an overall upward trend with the increase of temperature. The slight decrease at 250 ^o C is due to the decrease in the selectivity of the catalyst to dimethyl ether and methyl formate, while the conversion of methanol increases rapidly when the temperature is higher than 250 ^o C, and the conversion can be reduced at 350 ^o C. Up to 99.33%. It can be seen from the selectivity diagram of formaldehyde that the selectivity of formaldehyde increases with the increase of temperature. Similar to the change of methanol conversion rate, the selectivity of formaldehyde increases sharply when the temperature is higher than 250 ^o C, and the selectivity can reach 90.06% when the reaction temperature is 350 ^o C. The stability test of the catalyst for the direct dehydrogenation of methanol to anhydrous formaldehyde is shown in Figure 6. It can be seen that after 60 hours of catalytic reaction, the yield of formaldehyde is maintained at about 87%, while the conversion rate of methanol is maintained above 99%. Therefore, the catalyst has very good activity and stability. Figure 7 is the XRD spectrum of the catalyst before and after the stability test. It can be seen that the phase of the catalyst does not change before and after the reaction. According to the (104) diffraction peak, the Scherrer formula is used to calculate that the average particle diameter of the catalyst after the reaction is 15nm relative to that before the reaction. The 14nm has no obvious change, indicating that the catalyst has quite good stability.

Claims (8)

1. a kind of methanol direct dehydrogenation produces the V ₂ O ₃ preparation method of anhydrous formaldehyde catalyst, it is characterized in that: first V ₂ O ₅ powder is dispersed in organic reductant under stirring, sealing, heating, reaction time ; The separated solid is washed and dried, and then calcined to obtain the V ₂ O ₃ catalyst. 2 . The method for preparing V ₂ O ₃ catalyst according to claim 1 , characterized in that: the organic reducing agent is one or more mixtures of methanol, ethanol, ethylene glycol and formaldehyde. 3. The preparation method of V ₂ O ₃ catalyst according to claim 1, characterized in that: m(V ₂ O ₅ )/g:V(organic reducing agent)/ml=1:100～1:140, stirring The time is generally more than 0.5h; the reaction temperature is 120-300 ^o C, and the reaction time is 6-150h. 4. The preparation method of V ₂ O ₃ catalyst according to claim 1, characterized in that: the drying can be carried out under vacuum condition or inert atmosphere, the drying temperature is generally about 80-120 ^o C, and the drying time is more than 12 hours; Calcination should be carried out under vacuum or inert atmosphere, with programmed temperature above 400 ^o C and calcination time above 5h. The inert gas is generally argon, helium, nitrogen or their mixture. 5. A V ₂ O ₃ catalyst obtained by the preparation method according to any one of claims 1-4. 6. A method for preparing a supported V ₂ O ₃ catalyst for producing anhydrous formaldehyde by direct dehydrogenation of methanol, characterized in that: the V ₂ O ₃ catalyst according to claim 5 is impregnated in a certain concentration of soluble metal salt In an aqueous solution, stand still, dry, and calcined to obtain the target product. 7. supported V according to claim ₆ The preparation method of O ₃ catalyst is characterized in that: the soluble metal precursor is the nitrate, acetate and chloride etc. of noble metal or transition metal, and the concentration of impregnating solution is according to It needs to be adjusted and prepared. The load is 0.5%-20%, and the standing time is 8-24 hours; the drying temperature is about 80-120 ^o C, and the time is more than 12 hours; Vacuum or gas-flowing program-controlled temperature tube furnace, the program-controlled temperature is above 400 ^o C and the calcination time is above 5 hours, and the inert gas is argon, helium, nitrogen or their mixture, etc. 8. A supported V ₂ O ₃ catalyst obtained by the preparation method according to claim 6 or 7.

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