CN1795987A - Catalyst of Mo, V, Te, Nb in use for reaction of producing crylic acid by selective oxidation of propane - Google Patents

Abstract

A molybdenum-vanadium-tellurium-niobium catalyst used in the selective oxidation of propane to acrylic acid and its preparation. The fresh catalyst is subjected to high-temperature activation treatment by chemical methods; the high-temperature activation treatment is carried out under a reaction atmosphere, and the volume ratio of the reaction gas V(C ₃ H ₈ )/V(air)/V(vapor)=1/5～25/0～24, the reaction space velocity is 500～1500mL/g-cat/h, the activation temperature is 400～700℃, and the activation time is 2～ 20h. The invention can make propane conversion rate and acrylic acid selectivity as high as 59% and 64% respectively. In the 100h reaction, the reaction stability is very good, and the stable reaction state is reached in the initial stage of the reaction.

Description

A molybdenum vanadium tellurium niobium catalyst for selective oxidation of propane to acrylic acid and preparation method thereof

Technical field:

The invention relates to a Mo-V-Te-Nb-O catalyst used in the reaction of propane selective oxidation to acrylic acid, its preparation method and its application in the reaction of propane selective oxidation to acrylic acid.

Background technique:

Acrolein, acrylic acid and its ester series products are widely used in paint, chemical fiber, textile, light industry and other industries, as well as oil exploration and oil additives. There are many process routes for producing acrolein, acrylic acid and their esters, and now the industry is mainly based on the oxidation of propylene. However, the cost of propylene is relatively high, which is about 1 to 2 times the price of propane. Therefore, the direct oxidation of acrolein and acrylic acid by using cheap and easy-to-obtain propane instead of propylene has become one of the research hotspots in the development and utilization of low-carbon alkanes. At the same time, there are abundant sources of propane, which is a main component of oil field gas, natural gas and refinery gas. In my country's Daqing, Tarim and other oil fields, the gas contains about 6% propane, the condensate contains 3-6% propane, the liquefied petroleum gas contains about 60% propane, and the natural gas wet gas contains about 15% propane. In the past, propane was generally used as a fuel, a small amount as a solvent, or as a feedstock for steam cracking to produce ethylene and propylene. In recent years, the catalytic processing of propane into intermediate chemical products or chemical raw materials with high added value has attracted more and more attention. Among them, the selective oxidation of propane to acrolein and acrylic acid is one of the directions in exploration.

To sum up, due to the low price and abundant sources of propane, the one-step oxidation of propane to directly synthesize acrolein or acrylic acid has significant economic benefits and practical significance.

However, there are two major difficulties in the selective oxidation of propane to acrylic acid:

First. As a saturated hydrocarbon, propane has a strong C-H bond. Propane has low reactivity under most reaction conditions. The energy required to activate the methyl C–H bonds of propane is sufficient to break the C–C bonds in the partially oxidized products, resulting in the production of lower carbon products. Therefore, one of the difficulties is how to use the catalytic process to selectively activate the strong C-H bond on propane, so that the relatively inert propane undergoes partial oxidation reaction; at the same time, avoid breaking the weak C-C bond in the C3 product, protect the active C3 intermediate product, and prevent its depth. oxidation.

Second, acrylic acid is the target product of propane partial oxidation reaction. Among all C3 products, some intermediate products can be further oxidized to acrylic acid, such as propylene or acrolein; while other intermediate products will not regenerate acrylic acid, such as acetone. Therefore, the second problem is how to prevent and inhibit the occurrence of by-product pathways and improve the selectivity of acrylic acid.

The key to solving the above two difficulties is to find an efficient and practical catalyst to make the reaction proceed in the direction of producing the target product, and improve the conversion rate of the reactant and the selectivity of the target product.

The catalysts currently used for the selective oxidation of propane to acrylic acid are generally multi-component and multifunctional catalysts. V-P-O catalyst (Catalysis Today, Vol.13, p679 (1992)), Mn-P-O catalyst (Chemistry Letter, p1733 (1989)), Bi-V-Mo-O catalyst (Catalysis Today, Vol.13, p673 (1992) ), Bi-V-Nb-Sb-Mo-O catalyst (US Patent No.5198580) etc. have all been used in this reaction, but the yield of acrylic acid is not more than 10%.

Among the mixed metal oxide catalysts, the Mo-V-Te-Nb-O catalyst has good catalytic performance for this reaction, and has the possibility of replacing the traditional catalyst for the two-step selective oxidation of propylene to acrylic acid in the current industrial production. In the patents (European Patent No.0608838 and European Patent No.0962253) on Mo ₁ V _0.3 Te _0.23 Nb _0.12 O _n catalysts reported by Mitsubishi Kasei Company of Japan and Rohm and Haas Company of the United States, the yield of acrylic acid is as high as 48% and 42%, a result that has not been replicated by many research groups in the US and Europe. In most research results (Topics in Catalysis, Vol.23, p39 (2003) and Journal of Catalysis, Vol.200, p222 (2001)), the yield of acrylic acid is only between 14% and 23%.

The preparation method of the Mo-V-Te-Nb-O catalyst has a great influence on its crystal structure and catalytic performance in the selective oxidation of propane to acrylic acid, which is one of the important reasons why the performance of the catalyst is difficult to repeat. At the same time, the Mo-V-Te-Nb-O catalyst needs to go through a special activation process before use, so that the catalyst can form the necessary active phase and selective phase. However, in numerous patents and published documents, no catalyst activation method is mentioned. Moreover, the long-term reaction stability of the catalyst in the reaction has not been reported.

Invention content:

The object of the invention is to improve the catalytic performance of the Mo-V-Te-Nb-O catalyst in the reaction of propane selective oxidation to acrylic acid through the activation process.

Another object of the present invention is to improve the stability of the Mo-V-Te-Nb-O catalyst in the selective oxidation of propane to acrylic acid through the activation process.

To achieve the above object, the invention provides a molybdenum vanadium tellurium niobium catalyst for the reaction of propane selective oxidation to acrylic acid, the relative molar ratio of each element in the catalyst is as follows:

0.25<rMo<0.98

0.003<rV<0.5

0.003<rTe<0.5

0.003<rNb<0.5

It is characterized in that: the catalyst is obtained by chemically performing high-temperature activation treatment on the fresh catalyst; the high-temperature activation treatment is carried out under a reaction atmosphere, and the volume ratio of the reaction gas is V(C ₃ H ₈ )/V(air)/V(vapor )=1/5～25/0～24, the reaction space velocity is 500～1500mL/g-cat/h, the activation temperature is 400～700°C, and the activation time is 2～20h.

Among them, rMo, rV, rTe, and rNb are the relative molar ratios of metal elements Mo, V, Te, and Nb, respectively, which are calculated based on the contents of all elements except the element O. For example, the molecular formula of Mo-V-Te-Nb-O catalyst is represented by Mo _a V _{b Tec} Nb _d O _n , and the relative molar ratio of each metal element is calculated as follows:

rMo=a/(a+b+c+d)

rV=b/(a+b+c+d)

rTe=c/(a+b+c+d)

rNb=d/(a+b+c+d)

The molybdenum vanadium tellurium niobium catalyst used for the selective oxidation of propane to produce acrylic acid in the invention specifically refers to the catalyst whose chemical composition is Mo ₁ V _0.3 Te _0.23 Nb _0.12 O _x , wherein x=4.5-4.8.

The present invention also provides a method for preparing a molybdenum vanadium tellurium niobium catalyst for the selective oxidation of propane to acrylic acid, which is characterized in that: the fresh catalyst is subjected to high-temperature activation treatment by chemical method; the high-temperature activation treatment is carried out under a reaction atmosphere, and the reaction The volume ratio of gas V(C ₃ H ₈ )/V(air)/V(vapor)=1/5～25/0～24, the reaction space velocity is 500～1500mL/g-cat/h, and the activation temperature is 400 ~700℃, the activation time is 2~20h.

In the preparation method of the molybdenum vanadium tellurium niobium catalyst used in the reaction of propane selective oxidation to acrylic acid of the present invention, the volume ratio of the reaction gas V(C ₃ H ₈ )/V(air)/V(vapor)=1/12～ 15/10~15, the reaction space velocity is 600~900mL/g-cat/h. The preferred activation temperature is 450-600°C, and the activation time is 10-14 hours.

In the preparation method of the molybdenum vanadium tellurium niobium catalyst used in the reaction of propane selective oxidation to acrylic acid of the present invention, the catalyst after the high temperature activation treatment can be ground into a powder with a particle size of less than 20um, shaped and granulated, and sieved into 20-30 meshes Catalyst particles.

In the preparation method of the molybdenum vanadium tellurium niobium catalyst used in the reaction of propane selective oxidation to acrylic acid of the present invention, the high temperature activation treatment process is:

——Put fresh catalyst into the reactor, and raise the temperature to 380°C at a rate of 6°C/min under the protection of flowing _N2 atmosphere

——Switch the _N2 atmosphere to the reaction atmosphere, after the reaction is stable for 10 minutes, then slowly raise the temperature to the activation temperature at a heating rate of 2°C/min, and keep it for a certain period of time, then cool down to 380°C at a rate of 2°C/min;

——Change the reaction atmosphere to _N2 atmosphere, and drop to room temperature under the protection of _N2 atmosphere.

In the preparation method of the molybdenum vanadium tellurium niobium catalyst used for the selective oxidation of propane to acrylic acid of the present invention, when the catalyst is activated under the reaction atmosphere, the oxygen concentration in the tail gas needs to be between 2% and 10%, preferably between 3% and 5%. %between.

In the preparation method of the molybdenum vanadium tellurium niobium catalyst used in the selective oxidation of propane to acrylic acid of the present invention, the fresh catalyst is obtained by using a rotary evaporator to prepare a catalyst precursor and then roasting, and the roasting is carried out under the protection of static _N2 gas, The temperature is 550～650℃, and the time is 1～3h.

The molybdenum vanadium tellurium niobium catalyst used for the selective oxidation of propane to produce acrylic acid provided by the invention can make the conversion rate of propane and the selectivity of acrylic acid as high as 59% and 64% respectively. In the 100h reaction, the reaction stability is very good, and the stable reaction state is reached in the initial stage of the reaction.

Description of drawings:

Fig. 1 is the reaction stability of fresh Mo-V-Te-Nb-O catalyst; Wherein, ○ carbon oxide selectivity, ● acrylic acid selectivity, ■ propane conversion rate;

Figure 2 is the reaction stability of the activated Mo-V-Te-Nb-O catalyst; wherein, △Acrylic acid selectivity, ◆Propane conversion rate, ◇Acrylic acid yield, ○Carbon oxide selectivity, propylene selectivity, ▲Acetic acid selectivity, □Other compound selectivity;

Figure 3 is the XRD pattern of the Mo-V-Te-Nb-O catalyst before and after activation; wherein, a is before activation, and b is after activation;

Figure 4 is the XRD pattern of fresh and activated Mo-V-Te-Nb-O catalysts under various atmospheres, a. Fresh catalyst; b. Catalyst activated under air atmosphere; c. In the presence of air and water vapor The catalyst activated under the atmosphere; d. The catalyst activated under the atmosphere containing nitrogen and water vapor; e. The catalyst activated under the reaction atmosphere.

Figure 5 is the XRD pattern of the activated Mo-V-Te-Nb-O catalyst reacted under different conditions; a the activated Mo-V-Te-Nb-O catalyst; b the catalyst after the reaction under anhydrous conditions ; c reacts under anhydrous conditions and then adds water to the catalyst.

Detailed ways:

In the selective oxidation of propane to acrylic acid, the reaction product is divided into gas and liquid phases. Gas phase products include CO, CO ₂ and C ₃ H ₆ . The liquid phase products include the target product acrylic acid, a small amount of by-product acetic acid, and trace amounts of by-products acrolein, acetone and propionic acid.

Conversion and selectivity and productive rate are calculated with the following formula:

Yield (%)=conversion rate×selectivity×100

(Mi: the number of moles of a certain product; ni: the number of carbon atoms contained in a certain product molecule)

Example 1

Ammonium paramolybdate, ammonium metavanadate, telluric acid and niobium oxalate are used as raw materials, and the molar ratio between metal atoms is 1:0.3:0.23:0.12. Catalysts were prepared using a rotary evaporator. First, put 6.425g of ammonium paramolybdate, 1.275g of ammonium metavanadate and 1.925g of telluric acid in a rotary evaporator, add 105mL of distilled water, heat to 80°C to dissolve completely, and obtain an orange-yellow clear solution. After rotating for 2 hours, cool down to 40°C. Then add 41.1mL ( _CNb5+ =9.8mg/mL) niobium oxalate solution, at this time the solution gradually becomes turbid and precipitates appear. Rotate for another 2h. The samples were then vacuum dried at 40 °C. The dried precursor is ground, shaped, granulated, sieved into 20-30 mesh particles, and roasted at 600°C for 2h under the protection of a static _N2 atmosphere. The calcined catalyst was ground, shaped, granulated, and sieved into catalyst particles of 20-30 meshes to obtain a fresh Mo ₁ V _0.3 Te _0.23 Nb _0.12 O _x catalyst. The XRD pattern is shown in FIG. 3 .

Example 2

Put 2.14g of the fresh catalyst of Example 1 into the reaction tube, and under the protection of flowing _N2 atmosphere, the temperature was raised to 380°C at a heating rate of 6°C/min; then the _N2 atmosphere was switched to a reaction atmosphere, and the reaction conditions were: raw material gas The volume ratio V(C ₃ H ₈ )/V(air)/V(vapor)=1/15/12, the reaction space velocity is 800mL/g-cat/h, the reaction temperature is 400°C, and then 2°C/min The heating rate is slowly raised to the activation temperature. After keeping under this condition for a certain period of time, the temperature was lowered to 380° C. at a rate of 2° C./min under the same reaction atmosphere. Switch to _N2 atmosphere again, and drop to room temperature under the protection of _N2 atmosphere. An activated catalyst is obtained. The XRD pattern is shown in Figure 3.

Example 3

2.14 g of the activated catalyst of Example 2 was used in the selective oxidation of propane to acrylic acid for a stability test. The reaction raw material gas ratio is V(C ₃ H ₈ )/V(air)/V(Vapor)=1/15/12, the reaction temperature is 400°C, and the reaction space velocity is 800mL/g-cat/h. During the reaction period of 100 hours under investigation, the conversion rate of propane has been kept between 57% and 59%, the selectivity of acrylic acid is basically between 63% and 65%, and the selectivity of other various by-products is also in a stable state. The content is very low. It can be seen that the activated catalyst not only has excellent reaction performance, but also is in a stable reaction state at the initial stage of the reaction.

Example 4

2.14 g of the catalyst of Example 2 after activation was installed in the same reactor as in Example 3 to carry out the reaction of propane selective oxidation to acrylic acid. The reaction raw material gas ratio is V(C ₃ H ₈ )/V(air)/(Vapor)=1/15/12, the reaction temperature is 380°C, and the reaction space velocity is 800mL/g-cat/h. The results are shown in Table 1.

Example 5

2.45 g of the activated catalyst of Example 2 was installed in the same reactor as in Example 3 to carry out the reaction of propane selective oxidation to acrylic acid. The reaction raw material gas ratio V(C ₃ H ₈ )/V(air)/V(Vapor)=1/15/12, the reaction temperature is 400°C, and the reaction space velocity is 700mL/g-cat/h. The results are shown in Table 1.

Example 6

1.73 g of the activated catalyst of Example 2 was installed in the same reactor as in Example 3 to carry out the reaction of propane selective oxidation to acrylic acid. The reaction raw material gas ratio is V(C ₃ H ₈ )/V(air)/V(Vapor)=1/10/12, the reaction temperature is 400°C, and the reaction space velocity is 800mL/g-cat/h. The results are shown in Table 1.

Example 7

2.45 g of the activated catalyst of Example 2 was installed in the same reactor as in Example 3 to carry out the reaction of propane selective oxidation to acrylic acid. The reaction raw material gas ratio is V(C ₃ H ₈ )/V(air)/V(Vapor)=1/20/12, the reaction temperature is 400°C, and the reaction space velocity is 800mL/g-cat/h. The results are shown in Table 1.

Comparative example 1

3.0 g of the unactivated fresh catalyst of Example 1 was used in the selective oxidation of propane to acrylic acid for a stability test. The reaction raw material gas ratio is V(C ₃ H ₈ )/V(air)/V(Vapor)=1/15/12, the reaction temperature is 400°C, and the reaction space velocity is 560mL/g-cat/h. During the reaction period of 200 h under consideration, the conversion of propane remained at 19%, while the selectivity of acrylic acid increased from 32% to 50%, and the selectivity of CO _x decreased from 51% to 34%. Reaction performance is low and has been in an unstable state. As shown in Figure 1.

Comparative example 2

The unactivated fresh catalyst of Example 1 was used in the reaction of propane selective oxidation to acrylic acid. Reaction conditions: raw material gas volume ratio V(C ₃ H ₈ )/V(air)/V(vapor)=1/15/12, space velocity 800mL/g-cat/h, catalyst dosage 2.14g. During the reaction period of 200 h under consideration, the conversion of propane remained at 19%, while the selectivity of acrylic acid increased from 32% to 50%, and the selectivity of CO _x decreased from 51% to 34%. Reaction performance has been in an unstable state.

Comparative example 3

The fresh catalyst of Example 1 was activated under air atmosphere, and the operation process was the same as that of Example 2 with reaction gas activation. After the catalyst is kept at a high temperature in the atmosphere for a period of time, it is then ground and shaped, and sieved into catalyst particles of 20-30 meshes. 2.14 g of the catalyst was installed in the same reactor as in Example 2 for the selective oxidation of propane to produce acrylic acid. The reaction raw material gas ratio is V(C ₃ H ₈ )/V(air)/V(Vapor)=1/15/12, the reaction temperature is 400°C, and the reaction space velocity is 800mL/g-cat/h. In the reaction result, the conversion rate of propane was 1.23%, and no acrylic acid was produced.

Comparative example 4

The fresh catalyst of Example 1 is activated under an atmosphere containing air and water vapor, and the operation process is the same as the activation process with the reaction gas of Example 2. After the catalyst is treated at high temperature under the atmosphere for a period of time, it is ground and shaped, and sieved into catalyst particles of 20-30 meshes. 2.14 g of the catalyst was installed in the same reactor as in Example 2 for the selective oxidation of propane to produce acrylic acid. The reaction raw material gas ratio is V(C ₃ H ₈ )/V(air)/V(Vapor)=1/15/12, the reaction temperature is 400°C, and the reaction space velocity is 800mL/g-cat/h. In the reaction result, the conversion rate of propane was 0.32%, and no acrylic acid was produced.

Comparative Example 5

The fresh catalyst of Example 1 was activated under an atmosphere containing nitrogen and water vapor, and the operation process was the same as the activation process with the reaction gas of Example 2. After the catalyst is treated at high temperature under the atmosphere for a period of time, it is ground and shaped, and sieved into catalyst particles of 20-30 meshes. 2.14 g of the catalyst was installed in the same reactor as in Example 2 for the selective oxidation of propane to produce acrylic acid. The reaction raw material gas ratio is V(C ₃ H ₈ )/V(air)/V(Vapor)=1/15/12, the reaction temperature is 400°C, and the reaction space velocity is 800mL/g-cat/h. Among the reaction results, the conversion of propane was 58.4%, and the selectivity of acrylic acid was 41.4%.

Comparative example 6

2.14g of the activated Mo-V-Te-Nb-O catalyst was subjected to the selective oxidation of propane to acrylic acid under anhydrous conditions. The reaction raw material gas ratio is V(C ₃ H ₈ )/V(air)=1/15, the space velocity is 450mL/g-cat/h, and the reaction temperature is 400°C. After reacting for 5 hours, add water vapor to the raw material gas, the ratio of raw material gas becomes V(C ₃ H ₈ )/V(air)/V(vapor)=1/15/12, and the space velocity becomes 800mL/g-cat /h, the reaction temperature is still 400°C. The propane conversion and acrylic acid selectivity at this time were 57.4% and 64.5%, respectively. Same as the reaction result in Example 3. It can be seen that even if the catalyst activated by the reaction atmosphere has been reacted under the condition of anhydrous, the reaction performance of the catalyst will not be affected. It shows that the catalyst activated by the reaction atmosphere can withstand the fluctuation of the ratio of the reaction raw material gas in a wide range without causing the deactivation of the catalyst.

Comparative Example 7

Manhua Lin et al. investigated the Mo-V-Te-Nb-O catalyst in the selective oxidation of propane over a mixed metal oxide catalyst in the title of the article, Catalysis Today, 61(2000) 223-229 Catalytic performance in the oxidation to acrylic acid reaction. 20 g of catalyst were packed in a stainless steel tube reactor with an inner diameter of 11 mm. The reaction raw material gas ratio is V(C ₃ H ₈ )/V(air)/V(vapor)=3/50/47, the space velocity is 1200h ^-1 , the reaction pressure is 7psig, and the reaction temperature is 391°C. Experimental results: the conversion of propane and the selectivity of acrylic acid were 18.0% and 26.0% respectively. The molar concentration of acrylic acid in the liquid product was 68.4% (see Table 2).

Comparative Example 8

Lin Luo et al. titled the article "Comparison of Reaction Pathways for the PartialOxidation of Propane over Vanadyl Ion-Exchanged Zeolite Beta and Mo ₁ V _0.3 Te _0.23 Nb _0.12 O _x ", J.Catal.200(2001) 222-231 in the article Mo ₁ V _0.3 Te _0.23 Nb _0.12 O _x catalyst was studied for the selective oxidation of propane to acrylic acid. The amount of catalyst used was 1.75g, the reaction raw material gas ratio V(C ₃ H ₈ )/V(O ₂ )/V(He)=1/3.15/11.85, the total gas flow rate was 36.2mL/min, and the reaction temperature was 400°C. Experimental results: the conversion of propane and the selectivity of acrylic acid were 58.3% and 39.2% respectively. The molar concentration of acrylic acid in the liquid product was 85.0% (see Table 2).

Comparative Example 9

Table 2 shows the reactivity of the Mo ₁ V _0.3 Te _0.23 Nb _0.12 O _x catalyst prepared in this patent after being activated by the reaction atmosphere. The reaction conditions are as described in Example 3. The molar concentration of acrylic acid in the liquid product is as high as 93.3%. Much higher than other literature results (such as Comparative Example 7 and Comparative Example 8).

Because according to relevant European patent reports (European Patent No.0962253 and European Patent No.0608838), in the crystal structure diffraction peak of the Mo-V-Te-Nb-O catalyst with good catalytic performance for the selective oxidation of propane to acrylic acid, in There are five characteristic diffraction peaks at the diffraction angle 2θ of 22.1°, 28.2°, 36.2°, 45.2° and 50.0°. As can be seen from Fig. 3, embodiment 1 catalyst before activation is 36.2 ° and 50.0 ° place lacks two characteristic diffraction peaks at diffraction angle, only has three characteristic diffraction peaks at 22.1 °, 28.2 ° and 45.2 ° place at diffraction angle, and The relative intensity of the diffraction peaks is weak. This is the main reason for the poor reactivity of the fresh Example 1 catalyst. The activated catalyst has all five characteristic diffraction peaks, and the relative peak intensity ratio is consistent with the patent. Therefore, the reactivity of the activated catalyst is greatly improved.

Fig. 4 is the XRD pattern of the catalyst activated under four different atmospheres, such as reaction atmosphere, air, mixed atmosphere of air and water vapor, and mixed atmosphere of nitrogen and water vapor. It can be seen that only the catalyst activated by the reaction atmosphere has five characteristic diffraction peaks at the diffraction angles 2θ of 22.1°, 28.2°, 36.2°, 45.2° and 50.0°. However, catalysts activated by other atmospheres do not fully possess all five characteristic peaks. Therefore, the catalyst activated by the reaction atmosphere has good catalytic performance, while the catalytic performance of the catalyst activated by other atmospheres is not as good as the former.

Figure 5 shows the XRD patterns of several catalysts, a represents the catalyst activated by the reaction atmosphere; b represents the activated catalyst reacted for 5 hours under anhydrous conditions, and the catalyst was protected with N ₂ ; c represents the catalyst under anhydrous conditions After reacting in the presence of water for 5 hours, the catalyst was protected with N ₂ . By comparison, it is found that the XRD curves of b and c are exactly the same as a. It can be seen that even if the catalyst activated by the reaction atmosphere has been reacted under anhydrous conditions, the crystal phase structure of the catalyst will not be affected. It shows that the catalyst activated by the reaction atmosphere can withstand the fluctuation of the ratio of the reaction raw material gas in a large range without causing the change of the catalyst structure.

Partial reaction result in the embodiment of table 1 Propane Conversion (%) Acrylic acid selectivity (%) Acrylic acid yield (%) Example 4 45.6 71.8 32.7 Example 5 65.0 61.8 40.1 Example 6 55.0 68.8 37.9 Example 7 58.4 58.0 33.9

Partial reaction result in the comparative example of table 2 T(°C) Propane Conversion (%) Acrylic acid selectivity (%) Acrylic acid yield (%) Molar concentration of acrylic acid in liquid product (%) Comparative Example 7 391 18.0 26.0 4.7 68.4 Comparative Example 8 400 58.3 39.2 22.9 85.0 Comparative Example 9 400 59.1 63.6 37.6 93.3

Claims (10)

1. A molybdenum vanadium tellurium niobium catalyst for the reaction of propane selective oxidation to acrylic acid, the relative molar ratio of each element in the catalyst is as follows: 0.25<rMo<0.98 0.003<rV<0.5 0.003<rTe<0.5 0.003<rNb<0.5 It is characterized in that: the catalyst is obtained by chemically performing high-temperature activation treatment on the fresh catalyst; the high-temperature activation treatment is carried out under a reaction atmosphere, and the volume ratio of the reaction gas is V(C ₃ H ₈ )/V(air)/V(vapor )=1/5～25/0～24, the reaction space velocity is 500～1500mL/g-cat/h, the activation temperature is 400～700°C, and the activation time is 2～20h. 2. The molybdenum vanadium tellurium niobium catalyst for the selective oxidation of propane to acrylic acid according to claim 1, wherein the chemical composition of the catalyst is Mo ₁ V _0.3 Te _0.23 Nb _0.12 O _x , where x=4.5-4.8. 3. A method for preparing molybdenum, vanadium, tellurium, and niobium catalysts for the selective oxidation of propane to acrylic acid according to claim 1, characterized in that: the fresh catalyst is subjected to high-temperature activation treatment by chemical methods; the high-temperature activation treatment is carried out under a reaction atmosphere , the volume ratio of the reaction gas V(C ₃ H ₈ )/V(air)/V(vapor)=1/5～25/0～24, the reaction space velocity is 500～1500mL/g-cat/h, the activation temperature The temperature is 400~700℃, and the activation time is 2~20h. 4. The method for preparing molybdenum vanadium tellurium niobium catalyst for the reaction of propane selective oxidation to acrylic acid according to claim 3, characterized in that: the volume ratio of the reaction gas is V(C ₃ H ₈ )/V(air)/ V(vapor)=1/12～15/10～15, and the reaction space velocity is 600～900mL/g-cat/h. 5. The method for preparing the molybdenum vanadium tellurium niobium catalyst for the selective oxidation of propane to acrylic acid according to claim 4, characterized in that: the activation temperature is 450-600° C., and the activation time is 10-14 hours. 6. According to claim 3, the preparation method of the molybdenum vanadium tellurium niobium catalyst for the selective oxidation of propane to acrylic acid is characterized in that: the catalyst after the high temperature activation treatment is ground into a powder with a particle size of less than 20um, and molded into Granules, sieved into 20-30 mesh catalyst particles. 7. According to claim 3, the preparation method of the molybdenum vanadium tellurium niobium catalyst for the selective oxidation of propane to acrylic acid is characterized in that the high temperature activation treatment process is: ——Put fresh catalyst into the reactor, and raise the temperature to 380°C at a rate of 6°C/min under the protection of flowing _N2 atmosphere ——Switch the _N2 atmosphere to the reaction atmosphere, after the reaction is stable for 10 minutes, then slowly raise the temperature to the activation temperature at a heating rate of 2°C/min, and keep it for a certain period of time, then cool down to 380°C at a rate of 2°C/min; ——Change the reaction atmosphere to _N2 atmosphere, and drop to room temperature under the protection of _N2 atmosphere. 8. According to claim 3, the preparation method of molybdenum vanadium tellurium niobium catalyst for the selective oxidation of propane to acrylic acid is characterized in that: when the catalyst is activated under the reaction atmosphere, the oxygen concentration in the tail gas needs to be between 2% and 10% . 9. The method for preparing the molybdenum vanadium tellurium niobium catalyst for the selective oxidation of propane to acrylic acid according to claim 8, characterized in that: when the catalyst is activated under the reaction atmosphere, the oxygen concentration in the tail gas is between 3% and 5%. . 10. According to the preparation method of molybdenum vanadium tellurium niobium catalyst for the selective oxidation of propane to acrylic acid according to claim 3, it is characterized in that: the fresh catalyst is obtained by using a rotary evaporator to prepare a catalyst precursor and then roasting it. It is carried out under the protection of static N ₂ gas, the temperature is 550-650°C, and the time is 1-3 hours.

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