Application of carbon nitride material in catalytic oxidation dehydrogenation of low carbon alkanes to olefins

Abstract

The application belongs to the technical field of catalyst application, and particularly relates to application of carbon nitride material in preparation of olefins through low-carbon alkane oxidative dehydrogenation, wherein the carbon nitride material is activated under air, oxygen, carbon dioxide, nitrogen dioxide or water vapor atmosphere to obtain activated carbon nitride material, and the activated carbon nitride material is directly applied to the low-carbon alkane oxidative dehydrogenation reaction; the carbon nitride is low in preparation cost, simple and easy to obtain, suitable for industrialized production of the low-carbon alkane oxidative dehydrogenation to prepare olefins, high in olefin selectivity, free of carbon deposition, long in service life, and wide in application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalyst application, and particularly relates to application of carbon nitride material in catalytic oxidative dehydrogenation of low-carbon alkane to prepare olefin. BACKGROUND

[0002] With the increasing proven reserves of natural gas and the rapid development of mining technology, the cost of low-carbon alkanes is greatly reduced. The catalytic conversion of abundant low-carbon alkanes (C2-C5) in natural gas into corresponding olefins and oxygen-containing compounds and other chemical raw materials can greatly alleviate the crisis of the shortage of chemical raw materials. In low-carbon alkanes, the C-H bond is relatively stable, and it is difficult to activate, which leads to the need for high energy in the process of alkane dehydrogenation without oxygen, thereby increasing the production cost. The process of oxidative dehydrogenation of low-carbon alkanes is not limited by thermodynamics, and is the most promising method to replace the process of dehydrogenation without oxygen to produce olefins. However, the C-C bond energy in the product olefin is weaker than the C-H bond in the reactant, which causes deep oxidation products (CO, CO2) to easily appear in the process of oxidative dehydrogenation of low-carbon alkanes to produce olefins, thereby reducing the selectivity of the target product olefin. Therefore, developing a highly efficient catalyst is still a problem to be solved.

[0003] Currently, metal oxides are mostly used as catalysts for the oxidative dehydrogenation of low-carbon alkanes. However, due to the strong oxidizing property of such catalysts, the yield of olefins is rarely able to break through 20%. In recent years, researchers have found that boron nitride materials exhibit excellent olefin selectivity in the oxidative dehydrogenation of low-carbon alkanes, and the yield can reach more than 20% (Grant J T, Carrero CA, Goeltl F, et al. Selective oxidative dehydrogenation of propane to propene using boron nitride catalysts [J]. Science, 2016, 354(6319): 1570-1573; Venegas JM, Grant J T, McDermott W P, et al. Selective Oxidation of n-Butane and Isobutane Catalyzed by Boron Nitride [J]. ChemCatChem, 2017, 9(12): 2118-2127; Huang R, Zhang B, Wang J, et al. Direct Insight into Ethane Oxidative Dehydrogenation over Boron Nitrides [J]. ChemCatChem, 2017, 9(17): 3293-3297). The emergence of boron nitride catalysts has greatly promoted the industrialization of the oxidative dehydrogenation of low-carbon alkanes. However, the preparation process of boron nitride materials is complex and the cost is high. Therefore, it is still a great challenge to develop a catalyst with excellent catalytic performance and low price. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art and proposes the application of carbon nitride materials in the catalytic oxidative dehydrogenation of low-carbon alkanes to prepare olefins. The simple preparation process of carbon nitride non-metallic materials facilitates large-scale preparation, and the carbon nitride non-metallic materials show high selectivity and stability in the oxidative dehydrogenation of low-carbon alkanes such as propane, n-butane, isobutane and isopentane.

[0005] To achieve the above-mentioned purpose, the specific process of using carbon nitride materials to catalyze the oxidative dehydrogenation of low-carbon alkanes to prepare olefins is as follows:

[0006] (1) Activating the carbon nitride material in an air, oxygen, carbon dioxide, nitrogen dioxide or water vapor atmosphere to obtain an activated carbon nitride material, the activation temperature is 200-550℃, and the activation time is 6-72h;

[0007] (2) The activated carbon nitride material is directly applied to the low carbon alkane oxidative dehydrogenation reaction, the reaction temperature is 300-550 DEG C, wherein the propane is preferably 400-550 DEG C, the n-butane and isobutane are preferably 300-450 DEG C, and the pentane is preferably 300-450 DEG C, and the volume ratio of the reactant to the oxidant is (1-8):1, preferably (3-5):1.

[0008] The oxidant in the low carbon alkane oxidative dehydrogenation reaction is oxygen, air, carbon dioxide, carbon monoxide, carbon dioxide, carbon monoxide or steam, preferably air or oxygen; inert gas can be used as a diluent in the reaction, or no diluent can be used.

[0009] The inert gas is helium, nitrogen or argon, preferably nitrogen.

[0010] The working principle of the application is that after the carbon nitride is activated by the oxidant, the sawtooth position generates carbonyl through oxidation reaction, the carbonyl reacts with hydrogen in the low carbon alkane at a certain temperature to become hydroxyl, thereby removing hydrogen in the low carbon alkane to obtain the corresponding olefin, and since the carbon nitride has a stable two-dimensional structure, the selectivity of the olefin in the product is improved while the thermal stability of the material is ensured.

[0011] Compared with the commercial boron nitride in the prior art, the carbon nitride achieves similar olefin selectivity, but the cost of the carbon nitride catalyst is lower, and compared with the traditional vanadium catalyst, the selectivity of the olefin is increased by nearly 10% under similar alkane conversion rates; in the 48-hour stability test, the catalytic activity of the carbon nitride is almost unchanged, and the yield of the olefin reaches 20%; more importantly, when the alkane conversion rate is less than 10%, the total selectivity of the olefin reaches about 90%; the carbon nitride has low preparation cost, is simple and easy to obtain, is suitable for industrialized production of low carbon alkane oxidative dehydrogenation to olefin, has high olefin selectivity, no carbon deposition and long service life, and has a very broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The olefin selectivity of the carbon nitride in the application under different conversion rates in the propane oxidative dehydrogenation reaction.

[0013] Figure 2 The product selectivity comparison of the carbon nitride, boron nitride and silicon dioxide supported vanadium in the application under similar conversion rates in the propane oxidative dehydrogenation reaction.

[0014] Figure 3 The stability of the carbon nitride in the application in the propane oxidative dehydrogenation reaction. DETAILED DESCRIPTION

[0015] The application is further described below by way of examples and in conjunction with the drawings, but is not limited thereto.

[0016] The instruments described in the present embodiments can be obtained from commercial sources unless otherwise specified.

[0017] In the present embodiments, the conversion rate and selectivity are calculated as follows:

[0018] Alkane conversion rate (%) = [(moles of alkane before reaction - moles of alkane after reaction) / moles of alkane before reaction] x 100%

[0019] Product selectivity (%) = [number of carbon atoms in product / (number of carbon atoms in alkane before reaction - number of carbon atoms in alkane after reaction)] x 100%

[0020] Product yield (%) = alkane conversion rate (%) x product selectivity (%)

[0021] Example 1:

[0022] The application of the carbon nitride material in the present embodiments in catalyzing the oxidative dehydrogenation of low-carbon alkanes to prepare olefins includes the following steps:

[0023] 1) 1.0 g of the carbon nitride material was placed in a quartz tube in a fixed bed reactor and heated to 450°C at a rate of 1°C / min under the protection of air;

[0024] 2) After the temperature in step 1) was stabilized, a feed gas mixture was introduced, wherein the volume ratio of propane to air was 2:1, the total flow rate of the feed gas mixture was 20 ml / min, the reaction temperature was 450°C, the pressure was 0.1 MPa, and after half an hour of stabilization, data collection and testing were started. The test results showed that the conversion rate of propane was 3.1% and the selectivity of propylene was 87%.

[0025] Example 2:

[0026] The application of the carbon nitride material in the present embodiments in catalyzing the oxidative dehydrogenation of low-carbon alkanes to prepare olefins includes the following steps:

[0027] 1) 1.5 g of the carbon nitride material was placed in a quartz tube in a fixed bed reactor and heated to 500°C at a rate of 2°C / min under the protection of air;

[0028] 2) After the temperature in step 1) was stabilized, a feed gas mixture was introduced, wherein the volume ratio of propane to air was 2:1, the total flow rate of the feed gas mixture was 30 ml / min, the reaction temperature was 500°C, the pressure was 0.1 MPa, and after half an hour of stabilization, data collection and testing were started. The test results showed that the conversion rate of propane was 13% and the selectivity of propylene was 76%.

[0029] Example 3:

[0030] The application of the carbon nitride material in the catalytic preparation of olefins from low-carbon alkane oxidative dehydrogenation is as follows:

[0031] 1) 0.7 g of the carbon nitride material was placed in a quartz tube in a fixed bed reactor, and was heated to 460°C at a rate of 5°C / min under the protection of air;

[0032] 2) After the temperature in step 1) was stabilized, a raw material mixed gas was introduced, wherein the volume ratio of propane, oxygen and helium was 4:1:4, and helium was used as a diluent. The total flow rate of the raw material mixed gas was 18 ml / min, the reaction temperature was 460°C, and the pressure was 0.1 MPa. After being stabilized for half an hour, data was collected every 10°C to observe the changes in propane conversion and product selectivity, and the test results are shown in Table 1. Figure 1

[0033] Example 4:

[0034] In this example, the selectivity of the boron nitride catalyst was compared with that of the carbon nitride catalyst, and the specific steps were as follows:

[0035] 1.0 g of commercially available boron nitride (Sigma Reagent Company) was weighed, and then the steps in Example 3 were repeated. The changes in propane conversion and product selectivity were collected, and similar propane conversion data were selected for comparison. The test results are shown in Table 2. Figure 2

[0036] Example 5:

[0037] In this example, the selectivity of the vanadium catalyst was compared with that of the carbon nitride catalyst, and the specific steps were as follows:

[0038] 1) Ammonium metavanadate was directly loaded on commercially available high specific surface area SiO2 material, and then the V / SiO2 catalyst was obtained by treating at 500°C for three hours under an air atmosphere;

[0039] 2) 0.5 g of the V / SiO2 catalyst prepared in step 1) was weighed, and then the steps in Example 3 were repeated. The changes in propane conversion and product selectivity were collected, and similar propane conversion data were selected for comparison. The test results are shown in Table 3. Figure 2

[0040] Example 6:

[0041] The application of the carbon nitride material in the catalytic preparation of olefins from low-carbon alkane oxidative dehydrogenation is as follows:

[0042] 1) 1.0 g of the carbon nitride material was placed in a quartz tube in a fixed bed reactor, and was heated to 500°C at a rate of 5°C / min under the protection of air;

[0043] ​​​2) After temperature stabilization in step 1), the raw material mixed gas was introduced, wherein the volume ratio of propane, oxygen and helium was 4:1:4, helium was used as diluent, the total flow rate of raw material gas was 27 ml / min, the reaction temperature was 500℃, the pressure was 0.1 MPa, after stabilization for half an hour, data was collected every 2 hours, and continuous collection was performed for 48 hours, so as to observe the stability of the catalytic performance of the catalyst, and the test results are shown in Table 2. Figure 3 Table 2

Claims

1. Use of a carbon nitride material in the catalytic oxidative dehydrogenation of lower alkane to olefin, characterized in that, The low-carbon alkane is propane, and a specific process in which the carbon nitride material catalyzes the oxidative dehydrogenation of propane to prepare propylene includes the following steps: 1) 1.5 g of the carbon nitride material is placed in a quartz tube in a fixed bed reactor, and is heated to 500 DEG C at a rate of 2 DEG C / min under the protection of air; 2) After the temperature in step 1) is stabilized, the raw material mixed gas is introduced, wherein the volume ratio of propane to air is 2:1, the total flow rate of the raw material mixed gas is 30 ml / min, the reaction temperature is 500 DEG C, the pressure is 0.1 MPa, and after being stabilized for half an hour, data is collected and tested, and the test results show that the conversion rate of propane is 13% and the selectivity of propylene is 76%.

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