Current-responsive catalyst for enhancing cracking of light alkane to coproduce low-carbon olefins, and use

Abstract

The present application discloses a current-responsive catalyst for enhancing cracking of a light alkane to coproduce low-carbon olefins, and a use. The catalyst is mainly composed of an MFI-type HZSM-5 molecular sieve and a semiconductor-type metal oxide. The current-responsive catalyst of the present application can realize directional cracking of a light alkane under mild conditions (300-450ºC) to prepare low-carbon olefins, and compared with the case under the same conditions without an electric field, the conversion rate of the light alkane can be improved by 15-40%, and the selectivity for the low-carbon olefins can be improved by 5-20%. A light hydrocarbon cracking process based on the current-responsive catalyst has the advantages of mild reaction conditions, high energy utilization rate, etc., the problems of high temperatures (650-680ºC) and high energy consumption in traditional light hydrocarbon catalytic cracking processes are solved, and the concept of energy conservation, environmental protection, and green and sustainable development is met.

Description

Current response catalyst for strengthening light alkane cracking to produce low carbon olefins and application TECHNICAL FIELD

[0001] The present application belongs to the technical field of petroleum chemical industry, and particularly relates to a current response catalyst for strengthening light alkane cracking to produce low carbon olefins and application. BACKGROUND

[0002] With the sustained and rapid development of China's economy, the demand for basic chemical raw materials such as ethylene and propylene is increasing. The relatively mature process for preparing ethylene and propylene in industry is steam cracking of naphtha, which is an energy-intensive process with high energy consumption (reaction temperature higher than 800℃), large carbon emission and difficult product control.

[0003] The development of green and low-carbon chemical technology is of great significance to environmental protection and economic development, and is an inevitable choice for the sustainable development of the chemical industry. Low-carbonization refers to the replacement of high-carbon coal or oil resources with non-carbon or low-carbon renewable energy or other new energy, as well as the reduction and utilization of CO2 to achieve low-carbon emission in the whole process. The "double carbon" goal promotes the transformation of chemical processes to green and low-carbon, and the electrification of core chemical equipment, ultimately realizing clean and renewable energy-based heat and power supply.

[0004] At present, the catalytic technology under mild conditions mainly includes photocatalysis, plasma catalysis, electrocatalysis, biocatalysis, etc. Among them, the thermal-electric coupling catalytic technology realized under the action of an external electric field is one of the research hotspots, and the core lies in the development of high-activity current response catalysts. Current response catalysts are a kind of catalytic materials with suitable electrical conductivity and can generate current under the condition of applying an electric field. The current response catalysts reported at present include La / ZrO2, Ru / CeO2, Ni / SrTiO3, etc., and show excellent catalytic performance in the processes of ammonia synthesis, methane reforming, propane dehydrogenation, etc. For example, the Pt-In / TiO2 catalyst can reduce the temperature of the propane dehydrogenation reaction from 600℃ to 250℃, avoiding excessive energy consumption and forming a green new path for propane dehydrogenation.

[0005] The thermal-electric coupling process based on the current response catalyst is expected to make the reaction conditions of light hydrocarbon catalytic cracking more mild, and provide a new idea for the development of a transformative catalytic cracking process. However, the above-mentioned technology has not been reported in the field of catalytic cracking.

[0006] SUMMARY

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of protection of the claims.

[0008] The application provides a current response catalyst for strengthening light alkane cracking to produce low-carbon olefins, which has the advantages of greatly improving the conversion rate of light alkane and the selectivity of low-carbon olefins under mild conditions.

[0009] The technical solution adopted in the application is as follows: the current response catalyst for strengthening light alkane cracking to produce low-carbon olefins is obtained by compounding MFI type HZSM-5 molecular sieve (the molar ratio of SiO2 / Al2O3 includes 21, 25, 38, 50, 85, 120, 160, 200, 300 or 400:1) and semiconductor type metal oxide, and the preparation method is self-assembly, in-situ hydrothermal method or physical mixing method.

[0010] The self-assembly method comprises the following steps:

[0011] (1) a certain amount of HZSM-5 is added to anhydrous ethanol as a core, and stirred uniformly at room temperature, and then ultrasonic dispersion is performed;

[0012] (2) a certain amount of polyvinylpyrrolidone is dissolved in anhydrous ethanol, slowly added to the solution in step (1), stirred uniformly, and then ultrasonic treatment is performed;

[0013] (3) a certain amount of metal oxide precursor is dissolved in anhydrous ethanol, slowly added to the solution in step (2), ultrasonic treatment is performed, and then continuous stirring is performed;

[0014] (4) a certain amount of complexing agent is slowly added to the solution in step (3), stirring is maintained, and after the stirring is completed, standing is performed; and

[0015] (5) the solution after standing is completed is subjected to multiple centrifugation, washing and drying to obtain a preliminary solid product, which is calcined to obtain a core-shell type current response catalyst HZSM-5@MO x (M includes Ti, Ce or Sn).

[0016] The stirring time in steps (1) and (2) is 0.5-8 h, the ultrasonic power is 10-100 W, and the ultrasonic treatment time is 0.5-5 h; more preferably, the stirring time is 0.5-5 h, the ultrasonic power is 40-100 W, and the ultrasonic treatment time is 0.5-3 h.

[0017] The addition amount of polyvinylpyrrolidone in step (2) is 1-10 wt% of HZSM-5; more preferably, the addition amount of polyvinylpyrrolidone is 2-8 wt% of HZSM-5.

[0018] The metal oxide precursor in the above method step (3) is one or more of tetrabutyl titanate, isopropyl titanate, cerium nitrate, cerium ammonium nitrate or tin tetrachloride pentahydrate, the mass ratio of the metal oxide precursor to HZSM-5 is (0.5-10):1, the stirring time is 0.5-12 h, the ultrasonic power is 10-100 W, and the ultrasonic treatment time is 0.5-5 h; more preferably, the mass ratio of the metal precursor to HZSM-5 is (1-8):1, the stirring time is 0.5-10 h, the ultrasonic power is 40-100 W, and the ultrasonic treatment time is 0.5-3 h.

[0019] The complexing agent in the above method step (4) is one or more of anhydrous ethanol aqueous solution or hexamethylenetetramine, the amount of the complexing agent is 1-10 wt% of HZSM-5, and the standing time is 0.5-48 h; more preferably, the amount of the complexing agent is 2-8 wt% of HZSM-5, and the standing time is 0.5-36 h.

[0020] The drying temperature in the above method step (5) is 80-150℃, the drying time is 6-24 h, the calcination temperature is 400-700℃, the calcination time is 12-72 h, and the heating rate is 2-10℃.min -1 ; more preferably, the drying temperature is 100-120℃, the drying time is 8-12 h, the calcination temperature is 500-650℃, the calcination time is 12-48 h, and the heating rate is 2-5℃.min -1 .

[0021] The in-situ hydrothermal method comprises the following steps:

[0022] (1) a certain amount of NaCl, polyethylene glycol 600, a template agent and an aluminum source are dissolved in deionized water, ultrasonic treatment is performed, and stirring is uniformly performed, a certain amount of a silicon source is dissolved in water, and rapid addition is performed;

[0023] (2) then a certain amount of a semiconductor type metal oxide MO x (M includes Ti, Ce or Sn) is added to the solution of step (1), ultrasonic treatment is performed, and pre-crystallization is performed at room temperature for a certain time;

[0024] (3) the solution after the pre-crystallization is transferred to a hydrothermal kettle, and a two-step crystallization method is adopted: first, hydrothermal crystallization is performed at 50-150℃ for 12-72 h, and then hydrothermal crystallization is performed at 100-200℃ for 12-72 h;

[0025] (4) after the product obtained in step (3) is cooled, multiple centrifugation, washing, drying and calcination are performed, and a sodium type electric current response catalyst grown in-situ is obtained; and

[0026] (5) The sodium-type current response catalyst is ion exchanged with 1 mol / L NH4Cl solution, dried and calcined to obtain a hydrogen-type current response catalyst MO x @HZSM-5 (M includes Ti, Ce or Sn).

[0027] In the above method step (1), the template agent is tetrapropylammonium hydroxide, the aluminum source is one or both of aluminum isopropoxide and aluminum nitrate nonahydrate, and the silicon source is tetraethyl orthosilicate. The molar ratio of each substance is SiO2:Al2O3:TPAOH:Na2O:H2O = 1:(0.01-0.02):(0.2-0.5):(0.02-0.05):(20-200); more preferably, SiO2:Al2O3:TPAOH:Na2O:H2O = 1:(0.01-0.02):(0.2-0.3):(0.02-0.03):(50-150).

[0028] In the above method step (2), the semiconductor-type metal oxide MO x is one or more of anatase TiO2, rutile TiO2, CeO2 or SnO2, and MO x is in an amount of 1-8 wt% of HZSM-5, and the pre-crystallization time is 6-72 h; more preferably, MO x is in an amount of 2-6 wt% of HZSM-5, and the pre-crystallization time is 12-48 h.

[0029] In the above method steps (4) and (5), the calcination conditions are a temperature of 450-800°C, a time of 3-12 h, and a temperature increase rate of 2-10°C·min -1 ; more preferably, the calcination temperature is 550-650°C, the calcination time is 3-6 h, and the temperature increase rate is 2-5°C·min -1 .

[0030] In the above method step (5), the ion exchange conditions are: MO x @HZSM-5 and the NH4Cl solution have a mass ratio of 1:10, the ion exchange temperature is 80°C, the ion exchange time is 4 h, and the ion exchange number is 2.

[0031] The physical mixing method comprises the following steps:

[0032] HZSM-5 and a semiconductor-type metal oxide (one or more of anatase TiO2, rutile TiO2, CeO2 or SnO2) are placed in deionized water in a certain mass ratio, mechanically mixed under the condition of 10-100 W ultrasonic for 1-5 h, and then centrifuged and dried to obtain a composite current response catalyst HZSM-5 / MO x (M includes Ti, Ce or Sn).

[0033] The application also provides an application of the current response catalyst in catalyzing light alkane cracking to prepare low-carbon olefins, and the application process mainly comprises the following steps:

[0034] (1) The prepared current response catalyst is pressed into a tablet, and is sieved to 20-40 meshes, and 1.0 g of the above catalyst is loaded into a fixed bed reactor provided with an electrode;

[0035] (2) The reactor is raised to the target temperature in a N2 atmosphere, a direct current is applied, and is stabilized for 2 h; and

[0036] (3) The light alkane raw material is introduced to start the reaction, and the product composition is analyzed online by gas chromatography.

[0037] In the application of the above current response catalyst, the catalytic light alkane cracking to prepare low-carbon olefins reaction takes C4-C10 alkane as the raw material, and N2 as the carrier gas, wherein the space velocity of the light alkane is 10-80 mmol·g -1 ·h -1 , the N2 flow rate is 5-60 mL·min -1 , the cracking reaction temperature is 300-450℃, the direct current voltage is 0-1000V, the current is 0-3A, and the power is 0-50W; more preferably, the space velocity of the light alkane is 20-40 mmol·g -1 ·h -1 , the N2 flow rate is 10-50 mL·min -1 , the direct current voltage is 0-800V, the current is 0-2A, and the power is 0-30W.

[0038] Compared with the related art, the application has the following beneficial effects:

[0039] (1) The catalytic material prepared by the current response catalyst synthesis method provided by the application introduces a conductive layer on the basis of not destroying the topological structure of HZSM-5 molecular sieve, and has the current response characteristic under the action of a direct current field; and

[0040] (2) The current response catalyst provided by the application is applied to the reaction of catalyzing light alkane cracking to prepare low-carbon olefins, and under the condition of thermoelectric coupling, the reaction temperature is reduced, the catalytic activity is improved, the occurrence of side reactions is inhibited, and the selectivity of low-carbon olefins is improved.

[0041] Other aspects can be apparent after reading and understanding the detailed description. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the application and not to limit the application.

[0043] Example 1

[0044] Core-shell current response catalyst HZSM-5@TiO2

[0045] (1) 1.5 g of HZSM-5 was added as a core to anhydrous ethanol, stirred at room temperature for 1 h, and then ultrasonically treated at 60 W for 1 h;

[0046] (2) 2 wt% of polyvinylpyrrolidone was dissolved in anhydrous ethanol, slowly added to the solution of step (1), stirred uniformly, and then ultrasonically treated at 60 W for 1 h;

[0047] (3) 6.39 g of tetrabutyl titanate was dissolved in anhydrous ethanol, slowly added to the solution of step (2), ultrasonically treated at 60 W for 1 h, and then continuously stirred for 5 h;

[0048] (4) 2 wt% of anhydrous ethanol aqueous solution was slowly added to the solution of step (3), stirring was maintained, and after stirring was completed, standing was performed for 12 h; and

[0049] (5) The solution after standing was subjected to multiple centrifugation and washing, dried at 110°C for 10 h, and a preliminary solid product was obtained, which was calcined at 600°C for 24 h to obtain the core-shell current response catalyst HZSM-5@TiO2.

[0050] Example 2

[0051] The core-shell current response catalyst HZSM-5@TiO2 was prepared according to the same method and steps of Example 1, except that the amount of polyvinylpyrrolidone in step (2) was 4 wt% of HZSM-5 to regulate the electrostatic effect on the surface of HZSM-5.

[0052] Example 3

[0053] The core-shell current response catalyst HZSM-5@TiO2 was prepared according to the same method and steps of Example 1, except that the metal precursor in step (3) was isopropyl titanate.

[0054] Example 4

[0055] The core-shell current response catalyst HZSM-5@TiO2 was prepared according to the same method and steps of Example 1, except that the amount of anhydrous ethanol aqueous solution in step (4) was 3 wt% to regulate the hydrolysis rate of the titanium dioxide metal precursor.

[0056] Example 5

[0057] The core-shell current-responsive catalyst HZSM-5@TiO2 was prepared by the same method and steps as in Example 1, except that the amount of the aqueous ethanol solution in step (4) was 4wt% to control the hydrolysis rate of the titanium dioxide metal precursor.

[0058] Example 6

[0059] The core-shell current-responsive catalyst HZSM-5@TiO2 was prepared by the same method and steps as in Example 1, except that the standing time in step (4) was 24h.

[0060] Example 7

[0061] Core-shell current-responsive catalyst HZSM-5@CeO2

[0062] (1) 1.5g of HZSM-5 was added to anhydrous ethanol as the core, stirred at room temperature for 1h, and then ultrasonically treated at 60W for 1h;

[0063] (2) 2wt% of polyvinylpyrrolidone was dissolved in anhydrous ethanol, slowly added to the solution of step (1), stirred uniformly, and then ultrasonically treated at 60W for 1h;

[0064] (3) 1.8g of cerium nitrate was dissolved in anhydrous ethanol, slowly added to the solution of step (2), ultrasonically treated at 60W for 1h, and then continuously stirred for 5h;

[0065] (4) 1g of hexamethylenetetramine was dissolved in anhydrous ethanol, slowly added to the solution of step (3), and kept stirring, after which the solution was allowed to stand for 12h; and

[0066] (5) The standing completed solution was centrifuged and washed multiple times, dried at 110°C for 10h to obtain a preliminary solid product, which was calcined at 600°C for 24h to obtain the core-shell current-responsive catalyst HZSM-5@CeO2.

[0067] Example 8

[0068] The core-shell current-responsive catalyst HZSM-5@CeO2 was prepared by the same method and steps as in Example 7, except that the amount of polyvinylpyrrolidone in step (2) was 4wt% of HZSM-5 to control the electrostatic effect on the surface of HZSM-5.

[0069] Example 9

[0070] The core-shell current-responsive catalyst HZSM-5@CeO2 was prepared by the same method and steps as in Example 7, except that the metal oxide precursor in step (3) was cerium ammonium nitrate.

[0071] Example 10

[0072] The core-shell type current response catalyst HZSM-5@CeO2was prepared by the same method and steps as in Example 7, except that the mass of hexamethylenetetramine in step (4) was 1.8 g.

[0073] Example 11

[0074] The core-shell type current response catalyst HZSM-5@CeO2was prepared by the same method and steps as in Example 7, except that the mass of hexamethylenetetramine in step (4) was 3.6 g.

[0075] Example 12

[0076] The core-shell type current response catalyst HZSM-5@CeO2was prepared by the same method and steps as in Example 7, except that the standing time in step (4) was 24 h.

[0077] Example 13

[0078] In-situ growth type current response catalyst TiO2@HZSM-5

[0079] (1) 0.3 g of NaCl, 2.5 g of polyethylene glycol 600, 5.625 g of TPAOH, and 0.1 g of aluminum nitrate nonahydrate were dissolved in deionized water, ultrasonically treated, and stirred uniformly, 3.27 g of tetraethyl orthosilicate was dissolved in water, and quickly added;

[0080] (2) Then, 2 g of rutile TiO2was added to the solution of step (1), ultrasonically treated, and pre-crystallized at room temperature for 24 h;

[0081] (3) The pre-crystallized solution was transferred to an autoclave, and two-step crystallization was performed: first, hydrothermal crystallization at 80°C for 24 h, and then hydrothermal crystallization at 170°C for 36 h;

[0082] (4) The product obtained in step (3) was cooled, centrifuged and washed multiple times, dried at 110°C for 10 h, and calcined at 600°C for 4 h to obtain rutile TiO2@Na-ZSM-5; and

[0083] (5) The TiO2@Na-ZSM-5 was ion exchanged with 1 mol / L NH4Cl solution at 80°C for 4 h, repeated 2 times to form TiO2@NH4-ZSM-5, and then dried at 110°C for 10 h and calcined at 600°C for 4 h to obtain rutile TiO2@HZSM-5.

[0084] Example 14

[0085] The in-situ growth type current response catalyst TiO2@HZSM-5 was prepared according to the same method and steps of Example 13, except that the aluminum source in step (1) was aluminum isopropoxide.

[0086] Example 15

[0087] The in-situ growth type current response catalyst TiO2@HZSM-5 was prepared according to the same method and steps of Example 13, except that the titanium source in step (2) was anatase TiO2.

[0088] Example 16

[0089] The in-situ growth type current response catalyst TiO2@HZSM-5 was prepared according to the same method and steps of Example 13, except that the first step crystallization time in step (3) was 36 h.

[0090] Example 17

[0091] The in-situ growth type current response catalyst TiO2@HZSM-5 was prepared according to the same method and steps of Example 13, except that the second step crystallization time in step (3) was 48 h.

[0092] Example 18

[0093] The in-situ growth type current response catalyst CeO2@HZSM-5 was prepared according to the same method and steps of Example 13, except that the MO x was CeO2.

[0094] Example 19

[0095] The in-situ growth type current response catalyst SnO2@HZSM-5 was prepared according to the same method and steps of Example 13, except that the MO x was SnO2.

[0096] Example 20

[0097] The physical mixing type current response catalyst HZSM-5 / TiO2

[0098] HZSM-5 and anatase TiO2 were placed together in deionized water at a mass ratio m(TiO2: HZSM-5) = 1:1, mechanically mixed for 3 h under an ultrasonic power of 80 W, and then centrifuged and dried at 110°C for 10 h to obtain the physical mixing type current response catalyst HZSM-5 / TiO2.

[0099] Example 21

[0100] The physical mixture type current response catalyst HZSM-5 / TiO2 was prepared by the same method and procedure as in Example 20, except that the TiO2 was rutile type.

[0101] Example 22

[0102] The physical mixture type current response catalyst HZSM-5 / TiO2 was prepared by the same method and procedure as in Example 20, except that the mass ratio m(TiO2:HZSM-5) = 1.5:1.

[0103] Example 23

[0104] The physical mixture type current response catalyst HZSM-5 / TiO2 was prepared by the same method and procedure as in Example 20, except that the mass ratio m(TiO2:HZSM-5) = 2:1.

[0105] Example 24

[0106] The physical mixture type current response catalyst HZSM-5 / CeO2 was prepared by the same method and procedure as in Example 20, except that the MO x was CeO2.

[0107] Example 25

[0108] The physical mixture type current response catalyst HZSM-5 / SnO2 was prepared by the same method and procedure as in Example 20, except that the MO x was SnO2.

[0109] Application Example

[0110] A series of current response catalysts obtained in Examples 1-25 were used to catalyze the cracking of light alkanes, and the evaluation device was a microelectrode fixed bed reactor, and the specific process was as follows:

[0111] (1) The prepared current response catalyst powder was tabletted, sieved to 20-40 mesh, and 1.0 g of the above catalyst was loaded into the microelectrode fixed bed reactor;

[0112] (2) The carrier gas N2 flow was controlled at 40.0 mL·min -1 , the reactor was heated to the set temperature in N2 atmosphere, direct current was applied (0 / 5 W, 0 W represents no electric field, 5 W represents the power under applied electric field), and stabilized for 2 h; and

[0113] (3) The light alkane raw material was introduced to start the reaction, wherein the light alkane space velocity was 40 mmol·g -1 ·h -1 , and the product composition was analyzed online by gas chromatography, and sampling was performed once every 1 h.

[0114] Conversion and primary product selectivity are shown in Table 1 and Table 2 (in the tables "trienes" includes ethylene, propylene, and butylenes; "BTX" includes benzene, toluene, and xylenes).

[0115] Table 1 Properties of the current responsive catalysts prepared in the examples for cracking n-hexane with / without electric field Note: 0W represents no electric field, 5W represents power under applied electric field

[0116] Table 2 Properties of the current responsive catalysts prepared in the examples for cracking n-octane with / without electric field Note: 0W represents no electric field, 5W represents power under applied electric field

Claims

1. A method for preparing a current-responsive catalyst for enhancing the production of low-carbon olefins by cracking light alkanes, comprising: obtaining a current-responsive catalyst by compounding an MFI-type HZSM-5 zeolite and a semiconductor-type metal oxide; and using the current-responsive catalyst to catalyze the cracking of light alkanes to produce low-carbon olefins, including ethylene, propylene and butylene, and by-products of benzene, toluene and xylene.

2. The method of claim 1, wherein the current-responsive catalyst is prepared by the steps of: The molar ratio of SiO 2 / Al 2 O 3 in the MFI-type HZSM-5 zeolite is (21, 25, 38, 50, 85, 120, 160, 200, 300 or 400):

1.

3. The method of claim 1, wherein the current responsive catalyst is prepared by the steps of: The semiconductor-type metal oxide comprises anatase TiO 2, rutile TiO 2, CeO 2 or SnO 2.

4. The method of claim 1, wherein the current responsive catalyst is prepared by the steps of: The compounding method of the zeolite and the semiconductor-type metal oxide comprises a self-assembly method, an in-situ hydrothermal method or a physical mixing method.

5. The method of claim 1, wherein the current responsive catalyst is prepared by the steps of: The mass ratio of the semiconductor-type metal oxide to the HZSM-5 is (0.5-10):

1. 6.A current-responsive catalyst prepared by the method of any one of claims 1-5. 7.Use of the current-responsive catalyst of claim 6 in the cracking of light alkanes to produce low-carbon olefins, wherein a direct current is used in the thermoelectric coupling catalytic cracking of light alkanes, with a voltage of 0-1000 V, a current of 0-3 A and a power of 0-50 W.

8. Use according to claim 7, wherein, The catalytic cracking temperature of the light alkanes is 300-450℃.

9. Use according to claim 7 or 8, wherein, The light alkanes are alkanes with a chain length of C 4-C 10.

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