A stepwise calcination method for Cu / ZnO / Al2O3 catalyst

Abstract

The invention discloses a Cu / ZnO / Al 2 O 3 The catalyst is prepared by the calcination method of the present invention. The catalyst has uniform oxide particle size, uniform component distribution, and carrier Al, and the catalyst has uniform particle size, uniform component distribution, and uniform catalyst content. The catalyst is prepared by the calcination method of the present invention ... 2 O 3 The characteristic of not segregating and aggregating can effectively improve the thermal stability of the catalyst.

Description

Technical Field

[0001] The invention relates to a segmented roasting method of a Cu / ZnO / Al2O3 catalyst, in particular to a segmented roasting method of a Cu / ZnO / Al2O3 methanol synthesis catalyst. Background Art

[0002] Cu / ZnO / Al2O3 catalyst is a methanol synthesis catalyst with excellent performance and occupies a dominant position in methanol synthesis. Industrially, Cu / ZnO / Al2O3 catalyst is prepared by coprecipitation method, which includes precipitation, aging, washing, drying, calcination, reduction activation and other steps. After precipitation, aging, washing and drying, the catalyst precursor is obtained, and the main component phases are complex basic carbonates such as zinc malachite and green covellite and pseudo-boehmite. The calcination process is the process of decomposing the catalyst precursor into oxides under heating conditions. The process has high temperature and large structural changes, which has a huge impact on the final catalyst microstructure and catalytic performance.

[0003] The current calcination process uses direct heating to the final calcination temperature, or directly placing the precursor into a calcination furnace with the final calcination temperature and keeping it warm for a period of time. This calcination method does not take into account the differences in the temperature ranges of different components in the catalyst at different decomposition stages (Table 1). Therefore, the decomposition rates of the components are inconsistent during the calcination process, resulting in component segregation and aggregation, different particle sizes of copper oxide and zinc oxide, and uneven distribution of the components of the final catalyst. Agglomeration sintering and Ostwald ripening sintering are likely to occur during the reaction, resulting in decreased activity.

[0004] Table 1 Different components of the precursor and their decomposition process and decomposition temperature

[0005]

[0006] At present, the calcination process is carried out in the external atmospheric environment. The water and carbon dioxide produced by decomposition cannot be discharged in time, and are enriched near the catalyst, affecting the final catalyst structure. The decomposition of the precursor components zinc malachite and green cobalt zinc ore is a multi-step process. First, some hydroxyl groups are removed to form hydroxylated composite carbonates, and then hydroxyl groups and carbonates are further removed to generate copper oxide, zinc oxide and a small amount of high-temperature carbonates. The temperature is further increased, and the high-temperature carbonates are decomposed. The decomposition process of pseudo-boehmite is a dehydroxylation process. The water and carbon dioxide produced by these dehydroxylation and decarbonization processes have a great influence on the changes in the catalyst structure. The presence of water can accelerate the sintering and growth of the oxide particles generated by calcination, and can also accelerate the decomposition of high-temperature carbonates. The sintering and growth of oxide particles is obviously not conducive to catalytic performance. In addition, high-temperature carbonates help to disperse the active components, which is beneficial to improving the activity and stability of the catalyst. Therefore, timely removal of the water produced by decomposition can obtain oxide particles with smaller particle sizes and retain some high-temperature carbonates, which is beneficial to improving the activity and stability of the catalyst. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a staged roasting method to make the components of the Cu / ZnO / Al2O3 catalyst decompose evenly and controllably, prevent segregation and aggregation from causing uneven component distribution after roasting, sintering of oxide particles leading to uneven particle size, and excessive decomposition of high-temperature carbonates in the late stage of roasting.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A segmented calcination method for a Cu / ZnO / Al2O3 catalyst, wherein the segmented calcination method sets sequentially increasing constant temperature segments based on the temperature range differences of different thermal decomposition steps of different components of the catalyst, and gradually raises the temperature to a final calcination temperature.

[0010] The temperature ranges of the constant temperature sections respectively cover the decomposition temperatures of the thermal decomposition steps, preferably 140-230°C, 240-270°C and 300-330°C, and the final calcination temperature is 330-400°C.

[0011] The constant temperature is gradually increased from low temperature to high temperature until the final calcination temperature. The heating rate from room temperature to the first constant temperature, between the constant temperatures, and from the last constant temperature to the final calcination temperature is 0.1-10°C / min.

[0012] The holding time of each constant temperature section is 0 to 120 minutes, and the holding time of the final roasting temperature is 20 to 240 minutes.

[0013] The entire calcination process from heating to cooling to room temperature is carried out under any one of a dry air flow, a dry nitrogen flow and a dry argon flow, or under vacuum conditions.

[0014] The purge air velocity is not less than 5000h -1 , the vacuum condition pressure is not higher than 10kPa.

[0015] The specific operating steps of the staged roasting method are as follows: (1) placing a dried catalyst precursor in a roasting furnace; (2) starting a purge gas flow until the air in the furnace is completely replaced, or starting a vacuum until the pressure in the furnace is lower than 10 kPa; (3) starting a heated staged roasting; (4) continuing the purge gas flow or vacuuming until the temperature in the furnace drops to room temperature, then turning off the gas flow or removing the vacuum; (5) taking out the catalyst, and the roasting is completed.

[0016] The beneficial effects achieved by the staged roasting method of the present invention are as follows: based on the temperature range differences of different thermal decomposition steps of different components in the catalyst, the present invention sets constant temperature sections with different temperatures that increase in sequence, and by fine-tuning the temperature of each constant temperature section and the heating rate between different temperature sections, the components of the catalyst can be controlled and uniformly decomposed, preventing local overheating and component segregation and aggregation caused by inconsistent decomposition rates and different oxide particle sizes; at the same time, the present invention uses dry air flow blowing or vacuuming to promptly remove the moisture generated by decomposition, preventing oxide particle sintering and excessive decomposition of high-temperature carbonates caused by water vapor aggregation. Compared with the current direct temperature roasting process in ambient air, the staged roasting method of the present invention can obtain a catalyst with uniform oxide particle size and uniform distribution of different components, especially a carrier Al2O3 that will not segregate and aggregate and contains some high-temperature carbonates, which can effectively slow down the sintering deactivation caused by migration and agglomeration of active components and Ostwald ripening, and improve catalyst stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the XRD spectra of the catalysts obtained by calcining Example 2 (Cal-2), Example 4 (Cal-4), Example 5 (Cal-5), Example 6 (Cal-6) and Comparative Example 1 (Ref-1).

[0018] Figure 2 These are the TEM image, HRTEM image, and corresponding FFT of Example 3 (Cal-3).

[0019] Figure 3 It is the HAADF photograph and Al element distribution diagram of Example 5 (Cal-5).

[0020] Figure 4 This is a TEM photograph of Example 5 (Cal-5).

[0021] Figure 5 It is the HAADF photograph and Al element distribution diagram of Comparative Example 1 (Ref-1). DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0023] Example 1

[0024] The dried catalyst precursor (containing zinc malachite, pseudo-boehmite and a small amount of chalcanthite) was ground into fine powder, placed in a crucible and placed in a tube furnace. The dry air was turned on with an air velocity of 5000 h -1 , purge for 5 minutes to replace the original air, maintain the purge gas, start heating, heating rate of 5℃ / min, from room temperature to 200℃, keep constant temperature for 20 minutes, then increase to 300℃ at 5℃ / min and keep constant temperature for 20 minutes, then increase to 350℃ at 5℃ / min and calcine for 30 minutes, naturally cool to room temperature, turn off the purge gas, and obtain catalyst Cal-1.

[0025] Example 2

[0026] The dried catalyst precursor (containing zinc malachite, pseudo-boehmite and a small amount of chalcanthite) was ground into powder, placed in a quartz boat, and placed in a tube furnace. Dry nitrogen was turned on to a space velocity of 10,000 h -1 , purge for 2 minutes to replace the original air, maintain the purge gas, start heating, heating rate of 1℃ / min, from room temperature to 140℃, keep constant temperature for 10 minutes, then increase to 270℃ at 1℃ / min and keep constant temperature for 10 minutes, then increase to 330℃ at 1℃ / min and keep constant temperature for 10 minutes, then increase to 350℃ at 1℃ / min and roast for 20 minutes, naturally cool to room temperature, turn off the purge gas, and obtain catalyst Cal-2.

[0027] Example 3

[0028] The dried catalyst precursor (containing zinc malachite, pseudo-boehmite and a small amount of chalcanthite) was ground into powder, placed in a crucible and placed in a tube furnace. Dry nitrogen was turned on to a space velocity of 10,000 h -1 , purge for 2 minutes to replace the original air, maintain the purge gas, start heating, heating rate of 0.1℃ / min, from room temperature to 220℃, keep constant temperature for 30 minutes, then increase to 300℃ at 2℃ / min and keep constant temperature for 30 minutes, then increase to 350℃ at 2℃ / min and roast for 20 minutes, naturally cool to room temperature, turn off the purge gas, and obtain catalyst Cal-3.

[0029] Example 4

[0030] The dried catalyst precursor (containing zinc malachite, pseudo-boehmite and a small amount of green copper zinc ore) was ground into fine powder, put into a crucible, and placed in a tube furnace. The dry air was turned on with an air velocity of 100,000 h -1 , purge for 1 minute to replace the original air, maintain the purge gas, start heating, heating rate of 10℃ / min, from room temperature to 150℃, keep constant temperature for 120min, then increase to 400℃ at 5℃ / min and roast for 20min, cool naturally to room temperature, turn off the purge gas, and obtain catalyst Cal-4.

[0031] Example 5

[0032] The dried catalyst precursor (containing zinc malachite, pseudo-boehmite and a small amount of chalcanthite) was ground into fine powder, placed in a crucible and placed in a tube furnace. Dry air was turned on with an air velocity of 10,000 h / min. -1 , purge for 2 minutes to replace the original air, maintain the purge gas, start heating, heating rate of 0.5℃ / min, from room temperature to 200℃, keep constant temperature for 30 minutes, then increase to 350℃ at 1℃ / min and calcine for 30 minutes, cool naturally to room temperature, turn off the purge gas, and obtain catalyst Cal-5.

[0033] Example 6

[0034] The dried catalyst precursor (containing zinc malachite, pseudo-boehmite and a small amount of green cupreous zinc ore) was ground into fine powder, loaded into a crucible, and placed in a thick-walled tubular furnace. The vacuum was turned on, and when the pressure in the tube was less than 10 kPa, the vacuum was maintained, and the temperature was raised at a rate of 0.5 ° C / min from room temperature to 200 ° C, and the temperature was kept constant for 30 minutes, and then the temperature was raised to 350 ° C at 1 ° C / min for 30 minutes, and then the temperature was naturally lowered to room temperature, and the vacuum was slowly removed to obtain the catalyst Cal-6.

[0035] Comparative Example 1

[0036] The dried catalyst precursor (containing zinc malachite, pseudo-boehmite and a small amount of chalcocite) was ground into fine powder, put into a crucible, and calcined in a muffle furnace at 350° C. for 40 min. After natural cooling, the comparative catalyst Ref-1 was obtained.

[0037] Example 7

[0038] Testing of the catalyst obtained by the staged calcination method provided by the present invention

[0039] A micro-fixed bed continuous flow reactor was used, with a catalyst loading of 2 mL and a particle size of 16-40 mesh. The catalyst was reduced in a low hydrogen (H2:N2=5:95) atmosphere, with a programmed temperature increase (20°C / h) to 230°C for 10 hours. The reducing gas was switched to the feed gas for catalytic methanol synthesis testing. The test conditions were a reaction pressure of 8.0 MP and a space velocity of 10,000 h-1 , temperature 230℃, coal-based syngas composition: H2:CO:CO2:N2 = 65:14:4:17 (v / v) and a small amount of sulfide. After the reaction is stable for 2 hours, the liquid in the liquid collector is emptied and the timing is started. The collector is cooled by circulating water. After 2.5 hours, the collector liquid (crude methanol) is collected and the catalytic activity is measured, which is the initial activity. Then the catalyst is heat treated at 400℃ for 5 hours, and the activity is measured again under the above conditions, which is the heat-resistant activity. Methanol, ethanol, propanol and hydrocarbons in the liquid product were analyzed by Agilent-7890 gas chromatograph. Chromatographic conditions: hydrogen flame ionization detector (FID), HP-INNOWax type chromatographic column (column length 60m, inner diameter 0.32mm, wall thickness 0.5μm) programmed temperature, nitrogen as carrier gas, inlet temperature 250℃, constant pressure 10 psi, split mode 10:1, detection chamber temperature 300℃, hydrogen flow rate 30 mL / min, air flow rate 400 mL / min, tail flow rate 25 mL / min, and external standard method was used for quantification. The test results are shown in Table 2. The Ref-1 catalyst obtained in Comparative Example 1 was used as a reference. From the test results, it can be seen that the catalyst prepared by the staged roasting method has better activity and stability than the catalyst prepared by the conventional roasting method, showing the superiority of the present invention.

[0040] Table 2 Test results of methanol synthesis using staged calcination catalyst

[0041]

[0042] It should be noted that the above is only a preferred embodiment of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention. Although the present invention is directed to Cu / ZnO / Al2O3 catalyst, the same calcination method can be used for other methanol synthesis catalysts based on Cu / ZnO / Al2O3 and added with different additives, so the calcination of such catalysts should also be within the protection scope of the present invention.

Claims

1. A stepwise calcination method for a Cu / ZnO / Al2O3 catalyst, characterized in that Based on the difference in temperature range of different thermal decomposition steps of different components of the catalyst, a sequentially increasing constant temperature is set, and the temperature is gradually increased to the final calcination temperature; the catalyst precursor contains zinc malachite, pseudo-boehmite and green cobalt zinc ore, and the temperature range of each constant temperature is 140-230°C, 240-270°C and 300-330°C, respectively covering the decomposition temperature of each thermal decomposition step, and the final calcination temperature is 330-400°C; the step-by-step heating rate from room temperature to the first constant temperature, between each constant temperature, and from the last constant temperature to the final calcination temperature is 0.1-10°C / min; the insulation time of each constant temperature is 0-120min, and the left end value 0 is not taken, and the insulation time of the final calcination temperature is 20-240min; The calcination is carried out under a dry air flow purge, or under a dry nitrogen flow purge, or under a dry argon flow purge, or under a vacuum condition, and the vacuum pressure is not higher than 10 kPa.

2. The stepwise roasting method according to claim 1, characterized in that The air velocity of the purge gas flow is not less than 5000h -1 .

3. The stepwise roasting method according to claim 1, characterized in that The specific operation steps are as follows: (1) Place the dried catalyst precursor in the calcination furnace; (2) Start the purge gas flow until the air in the furnace is completely replaced, or start the vacuum until the pressure in the furnace is lower than 10kPa; (3) Start the heating stage calcination; (4) Continue the purge gas flow or vacuum until the temperature in the furnace drops to room temperature, then turn off the gas flow or release the vacuum; (5) Take out the catalyst and the calcination is completed.

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