A method for preparing a copper-zinc catalyst

Abstract

The application discloses a preparation method of a copper-zinc catalyst, which comprises the following steps: (1) a Zn and Cu-containing solution and a sodium metaaluminate solution are combined to carry out a gelation reaction to obtain a slurry; (2) the slurry obtained in the step (1) is continuously subjected to n times of third-stage pH value decreasing aging, 1 / n Al-containing solutions are added at the end of the first-stage pH value aging each time, and the material obtained after the aging is subjected to solid-liquid separation, the solid phase is subjected to first drying, tabletting and molding to obtain a molded material, and then the molded material is washed, subjected to second drying and calcination to obtain the copper-zinc catalyst. The catalyst prepared by the method has a large pore volume and pore diameter, and the stepwise pore distribution makes the active metal copper and the additive zinc have good dispersion performance and good synergistic effect, thereby improving the activity, selectivity and thermal stability of the copper-zinc catalyst and the service life of the catalyst.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a copper-zinc catalyst, in particular to a preparation method of a copper-zinc catalyst with high activity, high selectivity and good heat resistance. BACKGROUND

[0002] At present, the world generally adopts the middle and low pressure gas phase method to synthesize methanol, and the catalyst used is basically a mixed oxide of copper, zinc and aluminum. The three components of CuO, ZnO and Al2O3 in the copper-zinc catalyst have different functions, CuO is the main active component, and ZnO and Al2O3 are the additives. Al2O3 not only plays a skeleton role in the catalyst, but also can disperse the active components in the catalyst. Due to different catalyst preparation methods, carrier properties, compositions and contents, different copper dispersions and copper particle sizes are obtained, and the synergies between the metal active center copper and the oxide carrier are different, which have a great influence on the activity, methanol selectivity and stability of the copper-based catalyst. The higher the copper dispersion is, the more the number of metal atoms exposed on the surface is, and the less the sintering of the active center is, so as to maintain high activity of the catalyst. When the copper particle size is small, the copper particles have a large number of open surface and edge defect sites, which can strongly bind the key reaction intermediates and increase the methanol yield.

[0003] How to improve the specific surface area and pore volume of the catalyst, optimize the pore distribution, and thus improve the dispersion of the active component of the catalyst and the Cu-ZnO synergistic effect, so as to make the catalyst have excellent activity and good selectivity, has become the research focus of the copper-based catalyst.

[0004] CN101502803A discloses a preparation method of a catalyst for preparing 1,4-butanediol by selective hydrogenation of dimethyl maleate, which adds Mn, Mg, Cr and other metals as additives on the basis of a two-step method. CN1660490A discloses a preparation method of a copper-zinc catalyst, which adds a small amount of surfactant OP during the preparation process by the coprecipitation method. CN101733109A discloses a preparation method of a copper-based methanol synthesis catalyst, which adds an organic additive (one or more of ethylene glycol, diethylamine, glycerol, magnesium stearate and activated carbon) during the precipitation process. The above methods all add reagents during the precipitation process to improve the dispersion of CuO on the surface of the catalyst, but the addition of the additives does not increase the specific surface area, pore volume and optimize the pore distribution, and the improvement of the dispersion of the main active component CuO in the catalyst is limited.

[0005] CN103372440A discloses a preparation method of copper-zinc catalyst. The method is to prepare copper-zinc catalyst by co-flowing copper and zinc metal salt solution, sodium metaaluminate solution and CO2 gas to form a gel. The method can increase the specific surface area of the catalyst, has high active phase dispersion, and increases the number of active centers, but the material obtained by precipitation has poor adhesion and is not easy to be pressed into a tablet, and the number of active centers in the catalyst surface phase is not obviously increased.

[0006] CN201811114240.9 discloses a copper-zinc catalyst and a preparation method thereof. The catalyst contains an organic phosphonic acid compound and / or a carboxylic acid polymer and an organic carboxylic acid. The copper-zinc catalyst of the invention is prepared by mixing solution A and sodium metaaluminate solution to perform a co-flow gelation reaction to obtain slurry I, aging; then, solution B and sodium carbonate solution are co-flowed and added dropwise into the aged slurry I to perform a gelation reaction to obtain slurry II, then aging, drying and molding to obtain the catalyst. The specific surface area and pore volume of the catalyst are small, which affects the dispersion of active metals. CN107774263A discloses a preparation method of a copper-zinc catalyst. Sodium metaaluminate alkaline solution and Cu-containing soluble salt solution are simultaneously and co-flowingly added into a reaction tank containing pure water to perform a gelation reaction to generate slurry I, and then sodium metaaluminate alkaline solution is added dropwise into Zn-containing soluble salt solution to perform a gelation reaction to generate slurry II. The slurry I and the slurry II are uniformly mixed, aged, filtered, and then the obtained material is subjected to hydrothermal treatment with water vapor, wherein urea is added during the hydrothermal treatment, and then the material is washed, filtered, dried, calcined and pressed into a tablet to obtain the catalyst. Although the catalyst prepared by the method has a high content of active metal copper in the surface phase, the dispersion of copper and zinc in the surface phase of the catalyst is reduced under the action of water vapor pressure and the impact of water molecules, and the crushing strength is also poor.

[0007] The above methods change the dispersion of copper on the catalyst after reduction by changing the preparation process of copper-based catalyst or adding additives on this basis to improve the activity of the catalyst, but the specific surface area and pore volume of the catalyst are not obviously increased, and the dispersion effect of the active component is not obviously improved. SUMMARY

[0008] In view of the deficiencies in the prior art, the present application provides a preparation method of a copper-zinc catalyst. The catalyst prepared by the method has a large pore volume and pore size, and the step distribution of the active metal copper and the additive zinc has good dispersion performance and good synergistic effect, which improves the activity, selectivity and thermal stability of the copper-zinc catalyst and the service life of the catalyst.

[0009] The preparation method of the copper-zinc catalyst of the present application comprises the following contents:

[0010] (1) co-flow gelation reaction of Zn and Cu-containing solution and sodium metaaluminate solution to obtain a slurry;

[0011] (2) continuously aging the slurry obtained in step (1) for n times of three-stage decreasing pH value, adding 1 / n Al-containing solution at the end of the first-stage pH value aging each time, and obtaining a molding material through solid-liquid separation, first drying, tabletting and molding of the solid phase, washing, second drying and calcination of the molding material, to obtain a copper-zinc catalyst;

[0012] The three-stage decreasing pH value aging process is as follows: the aging temperature is 60-98°C, preferably 65-92°C; in the first stage, the pH value is 11.0-13.5, the aging time is 0.05-0.5 hours, and 1 / n Al-containing solution is added at the end of the first-stage aging; in the second stage, the pH value is adjusted to 8.5-10.5, and the aging time is 0.05-0.5 hours; in the third stage, the pH value is adjusted to 5.5-8.3, and the aging time is 0.05-0.5 hours; and n is an integer of 2-8.

[0013] In the method, the concentration of the soluble copper salt in the Zn- and Cu-containing solution in step (1) is 0.4-3.5 mol / L, preferably 0.5-3.0 mol / L, as calculated based on Cu 2+ ; and the concentration of the soluble zinc salt is 0.2-3.0 mol / L, preferably 0.3-2.5 mol / L, as calculated based on Zn 2+ ; the soluble copper salt is a copper-containing nitrate and / or acetate; and the soluble zinc salt is a zinc-containing nitrate and / or acetate.

[0014] In the method, the concentration of the sodium metaaluminate solution in step (1) is 10-90 g / L, preferably 15-85 g / L, as calculated based on Al2O3.

[0015] In the method, the gelation reaction conditions in step (1) are as follows: the reaction temperature is 30-90°C, preferably 40-85°C; the initial pH value is controlled to be 10.0-14.0, preferably 10.5-13.5; the final pH value at the end of the reaction is 6.8-8.5, preferably 7.0-8.3; and the gelation reaction time is 0.5-6.0 hours, preferably 0.6-5.0 hours.

[0016] Preferably, the pH value can be lowered in several steps from the initial value to the final pH value, and the method for lowering the pH value in several steps is to lower the pH value to the required value for the current step, and to keep the pH value of the reaction slurry constant until the next step of lowering the pH value starts; the number of times of lowering the pH value is 2-10, preferably 2-8.

[0017] Further preferably, the constant time after each pH reduction is 0.1-1.2 hours. The magnitude of each pH reduction can be the same or different, and preferably the magnitude of each pH reduction is equal to or less than the magnitude of the previous pH reduction. The time for each pH reduction is the time from the beginning of the pH reduction to the beginning of the next pH reduction, and further is the sum of the time for each pH reduction and the constant time at that pH. The time for each pH reduction can be the same or different, and preferably the times are the same.

[0018] In the method of the present application, in step (2), the acid and base used for adjusting the pH can be inorganic salts, inorganic acids and inorganic bases not containing aluminum element, and further can be one or more of hydrochloric acid and acetic acid, sodium carbonate and sodium bicarbonate. The concentration and amount of the acid and base solution can be adjusted according to the actual preparation needs.

[0019] In the method of the present application, in step (2), the Al added accounts for 5%-45% of the total Al in the obtained copper-zinc catalyst in terms of Al2O3, and preferably 6%-40%. When preparing the Al-containing solution, the aluminum source is generally a soluble aluminum salt, which can be one or more of aluminum nitrate, aluminum sulfate and aluminum chloride. The solution is divided into n parts by volume, and n is an integer of 2-8.

[0020] In the method of the present application, the solid-liquid separation in step (2) is generally carried out by filtration, centrifugation or the like.

[0021] In the method of the present application, in the forming process in step (2), a conventional forming aid can be added as needed. The forming aid refers to a substance that is beneficial to extrusion forming, such as one or more of carbon black and graphite powder, and the amount of the forming aid accounts for 1wt%-10wt% of the total material dry basis. The copper-zinc catalyst of the present application is in the form of cylindrical (solid) particles, and the particle size of the catalyst particles is 2-12 mm, and the length can be 1-8 mm.

[0022] In the method of the present application, the washing, first drying and calcination in step (2) can be carried out under conventional conditions in the art. The washing is carried out with deionized water until neutral. The first drying conditions are as follows: drying at 50-150°C, preferably 60-120°C, and the drying time is 0.5-24.0 hours, preferably 1-16 hours. The calcination conditions are as follows: calcination at 300-360°C for 1-16 hours, preferably 2-10 hours.

[0023] In the method of the present application, the second drying conditions in step (2) are as follows:

[0024] a. first drying the material at 60-100°C for 1.0-8.5 hours, preferably at 70-90°C for 2.0-8.0 hours;

[0025] b. Spraying water (preferably deionized water) on the material obtained in step a. The volume ratio of water to dry material is 1:4 to 4:1, and then drying at a temperature of 150 to 280°C, preferably 150 to 250°C, for 0.5 to 4.0 hours, preferably 0.6 to 3.5 hours;

[0026] c. Repeating step b for 2 to 9 times, preferably 3 to 8 times.

[0027] The volume ratio of water to dry material is greater than 1:1 in the first time, and less than 1:1 in the last time, and further, the volume ratio of water to dry material decreases with the increase of the number of drying.

[0028] The copper-zinc catalyst prepared by the method of the present application comprises the following components based on the weight of the catalyst: CuO 25% to 70%, preferably 30% to 65%, ZnO 12% to 38%, preferably 15% to 35%, and Al2O3 10% to 40%, preferably 15% to 38%.

[0029] The specific surface area of copper in the catalyst after reduction is 45 to 150 m 2 / g, preferably 50 to 140 m 2 / g. The dispersion of copper is 20% to 50%, preferably 25% to 45%.

[0030] The copper-zinc catalyst prepared by the method of the present application is in the form of (solid) particles, and preferably, the average pore diameter decreases from the outer surface layer to the center core. Preferably, the catalyst particle comprises an outer surface layer, an intermediate layer and a center core, and the average pore diameter decreases in a gradient, i.e. the average pore diameter of the outer surface layer is greater than that of the intermediate layer, and the average pore diameter of the intermediate layer is greater than that of the center core. The average pore diameter of the outer surface layer is 12 to 18 nm, the average pore diameter of the intermediate layer is 8 to 12 nm, and the average pore diameter of the center core is 4 to 8 nm, wherein the length from the outermost edge to the center point in the cross section of the catalyst particle is R. The thickness of the outer surface layer is 0.2R to 0.4R, the thickness of the intermediate layer is 0.2R to 0.5R, and the rest is the center core.

[0031] The copper-zinc catalyst prepared by the method of the present application is applied to the synthesis of methanol reaction, and the general process conditions are as follows: reaction temperature 210 to 320°C, preferably 230 to 290°C; pressure 2.0 to 10 MPa, preferably 2.0 to 8.0 MPa; volume space velocity 2000 to 15000 h -1 , preferably 4000 to 12000 h -1 .

[0032] Compared with the prior art, the present application has the following advantages:

[0033] (1) In the method of the present application, the pH value is decreased during the formation of the composite oxide of copper, zinc and aluminum, which can effectively improve the dispersion of copper and produce a good synergistic effect between Cu-ZnO.

[0034] (2) In the method of the present application, the solution containing Al is added in several times during the pH value fluctuation during aging, which further improves the support effect of Al2O3 skeleton, makes the pore unobstructed, is beneficial to the smooth passing of macromolecular reactants, promotes the dispersion of active metals and strengthens the promoting effect between active metals, which is beneficial to the improvement of catalyst activity, methanol selectivity and thermal stability.

[0035] (3) In the method of the present application, the drying method used in the second drying after shaping makes the average pore diameter of the catalyst particles from the outer surface layer to the center core of the catalyst particles decrease from large to small, which can weaken the influence of diffusion effect when the reactants enter and exit the pores of the catalyst, is beneficial to the improvement of catalyst selectivity and thermal stability, and further improves the interaction between Cu-ZnO. DETAILED DESCRIPTION

[0036] The scheme and effect of the present application are further illustrated by the following examples. In the present application, the specific surface area and pore volume and pore distribution are measured by low-temperature liquid nitrogen adsorption method, and the specific surface area (S Cu ) and dispersion (D Cu ) of the metal Cu of the catalyst after reduction are measured by N2O chemical reaction adsorption method. v% is volume fraction and wt% is mass fraction.

[0037] In the present application, the "cross section of the catalyst particle" refers to the entire surface exposed after cutting through the geometric center of the shape of a catalyst particle along the direction of the smallest dimension of the catalyst particle. For example, when the catalyst particle is spherical, the cross section refers to the entire surface exposed after cutting through the center of the sphere along the radius or minor axis direction of the sphere. Or, when the catalyst particle is columnar, the cross section refers to the entire surface exposed after cutting through the center point of the length dimension of the column perpendicularly to the direction of the length dimension of the column. The outer periphery of the exposed surface is referred to as the outermost edge of the cross section, and the geometric center (such as the center of the sphere or the center point of the length dimension mentioned above) is referred to as the center point on the cross section.

[0038] In the present application, the method for measuring the average pore diameter of different layers from the outer surface layer to the center core of the catalyst particles is as follows: first, the pore volume, specific surface area and average pore diameter of the sample are measured by low-temperature nitrogen adsorption method (BET); then, a certain amount of sample is placed in a catalyst attrition tester, and a certain amount of quartz sand is added to increase the attrition rate while the sample is being ground. When the particle size of the sample is reduced to a certain extent after grinding, the weight loss of the sample is measured and the pore structure is measured again. According to the relationship that the total pore volume and specific surface area of the sample are equal to the sum of each part, the pore volume and specific surface area of the ground part can be calculated. Meanwhile, 20-80 samples are measured to calculate the average pore diameter. Thus, the average pore diameters of different layers from the outer surface layer to the center core are measured.

[0039] Example 1

[0040] A solution containing Zn and Cu was prepared by dissolving 334 g of Cu(NO3)2-3H2O and 164 g of Zn(NO3)2-6H2O in deionized water. An aluminum chloride solution was prepared by dissolving aluminum chloride in deionized water, the Al in the aluminum chloride solution accounting for 30% of the Al in the resulting copper-zinc catalyst in terms of Al2O3, and the solution was divided into 5 equal parts by volume. Deionized water was added to a reaction tank, and a sodium aluminate solution (containing Al2O3 31 g / L) and the solution containing Zn and Cu were added to the reaction tank in parallel flow, the temperature of the gelation was 60°C, the initial pH value was controlled at 13.3, the final pH value at the end was adjusted to 7.7 by 7 times of pH value reduction, each time the pH value was reduced by 0.8, and after each time the pH value was adjusted to the set value, the pH value of the reaction slurry was controlled constant for 8 minutes. After the reaction was completed, a slurry containing copper, zinc and aluminum was obtained, the slurry was aged, the aging temperature was 76°C, the pH value during aging was first controlled at 13.2, 0.2 hours after the aging time, 1 part of the aluminum chloride solution was added, and the aging pH value was controlled at 9.5, 0.15 hours after the aging time, the pH value was then controlled at 7.6, 0.15 hours of aging time, the above operation was repeated 5 times, and the aging was completed. The aged slurry was filtered, the filter cake was dried at 90°C for 10 hours, an appropriate amount of graphite and water were added for rolling and pressing, and the material was formed into a tablet. The formed material was washed with deionized water until neutral, and then the washed formed material was subjected to a second drying according to the following steps: the material was first dried at 77°C for 5.0 hours, deionized water was uniformly sprayed on the dried material, and then the material was dried, the process of uniformly spraying deionized water and drying was repeated 6 times, the volume ratio of the first spraying of deionized water to the dried material was 1.5:1, the drying temperature was 180°C, and the drying time was 1.8 hours, the volume ratio of the second spraying of deionized water to the dried material was 1.2:1, the drying temperature was 180°C, and the drying time was 2.0 hours, the volume ratio of the third spraying of deionized water to the dried material was 1:1, the drying temperature was 180°C, and the drying time was 2.0 hours, the volume ratio of the fourth spraying of deionized water to the dried material was 1:1.2, the drying temperature was 150°C, and the drying time was 1.7 hours, the volume ratio of the fifth spraying of deionized water to the dried material was 1:1.8, the drying temperature was 170°C, and the drying time was 2 hours, and the volume ratio of the sixth spraying of deionized water to the dried material was 1:2.5, the drying temperature was 180°C, and the drying time was 2 hours. The dried formed material was calcined at 360°C for 3 hours to obtain catalyst A. The composition, pore distribution and main properties are shown in Table 1.

[0041] Example 2

[0042] The Cu(NO3)2.3H2O and Zn(NO3)2.6H2O were dissolved in deionized water to form a solution containing Zn and Cu according to the component content of catalyst B in Table 1, and the aluminum sulfate solution was prepared by dissolving aluminum sulfate in deionized water, and the Al in the aluminum sulfate solution accounted for 32.2% of the Al in the obtained synthetic copper-zinc catalyst in terms of Al2O3, and the aluminum sulfate solution was divided into 6 equal parts by volume. Deionized water was added to the reaction tank, and the sodium aluminate solution and the solution containing Zn and Cu were added to the reaction tank in parallel flow, the gelation temperature was 55°C, the initial pH value was controlled at 12.2, and the final pH value at the end was adjusted to 8.0 by 6 times of pH value reduction, and the pH value was reduced by 0.7 each time. After adjusting to the value each time, the adjusted reaction slurry pH value was constant for 10 minutes, and a slurry containing copper, zinc and aluminum was obtained. The obtained slurry was aged, the aging temperature was 77°C, and the pH value during aging was first controlled at 12.9, and after 0.2 hours of aging time, 1 part of the aluminum sulfate solution was added, and then the aging pH value was controlled at 9.8, and after 0.1 hours of aging time, the pH value was controlled at 6.5, and the aging time was 0.2 hours. The above operation process was repeated 6 times to end the aging. The aged slurry was filtered, the filter cake was dried at 90°C for 9 hours, an appropriate amount of graphite and water were added for rolling and pressing, and the tablet was formed. The formed material was washed with deionized water until it was neutral. The washed formed material was subjected to the second drying as follows: the material was first dried at 78°C for 6.5 hours, and then deionized water was uniformly sprayed on the dried material, and the process of uniformly spraying deionized water and drying was repeated 5 times. The volume ratio of the first spraying of deionized water to the dried material was 2:1, the drying temperature was 180°C, and the drying time was 2.1 hours. The volume ratio of the second spraying of deionized water to the dried material was 1.5:1, the drying temperature was 180°C, and the drying time was 2.0 hours. The volume ratio of the third spraying of deionized water to the dried material was 1:1, the drying temperature was 180°C, and the drying time was 2.0 hours. The volume ratio of the fourth spraying of deionized water to the dried material was 1:1.5, the drying temperature was 180°C, and the drying time was 1.5 hours. The volume ratio of the fifth spraying of deionized water to the dried material was 1:2.2, the drying temperature was 200°C, and the drying time was 1.5 hours. The dried formed material was calcined at 350°C for 4 hours to obtain catalyst B. The composition, pore distribution and main properties are shown in Table 1.

[0043] Example 3

[0044] The Cu(NO3)2.3H2O, Zn(NO3)2.6H2O were dissolved in deionized water to form a solution containing Zn and Cu according to the component content of catalyst C in Table 1, and the AlCl3.6H2O was dissolved in deionized water to form an aluminum chloride solution, the Al in the aluminum chloride solution accounted for 25.8% of the Al in the obtained synthetic copper-zinc catalyst in terms of Al2O3, and the solution was equally divided into 5 portions by volume. Deionized water was added to the reaction tank, and the sodium metaaluminate solution and the solution containing Zn and Cu were added to the reaction tank in parallel flow, the gelation temperature was 70°C, the initial pH value was controlled at 12.5, the final pH value at the end was adjusted to 7.5 by 5 times of pH value reduction, and the pH value was reduced by 1.0 each time. After adjusting to the value each time, the adjusted reaction slurry pH value was constant for 9 minutes, a slurry containing copper, zinc and aluminum was obtained, the obtained slurry was aged, the aging temperature was 80°C, the pH value during aging was first controlled at 12.8, 0.2 hours after aging, 1 portion of the aluminum chloride solution was added, and then the aging pH value was controlled at 9.4, 0.2 hours after aging, the pH value was controlled at 7.3, and the aging time was 0.15 hours. The above operation process was repeated 5 times to end the aging. The aged slurry was filtered, the filter cake was dried at 80°C for 8 hours, an appropriate amount of graphite and water were added for rolling and pressing, and the tablet was formed. The formed material was washed with deionized water until it was neutral, and then the washed formed material was subjected to the following step for the second drying: the material was first dried at 75°C for 5.5 hours, the dried material was then evenly sprayed with deionized water, and the process of evenly spraying deionized water and drying was repeated 6 times. The volume ratio of the first spraying of deionized water to the dried material was 1.6:1, the drying temperature was 180°C, and the drying time was 2.0 hours. The volume ratio of the second spraying of deionized water to the dried material was 1.3:1, the drying temperature was 1800°C, and the drying time was 2.0 hours. The volume ratio of the third spraying of deionized water to the dried material was 1:1, the drying temperature was 180°C, and the drying time was 2.0 hours. The volume ratio of the fourth spraying of deionized water to the dried material was 1:1.4, the drying temperature was 150°C, and the drying time was 1.3 hours. The volume ratio of the fifth spraying of deionized water to the dried material was 1:1.9, the drying temperature was 180°C, and the drying time was 2 hours. The volume ratio of the sixth spraying of deionized water to the dried material was 1:2.3, the drying temperature was 160°C, and the drying time was 2 hours. The dried formed material was calcined at 350°C for 5 hours to obtain catalyst C. The composition, pore distribution and main properties are shown in Table 1.

[0045] Example 4

[0046] The Cu(NO3)2.3H2O, Zn(NO3)2.6H2O were dissolved in deionized water to form a solution containing Zn and Cu according to the component content of catalyst D in Table 1, and the AlCl3.6H2O was dissolved in deionized water to form an aluminum chloride solution, the Al in the aluminum chloride solution accounted for 32% of the Al in the obtained copper-zinc catalyst in terms of Al2O3, and the solution was equally divided into 5 portions by volume. Deionized water was added to the reaction tank, and the sodium metaaluminate solution and the solution containing Zn and Cu were added to the reaction tank in parallel flow, the gelation temperature was 65°C, the initial pH value was controlled at 13.0, the final pH value at the end was adjusted to 7.4 by 7 times of pH value reduction, and the pH value was reduced by 0.8 each time. After adjusting to the value each time, the pH value of the adjusted reaction slurry was kept constant for 11 minutes, a slurry containing copper, zinc and aluminum was obtained, the obtained slurry was aged, the aging temperature was 78°C, the pH value during aging was first controlled at 13.3, 0.15 hours after aging, 1 portion of the aluminum chloride solution was added, and then the aging pH value was controlled at 9.6, 0.1 hours after aging, the pH value was controlled at 7.0, and the aging time was 0.2 hours. The above operation was repeated 5 times to end the aging. The aged slurry was filtered, the filter cake was dried at 90°C for 8 hours, an appropriate amount of graphite and water were added for rolling and pressing, and the pressed tablet was formed. The formed material after washing with deionized water to neutral was subjected to the following second drying: the material was first dried at 78°C for 6.8 hours, deionized water was uniformly sprayed on the dried material, and then the material was dried, the uniform spraying of deionized water and the drying process were repeated 6 times, the volume ratio of the first spraying of deionized water to the dried material was 1.9:1, the drying temperature was 190°C, and the drying time was 2.0 hours, the volume ratio of the second spraying of deionized water to the dried material was 1.4:1, the drying temperature was 180°C, and the drying time was 1.8 hours, the volume ratio of the third spraying of deionized water to the dried material was 1.2:1, the drying temperature was 190°C, and the drying time was 1.7 hours, the volume ratio of the fourth spraying of deionized water to the dried material was 1:1.2, the drying temperature was 180°C, and the drying time was 2 hours, the volume ratio of the fifth spraying of deionized water to the dried material was 1:1.5, the drying temperature was 190°C, and the drying time was 2 hours, and the volume ratio of the sixth spraying of deionized water to the dried material was 1:2.0, the drying temperature was 180°C, and the drying time was 1.8 hours. The dried formed material was calcined at 370°C for 4 hours to obtain catalyst D. The composition, pore distribution and main properties are shown in Table 1.

[0047] Comparative Example 1

[0048] A mixed solution was prepared by dissolving 334 g of Cu(NO3)2·3H2O and 164 g of Zn(NO3)2·6H2O in deionized water according to the component content of catalyst A in Table 1. Deionized water was added to a reaction tank, and a sodium metaaluminate solution and the mixed solution were added to the reaction tank in parallel flow, the gelation temperature was 60°C, the gelation time was 1 hour, and the reaction pH was 7.6, to obtain a reaction slurry. The slurry was aged under stirring, the aging pH was 7.6, the aging temperature was 76°C, and the aging time was 2.5 hours. The aged slurry was filtered, the filter cake was dried at 90°C for 10 hours, an appropriate amount of graphite and water were added for rolling and pressing, and the material after molding was washed with deionized water until neutral. The washed and molded material was dried at 100°C for 8 hours and then calcined at 360°C for 3 hours to obtain catalyst E. The composition, pore distribution, and main properties are shown in Table 1.

[0049] Comparative Example 2

[0050] According to the method disclosed in CN107774263A, a reference catalyst F having the same composition as the catalyst of Example 1 was prepared, and the specific process was as follows:

[0051] According to the catalyst composition of Example 1, 334 g of Cu(NO3)2·3H2O was dissolved in deionized water to prepare solution A. 164 g of Zn(NO3)2·6H2O was dissolved in deionized water to prepare mixed solution B. Deionized water was added to a reaction tank, and a sodium metaaluminate solution and mixed solution A were added to the reaction tank in parallel flow, the gelation temperature was 60°C, the gelation pH was 7.6, and the gelation time was 1.0 hour to obtain a slurry I containing copper and aluminum precipitates. The sodium metaaluminate solution was added to solution B under stirring, the gelation temperature was maintained at 60°C, the pH was controlled at 7.6 at the end, and the gelation time was controlled at 1 hour to generate a slurry II containing zinc and aluminum precipitates. The two above-mentioned slurry containing precipitates were mixed. Aging was started under stirring, the pH was 7.6 during aging, the temperature was 76°C, and the aging time was 2.5 hours. After aging, the material was filtered, the filter cake was hydrothermally treated in water vapor containing urea, the molar ratio of urea to the total amount of active metal atoms was 7:1, the temperature was 230°C, the pressure was 6.0 MPa, and the treatment time was 4 hours. The filter cake was dried at 90°C for 10 hours, an appropriate amount of graphite and water were added for rolling and pressing, and the material after molding was washed with deionized water until neutral. The washed and molded material was dried at 100°C for 8 hours and then calcined at 360°C for 3 hours to obtain catalyst F. The composition, pore distribution, and main properties are shown in Table 1.

[0052] Comparative Example 3

[0053] According to the method disclosed in CN103372440A, a reference catalyst G having the same composition as the catalyst of Example 1 was prepared, and the specific process was as follows:

[0054] To the dissolving tank 1, 500 mL of water was added, and 334 grams of Cu(NO3)2·3H2O and 164 grams of Zn(NO3)2·6H2O were dissolved respectively to prepare an acidic working solution A. To the dissolving tank 2, 500 mL of water was added, and sodium metaaluminate solution was dissolved to prepare an alkaline working solution B. Under stirring, solution A, solution B and CO2 were added into the reaction tank to form a gel, the CO2 concentration was 90 v%, the gel forming reaction temperature was 60℃, the gel forming time was 1 hour, and the pH value of the gel slurry was controlled at 7.6. The total amount of CO2 gas added during the gel forming process was 3.5 times the molar amount of Al2O3 in the alkaline working solution B. After gel forming, the material was aged at a pH of 7.6 and a temperature of 75℃ for 2.5 hours, then filtered, washed with deionized water, and the filter cake was dried at 100℃ for 8 hours and then calcined at 360℃ for 3 hours. The calcined material was added with an appropriate amount of graphite and water to form a tablet, and the tablet was obtained as catalyst G. The composition, pore distribution and main properties are shown in Table 1.

[0055] Comparative Example 4

[0056] According to the method disclosed in CN110935457A, a reference agent H with the same composition as the catalyst of Example 1 was prepared, and the specific process was as follows:

[0057] Cu(NO3)2·3H2O and AlCl3·6H2O were dissolved in deionized water to prepare a mixed solution B. Deionized water was added to the reaction tank, and sodium metaaluminate solution and mixed solution A were added into the reaction tank in parallel flow, the gel forming temperature was 60℃, the gel forming pH value was 7.5, and the gel forming time was 0.9 hours to obtain slurry I. The slurry I was aged under stirring, the stirring speed was 190 revolutions per minute, the aging temperature was 75℃, the pH value was 7.2, and the aging time was 0.7 hours. After aging, mixed solution B and sodium carbonate solution were added into the aged slurry I in parallel flow, the molar ratio of the amount of sodium carbonate to the total amount of copper and zinc was 2.0, the gel forming temperature was 60℃, the pH value was 9.2, and the gel forming time was 2.0 hours to obtain slurry II. The slurry II was aged under stirring, the stirring speed was 400 revolutions per minute, the aging temperature was 75℃, the pH value was 7.6, and the aging time was 3.0 hours. The aged slurry II was filtered, the filter cake was washed with deionized water, the filter cake was dried at 100℃ for 10 hours, and then calcined at 360℃ for 3 hours. The calcined material was added with an appropriate amount of graphite and water to form a tablet, and the tablet was obtained as catalyst H. The composition, pore distribution and main properties are shown in Table 1.

[0058] Comparative Example 5

[0059] The same as Example 1, except that the sodium metaaluminate solution and the Zn, Cu-containing solution are gelled at a fixed pH value, and the preparation process is as follows:

[0060] A Zn, Cu-containing solution was prepared by dissolving 334 g of Cu(NO3)2-3H2O and 164 g of Zn(NO3)2-6H2O in deionized water. An aluminum chloride solution was prepared by dissolving aluminum chloride in deionized water, and the Al content in the aluminum chloride solution was 30% of the Al content in the obtained copper-zinc catalyst in terms of Al2O3. The aluminum chloride solution was divided into five equal parts by volume. Deionized water was added to a reaction tank, and the sodium metaaluminate solution (containing Al2O3 31 g / L) and the Zn, Cu-containing solution were added to the reaction tank in parallel flow. The gelling temperature was 60°C, the gelling pH value was 7.7, and the gelling time was 56 minutes. After the reaction was completed, a slurry containing copper, zinc, and aluminum was obtained. The obtained slurry was aged, and the aging temperature was 76°C. The aging pH value was first controlled at 13.2, and after 0.2 hours of aging, one portion of the aluminum chloride solution was added. Then, the aging pH value was controlled at 9.5, and after 0.15 hours of aging, the pH value was controlled at 7.6, and the aging time was 0.15 hours. The above process was repeated five times to complete the aging. The aged slurry was filtered, and the filter cake was dried at 90°C for 10 hours. The dried filter cake was mixed with graphite and water, and then the mixture was pressed and formed into a tablet. The formed material was washed with deionized water until neutral, and then the washed formed material was subjected to a second drying process as follows. The material was first dried at 77°C for 5.0 hours. The dried material was then evenly sprayed with deionized water, and then dried. The above process of evenly spraying deionized water and drying was repeated six times. The volume ratio of the first spraying of deionized water to the dried material was 1.5:1, the drying temperature was 180°C, and the drying time was 1.8 hours. The volume ratio of the second spraying of deionized water to the dried material was 1.2:1, the drying temperature was 180°C, and the drying time was 2.0 hours. The volume ratio of the third spraying of deionized water to the dried material was 1:1, the drying temperature was 180°C, and the drying time was 2.0 hours. The volume ratio of the fourth spraying of deionized water to the dried material was 1:1.2, the drying temperature was 150°C, and the drying time was 1.7 hours. The volume ratio of the fifth spraying of deionized water to the dried material was 1:1.8, the drying temperature was 170°C, and the drying time was 2 hours. The volume ratio of the sixth spraying of deionized water to the dried material was 1:2.5, the drying temperature was 160°C, and the drying time was 2 hours. The dried formed material was calcined at 360°C for 3 hours to obtain catalyst I. The composition, pore distribution, and main properties are shown in Table 1.

[0061] Comparative Example 6

[0062] The same as Example 1, except that all of the aluminum chloride solution was added at one time during the aging process, and a fixed value was used for the aging pH value. The preparation process is as follows:

[0063] A Zn, Cu containing solution was prepared by dissolving 334 g of Cu(NO3)2-3H2O and 164 g of Zn(NO3)2-6H2O in deionized water. An aluminum chloride solution was prepared by dissolving aluminum chloride in deionized water, the Al in the aluminum chloride solution was 30% of the Al in the resulting copper zinc catalyst as Al2O3. Deionized water was added to a reactor vessel, a sodium aluminate solution (containing Al2O3 31 g / L) and the Zn, Cu containing solution were concurrently added to the reactor vessel, the temperature of the gelation was 60°C, the initial pH was controlled at 13.3, the final pH was adjusted to 7.7 at the end of the reaction by 7 times of pH reduction, each time the pH was reduced by 0.8, after each time the pH was reduced to the adjusted value, the pH of the reaction slurry was controlled constant for 8 minutes, after the reaction was completed, a slurry containing copper, zinc and aluminum was obtained, the slurry was aged, the entire aluminum chloride solution was added at the beginning of the aging, the temperature of the aging was 76°C, the pH was controlled at 8.5 during the aging, the aging was completed after 2.8 hours. The aged slurry was filtered, the filter cake was dried at 90°C for 10 hours, an appropriate amount of graphite and water were added to roll the material, and the material was tabletted. The tabletted material was washed with deionized water until neutral, and then the washed tabletted material was dried for the second time according to the following steps: the material was first dried at 77°C for 5.0 hours, the dried material was then evenly sprayed with deionized water, and the process of evenly spraying deionized water and drying was repeated 6 times, the volume ratio of the first spraying of deionized water to the dried material was 1.5:1, the drying temperature was 180°C, and the drying time was 1.8 hours, the volume ratio of the second spraying of deionized water to the dried material was 1.2:1, the drying temperature was 180°C, and the drying time was 2.0 hours, the volume ratio of the third spraying of deionized water to the dried material was 1:1, the drying temperature was 180°C, and the drying time was 2.0 hours, the volume ratio of the fourth spraying of deionized water to the dried material was 1:1.2, the drying temperature was 150°C, and the drying time was 1.7 hours, the volume ratio of the fifth spraying of deionized water to the dried material was 1:1.8, the drying temperature was 170°C, and the drying time was 2 hours, the volume ratio of the sixth spraying of deionized water to the dried material was 1:2.5, the drying temperature was 160°C, and the drying time was 2 hours. The dried tabletted material was calcined at 360°C for 3 hours to obtain catalyst J. The composition, pore distribution and main properties are shown in Table 1.

[0064] Comparative Example 7

[0065] The same as Example 1, the second drying of the tabletted material after washing used the first drying condition (conventional drying condition), and the preparation process was as follows:

[0066] 4Cu(NO3)2-3H2O 334 g and Zn(NO3)2-6H2O 164 g were dissolved in deionized water to prepare a Zn, Cu-containing solution. AlCl3 solution was prepared by dissolving AlCl3 in deionized water, the Al in the AlCl3 solution accounted for 30% of Al in the resulting Cu-Zn catalyst in terms of Al2O3, and the AlCl3 solution was equally divided into 5 portions by volume. Deionized water was added to a reaction tank, and the sodium aluminate solution (containing Al2O3 31 g / L) and the Zn, Cu-containing solution were added to the reaction tank in parallel flow, the gelation temperature was 60°C, the initial pH value was controlled at 13.3, the final pH value was adjusted to 7.7 at the end by 7 times of pH value reduction, the pH value was reduced by 0.8 each time, and the adjusted pH value was controlled constant for 8 minutes after each time of pH value reduction, after the reaction, a slurry containing copper, zinc and aluminum was obtained, the obtained slurry was aged, the aging temperature was 76°C, the pH value was controlled at 13.2 at the beginning of the aging, 0.2 hours after the aging, 1 portion of the AlCl3 solution was added, and then the aging pH value was controlled at 9.5, 0.15 hours after the aging, the pH value was controlled at 7.6, and the aging was repeated for 5 times. The aged slurry was filtered, the filter cake was dried at 90°C for 10 hours, an appropriate amount of graphite and water were added for rolling and pressing, and the pressed material was formed into a tablet. The formed material was washed with deionized water until neutral, and then the washed formed material was dried at 90°C for 10 hours, the dried formed material was calcined at 360°C for 3 hours, and a catalyst K was obtained. The composition, pore distribution and main properties are shown in Table 1.

[0067] Example 5

[0068] The Cu-Zn catalyst was crushed to 16-40 mesh, and was reduced with a hydrogen-nitrogen mixed gas with low concentration of hydrogen (H2 / N2=3 / 97 (volume ratio)) for 16-25 h before use, and the maximum reduction temperature was 235°C. The activity evaluation of the catalyst was carried out on a micro fixed bed reaction device. The catalyst loading amount was 5 ml, the raw gas composition was CO / H2 / CO2 / N2=13 / 70 / 6 / 11 (volume ratio), the reaction pressure was 5.0 MPa, the space velocity was 10000 h -1 -1, the reaction temperature was 245°C, and the conversion rates of CO and CO2 were determined as the initial activity of the catalyst. Then the catalyst was heat treated at 445°C for 5 h in a synthesis gas atmosphere, and then the conversion rates of CO and CO2 were determined at 250°C as the activity after heat treatment, i.e. the heat resistance. The products were analyzed by a gas chromatograph, and the time-space yield of methanol g·mL -1 ·h -1 was determined, i.e. the grams of methanol produced per hour per milliliter of catalyst, and the results are shown in Table 3.

[0069] As shown in Table 1 and Table 2, the metal dispersion in the catalyst of the present application is good, thereby improving the synergistic effect between Cu and ZnO in the catalyst, and the average pore diameter decreases from the outer surface layer to the core of the catalyst, so that the catalyst has high activity and selectivity. The copper-zinc catalyst of the present application has high activity, heat resistance and excellent selectivity, as shown by the test results.

[0070] Table 1 Catalyst composition and properties

[0071]

[0072] Table 1 (continued)

[0073]

[0074] Table 2 Dispersion and specific surface area of copper metal

[0075]

[0076] S Cu S is the specific surface area of copper, D Cu D is the dispersion of copper

[0077] Table 3 Catalyst activity evaluation and heat resistance test results

[0078]

Claims

1. A process for the preparation of a copper-zinc catalyst, characterized in that The method comprises the following steps: (1) a solution containing Zn and Cu and a sodium metaaluminate solution are co-currently gelled to obtain a slurry; the gelling reaction conditions of step (1) are as follows: the reaction temperature is 30-90 ℃, the initial pH value is controlled to be 10.0-14.0, the final pH value at the end is 6.8-8.5, and the gelling reaction time is 0.5-6.0 hours; the pH value is lowered in several times from the initial value to the final pH value, the method for lowering the pH value in several times is that the pH value is lowered to the required value at this time, and the pH value of the reaction slurry is kept constant until the next time of lowering starts, and the number of times of lowering is 2-10 times; (2) the slurry obtained in step (1) is continuously subjected to n times of three-stage pH value decreasing aging, and the material obtained after aging is subjected to solid-liquid separation, the solid phase is subjected to first drying and shaping to obtain a shaped material, and the shaped material is washed, subjected to second drying and calcination to obtain a copper-zinc catalyst. The three-stage pH value decreasing aging process is as follows: the aging temperature is 60-98 ℃; in the first stage, the pH value is 11.0-13.5, the aging time is 0.05-0.5 hours, 1 / n Al-containing solution is added at the end of the first-stage aging; in the second stage, the pH value is adjusted to 8.5-10.5, and the aging time is 0.05-0.5 hours; in the third stage, the pH value is adjusted to 5.5-8.3, and the aging time is 0.05-0.5 hours; wherein n is an integer of 2-8; the second drying conditions of step (2) are as follows: a, the material is dried at 60-100 ℃ for 1.0-8.5 hours; b, the dried material obtained in step a is evenly sprayed with water, and then dried at a temperature of 150-280 ℃ for 0.5-4.0 hours; c, the step b process is repeated for 2-9 times; wherein the volume ratio of the water to the dried material decreases with the increase of the number of drying, the volume ratio of the water to the dried material in the first time is greater than 1:1, and the volume ratio of the water to the dried material in the last time is less than 1:

1.

2. The method of claim 1, wherein: The concentration of the soluble copper salt in the solution containing Zn and Cu in step (1) is 0.4-3.5 mol / L, and the concentration of the soluble zinc salt is 0.2-3.0 mol / L; the soluble copper salt is a copper-containing nitrate and / or acetate, and the soluble zinc salt is a zinc-containing nitrate and / or acetate. 2+ The concentration of the soluble copper salt in the solution containing Zn and Cu in step (1) is 0.4-3.5 mol / L, and the concentration of the soluble zinc salt is 0.2-3.0 mol / L; the soluble copper salt is a copper-containing nitrate and / or acetate, and the soluble zinc salt is a zinc-containing nitrate and / or acetate. 2+ The concentration of the soluble copper salt in the solution containing Zn and Cu in step (1) is 0.4-3.5 mol / L, and the concentration of the soluble zinc salt is 0.2-3.0 mol / L; the soluble copper salt is a copper-containing nitrate and / or acetate, and the soluble zinc salt is a zinc-containing nitrate and / or acetate.

3. The method of claim 1, wherein: The concentration of the sodium metaaluminate solution in step (1) is 10-90 g / L in terms of Al2O3.

4. The method of claim 1, wherein: In step (2), the Al added accounts for 5%-45% of the total Al in the obtained copper-zinc catalyst in terms of Al2O3; when the Al-containing solution is prepared, the aluminum source is a soluble aluminum salt selected from one or more of aluminum nitrate, aluminum sulfate or aluminum chloride.

5. The method of claim 1, wherein: The first drying conditions of step (2) are as follows: the drying temperature is 50-150 ℃, and the drying time is 0.5-24.0 hours; the calcination conditions are as follows: the calcination temperature is 300-360 ℃, and the calcination time is 1-16 hours.

6. The copper-zinc catalyst prepared according to the method of any one of claims 1 to 5, characterized by: The catalyst comprises the following components in terms of the weight of the catalyst: CuO is 25%-70%, ZnO is 12%-38%, and Al2O3 is 10%-40%.

7. The copper-zinc catalyst of claim 6, wherein: The specific surface area of the metallic copper in the catalyst after reduction is 45-150 m 2 / g, and the dispersion of the metallic copper is 20-50%.

8. The copper-zinc catalyst of claim 6, wherein: The copper-zinc catalyst is a solid particle, and the average pore diameter decreases from the outer surface layer to the center core; the catalyst particle comprises an outer surface layer, an intermediate layer and a center core, and the average pore diameter decreases in a gradient, that is, the average pore diameter of the outer surface layer is greater than that of the intermediate layer, and the average pore diameter of the intermediate layer is greater than that of the center core; the average pore diameter of the outer surface layer is 12-18 nm, the average pore diameter of the intermediate layer is 8-12 nm, and the average pore diameter of the center core is 4-8 nm, wherein the length from the outermost edge to the center point on the cross section of the catalyst particle is R; the thickness of the outer surface layer is 0.2R-0.4R, the thickness of the intermediate layer is 0.2R-0.5R, and the rest is the center core.

9. Use of the copper-zinc catalyst prepared according to any one of the processes of claims 1 to 5 in the synthesis of methanol at a temperature of 210 to 320 °C, a pressure of 2.0 to 10 MPa and a space velocity of 2000 to 15000 h -1 .

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