CN112264026B - Preparation method of high-activity high-selectivity methanol synthesis catalyst - Google Patents
Preparation method of high-activity high-selectivity methanol synthesis catalyst Download PDFInfo
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- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
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- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/80—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with zinc, cadmium or mercury
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- C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
- C07C29/15—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of oxides of carbon exclusively
- C07C29/151—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of oxides of carbon exclusively with hydrogen or hydrogen-containing gases
- C07C29/153—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of oxides of carbon exclusively with hydrogen or hydrogen-containing gases characterised by the catalyst used
- C07C29/154—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of oxides of carbon exclusively with hydrogen or hydrogen-containing gases characterised by the catalyst used containing copper, silver, gold, or compounds thereof
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Abstract
The invention belongs to the technical field of catalysts, and particularly relates to a preparation method of a high-activity high-selectivity methanol synthesis catalyst. The method adopts a method combining a two-step precipitation method and a multi-step impregnation method, and specifically comprises the following steps: adding mixed zinc and aluminum salt and an alkali precipitator into a reactor in parallel flow at a certain speed, and precipitating to generate a carrier precursor; continuously adding the mixed salt of copper, zinc and aluminum and an alkali precipitator into the reactor in a parallel flow mode according to a certain speed, and carrying out a second-step reaction; aging and washing the precipitate, soaking in zinc nitrate solution for a period of time, washing, spray drying, roasting, soaking a certain amount of magnesium by an isometric soaking method, drying, roasting and forming to obtain the catalyst. After the second-step precipitation, the precipitate is soaked in a zinc nitrate solution, so that the copper-zinc substitution of the catalyst can be improved, and more active sites can be formed; the impregnated magnesium can neutralize the acidity of the catalyst surface, thereby improving the selectivity of the catalyst.
Description
Technical Field
The invention belongs to the technical field of catalysts, and particularly relates to a preparation method of a high-activity high-selectivity methanol synthesis catalyst.
Technical Field
Methanol is an important petrochemical raw material and can be used for manufacturing organic products such as formaldehyde, acetic acid, methylamine, methyl formate and the like; the fuel is also a clean fuel with excellent performance, and can be used as automobile fuel alone or mixed with gasoline. At present, the synthesis gas is widely applied to the industry for preparing the methanol, and the catalyst for synthesizing the methanol is the core of the whole process. The Cu-Zn-Al catalyst is a most researched methanol synthesis catalyst system at present due to good low-temperature activity and high-temperature stability. Wherein, Cu is the main active component, and the addition of ZnO can generate synergistic effect with CuO, thereby improving the activity of the catalyst. Al (Al)2O3As a carrier, the catalyst can be enhancedThe specific surface area of the catalyst and the dispersity of copper prevent the catalyst from being deactivated due to sintering of copper grains in the reaction process, and improve the stability of the catalyst.
The preparation of the traditional copper-based methanol synthesis catalyst mainly adopts a precipitation method, but the methanol synthesis catalyst prepared by the traditional precipitation method has a certain promotion space in the aspects of activity and selectivity, and how to develop a new precipitation method by adding other auxiliary means on the basis of the precipitation method is a main research direction for promoting the performance of the methanol synthesis catalyst at the present stage.
Disclosure of Invention
The invention aims to provide a preparation method of a high-activity high-selectivity methanol synthesis catalyst. The method adopts a method combining a two-step precipitation method and multi-step impregnation, and the precipitate is soaked in a zinc nitrate solution after the two-step precipitation, so that the copper-zinc substitution of the catalyst can be improved, and more active sites can be formed; the impregnated magnesium can neutralize the acidity of the catalyst surface, thereby improving the selectivity of the catalyst.
The invention is realized by the following technical scheme:
a preparation method of a high-activity high-selectivity methanol synthesis catalyst comprises the following steps:
(1) preparing a mixed aqueous solution of zinc nitrate and aluminum nitrate, and recording as a salt solution A; preparing a mixed aqueous solution of nitrates of copper, zinc and aluminum, and recording the mixed aqueous solution as a salt solution B; preparing a sodium carbonate solution, and recording as an alkali solution C; and preparing a zinc nitrate solution.
(2) Adding a proper amount of deionized water into the reactor, and respectively preheating the salt solution A, B, the alkali solution C and the deionized water in the reactor to the reaction temperature. And (3) dropwise adding the salt solution A and the alkali solution C into the reactor in a parallel flow manner under the condition of uniform stirring, and adjusting the pH value of the precipitation solution in the reactor to keep the precipitation solution in a proper range all the time. And stopping dripping the alkali solution C after the salt solution A is completely dripped. And after continuously stirring for 10-15min, adding the salt solution B in the same way, continuously dropwise adding the alkali solution C, and adjusting the pH value of the precipitation solution in the reactor to keep the precipitation solution in a proper range all the time. And stopping dropping the alkali solution C after the salt solution B is completely added into the reactor. After the precipitation is complete, aging is carried out in the reactor for a certain time.
(3) After aging is finished, carrying out centrifugal filtration on the precipitation liquid, washing a filter cake with deionized water and then filtering until no Na is detected in the filtrate+Until now. Preheating zinc nitrate solution to reaction temperature, soaking the washed filter cake in the preheated zinc nitrate solution for 2-3h, keeping the reaction temperature constant in the process, continuously stirring, and then filtering and washing for 3-4 times. And pulping the filter cake, then carrying out spray drying, and roasting the dried material to decompose the dried material to obtain roasted powder.
(4) An equal-volume impregnation method is adopted, and a proper amount of magnesium nitrate solution is impregnated on the roasted powder.
(5) And after the impregnation is finished, drying and roasting the materials, and adding graphite into the roasted powder for molding to obtain the synthetic methanol catalyst.
As a preferred embodiment of the present invention, the reaction temperature in the steps (2) and (3) is 70 to 90 ℃, preferably 70 to 80 ℃.
As a preferred embodiment herein, the pH in step (2) is controlled to be between 6.5 and 8.0, preferably between 7.0 and 7.5.
As a preferred embodiment of the present application, the aging time in step (2) is 2 to 3 hours, preferably 2 hours.
As a preferred embodiment of the present application, the initial concentration of the zinc nitrate solution in the step (3) is 0.05 to 0.1mol/L, preferably 0.05 mol/L.
As a preferred embodiment of the present application, the calcination temperature in steps (3) and (5) is 300-.
As a preferred embodiment herein, the amount of magnesium loaded in step (4) is 0.5 to 3 wt%, preferably 1 to 2 wt% of the calcined powder.
As a preferred embodiment in the present application, the amount of graphite added in step (5) is 1 to 3 wt% based on the mass of the catalyst.
The catalyst prepared by the preparation method of the high-activity high-selectivity methanol synthesis catalyst is prepared by the total mass of the catalystThe weight parts of the components are as follows: CuO: 60-75%, ZnO: 18-25% of Al2O3：5-15％，MgO：0.5-3％。
The catalyst is used for synthesizing the methanol catalyst, has good low-temperature activity and thermal stability, low byproduct content and better activity and selectivity.
Compared with the prior art, the preparation method of the high-activity high-selectivity methanol synthesis catalyst has the following advantages:
the preparation method of the high-activity high-selectivity methanol synthesis catalyst provided by the invention has the advantages that the materials obtained after the two-step precipitation are soaked in the zinc nitrate solution for a period of time, so that the copper-zinc substitution rate of the catalyst can be improved, more active sites can be formed, and the catalyst has higher low-temperature activity.
According to the preparation method of the high-activity high-selectivity methanol synthesis catalyst, a certain amount of magnesium element is introduced by adopting an isometric impregnation method in the preparation process of the catalyst, and the impregnated magnesium can neutralize the acidity of the surface of the catalyst, so that the selectivity of the catalyst is improved.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1:
weighing 24.51gZn (NO)3)2·6H2O、61.81g Al(NO3)3·9H2And O, dissolving in 500ml of deionized water, and stirring to completely dissolve to obtain a salt solution A. Weighing 332.6g Cu (NO)3)2·3H2O、85.14g Zn(NO3)2·6H2O and 15.45g Al (NO)3)3·9H2And O, dissolving in 1500ml of deionized water, and stirring to completely dissolve to obtain a salt solution B. 321.18g of Na were weighed2CO3Dissolving in 2000ml deionized water, and stirring to dissolve completely to obtain alkali solution C. Weighing 148.75gZn(NO3)2·6H2Dissolving O in 5L of deionized water, and stirring to completely dissolve O to obtain a zinc nitrate solution D.
The salt solution A, B and the alkali solution C are preheated to 70 ℃ respectively, and a proper amount of deionized water is added into the reactor, and the reactor is also preheated to 70 ℃. And (3) dropwise adding the salt solution A and the alkali solution C into the reactor in a cocurrent manner, continuously stirring in the whole process, controlling the pH value to be 7.0-7.5 by adjusting the feeding speed of the salt and the alkali, and controlling the temperature of the water bath to be 70 ℃. And stopping dripping the alkali solution C after the salt solution A is completely dripped. Continuously stirring for 10-15min, continuously adding the salt solution B in the same manner, and continuously dropwise adding the alkali solution C, wherein in the whole process, the pH value is controlled to be 7.0-7.5 by adjusting the feeding speed of the salt and the alkali, and the water bath temperature is maintained at 70 ℃. And stopping dropwise adding the alkali solution C after the salt solution B is completely added into the reactor, and aging the precipitate in the reactor for 2 hours at constant temperature. Thereafter, filtration was carried out, and after washing with deionized water, filtration was carried out again, and this step was repeated until no Na was detected+Is present. Putting the filter cake into a zinc nitrate solution D preheated to 70 ℃, continuously stirring for 2-3h, and maintaining the reaction temperature at 70 ℃ in the whole process. Then, filtration is carried out, and the mixture is washed 3 to 4 times by deionized water and then filtered. And pulping the filter cake, then carrying out spray drying, and roasting the dried material at 350 ℃ for 4h to decompose the dried material to obtain roasted powder. An equal-volume impregnation method is adopted, a proper amount of magnesium nitrate solution is impregnated on the roasted powder, and the loading capacity of magnesium is 2 wt% of the roasted powder. After the impregnation was completed, the material was dried at 120 ℃ for 24 hours and then calcined at 350 ℃ for 4 hours. And adding graphite into the roasted powder to form a synthetic methanol catalyst sample 1, wherein the adding amount of the graphite is 2 wt% based on the mass of the catalyst.
Example 2:
weighing 78.78gZn (NO)3)2·6H2O、99.34g Al(NO3)3·9H2And O, dissolving in 500ml of deionized water, and stirring to completely dissolve to obtain a salt solution A. Weighing 309.82g Cu (NO)3)2·3H2O、41.84g Zn(NO3)2·6H2O and 11.04g Al (NO)3)3·9H2And O, dissolving in 1500ml of deionized water, and stirring to completely dissolve to obtain a salt solution B. 321.18g of Na were weighed2CO3Dissolving in 2000ml deionized water, and stirring to dissolve completely to obtain alkali solution C. Weighing 74.37gZn (NO)3)2·6H2Dissolving O in 5L of deionized water, and stirring to completely dissolve O to obtain a zinc nitrate solution D.
The salt solution A, B and the alkali solution C are preheated to 80 ℃, and a proper amount of deionized water is added into the reactor, and the reactor is also preheated to 80 ℃. And (3) dropwise adding the salt solution A and the alkali solution C into the reactor in a cocurrent manner, continuously stirring in the whole process, controlling the pH value to be 7.5-8.0 by adjusting the feeding speed of the salt and the alkali, and controlling the temperature of the water bath to be 80 ℃. And stopping dripping the alkali solution C after the salt solution A is completely dripped. Continuously stirring for 10-15min, continuously adding the salt solution B in the same manner while continuously dropwise adding the alkali solution C, and controlling the pH value to be 7.5-8.0 and the water bath temperature to be 80 ℃ by adjusting the feeding speed of the salt and the alkali in the whole process. And stopping dropwise adding the alkali solution C after the salt solution B is completely added into the reactor, and aging the precipitate in the reactor for 2 hours at constant temperature. Thereafter, filtration was carried out, and after washing with deionized water, filtration was carried out again, and this step was repeated until no Na was detected+Is present. Putting the filter cake into a zinc nitrate solution D preheated to 80 ℃, continuously stirring for 2-3h, and maintaining the reaction temperature at 80 ℃ in the whole process. Then, filtration is carried out, and the mixture is washed 3 to 4 times by deionized water and then filtered. And pulping the filter cake, then carrying out spray drying, and roasting the dried material at 300 ℃ for 6 hours to decompose the dried material to obtain roasted powder. And soaking a proper amount of magnesium nitrate salt solution on the roasted powder by adopting an equal-volume soaking method, wherein the loading capacity of magnesium is 1 wt% of the roasted powder. After the impregnation was completed, the material was dried at 120 ℃ for 24 hours and then calcined at 300 ℃ for 6 hours. And adding graphite into the roasted powder to form a synthetic methanol catalyst sample 2, wherein the adding amount of the graphite is 2 wt% based on the mass of the catalyst.
Example 3:
weighing 73.53gZn (NO)3)2·6H2O、92.72g Al(NO3)3·9H2O, dissolved in 500mlAnd (4) stirring the mixture in ionized water to completely dissolve the mixture to obtain a salt solution A. Weighing 296.15g Cu (NO)3)2·3H2O、52.58g Zn(NO3)2·6H2O and 39.74g Al (NO)3)3·9H2And O, dissolving in 1500ml of deionized water, and stirring to completely dissolve to obtain a salt solution B. 321.18g of Na were weighed2CO3Dissolving in 2000ml deionized water, and stirring to dissolve completely to obtain alkali solution C. Weighing 118.98gZn (NO)3)2·6H2Dissolving O in 5L of deionized water, and stirring to completely dissolve O to obtain a zinc nitrate solution D.
The salt solution A, B and the alkali solution C are preheated to 85 ℃, and a proper amount of deionized water is added into the reactor and is also preheated to 85 ℃. And (3) dropwise adding the salt solution A and the alkali solution C into the reactor in a cocurrent manner, continuously stirring in the whole process, controlling the pH value to be 6.5-7.0 by adjusting the feeding speed of the salt and the alkali, and controlling the temperature of the water bath to be 85 ℃. And stopping dripping the alkali solution C after the salt solution A is completely dripped. Continuously stirring for 10-15min, continuously adding the salt solution B in the same manner while continuously dropwise adding the alkali solution C, and controlling the pH value to be 6.5-7.0 and the water bath temperature to be 85 ℃ by adjusting the feeding speed of the salt and the alkali in the whole process. And stopping dropwise adding the alkali solution C after the salt solution B is completely added into the reactor, and aging the precipitate in the reactor for 2 hours at constant temperature. Thereafter, filtration was carried out, and after washing with deionized water, filtration was carried out again, and this step was repeated until no Na was detected+Is present. Putting the filter cake into a zinc nitrate solution D preheated to 85 ℃, continuously stirring for 2-3h, and maintaining the reaction temperature at 85 ℃ in the whole process. Then, filtration is carried out, and the mixture is washed 3 to 4 times by deionized water and then filtered. And pulping the filter cake, then carrying out spray drying, and roasting the dried material at 400 ℃ for 4h to decompose the dried material to obtain roasted powder. An equal-volume impregnation method is adopted, a proper amount of magnesium nitrate solution is impregnated on the roasted powder, and the loading capacity of magnesium is 3 wt% of the roasted powder. After the impregnation was completed, the material was dried at 120 ℃ for 24 hours and then calcined at 400 ℃ for 4 hours. And adding graphite into the roasted powder to form a synthetic methanol catalyst sample 3, wherein the adding amount of the graphite is 2 wt% based on the mass of the catalyst.
In order to highlight the advantages of the preparation method of the methanol synthesis catalyst, comparative examples 1 to 3 are provided, and samples C1 to 3 prepared in comparative examples 1 to 3 have the same formulation as the sample in example 1 except that the conventional two-step precipitation method, the method of soaking only in zinc nitrate solution after two-step precipitation, and the method of soaking only in magnesium after two-step precipitation are respectively adopted, and the comparison is performed under the same conditions of the rest preparation processes, and in addition, comparative example 4 is provided, and sample C4 prepared in comparative example 4 has the same magnesium content as example 1, is coprecipitated with copper, zinc and aluminum, and is soaked in zinc nitrate solution, so as to highlight the advantages of magnesium impregnation.
Comparative example 1:
weighing 24.51gZn (NO)3)2·6H2O、61.81g Al(NO3)3·9H2And O, dissolving in 500ml of deionized water, and stirring to completely dissolve to obtain a salt solution A. Weighing 332.6g Cu (NO)3)2·3H2O、85.14g Zn(NO3)2·6H2O and 15.45g Al (NO)3)3·9H2And O, dissolving in 1500ml of deionized water, and stirring to completely dissolve to obtain a salt solution B. 321.18g of Na were weighed2CO3Dissolving in 2000ml deionized water, and stirring to dissolve completely to obtain alkali solution C.
The salt solution A, B and the alkali solution C were preheated to 70 deg.C, and an appropriate amount of deionized water was added to the reactor, which was similarly preheated to 70 deg.C. And (3) dropwise adding the salt solution A and the alkali solution C into the reactor in a cocurrent manner, continuously stirring in the whole process, controlling the pH value to be 7.0-7.5 by adjusting the feeding speed of the salt and the alkali, and controlling the temperature of the water bath to be 70 ℃. And stopping dripping the alkali solution C after the salt solution A is completely dripped. Continuously stirring for 10-15min, continuously adding the salt solution B in the same manner, and continuously dropwise adding the alkali solution C, wherein in the whole process, the pH value is controlled to be 7.0-7.5 by adjusting the feeding speed of the salt and the alkali, and the water bath temperature is maintained at 70 ℃. And stopping dropwise adding the alkali solution C after the salt solution B is completely added into the reactor, and aging the precipitate in the reactor for 2 hours at constant temperature. Thereafter, filtration was carried out, and the filtrate was washed with deionized water and then filtered, and this step was repeatedUntil no Na is detected+Is present. And pulping the filter cake, then carrying out spray drying, roasting the dried material at 350 ℃ for 4h to decompose the dried material, adding 2 wt% of graphite into the roasted powder, and forming to obtain a synthetic methanol catalyst sample C1.
Comparative example 2:
weighing 24.51gZn (NO)3)2·6H2O、61.81g Al(NO3)3·9H2And O, dissolving in 500ml of deionized water, and stirring to completely dissolve to obtain a salt solution A. Weighing 332.6g Cu (NO)3)2·3H2O、85.14g Zn(NO3)2·6H2O and 15.45g Al (NO)3)3·9H2And O, dissolving in 1500ml of deionized water, and stirring to completely dissolve to obtain a salt solution B. 321.18g of Na were weighed2CO3Dissolving in 2000ml deionized water, and stirring to dissolve completely to obtain alkali solution C. Weighing 148.75gZn (NO)3)2·6H2Dissolving O in 5L of deionized water, and stirring to completely dissolve O to obtain a zinc nitrate solution D.
The salt solution A, B and the alkali solution C were preheated to 70 deg.C, and an appropriate amount of deionized water was added to the reactor, which was similarly preheated to 70 deg.C. And (3) dropwise adding the salt solution A and the alkali solution C into the reactor in a cocurrent manner, continuously stirring in the whole process, controlling the pH value to be 7.0-7.5 by adjusting the feeding speed of the salt and the alkali, and controlling the temperature of the water bath to be 70 ℃. And stopping dripping the alkali solution C after the salt solution A is completely dripped. Continuously stirring for 10-15min, continuously adding the salt solution B in the same manner, and continuously dropwise adding the alkali solution C, wherein in the whole process, the pH value is controlled to be 7.0-7.5 by adjusting the feeding speed of the salt and the alkali, and the water bath temperature is maintained at 70 ℃. And stopping dropwise adding the alkali solution C after the salt solution B is completely added into the reactor, and aging the precipitate in the reactor for 2 hours at constant temperature. Thereafter, filtration was carried out, and after washing with deionized water, filtration was carried out again, and this step was repeated until no Na was detected+Is present. Putting the filter cake into a zinc nitrate solution D preheated to 70 ℃, continuously stirring for 2-3h, and maintaining the reaction temperature at 70 ℃ in the whole process. Then, filtration is carried out, and the mixture is washed 3 to 4 times by deionized water and then filtered. Filtering the filter cakeAnd (3) carrying out spray drying after pulping, roasting the dried material for 4 hours at 350 ℃ to decompose the dried material, and adding 2 wt% of graphite into the roasted powder to mold the mixture to obtain a synthetic methanol catalyst sample C2.
Comparative example 3:
weighing 24.51gZn (NO)3)2·6H2O、61.81g Al(NO3)3·9H2And O, dissolving in 500ml of deionized water, and stirring to completely dissolve to obtain a salt solution A. Weighing 332.6g Cu (NO)3)2·3H2O、85.14g Zn(NO3)2·6H2O and 15.45g Al (NO)3)3·9H2And O, dissolving in 1500ml of deionized water, and stirring to completely dissolve to obtain a salt solution B. 321.18g of Na were weighed2CO3Dissolving in 2000ml deionized water, and stirring to dissolve completely to obtain alkali solution C.
The salt solution A, B and the alkali solution C were preheated to 70 deg.C, and an appropriate amount of deionized water was added to the reactor, which was similarly preheated to 70 deg.C. And (3) dropwise adding the salt solution A and the alkali solution C into the reactor in a cocurrent manner, continuously stirring in the whole process, controlling the pH value to be 7.0-7.5 by adjusting the feeding speed of the salt and the alkali, and controlling the temperature of the water bath to be 70 ℃. And stopping dripping the alkali solution C after the salt solution A is completely dripped. Continuously stirring for 10-15min, continuously adding the salt solution B in the same manner, and continuously dropwise adding the alkali solution C, wherein in the whole process, the pH value is controlled to be 7.0-7.5 by adjusting the feeding speed of the salt and the alkali, and the water bath temperature is maintained at 70 ℃. And stopping dropwise adding the alkali solution C after the salt solution B is completely added into the reactor, and aging the precipitate in the reactor for 2 hours at constant temperature. Thereafter, filtration was carried out, and after washing with deionized water, filtration was carried out again, and this step was repeated until no Na was detected+Is present. And pulping the filter cake, then carrying out spray drying, and roasting the dried material at 350 ℃ for 4h to decompose the dried material to obtain roasted powder. An equal-volume impregnation method is adopted, a proper amount of magnesium nitrate solution is impregnated on the roasted powder, and the loading capacity of magnesium is 2 wt% of the roasted powder. After the impregnation was completed, the material was dried at 120 ℃ for 24 hours and then calcined at 350 ℃ for 4 hours. The calcined powder was then formed with 2 wt% graphite to give methanol catalyst sample C3.
Comparative example 4:
weighing 24.51gZn (NO)3)2·6H2O、61.81g Al(NO3)3·9H2And O, dissolving in 500ml of deionized water, and stirring to completely dissolve to obtain a salt solution A. Weighing 332.6g Cu (NO)3)2·3H2O、85.14g Zn(NO3)2·6H2O and 15.45g Al (NO)3)3·9H2O，19.62g Mg(NO3)2·6H2Dissolving O in 1500ml deionized water, stirring to dissolve completely to obtain salt solution B. 321.18g of Na were weighed2CO3Dissolving in 2000ml deionized water, and stirring to dissolve completely to obtain alkali solution C. Weighing 148.75gZn (NO)3)2·6H2Dissolving O in 5L of deionized water, and stirring to completely dissolve O to obtain a zinc nitrate solution D.
The salt solution A, B and the alkali solution C are preheated to 70 ℃ respectively, and a proper amount of deionized water is added into the reactor, and the reactor is also preheated to 70 ℃. And (3) dropwise adding the salt solution A and the alkali solution C into the reactor in a cocurrent manner, continuously stirring in the whole process, controlling the pH value to be 7.0-7.5 by adjusting the feeding speed of the salt and the alkali, and controlling the temperature of the water bath to be 70 ℃. And stopping dripping the alkali solution C after the salt solution A is completely dripped. Continuously stirring for 10-15min, continuously adding the salt solution B in the same manner, and continuously dropwise adding the alkali solution C, wherein in the whole process, the pH value is controlled to be 7.0-7.5 by adjusting the feeding speed of the salt and the alkali, and the water bath temperature is maintained at 70 ℃. And stopping dropwise adding the alkali solution C after the salt solution B is completely added into the reactor, and aging the precipitate in the reactor for 2 hours at constant temperature. Thereafter, filtration was carried out, and after washing with deionized water, filtration was carried out again, and this step was repeated until no Na was detected+Is present. Putting the filter cake into a zinc nitrate solution D preheated to 70 ℃, continuously stirring for 2-3h, and maintaining the reaction temperature at 70 ℃ in the whole process. Then, filtration is carried out, and the mixture is washed 3 to 4 times by deionized water and then filtered. Pulping the filter cake, spray-drying, roasting the dried material at 350 deg.C for 4h to decompose, adding 2 wt% graphite into the roasted powder, and molding to obtain the synthetic methanol catalyst sampleProduct C4.
And (3) sample testing:
the activity of the catalyst was tested using a fixed bed high pressure micro-reactor, and 7 catalyst samples prepared in examples 1-3 and comparative examples 1-4 were crushed, sieved through a 20-50 mesh sieve, and then packed with 4ml (2ml catalyst +2ml equi-sized ceramic rings). Temperature programmed reduction is required before activity testing, and the volume fraction is 5% H2-95％N2Heating and reducing under the atmosphere, heating from room temperature to 170 ℃ within 4h, keeping the temperature for 2h, heating to 220 ℃ within 2h, and keeping the temperature for 2 h.
The reaction conditions for synthesizing the methanol are as follows: the reaction pressure is 5.0MPa, the reaction temperature is 235-245 ℃, and the space velocity is 10000h-1(ii) a The volume composition of raw material gas is 13.0-14.0% of CO and its composition is2＝4.0-5.0％，N210%, the remainder is H2。
Heat resistance test conditions: the heat-resisting temperature is 400 ℃, the heat-resisting time is 10h, and the space velocity is 3000h-1。
Reaction conditions after heat resistance: the reaction pressure is 5.0MPa, the reaction temperature is 235-245 ℃, and the space velocity is 10000h-1。
Methanol synthesis was carried out under the above conditions, and the initial CO conversion (%) and methanol space-time yield (g. ml) of catalysts 1 to 3 and C1 to C3 were measuredcat -1·h-1) And initial CO conversion (%) and methanol space-time yield (g. ml) after the Heat resistance test thereofcat -1·h-1) The ratio of the space-time yield of methanol after the heat resistance test to the space-time yield of the initial methanol was used to compare the thermal stability of the catalyst, and the results are shown in Table 1. Meanwhile, the main byproduct content in the liquid phase product before and after the heat resistance test is analyzed by a chromatograph to compare the selectivity of the catalyst. In order to make the results more intuitive, the by-product contents of the sample C1 prepared by the conventional two-step method are used as the reference, and the by-product contents listed in the rest of the catalyst samples are relative ratios to the sample C1, and the results are shown in table 2.
Table 1 results of catalyst activity test
Table 2 catalyst selectivity test results
As can be seen from the data of table 1 and table 2, sample 1, sample 2 and sample 3 all showed excellent low temperature activity and thermal stability. Compared with the sample C1 prepared by the traditional two-step method, the initial activity and the thermal stability of the sample 1 are obviously improved, and the content of reaction byproducts is lower, which indicates that the sample 1 has better activity and selectivity; the sample C2 prepared by soaking zinc nitrate after the two-step precipitation has higher content of reaction by-products, but the activity and the thermal stability of the sample C2 are obviously improved compared with the sample C1 prepared by the traditional two-step method, and the activity level of the sample C1 is basically reached; the activity of the sample C3 soaked with magnesium nitrate after two-step precipitation is at the same level as that of the sample C1, which is obviously poorer than that of the sample C1 and the sample C2 soaked with zinc nitrate, but the content of the by-products is far lower than that of the sample C1, which indicates that the sample C3 has good selectivity. Comparing sample 1 with sample C4, it can be seen that the impregnated magnesium significantly reduces the by-product content relative to the precipitated magnesium, increasing the selectivity of the catalyst. The data can show that the precipitate is soaked in the zinc nitrate solution after the two-step precipitation, so that the activity of the catalyst is favorably improved; the impregnation of magnesium helps to reduce reaction by-products and improve the selectivity of the catalyst.
In conclusion, the catalyst sample prepared by the preparation method of the methanol synthesis catalyst has good activity and selectivity.
The above examples are only preferred embodiments of the patent, but the scope of protection of the patent is not limited thereto. It should be noted that, for those skilled in the art, without departing from the principle of this patent, several improvements and modifications can be made according to the patent solution and its patent idea, and these improvements and modifications should also be regarded as the protection scope of this patent.
Claims (8)
1. The preparation method of the high-activity high-selectivity methanol synthesis catalyst is characterized in that the methanol synthesis catalyst comprises the following components in percentage by mass: CuO: 60-75%, ZnO: 18-25% of Al2O3：5-15％，MgO：0.5-3％；
The preparation method comprises the following steps:
(1) preparing a mixed aqueous solution of zinc nitrate and aluminum nitrate, and recording the mixed aqueous solution as a salt solution A; preparing a mixed aqueous solution of nitrates of copper, zinc and aluminum, and recording the mixed aqueous solution as a salt solution B; preparing a sodium carbonate solution, and recording as an alkali solution C; preparing a zinc nitrate solution;
(2) adding a proper amount of deionized water into a reactor, preheating A, B saline solution, C alkali solution and the deionized water in the reactor to a reaction temperature, dropwise adding the saline solution A and the C alkali solution into the reactor in a cocurrent flow manner under uniform stirring, and adjusting the pH value of a precipitation solution in the reactor; stopping adding the alkali solution C after the salt solution A is added dropwise, and continuously stirring; adding the salt solution B and the alkali solution C in the same way, adjusting the pH value of the precipitation solution in the reactor, and stopping adding the alkali solution C after the salt solution B is dropwise added; after the precipitation is complete, aging for a certain time in the reactor;
(3) after aging is finished, filtering the precipitate, washing the filter cake with deionized water and filtering again until no Na is detected in the filtrate+Soaking the washed filter cake in preheated zinc nitrate solution, keeping the reaction temperature constant in the process, and continuously stirring; then filtering and washing for 3-4 times, pulping the filter cake, spray drying, and roasting for a certain time to obtain roasted powder;
(4) soaking a proper amount of magnesium nitrate solution on the roasted powder by adopting an isometric soaking method;
(5) after the impregnation is finished, drying and roasting the materials, adding graphite into the roasted powder, and molding to obtain the synthetic methanol catalyst;
the reaction temperature in the steps (2) and (3) and the preheating temperature of the zinc nitrate solution in the step (3) are both 70-90 ℃.
2. The preparation method of the methanol synthesis catalyst with high activity and high selectivity according to claim 1, wherein the preparation method comprises the following steps: the pH value in the reaction process of the step (2) is always maintained between 6.5 and 8.0.
3. The preparation method of the methanol synthesis catalyst with high activity and high selectivity according to claim 1, wherein the preparation method comprises the following steps: after the addition of the alkali solution C is stopped in the step (2), continuously stirring for 10-15 min; the aging time is 2-3 h.
4. The preparation method of the methanol synthesis catalyst with high activity and high selectivity according to claim 1, wherein the preparation method comprises the following steps: the roasting temperature in the steps (3) and (5) is 300-.
5. The preparation method of the methanol synthesis catalyst with high activity and high selectivity according to claim 1, wherein the preparation method comprises the following steps: the initial concentration of the zinc nitrate solution in the step (3) is 0.05-0.1 mol/L.
6. The preparation method of the methanol synthesis catalyst with high activity and high selectivity according to claim 1, wherein the preparation method comprises the following steps: the loading amount of magnesium in the step (4) is 0.5-3 wt% of the roasted powder.
7. The preparation method of the methanol synthesis catalyst with high activity and high selectivity according to claim 1, wherein the preparation method comprises the following steps: in the step (5), the adding amount of the graphite is 1-3% of the mass of the catalyst.
8. The method for preparing a high-activity high-selectivity methanol synthesis catalyst according to any one of claims 1 to 7, wherein: the catalyst is used for synthesizing the methanol catalyst, has better low-temperature activity and thermal stability, low byproduct content and better activity and selectivity.
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