CN102989463A - High-energy ball milling preparation method of CuZnO catalyst for methanol synthesis - Google Patents

Abstract

The invention discloses a high-energy ball milling method of CuZnO catalyst for methanol synthesis, which belongs to the field of preparation of new catalyst materials. The dry grinding method is to mix the metal powders of Cu, Zn and Al according to a certain ratio, add ball milling aids and then add them to the high-energy ball mill, and perform high-energy ball milling without any protective atmosphere to obtain high-activity alloy powders. The alloy powder after ball milling is mixed with the catalyst carrier in the air atmosphere, and then the CuZnO catalyst is prepared after high-energy ball milling without adding other ball milling aids; the wet milling method is to mix the metal powders of Cu, Zn, and Al, and then add ball milling aids. After the agent is added to a high-energy ball mill, water is added as a ball milling medium and a reaction solvent. Adopting the method of high-energy ball milling, the process flow is short, the cost is low, and no other harmful substances or wastes are produced in the process, which is green and environmentally friendly.

Description

Preparation method of CuZnO catalyst for methanol synthesis by high-energy ball milling

technical field

The invention relates to a preparation method of a catalyst, in particular to a high-energy ball mill preparation method for preparing a methanol catalyst from synthesis gas, and belongs to the field of preparation of new catalyst materials. the

Background technique

Copper-based catalysts are effective catalysts for synthesizing methanol or dimethyl ether. At present, copper-zinc or copper-zinc is used to add one or more metal oxides as auxiliary agents to prepare methanol through hydrogenation of synthesis gas or carbon monoxide and carbon dioxide. catalyst. The preparation method of this type of catalyst mainly adopts the chemical method, and the basic process of the chemical method preparation is to prepare the hydroxide precursor first, and the precursor is calcined to form an oxide to prepare the required catalyst. This type of preparation method requires a calcination process above 500°C to form oxide powder. As a result of calcination, the activity of the powder is reduced, the micropores of the powder are closed, the particles grow, and agglomeration will be formed in the powder. The agglomeration not only reduces the powder The specific surface area also reduces the catalytic activity of the powder accordingly, which has a great impact on the performance of the catalyst. the

The methods for preparing such catalysts by chemical methods mainly include co-precipitation, hydrothermal method, sol-gel method and alkoxide method. Co-precipitation is the most widely used and researched method among these methods. Different scholars have conducted a lot of discussions on the influence of precipitant, raw materials and process parameters on catalysis. The co-precipitation method uses chloride salts and nitrates. The existence of these anions is easy to destroy the properties of the synthetic powder. Removing these ions requires repeated washing, which is easy to change the component structure of the precipitated phase. In addition, the cost of these raw materials is relatively high. , the preparation process is complicated. The sol-gel method in the chemical preparation method is trivial, and relatively expensive metal alkoxides must be used to participate in the reaction. The chemical substances involved in the reaction are very sensitive to the environment, and the test technology is difficult. The hydrothermal method also has the problem of component segregation. The chemical preparation process of this type of catalyst is complicated and the cost is relatively high. Therefore, the search for efficient and low-cost catalyst preparation technology has become the focus of research. the

As a metastable metal alloy preparation method, mechanochemistry has developed rapidly in recent years. Mechanochemistry, as a branch of chemistry, focuses on the study of chemical or physical changes that occur when condensed matter is subjected to mechanical forces. Chemical transformation, which introduces the accumulation of mechanical energy through different modes of action of mechanical force, thereby changing the physical and chemical properties and structure of the object under force, improving its reactivity, thereby stimulating and accelerating the chemical reaction produced. Combining the research progress of mechanochemistry and the research results of Cu/ZnO catalysts prepared by chemical methods, exploring the use of mechanochemical methods to prepare such catalysts can not only explore a new preparation method, but also improve the theoretical research of mechanochemistry. Enrich the research content of high-energy ball milling and broaden its application fields. the

The research on the reaction activity center of CuZnO catalyst shows that the influence of the valence state of Cu on the catalysis is Cu ²⁺ , Cu ⁺ , and Cu ⁰ . The dispersion of Cu on its surface improves the catalytic performance. For the CuZnO composite carrier catalyst we want to study, mechanochemistry can synthesize alloys or supersaturated solid solutions in different phases at room temperature. The production of CuZn alloys by melting and casting and the research on their phases are relatively mature. As the amount increases, intermediate phases such as β, γ, and ε appear in sequence, and zinc and copper can form six phases such as α, β, γ, δ, ε, and η. Utilize mechanochemistry to prepare catalysts under the condition of high-energy ball milling; because the high-energy ball milling is used to prepare oxide catalysts, it can be directly ball-milled in the atmosphere without using a protective atmosphere, and Zn has high activity and is generally easy to oxidize, while Cu is not easy to oxidize Or partial oxidation, which not only promotes the diffusion of Cu in ZnO, but also forms different valence states of Cu. Different process parameters in the high-energy ball milling process correspond to different powder properties and phase states. If multiple analysis methods can be used , through the study of the relationship between the performance change of the catalyst and the powder phase state and various parameters in the bench experiment, the catalyst with good performance can be synthesized through the adjustment of the process. In addition, the characteristics and advantages of high-energy ball milling are the formation of unstable compounds. In the case of high-energy ball milling, the powder is refined and the activity of the powder is enhanced, thereby reducing the sintering temperature. In the presence of welds there occurs the phenomenon of calcination to form oxides. It is known in theory that as long as the time or energy of high-energy ball milling is sufficient, metal hydroxides can be converted into oxides at room temperature under the condition of high-energy ball milling, which not only avoids the formation of agglomerates under high-temperature calcination, but also improves the activity of the catalyst. During this reaction process, the surface activity of the hydroxide is large, coupled with the local high temperature phenomenon of high-energy ball milling and the sufficient energy provided, the hydroxide and the powdered alloy phase of CuZn will interact, which not only makes the active components of the catalyst Among them, the dispersion is uniform and a metastable mixture is formed, which has an obvious influence on the catalytic performance in the later stage.

Contents of the invention

In order to overcome the disadvantages of high cost and long process flow for preparing such catalysts by chemical methods, combined with the research results of preparing CuZn alloys by high-energy ball milling, the present invention provides a CuZnO catalyst that uses metal powder as raw material and uses high-energy ball milling technology to prepare CuZnO catalysts. The raw material is metal powder, and the method of high-energy ball milling is adopted, the cost is simple, and the process flow is short. the

The technical solution of the present invention is: the dry grinding method is to mix the metal powders of Cu, Zn and Al according to a certain proportion, add ball milling aids and then add them to a high-energy ball mill, and perform high-energy ball milling without any protective atmosphere. To obtain highly active alloy powder, the alloy powder after ball milling is mixed with the catalyst carrier in an air atmosphere without adding other ball milling aids, and then the CuZnO catalyst is prepared after high energy ball milling;

Or the preparation method can also be a wet milling method: in the absence of any protective atmosphere, after mixing the metal powders of Cu, Zn and Al, adding ball milling aids and adding them to a high-energy ball mill, adding water as a ball milling medium and a reaction solvent, The liquid-solid ratio of the added water to the metal powder is: 1-10:1mL/g. CuZn alloy and Zn hydroxide precursors are formed during the high-energy ball milling process. After the precursors are filtered and dried, they will not The CuZnO catalyst was prepared by adding other ball milling aids to carry out high energy ball milling on the precursor and the catalyst carrier.

The particle size of the metal powders of Cu, Zn and Al is less than 100 mesh. the

The metal powder mixing ratio of Cu, Zn and Al has a mass ratio of 4-5:4-5:2-1. the

The ball milling aid is stearic acid, and the mass ratio of the added ball milling aid to metal powder is 1-2:100. the

The ball-to-material ratio in the high-energy ball milling process is 5-40:1 (dry milling and wet milling processes do not include the ratio of water), the ball milling time is 1-2 hours, and the ball milling speed is 300-1200 rpm . the

The catalyst carrier is one of alumina, zirconia, and pseudo-boehmite or a mixture of several in arbitrary proportions, the mixing mass ratio of the alloy powder after ball milling and the catalyst carrier in the dry milling process, the precursor in the wet milling process The mixing mass ratio with the catalyst carrier is 2:1~5. the

The principle of the present invention is: the preparation method of mechanochemical wet grinding is to apply the principle of high-energy ball milling on the basis of mechanochemistry and mechanical alloying, so that a series of reactions occur between the solution and the solid phase under the action of mechanical force, and the added The solution not only serves as the medium of the ball milling process, but also reacts with the solid phase, and the generated substances are also soaked in it. Due to the existence of the ball milling medium, the local temperature of the reaction system changes little but will be accompanied by the generation of gas. the

The dry grinding of the present invention adopts three metal powders of Cu, Zn and Al. After adding certain ball milling aids, they are added to the high-energy ball mill according to a certain ratio, and the appropriate high-energy ball milling process parameters are selected, and the high-energy ball milling is carried out in an air atmosphere to form CuZn alloy precursor, the precursor mainly consists of different phases of CuZn alloy, due to ball milling in air atmosphere, it may contain part of ZnO and CuO. Since high-energy ball milling can refine the powder and increase the specific surface area of the powder, a large number of defects and fresh surfaces will be formed on the surface of the powder. These powders have strong activity. The process of ball milling is the process of powder alloying and activation; After the strong alloy precursor is obtained, choose a suitable catalyst carrier, mainly including alumina, zirconium hydroxide, and pseudoboehmite. One or more of them can be selected, and the precursor and the catalyst carrier are subjected to high-energy ball milling. Oxides can form oxides after high-energy ball milling. Since the alloy precursor is in an active state during the process, the alloy precursor of the active component of the catalyst is easy to combine with the catalyst carrier under high-energy ball milling to form a catalyst with strong activity. The catalyst active component can be uniformly dispersed in the catalyst carrier and also improves the specific surface area and catalytic activity of the catalyst. the

In the case of ball milling, the metal powder is surrounded by ball milling medium water, the specific surface area of the powder itself is large, and it can fully contact with water, the action of mechanical force makes the metal powder particles smaller, the specific surface area increases, and a large number of crystal lattice defects occur , accumulating a large amount of strain energy, reducing the activation energy of the reaction. Secondly, the generation of lattice defects and the instantaneous temperature rise caused by collisions provide favorable conditions for the diffusion of liquid molecules or ions into the interior of the particle, and the reaction layer is blown off to form a deposit and is taken away by the flowing liquid, exposing a new surface , the new surface continues to react with water, and so on, until the metal reacts completely. the

Cu/ZnO catalyst is a composite carrier catalyst composed of oxides of Cu and Zn and a carrier. The precursor or main active component of the catalyst is a highly dispersed oxide of Cu and Zn. The interaction has a great influence on the catalytic effect, and high-energy ball milling in water solvent is a better way to generate high dispersion and the interaction between the two. The precursor of CuZn alloy catalyst is a highly dispersed and mixed oxide of Cu and Zn. These two metals will react differently with water during the wet milling process of high-energy ball milling with water as the medium, and disperse in the water medium. In the case of an agent, the reaction is sufficient to form a different substance. the

In the case of water as the medium, controlling the pH of the ball milling medium and the milling parameters Cu and Zn can react with water to produce different substances, mainly oxides and hydroxides, which are the precursors of the catalysts we need to prepare The chemical composition is the same, and due to the existence of high-energy ball milling in the reaction process, the interaction and dispersion between the two metal elements and their oxides and hydroxides are improved, the specific surface area is increased, and some fresh surfaces are prepared. These are all for the preparation Catalyst precursors with excellent performance provide the possibility. the

During the wet milling process, due to the existence of water as the ball milling medium and reactant, the water and Zn in the ball mill react to form Zn(OH) ₂ , so that the reaction system is in an alkaline state. In this state, the formation of alloys and the formation of Cu The high-energy ball milling products of different valence states will have an impact. In this state, Cu and Zn can be highly dispersed, and the activity can be improved. In the subsequent high-energy ball milling process, the energy hydroxide of high-energy ball milling can be used The highly dispersed Cu and Zn active components and the high specific surface area and fresh surface formed by ball milling have laid a good foundation for the improvement of catalyst activity.

Advantages and positive effects of the present invention:

(1) The present invention mainly adopts the method of high-energy ball milling. During the process of high-energy ball milling, the powder is refined, a large number of fresh surfaces are produced, and the reactivity of the catalyst is improved. During the process of high-energy ball milling, the catalyst active components and the catalyst carrier undergo mechanochemical reactions. A catalyst with high specific surface area, non-equilibrium state, high dispersion and high activity is formed. This method uses metal powder, which is cheaper than the corresponding metal nitrate or other raw materials used in the chemical method. In addition, the method of high-energy ball milling is used, the process is short, the cost is low, and there are no other harmful substances or substances in the process. Waste generation, green environmental protection. The method has the advantages of normal temperature synthesis, large-scale production, simple process flow and low cost.

(2) In terms of the technical effect of wet grinding and dry grinding, the conversion rate of wet grinding catalyst is higher, which can reach or exceed the same type of catalyst prepared by chemical method, generally above 20%, and the highest conversion rate can reach 26% , the dry grinding may be worse, and the conversion rate is only below 10%. From the perspective of mechanism, wet grinding is the synthesis of catalyst after the metal is turned into hydroxide during the ball milling process and then calcined and mixed with the carrier ball mill of the oxide. The dry grinding process is to form an alloy phase. The alloy phase can be combined with the hydroxide catalyst The reaction takes place during ball milling to produce oxides. The carrier used in dry grinding is hydroxide, and the carrier used in wet grinding is a general oxide carrier. the

Detailed ways

The present invention will be further described below in conjunction with the examples, but the present invention is not limited to the scope described below. the

Example 1: This example adopts the dry grinding method to prepare CuZnO catalyst for methanol synthesis: after mixing Cu, Zn and Al metal powders with a particle size of 90 mesh according to the mass ratio of 2:2:1, add Add the ball milling aid to the high-energy ball mill (the milling aid is stearic acid, and the mass ratio of the added ball milling aid to metal powder is 1:100) and perform high-energy ball milling without any protective atmosphere to obtain a highly active alloy. Powder, ball milled alloy powder and catalyst carrier (catalyst carrier is alumina, the mixing mass ratio of ball milled alloy powder and catalyst carrier in the dry milling process is 2:1) and mixed in air atmosphere without adding other ball milling aids The CuZnO catalyst was prepared after high-energy ball milling, and the conversion rate was 8% (the ball-to-material ratio in the high-energy ball milling process was 5:1, the ball milling time was 2 hours, and the ball milling speed was 300 rpm)

Example 2: This example adopts the dry grinding method to prepare CuZnO catalyst for methanol synthesis: after mixing Cu, Zn, and Al metal powders with a particle size of 95 mesh according to the mass ratio of 4.5:4.5:1.5, add Add the ball milling aid to the high-energy ball mill (the milling aid is stearic acid, and the mass ratio of the added ball milling aid to metal powder is 1.5:100) and perform high-energy ball milling without any protective atmosphere to obtain a high-activity alloy Powder, ball milled alloy powder and catalyst carrier (catalyst carrier is zirconia, the mixing mass ratio of ball milled alloy powder and catalyst carrier in the dry milling process is 1:1) and mixed in air atmosphere without adding other ball milling aids The CuZnO catalyst was prepared after high-energy ball milling, and the conversion rate was 8% (the ball-material ratio in the high-energy ball milling process was 40:1, the ball milling time was 1 hour, and the ball milling speed was 800 rpm)

Embodiment 3: This embodiment adopts the dry milling method to carry out the preparation of CuZnO catalyst for methanol synthesis: after mixing the metal powders with a particle size of less than 100 meshes of Cu, Zn, Al according to the mass ratio of 5: 5: 1, After adding the ball milling aid, add it to the high-energy ball mill (the milling aid is stearic acid, and the mass ratio of the added ball milling aid to metal powder is 2:100) and carry out high-energy ball milling without any protective atmosphere to obtain high-activity Alloy powder, ball-milled alloy powder and catalyst carrier (catalyst carrier is a mixture of pseudo-boehmite and alumina in any proportion, and the mixing mass ratio of ball-milled alloy powder and catalyst carrier in the dry milling process is 2: 5) after mixing In the air atmosphere, the CuZnO catalyst was prepared after high-energy ball milling without adding other ball milling aids. turn/min)

Example 4: This example adopts wet grinding method to prepare CuZnO catalyst for methanol synthesis: in the absence of any protective atmosphere, after the metal powder particle size is less than 100 mesh Cu, Zn, Al metal powder mixed (metal The mass ratio of the powder mixing ratio is 4.8:4.3:2), adding the ball milling aid (the ball milling aid is stearic acid, and the mass ratio of the added ball milling aid to metal powder is 1:50) and then added to the high energy ball mill, Add water as the ball milling medium and reaction solvent. The liquid-solid ratio of the added water to the metal powder is: 1:1mL/g. CuZn alloy and Zn hydroxide precursors are formed during the high-energy ball milling process. After the precursors are filtered and dried , in an air atmosphere, without adding other ball milling aids to mix the precursor with the catalyst support (the catalyst support is a mixture of alumina and zirconia in any proportion, and the mixing mass ratio of the precursor to the catalyst support during the wet milling process is 2:3) The CuZnO catalyst was prepared after high-energy ball milling, and the conversion rate was 19% (the ball-to-material ratio in the high-energy ball milling process was 8:1, the ball milling time was 1.6 hours, and the ball milling speed was 900 rpm).

Example 5: This example adopts the wet grinding method to prepare CuZnO catalyst for methanol synthesis: without any protective atmosphere, after the metal powder has a particle size of 80 meshes, Cu, Zn, and Al are mixed (metal powder The mass ratio of the mixing ratio is 5: 5: 2), adding the ball milling aid (the ball milling aid is stearic acid, and the mass ratio of the added ball milling aid to metal powder is 1.3: 100) and then adding it to the high energy ball mill, adding Water is used as the ball milling medium and the reaction solvent, and the liquid-solid ratio of the added water to the metal powder is 2:1mL/g. During the high-energy ball milling process, CuZn alloy and Zn hydroxide precursors are formed. After the precursors are filtered and dried, the Under the air atmosphere, without adding other ball milling aids, the precursor and the catalyst support (the catalyst support is pseudo-boehmite, and the mixing mass ratio of the precursor and the catalyst support during the wet milling process is 1:2) are then subjected to high-energy ball milling. The CuZnO catalyst was prepared with a conversion rate of 17.8% (the ball-to-material ratio in the high-energy ball milling process was 15:1, the ball milling time was 1 hour, and the ball milling speed was 500 rpm). the

Example 6: This example adopts the wet grinding method to prepare the CuZnO catalyst for methanol synthesis: in the absence of any protective atmosphere, after the metal powder has a particle size of 95 meshes, Cu, Zn, and Al are mixed (the metal powder The mass ratio of the mixing ratio is 4:4:1), adding the ball milling aid (the ball milling aid is stearic acid, and the mass ratio of the added ball milling aid to metal powder is 1:100) and then adding it to the high-energy ball mill, adding Water is used as the ball milling medium and the reaction solvent. The liquid-solid ratio of the added water and metal powder is 10:1mL/g. During the high-energy ball milling process, CuZn alloy and Zn hydroxide precursors are formed. After the precursors are filtered and dried, the Under the air atmosphere, the precursor and the catalyst carrier were mixed without adding other ball milling aids (the catalyst carrier was a mixture of alumina, zirconia, and pseudoboehmite in any proportion, and the mixing mass ratio of the precursor and the catalyst carrier during the wet milling process was uniform. The CuZnO catalyst was prepared after high-energy ball milling, and the conversion rate was 18% (the ball-to-material ratio in the high-energy ball milling process was 40:1, the ball milling time was 2 hours, and the ball milling speed was 1000 rpm). the

Claims (6)

1. a methyl alcohol synthesizes the high energy ball mill method of using the CuZnO catalyst, it is characterized in that: the dry grinding method is after the metal dust of Cu, Zn, Al is mixed according to certain proportioning, add in the high energy ball mill after adding ball-milling additive, carry out high-energy ball milling in without the situation of any protective atmosphere and make highly active alloy powder, under air atmosphere, do not add other ball-milling additives and carry out again preparing the CuZnO catalyst behind the high-energy ball milling after alloy powder behind the ball milling and catalyst carrier are mixed; Perhaps the preparation method can also be wet grinding: in the situation without any protective atmosphere; after the metal dust of Cu, Zn, Al mixes; add in the high energy ball mill after adding ball-milling additive; add entry as ball-milling medium and reaction dissolvent; the water that adds and the liquid-solid ratio of metal dust are: 1～10:1mL/g; form the hydroxide presoma of CuZn alloy and Zn in the Process During High Energy Ball Milling; presoma is through behind the filtering drying; under air atmosphere, do not add other ball-milling additives presoma and catalyst carrier are carried out preparing the CuZnO catalyst behind the high-energy ball milling again.

2. methyl alcohol according to claim 1 synthesizes the high energy ball mill method with the CuZnO catalyst, it is characterized in that: the granularity of the metal dust of described Cu, Zn, Al is less than 100 orders.

3. methyl alcohol according to claim 1 synthesizes the high energy ball mill method with the CuZnO catalyst, and it is characterized in that: the mass ratio of the metal dust mixing match of described Cu, Zn, Al is 4～5:4～5:2～1.

4. methyl alcohol according to claim 1 synthesizes the high energy ball mill method with the CuZnO catalyst, and it is characterized in that: described ball-milling additive is stearic acid, and the ball-milling additive of adding and the mass ratio of metal dust are 1～2:100.

5. methyl alcohol according to claim 1 synthesizes the high energy ball mill method with the CuZnO catalyst, and it is characterized in that: ratio of grinding media to material is 5～40:1 in the described Process During High Energy Ball Milling, and Ball-milling Time is 1～2 hour, and rotational speed of ball-mill is 300～1200 and turns/min.

6. methyl alcohol according to claim 1 synthesizes the high energy ball mill method with the CuZnO catalyst, it is characterized in that: described catalyst carrier is one or several arbitrary proportion mixtures in aluminium oxide, zirconia, the boehmite, and the mixing quality ratio of presoma and catalyst carrier is 2:1～5 in the mixing quality ratio of the alloy powder in the dry grinding process behind the ball milling and catalyst carrier, the wet-milling process.