CN1139427C - Nano CuZnAl catalyst for synthesizing methanol and dimethylether and its preparing process - Google Patents

Abstract

The invention belongs to the technical field of chemical industry, and relates to a nano metal copper catalyst for synthesizing methanol or dimethyl ether and a preparation method thereof. The catalyst is composed of metal copper, zinc oxide and aluminum oxide. Between 2 and 10nm, the nano metal copper is highly dispersed on the zinc oxide-alumina composite carrier. The catalyst reduces the carbonate or oxalate coprecipitate of copper, zinc, aluminum soluble salt mixed solution with reducing agent such as alkali metal borohydride or hydrazine hydrate under the condition of 0-50°C, and suction filtration, It is prepared by washing, vacuum drying, and roasting under inert atmosphere. The catalyst prepared by the invention has better synthesis performance of methanol and _dimethyl ether than the CuO/ZnO/ _Al2O3 catalyst of the traditional carbonate co-precipitation method.

Description

A kind of nano-copper-zinc-aluminum catalyst for synthesizing methanol and dimethyl ether and preparation method thereof

technical field

The invention belongs to the technical field of chemical industry, and relates to a new preparation method of a catalyst for synthesizing methanol and dimethyl ether, in particular to a preparation method of a nanometer copper-zinc-aluminum catalyst used for synthesizing methanol or dimethyl ether.

Methanol synthesis is an extremely important chemical process. Copper-zinc-aluminum catalysts are the main components of low-pressure methanol synthesis catalysts and low-temperature water-gas shift industrial catalysts. At present, the copper-zinc-aluminum catalysts used in industry are all prepared by co-precipitation method. For example, the co-precipitation method proposed in British Patent 1,296,211 and 1,296,212 uses sodium carbonate as a precipitant to make the copper-zinc-aluminum nitrate mixture form a carbonate precipitate at a certain pH value and a certain precipitation temperature, and wash it with distilled water Sodium ions are then dried and roasted to form a copper-zinc-aluminum oxide mixture. This method has many disadvantages such as difficulty in washing sodium ions, easy overheating in the reduction process, which leads to a significant decrease in catalyst activity, and poor repeatability of catalyst activity. In particular, it should be pointed out that the above-mentioned industrial copper-zinc-aluminum catalysts must undergo complex pre-reduction treatment before they can be officially put into use, and the activation process is not only complicated and time-consuming, but also the changes in the subtle conditions during the reduction activation process have great impact on The catalytic performance is significantly affected. In addition, it was also found that when the industrial Cu/ZnO/Al ₂ O ₃ synthesis methanol catalyst prepared by the traditional co-precipitation method was used for CO ₂ hydrogenation to synthesize methanol and dimethyl ether, the activity of methanol and dimethyl ether was very low. Therefore, the design and development of the preparation method is simple, the catalytic performance is stable, it can fully activate CO ₂ under relatively mild conditions without complex pre-reduction process, and has a high selectivity for methanol or direct synthesis of dimethyl ether in one step. Catalysts are very necessary.

On the other hand, as environmental problems such as global industrial pollution and greenhouse effect become more and more serious, the exploratory research on how to effectively control and efficiently utilize carbon dioxide has attracted great attention. Catalytic conversion of carbon dioxide as raw material to produce chemicals such as methanol and dimethyl ether is one of the most important frontier research topics in modern carbon-one chemical industry. Methanol and dimethyl ether are extremely important basic raw materials for carbon-one chemical industry, which can be further oriented to synthesize many high value-added chemicals. In recent years, methanol and dimethyl ether are also considered to be a promising clean substitute fuel for gasoline and diesel. Therefore, the direct synthesis of methanol and dimethyl ether by hydrogenation of carbon dioxide can not only significantly improve the living environment of human beings, but also alleviate the increasingly serious energy crisis and resource crisis.

The 21st century is the century of new materials. As one of the most important basic materials in the new century, nanomaterials have attracted more and more attention from people from all walks of life. Nanoparticle catalysts have the characteristics of high specific surface area, high surface energy and many surface active sites, and exhibit unique catalytic properties different from conventional materials. As a new type of catalyst, they have good development prospects for carbon dioxide hydrogenation reaction. At present, domestic and foreign research reports in this area are increasing day by day. Therefore, according to the reaction characteristics of methanol synthesis, it is very attractive to design and prepare nano-catalysts that are suitable for the reaction characteristics of methanol synthesis and are easy to implement and use.

Contents of the invention

The purpose of the present invention is to propose a new type of nano-metal copper-zinc-aluminum catalyst that has high catalytic efficiency and can be directly used in the synthesis of methanol or one-step synthesis of dimethyl ether without complex reduction and activation treatment before the reaction, and proposes the preparation of the catalyst method.

The catalyst for synthesizing methanol or dimethyl ether provided by the present invention is a nano-metallic copper-based catalyst containing elemental copper, which is composed of multiple active components such as copper, zinc, aluminum, etc., and the molar ratio of each component is as follows: Bottom: Cu: 25-65%, NO: 65-25%, Al: 20-5%. The total amount of components is 100%. The preferred molar ratio is: Cu: 30-60%, Zn: 60-30%, Al: 15-10%. The size of metallic copper is 2 to 10 nm. Among them, nano-copper is highly dispersed on the zinc oxide-alumina composite carrier.

The preparation method of the nano-copper-zinc-aluminum catalyst that the present invention proposes is as follows:

According to the content ratio of each component, the co-precipitation slurry containing copper, zinc and aluminum compounds is first prepared by coprecipitation method, and the precipitate is light blue; then the precipitate slurry is directly reacted with a reducing agent to reduce copper. and release a large amount of hydrogen, and the reduced substance is a black precipitate; then the precipitate is filtered by suction, washed (usually first with deionized water, then with ethanol), and vacuum-dried; finally, the product can be directly pressed into tablets to obtain The catalyst is obtained by calcining the product at 250°C to 400°C under the protection of an inert gas (generally high-purity N ₂ ) or under vacuum.

In the present invention, the reducing agent used can be an aqueous or ethanol solution of alkali metal borohydride (such as NaBH ₄ , KBH _{4 ,} etc.) or hydrazine hydrate (N ₂ H ₄ ), and the amount thereof is 50-200% in excess.

In the present invention, the temperature condition of the reduction reaction may be 0°C to 50°C.

In the present invention, the coprecipitate of copper, zinc, aluminum compound is a kind of carbonate mixture containing copper, zinc, aluminum, or the alkaline color carbonate mixture containing copper, zinc, aluminum, or containing copper, zinc, An aluminum oxalate mixture, or a mixture of two or more of the above.

The method of the present invention destroys the sticky colloid-like structure of the original co-precipitate due to the treatment with the reducing agent after the precipitation process, so that the Na ⁺ ions harmful to the catalytic activity are extremely easy to clean. Washing with ethanol and vacuum drying in the preparation process of the present invention can prevent the collapse of the structure and the agglomeration of particles in the ordinary drying process of the precipitate to a certain extent.

The process is suitable for operation on a fluid or fixed bed, either batchwise or continuously, preferably continuously. The activity of catalyst provided by the invention can be tested by following method:

Activity evaluations were performed in a continuous flow pressurized stainless steel microreactor. The temperature of the catalyst bed in the reactor (200mm×Φ6mm) is controlled by a chrome-aluminum thermocouple through a program temperature controller. The reaction pressure is controlled by a constant pressure valve at the inlet. Reagent gas flow is controlled by trim valves and monitored by mass flow meters and soap film flow meters. The product was analyzed by on-line gas chromatography. The chromatographic carrier gas is H ₂ , which is detected by a thermal conductivity cell detector. Two parallel chromatographic columns (Poropak-Q and TDX-01, 2m) are used to separate CH ₃ OH, dimethyl ether, higher alcohols and CO, CO ₂ , CH ₄ and other products.

The method of the invention is based on the carbonate or oxalate co-precipitation method, and the co-precipitation slurry is treated with a liquid phase reducing agent, which can overcome many shortcomings of the traditional co-precipitation method. The washing process for removing sodium ions in the preparation process is fast and convenient, the post-treatment process is mild, and the catalyst activity and selectivity are high.

Compared with the prior art, the present invention has the following advantages:

1. The copper component in the catalyst is an elemental nanoparticle, and the other components are in an oxidized state. The distribution of each component is relatively uniform, and there is a strong interaction between each component;

2. The catalyst can be used directly after calcination, without the complicated, difficult and time-consuming reduction and activation process;

3. The preparation method of the catalyst is simple, easy to operate, and the repeatability of the catalyst performance is good. The catalytic activity and selectivity are superior to the traditional co-precipitation catalysts, and it is easy to realize industrial scale-up.

Detailed ways

The catalyst proposed by the present invention and its preparation method are further described below through the examples, and the examples of the catalyst prepared by the traditional sodium carbonate co-precipitation method are provided as a comparison.

Example 1

Take 10.22 grams of copper chloride (CuCl ₂ 2H ₂ O), 4.09 grams of zinc chloride (ZnCl ₂ ), and 2.42 grams of aluminum chloride (AlCl ₃ 6H ₂ O) and add water to form a solution (100 mL); another 11.13 gram of sodium carbonate (Na ₂ CO ₃ ) to make a solution (100mL); under vigorous stirring, add mixed metal solution and sodium carbonate solution into 100mL water at the same time, keep the pH value at about 7.0 during the precipitation process, and prepare light blue copper-zinc Aluminum mixed precipitates; under vigorous stirring, add 200ml of aqueous solution containing 19.4 grams of KBH ₄ to the fresh precipitates, the precipitates turn black and emit a large amount of hydrogen. The black precipitate was quickly suction filtered, washed three times with deionized water and three times with ethanol, and dried in vacuum. Samples can be directly compressed into tablets for catalytic reactions or after being calcined at 350°C for catalytic reactions. The loading amount of the catalyst on the flow reaction device is 0.5g, the catalyst is reacted without pre-reduction treatment, the CO ₂ /H ₂ is 1/3 (the total reaction pressure is 2.0MPa), the space velocity is 3600h ^-1 , 240℃ The methanol yield was 6.0%.

Example 2

At room temperature, under vigorous stirring, 0.2M KBH ₄ aqueous solution was added dropwise to a 0.5M copper chloride aqueous solution, reacted violently and released a large amount of hydrogen gas, washed and vacuum dried to obtain a brown-black nano-metallic Cu catalyst. The methanol synthesis reaction is implemented on the flow reaction device in Example 1, the catalyst is reacted without pre-reduction treatment, the loading of the catalyst is 0.5g, CO ₂ /H ₂ (2.0MPa) is 1/3, and the space velocity It is 3600h ^-1 , and the yield of methanol is 0.8% at 240°C.

Comparative Example 1

Take 10.22 grams of copper chloride (CuCl ₂ 2H ₂ O), 4.09 grams of zinc chloride (ZnCl ₂ ), and 2.42 grams of aluminum chloride (AlCl ₃ 6H ₂ O) and add water to form a solution (100 mL); another 11.13 1 gram of sodium carbonate was made into solution (100mL); under vigorous stirring, mixed metal solution and sodium carbonate solution were added to 100mL water simultaneously to prepare a mixed precipitate of copper, zinc and aluminum; the precipitate was washed 6 times with deionized water to remove residual Na ions, after drying at 110°C, bake at 350°C for 5 hours. The loading of the catalyst on the flow reaction device is 0.5g, the CO ₂ /H ₂ (2.0MPa) is 1/3, the space velocity is 3600h ^-1 , and the catalyst is reacted without pre-reduction treatment. The yield was 0.6%.

Comparative Example 2

Take 10.22 grams of copper chloride (CuCl ₂ 2H ₂ O), 4.09 grams of zinc chloride (ZnCl ₂ ), and 2.42 grams of aluminum chloride (AlCl ₃ 6H ₂ O) and add water to form a solution (100 mL); another 11.13 1 gram of sodium carbonate was made into solution (100mL); under vigorous stirring, mixed metal solution and sodium carbonate solution were added to 100mL water simultaneously to prepare a mixed precipitate of copper, zinc and aluminum; the precipitate was washed 6 times with deionized water to remove residual Na ions, after drying at 110°C, bake at 350°C for 5 hours. The loading capacity of the catalyst on the flow reaction device is 0.5g, the CO ₂ /H ₂ (2.0MPa) is 1/3, and the space velocity is 3600h ^-1 . The yield of methanol was 3.6%.

Example 3

Take 10.22 grams of copper chloride (CuCl ₂ 2H ₂ O), 4.09 grams of zinc chloride (ZnCl ₂ ), and 2.42 grams of aluminum chloride (AlCl ₃ 6H ₂ O) and add water to form a solution (100 mL); another 11.13 1 gram of sodium carbonate was made into solution (100mL); under vigorous stirring, mixed metal solution and sodium carbonate solution were added into 100mL water simultaneously to prepare a mixed precipitate of copper, zinc and aluminum; under vigorous stirring, 20ml hydrazine hydrate solution (40wt%) was added to obtain Yellow precipitate, wash the precipitate 6 times with deionized water to remove residual Na ⁺ ions, dry it at 110°C, and then bake it at 350°C. The loading of the catalyst on the flow reaction device is 0.5g, the CO ₂ /H ₂ (2.0MPa) is 1/3, the space velocity is 3600h ^-1 , the catalyst is reacted without pre-reduction treatment, and the methanol The yield was 2.2%.

Example 4

Take 10.22 grams of copper chloride (CuCl ₂ 2H ₂ O), 4.09 grams of zinc chloride (ZnCl ₂ ), and 2.42 grams of aluminum chloride (AlCl ₃ 6H ₂ O) and add water to form a solution (100 mL); another 22.63 gram of oxalic acid was made into a solution (100mL); under vigorous stirring, mixed metal solution and oxalic acid solution were added to 100mL water simultaneously to prepare a mixed precipitate of copper, zinc and aluminum; under vigorous stirring, 200ml was added to dissolve 19.4 grams of KBH ₄ in water to obtain a black For the precipitate, the black precipitate was quickly filtered by suction, washed three times with deionized water and three times with ethanol, dried in vacuum, and then calcined at 350°C. The loading of the catalyst on the flow reaction device is 0.5g, the CO ₂ /H ₂ (2.0MPa) is 1/3, the space velocity is 3600h ^-1 , the catalyst is reacted without pre-reduction treatment, and the methanol The yield was 6.2%.

Example 5

Take 13.40 grams of copper nitrate (Cu(NO ₃ ) ₂ 2H ₂ O), 5.68 grams of zinc nitrate (Zn(NO ₃ ) ₂ ), and 2.80 grams of aluminum nitrate (Al(NO ₃ ) ₃ 6H ₂ O) and add water to mix Take another 22.63 grams of oxalic acid to form a solution (100mL); under vigorous stirring, add mixed metal solution and oxalic acid solution to 100mL water at the same time to prepare a mixed precipitate of copper, zinc and aluminum; add 200ml of dissolved The aqueous solution of 19.4 grams of KBH ₄ obtained a black precipitate, which was quickly filtered by suction, washed 3 times with deionized water and 3 times with ethanol, dried in vacuum, and then roasted at 350°C. The loading of the catalyst on the flow reaction device is 0.5g, the CO ₂ /H ₂ (2.0MPa) is 1/3, the space velocity is 3600h ^-1 , the catalyst is reacted without pre-reduction treatment, and the methanol The yield was 6.5%.

Example 6

Connect to example 1. The vacuum-dried catalyst sample was mixed with γ-Al ₂ O ₃ at a weight ratio of about 3:1 to obtain a composite bifunctional nano-copper-based catalyst, which was used for direct synthesis of dimethyl ether in one step. The loading of the catalyst on the flow reaction device is 1.5g, the CO/CO ₂ /H ₂ (4.0MPa) is 33/3/64, the space velocity is 1800h ^-1 , the catalyst reacts without pre-reduction treatment, 240 The yield of dimethyl ether at °C was 84%.

Claims (8)

1. A nano-copper-zinc-aluminum catalyst for synthesizing methanol or dimethyl ether is characterized in that the nano-metal copper base containing elemental copper is composed of copper, zinc, and aluminum active ingredients, and the molar percentages of each component are: Cu: 25-65%, Zn: 65-25%, Al: 20-5%; the total amount of components is 100%, and the size of metal copper is 2-10hm. 2. The nano-copper-zinc-aluminum catalyst according to claim 1, characterized in that the mole percentage of each component is: Cu: 30-60%, Zn: 60-30%, Al: 15-10%, the total amount is 100%. 3. A method for preparing a nano-metallic copper-zinc-aluminum catalyst for synthesizing methanol or dimethyl ether as claimed in claim 1, wherein the coprecipitate slurry containing copper, zinc, and aluminum compounds is first prepared by coprecipitation; Then the co-precipitate slurry is directly reacted with a reducing agent to reduce copper; then the precipitate is suction filtered, washed, and vacuum-dried; finally, the product is directly compressed into a tablet, or the product is placed under the protection of an inert gas or under vacuum at 250 ℃ ~ 400 ℃ melting, the catalyst is prepared. 4. The preparation method of nanometer copper-zinc-aluminum catalyst according to claim 3, characterized in that the coprecipitate of copper, zinc and aluminum compounds is a carbonate mixture containing copper, zinc and aluminum. 5. The preparation method of nanometer copper-zinc-aluminum catalyst according to claim 3, characterized in that the coprecipitate of copper, zinc and aluminum compounds is a basic carbonate mixture containing copper, zinc and aluminum. 6. The preparation method of nanometer copper-zinc-aluminum catalyst according to claim 3, characterized in that the coprecipitate of copper, zinc and aluminum compounds is an oxalate mixture containing copper, zinc and aluminum. 7. The preparation method of nano-copper-zinc-aluminum catalyst according to claim 3, characterized in that the coprecipitate of copper, zinc, and aluminum compounds is a mixture of two or more of the following: a carbonate mixture containing copper, zinc, and aluminum , Basic carbonate mixture, oxalate mixture. 8. The preparation method of nanometer copper-zinc-aluminum catalyst according to claim 3, characterized in that the reducing agent is an aqueous or ethanol solution of alkali metal borohydride or hydrazine hydrate, and the amount of the reducing agent is 50-200% in excess.