CN101314134A - Preparation method of bifunctional catalyst for direct preparation of dimethyl ether from synthesis gas - Google Patents

Abstract

The invention discloses two preparation methods of bifunctional catalysts for directly preparing dimethyl ether from synthesis gas. The core principle is to add the active components of methanol synthesis to the methanol dehydration components in the form of oxalate precipitation, for example, by adopting The following steps: a. Dissolving the active component that can be used as a methanol synthesis catalyst in alcohol in the form of a soluble salt to prepare a mixed solution A; b. Adding the active component that can be used as a methanol dehydration catalyst to the above mixed solution A and stirring Obtain suspension B; c. add alcohol solution of oxalic acid to suspension B under stirring, the oxalate co-precipitate produced by the reaction is aged, filtered, dried, and finally roasted at 250-550°C to obtain the Bifunctional catalyst. The preparation process of the invention is simple, and the prepared bifunctional catalyst has low reaction temperature, high carbon monoxide conversion rate and good dimethyl ether selectivity.

Description

Preparation method of bifunctional catalyst for direct preparation of dimethyl ether from synthesis gas

technical field

The present invention relates to a catalyst for the preparation of dimethyl ether, more specifically to the preparation of a dual-functional catalyst used in the direct preparation of dimethyl ether by a one-step method of synthesis gas, which is composed of a methanol synthesis catalyst and a methanol dehydration catalyst method.

Background technique

Dimethyl ether is an important raw material for the production of various chemical products. In the 1980s, many countries in the world developed dimethyl ether as a safe atomization propellant. Freon was banned in the early 1990s, and dimethyl ether was used as an ideal substitute. In recent years, it has been found that it also has extremely good combustion performance and can achieve clean combustion. It is known as the "clean fuel" of the 21st century at home and abroad, so DME has attracted increasing attention internationally. DME was first produced by distillation of by-products in high-pressure methanol production. With the wide application of low-pressure methanol synthesis technology, the side reactions are greatly reduced, and the industrial production technology of dimethyl ether has quickly developed to methanol dehydration or direct synthesis of synthesis gas, which is the so-called two-step and one-step process. The two-step process is to first convert syngas to methanol, and then dehydrate the methanol to dimethyl ether. Methanol dehydration method includes liquid phase method and gas phase method. The former reaction is carried out in the liquid phase, and methanol is obtained by dehydration of concentrated sulfuric acid. The process has the advantages of mild reaction conditions (130-160° C.), high conversion rate of methanol per pass (about 90%), and the advantages of batch or continuous production. However, due to problems such as equipment corrosion, environmental pollution, and harsh operating conditions, this method was gradually eliminated. Due to the rapid growth of demand for dimethyl ether, countries have successively developed new methanol vapor phase dehydration processes with low investment, good operating conditions and no pollution. For example, in 1965, Mobil Corporation researched and developed a method for producing dimethyl ether by dehydration of methanol gas phase using crystalline aluminum silicate as a catalyst. In the early 1980s, Mobil improved the catalysis, and the selectivity of dimethyl ether and the conversion rate of methanol were greatly improved. In 1991, Japan's Mitsui Topress Chemical Company also developed a new catalyst. Domestic Southwest Research Institute of Chemical Industry and Shanghai Petrochemical Research Institute have also developed solid acid catalysts for methanol vapor phase dehydration to dimethyl ether, and have been applied in industrial devices of different scales.

The direct production of dimethyl ether from synthesis gas, that is, the one-step process is a new technology developed in recent years, which allows the two reactions of methanol synthesis and methanol dehydration to be carried out in the same reactor without intermediate processes, because there is methanol in the reaction system at the same time Synthesis and methanol dehydration are two types of reactions, thus breaking the thermodynamic equilibrium limitation in the pure methanol synthesis process and generating a large positive reaction driving force, which can effectively reduce the operating pressure and increase the single-pass conversion rate of CO. Generally speaking, the one-step method is better than the two-step method, so the research on the synthesis of dimethyl ether at home and abroad mainly focuses on the research on the one-step method. The catalyst used in the one-step synthesis of DME from syngas is a bifunctional catalyst composed of a methanol synthesis catalyst and a methanol dehydration catalyst. Methanol synthesis catalysts are mainly copper-based oxide catalysts, such as composite oxides such as Cu-Zn-Al or Cu-Zn-Cr. Methanol dehydration catalysts are mainly solid acid catalysts such as alumina or molecular sieves (such as HZSM-5, HY and mordenite). The reaction performance of the bifunctional catalyst used in the one-step synthesis of DME from syngas is not only related to the catalytic performance of the methanol synthesis component and the methanol dehydration component itself, but also related to the combination of two different functional components into a bifunctional catalyst. The preparation method is closely related. At present, there are mainly two composite methods used, namely mechanical mixing method and impregnation method.

The mechanical mixing method is to firstly prepare the composite oxides of methanol synthesis components such as copper, zinc and/or aluminum/or chromium through the co-precipitation method, and then directly mechanically mix them with methanol dehydration components such as alumina or molecular sieves . For example, the Chinese patent CN 1085824A (1994) entitled "a catalyst for producing dimethyl ether from synthesis gas and its process for preparing dimethyl ether" discloses the dehydration component by methanol (modified by B, P and Ti) Alumina) and methanol synthesis component (catalyst C ₃₀₂ for the industrial production of methanol produced by Southwest Chemical Industry Research Institute) is a dual-functional catalyst prepared by mechanical mixing, that is, the powders of the two catalysts are mixed evenly by mechanical stirring, and then pressed into tablets Forming to obtain a bifunctional catalyst. Under the reaction conditions of H ₂ /CO molar ratio of 2, reaction temperature of 260°C, reaction pressure of 3.5 MPa and feed gas space velocity of 1000h ^-1 , the conversion rate of carbon monoxide is 83-85%, and the selectivity of dimethyl ether is 84-94%. U.S. Patent No. 4,177,167 (1979) titled "Catalyst for the Preparation of Dimethyl Ether" uses silicon-modified activated alumina as a methanol dehydration catalyst, and prepares a double-layered catalyst with Cu-Zn-Al composite oxide, a methanol synthesis component, by mechanical mixing. Functional catalyst, that is, the powders of the two catalysts are mixed evenly by mechanical stirring, and then pressed into tablets. Under the reaction conditions of H ₂ /CO molar ratio of 3, reaction temperature of 300°C, reaction pressure of 5 MPa and feed gas space velocity of 3500h ^-1 , the conversion rate of carbon monoxide was 62%. After 475 hours of continuous reaction, the conversion rate of carbon monoxide was Decreased to 57%, the selectivity of dimethyl ether is basically unchanged. It can be seen that the conversion rate of carbon monoxide and the selectivity of dimethyl ether of the bifunctional catalyst are both low. It can be seen from the above that the disadvantage of the bifunctional catalyst prepared by the mechanical mixing method is that the two different functional components cannot be in close contact, which leads to a decrease in the reactivity of the catalyst.

The impregnation method to prepare the bifunctional catalyst is to introduce the active component with methanol synthesis function into the methanol dehydration component through the impregnation method. For example, U.S. Patent No. 4,375,424 (1983) entitled "Catalyst for the Preparation of Dimethyl Ether" discloses a bifunctional catalyst formed by supporting copper-zinc, a methanol synthesis component, on an acidic component γ-Al2O3 by impregnation. The specific preparation method in the examples is to dissolve 7.2 grams of copper nitrate and 7.8 grams of zinc nitrate in 30 milliliters of water, then add 30 grams of alumina, immerse for 0.5 hours, dry and roast to obtain the bifunctional catalyst. The catalyst has a carbon monoxide conversion rate of 60-70% under the reaction conditions of H2/CO molar ratio of 1:1, reaction temperature of about 300°C, reaction pressure of 12MPa and feed gas space velocity of 3000h ^-1 . It can be seen that the reaction pressure and reaction temperature required by the above-mentioned catalyst are relatively high, and the reaction activity is relatively low (the highest conversion rate of carbon monoxide is not more than 70%). The Chinese patent CN 1090222A (1994) titled "Preparation Method of Dimethyl Ether Catalyst" disclosed that alumina or alumina modified by silicon, tungsten, etc. was used as methanol dehydration component, and methanol synthesis component copper was introduced by impregnation method. and zinc bifunctional catalysts. The active reaction temperature of the catalyst is high (>290°C), and under the reaction conditions of reaction pressure 4MPa and raw material (semi-water gas) space velocity 2400h ^-1 , the maximum conversion rate of carbon monoxide does not exceed 61%. In addition, in order to achieve a certain content of active components, it is necessary to repeat the process of impregnation, drying and roasting many times. As can be seen from the above, although the preparation of bifunctional catalysts by impregnation has the advantage of simple preparation process, it also has obvious disadvantages, that is, it needs to repeat the processes of impregnation and roasting many times, and the working time is long, and the prepared catalyst is due to the active component Cu The particles are larger, so the conversion rate of CO is lower and/or the reaction temperature is higher.

In order to eliminate the shortcomings of the above-mentioned preparation methods, a new preparation method has been reported in a patent recently. For example, the Chinese patent CN 1356163A (2002) titled "Dual-functional Catalyst for Direct Synthesis of Dimethyl Ether from Synthesis Gas and Its Preparation Process" discloses that composite oxides such as copper and zinc are used as methanol synthesis components and alumina as methanol dehydration The components are bifunctional catalysts prepared by co-precipitation deposition method. The specific preparation method is to dissolve a certain amount of copper nitrate and zinc nitrate in water, then add acidic components and sodium carbonate solution for co-precipitation, deposit the active components on the surface of the acidic components, and wash and dry the precipitated deposits And calcined and compressed into tablets. Under the reaction conditions of H ₂ /CO molar ratio of 3.85, reaction temperature of 300°C, reaction pressure of 4 MPa and feed gas space velocity of 1490h ^-1 , the conversion rate of carbon monoxide is 81.75%, and the selectivity of dimethyl ether is 93.56%. Patents USP 6147125 (2000) and EP 1174408 (2002) of NKK Corporation of Japan also disclose two methods for preparing bifunctional catalysts for direct production of dimethyl ether from synthesis gas by coprecipitation deposition. (1) Add an acidic component such as γ-Al ₂ O ₃ to the mixed solution of active components such as copper, zinc and aluminum to make a suspension, and then add a precipitant sodium carbonate solution to co-precipitate the active components on γ-Al ₂ O ₃ surface, the resulting precipitate was filtered and washed to remove nitrate ions. In order to eliminate the adverse effect of alkaline sodium carbonate on the acidic components, the above-mentioned precipitate is soaked in a certain concentration of acid such as nitric acid solution, filtered, washed, dried and roasted after soaking for a certain period of time. (2) Replace the sodium carbonate in (1) with ammonia water as a precipitating agent to co-precipitate the active components on the surface of γ-Al ₂ O ₃ , because ammonia water is easily removed in the subsequent roasting process, so the obtained precipitate deposits The object does not need to be soaked in acid solution. Although the above-mentioned co-precipitation deposition method for syngas directly preparing dimethyl ether bifunctional catalyst has improved the degree of contact between two different functional components, it has the following disadvantages: (1) if sodium carbonate is used as precipitant to The active components co-precipitate on the surface of the acidic components. In order to eliminate the adverse effect of alkaline sodium carbonate on the acidic components, the resulting precipitated deposits need to be soaked in acid solution. Therefore, the preparation process is relatively cumbersome, and the repeated washing process will also have an adverse effect on the performance of the catalyst. (2) Using ammonia as a precipitant to co-precipitate the active components on the surface of the acidic component. Although the obtained precipitated deposits do not need to be soaked in acid solution, the performance of the catalyst prepared by using ammonia as a precipitant is poor.

It can be seen that the above-mentioned preparation methods for compounding methanol synthesis components and methanol dehydration components into bifunctional catalysts have obvious shortcomings, such as complicated preparation process, long time-consuming and/or the prepared bifunctional catalysts When it is used for the direct preparation of dimethyl ether from synthesis gas, its performance including the conversion rate of carbon monoxide and the selectivity of dimethyl ether are not quite satisfactory.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the complicated and time-consuming preparation process of the dimethyl ether bifunctional catalyst in the prior art, as well as the high temperature and low carbon monoxide conversion rate when the catalyst is used in the synthesis gas one-step method to prepare dimethyl ether. high, low selectivity of dimethyl ether and the like, and provides a catalyst preparation method with a simple preparation process, and the catalyst prepared by the method has the advantages of low reaction temperature, high conversion rate of carbon monoxide and good selectivity of dimethyl ether.

The core principle of the present invention is to add the active component of methanol synthesis to the methanol dehydration component in the form of oxalate precipitation, which specifically includes two ways:

The preparation method one of the bifunctional catalyst directly preparing dimethyl ether from synthesis gas comprises the following steps:

a. The active component that can be used as a methanol synthesis catalyst is dissolved in alcohol in the form of a soluble salt to prepare a mixed solution A, wherein the active component that can be used as a methanol synthesis catalyst is selected from Cu, Zn, Al, Cr wherein one or a mixture of them;

b. Add the active components that can be used as methanol dehydration catalysts to the above mixed solution A and stir to obtain suspension B, wherein the active components that can be used as methanol dehydration catalysts are selected from γ-Al ₂ O ₃ , HZSM-5 , one of HY;

c. Add the alcohol solution of oxalic acid to the suspension B under stirring, and the oxalate co-precipitate produced by the reaction is aged, filtered, dried, and finally roasted at 250-550° C. to obtain the bifunctional catalyst.

The alcohol is selected from one of anhydrous ethanol, n-propanol and isopropanol.

The oxalate co-precipitate produced by the reaction in step c is aged, filtered, dried, and finally calcined at 300-450° C. to obtain the bifunctional catalyst.

The preparation method two of the bifunctional catalyst directly preparing dimethyl ether from synthesis gas comprises the following steps:

a. The active component that can be used as a methanol synthesis catalyst is dissolved in alcohol in the form of a soluble salt to prepare a mixed solution A, wherein the active component that can be used as a methanol synthesis catalyst is selected from Cu, Zn, Al, Cr wherein one or a mixture of them;

b. oxalic acid is dissolved in alcohol to obtain alcohol solution B of oxalic acid;

c. Add the active component that can be used as a catalyst for methanol dehydration to alcohol to obtain a suspension C, wherein the active component that can be used as a catalyst for methanol dehydration is selected from γ-Al ₂ O ₃ , HZSM-5, and HY one;

d. Under stirring, drop the above two solutions of A and B into the suspension C at the same time, and the oxalate co-precipitate formed by the reaction is aged, filtered and dried directly, and finally roasted at 250-550 ° C. The bifunctional catalyst is prepared.

The alcohol is selected from one of anhydrous ethanol, n-propanol and isopropanol.

The oxalate co-precipitate produced by the reaction in step d is aged, filtered, dried, and finally calcined at 300-450° C. to obtain the bifunctional catalyst.

Beneficial effects of the invention: the core principle of the dimethyl ether bifunctional catalyst prepared by the method of the present invention is to add the active component of methanol synthesis to the methanol dehydration component in the form of oxalate precipitation, so the preparation process is simple. Repeated washing, drying and other steps are omitted in the method, and the disadvantages of cumbersome and time-consuming preparation of the dimethyl ether bifunctional catalyst in the prior art are overcome. Moreover, the method of the present invention greatly improves the degree of contact between two different functional components of the methanol synthesis active component and the methanol dehydration component, reduces the adverse effects of the preparation process on the catalyst, and the prepared bifunctional catalyst also has low reaction temperature. , high conversion rate of carbon monoxide and good selectivity of dimethyl ether and so on.

Detailed ways

The present invention is described in further detail below by preparation example and comparative example, the preparation method one of the bifunctional catalyst that directly prepares dimethyl ether by synthesis gas, comprises the following steps: a. The mode of salt is dissolved in alcohol and is formulated into mixed solution A, wherein the active component that can be used as methanol synthesis catalyst is selected from one of Cu, Zn, Al, Cr or their mixture; b. will be used as methanol dehydration The active component of the catalyst is added to the above mixed solution A and stirred to obtain a suspension B, wherein the active component that can be used as a catalyst for methanol dehydration is selected from one of γ-Al ₂ O ₃ , HZSM-5, and HY; c Add alcohol solution of oxalic acid to the suspension B under stirring, age, filter and dry the oxalate co-precipitate formed by the reaction, and finally roast at 250-550° C. to obtain the bifunctional catalyst. The alcohol is selected from one of anhydrous ethanol, n-propanol and isopropanol. The oxalate co-precipitate produced by the reaction in step c is aged, filtered, dried, and finally calcined at 300-450° C. to obtain the bifunctional catalyst.

The preparation method 2 of the bifunctional catalyst that directly prepares dimethyl ether from synthesis gas comprises the following steps: a. the active component that can be used as methanol synthesis catalyst is dissolved in alcohol in the form of soluble salt to prepare mixed solution A, wherein The described active component that can be used as methanol synthesis catalyst is selected from one of Cu, Zn, Al, Cr or their mixture; b. oxalic acid is dissolved in alcohol to obtain the alcohol solution B of oxalic acid; c. will be used as methanol dehydration The active component of the catalyst is added to the alcohol to obtain a suspension C, wherein the active component that can be used as a catalyst for methanol dehydration is selected from one of γ-Al ₂ O ₃ , HZSM-5, and HY; d. under stirring , the above two solutions of A and B are added dropwise to the suspension C at the same time, and the oxalate co-precipitate formed by the reaction is aged, filtered, dried, and finally roasted at 250-550 ° C to obtain the bis functional catalyst. The alcohol is selected from one of anhydrous ethanol, n-propanol and isopropanol. The oxalate co-precipitate produced by the reaction in step d is aged, filtered, dried, and finally calcined at 300-450° C. to obtain the bifunctional catalyst.

The bifunctional catalyst prepared by the invention can be used in a fixed bed reactor or a fluidized bed reactor, and can also be used in a gas-liquid-solid three-phase bed reactor, that is, a slurry bed reactor. The bifunctional catalyst prepared by the invention needs to be reduced before the reaction. The composition of the reducing gas is a mixture of hydrogen and an inert gas, and the inert gas is one or a mixture of nitrogen, helium and argon. The content of hydrogen in the reducing gas is 0.5-20%, preferably 1-10%; the reducing temperature is 180-300°C, preferably 220-280°C; the space velocity of the reducing gas is 500-5000h ^-1 , preferably 1000- 3000h ^-1 . The bifunctional catalyst prepared by the method of the present invention is used to directly prepare dimethyl ether from synthesis gas, and its applicable reaction conditions are: the molar ratio of synthesis gas raw material hydrogen to carbon monoxide is 0.8: 1～5: 1, preferably 1: 1～ 3:1; and the mixed gas preferably contains a certain amount of carbon dioxide, the content of which is 0.5-10%, preferably 1-5%. The volumetric space velocity of the reaction gas is 100 to 10000h ^-1 , preferably 500 to 3000h ^-1 . The reaction temperature is 200-400°C, preferably 220-300°C. The reaction pressure is 2.0-8.0 MPa, preferably 3.5-6.0 MPa.

One example of the process of the present invention using a fixed bed reactor is described below.

A certain amount of catalyst particles (20-40 meshes) is loaded into a stainless steel reactor with an inner diameter of 6 mm and a length of 300 mm. Electric heating is adopted, and the temperature is automatically controlled. The bottom of the reactor is filled with 20-40 mesh inert materials as supports, the inside of the reactor is filled with a certain amount of catalyst, and the upper part of the catalyst is filled with 20-40 mesh inert materials for preheating of raw materials. The raw material synthesis gas passes through the catalyst bed from top to bottom, where carbon monoxide hydrogenation and methanol dehydration reactions occur, and by-products such as dimethyl ether, methanol and a small amount of alkanes are produced. After the catalyst is loaded, use a reducing gas (5% H ₂ /95% N ₂ ) for reduction at elevated temperature (240° C.), and then switch the raw material gas for reaction. The composition (volume fraction) of the feed gas is CO: 31.1%, CO ₂ : 5.7%, and the rest is H ₂ ; the reaction pressure is 4.0 MPa; the reaction temperature is 230°C-290°C; the volume space velocity of the feed gas is 1500h ^-1 . HP 4890D gas chromatograph was used for online analysis, carbon monoxide and carbon dioxide were analyzed with thermal conductivity detector and carbon molecular sieve column; methanol, dimethyl ether and hydrocarbon by-products were analyzed with hydrogen flame ion detector and Porapak-N column.

According to the content of each component in the reaction tail gas, in the number of moles of carbon atoms, the conversion rate of carbon monoxide and the selectivity of hydrocarbons, methyl alcohol and dimethyl ether in the product are calculated by the following formula:

Carbon monoxide conversion (%) = (amount of carbon dioxide + amount of hydrocarbons + amount of methanol + amount of dimethyl ether × 2) / (amount of carbon monoxide + amount of carbon dioxide + amount of hydrocarbons + amount of methanol + dimethyl Amount of ether × 2) × 100%

The selectivity of dimethyl ether=the amount of dimethyl ether×2/(the amount of hydrocarbons+the amount of methanol+the amount of dimethyl ether×2)×100%

The selectivity of methanol = the amount of methanol / (the amount of hydrocarbons + the amount of methanol + the amount of dimethyl ether × 2) × 100%

The selectivity of hydrocarbons = the amount of hydrocarbons / (the amount of hydrocarbons + the amount of methanol + the amount of dimethyl ether × 2) × 100%

[Example 1]

43.5 grams of copper nitrate, 26.8 grams of zinc nitrate and 11.2 grams of aluminum nitrate were dissolved in absolute ethanol to make a mixed solution, and 11 grams of HZSM-5 (Si/Al=60) molecular sieves as methanol dehydration components were added to the above mixed solution. solution, and then stirred thoroughly to obtain a suspension. Add an ethanol solution containing 45 grams of oxalic acid to the above suspension under stirring to obtain a precipitate. The obtained sediment is aged at room temperature for half an hour, then filtered, dried, and then calcined at 350° C. for 6 hours to obtain a catalyst powder. Finally, the bifunctional catalyst A is obtained by tableting, crushing and sieving 20-40 mesh particles, wherein the weight percentage of each component is CuO 40%, ZnO 20%, Al ₂ O ₃ 7%, H-ZSM-5 33%.

[Example 2]

Dissolve 43.5 grams of copper nitrate, 26.8 grams of zinc nitrate and 11.2 grams of aluminum nitrate in absolute ethanol to make mixed solution a, dissolve 45 grams of oxalic acid in absolute ethanol to make solution b, and use 11 grams as methanol dehydration component The HZSM-5 (Si/Al=60) molecular sieve was added into absolute ethanol to prepare suspension c. Add solutions a and b simultaneously to the above suspension c under stirring to obtain a precipitate. The obtained sediment is aged at room temperature for half an hour, then filtered, dried, and then calcined at 350° C. for 6 hours to obtain a catalyst powder. Finally, bifunctional catalyst B was obtained by tableting, pulverizing and sieving 20-40 mesh particles, wherein the weight percentage of each component was the same as that of Example 1.

[Comparative example 1]

First, the methanol synthesis catalyst was prepared by co-precipitation method, that is, 43.5 grams of copper nitrate, 26.8 grams of zinc nitrate and 11.2 grams of aluminum nitrate were dissolved in distilled water to make a mixed solution, and the above mixed solution was mixed with sodium carbonate solution at 70 °C under strong stirring. A certain flow rate was dropped into a beaker at the same time to obtain a precipitate, and the obtained sediment was aged for one hour, then filtered, washed repeatedly with distilled water, dried at 110°C, and then roasted at 360°C for 6 hours to obtain methanol synthesis catalyst powder. Fully grind and mix 11 grams of HZSM-5 (Si/Al=60) molecular sieve as the methanol dehydration component with the obtained methanol synthesis component, then tablet, pulverize and sieve 20-40 mesh particles to obtain double Functional catalyst C, wherein the weight percentage of each component is the same as in Example 1.

[Comparative example 2]

43.5 grams of copper nitrate, 26.8 grams of zinc nitrate and 11.2 grams of aluminum nitrate were dissolved in distilled water to make a mixed solution, and 11 grams of HZSM-5 (Si/Al=60) molecular sieves as methanol dehydration components were added to the mixture under stirring. Immerse in the prepared mixed solution for 2 hours, then evaporate to dryness in a water bath, then dry at 110° C. and bake at 360° C. for 6 hours to obtain catalyst powder. Finally, bifunctional catalyst D was obtained by tableting, pulverizing and sieving 20-40 mesh particles, wherein the weight percentage of each component was the same as that of Example 1.

[Comparative example 3]

43.5 grams of copper nitrate, 26.8 grams of zinc nitrate and 11.2 grams of aluminum nitrate were dissolved in distilled water to make a mixed solution, and 11 grams of HZSM-5 (Si/A1=60) molecular sieves as methanol dehydration components were added to the above mixed solution , and then stirred thoroughly to obtain a suspension. Add a certain amount of ammonia solution to the above suspension at 70°C under vigorous stirring. After the dropwise addition, continue to stir the resulting precipitate in the mother liquor for 1 hour for aging, then filter, wash and dry, and then roast at 350°C Catalyst powder was obtained in 6 hours. Finally, bifunctional catalyst E was obtained by tableting, pulverizing and sieving 20-40 mesh particles, wherein the weight percentage of each component was the same as that of Example 1.

[Example 5]

Catalysts A, B, C, D and E prepared in Examples 1, 2 and Comparative Examples 1-3 were used for gas phase reaction in a continuous flow fixed bed pressurized reaction evaluation device, and the loading amount of the catalyst was 1 g. After the catalyst is loaded, the temperature is raised to 240°C under the condition of flowing reducing gas (5%H ₂ /95% N ₂ , the flow rate is 25ml/min). The temperature of the layer is lowered to 200°C, and then the raw material gas is switched and the temperature is gradually raised to the required reaction temperature for the reaction. The composition (volume fraction) of the feed gas is CO: 31.1%, CO ₂ : 5.7%, and the rest is H ₂ . The reaction conditions are pressure: 4 MPa, space velocity: 1500 ml/g _cat h ^-1 . After 3 hours of reaction, the system reached equilibrium, and then samples were taken for analysis. Use HP 4890D gas chromatograph on-line, use thermal conductivity detector, carbon molecular sieve chromatographic column to analyze carbon monoxide and carbon dioxide, use hydrogen flame ion detector, Porapak-N chromatographic column to analyze methanol, dimethyl ether and hydrocarbon by-products, catalyst The evaluation results can be seen in Table 1.

Table 1 Reaction performance of the catalyst

As can be seen from the data in Table 1, the bifunctional catalyst prepared by the method of the present invention, for the reaction of directly producing dimethyl ether from synthesis gas, the conversion rate of carbon monoxide and/or the selectivity of dimethyl ether are better than those prepared by the existing method. Compared with the bifunctional catalyst, it has been greatly improved.

The above content is only a basic description of the concept of the present invention, and any equivalent transformation made according to the technical solution of the present invention shall belong to the protection scope of the present invention.

Claims (6)

1. by the preparation method one of the bifunctional catalyst of direct preparation of dimethyl ether by using synthesis gas, comprise the following steps:

The active component that a. will can be used as methanol synthesis catalyst is dissolved in the mode of soluble-salt and is mixed with mixed solution A in the alcohol, and the wherein said active component that can be used as methanol synthesis catalyst is selected from the mixture of Cu, Zn, Al, Cr one of them or they;

The active component that b. will can be used as methanol dehydration catalyst joins to stir in the above-mentioned mixed solution A and obtains suspension B, and the wherein said active component that can be used as methanol dehydration catalyst is selected from γ-Al ₂O ₃, HZSM-5, HY one of them;

C. under agitation add the alcoholic solution of oxalic acid in suspension B, the oxalate coprecipitation thing that reaction generates 250～550 ℃ of following roastings, makes described bifunctional catalyst at last through aging, filtration, drying.

2. according to the preparation method of the described a kind of bifunctional catalyst by direct preparation of dimethyl ether by using synthesis gas of claim 1, it is characterized in that described alcohol be selected from anhydrous ethanol, normal propyl alcohol, isopropyl alcohol one of them.

3. according to the preparation method of the described a kind of bifunctional catalyst by direct preparation of dimethyl ether by using synthesis gas of claim 1, the oxalate coprecipitation thing that it is characterized in that reaction generation among the step c is through aging, filtration, drying, 300～450 ℃ of following roastings, make described bifunctional catalyst at last.

4. by the preparation method two of the bifunctional catalyst of direct preparation of dimethyl ether by using synthesis gas, comprise the following steps:

The active component that a. will can be used as methanol synthesis catalyst is dissolved in the mode of soluble-salt and is mixed with mixed solution A in the alcohol, and the wherein said active component that can be used as methanol synthesis catalyst is selected from the mixture of Cu, Zn, Al, Cr one of them or they;

B. oxalic acid is dissolved in the alcoholic solution B that obtains oxalic acid in the alcohol;

The active component that c. will can be used as methanol dehydration catalyst joins and obtains suspension C in the alcohol, and the wherein said active component that can be used as methanol dehydration catalyst is selected from γ-Al ₂O ₃, HZSM-5, HY one of them;

D. under agitation, two kinds of solution of above-mentioned A, B are added drop-wise among the suspension C simultaneously, the oxalate coprecipitation thing that reaction generates is after wearing out, and directly filtration, drying 250～550 ℃ of following roastings, make described bifunctional catalyst at last.

5. according to the preparation method of the described a kind of bifunctional catalyst by direct preparation of dimethyl ether by using synthesis gas of claim 4, it is characterized in that described alcohol be selected from anhydrous ethanol, normal propyl alcohol, isopropyl alcohol one of them.

6. according to the preparation method of the described a kind of bifunctional catalyst by direct preparation of dimethyl ether by using synthesis gas of claim 4, the oxalate coprecipitation thing that it is characterized in that reaction generation in the steps d is through aging, filtration, drying, 300～450 ℃ of following roastings, make described bifunctional catalyst at last.