Preparation method of silver-cobalt-silicon catalyst for synthesizing ethanol through oxalate hydrogenation

Abstract

The invention provides a silver-cobalt-silicon catalyst for synthesizing ethanol and ethylene glycol through catalytic hydrogenation of dimethyl oxalate and a preparation method of the silver-cobalt-silicon catalyst. The preparation method comprises the following steps: firstly, taking alkaline silica sol as a silicon source, taking soluble cobalt salt as a cobalt source, synthesizing a precursor of cobaltous silicate through an ammonia distillation method, then taking soluble silver salt as a silver source, and introducing a silver element into a cobaltous silicate layer through an impregnation method or the ammonia distillation method to prepare the silver-cobalt-silicon sphere catalyst through a synthesis method. The catalyst has high activity and high stability at a low reaction temperature. According to the novel silver-cobalt-silicon catalyst, the conversion rate of dimethyl oxalate can reach 99.9% in a wide temperature range, ethanol and ethylene glycol products with different proportions can be obtained at different temperatures, the total selectivity of ethanol and ethylene glycol reaches or exceeds 90%, and the novel silver-cobalt-silicon catalyst is suitable for producing ethanol and ethylene glycol products with different proportions according to different requirements.

Description

Technical Field

[0001] The present invention relates to the preparation of a catalyst for hydrogenating low-level fatty acid esters to synthesize alcohol, and more particularly to a method for preparing a catalyst for hydrogenating dimethyl oxalate to synthesize ethanol. The method can also be applied to hydrogenating dimethyl oxalate to synthesize ethylene glycol. Background Art

[0002] Ethanol is not only an important solvent and chemical raw material, but also an ideal high-octane pollution-free vehicle fuel and its additives. Entering the 21st century, in order to ease the tight energy supply situation and digest the stale grain inventory, my country began to promote the production of fuel ethanol using corn, wheat and other grains as raw materials, and my country's fuel ethanol industry began to develop. The upstream of the fuel ethanol industry is mainly the production of raw materials, including crops such as corn, cassava, sugarcane, beets, sweet sorghum, as well as wood cellulose, seaweed, etc.; the midstream is the manufacture of fuel ethanol, which can be divided into kerosene-based ethanol and bio-based ethanol according to the different production raw materials.

[0003] With the improvement of environmental quality requirements, MTBE automotive fuel additives that seriously pollute groundwater sources will be gradually eliminated. The development of ethanol fuel and the addition of alcohol or ether to gasoline have become the main way to improve automobile fuel. With the expansion of fuel ethanol production capacity, the research and development of ethanol production technology from coal resources through synthesis gas to replace the traditional grain fermentation route has important strategic significance for reducing my country's industrial consumption of grain and alleviating the contradiction of shortage of petroleum resources, as well as improving people's living standards and developing the national economy. The coal-based ethanol technology route can be divided into the following five: ① Coal is converted into C2 oxygen-containing compounds through synthesis gas, and then hydrogenated into ethanol; ② Coal is carbonylated to produce acetic acid, and acetic acid is directly hydrogenated to ethanol; ③ Dimethyl ether is carbonylated to produce methyl acetate, methyl acetate is hydrogenated to produce ethanol as a by-product of methanol, and methanol is dehydrated to produce dimethyl ether; ④ Olefin / acetic acid is esterified to acetate, and acetate is hydrogenated to produce ethanol and other alcohols; (⑤ Coal is converted into oxalate through synthesis gas and hydrogenated to synthesize ethanol technology.

[0004] Oxalate hydrogenation to ethanol is a technology related to coal-to-ethylene glycol. This technology can utilize existing coal-to-ethylene glycol equipment to synthesize ethanol by changing reaction conditions or replacing hydrogenation catalysts. Tianjin University has conducted some research on the process and catalysts for coal-to-ethanol. For example, Zhao Yujun et al. of Tianjin University reported a two-stage process for preparing ethanol by oxalate hydrogenation (publication number CN105085167B), with a mass space velocity of 1.0 h-1. -1When the oxalate conversion rate is 100%, the ethanol selectivity is as high as 85.0%. The "Catalyst for Hydrogenation of Oxalate to Ethanol and Its Preparation Method and Application" (CN102350358A) reported by Ma Xinbin et al. of Tianjin University discloses a hydrogenation catalyst for ethanol production with copper as the main active component, in which Co is one of the additives. The oxalate conversion rate of the catalyst in the oxalate hydrogenation reaction to ethanol production reaches 100%, the ethanol selectivity can reach 85%, and the low-carbon alcohol selectivity reaches 97%.

[0005] Since Guerbet reaction is easy to occur on copper-based catalysts under high temperature conditions to produce more butanol, isobutanol, propanol and isopropanol, it is difficult to further improve the selectivity of ethanol. In addition, the disadvantage of copper-based catalysts that they are easy to sinter at high temperatures is a difficult problem in this process route. Therefore, the development of non-copper-based catalysts has become an important breakthrough in the research of oxalate hydrogenation to ethanol reaction process. The non-copper-based catalysts used in the hydrogenation of dimethyl oxalate to ethanol mainly include two categories: Mo-based catalysts and Fe-based catalysts. In addition, there are nickel-based catalysts. In 2016, Chen Jiangang's team from the Institute of Coal Chemistry, Chinese Academy of Sciences reported the application of Mo2C / SiO2 and Cu / Mo2C catalysts in the hydrogenation of dimethyl oxalate to ethanol (Chemical Communications, 2016, 52(28):5030-5032. Applied Catalysis A: General, 2017, 529:143-155.). Under the optimal reaction temperature of 260°C, the conversion rate of dimethyl oxalate was 100%, and the selectivity of ethanol was 70.8% and 67.2%. In 2019, Zhao Yujun's team at Tianjin University reported a new carbonization process - methanol / hydrogen carbonization process, which converts more than 90% of metallic iron into Fe5C2 under mild conditions. In the hydrogenation of dimethyl oxalate, it is first hydrogenated to obtain the intermediate product methyl acetate and then hydrogenated to produce ethanol, and it shows higher ethanol selectivity. Under the optimal reaction temperature of 260°C, the conversion rate of dimethyl oxalate is 100%, and the selectivity of ethanol is 90% (Chemical Communications, 2017, 53(39): 5376-5379.). Existing Mo-based and Fe-based catalysts still have the problems of weak hydrogenation ability and insufficient active sites, and their catalytic performance is still a certain distance from industrialization. Ag-based catalysts are also a commonly used non-copper-based catalyst for the hydrogenation reaction of dimethyl oxalate. The relevant Ag-based catalysts are mainly used in the catalytic hydrogenation of dimethyl oxalate to produce methyl glycolate, and there are almost no reports on their application in the hydrogenation of dimethyl oxalate to produce ethanol. Summary of the invention

[0006] The purpose of the present invention is to provide an efficient and stable oxalate hydrogenation catalyst. The catalyst is mainly used in the dimethyl oxalate hydrogenation process, can synthesize ethanol and ethylene glycol, and can also simultaneously obtain ethanol and ethylene glycol in different proportions.

[0007] The technical scheme of the present invention is: silver is used as the main active component, cobalt is used as the auxiliary agent, and alkaline silica sol is used as the silicon source. First, the cobalt component is introduced by ammonia evaporation to obtain cobalt phyllosilicate, and then the silver component is introduced into the cobalt phyllosilicate layer by impregnation or ammonia evaporation, and finally a new type of silver cobalt silicon catalyst is prepared. The catalyst not only has high activity and high stability, but also can achieve high ethanol selectivity at higher temperatures and high ethylene glycol selectivity at lower temperatures, and obtain ethanol and ethylene glycol products in different proportions at intermediate temperatures.

[0008] The method steps for preparing the catalyst of the present invention are:

[0009] The preparation amount of the catalyst is first determined. The active component silver element accounts for 10-50% of the total mass of the catalyst, and the preferred content is 15-45%.

[0010] A. Dissolve the cobalt source in distilled water to form a 0.1-1 mol / L cobalt ion solution and stir it continuously until it is completely dissolved. Then place it in an ultrasonic instrument for ultrasonic oscillation. Then add urea. The weight ratio of cobalt element to urea is 0.1-1.5. Stir it continuously until it is completely dissolved. Then add ammonia water dropwise and stir it continuously until a transparent solution is formed. The pH value of the solution is controlled to be greater than 11.

[0011] The cobalt source is one or both of cobalt nitrate and cobalt acetate, and the amount of cobalt added is determined so that the cobalt element in the obtained catalyst accounts for 5% to 25% of the total mass of the catalyst;

[0012] B. Add alkaline silica sol containing 20% ​​to 40% by mass of SiO2 dropwise to the transparent solution obtained in A, stir thoroughly, place in a water bath at 40 to 90°C to evaporate ammonia until the pH of the solution is 7, stop stirring, filter and wash with distilled water for several times to obtain a filter cake, dry the filter cake in an oven at 120°C for 12 to 24 hours, and then place in a muffle furnace and roast at 300 to 500°C for 6 to 12 hours to obtain a solid powder containing cobalt phyllosilicate, i.e., Co / SiO2 precursor;

[0013] C. dissolving the silver source in distilled water and stirring continuously until completely dissolved, then adding ammonia water dropwise and stirring continuously until a transparent solution is formed, forming a 0.01-1 mol / L silver ammonium ion solution;

[0014] D. The Co / SiO2 precursor solid powder obtained in B is immersed in the silver ammonium ion solution obtained in C, and after being fully stirred, it is placed in an oven, and after standing at 40-60° C. for 12-24 hours, the water is completely evaporated to obtain a solid powder;

[0015] E. The solid powder obtained in D is placed in a muffle furnace and calcined at 300-500°C for 6-12 hours. The particles with a diameter of 1-2 mm are sieved out to obtain Ag@Co / SiO2 catalyst precursor.

[0016] The active components of the catalyst prepared by the method of the present invention are relatively evenly dispersed in the cobalt phyllosilicate layer. When the liquid hourly space velocity is constant, the conversion rate of oxalate can reach more than 99.99% at 190-280°C, the selectivity of ethanol can reach more than 85% at 240-280°C, the main products are ethanol and ethylene glycol, the total selectivity can reach more than 90% at 200-240°C, and the selectivity of ethylene glycol can reach more than 90% at 190-200°C.

[0017] The typical start-up procedure for synthesizing ethylene glycol using the catalyst of the present invention is: first, 5 mL of the precursor of the Ag@Co / SiO2 catalyst referred to in this method is reduced at 300° C. with hydrogen at a flow rate of 50 mL / min·mL·cat for 3 to 12 hours, and then the performance is evaluated; then, a prepared 0.2 g / mL methanol solution of dimethyl oxalate is introduced into the vaporization chamber and mixed with hydrogen, and the hydrogen is mixed with hydrogen at a hydrogen-to-ester molar ratio of 50 to 150, and the reaction temperature is controlled to 190 to 280° C.

[0018] Different from the copper-based catalyst used in the traditional synthesis gas to produce ethanol and ethylene glycol, the present method uses a non-copper-based silver-cobalt catalyst, which is not only conducive to improving the dispersion of silver species but also improves its catalytic hydrogenation ability. The use of silver-based catalysts for hydrogenation of dimethyl oxalate to synthesize ethanol in the present invention has not been reported before.

[0019] The invention has the beneficial effects of introducing silver species into the cobalt phyllosilicate layer by an impregnation method, inhibiting the agglomeration of Ag species to form smaller metallic silver, improving the electronic structure of the catalyst surface, and effectively improving the catalyst stability. Cobalt phyllosilicate can also act as a hydrogen storage pool to improve the catalytic hydrogenation activity of Ag, thereby realizing the hydrogenation of dimethyl oxalate to ethanol and ethylene glycol at a lower temperature. The method is easy to operate and standardize, which is conducive to ensuring batch stability during large-scale production of catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The activity evaluation results of Example 1 after 600 hours of reaction are shown in Figure 1. Curves A and B represent the conversion rate of dimethyl oxalate and the selectivity of ethanol, respectively. DETAILED DESCRIPTION

[0021] Embodiment 1:

[0022] (1) Preparation of catalyst

[0023] A. Dissolve 12.8g of cobalt nitrate in 100g of distilled water, and after fully dissolving, ultrasonic oscillate for 20min in an ultrasonic instrument at a frequency of 25kHz. Then add 5.0g of urea and stir to dissolve, then add 20mL of ammonia water dropwise and stir for 30min to obtain a transparent solution.

[0024] B. Add 24 g of alkaline silica sol with a SiO2 content of 40% dropwise to the transparent solution of A, mechanically stir the mixed solution and place it in a water bath at 80°C for 3 hours until the pH value of the solution reaches 7, stop heating, filter and wash with distilled water for several times to obtain a filter cake, and place the filter cake in an oven at 120°C to dry for 24 hours, then place it in a muffle furnace and calcine at 500°C for 6 hours to obtain a Co / SiO2 precursor solid powder.

[0025] C. Dissolve 11.2 g of silver nitrate source in 150 g of distilled water and stir continuously until completely dissolved, then add ammonia water dropwise and stir continuously until a transparent solution is formed.

[0026] D. Immerse the Co / SiO2 precursor solid powder obtained in B in the transparent solution obtained in C, stir it thoroughly and place it in an oven. After standing at 60°C for 12 hours, completely evaporate the water to obtain a solid powder.

[0027] E. The solid powder obtained in D was placed in a muffle furnace, calcined at 500°C for 6 hours, and then the solid particles with a diameter of 1 to 2 mm were screened out to obtain Ag@Co / SiO2 catalyst precursor, which was used for catalyst testing. The content of silver element was 33.5%, and the content of cobalt element was 12.2%.

[0028] (2) Catalyst application performance test

[0029] Ag@Co / SiO2 catalyst precursor particles with a diameter of 1 to 2 mm were loaded into a tubular fixed bed reactor. In a nitrogen atmosphere with a flow rate of 50 mL / min, the temperature was raised from room temperature to 300°C at a rate of 10°C / min and maintained for 5 hours. After that, the temperature was switched to hydrogen and the reaction temperature was gradually reduced from 280°C to 190°C for performance evaluation. At the same time, a prepared 0.2 g / mL methanol solution of dimethyl oxalate was introduced into the vaporization chamber and mixed with hydrogen to carry out oxalate hydrogenation reaction, wherein H2 / DMO=100 (mol / mol) and the mass liquid hourly space velocity of dimethyl oxalate was 0.3 g (DMO) / gcat·h. The results of the selective hydrogenation of dimethyl oxalate for 24 hours are shown in Tables 1 and 2, and the results after 500 hours of reaction are shown in Tables 1 and 2. Figure 1 .

[0030] Embodiment 2:

[0031] In Example 1, the amount of silver nitrate in the catalyst preparation step C was changed from 12.8 g to 3.7 g, which is the present example.

[0032] The performance evaluation conditions were the same as those in Example 1. The results of the selective hydrogenation of dimethyl oxalate for 24 hours are shown in Table 1.

[0033] Embodiment 3:

[0034] In Example 1, the amount of silver nitrate in the catalyst preparation step C was changed from 11.2 g to 18.7 g, which is the present example.

[0035] The performance evaluation conditions were the same as those in Example 1. The results after selective hydrogenation of dimethyl oxalate for 24 hours are shown in Table 1.

[0036] Embodiment 4:

[0037] In Example 1, the catalyst preparation step D "after fully stirring, place in an oven, let stand at 60°C for 12 hours and then completely evaporate the water to obtain a solid powder" is changed to "after fully stirring, place in a water bath at 80°C until the water is completely evaporated to obtain a solid powder", which is the current example.

[0038] The performance evaluation conditions were the same as those in Example 1. The results after selective hydrogenation of dimethyl oxalate for 24 hours are shown in Table 1.

[0039] Embodiment 5:

[0040] In Example 1, the catalyst preparation step B is changed to: "Add alkaline silica sol containing 20-40% SiO2 dropwise to the transparent solution obtained in A and stir continuously, then place in a water bath at 80°C to evaporate ammonia until the pH of the solution is 7, stop stirring, filter and wash with distilled water for multiple times to obtain a filter cake, place the filter cake in an oven at 120°C and dry it for 12-24 hours to obtain a Co / SiO2 precursor", which is this example.

[0041] The performance evaluation conditions were the same as those in Example 1. The results after selective hydrogenation of dimethyl oxalate for 24 hours are shown in Table 1.

[0042] Embodiment 6:

[0043] In Example 1, the 12.8 g of silver nitrate in A in the catalyst preparation step was changed to 17.0 g, which is the present example.

[0044] The performance evaluation conditions were the same as those in Example 1. The results after selective hydrogenation of dimethyl oxalate for 24 hours are shown in Table 1.

[0045] Embodiment 7:

[0046] In Example 1, 12.8 g of silver nitrate in A in the catalyst preparation step is replaced with 8.0 g of cobalt acetate, that is, this example.

[0047] The performance evaluation conditions were the same as those in Example 1. The results after selective hydrogenation of dimethyl oxalate for 24 hours are shown in Table 1.

[0048] Embodiment 8:

[0049] The catalyst was prepared as in Example 1.

[0050] In the performance evaluation conditions of Example 1, H2 / DMO=100 (mol / mol) was changed to H2 / DMO=70 (mol / mol), that is, in this example, the results after selective hydrogenation of dimethyl oxalate for 24 hours are shown in Table 1.

[0051] Embodiment 9:

[0052] The catalyst was prepared as in Example 1.

[0053] In the performance evaluation conditions of Example 1, H2 / DMO=100 (mol / mol) was changed to H2 / DMO=140 (mol / mol), that is, in this example, the results after selective hydrogenation of dimethyl oxalate for 24 hours are shown in Table 1.

[0054] Embodiment 10:

[0055] The catalyst was prepared as in Example 1.

[0056] In the performance evaluation conditions of Example 1, the mass liquid hourly space velocity of dimethyl oxalate was changed from 0.3 g (DMO) / gcat · h to 0.5 g (DMO) / gcat · h, that is, in this example. The results after selective hydrogenation of dimethyl oxalate for 24 hours are shown in Table 1.

[0057] Comparative Example 1

[0058] (1) Preparation of Catalyst The same steps A and B as in Example 1 were followed to obtain a Co / SiO2 catalyst precursor.

[0059] (2) Performance evaluation scheme

[0060] The performance evaluation conditions were exactly the same as those in Example 1. The results after 24 hours of selective hydrogenation of dimethyl oxalate to ethylene glycol are shown in Table 1.

[0061] Comparative Example 2

[0062] (1) Preparation of the catalyst The preparation method is the same as that of Comparative Example 1, except that cobalt nitrate is replaced by silver nitrate to obtain an Ag / SiO2 catalyst precursor.

[0063] (2) Performance evaluation scheme

[0064] The performance evaluation conditions are exactly the same as those in Comparative Example 1. The results after 24 hours of selective hydrogenation of dimethyl oxalate to ethylene glycol are shown in Table 1.

[0065] Comparative Example 3

[0066] (1) Preparation of catalyst

[0067] A. Dissolve 12.8g of cobalt nitrate and 11.2g of silver nitrate in 100g of distilled water. After fully dissolved, ultrasonic oscillate for 20min in an ultrasonic instrument at a frequency of 25kHz. Then add 5.0g of urea and stir to dissolve. Then add 20mL of ammonia water dropwise and stir for 30min to obtain a transparent solution.

[0068] B. Add 24g of alkaline silica sol with 40% SiO2 content dropwise to the transparent solution of A, mechanically stir the mixed solution and place it in a water bath at 80°C for 3-6 hours until the pH value of the solution reaches 7, then stop heating. Filter to obtain a filter cake, wash the filter cake with distilled water for several times, dry the obtained filter cake at 120°C in air for 24 hours, place it in a muffle furnace, and roast it at 500°C for 6-12 hours to obtain Ag-Co / SiO2 catalyst precursor solid powder, press it into tablets to screen out particles with a diameter of 1-2 mm.

[0069] (2) Performance evaluation scheme

[0070] The performance evaluation conditions are exactly the same as those in Comparative Example 1. The results after 24 hours of selective hydrogenation of dimethyl oxalate to ethylene glycol are shown in Table 1.

[0071] Table 1 Catalyst activity evaluation results for each case

[0072]

[0073] Table 2 Activity evaluation results of the catalyst in Example 1 at different reaction temperatures

[0074]

Claims

1. A method for preparing a silver-cobalt-silicon catalyst for ethylene glycol for catalytic hydrogenation of dimethyl oxalate to ethanol, characterized in that Here are the steps: A. dissolving a cobalt source in distilled water to form a 0.1-1 mol / L cobalt ion solution, stirring continuously until completely dissolved, placing the solution in an ultrasonic instrument for ultrasonic oscillation, and then adding urea, the weight ratio of cobalt element to urea being 0.2-1.0, stirring continuously until completely dissolved, adding ammonia water dropwise, and stirring continuously until a transparent solution is formed, and controlling the pH value of the solution to be greater than 11; the cobalt source is one or both of cobalt nitrate and cobalt acetate, and the amount thereof added is determined based on the content of cobalt element in the obtained catalyst being 5-25%, and the mass percentage concentration of ammonia water is 25%; B. Add alkaline silica sol containing 20% ​​to 40% by mass of SiO2 dropwise to the transparent solution obtained in step A and stir continuously, the molar ratio of the cobalt element added in step A to the silicon element added in step B is 0.1 to 0.5, and then place in a water bath at 40 to 90°C to evaporate ammonia until the pH of the solution reaches 7 and stop stirring; filter and wash the filter cake with distilled water for several times; dry the filter cake in an oven and then place the filter cake in a muffle furnace to roast to obtain a solid powder, that is, a Co / SiO2 precursor, the drying temperature is 100 to 150°C, the drying time is 12 to 24 hours, the roasting temperature is 300 to 500°C, and the roasting time is 6 to 12 hours; C. dissolving a silver source in distilled water and stirring continuously until completely dissolved; then adding ammonia water dropwise and stirring continuously until a transparent solution is formed to form a 0.1-1.5 mol / L silver ammonium ion solution, wherein the soluble silver salt is silver nitrate and the mass percentage concentration of the ammonia water is 25%; D. The solid powder Co / SiO2 precursor obtained in B is immersed in the silver ammonium ion solution obtained in C and placed in an oven to stand for evaporation to obtain a solid powder; or the solid powder Co / SiO2 precursor obtained in B is immersed in the silver ammonium ion solution obtained in C, and after sufficient mixing, ammonia is evaporated until the water is evaporated, and the temperature of the standing oven is 40 to 60° C., the time is 12 to 24 hours, the ammonia evaporation temperature is 60 to 80° C., and the molar ratio of silver element to cobalt element is 0.1 to 3; E. The solid powder obtained in D is placed in a muffle furnace for calcination, and the particles with a diameter of 1 to 2 mm are screened out through tableting to obtain the Ag-Co / SiO2 catalyst precursor. The calcination temperature is 300 to 500°C and the time is 6 to 12 hours.

2. A silver-cobalt-silicon catalyst prepared by the method according to claim 1.

3. The use of the copper-based catalyst according to claim 2, characterized in that: The catalyst sample was placed in a tubular fixed bed reactor. In a nitrogen atmosphere with a flow rate of 50 ml / min, the temperature was raised from room temperature to 150 °C at a rate of 2 °C / min, then switched to hydrogen. The temperature was continued to rise to 250 °C and maintained for 3 to 10 hours. The system temperature was then lowered to the reaction temperature. The prepared 0.2 g / ml The methanol solution of dimethyl oxalate is passed into the vaporization chamber and mixed with hydrogen, and the molar ratio of hydrogen to dimethyl oxalate is 50-150. The reaction is carried out at a temperature of 190 to 280° C. for 24 to 72 hours, and the liquid hourly space velocity of dimethyl oxalate is 0.2 to 1.0 g / g·h.

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