A transition metal oxide catalyst, its preparation method and application

Abstract

The present invention discloses a transition metal oxide catalyst, a preparation method thereof and an application. The catalyst is prepared by a solvent evaporation-induced sol-gel method, which has the advantages of simple preparation process, fine crystal grain size of the active components in the catalyst, close interaction between the components, good repeatability of the catalyst, etc. The catalyst exhibits excellent catalytic activity in the one-step catalytic synthesis of ethyl acetate from ethanol, and the selectivities of the main by-products 2-butanol and 2-butanone are low, thus significantly increasing the selectivity of the product ethyl acetate. At the same time, the reaction adopts a fixed-bed continuous reaction process, which has the advantages of simple process flow, convenient operation, mild reaction conditions, etc., and is suitable for the industrial production of the one-step catalytic synthesis of ethyl acetate from ethanol.

Description

Technical Field

[0001] The present invention relates to a transition metal oxide catalyst, a preparation method thereof, and an application thereof in the one-step catalytic synthesis of ethyl acetate from ethanol. Background Art

[0002] Ethyl acetate appears as a colorless clear liquid, with good solubility, quick drying property, water absorption property, etc. It is an important organic chemical raw material and industrial solvent, and is widely used in fields such as medicine, coatings, inks, adhesives, textiles, and daily-use fragrances. With the rapid growth of China's economy and the enhancement of people's environmental protection awareness, the proportion of high-grade coatings has increased significantly, the pharmaceutical industry has developed rapidly, and China's adhesive and polyurethane industries have grown from scratch and from small to large, which has greatly increased the demand for ethyl acetate.

[0003] Currently, the industrial production processes of ethyl acetate mainly include the following several kinds. The first one is the traditional method of producing ethyl acetate by esterification of acetic acid and ethanol, usually using sulfuric acid as a catalyst. The advantages of this process are that the catalyst is easy to obtain, the process is relatively simple, and other varieties of acetate esters can also be produced simultaneously; the disadvantages are that the production scale is limited, the equipment corrosion is serious, and the product quality is relatively poor. The second one is to produce ethyl acetate by acetaldehyde disproportionation, often using aluminum triethanolate as a catalyst. The advantages of this method are that only one raw material is needed and the by-products are few; the disadvantages are that the raw material acetaldehyde has strong toxicity and strong corrosiveness to production equipment. The third method is the ethylene-acetic acid method. This process uses clay and isopolyacid as catalysts to add acetic acid to ethylene to prepare ethyl acetate. However, the raw material ethylene is prone to explosion when heated under certain pressure conditions, and the risk level during transportation and production is too high. The last one is the one-step catalytic synthesis of ethyl acetate from ethanol, which produces ethyl acetate by catalytic dehydrogenation using noble metals, copper, vanadium and other catalysts. This technology was developed by Davy in the UK and Nippon Nitrogen Company in Japan in the late 1990s. It can convert ethanol into ethyl acetate by one-step dehydrogenation, and it is the most advanced technology in the world at present; its advantages are short process, stable operation, high product quality, easy large-scale production expansion, and it is very suitable for building factories to produce ethyl acetate in areas rich in ethanol.

[0004] For the one-step catalytic synthesis process of ethyl acetate from ethanol, the mainstream catalyst used is the Cu-based catalyst, which has the characteristics of high catalyst activity, low investment cost, basically no three wastes discharge, no corrosion, and high purity of the product ethyl acetate. In the published literature, in 2001, Davy carried out the reaction of dehydrogenating ethanol to ethyl acetate on a copper-chromium catalyst. Under the reaction conditions of 220 °C and 3.0 MPa, the selectivity of ethyl acetate was 94%, but the conversion rate of ethanol was only 27%, and the chromium-containing catalyst had certain toxicity [J Catal, 2005, 236(1): 21-33]. The copper-zinc-aluminum-zirconium composite oxide catalyst used by Nippon Nitrogen Petrochemical Co., Ltd. had an ethanol conversion rate of 45% and an ethyl acetate selectivity of 90-95% under the reaction conditions of 220 °C and 1.0 MPa [WO0053314]. The copper-zinc-aluminum-zirconium composite oxide catalyst prepared by the coprecipitation method at Tsinghua University showed an ethanol conversion rate of 46.3% and an ethyl acetate selectivity of 77.8% under the reaction conditions of 255 °C and 0.5 MPa [CN1062304A]. The Cu-SBA-15 catalyst prepared by the impregnation method at Jiangsu University showed an ethanol conversion rate of 73.7% and an ethyl acetate selectivity of 70.3% under the reaction conditions of 280 °C and atmospheric pressure. However, the reaction temperature was too high, resulting in a low product selectivity, and the carrier SBA-15 was expensive [CN103880661A]. The Cu-Mg-Al-F catalyst invented by the Institute of Coal Chemistry, Chinese Academy of Sciences showed an ethanol conversion rate of 52.3% and an ethyl acetate selectivity as high as 94.5% at 220 °C and 3 MPa. However, the reaction pressure was relatively high, requiring higher requirements for production equipment [CN110975895A]. The Southwest Research and Design Institute of Chemical Industry built a pilot plant for producing ethyl acetate by dehydrogenating ethanol with a capacity of 3000 t / a for Shandong Boxing. Using a Cu-ZnO-Al2O3 composite oxide catalyst, under the reaction conditions of 1.0 MPa and 250 °C, the ethanol conversion rate was 60-65%, but the ethyl acetate selectivity was only 85-90% [Chemical Industry Progress, 2004, 23(10): 1058-1061]. The copper-zinc-aluminum-zirconium composite oxide catalyst prepared by the coprecipitation method in the European patent [WO2022 / 066136A1] showed an ethanol conversion rate of 41.8% and an ethyl acetate selectivity of 93.2% under the reaction conditions of 210-240 °C and 1.3 MPa.

[0005] At present, the catalysts for the one-step catalytic synthesis of ethyl acetate from ethanol reported in the literature are all prepared by simple impregnation method or co-precipitation method. The activity or selectivity of the catalysts is relatively low, or it is difficult to balance the activity and selectivity indicators. In the catalysts prepared by the impregnation method, the dispersion degree, uniformity, etc. of the active components are not easy to control, so the activity of the prepared catalysts, especially the selectivity, is relatively low. In the catalysts prepared by the co-precipitation method, the crystal grain size of the active components is relatively large, resulting in relatively low catalytic activity of the catalysts. Moreover, some uncontrollable factors may occur during the preparation process, such as changes in solution concentration, fluctuations in feeding flow rate, uneven stirring, etc., resulting in poor repeatability of the catalysts. Therefore, the improvement of the catalyst preparation method is particularly important for the development of highly efficient catalysts for the one-step catalytic synthesis of ethyl acetate from ethanol. The present invention uses a solvent evaporation-induced sol-gel method to prepare a Cu-ZnO-Al2O3-ZrO2 composite oxide catalyst. The crystal grains of the active components in the catalyst are fine, and the interaction between them is close. The preparation process is simple and reliable. Therefore, the catalytic activity of the catalyst is high, and at the same time, the selectivity of the main by-products 2-butanone and 2-butanol is significantly reduced, so as to obtain a relatively high selectivity of ethyl acetate at the same time. Summary of the Invention

[0006] The first technical problem to be solved by the present invention is to provide a catalyst for the one-step catalytic synthesis of ethyl acetate from ethanol.

[0007] The second technical problem to be solved by the present invention is to provide a preparation method of the catalyst.

[0008] The third technical problem to be solved by the present invention is to provide the application of the catalyst in the reaction of the one-step catalytic synthesis of ethyl acetate from ethanol.

[0009] To solve the above technical problems, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a transition metal oxide catalyst, and the transition metal oxide catalyst is prepared by the following method:

[0011] Dissolve metal salts in a solvent, add an aqueous citric acid solution, stir evenly, rotate and evaporate the obtained mixed solution until it becomes gel-like, dry the obtained gel-like mixture, and put the obtained catalyst precursor into a muffle furnace and calcine it in an air atmosphere to obtain the transition metal oxide catalyst; the metal salts are a mixture of copper salts, zinc salts, aluminum salts and zirconium salts; the molar ratio of copper ions contained in the copper salt, zinc ions contained in the zinc salt, aluminum ions contained in the aluminum salt to zirconium ions contained in the zirconium salt is 2-6:2-6:0.5-3:0.1-1 (preferably 3-6:2.5-6:0.8-2:0.1-0.5, most preferably 5.8:3:1:0.2); the molar ratio of citric acid to metal ions in the metal salts in the aqueous citric acid solution is 0.4-1.5:1 (preferably 1:1);

[0012] The roasting procedure is as follows: heating up to 100 - 130°C at a rate of 5 - 11°C / min for the first round of heat preservation for 0.5 - 3 h, heating up to 220 - 260°C at a rate of 0.1 - 2°C / min for the second round of heat preservation for 0.5 - 3 h, and heating up to 300 - 600°C at a rate of 1 - 3°C / min for the third round of heat preservation for 2 - 10 h (preferably heating up to 120°C at a rate of 10°C / min for the first round of heat preservation for 1 h, heating up to 250°C at a rate of 0.5°C / min for the second round of heat preservation for 1 h, and heating up to 550°C at a rate of 2°C / min for the third round of heat preservation for 3 h).

[0013] By controlling factors such as the ratios of copper, zinc, aluminum, and zirconium, the dosage of citric acid, the solvent evaporation conditions, the drying temperature and time, the roasting temperature and the heating program, etc., not only can the dispersion degree and the degree of close interaction of the catalyst active components be effectively controlled, thereby improving the catalytic activity of the catalyst, but also the acid-base properties on the catalyst surface can be adjusted, reducing the selectivities of by-products 2-butanol and 2-butanone and increasing the selectivity of the product ethyl acetate, and then a highly efficient catalyst for the one-step catalytic synthesis of ethyl acetate from ethanol can be obtained. Setting different roasting temperature gradients is to allow the complexing agent citric acid to decompose / burn slowly, so that the crystal grain size of the catalyst active components is finer.

[0014] Further, the copper salt is at least one of copper nitrate, copper chloride, and copper acetate, and in the embodiments of the present invention, it is copper nitrate.

[0015] Further, the zinc salt is at least one of zinc nitrate, zinc chloride, and zinc acetate, and in the embodiments of the present invention, it is zinc nitrate.

[0016] Further, the aluminum salt is at least one of aluminum nitrate, aluminum chloride, and copper acetate, and in the embodiments of the present invention, it is aluminum nitrate.

[0017] Further, the zirconium salt is at least one of zirconium nitrate, zirconyl chloride, zirconium chloride, and zirconium acetate, and in the embodiments of the present invention, it is zirconium nitrate.

[0018] Further, the solvent is one or a mixed solvent of two or more of deionized water, methanol, and ethanol, and in the embodiments of the present invention, it is deionized water.

[0019] Still further, the volume of the solvent is 0.5 - 50 L / mol based on the amount of substance of the metal salt.

[0020] Further, the temperature of the rotary evaporation is 45 - 80°C, and the pressure is 0.005 - 0.1 MPa. In the embodiments of the present invention, the temperature of the rotary evaporation is 75°C, and the pressure is 0.01 MPa.

[0021] In a second aspect, the present invention provides the use of the transition metal oxide catalyst in the catalytic synthesis of ethyl acetate from ethanol.

[0022] Specifically, the use is as follows: The transition metal oxide catalyst is placed in a fixed-bed reactor. After being reduced by hydrogen, it catalyzes the reaction of ethanol to synthesize ethyl acetate.

[0023] Furthermore, the reduction conditions are: 200 °C, atmospheric pressure, using a mixed gas of H2 and N2 with a volume ratio of 1:9, and the space velocity of the mixed gas is 1800 h -1 , and the reduction time is 3 h. The reaction conditions are: 220 - 270 °C, atmospheric pressure - 2.0 MPa, and ethanol is introduced into the fixed-bed reactor at a liquid space velocity of 0.5 - 3.0 mL / (h·g cat ).

[0024] Preferably, nitrogen is also introduced in the reaction, and the volume ratio of nitrogen to ethanol is 100 - 1500:1. Under these conditions, the catalyst has high selectivity and yield for ethyl acetate and excellent stability.

[0025] The present invention particularly preferably has the reaction conditions as: 240 °C, 1 MPa, the liquid space velocity of ethanol is 1 mL / (h·g cat ), and the volume ratio of nitrogen to ethanol is 500:1.

[0026] The mechanism of the one-step catalytic synthesis of ethyl acetate from ethanol is as follows: Ethanol is first dehydrogenated on the Cu active center to form acetaldehyde, and then acetaldehyde undergoes a nucleophilic addition reaction with ethanol on the acid-base centers (provided by ZnO, Al2O3, and ZrO2 together, acid centers such as Zr 4+ , Al 3+ etc., and base centers such as O 2- ) to form hemiacetal, and finally the hemiacetal is dehydrogenated on the Cu center to form ethyl acetate. The overall reaction equation is 2C2H5OH → CH3COOC2H5 + 2H2.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) The present invention uses a solvent evaporation-induced sol-gel method to prepare the catalyst. The crystal grains of the active components in the catalyst are fine and the interaction between them is close. The highly dispersed Cu active component provides a large amount of ethanol dehydrogenation activity, and it closely cooperates with the equally highly dispersed oxides such as ZnO, Al2O3, and ZrO2 to provide a large number of acid-base active centers that promote the conversion of the intermediate product acetaldehyde, thus ultimately realizing the efficient conversion of ethanol to ethyl acetate.

[0029] (2) The catalyst of the present invention is safe, non-toxic, inexpensive, and the catalyst preparation method is simple, reliable, and has good repeatability.

[0030] (3) When the catalyst of the present invention is applied to the one-step catalytic synthesis of ethyl acetate from ethanol, a fixed-bed continuous reaction process is adopted. The process is simple, the reaction conditions are relatively mild, and at the reaction conditions of 240 °C and 1.0 MPa, the ethanol conversion rate is as high as 55.5%, and at the same time, the ethyl acetate selectivity reaches 96.3%. High conversion rate and high selectivity are achieved simultaneously, so it has good industrial application prospects. Description of the Drawings

[0031] Figure 1 It is the EDX mapping image of catalyst A.

[0032] Figure 2 It is the EDX mapping image of catalyst M.

[0033] Figure 3 It is the EDX mapping image of catalyst N.

[0034] Figure 4 It is the EDX mapping image of catalyst O.

[0035] Figure 5 It is the schematic diagram of the fixed-bed reaction device for the continuous catalytic conversion of the catalyst to synthesize ethyl acetate: 1 - hydrogen gas cylinder, 2 - nitrogen gas cylinder, 3 - raw material bottle, 4 - high-pressure constant flow pump, 5 - three-way valve, 6 - pressure reducing valve, 7 - stop valve, 8 - mass flowmeter, 9 - check valve, 10 - reaction tube, 11 - reaction furnace, 12 - condenser, 13 and 14 - condensate inlet and outlet, 15 - filter, 16 - back pressure valve, 17 - product collection tank. Detailed Embodiments

[0036] The present invention will be further described below through specific embodiments, but the protection scope of the present invention is not limited thereto.

[0037] Example 1

[0038] 1.2458 g of Cu(NO3)2·3H2O, 1.5338 g of Zn(NO3)2·6H2O, 0.8206 g of Al(NO3)3·9H2O and 0.1772 g of Zr(NO3)4·5H2O were added to 15 mL of deionized water. The molar ratio of copper, zinc, aluminum, and zirconium metal ions was 4:4:1.7:0.3. After dissolution and uniform mixing, 16 mL of 0.8 mol / L citric acid aqueous solution (the molar ratio of citric acid to the total amount of metal ions was 1:1) was added, and stirred for 1 h to form a metal ion-citric acid complex solution. The above solution was transferred to a rotary evaporator and rotary evaporated to a sol at 75 °C and 0.01 MPa, and then to a gel state. The obtained gel was dried in an oven at 100 °C for 72 h, and finally in a muffle furnace at a heating rate of 10 °C / min to 120 °C and held for 1 h, then at a heating rate of 0.5 °C / min to 250 °C and held for 1 h, and finally at a heating rate of 2 °C / min to 550 °C and held for 3 h to obtain catalyst A. The CuO content in catalyst A was 41.3 wt%, the ZnO content was 42.3 wt%, the Al2O3 content was 11.2 wt%, and the ZrO2 content was 5.2 wt%.

[0039] Figure 1 Figure 4 is the EDX mapping image of catalyst A prepared in Example 1. From Figure 1 it can be seen that no obvious nanoparticles were observed in catalyst A, indicating that the four elements of Cu, Zn, Al, and Zr were highly dispersed; and the signals of the four elements of Cu, Zn, Al, and Zr overlapped with each other, indicating that they were in close contact. The highly dispersed Cu active component provided a large amount of ethanol dehydrogenation activity, and its close cooperation with the equally highly dispersed oxides such as ZnO, Al2O3, and ZrO2 provided a large number of acid-base active centers for promoting the conversion of intermediate product acetaldehyde, thus finally realizing the efficient conversion of ethanol to ethyl acetate.

[0040] Example 2

[0041] The preparation method of catalyst B was the same as that of Example 1, but the masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O were 0.6040 g, 1.5338 g, 0.8206 g and 0.1772 g respectively, and the molar ratio of copper, zinc, aluminum, and zirconium metal ions was 2.5:5:2.1:0.4. 13 mL of 0.8 mol / L citric acid aqueous solution was added (the molar ratio of citric acid to the total amount of metal ions was 1:1). The CuO content in catalyst B was 25.5 wt%, the ZnO content was 53.7 wt%, the Al2O3 content was 14.3 wt%, and the ZrO2 content was 6.5 wt%.

[0042] Example 3

[0043] The preparation method of catalyst C is the same as that of Example 1, but the masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O are 0.9060 g, 2.2312 g, 0.4689 g and 0.1355 g respectively, and the molar ratio of copper, zinc, aluminum and zirconium metal ions is 2.9:5.9:1:0.2. 16 mL of 0.8 mol / L citric acid aqueous solution is added (the molar ratio of citric acid to the total amount of metal ions is 1:1). The content of CuO in catalyst C is 29.5 wt%, the content of ZnO is 60.4 wt%, the content of Al2O3 is 6.3 wt%, and the content of ZrO2 is 3.8 wt%.

[0044] Example 4

[0045] The preparation method of catalyst D is the same as that of Example 1, but the masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O are 1.8120 g, 1.1156 g, 0.4689 g and 0.1345 g respectively, and the molar ratio of copper, zinc, aluminum and zirconium metal ions is 5.8:3:1:0.2. 16 mL of 0.8 mol / L citric acid aqueous solution is added (the molar ratio of citric acid to the total amount of metal ions is 1:1). The content of CuO in catalyst D is 59.4 wt%, the content of ZnO is 30.4 wt%, the content of Al2O3 is 6.4 wt%, and the content of ZrO2 is 3.8 wt%.

[0046] Example 5

[0047] The preparation method of catalyst E is the same as that of Example 1. The masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O are 1.2458 g, 1.5338 g, 0.8206 g and 0.1772 g respectively, and the molar ratio of copper, zinc, aluminum and zirconium metal ions is 4:4:1.7:0.3. However, 12 mL of 0.8 mol / L citric acid aqueous solution is added (the molar ratio of citric acid to the total amount of metal ions is 0.75:1). The content of CuO in catalyst E is 41.3 wt%, the content of ZnO is 42.3 wt%, the content of Al2O3 is 11.2 wt%, and the content of ZrO2 is 5.2 wt%.

[0048] Example 6

[0049] The preparation method of catalyst F is the same as that of Example 1. The masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O, and Zr(NO3)4·5H2O are 1.2458 g, 1.5338 g, 0.8206 g, and 0.1772 g respectively. The molar ratio of copper, zinc, aluminum, and zirconium metal ions is 4:4:1.7:0.3. However, 8 mL of 0.8 mol / L citric acid aqueous solution is added (the molar ratio of citric acid to the total amount of metal ions is 0.5:1). The CuO content in catalyst F is 41.3 wt%, the ZnO content is 42.3 wt%, the Al2O3 content is 11.2 wt%, and the ZrO2 content is 5.2 wt%.

[0050] Example 7

[0051] The preparation method of catalyst G is the same as that of Example 1. The masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O, and Zr(NO3)4·5H2O are 1.2458 g, 1.5338 g, 0.8206 g, and 0.1772 g respectively. The molar ratio of copper, zinc, aluminum, and zirconium metal ions is 4:4:1.7:0.3. The molar ratio of citric acid to the total amount of metal ions is 1:1. However, the calcination procedure in the muffle furnace is as follows: heat up to 110°C at a heating rate of 10°C / min and hold for 1 h, then heat up to 250°C at a heating rate of 0.5°C / min and hold for 1 h, and finally heat up to 550°C at a heating rate of 2°C / min and hold for 3 h to obtain catalyst G. The CuO content in catalyst G is 41.3 wt%, the ZnO content is 42.3 wt%, the Al2O3 content is 11.2 wt%, and the ZrO2 content is 5.2 wt%.

[0052] Example 8

[0053] The preparation method of catalyst H is the same as that of Example 1. The masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O, and Zr(NO3)4·5H2O are 1.2458 g, 1.5338 g, 0.8206 g, and 0.1772 g respectively. The molar ratio of copper, zinc, aluminum, and zirconium metal ions is 4:4:1.7:0.3. The molar ratio of citric acid to the total amount of metal ions is 1:1. However, the calcination procedure in the muffle furnace is as follows: heat up to 120°C at a heating rate of 10°C / min and hold for 1 h, then heat up to 230°C at a heating rate of 0.5°C / min and hold for 1 h, and finally heat up to 550°C at a heating rate of 2°C / min and hold for 3 h to obtain catalyst H. The CuO content in catalyst H is 41.3 wt%, the ZnO content is 42.3 wt%, the Al2O3 content is 11.2 wt%, and the ZrO2 content is 5.2 wt%.

[0054] Example 9

[0055] The preparation method of Catalyst I is the same as that in Example 1. The masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O are 1.2458 g, 1.5338 g, 0.8206 g and 0.1772 g respectively. The molar ratio of copper, zinc, aluminum and zirconium metal ions is 4:4:1.7:0.3, and the molar ratio of citric acid to the total amount of metal ions is 1:1. However, the calcination procedure in the muffle furnace is as follows: heat up to 120 °C at a heating rate of 10 °C / min and hold for 2 h, then heat up to 250 °C at a heating rate of 0.5 °C / min and hold for 1 h, and finally heat up to 550 °C at a heating rate of 2 °C / min and hold for 3 h to obtain Catalyst I. The content of CuO in Catalyst I is 41.3 wt%, the content of ZnO is 42.3 wt%, the content of Al2O3 is 11.2 wt%, and the content of ZrO2 is 5.2 wt%.

[0056] Example 10

[0057] The preparation method of Catalyst J is the same as that in Example 1. The masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O are 1.2458 g, 1.5338 g, 0.8206 g and 0.1772 g respectively. The molar ratio of copper, zinc, aluminum and zirconium metal ions is 4:4:1.7:0.3, and the molar ratio of citric acid to the total amount of metal ions is 1:1. However, the calcination procedure in the muffle furnace is as follows: heat up to 120 °C at a heating rate of 10 °C / min and hold for 1 h, then heat up to 250 °C at a heating rate of 0.5 °C / min and hold for 2 h, and finally heat up to 550 °C at a heating rate of 2 °C / min and hold for 3 h to obtain Catalyst J. The content of CuO in Catalyst J is 41.3 wt%, the content of ZnO is 42.3 wt%, the content of Al2O3 is 11.2 wt%, and the content of ZrO2 is 5.2 wt%.

[0058] Example 11

[0059] The preparation method of catalyst K is the same as that of Example 1. The masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O are 1.2458 g, 1.5338 g, 0.8206 g and 0.1772 g respectively. The molar ratio of copper, zinc, aluminum and zirconium metal ions is 4:4:1.7:0.3, and the molar ratio of citric acid to the total amount of metal ions is 1:1. However, the final calcination temperature in the muffle furnace is 500 °C. The CuO content in catalyst K is 41.3 wt%, the ZnO content is 42.3 wt%, the Al2O3 content is 11.2 wt%, and the ZrO2 content is 5.2 wt%.

[0060] Example 12

[0061] The preparation method of catalyst L is the same as that of Example 1. The masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O are 1.2458 g, 1.5338 g, 0.8206 g and 0.1772 g respectively. The molar ratio of copper, zinc, aluminum and zirconium metal ions is 4:4:1.7:0.3, and the molar ratio of citric acid to the total amount of metal ions is 1:1. However, the final calcination temperature in the muffle furnace is 600 °C. The CuO content in catalyst L is 41.3 wt%, the ZnO content is 42.3 wt%, the Al2O3 content is 11.2 wt%, and the ZrO2 content is 5.2 wt%.

[0062] Comparative Example 1

[0063] Catalyst M is prepared by the co-precipitation method. Mix 16.5 mL of a 1.25 mol / L Cu(NO3)2·3H2O solution, 16.5 mL of a 1.25 mol / L Zn(NO3)2·6H2O solution, 7 mL of a 1.25 mol / L Al(NO3)3·9H2O solution and 8 mL of a 0.2 mol / L Zr(NO3)4·5H2O solution evenly. The molar ratio of copper, zinc, aluminum and zirconium metal ions is 4:4:1.7:0.3. Drop a 1.25 mol / L Na2CO3 solution and the above mixed solution into 60 mL of deionized water simultaneously to cause a co-current co-precipitation reaction. During the titration process, keep the slurry temperature at 70 °C, pH = 7 and stir vigorously. After the titration is completed, age the slurry at 80 °C for 1 h, then filter and wash the precipitate until the filtrate is neutral. Place the precipitate in an oven and dry it at 100 °C for 4 h, and then calcine it in a muffle furnace at 550 °C for 3 h in an air atmosphere to obtain catalyst M. The CuO content in catalyst M is 41.3 wt%, the ZnO content is 42.3 wt%, the Al2O3 content is 11.2 wt%, and the ZrO2 content is 5.2 wt%.

[0064] Figure 2 The EDX mapping image of catalyst M prepared in Comparative Example 1. It can be observed from Figure 2 that obvious Cu nanoparticles exist in catalyst M, but the three elements of Zn, Al, and Zr are highly dispersed; the low Cu dispersion may lead to low ethanol dehydrogenation activity, thus resulting in a low ethanol conversion rate, and partially covering the acid-base active centers on the catalyst surface that promote the conversion of acetaldehyde, thereby leading to a decrease in the selectivity of ethyl acetate.

[0065] Comparative Example 2

[0066] Catalyst N was prepared by the simple impregnation method. Weighed 0.2848 g of Cu(NO3)2·3H2O, 0.3507 g of Zn(NO3)3·6H2O, and 0.0358 g of Zr(NO3)4·5H2O and added them to 10 mL of deionized water (the molar ratio of copper, zinc, and zirconium metal ions is 4.8:4.8:0.4, with alumina as the carrier). After it was dissolved and mixed evenly, 1 g of alumina carrier was added thereto and oscillated for impregnation for 4 h. The above mixture was first dried at 50 °C and 0.01 MPa on a rotary evaporator for 3 h, and then dried in an oven at 110 °C for 4 h. The metal oxide precursors were uniformly loaded on the inner and outer surfaces of the alumina carrier. Subsequently, it was calcined in a muffle furnace at 550 °C in an air atmosphere for 3 h to obtain catalyst N. The content of CuO in catalyst N is 7.8 wt%, the content of ZnO is 8.0 wt%, the content of Al2O3 is 83.3 wt%, and the content of ZrO2 is 0.9 wt%.

[0067] Figure 3 The EDX mapping image of catalyst N prepared in Comparative Example 2. It can be observed from Figure 3 that larger Cu nanoparticles exist in catalyst N, but the three elements of Zn, Al, and Zr are highly dispersed; the lower Cu dispersion will significantly reduce the ethanol dehydrogenation activity, thus resulting in a decrease in the ethanol conversion rate, and partially covering the acid-base active centers on the catalyst surface that promote the conversion of acetaldehyde, thereby resulting in a low selectivity of the product ethyl acetate.

[0068] Comparative Example 3

[0069] Catalyst O was prepared by a conventional sol-gel method. Weighed 1.2458 g of Cu(NO3)2·3H2O, 1.5338 g of Zn(NO3)2·6H2O, 0.8206 g of Al(NO3)3·9H2O and 0.1772 g of Zr(NO3)4·5H2O were added to 15 mL of deionized water. The molar ratio of copper, zinc, aluminum and zirconium metal ions was 4:4:1.7:0.3. After they were dissolved and mixed evenly, 16 mL of 0.8 mol / L citric acid aqueous solution was added (the molar ratio of citric acid to the total amount of metal ions was 1:1), and stirred for 1 h. While stirring continuously, ammonia water (mass concentration was 25%) was added dropwise to the above solution until a sol was formed. The formed sol was heated in a water bath at 75 °C for 24 h to obtain a gel. The obtained gel was dried in an oven at 100 °C for 72 h, and finally heated in a muffle furnace at a heating rate of 10 °C / min to 550 °C and maintained for 3 h to obtain catalyst O. The content of CuO in catalyst O was 41.3 wt%, the content of ZnO was 42.3 wt%, the content of Al2O3 was 11.2 wt%, and the content of ZrO2 was 5.2 wt%.

[0070] Figure 4 It is the EDX mapping image of catalyst O prepared in Comparative Example 3. From Figure 4 it can be observed that obvious Cu nanoparticles exist in catalyst O, but the three elements of Zn, Al and Zr are highly dispersed; the low Cu dispersion degree leads to low ethanol dehydrogenation activity, and then low ethanol conversion rate, and makes the acid-base active centers promoting acetaldehyde conversion on the catalyst surface partially covered, thus resulting in low selectivity of the product ethyl acetate.

[0071] Comparative Example 4

[0072] The preparation method of catalyst P was the same as that of Example 1. The masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O were 1.2458 g, 1.5338 g, 0.8206 g and 0.1772 g respectively. The molar ratio of copper, zinc, aluminum and zirconium metal ions was 4:4:1.7:0.3, but 32 mL of 0.8 mol / L citric acid aqueous solution was added (the molar ratio of citric acid to the total amount of metal ions was 2:1). The content of CuO in catalyst P was 41.3 wt%, the content of ZnO was 42.3 wt%, the content of Al2O3 was 11.2 wt%, and the content of ZrO2 was 5.2 wt%.

[0073] Comparative Example 5

[0074] The preparation method of catalyst Q is the same as that in Example 1. The masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O are 1.2458 g, 1.5338 g, 0.8206 g and 0.1772 g respectively. The molar ratio of copper, zinc, aluminum and zirconium metal ions is 4:4:1.7:0.3, and the molar ratio of citric acid to the total amount of metal ions is 1:1. However, the final calcination temperature in the muffle furnace is 700 °C. The CuO content in catalyst Q is 41.3 wt%, the ZnO content is 42.3 wt%, the Al2O3 content is 11.2 wt%, and the ZrO2 content is 5.2 wt%.

[0075] Comparative Example 6

[0076] The preparation method of catalyst R is the same as that in Example 1, but the masses of Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O are 1.5338 g, 0.8206 g and 0.1772 g respectively. The molar ratio of zinc, aluminum and zirconium metal ions is 6.6:2.8:0.6. 10 mL of 0.8 mol / L citric acid aqueous solution is added (the molar ratio of citric acid to the total amount of metal ions is 1:1). The ZnO content in catalyst R is 72.1 wt%, the Al2O3 content is 19.2 wt%, and the ZrO2 content is 8.7 wt%.

[0077] Comparative Example 7

[0078] The preparation method of catalyst S is the same as that in Example 1, but the masses of Cu(NO3)2·3H2O, Al(NO3)3·9H2O and Zr(NO3)4·5H2O are 1.2458 g, 0.8206 g and 0.1772 g respectively. The molar ratio of copper, aluminum and zirconium metal ions is 6.6:2.8:0.6. 10 mL of 0.8 mol / L citric acid aqueous solution is added (the molar ratio of citric acid to the total amount of metal ions is 1:1). The CuO content in catalyst S is 71.6 wt%, the Al2O3 content is 19.5 wt%, and the ZrO2 content is 8.9 wt%.

[0079] Comparative Example 8

[0080] The preparation method of catalyst T is the same as that of Example 1, but the masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, and Zr(NO3)4·5H2O are 1.2458 g, 1.5338 g, and 0.1772 g respectively, and the molar ratio of copper, zinc, and zirconium metal ions is 4.8:4.8:0.4. 13 mL of 0.8 mol / L citric acid aqueous solution is added (the molar ratio of citric acid to the total amount of metal ions is 1:1). The CuO content in catalyst T is 46.6 wt%, the ZnO content is 47.6 wt%, and the ZrO2 content is 5.8 wt%.

[0081] Comparative Example 9

[0082] The preparation method of catalyst U is the same as that of Example 1, but the masses of Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, and Al(NO3)3·9H2O are 1.2458 g, 1.5338 g, and 0.8206 g respectively, and the molar ratio of copper, zinc, and aluminum metal ions is 4.1:4.1:1.8. 16 mL of 0.8 mol / L citric acid aqueous solution is added (the molar ratio of citric acid to the total amount of metal ions is 1:1). The CuO content in catalyst U is 43.6 wt%, the ZnO content is 44.6 wt%, and the Al2O3 content is 11.8 wt%.

[0083] The catalysts A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, and U prepared in the above examples and comparative examples are reduced in a fixed bed and then applied to the one-step continuous catalytic synthesis of ethyl acetate from ethanol in a fixed bed. The reaction device is as Figure 5 shown. The reduction conditions of the catalyst are: 200 °C, atmospheric pressure, using a mixed gas of H2 and N2 with a volume ratio of 1:9, and the space velocity of the mixed gas is 1800 h -1 , and the reduction time is 3 h. The reaction conditions and results of the catalytic synthesis of ethyl acetate are shown in Table 1.

[0084] Table 1 Catalytic performance of different catalysts in the one-step continuous catalytic synthesis of ethyl acetate from ethanol in a fixed bed

[0085]

Claims

1. A transition metal oxide catalyst, characterized in that The transition metal oxide catalyst is prepared by the following method: Dissolve the metal salts in a solvent, add an aqueous citric acid solution, stir evenly, rotary evaporate the obtained mixed solution until it becomes gel-like, dry the obtained gel-like mixture, and put the obtained catalyst precursor into a muffle furnace and calcine it in an air atmosphere to obtain the transition metal oxide catalyst; the metal salts are a mixture of copper salts, zinc salts, aluminum salts and zirconium salts; the molar ratio of copper ions contained in the copper salt, zinc ions contained in the zinc salt, aluminum ions contained in the aluminum salt to zirconium ions contained in the zirconium salt is 2-6:2-6:0.5-3:0.1-1; the molar ratio of citric acid in the aqueous citric acid solution to metal ions in the metal salts is 0.4-1.5:1; The program of the calcination is as follows: heat up to 100-130 °C at a rate of 5-11 °C / min for the first round of heat preservation for 0.5-3 h, heat up to 220-260 °C at a rate of 0.1-2 °C / min for the second round of heat preservation for 0.5-3 h, and heat up to 300-600 °C at a rate of 1-3 °C / min for the third round of heat preservation for 2-10 h.

2. The transition metal oxide catalyst according to claim 1, wherein: The copper salt is at least one of copper nitrate, copper chloride, and copper acetate; The zinc salt is at least one of zinc nitrate, zinc chloride, and zinc acetate; The aluminum salt is at least one of aluminum nitrate, aluminum chloride, and copper acetate; The zirconium salt is at least one of zirconium nitrate, zirconyl chloride, zirconium chloride, and zirconium acetate.

3. The transition metal oxide catalyst according to claim 1, wherein: The solvent is one or a mixed solvent of two or more of deionized water, methanol, and ethanol.

4. The transition metal oxide catalyst according to claim 1, wherein: The volume of the solvent is 0.5-50 L / mol based on the amount of substance of the metal salts.

5. The transition metal oxide catalyst according to claim 1, characterized in that: The temperature of the rotary evaporation is 45-80 °C, and the pressure is 0.005-0.1 MPa.

6. Use of the transition metal oxide catalyst according to claim 1 in the catalytic synthesis of ethyl acetate from ethanol.

7. The application according to claim 6, wherein The use is as follows: place the transition metal oxide catalyst in a fixed-bed reactor, after reduction with hydrogen, catalyze the reaction of ethanol to synthesize ethyl acetate.

8. The application according to claim 7, characterized in that The reduction conditions are as follows: 200 °C, atmospheric pressure, using a mixed gas of H2 and N2 with a volume ratio of 1:9, and the space velocity of the mixed gas is 1800 h -1 , and the reduction time is 3 h.

9. The application according to claim 7, wherein: The conditions of the reaction are as follows: 220 to 270 °C, atmospheric pressure to 2.0 MPa, and ethanol is introduced into the fixed-bed reactor at a liquid hourly space velocity of 0.5 to 3.0 mL / (h·g cat ).

10. The application according to claim 7, characterized in that: Nitrogen is also introduced into the reaction, and the volume ratio of the nitrogen to the ethanol is 100-1500:1.

Images