Method for preparing acetaldehyde from ethanol

Abstract

The invention discloses a method for preparing acetaldehyde from ethanol, which comprises the following steps: mixing Cu (NO3) 2, Zn (NO3) 2 and Al (NO3) 3 solutions to obtain a mixed solution, adding the mixed solution and Na2CO3 into a reaction kettle in a parallel flow manner, aging, washing to be neutral, drying to obtain a Cu-Zn-Al precursor, dipping the Cu-Zn-Al precursor into a Ce (NO3) 3 solution, transferring to a hydrothermal kettle for high-temperature reaction, roasting in a muffle furnace to generate a Cu-ZnO-Al2O3-CeO2 composite catalyst with a multi-stage pore structure, and drying to obtain the acetaldehyde. Tabletting and molding for later use; ethanol is used as a raw material, and the Cu-ZnO-Al2O3-coated CeO2 composite catalyst with the hierarchical porous structure is used for catalyzing ethanol to prepare acetaldehyde, so that the conversion rate of ethanol and the selectivity of acetaldehyde are improved, and the service life of the catalyst is prolonged.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, and in particular to a method for preparing acetaldehyde from ethanol. Background Technology

[0002] The dehydrogenation of ethanol to produce acetaldehyde is an important chemical reaction. Acetaldehyde, as a key chemical intermediate, is widely used in the production of chemicals such as acetic acid, ethyl acetate, and pentaerythritol. Currently, several technical routes exist for the dehydrogenation of ethanol to produce acetaldehyde, but each method has certain limitations.

[0003] Publication No. CN114054079 A discloses a method for catalytic dehydrogenation of ethanol in a fixed-bed reactor using a Cu / SiO2 catalyst at a reaction temperature of approximately 280℃. However, this method exhibits low selectivity, with acetaldehyde selectivity at only 69%, and numerous byproducts (such as ethyl acetate and butanol), increasing the difficulty of separation. Furthermore, it suffers from poor stability; Cu nanoparticles are prone to sintering and agglomeration, leading to catalyst deactivation and a short lifespan. Publication No. CN110385139A discloses a Cu-supported boron compound catalyst for the direct dehydrogenation of ethanol to acetaldehyde. While this catalyst demonstrates high selectivity for acetaldehyde and high ethanol conversion, it is essentially deactivated within 50 hours of testing. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing acetaldehyde from ethanol, which can solve the shortcomings of existing ethanol-to-acetaldehyde production processes mentioned in the background art, such as low yield, many by-products, and easy deactivation of catalysts.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing acetaldehyde from ethanol includes the following steps: A mixed solution was obtained by mixing Cu(NO3)2, Zn(NO3)2, and Al(NO3)3 solutions. The mixed solution was then added to the reactor in parallel with Na2CO3. After aging, the mixture was washed until neutral and dried to obtain the Cu-Zn-Al precursor. The Cu-Zn-Al precursor was impregnated with Ce(NO3)3 solution, transferred to a hydrothermal reactor for high-temperature reaction, and calcined in a muffle furnace to generate a multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst, which was then pressed into tablets for later use. Using ethanol as a raw material, acetaldehyde was prepared from ethanol using a multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst.

[0006] Furthermore, the concentrations of Cu(NO3)2 are 0.4-0.6 mol / L, Zn(NO3)2 are 0.2-0.4 mol / L, and Al(NO3) is 0.15-0.25 mol / L.

[0007] Furthermore, the mixed solution was added to the reactor in parallel with 1 mol / L Na2CO3, with the concentration of Na2CO3 controlled at 0.75-1.25 mol / L. The pH was adjusted to 8-10, and the mixture was aged at 60℃ for 12 hours.

[0008] Furthermore, the drying temperature is 110℃ and the drying time is 12 hours.

[0009] Furthermore, the Ce(NO3)3 concentration was controlled at 0.05-0.15 mol / L, and the reaction was carried out in a hydrothermal reactor at 180℃ for 6 hours.

[0010] Furthermore, the mixture is roasted in a muffle furnace at 450-600℃ for 4 hours.

[0011] Furthermore, the hierarchical porous Cu-ZnO-Al2O3@CeO2 composite catalyst was activated at 250°C for two hours in an atmosphere of 5% H2 / N2 at a rate of 30 mL / min before use. The activated hierarchical porous Cu-ZnO-Al2O3@CeO2 composite catalyst was then loaded into a fixed-bed reactor for reaction, and the reaction temperature, pressure, ethanol feed rate, and nitrogen flow rate were controlled.

[0012] Furthermore, a stainless steel fixed bed with an inner diameter of 20 mm was selected as the reaction device, and 10 mL of a multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst with a particle size of 20-40 mesh was loaded.

[0013] Furthermore, in the fixed-bed reactor, the reaction temperature is 170-400℃, the time is 3-5 hours, and the space velocity is 1.5-2.5 h⁻¹. -1 Pressure 0-0.12MPa.

[0014] Furthermore, in the fixed-bed reactor, N2 is selected as the carrier gas, and the feed molar ratio of ethanol to N2 is 1:1-3.

[0015] Mechanism of action of the hierarchical porous Cu-ZnO-Al2O3@CeO2 composite catalyst: This hierarchical porous Cu-ZnO-Al2O3@CeO2 composite catalyst achieves efficient dehydrogenation through a ternary synergistic mechanism. 0 Nanoparticles dissociate and adsorb ethanol to generate ethoxy groups; ZnO lattice oxygen extracts β-H to complete dehydrogenation, while Al2O3 stabilizes the structure; CeO2 coating layer inhibits carbon deposition through oxygen vacancy cycling and fixes Cu particle size; multi-level porous structure ensures efficient diffusion of reactants and improves acetaldehyde selectivity.

[0016] Compared with the prior art, the beneficial effects of the present invention are: The hierarchical porous Cu-ZnO-Al2O3@CeO2 composite catalyst prepared in this invention utilizes a CeO2 coating layer to promote surface hydroxyl desorption, reduce aldehyde condensation side reactions, and enhance ethanol diffusion efficiency while reducing internal diffusion resistance. Low-temperature operation delays Cu particle sintering, resulting in a catalyst lifetime >800 hours and ethyl acetate byproduct formation <0.5%. This invention provides a green and economical method for catalytic ethanol-to-acetaldehyde production, which is chromium-free and non-toxic, achieving an acetaldehyde yield >95%. Compared to other catalysts, it not only has a longer lifespan but also simplifies the process, allowing for operation at ambient pressure and low temperature, thus reducing equipment investment. Attached Figure Description

[0017] Figure 1 This is a scanning electron microscope image of the multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Process investigation of multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst at different calcination temperatures: Example 1: Preparation of 0.5 mol / L Cu(NO3)2, 0.3 mol / L Zn(NO3)2, and 0.2 mol / L Al(NO3)3: The three were mixed and then added to a reactor in parallel with 1 mol / L Na2CO3. The pH was adjusted to 9, and the mixture was aged at 60°C for 12 h. After washing until neutral, the mixture was dried at 110°C for 12 h to obtain a Cu-Zn-Al precursor. The Cu-Zn-Al precursor was impregnated in a 0.1 mol / L Ce(NO3)3 solution and transferred to a hydrothermal reactor to react at 180°C for 6 h. Finally, it was calcined in a muffle furnace at 400°C for 4 h to generate a multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst 1, which was then pressed into tablets for later use.

[0020] Example 2: Preparation of 0.5 mol / L Cu(NO3)2, 0.3 mol / L Zn(NO3)2, and 0.2 mol / L Al(NO3)3: The three were mixed and then added to a reactor in parallel with 1 mol / L Na2CO3. The pH was adjusted to 9, and the mixture was aged at 60°C for 12 h. After washing to neutrality, the mixture was dried at 110°C for 12 h to obtain a Cu-Zn-Al precursor. The Cu-Zn-Al precursor was impregnated in a 0.1 mol / L Ce(NO3)3 solution and transferred to a hydrothermal reactor to react at 180°C for 6 h. Finally, it was calcined in a muffle furnace at 450°C for 4 h to generate a multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst 2, which was then pressed into tablets for later use.

[0021] Example 3: Preparation of 0.5 mol / L Cu(NO3)2, 0.3 mol / L Zn(NO3)2, and 0.2 mol / L Al(NO3)3: The three were mixed and then added to a reactor in parallel with 1 mol / L Na2CO3. The pH was adjusted to 9, and the mixture was aged at 60℃ for 12 h. After washing until neutral, the mixture was dried at 110℃ for 12 h to obtain a Cu-Zn-Al precursor. The Cu-Zn-Al precursor was impregnated in a 0.1 mol / L Ce(NO3)3 solution and transferred to a hydrothermal reactor for reaction at 180℃ for 6 h. Finally, it was calcined in a muffle furnace at 500℃ for 4 h to generate a multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst 3, which was then pressed into tablets for later use.

[0022] Example 4: Preparation of 0.5 mol / L Cu(NO3)2, 0.3 mol / L Zn(NO3)2, and 0.2 mol / L Al(NO3)3: The three were mixed and then added to a reactor in parallel with 1 mol / L Na2CO3. The pH was adjusted to 9, and the mixture was aged at 60℃ for 12 h. After washing until neutral, the mixture was dried at 110℃ for 12 h to obtain a Cu-Zn-Al precursor. The Cu-Zn-Al precursor was impregnated in a 0.1 mol / L Ce(NO3)3 solution and transferred to a hydrothermal reactor to react at 180℃ for 6 h. Finally, it was calcined in a muffle furnace at 550℃ for 4 h to generate a multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst 4, which was then pressed into tablets for later use.

[0023] Example 5: Preparation of 0.5 mol / L Cu(NO3)2, 0.3 mol / L Zn(NO3)2, and 0.2 mol / L Al(NO3)3: The three were mixed and then added to a reactor in parallel with 1 mol / L Na2CO3. The pH was adjusted to 9, and the mixture was aged at 60℃ for 12 h. After washing to neutrality, the mixture was dried at 110℃ for 12 h to obtain a Cu-Zn-Al precursor. The Cu-Zn-Al precursor was impregnated in a 0.1 mol / L Ce(NO3)3 solution and transferred to a hydrothermal reactor to react at 180℃ for 6 h. Finally, it was calcined in a muffle furnace at 600℃ for 4 h to generate a multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst 5, which was then pressed into tablets for later use.

[0024] Ten mL of each of the hierarchical porous Cu-ZnO-Al2O3@CeO2 composite catalysts (catalysts 1-5) was loaded into a fixed-bed reactor. Before the reaction, the catalysts were activated for two hours at 250°C in a 5% H2 / N2 atmosphere (30 mL / min). Ethanol was used as the feedstock, preheated to 200°C, and then reacted at 230°C under normal pressure for 3 hours. N2 was used as the carrier gas, with a feed molar ratio of ethanol to N2 of 1:2, and the space velocity was controlled at 2.0 h⁻¹. -1 The results are shown in the table below.

[0025]

[0026] As shown in Table 1, controlling the calcination temperature of the Cu-Zn-Al precursor reaction with Ce(NO3)3 solution can improve the conversion rate and selectivity of ethanol. At 550℃, the ethanol conversion rate reaches 97.12%, and the selectivity reaches 98.29%. Meanwhile, the selectivity of the byproduct ethyl acetate can decrease to 0.38%. This is because if the temperature is too low, the catalyst precursor may not be completely converted into metal oxides, and the residual anions will occupy active sites, reducing catalytic activity. Furthermore, low temperatures can also cause insufficient crystallization of the components. Conversely, the temperature cannot be too high, as this can lead to sintering and deactivation of the active components.

[0027] The process conditions for the preparation of acetaldehyde from ethanol catalyzed by the hierarchical porous Cu-ZnO-Al2O3@CeO2 composite catalyst were investigated, and the results are shown in Table 2.

[0028] 10 mL of multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst 4 was loaded into a fixed-bed reaction tube. Before the reaction, the catalyst was activated for two hours at 250℃ in a 5% H2 / N2 atmosphere (30 mL / min). Nitrogen was used as the carrier gas, and the reaction was carried out at different molar ratios of nitrogen to ethanol, under different reaction temperatures and pressures, and for a reaction time of 4 hours. The results are shown in Table 2. Using catalyst 4, the conversion rate of ethanol reached 97.92% and the selectivity of acetaldehyde reached 98.23% at a reaction temperature of 230℃. At 400℃, the conversion rate decreased, possibly due to catalyst deactivation caused by high temperature. The catalytic effect was best when the molar ratio of nitrogen to ethanol was controlled at 2. Furthermore, the reaction at atmospheric pressure achieved a conversion rate of 97.31% and an acetaldehyde selectivity of 98.52%. Considering subsequent equipment wear and tear, the reaction was chosen to be carried out at atmospheric pressure.

[0029] Comparative Example 1: 0.5 mol / L Cu(NO3)2, 0.3 mol / L Zn(NO3)2, and 0.2 mol / L Al(NO3)3 were prepared and mixed. Then, 1 mol / L Na2CO3 was added to the reactor in a parallel flow. The pH was adjusted to 9, and the mixture was aged at 60℃ for 12 h. After washing until neutral, the mixture was dried at 110℃ for 12 h to obtain the Cu-Zn-Al precursor. The precursor was transferred to a hydrothermal reactor and reacted at 180℃ for 6 h. Finally, it was calcined in a muffle furnace at 550℃ for 4 h to generate the Cu-ZnO-Al2O3 composite catalyst. 。

[0030] A mixture of 0.5 mol / L Cu(NO3)2, 0.3 mol / L Zn(NO3)2, and 0.2 mol / L Al(NO3)3 was prepared and then added to a reactor in parallel with 1 mol / L Na2CO3. The pH was adjusted to 9, and the mixture was aged at 60℃ for 12 h. After washing until neutral, the mixture was dried at 110℃ for 12 h to obtain the Cu-Zn-Al precursor. This precursor was then impregnated in a 0.1 mol / L Ce(NO3)3 solution and transferred to a hydrothermal reactor to react at 180℃ for 6 h. Finally, the precursor was calcined in a muffle furnace at 550℃ for 4 h to generate a hierarchical porous Cu-ZnO-Al2O3@CeO2 composite catalyst. The scanning electron microscope (SEM) image is attached. Figure 1 Finally, the tablets are compressed and ready for use.

[0031] Ten mL of each of the two catalysts—Comparative Example 1 and the hierarchical porous Cu-ZnO-Al2O3@CeO2 composite catalyst—were taken and loaded into a fixed-bed reactor. The catalysts were activated for two hours at 250°C in a 5% H2 / N2 atmosphere (30 mL / min) before the reaction. Ethanol was used as the feedstock, preheated at 200°C, then heated to 230°C and reacted at atmospheric pressure for 3 hours. Nitrogen was used as the carrier gas, and the molar ratio of ethanol to N2 was 1:2. The space velocity was controlled at 2.0 h⁻¹. -1 The selectivity results for acetaldehyde are shown in the table below.

[0032]

[0033] As shown in Table 3, compared with the Cu-ZnO-Al2O3 composite catalyst alone, the conversion rate of ethanol using the multi-level porous Cu-ZnO-Al2O3@CeO2 composite catalyst was significantly increased by 37%, the selectivity was also increased to 98.29%, and the selectivity of the byproduct ethyl acetate could be reduced to 0.38%.

[0034] Comparative Example 2: A CuP / SiO2 catalyst was used and loaded into a fixed-bed reactor. Before the reaction, the catalyst was activated for two hours at 250°C in a 5% H2 / N2 atmosphere (30 mL / min). Ethanol was used as the feedstock. The ethanol was preheated at 200°C and then heated to 230°C and reacted at atmospheric pressure for 3 hours. Nitrogen was used as the carrier gas, and the molar ratio of ethanol to N2 was 1:2. The space velocity was controlled at 2.0 h⁻¹. -1 .

[0035] Comparative Example 3: A Cu / C / SiC catalyst was used and loaded into a fixed-bed reactor. Before the reaction, the catalyst was activated at 250°C for two hours in a 5% H2 / N2 atmosphere (30 mL / min). Ethanol was used as the feedstock. The ethanol was preheated at 200°C and then heated to 230°C and reacted at atmospheric pressure for 3 hours. Nitrogen was used as the carrier gas, and the molar ratio of ethanol to N2 was 1:2. The space velocity was controlled at 2.0 h⁻¹. -1 .

[0036] Comparative Example 4: A Cu-HB-deAL catalyst was used and loaded into a fixed-bed reactor. Before the reaction, the catalyst was activated at 250°C for two hours in a 5% H2 / N2 atmosphere (30 mL / min). Ethanol was used as the feedstock. The ethanol was preheated at 200°C and then heated to 230°C and reacted at atmospheric pressure for 3 hours. Nitrogen was used as the carrier gas, and the molar ratio of ethanol to N2 was 1:2. The space velocity was controlled at 2.0 h⁻¹. -1 .

[0037]

[0038] As shown in Table 4, the catalyst Cu-ZnO-Al2O3@CeO2 used for the preparation of acetaldehyde from ethanol not only has high conversion and selectivity, but also achieves higher catalytic activity at 230℃ compared to other catalysts, and its service life can be extended to 800h. This is because the catalyst is composed of CuO, ZnO, Al2O3 and CeO2 coating layers. The CeO2 coating layer is loaded on the surface of the Cu-Zn-Al precursor by in-situ hydrothermal method. The CeO2 coating layer promotes the desorption of surface hydroxyl groups and reduces the aldehyde condensation side reaction.

[0039] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A process for the preparation of acetaldehyde from ethanol, characterized in that, It comprises the following steps: Mixing Cu(NO3)2, Zn(NO3)2 and Al(NO3)3 solutions to obtain a mixed solution, adding the mixed solution and Na2CO3 into a reaction kettle in parallel flow, washing to neutral after aging, and drying to obtain a Cu-Zn-Al precursor; The Cu-Zn-Al precursor is immersed in a Ce(NO3)3 solution, transferred to a hydrothermal kettle for high-temperature reaction, and calcined in a muffle furnace to generate a multi-level pore structure Cu-ZnO-Al2O3@CeO2 composite catalyst, which is pressed into a tablet for use; Using ethanol as a raw material, the multi-level pore structure Cu-ZnO-Al2O3@CeO2 composite catalyst is used to catalyze ethanol to prepare acetaldehyde.

2. A process for the preparation of acetaldehyde from ethanol as claimed in claim 1 wherein, The concentration of Cu(NO3)2 is 0.4-0.6 mol / L, the concentration of Zn(NO3)2 is 0.2-0.4 mol / L, and the concentration of Al(NO3) is 0.15-0.25 mol / L. ​ 3. A process for the preparation of acetaldehyde from ethanol as claimed in claim 1 wherein, The mixed solution is added into the reaction kettle in parallel flow with 1 mol / L Na2CO3, the concentration of Na2CO3 is controlled at 0.75-1.25 mol / L, the pH is adjusted to 8-10, and the aging is performed at 60℃ for 12h.

4. The method for preparing acetaldehyde from ethanol as described in claim 1, characterized in that, The drying temperature is 110℃, and the drying time is 12h.

5. The process of claim 1 wherein the ethanol is prepared from a feedstock comprising corn, corn oil, corn syrup, corn starch, corn sugars, corn oil, corn syrup, corn starch, corn sugars, or combinations thereof. The concentration of Ce(NO3)3 is controlled at 0.05-0.15 mol / L, and the reaction is performed in a hydrothermal kettle at 180℃ for 6h.

6. The process of claim 1 wherein the ethanol is prepared from a feedstock comprising corn. The calcination is performed in a muffle furnace at 450-600℃ for 4h.

7. The method of claim 1, wherein the ethanol is prepared from a feedstock comprising corn, sugar, sugar beets, or a combination thereof. The multi-level pore structure Cu-ZnO-Al2O3@CeO2 composite catalyst is activated at 250℃ for two hours in an atmosphere of 5% H2 / N2 at a rate of 30mL / min before use, the activated multi-level pore structure Cu-ZnO-Al2O3@CeO2 composite catalyst is loaded into a fixed bed reaction device for reaction, and the reaction temperature, pressure, ethanol feed rate and nitrogen flow are controlled.

8. A process for the preparation of acetaldehyde from ethanol as claimed in claim 7 wherein, A stainless steel fixed bed with an inner diameter of 20mm is selected as the reaction device, the multi-level pore structure Cu-ZnO-Al2O3@CeO2 composite catalyst is loaded at 10mL, and the particle size of the multi-level pore structure Cu-ZnO-Al2O3@CeO2 composite catalyst is 20-40 mesh.

9. A process for the preparation of acetaldehyde from ethanol as claimed in claim 8 wherein, Reaction temperature 170-400°C, time 3-5h, space velocity 1.5-2.5h, pressure 0-0.12MPa in fixed bed reaction device -1 .

10. A process for the preparation of acetaldehyde from ethanol as claimed in claim 8 wherein, N2 is selected as the carrier gas in the fixed bed reaction device, and the feed molar ratio of ethanol to N2 is 1:1-3.

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