A process for continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor

Abstract

This invention relates to the field of compound technology, specifically to a process for the continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor. The process includes a modified catalyst, anhydrous ethanol, and benzaldehyde as a feedstock. In this process, the modified catalyst, employing a hollow nanocage-double active layer synergistic design, precisely anchors the aldehyde group in the benzaldehyde molecule and preferentially activates the C=O bond within it. This effectively reduces the attack of hydrogen on the benzene ring and the already generated benzyl alcohol, lowering the occurrence of side reactions such as benzene ring hydrogenation and deep hydrogenation of benzyl alcohol. Simultaneously, the highly efficient mass and heat transfer characteristics of the microchannel reactor rapidly remove the heat of reaction, preventing localized overheating, enhancing gas-liquid two-phase mixing, and improving hydrogen utilization. This effectively solves the problems of significantly reduced selectivity of the target product benzyl alcohol and low effective conversion rate of the feedstock benzaldehyde in traditional processes.

Description

Technical Field

[0001] This invention relates to the field of compound technology, and more specifically, to a process for the continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor. Background Technology

[0002] Currently, benzyl alcohol is a core fine chemical in the fields of fragrance, pharmaceutical intermediates and coating solvents. Its synthesis technology has long focused on the catalytic hydrogenation route, with benzaldehyde catalytic hydrogenation being the mainstream route in the industry. With the increasing demands for efficiency and safety in continuous production, microchannel reactors, due to their small liquid holdup and high mass and heat transfer efficiency, have gradually replaced traditional batch reactors in the catalytic hydrogenation process of benzyl alcohol. They can quickly remove the heat generated during the reaction to avoid local overheating and enhance the mixing of gas and liquid phases to improve hydrogen utilization, providing an equipment foundation for the continuous and safe production of benzyl alcohol.

[0003] However, the selective adsorption and activation capabilities of the aldehyde group and benzene ring in benzaldehyde molecules are insufficient. For example, it is difficult to accurately anchor the aldehyde group and preferentially activate the C=O bond in the aldehyde group. This not only easily leads to excessive hydrogen attack on the benzene ring or the already generated benzyl alcohol, triggering side reactions such as benzene ring hydrogenation and deep hydrogenation of benzyl alcohol, but also the uneven distribution of active sites in traditional catalysts, with some sites easily becoming deactivated due to reactant accumulation, resulting in a significant decrease in the selectivity of the target product benzyl alcohol. This also reduces the effective conversion rate of the raw material benzaldehyde, affecting the overall atom economy of the process and the purity of the product, thus limiting the effectiveness of microchannel reactors in the continuous catalytic hydrogenation process of benzyl alcohol.

[0004] Therefore, there is an urgent need for a process for the continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor. Summary of the Invention

[0005] The purpose of this invention is to provide a process for the continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor, in order to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, according to Figure 1 As shown, this invention provides a process for the continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor, comprising a modified catalyst, anhydrous ethanol, and benzaldehyde feedstock, and further comprising the following process steps:

[0007] S1.1 Raw material pretreatment: Benzaldehyde raw material is filtered through a filter to remove mechanical impurities with a particle size >1μm, to prevent solid impurities in the raw material from clogging the catalyst and entering the microchannel reactor, causing catalyst contamination. Then, it is added to a stirred tank with anhydrous ethanol at a mass ratio of 1:1.5 and stirred at 200-250r / min for 15-20min at room temperature to form a homogeneous solution. Finally, the solution is delivered to the preheating module by a constant phase feed pump and preheated at 40-45℃ until the solution temperature fluctuates within ±1℃. The benzaldehyde concentration is reduced by solvent dilution to obtain a temperature-stable benzaldehyde-ethanol solution free from impurity interference.

[0008] S1.2 Catalyst loading and activation: The modified catalyst is filled into the reaction chamber of the microchannel reactor. The catalyst loading amount is 60%-65% of the effective volume of the reaction chamber. Then, nitrogen gas with a purity of 99.99% is introduced to test the airtightness (the pressure is maintained at 0.8MPa, and the pressure drop within 30 minutes is ≤0.02MPa as qualified). After passing the test, hydrogen gas is switched to activate the catalyst at 0.5MPa and 120℃ for 2 hours to fully expose the active sites on the catalyst surface and form a catalytic system with high hydrogenation activity.

[0009] S1.3 Continuous hydrogenation reaction: Benzaldehyde-ethanol solution and hydrogen are delivered to the gas-liquid mixing module of the microchannel reactor by a metering pump at a volume ratio of 1:8. The mixture is dispersed at high speed in a static mixer at 2000-2200 rpm for 30-40 seconds to ensure thorough mixing of the gas and liquid phases and form a uniform gas-liquid emulsion system. Subsequently, the mixture is flowed into a reaction chamber containing a modified catalyst. Catalytic hydrogenation reaction is carried out under the conditions of reaction pressure of 1.2-1.5 MPa, reaction temperature of 70-75℃, and residence time of 8-10 minutes. Through the efficient heat transfer characteristics of the microchannel, the reaction temperature fluctuation is controlled to be ≤±1℃. The hollow cage structure and double active layer of the modified catalyst also work synergistically to preferentially activate and directionally hydrogenate the C=O bond of the aldehyde group, resulting in a mixture containing benzyl alcohol, unreacted hydrogen, and ethanol solvent.

[0010] S1.4 Product Separation: The mixture is fed into a gas-liquid separator. Under conditions of 0.3-0.5 MPa and 40-45℃, unreacted hydrogen is first separated. The separated hydrogen is then pressurized to 1.5 MPa by a compressor and recycled back to the reaction system for continued use. Next, the liquid product at the bottom of the separator is fed into a distillation column. Under conditions of -0.09 MPa vacuum and 100-105℃ at the top of the column, the ethanol solvent is separated. The recovered ethanol can be reused for raw material dissolution, while crude benzyl alcohol is obtained from the bottom of the distillation column.

[0011] S1.5 Purification: The crude benzyl alcohol product is fed into a precision distillation column. The vacuum level inside the column is first adjusted to -0.095 to -0.092 MPa to reduce the decomposition of benzyl alcohol or the side reaction of deep hydrogenation caused by high temperature. At the same time, the reflux ratio is set to 5:1 to 5.2:1. Through precise reflux control within a narrow range, the separation efficiency and energy consumption are balanced, and the production capacity is not wasted due to excessively high reflux ratio. The column bottom adopts segmented temperature control. When the temperature at the top of the column reaches 82-88℃, the fraction is collected. During this period, online equipment is used for real-time monitoring. Only the high-purity benzyl alcohol fraction is collected and sent to the finished product storage tank. The trace impurities remaining in the column bottom are collected and sent back to the raw material pretreatment step to participate in the reaction again. Finally, benzyl alcohol product with high purity and extremely low impurity content is obtained. At the same time, impurities are recycled, improving the overall economic efficiency of the process.

[0012] In this invention, a modified catalyst with a hollow nanocage-double active layer synergy is first prepared and combined with a microchannel reactor, along with a complete process chain of raw material pretreatment, continuous hydrogenation reaction, product separation, and purification. This not only anchors the aldehyde group in the benzaldehyde molecule and preferentially activates the C=O bond through the synergistic effect of the hollow cage structure and double active layer of the modified catalyst, reducing the attack of hydrogen on the benzene ring and the formation of benzyl alcohol, thus reducing side reactions such as benzene ring hydrogenation and deep hydrogenation of benzyl alcohol, but also enhances the two-phase dispersion and improves mass transfer efficiency through a gas-liquid mixing module. The product separation stage allows for the recycling of hydrogen and ethanol, and the purification stage employs low-vacuum segmented temperature control and impurity reflux, such as pressurizing the separated hydrogen back to the reaction system, recovering ethanol for raw material dissolution, and sending residual impurities from the reactor bottom back to the pretreatment step. This effectively improves the benzaldehyde conversion rate and benzyl alcohol selectivity, increases the benzyl alcohol purity compliance rate, reduces raw material waste and energy consumption, and enhances the overall economic efficiency and operational stability of the process.

[0013] Furthermore, this invention combines the dual-active-layer structure of the modified catalyst with the high-efficiency mass and heat transfer characteristics of the microchannel reactor, thereby enhancing reaction selectivity and efficiency. The main difference lies in the fact that the outer regulating layer of the modified catalyst preferentially adsorbs the aldehyde group in the benzaldehyde molecule and weakens the C=O bond energy through electronic effects and steric hindrance. Meanwhile, the Ru-Co active sites in the inner active layer rapidly activate hydrogen to generate active hydrogen species, which then directionally bind with the activated C=O bonds to complete the hydrogenation reaction. Simultaneously, the high-efficiency heat transfer of the microchannel reactor removes the heat of reaction in real time, preventing the active sites from becoming deactivated due to localized overheating. The high-efficiency mass transfer ensures rapid diffusion of hydrogen and benzaldehyde around the active sites, reducing reactant accumulation. The reaction formula is as follows: Under this combined effect, the side reactions of benzene ring hydrogenation to cyclohexylmethanol and benzyl alcohol deep hydrogenation to toluene can be reduced, thereby further improving the yield of the target product.

[0014] Furthermore, in step S1.5, the segmented temperature control includes the following steps:

[0015] Turn on the heating system of the precision distillation column reboiler and slowly raise the temperature to 95℃, controlling the heating rate at 2℃ / min to avoid local temperature surges that could lead to impurity carbonization. Maintain a constant temperature of 95℃ for 1 hour, and continuously stir the column reboiler at a stirring speed of 150r / min to fully dissolve any trace solid impurities (such as fine catalyst particles and high-boiling polymers) remaining in the crude benzyl alcohol, preventing blockage of the packing material inside the distillation column.

[0016] Then, the heating rate of the column bottom was adjusted to 1℃ / min, raising the temperature from 95℃ to 115℃. At the same time, the steam flow rate was observed through the steam flow meter at the top of the column to stabilize at 80-100mL / min, avoiding a sudden increase in vaporization due to excessively rapid heating, which would cause fluctuations in the purity of the top fraction. After the temperature reached 115℃, the temperature fluctuation of the column bottom was kept within ±0.5℃ to ensure that the benzyl alcohol component in the crude benzyl alcohol was fully vaporized. The vaporized mixed vapor entered the packing layer of the distillation column and came into full contact with the low-temperature benzyl alcohol liquid (cooled to 75-80℃) refluxed from the top condenser. This allowed the trace amounts of low-boiling-point impurities (such as incompletely separated ethanol) remaining in the mixed vapor to be absorbed by the low-temperature liquid and carried back to the column bottom, while the high-purity benzyl alcohol vapor continued to rise to the top of the column and became a liquid fraction after being cooled by the condenser.

[0017] Furthermore, according to Figure 2 As shown, the modified catalyst includes the following preparation steps:

[0018] S2.1 Preparation of hollow NiO nanocage carrier: Polystyrene microspheres and deionized water were added to a stirrer and stirred at 300-320 r / min for 20-25 min to form a uniform suspension; then nickel nitrate solution was added dropwise and stirring was continued for 30-35 min, followed by sodium hydroxide solution, with pH value monitored during addition, until the solution pH was 9.0-9.2, and stirring was continued for 1 h to obtain a mixture; this mixture was then transferred to a reaction vessel, sealed, and placed in an oven for hydrothermal reaction at 120-130℃ for 6 hours. -6.5h; After the reaction is completed, the reaction vessel is removed and naturally cooled to room temperature. The solid product is collected by filtration and washed repeatedly with deionized water until the pH of the washing solution is 7.0. The washed solid is placed in an 80℃ forced-air drying oven and dried for 12h; Finally, the dried solid is placed in a muffle furnace and heated to 500℃ at a heating rate of 5℃ / min, and calcined at this temperature for 4-4.5h to completely remove the polystyrene template, obtaining hollow NiO nanocages with a cage wall thickness of 15-20nm and an inner cavity diameter of 80-100nm;

[0019] S2.2 Construction of the inner active layer: Hollow NiO nanocages were placed in the reaction chamber of an atomic layer deposition apparatus and fixed. Then, ruthenium trichloride solution and cobalt chloride solution were prepared as precursors, and argon gas was used as the carrier gas. The carrier gas flow rate was adjusted to 50 mL / min. The deposition temperature in the reaction chamber was 180 °C. The apparatus was started to begin the deposition cycle. After deposition, the carrier gas in the reaction chamber was switched to hydrogen gas. The hydrogen flow rate was adjusted to 30 mL / min. The temperature of the reaction chamber was then raised to 280-300 °C for reduction for 2-2.5 h to obtain hollow NiO nanocages with a Ru-Co inner active layer.

[0020] S2.3 Construction of the external regulatory layer: First, prepare the precursor solution, add the hollow NiO nanocages to the precursor solution, and then place it in an ultrasonic cleaner to ultrasonically disperse it for 20-30 min at a power of 260-300W. Then, transfer the mixture to a three-necked flask, place it on a magnetic stirrer, and stir it at a speed of 400-420 r / min for 4-4.5 h at room temperature. Then, connect the three-necked flask to a rotary evaporator and remove ethanol by rotary evaporation at 80℃ and -0.09 MPa to obtain a solid powder. Then, place the solid powder in a muffle furnace and calcine it at a heating rate of 3℃ / min to 450℃ for 3 h to fully transform the precursor into a WO3-TiO2 composite regulatory layer. At the same time, Nb2O5 is uniformly doped, and finally, a hollow nanocage-double active layer synergistic modified catalyst is obtained.

[0021] Furthermore, in step S2.1, the amount of polystyrene microspheres used is 4.5-5.5g, and the particle size is 80-100nm; the amount of deionized water used is 90-110mL; the nickel nitrate solution used is a nickel nitrate solution with a concentration of 0.45-0.55mol / L, and the amount used is 28-32mL; the sodium hydroxide solution used is a sodium hydroxide solution with a concentration of 0.9-1.1mol / L, and the amount used is 14-19mL (to adjust the pH to 9.0-9.2).

[0022] In step S2.2, the amount of hollow NiO nanocages used is 2.8-3.2g, the amount of ruthenium trichloride solution with a concentration of 0.018-0.022mol / L is 9-11mL, the amount of cobalt chloride solution with a concentration of 0.058-0.062mol / L is 9-11mL, and the purity of argon and hydrogen is 99.99%.

[0023] In step S2.3, the amount of hollow NiO nanocages with Ru-Co inner active layer is 1.8-2.2g, and the amount of precursor solution is 48-52mL, wherein the precursor solution includes 0.28-0.32g ammonium tungstate, 1.4-1.6g tetrabutyl titanate, 0.09-0.11g niobium nitrate and 48-52mL anhydrous ethanol.

[0024] Furthermore, in S2.2, the atomic layer deposition equipment deposition cycle includes the following steps:

[0025] First, ruthenium trichloride solution is introduced for 10 seconds, then purged with argon gas for 20 seconds, then cobalt chloride solution is introduced for 10 seconds, and then purged with argon gas for 20 seconds, thus forming a complete deposition cycle.

[0026] The above deposition cycle was repeated, during which the Ru-Co alloy loading was monitored in real time by weighing until the loading reached 1.2%-1.8% of the mass of the hollow NiO nanocages, at which point deposition was stopped.

[0027] Furthermore, in step S2.3, the preparation of the precursor solution includes the following steps:

[0028] Take ammonium tungstate, tetrabutyl titanate and niobium nitrate, and add them together to anhydrous ethanol to obtain a mixture;

[0029] Place the mixture on a magnetic stirrer and stir it at 300-350 r / min for 30-40 min to allow the solid raw materials to initially dissolve and mix.

[0030] The mixture was then transferred to an ultrasonic cleaner and ultrasonically treated at 240-260W power for 15-20 minutes to break up the tiny solid particle agglomerates in the solution and to make the components evenly dispersed.

[0031] Finally, the sonicated solution was returned to the magnetic stirrer and stirred at 250-300 r / min for 1-1.5 h to obtain a clear and homogeneous WO3-TiO2-Nb2O5 precursor solution.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. In this microchannel reactor process for the continuous catalytic hydrogenation synthesis of benzyl alcohol, the use of a modified catalyst with a synergistic effect of hollow nanocages and a double active layer allows for precise anchoring of the aldehyde group in the benzaldehyde molecule and preferential activation of the C=O bond within the aldehyde group. This effectively reduces the attack of hydrogen on the benzene ring and the already generated benzyl alcohol, thus lowering the occurrence of side reactions such as benzene ring hydrogenation and deep hydrogenation of benzyl alcohol. Simultaneously, the highly efficient mass and heat transfer characteristics of the microchannel reactor can rapidly remove the heat of reaction, avoid localized overheating, enhance gas-liquid two-phase mixing, and improve hydrogen utilization. This effectively solves the problems of significantly reduced selectivity of the target product benzyl alcohol and low effective conversion rate of the raw material benzaldehyde in traditional processes.

[0034] 2. In this microchannel reactor continuous catalytic hydrogenation synthesis of benzyl alcohol, the dual-active-layer structure of the modified catalyst is combined with the high-efficiency mass and heat transfer characteristics of the microchannel reactor. The outer control layer of the modified catalyst preferentially adsorbs aldehyde groups and weakens the C=O bond energy through electronic effects and steric hindrance. The inner active layer rapidly activates hydrogen to generate active hydrogen species for directional hydrogenation. The microchannel reactor avoids deactivation of active sites due to local overheating through efficient heat transfer, and ensures rapid diffusion of reactants around the active sites through efficient mass transfer. In addition, the product separation stage allows for the recycling of hydrogen and ethanol, and the purification stage employs low-vacuum segmented temperature control and impurity reflux, effectively improving the conversion rate of benzaldehyde and the selectivity of benzyl alcohol, increasing the purity compliance rate of the benzyl alcohol product, reducing raw material waste and energy consumption, and improving the overall economic efficiency and operational stability of the process. Attached Figure Description

[0035] Figure 1 This is a process flow diagram of the continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor according to the present invention;

[0036] Figure 2 This is a flowchart illustrating the steps involved in preparing the modified catalyst of this invention.

[0037] Figure 3 This is a line graph showing the benzaldehyde conversion rate of this invention.

[0038] Figure 4 This is a line graph showing the selectivity of benzyl alcohol according to the present invention;

[0039] Figure 5 This is a line graph showing the purity of the benzyl alcohol product of this invention.

[0040] Figure 6 This is a line graph showing the raw material recycling rate of this invention. Detailed Implementation

[0041] The technical solutions in 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. Example 1

[0042] To prepare the modified catalyst, 4.5 g of polystyrene microspheres with a particle size of 80 nm were first added to 90 mL of deionized water in a stirrer and stirred at 300 r / min for 20 min to form a uniform suspension. 28 mL of a 0.45 mol / L nickel nitrate solution was added dropwise, and stirring continued for 30 min. Then, a 0.9 mol / L sodium hydroxide solution was added dropwise until the pH reached 9.0. After stirring for 1 h, the mixture was transferred to a reaction vessel and hydrothermally reacted at 120 °C for 6 h. After the reaction, the mixture was cooled to room temperature, the solid was collected by filtration, washed with deionized water until the pH reached 7.0, dried at 80 °C for 12 h, and finally calcined at 500 °C for 4 h at a rate of 5 °C / min to obtain hollow NiO nanocages with a wall thickness of 15 nm and an inner cavity diameter of 80 nm. 2.8 g of these nanocages were placed in the reaction chamber of an atomic layer deposition apparatus, and 99.99% argon gas was introduced at a flow rate of 50 mL / min as the carrier gas. The reaction was carried out at 180 °C using the "introduction" method. A cyclic deposition process was performed: 0.018 mol / L ruthenium trichloride solution for 10 s → argon purging for 20 s → 0.058 mol / L cobalt chloride solution for 10 s → argon purging for 20 s. The deposition was stopped when the Ru-Co loading reached 1.2% of the nanocage mass. Then, 99.99% hydrogen gas was introduced at a flow rate of 30 mL / min, and the nanocage was reduced at 280 °C for 2 h to obtain a Ru-Co-loaded nanocage with an inner active layer. Subsequently, a precursor solution containing 0.28 g ammonium tungstate, 1.4 g tetrabutyl titanate, 0.09 g niobium nitrate, and 48 mL anhydrous ethanol was prepared. 1.8 g of the above-mentioned nanocage with the inner active layer was added to the precursor solution, ultrasonically dispersed at 260 W for 20 min, transferred to a three-necked flask, stirred at 400 r / min at room temperature for 4 h, and then rotary evaporated at 80 °C and -0.09 MPa to remove ethanol to obtain a solid powder. Finally, the powder was calcined at 450 °C for 3 h at a rate of 3 °C / min to obtain the modified catalyst.In the synthesis of benzyl alcohol, benzaldehyde raw material is filtered to remove impurities with a particle size >1μm, and then added to a stirred tank with anhydrous ethanol at a mass ratio of 1:1.5. The mixture is stirred at 200 rpm at room temperature for 15 min, and preheated at 40℃ until the temperature fluctuation is ±1℃ to obtain a benzaldehyde-ethanol solution. A modified catalyst is filled into the reaction chamber of a microchannel reactor (filling volume is 60% of the effective volume). 99.99% nitrogen gas is introduced to 0.8 MPa to test the airtightness (pressure drop ≤0.02 MPa after 30 min). If qualified, the gas is switched to 0.5 MPa 99.99% hydrogen gas and activated at 120℃ for 2 h. Then, the benzaldehyde-ethanol solution and hydrogen gas are pumped to the gas-liquid mixing module at a volume ratio of 1:8 using a metering pump. A static mixer at 2000 rpm disperses the mixture for 30 s to form a gas-liquid emulsion system, which is then introduced into the reaction chamber. Catalytic hydrogenation was carried out at 0.2 MPa and 70℃ for 8 min. The resulting mixture was sent to a gas-liquid separator, where unreacted hydrogen was separated at 0.3 MPa and 40℃. The mixture was then pressurized to 1.5 MPa and recycled back to the reaction system. The liquid product was sent to a distillation column, where ethanol was separated at -0.09 MPa and 100℃ at the top of the column and recovered for use in raw material dissolution. Crude benzyl alcohol was obtained from the bottom of the column. The crude benzyl alcohol was then sent to a precision distillation column, where the vacuum was adjusted to -0.095 MPa and the reflux ratio was set to 5:1. The bottom of the column was heated to 95℃ at 2℃ / min and held at that temperature for 1 h (stirring at 150 r / min). The temperature was then increased to 115℃ at 1℃ / min and maintained with a temperature fluctuation of ±0.5℃. When the temperature at the top of the column stabilized at 82℃, the distillate was collected. After the purity was monitored online and found to be up to standard, the distillate was sent to the finished product storage tank. The residual impurities in the bottom of the column were sent back to the raw material pretreatment step. Example 2

[0043] In preparing the modified catalyst, 5.0 g of polystyrene microspheres with a particle size of 90 nm were added to 100 mL of deionized water in a stirrer and stirred at 310 r / min for 22 min to form a uniform suspension. 30 mL of 0.50 mol / L nickel nitrate solution was added dropwise, and stirring continued for 32 min. Then, 1.0 mol / L sodium hydroxide solution was added dropwise until the pH reached 9.1. After stirring for 1 h, the mixture was transferred to a reaction vessel and hydrothermally reacted at 125 °C for 6.2 h. After the reaction, the mixture was cooled to room temperature, the solid was collected by filtration, washed until the pH reached 7.0, dried at 80 °C for 12 h, and calcined at 500 °C for 4.2 h at a rate of 5 °C / min to obtain a cage with a wall thickness of 18 mm. Hollow NiO nanocages with an inner cavity diameter of 90 nm were prepared. 3.0 g of the nanocages were placed in an atomic layer deposition apparatus, and Ru-Co was deposited in a cycle at 180 °C with argon carrier gas at 50 mL / min until the loading reached 1.5%. The nanocages were then reduced with hydrogen at 290 °C for 2.2 h at 30 mL / min. A precursor solution containing 0.30 g ammonium tungstate, 1.5 g tetrabutyl titanate, 0.10 g niobium nitrate and 50 mL anhydrous ethanol was prepared. 2.0 g of the nanocages with the inner active layer were added, and the mixture was ultrasonically dispersed at 280 W for 25 min, stirred at 410 r / min for 4.2 h, and calcined at 450 °C for 3 h after rotary evaporation to remove ethanol. The modified catalyst was obtained. In the synthesis of benzyl alcohol, benzaldehyde is filtered and mixed with ethanol at a ratio of 1:1.5, stirred at 220 rpm for 18 min, and preheated at 42℃. The catalyst loading is 62%, and after passing the nitrogen leak test, it is activated with hydrogen at 0.5 MPa and 120℃ for 2 h. The reactants are fed with hydrogen at a ratio of 1:8, mixed at 2100 rpm for 40 s, and reacted at 1.3 MPa and 72℃ for 9 min. Hydrogen is separated and circulated at 0.4 MPa and 42℃, and ethanol is separated in a distillation column at -0.09 MPa and 102℃ at the top. The precision distillation column has a vacuum of -0.094 MPa and a reflux ratio of 5.1:1. The bottom of the column is temperature controlled in stages, and the top fraction at 85℃ is collected. Example 3

[0044] In preparing the modified catalyst, 5.5 g of polystyrene microspheres with a particle size of 100 nm were added to 110 mL of deionized water and stirred at 320 r / min for 25 min to form a uniform suspension. 32 mL of 0.55 mol / L nickel nitrate solution was added dropwise and stirring continued for 35 min. Then, 1.1 mol / L sodium hydroxide solution was added dropwise until the pH reached 9.2. After stirring for 1 h, the mixture was transferred to a reaction vessel and hydrothermally reacted at 130 °C for 6.5 h. The post-reaction treatment was the same as before: calcination at 500 °C for 4.5 h to obtain a cage with a wall thickness of 20 nm and an inner cavity diameter of [missing information]. Hollow NiO nanocages with a diameter of 100 nm were prepared. 3.2 g of the nanocages were placed in an atomic layer deposition apparatus and Ru-Co was cyclically deposited until the loading was 1.8%. The nanocages were then reduced with hydrogen at 300 °C for 2.5 h at a flow rate of 30 mL / min. A precursor solution containing 0.32 g ammonium tungstate, 1.6 g tetrabutyl titanate, 0.11 g niobium nitrate and 52 mL anhydrous ethanol was prepared. 2.2 g of the nanocages with the inner active layer were added, and the mixture was ultrasonically dispersed at 300 W for 30 min, stirred at 420 r / min for 4.5 h, and then calcined at 450 °C for 3 h after rotary evaporation to obtain the modified catalyst. In the synthesis of benzyl alcohol, benzaldehyde is filtered and mixed with ethanol at a ratio of 1:1.5, stirred at 250 rpm for 20 min, and preheated at 45 °C. The catalyst is filled to 65% and activated with hydrogen after leak testing. The reactants are fed with hydrogen at a ratio of 1:8, mixed at 2200 rpm for 40 s, and reacted at 1.5 MPa and 75 °C for 10 min. Hydrogen is separated and circulated at 0.5 MPa and 45 °C, and ethanol is separated in a distillation column. The precision distillation column has a vacuum of -0.092 MPa and a reflux ratio of 5.2:1. The temperature of the column bottom is controlled in stages, and the top fraction at 88 °C is collected. Example 4

[0045] In preparing the modified catalyst, 5.2 g of polystyrene microspheres with a particle size of 95 nm and 105 mL of deionized water were added to a stirrer and stirred at 315 r / min for 24 min to form a uniform suspension. 31 mL of 0.52 mol / L nickel nitrate solution was added dropwise, and stirring continued for 34 min. Then, 1.05 mol / L sodium hydroxide solution was added dropwise until the pH reached 9.1. After stirring for 1 h, the mixture was transferred to a reaction vessel and hydrothermally reacted at 128 °C for 6.4 h. The post-reaction treatment was the same as before: calcination at 500 °C for 4.3 h to obtain hollow Ni. O nanocages; 3.1 g of the nanocages were placed in an atomic layer deposition apparatus and Ru-Co was cyclically deposited until the loading was 1.6%, and reduced with hydrogen at 295 °C for 2.3 h at 30 mL / min; a precursor solution containing 0.31 g ammonium tungstate, 1.55 g tetrabutyl titanate, 0.105 g niobium nitrate and 51 mL anhydrous ethanol was prepared, and 2.1 g of nanocages with the inner active layer were added, ultrasonically dispersed at 290 W for 28 min, stirred at 415 r / min for 4.4 h, and calcined at 450 °C for 3 h after rotary evaporation to obtain the modified catalyst. In the synthesis of benzyl alcohol, benzaldehyde is filtered and mixed with ethanol at a ratio of 1:1.5, stirred at 240 rpm for 19 min, and preheated at 43 °C. The catalyst is filled to 63% and activated with hydrogen after leak testing. The reactants are fed with hydrogen at a ratio of 1:8, mixed at 2150 rpm for 35 s, and held at 1.4 MPa and 73 °C for 9.5 min. Hydrogen is separated and circulated at 0.45 MPa and 43 °C, and ethanol is separated in a distillation column. The precision distillation column has a vacuum of -0.093 MPa and a reflux ratio of 5.15:1. The temperature of the column bottom is controlled in stages, and the top fraction at 86 °C is collected.

[0046] To verify that the synthesized benzyl alcohol prepared in the embodiments of the present invention has good product selectivity and raw material conversion rate, the following experimental examples are used to illustrate the synthesized benzyl alcohol provided in the embodiments of the present invention.

[0047] Test case

[0048] The purpose of this experimental group is to investigate the effect of different component ratios on the synthesis of benzyl alcohol, and to test the benzaldehyde conversion rate, benzyl alcohol selectivity, benzyl alcohol product purity, and raw material recycling rate of the benzyl alcohol synthesized by this invention.

[0049] Experimental Objective: Experimental groups A, B, C, and D adopted the component ratios of the synthesized benzyl alcohol provided in Examples 1-4, respectively; the control group consisted of control groups A, B, C, D, E, and F, wherein:

[0050] Control group A

[0051] A commercially available Pd / C catalyst (5% Pd loading) was used. 10g of the catalyst, 100mL of benzaldehyde, and 150mL of anhydrous ethanol were added to a 500mL batch reactor. After sealing the reactor, nitrogen was purged three times, followed by hydrogen to 1.5MPa. The temperature was raised to 75℃, and the mixture was stirred (500r / min) for 2 hours. After the reaction was completed, the mixture was cooled to room temperature, the remaining hydrogen was released, the catalyst was removed by filtration, and the filtrate was sent to a distillation column. Ethanol was separated at 105℃ under normal pressure, and benzyl alcohol fraction was collected by distillation at 110℃ under reduced pressure (-0.08MPa). The residual impurities in the bottom of the column were directly discharged.

[0052] Control group B

[0053] In catalyst preparation, 3.0 g of NiO powder (50 nm particle size) was directly placed into the reaction chamber of an atomic layer deposition (ALD) apparatus. Argon gas (50 mL / min) was introduced, and deposition was carried out at 180 °C with only a 0.020 mol / L nickel chloride solution (without other metal precursors). The deposition was cyclically continued until the Ni loading reached 1.5%. Then, hydrogen gas (30 mL / min) was introduced for reduction at 290 °C for 2.2 h to obtain a catalyst with a single Ni active site (no hollow structure, no double active layer). The synthesis process of benzyl alcohol was the same as in Example 2: benzaldehyde was filtered and then reacted with ethanol at a ratio of 1: 1.5 Mixing (stirring at 220 r / min for 18 min), preheating at 42℃, catalyst loading at 62%, after passing nitrogen leak test, activation with 0.5 MPa hydrogen at 120℃ for 2 h, benzaldehyde-ethanol solution and hydrogen are fed at a volume ratio of 1:8, mixed at 2100 rpm for 40 s, reacted at 1.3 MPa and 72℃ for 9 min, hydrogen is separated and circulated at 0.4 MPa and 42℃, ethanol is separated in a distillation column at -0.09 MPa and 102℃ at the top, and purified in a precision distillation column at a vacuum of -0.094 MPa and a reflux ratio of 5.1:1.

[0054] Control group C

[0055] In preparing the catalyst, hollow NiO nanocages were prepared according to the method in Example 1. Atomic layer deposition was performed by passing only 0.018 mol / L ruthenium trichloride solution (without cobalt chloride solution) through the nanocage. The deposition was repeated until the Ru loading reached 1.2%. The subsequent construction of the external control layer was the same as in Example 1, and a single Ru active layer catalyst was obtained. The synthesis process of benzyl alcohol was the same as in Example 1.

[0056] Control group D

[0057] When preparing the catalyst, hollow NiO nanocages were prepared according to the method of Example 1 and loaded with Ru-Co inner active layer (loading amount 1.2%). The construction of the outer control layer was not carried out (i.e., the steps of precursor solution preparation, ultrasonic dispersion, calcination, etc. were omitted), and the nanocages loaded with inner active layer were directly used as catalysts. The synthesis process of benzyl alcohol was the same as that of Example 1.

[0058] Control group E

[0059] The preparation of the modified catalyst was exactly the same as in Example 1; the raw material pretreatment, catalyst loading and activation, continuous hydrogenation reaction, and product separation steps of benzyl alcohol synthesis were all the same as in Example 1. The only difference was that, in the purification stage, the trace impurities (benzaldehyde, toluene, etc.) remaining in the bottom of the precision distillation column were directly collected and treated as waste liquid, and were not sent back to the raw material pretreatment step.

[0060] control group F

[0061] When preparing the catalyst, polystyrene microsphere templates were not used. Instead, 2.8g of NiO powder (50nm particle size) was directly placed into an atomic layer deposition apparatus. The Ru-Co inner active layer (1.2% loading) was loaded according to the deposition parameters of Example 1. Then, the WO3-TiO2-Nb2O5 outer control layer was constructed according to the method of Example 1 to obtain a modified catalyst without hollow structure. The synthesis process of benzyl alcohol was the same as that of Example 1 (the raw material pretreatment, microchannel reaction parameters, and separation and purification steps were all the same).

[0062] Experimental methods: Based on the present invention, experiments were conducted to assess the benzaldehyde conversion rate, benzaldehyde selectivity, benzaldehyde product purity, and raw material recycling rate of benzyl alcohol. The specific experimental methods are as follows:

[0063] Benzaldehyde conversion rate: The conversion rate was calculated by detecting the benzaldehyde content before and after the reaction using gas chromatography (GC-2014 gas chromatograph, Shimadzu, Japan). The chromatographic conditions were as follows: HP-5 capillary column (30m × 0.32mm × 0.25μm), programmed temperature rise (initial temperature 60℃, hold for 2 min, increase to 180℃ at 10℃ / min, hold for 5 min), injection port temperature 200℃, and detector (FID) temperature 220℃. The carrier gas was nitrogen (99.999% purity), the flow rate was 1.0 mL / min, the injection volume was 1 μL, and the split ratio was 10:1. For detection, the benzaldehyde-ethanol solution before the reaction (referred to as sample 1) and the crude benzyl alcohol product after ethanol separation in step S1.4 (referred to as sample 2) were taken, filtered through a 0.22 μm organic phase filter membrane, and then subjected to gas chromatography analysis. The initial mass of benzaldehyde in sample 1 was calculated using the external standard method (a standard curve was plotted using benzaldehyde standard solutions of different concentrations). ) and the mass of residual benzaldehyde in sample 2 ( The formula for calculating the benzaldehyde conversion rate is: Benzaldehyde Conversion Rate (%) Each sample was tested in parallel three times, and the average value was taken as the final result.

[0064] Methanol selectivity: The content of benzyl alcohol and byproducts (toluene, cyclohexylethanol) in the reaction system was detected under the same gas chromatography conditions as described above to calculate the selectivity. The sample to be tested was the crude benzyl alcohol product after ethanol separation in step S1.4 (filtered through a 0.22 μm organic phase filter membrane). Standard curves for benzyl alcohol, toluene, and cyclohexylethanol were plotted using the external standard method, and the mass of benzyl alcohol produced in the crude benzyl alcohol product was calculated. ), mass of toluene produced ( ), the mass of cyclohexylmethanol produced ( Based on the molar mass of each substance (benzyl alcohol 108 g / mol, toluene 92 g / mol, cyclohexylethanol 114 g / mol), convert them to the corresponding amount of substance. , , The formula for calculating benzyl alcohol selectivity is: Benzyl alcohol selectivity (%) Each sample was tested in parallel three times, and the average value was taken as the final result.

[0065] Purity of benzyl alcohol: Dual verification was performed using gas chromatography (under the same chromatographic conditions as described above) combined with refractive index method (DR-A1 digital refractometer, Shanghai Yidian Physical Optical Instrument Co., Ltd.). During gas chromatography, the benzyl alcohol product collected in step S1.5 (referred to as sample 3) was filtered through a 0.22 μm organic phase filter membrane and injected. The mass fraction of benzyl alcohol in sample 3 was calculated using the external standard method (using a benzyl alcohol standard with a purity ≥99.9% to plot a standard curve). During refractive index testing, sample 3 was placed in a 25℃ constant temperature water bath for 30 minutes, and its refractive index (n) was measured. Based on the linear relationship between benzyl alcohol purity and refractive index (at 25℃, for every 1% increase in benzyl alcohol purity, the refractive index increases by approximately 0.00035; using the refractive index of 1.5392 for a 99.9% pure benzyl alcohol standard as a benchmark), the purity was calculated. The final purity of benzyl alcohol is the average of the results from the two methods, i.e.: Benzyl alcohol purity (%) Each sample was tested in parallel three times, and the average value was taken as the final result.

[0066] Raw material recycling rate: The raw material recycling rate is calculated by tracking the mass flow rate of benzaldehyde raw material and recycled materials. The specific method is as follows: During 10 hours of continuous and stable operation of the process, record the total mass of benzaldehyde initially added in step S1.1 ( The total mass of ethanol separated and recovered in step S1.4 ( (For subsequent raw material dissolution), residual impurities in the reboiler of step S1.5 (containing trace amounts of benzaldehyde) are returned to the total mass of step S1.1. The mass fraction of benzaldehyde in the impurities was determined by gas chromatography. Calculate the mass of circulating benzaldehyde. Simultaneously record the total mass of benzaldehyde consumed in step S1.5 to produce benzyl alcohol within 10 hours. Based on the total mass of benzyl alcohol and the molar conservation relationship between benzaldehyde and benzyl alcohol, the calculation is performed. =Total mass of benzyl alcohol finished product (106 represents the molar mass of benzaldehyde); the formula for calculating the raw material recycling rate is: Raw material recycling rate (%) (in Total consumption plus the mass of benzaldehyde from unreacted cycles. The total benzaldehyde mass (initial input + circulating return to the system) was monitored for 3 consecutive cycles (10 hours each), and the average value was taken as the final result.

[0067] Specific testing indicators are shown in Table 1.

[0068] Table 1 Detection indicators of each sample

[0069]

[0070] according to Figures 3-6 As shown in Table 2, the summary of the above comparative data is as follows:

[0071] From the perspective of benzaldehyde conversion rate, the conversion rates of the experimental groups AD all reached 98.2%-98.8%, which is higher than that of the control group A (92.5%) using a traditional batch reactor + Pd / C catalyst and the control group B (90.3%) using a catalyst without hollow structure + single Ni active site. Even compared with the control group C (94.6%) with a single Ru active layer, the control group D (95.3%) without an external control layer, and the control group F (96.2%) without hollow structure, it is still 3-8 percentage points higher. This indicates that the hollow NiO nanocage structure of the modified catalyst can provide a larger specific surface area and a more uniform distribution of active sites. Combined with the synergistic activation effect of the Ru-Co dual active layer, it effectively reduces the deactivation of active sites caused by reactant accumulation. At the same time, the efficient mass transfer characteristics of the microchannel reactor allow for sufficient contact between hydrogen and benzaldehyde, improving the raw material conversion efficiency. In contrast, the control group has a significantly lower conversion rate due to the lack of the mass transfer advantage of the hollow structure, the synergistic activation effect of the dual active layer, or the enhanced mixing ability of the microchannel.

[0072] Regarding the selectivity of benzyl alcohol, the selectivity of experimental group AD remained stable at 99.1%-99.4%, which was much higher than that of control group A (93.8%), control group B (91.5%), and also better than control group C (95.2%), control group D (94.8%), and control group F (97.3%). This was mainly due to the electronic effect and steric hindrance of the modified catalyst's external control layer (WO3-TiO2-Nb2O5). The external control layer anchors the aldehyde group in the benzaldehyde molecule and weakens the C=O bond energy, guiding the active hydrogen species generated in the inner active layer to bind to the C=O bond in an oriental manner, thus avoiding hydrogen attack on the benzene ring or the already generated benzyl alcohol. In contrast, the control groups had insufficient selective adsorption capacity due to the lack of an external control layer (control group D), a single active layer (control group C), or a lack of hollow structure (control group B, F), which easily triggered side reactions such as benzene ring hydrogenation and deep hydrogenation of benzyl alcohol, resulting in decreased selectivity. At the same time, the high-efficiency heat transfer characteristics of the microchannel reactor (temperature fluctuation ≤ ±1℃) avoided the aggravation of side reactions caused by local overheating, further enhancing the high selectivity.

[0073] Regarding the purity of benzyl alcohol, the purity of experimental group AD reached 99.6%-99.7%, which was higher than that of control group A (98.2%), control group B (97.8%), control group C (98.5%), control group D (98.6%), and control group F (99.0%). This was due to the low-vacuum segmented temperature control process in the purification stage. By controlling the vacuum degree (-0.095 to -0.092 MPa) and the segmented temperature rise of the tower bottom, the high-temperature decomposition of benzyl alcohol was reduced, and trace amounts of low-boiling point impurities were removed through sufficient contact between the packing layer and the reflux liquid. In contrast, the control groups used traditional distillation parameters (such as the vacuum degree of -0.08 MPa and atmospheric pressure separation of control group A) or lacked the inhibitory effect of modified catalysts on by-products, resulting in higher levels of residual toluene and cyclohexyl methanol impurities in the finished product, making it difficult to improve the purity.

[0074] Regarding the raw material recycling rate, the experimental group AD reached 95.8%-96.4%, which was higher than the control group E (88.7%) without recycling impurities and the control group A (82.3%) of the traditional batch process. This is because the present invention pressurizes the separated hydrogen back to the reaction system, recovers ethanol for raw material dissolution, and sends the residual impurities in the tower bottom back to the pretreatment step, realizing the recycling of materials throughout the entire process. In contrast, the control group E directly discharged tower bottom impurities, and the control group A had no recycling design, resulting in serious waste of raw materials. Even compared with the control groups B (90.1%), C (94.2%), D (94.5%), and F (93.6%), which had partial recycling but insufficient catalyst performance, the experimental group still improved the recycling rate by reducing the amount of impurities generated due to its higher conversion rate and selectivity.

[0075] In summary, by designing a hollow NiO nanocage-double active layer synergistic modification catalyst and combining it with a microchannel reactor to construct a complete and continuous process chain, the hollow structure of the modified catalyst provides a high specific surface area and uniform distribution of active sites. The Ru-Co inner active layer efficiently activates hydrogen to generate directional hydrogenation species, and the WO3-TiO2-Nb2O5 outer regulating layer precisely anchors the benzaldehyde aldehyde group and weakens the C=O bond energy. The combination of these three factors significantly reduces the occurrence of side reactions. The efficient mass transfer characteristics of the microchannel reactor enhance gas-liquid mixing and improve hydrogen utilization, while the efficient heat transfer characteristics precisely control the temperature to avoid deactivation of active sites. At the same time, the full-process material recycling design (hydrogen pressurization and reuse, ethanol recovery and dissolution, and impurity reflux reaction) reduces raw material waste.

[0076] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for the continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor, characterized in that, The raw materials include modified catalysts, anhydrous ethanol, and benzaldehyde, and also include the following process steps: S1.

1. Filter the benzaldehyde raw material through a filter to remove mechanical impurities with a particle size >1μm. Then, add it together with anhydrous ethanol into a mixing tank and stir to form a solution. Then, use a constant phase feed pump to deliver it to the preheating module for preheating. Reduce the benzaldehyde concentration by solvent dilution to obtain a benzaldehyde-ethanol solution. S1.

2. The modified catalyst is filled into the reaction chamber of the microchannel reactor, and then nitrogen is introduced to test the airtightness. After passing the test, hydrogen is introduced and activated at 0.5 MPa and 120℃ for 2 hours to form a catalytic system. S1.

3. Benzaldehyde-ethanol solution and hydrogen are delivered to the gas-liquid mixing module of the microchannel reactor at a volume ratio of 1:8 by a metering pump and stirred to form a uniform gas-liquid emulsion system. The system is then flowed into a reaction chamber with a modified catalyst for catalytic hydrogenation to obtain a mixture. S1.4 The mixture is fed into a gas-liquid separator to separate unreacted hydrogen. After being pressurized to 1.5 MPa by a compressor, it is recycled back to the reaction system. The liquid product at the bottom of the separator is then fed into a distillation column to separate ethanol. The ethanol is recovered and used to dissolve the raw materials. Crude benzyl alcohol is obtained from the bottom of the distillation column. S1.

5. The crude benzyl alcohol product is fed into a precision distillation column, and the vacuum degree is adjusted to -0.095 to -0.092 MPa and the reflux ratio is 5:1 to 5.2:

1. The column bottom is temperature controlled in stages. When the temperature at the top of the column is 82-88℃, the distillate is collected. The impurities in the column bottom are sent back for pretreatment, and finally the benzyl alcohol product is obtained. The modified catalyst includes the following preparation steps: S2.1 Add polystyrene microspheres and deionized water to a mixer and stir at 300-320 r / min for 20-25 min to form a uniform suspension; then add nickel nitrate solution dropwise and continue stirring for 30-35 min, followed by sodium hydroxide solution dropwise while monitoring the pH value until the solution pH is 9.0-9.2, and continue stirring for 1 h to obtain a mixture; transfer it to a reaction vessel, seal it, and place it in an oven for hydrothermal reaction at 120-130℃ for 6-6.5 h; After the reaction was completed, the reactor was removed and allowed to cool naturally to room temperature. The solid product was collected by filtration and washed repeatedly with deionized water until the pH of the washing solution reached 7.

0. The washed solid was then placed in an 80°C forced-air drying oven and dried for 12 hours. Finally, the dried solid was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min. The solid was then calcined at this temperature for 4-4.5 hours to completely remove the polystyrene template, resulting in hollow NiO nanocages with a cage wall thickness of 15-20 nm and an inner cavity diameter of 80-100 nm. S2.

2. Hollow NiO nanocages are placed in the reaction chamber of an atomic layer deposition apparatus and fixed. Next, ruthenium trichloride solution and cobalt chloride solution are prepared as precursors, and argon gas is used as the carrier gas. The carrier gas flow rate is adjusted to 50 mL / min. The deposition temperature in the reaction chamber is 180 °C. The apparatus is started to begin the deposition cycle. After deposition is completed, the carrier gas in the reaction chamber is switched to hydrogen gas. The hydrogen flow rate is adjusted to 30 mL / min. The temperature of the reaction chamber is then raised to 280-300 °C for reduction for 2-2.5 h to obtain hollow NiO nanocages with Ru-Co inner active layer. S2.3 First, prepare the precursor solution. Add the hollow NiO nanocages to the precursor solution and then place it in an ultrasonic cleaner. Disperse the mixture ultrasonically at 260-300W for 20-30 minutes. Then, transfer the mixture to a three-necked flask and place it on a magnetic stirrer. Stir at 400-420r / min at room temperature for 4-4.5 hours. Then, connect the three-necked flask to a rotary evaporator and remove the ethanol by rotary evaporation at 80℃ and -0.09MPa to obtain a solid powder. Then, place the solid powder in a muffle furnace and calcine it at 450℃ for 3 hours at a heating rate of 3℃ / min to fully transform the precursor into a WO3-TiO2 composite control layer. At the same time, Nb2O5 is uniformly doped, and finally, a hollow nanocage-double active layer synergistic modified catalyst is obtained.

2. The process for continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor according to claim 1, characterized in that, In step S2.1, the amount of polystyrene microspheres used is 4.5-5.5g, and the particle size is 80-100nm; the amount of deionized water used is 90-110mL; the nickel nitrate solution used is a nickel nitrate solution with a concentration of 0.45-0.55mol / L, and the amount used is 28-32mL; the sodium hydroxide solution used is a sodium hydroxide solution with a concentration of 0.9-1.1mol / L, and the amount used is 14-19mL. In step S2.2, the amount of hollow NiO nanocages used is 2.8-3.2g, the amount of ruthenium trichloride solution with a concentration of 0.018-0.022mol / L is 9-11mL, the amount of cobalt chloride solution with a concentration of 0.058-0.062mol / L is 9-11mL, and the purity of argon and hydrogen is 99.99%. In step S2.3, the amount of hollow NiO nanocages with Ru-Co inner active layer is 1.8-2.2g, and the amount of precursor solution is 48-52mL, wherein the precursor solution includes 0.28-0.32g ammonium tungstate, 1.4-1.6g tetrabutyl titanate, 0.09-0.11g niobium nitrate and 48-52mL anhydrous ethanol.

3. The process for continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor according to claim 1, characterized in that, In step S2.2, the atomic layer deposition equipment deposition cycle includes the following steps: First, ruthenium trichloride solution is introduced for 10 seconds, then purged with argon gas for 20 seconds, then cobalt chloride solution is introduced for 10 seconds, and then purged with argon gas for 20 seconds, thus forming a complete deposition cycle. The above deposition cycle was repeated, during which the Ru-Co alloy loading was monitored in real time by weighing until the loading reached 1.2%-1.8% of the mass of the hollow NiO nanocages, at which point deposition was stopped.

4. The process for continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor according to claim 2, characterized in that, In step S2.3, the preparation of the precursor solution includes the following steps: Take ammonium tungstate, tetrabutyl titanate and niobium nitrate, and add them together to anhydrous ethanol to obtain a mixture; Place the mixture on a magnetic stirrer and stir it at 300-350 r / min for 30-40 min to allow the solid raw materials to initially dissolve and mix. The mixture was then transferred to an ultrasonic cleaner and ultrasonically treated at 240-260W power for 15-20 minutes to break up the tiny solid particle agglomerates in the solution and to make the components evenly dispersed. Finally, the sonicated solution was returned to the magnetic stirrer and stirred at 250-300 r / min for 1-1.5 h to obtain a clear and homogeneous WO3-TiO2-Nb2O5 precursor solution.

5. The process for continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor according to claim 1, characterized in that, In step S1.1, the benzaldehyde raw material and anhydrous ethanol are mixed at a mass ratio of 1:1.5, and the mixture is stirred in a stirring tank at a speed of 200-250 r / min for 15-20 min at room temperature. The preheating module preheats the solution at 40-45℃ until the temperature fluctuation is within ±1℃.

6. The process for continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor according to claim 1, characterized in that, In step S1.2, the modified catalyst filling amount is 60%-65% of the effective volume of the reaction chamber, and the purity of nitrogen is 99.99%.

7. The process for continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor according to claim 1, characterized in that, In step S1.3, the gas-liquid mixing module is stirred and dispersed at high speed in a static mixer at 2000-2200 rpm for 30-40 seconds; the reaction chamber carries out catalytic hydrogenation reaction under the conditions of reaction pressure of 1.2-1.5 MPa, reaction temperature of 70-75℃, and residence time of 8-10 minutes.

8. The process for continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor according to claim 1, characterized in that, In step S1.4, the gas-liquid separator separates under conditions of 0.3-0.5 MPa and 40-45℃; the distillation column separates ethanol under conditions of -0.09 MPa vacuum and 100-105℃ at the top of the column.

9. The process for continuous catalytic hydrogenation synthesis of benzyl alcohol using a microchannel reactor according to claim 1, characterized in that, In step S1.5, the segmented temperature control includes the following steps: Turn on the heating system of the precision distillation column reboiler and slowly raise the temperature to 95℃, controlling the heating rate at 2℃ / min. Maintain the temperature at 95℃ for 1 hour, and continuously stir the column reboiler at a stirring speed of 150r / min to fully dissolve the trace solid impurities remaining in the crude benzyl alcohol. Then, the heating rate of the column bottom was adjusted to 1℃ / min, from 95℃ to 115℃. At the same time, the steam flow rate was observed through the steam flow meter at the top of the column and stabilized at 80-100mL / min. After the temperature reached 115℃, the temperature fluctuation of the column bottom was kept within ±0.5℃ to ensure that the benzyl alcohol in the crude benzyl alcohol was fully vaporized. The vaporized mixed steam moved up to the packing layer and came into contact with the low-temperature benzyl alcohol liquid refluxed at the top of the column. Low-boiling-point impurities were absorbed back to the column bottom, and high-purity benzyl alcohol vapor rose to the top of the column and was condensed into liquid fraction.

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