Solid base catalyst as well as preparation method and application thereof

Abstract

The invention discloses a solid base catalyst as well as a preparation method and application thereof. The preparation method of the solid base catalyst comprises the following steps: S1, mixing ZnCl2, Ca (NO3) 2.4 H2O and Al (NO3) 3.9 H2O according to a molar ratio of (0.3-2): 3: 1, and dissolving in water to obtain a mixed solution; s2, urea and the mixed solution are mixed and stirred and then subjected to a hydrothermal reaction, after the reaction is finished, cooling is conducted, precipitates are taken to be subjected to suction filtration and washed to be neutral, after surface moisture is removed, drying is conducted, then the precipitates are ground into powder, and a Zn-Ca-Al-LDH precursor is obtained; and S3, calcining the Zn-Ca-Al-LDH precursor at the temperature of 700 DEG C, so as to obtain the solid base catalyst. The solid base catalyst prepared according to the molar ratio of Zn to Ca to Al being 1: 3: 1 reacts with an acetaldehyde solution for 2 hours at 20 DEG C, the conversion rate of acetaldehyde reaches 87%, and the selectivity and yield of 3-hydroxybutyraldehyde are 73.4% and 63.85% respectively.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalysts, and more particularly relates to a solid base catalyst, a preparation method and application thereof. BACKGROUND

[0002] 1,3-Butanediol (1,3-BDO) is widely used in various industrial fields due to its high boiling point, low volatility, excellent water solubility, mild moisturizing property, good solubility for various organic components, and low biological toxicity. In the chemical industry, 1,3-BDO can be used as a monomer to generate alkyd resin and polyurethane coating, and can also be used as a plasticizer and modifier to improve the performance of high molecular materials. In the pharmaceutical industry, it can be used as a pharmaceutical intermediate to synthesize R,S-1,3-butanediol acetyl acetic acid diester and B-lactam antibiotics. In addition, in the cosmetics industry, about 35% of 1,3-BDO is used in moisturizing cream, skin toner, emulsion, shampoo and toothpaste, etc. Therefore, the research on 1,3-BDO has important scientific research value and application prospect.

[0003] Currently, there are three main processes for producing 1,3-BDO, namely acetaldehyde condensation hydrogenation, formaldehyde propylene condensation hydrolysis, and biological synthesis. The formaldehyde propylene condensation hydrolysis reaction product is complex, the yield is low, and the overall cost is high. The biological method is limited by the stability of the strain, and the energy consumption and cost are high. So far, the acetaldehyde condensation hydrogenation method is still the mainstream process. In this process, acetaldehyde undergoes aldol condensation reaction under alkaline conditions to generate 3-hydroxybutyraldehyde (3-HBA), and 3-HBA is converted into 1,3-BDO through catalytic hydrogenation reaction. Although this process is relatively mature, there are still obvious technical bottlenecks. The aldol condensation reaction is unstable, on the one hand, 3-HBA is easy to dehydrate to generate crotonaldehyde, and on the other hand, the 3-HBA generated by condensation will also react with acetaldehyde to generate 2,6-dimethyl-1,3-dioxane-4-ol (DDO) and other polymerization products, resulting in a complex composition of the reaction system.

[0004] Traditional acetaldehyde condensation is usually carried out in dilute alkaline solution. The research of acetaldehyde condensation to 3-hydroxybutyraldehyde shows that NaOH has the best catalytic activity at 5℃, but the energy consumption of low temperature restricts its industrial application. When the temperature rises to 30℃, Na2CO3 shows better temperature adaptability, and the selectivity is significantly improved from less than 10% to 50%. Solvent experiments show that water is the most suitable reaction medium. Pan Xia optimizes the acetaldehyde condensation process by using a micro-channel reactor, using NaOH and Na2CO3 composite catalyst at 20℃ for 7min, and the yield of 3-HBA reaches 35.15%, effectively solving the heat transfer problem in traditional reactors. Wuyanhui et al. research shows that the selectivity of acetaldehyde condensation catalyzed by strong base (NaOH) decreases significantly with reaction time, while weak base (Na2CO3) can maintain stable selectivity although the conversion rate is low. Overall, liquid alkali catalysts have good solubility and dispersibility. However, a proper amount of acid needs to be added to control the reaction progress during the reaction process, which leads to serious equipment corrosion, high salt content in wastewater, and difficulty in subsequent separation and purification, accompanied by a large amount of high-salt wastewater, which puts pressure on the environment. Moreover, liquid alkali catalysts are prone to deactivation and difficult to reuse, which restricts the economic and environmental friendliness of the process. SUMMARY

[0005] The present application is directed to the above problems, and provides a solid alkali catalyst, a preparation method and application thereof.

[0006] In order to achieve the above purpose, the present application is realized by the following technical scheme: The first aspect of the present application provides a preparation method of a solid alkali catalyst, comprising the following steps: S1. ZnCl2, Ca(NO3)2·4H2O and Al(NO3)3·9H2O are mixed and dissolved in water according to a molar ratio of (0.3-2):3:1 to obtain a mixed solution; S2. Urea and the mixed solution are mixed, stirred, and then subjected to hydrothermal reaction. After the reaction is completed, the precipitate is cooled, filtered and washed to neutral, and then dried after removing the surface moisture. The precipitate is ground into powder to obtain a Zn-Ca-Al-LDH precursor; S3. The Zn-Ca-Al-LDH precursor is calcined at 700℃ to obtain a solid alkali catalyst.

[0007] Preferably, the molar ratio of ZnCl2, Ca(NO3)2·4H2O and Al(NO3)3·9H2O is 1:3:1.

[0008] Preferably, the urea and the mixed solution are mixed according to a molar ratio of n(urea):n(NO3 - +Cl - )=1.5:1.

[0009] Preferably, the stirring condition is stirring at a speed of 50-1500 rpm for 2 hours at room temperature.

[0010] Preferably, the hydrothermal reaction condition is hydrothermal reaction at 120℃ for 12 hours.

[0011] Preferably, the heating rate of calcination is 5℃ / min, and the calcination time is 3 hours.

[0012] In the second aspect of the present application, a solid base catalyst prepared by any of the above methods is provided.

[0013] In the third aspect of the present application, the above solid base catalyst is used in an aldol condensation reaction, and the solid base catalyst is used as a catalyst.

[0014] Preferably, the above solid base catalyst is used to catalyze the aldol condensation of acetaldehyde to synthesize 1,3-butanediol.

[0015] Advantages of the present application (1) The present application uses a hydrothermal method to prepare a series of Zn-Ca-Al-O solid base catalysts. The precursor is obtained by hydrothermal reaction under the conditions of n(Zn):(Ca):(Al)=1:3:1, a precipitant according to (urea):n(NO3 - +Cl - )=1.5:1, hydrothermal reaction at 120℃ for 12 hours, and the Zn-Ca-Al-O solid base catalyst obtained by calcining the precursor at 700℃ for 3 hours has the best catalytic performance. The optimal reaction conditions for the catalyst to catalyze the aldol condensation of acetaldehyde to synthesize 3-hydroxybutyraldehyde are a reaction temperature of 20℃, a reaction time of 2 hours, and a catalyst:acetaldehyde solution ratio of 25:1. The conversion rate of acetaldehyde reaches 87%, and the selectivity and yield of 3-hydroxybutyraldehyde are 73.4% and 63.85%, respectively.

[0016] (2) As can be seen from the characterization of the catalyst, the Zn-Ca-Al-O solid base catalyst has ZnO and CaCO 3， with high crystallinity. This structure is the key to its weak basicity. The BET measurement shows that the BJH desorption cumulative specific surface area of the solid base catalyst is 29.4614m 2 / g, and the BJH desorption cumulative pore volume is 0.079494cm 3 / g. At the same time, the introduction of Zn changes the structure of the catalyst, making the catalyst present a porous stacking state. Through comparative experiments, it is found that this structure is more suitable for the condensation of acetaldehyde. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1XRD patterns of Ca-Al-O (a), Zn-Ca-Al-O3 (b), La-Zn-Ca-Al-O (c) catalysts and Zn-Ca-Al-LDH precursor (d) prepared in Example 3.

[0018] Figure 2 BET characterization curves of Ca-Al-O (a), Zn-Ca-Al-O3 (b), La-Zn-Ca-Al-O (c) catalysts and Zn-Ca-Al-LDH precursor (d) prepared in Example 3.

[0019] Figure 3 TG characterization curve of Zn-Ca-Al-LDH precursor prepared in Example 3.

[0020] Figure 4 SEM images of Ca-Al-O (a), Zn-Ca-Al-O3 (b), La-Zn-Ca-Al-O (c) catalysts and Zn-Ca-Al-LDH precursor (d) prepared in Example 3.

[0021] Figure 5 Effects of different catalyst addition amounts on conversion of acetaldehyde and selectivity and yield of 3-HBA.

[0022] Figure 6 Effects of different acetaldehyde aldol condensation reaction times on conversion of acetaldehyde and selectivity and yield of 3-HBA.

[0023] Figure 7 Effects of different acetaldehyde aldol condensation reaction temperatures on conversion of acetaldehyde and selectivity and yield of 3-HBA. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work should fall within the protection scope of the present application.

[0025] Unless otherwise defined, scientific and technical terms used in this text have meanings commonly understood by those skilled in the art. The experimental methods in the embodiments, unless otherwise specified, are conventional methods. The specific conditions not indicated in the embodiments are carried out according to conventional conditions or manufacturer's recommended conditions. The reagents or instruments used, unless otherwise indicated, are conventional products that can be obtained by purchase.

[0026] Example 1

[0027] A preparation method of a solid base catalyst, comprising the following steps: S1. ZnCl2, Ca(NO3)2.4H2O and Al(NO3)3.9H2O are mixed and dissolved in deionized water (water:salt=2:1) according to a molar ratio of Zn:Ca:Al=0.3:3:1 to obtain a mixed solution; S2. Urea and the mixed solution are poured into a hydrothermal synthesis reaction kettle according to a molar ratio of n(urea):n(NO3 - +Cl - )=1.5:1, stirred at room temperature for 2h, then transferred to an electric heating drying oven, and hydrothermally reacted at 120℃ for 12h, after the reaction, naturally cooled to room temperature, the precipitate is taken out for suction filtration, washed repeatedly with deionized water until the filtrate pH=7, then the surface moisture of the catalyst is removed with anhydrous ethanol, the obtained filter cake is dried at 85℃ for 10h, then ground into powder to obtain a Zn-Ca-Al-LDH precursor; S3. The Zn-Ca-Al-LDH precursor is loaded into a crucible and placed in a muffle furnace, heated to 700℃ at a heating rate of 5℃ / min for 3h to obtain a Zn-Ca-Al-O solid base catalyst, denoted as Zn-Ca-Al-O1.

[0028] Example 2

[0029] A preparation method of a solid base catalyst, comprising the following steps: S1. ZnCl2, Ca(NO3)2.4H2O and Al(NO3)3.9H2O are mixed and dissolved in deionized water (water:salt=2:1) according to a molar ratio of Zn:Ca:Al=0.5:3:1 to obtain a mixed solution; S2. Urea and the mixed solution are poured into a hydrothermal synthesis reaction kettle according to a molar ratio of n(urea):n(NO3 - +Cl - )=1.5:1, stirred at room temperature for 2h, then transferred to an electric heating drying oven, and hydrothermally reacted at 120℃ for 12h, after the reaction, naturally cooled to room temperature, the precipitate is taken out for suction filtration, washed repeatedly with deionized water until the filtrate pH=7, then the surface moisture of the catalyst is removed with anhydrous ethanol, the obtained filter cake is dried at 85℃ for 10h, then ground into powder to obtain a Zn-Ca-Al-LDH precursor; S3. The Zn-Ca-Al-LDH precursor is loaded into a crucible and placed in a muffle furnace, heated to 700℃ at a heating rate of 5℃ / min for 3h to obtain a Zn-Ca-Al-O solid base catalyst, denoted as Zn-Ca-Al-O2.

[0030] Example 3

[0031] A preparation method of a solid base catalyst, comprising the following steps: S1. ZnCl2, Ca(NO3)2.4H2O and Al(NO3)3.9H2O are mixed and dissolved in deionized water (water:salt=2:1) according to a molar ratio of Zn:Ca:Al=1:3:1 to obtain a mixed solution; S2. Urea and the mixed solution are poured into a hydrothermal synthesis reaction kettle according to a molar ratio of n(urea):n(NO3 - +Cl - )=1.5:1, stirred at room temperature for 2h, transferred to an electric heating drying oven, hydrothermally reacted at 120℃ for 12h, naturally cooled to room temperature after the reaction, the precipitate is taken out for suction filtration, washed repeatedly with deionized water until the filtrate pH=7, the surface moisture of the catalyst is removed with anhydrous ethanol, the obtained filter cake is dried at 85℃ for 10h, ground into powder to obtain a Zn-Ca-Al-LDH precursor; S3. The Zn-Ca-Al-LDH precursor is loaded into a crucible and placed in a muffle furnace, heated to 700℃ at a rate of 5℃ / min for 3h to obtain a Zn-Ca-Al-O solid base catalyst, denoted as Zn-Ca-Al-O3.

[0032] Comparative Example 1 A preparation method of a solid base catalyst, comprising the following steps: S1. Ca(NO3)2.4H2O and Al(NO3)3.9H2O are mixed and dissolved in deionized water (water:salt=2:1) according to a molar ratio of Ca:Al=3:1 to obtain a mixed solution; S2. Urea and the mixed solution are poured into a hydrothermal synthesis reaction kettle according to a molar ratio of n(urea):n(NO3 - )=1.5:1, stirred at room temperature for 2h, transferred to an electric heating drying oven, hydrothermally reacted at 120℃ for 12h, naturally cooled to room temperature after the reaction, the precipitate is taken out for suction filtration, washed repeatedly with deionized water until the filtrate pH=7, the surface moisture of the catalyst is removed with anhydrous ethanol, the obtained filter cake is dried at 85℃ for 10h, ground into powder to obtain a Ca-Al-LDH precursor; S3. The Ca-Al-LDH precursor is loaded into a crucible and placed in a muffle furnace, heated to 700℃ at a rate of 5℃ / min for 3h to obtain a Ca-Al-O solid base catalyst, denoted as Ca-Al-O.

[0033] Comparative Example 2 A preparation method of a solid base catalyst, comprising the following steps: S1. La(NO3)3·6H2O, ZnCl2, Ca(NO3)2·4H2O and Al(NO3)3·9H2O were mixed and dissolved in deionized water (water:salt = 2:1) according to La:Zn:Ca:Al = 0.6:1:3:1 to obtain a mixed solution; S2. Urea and the mixed solution were poured into a hydrothermal synthesis reaction kettle according to a molar ratio of n(urea):n(NO3 - )=1.5:1, stirred at room temperature for 2h, then transferred to an electric heating drying oven, hydrothermal reaction at 120℃ for 12h, after the reaction was completed, naturally cooled to room temperature, the precipitate was taken out and filtered, washed repeatedly with deionized water until the filtrate pH = 7, then the surface moisture of the catalyst was removed with anhydrous ethanol, the filter cake was dried at 85℃ for 10h, then ground into powder to obtain a La-Zn-Ca-Al-LDH precursor; S3. The La-Zn-Ca-Al-LDH precursor was loaded into a crucible and placed in a muffle furnace, heated to 700℃ at a rate of 5℃ / min for 3h to obtain a La-Zn-Ca-Al-O solid base catalyst, denoted as La-Zn-Ca-Al-O.

[0034] Comparative Example 3 A preparation method of a solid base catalyst, comprising the following steps: S1. ZnCl2, Ca(NO3)2·4H2O and Al(NO3)3·9H2O were mixed and dissolved in deionized water (water:salt = 2:1) according to a molar ratio of Zn:Ca:Al = 1:3:1 to obtain a mixed solution; S2. Urea and the mixed solution were poured into a hydrothermal synthesis reaction kettle according to a molar ratio of n(urea):n(NO3 - +Cl - )=1.5:1, stirred at room temperature for 2h, then transferred to an electric heating drying oven, hydrothermal reaction at 120℃ for 12h, after the reaction was completed, naturally cooled to room temperature, the precipitate was taken out and filtered, washed repeatedly with deionized water until the filtrate pH = 7, then the surface moisture of the catalyst was removed with anhydrous ethanol, the filter cake was dried at 85℃ for 10h, then ground into powder to obtain a Zn-Ca-Al-LDH precursor; S3. The Zn-Ca-Al-LDH precursor was loaded into a crucible and placed in a muffle furnace, heated to 600℃ at a rate of 5℃ / min for 3h to obtain a Zn-Ca-Al-O solid base catalyst, denoted as Zn-Ca-Al-O5.

[0035] Comparative Example 4 A preparation method of a solid base catalyst, comprising the following steps: S1. ZnCl2, Ca(NO3)2·4H2O and Al(NO3)3·9H2O were mixed and dissolved in deionized water (water: salt = 2:1) according to the molar ratio of Zn:Ca:Al = 1:3:1 to obtain a mixed solution; S2. Urea and the mixed solution were poured into a hydrothermal synthesis reactor according to the molar ratio of n(urea):n(NO3 - +Cl - )=1.5:1, stirred for 2h at room temperature, then transferred to an electric heating drying oven, and hydrothermally reacted at 120℃ for 12h. After the reaction, it was naturally cooled to room temperature, the precipitate was taken out and filtered, washed with deionized water until the filtrate pH = 7, then the surface water of the catalyst was removed with anhydrous ethanol, the obtained filter cake was dried at 85℃ for 10h, then ground into powder to obtain a Zn-Ca-Al-LDH precursor; S3. The Zn-Ca-Al-LDH precursor was loaded into a crucible and placed in a muffle furnace, and heated to 800℃ at a rate of 5℃ / min for 3h to obtain a Zn-Ca-Al-O solid base catalyst, denoted as Zn-Ca-Al-O6.

[0036] The solid base catalyst prepared above will be characterized and tested for catalytic activity respectively.

[0037] 1. Characterization of solid base catalyst 1.1 Powder X-ray diffraction analysis (XRD) The physical structure of the catalyst was analyzed by a D8 X-ray diffractometer (XRD) produced by Bruker Company, Germany, using CuKa radiation, working voltage 40kV, working current 40mA, scanning range 10~80°, scanning speed 0.2Sec / Step.

[0038] Figure 1 XRD patterns of Zn-Ca-Al-O1, Zn-Ca-Al-O2, Zn-Ca-Al-O3, Zn-Ca-Al-O4 solid base catalysts and Zn-Ca-Al-LDH precursor prepared in Example 3. From the XRD patterns, it can be seen that the Zn-Ca-Al-LDH precursor prepared in Example 3 has a typical layered double hydroxide structure, and the Zn-Ca-Al-O1, Zn-Ca-Al-O2, Zn-Ca-Al-O3, Zn-Ca-Al-O4 solid base catalysts have a typical spinel structure. Figure 1It can be seen that the XRD pattern of the Zn-Ca-Al-LDH precursor shows a broadened and low-intensity diffuse scattering signal, indicating that it is mainly composed of an amorphous layered hydrotalcite structure with few crystalline phases, providing a structural basis for the formation of weak to medium-alkaline sites in the subsequent catalyst. After calcination at 700℃, samples with different Zn:Ca:Al molar ratios all showed characteristic crystalline phase signals of CaCO3 and ZnO. The stable coexistence of these two phases, as related weak to medium-alkaline phases, is the core structural guarantee for the catalyst to possess weak to medium-alkaline properties. As the Zn component ratio increases from 0.3:3:1 to 2:3:1, the intensity of the ZnO diffraction peak gradually increases and the peak shape becomes sharper, indicating that the increase in Zn content can promote the formation of ZnO crystalline phase and improve crystallinity, thereby regulating the number and intensity of weak to medium-alkaline sites. The peaks of Al2O3 that do not appear in the figure are mainly highly dispersed in the crystalline phase in an amorphous state. This figure confirms that the catalyst after calcination is mainly composed of a composite crystalline phase of ZnO and CaCO3, which is the key to its weak to moderate alkalinity.

[0039] 1.2 Low-temperature N2 adsorption-desorption (BET) Specific surface area was determined using a BET (Beijing Electron Technology) ASAP2460 fully automated specific surface area and porosity analyzer from Micron Technology Corporation (USA) after nitrogen adsorption-desorption and degassing treatment at 120°C.

[0040] Figure 2 BET characterization curves for Ca-Al-O (a), Zn-Ca-Al-O3 (b), La-Zn-Ca-Al-O (c) solid base catalysts and the Zn-Ca-Al-LDH precursor (d) prepared in Example 3. Figure 2 The nitrogen adsorption-desorption isotherms shown in figures a~2c indicate that all three catalysts exhibit typical type IV isotherms with a significant hysteresis loop, suggesting that they possess mesoporous structural characteristics. BET characterization results show that the Zn-Ca-Al-O3 solid base catalyst has the largest BET specific surface area, at 21.7820 m². 2 / g, slightly higher than 21.5334m for Ca-Al-O solid base catalysts. 2 / g, and significantly greater than 10.4323m for La-Zn-Ca-All-O solid base catalyst. 2 The concentration of 20.6216 m² / g indicates that it can provide more active sites, which is beneficial to improving reaction kinetics. Further t-plot analysis showed that the Zn-Ca-Al-O solid base catalyst has an external specific surface area of ​​20.6216 m² / g. 2 / g, with a micropore area of ​​only 1.1604m². 2 The / g indicates that its pore system is predominantly mesoporous, which facilitates the diffusion and transport of reactants and products. Furthermore, the cumulative BJH adsorption and desorption surface areas of this catalyst are 24.2623 m². 2 / g and 29.4614m2 / g, and the average pore size was 14.5494 nm, which were better than those of the other two catalysts, indicating that the pore structure was more conducive to the mass transfer process, which could effectively reduce the internal diffusion resistance and improve the reaction selectivity. In summary, the Zn-Ca-Al-O solid base catalyst had higher specific surface area, suitable pore structure, and excellent surface accessibility, and showed better catalytic potential in the acetaldehyde condensation reaction.

[0041] From Figure 2 b and 2d, it can be seen that calcination treatment has a key regulating effect on the microstructure and catalytic performance of the material. The uncalcined sample Zn-Ca-Al-LDH precursor showed a complete mesoporous-microporous composite system, with a BET specific surface area of 67.3974 m 2 / g, an average pore size of about 5.26 nm, and a total pore volume of 0.088742 cm 3 / g. After calcination at 700°C, the material underwent layer collapse and guest species removal, resulting in a decrease in the BET specific surface area to 21.7820 m 2 / g, a decrease in the t-Plot micropore area to 1.1604 m 2 / g, and a decrease in the BJH adsorption and desorption cumulative surface area to 24.2623 m 2 / g and 29.4614 m 2 / g, respectively. However, this process significantly exposed the Zn, Ca, Al, and other metal active sites, while the average pore size increased to 14.5494 nm, making the calcined sample perform much better than the uncalcined sample in terms of reaction conversion rate.

[0042] 1.3 Thermogravimetric analysis (TG) The TG-DTA8121 thermogravimetric differential thermal analyzer from Rigaku was used for analysis, with a temperature increase rate of 10°C / min from room temperature to 800°C.

[0043] Figure 3 TG characterization curve of the Zn-Ca-Al-LDH precursor prepared in Example 3. From Figure 3It can be seen that Zn-Ca-Al hydrotalcite-like shows a continuous mass loss in the range of 25-800℃, which is mainly attributed to its step-by-step thermal decomposition process: first, the physical adsorbed water and interlayer crystallization water are removed, then the layer plate hydroxyl and carbonate are decomposed to release H2O and CO2. When the calcination temperature reaches 700℃, the sample is converted into a composite oxide mainly composed of CaCO3, ZnO and amorphous CaO. At this time, the surface of the catalyst is mainly composed of medium and weak basic sites, which shows the best selectivity in the condensation reaction of acetaldehyde. After continuing to heat to 800℃, the sample is further converted into a strong basic calcium oxide-based solid base. Although the strength of the basic site reaches the maximum, it is easy to cause side reactions such as over-condensation, resulting in a decrease in its catalytic performance. Therefore, the appropriate calcination temperature is balanced between the formation of moderate basic sites and the stability of the composite structure, which plays a key role in obtaining a high-selectivity acetaldehyde condensation catalyst.

[0044] 1.4 Field emission scanning electron microscope (SEM) The morphology of the catalyst was observed by a JSM-6490LV high-performance scanning electron microscope (SEM) produced by JEOL Company, and the voltage used was 5 kV.

[0045] Figure 4 SEM images of Ca-Al-O (a), Zn-Ca-Al-O3 (b), La-Zn-Ca-Al-O (c) solid base catalysts and Zn-Ca-Al-LDH precursor (d) prepared in Example 3. From Figure 4 It can be seen from a that the Ca-Al-O solid base catalyst shows a crystal stacking microstructure, which belongs to a fibrous catalyst with uniform morphology. From Figure 4 It can be seen from b that with the introduction of Zn, the catalyst shows a porous stacking state, and small particles are aggregated on the surface of the catalyst, and the disorder is better. From Figure 4 It can be seen from c that the addition of La makes the catalyst morphology not regular, and the particle size distribution is uneven, which is also the main reason for the decrease of the specific surface area. Figure 4 d comparison Figure 4 It can be seen from b that the catalyst before calcination is mainly a thin-layer distributed microstructure, and the calcination process significantly refines the catalyst particles, greatly improves the dispersion, and tends to be clear and regular in morphology. This also makes it expose more basic sites and thus improve the conversion rate of acetaldehyde.

[0046] 2. Catalyst activity test 2.1 Effect of different catalysts on acetaldehyde aldol condensation The solid base catalysts prepared in Examples 1-4 and Comparative Examples 1-4 were tested for activity using acetaldehyde as the reactant. 0.4 g of the catalyst and 15 g of an acetaldehyde aqueous solution with a concentration of 66.7% were placed in a 100 mL flask, and the reaction was carried out in a water bath at a constant temperature of 17°C for 2 h. After the reaction was completed, a gas chromatograph (GC9790H OV-1701 capillary column 30 m) equipped with a flame ionization detector was used for analysis. The reactants and products in the reaction mixture were analyzed quantitatively by normalization. The sample should be diluted before testing to make the test results more accurate. The acetaldehyde conversion rate, 3-hydroxybutyraldehyde selectivity, and 3-hydroxybutyraldehyde yield were calculated according to formulas (1), (2), and (3) as follows: (1) (2) (3) In formulas (1)-(2), W 0 represents the amount of acetaldehyde feed; W 1 represents the amount of acetaldehyde outflow; W 2 represents the amount of 3-HBA outflow.

[0047] Table 1. Test results of acetaldehyde conversion rate and 3-HBA selectivity and yield Catalyst Conversion of acetaldehyde 3-HBA selectivity 3-HBA yield Zn-Ca-Al-O1 80% 66% 52.8% Zn-Ca-Al-O2 71% 60% 42.6% Zn-Ca-Al-O3 87% 61% 53.07% Zn-Ca-Al-O4 83% 54% 44.82% Ca-Al-O 92% 42% 38.64% La-Zn-Ca-Al-O 78% 36% 28.08% Zn-Ca-Al-O5 5% 61% 3.05% Zn-Ca-Al-O6 98% 11% 10.78% Table 1 is the test results of acetaldehyde conversion rate and 3-HBA selectivity and yield of the solid base catalysts prepared in Examples 1-4 and Comparative Examples 1-4. The experimental results show that the yield of 3-HBA in the presence of the Zn-Ca-Al-O catalysts prepared in Examples 1-4 is significantly higher than that in the presence of the solid base catalysts prepared in Comparative Examples 1-4.

[0048] When Ca:Al=3:1, compared with Ca-Al-O without the introduction of Zn element, the selectivity and yield of 3-HBA are significantly improved in the presence of Zn-Ca-Al-O1, Zn-Ca-Al-O2, Zn-Ca-Al-O3, or Zn-Ca-Al-O4, indicating that the introduction of Zn element can significantly improve the selectivity of 3-HBA, thereby achieving the purpose of improving the yield of 3-HBA. When Zn:Ca:Al=1:3:1, compared with La-Zn-Ca-Al-O with the introduction of La element, the selectivity and yield of 3-HBA are significantly improved in the presence of Zn-Ca-Al-O3, indicating that the introduction of La element significantly reduces the selectivity of 3-HBA, thereby leading to a decrease in the yield of 3-HBA.

[0049] The calcination temperature of the catalyst has a decisive influence on the phase structure and surface basic sites of the catalyst, thereby regulating the catalytic performance of acetaldehyde in the aldol condensation reaction to prepare 3-hydroxybutyraldehyde (3-HBA).

[0050] Comparing the Zn-Ca-Al-O3, Zn-Ca-Al-O5 and Zn-Ca-Al-O6 solid base catalysts prepared at different calcination temperatures, the active phase of Zn-Ca-Al-O3 prepared at 700 ℃ was the best, which made the conversion of acetaldehyde reach 87% and achieved high selectivity of 3-HBA; when the temperature increased to 800 ℃, although the conversion increased to 98%, the excessive condensation caused by excessive basicity led to a significant decrease in the selectivity of 3-HBA, so 700 ℃ was the optimal condition for considering activity and selectivity.

[0051] 2.2 Effect of reaction conditions on acetaldehyde aldol condensation According to the experimental method provided in section 2.1, with Zn-Ca-Al-O3 as the catalyst, the effects of catalyst dosage, reaction time and reaction temperature on acetaldehyde aldol condensation were investigated by controlling the variable experiment. Except for the single factor investigated, the other reaction factors were the same as those in section 2.1.

[0052] The conversion of acetaldehyde and the selectivity and yield of 3-HBA under the action of Zn-Ca-Al-O3 when the catalyst dosage was 0.1 g, 0.2 g, 0.3 g, 0.4 g and 0.5 g were investigated respectively, and the results are shown in Figure 5 and Table 2.

[0053] Table 2 Effect of catalyst dosage on the conversion of acetaldehyde and the selectivity and yield of 3-HBA Zn-Ca-Al-O3 mass Conversion of acetaldehyde 3-HBA selectivity 3-HBA yield 0.1g 52% 55% 28.6% 0.2g 76% 45% 34.2% 0.3g 83% 49% 40.7% 0.4g 87% 61% 53.07% 0.5g 86% 41% 35.3% From Figure 5 and Table 2, it can be seen that with the increase of catalyst dosage, 3-HBA reached a peak at 0.4 g, and further increasing the catalyst dosage led to a decrease in catalyst yield, which was mainly due to the increase of the total surface area of the solid base catalyst with the increase of the catalyst dosage, which increased the active sites and accelerated the occurrence of condensation side reactions.

[0054] The conversion of acetaldehyde and the selectivity and yield of 3-HBA under the action of Zn-Ca-Al-O3 when the reaction time was 2 h, 3 h, 4 h, 5 h and 6 h were investigated respectively, and the results are shown in Figure 6 and Table 3.

[0055] Table 3 Effect of reaction time on the conversion of acetaldehyde and the selectivity and yield of 3-HBA Reaction time Conversion of acetaldehyde 3-HBA selectivity 3-HBA yield 2h 87% 61% 53.07% 3h 89.9% 58% 52.14% 4h 90% 56.9% 51.2% 5h 90% 58.3% 52.5% 6h 90.4% 56% 50.62% From Figure 6 and Table 3, it can be seen that the appropriate reaction time was 2 h, and further prolonging the reaction time led to a slight decrease in the yield, which was due to the further condensation of acetaldehyde and 3-HBA to form trimers and DDO, etc.

[0056] The conversion rate of acetaldehyde, as well as the selectivity and yield of 3-HBA, under the action of Zn-Ca-Al-O3 at reaction temperatures of 5℃, 10℃, 15℃, and 20℃ were investigated. The results are as follows: Figure 7 As shown in Table 4.

[0057] Table 3. Effects of reaction temperature on acetaldehyde conversion, selectivity, and yield of 3-HBA. Reaction temperature Conversion of acetaldehyde 3-HBA selectivity 3-HBA yield 5℃ 81% 59% 47.79% 10℃ 81% 58% 46.98% 15℃ 88% 61% 53.68% 20℃ 87% 73.4% 63.85% Depend on Figure 7 As shown in Table 4, the selectivity of 3-HBA and the conversion rate of acetaldehyde both increase with increasing temperature. The yield of 3-HBA reaches its maximum of 63.85% at a reaction temperature of 20℃. Above 20℃, liquid-phase catalysis is no longer suitable due to the low boiling point of acetaldehyde. Therefore, considering the above, the optimal reaction conditions for the condensation of acetaldehyde to 3-HBA using the Zn-Ca-Al-O solid base catalyst are: catalyst dosage of 0.4 g, reaction time of 2 h, and reaction temperature of 20℃.

[0058] 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 method for preparing a solid base catalyst, characterized in that, Includes the following steps: S1. Mix ZnCl2, Ca(NO3)2·4H2O and Al(NO3)3·9H2O in water at a molar ratio of (0.3~2):3:1 to obtain a mixed solution; S2. Mix urea and the mixed solution, stir and carry out hydrothermal reaction. After the reaction is completed, cool, take the precipitate, filter and wash until neutral, remove surface moisture, dry, and grind into powder to obtain Zn-Ca-Al-LDH precursor. S3. The Zn-Ca-Al-LDH precursor was calcined at 700℃ to obtain a solid base catalyst.

2. The method for preparing the solid base catalyst according to claim 1, characterized in that, The molar ratio of ZnCl2, Ca(NO3)2·4H2O and Al(NO3)3·9H2O is 1:3:

1.

3. The method for preparing the solid base catalyst according to claim 1, characterized in that, Urea and the mixed solution are in the order of n(urea):n(NO3) - +Cl - They were mixed in a molar ratio of 1.5:

1.

4. The method for preparing the solid base catalyst according to claim 1, characterized in that, The stirring conditions were 50-1500 rpm at room temperature for 2 hours.

5. The method for preparing the solid base catalyst according to claim 1, characterized in that, The hydrothermal reaction conditions were 120℃ for 12 hours.

6. The method for preparing the solid base catalyst according to claim 1, characterized in that, The calcination heating rate was 5℃ / min, and the calcination time was 3h.

7. A solid base catalyst prepared by the method according to any one of claims 1 to 6.

8. The application of the solid base catalyst according to claim 7 in the aldol condensation reaction, characterized in that, Solid base catalysts are used as reaction catalysts.

9. The application of the solid base catalyst according to claim 8 in the aldol condensation reaction, characterized in that, It is used to catalyze the aldol condensation of acetaldehyde to synthesize 1,3-butanediol.

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