A high-efficiency catalyst for preparing citronellal by selective reduction of citral and preparation method thereof

Abstract

The invention discloses a catalyst for preparing citronellal by selective reduction of citral and a preparation method thereof. A magnesium oxide carrier is obtained by calcining a magnesium salt at high temperature, a palladium precursor is uniformly loaded on magnesium oxide by adsorption, palladium is reduced with sodium borohydride, potassium borohydride or sodium formate, and then a hydrophobic hydrogenation catalyst is obtained by modification with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane. The catalyst prepared in this way has high catalytic activity and selectivity for the reaction of preparing citronellal by selective reduction of citral. The catalyst active components of the present invention are highly dispersed, highly active, and have a selectivity of ≥98%, and the catalyst cost is low, and has a high industrial application value.

Description

Technical Field

[0001] The invention belongs to the field of organic chemistry and relates to a high-efficiency catalyst for preparing citronellal by selectively reducing citral and a preparation method thereof. Background Art

[0002] Citronellal is an important flavoring agent with a fresh, green citrus-like, slightly woody aroma. It can be used as a fixative, coordinator and modifier. It is widely used in edible flavors, citrus and cherry flavors, and is also used to prepare low-grade soap flavors. Citronellal has the special aroma of vanilla beans and is widely used in the food, flavoring and cosmetics industries. In addition, citronellal is also a raw material for preparing flavors such as hydroxycitronellal, menthone, isopulegol and menthol.

[0003] Citronellal comes from two sources: natural extraction and chemical synthesis. Naturally extracted citronellal is subject to changes in natural conditions, resulting in large fluctuations in its yield and quality, which cannot meet the market's stability requirements. Synthetic citronellal can avoid the above situation. The main synthesis routes include: (1) using β-pinene as a raw material and performing multiple steps such as pyrolysis and chlorination to obtain it. The β-pinene used in this route also comes from natural extracts, and its supply is subject to natural conditions. In addition, the synthesis process is complex, the yield of citronellal is low, and there are more three wastes; (2) using citral as a raw material to hydrogenate citronellal. The citronellal obtained by this route has a pure aroma and is the mainstream synthesis route. However, considering the special structure of citral, it is technically very challenging to obtain citronellal by hydrogenation with a high yield.

[0004] CN1234385A discloses a method for preparing citronellal by selective liquid phase hydrogenation of citral in the presence of powdered rhodium and / or palladium catalysts and in the presence of organic bases. The highest selectivity of citronellal in this method is 94%. However, this method cannot realize the application of catalyst Pd / C. The catalyst loses its activity after one use, and its activity cannot be restored by washing the catalyst with a solvent. CN110961154A adds rare earth and metal oxides to the palladium catalyst, and adds nitrogen heterocyclic additives to coordinate with CO generated during the reaction to reduce the absorption of CO by Pd and thus reduce the activity of the catalyst. The activity and selectivity of the 4wt% Pd / LaH3 catalyst did not change significantly after 10 applications. Although the activity of this type of catalyst is relatively stable, the activity is relatively low and it needs to react at 70-160°C.

[0005] The new synthesis patent CN108794314A discloses a method for synthesizing citronellal by hydrogenation of citral, using 7% palladium-molybdenum catalyst (containing 98% palladium and 2% molybdenum) as raw material, anhydrous ethanol as solvent, diethanolamine as co-catalyst, 130°C, 1Mpa for 55 minutes, and the yield of citronellal is only 89%.

[0006] Citral is generally hydrogenated and reduced to produce citronellal under alkaline conditions. However, under alkaline conditions, when the temperature is high, citral and citronellal are prone to undergo aldol condensation side reactions, which reduces the yield. Moreover, the high reaction temperature and high energy consumption do not conform to the concept of green environmental protection and run counter to the "dual carbon" goal. In order to overcome the problems existing in the above processes and successfully achieve the "dual carbon" goal, it is very necessary to develop a highly active and selective catalyst for the selective hydrogenation of citral to produce citronellal. Summary of the invention

[0007] In view of the problems existing in the above processes, the present invention aims to develop a highly active and selective catalyst for selective reduction of citral to prepare citronellal. Under the action of the catalyst, the reaction of selective reduction of citral to prepare citronellal is carried out at relatively low temperature and pressure, and high-content citronellal can be obtained efficiently.

[0008] The technical solution of the present invention is: the present invention first provides a hydrogenation catalyst.

[0009] The hydrogenation catalyst provided by the present invention is prepared by a method comprising the following steps: calcining a magnesium salt to obtain a mesoporous magnesium oxide sheet, then loading a palladium precursor onto a magnesium oxide carrier by adsorption, reducing with a reducing agent, and then modifying with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane to obtain a hydrogenation catalyst.

[0010] The magnesium salt is selected from at least one of magnesium nitrate hexahydrate, magnesium chloride, and magnesium carbonate;

[0011] The calcination temperature may be 450-550°C, and the calcination time may be 4h-6h; specifically, calcination may be performed at 550°C for 4h; calcination may be performed at 500°C for 5h;

[0012] The palladium precursor is selected from at least one of palladium acetate, palladium chloride, chloropalladic acid, palladium acetylacetonate, and palladium nitrate;

[0013] The palladium loading is 0.5-5%;

[0014] The reducing agent may specifically be one or more of sodium borohydride, potassium borohydride or sodium formate;

[0015] The molar ratio of the amount of the reducing agent added to the palladium is 2-10:1;

[0016] The reduction temperature is 0-85°C and the time is 1-3h.

[0017] The modification operation is: impregnation with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane ethanol solution, suction filtration, and vacuum drying to obtain a hydrogenation catalyst;

[0018] Wherein, the mass ratio of 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane to the mesoporous magnesium oxide sheet can be 2-10:1, specifically 2:1;

[0019] The mass concentration of 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane in the 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane ethanol solution is 1-5%.

[0020] The modification treatment was carried out at 25°C for 24 h.

[0021] The application of the above hydrogenation catalyst in the selective reduction of citral to prepare citronellal also falls within the protection scope of the present invention.

[0022] The invention also provides a method for preparing citronellal by hydrogenating citral.

[0023] The method for preparing citronellal by hydrogenating citral provided by the present invention comprises the following steps: under the action of the above-mentioned hydrogenation catalyst and alkaline water conditions, selectively hydrogenating citral to obtain citronellal.

[0024] Wherein, the amount of the hydrogenation catalyst is 0.5-4wt% of the weight of citral;

[0025] The amount of alkaline water added is 10-25% of the mass of citral, wherein the alkaline water is a sodium hydroxide aqueous solution with a mass concentration of 1%-10%;

[0026] The reaction temperature of the hydrogenation reaction is 20-50°C.

[0027] The reaction pressure of the hydrogenation reaction is 1-3.5 MPa, preferably 1.5-2.5 MPa.

[0028] The invention obtains a magnesium oxide carrier by calcining a magnesium salt at high temperature, uniformly loads a palladium precursor onto the magnesium oxide by adsorption, reduces the palladium by sodium borohydride, and then obtains a hydrophobic hydrogenation catalyst by modification with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane. The catalyst prepared by the method has high catalytic activity and selectivity for the reaction of selectively reducing citral to prepare citronellal. The catalyst active components of the catalyst of the invention are highly dispersed, highly active, and have a selectivity of ≥98%, and the catalyst cost is low, and has high industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the TEM image of the mesoporous magnesium oxide sheet prepared in Example 1 of the present invention.

[0030] Figure 2 This is a TEM image of catalyst A-1 prepared in Example 1 of the present invention.

[0031] Figure 3 This is a TEM image of catalyst B-1 prepared in Example 2 of the present invention.

[0032] Figure 4 This is a TEM image of catalyst C-1 prepared in Example 3 of the present invention.

[0033] Figure 5 This is a TEM image of catalyst D-1 prepared in Example 3 of the present invention.

[0034] Figure 6 It represents the contact angle between the catalyst CatA prepared in Example 1 of the present invention and water.

[0035] Figure 7 It represents the contact angle between the catalyst CatB prepared in Example 2 of the present invention and water.

[0036] Figure 8 It represents the contact angle between the catalyst CatC prepared in Example 3 of the present invention and water.

[0037] Fig. 9 It represents the contact angle between the catalyst CatD prepared in Example 4 of the present invention and water. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with specific embodiments, and the examples provided are only for illustrating the present invention, rather than for limiting the scope of the present invention. The examples provided below can be used as a guide for further improvements by those of ordinary skill in the art, and do not constitute a limitation of the present invention in any way.

[0039] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels.

[0040] The content and purity of the citral and citronellal reaction solution in the present invention are detected by gas chromatography.

[0041] The amount of the hydrogenation catalyst is 0.5-4wt% of the weight of citral; the reaction temperature of the hydrogenation reaction is 20-50°C, and the reaction pressure of the hydrogenation reaction is 1-3.5Mpa, preferably 1.5-2.5Mpa.

[0042] Example 1

[0043] Magnesium nitrate hexahydrate was calcined at 550° C. for 4 h and then naturally cooled to obtain a mesoporous magnesium oxide sheet carrier 1. Figure 1 TEM image of the prepared mesoporous magnesium oxide sheet.

[0044] 5g of carrier 1 was added to 500g of anhydrous ethanol and ultrasonicated for 0.5h, which was recorded as A. 0.32g of palladium acetate was dissolved in 320g of acetonitrile, which was recorded as B. 0.5g of sodium borohydride was dissolved in 75g of anhydrous ethanol, which was recorded as C. B was slowly added to A under magnetic stirring and stirred at 0℃ for 2h. Then, C was slowly added to the above mixture under nitrogen protection. After the addition, it was continued to stir at 0℃ for 2h so that the palladium was fully reduced. After that, it was filtered and washed with anhydrous deionized water and anhydrous ethanol, and dried at 50℃ under vacuum for 10h to obtain catalyst A-1 ( Figure 2 3g of catalyst A-1 was dispersed in 300g of 2wt% 1H,1H,2H,2H-perfluorooctyltriethoxysilane ethanol solution and treated at 25°C for 24h. Afterwards, it was filtered and washed with anhydrous deionized water and anhydrous ethanol, and dried at 50°C under vacuum for 10h to obtain CatA.

[0045] Figure 6 It represents the contact angle between the prepared catalyst CatA and water.

[0046] Example 2

[0047] Magnesium nitrate hexahydrate was calcined at 500° C. for 5 h and then cooled naturally to obtain carrier 2. The remaining conditions were the same as those in Example 1 to obtain CatB.

[0048] Figure 3 This is the TEM image of the prepared catalyst B-1.

[0049] Figure 7 It represents the contact angle between the prepared catalyst CatB and water.

[0050] Example 3

[0051] 5g of carrier 2 was added to 500g of anhydrous ethanol and ultrasonicated for 0.5h, which was recorded as A. 0.43g of palladium acetate was dissolved in 430g of acetonitrile and recorded as B. 0.67g of sodium borohydride was dissolved in 75g of anhydrous ethanol and recorded as C. B was slowly added to A under magnetic stirring and stirred at 0℃ for 2h. Then, C was slowly added to the above mixture under nitrogen protection. After the addition, it was continued to stir at 0℃ for 2h so that the palladium was fully reduced. After that, it was filtered and washed with anhydrous deionized water and anhydrous ethanol, and dried at 50℃ under vacuum for 10h to obtain catalyst C-1. Take catalyst C-13g and disperse it in 300g4wt% 1H, 1H, 2H, 2H-perfluorooctyl triethoxysilane ethanol solution and treat it at 25℃ for 24h. After that, it was filtered and washed with anhydrous deionized water and anhydrous ethanol, and dried at 50℃ under vacuum for 10h to obtain CatC.

[0052] Figure 4 This is the TEM image of the prepared catalyst C-1.

[0053] Figure 8 It represents the contact angle between the prepared catalyst CatC and water.

[0054] Example 4

[0055] 5g of carrier 1 was added to 500g of anhydrous ethanol and ultrasonicated for 0.5h, which was recorded as A. 0.50g of palladium nitrate was dissolved in 250g of toluene, which was recorded as B. 0.57g of sodium borohydride was dissolved in 75g of anhydrous ethanol, which was recorded as C. B was slowly added to A under magnetic stirring and stirred at 0℃ for 2h. Then, C was slowly added to the above mixture under nitrogen protection. After the addition, it was continued to stir at 0℃ for 2h so that the palladium was fully reduced. After that, it was filtered and washed with anhydrous deionized water and anhydrous ethanol, and dried at 50℃ under vacuum for 10h to obtain catalyst D-1. Take 3g of catalyst D-1 and disperse it in 300g of 4wt% 1H, 1H, 2H, 2H-perfluorooctyl triethoxysilane ethanol solution and treat it at 25℃ for 24h. After that, it was filtered and washed with anhydrous deionized water and anhydrous ethanol, and dried at 50℃ under vacuum for 10h to obtain CatD.

[0056] Figure 5 This is the TEM image of the prepared catalyst D-1.

[0057] Fig. 9 It represents the contact angle between the prepared catalyst CatD and water.

[0058] Example 5

[0059] 0.4g of the above catalyst (catalytic citral) was hydrogenated and selectively reduced to citronellal. The specific hydrogenation experiment process is: 0.4g of the above catalyst, 40g of citral, and 8g of alkaline water were added to a 500mL high-pressure reactor with magnetic stirring in sequence and sealed. The air in the reactor was replaced by low-pressure hydrogen, and the initial pressure, reaction temperature, reaction, and stirring speed were given at 500 rpm. The specific results are as follows:

[0060] Table 1 Catalyst evaluation results

[0061]

[0062] a The catalyst is a fresh catalyst;

[0063] b The catalyst was applied five times;

[0064] c Alkaline water: Aqueous solution of sodium hydroxide with a mass concentration of 1%.

[0065] Comparative Example 1

[0066] 0.4g of commercial Pd / C catalyst with a loading of 5% was selectively reduced to citronellal by hydrogenation under alkaline conditions: 0.4g of commercial Pd / C catalyst with a loading of 5%, 40g of citral, and sodium hydroxide aqueous solution were added to a 500mL high-pressure reactor with magnetic stirring in sequence and sealed. The air in the reactor was replaced with low-pressure hydrogen, and the initial pressure, reaction temperature, reaction, and stirring speed were given at 500r / min. The specific results are shown in Table 2.

[0067] Comparative Example 2

[0068] 0.4g of commercial Pd / C catalyst with a loading of 5% was selectively reduced to citronellal by hydrogenation under the conditions of a microemulsion formed by water and citral: 0.4g of commercial Pd / C catalyst with a loading of 5%, 40g of citral, and water were added to a 500mL high-pressure reactor with magnetic stirring in sequence and sealed. The air in the reactor was replaced by low-pressure hydrogen, and the initial pressure, reaction temperature, reaction, and stirring speed were given at 500r / min. The specific results are shown in Table 2.

[0069] Comparative Example 3

[0070] 0.4g CatA, 40g citral, and 8g water were added to a 500mL high-pressure reactor with magnetic stirring in sequence and sealed. The air in the reactor was replaced by low-pressure hydrogen, and the initial pressure, reaction temperature, reaction, stirring speed were set at 500r / min. Citral was selectively reduced to citronellal by hydrogenation. The specific results are shown in Table 2

[0071] Table 2 Comparative evaluation results

[0072]

[0073] a The catalyst is a fresh catalyst;

[0074] b The additive is a sodium hydroxide solution with a concentration of 1%;

[0075] c The additive is deionized water.

[0076] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, and without the need to carry out unnecessary experimental conditions, the present invention can be implemented in a wide range under equivalent parameters, concentrations and conditions. Although the present invention provides specific embodiments, it should be understood that the present invention can be further improved. In a word, according to the principles of the present invention, the application is intended to include any changes, uses or improvements to the present invention, including departure from the disclosed scope in the application, and changes made with conventional techniques known in the art.

Claims

1. A method for preparing a hydrogenation catalyst for selective reduction of citral to prepare citronellal, comprising the following steps: calcining a magnesium salt to obtain a mesoporous magnesium oxide sheet, then loading a palladium precursor onto a magnesium oxide carrier by adsorption, reducing it with a reducing agent, and then modifying it with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane to obtain a hydrogenation catalyst; The reducing agent is one or more of sodium borohydride, potassium borohydride or sodium formate.

2. The method according to claim 1, characterized in that: The magnesium salt is selected from at least one of magnesium nitrate hexahydrate, magnesium chloride, and magnesium carbonate; The calcination temperature is 450-550° C. and the calcination time is 4h-6h.

3. The method according to claim 1, characterized in that: The palladium precursor is selected from at least one of palladium acetate, palladium chloride, chloropalladic acid, palladium acetylacetonate, and palladium nitrate; The palladium loading is 0.5-5%.

4. The method according to claim 1, characterized in that: The modification operation is: impregnation with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane ethanol solution, suction filtration, and vacuum drying to obtain a hydrogenation catalyst; The mass ratio of 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane to mesoporous magnesium oxide sheet is 2-10:1; The mass concentration of 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane in the ethanol solution of 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane is 1-5%; The modification treatment was carried out at 25°C for 24 h.

5. The method according to claim 1, characterized in that: The molar ratio of the amount of the reducing agent added to the palladium is 2-10:1; The reduction temperature is 0-85°C and the time is 1-3h.

6. A hydrogenation catalyst for selective reduction of citral to prepare citronellal, prepared by the method according to any one of claims 1 to 5.

7. Use of the hydrogenation catalyst for selective reduction of citral to prepare citronellal according to claim 6 in the reaction of selective reduction of citral to prepare citronellal.

8. A method for preparing citronellal by hydrogenating citral, comprising the following steps: subjecting citral to a selective hydrogenation reaction under alkaline water conditions under the action of the hydrogenation catalyst as claimed in claim 6 to obtain citronellal; The alkaline water is a sodium hydroxide aqueous solution with a mass concentration of 1%-10%; The amount of alkaline water added is 10-25% of the mass of citral; The reaction temperature of the selective hydrogenation reaction is 20-50°C; The reaction pressure of the selective hydrogenation reaction is 1-3.5 MPa.

9. The method according to claim 8, characterized in that: The amount of the hydrogenation catalyst used is 0.5-4wt% of the weight of citral.

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