Bromide ion intercalated magnesium-aluminum layered hydroxide as well as preparation method and application thereof

Abstract

The invention relates to the technical field of preparation of propylene carbonate, and discloses a bromide ion intercalated magnesium-aluminum layered hydroxide as well as a preparation method and application thereof. The method comprises the following steps: (1) providing an aqueous solution containing an aluminum source and a magnesium source, mixing the aqueous solution containing the aluminum source and the magnesium source with an alkali source, aging the obtained mixed solution, and then separating out a solid phase; and (2) mixing the solid phase obtained in the step (1) with an aqueous solution containing a bromine source, aging the obtained turbid liquid, and then carrying out solid-liquid separation. The bromide ion intercalated magnesium-aluminum layered hydroxide prepared by the method provided by the invention can effectively catalyze ring opening of epoxypropane, can obtain obviously higher propylene carbonate yield under mild conditions, cannot be inactivated after being used as a catalyst for many times, and has higher stability.

Description

Technical Field

[0001] The present invention relates to the technical field of propylene carbonate preparation, and particularly relates to a bromide ion intercalated magnesium-aluminum layered hydroxide, a preparation method thereof, and an application thereof. Background Art

[0002] As a carbon source with wide sources, non-toxicity, and recyclability, the resource utilization of CO2 can produce high-value chemicals. However, the carbon atom in CO2 is in the highest oxidation state of carbon, its molecular structure is very stable, with very high thermodynamic stability and kinetic inertness. Utilizing CO2 to synthesize high-value chemicals often requires a relatively high energy input. Based on the selection of epoxides (highly reactive substrates), the energy requirement can be reduced, and the limitations in terms of thermodynamics and kinetics of the inert CO2 molecule can be overcome. Therefore, the preparation of cyclic carbonates by the ring-opening addition of CO2 and epoxides has the characteristics of simple process, low cost, wide raw material sources, and environmental friendliness.

[0003] Propylene carbonate is a colorless, non-corrosive, low-toxic, high-boiling-point, low-vapor-pressure polar aprotic liquid, and is often used as an electrolyte for lithium batteries, a polymer precursor (such as polycarbonate), a cosmetic, and an intermediate for pharmaceutical and chemical products (such as dialkyl carbonates, ethylene glycol, carbamates, pyrimidines, purines). In addition, propylene carbonate has the property of biodegradability and is an emerging green solvent with a broad market.

[0004] The earliest method for synthesizing propylene carbonate was the phosgene method. However, due to the toxicity of phosgene and the serious environmental pollution caused by the synthesis method, it has been gradually eliminated by the market. The existing main synthesis methods include the CO2-propylene glycol method, the urea alcoholysis method, the transesterification method, the CO2-propylene oxide ring-opening addition method, etc. The CO2-propylene glycol method has the disadvantages of more by-products and poor atom economy. The reaction of urea with glycol can also produce propylene carbonate, but its single-pass conversion rate is not high and the operating conditions are relatively harsh. The synthesis of propylene carbonate using chloropropanol as a raw material usually produces by-products such as halogenated salts, which corrode the equipment. The ring-opening addition of carbon dioxide and propylene oxide to prepare propylene carbonate is the most widely studied method and the main method for industrial production of propylene carbonate. The atom economy of this route is 100%, and it has good economic value.

[0005] At present, ionic liquids, metal oxides, metal Schiff base complexes, metal organic framework materials, etc. are widely used in this system. For example, patent application CN112827510A discloses a porous composite material, which complexes Schiff base with transition metal to make the catalyst have bimetallic catalytic activity, but the synthesis process of the catalyst is complicated, and a co-catalyst needs to be added during the reaction to increase the yield of propylene carbonate. Patent application CN114433228A discloses a core-shell polymer ionic liquid, which has high preparation cost and strong toxicity. Patent application CN106831583B discloses an N,N-dialkyl substituted pyrazole ionic liquid, which has harsh synthesis conditions and is a homogeneous catalyst, and it is difficult to separate from the reaction system after the reaction is completed.

[0006] In summary, immobilized catalysts still have problems such as complex synthesis process, difficulty in regulating active sites, and loss of active sites during long-term use, which leads to decreased catalyst stability. Therefore, it is an urgent technical problem to find a heterogeneous catalyst with simple and environmentally friendly preparation process, high activity, high stability and easy product separation. Summary of the invention

[0007] The purpose of the present invention is to overcome the problem that the active sites of the immobilized catalyst for synthesizing propylene carbonate in the prior art are difficult to control and the active sites are lost during long-term use, resulting in a decrease in the stability of the catalyst, and to provide a bromide-intercalated magnesium aluminum layered hydroxide and a preparation method and application thereof. The bromide-intercalated magnesium aluminum layered hydroxide prepared according to the method of the present invention retains the pore structure of the magnesium aluminum double hydroxide layer, and inserts water-soluble nucleophilic anions (i.e., bromide ions) into the interlayer of the layered hydroxide through ion exchange, and directionally controls their placement; a propylene carbonate yield of >90% can be achieved under solvent-free and auxiliary agent-free conditions, and the catalyst will not be deactivated after multiple uses, and has strong stability.

[0008] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a bromide ion intercalated magnesium aluminum layered hydroxide, the method comprising the following steps:

[0009] (1) providing an aqueous solution containing an aluminum source and a magnesium source, mixing the aqueous solution containing the aluminum source and the magnesium source with an alkali source, aging the obtained mixed solution, and then separating a solid phase;

[0010] (2) The solid phase obtained in step (1) is mixed with an aqueous solution containing a bromine source, the obtained suspension is aged, and then the solid-liquid separation is performed.

[0011] Preferably, in step (1), in the aqueous solution containing an aluminum source and a magnesium source, the magnesium source is Mg 2+ Al 3+The molar content ratio is (1 - 20):1, preferably (2 - 12.5):1.

[0012] Preferably, in the aqueous solution containing the aluminum source and the magnesium source, the concentration of the aluminum source in terms of Al 3+ is 0.1 - 5 mol / L, preferably 0.1 - 2 mol / L.

[0013] Preferably, in the aqueous solution containing the aluminum source and the magnesium source, the concentration of the magnesium source in terms of Mg 2+ is 0.1 - 10 mol / L, preferably 0.1 - 3 mol / L.

[0014] Preferably, the aluminum source is at least one of aluminum nitrate, aluminum acetate, aluminum carbonate, and aluminum chloride.

[0015] Preferably, the magnesium source is at least one of magnesium nitrate, magnesium acetate, magnesium carbonate, and magnesium chloride.

[0016] Preferably, in step (1), the amount of the base source is such that the pH value of the mixed solution is 7 - 13, preferably 9 - 11.

[0017] Preferably, the base source is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, ammonium bicarbonate, urea, ammonia water, n - butylamine, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium bromide.

[0018] Preferably, in step (1), the aging conditions include: the temperature is higher than 25°C and lower than 200°C, preferably higher than 25°C and lower than 100°C; the time is 10 - 36 h, preferably 15 - 30 h.

[0019] Preferably, in step (2), in the aqueous solution containing the bromine source, the concentration of the bromine source in terms of Br - is 0.1 - 10 mol / L, preferably 0.1 - 2 mol / L.

[0020] Preferably, the bromine source is at least one of potassium bromide, calcium bromide, and zinc bromide.

[0021] Preferably, in step (2), the mass ratio of the bromine source to the solid phase is (10 - 70):1.

[0022] Preferably, in step (2), the pH value of the suspension is 5 - 13, preferably 5 - 10.

[0023] Preferably, in step (2), the aging conditions include: the temperature is higher than 25°C and lower than 200°C, preferably higher than 25°C and lower than 100°C; the time is 10 - 36 h, preferably 15 - 30 h.

[0024] The second aspect of the present invention provides a bromide ion-intercalated magnesium-aluminum layered hydroxide prepared by the above method.

[0025] The third aspect of the present invention provides a method for preparing propylene carbonate, which includes: reacting propylene oxide and carbon dioxide in the presence of a catalyst, wherein the catalyst is the bromide ion-intercalated magnesium-aluminum layered hydroxide described above.

[0026] Through the above technical solution, the bromide ion-intercalated magnesium-aluminum layered hydroxide prepared by the method according to the present invention has a typical layered hydroxide structure. Compared with the existing immobilized catalysts, the bromide ion-intercalated magnesium-aluminum layered hydroxide not only retains the excellent pore structure of the layered hydroxide structure and the adsorption capacity for carbon dioxide, but also allows the nucleophilic anion (i.e., bromide ion) to be inserted into the interlayer of the layered hydroxide to directionally regulate its location, thereby being able to effectively catalyze the ring-opening of propylene oxide and remaining inactive even after being used as a catalyst multiple times, with strong stability; moreover, when used for synthesizing propylene carbonate, compared with traditional heterogeneous catalysts, in the reaction process using the bromide ion-intercalated magnesium-aluminum layered hydroxide of the present invention as a catalyst, no additional cocatalyst needs to be added, and a propylene carbonate yield of more than 90% can be achieved under mild conditions.

[0027] In addition, in the preparation method of the bromide ion-intercalated magnesium-aluminum layered hydroxide of the present invention, the raw materials used are all commercially available, inexpensive and easily obtained; and there is no need for calcination and crystallization at high temperature during the preparation process, significantly reducing energy consumption, greatly reducing the synthesis time and shortening the synthesis steps, without waste gas emission, and the process is green and environmentally friendly. Description of the Drawings

[0028] Figure 1 is the XRD spectrum of the bromide ion-intercalated magnesium-aluminum layered hydroxide prepared in Example 1;

[0029] Figure 2 is the nitrogen physical adsorption graph of the bromide ion-intercalated magnesium-aluminum layered hydroxide prepared in Example 1;

[0030] Figure 3 is the pore size distribution graph of the bromide ion-intercalated magnesium-aluminum layered hydroxide prepared in Example 1;

[0031] Figure 4 is the TEM graph of the bromide ion-intercalated magnesium-aluminum layered hydroxide prepared in Example 1. Detailed Embodiments

[0032] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0033] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0034] The preparation method of the bromide ion-intercalated magnesium-aluminum layered hydroxide according to the present invention comprises the following steps:

[0035] (1) Providing an aqueous solution containing an aluminum source and a magnesium source, mixing the aqueous solution containing the aluminum source and the magnesium source with an alkali source, aging the obtained mixed solution, and then separating out the solid phase;

[0036] (2) Mixing the solid phase obtained in step (1) with an aqueous solution containing a bromine source, aging the obtained suspension, and then performing solid-liquid separation.

[0037] The bromide ion-intercalated magnesium-aluminum layered hydroxide prepared by the method according to the present invention not only retains the excellent pore structure of the layered hydroxide structure and the carbon dioxide adsorption capacity, but also enables the nucleophilic anion (i.e., bromide ion) to be inserted into the interlayer of the layered hydroxide to directionally regulate its location, so that it can effectively catalyze the ring-opening of propylene oxide and still not deactivate after being used as a catalyst multiple times, with strong stability.

[0038] In step (1), in the aqueous solution containing the aluminum source and the magnesium source, the molar content ratio of the magnesium source calculated as Mg 2+ to the aluminum source calculated as Al 3+ is (1 - 20):1, preferably (2 - 12.5):1.

[0039] In step (1), in the aqueous solution containing the aluminum source and the magnesium source, the concentration of the aluminum source calculated as Al 3+ can be 0.1 - 5 mol / L, preferably 0.1 - 2 mol / L.

[0040] In step (1), in the aqueous solution containing the aluminum source and the magnesium source, the concentration of the magnesium source calculated as Mg 2+ can be 0.1 - 10 mol / L, preferably 0.1 - 3 mol / L.

[0041] In some embodiments, the process of providing an aqueous solution containing an aluminum source and a magnesium source in step (1) includes: stirring and mixing the aluminum source, the magnesium source, and water in proportion to form a homogeneous solution.

[0042] In the present invention, the aluminum source may be selected from water-soluble or water-dissolvable aluminum-containing compounds. Preferably, the aluminum source is at least one of aluminum nitrate, aluminum acetate, aluminum carbonate, and aluminum chloride. Further preferably, the aluminum source is aluminum nitrate and / or aluminum chloride.

[0043] In the present invention, the aluminum chloride is preferably AlCl3·9H2O.

[0044] In the present invention, the magnesium source may be selected from water-soluble or water-dissolvable magnesium-containing compounds. Preferably, the magnesium source is at least one of magnesium nitrate, magnesium acetate, magnesium carbonate, and magnesium chloride. Further preferably, the magnesium source is magnesium nitrate and / or magnesium chloride.

[0045] In the present invention, the magnesium chloride is preferably MgCl2·6H2O.

[0046] In step (1), the amount of the base source is such that the pH value of the mixed solution is 7-13, preferably 9-11.

[0047] In the present invention, the base source may be selected from water-soluble or water-dissolvable basic compounds. Specifically, the base source may be selected from at least one of inorganic base sources and organic base sources. Preferably, the base source is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, ammonium bicarbonate, urea, ammonia water, n-butylamine, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium bromide. Most preferably, the base source is sodium hydroxide.

[0048] In the present invention, the base source is used in the form of an aqueous solution. In the aqueous solution of the base source, the concentration of the base source may be 0.5-5 mol / L, preferably 1-3 mol / L.

[0049] In some embodiments, the process of mixing the aqueous solution containing the aluminum source and the magnesium source with the base source in step (1) includes: rapidly dropping the aqueous solution of the base source into the aqueous solution containing the aluminum source and the magnesium source, stirring and mixing to form a homogeneous mixed solution.

[0050] In step (1), the conditions for aging may include: the temperature is higher than 25°C and lower than 200°C, preferably higher than 25°C and lower than 100°C; the time is 10 - 36 h, preferably 15 - 30 h, and more preferably 23 - 28 h. In the method of the present invention, by controlling the temperature and time of aging within the above ranges, a typical layered hydroxide structure can be ensured in the finally prepared product.

[0051] In step (1), the aging can be static aging or dynamic aging, preferably dynamic aging.

[0052] In step (1), the process of separating the solid phase may include: sequentially performing solid-liquid separation, washing, and drying on the aged mixture. The operation mode of solid-liquid separation can be centrifugal separation or suction filtration separation, preferably suction filtration separation. The process of suction filtration separation can be implemented according to the conventional methods and conditions in the art. The process of washing can be alternately washing with deionized water and ethanol several times (such as 2 - 5 times). The drying temperature is preferably lower than the decomposition temperature of the solid phase. Specifically, the drying temperature can be 40 - 120°C, preferably 70 - 90°C.

[0053] In step (2), in the aqueous solution containing the bromine source, the concentration of the bromine source in terms of Br - can be 0.1 - 10 mol / L, preferably 0.1 - 2 mol / L.

[0054] In step (2), the mass ratio of the bromine source to the solid phase can be (10 - 70):1, preferably (15 - 50):1, and more preferably (20 - 40):1.

[0055] In the present invention, the bromine source is selected from water-soluble or bromine-containing compounds that can dissolve in water. In a preferred case, the bromine source is at least one of potassium bromide, calcium bromide, and zinc bromide. Most preferably, the bromine source is potassium bromide.

[0056] In step (2), the specific operation of mixing the solid phase with the aqueous solution containing the bromine source can be: under stirring, adding the solid phase obtained in step (1) to the aqueous solution containing the bromine source to form a suspension.

[0057] In step (2), in a preferred case, the pH value of the suspension is controlled to be 5 - 13, preferably 5 - 10. By adjusting the pH value of the suspension, bromide ions can be promoted to insert into the interlayer of the layered hydroxide, and their deposition can be directionally regulated. Furthermore, when the prepared bromide ion-intercalated magnesium-aluminum layered hydroxide is used as a catalyst, it has strong stability.

[0058] In step (2), the aging conditions may include: the temperature is higher than 25 °C and lower than 200 °C, preferably higher than 25 °C and lower than 100 °C; the time is 10 - 36 h, preferably 15 - 30 h, more preferably 23 - 28 h. In the method of the present invention, by controlling the aging temperature and time within the above ranges, bromide ions can be promoted to insert into the interlayers of the layered hydroxide, and their deposition can be directionally regulated. Furthermore, when the prepared bromide ion-intercalated magnesium-aluminum layered hydroxide is used as a catalyst, it has strong stability.

[0059] In step (2), the aging can be static aging or dynamic aging, preferably dynamic aging.

[0060] In step (2), the process of solid-liquid separation may include: sequentially performing solid-liquid separation, washing, and drying on the aged mixture. The operation mode of solid-liquid separation can be centrifugal separation or suction filtration separation, preferably suction filtration separation. The process of the suction filtration separation can be implemented according to the conventional methods and conditions in the art. The process of the washing can be washing with deionized water. The drying temperature is preferably lower than the decomposition temperature of the prepared bromide ion-intercalated magnesium-aluminum layered hydroxide. Specifically, the drying temperature can be 40 - 120 °C, preferably 70 - 90 °C.

[0061] The present invention also provides a bromide ion-intercalated magnesium-aluminum layered hydroxide prepared by the above method. The bromide ion-intercalated magnesium-aluminum layered hydroxide has a typical layered hydroxide structure. Compared with the existing immobilized catalysts, the bromide ion-intercalated magnesium-aluminum layered hydroxide not only retains the excellent pore structure of the layered hydroxide structure and the adsorption capacity for carbon dioxide, but also enables nucleophilic anions (i.e., bromide ions) to insert into the interlayers of the layered hydroxide, and their deposition can be directionally regulated. Thus, it can effectively catalyze the ring-opening of propylene oxide and will not deactivate even after being used as a catalyst multiple times, with strong stability.

[0062] The present invention also provides a method for preparing propylene carbonate, which includes: reacting propylene oxide and carbon dioxide in the presence of a catalyst, wherein the catalyst is the bromide ion-intercalated magnesium-aluminum layered hydroxide described above. According to the method for preparing propylene carbonate of the present invention, the bromide ion-intercalated magnesium-aluminum layered hydroxide as a catalyst can effectively catalyze the ring-opening of propylene oxide and will not deactivate even after being used multiple times, with strong stability; moreover, compared with traditional heterogeneous catalysts, in the reaction process using the bromide ion-intercalated magnesium-aluminum layered hydroxide of the present invention as a catalyst, no additional cocatalyst needs to be added, and a propylene carbonate yield of more than 90% can be achieved under mild conditions.

[0063] The bromide ion-intercalated magnesium-aluminum layered hydroxide, its preparation method and application according to the present invention will be further described below by way of examples. The examples are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0064] In the following examples, the experimental methods, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, can all be obtained commercially.

[0065] Example 1

[0066] (1) Weigh 6.099 g of MgCl2·6H2O (0.03 mol) and 2.39 g of AlCl3·9H2O (0.008 mol), dissolve them in 30 ml of solution and stir for more than 10 min. Dropwise add 2 mol / L NaOH solution to the stirred mixed solution, and adjust the pH = 10 ± 0.5. Continue to stir for 30 min, age at 60 °C for 24 h, filter by suction, wash alternately with deionized water and ethanol 3 times, and then dry overnight under vacuum at 80 °C to obtain the precursor Cl-LDH.

[0067] (2) Dissolve 0.2 mol of KBr in 300 ml of water and stir until the solid is evenly dispersed. Then add 0.6 g of the precursor Cl-LDH, adjust the pH value of the obtained suspension to 8, age at 60 °C for 24 h under stirring, filter by suction, wash, and then dry overnight under vacuum at 80 °C to obtain the bromide ion-intercalated magnesium-aluminum layered hydroxide Cat-1.

[0068] The XRD pattern of the bromide ion-intercalated magnesium-aluminum layered hydroxide Cat-1 is as Figure 1 shown, its nitrogen physical adsorption diagram is as Figure 2 shown, its pore size distribution diagram is as Figure 3 shown, and its TEM diagram is as Figure 4 shown. It can be seen from the figures that the bromide ion-intercalated magnesium-aluminum layered hydroxide has crystal planes at (003), (006), (012), (015), (018), and (100), which is consistent with the crystal plane distribution of the traditional Mg / Al layered hydroxide, indicating that the incorporation of Br does not affect the crystal structure of the magnesium-aluminum layered hydroxide; the N2 physical adsorption-desorption isotherm diagram of the bromide ion-intercalated magnesium-aluminum layered hydroxide is a typical type IV isotherm; it can be seen from the figures that the bromide ion-intercalated magnesium-aluminum layered hydroxide belongs to mesoporous materials; it can be seen from the TEM diagram that the bromide ion-intercalated magnesium-aluminum layered hydroxide is in the form of irregular stacking of lamellae.

[0069] Example 2

[0070] (1) Weigh 7.692 g of magnesium nitrate hexahydrate (0.03 mol) and 1.099 g of aluminum nitrate nonahydrate (0.003 mol), dissolve them in 30 ml of solution, and stir for more than 10 min. Dropwise add 1 mol / L NaOH solution to the stirred mixed solution to adjust the pH to 10 ± 0.5. Continue stirring for 30 min, age at 80 °C for 24 h, filter by suction, wash alternately with deionized water and ethanol three times, and then vacuum dry overnight at 80 °C to obtain the precursor Cl-LDH.

[0071] (2) Dissolve 0.2 mol of KBr in 300 ml of water, stir until the solid is evenly dispersed, then add 0.6 g of the precursor Cl-LDH, adjust the pH value of the resulting suspension to 8, age at 80 °C for 24 h with stirring, filter, wash, and then vacuum dry overnight at 80 °C to obtain bromide ion intercalated magnesium-aluminum layered hydroxide Cat-2.

[0072] Example 3

[0073] (1) Weigh 6.099 g of MgCl2·6H2O (0.03 mol) and 2.39 g of AlCl3·9H2O (0.008 mol), dissolve them in 30 ml of solution, and stir for more than 10 min. Dropwise add 1 mol / L NaOH solution to the stirred mixed solution to adjust the pH to 10 ± 0.5. Continue stirring for 30 min, age at 50 °C for 24 h, filter by suction, wash alternately with deionized water and ethanol three times, and then vacuum dry overnight at 80 °C to obtain the precursor Cl-LDH.

[0074] (2) Dissolve 0.2 mol of KBr in 300 ml of water, stir until the solid is evenly dispersed, then add 0.6 g of the precursor Cl-LDH, adjust the pH value of the resulting suspension to 8, age at 50 °C for 24 h with stirring, filter, wash, and then vacuum dry overnight at 80 °C to obtain bromide ion intercalated magnesium-aluminum layered hydroxide Cat-3.

[0075] Example 4

[0076] (1) Weigh 17.4 g of MgCl2·6H2O (0.086 mol) and 2.39 g of AlCl3·9H2O (0.008 mol), dissolve them in 30 ml of solution, and stir for more than 10 min. Dropwise add 1 mol / L NaOH solution to the stirred mixed solution to adjust the pH to 10 ± 0.5. Continue stirring for 30 min, age at 40 °C for 24 h, filter by suction, wash alternately with deionized water and ethanol three times, and then vacuum dry overnight at 80 °C to obtain the precursor Cl-LDH.

[0077] (2) Dissolve 0.2 mol of KBr in 300 ml of water and stir until the solid is uniformly dispersed. Then add 0.6 g of the precursor Cl-LDH. Adjust the pH value of the resulting suspension to 8, age it at 40 °C for 24 h under stirring, filter, wash, and then dry it under vacuum at 80 °C overnight to obtain bromide ion-intercalated magnesium-aluminum layered hydroxide Cat-4.

[0078] Example 5

[0079] (1) Weigh 17.4 g of MgCl2·6H2O (0.086 mol) and 2.39 g of AlCl3·9H2O (0.008 mol) and prepare a 30 ml solution, stirring for more than 10 min. Slowly add 1 mol / L NaOH solution drop by drop to the stirred mixed solution to adjust the pH = 10 ± 0.5. Continue stirring for 30 min, age at 30 °C for 15 h, perform suction filtration, and wash it alternately with deionized water and ethanol three times to obtain the wet precursor Cl-LDH.

[0080] (2) Dissolve 0.2 mol of KBr in 300 ml of water and stir until the solid is uniformly dispersed. Then add 0.6 g of the wet precursor Cl-LDH. Adjust the pH value of the resulting suspension to 7, age it at 30 °C for 15 h under stirring, filter, wash, and then dry it under vacuum at 80 °C overnight to obtain bromide ion-intercalated magnesium-aluminum layered hydroxide Cat-5.

[0081] Example 6

[0082] (1) Weigh 17.4 g of MgCl2·6H2O (0.086 mol) and 2.39 g of AlCl3·9H2O (0.008 mol) and prepare a 30 ml solution, stirring for more than 10 min. Slowly add 2 mol / L NaOH solution drop by drop to the stirred mixed solution to adjust the pH = 10 ± 0.5. Continue stirring for 30 min, age at 70 °C for 24 h, perform suction filtration, and wash it alternately with deionized water and ethanol three times to obtain the wet precursor Cl-LDH.

[0083] (2) Dissolve 1 mol of KBr in 300 ml of water and stir until the solid is uniformly dispersed. Then add 0.6 g of the wet precursor Cl-LDH. Adjust the pH value of the resulting suspension to 7, age it at 70 °C for 24 h under stirring, filter, wash, and then dry it under vacuum at 80 °C overnight to obtain bromide ion-intercalated magnesium-aluminum layered hydroxide Cat-6.

[0084] Example 7

[0085] (1) Weigh 6.099 g of MgCl₂·6H₂O (0.03 mol) and 2.39 g of AlCl₃·9H₂O (0.008 mol), dissolve them in 30 ml of solution, and stir for more than 10 min. Dropwise add 1 mol / L NaOH solution to the stirred mixed solution to adjust the pH to 9 ± 0.5. Continue stirring for 30 min, age at 90 °C for 24 h, perform suction filtration, wash alternately with deionized water and ethanol three times, and then vacuum dry overnight at 80 °C to obtain the precursor Cl-LDH.

[0086] (2) Dissolve 0.2 mol of zinc bromide in 300 ml of water and stir until the solid is evenly dispersed. Then add 0.6 g of the precursor Cl-LDH, adjust the pH value of the resulting suspension to 8, age at 90 °C for 24 h under stirring, filter, wash, and then vacuum dry overnight at 80 °C to obtain the bromide ion intercalated magnesium-aluminum layered hydroxide Cat-7.

[0087] Example 8

[0088] (1) Weigh 7.692 g of magnesium nitrate hexahydrate (0.03 mol) and 2.39 g of AlCl₃·9H₂O (0.008 mol), dissolve them in 30 ml of solution, and stir for more than 10 min. Dropwise add 2 mol / L NaOH solution to the stirred mixed solution to adjust the pH to 11 ± 0.5. Continue stirring for 30 min, age at 60 °C for 24 h, perform suction filtration, wash alternately with deionized water and ethanol three times, and then vacuum dry overnight at 80 °C to obtain the precursor Cl-LDH.

[0089] (2) Dissolve 0.2 mol of zinc bromide in 300 ml of water and stir until the solid is evenly dispersed. Then add 0.6 g of the precursor Cl-LDH, adjust the pH value of the resulting suspension to 8, age at 60 °C for 24 h under stirring, filter, wash, and then vacuum dry overnight at 80 °C to obtain the bromide ion intercalated magnesium-aluminum layered hydroxide Cat-8.

[0090] Example 9

[0091] Prepare the bromide ion intercalated magnesium-aluminum layered hydroxide according to the method of Example 1, except that in step (1), add NaOH solution to adjust the pH value of the mixed solution to 13 to obtain the bromide ion intercalated magnesium-aluminum layered hydroxide Cat-9.

[0092] Example 10

[0093] Prepare the bromide ion intercalated magnesium-aluminum layered hydroxide according to the method of Example 1, except that in step (1), the amount of NaOH solution used is such that the pH value of the mixed solution is adjusted to 7 to obtain the bromide ion intercalated magnesium-aluminum layered hydroxide Cat-10.

[0094] Example 11

[0095] The bromide ion intercalated magnesium-aluminum layered hydroxide was prepared according to the method of Example 1, except that in step (2), the pH value of the suspension was adjusted to 13 to obtain the bromide ion intercalated magnesium-aluminum layered hydroxide Cat-11.

[0096] Comparative Example 1

[0097] The precursor Cl-LDH was prepared according to the method of Example 1, and was called magnesium-aluminum layered hydroxide D1.

[0098] Comparative Example 2

[0099] The operation was carried out according to the method of Example 1, except that KI with the same molar amount was used instead of KBr to prepare magnesium-aluminum layered hydroxide D2.

[0100] Application Example 1

[0101] The magnesium-aluminum layered hydroxides prepared in Examples 1-11 and Comparative Examples 1-2 were used as catalysts in the reaction of propylene oxide cycloaddition to prepare propylene carbonate. The reaction conditions included: the catalyst dosage was 0.2 g, the propylene oxide (PO) dosage was 5 mmol, the reaction was carried out in a 10 ml batch reactor, and magnetic stirring was used to promote the uniform mixing of the reactants. The reaction was carried out at 80 °C and 2 MPa CO2 partial pressure for 12 hours. The solid-liquid mixture was separated by centrifugation, and then the liquid was passed through a liquid chromatograph for analysis. The results are shown in Table 1 below.

[0102] Table 1

[0103] Example Number Propylene Oxide Conversion Rate Propylene Carbonate Selectivity Propylene Carbonate Yield Example 1 94.4％ 98.6％ 93.1％ Example 2 95.5％ 97.2％ 92.8％ Example 3 94.7％ 97.7％ 92.5％ Example 4 95.1％ 96.9％ 92.2％ Example 5 95.9％ 96.4％ 92.4％ Example 6 94.4％ 97.8％ 92.3％ Example 7 94.4％ 97.2％ 91.7％ Example 8 94.0％ 98.3％ 92.4％ Example 9 92.7％ 97.5％ 90.4％ Example 10 92.4％ 97.5％ 90.1％ Example 11 94.3％ 95.8％ 90.3％ Comparative Example 1 73.5％ 50.1％ 36.8％ Comparative Example 2 38.9％ 67.2％ 26.1％

[0104] Application Example 2

[0105] The magnesium-aluminum layered hydroxides prepared in Examples 1-11 and Comparative Examples 1-2 were used as catalysts in the reaction of propylene oxide cycloaddition to prepare propylene carbonate. The reaction conditions included: 5 mmol of PO and 0.2 g of the catalyst as the reaction raw materials were added to a 25 ml micro high-pressure reactor, 2 MPa of CO2 was charged, the reaction parameters were set at 80 °C, the reaction was carried out for 12 h, and the rotation speed was 600 r. After the reaction, it was naturally cooled to room temperature. 25 ml of ethyl acetate was used to absorb the tail gas after the reaction. The tail gas absorption liquid was mixed evenly with the reaction liquid. The solid-liquid mixture was separated by centrifugation, and then the liquid was passed through a liquid chromatograph for analysis. Then the mixed solution was centrifuged, washed 4 times with ethanol, dried at 80 °C, and the above experimental operation was repeated until the catalytic effect of the catalyst decreased by 5-10%.

[0106] The results are shown in Table 2 below.

[0107] Table 2

[0108] Example Number Stability Example 1 The conversion rate can still be maintained at 91.2 - 93.0% after 4 cycles Example 2 The conversion rate can still be maintained at 89.6 - 91.8% after 4 cycles Example 3 The conversion rate can still be maintained at 89.3 - 91.0% after 4 cycles Example 4 The conversion rate can still be maintained at 86.8 - 89.9% after 4 cycles Example 5 The conversion rate can still be maintained at 88.1 - 90.4% after 4 cycles Example 6 The conversion rate can still be maintained at 86.9 - 89.9% after 4 cycles Example 7 The conversion rate can still be maintained at 88.3 - 89.9% after 4 cycles Example 8 The conversion rate can still be maintained at 87.8 - 89.0% after 4 cycles Example 9 The conversion rate can still be maintained at 88.2 - 90.2% after 4 cycles Example 10 The conversion rate can still be maintained at 87.3 - 90.0% after 4 cycles Example 11 The conversion rate can still be maintained at 87.2 - 90.0% after 4 cycles Comparative Example 1 The conversion rate can only be maintained at 33.5 - 36.8% after 2 cycles Comparative Example 2 The conversion rate can only be maintained at 23.2 - 26.1% after 3 cycles

[0109] It can be seen from the results of Table 1 and Table 2 that the bromide ion intercalated magnesium-aluminum layered hydroxide prepared by the method according to the present invention can effectively catalyze the ring-opening of propylene oxide, and significantly higher yields of propylene carbonate can be obtained under mild conditions. Moreover, it will not deactivate even after being used as a catalyst multiple times, and has strong stability.

[0110] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A preparation method of bromide ion-intercalated magnesium-aluminum layered double hydroxides, characterized in that, The method comprises the following steps: (1) Provide an aqueous solution containing an aluminum source and a magnesium source, mix the aqueous solution containing the aluminum source and the magnesium source with a base source, age the resulting mixed solution, and then separate out the solid phase; (2) Mix the solid phase obtained in step (1) with an aqueous solution containing a bromine source, age the resulting suspension, and then perform solid-liquid separation.

2. The method according to claim 1, characterized in that In step (1), in the aqueous solution containing an aluminum source and a magnesium source, the molar content ratio of the magnesium source calculated as Mg 2+ to the aluminum source calculated as Al 3+ is (1 - 20):1, preferably (2 - 12.5):1; Preferably, in the aqueous solution containing an aluminum source and a magnesium source, the concentration of the aluminum source in terms of Al 3+ is 0.1 - 5 mol / L, preferably 0.1 - 2 mol / L; Preferably, in the aqueous solution containing an aluminum source and a magnesium source, the concentration of the magnesium source in terms of Mg 2+ is 0.1-10 mol / L, preferably 0.1-3 mol / L; Preferably, the aluminum source is at least one of aluminum nitrate, aluminum acetate, aluminum carbonate, and aluminum chloride; Preferably, the magnesium source is at least one of magnesium nitrate, magnesium acetate, magnesium carbonate, and magnesium chloride.

3. The method according to claim 1 or 2, characterized in that, In step (1), the amount of the base source is such that the pH value of the mixed solution is 7 - 13, preferably 9 - 11; Preferably, the base source is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, ammonium bicarbonate, urea, ammonia water, n-butylamine, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium bromide.

4. The method according to any one of claims 1-3, characterized in that, In step (1), the aging conditions include: the temperature is higher than 25°C and lower than 200°C, preferably higher than 25°C and lower than 100°C; the time is 10 - 36 h, preferably 15 - 30 h.

5. The method according to claim 1, characterized in that, In step (2), in the aqueous solution containing a bromine source, the concentration of the bromine source in terms of Br - is 0.1 - 10 mol / L, preferably 0.1 - 2 mol / L; Preferably, the bromine source is at least one of potassium bromide, calcium bromide, and zinc bromide.

6. The method according to claim 1 or 5, characterized in that, In step (2), the mass ratio of the bromine source to the solid phase is (10 - 70):

1.

7. The method according to claim 1, 5 or 6, characterized in that, In step (2), the pH value of the suspension is 5 - 13, preferably 5 - 10.

8. The method according to claim 1, 5, 6 or 7, characterized in that, In step (2), the aging conditions include: the temperature is higher than 25°C and lower than 200°C, preferably higher than 25°C and lower than 100°C; the time is 10 - 36 h, preferably 15 - 30 h.

9. A bromide ion-intercalated magnesium-aluminum layered hydroxide prepared by the method according to any one of claims 1 - 8.

10. A method for preparing propylene carbonate, the method comprising: In the presence of a catalyst, propylene oxide and carbon dioxide are reacted, characterized in that the catalyst is the bromide ion-intercalated magnesium-aluminum layered hydroxide according to claim 9.

Images