Preparation method of a specific crystal form of manganese dioxide and application thereof in CO2 and propylene oxide cycloaddition reaction

Abstract

The present application relates to a kind of preparation method of specific crystal form manganese dioxide and its application in the ring addition reaction of CO2 and propylene oxide, belong to catalyst preparation and application technical field, its preparation method is as follows: the potassium permanganate of certain concentration and manganese sulfate are fused and heated to specified temperature, under the control of microflow, with certain flow rate is uniformly mixed in the reaction kettle and is reacted, after standing, washing, adjusting pH, drying, grinding, the target catalyst is obtained.In the catalyst prepared, the catalytic activity of δ-MnO2 is the best, the conversion rate of propylene oxide is the largest and reaches 100%, the selectivity of propylene carbonate reaches more than 99%.The preparation method is simple, δ-MnO2 can be mass-produced, the production cost is low, the yield is higher, is used to catalyze propylene oxide and CO2 conversion into propylene carbonate, the selectivity is high, and can be recycled four times, has extensive industrialization prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalyst preparation, and particularly relates to a method for preparing a specific crystal form of manganese dioxide and application of the specific crystal form of manganese dioxide in a CO2 and propylene oxide cycloaddition reaction. BACKGROUND

[0002] Propylene carbonate has good biodegradability, solubility, and physical properties such as high polarity and high boiling point, and is widely used in the fields of high polymer industry, electronic industry, textile, dye and chemical reagent, etc. At present, propylene carbonate is prepared by the addition of propylene oxide and CO2 under certain pressure, followed by distillation under reduced pressure. However, the above production conditions are harsh, and therefore the development of a high-efficiency catalyst for catalyzing the cycloaddition reaction of CO2 and epoxide has been a focus of attention.

[0003] In early studies, propylene carbonate was mainly prepared from propylene oxide and CO2 by using a homogeneous catalyst such as an ionic liquid, an alkali metal salt and an organic base. These catalysts generally use a halogen-containing catalyst such as potassium iodide, and the reaction is carried out at a temperature above 200℃ and a pressure higher than 6 MPa, which not only has the disadvantages of high energy consumption and environmental pollution, but also has a certain risk in production safety. Compared with heterogeneous catalysts, homogeneous catalysts have the disadvantages of difficult recovery and poor stability, and therefore the development of a heterogeneous catalyst for efficiently catalyzing the cycloaddition reaction of CO2 and propylene oxide under mild conditions has attracted wide attention. Up to now, heterogeneous catalysts such as metal oxides, functionalized molecular sieve materials, functionalized polymers and metal organic frameworks have a good industrial application prospect.

[0004] Metal oxides are low in price and easy to produce. The catalysis of metal oxides in the preparation of propylene carbonate from the cycloaddition reaction of CO2 and propylene oxide is a green, economic and efficient process route, and the reaction also has the advantages of good product, high yield and recyclable catalyst. At present, most of the metal oxide catalysts used in the cycloaddition reaction of CO2 and propylene oxide are MgO, CeO2, La2O3, ZrO2, ZnO, Al2O3 and composite metal oxides. For example, Bhanage et al. investigated the catalytic performance of common alkaline earth metal oxides, transition metal oxides and post-transition metal oxides in the reaction, and found that La2O3 and MgO had good performance in the cycloaddition reaction of CO2 and epoxide due to the presence of strong and medium-strong alkali sites. Islamb et al. synthesized porous MgO nanosheets and ZnO hollow nanospheres by ammonia precipitation and citrate precipitation, respectively. The MgO sample had a nanoscale narrow mesoporous structure and a specific surface area of 34.2 m 2 / g, while the ZnO sample exhibits a hollow porous structure, both of which can make the yield of cyclic carbonate reach more than 98% under normal temperature and pressure. For the composite metal oxides, for example, Kazuya et al. prepared Mg-Al composite catalyst with Mg / Al molar ratio of 5 by calcining layered hydrotalcite structure, and used it in the cycloaddition reaction of CO2 and epoxide. Since Mg 2+ was replaced by Al 3+ , the isomorphic substitution formed Mg-O-Al bond, increased the surface acidity and strong basic sites, and the higher reactivity proved the importance of acid-base synergistic catalysis. Rasal et al. pointed out that in the Mg-Li composite oxide prepared by gel combustion method, since Li + and Mg 2+ had different valence states, Li + substituted Mg 2+ resulted in the formation of defect centers in the lattice as the activation sites of CO2, which strengthened the basicity of the catalyst and improved the catalytic performance. It can be seen that both single component and composite metal oxide catalysts have good reactivity and selectivity. However, most of the above catalysts have low production yield, and the conditions required to control the appropriate acid-base sites are harsh.

[0005] Among metal oxides, manganese oxides have low preparation cost, high activity, and various crystal structures. Different crystal structures of manganese oxides have different surface microstructures and chemical compositions, resulting in different catalytic performances. Due to the unique two-dimensional layered structure of δ-manganese dioxide, it has rich acid-base active sites, and has high activity for catalytic conversion of CO2, so it has attracted widespread attention in the field of catalytic conversion of CO2.

[0006] In summary, the catalytic CO2 and propylene oxide cycloaddition reaction to prepare cyclic carbonate is an efficient and applicable method, so it is of great significance to develop a simple, green, low-cost and large-scale preparation of δ-MnO2 for catalyzing the cycloaddition reaction of CO2 and propylene oxide to prepare propylene carbonate. SUMMARY

[0007] In view of the above problems existing in the prior art of catalytic CO2 and propylene oxide cycloaddition reaction, the purpose of the present application is to provide a preparation method of a specific crystal type manganese dioxide catalyst and the application of the catalyst in the cycloaddition reaction of CO2 and propylene oxide. The preparation method of the catalyst has simple process, low price, high product yield, and can realize large-scale preparation. The activity and selectivity of the catalyst in the cycloaddition reaction of CO2 and propylene oxide to prepare propylene carbonate are high, and the catalyst has good economic and practical value.

[0008] To achieve the above purpose, the technical scheme of the present application is as follows.

[0009] The application provides a preparation method of a specific crystal form manganese dioxide catalyst, comprising the following steps:

[0010] (1) preheat a potassium permanganate solution with a certain concentration and a manganese sulfate solution to a specified temperature T respectively;

[0011] (2) simultaneously add the potassium permanganate solution and the manganese sulfate solution into a reaction kettle of a microfluidic reaction device at a certain feeding flow rate, and carry out reaction at a constant temperature, wherein the reaction temperature is T, and the reaction time is 1 h;

[0012] (3) place the product obtained by reaction for 24 h, perform suction filtration and washing until the pH value is 7, carry out constant temperature drying at 80 DEG C, cool to room temperature, and then grind, so as to obtain the specific crystal form manganese dioxide.

[0013] In the above preparation method, the microfluidic reaction device uses a technology scheme disclosed in the prior art, for example, an invention patent with the authorized announcement number CN 114956188 B, a method for continuously preparing a specific crystal form manganese dioxide by using a microfluidic device, the microfluidic reaction device comprises a first raw material tank, a second raw material tank, a hastelloy pump, a stainless steel pump, a reaction kettle and a product tank, the first raw material tank is used for storing a potassium permanganate solution, the second raw material tank is used for storing a manganese sulfate solution, the bottom of the first raw material tank and the bottom of the second raw material tank are provided with first temperature control devices for preheating the solutions, the inlet and the outlet of the hastelloy pump are connected with the first raw material tank and the reaction kettle through heat preservation pipelines respectively, the inlet and the outlet of the stainless steel pump are connected with the second raw material tank and the reaction kettle through heat preservation pipelines respectively, the bottom of the reaction kettle is provided with a second temperature control device, and the discharge port of the reaction kettle is connected with the product tank through a pipeline.

[0014] Preferably, in the step (1), the feeding concentration c1 of the potassium permanganate solution is controlled to be 0 mol / L < c1≤1 mol / L.

[0015] Preferably, in the step (1), the feeding concentration c2 of the manganese sulfate solution is controlled to be 0 mol / L < c2≤1 mol / L.

[0016] Preferably, in the step (2), the feeding flow rate Q1 of the potassium permanganate solution is controlled to be 60 g / min≤Q1≤80 g / min.

[0017] Preferably, in the step (2), the feeding flow rate Q2 of the manganese sulfate solution is controlled to be 70 g / min≤Q2≤120 g / min.

[0018] Preferably, the specified temperature in the step (1) and the reaction temperature T in the step (2) are controlled to be 0 DEG C≤T≤150 DEG C.

[0019] Preferably, when the reaction temperature T is controlled at 0℃≤T<80℃, the product generated by the reaction is α-type manganese dioxide.

[0020] Preferably, when the reaction temperature T is controlled at 80℃≤T<90℃, the product generated by the reaction is δ-type manganese dioxide.

[0021] Preferably, when the reaction temperature T is controlled at 90℃≤T≤150℃, the product generated by the reaction is γ-type manganese dioxide.

[0022] The application also provides the use of the δ crystal form MnO2 catalyst in the CO2 and propylene oxide ring addition reaction for preparing propylene carbonate. Under the reaction conditions of 3 MPa CO2 pressure, 120-160℃ reaction temperature, and 1 h reaction time, the conversion rate of the δ crystal form MnO2 catalyst to propylene oxide reaches 10.6-38.23%, the conversion rate of propylene oxide can reach 100% when the reaction time is 24 h, and the selectivity of propylene carbonate reaches more than 99%.

[0023] The δ crystal form manganese dioxide prepared by the application has a unique two-dimensional layered structure, and its surface has rich Lewis acid-base active sites, has better activation effect on the reaction of carbon dioxide and propylene oxide, has higher catalytic activity for the ring-opening of propylene oxide and the insertion of carbon dioxide, and has higher catalytic stability. The α-type manganese dioxide is a chain structure, and the γ-type manganese dioxide is a grain structure, the surface thereof has few acid-base active sites, and the catalytic activity thereof is relatively low. Therefore, the δ crystal form manganese dioxide has better catalytic activity than other crystal forms of manganese dioxide.

[0024] By using the above technology, the application has the following beneficial effects compared with the prior art.

[0025] 1) The application uses a microfluidic method to mass-produce specific crystal form manganese dioxide, uses cheap raw materials, and has low production cost, so that industrial production can be realized.

[0026] 2) The δ-type manganese dioxide catalyst prepared by the application has good performance in catalyzing the CO2 and propylene oxide ring addition reaction for preparing propylene carbonate; under the reaction conditions of 3 MPa CO2 pressure, 120-160℃ temperature, 1 h reaction time, and 400 mg catalyst, and 14.52 g propylene oxide, the conversion rate of the δ crystal form MnO2 catalyst to propylene oxide reaches 10.6-38.23%, the selectivity of propylene carbonate reaches more than 99%, the conversion rate of propylene oxide can reach 100% when the reaction time is 24 h, has the advantage of high yield, the selectivity of propylene carbonate reaches more than 99%, and the catalyst can be recycled four times, so that the application has wide industrialization prospects. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 XRD pattern of δ-MnO2 catalyst;

[0028] Figure 2 XRD pattern of α-MnO2 catalyst;

[0029] Figure 3 XRD pattern of γ-MnO2 catalyst;

[0030] Figure 4 TEM pattern of three different crystal form MnO2 catalysts;

[0031] Figure 5 TEM magnification pattern of γ-MnO2 catalyst;

[0032] Figure 6 Time course analysis pattern of δ-MnO2 catalyst;

[0033] Figure 7 Performance pattern of stability experiment of δ-MnO2 catalyst;

[0034] Figure 8 Schematic diagram of microfluidic reaction device.

[0035] In the figure: 1 - first raw material tank; 2 - second raw material tank; 3 - hastelloy pump; 4 - stainless steel pump; 5 - heat preservation pipeline; 6 - microfluidic reactor; 7 - first temperature control device; 8 - second temperature control device; 9 - product tank. DETAILED DESCRIPTION

[0036] The technical solutions of the present application are further described below with specific examples, but the protection scope of the present application is not limited thereto. The steps in the present application are arranged with labels, but are not used to limit the sequence of the steps, unless the sequence of the steps is explicitly described or the execution of a step needs other steps as a basis, otherwise the relative sequence of the steps can be adjusted. Unless otherwise specified, the chemical reagents and materials in the present application are purchased through market channels or synthesized from raw materials purchased through market channels.

[0037] In the examples of the present application, the products prepared under different temperature conditions, i.e. δ-type, α-type and γ-type manganese dioxide catalysts, are used as examples to test the performance and parameters of the products and determine the optimal performance of the products.

[0038] Example 1: Preparation of δ-MnO2

[0039] The 1 mol / L potassium permanganate solution and the 0.8 mol / L manganese sulfate solution are preheated to 85°C, and then the potassium permanganate solution is fed into the reaction kettle of the microfluidic reaction device at a feeding rate of 60 g / min, and the manganese sulfate solution is fed into the reaction kettle at a feeding rate of 100 g / min to react, so as to obtain δ-manganese dioxide.

[0040] The specific steps for preparing δ-manganese dioxide are as follows: referring to the process flow in FIG. 1, the potassium permanganate solution and the manganese sulfate solution are respectively placed in the first raw material tank 1 and the second raw material tank 2, the potassium permanganate solution and the manganese sulfate solution are heated to a predetermined temperature by the first temperature control device 7, the heated potassium permanganate solution is fed into the reaction kettle 6 through the hastelloy pump 3 via the heat preservation pipeline 5, and the heated manganese sulfate solution is fed into the reaction kettle 6 through the stainless steel pump 4 via the heat preservation pipeline 5, the two solutions are controlled to enter the reaction kettle 6 at the same time to react, the temperature of the reaction kettle 6 is adjusted and controlled by the second temperature control device 8, the manganese dioxide generated by the reaction is transported to the product tank 9 via the heat preservation pipeline 5, the product in the product tank 9 is left to stand for 24 h, and then is washed by filtration until the pH value is 7, and then is placed in a drying box at 80°C to be dried, and after being cooled to room temperature, the product is ground, and the obtained product is δ-manganese dioxide. Figure 8

[0041] In addition, the specific preparation process of the manganese dioxide with different crystal forms obtained in the subsequent examples is the same as that of Example 1.

[0042] Under the reaction conditions of a CO2 pressure of 3 MPa, a temperature of 120°C, a reaction time of 1 h, δ-manganese dioxide of 400 mg, 20 mL of N,N-dimethylformamide, and propylene oxide of 14.52 g, the conversion rate of the catalyst to propylene oxide reaches 10.6%, the conversion rate of propylene oxide can reach 100% when the reaction time is 24 h, the selectivity of propylene carbonate reaches more than 99%, and the catalyst can be recycled four times.

[0043] The performance test of the δ-manganese dioxide catalyst prepared in this example is as follows:

[0044] 400 mg of the catalyst is weighed in a high-pressure reaction kettle, and then (14.52 g) of propylene oxide and 20 mL of N,N-dimethylformamide are weighed and uniformly mixed, and then the mixed solution is transferred into the high-pressure reaction kettle. The high-pressure reaction kettle is sealed and placed in a magnetic heating stirrer. After 1 MPa of CO2 is introduced to check the airtightness of the high-pressure reaction kettle, if there is no CO2 leakage, the CO2 in the kettle is discharged, and the air in the kettle is replaced three times to ensure that there is no air in the kettle. Finally, the high-pressure reaction kettle is filled with a certain pressure.

[0045] ​The magnetic speed was adjusted to 500 rpm, and the temperature of the reactor was raised to 120°C. The reaction was started when the timer was started. After 1 h of reaction, the reactor was removed and allowed to cool to room temperature. The high-pressure reactor was then placed in an ice water bath to reduce the temperature to below 10°C. The gas valve of the high-pressure reactor was opened to release the CO2 until the pressure was 0 MPa. Finally, the high-pressure reactor was opened and the reaction liquid was removed. The reaction liquid was filtered using a filter needle. A gas chromatography micro-liquid inlet needle was used to extract 0.4 μl of the filtered liquid, and the components were analyzed by gas chromatography. The gas chromatography H2 flow was set to 50-80 mL / min, the air flow was 200-300 mL / min, the carrier gas flow was 3-5 mL / min, the sample injection temperature was set to 280.0°C, the column oven initial temperature was set to 60°C for 6 min, then increased to 220°C at a rate of 25°C / min for 10 min, and the FID temperature was set to 280.0°C.

[0046] After the chromatographic peak was obtained, the conversion rate of propylene oxide was calculated by peak area.

[0047] Example 2: Preparation of δ-MnO2

[0048] A 1 mol / L potassium permanganate solution and a 0.6 mol / L manganese sulfate solution were separately preheated to 85°C. The potassium permanganate solution was then added to the reactor of the microfluidic reaction device at a feed rate of 60 g / min, and the manganese sulfate solution was added at a feed rate of 100 g / min to obtain δ-manganese dioxide.

[0049] Under the reaction conditions of CO2 pressure 3 MPa, temperature 120°C, reaction time 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide, and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 7.52%, and the selectivity of propylene carbonate reached more than 99%.

[0050] The application of α-MnO2 catalyst was tested under the same conditions and steps as in Example 1.

[0051] Example 3: Preparation of δ-MnO2

[0052] A 1 mol / L potassium permanganate solution and a 1 mol / L manganese sulfate solution were separately preheated to 85°C. The potassium permanganate solution was then added to the reactor of the microfluidic reaction device at a feed rate of 60 g / min, and the manganese sulfate solution was added at a feed rate of 100 g / min to obtain δ-manganese dioxide.

[0053] Under the reaction conditions of CO2 pressure 3 MPa, temperature 120 ℃, reaction 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 6.39%, and the selectivity of propylene carbonate reached more than 99%.

[0054] The application of the α-MnO2 catalyst, and the reaction performance test conditions and steps are the same as in Example 1.

[0055] Example Four: Preparation of δ-MnO2

[0056] The 1 mol / L potassium permanganate solution and the 0.8 mol / L manganese sulfate solution were preheated to 85 ℃ respectively, and then the potassium permanganate solution was added into the reaction kettle of the microfluidic reaction device at a feeding flow rate of 60 g / min, and the manganese sulfate solution was added into the reaction kettle at a feeding flow rate of 80 g / min to obtain δ-manganese dioxide.

[0057] Under the reaction conditions of CO2 pressure 3 MPa, temperature 120 ℃, reaction 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 6.83%, and the selectivity of propylene carbonate reached more than 99%.

[0058] The application of the α-MnO2 catalyst, and the reaction performance test conditions and steps are the same as in Example 1.

[0059] Example Five: Preparation of δ-MnO2

[0060] The 1 mol / L potassium permanganate solution and the 0.8 mol / L manganese sulfate solution were preheated to 85 ℃ respectively, and then the potassium permanganate solution was added into the reaction kettle of the microfluidic reaction device at a feeding flow rate of 60 g / min, and the manganese sulfate solution was added into the reaction kettle at a feeding flow rate of 120 g / min to obtain δ-manganese dioxide.

[0061] Under the reaction conditions of CO2 pressure 3 MPa, temperature 120 ℃, reaction 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 5.37%, and the selectivity of propylene carbonate reached more than 99%.

[0062] The application of the α-MnO2 catalyst, and the reaction performance test conditions and steps are the same as in Example 1.

[0063] Example Six: Preparation of α-MnO2

[0064] Preheat 0.3 mol / L potassium permanganate solution and 0.5 mol / L manganese sulfate solution to 60℃, then feed the potassium permanganate solution into the reactor of the microfluidic reaction device at a flow rate of 65 g / min and the manganese sulfate solution at a flow rate of 70 g / min to carry out the reaction, and obtain α-manganese dioxide.

[0065] Under the reaction conditions of CO2 pressure 3 MPa, temperature 120℃, reaction 1 h, α-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reaches 4.13%, the conversion rate of propylene oxide can reach 62.82% when the reaction time is 24 h, and the selectivity of propylene carbonate reaches more than 99%.

[0066] The application of α-MnO2 catalyst, the reaction performance test conditions and steps are the same as in Example 1.

[0067] Example Seven: Preparation of γ-MnO2

[0068] Preheat 0.3 mol / L potassium permanganate solution and 0.5 mol / L manganese sulfate solution to 60℃, then feed the potassium permanganate solution into the reactor of the microfluidic reaction device at a flow rate of 65 g / min and the manganese sulfate solution at a flow rate of 70 g / min to carry out the reaction, and obtain α-manganese dioxide.

[0069] Under the reaction conditions of CO2 pressure 3 MPa, temperature 120℃, reaction 1 h, α-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reaches 4.13%, the conversion rate of propylene oxide can reach 62.82% when the reaction time is 24 h, and the selectivity of propylene carbonate reaches more than 99%.

[0070] The application of α-MnO2 catalyst, the reaction performance test conditions and steps are the same as in Example 1.

[0071] Example Eight: The mass of propylene oxide is 11.62 g

[0072] Under the reaction conditions of CO2 pressure 3 MPa, temperature 120℃, reaction 1 h, α-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reaches 4.13%, the conversion rate of propylene oxide can reach 62.82% when the reaction time is 24 h, and the selectivity of propylene carbonate reaches more than 99%.

[0073] The application of α-MnO2 catalyst, the reaction performance test conditions and steps are the same as in Example 1.

[0074] Example Nine: The mass of propylene oxide was 17.42 g

[0075] Under the reaction conditions of CO2 pressure 3 MPa, temperature 120 °C, reaction 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 17.42 g, the conversion rate of propylene oxide reached 5.85%, and the selectivity of propylene carbonate reached more than 99%.

[0076] The application of the δ-MnO2 catalyst, the reaction performance test conditions and steps were the same as in Example 1.

[0077] Example Ten: The reaction temperature was 40 °C

[0078] Under the reaction conditions of CO2 pressure 3 MPa, temperature 40 °C, reaction 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 0.12%, and the selectivity of propylene carbonate reached more than 99%.

[0079] The application of the δ-MnO2 catalyst, the reaction performance test conditions and steps were the same as in Example 1.

[0080] Example Eleven: The reaction temperature was 100 °C

[0081] Under the reaction conditions of CO2 pressure 3 MPa, temperature 100 °C, reaction 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 4.25%, and the selectivity of propylene carbonate reached more than 99%.

[0082] The application of the δ-MnO2 catalyst, the reaction performance test conditions and steps were the same as in Example 1.

[0083] Example Twelve: The reaction temperature was 140 °C

[0084] Under the reaction conditions of CO2 pressure 3 MPa, temperature 140 °C, reaction 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 32.45%, and the selectivity of propylene carbonate reached 99%.

[0085] The application of the δ-MnO2 catalyst, the reaction performance test conditions and steps were the same as in Example 1.

[0086] Example Thirteen: The reaction temperature was 160 °C

[0087] Under the reaction conditions of CO2 pressure 3 MPa, temperature 160°C, reaction 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 38.23% and the selectivity of propylene carbonate reached more than 99%.

[0088] The application of the δ-MnO2 catalyst, the reaction performance test conditions and steps are the same as in Example 1.

[0089] Example Fourteen: reaction temperature is 180°C

[0090] Under the reaction conditions of CO2 pressure 3 MPa, temperature 180°C, reaction 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 46.52% and the selectivity of propylene carbonate reached 95%. It can be seen that when the catalytic reaction temperature is increased to 180°C,

[0091] The application of the δ-MnO2 catalyst, the reaction performance test conditions and steps are the same as in Example 1.

[0092] Example Fifteen: reaction temperature is 200°C

[0093] Under the reaction conditions of CO2 pressure 3 MPa, temperature 200°C, reaction 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 52.45% and the selectivity of propylene carbonate reached 88%.

[0094] The application of the δ-MnO2 catalyst, the reaction performance test conditions and steps are the same as in Example 1.

[0095] Example Sixteen: CO2 reaction pressure is 1.5 MPa

[0096] Under the reaction conditions of CO2 pressure 1.5 MPa, temperature 120°C, reaction 1 h, δ-MnO2 400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 10.35% and the selectivity of propylene carbonate reached more than 99%.

[0097] The application of the δ-MnO2 catalyst, the reaction performance test conditions and steps are the same as in Example 1.

[0098] Example Seventeen: CO2 reaction pressure is 4.5 MPa

[0099] Under the reaction conditions of CO2 pressure 4.5 MPa, temperature 120℃, reaction 1h, δ-MnO2400 mg, 20 mL N,N-dimethylformamide and propylene oxide 14.52 g, the conversion rate of propylene oxide reached 10.89% and the selectivity of propylene carbonate reached more than 99%.

[0100] The application of the δ-MnO2 catalyst, and the reaction performance test conditions and steps are the same as those in Example 1.

[0101] The XRD pattern of the δ-MnO2 catalyst prepared in Example 1 shows that there are six diffraction peaks at about 2θ = 12.51°, 25.21°, 37.31°, 40.01° and 66.21°, corresponding to the six crystal faces of (001), (002), (100), (201) and (110) of the crystal.

[0102] Figure 2 The XRD pattern of the α-MnO2 catalyst shows that there are 14 diffraction peaks at about 2θ = 12.71°, 18.11°, 25.71°, 28.81°, 37.51°, 39.01°, 41.91°, 47.31°, 49.81°, 56.31°, 60.21°, 65.11°, 69.71° and 72.71°, corresponding to the 14 crystal faces of (110), (200), (220), (310), (211), (330), (301), (510), (411), (600), (521), (002), (541) and (312) of the crystal.

[0103] Figure 3 The XRD pattern of the γ-MnO2 catalyst shows that there are six diffraction peaks at about 2θ = 22.41°, 34.41°, 38.71°, 42.61°, 57.31° and 68.81°, corresponding to the six crystal faces of (120), (031), (131), (300), (160) and (003) of the crystal.

[0104] Figure 4 The transmission electron microscope patterns of the three different crystal forms of γ-MnO2 catalysts show that, Figure 4 the α-MnO2 catalyst of (a) presents a nanofiber shape, Figure 4 the δ-MnO2 catalyst of (b) is composed of a daisy structure of nanosheet superposition, Figure 4 and the γ-MnO2 catalyst of (c) presents a grain-like structure.

[0105] Figure 5 is a magnified transmission electron microscope pattern of the γ-MnO2 catalyst.

[0106] Figure 6 The time course analysis chart of the δ-MnO2 catalyst shows that the conversion of propylene oxide is 0.0%, 10.6%, 31.9%, 58.4%, 83.5%, 97.3% and 100.0% at the reaction time of 0 h, 1 h, 3 h, 6 h, 12 h, 18 h and 24 h respectively, and the selectivity of propylene carbonate is maintained at more than 99%, so it can be concluded that the δ-MnO2 catalyst has high catalytic activity.

[0107] Figure 7 The stability experiment performance chart of the δ-MnO2 catalyst shows that the conversion of propylene oxide is 10.62%, 10.0%, 9.63% and 10.25% at the catalyst cycle times of the first time, the second time, the third time and the fourth time respectively, and the selectivity of propylene carbonate is maintained at more than 99%, so it can be concluded that the δ-MnO2 catalyst has high stability.

[0108] The catalytic performance of the three kinds of manganese dioxide catalysts on propylene oxide under the same reaction conditions is shown in Table 1.

[0109] Table 1

[0110]

[0111] The reaction conditions in Table 1 are as follows: 14.52 g of propylene oxide, 0.4 g of catalyst, reaction temperature 120°C, carbon dioxide pressure 3 Mpa, 20 mL of N,N-dimethylformamide, reaction time 24 h.

[0112] According to the data analysis of Table 1, it can be concluded that the δ-MnO2 catalyst can achieve complete catalytic conversion of propylene oxide to propylene carbonate without by-product generation when the reaction time is 24 h, and the δ-MnO2 catalyst has the best performance under the same reaction conditions.

[0113] The catalytic stability experiment performance chart of the three kinds of manganese dioxide catalysts on propylene oxide under the same reaction conditions is shown in Table 2.

[0114] Table 2

[0115]

[0116]

[0117] The reaction conditions in Table 2 are as follows: 14.52 g of propylene oxide, 0.4 g of catalyst, reaction temperature 120°C, carbon dioxide pressure 3 Mpa, 20 mL of N,N-dimethylformamide, reaction time 1 h.

[0118] The data analysis in Table 2 shows the experimental performance of the catalytic stability of δ-MnO2 catalyst for propylene oxide under the same reaction conditions. It can be concluded that δ-MnO2 has the best performance under the same reaction conditions.

[0119] Through Examples 1, 10 to 15, it can be seen that the catalytic performance of δ-MnO2 catalyst on propylene oxide under different temperature reaction conditions is shown in Table 3.

[0120] Table 3

[0121]

[0122]

[0123] Table 3 Reaction conditions: 14.52g propylene oxide, 0.4g catalyst, reaction temperature 40-200℃, carbon dioxide pressure 3MPa, 20mL N,N-dimethylformamide, reaction time 1h.

[0124] The data analysis in Table 3 shows the catalytic performance of δ-MnO2 catalyst on propylene oxide at different reaction temperatures. It can be concluded that under the same reaction conditions, the conversion rate of δ-MnO2 catalyst on propylene oxide increases with increasing reaction temperature, but the selectivity of propylene carbonate remains high at first and then decreases.

[0125] Through data analysis of Examples 1, 16, and 17, the catalytic performance of δ-MnO2 catalyst on propylene oxide under different pressure conditions was studied. It was found that the catalytic performance of δ-MnO2 catalyst on the conversion rate of propylene oxide and the selectivity of propylene carbonate was minimal under different pressure conditions, but the catalytic performance was best at 3 MPa.

[0126] Through data analysis of Examples 1, 8, and 9, the catalytic performance of the δ-MnO2 catalyst on propylene oxide under different concentrations of propylene oxide was studied. It was found that under different reactant concentrations, both excessively high and low concentrations of propylene oxide would affect the conversion rate of propylene oxide by the catalyst, but would not affect the selectivity of propylene carbonate.

[0127] The above description is only a partial embodiment of the present invention and is not intended to limit the present invention. Any equivalent changes and modifications made based on the content of this invention are within the protection scope of this invention.

Claims

1. The application of a δ-crystalline manganese dioxide catalyst in the cycloaddition reaction of CO2 with propylene oxide to prepare propylene carbonate, characterized in that, Under the reaction conditions of 14.52 g propylene oxide, 0.4 g δ-crystalline manganese dioxide catalyst, 3 MPa CO2 pressure, 120–160 °C reaction temperature, and 1 h reaction time, the conversion rate of propylene oxide by the δ-crystalline manganese dioxide catalyst reached 10.6–38.23%. After 24 h of reaction, the conversion rate of propylene oxide by the δ-crystalline manganese dioxide catalyst reached 100%, and the selectivity for propylene carbonate reached over 99%. The specific steps for developing this δ-crystalline manganese dioxide catalyst are as follows: (1) Preheat the potassium permanganate solution and manganese sulfate solution to 80 ℃≤T<90 ℃ respectively; (2) Potassium permanganate solution and manganese sulfate solution are added to the reaction vessel of the microfluidic reaction device at the same time, and the reaction is carried out at a constant temperature of 80 ℃≤T<90 ℃ for 1 h. (3) The product obtained from the reaction was allowed to stand for 24 h, filtered and washed until the pH value was 7, dried at 80°C, cooled to room temperature, and then ground to obtain δ-crystal manganese dioxide with a two-dimensional layered structure.

2. The application according to claim 1, characterized in that, In step (1), the concentration c1 of the potassium permanganate solution is controlled to be 0 mol / L < c1 ≤ 1 mol / L.

3. The application according to claim 1, characterized in that, In step (1), the concentration of manganese sulfate solution c2 is controlled to be 0 mol / L < c2 ≤ 1 mol / L.

4. The application according to claim 2, characterized in that, In step (2), the feed flow rate Q1 of the potassium permanganate solution is controlled to be 60 g / min≤Q1≤80 g / min.

5. The application according to claim 3, characterized in that, In step (2), the feed flow rate Q2 of the manganese sulfate solution is controlled to be 70g / min≤Q2≤120g / min.

Images