Catalyst and method for preparing dimethyl carbonate by catalyzing reaction of methanol and propylene carbonate

Abstract

The invention provides a catalyst and a method for preparing dimethyl carbonate by catalyzing reaction of methanol and propylene carbonate. The structural formula of the catalyst is M1O-M1M2O; wherein the metal M1 is alkali metal or alkaline earth metal, the alkali metal is one of lithium, sodium and potassium, and the alkaline earth metal is one of calcium, magnesium and barium; the metal M2 is one of zirconium, titanium, silicon and tin; the catalyst can be prepared by a sol-gel method or an impregnation method. According to the method, a catalyst is adopted, and methanol and propylene carbonate are catalyzed to be subjected to transesterification in a tank reactor under mild reaction conditions, so that dimethyl carbonate is prepared. The solid base catalyst adopted by the invention has the advantages of high activity, high selectivity and difficulty in loss of active components, and has the characteristics of strong applicability and high economical efficiency when being applied to industrial production of dimethyl carbonate prepared by ester exchange reaction of methanol and propylene carbonate.

Description

Technical Field

[0001] The invention belongs to the field of chemical multiphase catalytic technology and chemical process, and specifically relates to a catalyst and a method for catalyzing the reaction of methanol and propylene carbonate to prepare dimethyl carbonate. Background Art

[0002] With the strengthening of people's environmental awareness and the implementation of sustainable development strategies, many traditional chemical industries are facing severe challenges due to environmental pollution and other problems. The green chemical industry, which uses chemical principles and methods to fundamentally reduce or eliminate the pollution of traditional industries to the environment, improve the human living environment and significantly increase economic benefits, is booming around the world.

[0003] Dimethyl carbonate is non-corrosive and non-toxic. It contains carbonyl, methyl, methoxy and carbonylmethyl groups, so its chemical properties are very active. It can synthesize many compounds with special properties in organic synthesis. It is an important organic synthesis intermediate and can replace some toxic compounds. Since dimethyl carbonate was registered as a non-toxic chemical in Europe in 1992, its development and research has received increasing attention. In recent years, its synthesis methods and application fields have been continuously expanded, and it is considered to be a newly emerging "green" chemical product with great development prospects.

[0004] Generally, the transesterification reaction is carried out in the presence of a suitable catalyst. Chinese patent CN1488439A discloses a homogeneous catalyst, which mainly includes alkali metal hydroxides, alkali metal salts, alcohol salts, organic bases, etc. Since it is a homogeneous reaction, it is difficult to separate and recover the catalyst and the product after the reaction, and it is corrosive to the equipment and is not conducive to maintenance.

[0005] U.S. Patent No. 4196041 discloses several heterogeneous catalysts, including quaternary amine type, tertiary amine type, sulfonic acid and carboxylic acid functional group ion exchange resins and silica impregnated with alkali metal and alkaline earth metal silicates. This type of catalyst does not have the separation problem, but the ion exchange resin generally has problems such as temperature resistance and easy swelling, and poor activity.

[0006] Metal oxides such as CaO, ZrO2, MgO, ZnO, CeO2, etc. in heterogeneous catalysts have attracted much attention due to their simple preparation, easy separation and abundant basic sites. The prior art uses CaO as a catalyst for the transesterification of methanol and propylene carbonate to synthesize dimethyl carbonate at room temperature. It can be seen that CaO has good activity at room temperature, and it is simple to prepare, easy to separate and has abundant basic sites. However, its disadvantage is that CaO, as an active component of the catalyst, is easy to lose, and the stability of CaO alone as a catalyst is not good. Studies have shown that when a new metal is introduced into a single metal oxide, the composition and structure of the active sites will change, thereby changing the activity of the catalyst. Summary of the invention

[0007] In order to solve the shortcomings of the prior art, the present invention provides a catalyst and method for catalyzing the reaction of methanol and propylene carbonate to prepare dimethyl carbonate. The catalyst has the characteristics of high activity, high selectivity and low loss of active components, thus solving the problem of poor catalyst stability in the prior art.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] The present invention discloses a catalyst for preparing dimethyl carbonate by catalyzing the reaction of methanol and propylene carbonate. The catalyst is M1O-M1M2O. The metal M1 is an alkali metal or an alkaline earth metal. The alkali metal is any one of lithium, sodium and potassium, and the alkaline earth metal is one of calcium, magnesium and barium. The metal M2 is one of zirconium, titanium, silicon and tin. The loading amount of M1 is 5-30wt%, the loading amount of M2 is 10.5-15.5wt%, and the ratio of the amount of M1 to the sum of the amounts of M1 and M2 is 0.7-0.9.

[0010] Furthermore, the catalyst is prepared by a sol-gel method or an impregnation method.

[0011] Furthermore, the sol-gel method comprises: mixing a soluble salt of M1 、 The soluble salt of M2 is dissolved in an ethanol solution to obtain solution A, citric acid is dissolved in anhydrous ethanol to obtain a 0.8-1.2 mol / L citric acid ethanol solution, the citric acid ethanol solution is added to solution A, and vigorously stirred at 24-26°C for 20-30 hours to obtain a mixture, the mixture is heated to 70-90°C to evaporate the solvent to obtain a gel, and then dried at 70-90°C for 20-30 hours, and calcined at 750-850°C in air for 3-6 hours to obtain the catalyst. The molar ratio of citric acid to the soluble salt of M1 is 1:0.7-0.9.

[0012] Furthermore, the M1 soluble salt is one of the nitrate, acetate and carbonate of the corresponding metal, and more preferably Ca(NO3)2·4H2O.

[0013] Furthermore, the impregnation method includes: placing the oxide of M1 in a beaker, dissolving the soluble salt of M2 in water to obtain an aqueous solution of the soluble salt of M2, dripping the aqueous solution of the soluble salt of M2 into the beaker, shaking evenly, and immersing in a constant temperature water bath at 35-45°C for 20-30 hours, and then calcining at 750-850°C in air for 3-6 hours to obtain the catalyst.

[0014] Furthermore, the M2 soluble salt is one of the nitrate, acetate and carbonate of the corresponding metal. Zr(NO3)4·5H2O is further preferred.

[0015] Furthermore, the oxide of M1 is one of calcium oxide, magnesium oxide and barium oxide, and CaO is more preferred.

[0016] Another aspect of the present invention discloses a method for preparing dimethyl carbonate by reacting methanol with propylene carbonate catalyzed by the above catalyst. Methanol and propylene carbonate with a molar ratio of 6 to 8:1 are placed in a kettle reactor, stirring and condensing water are started; after the reaction liquid in the kettle reactor reaches 55 to 75° C., the catalyst is immediately added, the pressure is normal pressure, and stirring is carried out for 2 to 4 hours. The ester exchange reaction is completed to obtain dimethyl carbonate.

[0017] Furthermore, the mass percentage of the catalyst in the reaction solution is 0.134-9.2wt%.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are:

[0019] (1) The catalyst of the present invention has the advantages of high activity, high selectivity, mild reaction conditions, good stability, and easy product separation in the ester exchange reaction of methanol and propylene carbonate to prepare dimethyl carbonate, and is used to meet the requirements of the new environmentally friendly catalytic process.

[0020] (2) The catalyst of the present invention is easy to separate and recover from the product after the reaction, has a high reuse rate, and will not corrode the equipment, thus solving the problem of easy loss of active components and poor stability of heterogeneous catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the XRD pattern of the CaO-CaZrO3 catalyst prepared by the sol-gel method in Example 1 of the present invention;

[0022] Figure 2 is the XRD pattern of the CaO-CaZrO3 catalyst prepared by the impregnation method in Example 2 of the present invention;

[0023] Figure 3 is the XRD pattern of the CaO-CaZrO3 catalyst prepared by the co-precipitation method in Example 3 of the present invention;

[0024] Figure 4 is the FID chromatogram of the raw material and the product after the transesterification reaction in Example 4 of the present invention;

[0025] Figure 5 The continuous sampling and analysis comparison of the CaO-CaZrO3 catalyst with Ca / (Ca+Zr)=0.9 in Example 7 of the present invention;

[0026] Figure 6It is a comparison of continuous sampling and analysis of the CaO-CaZrO3 catalyst with Ca / (Ca+Zr)=0.8 in Comparative Example 2 of the present invention;

[0027] Figure 7 It is a comparison of continuous sampling and analysis of the CaO-CaZrO3 catalyst with Ca / (Ca+Zr)=0.7 in Comparative Example 3 of the present invention;

[0028] Figure 8 The continuous sampling and analysis comparison of the CaO-CaZrO3 catalyst with Ca / (Ca+Zr)=0.9 prepared by the sol-gel method in Example 10 of the present invention;

[0029] Fig. 9 This is a comparison of continuous sampling and analysis of the CaO-CaZrO3 catalyst prepared by the impregnation method in Example 11 of the present invention;

[0030] Fig.10 is the stability curve of the CaO-CaZrO3 catalyst on a fixed bed in Example 12 of the present invention;

[0031] Fig.11 It is the stability curve of the CaO catalyst on the fixed bed in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and through specific embodiments. The following embodiments are merely illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0033] Example 1

[0034] CaO-CaZrO3 catalyst was prepared by sol-gel method.

[0035] The specific method is as follows: 0.09 mol of Ca(NO3)2·4H2O and 0.01 mol of Zr(NO3)4·5H2O, 0.08 mol of Ca(NO3)2·4H2O and 0.02 mol of Zr(NO3)4·5H2O, 0.07 mol of Ca(NO3)2·4H2O and 0.03 mol of Zr(NO3)4·5H2O are dissolved in 100 ml of anhydrous ethanol to prepare a 1 mol / L metal nitrate ethanol solution (solution A). At the same time, 0.1 mol of C6H8O7·H2O is weighed and dissolved in 100 ml of anhydrous ethanol to prepare a 1 mol / L citric acid ethanol solution (solution B). Solution B is added to solution A, and after vigorous stirring at room temperature for 24 hours, the mixture is heated to 80°C to evaporate the solvent to obtain a gel. Subsequently, it is dried at 80°C for 24 hours and calcined at 800°C in air for 4 hours to obtain a composite metal oxide catalyst. The Ca / (Ca+Zr) of the obtained catalysts were 0.9, 0.8 and 0.7 respectively.

[0036] The phase composition of the prepared catalyst with Ca / (Ca+Zr) ratio of 0.9 was analyzed by X-ray diffraction. Figure 1 As shown, the main phase components are CaZrO3 and CaO.

[0037] Example 2

[0038] CaO-CaZrO3 catalyst was prepared by impregnation method.

[0039] The specific method is as follows: 8.4g of Zr(NO3)4·5H2O is weighed and dissolved in 100ml of deionized water. At the same time, 12.936g of CaO is weighed in a 500ml beaker. The fully dissolved Zr(NO3)4 solution is added to the beaker containing CaO, shaken evenly, and immersed in a 40℃ constant temperature water bath for 24h to evaporate the water. Then, it is calcined in air at 800℃ for 4h to obtain the CaO-CaZrO3 catalyst.

[0040] The phase composition of the prepared CaO-CaZrO3 catalyst was analyzed by X-ray diffraction. Figure 2 As shown, the main phase components are CaZrO3 and CaO.

[0041] Example 3

[0042] CaO-CaZrO3 catalyst was prepared by co-precipitation method.

[0043] Weigh 0.09 mol of Ca(NO3)2·4H2O, 0.01 mol of Zr(NO3)4·5H2O and 100 ml of distilled water into a 500 ml beaker and stir evenly. Add 1:1 ammonia water dropwise into the beaker under stirring, control the pH to 9-10, stir for 30 minutes after precipitation is complete, age in the mother liquor for a period of time, filter the precipitate and dry at 110°C for 12 hours. Then calcine at 800°C in air for 4 hours to obtain CaO-CaZrO3 catalyst.

[0044] The phase composition of the prepared catalyst was analyzed by X-ray diffraction. Figure 3 As shown, the main phase components are CaZrO3 and CaO.

[0045] Example 4

[0046] The reaction products of methanol and propylene carbonate were measured on an Agilent GC-2010Pro gas chromatograph equipped with a flame photometric detector (FID). Nitrogen was used as the carrier gas, the injection port temperature was 280°C, the split ratio was 50, and the injection volume was 1 μL. The capillary column model was DB-WAX, constant pressure mode, pressure 22.06 KPa, and the temperature program was 40°C for 0.5 min, then increased to 195°C at a heating rate of 25°C / min, maintained at 195°C for 8.7 min, then increased to 230°C at a heating rate of 25°C / min, and maintained at 230°C for 29.1 min. The FID detector temperature was 275°C. The area normalization method was used for quantitative analysis. The chromatograms of the reactants are shown in Figure 4 It can be seen that the residence times of methanol, DMC (dimethyl carbonate), PG (propylene glycol), and PC (propylene carbonate) are 1.977 min, 2.244 min, 5.166 min, and 6.301 min, respectively.

[0047] Example 5

[0048] First, weigh 1g of CaO-CaZrO3 with Ca / (Ca+Zr)=0.9 prepared in Example 1, then weigh 10.23g of PC and 22.42g of methanol and place them in a 100mL three-necked flask, open the condenser, and wait until the water bath temperature rises to 65°C before placing the flask in a water bath. Quickly add the catalyst to the flask. After reacting for 180min under strong stirring conditions, take samples for analysis.

[0049] The product composition was analyzed by the method described in Example 4. The results are shown in Table 1. It can be seen that the concentration of PC was significantly reduced, the total conversion rate was 70.3%, and the yield of DMC was 69.8%.

[0050] Example 6

[0051] The reaction of methanol and propylene carbonate was carried out in the same manner as in Example 5, except that the catalyst used was 1 g of CaO-CaZrO3 prepared in Example 2. The product composition was analyzed by the method described in Example 4. The results are shown in Table 1. It can be seen that the concentration of PC was significantly reduced, the overall conversion rate was 70.9%, and the yield of DMC was 70.4%.

[0052] Comparative Example 1

[0053] The reaction of methanol and propylene carbonate was carried out in the same manner as in Example 5, except that the catalyst used was 1 g of CaO-CaZrO3 prepared in Example 3. The composition of the product was analyzed by the method described in Example 4, and the results are shown in Table 1. It can be seen that the concentration of PC was reduced, the total conversion rate was 28.1%, and the yield of DMC was 26.6%. The catalytic activity was significantly lower than that of the CaO-CaZrO3 prepared in Examples 1 and 2.

[0054]

[0055] Example 7

[0056] First, weigh 0.11g of CaO-CaZrO3 with Ca / (Ca+Zr)=0.9 prepared in Example 1, then weigh 25.575g of PC and 56.05g of methanol and place them in a 150mL three-necked flask, turn on the condensation water, and wait until the water bath temperature rises to 65°C before placing the flask in a water bath. Rapidly add the catalyst to the flask under strong stirring conditions, sample every 5min for the first 80min, and then sample and analyze every 10min until the reaction ends at 120min. The composition of the product in the product was analyzed using the method described in Example 4, and the results are shown in Figure 5 It can be seen that the final conversion rate of PC in the reaction solution is 56.08%.

[0057] Comparative Example 2

[0058] The reaction of methanol and propylene carbonate was carried out in the same manner as in Example 7, except that the catalyst used was 0.11 g of CaO-CaZrO3 with a Ca / (Ca+Zr) of 0.8 prepared in Example 1. The composition of the product was analyzed using the method described in Example 4. The results are shown in Figure 6 It can be seen that the final conversion rate of PC in the reaction solution is 35.36%.

[0059] Comparative Example 3

[0060] The reaction of methanol and propylene carbonate was carried out in the same manner as in Example 7, except that the catalyst used was 0.11 g of CaO-CaZrO3 prepared in Example 1 with a Ca / (Ca+Zr)=0.7. The composition of the product was analyzed by the method described in Example 4. The results are shown in Figure 7 It can be seen that the final conversion rate of PC in the reaction solution is 24.9%.

[0061] Example 8

[0062] First, weigh 1g of CaO-CaZrO3 prepared in Example 1, then weigh 10.23g of PC and 22.42g of methanol and place them in a 100mL three-necked flask, open the condenser, and wait until the water bath temperature rises to 55°C, 65°C or 75°C before placing the flask in a water bath. Quickly add 1g of CaO-CaZrO3 to the flask under strong stirring conditions, react for 3h under strong stirring conditions, and then take samples for analysis.

[0063] The composition of the product was analyzed by the method described in Example 4, and the results are shown in Table 2. As can be seen from the table, 65°C is a relatively optimal reaction temperature. When the reaction temperature is further increased after 65°C, the yield of DMC decreases.

[0064] Table 2

[0065]

[0066] Example 9

[0067] The reaction of methanol and propylene carbonate was carried out in the same manner as in Example 8, except that the catalyst used was 1 g of CaO-CaZrO3 prepared in Example 2. The composition of the product was analyzed by the method described in Example 4, and the results are shown in Table 3. As can be seen from the table, 65 o C is the optimal reaction temperature. When the reaction temperature continues to rise after 65°C, the yield of DMC decreases.

[0068] Table 3

[0069]

[0070] Example 10

[0071] First, weigh 0.11g of CaO-CaZrO3 prepared in Example 1 with Ca / (Ca+Zr)=0.9. Then weigh 25.575g of PC and 56.05g of methanol and place them in a 150mL three-necked flask, turn on the condensation water, and place the flask in a water bath after the water bath temperature rises to 65°C. Rapidly add the catalyst to the flask under strong stirring conditions, sample every 5 minutes for the first 80 minutes, and then sample and analyze every 10 minutes until the reaction ends after 100 minutes. The composition of the product in the product was analyzed using the method described in Example 4, and the results are shown in Figure 8 It can be seen that the final conversion rate of PC is 56.11%, and it can be seen that CaO-CaZrO3 has a very high reaction rate in the early stage of the reaction.

[0072] Embodiment 11

[0073] The reaction of methanol and propylene carbonate was carried out in the same manner as in Example 8, except that the catalyst used was 0.11 g of CaO-CaZrO3 prepared in Example 2. The composition of the product was analyzed using the method described in Example 4. The results are shown in Fig. 9 It can be seen that the final conversion rate of PC is 51.82% but the reaction rate is not very ideal.

[0074] Example 12

[0075] First, weigh 1g of CaO-CaZrO3 prepared in Example 2 with Ca / (Ca+Zr)=0.9. Press the catalyst into 20-40 mesh and install it in the constant temperature section of the fixed bed reactor; adjust the reactor temperature to stabilize the fixed bed constant temperature section at 65°C; feed the mixed solution of methanol:PC=7 at a feed rate of 0.4ml / min, and take samples every 1h after the reaction is stable for 1h. The composition of the product was analyzed using the method described in Example 4, and the results are shown in Fig.10It can be seen that after 12 hours of reaction, the conversion rate of PC is still 62.5%, which shows that CaO-CaZrO3 has good stability.

[0076] Comparative Example 4

[0077] The reaction of methanol and propylene carbonate was carried out in the same manner as in Example 12, except that the catalyst used was 1 g of CaO calcined at 800°C. The composition of the product was analyzed and calculated using the method described in Example 4. The results are shown in Fig.11 It can be seen that in the initial stage of the reaction, CaO has a high activity, and the conversion rate of PC is 66.5%. However, as the reaction time increases, the active components of the catalyst are lost, and the catalyst activity decreases until the PC conversion rate is only 8.8% after 12 hours.

[0078] Through the above description, the two catalysts for preparing dimethyl carbonate by catalyzing the reaction of methanol with propylene carbonate of the present invention and their preparation and method have been clearly disclosed. It is well known to those skilled in the art that some modifications and improvements may be made to the present invention, but any modifications and improvements made to the present invention should be within the scope of the present invention as long as they do not depart from the spirit of the present invention.

Claims

1. A catalyst for catalyzing the reaction of methanol and propylene carbonate to prepare dimethyl carbonate, characterized in that: The structural formula of the catalyst is M1O-M1M2O; wherein the metal M1 is an alkali metal or an alkaline earth metal, the alkali metal is one of lithium, sodium, and potassium, and the alkaline earth metal is one of calcium, magnesium, and barium; the metal M2 is one of zirconium, titanium, silicon, and tin, the loading amount of M1 is 5 to 30 wt%, the loading amount of M2 is 10.5 to 15.5 wt%, and the ratio of the amount of M1 substance to the sum of the amounts of M1 and M2 substances is 0.7 to 0.

9.

2. The catalyst according to claim 1, characterized in that The catalyst is prepared by a sol-gel method or an impregnation method.

3. The catalyst according to claim 2, characterized in that The sol-gel method comprises: dissolving M1 soluble salt and M2 soluble salt in ethanol solution to obtain solution A, dissolving citric acid in anhydrous ethanol to obtain 0.8-1.2 mol / L citric acid ethanol solution, adding the citric acid ethanol solution to solution A, vigorously stirring at 24-26° C. for 20-30 hours to obtain a mixture, heating the mixture to 70-90° C. to evaporate the solvent to obtain a gel, then drying at 70-90° C. for 20-30 hours, and calcining at 750-850° C. in air for 3-6 hours to obtain the catalyst, wherein the molar ratio of citric acid to M1 soluble salt is 1:0.7-0.

9.

4. The catalyst according to claim 3, characterized in that The M1 soluble salt is one of the nitrate, acetate and carbonate of the corresponding metal.

5. The catalyst according to claim 2, characterized in that The impregnation method comprises: placing the oxide of M1 in a beaker, dissolving the soluble salt of M2 in water to obtain an aqueous solution of the soluble salt of M2, dripping the aqueous solution of the soluble salt of M2 into the beaker, shaking evenly, and then immersing in a constant temperature water bath at 35-45° C. for 20-30 hours, and then calcining at 750-850° C. in air for 3-6 hours to obtain the catalyst.

6. The catalyst according to claim 3 or 5, characterized in that The M2 soluble salt is one of the nitrate, acetate and carbonate of the corresponding metal.

7. The catalyst according to claim 5, characterized in that The oxide of M1 is one of calcium oxide, magnesium oxide and barium oxide.

8. A method for preparing dimethyl carbonate by reacting methanol with propylene carbonate using a catalyst according to any one of claims 1 to 7, characterized in that: Methanol and propylene carbonate in a molar ratio of 6 to 8:1 are placed in a tank reactor, stirring and condensing water are started; after the reaction liquid in the tank reactor reaches 55 to 75° C., the catalyst is immediately added, the pressure is normal pressure, and stirring is performed for 2 to 4 hours, and the ester exchange reaction is completed to obtain dimethyl carbonate.

9. The method according to claim 8, characterized in that The mass percentage of the catalyst in the reaction solution is 0.134-9.2wt%.

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