阅读说明：本技术 一种酯交换合成碳酸二甲酯催化剂的制备方法、催化剂及应用 (Preparation method of catalyst for synthesizing dimethyl carbonate through ester exchange, catalyst and application ) 是由 杨先贵 魏强 王公应 于 2020-06-09 设计创作，主要内容包括：本发明公开了一种酯交换合成碳酸二甲酯催化剂的制备方法、催化剂及应用。所述方法包括：柠檬酸钙经碳化后制得所述催化剂。碳化温度为500-900℃；碳化时间1～3小时。本发明的催化剂在保持较高转化率的同时,可以减少催化剂的用量,大大缩短反应时间,降低了生产成本。(The invention discloses a preparation method of a catalyst for synthesizing dimethyl carbonate by ester exchange, the catalyst and application. The method comprises the following steps: the catalyst is prepared by carbonizing calcium citrate. The carbonization temperature is 500-900 ℃; the carbonization time is 1-3 hours. The catalyst of the invention can reduce the dosage of the catalyst, greatly shorten the reaction time and reduce the production cost while keeping higher conversion rate.)

1. A preparation method of a catalyst for synthesizing dimethyl carbonate by ester exchange is characterized by comprising the following steps:

the catalyst is prepared by carbonizing calcium citrate.

2. The method of claim 1, wherein:

the carbonization temperature is 500-900 ℃; and/or the presence of a gas in the gas,

the carbonization time is 1-3 hours.

3. The method of claim 2, wherein:

the carbonization temperature is 700-800 ℃.

4. The method of claim 3, wherein:

and during carbonization, heating to the carbonization temperature at the heating rate of 3-5 ℃/min.

5. A catalyst prepared by the process of any one of claims 1 to 4.

6. Use of a catalyst according to claim 5 for the transesterification synthesis of dimethyl carbonate.

7. The use of claim 6, wherein:

methanol and ethylene carbonate are taken as raw materials, and the dimethyl carbonate is synthesized by adopting the catalysis;

the molar ratio of the methanol to the ethylene carbonate is 4-12: 1; and/or the presence of a gas in the gas,

the dosage of the catalyst is 0.5-2.5% of the mass of the ethylene carbonate.

8. The use of claim 6, wherein:

the reaction temperature is 70-120 ℃, and the reaction time is 5-30 min.

9. The use of claim 6, wherein:

the dosage of the catalyst is 1.0-2.0 wt% of the ethylene carbonate.

10. The use of claim 8, wherein:

the reaction temperature is 90-110 ℃; the reaction time is 15-25 min.

Technical Field

The invention relates to the technical field of solid base catalysts, in particular to a heterogeneous catalyst, and relates to a preparation method of a catalyst for synthesizing dimethyl carbonate by ester exchange, the catalyst and application of the catalyst in synthesizing dimethyl carbonate by ester exchange.

Background

Dimethyl carbonate (DMC) is an important environment-friendly chemical intermediate, has the advantages of high dielectric constant, high oxygen content (53%), high octane number (105), low toxicity, high biodegradability and the like, and is widely applied to the fields of polycarbonate raw materials, electrolyte solvents, additives of fuel oil and the like; in recent years, research on DMC and its derivatives has become one of the hot spots of the world chemical research. The DMC synthesis mainly comprises a phosgene route, a carbonylation route and a transesterification route; compared with other routes, the ester exchange route has mild reaction conditions and environment-friendly raw materials, not only accords with the current green synthesis process, but also has extremely high industrial value for co-producing the product ethylene glycol; therefore, it is becoming a mainstream route for DMC synthesis.

The catalysts currently used for the transesterification process for the synthesis of DMC can be largely divided into two main classes, homogeneous and heterogeneous. Homogeneous catalysts include triethylamine, sodium methoxide, metal acetate, alkali metal salts and the like; but has great defects in the later separation and use. The most advantage of the heterogeneous catalyst is that the separation of the product from the catalyst can be achieved in a simple manner (such as centrifugation, filtration, etc.) at a later stage; patent 200310109693 discloses a method for preparing a zirconium oxide and calcium fluoride composite catalyst; when the reaction temperature is 120 ℃ and the reaction time is 48 hours, the yield of the dimethyl carbonate can reach 97 percent. Patent 201510700289.2 discloses a preparation method of a graphene oxide based magnesium oxide supported catalyst; the method has high preparation cost, is not beneficial to the industrialized mass production in the later period, and the selectivity and the yield of the dimethyl carbonate are respectively 99.3 percent and 87.1 percent. Patent 201610988571.x discloses a method for synthesizing dimethyl carbonate by using ethylene carbonate and methanol as raw materials and activated carbon as a catalyst, which is carried out in a high-pressure reaction kettle, wherein when the amount of activated carbon is 20% (compared with the mass fraction of ethylene carbonate), the pressure is 0.3MPa, the reaction temperature is 160 ℃, and the reaction time is 8h, the conversion rate and selectivity of ethylene carbonate are as high as 97% and 99%; however, the reaction needs to be carried out under high pressure and high temperature, and the reaction time is long.

In summary, the heterogeneous catalyst used for synthesizing DMC by ester exchange method generally has the problems of large catalyst reaction dosage, high reaction temperature, long reaction time and the like. In view of this, it is important to design and develop a heterogeneous catalyst with low preparation cost, good catalytic performance and short reaction period.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a preparation method of a catalyst for synthesizing dimethyl carbonate by ester exchange, the catalyst and application. The catalyst of the invention is a heterogeneous catalyst, has lower preparation cost and better catalytic performance, can obviously shorten the reaction time and reduce the reaction temperature, and is relatively suitable for large-scale production.

The invention aims to provide a preparation method of a catalyst for synthesizing dimethyl carbonate by ester exchange.

The method comprises the following steps:

the catalyst is prepared by carbonizing calcium citrate.

In a preferred embodiment of the present invention,

the carbonization temperature is 500-900 ℃;

the carbonization time is 1-3 hours.

In a further preferred embodiment of the invention,

the carbonization temperature is 700-800 ℃.

In a further preferred embodiment of the invention,

and during carbonization, heating to the carbonization temperature at the heating rate of 3-5 ℃/min.

In a more preferred embodiment of the present invention,

calcium citrate is used as a raw material, and the carbonization temperature is adjusted to promote the calcium citrate to be cracked, so that the CaC-based catalyst is prepared.

The catalyst is typically prepared by, but not limited to, the following methods: weighing a certain mass of calcium citrate in a clean quartz square boat, placing the quartz square boat in a tubular furnace capable of temperature programming under the protection of nitrogen, heating to 500-.

In the catalyst of the invention, the carbonization temperature is 500-900 ℃, preferably 700-800 ℃, and when the carbonization temperature is lower than 500 ℃, calcium carbonate is embedded in the carbonaceous matrix, but the activity is lower and is not enough to effectively catalyze the transesterification reaction. When the carbonization temperature is higher than 500 ℃ but lower than 700 ℃, the mixture of calcium carbonate and calcium oxide is embedded in the carbonaceous matrix, and the activity of the catalyst is greatly improved due to the generation of the calcium oxide. When the carbonization temperature is higher than 800 ℃ but lower than 900 ℃, the catalyst is easily sintered during the carbonization process, so that the catalytic performance is reduced, but the transesterification reaction can still be effectively catalyzed. Preferably, the carbonization temperature is 800 ℃, the carbonization time is 2h, the content of the obtained active component is the maximum in the carbonization process, and the catalytic performance of the catalyst is optimal.

It is a further object of the present invention to provide a catalyst prepared by the process according to one of the objects of the present invention.

The invention also aims to provide application of the catalyst in synthesizing dimethyl carbonate by ester exchange.

In a preferred embodiment of the present invention,

methanol and ethylene carbonate are taken as raw materials, and the dimethyl carbonate is synthesized by the catalysis, wherein the reaction temperature is 70-120 ℃, and the reaction time is 5-30 min;

the dosage of the catalyst is 0.5-2.5% of the mass of the ethylene carbonate;

the molar ratio of the methanol to the ethylene carbonate is 4-12: 1.

In a further preferred embodiment of the invention,

the reaction temperature is 90-110 ℃; the reaction time is 15-25 min;

the dosage of the catalyst is 1.0-2.0 wt% of the ethylene carbonate.

The reaction of ethylene carbonate and methanol to dimethyl carbonate belongs to the field of ester exchange, Kabashima et al^[3]The studies show that methoxy (available from methanolysis) as a strong basicity point has a high catalytic activity in the transesterification reaction, and in the presence of methoxy, the transesterification reaction starts to occur. Secondly, in the case of the transesterification catalyst, what is needed is to promote the decomposition of methanol to methoxy (CH)₃OH＝CH₃O^-+H⁺). The CaC-based catalyst has appropriate alkali amount and alkalinity, and can make H in methanol⁺Adsorbing on lattice oxygen of calcium oxide in catalyst to generate great amount of methoxyl radical to promote reactionAnd (6) rows.

[3]Kabashima H,Tsuji H,Hattori H.Michael addition of methyl crotonate over solid base catalysts[J].Applied Catalysis A General,1997,165(1-2):319-325.

The invention provides a preparation method of a supported catalyst; the carrier is a supported type, and consists of an active species and a carrier, and the general expression method is A/B, wherein A represents the active species, and B represents the carrier; whereas conventional preparation methods are generally divided into two steps, the first step being the loading of the active species on the support and the second step being the activation.

However, we have found that calcium citrate, due to its special structure, is easily cracked under the protection of inert gas at high temperature to generate active species and gas small molecules, and at the same time, a large amount of carbon species is also preserved, and these carbon species can be used as carriers of these active species; that is, only one step (carbonization) is required to obtain a supported carbon-based catalyst; compared with the traditional preparation method of the catalyst, the preparation method has the advantages of making breakthrough progress and greatly reducing the preparation cost.

The invention has the beneficial effects that:

(1) the preparation cost of the catalyst is low, the method is simple, and the heterogeneous catalyst can be quickly obtained in batches through carbonization treatment.

(2) The catalyst of the invention is applied to the synthesis of dimethyl carbonate, the ester exchange reaction condition is mild, and the reaction time is short and the reaction rate is high on the basis of keeping higher conversion rate of reactant vinyl carbonate and selectivity of product dimethyl carbonate.

Detailed Description

While the present invention will be described in detail with reference to the following examples, it should be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the present invention.

Example 1:

preparing a catalyst, namely putting a certain mass of calcium citrate into a clean quartz ark, placing the quartz ark into a tubular furnace under the protection of nitrogen, heating the quartz ark to 800 ℃ at the heating rate of 4 ℃/min, preserving the temperature for 2h, cooling the quartz ark to room temperature, and grinding the quartz ark to obtain the CaC-based catalyst.

And (2) carrying out catalytic reaction, namely adding 0.088g of CaC-based catalyst, 8.8g of ethylene carbonate and 25.6g of methanol into a 150ml round-bottom flask, stirring at 100 ℃ for reaction for 30min, and detecting and analyzing products in the flask, wherein the analysis results comprise that the conversion rate of the ethylene carbonate is 78.5%, and the selectivity and the yield of the dimethyl carbonate are 99.0% and 77.7% respectively.

Example 2:

according to the preparation method of the catalyst in the embodiment 1, the temperature is raised to 700 ℃ at the heating rate of 3 ℃/min, the temperature is kept for 2h, then the catalyst is cooled to the room temperature, and the CaC-based catalyst is obtained after grinding.

0.088g of the catalyst, 8.8g of ethylene carbonate and 25.6g of methanol are added into a 150ml round bottom flask, the mixture is stirred and reacted for 30min at the temperature of 100 ℃, products in the flask are taken for detection and analysis, and the analysis results show that the conversion rate of the ethylene carbonate is 73.7 percent, and the selectivity and the yield of the dimethyl carbonate are 97.7 percent and 72.0 percent respectively.

Example 3:

according to the preparation method of the catalyst in the embodiment 1, the temperature is raised to 900 ℃ at the heating rate of 5 ℃/min, the temperature is kept for 2h, then the catalyst is cooled to room temperature, and the CaC-based catalyst is obtained after grinding.

0.088g of the catalyst, 8.8g of ethylene carbonate and 25.6g of methanol are added into a 150ml round bottom flask, the mixture is stirred and reacted for 30min at the temperature of 100 ℃, products in the flask are taken for detection and analysis, and the analysis results show that the conversion rate of the ethylene carbonate is 77.8 percent, and the selectivity and the yield of the dimethyl carbonate are 98.6 percent and 76.7 percent respectively.

Example 4:

the catalyst prepared in example 1 was used.

0.132g of the catalyst, 8.8g of ethylene carbonate and 25.6g of methanol are added into a 150ml round-bottom flask, after the mixture is stirred and reacts for 20min at the temperature of 100 ℃, products in the flask are taken for detection and analysis, and the analysis results show that the conversion rate of the ethylene carbonate is 81.2 percent, and the selectivity and the yield of the dimethyl carbonate are 99.3 percent and 80.6 percent respectively.

Comparative example 1:

0.088g of sodium methoxide, 8.8g of ethylene carbonate and 25.6g of methanol are added into a 150ml round-bottom flask, the mixture is stirred and reacted for 20min at the temperature of 100 ℃, products in the flask are taken for detection and analysis, and the analysis result shows that the conversion rate of the ethylene carbonate is 69.6 percent, and the selectivity and the yield of the dimethyl carbonate are 99.3 percent and 69.1 percent respectively.

Comparative example 2:

0.132g of sodium methoxide, 8.8g of ethylene carbonate and 25.6g of methanol are added into a 150ml round-bottom flask, the mixture is stirred and reacted for 20min at the temperature of 100 ℃, and then products in the flask are taken for detection and analysis, wherein the analysis result shows that the conversion rate of the ethylene carbonate is 74.9 percent, and the selectivity and the yield of the dimethyl carbonate are 99.1 percent and 74.2 percent respectively.

The sodium methoxide is the only homogeneous catalyst for industrial production at home at present, and the data of the examples and the comparative examples show that compared with the sodium methoxide, the catalyst has higher conversion rate under the same conditions, and can be easily separated from the product and reused.

Table 1 shows some data of heterogeneous catalysts in some published documents, and it can be seen from the data in table 1 that the catalyst of the present application has a reduced amount of catalyst and a greatly reduced reaction time while maintaining a high yield.

TABLE 1

Note: the last column is the catalyst prepared in example 4.

The above-described embodiments are intended to illustrate the substance of the present invention, but are not intended to limit the scope of the present invention. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention.