CN105344341B - Preparation method of solid catalyst for synthesizing dimethyl carbonate - Google Patents

Abstract

The invention relates to a method for preparing a solid catalyst for synthesizing dimethyl carbonate. The method uses graphene oxide as a carrier and magnesium nitrate as an active component precursor, and can be obtained by impregnating, drying and roasting. A solid catalyst for synthesizing dimethyl carbonate by transesterification of ethylene carbonate and methanol. The method is simple to operate, and the obtained solid catalyst not only has high efficiency and low cost, but also can be continuously recycled after being filtered, has a long service life and is pollution-free. The catalyst is used to synthesize dimethyl carbonate through transesterification, and the yield of dimethyl carbonate can be up to 87.1%, and the selectivity is 99.3%.

Description

A kind of preparation method for the solid catalyst of synthesizing dimethyl carbonate

technical field

The invention relates to the field of preparation of solid catalysts, in particular to a preparation method of a solid catalyst for synthesizing dimethyl carbonate.

Background technique

Dimethyl Carbonate (Dimethyl Carbonate, DMC), is a colorless and transparent liquid at room temperature, hardly soluble in water, but miscible with almost all organic solvents such as alcohols, ethers, and ketones. DMC has very low toxicity and was listed as a non-toxic product in Europe in 1992. It is an environmentally friendly chemical raw material that meets the requirements of modern clean technology. Therefore, the synthesis technology of DMC has received extensive attention from the chemical industry at home and abroad.

The original production method of DMC was the phosgene method, which was successfully developed in 1918, but the toxicity and corrosiveness of phosgene limited the application of this method, especially with the increasing attention to environmental protection in the world, the phosgene method has been Be eliminated. In the early 1980s, the EniChem company in Italy realized the commercialization of the synthesis of DMC by oxidative carbonylation of methanol using CuCl as a catalyst. This is the first industrialized non-phosgene synthesis of DMC, and it is also the most widely used. craft. The defect of this process is that the deactivation of the catalyst is serious when the conversion rate is high, so the conversion rate per pass is only 20%. In the 1990s, the research on DMC synthesis technology developed rapidly. Ube of Japan improved the DMC synthesis process of methanol oxidative carbonylation in EniChem Company, and the conversion rate almost reached 100%. This process has been industrialized. However, this process uses CO as a raw material, and CO is a poisonous gas, so the safety problems caused by CO limit the application of this process.

Texaco Corporation of the United States developed a process of producing ethylene carbonate by reacting ethylene oxide with carbon dioxide, and then transesterifying with methanol to produce DMC. This process co-produces ethylene glycol and was industrialized in 1992. Ethylene oxide and carbon dioxide are used as raw materials to synthesize ethylene carbonate under the action of a catalyst, and then ethylene carbonate and methanol are transesterified to obtain dimethyl carbonate and by-product ethylene glycol is currently the most widely used dimethyl carbonate in China. Method for industrial production of esters.

The catalytic system for synthesizing dimethyl carbonate by transesterification reaction can be divided into homogeneous catalytic reaction and heterogeneous catalytic reaction according to different catalytic systems. At present, the synthesis of DMC at home and abroad is mainly through the homogeneous catalytic reaction system. The catalysts used in the reaction are, Alkali metal oxides, alkali metal hydroxides, alkali metal alkoxides, alkali metal carbonates, alkali metal oxalates, quaternary ammonium halides and organic bases, etc. Alkali metal oxides, hydroxides, carbonates and oxalates all exhibit good catalytic performance, but due to their small specific surface area and poor dispersion in the reaction system, the catalytic efficiency is low, and the amount of catalyst used is generally higher. Large; quaternary ammonium salts and organic bases are not only expensive, but also difficult to separate after the reaction, which can easily cause catalyst loss, which not only increases production costs, but also reduces product purity. Industrially, the used catalyzer of synthesizing dimethyl carbonate by ethylene carbonate and methyl alcohol is sodium methylate, and the use of sodium methylate catalyst has many shortcomings, which can be summarized as follows: (1) the consumption of catalyst is large, and now every ton of carbonic acid produced in industry Dimethyl ester needs about 80-110kg of sodium methylate 25-30% by mass percentage; (2) after the catalyst fails, a large amount of waste residue is produced, causing environmental pollution; (3) the separation of solids in the catalytic system affects the continuous production of the system Stability, blockage of pipelines and equipment, seriously affecting the continuity of production; (4) The synthesis process is complicated, in order to remove the catalyst waste residue from the reaction material system, and prevent the solid waste from being precipitated during rectification, it is attached to the inner wall surface of the heat exchanger tube And attached to the filler, the heavy component from the reactor of the reactive distillation column should be added to desalted water and carbon dioxide, so that the remaining catalyst sodium methoxide becomes invalid and becomes sodium hydroxide, and then reacts with carbon dioxide to become inorganic salt sodium carbonate. Then filter out sodium carbonate by filter, which makes the production process very complicated; (5) the catalyst cannot be reused, because after the catalyst fails, it generates sodium carbonate inorganic salt, which no longer has catalytic effect.

Therefore, the object of the present invention is to develop and operate simply, product and catalyzer are separated conveniently, and gained product purity is high, and the method for the good synthetic dimethyl carbonate of catalyzer recovery and reuse performance. However, so far, there has been no literature report on the preparation of supported catalysts for the synthesis of dimethyl carbonate using graphene oxide as a carrier.

Contents of the invention

The technical problem to be solved in the present invention is to provide a kind of simple operation, easy to separate the product and the catalyzer for the problems such as large amount of catalyst used in the synthesis of DMC by transesterification, difficulty in catalyst separation and recovery, and low yield of product DMC. The method for synthesizing dimethyl carbonate has high product purity and good catalyst recovery and reuse performance.

In order to solve the above problems, the present invention provides a solid catalyst for synthesizing DMC and a preparation method thereof, which can realize high catalytic activity and high selectivity of the solid catalyst in the transesterification reaction of ethylene carbonate and methanol, and catalyst recovery and recycling The use is simple, and the reaction cost is greatly reduced.

The technical solution adopted by the present invention to solve its technical problems is:

Catalyst preparation method:

(1) Add a certain amount of graphene oxide into deionized water, the mass ratio of graphene oxide to deionized water is 1:10-1:20, ultrasonically disperse at room temperature for 30-60 minutes, and the power is 120-240W;

(2) Magnesium nitrate is added in the material of step (1) gained, and at room temperature magnetic stirring 12h, wherein the mass ratio of magnesium nitrate and graphene oxide is 1:10～1:20;

(3) Evaporate the substance obtained in step (2) to dryness in a water bath, then transfer it to an oven for drying, then transfer it to a tube furnace, heat up to 400-450 ° C under a nitrogen atmosphere or an argon atmosphere, and Keep at the temperature for 3h-6h, then drop to room temperature.

Wherein carrier graphene oxide is prepared by the following method:

In an ice-water bath, mix 5g flake graphite and 2.5g sodium nitrate with 115mL of concentrated sulfuric acid evenly, slowly add 15gKMnO ₄ while stirring, keep the reaction below 2°C for 1h, transfer it to a 35°C water bath for 30min, and gradually add 250mL After deionized water, the temperature was raised to 98°C and the reaction was continued for 1 h. It was clearly observed that the mixture changed from brown to bright yellow. Further dilute with water continuously, and treat with 30% H ₂ O ₂ solution. Suction filter the above solution, wash with 5% HCl solution until neutral, put the filter cake in an oven at 80°C and fully dry to obtain graphite oxide. Take 0.1g of graphite oxide and put it into 50mL of deionized water, ultrasonically treat it for 1.5h (180W, 60Hz), then perform suction filtration, put the filter cake in a vacuum oven at 40°C (10Pa) and dry for 6h to obtain the desired graphene oxide .

The present invention uses graphene oxide as a carrier and magnesium nitrate as a precursor to successfully prepare a graphene oxide-supported magnesium oxide catalyst. Compared with the traditional catalyst carrier molecular sieve or activated carbon, graphene oxide is low in cost and is an ideal material as a catalyst carrier. In addition, graphene oxide has the advantage of small mass transfer resistance as a catalyst carrier, because it is only a planar two-dimensional structure, which is unmatched by materials such as molecular sieves or activated carbon; in addition, a large number of carboxyl functional groups on graphene oxide can be combined with Metal magnesium ions form a coordination bond, which not only makes the magnesium oxide uniformly dispersed on the surface of the carrier during the impregnation process, but also can fix the magnesium oxide well, thereby avoiding the loss of active components. The method of the invention is simple, low in cost, good in immobilization effect and high in catalyst activity, is an effective method for preparing a supported catalyst, and successfully overcomes the disadvantages of the traditional method.

Applying the solid catalyst of the present invention to the transesterification reaction of ethylene carbonate and methanol to synthesize dimethyl carbonate has achieved good results. During the reaction process, the catalyst not only has high catalytic activity, but also can be recycled and reused after simple filtration after the reaction, has a long service life, no pollution, and greatly reduces the preparation cost of the catalyst.

Detailed ways

The present invention will be further described with reference to the following examples, but it should be understood that these examples are for illustrative purposes only and should not be construed as limitations on the implementation of the present invention.

Example 1

Take 0.2g of graphene oxide and add it to 2mL of deionized water, then sonicate at room temperature for 30 minutes with an ultrasonic power of 200W; then add 0.03g of magnesium nitrate to the above solution, stir at room temperature for 12h; evaporate the obtained substance to dryness in a 70°C water bath , then transferred to an oven and dried at 100°C for 6h; then transferred to a tube furnace, heated to 450°C at a rate of 10°C/min under nitrogen, and kept at this temperature for 3h, then dropped to At room temperature, catalyst A was obtained.

Example 2

Take 0.2g of graphene oxide and add it to 2mL of deionized water, and then ultrasonicate at room temperature for 60 minutes, with an ultrasonic power of 120W; then add 0.03g of magnesium nitrate to the above solution, and stir at room temperature for 12h; evaporate the resulting substance to dryness in a 70°C water bath , then transferred to an oven and dried at 100°C for 6h; then transferred to a tube furnace, heated to 450°C at a rate of 10°C/min under nitrogen, and kept at this temperature for 3h, then dropped to At room temperature, catalyst B was obtained.

Example 3

Take 0.2g of graphene oxide and add it to 4mL of deionized water, then sonicate at room temperature for 60 minutes with an ultrasonic power of 240W; then add 0.04g of magnesium nitrate to the above solution, stir at room temperature for 12h; evaporate the resulting substance to dryness in a 70°C water bath , then transferred to an oven and dried at 100°C for 6h; then transferred to a tube furnace, heated to 450°C at a rate of 10°C/min under nitrogen, and kept at this temperature for 3h, then dropped to At room temperature, catalyst C was obtained.

Example 4

Take 0.2g of graphene oxide and add it to 4mL of deionized water, then sonicate at room temperature for 60 minutes with an ultrasonic power of 240W; then add 0.02g of magnesium nitrate to the above solution, stir at room temperature for 12h; evaporate the resulting substance to dryness in a 70°C water bath , then transferred to an oven and dried at 100°C for 6h; then transferred to a tube furnace, heated to 450°C at a rate of 10°C/min under nitrogen, and kept at this temperature for 3h, then dropped to At room temperature, the catalyst D was obtained.

Comparative example 1

In this comparative example, graphene oxide is used as a catalyst, which is denoted as catalyst E.

Above-mentioned catalyst is used for the reaction of ethylene carbonate and methyl alcohol respectively, and reaction condition is:

The molar ratio of ethylene carbonate to methanol is 1:10, the amount of catalyst used is 1% of the mass of ethylene carbonate, the reaction temperature is 70°C, and the reaction time is 4h.

The reaction product is analyzed by gas chromatography. The conditions of chromatographic analysis are: OV-101 capillary chromatographic column, the temperature of the gasification chamber and the detector is 250 ° C, and the temperature of the column oven is 80 ~ 180 ° C. The temperature is programmed to determine the yield and selectivity of the product. The specific results are shown in Table 1.

Catalytic activity of table 1 catalyst

catalyst Dimethyl carbonate selectivity (%) Dimethyl carbonate yield (%) A 98.7 79.3 B 99.1 81.1 C 99.3 87.1 D. 98.2 75.2 E. 99.5 2.4

As can be seen from Table 1, the catalyst of the present invention is applied in the transesterification reaction, and the catalyst has higher activity.

The catalyst in the reaction solution was recovered by filtering, and reused after drying. The results of repeated use of catalyst C in the transesterification reaction of ethylene carbonate and methanol are shown in Table 2.

Table 2 Catalyst Repeated Experiment Results

Cycles Dimethyl carbonate selectivity (%) Dimethyl carbonate yield (%) 1 99.3 87.1 2 99.1 87.0 3 98.8 86.9

As can be seen from Table 2, after the catalyst has been recycled three times, the selectivity and yield of dimethyl carbonate are basically stable, indicating that the catalyst can be reused without reducing its catalytic activity, and has a good effect.

Inspired by the above-mentioned ideal embodiment according to the present invention, through the above-mentioned description content, relevant workers can make various changes and modifications within the scope of not departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, but must be determined according to the scope of the claims.

Claims (1)

1. a kind of preparation method of solid catalyst for Synthesis of dimethyl carbonate, it is characterised in that this method is to aoxidize stone Black alkene be carrier, using magnesium nitrate as presoma, by dipping, drying, roasting method by MgO-Supported in graphene oxide On, what this method specifically carried out as steps described below：

(1) a certain amount of graphene oxide is added in deionized water, the mass ratio of graphene oxide and deionized water is 1:10 ~1:20, ultrasonic disperse 30~60 minutes under room temperature, 120~240W of power；

(2) magnesium nitrate is added in the substance obtained by step (1), and magnetic agitation 12h at room temperature, wherein magnesium nitrate and oxidation The mass ratio of graphene is 1:10~1:20；

(3) step (2) obtained material is evaporated in a water bath, is subsequently transferred to dry in baking oven, is subsequently transferred in tube furnace, It is warming up to 400~450 DEG C under nitrogen atmosphere or argon gas atmosphere, and keeps 3h~6h at this temperature, is subsequently reduced to room temperature.