CN109647497B

CN109647497B - Catalyst for preparing dimethyl carbonate from epoxide, methanol and carbon dioxide, preparation method and application thereof

Info

Publication number: CN109647497B
Application number: CN201811460299.3A
Authority: CN
Inventors: 宋清文; 韩丽华; 刘平; 张侃; 吉可明
Original assignee: Shanxi Institute of Coal Chemistry of CAS
Current assignee: Shanxi Institute of Coal Chemistry of CAS
Priority date: 2018-11-30
Filing date: 2018-11-30
Publication date: 2022-05-24
Anticipated expiration: 2038-11-30
Also published as: CN109647497A

Abstract

A catalyst for preparing dimethyl carbonate from epoxide, methanol and carbon dioxide comprises metal oxide and HZSM-5 molecular sieve, and the weight percentage of the catalyst is as follows: 0.005-20% of metal oxide and the balance of HZSM-5 molecular sieve. The invention is directly realized for CO₂The methyl carbonate is prepared by the one-pot reaction of the methanol and the epoxide, and the method has the advantages of simple reaction steps, low cost and wider application prospect.

Description

Catalyst for preparing dimethyl carbonate from epoxide, methanol and carbon dioxide, preparation method and application thereof

Technical Field

The invention relates to a catalyst for preparing dimethyl carbonate from epoxide, methanol and carbon dioxide, a preparation method and application thereof.

Background

Carbon dioxide is an environmentally friendly carbon resource, which is abundant, non-toxic, non-flammable, inexpensive, readily available, and recyclable. CO, whether from the point of view of environmental protection or renewable resource utilization₂The research on the aspects of fixation and chemical transformation has great significance. In organic synthesis, CO₂Can partially replace traditional toxic compounds such as CO, phosgene and the like to synthesize organic carbonate, polycarbonate, urea and the like, and the three compounds are all industrially produced at present.

The organic carbonate is a green chemical with the characteristics of high boiling point, low vapor pressure, low toxicity and the like, and is widely applied to a plurality of fields of organic solvents, detergents, lithium battery electrolytes, fuel additives and the like. Organic carbonates can be classified into chain carbonates and cyclic carbonates. Chain carbonates of industrially important utility include: dimethyl carbonate (DMC), diphenyl carbonate (DPC), methylethyl carbonate, and the like; the cyclic carbonate includes: ethylene Carbonate (EC), Propylene Carbonate (PC), and the like. Wherein, the Dimethyl Carbonate (DCM) is colorless and transparent liquid at normal temperature and can be mutually dissolved with most organic solvents, in particular polar solvents such as alcohol, ketone, ether, ester and the like. DMC can replace Freon, trichloromethane, etc. as solvent, methyl tert-butyl ether (MTBE) as oil additive, halogenated methane and dimethyl sulfate as methylating agent and phosgene as carbonylating agent. DMC has wide application prospect in the fields of pesticide, medicine, plastic fuel, coating, new material and the like. Therefore, the synthesis of the dimethyl carbonate has very large practical application value and economic value.

The preparation method of the existing dimethyl carbonate at home and abroad mainly comprises the following steps: methanol oxidation carbonylation method, ester exchange method, urea alcoholysis method, methanol and CO₂A synthesis method and a phosgene method. In actual industrial production in China, the ester exchange method, the methanol oxidative carbonylation method and the phosgene method are mainly used. Phosgene is now being phased out because it is a toxic raw material and causes severe environmental pollution. The processes mainly used at present are the transesterification process and the methanol-carbonyl oxide process. The carbonyl oxide method has the advantages of high technical difficulty, strict requirements on process design and equipment material selection and high investment. The ester exchange method has the advantages of high yield of dimethyl carbonate, mild reaction conditions and nontoxic reaction process, and the byproduct diol compound is also an important chemical raw material. At present, the route is mainly divided into two steps, firstly, the cycloaddition reaction of carbon dioxide and epoxide is carried out to generate cyclic carbonate, and then the cyclic carbonate and methanol are subjected to ester exchange to generate dimethyl carbonate. The transesterification of cyclic carbonates with methanol can be carried out using acid and base catalysts, but the base is effective. All adopt in industry at presentHomogeneous catalysts, such as soluble bases like sodium methoxide, are used as transesterification catalysts. The disadvantages of the two-step process are high energy consumption and high investment. If the two reactions can be combined into one step, the separation process in the two steps of cycloaddition and ester exchange is avoided, the production cost is greatly reduced, and the method is the most promising method for producing the dimethyl carbonate. The most key step for realizing the three-component one-pot high-efficiency reaction is to simultaneously activate a reaction substrate and carbon dioxide by an active catalytic component, so that the reaction can be rapidly carried out under mild conditions. Several strategies are described below for the activation of carbon dioxide, epoxides and methanol.

CO₂The oxygen has weak Lewis basicity and can be used as a nucleophilic site, and the carbonyl carbon has weak Lewis acidity and can be used as an electrophilic site and is easy to react with an electron donor. Typical activated CO₂The strategy of (A) is to use nucleophiles to alter CO₂Linear molecular structure, giving it higher reactivity, further promoting CO₂The effective transformation of (1). Representative activating systems are strong organic bases, super bases and alcohol two-component systems, azacyclo-carbenes, ammonium tungstate, and the like. Another effective CO activation₂By using transition metal compounds to adjust their structure or charge distribution, e.g. nickel catalysts and d⁸-d¹⁰Late transition metal (Fe)⁰,Rh^I,Pd⁰,Pd^II) Catalysts, and the like.

After the epoxide is activated, the electron cloud density of the epoxy atom on the ring is reduced, and the ring-opening reaction is easier to occur. Thus activating the reaction substrate pair CO₂The chemical conversion reaction has a crucial role, and according to previous research reports, the activation modes of the epoxide are mainly divided into three types: 1) main group/transition metal as Lewis acid activating center; 2) as proton carriers

an acid activation center; 3) organic molecule cations (quaternary ammonium salt cations, quaternary phosphonium salt cations, ionic liquid and the like) are used as the activation centers. Among the most cost effective systems are quaternary ammonium salts as nucleophiles, using transition metal species to activate the reaction substrateAnd CO₂Thereby realizing high-efficiency catalytic conversion under low pressure and mild conditions.

Methanol acts as a nucleophile in this reaction, and thus, increasing the nucleophilicity of methanol helps to enhance the activity of the reaction. Such an activation effect can be achieved by the action of strongly electron donating species such as strong organic bases. The nitrogen atom in the organic alkali molecule is rich in electrons, and has hydrogen bond effect with the methanol hydroxyl group, so that the charge density on the methanol oxygen atom is improved, and the nucleophilicity is further improved.

ZSM-5 is aluminosilicate mesoporous zeolite molecular sieve with three-dimensional through pore channel structure, and has excellent thermal stability, acid and alkali resistance, oleophilic hydrophobicity and the like. The hydrogen type HZSM-5 has Lewis acid (Lewis acid) and Bronsted acid (Bronsted acid) at the same time, and the acid site and the acid density are adjustable. In addition, the acid-base catalytic property of the HZSM-5 can be adjusted in a targeted manner by simple methods such as supported metal or framework atom replacement. HZSM-5 molecular sieves have gained increasing attention as high-performance carriers or catalysts in the field of organic synthesis, and they can also be applied to CO₂Catalytic conversion reaction and easy recovery and reuse.

The invention is to mix CO₂Methanol and epoxide are added into a reactor at the same time, and dimethyl carbonate is directly synthesized under the condition of a proper catalyst. The process requires that the catalyst has catalytic activity for both cycloaddition and cyclic carbonate alcoholysis reactions, and the optimal reaction conditions are close. The catalyst consisting of metal species and the HZSM-5 molecular sieve is applied to three components to synthesize the dimethyl carbonate, is effective to cycloaddition reaction and alcoholysis reaction, and no relevant research report exists at present.

Disclosure of Invention

The invention aims to provide a method for preparing CO₂The catalyst for preparing dimethyl carbonate by the reaction of methanol and epoxide and the preparation method and application thereof.

The invention adopts a new heterogeneous catalysis mode, and constructs a multifunctional heterogeneous catalyst (M)/HZSM-5 based on an HZSM-5 molecular sieve. The catalyst has multiple activation sites and can be used for treating CO₂Double activation with reaction substrate to raise catalytic capacity greatlyThe compatible aims of high activation and catalytic capability and simple recycling are realized.

The functionalized (M)/HZSM-5 catalyst has rich and adjustable acid-base sites and can treat CO₂And organic reaction substrate, and the synergistic effect enables the heterogeneous catalytic system to be under low-pressure CO₂And high-efficiency catalytic conversion is realized under mild conditions. By the invention, the defects of high pressure, high catalytic amount and long reaction time of the traditional catalytic system are overcome, and a cheap and efficient heterogeneous catalytic method is provided, so that the method is convenient for large-scale application.

The catalyst composition of the invention comprises metal oxide and HZSM-5 molecular sieve.

The weight percentage of the catalyst is as follows: 0.005-20% of metal oxide and the balance of HZSM-5 molecular sieve.

The metal oxide is one or more of Zn, Mg, Ce, Ca, Co, La, Ga and Zr oxide.

The Si/Al molar ratio of the HZSM-5 molecular sieve is 10-130, and the specific surface area is 200-1000 m²·g^-1The particle diameter is 20-10000 nm, and the average pore diameter is 0.5-20 nm.

In order to achieve the purpose, the invention provides a modified HZSM-5 molecular sieve catalyst prepared by an impregnation method, and the specific preparation method comprises the following steps:

the concentration of the prepared metal cation is 0.01-0.50 g/ml^-1Adding the HZSM-5 molecular sieve into the metal nitrate solution, soaking for 1-24 h, drying for 2-24 h at 60-150 ℃, grinding the obtained solid, and roasting for 3-12 h at 200-450 ℃.

The metal nitrate is the nitrate of Zn, Mg, Ce, Ca, Co, La, Ga, Zr.

The application of the catalyst in preparing dimethyl carbonate has the following reaction conditions:

epoxide and methanol account for 10-50% of the volume of the reactor, quaternary ammonium salt and catalyst are added in the reaction system, and CO is filled in the reaction system at the reaction temperature of 60-180 DEG C₂The residence time of reactants in a reaction bed layer is controlled to be between 0.1 and 6MPa1-8 hours, wherein the molar ratio of epoxide to methanol is 1: 1-1: 30, the molar ratio of quaternary ammonium salt to epoxide is 0.05-0.2, and the ratio of the number of moles of epoxide to the mass of catalyst is 0.05-0.2 mmol/g based on the metal content in the metal oxide_cat，

The epoxide as described above is ethylene oxide or propylene oxide.

The quaternary ammonium salt is one of tetrapropylammonium bromide, tetraethylammonium chloride, tetrapropylammonium chloride, tetrabutylammonium chloride and tetrabutylammonium bromide.

The technical advantages of the invention are as follows:

the invention discloses an HZSM-5 molecular sieve catalyst modified by an impregnation method. Compared with the existing industrial catalyst, the invention has the substantive characteristics and the progress that:

(1) the industrial step catalyst is operated under higher reaction pressure, and provides more rigorous requirements for the design, manufacture and use conditions of a reactor, the working HZSM-5 molecular sieve is convenient for metal modification by a simple method, the reaction pressure is low, and the method has important significance for reducing the manufacturing cost of products;

(2) the HZSM-5 molecular sieve has Lewis acid and Bronsted acid, can activate and activate a plurality of substrates, and the (M)/HZSM-5 molecular sieve is used as a high-efficiency functional catalyst and is used for preparing dimethyl carbonate by three-component reaction, which is not reported;

(3) the HZSM-5 molecular sieve has oleophylic and hydrophobic characteristics, and compared with species such as metal oxide and the like, the surface of the HZSM-5 molecular sieve is easier to contact with a reaction substrate and interact with the reaction substrate, so that the reaction can be carried out efficiently;

(4) the functional molecular sieve is used as a catalyst, the three-component one-pot reaction is directly realized to prepare the dimethyl carbonate, the reaction steps are simple, the cost is low, and the application prospect is wider.

(5) Catalytic efficiency of the catalyst: the conversion rate is more than or equal to 99 percent, the yield of the carbonic ester is more than or equal to 99 percent, the catalyst is recycled for at least more than 6 times, and the activity is not reduced.

Detailed Description

The following provides a more detailed description of embodiments of the present invention by way of specific examples.

Example 1

The concentration of zinc ion is 0.2 g/ml^-1Adding HZSM-5 molecular sieve to dip the zinc nitrate solution for 12 hours, wherein the silicon-aluminum ratio of the ZSM-5 molecular sieve is 70, and the specific surface area is 700m²·g^-1The particle size is 10000nm, and the average pore diameter is 0.5 nm. And then drying at 80 ℃ for 2h, grinding the obtained solid, and roasting at 250 ℃ for 9h to obtain the required modified molecular sieve catalyst. The modified ZSM-5 molecular sieve catalyst prepared has the zinc oxide content of 0.5 percent by mass.

The catalyst is used for the reaction for preparing the dimethyl carbonate. The reaction raw materials are epoxypropane and methanol which account for 30 percent of the total volume of the reactor, the mol ratio of the epoxide to the methanol is 5, tetraethylammonium chloride is added into the reaction system, and the mol ratio of the tetraethylammonium chloride to the epoxypropane is 0.2. The molar ratio of the metal component in the (M)/HZSM-5 molecular sieve catalyst added in the reaction system to the epoxypropane is 0.2, the reaction temperature is 100 ℃, and CO is in the reactor₂The pressure is increased to 1MPa, and the residence time of reactants in the reaction bed is controlled to be 4 h.

Examples 2 to 11

On the basis of example 1, the catalyst composition, the preparation process and the reaction conditions were adjusted in examples 2 to 11, and the specific data are shown in attached table 1 and attached table 2. The reaction conditions and results are shown in Table 3.

Comparative example 1

The reaction raw materials are epoxypropane and methanol which account for 30 percent of the total volume of the reactor, the mol ratio of the epoxide to the methanol is 1:5, tetraethylammonium chloride is added into the reaction system, and the mol ratio of the tetraethylammonium chloride to the epoxypropane is 0.07. No catalyst is added in the reaction system, and CO is in the reactor at the reaction temperature of 100 DEG C₂The pressure is increased to 1MPa, and the residence time of reactants in the reaction bed is controlled to be 4 h. The data are shown in attached table 3.

Comparative example 2

On the basis of example 1, the catalyst composition and the reaction conditions were adjusted in comparative example 2, and the reaction raw materials were propylene oxide and methanol, which accounted for 30% of the total volume of the reactorAnd the molar ratio of the epoxide to the methanol is 1:5, and tetraethylammonium chloride is added into the reaction system, wherein the molar ratio of the tetraethylammonium chloride to the propylene oxide is 0.07. Adding unmodified HZSM-5 molecular sieve catalyst into a reaction system, wherein the mass ratio of the epoxide to the unmodified HZSM-5 molecular sieve catalyst is 10.0, and CO in a reactor is reacted at the temperature of 100 DEG C₂The pressure is increased to 1MPa, and the residence time of reactants in the reaction bed is controlled to be 4 h. The data are shown in attached table 3.

Catalyst preparation conditions according to FIG. 1

TABLE 2 catalyst composition

Examples	The composition of the metal oxide in the catalyst and the proportion/wt percent thereof
		1	Zinc oxide, 0.5
2	Magnesium oxide, 15
		3	Cerium oxide, 10
4	Calcium oxide, 10
		5	Cobalt oxide, 5
6	Lanthanum oxide, 10
		7	Gallium oxide, 2
8	Zirconium oxide, 5
		9	Zinc oxide, 5; magnesium oxide, 5
10	5 parts of calcium oxide; lanthanum oxide, 5
		11	Magnesium oxide, 8; cerium oxide, 7

Reaction conditions and results of attached Table 3

Claims

1. A catalyst for preparing dimethyl carbonate from epoxide, methanol and carbon dioxide is characterized in that: the concentration of the prepared gallium ions is 0.45 g/ml^-1Adding HZSM-5 molecular sieve to soak for 8h, wherein the HZSM-5 molecular sieve has a silica-alumina ratio of 10 and a specific surface area of 900m²·g^-1The particle size is 470nm, and the average pore diameter is 7 nm; then drying at 110 ℃ for 10h, grinding the obtained solid, and roasting at 300 ℃ for 8h to obtain the required modified molecular sieve catalyst; the gallium oxide mass percentage content in the prepared modified HZSM-5 molecular sieve catalyst is 2%;

the catalyst is used for the reaction for preparing the dimethyl carbonate; the reaction raw materials are epoxypropane and methanol, which account for 20 percent of the total volume of the reactor, and the molar ratio of the epoxide to the methanol is 1: adding tetrabutylammonium bromide into the reaction system, wherein the molar ratio of the tetrabutylammonium bromide to the propylene oxide is 0.17; ga added to the reaction system₂O₃The mol ratio of the metal component in the HZSM-5 molecular sieve catalyst to the epoxypropane is 0.17, the reaction temperature is 130 ℃, and CO is in the reactor₂The pressure is increased to 0.1MPa, and the residence time of reactants in a reaction bed layer is controlled to be 1.5 h.