阅读说明：本技术 一种碳酸二甲酯合成专用催化剂及其制备方法 (Special catalyst for synthesizing dimethyl carbonate and preparation method thereof ) 是由 姚元根 郭榕 覃业燕 陈建珊 丁一凡 朱焜 于 2020-06-11 设计创作，主要内容包括：本发明公开了一种碳酸二甲酯合成专用催化剂及其制备方法,该催化剂表示为PdCu/M<Sub>x</Sub>O<Sub>y</Sub>-Y,其中M<Sub>x</Sub>O<Sub>y</Sub>-Y代表氧化物修饰的分子筛,活性金属组分Pd和助剂Cu负载在该分子筛上,Pd的负载量为0.5-1％,Cu的负载量为1-2％。该催化剂的制备特点在于对分子筛载体的改性,将分子筛通过金属离子交换、沉淀和焙烧等过程,生成金属氧化物修饰分子筛表面结构,该载体的相比于传统的Y分子筛,其表面酸性降低。将该载体制备成催化剂应用于亚硝酸甲酯羰基化合成碳酸二甲酯的过程中,能够有效抑制亚硝酸甲酯的分解,从而提高催化剂的选择性和时空收率。(The invention discloses a special catalyst for synthesizing dimethyl carbonate and a preparation method thereof, wherein the catalyst is represented as PdCu/M x O y -Y, wherein M x O y Y represents an oxide modified molecular sieve, an active metal component Pd and an auxiliary agent Cu are loaded on the molecular sieve, the load of Pd is 0.5-1%, and the load of Cu is 1-2%. TheThe preparation of the catalyst is characterized in that the molecular sieve carrier is modified, the molecular sieve is subjected to metal ion exchange, precipitation, roasting and other processes to generate a metal oxide modified molecular sieve surface structure, and the surface acidity of the carrier is reduced compared with that of the traditional Y molecular sieve. The catalyst prepared from the carrier is applied to the process of synthesizing dimethyl carbonate by carbonylation of methyl nitrite, and can effectively inhibit the decomposition of methyl nitrite, thereby improving the selectivity and the space-time yield of the catalyst.)

1. A preparation method of a special catalyst for synthesizing dimethyl carbonate comprises the following specific preparation steps:

A. dissolving soluble metal salt in water to prepare 0.4-1mol/L metal salt solution, adding a commercially available Y-type molecular sieve according to the mass ratio of the metal simple substance to the Y molecular sieve of 0.05-0.2:1, and carrying out ultrasonic treatment for 30-35min to obtain a mixed solution;

the metal salt is one of nitrate, sulfate and chloride of aluminum, titanium, zirconium, lanthanum, cerium and neodymium;

B. slowly dripping alkali solution into the mixed solution under the stirring condition of 30-60 ℃ until the metal and the alkali completely react to generate precipitate, continuing stirring for 20-30min after the dripping of the alkali solution is finished, performing suction filtration and washing, drying for 4-8h at the temperature of 100-650 ℃, and roasting for 4-8h at the temperature of 350-650 ℃ to obtain the oxide modified molecular sieve, which is marked as M_xO_y-Y；

C. An active metal component Pd and an auxiliary agent Cu are loaded on M by an ion exchange method_xO_yLoading the catalyst on Y according to the loading amounts of Pd0.5-1% and Cu 1-2%, and preparing the catalyst expressed as PdCu/M_xO_y-Y。

2. The catalyst prepared by the method of claim 1 and used for synthesizing dimethyl carbonate, wherein the catalyst is PdCu/M_xO_y-Y, wherein M_xO_yY represents an oxide modified molecular sieve, an active metal component Pd and an auxiliary agent Cu are loaded on the molecular sieve, the load of Pd is 0.5-1%, and the load of Cu is 1-2%.

Technical Field

The invention belongs to the technical field of catalysis for synthesizing dimethyl carbonate by carbonylation of methyl nitrite, and particularly relates to a preparation technology of a composite carrier.

Background

Dimethyl Carbonate (DMC) is an important green chemical, and is widely used in the fields of polycarbonate synthesis, electrolyte additives, coatings and the like. At present, dimethyl carbonate is mainly prepared at home and abroad by adopting an ester exchange method, which has the problems of mild reaction conditions and low equipment corrosivity, but has the problems of low conversion rate and high energy consumption. With the continuous development of the market of dimethyl carbonate, the development of a new process route is imperative.

In recent years, the coal chemical industry is continuously developed, coal is used as a raw material, synthesis gas is extracted through conversion, and then different chemicals such as ethanol, ethylene glycol, low-carbon olefin and the like can be produced through a series of reactions. On the basis of the development of the technology for preparing the ethylene glycol from the coal, the technology for preparing the dimethyl carbonate from the coal is carried out. Through the introduction of intermediate methyl nitrite, the carbon monoxide and methyl nitrite can synthesize dimethyl carbonate under the action of a catalyst. In the technology of preparing dimethyl carbonate from coal, the development of a high-efficiency catalyst required for synthesizing dimethyl carbonate is crucial.

Catalysts used in the technology of preparing dimethyl carbonate from coal are mainly divided into two types, one type is a chlorine system catalyst taking activated carbon and lithium aluminum spinel as carriers (U.S. Pat. No. 5,5426209 and U.S. Pat. No. 5,5688984); the other is a chlorine-free system catalyst using Y molecular sieve as carrier (patent CN 1227839A). The catalyst stability is poor due to the problem of chlorine loss of the catalyst containing chlorine system, and the chlorine loss also has certain influence on equipment corrosion. The stability of the catalyst can be improved by a series of chlorine supplementing measures, but the problem of poor stability cannot be thoroughly solved. The chlorine-free system catalyst has excellent stability due to the pore structure characteristics of the molecular sieve, and has the defects of low conversion per pass of carbon monoxide, low selectivity of dimethyl carbonate product and low selectivity, and the problem of low selectivity mainly shows that methyl nitrite is decomposed to generate methanol, Methyl Formate (MF) and Dimethoxymethane (DMM). Aiming at the defects of the catalyst of the chlorine-free system, the design of a novel catalyst is the current research focus.

The McClin subject group at Tianjin university regulates and controls the electron cloud density of the active component Pd by a K additive modification method, and further influences the Activation of Carbon Monoxide (ChemCatchem, Synergy between Palladium and Potasassspeces for Efficient Activation of Carbon Monoxide in the Synthesis of dimethyl Carbonate, 2015, Vol 7, 2460-one 2466). The clever subject group of Fujian substance structure research institute of Chinese academy of sciences prepares the monatomic Pd/NaY catalyst by ion exchange and ammonia evaporation methods, and greatly improves the yield of the chlorine-free system catalyst (ACS catalyst, Synthesis of High-Performance and High-Stability Pd (II)/NaYCatacatalyst for CO Direct Conversion to Dimethyl Carbonate by ratio design, 2019, Vol 9, 3595 3603). In patent 201911100067.1, Yuangen subject group Yao, a institute of Fujian substance Structure, of Chinese academy of sciences, autonomously synthesizes a Y molecular sieve, and modulates a Y molecular sieve skeleton structure by adding components such as titanium, phosphorus and the like, so that the electron cloud density of active components is influenced, the activation of reactant CO is further regulated and controlled, and the catalyst performance is improved. It can be seen that the performance of the chlorine-free system catalyst can be effectively improved by optimally designing the active center, but no clear effective measure exists for the problem of methyl nitrite decomposition at present.

Disclosure of Invention

Aiming at the problem of methyl nitrite decomposition in a chlorine-free system catalyst for synthesizing dimethyl carbonate by using carbon monoxide and methyl nitrite, the invention designs a novel catalyst which can effectively reduce the decomposition of methyl nitrite and improve the selectivity of dimethyl carbonate.

The carbonic acid provided by the inventionThe catalyst special for synthesizing dimethyl ester is PdCu/M_xO_y-Y, wherein M_xO_yY represents an oxide modified molecular sieve, an active metal component Pd and an auxiliary agent Cu are loaded on the molecular sieve, the load of Pd is 0.5-1%, and the load of Cu is 1-2%.

The preparation method of the novel carrier provided by the invention comprises the following steps:

A. dissolving soluble metal salt in water to prepare 0.4-1mol/L metal salt solution, adding a commercially available Y-type molecular sieve according to the mass ratio of the metal simple substance to the Y molecular sieve of 0.05-0.2:1, and carrying out ultrasonic treatment for 30-35min to obtain a mixed solution.

The metal salt is one of nitrate, sulfate and chloride of aluminum, titanium, zirconium, lanthanum, cerium and neodymium;

B. slowly dripping alkali solution into the mixed solution under the stirring condition of 30-60 ℃ until metal and alkali completely react to generate precipitate, continuing stirring for 20-30min after the dripping of the alkali solution is finished, performing suction filtration, washing, drying at 100-650 ℃ for 4-8h, and finally roasting at 350-650 ℃ for 4-8h to obtain the oxide modified molecular sieve, which is marked as M_xO_y-Y。

C. An active metal component Pd and an auxiliary agent Cu are loaded on M by an ion exchange method_xO_yLoading the catalyst on Y according to the loading amounts of Pd0.5-1% and Cu 1-2%, and preparing the catalyst expressed as PdCu/M_xO_y-Y。

The invention disperses exchangeable metal ions by an ultrasonic-assisted ion exchange method, so that the exchangeable metal ions enter a molecular sieve pore passage; the alkali liquor is added to make metal ions form precipitates, and the precipitates can be decomposed by a high-temperature roasting method, so that the Y molecular sieve modified by the metal oxide is formed.

FIGS. 1, 2 and 3 show the comparison of the physicochemical properties of the metal oxide modified Y molecular sieve prepared by the present invention and the unmodified Y molecular sieve.

As can be seen from FIG. 1, in the metal oxide-modified Y molecular sieve, the intensity of the diffraction peak characteristic of the Y molecular sieve is greatly reduced, while the intensity of the diffraction peak characteristic of the corresponding metal oxide is significant, wherein the Nd in example 4₂O₃Easily react with water to generate Nd (OH)₃The precipitate is attached to the pore canal of the molecular sieve, so the characteristic peak is attributed to Nd (OH)₃. Indicating that the metal oxide was successfully added to the Y molecular sieve structure.

Fig. 2 shows that the pore size of the Y molecular sieve modified by metal oxide is reduced, and the introduction of metal oxide does not significantly increase the mesoporous structure.

From fig. 3, it can be seen that the surface acidity of the Y molecular sieve modified by the metal oxide is significantly changed. The desorption curves of examples 1, 2 and 3 are basically consistent with those of the unmodified Y molecular sieve, but the acid amount is obviously reduced, which shows that the acidity of the surface of the Y molecular sieve can be effectively reduced by proper metal oxide modification. Example 4 has two more desorption peaks at 290 ℃ and 430 ℃, which indicates that the number of strong acid sites in the sample is increased, and this may be related to the generation of Nd (OH) 3.

The catalyst of the invention is mainly used in the process of generating dimethyl carbonate by the reaction of carbon monoxide and methyl nitrite, the table 2 shows the application examination result of the catalyst, and the examination process conditions are as follows: the reaction temperature is 120-140 ℃; the reaction pressure is normal pressure; the space velocity is 2400-^-1(ii) a The raw material components are respectively CO 10%; CH (CH)₃ONO 20-40％；N₂50-70% by volume. As can be seen from Table 2, the catalyst of the present invention has high selectivity to both carbon monoxide and methyl nitrite, and the space-time yield of dimethyl carbonate reaches about 700 g/(l.h).

The invention has the beneficial effects that: the Y molecular sieve is modified by proper metal oxide, so that the surface structure of the Y molecular sieve is changed, and acid sites on the surface of the molecular sieve can be reduced. The molecular sieve is applied to the process of synthesizing dimethyl carbonate by carbonylation of methyl nitrite, so that the decomposition of the methyl nitrite is effectively inhibited, and the selectivity and the space-time yield of the catalyst are improved.

Drawings

FIG. 1 is an XRD comparison of the sample obtained in step A of examples 1-4 with a commercially available Y molecular sieve, wherein a, b, c, d correspond to the oxide modified Y molecular sieve of step A of examples 1-4, respectively, and e is the commercially available Y molecular sieve.

FIG. 2 is a graph comparing the pore size distribution of the sample obtained in step A of examples 1-4 with that of a commercially available unmodified Y molecular sieve, wherein a, b, c, d correspond to the oxide-modified Y molecular sieve in step A of examples 1-4, respectively, and e is a commercially available Y molecular sieve.

FIG. 3 shows the samples obtained in step A of examples 1-4 and commercial unmodified Y molecular sieve NH₃TPD comparison scheme, wherein a, b, c, d correspond to the oxide modified Y molecular sieves of steps A of examples 1-4, respectively, and e is a commercially available Y molecular sieve.

Detailed Description