Preparation method of modified molecular sieve loaded Pd catalyst and application of modified thereof in synthesis of dimethyl carbonate by gas phase process

Abstract

The invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method of a modified molecular sieve loaded Pd catalyst and application thereof in synthesis of dimethyl carbonate by a gas phase process. The carrier of the catalyst is a modified FAU or EMT molecular sieve, main active components are zero-valent palladium (Pd) and valence state Pd, themass fraction of Pd in the catalyst is 0.1%-2.5%, and the average particle size of Pd particles is 0.2-15 nanometers. The catalyst is applied to a reaction for synthesizing dimethyl carbonate from carbon monoxide and methyl nitrite by a low-pressure gas phase process, solves the problems of equipment corrosion and inactivation caused by a traditional chlorine-containing catalyst, and is a high-performance catalyst which is high in stability, selectivity and conversion rate, resistant to sintering, free of chlorine and adjustable in Pd nanoparticle size. The preparation method of the catalystis simple, low in equipment requirement and low in production cost, is suitable for large-scale production, and has certain industrial application prospect.

Description

technical field [0001] The invention belongs to the technical field of catalyst preparation, and in particular relates to a preparation method of a modified molecular sieve supported Pd catalyst and its application in gas-phase synthesis of dimethyl carbonate. Background technique [0002] Dimethyl carbonate (Dimethyl carbonate, DMC) is an important environment-friendly chemical raw material. It has been listed as a non-toxic chemical as early as 1992. It can be used to produce polycarbonate, pharmaceuticals, pesticides and other products, instead of phosgene and halogenated Methane and dimethyl sulfate are used as carbonylation and methylation reagents, and are used as solvents in the lithium battery electrolyte and paint coating industries (accounting for more than 50% of my country's total DMC consumption), and are expected to replace toxic methyl tert-butyl ether ( MTBE) as gasoline and diesel additives. According to statistics, the market demand for DMC in my country has...

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Problems solved by technology

The phosgene method is being phased out due to the disadvantages of high raw material toxicity, poor safety, and serious environmental pollution; although the transesterification method has the advantages of simple operation and mild reaction conditions, it is relatively difficult to separate and purify the target product, and the cost is relatively high The uric acid alcoholysis method also encounters the problem of subsequent separation difficulties due to the use of a homogeneous catalyst; although the one-step synthesis method of methanol and carbon dioxide is simple, the activity of the catalyst is relatively low

The conversion rate of methanol and carbon dioxide reported in the Chinese patent CN110479287A is only 11.2%, the selectivity of dimethyl carbonate is 75.6%, and the yield is only 8.5%.

Chinese patent application publication number CN106423289A publicly reports a kind of catalyst used for synthesizing dimethyl carbonate and preparation method thereof, adopts copper and potassium as the auxiliary agent of molecular sieve loaded Pd catalyst, and the space-time yield of this catalyst is 690g / (Lh), yet The selectivity of dimethyl carbonate based on methyl nitrite is only 45% to 51%, which shows that the selectivity of the catalyst is relatively low

A molecular sieve-loaded Pd catalyst was prepared by Japan Ube Corporation Yamamoto et al. The selectivity of dimethyl carbonate based on methyl nitrite was 75%, and the CO conversion rate even decreased to 75% of the initial conversion rate after 150 hours of operation. It can be seen that the company The stability of prepared molecular sieve supported Pd catalyst is poor, (Catalysis and characterizationof Pd / NaY for dimethyl carbonate synthesis from methyl nitrite and CO, Yamamoto etc., J.Chem.Soc.Faraday Trans., 1997, volume 93, No. 3721 pages)

In summary, the introduction of chlorine in chlorine-containing catalysts will lead to serious corrosion of equipment and low purity of DMC products, while the conversion and selectivity of chlorine-free Pd / molecular sieve catalysts are low and their stability is poor, and there are still problems. big room for improvement

[0005] In the catalyst preparation process, due to the imperfect preparation method or the unsatisfactory distribution of the noble metal catalyst, the noble metal catalyst will have larger metal particles. For example, when the traditional palladium-based catalyst is prepared by excess or equal impregnation method, this impregnation method prepares The distribution of Pd particles in the palladium-based catalyst is often uneven, and larger Pd particles will be produced, resulting in a catalyst with a lower degree of metal dispersion, thereby increasing the production cost of the Pd catalyst

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