Chemical catalysts controlled by foreign patent holders: anhydride catalysts

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Chemical catalysts controlled by foreign patent holders: Anhydride catalysts. Immersive reading in a novel reader. Dicyanodiphenylmethane anhydride (PMDA) and its derivatives have a wide range of applications; they are used primarily as monomers for high-temperature resistant specialty engineering resins such as polyimides (PI), as high-performance plasticizers, as curing agents for epoxy resins, as intermediates in the pharmaceutical industry, as intermediates for matting agents in powder coatings, and for modifying alkyd and polyester resins. Products made from these materials are widely utilized in cutting-edge technologies across fields such as aerospace and the electronics industry. The mainstream production process for symmetrical anhydrides involves catalytic oxidation using p-toluenetetramethyl (1,2,4,5-tetramethylbenzene). The methods for the gas-phase oxidation of p-menthane to p-anhydride mainly include: ① Air oxidation method ； ②Nitric acid oxidation method ； ③Chromic acid oxidation method ； ④Potassium permanganate oxidation method ； ⑤At 300 atmospheres, using methods such as SO2 oxidation in the presence of HBr or other hydrogen halides. Among them, nitric acid oxidation, chromic acid oxidation, potassium permanganate oxidation, and halogenated hydroxide oxidation all cause serious pollution and equipment corrosion problems. The commonly used oxidation method at present is a one-step oxidation process using p-tertoluenes as the raw material in the presence of air. The air-phase oxidation of tetramethylbenzene is a complex organic reaction. P-tertoluenes undergo demethylation to yield o-xylene, m-xylene, p-xylene, and benzene, which are then oxidized on the catalyst to phthalic anhydride, isophthalic anhydride, and trimellitic anhydride respectively, resulting in a low yield of the anhydrides. Therefore, it is of extreme importance for manufacturing companies to develop catalysts that facilitate the conversion of p-tertoluenes to pyromellitic anhydride, as this can significantly improve economic efficiency. Research on anhydride catalysts both domestically and internationally has been quite active; vanadium (V) is almost always used as the main active component, while the promoters are selected from oxides of elements such as Sb, Cr, Mn, Ti, Bi, P, Cu, Al, as well as oxides of elements from group VIIIB of the periodic table, oxides of alkali metals and/or alkaline earth metals, and oxides of rare earth metals. In recent years, research on anhydride catalysts has mainly focused on using V as the main component, with anatase TiO2 powder as the carrier, and adding oxides of one or more elements to create ternary and multi-component composite catalysts. This approach is simple, allows for continuous production, is easy to automate, results in low pollution, and has low production costs; it is therefore the primary method used for manufacturing anhydride catalysts. As early as 1947, California Research Corp in the United States used a gas-phase method to oxidize p-tert-butylbenzene to produce pyromellitic anhydride, employing a V2O5 composite oxide catalyst for the first time. Since then, V-based phosgene catalysts have attracted widespread attention. In 1987, Nippon Shokubai used a V-Ti-based catalyst in the catalytic process for producing terephthalic acid or its anhydride, adding Nb2O5, P2O5, and Sb2O3 as promoters. A few years later, the company developed another V-Ag series catalyst, in which the ratio of Ag to V, the main active components, was between 0.001 and 0.2; elements such as Ti, P, Mo, and W were also added to this catalyst, giving it a longer service life. In industrial installations, the advantage of the gas-phase oxidation method is that it enables one-step conversion to the target product, with no solvent interfering with the raw materials or the product. However, in coated catalysts, the coating inevitably peels off during the loading process and under high space velocities during the reaction, which affects the catalyst’s lifespan. Therefore, in addition to studying the active components of the catalysts, researchers have also investigated the carrier and the issue of the bonding between the coating and the carrier. At present, there is considerable research in China on anhydrides and catalysts. Institutions such as the Beijing Research Institute of Chemical Technology and the Shanghai Research Institute of Chemical Technology, which are part of the Sinopec group, have carried out relevant work. In addition, some private chemical and catalyst companies have also developed catalyst products and achieved successful industrial applications. Overall, however, the catalysts and related production processes for anhydride in our country are still relatively underdeveloped. There are still issues such as small production scales, low yields, and unsatisfactory product quality when it comes to anhydide production; in particular, the actual quality yield of anhydride is still far from the theoretical yield. Furthermore, due to the high technical barriers, anhydride catalysts imported from abroad are expensive, costing around several hundred thousand yuan per ton. Moreover, they need to be replaced regularly on a yearly basis during the production process, which represents a significant burden on a company’s production costs. To improve the domestic production level of maleic anhydride, it is also necessary to increase research on maleic anhydride catalysts, particularly in terms of the selection and optimization of the active components and additives used in these catalysts. The development of functional composite oxide carriers with TiO2 as the main component, as well as processes such as slurry spraying and calcination, are important steps to enhance the conversion rate and selectivity of the oxidation reaction, thereby reducing the generation of by-products and waste, as well as pollutant emissions