Liquid-phase Beckmann Rearrangement Of Cyclohexanone Oxime Over Solid Acid

Solid acid catalyst is a new type of environmentally friendly catalytic material with the advantages of high catalytic activity,good selectivity,low corrosion,easy recovery and recycling.As the environmental awareness and green chemistry concept continue to deepen,environmentally friendly green catalytic technology has received more and more attention.Appling of solid acid catalyst in the liquid phase Beckmann rearrangement of cyclohexanone oxime is of great importance for developing environment-friendly caprolactam production process,which not only can alleviate the coking of the catalyst for longer lifetime,but also realize the rapid separation of the catalyst from the reaction solution.In this thesis,four kinds of solid acid catalysts were prepared and characterized,whose catalytic performance were evaluated in the liquid phase Beckmann rearrangement of cyclohexanone oxime.The reaction mechanism for the active center and rearrangement products were also investigated.Firstly,sulfated zirconia S-ZrO₂ was synthesized by precipitation-impregnation method.Fourier infrared spectroscopic analysis,thermogravimetric analysis,pyridine adsorption infrared spectrum and NH3 temperature-programmed desorption were used to characterize the structure of the S-ZrO₂.Its catalytic performance was studied in the liquid phase Beckmann Rearrangement.The results showed that the acid active site from SO₄^2-and Zr was favorable for the formation of caprolactam,while low conversion of cyclohexanone oxime was obtained because of the lower specific surface area of S-ZrO₂.In addition to cyclohexanone,the main by-products of the system were the polycondensation and polymerization products of cyclohexanone oxime and the polymerization product of the caprolactam.The hydrolysis reaction of the cyclohexanone oxime to cyclohexanone may occure with the forming of water from the polymerization of the cyclohexanone oxime.Secondly,the sulfated Zirconium silicate molecular sieve S-ZS was prepared by using MFI-type Zeolite as the carrier,after incorporation of heteroatom Zr into zeolite,the impregnation of sulfuric acid was carried out resulting in the composite catalyst with Zr and SO₄^2-as the superacid.The performance of the catalyst in the liquid phase Beckmann rearrangement was investigated.The results showed that the incorporation of Zr atoms and the further treatment of SO₄^2-can increase the activity of the catalyst to cyclohexanone oxime and the selectivity to caprolactam,what's more,reduce theselectivity to cyclohexanone.The caprolactam produced by the strong acid center of S-ZS was more difficult to desorption and can be further reacted to produce high boiling products.The kinds of byproducts and the formation approach of water in the system is the same as that of S-ZrO₂.Further,two kinds of aluminum-containing molecular sieves,TIE-MCM-41 and SA20-MCM-41,were prepared by template ion exchange method and in situ synthesis method,respectively.The obtained catalysts were characterized and used in the Beckmann rearrangement for comparision.The results showed that the activity of TIE-MCM-41 and SA20-MCM-41 were improved compared with Si-MCM-41,which were due to the increase of total amount of acid in two kinds of aluminum-containing molecular sieves.The reason for the increase of the selectivity of TIE-MCM-41 to caprolactam was that the Br?nsted acid had a slight increase and the decrease in the acidity and amout of the silanol OH groups.The SA20-MCM-41 with the highest selectivity to caprolactam was due to its highest content of Br?nsted acid and weak acid strength of o-adjacent silicon hydroxyl groups with reducing acid amount,which further inhibit the formation of cyclohexanone.Finally,two sulfonated functional mesoporous molecular sieves M-SO3H-P6 and M-SO3H-Y were prepared by post-grafting method and in situ synthesis method.The two catalysts were characterized and the performance differences were compared in the reaction of Beckmann Rearrangement.The results showed that the sulfonic acid functionalized materials synthesized by the two methods improved the catalytic activity for cyclohexanone oxime because of the increasing of the strong acid sites from sulfonic acid groups compared with pure silicon MCM-41.The content of Br?nsted acid in M-SO3H-Y was greater than that of M-SO3H-P6,and the former catalyst with in situ sulfonic acid functionalization almost had no surface silicon hydroxyl groups,which inhibited the hydrolysis of cyclohexanone oxime resulting in the higher selectivity to caprolactam.