Preparation Of Montmorillonite Composite Incorporated With Phosphotungstic Acid And Study On Its Catalytic Performance In Direct Synthesis Cyclohexanone Oxime From Cyclohexanol

Cyclohexanone oxime is an important intermediate to produce?-caprolactam.The traditional way to obtain cyclohexanone oxime is from cyclohexanone and hydroxylamine or hydroxylamine formed in situ with aqueous NH₃ and H₂O₂.The synthesis of cyclohexanone oxime using hydroxylamine as raw material suffers high cost and potential security liability.The hydroxylamine could be formed by in situ reaction of aqueous NH₃and H₂O₂ in the presence of TS-1.The process possesses the advantages of environment friendliness,mild reaction condition,high cyclohexanone conversion and selectivity to cyclohexanone oxime.However,the application of TS-1 zeolites is limited due to its difficulties of separation and recovery and high production cost.Phosphotungstic acid?HPW?is efficient multifunction catalysts in the process of ammoximation of cyclohexanone to produce cyclohexanone oxime.The synthesis of cyclohexanone oxime directly from cyclohexanol combined oxidation with simultaneous cyclohexanone oximation using hydrogen peroxide and aqueous ammonia on a single site multifunctional catalyst in a pot type reactor is an alternative route.Firstly,HPW-ex-MMT was prepared by introducing HPW to exfoliated MMT.HPW-ex-MMT was characterized by FT-IR,XRD,TGA,N₂ adsorption-desorption,UV-vis DRS,³¹P MAS-NMR,contact angle and SEM.And the results indicate that HPW is introduced and well dispersed on ex-MMT.A 90.1%conversion of cyclohexanol and 85.5%selectivity for cyclohexanone oxime was obtained under optimum reaction conditions.HPW-ex-MMT exhibited good catalytic performance in direct synthesis of various oximes from corresponding alcohols.The catalyst was reused for four times without the significant loss of catalytic performance.Secondly,the direct synthesis of cyclohexanone oxime is water-organic tandem process and hydrophobicity-hydrophilicity micro-environment is especially crucial for the water-organic tandem processes.HPW?in situ?-CTAB-MMT was synthesized in situ from Na₂WO₄ and Na₂HPO₄.The structure information,morphology properties and hydrophobicity of HPW?in situ?-CTAB-MMT were characterized by FT-IR,³¹P MAS-NMR,UV-vis DRS,XPS,XRD,N₂ adsorption-desorption and SEM,respectively.The results of distribution in a water-cyclohexanol biphasic system and adsorption tests of cyclohexanol and cyclohexanone oxime indicated HPW?in situ?-CTAB-MMT has high adsorption ability of cyclohexanol.A 95.8%conversion of cyclohexanol and 75.5%selectivity for cyclohexanone oxime was obtained over HPW?in situ?-CTAB-MMT.The good catalytic performance of HPW?in situ?-CTAB-MMT is attributed to the high dispersion of HPW in the interlayers of CTAB-MMT and high enrichment of the superhydrophobic HPW?in situ?-CTAB-MMT for the reactants.The anchor effect of HPW on interlayers of CTAB-MMT inhibits the active sites leaching,leading to its high catalytic recyclability with almost unchanged catalytic efficiency for more than 6 times.