Study On Ammoximation Of Cyclohexanone Catalyzed By Magnetic Titanium Silicalite Molecular Sieve

Cyclohexanone oxime is the important precursors of caprolactam in the industry field.About90%of caprolactam is produced by using cyclohexanone oxime as raw materialthrough Beckmann rearrangement method. However, the traditional process exist someshortcomings such as complex technologies, more intermediate steps and discharge oflow-product ammonium sulfate and contaminate nitrogen oxides for the synthesis of massivehydroxylammonium salts, which resulting in inefficient production of caprolactam andserious environmental pollution problems. Cyclohexanone oxime can be obtained in the mildreaction conditions with high selectivity by titanium silicate molecular sieves. The noveltechnology has showed a lot of advantages such as brief process, environment-friendly andmild reaction conditions and so on. However, there is a problem with the liquid-solidseparation and recycle of the catalytic agent due to its small particle size. Magnetic titaniumsilicalite molecular sieves was proposed and prepared to achieve a fast and efficient recoveryof the catalyst by means of an external magnetic field. In this paper ammoximation ofcyclohexanone catalyzed by magnetic titanium silicalite molecular sieve was studieddetailedly and optimum operating conditions and reaction kinetics parameters was achieved toprovide theoretical references for industrialization.Magnetic titanium silicalite molecular sieves was synthesized via the process ofhydrothermal synthesis and solvent vaporation method by using orthosilicate ester as silicasource, tetrabutyl titanate as the titanium source, tetrapropylammonium ammonium hydroxideas a template agent and nanosized nickelferrite as nuclear magnetic. The influences ofreactants ratios, reaction temperature, reaction time, catalyst amount and ratio of solvent tothe cyclohexanone conversion and oxime selectivity in ammoximation of cyclohexanone wereinvestigated. The experiments results indicated that the optimum operating conditions were amixture of water and t-butanol with volume ratio of1:1as reaction solvent system and ancyclohexanone: hydrogen peroxide: ammonia molar ratio of1:1.2:1.8at a reactiontemperature of80℃and a residence time about2.5h. And the catalyst/cyclohexanone ratio was0.2g/g. The cyclohexanone conversion, oxime selectivity and oxime yield can amount to96%,98%and94%respectively. And the recovery of magnetic titanium silicalite molecularsieves in the external magnetic field can achieve100%.Through the research of reaction kinetics of liquid phase ammoximation ofcyclohexanone the kinetic parameters are confirmed. The orders of the reaction are0.65,0.27and1.06respect to cyclohexanone, hydrogen peroxide and ammonia respectively. Thereaction activation energy is101.362kJ·mol^-1and the per-exponential factor is5.923×10¹²(mol^-0.98L^0.98/min.