Studies On Reaction Mechanism Of MOCA Synthesis Over Molecular Sieves And Mechanism Of Catalyst Deactivation

In this work,the reaction mechanism of catalytic synthesis of 3,3'-dichloro-4,4'-diaminodiphenylmethane?MOCA?from o-chloroaniline and formaldehyde over molecular seives and the mechanism of catalyst deactivation have been studied in a fixed bed reactor.Firstly,the performance of molecular sieves with different types and ratios of silicon and aluminum for MOCA synthesis by condensation of chloroaniline and formaldehyde were investigated,indicating that HY?11?gave the best performance;Secondly,with using HY?11?as the catalyst,the effects of reactiontemperature on the selectivity of product MOCA and the conversion of reactant HCHO were investigated,and the reaction conditions were optimized;Moreover,based experimental data and literature review,the micro mechanisms of MOCA synthesis and by-products formations in reaction of chloroaniline and formaldehyde condensation over HY?11?molecular sieve were described;Afterwards,through the analysis and calculation of experimental data,the kinetic parameters of the reaction and the deactivation were estimated;Finally,from the experiments of catalyst deactivation and regeneration in combination with characterization of the fresh,deactivated and regenerated molecular sieve,the causes of molecular sieve deactivation were analyzed.Under the optimal condition of n?o-chloroaniline?:n?formaldehyde?)=4:1,temperature 170?,LHSV=3.5h-1,N₂ flow rate=10ml/min and pressure 0.55MPa,the reaction of o-chloroaniline and formaldehyde condensation over HY?11?molecular sieve gave MOCA selectivity of 0.71 and HCHO conversion of 0.92.The identification and analysis of reaction intermediates and by-productus have suggested that the micro reaction mechanism of MOCA synthesis from o-chloroaniline and formaldehyde over HY?11?molecular sieve included three main steps:firstly,o-chloroaniline and formaldehyde condensate into N,N'-bis?2-chlorophenyl?-methane-diamine,2-chloro-6-[?2-chloroaniline?-methyl]-aniline or 2-chloro-4-[?2-chloroaniline?-methyl-]aniline;secondly,intra-molecular rearrangement of N,N'-bis?2-chlorophenyl?methanediamine into 2-chloro-6-[?2-chloroaniline?-methyl]aniline or 2-chloro-4-[?2-chloroaniline?-methyl]aniline;finally,intra-molecular rearrangement of 2-chloro-4-[?2-chloroaniline?-methyl]aniline into MOCA.Based on the reaction mechanism,the kinetic models of reaction and deactivation were established,and evaluation with using the experimental data gave,the reaction activation energy of 81.43kJ/mol,the deactivation activation energy of 177.63kJ/mol and the deactivation coefficient of 2.36,respectively.Also,all the kinetic parameters were verified by a variety of statistical analysis methods.To regenerate the deactivated HY?11?molecular sieve,the treatments were conducted with air calcinations in 550? or 400?,DMF or benzene wash.It was found that the calcinations in 550? could completely recover the pore structure and acidity of HY?11?molecular sieve,the calcinations in 400? and DMF wash partially recover the activity of HY?11?molecular sieve,and benzene wash barely have any effect.The fresh,deactivated and regenerated HY?11?molecular sieve were characterized by BET,NH3-TPD and XRD.The results showed that the pore volume and acid amout of the deactivated HY?11?molecular sieve were siginificantly dropped,but its crystal structure and acidic strength were almost unchanged.indicating that the block of catalyst pore could be the main reason to cause HY?11?molecular sieve deactivation.