N-methylation of Benzylamine to N,N-dimethylbenzylamine by Using Dimethyl Carbonate as a Methylation Agent over Aluminophosphate Molecular Sieves

Aluminophosphate molecular sieves (AlPxO) were synthesized by the sol-gel method using Al(NO3)(3) and H3PO4 as the raw materials. The effect of the different P/Al ratios on the structures of AlPxO and the influence of AlPxO on the catalytic activity of N-methylation of benzylamine with dimethyl carbonate (DMC) were investigated. The products of N-methylation of dimethyl carbonate with benzylamine were qualitatively analyzed by GC-MS; based on the results of the analysis, the possible pathways of the main products were assumed. The AlPxO samples were characterized by X-ray diffraction, NH3-TPD, specific surface area and pore size analysis and TG. Meanwhile, the effect of process conditions on the N-methylation of dimethyl carbonate and benzylamine was investigated. The results have shown that synthesized AlPxO was a more efficient catalyst compared with other molecular sieves. Aluminophosphate molecular sieves of amorphous structure have a higher total selectivity to target amine, which containing the large specific surface area, more acidic sites and the amount of acid. Under the optimal conditions that n(dimethyl carbonate): n(benzylamine) = 1: 1, m(AlP0.9O): m(benzylamine) = 0.06, T = 200 degrees C and t = 4 h, the conversion of benzylamine and the total selectivity of the products from N-methylation of benzylamine were 59.16% and 77.18%, respectively. The mechanism on formation of target product was proposed based on the experimental results.