Research On The N-Methylation With Catalytic Hydrogenation

N-methyl amines play an important role in the production of many chemical compounds including surfactants,dyes,pesticides,herbicides and medicinal intermediates.The amination with halomethane is a common route of N-methylation with drawbacks such as batch process,more halogeno salt by-products,low atom economy and serious equipment corrosion.The amination of methanol adopting continuous process in the fixed-bed is another route of N-methylation.Because of the high temperature and pressure involved,the demand for production equipments,catalysts and process control also increases constantly.Therefore,it is important to develop a new method for N-methylation with simple process,environmental friendliness and remarkable economic efficiency.The catalytic hydrogenation N-methylation using paraformaldehyde and amine as raw materials,hydrogen as reductant has become a hotspot because of its recyclable catalyst,nonpolluting by-product and suitability for industrialized production.The synthesis of N,N-dimethylbutylamine from n-butylamine and paraformaldehyde in the autoclave was designed to screen a series of potential catalysts of hydrogenation reduction.Raney Ni was chosen as the most suitable catalyst because of its moderate catalytic activity,low price and recyclability.Moreover,the reaction system was analyzed and the optimum condition was found:reaction temperature=115?,reaction pressure=1.6MPa,reaction time=4h,methanol as solvent,Raney Ni as catalyst(4 wt%),n(methanal):n(n-butylamine)=2.2:1.The product was separated via atmospheric distillation with the yield of 92.9%and purity of 99.1%.This dissertation further examined the applicability of this catalytic reductive amination system with different amines as substrates.And the range of optimum condition was found:reaction temperature=100-130?,reaction pressure=1.3-2.0MPa,reaction time=3-4.5h,Raney Ni as catalyst(3-5 wt%),paraformaldehyde consumption=1.05-1.2 times theoretical values.Most of the reactions showed a yield nearly 90%,which indicated that the Raney Ni catalytic reductive amination system is suitable for most of fatty amines.In addition,the N-alkylation steric hindered amines needed more harsh condition and the yeild was relevantly lower.The reaction activities of aromatic amines were far those of below fatty amines.Electron-donating groups on aromatic amines can improve the reaction activity of amino group and the yeild increased obviously.At last,the conversion rule of raw materials and intermediates was analyzed by GC and the intermediates were characterized by MS.The reaction route of the N,N-dimethylbutylamine synthesis catalyzed by Raney Ni including addition reaction of n-butylamine and methanal,dehydration reaction of intermediates and hydrogenation reaction of imine was estimated.What's more,the mechanism of the reaction above was researched and calculated by Materials Studio based on the estimated reaction route.The role of Raney Ni during the catalytic reaction and the dehydration reduction processes of intermediates were studied in details.The N-methylation of the other amines was firstly estimated by the calculation of Materials Studio.The established results have guiding significance for adjusting the reaction conditions and increasing test efficiency.