Research On The Synthesis Of Morpholine And Its Alkyl Derivatives

Morpholine and its derivatives, as important intermediates of fine chemicals, have been widely used for the preparation of rubber assistants, medicines, pesticides and so on. By now the main process to synthesize morpholine and its derivatives based on the reaction of diethylene giycol (DEG) with aliphatic amines or ammonia under pressure and in the presence of catalysts. The major problems of the process above-mentioned are the low activity of the catalyst and the low yields of the products. Therefore, it is important to improve the catalysts and optimize the conditions to reduce the costs and improve the yields of morpholine and its derivatives.The support γ-Al2O3was pretreated by calcination with programed temperature regulation. The rules of pore structure variating with temperature and the relationship between support structure and molecular size were obtained to determine the pre-conditions of the support. The catalyst was prepared with Cu and Ni as the active components, and the optimum active component formulations were got by screening experiments. The catalyst was prepared by an isovolume impregnation method, and the Ni and Cu content of the catalyst were4.2-4.4%and16.8-18.9%, respectively.The optimized conditions of N-alkyl morpholine were obtained through single factor and orthogonal experiments. It was found that morpholine, N-methyl morpholine and N-ethyl morpholine almostly shared the same reaction conditions. The optimized conditions were got as follows:220℃,1.2MPa,0.15h-1, and the molar ratio of raw material was1:9. For. N-propyl morpholine and N-butyl morpholine, the reaction conditions became harder, that was:230℃,1.4MPa,0.13h-1, the molar ratio of raw material was1:9. The yields of N-alkyl morpholine were75.74%,75.12%,74.39%,66.32%and60.72%, respectively. The yields declined and the reaction conditions became more harsh when the products changing from morpholine to N-butyl morpholine, which indicated that the steric hindrance increased with the growing in the number of carbon atoms of low-carbon aliphatic amines. The performance of catalysts was found stable within500h by stability analysis,while the conversion of diethylene glycol and the yield of morpholine decreased rapidly through catalyst destructive testing.The causes of catalyst deactivation were found by using SEM, XRD, TGA and N2adsorption-desorption. Firstly, the catalyst was covered with coke, which stunted the active center of catalyst surface and blocked the pores of the support. Secondly, the active metal Cu sintered due to high temperature, resulting in reunion of active metal and reduce of the active sites, which gave rise to the deactivation of the catalyst. In addition, the catalysts were regenerated by calcination with high temperature, and the catalysts regained88.9%of the original activity. The pore volume was partially restored when the coke on the catalyst surface was removed, and the Cu particles were dispersed again after calcination and reduction.Finally, the synthesis mechanism of N-methyl morpholine was investigated in the presence of diethylene glycol, ammonia and methanol using in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The in situ infrared cell was used to simulate the fixed bed reactor, and the results showed that the N-methyl morpholine was obtained from diethylene glycol and methylamine after the synthesis of methylamine with methanol and ammonia as raw materials.