Study On The Cyclization Of Ethanolamine To Piperazine

Piperazine is an important intermediate and raw material of fine chemicals, which is widely used in medicine, pesticide, and dye industries. There are many ways of synthesis of piperazine in accordance with the raw material. At present, the mostly used method is using ethanolamine as relatively cheap raw material. In this paper, cyclization of ethanolamine to piperazine over Raney Ni catalyst in the presence of hydrogen was mainly studied.As for the synthetic process, the effects of reaction temperature, reaction time, hydrogen pressure, solvent and other factors on the conversion of ethanolamine and the selectivity and yield of piperazine were investigated through the single factor experiment. The results show that the best reaction temperature is200℃. Under the best reaction temperature, the conversion of ethanolamine is95.93%and the selectivity of piperazine is up to49.58%. The best reaction time is4h under the best temperature and the best hydrogen pressure is3MPa. The best mass of catalyst is20%of the mass of ethanolamine. The best solvent for the reaction is water which can prevent the polymerization of ethanolamine and help piperazine separate from the surface of the catalyst quickly in order to improve the selectivity of piperazine. Orthogonal experiments show that the reaction temperature is the most critical factor which affects the conversion and selectivity, followed by the reaction time and hydrogen pressure. The optimum reaction conditions for the conversion of ethanolamine were determined by experiments as follows:the temperature is200℃, the reaction time is6h, the hydrogen pressure is3MPa. Under such condition, the conversion of ethanolamine is95.00%. The optimum reaction conditions for the selectivity of piperazine were also determined by experiments as follows:the temperature is200℃, the reaction time is6h, the hydrogen pressure is7MPa. Under such condition, the selectivity of piperazine is54.67%.Based on qualitative analysis of reaction products with GC-MS, the hydroxyethyl piperazine and ammoniaethyl piperazine are the main byproducts. The experiments show that the hydrogen participates in the hydrogenation reaction as a reactant. Meanwhile, the presence of hydrogen makes the reaction system have a certain pressure that inhibits the occurrence of side reaction such as dehydrogenation and deamination. The process route of the synthesis of piperazine in the presence of carbon dioxide is firstly proposed, the experiments show that ethanolamine absorbs carbon dioxide into ethanolamine formic acid, which is hard to ring up into piperazine.The reaction kinetics under hydrogen pressure of3MPa was studied. The results show that the reaction of ethanolamine complies with second-order reaction kinetics model. The kinetic equation is-r=-dC z??/dt=1.687*1015exp(-141973/RT)C???2, and the activation energy is141.973kJ/molThe thermodynamics of the main and side reactions were studied. Firstly, the group contribution method was used to estimate the thermodynamic date of the reaction substances. According to that, the enthaipy change, gibbs free energy change and equilibrium of reactions in standard state were calculated. Secondly, the enthaipy change, gibbs free energy change and equilibrium of reactions in the temperature of423-523K were also calculated by designing reversible process. The calculation results show that although cyclization of ethanolamine to piperazine over Raney Ni catalyst is feasible in thermodynamics, but the main and side reactions are all exothermic reactions, the main reaction is not dominant in the thermodynamics. So, the synthesis of piperazine should be carried out under an appropriate temperature, too high or too tow of the temperature is not good for the synthesis of piperazine.