Research On In-Situ Liquid-Phase Hydrogenation For N-Alkylation

N-alkylated amines are widely used in many important areas such as pesticide,pharmacy,' dyestuff,pigment,commodity chemistry,material science,fine chemical engineering and so on,which are frequently manufactured through N-alkylation of certain primary amine or secondary amine.The N-alkylations of amines are the most fundamental and important reactions for preparation of N-alkylated amines.The traditional routes of N-alkylation mainly consists of homogeneous and heterogeneous method.The homogeneous N-alkylation used in industry are usually catalyzed by H₂SO₄,H₃PO₄,hydrohalogenic acid or likes which will bring many disadvantages of high capital cost,reactor corrosion,formation of by-products and environment pollution. Heterogeneous method usually undergoes carbonium ion mechanism needing quite high activation energy to activate the reactants,and it will have a good yield only with high temperature.The mechanism of N-alkylation is changed into elimination-addition while hydrogen as a reductant is added to the reaction,resulting in higher yields at lower temperature because of the lower activation energy of the N-alkylation. The N-alkylation needing hydrogen is called reduction-alkylation,which gets lots of attentions of scientists recent years for its high activity. However,the dangerous and difficulties of hydrogen reservation restrict the application of these reactions to scale-up manufacture of alkylation amines.A convenient and environment-friendly liquid-phase catalytic N-alkylation,called in-situ liquid-phase hydrogenation N-alkylation is proposed in this thesis,which is a coupling process of hydrogen reforming of alcohol and reduction-alkylation of amine with alcohol.The transfer of hydrogen is usually the rate-determining steps of reduction-alkylation,and the atoms of hydrogen coming from the alcohol are obtained by the intermediates of N-alkylation directly in in-situ liquid-phase hydrogenation N-alkylation,which will enhance the activity very much without adding additional H₂.Three parts of work are contained in this thesis:(1)compare the activity,selectivity and stabilities of different catalysts for the N-ethylation of aniline to find the best catalyst for in-situ liquid-phase hydrogenation N-alkylation;(2)study the in-situ liquid-phase hydrogenation N-alkylation for nitrobenzene with alcohol;(3)discuss the influences of reaction conditions such as temperature,flow rate of raw materials,pressure and concentration,on in-situ liquid-phase hydrogenation N-alkylation for different kinds of amines with alcohols. Ni(5%)-Sn(5%)/Al₂O₃ was the efficient catalyst for in-situ liquid-phase hydrogenation N-alkylation of aniline in this research.The yields of N-ethylated were no less than 99%while the reaction was catalyzed by Ni(5%)-Sn(5%)/Al₂O₃.Except for great activity and selectivity,this catalyst had much longer life than the others,which kept 99%conversion more than 470h.Acording to a serious of characterization such as XRD,TEM,the reason why the decline of the activity of the catalyst was discussed.The N-ethylation of nitrobenzene with different concentrations of water and different temperatures was studied.Both increasing water and raising the reaction temperature resulted in higher yields of N-ethylated amines.When the temperature was 220℃and the concentration of water was 30%,77%N-ethylated aniline would be obtained.The N-alkylations for different kinds of amines with alcohols were studied,including:aniline,toluidine(o-,m-,p-),chloroaniline(o-,m-,p-), naphthalen-1-amine,p-aminophenol,p-methoxyaniline,butyl amine, ethylenediamne,dodecan-1-amine,morpholine,piperazirte and so on. Majority of these amines had yields more than 85%in in-situ liquid-phase hydrogenation N-alkylation,especially while ethanol as the alkylated reagent.Apparently that in-situ liquid-phase hydrogenation N-alkylation could be a widely used as a high efficient method.The influence of reaction condition such as temperature,flow rate and so on,on in-situ liquid-phase hydfogenation N-alkylation was proposed in this thesis.Some phenomenon were explained qualitatively according to the mechanism and principles of thermodynamics.In conclusion,in-situ liquid-phase hydrogenation N-alkylation was a convenient and high efficient method suitable for N-alkylations for a lot of kinds of amines with different alcohols,which not only displayed good conversion and selectivity,but also simplified the production process and reduced the environment pollution.