Study On Synthesis Of Isopropanolamines Via Reaction Distillation

Isopropanolamines include three kinds of homologues:mono-isopropanolamine?MIPA?,di-isopropanolamine?DIPA?and tri-isopropanolamine?DIPA?.MIPA and DIPA are widely used in industry,which MIPA has best cost performance,and TIPA has the highest cost with lowest price.Traditional process is generally carried out by the consecutive reaction with the system of the liquid ammonia and propylene oxide.The ratio of liquid ammonia and propylene oxide is about 15:1⁵0:1 that can produce three kinds of isopropanolamines,in which the ratio of MIPA is 40⁵0%and the ratio of TIPA is up to15%²0%.Therefore,A novel one-step reactive distillation approach was proposed to streamline and economize the production which can reduce ratio of ammonia and propylene oxide and reduce the selectivity of TIPA,meanwhile increase the selectivity of MIPA and DIPA.The law of reaction of ammonia water and propylene oxide?PO?was researched,it showed that selectivity of isopropanolamines in product can not be changed by changing temperature or pressure.Only molar ratio of NH₃ to PO determined the selectivity,the high molar ratio of NH₃ to PO,the high selectivity of MIPA can get.Select ELECNRTL thermodynamic equation,radfrac equilibrium stage model theory,to simulate the process by simulation in Aspen plus.The theoretical stage number,the mass flow of H2O,the feed stage,operating pressure?the ratio of the materiel are researched.The optimal conditions are that the operation pressure is 0.8MPag?gauge pressure?,the feed stage of H2O which the mass flow is about 20%of the total mass flow is at the top of the column,besides the feed stage of liquid ammonia and propylene oxide which the molar ratio is 1:1 is at the third theoretical stage number from the upper of the column.In addition,it was operated under a total reflux of the unreacted ammonia to achieve a high ratio of ammonia to PO in the column.The product selectivity of MIPA and TIPA are respectively86.7%and 0.14%.Reactive distillation process was used to synthesize MIPA in a stainless steel tower at high pressure.The reactive distillation column packed with Dixon packing was 1.5 meters high,0.038 meter in diameter.The result showed that suitable operating parameters as follows:Water,was introduced above the first stage,the feed stage of H2O which the mass flow is about 20%of the total mass flow.PO was fed above the second stage.NH3 was introduced above the third stage.The mole ratio of NH3 and PO is 1:1.The pressure control valve at the top of tower kept pressure at 0.8MPa?gauge pressure?.The final product contained 85.0%MIPA and 1.5%TIPA.This example showed that the extremely high conversion of PO to MIPA could be obtained by using the reactive distillation technique even with the use of the initial low molar ratio of ammonia to PO in the fresh feed mixture.The experimental datas and the simulation values coincide well.