Study On Equipment And Process Of Microwave-induced Evaporation And Intensified Separation

As an important external energy field technology for process intensification(PI),microwave field has been widely studied in the field of chemical separation.It has been found that microwave irradiation can affect the vapor-liquid equilibrium(VLE)and change the relative volatility of some binary mixtures based on its special heating property.However,there is still a lack of research on the application of microwave technology to the operation of special chemical separation units and the realization of separation enhancement of binary mixtures.Thus,the main purpose of this article is to develop a new microwave field intensifying separation technology – microwave induced thin film evaporation process.And several binary systems were selected to investigate the strengthening influence of microwave irradiation on scraped-film evaporation separation.In this paper,the relationship between the influence of microwave irradiation on VLE and the polarity and boiling point differences of components were firstly explored.The VLE results show that microwave irradiation only has obvious influence on the VLE data of cyclohexane-n-propanol(polar-nonpolar system),and the impact is different in the different concentration range,which is mainly caused by the different collision and heat transfer rate related to the larger difference of boiling points of two components.However,microwave irradiation has almost no effect on the VLE of ethyl acetate-isopropanol system(polar-polar system),which has the smaller polarity difference between two components.Based on the above different effect of microwave on different binary systems,a scraped-thin film evaporation separation technology was developed to achieve the intensification of microwave irradiation on separation of binary mixtures.And the scraped-thin film evaporator suitable for the microwave field was self-designed and constructed.The residence time distribution of liquid film in the evaporator was investigated by the pulse tracing method.The results showed that the average residence time of liquid film was mainly affected by the feeding flowrate,then the rotation speed,and the influence of the operating parameters on the action time of the liquid film and microwave in the device were determined.Finally,the evaporation separation experiments of cyclohexane-isopropanol system were conducted under microwave irradiation and conventional heating using the above experimental device.The results verified the feasibility of enhancement of microwave irradiation for the evaporation of isopropanol on non-equilibrium steady state separation.Besides,the effects of feeding content,flowrate,initial temperature and microwave power density on evaporation separation of isopropanol-cyclohexane system were investigated by single factor analysis.Then,by comparing and analyzing the evaporation separation results of ethyl acetate-isopropanol,isopropanol-ethanol and cyclohexane-ethanol systems,it was found that the microwave induced evaporation separation depends mainly on the difference of polarity and dielectric properties of the substances,not the boiling point sequence and the conventional separation order of binary mixtures.It was proved in this paper that microwave irradiation can be applied to the scraped-film evaporation and realize the intensification on separation of binary systems.This is because that the polar component molecules could leave the evaporator quickly after absorbing microwave energy and vaporizing,which reduce the collision,heat and mass transfer between the two components.These studies can provide theoretical basis and data support for further research,design and development of microwave-enhanced separation process and experimental equipment.