Study On Cascaded Semi-continuous Distillation Process With Constant Total Reflux And Liquid Exchange

A novel operation mode of constant total reflux semi-continuous distillation with liquid exchange is proposed in this article.The main purpose of the new operation mode is to realise the connection of columns and separate binary mixtures with small relative volatility.The continuity and feasibility of proposed operation mode is verified by experiment and simulation.Operation time of different feeding concentration,exchange time holdup in vessels are compared and discussed.The main steps of the new operation mode are confirmed,which include start-up,liquid exchange,recovery-exchange-feed of the light component product,recoveryexchange-feed of the heavy component product as well as recovery-exchange-feed of the light and heavy component simultaneously.Depending on the operating characteristics and some basic assumptions,a mathematical model is setup.4-5 RungeKutta method(ODE45)is used to solve the functions.The new operating mode is simulated by programming Matlab software.The simulation results reveal that the product can reach the desired purity and the continuity of the operation is good.Different conditions are simulated to compare the influence on operation results by changing the feed concentration,relative volatility,vessel holdup and liquid exchange time.Compared with repeated batch distillation,the new operation mode has great advantages in high separation efficiency,flexible feeding,product yield and time saving.The total operation time can save 9.86%~17.49%.Binary mixture,ethanol-1-propannol,is used in the experiment.The experimental data and simulation results were compared.Experimental data accord with simulation results well.It proves that the new operation mode has good performance on the continuity and feasibility,and the mathematical model is reasonable.