Dynamic Model And Simulation Of Catalytic Distillation For The Synthesis Of Ethylene Glycol Monobutyl Ether

Reactive/Catalytic distillation is a newly developed process intensification techniques in the fields of chemical process research and development which has been developed since 1980s. It integrates chemical reaction and separation, two key processes in chemical engineering field, into one unit equipment, which can be seen as a representative technology in process intensification and used to innovate the conventional unit operation. Recently, Liaoning Oxiranchem Group proposed a new synthesis process of ethylene glycol monobutyl ether (EGMBE) through catalytic distillation (CD), aiming at applying catalytic distillationto innovate the conventional ethoxylation processes in ethylene oxide (EO) related industry, which suffers from several disadvantages such as low yield of desired product, high energy consumption, and ineffective reaction heat utilization. A pilot-scale catalytic distillation column was developed. Based on the former developed steady-state mathematical model and research in our laboratory, the present paper focuses on developing dynamic mathematical model and simulation. The results obtained in this paper will be further used to guide industrial experiments, operation, control and equipment scale-up and so on.The main work and the results obtained involve the following aspects:(1) A vapor-liquid equilibrium model is developed. The dynamic simulation has been taken out using the simulation software, Aspen Plus and Aspen Dynamics.(2) The semi-batch catalytic distillation is simulated through Aspen Plus. The optimal operation parameters are determined to be:pressure 0.2 Mpa and the EO feed rate 0.036-0.4 kmol·h-1. The simulations also provide the typically dynamic profiles of the liquid and vapor flow rates, compositions and temperature. Through simulation under the established operating conditions, it is showed that, after reacting for 5 hours, the total molar feed ratio of n-butanol to EO is 1.6:1, the EO conversion is more than 99%, n-butanol more than 91% and a as high as 87% selectivity of EGMBE could be achieved, which indicated the potential advantage of using CD for the production of EGMBE. The compared results between model predictions and experimental data demonstrate that the model developed in this research predicts the semi-batch behavior of the CD process well. The predicted temperature profiles are good agreement with experimental data with an average error less than 10%. The comparisons of product composition in the bottom stream between the model predictions and experimental results are also satisfactory.(3) Using the dynamic mathematic model established, the start-up process for the CD column is simulated. The dynamic profiles for the vapor and liquid composition in the reflux drum and reboiler, the heat duty and temperature of condenser and reboiler, the liquid and vapor flow rate along the column as well as the reaction rate for the components involved in this system are simulated and analyzed. The results obtained show that during the period from the reactants were fed into the column to the steady operation was obtained, the response time of the items, including the heat duty, the temperature, the composition and the flow rate for the condenser, which is 2:5 hours, is much shorter than that of reboiler, which is 5 hours.(4) The disturbance of EO feed rate has been studied. The results obtained show that under the same disturbance, controlling project one, that is:the liquid level of reflux drum is controlled by reflux flow rate; the liquid level of reboiler is controlled by heat duty of reboiler, the system could return to a new steady-state within 10 hours and there are few fluctuations during this period while controlling project two, that is: the liquid level of reflux drum is controlled by feed rate of butanol; the temperature of stage 9 is controlled by heat duty of reboiler, the system could response immediately, but it needs 12 hours to return to steady-state with lots of fluctuations. But the new steady-state is much close to the former one. When the disturbance is as much as±20%, the final selectivity of EGMBE under the two controlling project is still higher than 87%, which shows the effectiveness of the controlling projects.