Developing Reactor Scale Kinetics Model Integrated with Hydrodynamics Towards Scale-up of a Packed Bed Reactor

Assessing the reactor performance for trickle bed and two-phase upflow packed bed reactors needs optimized experimentation supplemented by validation of a reliable mathematical model at different scales. Various factors like catalyst wetting, liquid maldistribution, and transports are necessary to predict the performance of these reactors. At Multiphase Flows and Reactors Engineering and Applications laboratory (mFReal), a lab-scale packed bed reactor experimental unit equipped with a blast shield has been designed to conduct flow reaction investigations at high-pressure and temperature. The unit was tested for selected operating conditions for the acetylene hydrogenation in the liquid phase to understand the conversion and optimize the process towards scaleup aided with the model. Reactor scale models have been developed towards this study based on different approaches incorporating the kinetics and hydrodynamics with the effectiveness factor evaluated from a pellet scale model.

Catalytic hydrogenation of acetylene in the gas phase to form ethylene has widely been used in industrial practice. This reaction is highly exothermic which may lead to thermal runaway. Moreover, many studies have reported the formation of green oil (C₆⁺) due to the oligomerization of the reaction leading to catalyst deactivation. The hydrogenation of acetylene in the liquid phase using a selective solvent is a study of interest to overcome the issues of green oil formation and controlling the heat of the reaction. The solvent used in this study is N-Methyl Pyrrolidone (NMP), a polar solvent generally used to strip acetylene selectively from the cracker effluent. The reaction kinetics of the acetylene hydrogenation over a commercial 0.5 wt% Pd/Al₂O₃ catalyst was investigated in a stirred tank reactor. The reaction was studied for various operating conditions to mention temperature, catalyst loading at a pressure of 250 psig. The kinetic parameters were estimated by Langmuir-Hinshelwood-Hougen-Watson based reaction mechanism by fitting the model equation to the experimental data. The kinetics of the reaction will be integrated into the model to predict the reactor performance of a packed bed reactor at scale. Cold flow experiments in a trickle-bed reactor at scaled-down operating conditions using a liquid tracer were conducted to obtain the residence time distribution (RTD). The operating conditions were chosen from literature and industrial conditions. From the RTD information, the liquid dispersion and liquid holdup were evaluated. Integrating both the kinetics and hydrodynamics, the reactor scale model was enhanced and validated against experimental data obtained from the flow hydrogenation experiments conducted at optimized operating conditions. This information will help us to evaluate and suggest ideal scale-up parameters for this reaction. This study can be expanded to various sensitive catalytic reactions.