(231c) Residence Time Distribution Studies in a Laboratory Scale Trickle-Bed Reactor for Liquid Phase Hydrogenation of Acetylene

Humayun Shariff, Premkumar Kamalanathan, and Muthanna H. Al-Dahhan

Multi-phase Reactors Engineering and Applications Laboratory(mReal), Department of Chemical and Biochemical Engineering, Missouri University of Science and Technology, Rolla, MO, USA

Liquid phase hydrogenation of acetylene for ethylene production has recently gained interest for its safe operation and better catalyst life in comparison with gas phase process [1]. A selective solvent is used as the liquid medium which not only selectively absorbs acetylene from a gas mixture but also reduces the formation of green oil due to oligomerization in the reaction. The gas phase hydrogenation of acetylene itself is a highly exothermic reaction leading to thermal runaway [2]. In industries, trickle bed reactors are widely used for gas-solid-liquid contacting due to the inherent advantages of high pressure operations and high catalyst to liquid ratio [3]. Naturally, trickle bed reactors are the choice for the liquid phase hydrogenation of acetylene. Due to the complex flow behavior in TBRs, in addition to the kinetics, factors such as wettability of the liquid, mixing, holdup (gas and liquid) affect the conversion and selectivity. As part of our continued effort to understand and develop the scale models for liquid phase hydrogenation, in this work, global mixing is quantified using Residence Time Distribution (RTD) studies. Thereby, the performance of the reaction in TBR. RTD experiments were investigated in a stainless-steel lab scale TBR (1 inch I.D. and 60 cm long) with 2mm spherical particles of 30 cm catalyst bed length. RTD studies were conducted at the similar bed conditions as the reaction studies of liquid phase hydrogenation of acetylene for ethylene production. The experiments were conducted for liquid velocities of 0.10 x 10^-3 – 3x10^-3 m/s and for gas superficial velocities of 0.02 – 0.45 m/s. RTD were determined using conductivity measurements from the pulse-input liquid-tracer injection. Mean residence time and standard deviation were determined from the C - curve. Axial dispersion model (ADM) was used to obtain the dispersion coefficient by regressive fitting. D_ax was compared with the available correlations from literature to predict the reactor performance for a developed reactor scale model. The influence of the liquid and gas velocities on the model parameters is also studied.

Keywords: Trickle Bed Reactor, Liquid phase hydrogenation, Acetylene, Residence time distribution, Axial Dispersion

References

[1] Edvinsson, R. K., Holmgren, A. M., & Irandoust, S. (1995) Ind. & Engg. Chemistry Research, 34(1), 94-100

[2] Borodziński, A., & Bond, G. C. (2006) Catalysis Reviews, 48(02), 91-144

[3] Al-Dahhan, M.H., et al. (1997) Ind. & Engg. Chemistry Research 36(8), 3292-3314