Simulation Of Multiphase Hydrodynamics And Mass Transfer In The Structure Catalysts

Structured catalysts have been widely used in unit operations of chemical engineering, own to their unique advantages such as large surface area, small pressure drop, high percent conversion, and enhanced multiphase flow mass transfer. Therefore, more and more researchers have paid attention to their performances studies in the process intensification.Firstly, benzene and propylene two-phase flow patterns and characteristics in the Taylor flow regime in the vertical microchannel contactors of 2 mm hydraulic diameters, which consists of a T-type circle microchannel injection, were investigated. The simulations were carried out using 2D grid. The volume of fluid method (VOF) in the commercial CFD software (FLUENT 6.3.26) was used for tracking free fluid surfaces accurately in the simulation. The simulation results show that four types of flow patterns (i.e., bubbly flow, Taylor flow, Taylor-annular flow, and annular flow) are observed in the range of gas velocity from 0.01 to 3.0 ms-1 and liquid velocity from 0.01 to 0.05 ms-1. Then, the hydrodynamic performances including bubble velocity, wall adhesion, unit cell length, pressure drop and the pressure profile along the axis in the Taylor flow regime were investigated in detail. It was found that the increase of gas superficial velocity leads to longer bubbles and shorter liquid slugs under a fixed liquid superficial velocity. Meanwhile, a critical point is observed in the unit cell length, when the gas superficial velocity equals to liquid superficial velocity the unit cell length reaches a lowest value. Furthermore, when the gas superficial velocity is above a certain value, the slug flow became unstable, which means that the length of liquid slugs and Taylor bubbles could not remain constant. Furthermore, it is found that the pressure drop mainly exists in the liquid slug, while in the bubble the pressure nearly keeps a constant. Finally, the two mechanisms (i.e., squeezing regime and dripping regime) proposed by Garstecki et al are also found in this work in the Taylor bubble formation process.Then, the mass transfer performance of benzene and propy lene two-phase flow in the capillary was investigated using one Taylor unit cell model. The simulation results indicate that the mass transfer coefficient in the structured catalyst in Taylor flow regime is at least one order of magnitude higher than that in the traditional particle catalyst.