Hydrodynamics and Mass Transfer Studies in Three-Phase Slurry Bubble Column for Synthesis of Methanol Using Biomass-Derived Syngas

Abstract

Methanol and DME (dimethyl ether) are increasingly emerging as a potential alternative to the conventional non-renewable petroleum fuels and can be produced from biomass-derived syngas as a feedstock. Methanol synthesis via liquid-phase processes carried in slurry bubble column offers advantages of effective control system for heat produced by highly exothermic reactions during process. Although liquid-phase process provides higher conversion and better catalyst life compared to gas-phase processes, however additional mass transfer resistance due to the presence of liquid-phase is one of the major constraints which limits its commercial usage. Also, slurry bubble column reactor (SBCR) employed in methanol synthesis are operated at high superficial velocity in heterogeneous complex turbulent conditions. Therefore, understanding of hydrodynamics, bubble size distribution, and mass transfer characteristics (mass transfer coefficients, interfacial area) during liquid-phase methanol process in SBCR becomes important to achieve higher conversion. In the present work, a computational fluid dynamic (CFD) based Eulerian approach is used to simulate the effect of syngas on the dynamic and mass transport properties in a rectangle SBCR. Eulerian multiphase model along with UDS transport equation is used to incorporate the interfacial mass transfer coefficient (𝑘H𝑎). Mass transfer is studied as tracer uptake dynamics in the liquid phase. The effect of superficial velocity and liquid viscosity on dynamics and mass-transfer rates is studied in a the SBCR. Three gas-liquid systems, i.e. air water, syngas-paraffin, and syngas-glycerol, are studied for different superficial velocities, ranging from 0.02–0.10 m/s. Mass transfer coefficient is modelled as constant and using correlation to examine influence of liquid property. Mass transfer characteristics have found to be dependent on gas holdup and mirror its trend. The study shows that gas holdup and mass transfer increases with increase in superficial velocity and decreases for increase in liquid viscosity.