Characterization of gas-liquid two-phase flow and mass transfer in single pellet string microreactors

The single pellet string microreactor (SPSM) presents a promising approach for intensifying multiphase catalytic reactions due to its enhanced heat/mass transfer characteristics and relatively simple flow behavior resulting from a regular packing configuration. Understanding hydrodynamics and mass transfer characteristics of SPSMs is essential for their application in heterogeneous catalyst screening, reaction kinetic studies and performance optimization. In this work, the gas-liquid flow regimes in SPSMs were studied using CO₂-water model fluid system. Slug flow, bubble-slug flow, film flow and churn flow were observed, and the corresponding flow regime maps were proposed, which are similar to those in empty microreactors. The transition from slug flow to other flow regimes occurred at higher phasic velocities in the bed with smaller particles due to the increased importance of capillary force. The mass transfer parameters (liquid-side volumetric mass transfer coefficient and interfacial area) were then investigated in SPSMs via CO₂ absorption into alkaline solutions within slug flow and bubble-slug flow regimes. The increased (gas or liquid) flow rate and decreased particle/reactor size are beneficial for improving mass transfer performance. Based on the flow analogy to empty microreactors, the measured liquid-side volumetric mass transfer coefficients in SPSMs were correlated using the literature correlation for empty microreactors with additional consideration of bed properties (i.e., porosity and particle size). Finally, a comparative analysis of mass transfer between SPSMs and conventional reactors as well as other types of packed bed microreactors was conducted, highlighting the superior mass transfer and energy efficiency of SPSMs. • Gas-liquid flow regime map in single pellet string microreactors was proposed. • Enhanced influence of capillary force in SPSMs on flow transition was observed. • Existing pressure drop model in SPSMs was modified to address absorption effect. • Mass transfer coefficient and interfacial area in SPSMs were determined. • Increased flow rate and reduced particle size improved mass transfer performance.