Evaluation of Multiphase Gas-Liquid Mass Transfer in a Slurry Reactor

Introduction: In this study, the mass transfer effects in a triphasic reaction conducted in a slurry reactor were evaluated to optimize operational parameters (gas flow, stirring speed, temperature, and solid mass), aiming to understand how these parameters influence the efficiency of the reactor. The reactor was operated at 25°C and 1.0 bar under mechanical stirring, in a semi-batch mode, where the liquid and solid phases were in batch mode, while the gas phase was in continuous mode. The evaluation was performed at stirring speeds ranging from 200 to 500 rpm and airflow rates between 50 and 200 L h⁻¹. The results highlighting the limiting effects of mass transfer indicated that the gas-liquid volumetric mass transfer coefficient (kLa) ranged from 0.0152 to 0.0768 s⁻¹. For glycerol oxidation in a slurry reactor, the mass transfer of oxygen in a 30 g L-1 glycerol solution was evaluated, yielding a kLa value of 0.046 s⁻¹. Objective: The objective of this study is to investigate the mass transfer effects in a three-phase reactor, characterizing mechanical agitation and gas dispersion to enhance oxygen transfer, as demonstrated by the model reaction. Theoretical Framework: The main concepts and theories that underpin the research are mass transfer in multiphase and reactive systems, including two-film theory, the effects of operational parameters on a slurry reactor, and its behavior. Also, the development of a dynamic measurement. Method: The methodology adopted for this research comprises a three-phase reactor, and a kinetic study was conducted. Data collection was carried out by measuring the concentration of oxygen and applying the subtle equations shown in the main text. Results and Discussion: The study found that increasing the stirring speed and gas flow significantly enhanced the volumetric mass transfer coefficient (kLa), reaching a maximum value of 0.076 s⁻¹. Temperature had a positive influence on kLa, especially at higher gas flows, while glycerol concentration reduced oxygen transfer due to increased viscosity. The solid mass had a lesser effect compared to the gas flow. These findings support efficient reactor operation with minimal resource usage. Research Implications: These insights contribute to a deeper understanding of the transport phenomena that govern catalytic oxidation processes, offering a valuable tool for rational reactor design and scale-up, especially in systems limited by gas-liquid transfer. Moreover, the methodology and results support the development of efficient and cost-effective oxidation systems for applications such as glycerol valorization. Originality/Value: This study presents an integrated analysis of operational parameters affecting gas-liquid mass transfer in a slurry reactor. Using a dynamic and precise method based on in situ oxygen measurements, it accurately quantifies kLa under varying conditions. The approach enables optimized slurry reactors, reducing excess and improving efficiency.