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This post was originally posted as a 3-part series, which are combined below.

Part 1

Gas-liquid mass transfer (GLMT) is a fundamental interphase transport process that we rely on in our everyday lives: drying washed clothes, preparing a carbonated drink, or using perfume. This transport phenomenon plays a crucial role in many industrial and natural systems where efficient mass transfer is essential for achieving desired reactions and products:

• Chemical and Petrochemical Processes: GLMT is extensively used for the absorption of gases into liquid solvents or the stripping of gases from liquids. This is crucial for separating valuable components or removing impurities in processes like natural gas sweetening and acid gas removal.
• Mining and Metallurgy: GLMT is involved in various processes such as hydrometallurgy, where gases like oxygen are transferred into liquid solutions to facilitate leaching and extraction of metals from ores.
• Carbon capture: GLMT in carbon capture technologies is a dynamic and intricate process that sees many applications such as absorption and desorption of CO2 in a solvent, selective permeation of CO2 through membranes, precipitation and crystallization, and pressure swing adsorption.
• Environmental Engineering: Mass transfer is important in environmental processes like air-water interactions, such as gas exchange in natural bodies of water. It influences processes like oxygen transfer in wastewater treatment, gas transfer in water ecosystems, and air pollution control.
• Biotechnology: In bioreactors for cell culture, efficient GLMT is essential to provide oxygen to cells and remove carbon dioxide. This is critical for the growth and production of cells used in the production of bio-based products.
• Pharmaceuticals: GLMT plays a pivotal role in pharmaceutical processes, such as drug formulation and dissolution. Microorganisms in fermentation process metabolize substrates to produce pharmaceuticals, enzymes, or other bio-based products. Oxygen transfer is a critical factor in these processes.

Part 2

In our previous post, we discussed applications of gas-liquid mass transfer (GLMT) over a wide range of industries and natural systems. Understanding GLMT is essential for designing a robust and efficient system.

Gas-liquid mass transfer is governed by two primary mechanisms: convection and diffusion.

Convection occurs due to the bulk movement of the liquid or gas phase as a whole. It facilitates the transfer of mass by renewing the gas-liquid interface, where mass transfer occurs.

Diffusion, on the other hand, is the random movement of molecules from an area of higher concentration to an area of lower concentration. It is responsible for the molecular-level transport of mass between the gas and liquid phases.

Based on these considerations, the scaling of gas-liquid mass transfer processes usually relies on correlations between the Sherwood number (which rationalizes convective mass transfer to diffusive mass transfer), the Reynolds number (which rationalizes inertial flow to viscous flow) and the Schmidt number (which rationalizes viscosity to diffusion).

Several factors influence the rate of gas-liquid mass transfer, and we will discuss these in our final post of the three-part series.

Part 3

The first two posts in this series introduced gas-liquid mass transfer (GLMT), its applications and primary mechanisms. Today we will explore the factors which influence the rate of gas-liquid mass transfer:

-Mass Transfer Area: The interfacial area between the gas and liquid phases significantly affects mass transfer. Increasing the surface area, such as through the use of packing materials or agitation, enhances the contact between the phases and promotes efficient mass transfer.
-Concentration Difference: The driving force for mass transfer is the difference in concentration between the gas and liquid phases. A larger concentration difference leads to a higher mass transfer rate. This difference can be influenced by factors such as the solubility of the gas in the liquid and the partial pressure of the gas in the gas phase.
-Diffusion Coefficient: The diffusion coefficient characterizes the ease with which a substance can diffuse through a particular medium. It depends on properties such as temperature, pressure, and the nature of the gas and liquid involved. Higher diffusion coefficients result in faster mass transfer.
-Thickness of the Diffusion Layer: The thickness of the diffusion layer, which is the region where diffusion occurs adjacent to the gas-liquid interface, impacts mass transfer. A thinner diffusion layer reduces the resistance to mass transfer and increases the overall rate.

Depending on a specific scenario, several methods can be employed to enhance mass transfer rates such as optimization of feed system, use of packing material, gas sparging, agitation and enhanced mixing, solvent and catalyst selection, and temperature and pressure control.