Diffusion and Mass Transfer of Gases in Surfactant Solutions and Nanofluids

Abstract

The investigation of gas-liquid mass transfer process is critical in many fields, such as petroleum engineering, environmental science, and chemical engineering. Mass transfer coefficient (k) and diffusion coefficient (D) are the key parameters affecting mass transfer process. A reliable method to measure and optimize these parameters can be very useful and have many applications, such as optimizing gas solvent-based oil recovery processes, enhancing efficiency of the sequestration of greenhouse gases in reservoirs, and controlling the gas-liquid mass transfer rate in liquid-gas reactor or an effective scheme of fermentation. The pressure decay technique is a simple but effective method to measure k and D accurately and efficiently. The application of surfactants and nanoparticles in optimizing the gas-liquid mass transfer is rarely reported previously. In this study, pressure-decay-based methods, with a large number of experiments, are proposed to systematically measure the k and D of CH4 and N2 in pure water, surfactant solutions, and nanofluids. A designed apparatus is used to measure the gas pressure change with time using a high-resolution pressure transducer. Diffusion dominated (DD) model and interface-resistance diffusion (IRD) model, based on the experiments, are presented. The exact solutions of these two models are further obtained to estimate the k and D using pressure data through a global optimization method. The DD and IRD models extend previous pressure-decay models and resolve several existed issues. The methods, proposed in this work, are used to investigate the effect of surfactants and nanoparticles on the gas-liquid mass transfer. The results provide new insight into the mechanisms of gas mass transfer in the surfactant solutions and nanofluids. The effect is significant. Compared with pure water, the smallest k is a decrease ratio of 8.6. It takes place at a concentration of 10,000 ppm for modified-oleic acid (OA) nanofluid. The greatest D enhancement ratio is about 2.5, which is achieved in modified-OA nanofluid at a concentration of 5,000 ppm.