Abstract
Differing experimental results have been obtained for gas absorption into horizontal stagnant liquid pools, with and without chemical reaction, using a novel simultaneous optical birefringent interferometric and pressure transducer technique. The thesis is divided into two parts. Section one is mainly concerned with physical gas absorption. The systems investigated were carbon dioxide/water, acetylene/water, ammonia/water, sulphur dioxide/water and carbon dioxide/propylene carbonate. The take-up of gas (M[t]) by the absorbing solutions, concentrations and concentration profiles of gas in liquid have been obtained relative to exposure times from both experimental and,generally, theoretical considerations. The possibility of a surface resistance (1/k[s]) for the absorption of carbon dioxide by water and propylene carbonate, and acetylene by water, has been considered. The method of analysis indicates an appreciable resistance to exist in all cases. The effect of a soluble surfactant on the transfer process has also been studied. It has been demonstrated that for all the systems studied, convective disturbances (perhaps in the form of microflows or eddies) are produced almost instantaneously (0.04 sec was the shortest time of investigation possible in this study) upon exposure of absorbing gas to liquid. This convective disturbance could be responsible for a much larger transport of solute from the liquid surface than can occur by molecular diffusion alone. Further studies on convection involved examining the effect of pool depth on the absorption of carbon dioxide and acetylene by a 3% aqueous solution of wetting agent (pool depths from less than 0.4 mm to 25 mm), and sulphur dioxide by pure water (approximately 2 mm to 25 mm). In all cases, there was a peak depth at which absorption was greatest. This phenomenon is suggested to be due to the presence of convection in the liquid pool. An analysis, based on hydrodynamic stability theory, was carried out for buoyancy-driven convection in the sulphur dioxide/water system. Calculated values of critical Rayleigh numbers from experimental results were shown to be larger than theoretically predicted values. Section two of the thesis deals with interfacial turbulence and absorption of an acid-gas in several systems of absorption accompanied with chemical reaction. These were carbon dioxide absorption by aqueous solutions of mono-di- and tri-ethanolamine, sodium and potassium hydroxide, and hydrogen sulphide absorption by aqueous solutions of mono-di- and tri-ethanolamine. All the systems were examined optically and by the transducer technique. The carbon dioxide/monoethanolamine system for concentrations less than IN was studied using a laminar jet absorption apparatus. Photographs of turbulence are shown, and a time-scale for the onset of visible convection in the form of roll cells is presented for all the systems. A minimum time of several seconds for this onset time, which varied with concentration, was found for all the systems. However, analysis of interferograms for absorption of carbon dioxide by IN monoethanolamine, suggests that some form of convection is almost instantaneously generated upon exposure of gas to liquid, as in the case of physical absorption. Transducer absorption studies, when compared to theoretical predictions, suggest there is an accumulation of reaction product at the gas/liquid interface until viscous forces in the liquid bulk are overcome. At this point, roll cell convection commences and the amount of gas absorbed begins to exceed that predicted by theory.