Colloidal Gas Aphrons

Abstract: The removal of Solvent Yellow 1 in a range from 0.25 to 10 ppm by weight from an aqueous solution using a predispersed solvent extraction (PDSE) was investigated and compared with conventional solvent extractions in batch mode. Colloidal liquid aphrons (CLAs) made out of kerosene were used as a predispersed organic solvent. To form CLAs, Tergitol 15-S-3 and sodium dodecylbenzene sulfonate were used as oil-soluble and water-soluble surfactants, respectively. The ratio of solvent volume to pregnant solution volume was less than 0.025. The efficiency of the extraction with CLAs can be higher than that of a single-staged conventional extraction process with a shorter contact time. The recovery of used CLAs with a colloidal gas aphrons (CGAs) flotation was measured using different surfactants. CLAs with an extremely large surface area can also reduce processing time and energy cost. PDSE is therefore a promising process for the removal of organic materials from water.

Abstract: Colloidal gas aphrons (CGAs) were first reported by Sebba (J. Colloid Interface Sci., 35 (4) (1971) 643) as micro bubbles (10-100 μm), composed of a gaseous inner core surrounded by a thin surfactant film, which are created by intense stirring of a surfactant solution. Since then, these colloidal dispersions have been used for diverse applications (clarification of suspensions, removal of sulphur crystals, separation of organic dyes from wastewater, etc.). However, there have been no reports, as yet, of their direct application for protein recovery. In this study, CGAs are created from an anionic surfactant (AOT) and are characterised in terms of stability and gas hold-up for a range of process parameters relevant to their proposed use for protein recovery, at a later stage. A statistical experimental design was developed in order to study the effect of different factors (surfactant concentration, salt concentration, pH, time of stirring and temperature) on the stability and gas hold-up of CGAs. The analysis of results from the experimental design provides predictive statistical models. Stability was found to depend mainly on salt and surfactant concentration. Several interactions are shown to be significant including the time-temperature interaction. Gas hold-up was found to depend mainly on salt and surfactant concentration and time of stirring. Also, results from power measurements are presented and the minimum energy for the formation of CGAs, for one set of solution properties, is determined.

Abstract: Colloidal gas aphrons (CGA) have previously been defined as surfactant stabilized gas microbubbles and characterized for a number of surfactants in terms of stability, gas holdup and bubble size even though there is no conclusive evidence of their structure (that is, orientation of surfactant molecules at the gas–liquid interface, thickness of gas–liquid interface, and/or number of surfactant layers). Knowledge of the structure would enable us to use these dispersions more efficiently for their diverse applications (such as for removal of dyes, recovery of proteins, and enhancement of mass transfer in bioreactors). This study investigates dispersion and structural features of CGA utilizing a range of novel predictive (for prediction of aphron size and drainage rate) and experimental (electron microscopy and X-ray diffraction) methods. Results indicate structural differences between foams and CGA, which may have been caused by a multilayer structure of the latter as suggested by the electron and X-ray diffraction analysis.