A Novel Method for Decomposing and Recycling Ammonium Bicarbonate Solutions

A new way of decomposing and recycling ammonium bicarbonate (AB) in aqueous solution has been achieved using a membrane transport process with both dense and porous hollow fibre membranes, which offer efficient heat and mass transfer coefficients. It has been established that the decomposition of AB solutions occurs via contact through a permeable membrane, of AB solutions pre-heated to 80 °C, with a continuous counter-flow of dehumidified air at room temperature. In this process, ammonia (NH3) and carbon dioxide (CO2) gases permeate through the membrane and are thereby separated from the feed solution and they can then be collected into aqueous solution, for recycling purposes. The new process could, for example, be applied to the treatment of concentrated AB solutions used as draw solutions in forward osmosis (FO) or in the regeneration of depleted ion exchange resins. The results also show that AB recovery depends largely on the membrane surface area. The membrane can be used and optimised to achieve a high decomposition rate for AB with a single pass system to avoid additional pumping of the solution

Applied Colloid And Surface Chemistry

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Further studies into oil droplet size manipulation

Recent work has shown that heating degassed oil-in-water emulsions causes a significant reduction in the oil droplet size. The results presented here report further work on the effect of changes in salt concentration, oil/water ratio, pH and heating, on the oil droplet sizes of dispersions produced by the de-gassing process. The change in particle or droplet size for long, straight chain hydrocarbon oils, dispersed in water by degassing, is also reported here. These oils, of 20-24 carbon units in length, are liquid when heated above 50 °C but are solid at room temperature. The particle size of these dispersions was also monitored during the phase transition from liquid to solid, on cooling

Oil droplet size manipulation applied to surfactant-free emulsion polymerization

Recently reported results indicate that heating of degassed oil in water emulsions reduces the size of the droplets and can produce a more mono-disperse dispersion, in the absence of surfactants. In this work, these results were applied to the field of emulsion polymerization, to create meta-stable, mono-disperse monomer solutions, which were then polymerized to produce stable dispersions of polymer spheres. The product particle size depended on a range of factors, including: salt concentration, type of thermal initiator, temperature changes, creaming time, pH and monomer/initiator concentration ratio

Changing the size of oil droplets dispersed in water without added surfactants

Electrophoresis studies on pure hydrocarbon oil droplets, dispersed in water, have established that a significant charge is naturally developed on the droplets surface due to the spontaneous adsorption of hydroxyl ions. It has subsequently been pointed out that this charge should ensure the meta-stability of fine, micron-sized oil droplets dispersed in water. Further studies have demonstrated that such dispersions can be produced by the vigorous shaking of de-gassed mixtures of oil and water. De-gassing appears to enhance the dispersion process and the natural charging of the oil droplets ensures their meta-stability. Using this enhanced dispersion process, we have found that subsequent heating and cooling cycles, carried out over several minutes, can alter the average droplet size and the droplet size distribution, in some cases producing narrower distributions

The hydrophobicity of non-aqueous liquids and their dispersion in water under de-gassed conditions

Several recent studies have shown that many oils, such as hydrocarbons, fluorocarbons, silicone and natural oils, are more readily dispersed as fine (micron-sized) droplets in water when the mixtures are almost completely degassed. These observations have not yet been fully explained and so this paper examines the nature of hydrophobicity of a wide range of oils and considers both the cavitation process and the surface charging expected during the separation of hydrophobic materials in water. Cavitation inside porous hydrophobic solids immersed in water is also considered. We also introduce a quick, easy and alternative method to freeze-thaw degassing, by which enhanced dispersions can be formed, which gives further support to the central role of degassing

Novel applications of non Hofmeister ion specificity in bubble interactions

The ion specificity of bubble-bubble interactions in water remains unexplained. Whatever their valence all ion pairs either completely inhibit bubble coalescence or have no effect whatever. The phenomenon appears unrelated to Hofmeister specificity. Salts which inhibit coalescence enable the formation of a high density bubble column evaporator (BCE). If hot gas bubbles are injected into the bubble column evaporator at a significantly higher temperature than the water, the hot bubble surfaces can be used to produce thermal effects in dissolved and dispersed solutes. These two properties can be exploited for a wide range of applications. Among these, high temperature aqueous reactions catalyzed at low solution temperatures, measurement of enthalpies of vaporization of concentrated salt solutions, wastewater treatments by sterilization and de-watering and desalination are a few