The influence of different factors on the stability and ultrafiltration of emulsified oil in water

The effects of different operating conditions on ultrafiltration (regenerated cellulose with a cut-off of 100 kg/mol) of cutting oil were studied for two different cases. The factors, examined at three levels, included: pH, oil concentration, feed flow velocity, and temperature. The salt (NaCl and CaCl(2)) concentration was examined at three levels as well. A lower concentration range was used initially and was increased in the second case. In each case different combinations of operating conditions were studied by using the Taguchi experimental design. The designed experimental set consisted of eighteen trials with three levels of variation for each factor. For each trial permeate flux, oil drop size and the zeta potential of the oil were measured. The obtained results showed that with a low salt concentration (NaCl and CaCl(2)), pH is the most important factor. With increasing salt concentration, temperature becomes the most important factor. pH affects mainly emulsion stability while temperature has an influence on viscosity. Further, a statistical analysis of variance (ANOVA) was performed to determine the significance of controlling factors. It was observed that for both cases salts have the least influence on the increase of permeate flux. The best optimum conditions for both cases were achieved when salt and oil concentration remained at the lowest level, whereas temperature, pressure and flow velocity were at the highest level. (C) 2008 Elsevier B.V. All rights reserved.