Študija vpliva obratovalnih pogojev in predčiščenja na mašenje membrane pri ultrafiltraciji hladilno mazalnih sredstev

slovenian

doktorska dela

2014

Univerza v Mariboru, Fakulteta za kemijo in kemijsko tehnologijo

The context of the doctoral dissertation is based on the study of various factors on the membrane fouling during the ultrafiltration of metalworking fluids. One of the possible ways to prevent the membrane fouling and consequent flux reduction is by controlling the operating conditions. Therefore, in the first part of the doctoral thesis Taguchi experimental design methodology was used to determine the optimal combination and relative importance of process parameters influencing the ultrafiltration (UF) of cutting oil emulsions. Four parameters, including pH, oil concentration, transmembrane pressure and temperature, were researched at three levels. The highest flux was used as optimization criterion. In order to reduce the number of experiments, the Taguchi method was applied. Analysis of variance (ANOVA) was used to determine the most significant parameters affecting the optimization criterion. Filtration experiments were performed in cross-flow operation at total recycle condition in a lab-scale plant. The ceramic UF membrane was employed in the tubular type module. During the experiments permeate flux was measured. Based on the results of the chemical analysis, the retention of individual components was calculated. The optimum conditions of UF providing the highest flux were found at %p = 5 bar, pH = 7, and % = 0,5 v/v % and T = 45 °C. The pH of emulsion had the greatest impact on the removal efficiency of organic compounds. The surface and structural properties of the membrane are very important for their permeability (which defines the capacity of filtration device) and play a crucial role in determining the fouling resistance property of the membranes. It is a general rule that hydrophilic materials are less sensitive to adsorption when compared to hydrophobic ones. Also, electrostatic phenomena, often quanti%ed by the membrane zeta potential, in%uence permeate flux and the fouling behaviour. In the second part of the study, the ultrafiltration of the cutting oil with three different polymeric membranes (regenerated cellulose (RC), polyacrylonitrile (PAN) and polyetherimide (PEI)) was studied. The permeate flux in dependence of ultrafiltration time was studied using two devices with cross-flow and dead-end flow. According to permeate flux reduction fouling mechanisms using Hermia%s model and modified membrane fouling index (MFI) were determined. Also, physical parameters as contact angle and streaming potential of membranes were analysed. The tests showed that among the three different UF membrane materials, regenerated cellulose showed the best performance in terms of the water flux and fouling tendency, due to its good hydrophilicity, in cross-flow operation. The dominant fouling mechanism was the cake layer formation model followed by the intermediate blocking model. In the third part of the doctoral thesis we solved the problem of membrane fouling by pre-treatment of oily emulsion. The aim of the pre-treatment was to reduce the organic fraction and to improve the ultrafiltration performance. Electrocoagulation and ultrafiltration experiments were carried out with cutting oil solutions at different concentrations. Electrocoagulation experiments were performed with aluminium electrodes. Ultrafiltration experiments were performed in a lab-scale cross-flow cell using flat sheet regenerated cellulose membrane. Electrocoagulation as a pre-treatment considerably improved the overall flux in UF of cutting oils. It also reduced fouling and cake layer resistance. Irreversible fouling was eliminated completely after 30 minutes of pre-treatment by electrocoagulation. Electrocoagulation increased the size of particles/droplets and improved removal of cutting oil up to 10 %.

07.08.2023