Abstract
M.Tech. (Chemical Engineering)
The legislation on environmental conservation in South Africa, as outlined in the National Environmental Management: Air Quality Act 39 of 2004, has forced all industries to closely monitor any effluents emitted into the environment. This work investigated the suitability of biodiesel (specifically methyl linolenate, methyl palmitate, methyl oleate and methyl stearate) as an absorbent for the recovery of VOCs from waste gas process streams through absorption. The objective was to predict the vapour liquid equilibria (VLE) data, in the form of infinite dilution activity coefficients for five VOC families, in fatty acid methyl ester solvents. The Original Universal Functional Group Activity Coefficient (UNIFAC) model (Fredenslund et al., 1975), Modified UNIFAC (Larsen et al., 1981) and Modified UNIFAC (Bastos et al., 1988) were used to predict the infinite dilution activity coefficients. The solubility of alkanes, amines, alkenes, organic acids and alcohols showed a decrease in activity coefficients with an increase in molecular weight. Shorter chained esters with a lower carbon count had higher activity coefficients when compared to longer chained esters with a higher carbon count. The solubility of VOCs in biodiesel decreases with increases in ester hydrocarbon unsaturation. This work also investigated the vapour liquid equilibria (VLE) data in the form of infinite dilution activity coefficients for five VOC families, in fatty acid methyl ester solvents at varying temperature. Alkanes, alcohols and acids/ester interactions showed increases in activity coefficients with increases in temperature. The influence of temperature on the activity coefficients for alkene and amine families was negligible. The solubility of VOCs in biodiesel decreased with increases in ester hydrocarbon unsaturation and the solubility increased with an increase in ester molecular weight. The results for the modified UNIFAC Bastos and UNIFAC Fredenslund showed good agreement with the experimental measurements for 1,2-Dichloroethane, 2-Chlorobutane and Toluene. This study substantiates the hypothesis biodiesel is well suited as an absorbent for removal of VOC solutes from waste gas streams. The results presented in this report are comprehensive and it is envisaged that this work will assist engineers in making informed decisions when using biodiesel as a scrubbing solvent.