oa South African Journal of Chemical Engineering - Influence of temperature on volatile organic compounds - ester solvent interactions
The influence of temperature on the solubility of 27 volatile organic compounds (VOCs) representing seven VOC families in biodiesel esters was investigated. Phase equilibrium data in the form of infinite dilution activity coefficients were predicted for a temperature range of 30° to 50°C using the Modified UNIFAC Dortmund Group Contribution Model. The desired phase equilibrium data were computed using a Microsoft Excel spreadsheet designed for this purpose. It was found that alkane activity coefficients decreased with increasing temperature, but do not approach ideality with increasing temperature. With the exception of the acroleins, activity coefficients of the aldehydes decreased with increasing temperature, approaching ideality. Activity coefficients of organic acids in unsaturated esters tended towards ideality whilst interactions with unsaturated esters deviated from ideality. With the exception of tetrahydrofuran and tetrahydropyran, ether interactions with ester solvents generally tended towards ideality. It was also observed that the activity coefficients of formates and carbonates particularly ethyl formatein biodiesel generally tended towards ideality with increasing temperature. The interactions in this study show that ester/solute interactions yielding activity coefficients greater than 1 favour higher absorption temperatures whilst those with coefficients less than 1 favour lower absorption temperatures.
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