M.Tech. (Chemical Engineering) / Increasing pressure on industry from national and international communities for more environmentally friendly operations has generated a drive towards the use of ‘green’ absorbents in the removal of volatile organic compounds from contaminated air streams. The objective of this work was to investigate the use of ester solvents, especially biodiesel esters, as suitable ‘green’ scrubbing solvents for the absorption of volatile organic compounds (VOCs) from gaseous waste streams. The objective was accomplished by investigating the nature of molecular interactions between ester solvents and various families of VOC solvents, and by studying the effect of temperature on absorption, through the analysis of infinite dilution activity coefficients. Activity coefficients were computed with a Microsoft Excel generated spread sheet using Modified UNIFAC Dortmund (1987) as a thermodynamic predictive model. Results show that non-polar solutes are more soluble in long chain ester solvents whilst polar solutes absorb easier in short chain ester solvents. The solubility of non-polar solutes decreases with increasing ester solvent unsaturation, whilst the opposite is true for polar solutes in esters. Short chain length non-polar solutes are more soluble than long chain length non-polar solutes in ester solvents, whilst the opposite trend occurs for polar solutes in ester solvents. An increase in branching of polar solutes results in the solute behaving more like a non-polar solute. Unfortunately UNIFAC models fail to account for functional group proximity effects, which may result in inaccurate results for systems involving highly branched solutes. However given that the purpose of this study was only to establish trends for generating an understanding of molecular interactions between the solutes and the solvent, it was acceptable to assume that these inaccuracies would be minor for the intended purpose. It was found that activity coefficients of ester/ solute interactions generally tend towards ideality with increasing temperature with the exception of alkanes and the nitrogen based VOCs, as well as tetrahydrofuran and tetrahydropyran, methacrolein and organic acid/ unsaturated ester interactions. In the case of the alkanes, tetrahydrofuran and tetrahydropyran, high-temperature absorption is preferred whilst for methacrolein lower temperature absorption is preferred. It was concluded that ester solvents ,especially biodiesel esters, are well suited for the removal of non-polar to moderately polar VOC solutes from waste gas streams due to the favourably low activity coefficients obtained for these ester/ solute interactions. The results presented in this report are comprehensive and can assist in making informed decisions in using biodiesel as a scrubbing solvent.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:11392 |
| Date | 04 June 2014 |
| Creators | Scheepers, Jacques Johan |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Johannesburg |
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