The labelling of methyl tertiary butyl ether (MTBE), an oxygenate additive used extensively in gasoline blending, as an environmentally harmful chemical has led to the banning and subsequent phasing-out of this additive in California (USA). In response, the global petroleum industry is currently considering replacement strategies, which include the use of tertiary amyl methyl ether (TAME) or ethanol. Subsequently, SASOL (South African Coal and Oil Limited), a local petrochemical company, in its capacity as an environmentally responsible player in the global petroleum and aligned chemical markets, has commissioned this investigation into the environmental fate of the fuel oxygenates: TAME, ethanol and MTBE. In order to evaluate the environmental fate of the oxygenates, this dissertation has formed a three-tiered approach, using MTBE as a benchmark. The first tier assessed the general fate behaviour of the oxygenates using an evaluative model. A generic evaluative model, developed by Mackay et al. (l996a), called the Equilibrium Criterion (EQc) model was used for this purpose. This fugacity based multimedia model showed MTBE and TAME to have similar affinities for the water compartment. Ethanol was demonstrated to have a pre-disposition for the air compartment. Parameterisation of the EQC model to South African conditions resulted in the development of ChemSA, which reiterated the EQC findings. The second tier quantified the persistence (P), bioaccumulation (B) and long-range transport (LRT) potential of the additives. This tier also included a brief toxicity (T) review. MTBE and ethanol were demonstrated to be persistent and non-persistent, respectively, according to three threshold limit protocols (Convention on the Long Range Trans-boundary Air Pollution Persistent Organic Chemical Protocol; the United Nations Environment Programme Global Initiative; and the Track 1 criteria as defined by the Canadian Toxic Substances Management Policy, as referred to by the Canadian Environmental Protection Act 1999). These protocols were not unanimous in the persistence classification of TAME. Further investigation of persistence was conducted using a persistence and long-range transport multimedia model, called TaPL3, developed by Webster et al. (1998) and extended by Beyer et al. (2000). TaPL3 reiterated the conclusions drawn from the threshold limit protocols, indicating that TAME's classification worsened from non-persistent to persistent on moving from an air emission to a water emission scenario. This served to emphasise the negative water compartment affinity associated with TAME. Using classification intervals defined by Beyer et al. (2000), TaPL3 demonstrated that the long-range transport potential of the oxygenates increased in the order of TAME, ethanol and MTBE; however, it was concluded that none of the oxygenates were expected to pose a serious long-range transport threat. Bioaccumulation was not expected to be a pertinent environmental hazard. As expected, the oxygenates were dismissed as potential bioaccumulators by the first level of a screening method developed by Mackay and Fraser (2000); as well as by the threshold limit protocols listed above. Simulation of biomagnification, using an equilibrium food chain model developed by Thomann (1989), demonstrated that none of the oxygenates posed a biomagnification threat. A review of toxicity data confirmed that none of the three oxygenates are considered particularly toxic. LDso values indicated the following order of increasing toxicity: ethanol, MTBE and TAME. The third tier focussed on oxygenate aqueous behaviour. A simple equilibrium groundwater model was used to analyse the mobility of the oxygenates in groundwater. TAME was found to be 21 % less mobile than MTBE. Ethanol was shown to be very mobile; however, the applicability of the equilibrium model to this biodegradable alcohol was limited. An analysis of liquid-liquid equilibria comprised of oxygenate, water and a fuel substitution chemical was performed to investigate fuel-aqueous phase partitioning and the co-solvency effects of the oxygenates. Ethanol was shown to partition appreciably into an associated water phase from a fuel-phase. Moreover, this alcohol was shown to act as a co-solvent drawing fuel chemicals into the water phase. MTBE was found to partition sparingly into the water phase from a fuel-phase, with TAME partitioning less than MTBE. Neither ether was shown to act as a co-solvent. It was concluded that TAME and ethanol pose less of a burden to the environment than MTBE. Ethanol was assessed to be environmentally benign; however, it was concluded that ethanol's air compartment affinity and the extent of its co-influence on secondary solutes justified the need for further investigation before its adoption as a fuel additive. This project showed sufficient variation in the environmental behaviour of TAME and MTBE to justify the abandonment of the axiom that MTBE and TAME behave similarly in the environment. However, as MTBE is a significant water pollutant, and TAME has been shown to share a similar water affinity, it is cautiously recommended that the assumption of environmental similarity be discarded, except for the water compartment. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2002.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

The United States Environmental Protection Agency has estimated that over 111 million people reside in areas that exceed the National Ambient Air Quality Standards for ozone. One major source of the chemical precursors (nitrogen dioxides and volatile organic compounds (VOCs)) for ozone are motor vehicles. The overall goal of this research is to improve the knowledge base related to VOC refueling and evaporative emissions from motor vehicles. Refueling, running loss, hot soak, and diurnal loss total and speciated VOC emissions were investigated. A total of 12 uncontrolled refueling events were completed and involved the determination of volumetric flow rates of gasoline vapor during refueling, as well as total and speciated VOC concentrations. Total VOC emissions were compared with two commonly used algorithms. Speciated VOC vapor profiles were compared with two published gasoline vapor profiles and theoretical predictions based on knowledge of liquid composition and environmental conditions. An evaluation of refueling emissions impacts on ozone formation potentials using MIR was completed and results were compared against speciated emissions and MOBILE-based total VOC emissions estimates coupled with a default speciation profile. Refueling VOC emissions and resultant ozone formation potential may be underestimated in existing emission inventories, particularly during the summer ozone season, A model was developed to predict the speciation of VOCs associated with evaporative emissions from motor vehicles. Model-predicted speciation profiles were evaluated using SHED studies. Running loss, hot soak and diurnal emissions were included in each test. Total VOC emissions measured during each test were compared against MOBILE6 predicted emissions. An evaluation of evaporative emissions impacts on ozone formation potentials using MIR was completed, comparing measured and predicted emissions. The measured:predicted speciation results ranged between 0.93 and 1.11 and had an average value of 1.02. For the conditions tested, MOBILE6 underestimated evaporative emissions in 20 of 24 comparisons. MOBILE6-based ozone formation potentials may be underestimated.