Indirect Positive Effects of Ethers Use
The use of ethers also entails positive indirect effects, arising from the dilution of other, less desirable, gasoline pool components—such as olefins, aromatics, sulfur, and benzene levels.
The extent of MTBE’s air quality benefits depends on various parameters, such as the percentage of blended MTBE, the presence of catalyst devices, the type and age of engine and the driving cycle. Nevertheless, there is general agreement in the industrial and scientific communities on broad values, as reported in the chart below.
- Carbon monoxide: CO emission is reduced on average by at least the same percentage as MTBE content in gasoline.
- Unburned hydrocarbons: For each 1 or 2% of MTBE, there is a 1% reduction in total HC emissions.
- Particulate matter: It is estimated that each 1% of MTBE results in a 2 to 3% PM emission reduction.
- Ozone: MTBE generates about half the ozone compared with iso/alkylates and one-tenth that of aromatics.
- Benzene: It is estimated that, for each 1% of MTBE, there is an equivalent percentage reduction in benzene emissions, both evaporative and exhaust.
- Olefins: MTBE displays low vapour pressure and low volatility compared to olefins. Converting olefins to MTBE in the refinery removes some of the most reactive and volatile components from the gasoline pool.
- Lead: MTBE is an effective substitute for lead, a toxic compound that has been phased out in most parts of the world.
Moreover, as an example of the potential air quality benefits of MTBE, the following significant reductions of pollutants have been achieved through the use of reformulated gasoline containing 10-15% MTBE, compared to conventional gasoline:
- 20-25 % less carbon monoxide
- 10-15% less unburned hydrocarbons
- About 30% less particulate matter
- 20-30% less benzene
- 5% less nitrogen oxides
- 15% less evaporative emissions
- Reduction of ground-level ozone