Effect of the Properties of MTBE and Other Oxygenates on Treatment

In an SVE system, the primary mechanism for contaminant removal from the soil to the vadose zone is the volatilization of contaminants present in the pure or adsorbed phase onto soil into the vapor phase, as the vapor phase is continually extracted. The property that shows the extent to which this transfer can take place during SVE is vapor pressure, which provides an indication of the extent to which each contaminant will partition between the liquid phase and the vapor state at equilibrium conditions. Generally, a contaminant with a greater vapor pressure more readily volatilizes than one with a lesser vapor pressure.

Figure 24.4 shows the vapor pressures, in units of millimeters of mercury (mm Hg), for the common fuel oxygenates as compared with BTEX.1 Generally, contaminants with vapor pressures greater than 10 mm Hg are considered to be amenable to treatment using SVE. As shown in the figure, each of the common oxygenates has vapor pressures >10 mm Hg, with ether-based oxygenates generally having greater vapor pressures than alcohol-based oxygenates. In addition, most of the common oxygenates (with the exception of TBA, TAME, and ethanol) have greater vapor pressures than BTEX, suggesting that they are more readily extracted using SVE than BTEX, which are commonly addressed with SVE.

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