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The Henry's Law Constant for benzene is 0.152 at 15oC. For xylene the average Kh for the three isomers is 0.261 at 25oC. MTBE has a HLC of 0.0224 at 25oC or 44.6 molecules in the water for every one in air. Another way to look at it is that approximately 98% of the MTBE prefers to stay in the water.

Lyman et al. (1982) give the following general guidelines for volatility based on the Henry's constant in units of atm m3/mol:

Volatility Guide
Relative Volatility Henry's Constant
atm m3/mol
Chemicals of Interest
low less than 10-7 --
slow 10-7 to 10-5 --
significant 10-5 to 10-3 MTBE
rapid greater than 10-3 benzene, xylenes

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