Handbook of Solvents - George Wypych - ChemTech - Ventech!

1198 Michelle Bergin, Armistead Russell
Figure 17.4.2. Solvent relative reactivities based on mass of ozone formed per gram of solvent emitted into the gas
phase. PCBTF is para-chlorobenzo-trifluoride, BTF is benzo-trifluoride and TBA is tertiary butyl acetate.
[Adapted from M.S. Bergin et al., Env. Sci. Technol., 29, 3029 (1998) and M. Khan et al., Atmos. Env., 33, 1085
(1999)].
used, e.g., by switching to ethers, alcohols, alkanes or halogenated compounds. Solvent
substitution, however, is complicated by the need to maintain product quality.
17.4.4 REGULATORY APPROACHES TO OZONE CONTROL AND
SOLVENTS
Historically, regulatory approaches to reducing ozone concentrations have relied reducing
the mass emissions of VOCs, 2,4 and this has led to stringent controls on solvents. Two factors
are important in determining if an organic solvent is considered a VOC: its reactivity
(discussed above) and its vapor pressure. In the U.S., traditionally, if a compound was less
reactive than ethane, it was considered unreactive. Such compounds include many
halogenated species and some acetates and ethers. Recently, acetone was also added as an
unreactive compound. A vapor pressure threshold is also used in many areas (e.g., Europe)
since it is viewed that compounds with very low vapor pressures will not be emitted rapidly
into the atmosphere. It has been argued that a vapor pressure limit may not be appropriate
since, given time, even lower vapor pressure compounds will have ample time to evaporate.
Just recently, California is considering regulations that more fully account for the full range
of reactivities that solvents possess. This is due, in part, to make it easier for manufacturers
to meet stringent regulations being adopted in that state to help them meet their air quality
goals. It is likely that other areas will also have to employ increasingly more stringent regulations,
to both lower ozone and alleviate other environmental damage.
In many countries, greater focus is now being placed on reducing NOx emissions to
mitigate ozone formation. This has important ramifications for solvent use, indicating the