The quality of these a priori estimates of blend flashpoints
testifies to the quality of representation of molecularinteractions
by HSPs.
Lower Explosive Limit (LEL). Consider a blend ofmethyl formate
and dimethyl etherdnot a likely blend ofcleaning solvents, but one
for which blend LEL data areavailable. From Appendix A1, the
component LEL valuesare 4.5 and 3.3 volume percent, respectively.
The blendcomposition, in air, is 75 and 25 volume %,
respectively.Accordingly, the blend LEL was calculated using
EquationA2-18 as 3.56 vol.%, as shown in Equation A2-18.
Themeasured value was 3.65 vol.%AA.
LELblend 0:75 0:25
0:750:045
0:250:033
0:0356A218
Notice that the total composition is not needed in
thiscalculation, because it appears in both the numerator
anddenominator.
Upper Explosive Limit (UEL). Consider a blend ofheptane and
chloroform. This blend was tested by the USArmy in 1950 to
determine whether chloroform was aneffective flame suppressantBB.
They measured its upperexplosive limit in heptane (and air), and
compared themeasured values to those of other blends to learn
whichhalogenated solvents best suppressed combustion.
Heptane and chloroform were present at equal volumes(5%), in the
vapor phase. Testing was done at 25C. FromAppendix A1, literature
values of the UELs for chloro-form and heptane are 12.9 and 6.7
volume percent,respectively.
Accordingly, the blend UEL was calculated as 8.8 vol.%, asshown
inEquationA2-18. Themeasured valuewas9.3vol.%.
UELblend 0:05 0:05
0:05:129
0:050:067
0:088 A218
Relative Evaporation Rate (RER) of Blends. Considera blend of
octane and toluene, two solvents with relativelysimilar HSPs as
their RA is only 5.5 MPa
. The blend of70.56 wt. % octane is prepared and allowed to
evaporate,and both the overall and individual evaporation rates
aremeasured with the aid of a gas chromatographCC over timeuntil
the blend is fully evaporated.
From Appendix A1, Table 4, RER values for octane andtoluene are
1.984 and 1.230, both evaporating morereadily than n-butyl
acetate.
RERblend n BuAc 1 1
0:66021:984
0:33981:230
1:642
AA219A
Estimation of Properties of Solvent Blends A2 Appendix
499
