Handbook of Solvents - George Wypych - ChemTech - Ventech!

2.3 Basic physical and chemical properties 53
Minimum spark ignition energy, mJ
1.4
1
0.6
0.2
0.9 1.1 1.3 1.5 1.7
Stoichiometric air to solvent ratio
Figure 2.3.14. Minimum ignition energy vs.
stoichiometric ratio of air to methyl ethyl ketone.
[Data from H F Calcote, C A Gregory, C M Barnett,
R B Gilmer, Ind. Eng. Chem., 44, 2656 (1952)].
Autoignition temperature, o C
500
450
400
350
300
alcohols
aromatic CH
esters
ketones
250
20 40 60 80 100 120 140 160
Molecular weight, Daltons
Figure 2.3.16. Autoignition temperature of selected
solvents vs. their molecular weight.
0.1
20 60 100 140
Figure 2.3.14 shows the effect of
changing the ratio of air to methyl ethyl
ketone on the minimum spark ignition energy.
The ignition energy decreases within
the studied range as the amount of air
increases (less flammable content). Figure
2.3.15 shows the effect of temperature on
the minimum ignition energy of selected
solvents. There are differences between
solvents resulting from differences in
chemical structure as discussed above but
the trend is consistent − a decrease of required
energy as temperature increases.
The autoignition temperature is the
minimum temperature required to initiate
combustion in the absence of a spark or
flame. The autoignition temperature depends
on the chemical structure of solvent,
the composition of the vapor/ air mixture, the oxygen concentration, the shape and size of
the combustion chamber, the rate and duration of heating, and on catalytic effects. Figure
2.3.16 shows the effect of chemical structure on autoignition temperature. The general trend
for all groups of solvents is that the autoignition temperature decreases as molecular weight
increases. Esters and ketones behave almost identically in this respect and aromatic hydrocarbons
are very similar. The presence of a hydroxyl group substantially reduces
autoignition temperature.
Minimum ignition energy, mJ
0.4
0.3
0.2
Temperature, o C
ethyl acetate
toluene
ethanol
Figure 2.3.15. Minimum ignition energy vs.
temperature for selected solvents. [Data from
V S Kravchenko, V A Bondar, Explosion Safety of
electrical Discharges and Frictional Sparks,
Khimia, Moscow, 1976].