Handbook of Solvents - George Wypych - ChemTech - Ventech!

18.3 Indoor air pollution by solvents 1241
VOCC (volatile organic compound content) is defined as follows: 1 Mass of the volatile organic
compounds in a coating material, as determined under specified conditions.
Table 18.3.3. Example for basic calculations of VOC-emissions during application of
emulsion paints (after references 2,5,6,13)
1. At the beginning of the application process (t=0) the mass of VOC changes positively (vSTdscw),onthe other hand VOC evaporates (first order of kinetics).
dmw/dt=vSTdscw -klmw/ds [18.3.1]
2. In the ambient air the mass of VOC increases because of the evaporation out of the wall and decreases
according to the ventilation rates.
dmL/dt=k1mw/ds -k2mL [18.3.2]
3. If the connected differential equations are solved and integrated (from t=0 until the end of application
t=A/vST), the following equations are received:
2
mw(t)=vSTds cw/k1(1-exp(-klt/ds)) [18.3.3]
and
mL(t) = ((1-exp(Bt)/B - (1-exp(k2t)/k2)vSTdscwexp(-k2t)) [18.3.4]
with
B=k2-k1/d2 [18.3.5]
4. After finishing application only evaporation is relevant (equation [18.3.1] is simplified):
dmw/dt=-k1mW/ds [18.3.6]
5. The course of VOC in the ambient air does not change (equation [18.3.2] corresponds to equation [18.3.7]):
dmL/dt=k1mw/ds -k2mL [18.3.7]
6. The solution of these differential equations describes the quantities of VOC in the wall (equation [18.3.8]
and the course of VOC in the ambient air [18.3.9]:
mw(t)=mw,AEexp(-k1(t-tAE)/ds) [18.3.8]
mL(t) = ((k1mw,AE/ds) (exp(B(t- tAE))-1)/B + mL, AE) exp(-k2(t-tAE)) [18.3.9]
with
B=k2-k1/ds [18.3.5]
where:
A area of the wall
a coating thickness
B fraction of binder
cW VOC-concentration in the wall
cL VOC-concentration in the ambient air
D density
ds thickness of the layer of the paint application (=a/D)
k1 constant of evaporation
k2 ventilation rate of the indoor air
mL mass of VOC in the indoor air
mL,AE mL at the end of the application
mw mass of VOC in the wall
mW,AE mW at the end of the application
RM VOC-content in the dispersion
t time
V volume of the indoor air
vST spreading velocity
In VOCs, especially these emitted from coating materials, the evaporation temperature
is specified by European regulations: b.p. max. 250 o C (according to DIN ISO
11890-1,-2 or 96/13/EC) 14 or b.p. max. 260 o C (according to VDI Guidelines 4300-6). 15 In