Exp. G notes
Fractional Distillation, 30Aug2004
page 1
Prelab: provide only for 1-propanol, 1-butanol, and methanol Properties 1-propanol
M.W.
M.P.
B . P.
Den.
Sol. (> 10%)
60.10
-127o
970
0.804
H2O, EtOH
Hazard 3 0
1
1-butanol
74.12
-900
117.70
0.810
EtOH
3 0
1
methanol
32.04
-98
64.6
0.791
Water, ethanol
3 1
0
1. do not plug plug mantle mantle directly directly electric electric outlet outlet,, use controlle controllerr
2. Use 40/60 mol percent percent 1-propano 1-propanol/1-b l/1-butan utanol ol (no cyclohexan cyclohexanee or toluene) – less toxic 3. Set up fractional fractional distillat distillation ion (OP27) (OP27) 4. Set heat at highest highest level level to start, insula insulate te distillatio distillation n column with with glass wool wool after boiling begins to save time 5. not too fast fast or slow, slow, distillati distillation on should should take about about 30 min min 6. turn back back down to 60-80% 60-80% when vapor vapor starts starts up column, column, collect collect first sample sample then adjust heat as needed 7. 40/60 40/60 solu solutio tion n is standa standard rd 8. write procedure during distillation not when finished you may split page, left side procedure, right side table (no scratch paper)
Additional material for Postlab Report 1. Rete Retent ntio ion n time timess 2. C and XP,v (mole fraction of propanol vapor), and X B,v (mole fraction of butanol vapor).
Exp. G notes
Fractional Distillation, 30Aug2004
page 2
3. table with area of propanol (A P), area of butanol (A B), AP/AB, R, XP (mole fraction of propanol), and X B (mole fraction of butanol). sample standard 1 AP AB AP/AB R XP XB 4. example of each calculation. 5. plot of boiling point versus volume 6. calculate HETP 7. copy of chromatograms
Exp. G notes
Fractional Distillation, 30Aug2004
page 3
Calculation of Theoretical plates from mole fractions
1. theoretical plate – result of simple distillation 2. each distillation (plate) creates vapor more rich in more volatile component 3. column can have several theoretical plates 4. n is total theoretical plates in apparatus 5. n-1 is total theoretical plates of column 6. determine n from mole fraction (X) of components Use complete equation on OP 27. log n α
=
X P ,v
−
X P ,l
log
X B ,v X B ,l
log α
is the volatility ratio = 1.49
X P = n P =
n P n p
+
X B
n B
moles of propanol,
n B
=
n B n p
+
n B
= moles of butanol
XP,v and XB,v = mole fractions in the vapor at the top of the column, X P,l and X B,l = mole fractions in the pot For this experiment X P,v and XB,v are obtained from first fraction, X P,l and XB,l are obtained from original mixture Calculation of mole fractions from GC data
AP = area of propanol under peak, A B = area of butanol under peak (AP/nP)std = (AP/nP)sample and (AB/nB)std = (AB/nB)sample (AP/nP)std/(AB/nB)std = (AP/nP)sample /(AB/nB)sample (nP/nB)sample = R = (A P/AB)sample*(AB/nB)std/(AP/nP)std = (AP/AB)sample*(AB/AP)std*(nP/nB)std
Exp. G notes
Fractional Distillation, 30Aug2004
page 4
Let C = (AB/AP)std*(nP/nB)std = a calibration factor from standard Then R = (AP/AB)sample*C (mole ratio) = (area ratio of sample)*(calibration factor) R can be used to calculate mole fractions X and X n P X P / X B
n p
=
+
n B n p
X P + X B
R
= X P
n B
+
/ X B
R − RX P
n B
=
R
n B
=
X P
1 − X P
= X P
log
= X P
R
= X P + RX P
R
= X P (1 + R )
X B
n P
= 1, X B = 1 - X P
R (1 − X P )
X P
=
n
=
X P ,v X P ,l
−
log
X B , v X B ,l
log α
R =
=
1 + R 1−
R
1 + R
HETP =
length of column packing n −1
