Reaction with phase change, conducted in a PFR
P3-21B. The gas phase reaction between chlorine and methane to form carbon tetra chloride
and hydrochloric acid is to be carried out at 75 C and 950 kPa in a PFR. The vapor pressure
of CCl4 at 75 C is 95 kPa. The feed is stoichiometric and the volumetric flow rate is 0.4 lit/s
a. Setup a stoichiometric table for this reaction, before and after phase change.
b. What if the feed were equimolar ?
Answer. CH4 + 4Cl2 ==> CCl4 +4 HCl
Species
Inlet
X≤Xc
X ≥ Xc
CH4
FAin
FAin (1-x)
FAin (1-x)
Cl2
4FAin
4FAin (1-x)
4FAin (1-x)
CCl4 (G)
0
FAin x
ysat × FTotal(g)
CCl4 (L)
0
0
FAin x- ysat × FTotal(g)
CCl4 (Total)
0
FAin x
FAin x
HCl
0
4 FAin x
4 FAin x
Total (g)
5 FAin
5 FAin
FTotal(g)
Total (L)
0
0
FAin x- ysat × FTotal(g)
Total
5 FAin
5 FAin
5 FAin
When partial pressure of CCl4 becomes 95 kPa, condensation will occur. Total pressure is 950
kPa. i.e. Ysat = 0.1.
FAin x x
  0.1 , i.e. when the conversion is 50%, condensation will occur.
5FAin 5
FTotal(g) = 5 Fain – Fain × x + 0.1 FTotal(g)
i.e. FTotal(g) =
FAin  5  x 
0.9
(b) If we send equimolar feed, then chlorine is the limiting reactant. We should write the
conversion based on chlorine.
Species
Inlet
X≤Xc
X ≥ Xc
CH4
FAin
FAin (1-0.25x)
FAin (1-0.25x)
Cl2
FAin
FAin (1-x)
FAin (1-x)
CCl4 (G)
0
0.25 FAin x
ysat × FTotal(g)
CCl4 (L)
0
0
0.25 FAin x- ysat × FTotal(g)
CCl4 (Total)
0
0.25 FAin x
0.25 FAin x
HCl
0
FAin x
FAin x
Total (g)
2 FAin
2 FAin
FTotal(g)
Total (L)
0
0
FAin x- ysat × FTotal(g)
Total
2 FAin
2 FAin
2 FAin
When partial pressure of CCl4 becomes 95 kPa, condensation will occur. Total pressure is 950
kPa. i.e. Ysat = 0.1.
0.25  FAin x x
  0.1 , i.e. when the conversion is 80%, condensation will occur.
2 FAin
8
FTotal(g) = 2 Fain – 0.25 Fain × x + 0.1 FTotal(g)
i.e. FTotal(g) =
FAin  2  0.25x 
0.9