Page 66 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Distillation 55

Mols dimethyl ether overhead = 76 - 0.335 = 75.665 Bubble Point of Initial Charge
xiM01. Q 50°F Assumed q 50" a105 a
Composition of total overhead collected: Component Fract I$ y=k, 105",I(i I$/% Avg
__.__._
~ ~~ ~
C2H6 0.10 4.5 0.45 7.2 3.81 3.28 3.54
75'665
(100)
Dimethyl ether = - 99.6% CSHS 0.25 1.18 0.295 2.2 1.0 1.0 1.0
=
76.0 n-C4Hlo 0.35 0.33 0.115 0.75 0.28 0.341 0.310
i-C&lo 0.48 Q&g 1.0 0.407 0.454 0.430
1.00 1.004
Methanol = 100.0 - 99.6 = 0.4%
O.K. _-
Differential DistiUation4imple Batch, Without Trays, Note: K values at 80 psia from Natural Gasoline Supply
Multicomponent Mivture Man's Assoc. Data Book [48].
Propane is reference material.
For muhicomponent systems, the relation of the system
can be expressed using the relative volatility: ai500= Ki =-= 4'5 3.81
Kpropane 1.18
qlojo Ki = -= 7.2 3.28
=
(8 - 102) Kpropane 2-2

where Bi = mols of component, i, after a given time of
distillation
Bi, = mols of component, i, at start of distillation 3.54 10
=
Bb = mols of component, b, used as reference for B(ethane) = (10) - = - 0.39 mols in bottoms
(i!) 25.6
volatility after a given time of distillation
_.
-.
-- __ - - - .- .- -. ._ - -.
.-
Bbo = mols of component, b, used as reference for Vapor
volatility, at start of distillation. Fii Press.
Component Bi Bottoms at 105", Pi pi = Pix1
~ ~ ~~
Knowing the amount of components present at the C2H6 0.39 0.00686 840 psia 5.73
beginning, the quantity remaining after the distillation C3HS 10.00 0.176 200 35.2
can be calculated. n-C4H10 26.30 0.463 57 26.4
0.355
20.20
2'7.6
i'C4H10 --_ -- - 78 -
56.89 1.000 94.9
Example 8-17: Multicomponent Batch Distillation (Too high,
assume
lower
A mixture of hydrocarbons at 80 psia is to be differen- tem-
tially distilled until the mols of propane is reduced to 10 perature
mols per 100 mols of bottom feed material. A kettle with and re-
bottom coil is to be used, and no trays. calculate)
-.
_-
- -_.-_-_ _.-- - - - --
Material in kettle at start of distillation: xi = 0.39/56.89 = 0.00686
Vapor pressure from N.K. Rector chart in Reference 48.
Comoonent Mol Fraction
C2H6 0.10 Second Tr);
.-
.-
C3HS 0.25 --- - .- . - - __
Initial q Assume a95 a
N-C~HI 0 0.35 Component xj 50" 95",& &/I$, Avg.
-_-_
-.
i-C4H10 - -
C2H6 0.10 3.81 6.7 3.35 3.58
1.00 C3H8 0.25 1.0 2.0 1.0 1.0
n-C4H10 0.35 0.28 0.6'7 0.335 0.307
Basis: 100 mols of bottoms feed i-CdHin 0.30 0.407 0.92 0.46 0.432