Exercise 1.1 (i)
Known: Fluorocarbons can be produced from the reaction of carbon tetrachloride and
hydrogen fluoride followed by a number of separation steps.
Given: Flow diagram and a brief description of a fluorocarbons production process in
"Chemical Process Industries" , 4th edition, by Shreve and Brink and also in "Shreve's
Chemical Process Industries", 5th edition, by G. T. Austin, pages 353-355 (Fig. 20.4).
Find: Draw a process flow diagram and describe the process.
Description of Process: Two main reactions occur:
CCl4 + HF CCl3F + HCl
CCl3F +HF CCl2F2 + HCl
Excess carbon tetrachloride is reacted in R1 with HF in the presence of antimony
pentoxide catalyst and a small amount of chlorine to maintain catalyst activity. The HF
contains a small amount of water as an impurity. The effluent from the R1 is HCl,
CCl3F, CCl2F2, unreacted CCl4, and small amounts of water and chlorine. The normal
boiling points in oC of these components in the order of decreasing volatility are:
HCl -84.8
Cl2 -33.8
CCl2F2 -29.8
CCl3F 23.7
CCl4 76.7
H2O 100
, Exercise 1.1 (i) (continued)
The reactor effluent is distilled in D1 to remove the CCl4 as bottoms, which is
recycled to R1. The distillate enters absorber A1, where HCl is absorbed by water to
produce a byproduct of aqueous HCl. The gas from A1 contains residual HCl, which is
neutralized, and chlorine, which is absorbed, by aqueous NaOH, in A2. The effluent
liquid from A2 is waste. Moisture is removed from the gas leaving A2 by absorption
with H2SO4 in A3. The exit liquid from A3 is also waste. The gas leaving A3 is distilled
in D2 to obtain CCl2F2 as a distillate, which is then dried in S1 by adsorption with
activated alumina. Bottoms from D2 is distilled in D3 to recover a distillate of CCl3F,
which is dried with activated alumina in S2. Bottoms from D3, containing residual CCl4,
is recycled to reactor R1.
, Exercise 1.2
Subject: Mixing is spontaneous, but separation is not.
Given: Thermodynamic principles.
Find: Explanation for why mixing and separation are different.
Analysis: Mixing is a natural, spontaneous process. It may take time, but concentrations
of components in a single fluid phase will tend to become uniform, with an increase in
entropy. By the second law of thermodynamics, a natural process tends to randomness.
The separation of a mixture does not occur naturally or spontaneously. Energy is
required to separate the different molecular species.
Exercise 1.3
Subject: Separation of a mixture requires a transfer of energy to it or the degradation of
its energy.
Given: The first and second laws of thermodynamics.
Find: Explain why the separation of a mixture requires energy.
Analysis: As an example, consider the isothermal minimum (reversible) work of
separation of an ideal binary gas mixture. Therefore, the change in enthalpy is zero.
However, there is a change in entropy, determined as follows. From a chemical
engineering thermodynamics textbook or Table 2.1, Eq. (4):
Wmin = n(h − T0 s) − n(h − T0 s)
out in
= RT0 nk yi ,k ln yi , k − nj yi , j ln yi , j
out in
It can be shown that regardless of values of y between 0 and 1, that Wmin is always
positive. This minimum work is independent of the process.
, Exercise 1.4
Subject : Use of an ESA or an MSA to make a separations.
Given: Differences between an ESA and an MSA.
Find: State the advantages and disadvantages of ESA and MSA.
Analysis: With an MSA, an additional separator is needed to recover the MSA. Also,
some MSA will be lost, necessitating the need for MSA makeup. If the MSA is
incompletely recovered, a small amount of contamination may result. The use of an
MSA can make possible a separation that can not be carried out with an ESA. An ESA
separation is easier to design.
Exercise 1.5(b)
Subject: Producing ethers from olefins and alcohols.
Given: Process flow diagram and for production of methyl tert-butyl ether (MTBE).
Find: List the separation operations.
Analysis: The reactor effluent contains 1-butene, isobutane, n-butane, methanol, and
MTBE. The separation steps are as follows:
Separation Step Products
Distillation Distillate: all C4s, methanol
Bottoms: 99 wt% MTBE
L/L Extraction with water Extract: methanol, water
Raffinate: C4s
Distillation Distillate: methanol to recycle
Bottoms: water for recycle
Known: Fluorocarbons can be produced from the reaction of carbon tetrachloride and
hydrogen fluoride followed by a number of separation steps.
Given: Flow diagram and a brief description of a fluorocarbons production process in
"Chemical Process Industries" , 4th edition, by Shreve and Brink and also in "Shreve's
Chemical Process Industries", 5th edition, by G. T. Austin, pages 353-355 (Fig. 20.4).
Find: Draw a process flow diagram and describe the process.
Description of Process: Two main reactions occur:
CCl4 + HF CCl3F + HCl
CCl3F +HF CCl2F2 + HCl
Excess carbon tetrachloride is reacted in R1 with HF in the presence of antimony
pentoxide catalyst and a small amount of chlorine to maintain catalyst activity. The HF
contains a small amount of water as an impurity. The effluent from the R1 is HCl,
CCl3F, CCl2F2, unreacted CCl4, and small amounts of water and chlorine. The normal
boiling points in oC of these components in the order of decreasing volatility are:
HCl -84.8
Cl2 -33.8
CCl2F2 -29.8
CCl3F 23.7
CCl4 76.7
H2O 100
, Exercise 1.1 (i) (continued)
The reactor effluent is distilled in D1 to remove the CCl4 as bottoms, which is
recycled to R1. The distillate enters absorber A1, where HCl is absorbed by water to
produce a byproduct of aqueous HCl. The gas from A1 contains residual HCl, which is
neutralized, and chlorine, which is absorbed, by aqueous NaOH, in A2. The effluent
liquid from A2 is waste. Moisture is removed from the gas leaving A2 by absorption
with H2SO4 in A3. The exit liquid from A3 is also waste. The gas leaving A3 is distilled
in D2 to obtain CCl2F2 as a distillate, which is then dried in S1 by adsorption with
activated alumina. Bottoms from D2 is distilled in D3 to recover a distillate of CCl3F,
which is dried with activated alumina in S2. Bottoms from D3, containing residual CCl4,
is recycled to reactor R1.
, Exercise 1.2
Subject: Mixing is spontaneous, but separation is not.
Given: Thermodynamic principles.
Find: Explanation for why mixing and separation are different.
Analysis: Mixing is a natural, spontaneous process. It may take time, but concentrations
of components in a single fluid phase will tend to become uniform, with an increase in
entropy. By the second law of thermodynamics, a natural process tends to randomness.
The separation of a mixture does not occur naturally or spontaneously. Energy is
required to separate the different molecular species.
Exercise 1.3
Subject: Separation of a mixture requires a transfer of energy to it or the degradation of
its energy.
Given: The first and second laws of thermodynamics.
Find: Explain why the separation of a mixture requires energy.
Analysis: As an example, consider the isothermal minimum (reversible) work of
separation of an ideal binary gas mixture. Therefore, the change in enthalpy is zero.
However, there is a change in entropy, determined as follows. From a chemical
engineering thermodynamics textbook or Table 2.1, Eq. (4):
Wmin = n(h − T0 s) − n(h − T0 s)
out in
= RT0 nk yi ,k ln yi , k − nj yi , j ln yi , j
out in
It can be shown that regardless of values of y between 0 and 1, that Wmin is always
positive. This minimum work is independent of the process.
, Exercise 1.4
Subject : Use of an ESA or an MSA to make a separations.
Given: Differences between an ESA and an MSA.
Find: State the advantages and disadvantages of ESA and MSA.
Analysis: With an MSA, an additional separator is needed to recover the MSA. Also,
some MSA will be lost, necessitating the need for MSA makeup. If the MSA is
incompletely recovered, a small amount of contamination may result. The use of an
MSA can make possible a separation that can not be carried out with an ESA. An ESA
separation is easier to design.
Exercise 1.5(b)
Subject: Producing ethers from olefins and alcohols.
Given: Process flow diagram and for production of methyl tert-butyl ether (MTBE).
Find: List the separation operations.
Analysis: The reactor effluent contains 1-butene, isobutane, n-butane, methanol, and
MTBE. The separation steps are as follows:
Separation Step Products
Distillation Distillate: all C4s, methanol
Bottoms: 99 wt% MTBE
L/L Extraction with water Extract: methanol, water
Raffinate: C4s
Distillation Distillate: methanol to recycle
Bottoms: water for recycle
