CBE 40 Homework 5
Due September 30, 2020
15 points total
Please review the course homework guidelines
Reading for next week: D&R 2nd Ed. Section 3.4, D&R 1 s t Ed. Sections 3.14-3.15
Note: Only first three problems are graded.
Problem 1 (5 Points)
1. Following a nuclear plant accident, groundwater is contaminated with a compound A. It
can be removed from the water phase by extraction in an oily solvent; the A is transferred
from the water to the oil as the two liquids flow through the extractor, as shown below.
Whereas absorption is transfer from a gas phase to a liquid phase, extraction is transfer
from one liquid phase to another liquid phase. To maintain two distinct liquid phases, the
liquids must be immiscible.
oil
1
water with A (1%)
2
oil with A
oil phase
water phase
3
water with A (0.1%)
4
Stream 1 is pure oil and stream 3 contains A. The extractor is long enough so that by the time
the two phases exit (streams 3 and 4) they have reached equilibrium: no more A transfers into
the oil. The equilibrium relationship for this particular system is given by the following
empirical equation:
xA,w = K xA,o
Where xA,w and xA,o refer to the mass fractions of A in the water and oil phases, respectively,
and K is an experimentally determined equilibrium constant. For this system K = 5.00.
The flow rate of stream 2 is 100. kg/min, xA,2 = 0.010, and the extractor removes 90.% of the
A from stream 2. (Hint: xA,4 = K x3,A)
a) Calculate the flow rate of A in the oil phase leaving the extractor (stream 3).
b) Calculate the flow rate of oil entering the extractor (stream 1).
c) Now assume the extractor removes 99% of the A from stream 2. All other parameters
remain the same and streams 3 and 4 are again in equilibrium. Calculate the flow rate
of oil entering the extractor (stream 1) needed to achieve this.
Give your answers in 2 significant figures.
CBE 40 Homework 5
Due September 30, 2020
15 points total
Problem 2 (5 Points):
2. D & R 2nd Ed 3.43
(E to X by two schemes)
CBE 40 Homework 5
Due September 30, 2020
15 points total
Problem 3 (5 Points):
3. A high temperature blast furnace converts iron oxide (from magnetite ore) to iron as part of
the steel production process:
Fe2O3 + 3C → 2Fe + 3CO
After mixing 600. g/s of carbon (“coke”) with 2400. g/s of pure iron oxide (Fe2O3), the process
produces 1200. g/s of pure iron. Report answers with 2 significant figures. Molecular weights
are given below.
a. Determine the percentage of excess carbon: _______% excess carbon
b. Determine the percentage conversion of Fe2O3 to Fe: _____% conversion
c. Calculate the flow rates of each substance in the product stream, in g/s.
Molecular weights (g/mole)
Fe2O3
160.
C
12.
Fe
55.8
CO
28
* The following three optional problems are for your practice and won’t be graded. Solutions
will be posted for you to look at on your own.
CBE 40 Homework 5
Due September 30, 2020
15 points total
Optional Problem 4:
4. D & R 2nd Ed 3.17 (batches of elixir)
CBE 40 Homework 5
Due September 30, 2020
15 points total
Optional Problem 5:
5. A chemical process converts reactant A into product B in accordance with the process flow
diagram below. How much of the reactant in stream 3 must be separated in order to have a
flow rate of 95.0 mol/min for the product in stream 4
A 100.
mol/min
F1
F2
A
A->B
(80.0%
conversion)
F5
A
Optional Problem 6:
6. D & R 2nd Ed 3.53 (A, B -> P, Q)
F3
A
B
Separator
X% A
removed
B 95.0
mol/min
A 5 .00
mol/min
F4