2100
Homework Name________________________________________________________________________________
ChBE #3
Due Friday, Feb. 3
Please follow the homework guidelines outlined in the syllabus. Sign the Honor Code and use this page
as a coversheet for your solutions.
Honor Code:
I commit to uphold the ideals of honor and integrity by refusing to betray the trust bestowed upon me
as a member of the Georgia Tech community.
_______________________________________
Signature
1. Sugar is produced from sugarcane by
M (Sugar)
the process shown. The mill washes,
1000 lb/hr
chops, and uses revolving knives to
shred the cane. Shredded cane is
repeatedly mixed with water and
Crystallizer
L (Water)
crushed between rollers. The collected
F (Cane)
juices contain 1015 percent sucrose
16 % Sugar
25% Water
and are screened to further remove
K 40% Water
59% Pulp
pulp; the remaining fibrous solids,
called bagasse, are burned for fuel.
E
H
Evaporator J (Water)
The clarified juice is concentrated in a
Mill
Screen
13 % Sugar
multiple-effect evaporator to make a
14% Pulp
syrup which is further concentrated
under vacuum and then seeded with
95% Pulp
80% Pulp
crystalline sugar. On cooling, more
G (Solids)
D (Bagasse)
sugar crystallizes from the syrup.
Calculate the flow rates of every
stream and the fraction of the sugar in the cane that is recovered if we want to recover 1000
lb/hr of sugar.
2. Propylene oxide (C3H6O) is produced by the oxidation of propylene (C3H6), according to the
reaction: 2 C3H6 + O2 2 C3H6O
9
There is also an unwanted side-reaction: C3H6 + O2 3CO2 + 3H2O
2
The stream entering the reactor contains 75 mole% propylene and the balance oxygen. The
reactor achieves a (single-pass) propylene conversion of 20%, and 0.9 moles of propylene oxide
exit the reactor for every mole of propylene consumed in the reactor. The exit stream from the
reactor is separated into three different streams. One stream, containing propylene and oxygen,
is recycled to the reactor. The second stream is propylene oxide and is sold, while the third
stream contains carbon dioxide and water and is discarded. Calculate all the unknown flow rates
and compositions (including that of the fresh feed), for a pure propylene oxide production rate
of 1000 kg/hr.
3. The vitamin company you work for produces alanine (C3H7NO2). Alanine is a nonessential amino
acid, meaning it can be manufactured by the human body and does not need to be obtained
directly through the diet. It is important as a source of energy for muscle tissue, the brain, and
the central nervous system. Alanine also helps in the metabolism of sugars and organic acids.
Alanine is produced in a reactor in a continuous process. There are two separate streams
that inlet contain glutamine (C5H10N2O3; 100 mol/min) and pyruvic acid (C3H4O3; 50 mol/min),
respectively. The ratio of the molar flow rate of pyruvic acid in the outlet stream to that in the
inlet is 0.6.
C5H10N2O3 + C3H4O3
C5H7NO4 (-ketoglutamic acid) + C3H7NO2
a. Find the extent of reaction.
b. What is the limiting reagent?
c. Find the fractional conversion of glutamine, fG & pyruvic acid, fPA.
d. Find the outlet molar flow rates of alanine, -ketoglutamic acid, pyruvic
acid, and glutamine.
4. Acetylene is hydrogenated to ethylene in catalytic reaction:
C2H2 + H2
C2H4
In the reactor a single-pass conversion of 10% (based on acetylene) is obtained. The effluent
form the reactor is sent to a separator where all of the ethylene and 1.0 mol% of the hydrogen
are removed. The remaining flow is recycled. The process operates in steady state with a feed
stream that consists of 100 mol C2H2/min and 120 mol H2/min.
a. Draw and label the flow chart for this process.
b. Perform degree-of-freedom analyses based on an atomic species balances for the overall
process and for each unit.
c. Specify the flow rates of acetylene, ethylene, and hydrogen in the process outlet stream.
d. Specify the flow rates of acetylene, ethylene, and hydrogen in the recycle stream.
e. A new catalyst for hydrogenation of acetylene to ethylene becomes available. With this
catalyst the single-pass conversion can be increased to 20%. How much can you increase the
production of ethylene if the feed to the reactor remains constant? How do the feed and
product streams change?
5. Fresh orange juice contains 12 wt% solids and the balance water, and concentrated orange juice
contains 42 wt% solids. Initially a single evaporation process was used for concentration, but
volatile constituents of the juice escaped with the water, leaving the concentrate with a flat
taste. The current process overcomes this problem by bypassing the evaporator with a fraction
of the fresh juice. The juice that enters the evaporator is concentrated to 58 wt% solids, and the
evaporator product stream is mixed with the bypassed fresh juice to achieve the desired final
concentration.
a. Draw and label a flowchart for this process, neglecting vaporization of anything but water.
b. Calculate the amount of product produced per 100 kg fresh juice fed to the process and the
fraction of the feed that bypasses the evaporator.
6. Technical writing assignment: Consider the following flow chart for a process for the reaction A
B:
Solvent
A
Reactor
A
B
Extraction
A
B
Solvent
A
Compare the single-pass conversion and the overall conversion qualitatively (i.e. which one is
higher). Provide an explanation for your answer.