Material and Energy Balances, 313a
Assignment # 5
Oct. 7, 2003
Due date : Oct. 14, 2003
1) In the following reaction the once-through conversion of component B is 60 %
and in the fresh feed A is 20% in excess. Overall conversion of B to products for
the overall process is 90%. After the products exit from the reactor, a stream of
pure B is separated from the products and forms the recycle stream as shown in
Figure below. Determine the ratio of recycle stream to feed.
2A +5B
3C = 6D
R, Pure B (100%)
Products
Feed
Reactor
2) A three stage separation is shown in figure below. The ratio of P3 to D3 is 3, and P2 =
D2. If the ratio of mass flow rate of A to B in stream P2 is 4, calculate the flow rate and
compositions in stream E. See the figure for additional information. All data are wt% and
the flow rate of D3 is 10% of the Feed entering stage 1. (hint: make an assumption for the
feed and start with overall balance).
D1
A = 0.50
B = 0.23
C = 0.27
F
A = 0.50
B = 0.20
C = 0.30
Stage 1
D3
A=?
B=?
C = 0.00
D2
A = 0.17
B = 0.10
C = 0.73
Stage 2
P1
E
Stage 3
P2
P3
A = 0.70
B = 0.30
C = 0.00
3) Ethylene oxide ((CH2)2O) is produced by the oxidation of ethane (C2H6) in the gas
phase based on the following reaction:
C2H6 + O2
(CH2)2O + H2O
The ratio of air to the ethane in the feed to the reactor (after mixing point) is 10 to 1 and
the conversion of ethane on one pass through the reactor is 18%. The unreacted ethane is
separated from the reactor products and recycled as shown in Fig. below. Calculate the
composition of the exit stream from the reactor (before separation). What is the ratio of
the recycle stream to the feed stream?. What is the composition of Feed before mixing
point. Air is assumed to be 20% oxygen and 80% nitrogen. Separator is capable of
complete separation of water, ethane and ethylene oxide.
N2 + O2
Feed
Ethane
Air
Water
Reactor
Separator
Ethylene
oxide
Recycle 100% ethane
4) Methanol (CH3OH) can be converted to formaldehyde (HCHO) either by oxidation to
from formaldehyde and water or by direct decomposition to formaldehyde and hydrogen.
Suppose that pure oxygen is supplied in the fresh feed to the process and the ratio of
methanol to oxygen is 4 moles to 1, the conversion per pass of methanol in the reactor is
50%, and all of the oxygen reacts in the reactor (none leaves with the hydrogen). After
the reaction a separation process removes first all the formaldehyde and water, and then
all the hydrogen is removed from the recycled methanol. Determine the flow rate of each
species and the total flow rate at each point in the process.
CH3OH + ½ O2
HCHO + H2O
CH3OH
HCHO + H2
Recycle Pure methanol
Hydrogen
Separator
Reactor
HCHO
Water
Separator