In a plant for the synthesis of sulfuric acid a feed stream of 50 m 3 /min that
ID: 939186 • Letter: I
Question
In a plant for the synthesis of sulfuric acid a feed stream of 50 m3/min that has a molar composition of ySO2=0.5 and yO2=0.5 is fed into a reactor at a pressure of 3 atmospheres and a temperature of 450 Kelvin. The outlet from the reactor is then mixed with a water stream to form sulfuric acid. Draw a diagram with the two unit operations, write out the relevant reactions in each unit and mark all streams entering and leaving them.
1. Convert from volumetric flow rate to molar flow rates using the ideal gas law
(PV=n8.314T) where V, n are the volumetric and molar flow rates.
2. The reaction to form SO3 in the reactor goes to full extent. Calculate the outlet composition of the reactor.
3. The outlet stream from the reactor is fed into a contact vessel where it mixes with another incoming stream of water. The water and SO3 reacts to form sulfuric acid. How much water must be fed into the reactor to prepare a final product of 4 molar sulfuric acid?
Explanation / Answer
1) since volume is proportional to the number of moles, volumetric flow rate is proportional to that of molar flow rate. Hence, the molar flow rate of both SO2 and O2 will be equal.
so, let the molar flow rate of SO2 and O2 be x moles/min
3 * 50*10^3 = n*(1/12)*450
or n=4000 moles/min
so the molar flow rate of O2 and that of SO2 is 4000 moles/min
2) 2SO2 + O2 -> 2SO3
since the number of moles of O2 and SO2 are equal in the reactor,
the output molar flow rate fraction of SO3 will be 2/3 and that of O2 will be 1/3.
since the molar flow rate of SO3 will be 4000 and that of O2 will be 2000 moles/min.
3)SO3 + H2O -> H2SO4
since the molarity is 4,
molarity = incoming moles per minute/ volume of water per minute
4=4000/x(L/min)
or x=1000 liters/min
so the volume flow rate of water is 1000 L/min.
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