# Yale University Mass Balance with Reaction Problem Solving Questions

Description

Mass Balances with Reaction Problem 1 – Steady-State problem with a reaction.A gasoline powered car travels at a speed of 60 miles per hour. The car typically gets 35 miles to the gallon. Gasolineisa mixture of many chemicals, but for simplicity assume it has the formula of octane, C8H18. Use a density of 790 g/liter. For purposes of this problem, assume that only carbon dioxide and water (no carbon monoxide) is produced in the reaction.What is the required air flow rate per liter of gasoline, for air fed in stoichiometric proportion? Give your answer in molar units (mol air/liter gasoline), in mass units (grams air/liter gasoline) and in standard volume units (standard liters air/liter gasoline)Estimate the rate at which gasoline is fed in grams per minute and moles per minute, using the information given earlier in the problemDetermine the flowrate (mol/min) and composition (mol fraction) of the exhaust gases if gasoline is fed at the rate you found above with 4 % excess air and 98% conversion of the gasoline.Note: you may find it easier to find the air needed per mol of gasoline and then use the number of moles of gasoline in a liter to scale your air requirement.Problem 2 – Saterbak Textbook problem 3-26 (3-21 in first edition of the book). This probleminvolvesmodeling a process that converts carbon dioxide (CO2) and water (H2O) to propane (C3H8). Make the following modifications to the problem in the book:use a carbon dioxide feed flowrate of 136.4 standard liters per minute (convert to moles per minute)use a carbon dioxide conversion of 90% (not 100%)assume that the gas exiting the reactor has 3 mol % water vapor, but water in the reactor remains in the liquid state, thus there may also be a liquid stream leavingset the water feed rate to provide 12% excess water (same as in the problem)Do the following: draw and fully label a flow diagram for the systemwritea balanced reaction (stoichiometric) equation, assuming oxygen (O2)isproducedalong with propane (the oxygen atoms need to come out in some form)Determine the feed water rate in grams per minuteUse appropriate mass balances to find the flow of the exit stream in moles/minute and standard liters per minute, and the composition of this stream in mole %.Determine the rate of propane production in kg per day if the process runs 24 hr/dayDetermine the water feed rate such that no liquid water leaves the reactor Comment on the safety of this process

Mass Balances with Reaction
Problem 1 – Steady-State problem with a reaction.
A gasoline powered car travels at a speed of 60 miles per hour. The car typically gets 35 miles to the gallon.
Gasoline is a mixture of many chemicals, but for simplicity assume it has the formula of octane, C8H18. Use a
density of 790 g/liter. For purposes of this problem, assume that only carbon dioxide and water (no carbon
monoxide) is produced in the reaction.
a) What is the required air flow rate per liter of gasoline, for air fed in stoichiometric proportion? Give
your answer in molar units (mol air/liter gasoline), in mass units (grams air/liter gasoline) and in
standard volume units (standard liters air/liter gasoline)
Note: you may find it easier to find the air needed per mol of gasoline and then use the
number of moles of gasoline in a liter to scale your air requirement.
b) Estimate the rate at which gasoline is fed in grams per minute and moles per minute, using the
information given earlier in the problem
c) Determine the flowrate (mol/min) and composition (mol fraction) of the exhaust gases if gasoline is
fed at the rate you found above with 4 % excess air and 98% conversion of the gasoline.
Problem 2 – Saterbak Textbook problem 3-26 (3-21 in first edition of the book). This problem involves
modeling a process that converts carbon dioxide (CO2) and water (H2O) to propane (C3H8). Make the following
modifications to the problem in the book:
• use a carbon dioxide feed flowrate of 136.4 standard liters per minute (convert to moles per minute)
• set the water feed rate to provide 12% excess water (same as in the problem)
• use a carbon dioxide conversion of 90% (not 100%)
• assume that the gas exiting the reactor has 3 mol % water vapor, but water in the reactor remains in the
liquid state, thus there may also be a liquid stream leaving
Do the following:
a) draw and fully label a flow diagram for the system
b) write a balanced reaction (stoichiometric) equation, assuming oxygen (O2) is produced along with
propane (the oxygen atoms need to come out in some form)
c) Determine the feed water rate in grams per minute
d) Use appropriate mass balances to find the flow of the exit stream in moles/minute and standard liters per
minute, and the composition of this stream in mole %.
e) Determine the rate of propane production in kg per day if the process runs 24 hr/day
f) Determine the water feed rate such that no liquid water leaves the reactor
Comment on the safety of this process