Assignment # 7

Material and Energy Balances, 313 a
Assignment # 7,
Oct. 21, 03
Due date: Oct. 28, 03
1) A cylinder contains ethylene (C2H4) at 200 psig. The cylinder and gas weight is 222 lb.
The supplier refills the cylinder with ethylene until the pressure reaches 1000 psig, at
which the cylinder and gas weigh 250 lb. The temperature is assumed to be constant at 25
C. Calculate the charge to be made for the ethylene if the ethylene is sold at $0.41/
pound. Calculate the weight of empty cylinder and its volume. a) Use compressibility
factor charts. b) Use Van der Waals eqn.
2) A sample of natural gas taken at 3500 kPa (absolute) and 120 C contains the following
components. What is the density of this sample? Use compressibility factor charts.
CH4 = 100 g,
C2H6 240 g,
C3H8 = 150 g,
N2 = 50 g
Pc =
Pc =
Pc =
Pc =
atm Tc = 191 K
atm Tc = 305 K
atm Tc = 370 K
atm Tc = 126 K
3) You are asked to design a steel tank to store CO2 at 290 K. The tank volume is 10.4
m3 and it is required to store 460 kg of CO2 in it. Using Redlich-Kwong equation
a) calculate the pressure in the tank.
b) Due to safety consideration the pressure should not exceed 1200 kPa, what would
be the mass of CO2 stored at this pressure.
a = 0.37 (K0.5)(m6)(Pa)(g mol)2, b = 2.97 x 10-5 m3 /g mol
4) The vapor pressure of a solid material is given as;
Log Pv = 8.3647 – (2642/T)
The vapor pressure of the same material in liquid phase can be found from the following
Log Pv = 10.3822 – (3392/T)
What is the melting point of this material?
5) A storeman recently lost an eye when an old 1-L bottle of 100% formic acid (HCO2H)
exploded as he lifted it off the shelf in the main store of the chemistry department. He
was not wearing safety glasses. Concentrated formic acid slowly decomposes to carbon
monoxide and water upon prolonged storage, and the gas pressure can be sufficient to
rupture sealed glass container. Assume that the pressure in the vapor space in the bottle
above the formic acid reached 210 kPa and that the vapor space occupied 10 cm3. If the
bottle was at room temperature (25 C), estimate the fraction of the formic acid that
decomposed. Assume the water and carbon monoxide are both in the vapor phase only
(the worst case scenario). Specific gravity of formic acid is 1.22 and its MW = 43.06.
The parameters in Antoine equation for formic acid is A = 19.45, B = 5085, C = 25.56.
Assume ideal gas law.
6) A synthetic gas generated from coal has the following composition: CO2, 7.2%; CO,
24.3%; H2, 14.1%; CH4, 3.5%; N2, 50.9%.
a) Calculate the cubic feet of air necessary for complete combustion per cubic foot of
synthetic gas at the same conditions.
b) If 38% excess air were used for combustion, what volume of flue gas at 750°F and
738 mm Hg would be produced per cubic foot of synthetic gas at standard
7) Polymeric membranes are proposed to be used to reduce the SO2 concentration in the
waste gas of a sulfuric acid plant from 1.5% to 0.01%. Hollows fibers (made of
polymeric membrane) fill the separations unit. The waste gas containing 1.5% SO2 is the
fresh feed in the amount of 1000 m3/hr at 25°C and 1 atm (101.3 kPa). To meet the
product gas specifications, part of the product stream has to be recycled to reduce the
concentration of SO2 entering the separator itself to 1.10% SO2 in G, the process feed.
The process is isothermal at 25°C and isobaric at 1 atm.
(a) Determine the recycle stream flow rate R in m3 /hr.
(b) Determine the waste stream flow rate W in m3 /hr.