\"24.1 Liquified natural gas, LNG, is to be shipped from the Alaskan Kenai Penin
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"24.1 Liquified natural gas, LNG, is to be shipped from the Alaskan Kenai Peninsula by an ocean carrier to processing plant on Yaquina Bay, Oregon. The molar composition of the com- mercial LNG is methane, CH4 93.5 mol % ethane, C2H6 4.6% Propane, C5H8 1.2% Carbon dioxide, CO2 0.7%" (Benitez 45) Benitez, Jamie, James Welty. Transport Phenomena II. Wiley Custom Select, 12/2012. . "a. the weight fraction of ethane; b. the average molecular weight of the LNG mixture; c. the density of the gas mixture when heated to 207 K and at 1.4*10^5 Pa; d. the partial pressure of methane when the total pressure is 1.4*10^5 Pa; e. the mass fraction of carbon dioxide in parts per million by weight.Explanation / Answer
Let there are 100 moles total
Moles of methane = 93.5 , mass of methane = Moles X molar mass = 93.5 X 16 = 1496 grams
Moles of ethane = 4.6 . mass of ethane = Moles X molar mass = 4. 6 X 30 = 138 grams
moles of propane = 1.2 , mass of propane = mole X molar mass = 1.2 X 44 = 52.8g
moles of CO2 = 0.7 moles, mass of CO2 = mole X molar mass = 0.7 X 44 = 30.8g
a) total weight = 1496 + 13 8+ 52. 8 + 30. 8 = 1717.6 grams
wt % of ethane = 138 X 100 / 1717.6 = 8.03 %
b) Avg molar mass = sum of mole fraction X molar mass
avg molar mass = 0.935 X 16 + 0.046 X 30 + 0.012 X 44 + 0.007 X 44 = 14.96 + 1.38 + 0.528 + 0.308 = 17.18 g / mole
c) Density = Mass / volume
Volume = nRT / P = mass X RT / P Xmolar mass
Density = Mass X P Xmolar mass/ mass X RT = Molar mass X P / RT
R = 8.314 L?kPa K?1?mol?1
P = 140 kPa
T = 207 K
Density = 17.18 X 140 / 8.314 X 207 = 1.4 L
d) partial pressure of methan = mole fraction X total pressure = 0.935 X 1.4 X 10^5 = 1.309 X 105 Pa
e) mass fraction of CO2 = 30.8g / 1717.6 = 0.0179 w/w = 0.0179 X 10^6 ppm by weight = 17900 ppm
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