SEPR3002- UNIT OPERATIONSI Question 1: The vapour coming off the top tray of a d
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SEPR3002- UNIT OPERATIONSI Question 1: The vapour coming off the top tray of a distillation tower has the following molar composition: methanol0.80 ethanol n-propano 0.05 n-butanol 0.14 - 0.01 If the pressure entering the condenser is 1520mmHg and the pressure drop through the condenser is 520mmHg then a) Determine the temperature to which the vapour must be cooled to give a saturated liquid product. (Note: Use only the data points provided. Do not interpolate data for other temperature points.) If instead the vapour is cooled to 80°C, i. Determine the fraction of the stream that is condensed and the c b) of the liquid reflux produced. i. Determine the composition of the vapour in equilibrium with the reflux. Vapour Pressure Data T(ec) Vapour Pressure (mmHg) Methanol 415 629 767 929 1119 1339 1593 1884 2598 Ethanol 50 60 65 70 75 80 85 90 100 n-Propanol 88.9 148.9 190.1 240.6 301.9 376 465 571 843 n-Butanol 33.7 59.2 77.7 99.6 131.3 165.0 206.1 225.9 387.6 220 351.5 438 542 665 812 984 1185 1706Explanation / Answer
Condenser outlet pressure =1520-520 =1000 mg
A) since we can refer data points only given in table and we can not extrapolate any number (assumption made in question) for total condensation we have to find the maximum temperature where vapor pressure of all 4 components is less than condenser outlet pressure of 1000 mmHg
Such point is 70 Degc from table thus vapor must be cooled to 70 degc to condense everything
b) I) at 80 degc all streams except methanol has a vapor pressure of lower than 1000 mmHg thus except methanol everyone stream will condense
Fraction of stream condensed =( 0.14+0.05+0.01)/1 = 0.2
Liquid will have 0.14, 0.05,0.01 moles of ethanol, n-propanol and n-butanol respectively for every mole of column vapor.
Thus ethanol fraction In reflux = 0.14/0.2 = 0.7
n-propanol fraction = 0.05/0.2 =0.25
n-butanol fraction = 0.01/0.2 = 0.05
Ii) since at equilibrium only methanol will be the only stream in vapor phase thus methanol mole frac will be 1 in vapor stream
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