work. Attach your OWN EXCEL Sheets/MATLAB Codes if used. a Bubble-Point Temperat

Question

work. Attach your OWN EXCEL Sheets/MATLAB Codes if used. a Bubble-Point Temperature Calculation: (30 points) Feed (z) comprising of ethane (6 kmol/h), propane (19 kmol/h), n-butane (36 kmol/h), n pentane (26 kmol/h), and n-hexane (7 kmol/h) enters a distillation column as saturated liquid at 1.5 MPa. Calculate the bubble-point temperature using K-values given below 9 Tin K, P in kPa 90,389 -185,209 212,114 285,026 299,595 360,138 395,23 9.9730 -0.8951 2,846.4 .5411 -0.8468 2,042.6 9.6178 -0.886 2,331.8 4141 -0.8787 2,267.6 8.6372 -0.7698 0 9.5073 -0.922 0 9.8124-0.9646 0 9.3796 -0.9316 0 9.0527 -0.8914 0 8.6021 -0.8463 0 8.0651 -0.7954 0 methane ethylene propylene propane isobutane 47.602 isopentane n-pentane n-hexane 470,645 549,044 621,544 b Isothermal Flash: (70 points) 100 kmol/h of a feed (z) composed of 20 mol% n-butane, 43 mol% n-pentane, and 37 mol% n-hexane is flashed. If 70% (by moles) of the n-hexane is in the liquid at 400 K. what is the pressure (P) and the liquid (xi) and vapor (yi) compositions? Obtain K-values from the above table Hint: Calculate bubble point and dew point pressures first to get an estimate for an initial input value for equilibrium pressure in the flash calculations.)

Explanation / Answer

a) Molar fraction of component i, xi = molar flowrate of component i/Total Molar flowrate

Let nbutane be the reference molecule

Assume T= Boiling Point of nbutane = 272 K

Keeping T = 272 K and P = 1.5 MPa = 1500 KPa, Obtained K values using given formula are

Because, yi = ki*xi

Therefore, yi = ki*xi = 15.71

New K value for our reference Molecular n butane = K(nbutane)/yi = 16.1/15.71 = 1.02

Now for nbutane, keeping K = 1.02 in the formula, obtained T = 11.94 K,

Using T=11.94, again calculation K values of all the molecules

Because, yi = ki*xi

Therefore, yi = ki*xi = 1.35

New K value for our reference Molecular n butane = K(nbutane)/yi = 1.02/1.35 = .75

Now for nbutane, keeping K = 1.02 in the formula, obtained T = 11.33 K,

Using T=11.33, again calculation K values of all the molecules

Because, yi = ki*xi

Therefore, yi = ki*xi = 1.07

Because in Vapor phase, yi = 1,

Our obtained value in last iteration ~=1,

Therefore, Bubble point of given mixture = 11.33 K

2) Let's 1st find Bubble Point Pressure of Mixture,

For that, let's assume whole feed is in liquid phase,

Therefore, Feed fraction, zi = liquid fraction, xi

Now, yi =Ki*xi = 1

Putting T=400 K the formula of K and using above equation,

Obtained Bubble Point Pressure, Pb = 26308 Kpa

Let's find dew Point Pressure of Mixture,

For that, let's assume whole feed is in vapor phase,

Therefore, Feed fraction, zi = vapor fraction, yi

Now, xi =yi/Ki = 1

Putting T=400 K the formula of K and using above equation,

Obtained Dew Point Pressure, Pd = 26228 Kpa

Now, flash Pressure will lie between these two values

By Rachford rice flash equation, i zi(Ki 1)/(1 + V/ F (Ki 1) )= 0

Assuming P = Pb = 26228 KPa

Using Rachford rice equation, V/f = .24

F = 100 kmol/hr

Therefore,

Vapor flowrate = 24 Kmol/hr

Liquid flowrate = F-V = 76 Kmol/hr

Given, 70% of nhexane feed is in liquid,

Therefore, moleflowrate of nHexane in Liquid = 0.7*37 = 25.9 Kmol/hr

Therefore, moleflowrate of nHexane in Vapor = 37-25.9 = 11.1 Kmol/hr

Therefore, molefraction of nHexane in Liquid, . = 25.9/76 = .34

Therefore, molefraction of nHexane in Vapor, ynHexane = 11.1/24= .46

For component i,

yi = ki*xi

zi*F = L*xi+V*Ki*xi

Using these equations and above derived value, Liquid and Vapor phase composition are as below

Component, i Molar flowrate mole fraction Ethane 6 .06 Propane 19 .2 nbutane 36 .38 npentane 26 .27 nhexane 7 .07 Total flowrate 94

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