Set5ans.docx

CHE425: Problem set #5 1. (Seader 4.23) An equimolar mixture of ethane, propane, n-butane, and n-pentane is subjected to flash vaporization at 610oR and 205 psia. What are the expected amounts and compositions of the products? Determine the temperature and pressure of a single-stage flash to recover 70% of the ethane in the vapor without losing more than 5% of the nC4 to the vapor.

 

Equilibrium K values for light hydrocarbon systems ============================================================= ln K = A/T2 + B  C ln(P) + D/P + E/P2,  where P is in psia, T is in oR Compound A B C       D           E ============================================================= Ethane 687248.2 7.90694 .866 0 49.02654 Propane 970688.6 7.15059 .76984 6.90224 0 n­Butane 1280557 7.94986 .96455 0 0 n­Pentane 1524891 7.33129 .89143 0 0 ============================================================= Solution

P(psia) = 205 Drum temperature T(R) = 610 Flash temperature, T(R) = 610.00, V/F = 0.4537 Species: Ethane Propane n-Butane n-Pentane Feed z = 0.2500 0.2500 0.2500 0.2500 x=

0.1007

0.1956

0.3169

0.3868

y=

0.4298

0.3155

0.1695

0.0853

Ki =

4.2692

1.6124

0.5348

0.2205

Percentage recover of ethane in vapor = 78.0008 Percentage lost of n-butane in vapor = 30.7537 >> y11s5p1 P(psia) = 14.6 Drum temperature T(R) = 420 Flash temperature, T(R) = 420.00, V/F = 0.2570 Species: Ethane Propane n-Butane n-Pentane Feed z = 0.2500 0.2500 0.2500 0.2500 x=

0.1002

0.2463

0.3198

0.3336

y=

0.6831

0.2607

0.0480

0.0082

Ki =

6.8156

1.0583

0.1502

0.0246

Percentage recover of ethane in vapor = 70.2132 Percentage lost of n-butane in vapor = 4.93896 2) Run program CASCADES. You need to copy the folder CHE425 into the H: drive or your flash drive. Open the folder CHE425 and double click on DOSBox.exe. When the prompt “C:\>” appears, type CASCADES and press “ENTER” to run the program. Copy and report the score and performance number from the program. Type “e” or “exit” and press “ENTER” to exit the DOSBox program. 3) Run program MCCABE. You need to copy the folder CHE425 into the H: drive or your flash drive. Open the folder CHE425 and double click on DOSBox.exe. When the prompt “C:\>” appears, type MCCABE and press “ENTER” to run the program. Copy and report the score and performance number from the program. Type “e” or “exit” and press “ENTER” to exit the DOSBox program. 4) Run program VLE. You need to copy the folder CHE425 into the H: drive or your flash drive. Open the folder CHE425 and double click on DOSBox.exe. When the prompt “C:\>” appears, type VLE and press “ENTER” to run the program. Copy and report the performance number from the program. Type “e” or “exit” and press “ENTER” to exit the DOSBox program. 5) Run program BASIS. You need to copy the folder CHE425 into the H: drive or your flash drive. Open the folder CHE425 and double click on DOSBox.exe. When the prompt “C:\>” appears, type BASIS and press “ENTER” to run the program. Copy and report the performance number from the program. Type “e” or “exit” and press “ENTER” to exit the DOSBox program. 6) A 1000 lb-mole per hour mixture of 5% methane, 20% ethane, 25% propane, 30% nbutane, and 20% n-pentane at 47 psia and 90F is to be separated by a flash drum. Write a Matlab program using the data in Table 2 to determine the fraction of the feed vaporized and the compositions of the vapor and liquid streams leaving the flash drum. Compare the results with those from Provision. Table 2 Equilibrium K values for light hydrocarbon systems ============================================================= (1) ln K = A/T2 + B  C ln(P) + D/P2 (2) ln K = A/T2 + B  C ln(P) + D/P  

Compound A B C D Form ============================================================= Methane 292860 8.2445 .8951 59.8465 (1) Ethane 687248.2 7.90694 .866 49.02654 (1) Propane 970688.6 7.15059 .76984 6.90224 (2) n­Butane 1280557 7.94986 .96455 0 (1)

Ans:

n­Pentane 1524891 7.33129 .89143 0 (1) ======================================================== V/F = 0.97709 Species Feed mole fraction x y Methane 0.05 .00108 .05115 Ethane 0.20 .02001 .20422 Propane 0.25 .08247 .25393 n-Butane 0.3 .29914 .30002 n-Pentane 0.2 .59730 .19068 Solution Flash temperature, T(R) = 550.00, V/F = 0.9771 Species: Methane Ethane Propane n-Butane n-Pentane Feed z = 0.0500 0.2000 0.2500 0.3000 0.2000 x=

0.0011

0.0200

0.0825

0.2992

0.5973

y=

0.0511

0.2042

0.2539

0.3000

0.1907

Ki =

47.3323 10.2064

3.0789

1.0029

0.3192

7) The equilibrium data for the acetone (1)­water (2) system are given at 25oC as follows: x1

0.0194

0.0289

0.0449

0.0556

0.0939

y1

0.5234

0.6212

0.7168

0.7591

0.8351

50.1

61.8

81.3

91.9

126.1

P(mmHg)

At 25oC the vapor pressures are: P1sat = 230.05 mmHg and P2sat = 23.76 mmHg. Use these data to calculate the following for the air-water-acetone system.

Ans:

(a) The vapor mol fraction of acetone in equilibrium with a liquid containing 0.0939 mol fraction acetone at 25oC and a pressure of 2 atm. (b) The vapor mol fraction of water in equilibrium with the liquid described in part (a). a) 0.0693 b) 0.0137

8. 1A distillation column is fed 100 kmol/h of a mixture of 50 mol % benzene and 50 mol % toluene at 101.32 kPa abs pressure. The feed is liquid at the boiling point. The distillate is to contain 90 mol % benzene and the bottoms 10 mol % benzene. The reflux ratio is 4.52:1. Calculate the kmol/h distillate, kmol/h bottoms, and the number of theoretical trays needed using the McCabe-Thiele method. Equilibrium data for benzene-toluene system at 101.32 kPa are given below, where x and y are mole fraction of benzene. x y

0 0

0.130 0.261

0.258 0.456

0.411 0.632

0.581 0.777

0.780 0.900

1.000 1.000

Solution From the graph, we have about 6 theoretical stages or 5 theoretical trays plus a reboiler.

11 Geankoplis, C.J., Transport Processes and Separation Process Principles, 4th edition, Prentice Hall, 2003, p. 753