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CONFIDENTIAL EH/OCT 2009/CPE521

UNIVERSITI TEKNOLOGI MARA

FINAL EXAMINATION

COURSE

COURSE CODE

EXAMINATION

TIME

PROCESS UNIT OPERA TION

CPE521

OCTOBER 2009

3 HOURS

INSTRUCTIONS TO CANDIDATES

1 . This question paper consists of five (5) questions.

Answer ALL questions in the Answer Booklet. Start each answer on a new page..

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CONFIDENTIAL 2 EH/OCT 2009/CPE521

QUESTION 1

a) Many biological and inorganic or organic substances occur in a mixture of differentcomponents in a solid. In order to separate the desired solute constituent or remove anundesirable solute component from the solid phase, the solid is contacted with a liquidphase. Explain the leaching process for biological substances and inorganic or organicmaterials by citing an example for each of the process.

(4 marks)

b) Leach oil is to be ex tracted from palm kernel in a countercurrent m ulti-batch extractorwhere hexane is used as the extracting solvent. The process is to treat 2880 kg/h ofpalm kernel consisting of 69.44 wt inert solid (B), 28.4 7 wt of oil (A) and also 2.09wt of hexane (C). The fresh solvent mixture contains 1 350 kg/h hexane and 25 kg/h oil.The leached solids are to contain 125 kg/h oil. The concentration of insoluble solid in thesolution mixture (A/) for the slurry underflow is essentially constant at 2.0 kg insoluble

solid/kg soluble retained.

i) Calculate the amo unts (LN, \A,) and compositions (yN, x-,) of the two exit strea ms .(18 marks)

ii) Calculate the number of theoretical stages.(3 marks)

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QUESTION 3

A feed stream containing 51 mol methano l and the rema inder methyl ethyl ketone is fedas a two phase mixture that is 80 vapor to a distillation column at 1 .013 bar. It is desired toseparate this mixture into a stream containing 80 mol me thanol and a stream containing95 mol methyl ethyl ketone. The column has a total condenser and a partial reboiler. Theequilibrium data for methanol at 1.013 bar are given in Table 1.

Table 1 Equilibrium data for methanol at 1.013 bar

xA

00.047

0.1

0.1530.201

0.310

0.420

YA

00.1590.252

0.3280.386

0.486

0.572

xA

0.614

0.713

0.809

0.8570.903

0.948

1

yA

0.6930.7510.817

0.8560.895

0.939

1

i) From the equilibrium data in Table 1 , construct the vapo r-liquid equilibrium curve.(2 marks)

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QUESTION 4

a) Describe and explain the following phenomena which occur in gas absorption:

i) Loading pointii) Flooding point

(4 marks)

b) It is desired to remove 92 of the ammon ia from the entering gas stream from a chem icalreactor contains 25 mol amm onia and the rest inert gases. The total flow is 1 81 .4 kgmol/h to an absorption tower at 303K and 1.013 x 10

5 Pa pressure, where water

containing 0.005 mol fraction ammonia is in the scrubbing liquid. The equilibrium data forAmm onia-Water system are given in Appendix 1 .

i) Construct the equilibrium curve for Am monia-Water system(2 marks)

ii) Determine the minimum flow L min(5 marks)

iii) Using 1.5 times the minimum flow, plot the equilibrium and operating line.(5 marks)

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CONFIDENTIAL APPENDIX 1 EH OCT 2009 CPE521

A.3-22 Equilibrium Data for Ammonia-Water System

Mote FractionNHs inLiquid xA

0

0.0126

0.0167

0.0208

0.0258

0.0309

0 0405

0 0503

0.0737

0.0960

0.137

0.175

Partial Pressure ofNH2

in Vapor pA mm Hg)

20°C 293 K)

0

12

15

18.2

24.931.7

50.0

69.6

114

166

30°C 303 K)

0

11.5

15.3

19.3

24.4

29.6

40.151.0

79.7

110

179

260

Mole Fraction NH3

in Vapor yA\ P — 1 Atm

20°C

0

0.0158

0.0197

0.0239

0.03280.0416

0.0657

0 0915

0.150

0.218

30°C

0

0 0151

0 0201

0.0254

0 0321

0.0390

0.05270 0671

0.105

0.145

0 235

0 342

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