che571_che584_che594

CONFIDENTIAL EH/OCT 2009/CHE571/584/594

UNIVERSITI TEKNOLOGI MARA FINAL EXAMINATION

COURSE

COURSE CODE

EXAMINATION

TIME

CHEMICAL REACTION ENGINEERING

CHE571/584/594

OCTOBER 2009

3 HOURS

INSTRUCTIONS TO CANDIDATES

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

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

3. Do not bring any material into the examination room unless permission is given by the invigilator.

4. Please check to make sure that this examination pack consists of:

i) the Question Paper ii) an Answer Booklet - provided by the Faculty iii) a one - page Appendix iv) a graph paper - provided by Faculty

DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SO

This examination paper consists of 6 printed pages © Hak Cipta Universiti Teknologi MARA CONFIDENTIAL

CONFIDENTIAL 2 EH/OCT 2009/CHE571/584/594

QUESTION 1

The elementary liquid-phase irreversible reaction of C2H4 + H20 -» C2H5OH is to be carried out in a flow reactor. Two reactors available are an 800 dm3 PFR that can only be operated at 300 K and a 200 dm3 CSTR that can be operated at 350 K. The two feeds stream to the reactor mix to form a single feed stream that is equal molar in C2H4 and H20, with a total volumetric flowrate of 10 dm3/min. Determine the best reactor for this reaction and justify your answer.

Additional information: At 300 K, k = 0.07 dm3/mol.min

E = 85000 J/mol.K CAO = CBO = 2 mol/dm3

VAO - VBO = 0.5v0 = 5 dm3/min (20 marks)

QUESTION 2

a) In each of the following reactions determine the specific reaction rate constant for each of the other species in the reaction. Assume that k in each case has a value of 25 with the approximate combination of units of mol, dm3 and s.

i. For the reaction of

~N2+-H2 -+NH2

The rate law is - rNi = kNCNCHi

ii. For the solid catalyzed reaction,

4NH3 + 502 -> ANO + 6H20

The rate law is -r'NHi = kNHC2NHC0i

(7 marks)

b) In the homogeneous gas-phase reaction,

CH4 + -02 -> HCOOH + H20

State the relationship between /"c/-/4 and r0^ .

(2 marks)

© Hak Cipta Universiti Teknologi MARA CONFIDENTIAL


c) State the rate expression for each species in the following reaction

i. For the reaction of

ii. For the reaction of

"1 . D "2 ->s- •>C

A-

A-

+D

^U (6 marks)

QUESTION 3

Typical curve of a reaction carried out isothermally is shown in Figure 1, while the curve shown in Figure 2 is typical of an exothermic reaction carried out adiabatically.

a) Assuming that you have a CSTR and a PBR containing equal weights of catalyst, suggest the arrangement of the reactor for an isothermal reaction and adiabatic reaction.

(4 marks)

b) Calculate the catalyst weight necessary to achieve 80% conversion for single CSTR and PBR. Comment your answer.

(8 marks)

c) Recommend the best reactor arrangement for different -rA versus X curves. (3 marks)

1000

o E w

E

0.2 0.4 0.6 0.I

Conversion, x

Figure 1 Processed data

1.0



60

50

>> 4 0

-•—• CD O O)

XL 30

<

20

10

0.2 0.4 0.6 Conversion, x

0.8 1.0

Figure 2 Exothermic reaction

QUESTION 4

CSTR frequently is less costly and easier to maintain and one or more CSTRs can frequently be preferred over a PFR. However, when selectivity and yield of a given product need to be maximized, the design issues become more complicated.

Engineers, Aqso and Madina are assigned to design the reactor for production of ethylene from ethane with acetylene as a byproduct. If the reaction can be considered as first order series reaction, for 90% conversion determine the followings:

Holding time Reactor volume Concentration of ethylene

iv. Selectivity v. Yield

Based on the determined criteria above, recommend the best reactor that should be designed for this system and justify your answer.

Given, v = 4 liter/min

CA 0 = 2 moles/liter

k-i =0.5min"1

k-, =0.1min -1

(20 marks)



QUESTION 5

a) The second order irreversible liquid phase isomerisation reaction of normal butane to isobutene,

nCAHw -> iC4Hl0

is carried out adiabatically in a CSTR. Butane and an inert I (which contains the catalyst) are fed to the reactor in equal molar amounts at a temperature of 57°C and a total volumetric flow rate of 163 kg.mol/hr. The concentration of butane entering the reactor is 9.5 kg.mol/m3. Determine the reactor volume to achieve 80% conversion.

Additional information: AH°nn =-6900 J Imol

k = 31.1/hr at S7°C

E = 65.7kJImol

CPA =\4U/mol.K

CPB = \4Ulmol.K

Cn =\6U/mol.K

x - &,C»[T-TQ] EB -AH^+AC^T-T,]

(10 marks)

b) The following reversible elementary liquid phase reaction of vinyl allyl ether to n-pentaldehyde-ene-4 occurs in a PFR:

CH2 = CHCH2OCH = CH2 ^ = > CH2 = CHCH2CH2CHO

The entering flow rate is 10 dm3/s with an entering concentration of 2M of pure vinyl allyl ether and the feed temperature is 310 K. The specific reaction rate and equilibrium constant are shown in Figure 3 and Figure 4 respectively. Determine the reactor volume necessary to achieve 90% of the adiabatic equilibrium conversion in one operated adiabatically.

Additional information: CP =CP = 50 cal fmol.K

'A r f l

^H'RXN = -10000 cal I molA

-rA =k r

C B A Kc

(20 marks)



zu -

1o -

•1C ID

14 "

19 -

*•" m -{/> lU

O "

D ~

A -

9 .

0 -

300 320 340 360 380 400 420 440 460 480 500

Temperature (K)

Figure 3 Specific rate reaction

uu

90

on -OU

7D

Rn -DU

ou

40 -

"3ft OU

on

1 n -I u

0-300 320 340 360 380 400 420 440 460 480 500

Temperature (K)

Figure 4 Equilibrium constant

END OF QUESTION PAPER


CONFIDENTIAL APPENDIX 1 EH/OCT 2009/CHE571/584/594

Simpson's one third rule:

fV(x)cfx = ̂ ( x 0 ) + 4f(x1) + /r(x2)] Jx0 j

Simpson's three-eighths rule:

j * V (x)dx =h[f (x0) + 3f (x,) + 3f (x2) + f (x3)] JX0 5

Five-point quadrate formula:

f4f(x)dx=l[f0+4fl+2f2+4f3+f4] Jx0 i


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