Msc (Chemical and Pharmaceutical Process Technology)

DUBLIN INSTITUTE OF TECHNOLOGY

KEVIN STREET, DUBLIN 8

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MSc (Chemical and Pharmaceutical Process Technology)

Stage 1

MODULAR EXAMINATIONS 2008/2009

Semester 2

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Separation Processes II

CPPT9005

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Mr G. Duffy

Dr. H. Ali

Dr. D. McCormack

Dr. D. Coveney

DATE:

TIME:

Answer ONE question from Section A and

ONE question from Section B.

Graph paper is available on request.

SECTION A

1. Answer ALL parts

(a) Describe the rotary (drum type) filter, and discuss its advantages and disadvantages.

[10 marks]

(b) A rotary drum filter of area 3m2 operates with an internal pressure of 30kN/m2 and with 30% of its surface submerged in the slurry. Calculate the rate of production of production of filtrate and the thickness of cake when it rotates ½ revolutions per minute. Given that:

Voidage of cake = 0.4

Specific resistance of cake = 2x1012m-2

Density of solids = 2x103kg/m3

Density of filtrate = 1x103kg/m3

Viscosity of filtrate = 1x10-3Ns/m2

Slurry concentration = 20% by weight solids

Cake equivalent thickness = 1x10-3m

Atmospheric pressure = 101.3kN/m2

dV = [{A2 ( − ∆P )} / {rµν (V + LA/ν)}] dt

[30 marks]

(c) (i) Adsorption processes have a wide range of applications in industrial processes. Define adsorption phenomena and then explain what makes molecules adsorb on activated carbon.

[5 marks]

(ii) What factors govern and control the rate of adsorption?

[5 marks]

(iii) Write brief notes on pressure – swing adsorption.

[10 marks]

2. Answer ALL parts

(a) A rotary disc filter rotates at 1/4 revolution per minute with 25% of its surface submerged and an internal pressure of 35.5 kN m-2 absolute is maintained during filtration process of an industrial slurry. Some of the slurry was tested on a plate and frame press filter in the laboratory at a constant pressure differential of 75 kN m-2and gave the following results.

Time (min) 10.0 20.0 30.0 40.0

Filter volume (m3) per surface area (m2) 4.17 6.25 7.50 9.09 (V/A)

Determine the area required for the disc filter if 69.4 kg/min of solid are to be

filtered from a slurry containing 8% by weight of solid.

Atmospheric pressure = 101.3 kN m-2

Density of liquid = 1000 kg m-3

Useful relationships:

t / V = (rµv /A2 ∆P). V and

(t-t1) / (V-V1) = (rµv / A2 ∆P)V1 + (rµv /2A2 ∆P). (V-V1)

t / V = (rµL /A ∆P) + (rµv /2A2 ∆P).V

[20 marks]

(b) Write notes on the design, applications, advantages and disadvantages of the filter press.

[20 marks]

Symbols definition

U = velocity
A = area
V = volume
e = voidage
r = cake specific resistance
v = volume of cake deposited by unit
volume of filtrate
t = time / DP = applied pressure difference
ℓ = cake thickness
S = specific surface of particle
dV/dt = volume per time
m = viscosity
L = equivalent thickness
c = concentration

SECTION B

3. Answer ALL parts

(a) Outline an experimental procedure to measure the metastable zone width of a solution.

Discuss the effect the rate of cooling and heating will have on the width of the metastable zone.

[20 marks]

(b) Why are unseeded crystallisations often avoided in industry? Discuss some of the problems caused by unseeded crystallisations to illustrate your answer.

Figure Q3 below shows the progress of a typical unseeded crystallisation.

(i) Explain the diagram depicting the progress of the crystallisation from points A to D. Identify where supersaturation, nucleation and crystal growth occur.

(ii) Where would you recommend seeding should occur and why?

Figure Q3

[20 marks]

4. Answer ALL parts

(a) Compare and contrast the optimal and linear rate methods of cooling during a crystallisation. For each option, draw a sketch of temperature and supersaturation over time for the duration of the crystallisation.

What is the justification for using optimal cooling?

How is optimal cooling implemented and what property of the solution must be measured?

[20 marks]

(b) The following is an extract taken from a crystallisation procedure in a pharmaceutical company:

Ensure that the organic phase containing the product in solution is charged to the crystalliser and distilled down to the crystallisation volume. Agitate the mixture at all times.

Step1. Reduce the temperature of the solution to 80°C.

Step 2. While maintaining the temperature at 80ºC, add 25% of the total charge of anti solvent.

Step 3. Seed the crystalliser with 5% of the product from a previous batch.

Step 4. Hold the solution in this state for 30 minutes.

Step 5. Add the remaining anti solvent at a constant rate for 180 minutes at a constant temperature of 80°C.

Step 6. Hold the slurry in this state for 30 minutes.

Step 7. Next cool the slurry to 20°C by reducing the

temperature at a constant rate for 60 minutes.

Filter the product.

Identify where the following events happen in the above procedure and give a brief explanation as to why:

· Nucleation

· Supersaturation

· Crystal growth

Suggest ways of modifying the above procedure in order to minimise the creation of fines.

[20 marks]