MSc DT275 lab manual PDF

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MSc Pharmaceutical and Chemical Process Technology

LABORATORY MANUAL

September 2008

CONTENTS 1.

Filtration at constant pressure.

2.

Aspen Plus tutorials (version 11): Separation Processes (I and II)

3.

Drying of solids – (i) tray drying (ii) spray drying (iii) fluid bed drying

4.

Heat Transfer – double tube and shell and tube heat exchangers.

5.

Reactor experiments: Batch reactor

6.

Distillation: Vapour – liquid equilibrium curve and application.

7.

Fluid flow: Flowmeter demonstration Energy losses in pipes

8. 9. 10. 11. 12.

Continuous column extraction GMP 1/2 PID control Membrane separation - pervaporation Pharmaceutical Plant visit.

Introduction Students are required to complete practicals from the list provided.

Ensure that you read through each experiment prior to commencement and discuss with the laboratory supervisor.

Laboratory reports must be written following the completion of each experiment and handed into the laboratory supervisor for assessment.

Laboratory reports should be written using the following format:



Title



Introduction (statement of objectives, theory, background)



Experimental methods (a concise account of all experimental methods used including equipment, materials)



Results (tabulation of results, figures, calculations etc)



Discussion (of results)



Conclusions



References

Reports should be contained in plastic envelopes and folders. All reports must be written using Microsoft Word/Excel.

Filtration at Constant Pressure Safety information Refer to CRA and MSDS Hazard identification and risk assessment Chemical Hazard class

Calcium carbonate

Xi

Hazard identification and risks Xi

Risk phrases

R 37/38, 41

Precautions  Avoid inhalation of dust Waste  Calcium carbonate must be dried and reused. Spillage  Clear up and dispose of as non-hazardous waste 1. Introduction The integrated form of the filtration equation for constant pressure filtration (assuming an incompressible filter cake) gives: V2 + AVL = A2 Pt 2 v r v

i.e.

V = 2A2 Pt - 2AL r v V v

(V is linear with t/v)

where V=

volume of filtrate (m3)

A=

filter area (m2)

r=

specific resistance of filter cake

=

filtrate viscosity (Nsm-2)

v=

Volume of cake Volume of filtrate

L=

filter cake equivalent thickness to cloth or paper (m)

P =

pressure drop (Nm-2)

t=

filtration time (s)

The terms L and rv are termed the filtration constants and may be determined by v obtaining values for V and t, plotting V versus t and V obtaining slope and intercept. Having obtained these, the values can be used to scale-up a filtration. If the viscosity of the filtrate is known and a value for v obtained, then values for r and L may be obtained also. The viscosity at any temperature may be obtained by using the attached nomograph. Another parameter of interest is the fractional porosity of the cake, e, and this may be obtained from measuring cake volume and calculating particle volume from specific gravity. In summary, the objective of the experiment is to operate a laboratory scale filtration at constant pressure, estimate the filtration constants, calculate r, L and use the filtration constants to carry out a preliminary design for a filter press.

2. Experimental Procedure 2.1 Equipment As assembled. 2.2 Method Make up a suspension of 5%w/w CaCO3 (or CaSO4. 2H2O as available) in water and place in reservoir. Start the stirrer motor. Start the vacuum pump with stopcock A closed and using stopcock B obtain a steady pressure reading of between 50 and 60 cm Hg (i.e. between 67,763 and 78,947 Nm-2) to give a steady filtrate flowrate. Use safety screen provided. Maintain this pressure at a steady reading. Fill the funnel about half-way, at the same time opening A fully. Adjust B to obtain a steady pressure reading as before. Maintain the level in the funnel as constant as possible and take filtrate volume readings at suitable time intervals i.e. try and include at least five readings for each run. Do not exceed the capacity of the filtrate vessel. Record final filtrate volume. Repeat the experiment twice more, for each run changing the P to give sensible filtrate flowrates. Record P values Dry filter cakes in drying oven to constant weight. Record weight, diameter and thickness of each filter cake. Retain filter cakes for further use. 3.

Calculations

3.1

Plot V against t/V for the separate P runs and calculate rv, L, r and L. Compare values. v

Use the rv, and L average values obtained to carry out design calculation in 3.2 v 3.2

Filter Design

A filter press consisting of 12 frames is to be operated on a 15 minute cycle using the slurry above. It is required that the volume of filtrate processed on each cycle should be 80.0 litres. If the pressure drop across the filter is maintained at 4.0 X 105 Nm-2, what is the required area of each frame? (Note: A filter frame contains two filtration areas).

4. Report The following should be included: 4.1 Comments on control of process, appearance of filter cake etc. 4.2

Tabulation of r v and L results. v

4.3

r and L values.

4.4 4.5

e values for each filtration. The calculated filter-frame area in scale-up.

Note: (i) (ii)

All calculations and units of measurement are to be clearly shown. S.I. units are to be used throughout.

Modelling of Chemical Processes – Separation Processes (I) Introduction This practical is concerned with the use of Aspen Plus as a modeling tool for the operation of continuous fractional distillation. Objectives 1. To obtain operating results for a continuous fractional distillation system. 2. To perform a sensitivity analysis for a continuous fractional distillation system. 3. To develop a process flowsheet. 4. To meet a process design specification.

Method Complete the tutorials in ‘Building and running a process model version 11’ as follows: Ch.1 Aspen plus basics (20 min.) Ch.2 Building and running a process simulation model (50 min.) Ch. 3 Performing a sensitivity analysis (20 min.) Ch.4 Meeting process design specifications (20 min.) Ch.5 Creating a process flow diagram (20 min.) When the tutorials have been completed build and run a process simulation model using the following process parameters/system specification: Feed: 10 kmol h-1 benzene/toluene Feed composition: 60 mol %toluene/40 mol % benzene (xf = 0.4) Reflux ratio (R): 4 Feed temperature: 95oC Theoretical plates: 7 (N) Distillate flow: 3.75 kmol h-1 Feed stage: 4 Pressure: 1 atm. Obtain operating results for the above system. Choose ‘Template’/’Metric units’ for your model. Use the RadFrac unit operation model and the UNIFAC activity coefficient model or IDEAL model. Obtain operating results for a system with 12 stages instead of 7 (N = 12). Perform a sensitivity analysis on the above system (variation of xd, distillate composition, with R) Develop the process flowsheet as described in the tutorial. Meet a process design specification (say xd = 0.90). Save results on disc. Print results and include with your report. Reference Building and Running a Process Model Version 11.

Modeling of Industrial Chemical Processes – Separation Processes (II) Introduction This practical is concerned with the use of Aspen Plus as a modeling tool for the operation of liquid-liquid extraction. Objectives:

To obtain operating results for a liquid-liquid extraction system.

1

3 L2

48 kmol s-1 water

4

2

7.69 kmol s-1 benzene 2.31 kmol s-1 acetone

Method Complete the tutorials in ‘Building and running a process model version 11’ as follows: Ch.1 Aspen plus basics (20 min.) Ch.2 Building and running a process simulation model (50 min.) Ch.3 Performing a sensitivity analysis (20 min.) Ch.4 Meeting process design specifications (20 min.) Ch.5 Creating a process flow diagram (20 min.) When the tutorials have been completed build and run a process simulation model using the following process parameters/system specification: Continuous counter-current liquid – liquid extraction Use Type-Column and Model-EXTRACT. Use UNIQUAC activity coefficient model. System specifications. solvent: 48 kmol s-1 water. feed: 7.69kmol s-1 benzene/2.31kmol s-1 acetone. T: 298 K P: 101325 Pa. (1 atm) N (stages): 3 Vary N (say N = 2, 4, 5, 6) and examine the effect on the raffinate composition. Print results. Reference Building and Running a Process Model Version 11.

Drying of solids – tray drying Safety information Hazard identification and risk assessment Precautions  sand is used in this experiment  oven and contents are hot! Waste  Sand must be dried and reused. Spillage  Sweep up and dispose of as non-hazardous waste Oven  Avoid direct contact with any hot item, use tong to manipulate hot apparatus or use special gloves. Objectives Experimental determination of the rate of drying curve for solid, at constant drying conditions (constant air flow, temperature and humidity).The experiment is carried out in a batch dryer and heat is supplied by direct contact with heated air at atmospheric pressure. The drying oven is operated at three temperatures – 100, 110 and 120 deg. cent. Important Definitions 

Humidity of an air-water vapor mixture (H): H = Mass of Water (kg)  Mass of Dry Air (kg)



Moisture content of a solid (X): X = Mass of Water (kg)  Mass of Dry Solid (kg)



Equilibrium Moisture Content of a Solid (Xe): Is the final moisture content of a solid after being brought into contact with a stream of air (having humidity “H” and temperature “T”) long enough, for equilibrium to be reached. Is expressed in the same way as X.



Free Moisture Content of a solid: Is the moisture above the equilibrium moisture content. Is the only moisture that can be removed by drying under the given drying conditions.



Critical Moisture Content of a solid (Xc): Is the solid moisture content attained, during the drying process, when the entire surface of the solid is no longer wetted.

Experimental Determination of the Rate of Drying Curve The rate of drying “R” is defined as the mass of liquid evaporated by unit time and by unit of exposed surface area for drying. It can be mathematically expressed by S dX R =    A

(1)

dt

Where R = drying rate (kg H2O/sm2) S = weight of dry solid (kg) A = exposed surface area for drying (m2) X = solid moisture content (kg H2O/kg dry solid) t = time (s) To experimentally determine the rate of drying for a given material (case study sand), a sample is placed in a dryer and under constant drying conditions, the loss in weight of moisture during the drying process is determined at constant time intervals. With the data obtained from the batch experiment, a plot of the solid moisture content “X” versus time can be made (Figure 1). From this plot, the rate of drying curve can be obtained by measuring the slopes of the tangents drawn to the curve, which give the values of dX/dt at given values of t. The drying rate “R” is calculated for each point using equation (1). The drying rate curve is obtained by plotting R versus the solid moisture content “X” as in figure 2. The plot of the rate of drying curve can presents several shapes but generally the two major points – constant and falling rate period – are present. At time zero the initial moisture content of the solid is shown at point A or A’ depending on the solid temperature. At point B the surface temperature as attained its equilibrium value and the constant rate period starts. This period continues as long as the water is supplied to the surface as fast as it evaporates. At point C, the solid critical moisture content “Xc” is attained. At this point there is no insufficient water on the surface to maintain a continuous film of water and the first falling rate period starts. The wetted area of the solid continually decreases until the surface is totally dry at point D. At this point begins the second falling rate period, that continues until the equilibrium moisture content of the solid is reached, at point E.

Figure1: solid moisture content “X” versus time for constant drying conditions

Figure2: drying rate “R“ versus solid moisture content “X” for constant drying conditions

Date : ………/………./ Weight of dry solid …………………………………..

kg

Weight of added water………………………………..

kg

Initial moisture content………………………………..

%

Total sample weight (tray + solid + water)…………….

kg

Air temperature…………………………………………

o

Air velocity……………………………………………..

m/s

Surface area……………………………………………..

m2

Time (s)

Time

(s)

.

X

C

Weight of solid (kg)

(kg H2O/kg dry solid)

.

dX/dt

.

R

(kg/s m2)

Calculations 

Plot experimental X versus time t



Plot experimental R versus experimental X

Practical Formulas W  Ws X =  Ws

I

Ws dX R =    A dt

II

where W = weight of total solid Ws = weight of dry solid

(kg) (kg)

References Geankoplis, Christie, J (1983). Transport Processes and Unit Operations, 2nd ed. Massachusetts, Allyn and Bacon. Inc., pg 508-552

Spray drying The aims of this experiment are:  To investigate the performance of the spray drier  To investigate parameters that control the spray drying process  To examine and study spray dried product properties e.g. particle size and shape See operating manual for experimental details.

Drying of solids – fluid bed drying Introduction: When a stream of gas is passed upwards through a bed of material at a certain velocity the bed will first expand, then become suspended and agitated by the gas stream to form a fluidised bed. This has the appearance of boiling liquid due to the formation of many small bubbles-the so-called ‘bubbling fluidisation’. At higher gas velocity, larger bubbles and plugs of material are formed resulting in a more violent type of fluidisation called slugging or spouting. The optimum operating gas velocity for bubbling fluidisation lies above the minimum fluidising velocity but below the velocity of entrainment of the material. If a bed of wet material is fluidised by a heated air stream, as in the laboratory batch dryer, the conditions are ideal for drying. The very efficient contact between gas and solid particles results in heat transfer rate causing evaporation (mass transfer) of moisture which is carried away with the exit air. The same principles apply for industrial fluid bed dryers-both batch and continuous types, therefore the laboratory fluid bed dryer can be used to assess the feasibility of different materials for large scale fluidised drying. Operating method: 1- Determine the optimum bed depth The optimum bed depth is that which can be fluidised at the required temperature by relative high air velocity. The optimum bed depth will vary appreciably with the material-an initial bed depth of about 75mm is typical. 1- Remove any excess water from the solid sample by decanting and / or using a filter pump. 2- Place the sample of material in the tub to an appropriate bed depth. Weigh the tub alone then with the material. 3- Locating the sealing ring into the groove. 4- Switch on the mains supply and select the drying temperature required (select three temperatures). 5- Note the wet and dry bulb temperatures of the inlet air to the fan and outlet air from the fluidised bed. 6- Weigh the tub with material at 2 minutes intervals for about 15 minutes (or as long as it takes to attain constant weight) recording the wet and dry temperature before removing the tub for weighing. Then weigh at 5 minutes intervals until constant weigh is achieved indicating that the equilibrium moisture content has been reached. Record the drying time and moisture content. From these results plot drying curves of moisture content vs time and drying rate vs moisture content.

Calculation of Heat Transfer Coefficient Heat transfer coefficient could be calculated as follows; Heat lost by entering gas = heat transferred to solids to vaporise the liquid Therefore (dw/dt) = -h A (Ta – Ts)log mean .1/L This equation can be integrated to give

h = (Wo – Wc).L /t.A (Ta – Ts)log mean where dw/ dt = constant drying rate, kg.s -1 L = latent heat of vaporisation, J.kg -1 H = heat transfer coefficient, W.m -2. oC-1 A = surface area, m2 o Ta = dry bulb air temperature, C o Ts = wet bulb air temperature, C Wo = initial moisture content, kg water/kg dry solid Wc = critical moisture content at end of constant rate period, kg water/kg dry solid t = constant rate drying time, s

Heat transfer/Heat exchangers This aim of this practical is to examine the performance of a double tube heat exchanger and a shell and tube heat exchanger. Hot and cold water flow rates, hot water temperature and mode of operation are varied and comparisons are made between the two types of heat exchanger. (see operating manual for details of procedures, observations and calculations)

Reactor experiments Safety information Refer to CRA and MSDS sheets Hazard identification and risk assessment Chemical Hazard class

Sodium hydroxide solution Ethyl acetate

C F, Xi

Sodium acetate Ethanol

none F

Hazard identification and risks Causes severe burns

Risk phrases

Highly flammable. Irritating to eyes. none Highly flammable

R11, 36, 66, 67

R35

none R11

Precautions  Avoid contact with sodium hydroxide solution. Wash with water.  Avoid contact with ethyl acetate. Wash with water.  Use sodium hydroxide solution and ethyl acetate solution in sealed containers.  No ignition sources. Waste  Reactor contents may be diluted with water and washed down the laboratory sink at the end of the experiment. Spill  No ignition sources  Wear appropriate PPE  For ethyl acetate solution use spill kit  For sodium hydroxide solution dilute with water and clean up with suitable absorbent material Further information: see MSDS’s and chemical risk assessment

Isothermal batch reactor Safety Information Refer to CRA and MSDS sheets Hazard identification and risk assessment Chemical

Hazard Class

Hazard Identification & Risks

Risk Phrases

Sodium hydroxide solution Ethyl acetate

C

Causes severe burns

R35

F, Xi

R11, 36, 66, 67

Sodium acetate Ethanol

None F

Highly flammable. Irritating to eyes None Highly flammable

none R11

Precautions    

Avoid contact with sodium hydroxide solution. Wash with water. Avoid contact with ethyl acetate. Wash with water. Use sodium hydroxide solution and ethyl acetate solution in sealed containers. No ignition sources.