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BACKGROUND
Filtration may be defined as a process of separation of solids from a fluid by passing the same through a porous medium that retains the solids, but allows the fluid to pass through. The following terms are used with respect to filtration. The suspension to be filtered is known as slurry. The porous medium used to retain solids is described as filter medium. The solid retained on filter is known as filter cake, while the clear liquid that passes through is known as filtrate. When the solids are present in a very low concentration i.e. 1% w/v, the process of its separation from liquid is called clarification.
Surface filtration type is employed, i.e. pores and holes of the medium prevent the passage of solids. Filter paper is used as a filter medium. The mechanisms involved are straining and impingement. The effect of concentration of suspension, effect of viscosity of the vehicle, and effect of filter aid are the material related factors that are studied in this experiment.1
The rate of filtration depends on concentration of solids. As the concentration of solids in the suspension increases, the thickness of the filter cake increases. As a result, the rate of filtration decreases.
The rate of filtration depends on the viscosity of the slurry. Viscosity of the suspension may be due to presence of solids and or viscosity of the vehicle. The vehicles containing different concentrations glycerine-water mixture are used. Viscosity increases with increase in the concentration of glycerine in the mixture. With increase in the viscosity of the suspension, the rate of filtration decreases.2
Aim: To study the effect of materials related factors on the rate of filtration, using calcium carbonate suspension.
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REQUIREMENTS
Apparatus: Measuring cylinder
Mortar and pestle
Beakers
Buckner flask
Buckner funnel
Balance
Filter paper
Chemicals: Calcium carbonate
Glycerine
Kieselguhr
Talc
Bentonite
Charcoal
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PROCEDURE
Preparation of calcium carbonate suspension
5gm of calcium carbonate was weighed and transferred to a mortar. 50 ml of water was added and triturated to get a smooth paste. The contents were transferred into a measuring cylinder (100 ml). The mortar and pestle were washed with 10 ml of water (2 or 3 times if necessary).The washings were transferred into the measuring cylinder. The volume was made up to the mark (100ml) by adding water. The suspension was shaken thoroughly. The same procedure was repeated to prepare 10% and 15% suspensions using 10.00 and 15.00 g of calcium carbonate, respectively.
Method of studying the effect of concentration
The apparatus was assembled as shown in the figure 1. The filter paper of appropriate size (10 cm diameter) was placed into the Buckner funnel. 100 ml of 5% calcium carbonate was poured over the Buckner funnel.Time required to collect 50 ml of the filtrate was recorded and reported in table 1 The experiment (steps 2 to 4) was repeated for the same concentration of calcium carbonate suspension for two more trials. The experiment was repeated for other concentrations also. The reading was recorded in the given table. A graph was plotted by taking concentration in of calcium carbonate on x- axis and rate of filtration on y- axis.
Method of studying the effect of viscosity
The filter paper of appropriate size was placed into the Buckner funnel.100 ml of calcium carbonate aqueous solution containing 5% glycerine was poured over the Buckner funnel. Time required to collect 50 ml of the filtrate was recorded. The experiment (steps 1 to 3) was repeated for the same suspension two more times. The experiment was repeated for the suspension containing increased concentration of glycerin. The reading was recorded. A graph was plotted by taking viscosity of the vehicle of calcium carbonate suspension on x-axis and rate of filtration on y-axis.
Method for studying the effect of filter aid
The filter paper of appropriate size was placed into the buckner funnel. 100 ml of 15% calcium carbonate suspension was poured over the buckner funnel. Time required to collect 50 ml of the filtrate was recorded. The experiment (steps 1-4 ) was repeated for the same concentration of the calcium carbonate suspension for two more trials. The experiment was repeated (steps 1-5) for the suspension containing 1% keiselguhr, 1% bentonite and 1% charcoal. The readings were recorded in the table and processed. A bar graph was plotted by taking 15% calcium carbonate suspension with filter aid on x-axis and rate of filtration on y-axis.
Table 1(a) Study the effect of concentration of slurry
| Concentration of slurry | Trial | Volume of filtrate collected(ml) | Time of collection of filtrate(min) | Time of collection of filtrate (sec) | Rate of filtration ml/sec |
Rate of filtration m3/sec | |
| (3)/(5) | (6) *10-6 | ||||||
| (1) | (2) | (3) | (4) | (5) | (6) | (7) | |
| 5% | 1 | ||||||
| 2 | |||||||
| 3 | |||||||
| Mean | |||||||
Table 1(b):
| Concentration of slurry | Trial | Volume of filtrate collected(ml) | Time of collection of filtrate(min) | Time of collection of filtrate (sec) | Rate of filtration ml/sec |
Rate of filtration m3/sec | |
| (3)/(5) | (6) *10-6 | ||||||
| (1) | (2) | (3) | (4) | (5) | (6) | (7) | |
| 10% | 1 | ||||||
| 2 | |||||||
| 3 | |||||||
| Mean | |||||||
Table 1(c)
| Concentration of slurry | Trial | Volume of filtrate collected(ml) | Time of collection of filtrate(min) | Time of collection of filtrate (sec) | Rate of filtration ml/sec |
Rate of filtration m3/sec | |
| (3)/(5) | (6) *10-6 | ||||||
| (1) | (2) | (3) | (4) | (5) | (6) | (7) | |
| 15% | 1 | ||||||
| 2 | |||||||
| 3 | |||||||
| Mean | |||||||
Table 2 Study the effect of viscosity of the vehicle
| Composition and viscosity of the vehicle | Trial | Volume of filtrate collected(ml) | Time of collection of filtrate(min) | Time of collection of filtrate (sec) | Rate of filtration ml/sec |
Rate of filtration m3/sec | |
| (3)/(5) | (6) *10-6 | ||||||
| (1) | (2) | (3) | (4) | (5) | (6) | (7) | |
| 5% glycerine and 1.010 centi poise | 1 | ||||||
| 2 | |||||||
| 3 | |||||||
| Mean | |||||||
Table 3: Study of effect of filter aid.
| Name of the filter aid | Trial | Volume of filtrate collected(ml) | Time of collection of filtrate(min) | Time of collection of filtrate (sec) | Rate of filtration ml/sec |
Rate of filtration m3/sec | |
| (3)/(5) | (6) *10-6 | ||||||
| (1) | (2) | (3) | (4) | (5) | (6) | (7) | |
| Bentonite | 1 | ||||||
| 2 | |||||||
| 3 | |||||||
| Mean | |||||||
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CONCLUSION
As the concentration of calcium carbonate suspension increases, the rate of filtration increases/ decreases. A graph was plotted by taking concentration of calcium carbonate on x-axis and rate of filtration on y-axis. As the viscosity of the vehicle used in the suspension increases, the rate of filtration increases/ decreases. A graph was plotted by taking viscosity of the vehicle on x-axis and rate of filtration on y-axis. Presence of filter aid increases the rate of filtration. Different filter aids increases the rate of filtration to different magnitudes. A bar graph was plotted by taking filter aids on x-axis and rate of filtration on y-axis.
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REFERENCES
- Subrahmanyam CVS, Setty JT, Sarasija S. Laboratory manual of pharmaceutical engineering ( Unit operations) , Delhi Vallabh Publications.
- Pharmaceutical Engineering by K.Sanbamurty (New Age International, New Delhi)
