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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.
A simple straining process does not provide complete description of how particles are removed from a suspension. The particles are exposed
to a number of forces including gravity or electric fields. The rate of filtration will be greatest at the beginning of the process, since resistance is minimum and will be proportional to the filtering area. Once the filter cake is formed, its surface acts as a filter medium and solids continuously deposit adding to the thickness of the cake. Hence resistance to filtration is observed. Among several factors, pressure drop is one of the main factors to enhance the rate of filtration. This can be achieved by following methods.
Gravity
Applying pressure
Reducing the pressure
The rate of filtration under atmospheric condition and under vacuum is studied using calcium carbonate suspension. The effect of thickness and surface area of the filter medium on rate of filtration are studied.
Aim:
To study the effect of process related factors on the rate of filtration, using calcium carbonate suspension.
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REQUIREMENTS
Apparatus: Measuring cylinder
Mortar and pestle
Beakers
Buckner funnel
Buckner flask
Balance
Filter paper
Vacuum pump
Chemicals:Calcium carbonate
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PROCEDURE
Preparation of calcium carbonate suspension
5 g 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 (100 ml) by adding water. The suspension was shaken thoroughly.
Method to study the effect of surface area of filter medium
The filter paper of appropriate size was placed into small Buckner funnel. Hundred ml of 5 % calcium carbonate suspension was poured over the Buckner funnel. Time required to collect 50 ml of filtrate was recorded. The experiment steps 1-3 was repeated for the same concentration of calcium carbonate suspension for two more trials. The experiment was repeated for big and bigger size Buckner funnels. Reading was recorded in table and the rate of filtration was calculated. A graph was plotted by taking surface area of filter medium on x-axis and rate of filtration on y-axis.
Method to study the Effect of Thickness of Filter Medium
The filter paper of known thickness (one filter paper) was placed into the small Buckner funnel. Hundred ml of 5% calcium carbonate suspension was poured over the Buckner funnel. Time required to collect 50 ml of the filtrate was recorded in table. The experiment steps 1-3 was repeated for the same concentration of calcium carbonate suspension for two more trials. The experiment was repeated for two more filter media of same material of different thickness. The readings were recorded in the table and the rate of filtration was calculated. A graph was plotted by taking thickness of filter medium on x-axis and rate of filtration on y- axis.
Method to study the effect of pressure
–Under atmospheric conditions
The filter paper of known thickness(one filter paper) was placed into the small Buckner funnel.Hundred ml of 5 % calcium carbonate suspension was poured over the Buckner funnel.Time required to collect 50 ml of the filtrate was recorded in table.
The experiment steps 1-3 was repeated for the same concentration of calcium carbonate suspension for two more trials.The readings were recorded in the table and the rate of filtration was calculated.
-Under negative pressure
The apparatus was assembled as shown as above fig. Filtrate receiver was marked with glass marker for 50 ml level. The filter paper of appropriate size was placed into Buckner funnel. Hundred ml of 5 % calcium carbonate suspension was poured over the Buckner funnel. Time required to collect 50 ml of the filtrate was recorded in table. The filtration unit was disconnected to throw the contents. The experiment steps 1-3 was repeated for the same concentration of calcium carbonate suspension for two more trials.The readings were recorded in the table and the rate of filtration was calculated.All the result of 2 experiments were compared. A bar graph was plotted by taking atmospheric pressure and vacuum pressure on x-axis and rate of filtration on y-axis.
Observations and calculations
Table 1: the effect of surface area of filter medium on the rate of filtration.
| Surface area of filter medium,m2 | 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) |
| 1 | ||||||
| 2 | ||||||
| 3 | ||||||
| Mean |
Table 2: Effect of Thickness of Filter Medium on the rate of filtration.
| Thickness of the filter medium | 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) |
| 1 | ||||||
| 2 | ||||||
| 3 | ||||||
| Mean |
Table 3: The effect of pressure on the rate of filtration.
| Type of pressure | 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) |
| 1 | ||||||
| 2 | ||||||
| 3 | ||||||
| Mean |
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CONCLUSION
- With increase in surface area, rate of filtration increases/decreases.
- A graph was plotted by taking surface area of filter medium on x-axis and rate of filtration on y-axis.
- With the increase in thickness, rate of filtration increases/ decreases
- A graph was plotted by taking thickness of filter medium on x-axis and rate of filtration on y- axis.
- With the application of vacuum, rate of filtration increases/decreases.
-
A bar graph was plotted by taking atmospheric pressures and vacuum 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.
- Sanbamurty K. Pharmaceutical Engineering (New Age International, New Delhi)
- Carter SJ. Cooper and Gunn’s Tutorial Pharmacy Edited by (CBS Publishers, Delhi)
- Pharmaceutical Dosage forms by Aulton. (Churchill Livingstone, Edinburg)
