In the final stages of manufacture of bulk drugs, it is necessary to clarify the reaction mixture to remove extraneous and other suspended matter which may be present. This is done by means of filtration of the reaction mixture. This document gives the procedure for clarification of reaction mixtures by filtration through horizontal plate filters.
a) It is advisable to use freshly boiled and cooled purified water .
b) The suitability of the filter paper and filter cloth used for filtration must be ascertained before use.
c) It must be ensured that flexible tubings used in the filter asembly have been cleaned. Where they have been stored away after cleaning, the open ends should have been covered with polythene sheets. If this has not been done or there is evidence of dust on the tubings, they should be cleaned and dried before use.
3.0 SETNNG OF THE FILTERATION MACHINE
a) All the removable parts of the filter assembly should be cleaned with hot water and steam. Hot water should be passed through flexible tubings followed by steam. The water should then be drained out.
b) The filter plates should then be assembled with the cloth filters or papers in place. The battery of filters should then be positioned in the filter chamber and the lid should be fitted.
c) The required lengths of flexible tubing should then be attached to both ends of the filter assembly.
d) The required quantity of filter aid or clarifying agent should be suspended in a suitable quantity of purified water. After it is uniformly mixed it should be pumped into the filter and circulated through the filter unit until a uniform bed is formed on the filter and the water coming out of the outlet end of the assembly is clear .
e) The bed should be washed with fresh quantities of purified water until the pH of the water from the outlet is the same as that of the feed water (range 5.5 to 6.5)
f) The pump should be stopped and the water in the filter assembly should be drained out.
4.0 FILTERATION PROCESS
4.1 The inlet tubing should be dipped into the product to be filtered. The outlet tubing should be placed in a clean container and the pump should be started.
4.2 The air vent should be closed after air is removed from the assembly and the liquid starts flowing thorough the outlet tube.
4.3 The first few liters of liquid should be discarded as it normally consists of the product diluted with water trapped in the filter assembly.
4.4 The clarity of the first few litres should be checked and if found satisfactory, the filtered liquid should be returned to the main product tank.
4.5 Filtration should continue and the clear product should be collected in a clean dry tank. During filtration the clarity of the liquid should be checked at suitable intervals.
4.6 If the clarity is not satisfactory at any stage, the collection of filtered liquid should be stopped and the liquid in the assembly should be returned to the main tank.
4.7 The filter should be re-set as described
4.8 After filtration is over, the inlet valve should be closed and the pump stopped immediately. Pressure should be applied through the air vent and the filtrate should be collected and added to the main filtered bulk.
4.9 When air starts coming out, the outlet value should be closed and the trapped liquid in the assembly should be collected through the scavenger outlet.
4.10 Liquid coming through the scavenger outlet should be checked for clarity before adding it to the main filtered bulk.
4.1 The electrical connections should be removed and the tubings and filter assembly should be taken away for washing.