NEWSLETTER
ISSUE
Apr to Jun, 2020 Volume 12
Importance of Sterilization and Various cycles in Pharmaceutical manufacturing – Part 2
In line with the discussion on the importance of sterilization cycles in the previous issue of TECH SPARK, we will discuss the following cycles in the current issue.
- Liquid Cycle
- Air-Over Pressure Cycle
- Steam-Air mixture Cycle
LIQUID CYCLE
Sterilization of liquid is a regular requirement in day to day operation. The liquid in an open or vented container cannot be sterilized using a normal Gravity or Vacuum cycle. Use of these cycles causes substantial spillage and loss of liquid due to rigorous fluid boiling during the cycle operation. The boiling phenomenon occurs due to the quick release of pressure during the exhaust phase. If the pressure is released at once in the exhaust phase, the temperature of the liquid will be above the boiling point, which may result in rigorous boiling.
A liquid cycle is used to overcome this excessive boiling, thereby reducing the spillage and loss of liquid.This cycle is a modified version of gravity cycle. In aliquid cycle, the pressure is released with a slower rate during the exhaust phase compared to gravity cycle. The slower exhaust rate allows the temperature of the liquid to remain below boiling point, thus eliminating excessive boiling.
Purge Phase: Like Liquid cycle, during the Purge phase, the steam enters the sterilizer chamber and displaces the air within the chamber through a chamber drain port. The temperature and pressure of the chamber gradually increase and attains the sterilization temperature.
Sterilization Phase: On attaining sterilization temperature, the sterilizer holds (maintains) the temperature and pressure of the chamber till predefined time. Usually, it is 121 degrees C and time for 20 minutes (considering the overkill approach) for steam sterilization.
Exhaust Phase: Once the sterilization hold time is over, the cooled air is purged in the chamber during the exhaust of steam. The cooled air purging increases the chamber pressure and at the same time,reduces the load temperature. Thus, the sterilized material is ready for unloading from the chamber without evaporation losses.
Steam-Air Mixture Cycle
Sterilization methodchanges not only with the type of load but also with thekind of 
holding or storage. i.e. liquid stored in an open or partially open container can be sterilized with Liquid or Air-over pressure cycle (as discussed above). In contrast, the liquid in asealed container requires a differentcycle. During sterilization of a sealed load, the pressure inside the container increases with a rise in the liquid temperature. This increased pressure may deform or damage the container permanently and lead to spillage and loss of the liquid.It is advisable to use Steam-Air Mixture cycle toavoid such losses. Here, the additional air pressure is maintained during sterilization and exhaust phase.
Purge Phase: Cycle starts with the purge phase, wherein the steam and sterile air are purged into the chamber. The steam and air within the chamber are mixed homogenously with the help of blowers installed in the chamber. While the steam & air are purged, the condensate is simultaneously removed through the chamber drain. The temperature and pressure of the chamber gradually increase and attains the sterilization temperature.
Sterilization Phase: On attaining sterilization temperature, the sterilizer holds (maintains) the temperature and pressure of the chamber till predefined time. Usually, it is 121 degrees C and time of 20 to 30 minutes (considering the overkill approach) for steam-air mixture sterilization.The pressure across the wall of the container is balanced by regulating the air purging in the chamber.
Exhaust Phase: After the sterilization phase, the air, used for maintaining the chamber pressure, is cooled down to reduce the load temperature.With a reduction in the load temperature, the pressure inside the container also reduces. This reduced pressure inside the container can too create a pressure imbalance across the wall of the container anddamage the load. Therefore, to avoid such damages, the external air pressure is gradually reduced by monitoring the load temperature during exhaust. Once the chamber temperature reaches the desired value, the chamber pressure is released, and the load is ready for unloading from the chamber.
More sterilization cycle to continue in next newsletters.
