The freeze-drying process consists of two stages: pre-freezing and drying. Traditional freeze dryers, regardless of processing capacity, generally consist of two separate chambers. Pre-freezing is completed in one quick-freezing chamber, and the product is then transferred to a drying chamber for drying. This two-chamber design requires a larger footprint, and transferring the product between the two chambers requires manual labor. Beyond the extra floor space and labor cost, the transfer step also exposes the pre-frozen product to ambient temperature and humidity, which risks partial thawing, surface condensation, and even contamination — all of which can compromise product quality and batch consistency.
Kemolo has advanced this technology by combining the two chambers into one, completing both pre-freezing and drying within a single chamber. This integrated design not only saves valuable production floor space and eliminates manual handling between chambers, but also shortens the overall cycle time and reduces the risk of product damage during transfer. During the pre-freezing stage, the target product temperature is -40 to -35°C, which is relatively low, while during the heating stage, the temperature may reach 70–80°C. These demanding conditions mean the heat-transfer medium must operate reliably across a very wide temperature span — if pure water were used as the heat-transfer medium, it would freeze solid and be unable to circulate during the pre-freezing stage.
This is where silicone oil proves indispensable. Silicone oil has excellent low-temperature flowability: it neither freezes nor solidifies, nor boils, within the range of -80 to 150°C, and it always maintains a stable liquid state throughout the entire freeze-drying cycle. Its viscosity remains low and pumpable even at deep sub-zero temperatures, ensuring uniform, efficient heat transfer to and from the shelves. At the same time, it does not boil or vaporize at elevated heating temperatures, preventing pressure fluctuations inside the circulation system.
Silicone oil also offers excellent chemical stability and is non-corrosive, making it highly suitable for use in the freeze-drying industry. It does not react with the metal components of the shelf and piping system, which extends the service life of the equipment and minimizes maintenance. Furthermore, silicone oil has a very low vapor pressure, meaning it does not easily volatilize into the drying chamber and contaminate the product — a critical advantage for pharmaceutical, food, and biological applications that demand strict purity. Its low oxidation tendency and long service life further reduce the frequency of oil replacement and the associated downtime and operating costs.
It should be noted that because silicone oil has a relatively high flash point and is flammable under certain conditions, freeze-dryer manufacturers equip the system with temperature and pressure monitoring, oil-quality alarms, and proper ventilation to ensure safe operation. Nevertheless, thanks to its stable liquid state across the full operating range, excellent chemical inertness, low volatility, and long service life, silicone oil remains the preferred heat-transfer medium in modern single-chamber freeze dryers — and the key to Kemolo's integrated, labor-saving, and high-efficiency design.
