Freeze drying is a widely used technology for preserving food and medicines. It can reduce product wastage and make food taste better and healthier.
Freeze drying is done by freezing a product and then sublimating it under vacuum to remove water. The vacuum level and temperature of the product must be controlled properly in order to produce good quality products.
Heating and Cooling
Freeze drying is the process of dehydrating a sample or food product by freezing it and then collecting the resulting vapors for use in other applications. This process is known as “lyophilization.” It is a cost-effective and environmentally friendly method of preserving products.
The Vacuum Freeze Dryer must have a heating system that is capable of sublimating the water molecules in a frozen sample. This requires a very high amount of heat, almost ten times the amount required to freeze a gram of water.
For this reason, a freeze dryer must be very careful to apply the proper temperature and pressure. A temperature that is too low will not allow ice to be sublimated, while a temperature that is too high will prevent the vapor from being collected in the ice trap.
As shown in the Water Triple Point Graphic, water can transition from solid phase (ice) to liquid phase and then back to vapor phase at certain temperatures and pressures. This can be accomplished by a vacuum pump.
Vacuum pumps are important for reducing the pressure in the drying chamber, which helps to lower the freezing point of water and increase its evaporation rate. They also help to eliminate any potential contamination from moisture and oxygen present in the environment during the freeze drying process.
A vacuum system is also essential for preventing the accumulation of ice in the ice collector. A cold trap is placed in the ice collector and the vacuum pressure is reduced to below the vapor pressure of the ice. This causes the ice to migrate from the higher pressure area into the lower pressure area. The ice collector then collects the resulting vapor.
image source: https://www.pinterest.ph
Vacuum Pumping
Vacuum pumps work by reducing the pressure inside a sealed chamber. This causes water vapor to evaporate more easily and can shorten the drying process.
It’s important to choose the right vacuum pump for your freeze drying needs, as different types of pumps have varying advantages and drawbacks. They may also require specialized maintenance to ensure they last as long as possible and function properly.
Positive displacement pumps are the most commonly used type, but there are other kinds that can be used in certain applications. Some pumps are oil-free, which helps prevent contamination from affecting the pumping process.
Regardless of the type of pump you use, it’s important to regularly check the parts for any damage or deterioration. This can increase the lifespan of the vacuum pump and make it more reliable, preventing costly emergency repairs in the future.
If your vacuum pump is oil-based, you’ll need to change the oil every 20-25 uses. This is an important part of maintaining your freeze dryer, as contaminating the oil can reduce its lubricity and effectiveness.
In addition to oil changes, vacuum pumps and Quick-Freezing Equipment should be inspected for other signs of wear and tear. This can include the vanes, bearings and belts. It’s best to replace these components in sets to avoid contaminants from accumulating over time and damaging the machine.
In addition to regular maintenance, you can also keep your freeze dryer’s vacuum pump in good condition by removing any debris and cleaning the unit. This will help it last longer and function better, making it a great investment.
Dew Point Monitoring
Dew point monitoring is used in industrial settings to prevent moisture damage to equipment, save energy, and avoid corrosion. Moisture control is especially important in places that use compressed air. If the air is too damp, it could cause pipes to clog and machines to break down.
A number of factors influence the dew point in the air, including the humidity level. High moisture levels in the air can lead to condensation that ruins products, change test results, lower product quality, and accelerate wear and tear of piping systems.
Some types of temperature sensors are suitable for use in freeze dryers, such as thermocouples and resistance temperature detectors (RTDs). However, these devices require calibration in order to be accurate.
Another type of device is a data logger. This device is often a portable unit with a battery and wireless technology. It can be connected to the control system of a freeze dryer and provides real-time data that can be transmitted to a reader station.
It is possible to use tunable diode laser absorption spectroscopy (TDLAS) to monitor the mass flow rate of water vapor through the freeze dryer chamber and condenser. While TDLAS has been well established at laboratory scale, more work is needed to apply the technology to production-scale equipment.
This is due to the fact that some "drift" occurs within the axi-symmetric gas flow of the freezing dryer's connecting duct, resulting in measurement errors. This is especially true when a single-vial technique is applied.
The best practice for pressure monitoring in freeze drying is to have both a capacitance manometer and a Pirani gauge on the chamber and condenser, respectively. This configuration enables what has come to be known as comparative pressure measurement, which is useful for process analytical methods.
Controlled Crystallization Technology
Crystallization plays an important role in many industries, including pharmaceuticals and fine chemicals. Its control is crucial for the production of high-quality products with desired solid-state properties.
However, crystallization is not only governed by thermodynamics but also heavily influenced by kinetics. This is especially the case during process scale-up, where unexpected issues can arise that are not readily seen in a lab-scale environment. Typical issues include the appearance of transient polymorphs, oiling out and even undesirable and unwanted solid forms.
For this reason, there is a need to identify and understand the mechanisms that are responsible for impurity incorporation during solution crystallization and to develop effective methods to prevent them from occurring. This can be done by using advanced techniques such as particle size analyzers that quickly provide accurate and reliable data for assessing impurity concentration.
To achieve this, we have developed a stochastic model that accounts for drying heterogeneity at the shelf temperature and chamber pressure level by using a new semiempirical energy balance to keep the number of equipment-dependent parameters to a minimum. Furthermore, we have applied nonlinear dynamic optimization to minimize the primary drying duration while still ensuring that tight constraints on the product temperature and sublimation rate are met.
This approach enables us to address two key issues with existing models: the lack of a stochastic formulation and the limited ability to capture time-varying operating conditions. To solve these issues, we have incorporated macroscopic energy and mass balances within the model and allocated intralot variability as a parametric uncertainty in the model parameter with the highest sensitivity to the process KPIs (product temperature, total sublimation flux and length of the frozen layer). The result is a robust stochastic model that allows time-varying operating conditions to be handled while limiting the number of equipment-dependent parameters that need to be estimated.
Solvent Trapping System
Freeze drying is a widely used method of stabilisation for drugs, vaccines, antibodies and other biological material. However, despite significant improvements in analytical and process science a number of misconceptions persist which are preventing the effective management of this critical laboratory procedure.
The solvent trapping system is a key part of the Experimental Vacuum Freeze Dryer process. This is a system that collects and recovers the organic solvent from the frozen sample, ensuring that it remains in a pure form that can be easily redissolved and weighted, or sub-sampled and redissolved in another solvent.
Choosing the right solvent trapping system for your freeze drying application is important for optimum performance. This includes selecting a vacuum pump, cold trap or condenser, and the pressure control that will ensure optimum solvent removal and recovery.
image source: https://www.pinterest.ph
Vacuum Pumps
The most suitable vacuum pumps for freeze drying are oil sealed rotary vane pumps. These are the most reliable and provide near 100% of their ultimate achievable vacuum across the typical working range of freeze drying requirements – typically 1mtorr at full load.
In order to maximise the performance of your vacuum pump for freeze drying, it is essential that it has a sufficient degree of oil compatibility and a high tolerance to water vapour. In addition, it is often a good idea to operate a “gas ballast” valve for a short period after the freeze drying run has finished, in order to degas the pump and remove any excess oil that may have built up.
In addition, the pressures achieved in a freeze dryer chamber must be low enough to allow a solvent to sublime directly from ice to vapour. A chamber with too high a pressure is not capable of this and will cause samples to boil out.
No comments yet