Lyophilizer, also known as freeze dryer or liofilizador, they are synonymous. A lyophilizer is the equipment execute dehydrate process that typically used to preserve perishable materials, to extend shelf life, or make the material more convenient for storage or transport. Lyophilizer works by freezing the material, then reducing the surround to allow the frozen water(ice) to sublimate.
That means, a lyophilizer will have systems of: refrigeration, vacuum, heating, drying chamber, vapor collect condenser and controller, as well as the auxiliary components like temperature probes, vacuum sensors, software and so on.
Working Principle of Lyophilization
Lyophilization is based on a simple principle of physics called “SUBLIMATION”. Sublimation is the process of transition of a substance from solid to the vapor state without passing through an intermediate liquid phase. The process of lyophilization consists of:
- Freezing of the product to convert the water in the product to ice form,
- Sublimation of ice directly into water vapor under vacuum.
- Drawing off the water vapor
- Once the ice has been sublimated, the products are freeze-dried and can be removed from machine.
The principle advantages of lyophilization as a drying process are:
- Minimum damage and loss of activity in delicate heat-liable materials
- Speed and completeness of rehydration
- Possibility of accurate, clean dosing into final product containers
- Porous, friable structure
The principle disadvantages of lyophilization are:
- High capital cost of equipment (about three times more than other methods)
- High energy costs (2-3 times more than other methods)
- Long process time (typically 24 hour drying cycle)
A Lyophilizer’s 3 Primary Stages
A lyophilizer functions in three phases, with the first and most critical being the freezing phase. Proper lyophilization, otherwise known as freeze drying, can reduce drying times by 30%.
A lyophilizer uses various methods to freeze the product. Freezing can be done in a freezer, a chilled bath (shell freezer), or on a shelf in the lyophilizer. The lyophilizer cools the material below its triple point to ensure that sublimation, rather than melting, will occur. This preserves the material’s physical form.
A lyophilizer most easily freeze dries large ice crystals, which can be produced by slow freezing or annealing. However, with biological materials, when crystals are too large they may break the cell walls, and that leads to less-than-ideal freeze drying results. To prevent this, the freezing is done rapidly. For materials that tend to precipitate, annealing can be used. This process involves fast freezing, then raising the product temperature to allow the crystals to grow.
Primary Drying (Sublimation) Phase
A lyophilizer’s second phase is primary drying (sublimation), in which the pressure is lowered and heat is added to the material in order for the water to sublimate. The lyophilizer’s vacuum speeds sublimation. The lyophilizer’s cold condenser provides a surface for the water vapor to adhere and solidify. The condenser also protects the vacuum pump from the water vapor. About 95% of the water in the material is removed in this phase. Primary drying can be a slow process. Too much heat can alter the structure of the material.
Secondary Drying (Adsorption) Phase
A lyophilizer’s final phase is secondary drying (adsorption), during which the ionically-bound water molecules are removed. By raising the temperature higher than in the primary drying phase, the bonds are broken between the material and the water molecules. Freeze dried materials retain a porous structure. After the lyophilizer completes its process, the vacuum can be broken with an inert gas before the material is sealed. Most materials can be dried to 1-5% residual moisture.
Thoroughly freezing raw materials.
Mostly, freezing temperature should 5 ~ 10C lower than product’s eutectic temperature, halfway freezing (typically show external freezing, internal still in liquid phase) may cause dried products out of shape or nutrition lose.
Eutectic point (freezing point), which mentioned above, is the lowest temperature that could completely freezing material to solid. Normally, when freezer reach products’ eutectic point needs last 1 to 2hrs.
Proper give energy in sublimation step
Heating the product too high in temperature can cause many troubles:
- Product melt. For example, carbohydrate will block the vapor channel, cause drying fail.
- Too much vapor creation. Condenser cannot collect in time, and the temperature will have a drastic raise.
- Vacuum pump broken. Vapors that cannot collect by condenser in time may go to vacuum pump, oil pump will broken.