How to freeze dry liquids

Freeze dryer is a technique of drying by using the principle of sublimation. It is to freeze the dried material at low temperature and then sublimate the frozen water molecules in a proper vacuum oven environment. It is a process that makes frozen water molecules into water vapor evolution.

The vacuum system of the freeze dryer consists of a freeze dryer, a water vapor condenser, a vacuum valve, and a vacuum pump. The degree of vacuum during lyophilization is approximately 67 to 0.13 Pa (5 x 10-1 to 1 x 10-3Torr). The pre-vacuum of the freeze-drying system requires that the required vacuum should be achieved in about 30 minutes.

Then people maybe wonder how to freeze dry liquids, next let’s go through the process together : Before freeze drying materials, we need to compound the materials into liquids with certain concentration. And materials that need to be freeze dried should be compounded into liquids with 4%-25% solid substances concentration(10%-15% is the best), so that the materials could have a good shape finally. The freeze-drying process generally consists of three steps: pre-freezing, sublimation drying (or the first stage drying), analytical drying (or the second stage drying).

Firstly, pre-freezing is to solidify the free water in the solution and give the product the same shape after drying as before, and to prevent irreversible changes such as foaming. Secondly, when frozen products are heated in sealed vacuum containers, their ice crystals will sublimate to vapor and escape, resulting in dehydration and drying of the products. Thirdly, in order to improve the storage stability and prolong the shelf life of the product, it is necessary to remove moisture that is adsorbed on the capillary wall and polar groups of dry matter.

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