Vacuum freeze dryers are highly efficient drying equipment that removes moisture from materials through low-temperature sublimation. They are widely used in the food, pharmaceutical, biological products, and chemical industries. Their core principle is to lower the material temperature below freezing point in a vacuum environment, causing moisture to directly sublimate from a solid to a gaseous state, thus avoiding the damage to the active ingredients of the material caused by high temperatures. The following details the usage method from three aspects: pre-operation preparation, operating procedures, and precautions.
Pre-operation Preparation
Equipment Inspection: Confirm that the cold trap, vacuum pump, heating system, and control system are in normal working order. Check if the cold trap temperature has reached the preset value (usually requiring pre-cooling to below -40℃), if the vacuum pump oil level is within the standard range, and if the sealing rings are intact.
Material Pretreatment: Perform pre-freezing treatment according to the material characteristics. For example, food materials need to be frozen at -30℃ to -40℃ for 12-24 hours to ensure complete freezing; pharmaceutical materials require controlled freezing rates to avoid crystal damage. Insufficient pre-freezing can lead to collapse during the sublimation stage, affecting the quality of the finished product.
Loading and Layout: Spread the material evenly on the material trays, with a recommended thickness of 5-10mm. Multiple material trays should maintain a spacing (e.g., 38mm) to avoid hindering vapor diffusion. For materials with volatile components, use packaging materials with good air permeability.
Operating Procedures
Pre-freezing Stage: Set the pre-freezing temperature (-40℃ to -50℃) and time (adjust according to the amount of material, usually 2-4 hours) via the intelligent control panel. During this stage, ensure the cold trap temperature is stable to avoid excessive ice crystal formation due to temperature fluctuations.
Vacuuming and Sublimation Drying: After pre-freezing, start the vacuum pump to reduce the system pressure to below 10Pa (achieving a standard vacuum of 5Pa under no-load). At this point, the ice in the material begins to sublimate, requiring energy from a conductive heating system (e.g., shelf heating). The heating temperature should be gradually increased (recommended to start from -20℃, increasing by 5-10℃ each stage) to avoid localized overheating.
Desorption Drying Stage: When the material temperature approaches ambient temperature, the desorption drying stage begins. At this point, the vacuum level needs to be further reduced (to below 2 Pa), and the shelf temperature increased to 30-50℃ to remove residual bound water. During this stage, the sample temperature display needs continuous monitoring to prevent excessive temperature from causing material denaturation.
Shutdown and Sampling: After drying, first turn off the heating system, and then turn off the vacuum pump after the material temperature has dropped to room temperature. Finally, introduce drying nitrogen to break the vacuum and remove the material. For high-value materials, it is recommended to use the one-button electric defrost function to quickly restore the equipment to its normal state.
