Abstract: A method to monitor a secondary drying phase of a freeze-drying process comprises initial steps in which is provided to perform pressure rise tests at different time and to calculate a respective value of experimental desorption rate of product (steps 1 to 3). Subsequently, the method provides to estimate initial conditions and kinetic constants of a kinetic model of the process (step 4) and to calculate at time t=t2 a respective residual moisture content and a respective desorption rate (step 5). The method can be performed in a freeze-dryer apparatus which includes a drying chamber that contains a product to be dried and can be isolated to perform pressure rise tests.

Abstract: A freeze-drying process includes a primary drying phase. Within this phase, a test is performed for causing a variation of partial pressure of solvent inside a drying chamber. At the beginning of the test, a product sublimation flux, a total pressure and a partial pressure of the solvent in the drying chamber are measured. A product temperature is estimated at the interface of sublimation at the beginning of the test. The solvent vapor pressure at the interface of sublimation is calculated as is a resistance of a dried layer of the product to the vapor flow of the solvent. Next, a thickness of a frozen layer of the product is calculated and a coefficient of heat transfer between heating surface and product is also calculated. An initial temperature profile of the frozen product is then calculated as is a total pressure in the drying chamber. A value of the product temperature at the interface of sublimation at the beginning of test is determined and a time constant of the freeze-drying process is calculated.

Abstract: A freeze-drying process includes a primary drying phase. Within this phase, a test is performed for causing a variation of partial pressure of solvent inside a drying chamber. At the beginning of the test, a product sublimation flux, a total pressure and a partial pressure of the solvent in the drying chamber are measured. A product temperature is estimated at the interface of sublimation at the beginning of the test. The solvent vapor pressure at the interface of sublimation is calculated as is a resistance of a dried layer of the product to the vapor flow of the solvent. Next, a thickness of a frozen layer of the product is calculated and a coefficient of heat transfer between heating surface and product is also calculated. An initial temperature profile of the frozen product is then calculated as is a total pressure in the drying chamber. A value of the product temperature at the interface of sublimation at the beginning of test is determined and a time constant of the freeze-drying process is calculated.

Abstract: A method to monitor a secondary drying phase of a freeze-drying process comprises initial steps in which is provided to perform pressure rise tests at different time and to calculate a respective value of experimental desorption rate of product (steps 1 to 3). Subsequently, the method provides to estimate initial conditions and kinetic constants of a kinetic model of the process (step 4) and to calculate at time t=t2 a respective residual moisture content and a respective desorption rate (step 5). The method can be performed in a freeze-dryer apparatus which includes a drying chamber that contains a product to be dried and can be isolated to perform pressure rise tests.