Comparative Rates of Freeze-Drying for Lactose and Sucrose Solutions as Measured by Photographic Recording, Product Temperature, and Heat Flux Transducer

Abstract

Sublimation from lactose and sucrose solutions has been monitored by temperature measurement, visual observation, heat flux sensing and manometric measurements. Estimates of energy transfer rates to the subliming mass made from visual observations and heat flux measurements are in broad agreement, demonstrating for the first time that heat flux sensors can be used to monitor the progress of lyophilization in individual vials with low sample volumes. Furthermore, it is shown that under identical lyophilization conditions the initial rate of drying for lactose solutions is low with little water sublimation for up to 150 minutes, which contrasts markedly with the much faster initial rate of drying for sucrose solutions. Measurement of the initial heat flux between shelf and vial indicated a lower flux to a 10% lactose solution than to a 10% sucrose solution.

Keywords:

• lyophilization
• freeze-drying
• heat flux
• drying rate
• heat flux transducer

ACKNOWLEDGMENTS

We are grateful to Dr Sergei Tchesalov for suggesting the use of the heat flux transducer, Mr W. Petre for initial experiments with the heat flux transducer, and to Mr Surinder Sall of the Department of Chemical Engineering, University of Cambridge, for valuable assistance with the implementation of this technique.