Gap Freezing for Uniform Lyophilized Cake Crystallization
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Solution Overview
Problem
Lyophilization of materials, such as sugars, often results in the formation of solute layers on the top of the frozen solution, leading to inhibited sublimation due to amorphous solid formation, requiring higher drying temperatures and longer times, which negatively impact the process integrity and economics.
Innovation Solution
A method and apparatus involving a thermal insulator to maintain a fixed distance between the heat sink and the tray or container, allowing for simultaneous freezing from the top and bottom surfaces, preventing solute concentration and promoting uniform sublimation, including a heat sink with a refrigerant conduit and a thermal insulator with low thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the solution is frozen using conventional direct contact with heat sink, then freezing efficiency is improved, but solute layers form on the top surface inhibiting sublimation
Solution Approach 1:
The heat transfer system is segmented into multiple heat sinks positioned at different locations (top and bottom) of the container, allowing independent temperature control of each surface to prevent solute concentration at the top
Solution Approach 2:
A thermal insulator is introduced as an intermediary between the heat sink and the container bottom, enabling controlled heat transfer that prevents excessive cooling and solute layer formation while maintaining freezing efficiency
2Productivity
If higher drying temperatures are used to overcome solute layer inhibition, then sublimation rate is improved, but product integrity deteriorates
Solution Approach 1:
The freezing process is modified in advance by using dual heat sinks and thermal insulators to prevent solute layer formation before sublimation begins, eliminating the need for higher drying temperatures and protecting product integrity
3Reliability
If longer drying times are used to overcome solute layer inhibition, then sublimation completeness is improved, but process economics deteriorate
Solution Approach 1:
The freezing stage is optimized beforehand using thermal insulators and dual heat sinks to create ideal sublimation conditions, enabling complete sublimation in shorter times and improving process economics
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach prevents the formation of impermeable solute layers, enabling efficient sublimation and producing lyophilized cakes with larger, consistent pore sizes, reducing drying time and maintaining product integrity.
Implementation Method 1
a thermal insulator disposed between the heat sink surface and the tray surface
Implementation Method 2
a heat sink with a heat sink surface in thermal communication with a refrigerant
Implementation Method 3
the frozen solvent is removed by sublimation under reduced pressure
Data Source
AI summary
This application discloses devices, articles, and methods useful for producing lyophilized cakes of solutes. The devices and articles provide for a method of freezing liquid solutions of the solute by the top and the bottom of the solution simultaneously and at approximately the same rate. The as frozen solution can then provide a lyophilized cake of the solutes with large and uniform pores.