Drying Flashcards
During manufacturing, drying is essential to guarantee process performances e.g. granulation and compaction. True or false?
True
What is moisture content defined as?
the amount of water contained in a material
What is % moisture by volume defined as?
The molecules of water per unit volume
Moisture content and relative humidity are the same thing. True or false?
False
What is humidity defined as?
The amount of water vapour present in the air
Relative humidity indicates the amount of moisture in the air as a percentage of the maximum amount of moisture that the air can hold. True or false?
True
Water content in the air increases as temperature increases. True or false?
True
An increase in temperature results in an increase in relative humidity. True or false?
false, decrease in relative humidity because the air can hold a greater amount of water vapour
What is the dew point?
The temperature to which moisture condenses and evaporates at the same rate
During drying, only moisture content can change. True or false?
False
Temperature also changes
What transfers happen during drying?
heat transfer from heating source to the product, and mass transfer of moisture from internal to surface then surface to surrounding
In practice, heat can be transferred to drying materials through what modes?
Convection Conduction Radiation Microwave Radiofrequency Joule heating
Name 4 drying methods
spray drying, convective drying, vacuum drying and microwave drying
Which 2 factors should be considered to preserve the stability of moisture sensitive medicines during storage?
temperature (reduction of water solubility in air and condensation) & (air exchange (avoid saturation of drying air
Paper is non-hygroscopic. True or false?
False, it is hygroscopic
When there is less moisture in the air, paper releases moisture. True or false?
True
When there is more moisture in the air, water absorbs moisture. True or false?
True
What is meant by total moisture?
Total amount of water associated with a wet solid
total = free + equilibrium
Free moisture content is the amount of water that can be easily removed. True or false?
true, also known as unbound water
What is meant by equilibrium moisture content?
The portion of water that is more difficult to remove, also known as bound water
What are the factors that need to be considered when selecting the drying method?
Heat sensitivity of materials used
Materials physical characteristics
Solvent/liquid to be removed e.g. boiling point
Efficient mass transfer of evaporated liquid
Efficient vapour removal from drying air
Amount of material to be processed e.g. scale up considerations
Sterility
What are the advantages of a fluidised bed dryer?
Efficient heat transfer (minimise effects on thermo-sensitive materials), Homogenous process - movement of particles guarantees drying of all individual ones, Free movement of particles reduces the migration process and separation/aggregation phenomena
What are the disadvantages of a fluidised bed dryer?
Turbulence might damage granules, Small particles might need specific attention to be removed from the fluidising air, Particle movement in turbulence and warm environment might cause charges of static electricity
What are the advantages and disadvantages of microwave drying?
Adv: Rapid drying at controlled temp, energy absorbed in the wet material not in the air, stationary conditions decreases small particle movement , uniform heating reduces solute migration effect . Disadv – small batch size & shielding from radiation is essential
Microwave drying has been used to process yeast, enzymes, small molecule pharmaceuticals and various biopharmaceuticals. True or false?
True
Vacuum ovens are generally used for large scale processes. True or false?
false, small scale
Which type of dryer is used with heat-sensitive materials?
Freeze dryer
A spray dryer generates a large surface area to promote what?
heat exchange and heat transfer
The higher the flow rate of a spray dryer, the smaller the droplets. True or false?
True
In a vacuum oven, a temperature of 25-35 degrees is sufficient to boil water. This is convenient for thermo-sensitive drugs.
True
What is solute migration?
movement of solution in a wet system during drying
What is the difference between inter-granular migration and intra-granular migration?
inter-granular the solute moves between granules towards the surface but in intra-granular granules are separated during the process and there is even distribution of solute within a granule.
Explain the impact of dew point on manufacture
During the drying process of temperature sensitive material it might be necessary to cool down the supplied air
Important to avoid to design a drying process with conditions close to the dew point
Inhomogeneity between granules impact what?
Quality aspects
Dose
Manufacturing
Appearance
Therefore important to reduce solute migration
How to reduce solute migration phenomena
Initial moisture content
Slow convective drying
Drying by microwave radiation
Dynamic drying methods (“granules in motion”)
