Drying Flashcards
Drying Def
Process where most/all liquid is removed from product. Involves evaporation and sublimation. May improve powder flowability and prevent degradation by hydrolysis. Uses 3 methods of heat transfer
Sublimation Def
Removal of liquid vapour by using latent heat stage
Purpose of drying
Improve flowability, increases stability (no hydrolysis degradation) and prevents adhesion during compaction
3 methods of heat transfer
conduction (heat tranfer through a solid), convection (heat transfer through liquid/gas, heat rises) and radiation (heat transfer through electromagnetic rays)
Total Moisture Content Def
wet solid mass containing easily unbound (water easily removed) and bound water(water not easily removed)
Free moisture content def
Unbound water in a solid that easily air dried
Equilibrium moisture content def
Water within solid (mainly bound) that is at equilibrium concentration between solid and enviornment
Ambient air def
solution of water in a mix of gases
Relationship between water solubility and enviormental temp
increased temp = increased water solubility = increase mositure in atmosphere = decreased unbound water
Relative Humidity Def
percentage saturation (conc of water) in air at a given temp
Relationship between temp, relative humidity and water removed from solid
Decreased temp = decreased relative humidity = increased unbound water = more water loss to atmosphere
Drying Considerations
Material thermosensitivity, material physical characteristics, liquid nature and scale
Dryer Types
Fluidised bed dryer (convection), vacuum oven (conduction), microwave (radiation), spray dryer and freeze dryer
Fluidised Bed Drying Outline
Convection Drying. Powder fluidised in air stream. High heat and mass transfer rates
Fluidised Bed Dryers Advantages
High drying rates, uniform + homogenous drying, minimal solute migration (intergranular heating) and large volume
Fluidised bed dryer limitations
Expensive, attrition (particle size reduction) and static electricity
Vacuum Oven Outline
Conduction, small scale drying. Reducing pressure in a sealed chamber creates vacuum, heat shelves, water boils at low temp, vapour removed by vacuum.
Vacuum Oven Advantages
Low temps, lower oxidation risk
Vacuum Oven Limitations
Scale issues with drying uniformity and solute migration occurs
Solute Migration Def
Drying process starts at surface, solvent soaked in particles moves to surface when being removed. Particles are pushed together wearing eachother down. Impacting uniformity of dose
Microwave Dryers Outline
Radiation drying. Magnetron produces electromagnetic waves, electromagnetic waves enter through a window, resonance of electrons in solids mass transfers energy and heat is generated
Microwave Dryers Advantages
Low temps, rapid heat transfer, efficient (energy not transferred to heat), powder can be stationary and uniform drying
Microwave Dryer Limitation
smaller batch size and radiation hazards
Spray Drying Outline
Method of drying solution/suspension particles. Generates large surface area increasing rate particles are dried. Liquid preparation fed to spray dryer, pressururised air turns into drying chamber as droplets, droplet warmed un warm air currentsand dry product is collected
Spray Drying Advantages
Low temp, rapid heat transfer, uniform drying and uniform particle size shape
Spray Drying Disadvantages
Expensive, inefficient energy (heat) and polymorphism/amorphism
Freeze Drying Outline
Removal of liquid by freezing and sublimation, low temps, low pressure. Reduce temp below water freezing at atmospheric pressure. At this temp, reduce pressure to vacuum below triple point of liquid and at pressure increase temp
Freeze drying advantages
Low temp (stability), little oxidation, light/porous products and used in protein formulation
Freeze Drying Disadvantages
Expensive, time cosnuming, product formed is hygroscopic
