Spray Drying Flashcards
What is the difference between bound and unbound water?
unbound water - free moisture content
- exists as moisture/liquid therefore exerts vapour pressure
- can be easily removed by drying resulting in air dry material
bound water - equilbrium moisture content
- doesnβt exert any vapour pressure as strongly bound to solid material by
= adsorption on the surface OR absorbed within the solid structure (trapped in capillaries by surface tension)
- difficult to remove
What is drying?
removal of all or most of the liquid associated with a wet pharmaceutical product
How can relative humidity be calculated?
%RH = π£ππππ’π ππππ π π’ππ ππ π€ππ‘ππ π£ππππ’π ππ πππ/π£ππππ’π ππππ π π’ππ ππ π€ππ‘ππ π£ππππ’π ππ π ππ‘π’πππ‘ππ πππ ππ‘ π‘βπ π πππ π‘πποΏ½
How can the relative humidity of ambient air be reduced?
can be done by silica gel or phosphorous pentoxide.
What are the advantages of spray drying?
flowability increases compared to drug powders where flowability is inhibited by static charge
compaction properties enhance as well
What must be considered before spray drying?
Heat sensitivity of the materials Physical characteristics of the material Nature of the liquid to be removed Scale of the drying operation Available source of heat
What are the principle for efficient drying?
- large surface area for drying
- efficient heat transfer per unit area - provide sufficient latent heat of vaporization
- efficient mass transfer of evaporated water - turbulence to minimize boundary layer thickness
- efficient vapour removal - using low RH air
What are the types of drying methods?
Convection - energy is transferred by mass motion of molecules (fluidized-bed drying)
Conduction - wet solid is in thermal contact with hot surface (oven)
Radiation - no need for transfer medium (microwave)
What is simple jet atomiser?
Can be blocked easily (solid deposition after rapid evaporation
Variation in flow rate (uniformity of the droplet size
What is rotary type atomiser?
Break down article via rotation
- disc that rotate at high speed (10,000- 30,000 rotation/minute)
Form a film that spread from a small disc to a larger disc and disperse form edge into a finespray
- effective in both solutions and suspension of solids
Can operate effectively at various flow rate
What are the advantages of spray drying?
Atomise solutions into very small droplet which give large surface area for mass and heat transfer
- takes only fraction of second to dry droplets
droplets donβt attain high temperature because the evaporation is rapid
- hence most of the heat used are latent heat of vaporization and the temperature of the particles kept low by evaporative cooling
Product is almost spherical particles hence it is free-flowing which is convenient for tablet manufacturing
Usually spray-dried powders have higher dissolution and hence better bioavailability (Why!)as large surface area , crystalline (energy to break down crystalline sturcture) β amorphous (high solubility)
It can be used as a continuous process
Low labour cost
What are the uses of spray drying?
Spray dryer is capable of drying both solution and suspensions (soluble and insoluble substances)
- examples citric acid, barium sulfate, calcium phosphate and antibiotics.
Spray drying can produce spherical particles in respirable range of 1-7Β΅m that are used for dry powder inhaler
Spray drying can be operated aseptically using heated filtered air. e.g. serum hydrolysate
Spray dryers can operate in a closed circuit mode under inert gas to minimise product oxidation.
Sustaining the drug release.
