MDM: Pharmaceutical drying Flashcards
What is the importance of drying in primary and secondary manufacturing?
- Primary: hydroyltic degradation, effects flow
- Secondary: effects flow properties and stability
What is total moisture content?
What is water called if it can easily be removed?
What is Equilibrum moisture content?
What effects this?
- The total water content of a wet solid
- Unbound water or free moisture content
- Moisture content the solid is neither losing or gaining. It is in equilibrium with the moisture present in air
- Temperature and humidity
what methods are used to determine moisture content?
IMPORTANT!
- Karl - Fischer potentiometric titration
Measure amount of water by the electrical conductivity of a REDOX titration
- Dynamic vapour sorption
Measure weight change as a function of both temperature and humidity
- Thermogravametric analysis
Measure weight change as a function of temperature
Describe Relative Humidity
- Relative humidity is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature.
- At a given temperature air will take up water. When no more vapour can be taken up the humidity is saturated
Solute (water) dissolve in solvent (air):
- Increasing solubility with temperature
- Max solubility at particular temperature
- Precipitation on cooling
How do you calculate Relative Humidity?
What is it important to consider prior to drying?
IMPORTANT!
- Heat sensitivity of material to be dried
- Physical characterisitics of material to be dried
- Requirement for aseptic conditions
- Nature of liquid to be removed
- Scale of opperation
- Available sources of heat
What are the classifications of drying methods?
- Convection:
Macroscopic movement of molceules and their associated heat energy
- Conduction:
Vibration of atoms/ molecules with no appreciable movement of molecules
- Radiation:
Absorption of EM rays resulting in an increase in temperature
Describe the phase changes between solid,liquids, gases.
What processes are endothermic? which are exothermic?
- Condensation and freezing are EXOTHERMIC (-Q)
- Melting, sublimation and evaporation are ENDOTHERMIC (+Q)
Define:
- Evaportation
- Vapour pressure
- Boiling point
- Phase change from a liquid to a vapour
- The pressure of a vapour in equilibrium with the liquid at any given temperature
- When vapour pressure is equal to or greater than external /atomospheric pressure the liquid boils
What is the difference betwee sensible and latent heat?
Equations?
Sensible heat is associated with an appreciable rise in temperature
Q=mc►T
Latent heat (heat of transformation) is the heat evolved/ absorbed by unit mass when changing phase without temperature change
Q=mL
L = heat absorbed/ liberated
What is the relationship between Watts and Joules?
1 Js-1 = 1 W
Drying equipment?
- Fluidised bed drier
- spray drier
What are the advantages of a fluidised bed drier?
- Efficent heat and mass transfer
- Drying occurs from the surface of particles
- Temperature of fluidised bed is uniform throughout
- Some attrition of particles cause particle sphericity
- Short drying times
What are the disadvantages of a fluidised bed drier?
- Excessive attrition due to turbulent state
- Production of fines/ dust - must be filtered
- Generation of static electricity - explosion
Describe the use of a spray drier
- Solution is atomised by a high pressure gradient through a nozzle
- The small spherical droplets are sprayed into stream of hot air
- Evapporation of solvent is extremely fast due to very high surface area of the droplets
- Most heat is latent and a degree of evapporative cooling takes place - keeps particles from overheatig
- each droplet dries to a sphere
