MDM: Pharmaceutical drying

Question 1

What is the importance of drying in primary and secondary manufacturing?

Answer 1

• Primary: hydroyltic degradation, effects flow
• Secondary: effects flow properties and stability

Question 2

What is total moisture content?

What is water called if it can easily be removed?

What is Equilibrum moisture content?

What effects this?

Answer 2

• 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

Question 3

what methods are used to determine moisture content?

IMPORTANT!

Answer 3

• 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

Question 4

Describe Relative Humidity

Answer 4

• 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

Question 5

How do you calculate Relative Humidity?

Answer 5

Question 6

What is it important to consider prior to drying?

IMPORTANT!

Answer 6

• 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

Question 7

What are the classifications of drying methods?

Answer 7

• 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

Question 8

Describe the phase changes between solid,liquids, gases.

What processes are endothermic? which are exothermic?

Answer 8

• Condensation and freezing are EXOTHERMIC (-Q)
• Melting, sublimation and evaporation are ENDOTHERMIC (+Q)

Question 9

Define:

1. Evaportation
2. Vapour pressure
3. Boiling point

Answer 9

1. Phase change from a liquid to a vapour
2. The pressure of a vapour in equilibrium with the liquid at any given temperature
3. When vapour pressure is equal to or greater than external /atomospheric pressure the liquid boils

Question 10

What is the difference betwee sensible and latent heat?

Equations?

Answer 10

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

Question 11

What is the relationship between Watts and Joules?

Answer 11

1 Js-1 = 1 W

Question 12

Drying equipment?

Answer 12

• Fluidised bed drier
• spray drier

Question 13

What are the advantages of a fluidised bed drier?

Answer 13

• 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

Question 14

What are the disadvantages of a fluidised bed drier?

Answer 14

• Excessive attrition due to turbulent state
• Production of fines/ dust - must be filtered
• Generation of static electricity - explosion

Question 15

Describe the use of a spray drier

Answer 15

• 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

Question 16

Advantages of spray drier

Answer 16

• Millions of small droplets give massive SA/ mass transfer and hence fast evapporation of solvent
• The characteristic (spherical) particle shape gives the product a high bulk density
• Uniform and controllable particle size
• Labour costs low - single opperation

Question 17

Disadvantages of spray drier

Answer 17

• Bulky equipment
• Heat transfer from air inefficent

Question 18

Application of spray drying

Answer 18

• Used for drying solutions/ suspension
• highout puts possible
• capable of producing spherical particles suitable for dry powder inhalation products
• can be operated aseptically