Pharmaceutical drying

Question 1

importance of drying

Answer 1

primary manufacturing
-water is capable of degrading many types of drug
-hydrolytic degredation is to be discouraged
-dry product is free flowing

secondary manufacturing
-wet granulation is commonly used to prepare formulations prior to tablet compaction
-stability, flow properties and compactability are all influenced by residual water content

Question 2

Total moisture content

Answer 2

-total water content of a wet solid
-not all of this water can be easily removed
-easily removable water is sometimes reffered to as free moisture content or unbound water

Question 3

equilibrium moisture content

Answer 3

-all solids will equilibrate with moisture present in air
-this water is called the eqilibrium moisture content
the absolute amount is dynamic as it changed with chamges in temperature and humidity
-each type of solid has its own inherent hygroscopicity.

Question 4

karl-fischer potentiometric titration

Answer 4

measures the amount of water by the electrical conductivity of a redox titration - most accurate

Question 5

dynamic vapour sorption

Answer 5

measures the weight change as a function of both temperature and humidity

Question 6

thermogravimetric analysis

Answer 6

measures the weight change as a funciton of temperature

Question 7

relative humidity (RH)

Answer 7

increased temperature will increase solubility
maximum solubility at a particular temperature
precipitation of the solute on cooling

-air at a given temperature will take up water vapour
-when no more vapour can be taken up the humidity is considered to be saturated

Question 8

Relative humidity formula

Answer 8

RH % = (vapour pressure of water vapour in air/vapour pressure of water vapour in air at saturated temperature) X100

Question 9

considerations prior to drying

Answer 9

-heat sensitivity of the material to be dried
-physical characteristics of the material
-requirment of aseptic conditions
-nature of the liquid to be removed
-scale of the operations
available sources of heat eg.electrial or steam

Question 10

3 classification of drying methods

Answer 10

conduction, convecton, radiation

Question 11

states of matter

Answer 11

latent heat is associated with all these phase changs
solid to liquid - melting
liquid to solid - freezing
solid to gas - sublimation
gas to liquid - cindensation
liquid to gas - evaporation

Question 12

endothermic processes (+Q)

Answer 12

melting
sublimation
evaporation

Question 13

exothermic procceses (-Q)

Answer 13

condensation
freezing

Question 14

evaporation

Answer 14

change from liquid to vapour
-the pressure of a vapour in equlibirium is called the vapour pressure
-when the vapour pressure is equal to the external pressure, the liquid boils (boiling point)

Question 15

conduction

Answer 15

vibration of atoms/molecules with no appreciable movement of molecules

Question 16

convection

Answer 16

macroscopic movement of molecules and their associated heat energy

Question 17

radiation

Answer 17

absorption of electromagnetic rays resultiing in increase in temperature

Question 18

practical heat transfer

Answer 18

-conductioin is the most important heat transfer process in industrial pharmacy
-convection in industrial processes is normally of a forced nature rather than being natural

Question 19

sensible heat

Answer 19

-sensible heat is an appreciable rise in temperature
Q = mc(change in temp
Q - heat energy
c = specific heat capacity

Question 20

Latent heat

Answer 20

-heat evolved or absorpbed by unit mass when it changes phases without a change in temperature

Question 21

Latent heat formula

Answer 21

Q=mL

Q-heat energy
m-mass
L-heat absorbed/liberated in the change of phase of unit mass

Question 22

fluidised-bed drier

Answer 22

equipment used for pharmaceutical drying

Question 23

effect of air velocity on pressure drop
Describe all points on this graph

Answer 23

A - air velocity low / no disturbance on particles
B - frictional drag on particles is equal to force of gravity
C- rearrangement to offer least resistence / suspension
D - particle porosity produces small pressure drop

Question 24

Advantages of fluidised bed granulator

Answer 24

-Efficient heat and mass transfer
-drying occurs from the surface of individual particles
-temperature of fbd is uniform throughout
-some attrition of particles cause particle spherity
-short drying times

Question 25

disadvantages of fluidised bed drier

Answer 25

excessive attrition due to turbulent state
production of fines - must be filtered
generation of static electricity - explosion risk

Question 26

Spray drier

Answer 26

-solution is atomised by high pressure gradient through a nozzle
-the small spherical droplets are sprayed into a steam of hot air
-evaporation of the solvent is extremely fast due to the very high surface area of the droplets
- most of the heat used as latent heat and as a degree of evaporative cooling takes place - this keeps the particles from overheating
-each droplet dries an individual solid particle

Question 27

advantages of spray drying

Answer 27

-millions of small droplets give a massive surface area heat/mass transfer and hence fast evaporation of solvent
-the characteristic particle shape gives the product a high bul density - good flowability, fast dissolution
-uniform and controllable particle size
-labour costs are low - single operation

Question 28

disadvantages of spray drying

Answer 28

equipment is bulky
heat trasnfer from air is relatively inefficient

Question 29

applications of spray drying

Answer 29

-used for drying solutions and suspensions
-reasonably useful for thermolabile materials
-high outputs are possible
-capable of producing spherical particles suitable for dry powder inhalation products
-can be operated aseptically
-examples of materials that are spray dried: starch, lactose, calcium, citric acid