Drying

Question 1

During manufacturing, drying is essential to guarantee process performances e.g. granulation and compaction. True or false?

Answer 1

True

Question 2

What is moisture content defined as?

Answer 2

the amount of water contained in a material

Question 3

What is % moisture by volume defined as?

Answer 3

The molecules of water per unit volume

Question 4

Moisture content and relative humidity are the same thing. True or false?

Answer 4

False

Question 5

What is humidity defined as?

Answer 5

The amount of water vapour present in the air

Question 6

Relative humidity indicates the amount of moisture in the air as a percentage of the maximum amount of moisture that the air can hold. True or false?

Answer 6

True

Question 7

Water content in the air increases as temperature increases. True or false?

Answer 7

True

Question 8

An increase in temperature results in an increase in relative humidity. True or false?

Answer 8

false, decrease in relative humidity because the air can hold a greater amount of water vapour

Question 9

What is the dew point?

Answer 9

The temperature to which moisture condenses and evaporates at the same rate

Question 10

During drying, only moisture content can change. True or false?

Answer 10

False

Temperature also changes

Question 11

What transfers happen during drying?

Answer 11

heat transfer from heating source to the product, and mass transfer of moisture from internal to surface then surface to surrounding

Question 12

In practice, heat can be transferred to drying materials through what modes?

Answer 12

Convection
Conduction
Radiation
Microwave
Radiofrequency
Joule heating

Question 13

Name 4 drying methods

Answer 13

spray drying, convective drying, vacuum drying and microwave drying

Question 14

Which 2 factors should be considered to preserve the stability of moisture sensitive medicines during storage?

Answer 14

temperature (reduction of water solubility in air and condensation) & (air exchange (avoid saturation of drying air

Question 15

Paper is non-hygroscopic. True or false?

Answer 15

False, it is hygroscopic

Question 16

When there is less moisture in the air, paper releases moisture. True or false?

Answer 16

True

Question 17

When there is more moisture in the air, water absorbs moisture. True or false?

Answer 17

True

Question 18

What is meant by total moisture?

Answer 18

Total amount of water associated with a wet solid

total = free + equilibrium

Question 19

Free moisture content is the amount of water that can be easily removed. True or false?

Answer 19

true, also known as unbound water

Question 20

What is meant by equilibrium moisture content?

Answer 20

The portion of water that is more difficult to remove, also known as bound water

Question 21

What are the factors that need to be considered when selecting the drying method?

Answer 21

Heat sensitivity of materials used
Materials physical characteristics
Solvent/liquid to be removed e.g. boiling point
Efficient mass transfer of evaporated liquid
Efficient vapour removal from drying air
Amount of material to be processed e.g. scale up considerations
Sterility

Question 22

What are the advantages of a fluidised bed dryer?

Answer 22

Efficient heat transfer (minimise effects on thermo-sensitive materials), Homogenous process - movement of particles guarantees drying of all individual ones, Free movement of particles reduces the migration process and separation/aggregation phenomena

Question 23

What are the disadvantages of a fluidised bed dryer?

Answer 23

Turbulence might damage granules, Small particles might need specific attention to be removed from the fluidising air, Particle movement in turbulence and warm environment might cause charges of static electricity

Question 24

What are the advantages and disadvantages of microwave drying?

Answer 24

Adv: Rapid drying at controlled temp, energy absorbed in the wet material not in the air, stationary conditions decreases small particle movement , uniform heating reduces solute migration effect . Disadv – small batch size & shielding from radiation is essential

Question 25

Microwave drying has been used to process yeast, enzymes, small molecule pharmaceuticals and various biopharmaceuticals. True or false?

Answer 25

True

Question 26

Vacuum ovens are generally used for large scale processes. True or false?

Answer 26

false, small scale

Question 27

Which type of dryer is used with heat-sensitive materials?

Answer 27

Freeze dryer

Question 28

A spray dryer generates a large surface area to promote what?

Answer 28

heat exchange and heat transfer

Question 29

The higher the flow rate of a spray dryer, the smaller the droplets. True or false?

Answer 29

True

Question 30

In a vacuum oven, a temperature of 25-35 degrees is sufficient to boil water. This is convenient for thermo-sensitive drugs.

Answer 30

True

Question 31

What is solute migration?

Answer 31

movement of solution in a wet system during drying

Question 32

What is the difference between inter-granular migration and intra-granular migration?

Answer 32

inter-granular the solute moves between granules towards the surface but in intra-granular granules are separated during the process and there is even distribution of solute within a granule.

Question 33

Explain the impact of dew point on manufacture

Answer 33

During the drying process of temperature sensitive material it might be necessary to cool down the supplied air

Important to avoid to design a drying process with conditions close to the dew point

Question 34

Inhomogeneity between granules impact what?

Answer 34

Quality aspects
Dose
Manufacturing
Appearance

Therefore important to reduce solute migration

Question 35

How to reduce solute migration phenomena

Answer 35

Initial moisture content
Slow convective drying
Drying by microwave radiation
Dynamic drying methods (“granules in motion”)