Drying lecture 20

Question 1

Why is drying important in quality tests, in what concepts?

Answer 1

flowability
stability
dry granulation
compaction

Question 2

Define moisture content:

Answer 2

the amount of water contained in a material

Question 3

Define Mv:

Answer 3

% moisture by volume: the molecules of water per unit volume by the total number of molecules per unit volume

Question 4

Define relative humidity:

Answer 4

the amount of moisture in the air as a % of the max amount of moisture that the air can hold

Question 5

What is the relation between temp, RH and water vapour?

Answer 5

the higher the temp, the more water vapour that the air can hold and so there is a decrease in RH

Question 6

Define dew point:

Answer 6

just as increasing temp decreases RH, decreasing temp will increase RH and when RH reaches 100%, water vapour will condense to form dew

Question 7

During drying, what 2 factors can change?

Answer 7

1. moisture content (water can evaporate)

2. temperature (can decrease to reduce heat-exchange with the material)

Question 8

Define hygroscopic substances:

Answer 8

attract and hold water molecules from the surrounding environment e.g. paper (if less moisture in the air, paper will release water) and some plastics

Question 9

Total moisture = …

Answer 9

FREE (unbound) + EQUILIBRIUM (bound)

Question 10

How can equilibrium moisture be varied?

Answer 10

by varying external conditions such as adding a desiccant like silica gel or phosphorous pentoxide to reduce RH

Question 11

What are the 2 types of solute migration?

Answer 11

1. inter-granular migration = solute moves between granules towards the surface (differences in solute composition between granules)
2. intra-granular migration = granules are separated during the process (even distribution of solute within a granule)

Question 12

How can you reduce solute migration (to ensure homogeneity)?

Answer 12

a) Initial moisture content
b) Slow convective drying
c) Drying by microwave radiation
d) Dynamic drying methods

Question 13

What are the 3 methods to dry wet solids?

Answer 13

1. fluidised bed dryer (convection)
2. microwave (radiation)
3. vacuum oven (conduction)

Question 14

What are the 2 methods to dry solutions and suspensions?

Answer 14

1. spray dryer

2. freeze-drying

Question 15

Why is solvent removal useful?

Answer 15

to prevent chemical and microbial degradation

Question 16

Is a low temp or high temp better to prevent drug degradation?

Answer 16

low