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S2 Case 1 - IBD > Drying > Flashcards

Drying Flashcards

1
Q

What is drying?

A

Mass transfer of volatile component out of a solid-liquid mixture

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2
Q

What is drying important for?

A

Purification of drug + granulation for tabletting

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3
Q

What does moisture content effect?

A

Product stability
Physical properties

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4
Q

What can H2O do?

A

Cause microbial growth
Affect degradation = increase hydrolysis
Clump together = decrease flowability

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5
Q

What is a substance called that is normally a gas?

A

Gas

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6
Q

What is a substance called that is normally a liquid?

A

Vapour

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7
Q

What is it called when goes liquid to gas?

A

Vaporisation

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8
Q

Evaporation

A

Liquid surface only
= below boiling point

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9
Q

Boiling

A

Throughout body of liquid
= at boiling point only

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10
Q

Solid to gas

A

Sublimation

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11
Q

Gas to liquid

A

Condensation

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12
Q

Liquid to solid

A

Freezing

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13
Q

Gas to solid

A

Deposition

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14
Q

Solid to liquid

A

Melting

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15
Q

Liquid to gas

A

Vaporisation

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16
Q

What will it have if it has a large SA?

A

Effective heat transfer
Effective mass transfer

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17
Q

What is the equation for heat transfer?

A

Q = hAΔT
Q = heat transfer
h = heat transfer coefficient
A = SA
ΔT = Temp difference (k)

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18
Q

What is relative humidity (RH)?

A

H2O content in air
Affects eqm moisture content in solids

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19
Q

What RH equation?

A

RH (%) = Pcurrent
————-
Psaturation
p = partial pressure

20
Q

What does it mean higher relative humidity?

A

Closer to saturation point
= harder liquid is to evaporate
= lower drying rate

21
Q

What does it mean H2O evaporating off?

A

Increases surrounding humidity
= if vapour NOT cleared quickly
= drying decreases

22
Q

What does it mean if sample is in high humidity environment?

A

Sample gains moisture

23
Q

What is FMC?

A

Free moisture content
= unbound H2O
= readily removed by evaporation

24
Q

What is EMC?

A

Eqm moisture content (EMC)
= bound H2O
= NOT removed by evaporation

25
Q

How is bound H2O removed + problem?

A

Forcibly
= as soon as drying stops
= sample regains moisture

26
Q

WET —-> AIR-DRY —-> BONE-DRY

A

WET —-> AIR-DRY = remove FMC
AIR-DRY —-> BONE-DRY = remove EMC BUT has to be stored in protective environment

27
Q

What are the modes of heat transfer?

A

Convection
Conduction
Radiation

28
Q

What is convection?

A

Mass transfer of hot fluid

29
Q

What is conduction?

A

Heat transfer through contact with medium

30
Q

What is radiation?

A

Electromagnetic waves, no medium

31
Q

Describe static tray oven

A

Fan-assisted ventilation + vapour removal
Conduction

32
Q

What does drying rate depend on in static tray oven?

A

Thickness

33
Q

What is static tray oven susceptible to?

A

Solute migration

34
Q

Describe vacuum oven

A

Low pressure = evaporation at lower temp
Convection

35
Q

What does vacuum oven reduce risk of?

A

Oxidative degradation

36
Q

Describe oven drying

A

Heat absorbs moisture + fan removes it

37
Q

Describe solute migration

A

Solvent diffuses from centre of particle-to-particle surface
= brings dissolved solute with it
Solvent evaporates leaving behind solute concentrated at surface

38
Q

What does solute migration do?

A

Reduce content uniformity

39
Q

Describe microwave dryer

A

Uniform heating = reduces solute migration
High thermal efficiency

40
Q

What is pro of high thermal efficiency?

A

Rapid drying with loss of thermal stress

41
Q

Describe fluidised-bed dryer

A

Large drying SA = rapid drying
Particle movement prevents aggregation
Uniform heating
Particle attrition rounds particles = better flow

42
Q

What is fluidised-bed dryer only suitable for?

A

Granules

43
Q

Describe spray drying

A

Liquid samples
Suspension sprayed into hot air stream
Solvent evaporates, leaving behind solid
Particles collected

44
Q

Describe freeze-drying cycle

A

Cytoprotectants used
Primary drying
Secondary drying

45
Q

Describe primary drying
Freeze-drying cycle

A

Pressure lowered below solid-gas phase boundary
= sublimation
= bound moisture removed

46
Q

Describe secondary drying
Freeze-drying cycle

A

Warming under sustained low pressure
= desorption of bound moisture

47
Q

What are some particle considerations?

A

Sample type = solid/solution/suspension
Liquid to be removed = volatile/flammable
Extent of drying
Solute migration
Cost

S2 Case 1 - IBD (18 decks)

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