Drying

Question 1

What is primary manufacturing?

Answer 1

Synthesis of Actives

Question 2

What is secondary manufacturing?

Answer 2

Production of dosage form

Question 3

What is easily removable water called?

Answer 3

Free moisture content or unbound water

Question 4

What does residual water content influence?

Answer 4

Stability, flow properties and compactability

Question 5

What is equilibrium moisture content?

Answer 5

Solids equilibrate with moisture present in the air

Question 6

Why is the absolute equilibrium moisture content dynamic?

Answer 6

Moisture content changes with temperature and humidity

Question 7

What is hygroscopicity?

Answer 7

How strongly a material absorbs moisture from the atmosphere

Question 8

What does the Karl-Fischer Potentiometric Titration do?

Answer 8

Measures the amount (moles) of water by the electrical conductivity of a REDOX titration

Question 9

How does the dynamic vapour sorption work?

Answer 9

Measures the weight change as a function of both temperature and humidity in an environmental chamber

Question 10

How does thermogravimetric analysis work?

Answer 10

Measures the weight change as a function of temperature

Question 11

When is humidity considered saturated?

Answer 11

When no more vapour can be taken up

Question 12

What is relative humidity dependent on?

Answer 12

Air temperature

Question 13

How does conduction drying work?

Answer 13

Heat is directly transferred through the material where there is a difference in temperature

Question 14

How does convection drying work?

Answer 14

Movement of particles through a substance, transporting their heat energy from hotter areas to cooler areas

Question 15

How does radiation drying work?

Answer 15

Emission of energy in the form of waves or particles

Question 16

What is latent heat?

Answer 16

Heat evolved or absorbed by a unit mass when it changes phase without a change in temperature

Question 17

What considerations should be made prior to drying?

Answer 17

Heat sensitivity of the material
Requirement for aseptic conditions
Nature of the liquid to be removed
Scale of operation
Physical characteristics of the material

Question 18

Are condensation and freezing exo- or endo- thermic?

Answer 18

Exothermic

Question 19

Definition of evaporation

Answer 19

To change from liquid state to vapour

Question 20

What is vapour pressure?

Answer 20

The pressure of a vapour in equilibrium with the liquid at any given temperature

Question 21

What happens to vapour pressure when a liquid boils?

Answer 21

The vapour pressure is equal to external pressure

Question 22

Equation for sensible heat

Answer 22

Q=mcΔT
m = mass of substance
c = specific heat capacity
T = change in temperature (K)

Question 23

Equation for latent heat?

Answer 23

Q=ml
m= mass of substance
l = heat absorbed or liberated in the change of phase of unit mass (JKg-1)

Question 24

What are advantages of a fluidised bed drier?

Answer 24

Efficient heat and mass transfer
Drying occurs from the surface of all individual particles
Short drying time

Question 25

What are disadvantages of fluidised bed drier?

Answer 25

Excessive attrition due to turbulent state Production of fine dust - must be filtered Generation of static electricity

Question 26

How does a spray drier work?

Answer 26

Solution is atomised by high pressure gradient through a nozzle Small spherical droplets are spread into a stream of hot air Evaporation of the solvent is extremely fast due to the very high surface area of the droplets Most of the heat is latent heat and so the particles don't overheat Each droplet dries to an individual solid partice

Question 27

What are the advantages of spray drying?

Answer 27

Millions of small droplets give a massive surface area so fast evaporation occurs Uniform and controllable particle size Single operation - low cost

Question 28

What are the disadvantages of spray drying?

Answer 28

Equipment is bulky Heat transfer from air is relatively inefficient

Question 29

When is spray drying used?

Answer 29

Drying solutions and suspensions High outputs of <2000kg/hr Can be aseptic

Question 30

What is solute migration?

Answer 30

Results from the movement of a solution within a wet formulation Solvent moves towards the surface of a solid taking undissolved solute with it Results in localised variation of solubilized formulation components

Question 31

When is intergranular solute migration common?

Answer 31

In static bed methods such as tray driers

Question 32

When is intragranular solute migration common?

Answer 32

In fluidised-bed and vacuum tumbling