drying

Question 1

what is drying?

Answer 1

removal of moisture, in particular water by: evapouration/ vaporisation / sublimation

Question 2

what are the aims of drying?

Answer 2

To improve product stability
To improve resuspensionor dissolution
To ensure processability
powder flow
reduced stickiness
Tabletability

Question 3

what does the equilibrium pressure- temperature diagram for water show?

Answer 3

a graph of pressure vs temp and the requirements for freezing/ evapouration/ sublimination

Question 4

in relative humidity how do air and water behave?

Answer 4

Air and water vapourbehave like ideal gases

Air and water are completely miscible

Question 5

what is the relationship like between the total pressure of air-water vapor mixture and partial pressures of air and vapor?

Answer 5

p=pa+pv

Question 6

why is there a restriction for relative humidity at a given temp?

Answer 6

at given temperature Pv≤ Ps(Ps: saturation vapour pressure of water)

Question 7

what is the equation for relative humidity?

Answer 7

=pv/px X 100%

Question 8

what is the dew point?

Answer 8

it is the cooling of air until pv exceeds ps for a given temp
liquid water will be deposited

Question 9

what are the requirements of the psychrometer to measure relative humidity?

Answer 9

• wick must be kept moist

- min air flow velocity of 3m/s

Question 10

how do you measure the relative humidity using the psychrometer?

Answer 10

measure the difference between the two thermometers

Question 11

what does an increase in the difference in the psychrometer indicate?

Answer 11

The difference increases with decrease in relative humidity

Question 12

what drying method would you use for a wet particle?

Answer 12

convective drying

Question 13

what would be an example of convective drying?

Answer 13

tray drier

Question 14

what would you use for convective drying of wet solids?

Answer 14

dynamic fluid bed dryer

Question 15

which is better a tray drier or a fluid bed dryer?

Answer 15

fluid bed drier-5% moisture content vs 10% for tray drying

Question 16

what occurs in convective drying of wet solids heat transfered during fluid bed drying?

Answer 16

gas to particle- convective particle
chamber wall to fluid bed- conductive aspect
particle to particle- smaller to coarser particles

Question 17

what are some of the advantages of fluid bed drying?

Answer 17

Eeffective heat and mass transfer
Temperature exposure of temperature labilematerial to heat is minimal
Drying of individual particles
Precise control of bed temperature

Question 18

what are some of the disadvantages of fluid bed drying?

Answer 18

Attritiondue to turbulent air flow
Fine particle elutriation
Electrostatic charging
restriction- insufficient fluidisation of particles below 100 or above 1000um

Question 19

what is an example of conductive drying for wet solids?

Answer 19

vaccum oven

Question 20

what are some of the advantages of vaccum oven?

Answer 20

Drying at low temperatures

Minimum risk of oxidation

Question 21

what are some of the advantages of microwave drying?

Answer 21

Rapid drying at low temperatures
High thermal efficiency
Uniform heating of the wet mass
Granulation end point: microwave energy rises when there is little solvent in the wet mass

Question 22

what are some of the disadvantages of microwave drying?

Answer 22

Batch size is smaller compared with that of fluid-bed driers
Care: microwave radiation can harm operators

Question 23

what are the applications of drying using fluid bed dryer and vaccuum oven ?

Answer 23

analyse drying conditions/ dissolution time/ disintegration time na dtensile strength

Question 24

what affects does drying of pelets have?

Answer 24

improve drug dissolution

Question 25

what is freeze drying also known as?

Answer 25

lyophilisation

Question 26

what is freeze drying?

Answer 26

removal of moistire in particular water by sublimination ( ice- gas without passing through the liquid state)

Question 27

what are the aims of freeze drying?

Answer 27

to dry heat sensitive materials without damage e.g.- proteins or blood products

Question 28

what pressure is used in freeze drying?

Answer 28

Solid ice maintained below triple point pressure (610 Pa)

Question 29

what occurs in freeze drying?

Answer 29

sublimination

Question 30

what are the min freezing temp’s in sublimination?

Answer 30

pharmaceutical material :-40–50

biological material -10 to -30

Question 31

what are the 4 stages of the freeze drying process?

Answer 31

freezing stage-
vacuum stage
primary drying
secondary drying

Question 32

what happens in the freezing stage?

Answer 32

Eutectic formation- not as good freezing

Glass formation- good freezing

Question 33

what is the differnce in primary and secondary drying in the freeze drying process?

Answer 33

1= sublimination of ice and vapour removal
2= for bound water desorption

Question 34

what is the residual moisture content for primary freeze drying?

Answer 34

about 6%

Hence, secondary drying is required to reduce the residual moisture content to optimum value (<1%

Question 35

what size particles can lyophilisation analyse?what else does it analyse?

Answer 35

particles down to nano meters

particle size, zeta potential, and dynamic viscosity

Question 36

what is the cycle summary of freeze drying?

Answer 36

During freezing, water crystallises as ice, therefore the concentration of solutes increases and changes the solution from a viscous liquid to a glass
The temperature for this transition is called glass transition temperature (Tg)of the freeze concentrate (Tg) represents the optimal temperaturefor primary drying Secondary drying removes the non-frozenor bound water at elevated temperature
The shelf life of the product depends on the residual moisture content

Question 37

what happens if you go above the critical parameters?

Answer 37

T`g
Tcol (collapse temperature)
Tcry (crystallisation temperature)
Teut (eutectic temperature)

Question 38

what kind of stabilising additives do you add to freeze dried products?

Answer 38

Sugars: sucrose, trehalose, and lactose
Polyols: glycerol Amino acids: glycine and alanine
Salts: organic or inorganic
Polymers: dextrane, poly vinyl alcoholand carboxymethyl cellulose
Surfactants: Tween 80

Question 39

what are some advantages of freeze drying products?

Answer 39

Drying at very low temperatures
Enhancement of product solubility
Preparation of stable pharmaceutical products
No contact with air

Question 40

what are some disadvantages of freeze dry products?

Answer 40

Freeze dried products are very hygroscopic
Very slow process
Difficult to control the particle size of the solid

Question 41

what are some of the pharmaceutical applications of freeze drying?

Answer 41

Used for drying of heat sensitive products for example: antibiotics, blood products and vaccines
Development of solid protein pharmaceuticals (for long term storage)
Instantaneously dissolving tablets Lyophilised nasal inserts
Drying of micro-and nano-particles

Question 42

what would not be ideal with a freeze dry product?

Answer 42

for it to collapse