drying Flashcards

1
Q

what is drying?

A

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

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2
Q

what are the aims of drying?

A
To improve product stability
To improve resuspensionor dissolution
To ensure processability
powder flow
reduced stickiness
Tabletability
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3
Q

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

A

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

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4
Q

in relative humidity how do air and water behave?

A

Air and water vapourbehave like ideal gases

Air and water are completely miscible

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5
Q

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

A

p=pa+pv

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6
Q

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

A

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

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7
Q

what is the equation for relative humidity?

A

=pv/px X 100%

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8
Q

what is the dew point?

A

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

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9
Q

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

A
  • wick must be kept moist

- min air flow velocity of 3m/s

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10
Q

how do you measure the relative humidity using the psychrometer?

A

measure the difference between the two thermometers

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11
Q

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

A

The difference increases with decrease in relative humidity

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12
Q

what drying method would you use for a wet particle?

A

convective drying

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13
Q

what would be an example of convective drying?

A

tray drier

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14
Q

what would you use for convective drying of wet solids?

A

dynamic fluid bed dryer

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15
Q

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

A

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

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16
Q

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

A

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

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17
Q

what are some of the advantages of fluid bed drying?

A

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

18
Q

what are some of the disadvantages of fluid bed drying?

A

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

19
Q

what is an example of conductive drying for wet solids?

A

vaccum oven

20
Q

what are some of the advantages of vaccum oven?

A

Drying at low temperatures

Minimum risk of oxidation

21
Q

what are some of the advantages of microwave drying?

A

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

22
Q

what are some of the disadvantages of microwave drying?

A

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

23
Q

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

A

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

24
Q

what affects does drying of pelets have?

A

improve drug dissolution

25
what is freeze drying also known as?
lyophilisation
26
what is freeze drying?
removal of moistire in particular water by sublimination ( ice- gas without passing through the liquid state)
27
what are the aims of freeze drying?
to dry heat sensitive materials without damage e.g.- proteins or blood products
28
what pressure is used in freeze drying?
Solid ice maintained below triple point pressure (610 Pa)
29
what occurs in freeze drying?
sublimination
30
what are the min freezing temp's in sublimination?
pharmaceutical material :-40--50 | biological material -10 to -30
31
what are the 4 stages of the freeze drying process?
freezing stage- vacuum stage primary drying secondary drying
32
what happens in the freezing stage?
Eutectic formation- not as good freezing | Glass formation- good freezing
33
what is the differnce in primary and secondary drying in the freeze drying process?
``` 1= sublimination of ice and vapour removal 2= for bound water desorption ```
34
what is the residual moisture content for primary freeze drying?
about 6% | Hence, secondary drying is required to reduce the residual moisture content to optimum value (<1%
35
what size particles can lyophilisation analyse?what else does it analyse?
particles down to nano meters | particle size, zeta potential, and dynamic viscosity
36
what is the cycle summary of freeze drying?
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 (T`g)of the freeze concentrate (T`g) 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
37
what happens if you go above the critical parameters?
T`g Tcol (collapse temperature) Tcry (crystallisation temperature) Teut (eutectic temperature)
38
what kind of stabilising additives do you add to freeze dried products?
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
39
what are some advantages of freeze drying products?
Drying at very low temperatures Enhancement of product solubility Preparation of stable pharmaceutical products No contact with air
40
what are some disadvantages of freeze dry products?
Freeze dried products are very hygroscopic Very slow process Difficult to control the particle size of the solid
41
what are some of the pharmaceutical applications of freeze drying?
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
42
what would not be ideal with a freeze dry product?
for it to collapse