This document provides an overview of various drying techniques used in pharmaceutical engineering. It discusses the objectives, mechanisms, and principles of operation for common dryers like tray dryers, drum dryers, spray dryers, fluidized bed dryers, vacuum dryers, and freeze dryers. The document also covers topics like drying applications, measurements of equilibrium moisture content, and rate of drying curves. Overall, it serves as a comprehensive introduction to drying as a crucial process in pharmaceutical manufacturing.

1. PHARMACEUTICAL ENGINEERING
B. Pharma
3rd Semester
Unit -3
Presented by – Nikita Gupta
( Assistant Professor )

2. Chapter - 7
Drying

3. Syllabus
• Drying
• Objectives
• Applications
• Mechanism of drying process
• Measurements & applications of Equilibrium Moisture
content
• Rate of drying curve

4. • Principles, construction, working, uses, merits and
demerits of
• Tray dryer
• Drum dryer
• Spray dryer
• Fluidized bed dryer
• Vacuum dryer
• Freeze dryer

5. Drying
Drying is a mass transfer process consisting
of the removal of water or another solvent
by evaporation from a solid, semi-solid or
liquid.

6. Objectives
(i) To overcome common challenges in pharmaceutical
drying development, including material constraints for
scale-up studies and transferring to different equipment
types and sizes.
(ii) To understand drying development related to chemical
and physical stability, drying kinetics, and powder
properties and highlights common development gaps for
improving drying development workflows within the
industry.

7. (iii) To encourage further fundamental research and
technological advancements for improving the drying
process.
(iv) Other objectives are to carry outsize reduction, to avoid
deterioration on storage, to dry the tablet granules to reduce
the moisture, to reduce the bulk and weight to lower
transportation charges and for certain preparations such as
spray dried lactose.

8. (v) To design and produce a dryer that conserves
energy consumption for optimal utilization in terms of
acquisition and operating cost and with optimal local
content and versatility.
(vi) To understand the impact of factors and establish
the product specifications, as well as the nature and
limits of residual solvents, in agreement with current
regulations.

9. Applications
In the manufacturing of pharmaceuticals, the last stage of
processing is drying, which is carried out for one or more of
the following applications:
1.Drying is used to remove excess moisture or other volatiles
from coatings and various substrates.
2. It is used to reduce and control moisture levels in solid
materials in the manufacture of many materials.
microbiological cultures, hormones and antibiotics

10. 3.It is most important in the processing of highly thermolabile
products which are not stable in liquid form. The lyophilization
enables longer shelf life of thermolabile materials and make them
suitable for storage and transport of the product.
For example, drying of biological products such as blood plasma,
vaccines, enzymes
4. Drying is necessary to make material light in weight that help to
reduce the cost of transportation of large volume materials
(liquids).

11. 5. Drying is used to make the material easy or more suitable for
handling and processing. In the manufacturing of bulk drugs or for
large-scale production of synthetic drugs, drying is essential to get
free-flowing materials. For example, dried aluminum hydroxide,
spray-dried lactose, etc.
6. Drying is used as the final step in evaporation, filtration, and
crystallization and to preserve materials from environmental
factors.

12. 7. Drying is used to maintain and improve shelf life of
thermolabile and hydrolytic substances for longer period of
time. It is necessary to avoid deterioration of blood products,
skin and tissue that undergo microbial decomposition.
8. Drying significantly decreases rate of chemical reactions as
well as chances of microbial attack or enzymatic actions and
thus improves stability

13. Mechanism of drying process
• Drying is governed by the principles of heat and
mass transfer.
• When a moist solid is heated to an appropriate
temperature, moisture vaporizes at or near the solid
surface.
• The heat required for evaporating moisture from
the drying product is supplied by hot air or a gas.
• Drying involves diffusion in which the transfer of
moisture to the surrounding medium takes place by
the evaporation from the surface.

14. • As some of the moisture from the surface vaporizes more
moisture is transported from bulk of the solid to its surface.
• The mechanism involved in moisture transport in those solids
is classified as:
(i) Transport by liquid or vapors diffusion
(ii) Capillary action
(iii) Pressure-induced transport.

15. • A specific mechanism that involves in drying a specific solid
depends on its nature, pore structure and the rate of drying.
• Moisture content of a substance which exerts as equilibrium
vapors pressure less than of the pure liquid at the same
temperature is referred to as bound moisture.
• Moisture content of the solid which exerts an equilibrium
vapour pressure equal to that of pure liquid at the given
temperature is the unbound moisture.

16. Measurements & applications of Equilibrium
Moisture content
Rate of drying in a bed of powder:
The rate at which drying occurs has been found to show certain phases in
which the change in moisture content is plotted against time.
From A to B the relationship is linear, which is known as the constant-rate
period , whereas from B to C the rate of loss of moisture decreases and is
known as the falling-rate period. The endof the constant rate period, B,is
referredto as the critical moisture content.

18. The first falling- rate period has
a linear relationship, that is , the decrease in drying rate is uniform,
whereas in the second falling-rate period there is a continuous decrease
in the rate of drying until the EMC is reached.
Constant-rate period: The evaporation rate from the drying bed is
similar to that of the solvent alone from a free liquid surface under the
same conditions, indicating that the evaporation takes place from the wet
surface of the solid, and that the surface remains wet in this period as a
result of the liquid being replaced from below as fast as it is vaporized.

19. First falling-rate period: As moisture is removed from the surface,
a point will be reached when the rate of vaporization is insufficient
to saturate the air in contact with the surface. Under these
conditions, the rate of drying will be limited by the rate of capillary
transfer of the liquid to the surface of the wet bed , and this
becomes increasingly difficult as the bed dries, the solvent level
decreases and thus has further to travel to the point of evaporation .
Consequently, the rate of drying decreases continuously.

20. Second falling-rate period: Any moisture that remains within
the drying bed at the end of the first falling rate period is unable
to move, so that drying cannot take place on the surface. i.e. the
drying rate depends on the movement of the vapour through the
pores of the bed to the surface, in general by molecular
diffusion.

21. Rate of drying curve

22. Tray dryer
Principal - In tray dryer hot air is continuously passed over wet
mass. Heat transfer takes place by forced convection.
Tray Dryer is the most commonly used dryer.
Tray dryer is the device used for drying of wet products of the
crude drugs, chemicals, powders or the granules, etc.

23. Principle of Tray Dryer. In tray dryer, hot air is continuously
circulated.
Forced convection heating takes place to remove moisture
from the solids placed in trays.
Simultaneously , the moist air is removed partially.

25. Drum dryer or Roller Dryer
Principle - In drum dryer heated hollow cylindrical drum is
rotate on longitudinal axis, which is dipped into the solution
to be dried. The solution is carried as a film on the surface
of the dryer and dried to form a layer. Dried material is
removed with the help of the knife.

27. Spray dryer
Spray drying is a method of changing a dry powder from a
liquid or slurry by rapidly drying with a hot gas. This is the
preferred method of drying of many thermally-sensitive
materials such as foods and pharmaceuticals,

29. Fluidized bed dryer
Principle - The bottom of the fluidized-bed dryer is
perforated, where hot air moves through the granules to be
dried. The granules rise from the bottom of the air stream as
they are suspended in it. The process is known as fluidization
To dry each granule completely, hot air surrounds it. This
results in uniform drying of the materials.

31. Vacuum dryer
Vacuum drying is the mass transfer operation in which the
moisture present in a substance, usually a wet solid, is
removed by means of creating a vacuum.

32. Principle - By creating a vacuum, moisture present in a wet solid
is removed during vacuum drying.
In this process, there is an attempt to lower the pressure beneath
the water's vapor pressure by creating a vacuum.
Drying substances are made possible by reducing the pressure
around them using vacuum pumps.
Consequently, the boiling point of water inside of the product is
lowered, increasing evaporation rates tremendously.

34. Freeze dryer
Freeze-drying or lyophilization is a drying process used to
convert solutions of labile materials into solids of sufficient
stability for distribution and storage.

35. Principle - The main principle involved in lyophilization is a
phenomenon called sublimation. The water passes directly from
the solid-state (ice) to the vapor state without passing through the
liquid state. Water is removed from the frozen state material and
then subjected to high vacuum to heat (by conduction or radiation
or by both) so that the sublime frozen liquid leaves only solids or
the dry components of the original liquid. Drying is achieved by
subjecting the material to temperature and pressures below the
triple point.

37. Chapter - 8
Mixing

38. Syllabus
• Mixing
• Objectives
• Applications
• Factors affecting mixing
• Difference between solid and liquid mixing
• Mechanism of solid mixing
• Liquids mixing and semisolids mixing.

39. Principles, Construction, Working, uses,
Merits and Demerits of -
• Double cone blender
• Twin shell blender
• Ribbon blender
• Sigma blade mixer
• Planetary mixers
• Propellers
• Turbines
• Paddles
• Silverson Emulsifier

40. Mixing - Mixing may be defined as a unit
operation in which two or more components,
in an unmixed or partially mixed state, are
treated so that each unit (particle, molecule
etc.) of the components lies as nearly as
possible in contact with a unit of each of the
other components.

41. Objective
 To ensure uniformity .
 To initiate or to enhance the physical or
chemical reactions e.g. diffusion, dissolution
etc.
 To make the following products:
 Tablets
 Suspensions
 Emulsions
 Pastes
 Creams

42. Applications
➢ Mixing is an intermediate step in production
of tablet or capsule. Mixing of powders in
different proportion prior to granulation or
tableting.
➢ Dry mixing of materials for direct
compression in to tablets.
➢ Dry mixing of powder or composites
powders in capsule and insufflations
respectively.

43. ➢ Blending of powders are also important in
preparation of cosmetic products such as facial
powder or dental powder.
➢ In case of potent drugs where dose is low,
mixing is critical factor. Otherwise it will affect
content uniformity of tablet
 Dispersion - In suspension and pastes solid
particles are dispersed in a liquid by mixing.
 Promotion of reaction - Mixing encourages
and controls a chemical reaction, so ensuring
uniform products.

44. • Factors affecting mixing
1. Nature of product: For effective mixing
particle surface should be smooth.
2. Particle size: It is easier to mix powder of
same particle size. Increasing the difference
in particle size will lead to segregation.
3. Particle shape: Particle should be spherical
in shape to get a uniform mixture.

45. 4. Particle charge: some particle due to
electrostatic charge exerts attractive force which
leads to separation.
5. Proportion of material: It is easier to mix
powders if available in same quantities.
6. Relative density: If the components have a
different density, the denser material will sink
through lighter material.
7. Viscosity: An increase in viscosity reduces the
extent of mixing.

46. 8. Surface tension of liquids: High surface tension
reduces the extension of mixing.
9. Temperature: Temperature also affects the mixing
because viscosity changes with increase in temperature.
10. Mixture volume: Mixing efficiency depends on
mixture volume.
11. Agitator type: The shape, size, location and type of
agitator also affect affects the degree of mixing.
12. Speed/rpm of the impeller: Mixing at less rpm is
more homogenous than at higher rpm.
13. Mixing time: Mixing time is also very important for
appropriate mixing.

47. Difference between solid and liquid mixing
Mechanism of Solid Mixing: Mechanism in
involved in solid mixing are Convective
mixing, In which group of particles move
from one position to another. It also referred
to as macromixing.
Shear mixing - In this, shearing force is
created within the mass of material by the use
of a stirring arm or a burst of air.

48. Diffusive mixing - During this mixing,
gravitational forces cause the upper layers of
material to slip and random motion of
individual particles take place on newly
developed surfaces. Also known as micro
mixing
Mechanism of Liquid Mixing: Mechanism
of liquid mixing are Bulk transport. It is the
movement of large portion of material from
one location to another location. The
movement is done by rotating blades or
paddles.

49. Turbulent mixing: In this mixing is due to
turbulence. Turbulence is a function of velocity
gradient between two adjacent layers of a liquid.
Laminar mixing/Streamline mixing: When two
dissimilar liquid are mixed through a laminar
flow, the shear that is generated stretches the
interface between them.

50. Molecular diffusion: The mechanism
responsible for mixing at molecular level is
the diffusion resulting from thermal
movement of molecules.
Primary mechanism responsible for mixing at
the molecular level is the thermal motion of
molecules.
Mechanisms of Semi-Solid Mixing: The
mechanisms involved in mixing semi solids
depend on the character of the material

51. Double cone blender
Principles of Double Cone Blender:
• Materials being blended are constantly
being intermixed as the Double Cone
rotates.
• Normal cycle times are typically in the
range of 10 minutes.
• The slant double cone design eliminates
dead spots which occasionally occur in
conventional double cone mixer.

52. • The conical shape at both ends enables
uniform mixing and easy discharge.
• The cone is statically balanced which
protects the gear box and motor from any
excessive load.
• Powder is loaded into the cone through a
wide opening and discharged through a
butterfly or a Slide valve.

53. • Depending upon the characteristic of
the product, paddle type baffles can
be provided on the shaft.
• Dust free bin charging system
ensures minimum material handling.
• Mixing, uniform blending and de-
agglomeration.

55. Twin shell blender
Principle of Twin Shell Blender: The mixing occurs due
to tumbling motion.

56. Ribbon blender
Principle of Ribbon Blender:
• The mechanism of mixing is shear
which is transferred by moving blades
(ribbon shaped) in a fixed (non-
movable) shell.
• Convective mixing is the macro
movement of large portions of the
solids

57. • Convection mixing occurs when
the solids are turned over along the
horizontal axis of the agitator
assembly.
• High shear rates are effective in
breaking lumps and aggregates.
• An equilibrium state of mixing can
be achieved.

59. Sigma blade mixer
Principle of Sigma Blade Mixer:
• The mechanism of mixing is shearing.
• The inter meshing of sigma shaped blades
creates high shear and kneading actions.
• The mixing action is a combination of bulk
movement, shearing, stretching, folding,
dividing, and recombining as the material is
pulled and squeezed against blades, saddle,
and side walls.
• This is used for high viscosity material.

61. Planetary mixers
Principle of Planetary Mixer:
The principle of planetary mixers is very
simple, which usually have two or three multi
hinged blades, when the paddles are revolution
and rotation running at the same time, so that
the material will flows up and down as well as
around the inner cylinder, which can reach the
mixing effect in a very short time. It is also
known as change can mixer

62. • The Planetary Mixer have two blades
which rotate on their own axes, while
they orbit the mix vessel on a common
axis.
• The blades continuously advance along
the periphery of the vessel, removing
material from the vessel wall and
transporting it to the interior.
• These mixers are ideal for mixing and
kneading viscous pastes or putty-like
materials

64. Propellers - Propellers are the mechanical device
that are used to mix liquid materials using blades.
• A three bladed design is generally used for
liquids
• Principle of Propeller Mixer: The propeller
mixer mainly works on the principle of
shearing force.
• It consists of vessel and propeller.
• A propeller has angled blades, which cause
the fluid to circulate in both an axial and
radial direction.

66. Turbines –
Principle of Turbine Mixer
• A turbine mixer is a mechanical device
that is used in mixing different type of
liquids.
• The turbine mixer works mainly on the
principle of shearing action.

67. Construction of Turbine Mixer:
• Turbine consists of number of blades
attached to the circular disk.
• The blades used in the mixture are of
various types:- flat blades, disk-type flat
blades, inclined blades, curved blades,
arrow headed blades, and so on.
• The diameter of turbine varies from 30
to 50 percentage of the diameter of
vessel.
• As compared to propeller turbines
rotates at lower speed.

69. Paddles
Principle of Paddles:
Paddles consist of two long flat blades
attached vertically to a shaft.
It rotates at low speed.
Paddle mixer is suitable to mix viscous
liquids or semisolids.
Construction of Paddles: Blades used in this
mixer are dished or hemispherical in shape.
The diameter of paddle is 50-80 percentage
of inside diameter of vessel.

71. Silverson Emulsifier - In silverson
homogenizer the droplets are subjected to a high
shear rates.
It consists of an emulsifying head to which
blades are attached , surrounded by a fine mesh
sieve made up of a stainless steel .
The emulsifying head is immersed in the liquid
to be emulsified.
The head is rotated by a small motor at very
high speed.

72. The liquids to be mixed are sucked through fine mesh
into the base of the emulsifying head where they are
subjected to vigorous mixing by high speed rotation
of blades.
The mixed material is then expelled with a great
force through the sieve band.
This sucking in and forcing out sets up a pattern of
circulation, and thus large size globules are reduced
to small size globules.

74. Thank You
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