Industrial Pharmacy I - suli-pharma.com · 1/10/2017 Industrial Pharmacy I 3 . Outlines • Mixing definition and mechanism of fluid mixing • Batch mixing • Impeller • Air jet

University of Sulaimani School of Pharmacy

Dept. of Pharmaceutics 5th stage

Industrial Pharmacy I

Dr. rer. nat. Rebaz H. Ali

1/10/2017 Industrial Pharmacy I 1

Eman 2016

Typewriter

2


Outlines

1. Principles of pharmaceutical processing

• Mixing

• Milling

• Drying

• Compression and consolidation of powdered solids

2. Pharmaceutical dosage form design

• Preformulation

3. Pharmaceutical dosage forms

• Sterilization

Reference: the theory and practice of industrial pharmacy by Leon Lachman


Outlines

• Mixing definition and mechanism of fluid mixing

• Batch mixing

• Impeller

• Air jet

• Fluid jet

• Continues mixing

• Mixer selection

• Mechanism of solid mixing


Mixing

• Mixing is defined as a process that tends to result in a randomization of dissimilar

particles within a system.

Objectives

1. To make simple physical mixture, as in production of tablet, capsules, creams and

etc.

2. Physical changes as preparation of solutions.

3. Promotion of reaction.


Types of mixing

1. Positive

• They are formed from materials such as gases or miscible liquids, which mix

spontaneously and irreversibly.

2. Negative

• After mixing, the components will tend to separate out.

• Energy must be continuously input to keep the components in dispersed state like

Calamine lotion.

3. Neutral

• They are static in their behavior, the components having no tendency to mix

spontaneously, nor do they segregate when mixed, like ointments, paste, mixed

powders.


Mechanisms of liquid-liquid mixing

1. Bulk transport: is the movement of a relatively large portion of the material being

mixed from one location in the system to another which accomplished by means of

paddles or revolving blades.

2. Turbulent mixing: it characterizes by random fluctuation of the fluid velocity at any

given point within the system

• The fluid has different velocities at different locations at the same time.

• Turbulent flow can be conveniently visualized as a composite of eddies of

various sizes.

• An eddy is a portion of fluid moving as a unit in a direction often contrary to

that of the general flow.

• Large eddies tend to break up; forming eddies of smaller and smaller size until

they are no longer distinguishable.


Mechanisms of liquid-liquid mixing cont.

• Scale of turbulence: is the size distribution of eddies within a turbulent region,

when small eddies are predominant, the scale of turbulence is low.

• Intensity of turbulence: is the velocities of the eddies.

3. Laminar mixing: (streamline) is frequently encountered when highly viscous fluids

are being processed.

• It can also occur if stirring is relatively gentle.

• The velocity components at a given point in the flow field remain constant.

4. Molecular diffusion: is the primary mechanism for mixing at the molecular level

resulting from the thermal motion of the molecules.


Degree of mixing

• The degree of mixing is described by scale and intensity of segregation

A. Scale of segregation

• Linear scale which represent an

average value of the diameter of

the lumps present,

• Volume scale roughly corresponds

to the average lump volume.

B. Intensity of segregation is a measure of the variation in composition among

the various portions of the mixture

• When mixing is complete; the intensity of segregation is zero.


Outlines


• Batch mixing

• Impeller

• Air jet

• Fluid jet


• Mixer selection



Batch mixing

• Batch mixing: a system for batch mixing commonly consist of two components:

1. A tank or other container suitable to hold the material being mixed,

2. A means of supplying energy to the system so as to bring about rapid mixing.

• Power may be supplied to the fluid mass by means an impeller, air

stream, or liquid jet.

• Baffles, vanes or ducts also are used to direct the bulk movement of

material so as to increase their efficiency.


Batch mixing

Factors affecting the flow pattern of liquids:

• Form of impeller and its position; e.g. whether it is high or low in the vessel,

whether mounted centrally or to one side, or whether the shaft is vertical or

inclined.

• Container shape.

• Presence of baffles.

• Liquid properties.

• High viscosity, such as paste, will need a D/d ratio of 1 and low speed of

rotation.


Impellers

Mixing equipment for liquid

1. Impeller: is the rotating part of a machine which imparts energy to the liquid to be

moved.

• The distinction between impeller types is often made on the bases of type of flow

pattern they produce, or on the basis of the shape and pitch of the blade.

• Three basic of flow may be produced:

A. Tangential

B. Radial

C. Axial or longitudinal


Impellers cont.

A. Propeller mixers

• The propellers are small impellers that produce a

longitudinal movement of liquids.

• They generally operates at high speeds: up to 8000 rpm.

• Propeller mixer is not normally effective for liquids of

high viscosity.

Vortexing and its remedies

• Due to the high speed of the propellers, air may get

entrapped which may be difficult to remove from the

product.

fig (a) fig (b)

fig (c) fig (d)

fig (e)

fig (f)


Impellers cont.

B. Turbine mixers

• A turbine mixer uses a circular disc impeller, to which are attached a number of

vertical blades, which may be straight or curved.

• The blades are usually flat, hence, very little axial or tangential flow, the liquid moves

rapidly in a radial direction.

• They can deal with more viscous liquids than the propeller mixer


Impellers cont.

C. Paddle mixers

• Paddle mixers consists of flat blades attached to a vertical shaft and rotating at low

speed (50-100 rpm).

• Their blades have a large surface area in relation to the tank in which they are

employed, a feature that permits them to pass close to the tank walls and effectively

mix viscous liquids or semisolids, which tend to cling to these surfaces.


Impellers cont.

• Baffles: they are auxiliary devices for directing the flow of the fluid.

• Sidewall baffles, when vertically mounted in cylindrical tanks, are effective in

eliminating excessive swirl and further aid the overall mixing process by inducing

turbulence.

Baffles


Batch mixing

2. Air jets: the liquids must be of low viscosity, non-foaming, un-reactive with the gas

employed, and reasonably nonvolatile.

• The jets are usually arranged so that the buoyancy of the bubbles lifts liquids

from the bottom to the top of the mixing vessel.

3. Fluid jet: used when liquids are to be pumped into a tank for mixing.


Outlines


• Batch mixing

• Impeller

• Air jet

• Fluid jet


• Mixer selection



Continuous mixing

• Continuous mixing: is an uninterrupted supply of freshly mixed material and is

often desirable when very large volumes of material are to be handled.

• It can be accomplished essentially in two ways:

• in a tube or pipe through which the material flows and in which there is very

little back flow or recirculation,

• or in a chamber in which a considerable amount of holdup and recirculation

occur.


Outlines


• Batch mixing

• Impeller

• Air jet

• Fluid jet

• Baffles


• Mixer selection



Mixer selection

• Factors that must be taken into consideration include:

1. The physical properties of the materials to be mixed such as density, viscosity,

and miscibility

2. Economic considerations regarding processing, e.g. time required for mixing

and the power expenditure necessary.

3. Cost of equipment and its maintenance.

• Monophase systems: Fluids of relatively low viscosity are best mixed by methods

that same time circulate the entire mass of material.

• For this, air jets, fluid jets, and the various high-speed impellers can be used.

• Thick creams, ointments, and pastes are of such high viscosity that it is difficult to

generate turbulence within their bulk and relied on laminar mixing.

• Mixing of such fluids may be done with turbine of flat blade design


Mixer selection

• Polyphase systems: the mixing of systems composed of several liquid or solid phase.

In a general, the processes of homogenization, suspension formation, and

emulsification may be considered forms of mixing.

• The mixing of two immiscible liquids requires the subdivision of one of the phases

into globules, which are then distributed throughout the bulk of the fluid.

• The interfacial tension of the globules tends to resist the distortion of globules

shape that necessary for fragmentation into smaller globules

• Forces of shear act to distort and ultimately disrupt the globules (homogenizer).


Roller mill

• Roller mill

• Three roll tube is preferred for semisolid preparations.

• The rollers rotate at different speed.

Scrapper


Outlines


• Batch mixing

• Impeller

• Air jet

• Fluid jet

• Baffles


• Mixer selection


• Equipment


Solid mixing

Forces acting in multi-particulate solids systems are essentially of two types:

A. Force that tend to result in movement of two adjacent particles or groups of

particles relative to each other

• Such motion can result either from contact with the mixer surfaces or from

contact with other particles.

B. Force that tend to hold neighboring particles in a fixed relative position.

• It results from interparticulate interactions associated with the size, shape, and

surface characteristics of the particles themselves.

• Powders that have high cohesion forces have more resistant to mixing.

• Surface charge, and adsorbed substances such as moisture among factors that

increased cohesiveness.


Segregation

• Particulate solids tend to segregate because of difference in their size, density and

shape.

• It is most pronounced with free-flowing powders and less with powder having high

cohesion and adhesion, due to high interparticulate force.


Outlines


• Batch mixing

• Impeller

• Air jet

• Fluid jet

• Baffles


• Mixer selection


• Equipment


Tumbling mixer

• Used for mixing / blending of granules or free-flowing powders

• It consists of a container of one of several geometric forms, which is mounted so that

it can be rotated about an axis.

• The tumbling motion is accentuated by means of baffles or simply by virtue of the

shape of the container.

• Examples like drum, cubical-shaped, double-cone and twin shell blenders

• Tween shell is the most efficient one!


Tumbling mixer cont.

The efficiency of tumbling mixers is highly dependent on the speed of rotation.

• Rotation that is too slow does not produce the desired intense tumbling or

cascading motion, nor does it generate rapid shear rates.

• Rotation that is too rapid tends to produce centrifugal force sufficient to hold

the powder to the sides of the mixer and thereby reduce efficiency.

• The optimum rate is 30 to 100 rpm.


Agitator mixer

• This type of mixers employs a stationary container to hold the material and brings

about mixing by means of moving screws, paddles or blades.

• Use: Since the mixing process does not depend on gravity as do the tumblers, it is

useful in mixing wet solids, sticky pastes etc.

• Ribbon mixer

• It consists of horizontal cylindrical tank usually opening at the top and fitted with

helical blades.


Nautamixer

• Conical orbital screw mixer (Nautamixer)

• It consists of a conical vessel fitted at the base with a rotating screw, which is

fastened to the end of a rotating arm at the upper end.

• The mixer thus combines convective mixing and shear and diffusive mixing

Motor

Rotating arm

Helical conveyor

Discharge

Fig. Conical orbital mixer (Nautamixer)


Thank you for your attention!

Documents

Industrial Pharmacy I - suli-pharma.com · 1/10/2017 Industrial Pharmacy I 3 . Outlines • Mixing definition and mechanism of fluid mixing • Batch mixing • Impeller • Air jet