Pharmaceutical Engineering and Industrial Process Principles

Posted on Feb 16, 2026 in Electromechanical Engineering

Distillation Principles and Processes

Distillation is a process by which a liquid mixture is separated into fractions with higher concentrations of certain components by exploiting differences in relative volatility. Distillation is a separation process used to separate components of a liquid mixture based on differences in their boiling points. The process involves heating the mixture to vaporize the most volatile component(s), followed by cooling the vapor to condense it back into liquid form, thereby isolating the different components.

Steam Distillation

Principle: The principle behind steam distillation is a way of separating miscible liquids based on their volatilities. The boiling point of the products is minimized so that it permits the constituents to be vaporized. The vapor pressure exerted by the liquids differs in strength, which is a function of temperature. The boiling of the liquids takes place, and at a certain instance, the boiling point of the natural products in the liquid form surpasses the atmospheric pressure. The result is that the vapor pressure of the whole system increases.

Working: Steam distillation is a process employed to extract essential oils from organic plant matter by passing steam generated through the plant material. Usually, a chamber is filled with holes (perforations) in the bottom for steam to come through with either fresh or dried herbs.

Advantages and Disadvantages

  • Advantages: (i) Steam distillation is useful for extracting most fats, oils, and waxes. This process works well for types of substances that do not mix with water. (ii) It can be a cost-effective method to invest in for extracting a diverse array of immiscible substances.
  • Disadvantages: (i) Needs a trained operator in order to operate the equipment. (ii) The process has a hidden cost of maintaining and repairing equipment.

Applications of Steam Distillation

  • (i) Used to extract essential oils from aromatic plants to flavor liqueurs.
  • (ii) Used at a wide scale for the manufacturing of essential oils like perfumes.
  • (iii) Used in the synthesis of complex organic compounds.
  • (iv) Orange oil and eucalyptus oil are obtained at an industrial scale using this method.
  • (v) Used in petroleum industries and in the production of consumer food products.
  • (vi) Used for the extraction of peppermint and spearmint oils.

Mixing of Semisolids and Ribbon Blenders

Classification of Mixers

Mixing equipment is most commonly classified based on the type of materials being mixed. The three main classes of mixing equipment are described below:

Blenders

Blenders are mixers used for solid-solid blending. Considering the multitude of industrial operations that require blending of bulk solids, there are a wide range of blenders available. Based on the principle mechanism of mixing, mixer blenders are classified as follows:

  • Tumbler Blenders: These blenders are used for gentle mixing and are often employed in industries like food and pharmaceuticals. Examples include: 1. Double Cone Blender, 2. V-Cone Blender, 3. Octagonal Blender.
  • Convective Blenders: These mixers rely on the motion of a continuous blade to move the materials for blending. They are typically used for powders and granules. Examples include: 1. Ribbon Blender, 2. Paddle Blender, 3. Vertical Screw Blender.

Ribbon Mixer Blender

Principle: Ribbon blenders operate on the combined convection and diffusion mechanisms. Convective mixing is the macro movement of large portions of the solids. Convection mixing occurs when the solids are turned over along the horizontal axis of the agitator assembly. Diffusion mixing involves the micro-mixing that occurs when individual particles are moved relative to the surrounding particles. In the ribbon blender, diffusion occurs when the particles in front of the ribbon are moved in one direction while nearby particles are not moved or lag behind. Together, these two types of action result in the mixing and blending of solids.

Construction: A ribbon blender consists of a U-shaped horizontal trough containing a double helical ribbon agitator. The agitator’s shaft is centrally positioned within the trough and has welded spokes that hold the inner and outer helical ribbons (spirals), forming a “double” helical ribbon agitator. The gap between the outer ribbon edge and the trough wall ranges from 3 to 6 mm, depending on the application. The ribbons are pitched to move the material both axially and radially, ensuring fast and thorough blending.

Working: The ribbon blender works by charging the feed material through nozzles or hoppers mounted on the top.

Fluid Flow and the Venturi Meter

Fluid Flow: Refers to the movement of fluids (liquids or gases) driven by forces like pressure differences or gravity. It can be classified as steady or unsteady, laminar or turbulent, and compressible or incompressible, depending on the nature of the flow.

  • Fluid Statics: The study of fluids at rest. It focuses on pressure distribution, buoyancy, and hydrostatic pressure. Key principles include Pascal’s law (pressure transmission) and Archimedes’ principle (buoyancy force).
  • Fluid Dynamics: Deals with fluids in motion, including the forces that cause the fluid to move and how it interacts with its surroundings. Important concepts include the continuity equation (mass conservation), Bernoulli’s equation (relationship between pressure and velocity), and Navier-Stokes equations (fluid motion). The flow can be characterized by the Reynolds number.

Venturi Meter

A Venturi meter measures the flow rate of fluid by generating a pressure difference as a result of the reduction in the cross-sectional flow area in the flow path.

Principle: In the pipeline of a Venturi meter, two tapered segments along with a constriction (or throat) at the center are present. In comparison to the upstream velocity, the fluid velocity at the Venturi rises when the fluid stream is passed through the narrow constriction. As a result, the pressure head reduces consistently. Using Bernoulli’s theorem, the increase in velocity head can be correlated with the decrease in pressure head between the two points. A manometer can be used for determining the value of the pressure difference (ΔH). At the point before entering the Venturi, the fluid velocity might be considered insignificant if the Venturi diameter is smaller than the pipe diameter. As a result, fluid velocity is directly obtained by the manometer reading.

Construction: A Venturi meter consists of two tapered sections inserted in a pipeline. To prevent any changes in the flow rate by other fittings during measurements, the Venturi meter is placed between long straight pipes. In comparison to the downstream cone, the upstream is shorter. In the downstream cone, eddies are absent and there is no power loss due to smooth and gradual tapers. It also has a distinct cross-section of the stream which is a high-velocity portion.

Reynolds Experiment and Flow Regimes

1. Reynolds Experiment Setup: Fluid flows through a closed channel (e.g., pipeline), regulated by a valve. A colored solution is injected into the fluid via a nozzle, allowing visualization of the flow.

2. Types of Flow:

  • Laminar (Viscous) Flow: Fluid particles move in layers with minimal mixing between them. Momentum transfer between layers is absent.
  • Turbulent Flow: Fluid particles are disturbed and mixed, leading to constant momentum transfer between layers, resulting in a chaotic, diffused flow.

3. Critical Velocity: The critical velocity is the average fluid velocity at which laminar flow transitions into turbulent flow. It marks the transition point between the two flow regimes.

Significance of Reynolds Number

  • 1) A special significance of the Reynolds number is that it can be used to predict the nature of flow in a particular set of circumstances.
  • 2) The type of flow, either viscous or turbulent, also determines the rate of heat transfer in liquids.
  • 3) Sedimentation rate or settling rate of particles determined by Stokes’ Law regulates the physical stability of suspensions or emulsions. It is also necessary that the rate of sedimentation of particles should not be too rapid that it creates turbulence, so the Stokes equation is modified to include the Reynolds number.

Perforated Basket Centrifuge

Principle: The perforated basket centrifuge is a filtration-type centrifuge in which separation occurs on the basis of density differences between solid and liquid phases. The basket has a perforated side-wall. When centrifugal force is applied, the liquid phase moves through the perforated wall and the solid phase remains in the bowl. On completion of centrifugation, the sediment is removed with a blade.

Construction: It consists of a basket of steel (sometimes covered with vulcanite or lead), copper, monel, or any other suitable metal. The construction material should be highly corrosion-resistant. The diameter of the basket should be 0.90m and its capacity should be 0.085m³. The diameter of the perforations should be selected based on the size of crystals to be separated. A filter cloth is used if the perforations are bigger than the particles. The basket is mounted on a vertical shaft and is operated via motor using power systems like belt pulleys, water turbines, and electric motors. Around 5 kilowatts of power is consumed to start the basket and 2 kilowatts for its operation. Steel hoops are externally employed for strengthening. A stationary casing collects the filtrate and discharges it at the outlet.

Working: Material is kept in the stationary basket. An optimum amount should be placed and evenly loaded to avoid strain. The basket is rotated, reaching around 1000 rpm quickly. During centrifugation, the solid phase remains in the basket while the liquid passes through the perforated wall. The cake is dried by rotating at higher speeds. After a fixed duration, the centrifuge is stopped by applying a brake. A blade is used to cut the solid cake, which is then manually unloaded.

Ball Mill Principles and Operation

Principle: A ball mill works on the principle of impaction occurring between the rapidly moving balls and the powder contained in a hollow cylinder. At low speeds, the balls roll over each other and attrition is the major mode of action. Thus, in ball mills, impact, attrition, or both are responsible for size reduction.

Construction

  • 1) Hollow Cylinder: Formed of metal with a chromium lining. The metallic frame attaches the cylinder so it can rotate on its longitudinal axis. About 30-50% of the volume is occupied by steel balls.
  • 2) Balls: Formed of metals and coated with chromium. Sometimes lined with rubber or porcelain. Their weight is kept constant. The size depends on the diameter of the mill and the feed.

Working of a Ball Mill

  • 1. Filling and Rotation: The cylinder is filled with the drug substance and rotated.
  • 2. Speed of Rotation:
    • At Low Speed (Sliding): Balls roll and slide, resulting in minimal size reduction.
    • At High Speed (Centrifugation): Centrifugal force moves balls to the walls, preventing grinding.
    • At Correct Speed (Cascading): Balls move to the roof and fall, leading to attrition and impact for maximum size reduction.
  • 3. Final Product: The material is withdrawn and passed through a sieve.

Uses of Ball Mill

  • 1. Key equipment for regrinding materials.
  • 2. Widely used in the production of cement, silicate products, building materials, fire-proof materials, chemical fertilizers, black and non-ferrous metals, glass, and ceramics.

Filtration Theory and Factors

Theory: The liquid flowing through a filter follows basic rules governing flow through a medium offering resistance. Rate = Driving force / Resistance. Filtration rate is the volume of solution passing per unit time (dv/dt). The driving force is the pressure difference between upstream and downstream. Resistance increases as solids deposit. Filtration is not a steady state. Initially, the flow rate is greatest. After cake formation, the cake acts as the medium. Resistance to movement = (Pressure upstream – Pressure downstream) / Length of capillaries. Theory is explained by Poiseuille’s, Darcy’s, and Kozeny-Carman equations.

Factors Influencing the Rate of Filtration

  • 1. Pressure: Rate increases with higher pressure difference.
  • 2. Viscosity: Rate decreases as viscosity increases.
  • 3. Surface Area: Larger surface area increases the rate.
  • 4. Temperature: Higher temperatures reduce viscosity, increasing the rate.
  • 5. Particle Size: Larger particles are easier to filter.
  • 6. Pore Size: Larger pore size increases the rate for coarse particles.
  • 7. Thickness of Cake: As cake builds up, the rate decreases.
  • 8. Porosity of Cake: Higher porosity increases the filtration rate.

Cyclone Separator Mechanics

Principle: A cyclone separator is a sedimentation technique working on the principle of centrifugal force rather than gravitational force. Based on fluid velocity, it enables the separation of all particles or just coarse particles, leaving fine particles behind.

Construction: Consists of a cylindrical vessel with a conical base. The upper part has a tangential inlet and a central fluid outlet. The lower part has an outlet for solid particles.

Working: Suspension is introduced through the tangential inlet at high speed to provide rotary movement. The fluid outlet at the top removes the fluid. Solid particles are thrown towards the walls due to centrifugal force and fall to the conical base to be removed from the bottom outlet.

Fluidized Bed Dryer Operation

Principle: Involves introducing hot air or gas at high pressure through a perforated bottom. The gas lifts granules and suspends them in the air stream, resulting in a fluidized state. This ensures uniform drying as hot gas surrounds all granules.

Construction: Available in vertical and horizontal types. A vertical dryer is made of stainless steel or plastic with a detachable bowl at the bottom. The bowl has a perforated bottom with wire mesh. The upper part has a fan, fresh air inlet, pre-filter, and heat exchanger. Filter bags recover fines.

Working: Wet granules are placed in the bowl. Fresh air passes through a pre-filter and heat exchanger. Hot air flows through the bowl. As air velocity exceeds the settling velocity, granules become suspended. At a specific pressure, frictional drag equals gravity. Granules rise and fall in a random boiling motion (fluidized state). Drying is achieved at a constant rate. Residence time is about 40 minutes.

Uses and Merits

  • Uses: Drying granules for tablets, mixing, granulation, and coating.
  • Merits: Faster than tray dryers (20-40 mins vs 24 hours), simple handling, mobile containers, high thermal and mixing efficiency.

Evaporation, Distillation, and Drying

Evaporation vs. Distillation

  • Evaporation: Transforming liquid to gas under heat; occurs only at the surface; liquid vaporizes below boiling point; slow process; not a separation technique.
  • Distillation: Obtaining gas from liquids by heating and condensing; occurs throughout the liquid; liquid vaporizes at boiling point; rapid process; a separation technique.

Evaporation vs. Boiling

  • Evaporation: Takes place at all temperatures; temperature may change; takes place only at the surface; rate depends on surface area.
  • Boiling: Takes place at a definite temperature; temperature remains constant; takes place in every region; rate is independent of surface area.

Evaporation vs. Drying

  • Evaporation: Removal of large amounts of water; yields concentrated syrupy liquid; water removed by boiling; not the final stage.
  • Drying: Removal of small amounts of water from solids; yields solid product; removal by boiling below boiling point; uses circulating hot air; final stage of preparation.

Factors Affecting Evaporation

  • 1) Surface Area: Rate increases with area.
  • 2) Temperature: Rate increases with temperature.
  • 3) Humidity: Rate decreases with increased humidity.
  • 4) Speed of Wind: Rate increases with wind speed.

Molecular Distillation Principles

Principle: Many substances (viscous liquids, oils, waxy materials) exhibit low vapor pressures and require high temperatures to boil. High vacuum reduces the boiling point. At very low pressure, the distance between the evaporating surface and the condenser is approximately equal to the mean free path of the vapor molecules. Molecules leaving the surface are more likely to hit the condenser than collide with other molecules. Little or no re-condensation takes place.

Planetary Mixer Construction and Use

Principle: Blades tear the mass apart and shearing action is applied between the moving blade and fixed wall. The blade reaches every spot by moving in two directions (around its own axis and the central axis). Convective action is achieved by sloping plates moving powder upward.

Construction: Consists of a stationary stainless steel vessel. The vessel is detached by raising the blade or lowering the vessel. The blade is moved by an electric motor and planetary gear. Initially, it moves slowly for pre-mixing, then speeds up for active mixing. Narrow clearance provides kneading and shearing.

Working: The agitator undergoes planetary motion. The blade passes closely over the side and bottom, creating no dead spaces. It is variable speed driven. High shearing force can be applied.

Uses: Mixing light to medium viscosity products in pharmaceutical, food, and cosmetic industries. Double planetary mixers are used for rubber and chemicals. Steam jacketed bowls are used for ointments and sustained-release products.

Ferrous Metals in Plant Construction

Ferrous metals, primarily iron-based, are widely used due to mechanical properties and cost-effectiveness.

Types of Ferrous Metals

  • 1. Mild Steel (Low Carbon Steel): Contains <0.3% carbon. Ductile, malleable, good weldability. Used for beams, columns, and pipelines.
  • 2. Carbon Steel: 0.3% to 1.5% carbon. Stronger and more durable but less ductile and prone to corrosion. Used for pressure vessels.
  • 3. Alloy Steel: Contains chromium, nickel, etc. Enhanced strength, toughness, and heat resistance. Used in furnaces and boilers.
  • 4. Stainless Steel: Contains at least 10% chromium. Superior corrosion resistance. Used in chemical and food plants.

Advantages of Ferrous Metals

  • 1. Strength and Durability: Excellent tensile strength for heavy loads.
  • 2. Cost-Effectiveness: Inexpensive compared to non-ferrous metals.
  • 3. Weldability: Easily fabricated into various shapes.
  • 4. Corrosion Resistance: Specifically in stainless steel.
  • 5. Recyclability: Highly recyclable without loss of properties.

Centrifugation and Size Reduction

Centrifugation: The process by which solid particles are sedimented and separated from a liquid using centrifugal force as a driving force. Force is exerted away from the center of path curvature.

Size Reduction

  • Advantages: Maintains content uniformity, enables effective extraction/drying, improves absorption/dissolution, enhances viscosity, and improves bioavailability.
  • Disadvantages: May degrade the drug, lead to poor mixing, cause contamination, or create noise.

Factors Affecting Size Reduction

  • 1. Toughness: Fibrous or high-water content drugs are harder to reduce.
  • 2. Hardness: Soft materials are easier than hard substances.
  • 3. Stickiness: Resinous materials stick to surfaces; heat generation can worsen this.
  • 4. Moisture Content: Affects stickiness, toughness, and hardness.

Short Tube Evaporator and Vortex Formation

Short Tube Evaporator

A type of heat exchanger used to concentrate liquids. Consists of a vertical shell-and-tube arrangement with short tubes. Used for low-viscosity feeds in food and pharma.

  • Construction: Includes a vertical shell, short vertical tubes, a heating medium (steam) inside tubes, and a feed liquid in the shell.
  • Working: Steam transfers heat through tube walls to the feed liquid. Solvent evaporates, rises to the top, and is condensed. Concentrated liquid is discharged from the bottom.

Vortex Formation

Theory: A flow pattern where fluid revolves around an axis. Occurs when flow is disturbed by obstacles or velocity changes. Characterized by centripetal force and a low-pressure core.

  • Causes: Sudden changes in direction, velocity variations, obstructions, or excessive flow rates.
  • Prevention: Use of vortex breakers or baffles to reduce cavitation and inefficient mixing.

Filter Aids and Materials of Construction

Filter Aids

Substances added to improve filtration efficiency by increasing porosity and preventing clogging.

  • Why Used: Improve rate, prevent clogging, enhance cake structure, and improve clarity.
  • Common Aids: Diatomaceous earth (kieselguhr), talc, charcoal (activated carbon), Fuller’s earth, silica gel, cellulose, and perlite.

Classification of Materials

  • 1. Metals: Ferrous and Non-ferrous.
  • 2. Polymers: Thermoplastics and Thermosetting plastics.
  • 3. Ceramics: Glass, brick, tiles.
  • 4. Composites: Fiberglass, carbon fiber.
  • 5. Wood and Concrete.

Ferrous Metals: Cast Iron

Contains 2-4% carbon and 1-3% silicon. Types include Gray (good damping), White (hard/brittle), Malleable (heat-treated), and Ductile (nodular graphite for strength).

Heat Transfer and Mixing Factors

Modes of Heat Transfer

  • 1. Conduction: Transfer through solids via molecular collisions. Examples: Heating a metal rod, cooking with a pan, insulated pipes.
  • 2. Convection: Transfer by physical movement of fluid. Natural convection (density differences) or Forced convection.
  • 3. Radiation: Transfer via electromagnetic waves.

Factors Influencing Mixing of Solids

  • 1. Particle Size: Smaller particles disperse faster; wide distributions lead to segregation.
  • 2. Particle Shape: Spherical particles flow better; irregular shapes may interlock.
  • 3. Density: Differences lead to stratification; denser particles settle at the bottom.

Hammer Mill Principles

Principle: Operates on the principle of impact between rapidly moving hammers and a stationary powder bed. Material is pulverized until fine enough to pass through a bottom sieve.

Construction: Consists of a stout steel casing, a central shaft with swinging hammers, and a replaceable sieve. Some have projecting sections for a cutting action on fibrous materials.

Working: Uses gravity or metered feeding (like pneumatic rotary valves). Hammers swing radially when the motor rotates the shaft, crushing the material against the casing.