Fundamentals of Drying in Pharmaceutical Manufacturing

1. By Moizul Hasan Assistant Professor DRYING

2. Definition Drying is defined as the removal of small amounts of water or other liquid from a material by the application of heat.

3. Applications • Preservation of drug products • Improved characteristics • Preparation of Bulk drugs • Improved Handling

4. Background EMULSIONS Bound water is the minimum water held by the material that exerts an equilibrium vapour pressure less than the pure water at the same temperature.  Unbound water is the amount of water held by the material that experts an equilibrium vapour pressure equal to that of pure water at the same temperature. Unbound water exists largely in the voids of the solid. Emulsion Type and Means of Detection: 1) Dilution Test: - o/w emulsion can be diluted with water. - w/o emulsion can be diluted with oil.

5. Background Hygroscopic Materials Water in: -fine capillaries -cell and fibre walls -physical interaction Vapour pressure of wet solids is Less than the vapour pressure of pure water Contains Condition Bound water Non-hydroscopic materials Water in void spaces Contains Condition Vapour pressure of wet solids is equal to vapour Pressure of pure water Unbound water

6. Preamble Equilibrium moisture content (EMC): It is the amount of water present in the solid which exerts a vapour pressure equal to the vapour pressure of the atmosphere surrounding it. Free moisture content (FMC): Free moisture content (FMC) is the amount of water that is free (easy) to evaporate from the solid surface.

7. Calculations mass of water in sample (kg) % Loss on drying = -------------------------------------- x 100 (LOD) total mass of wet sample (kg) mass of water in sample (kg) % Moisture content = ------------------------------------- x 100 (MC) mass of the dry sample (kg) weight of water lost from sample(kg) Drying rate = -------------------------------------------------------------- Time(h) x weight of the dry solid(kg) X Unit area

8. Interpretation Data Drying rate curve: The moisture at point ‘C’ is called CMC = Critical moisture content, E= EMC AB= Initial adjustment, BC = Constant rate period, CD=First falling period, DE= second falling period, A’A B C Drying Rate D E Free Moisture content 

10. Equipment TRAY DRIER 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. 

12. DRUM DRYER OR ROLLER DRYER   In drum dryer, a heated hallow metal drum rotates on its longitudinal axis, which is partially dipped in the solution to be dried. The solution is carried as a film on the surface of the dryer and dried to form a layer. A suitable knife scraps the dried material, while the drum is rotating.

14. SPRAY DRYER In spray dryer, the fluid to be dried is atomized into fine droplets, which are thrown radially into a moving stream of hot gas. The temperature of the droplets is immediately increased and fine drop-lets get dried instantaneously in the form of spherical particles. 

16. FLUIDISED BED DRYER (FBD) In fluidized bed dryer, hot air (Gas) is passed at high pressure through a Perforated bottom of the container containing granules to be dried. The granules are lifted from the bottom and suspended in the stream of air. The condition is called fluidized state. The hot gas is surrounding every granule to completely dry them. Thus, materials or granules are uniformly dried.

18. Vacuum Dryer In vacuum dryer, material is dried by the application of vacuum. When pressure is lowered,the water boils at low temperature . Hence the evaporation is faster. The rate of drying enhance d substantially

20. Freeze Dryer Freeze drying is also known as lyophilization. Principle: In freeze drying, water is removed from the frozen state by sublimation, i.e., direct change of water from solid into vapour without conversion to a liquid phase.

22. Pharmaceutical granulation drying method • Tray drying • Fluid bed drying • Vacuum drying • Dry electric ( MICRO WAVE DRYING) • TUNNEL DRYING

27. DIELECTRIC OR MICROWAVE DRYING • It is the method of drying in which electromagnetic radiation (radio frequency from 3-150 MHz or microwave frequency at 915 or 2450 MHz) is applied to material dried. • If polar solvent molecules are present, the electromagnetic field induce orientation of the dipoles in molecules

28. As the field oscillates, the polar solvent molecules oscillate with the field, resulting in increased kinetic energy from dipolar molecules and their collisions with others • This manifested in thermal or heat energy

30. Theory • The rate of heating is proportional to the dielectric constant of materials placed in the field • Water has dielectric constant 70 and the granule around 10, then water will be heated more rapidly than other components in granule.

31. Factors P= Z f E2 ε’ tanδ • P= POWER ABSORBED (watts/ unit volume) • Z= Geometric constant times the dielectric constant of vacuum • f = The frequency of applied field • E = The field strength (volts/unit distance) • ε’ = the relative dielectric constant of material • tan δ = the loss tangent or dissipation factor of material

32. Applications • Since the EM radiation penetrate entire granule and bed of granules, heating and vaporization of solvent can occur evenly throughout the mass • Drying rates are proportional to rate of vapor diffusion rather than liquid diffusion • Energy savings of 70% compared to fluid bed drying

35. Combinations • Micro wave drying – Batch or continuous • Micro wave – fluid bed drying • Bed thickness and airflow variations • Micro wave – vacuum drying

36. Conclusion The different drying equipments are available, but the suitable dryer is selected based on the Nature of material,cost, time and nature of the product required.