Industrial Pharmaceutical Drying

1. Industrial Pharmaceutical Drying Faculty of Pharmacy OCTOBER 6 University

2. Wet granulation in manufacture of tablet • 1- increasing P.S. 2-suppert in formulation 3- improving flow 4- compression character. 5-improving content uniformity . DRYING: removal of water from a solid or semisolid mass by evaporative processes

3. DRYING OF SOLID • Solid drying involves two fundamental : 1- heat is transferred to the granule to evaporate liquid . 2- mass is transferred as a liquid or vapor within solid and as a vapor from the surface into the surrounding gas phase . DRYING RATES :factors that influence the rates of these processes .

4. MODES OF HEAT TRANSFER • 1- CONDUCTION: transfer of heat from a- one part to another part of the same body. b-one body to another body in direct physical contact with it .Transfer must occur without displacement of particles of body other than AT OR MOL VIBRATION . 2- CONVECTION : transfer from one point to another within a fluid , by mixing with other fluid. Nature : motion of fluid caused by gradient in density by temp ,gravity Forced : motion caused by mechanical means .

5. 3- Radiation : transfer of heat between two different body by electromagnetic waves . • DRYING TRMINOLGY : • (E.M.C) : bone dry depending on temp. & hum. Dryer outlet ,avoid over drying when reach (E.M.C).

6. MOISTURE CONTENT • 1- Bound moisture : liquid exerts V.P. < then pure liquid . • Unbound mois.: liquid exerts V.P.= to free liquid . • 2- Free moisture :liquid > (E.M.C) ,under satur. Hum. free = unbound, in other case free may consist of both BO. & UNBO. • MOISTURE CONTENT : % mois. Content ,dry basis , NO. of parts by weight of mois. Per 100 parts of BONE DRY, PARTS / PARTS .

7. RATE OF DRYING

8. INTERNAL MECHANISM OF MOISTURE FLOW • There are three kinds of transport of moist. • 1-CAPILLARY FLOW :moisture hold in interstices as liquid on surface or in cap. Moves by gravity & capillary forces . • 2- VAPOR PRESSURE : moist. Moves via V.P. either by heating or subject to atmos. where V.P. of solvent < V.P. granule solvent

9. 3- LIQUID DIFFUSION : restricted to granule (E.M.C) < point of atmospheric saturation or system moisture & solid are soluble exp paste. 4-EXTERNAL CONDITIONS :which affect drying rate 1-humidity 2-airflow 3-temp. 4- P.S. 5-Degree of agitation of the granule bed. 6- method of supporting the granules,7- degree of contact between the drying phase & wet granules.

10. PHYCHROMETRY : Relationships bet. the material & energy balances of W.V./air mix • HUMIDITY : Conc. Of W.V. in air ,it can be expressed in several ways : a- Absolute humidity :mass of W.V. per unit mass air. b- Saturation humidity : absolute humidity at which partial pressure of W.V. in air = V.P. of pure bulk water at a particular temp.

11. Dew point :temp. to which a particular mix. Of air & W.V. must cooled to become saturated with respect to W.V. • Relative humidity : ratio of actual conc. Of W.V. in air to the satur. Conc. Of W.V. air. • measured VP of water in air 100 saturation VP of water in air

12. Dry-bulb temp. : temp. measured by an ordinary thermometer. • Wet bulb : temp. read from therm. Whose tip containing the temp. indicating medium is wrapped in material which soaked in water • If there is difference bet. V.P. of water surround tip of thermom. & V.P. of water in surr. atom. , some of the water will evaporate . Etc.

13. DRYING MECHANISMS-PERIODS OF DRYING

14. Constant rate (steady state) period : in C.D. rate ,granulation behaves as if there is free liquid. Surface of constant comp. & V.P. Rate of drying governed by rate of heat transfer to evaporating Surface . • Critical moisture content : moisture content of the granulation. At the end of C.D.R. period. • Falling rate period : after C.D.P. ends, falling rate period begins .

15. MEASUREMENT OF HUMIDITY • 1- Gravimetric method : depend on Weight p205. • 2- Psychrometric method (sling psychometer ) :two thermometers one dry &wet ,temp. measured at different time until constant temp. • 3- Dew point method : Polished surface until drop of water , attained temp. is dew point, use temp. aid of a psychrometric chart . • 4- Hygrometer : two types a- mechanical hygrometer : used hair, wool fiber , or plastic , change their length by humidity. b- electric hygrometer :measure the change in electric resistance of moisture absorbing materials with humidity .

16. MATERIAL NOT AGITATED

17. DRYERS • Classified in different ways depend on criteria used : • First :based on method of heat transfer . • Second :used when special attention must be given to the nature of the material to be dried depend presence or absence of agitation e.g. not when friable or sub to attrition ,& agitation used when intended to be pulverized .

18. Static bed : no relative movement among the solid particles being dried . • Moving bed :drying particles flow over each other ,induced by gravity or Mech. Agitation . • Fluidized bed :S.P. suspended in upward moving gas stream, like boiling liquid. • Pneumatic : drying particles are entrained & conveyed in a high velocity gas stream .

19. THE MOST COMMON DRYERS • 1- TRAY/ TRUCK DRYER : It is a common method, for wet granulation Or wet product ,slow & relative inefficient ,made of metal, tray placed on large rack with wheels (truck) then put in large oven or room . It is direct dryers ,air circulated over Granul. Bed Drying from upper surface ,take 48 HR. T&T useful in drying of soft shell CAP. Temp.=37 with relative humidity of 10 %.

21. COUNTERCURRENT DRYING • Countercurrent drying carried out in rotary dryers .long cylinder, which direct product opposite to that of air flow . • It is applied to large volume product ,in automated or semi-automated processes. • The rate-limiting step is moisture movement within the granule .

22. FLUID BED DRYING • Rate limiting step is diffusion of WV through air film surrounding granule , it is function of particle diameter, SA EFFECT RATE OF DRYING. • Humidity of DA is most parameter of drying rate because VP difference bet. M.S.& D.A. • At end of drying some G. reach D.BULB TEMP. of drying gas so H.Sens.M. dried at appropriate temp. • FBD conducted in a batch vertical design> or continuous manner used horizontal FBD.

24. ADV. : allows material to be dried with temp. profile which programmed or controlled autom., using different drying rate periods. Moist. Evap. Cool drying air. • IN case of flammable organic solvent using noncombustible gases as N2 & CO2 or using air flow rates which allow air vap. below explosion limits .

25. Continuous processes , horizontal FB desi

26. fluidised be vertical bed.

27. VACUUM DRYING • Drying potential is the difference between the VP of solvent in or at surface of wet granule & VP of solvent in surrounding gas • DRYING RAT =N A /L( Po – P1 ) inversely proportional to the heat of evaporation of liquid L(J/KG), Po VP of solvent at W. granule Surface P1 VP solvent in gas, N (constant )is transfer coefficient Depend on both heat & mass transfer . # adv. 1- capability of drying at low temp. 2- More rapid then T&T CD but not as rapid as fluid bed drying . High Vacuum fast drying but case hardening .

29. Vacuum oven • It is a jacketed vessel, of stout material . • Shelves form part of jacket ,for large area & door • Adv.1- Good for thermo labile sub.2- Good for dry extracts porous & friable product. -3-Solvent recovery . • Disadv. 1- Low heat transfer coefficients . 2- Limited capacity . 3- High labor & running cost 4- Overheating & decomposition can occur .

31. DIELECTRIC OR MICROWAVE DRYING • Depend on electromagnetic radiation . • ELM field induce orientation of the dipoles in the molecules & solvent molecule oscillate resulting in increase kinetic energy, indicated as heat EN. • Heat generation within granule so solvent vaporization result in VP gradient = drying. • Drying rate proportional to V diffusion rather L dif • Microwave in batch or continuous manner with or without fluidization .

32. MICROWAVE- VACUUM DRYING • Depend on very low VP combined with mol. Selective energy. Polar solvent may evaporated at low temp. exp water based granulation evaporated at 35 mm mercury & water based granulation dried at 31C . • It is very efficient & recovery of solvent .

34. DRYERS FOR DILUTE SOLUTION & SUSPENSION • Object : to spread liquid surface area & to collect the dry solid . There are two methods • 1- Drums dryer ( film) : Drum heated internally by steam & rotated, liquid is applied to surface & spread to film. Rate of drying controlled by speed of rotation & drum temp. ADV. : 1- rapid, economic. 2- compact. 3- used under vacuum. 4- convenient product as flakes . DI ADV. : It necessary to control feed rate ,film thickness, speed of rotation & temp. difference.

36. 2- SPRAY DRYER • Using atomizer to produce small droplets of liquid to increase surface area . • It sprayed in steam of hot air .Drying chamber resembles cyclone to ensure good air circulation ,to facilitate heat transfer & dried particle separated by centrifugal action . • Two types of atomizers used jet or rotary . • Adv. : 1-rapid.2-high bulk density & readily soluble . 3- uniform PS. 4- Free flowing . Dis adv. :1- Equipment bulky & expensive .2- thermal efficiency is low .

39. FREEZE DRYING ( SUBLIMATION DRYING ) • Reducing temp. & pressure to values below the triple point .so any heat transfer is used as latent heat & ice sublimes directly to vapour state. • 1- temp. must kept below triple point . • 2- the same for pressure . • 3- material is frozen & vapour sublimes ,so it required large area.4- used a thin layer to reduce distance between ice & solid.5- avoid contact with atmosphere as it contain very low moisture & final container should be sealed .

41. STGES: freezing – vacuum – drying . • ADV. 1- drying at low temp. 2- product light & porous so it readily soluble. 3- oxid is minimized . DIS ADV. 1- hygroscopic 2- process is very slow complicated & expansive .