Industrial Pharmaceutical Drying

Faculty of Pharmacy

OCTOBER 6 University

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

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 .

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 .

• 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).

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 .

RATE OF DRYING

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

• 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.

• 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.

• 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

• 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.

DRYING MECHANISMS-PERIODS OF DRYING

• 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 .

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 .

MATERIAL NOT AGITATED

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 .

• 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 .

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 %.

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 .

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.

• 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 .

• Continuous processes , horizontal FB desi

fluidised be vertical bed.

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 .

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 .

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 .

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 .

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.

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 .

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 .

• 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 .