ChemicalEngineering3

Lecture9:Spraydrying

Outline

•  Principlesofspraydrying

•  Macroscopicview:massandenthalpybalance

•  Microscopicview:singledropletevaporaAon

•  ControlofparAcleproperAes

Spraydryingprocess

liquid powderspray

Spraydryingprocess

Drying air Feed to atomizer Exhaust air Powder discharge

27

GEA Niro spray congealing systems

Spray atomization and final powder in spray congealing of melted fat and hydrogenated vegetable oils.

Feed

Mainpowderfraction

Fines

Cyclone

HEP

AH

eate

r

Bag filter HEPA Condenser

N2 out

N2 in

Solvent

Closed-cycle spray drying process Spray cooling

Co-current, flat base with rotary atomizer, for special products. Also suitable for spray congealing.

Spraydryingprocess

Laboratoryscale Pilotplantscale

Spraydryingprocess

Industrialscale

ParAclemorphologiespolymersoluAon(chitosan) colloidaldispersion(colloidalSiO2)

parAcleslurry(lactose) saltsoluAon(NaCl) milkpowderdriedatdifferenttemperatures

Processparameters

! FeedconcentraAon! Dropletsize(atomisaAonpressure)

! Choiceofsolvent*! ChoiceofaddiAves

! Feedflowrate! Dryinggasflowrate! Dryinggashumidity

! Dryinggastemperature*

ParAclesizeandmorphology

Producttemperatureandresidualmoisture

Massandenthalpybalance

moisturecontentinsolids

€

X =mA

mC

A…solventB…drygasC…drysolids

moisturecontentofgas

€

Y =mA

mB

€

˙ m C

€

˙ m B

assumpAons:1)  non-volaAlesolids2)  non-condensiblegas

€

Xin

€

Yin

€

˙ m A

vap

€

˙ m C

€

˙ m B

€

Xout

€

Yout

moisturemassbalance:

€

˙ m C Xin − Xout( ) = ˙ m B Yout −Yin( ) = ˙ m Avap

⇒ evaporaAonrate⇒ gasconsumpAon

€

˙ m A

vap

€

˙ m B

Massandenthalpybalance

specificenthalpyofwetsolids

€

J =HA +HC

mC

= (Xcp,A + cp,C )T

€

˙ m C

€

˙ m B

assumpAon:isenthalpicdrying

€

Xin

€

Yin

€

˙ m A

vap

€

˙ m C

€

˙ m B

€

Xout

€

Yout

€

TC ,out = TB ,out

€

˙ Q €

TC ,in

€

TB ,in

esAmateofminimumheaAngduty

€

˙ Q = ˙ m AvapΔhvap,A

specificenthalpyofwetgas

€

I =HA +HB

mB

= (Ycpg,A + cp,B )T +YΔhvap,A

€

TB ,ambient

enthalpybalances:

€

˙ m B Iin = ˙ Q + ˙ m B Iambient

€

˙ m C Jin + ˙ m B Iin = ˙ m cJout + ˙ m B Iout

specificenthalpy[kJ/kg]

€

I =HA +HB

mB

= (Ycpg,A + cp,B )T +YΔhvap,A

moisturecontent[kg/kg]

€

Y =mA

mB

relaAvehumidity[%]

€

ϕ =pA

pAsat (T)

=xAPpAsat (T)

=P

pAsat (T)

nAnA + nB

=P

pAsat (T)

Y Mw ,BM w ,A

1+Y Mw ,BM w ,A

saturatedvapourpressure[Pa]

€

log10 pAsat = a − b

c +T

(AntoineequaAon)

Massandenthalpybalance

Condi&on:RelaAvehumidityatoutlet<100%

GraphicalrepresentaAon:Ramzindiagram

Step1:1)  Takeairat20°C

and60%RH2)  FindYandI

Step2:1)  Takeairfromstep12)  Heatitupto120°C3)  FindI

Step3:1)  Takeairfromstep22)  FinditsadiabaAc

saturaAontemperature

ProperAesofwetsolids

EquilibriummoisturesorpAonisotherm Samematerial,differenttemperatures

Sametemperature,differentmaterials

“sAckypoint”temperature!

DVS(DynamicVapourSorpAon)

Processparameters

! FeedconcentraAon! Dropletsize(atomisaAonpressure)

! Choiceofsolvent*! ChoiceofaddiAves

! Feedflowrate! Dryinggasflowrate! Dryinggashumidity

! Dryinggastemperature*

ParAclesizeandmorphology

Producttemperatureandresidualmoisture

Singledropletdrying

Dryingcurve

17

VOLATILE CONTENT POWDER TEMPERATURE

Time

PRODUCT DRYING CURVE1stperiodofdrying:EvaporaAonfromfreesurfaceWetbulbtemperature

2ndperiodofdrying:DiffusionacrosssolidshellFormaAonofhollowcore

SingledropletdryingWetbulbtemperature

heattransfer

masstransfer

boundarylayer

droplet

evaporaAonrate

€

˙ m A = kmS pAsat (Tsurf ) − pA

bulk( )

Ranz-MarshallcorrelaAon

€

Sh = 2.0 + 0.6Re12 Sc 13

€

Nu = 2.0 + 0.6Re12 Pr 13

heat-transferrate

€

˙ Q = kqS Tbulk −Tsurf( ) = ˙ m AΔhvap,A

Reynoldsnumber

Nusseltnumber Prandtlnumber

Sherwoodnumber Schmidtnumber

€

Re =udρη

€

Sh =kmdD

€

Nu =kqdλ

€

Sc =η ρD

€

Pr =η

λ cp

DropletmorphologyevoluAon

non-skinforming

nuclea7on

porouspar7cles

skinforming

smoothpar7cles

“strong”skin

“weak”skin

collapsedshells

buckling

“puffing”

media were aqueous buffers at pH 6.8 with 0.001% (w/v) SDS(sodium dodecyl sulphate) and pH 2 with 0.001% (w/v) Tween 20.The rotational speed was 75 rpm at pH 6.8 and 100 rpm at pH 2. Thedissolution profile was obtained at 37 !C by the paddle method fromthe powder. The concentration of Valsartan in the solution wasdetermined using the UV technique at predetermined time points(2, 5,10,15, 20, 25, 30, 40, 50, 60, 70, 80, 90 min and at pH 2 also 100,110 and 120 min). The wavelength of 250 nm was used formeasurements.

3. Results and discussion

3.1. Characterisation of solid dispersions

SEM micrographs of spray dried solid dispersions and physicalmixtures of microparticles are shown in Fig. 2. SEM analysisrevealed a particle size distribution between 2 mm and 30 mm anda hollow spherical particle shape of the spray dried particles. Theamorphous form of Valsartan in the solid dispersions was

confirmed by XRD analysis as shown in Fig. 3. The spray driedsamples were compared with the reference sample of semicrys-talline Valsartan. The stability of the amorphous form understorage conditions was also measured after 45 days. No crystallineform of the API was noticed in the stability study of the soliddispersion after this period. Pure Valsartan used in the physicalmixtures was prepared by milling step and the volume-meanparticle diameter of the amorphous semi-crystalline particles was34 mm and 82 mm, respectively.

3.2. Sorption of water

A water sorption isotherm provides information about theaffinity between the material and water. The water sorptionisotherms of pure polymers are shown in Fig. 4. From the testedpolymers, the most hygroscopic character was revealed by PVP K30(87.7% change of mass at 95% RH). The polymer Soluplus also showsa hygroscopic character with 37.6% change of mass at 95% RH.However, the water sorption of Eudragit EPO shows a hydrophobic

Fig. 1. Example of the evolution of RH and sample mass of physical mixture of amorphous Valsartan and PVP during a single DVS measurement.

Fig. 2. SEM micrographs of microparticles a) Valsartan:Soluplus solid dispersion, b) Valsartan:PVP solid dispersion, c) Valsartan:Eudragit solid dispersion, d) Valsartan:Soluplus physical mixture, e) Valsartan:PVP physical mixture and f) Valsartan:Eudragit physical mixture.

K. Pun9cochová et al. / International Journal of Pharmaceutics 469 (2014) 159–167 161

DropletmorphologyevoluAon

Skinformingvs.Nonskinforming

CompeAAon:- EvaporaAonrate- Internaldiffusionrate

€

α =dS dtDeff

Strongvs.weakshell

“baAscafo”equaAoncondiAonforshellbuckling

GEA Process Engineering

Building a better spray dryer drop by drop

GEA Niro DRYNETICSTM

engineering for a better world

TECHNOLOGICAL BREAKTHROUGH

DirectobservaAon:- AcousAclevitaAon- High-speedcamera- Contactlessthermometer- Ramanspectroscopy

GEA/NiroDryneAcsTM