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Outline
• Principlesofspraydrying
• Macroscopicview:massandenthalpybalance
• Microscopicview:singledropletevaporaAon
• ControlofparAcleproperAes
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.
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