Chemical Engineering 3. Lecture 9: Spray drying

Transcription

1 Chemical Engineering 3 Lecture 9: Spray drying

2 Outline Principles of spray drying Macroscopic view: mass and enthalpy balance Microscopic view: single droplet evaporaaon Control of paracle properaes

3 Spray drying process liquid spray powder

4 Spray drying process Feed Cyclone Bag filter HEPA Condenser HEPA Heater Main powder fraction Fines Solvent N2 out N2 in

5 Spray drying process Laboratory scale Pilot plant scale

6 Spray drying process Industrial scale

7 ParAcle morphologies polymer soluaon (chitosan) paracle slurry (lactose) colloidal dispersion (colloidal SiO2) salt soluaon (NaCl) milk powder dried at different temperatures

8 Process parameters! Feed concentraaon! Droplet size (atomisaaon pressure)! Choice of solvent*! Choice of addiaves ParAcle size and morphology! Feed flowrate! Drying gas flowrate! Drying gas humidity! Drying gas temperature* Product temperature and residual moisture

9 Mass and enthalpy balance X in m C Y in m B A solvent B dry gas C dry solids assumpaons: 1) non-volaale solids 2) non-condensible gas vap m A moisture content in solids moisture content of gas moisture mass balance: X = m A m C Y = m A m B m C vap ( X in X out ) = m B ( Y out Y in ) = m A X out Y out m C m B evaporaaon rate gas consumpaon vap m A m B

10 Mass and enthalpy balance X in m C T C,in vap m A T B,in Y in m B Q T B,ambient assumpaon: isenthalpic drying specific enthalpy of wet solids J = H A + H C m C = (Xc p,a + c p,c )T specific enthalpy of wet gas I = H A + H B m B = (Yc pg,a + c p,b )T +YΔh vap,a enthalpy balances: m B I in = Q + m B I ambient m C J in + m B I in = m c J out + m B I out X out Y out esamate of minimum heaang duty m C T C,out = T B,out m B Q = m A vap Δh vap,a

11 Mass and enthalpy balance Condi&on: RelaAve humidity at outlet < 100 % specific enthalpy [kj/kg] I = H A + H B m B = (Yc pg,a + c p,b )T +YΔh vap,a moisture content [kg/kg] Y = m A m B relaave humidity [%] ϕ = p A p A sat (T) = x AP p A sat (T) = P p A sat (T) n A n A + n B = P p A sat (T) Y M w,b M w,a 1+Y M w,b M w,a saturated vapour pressure [Pa] log 10 p A sat = a b c + T (Antoine equaaon)

12 Graphical representaaon: Ramzin diagram Step 1: 1) Take air at 20 C and 60 % RH 2) Find Y and I Step 2: 1) Take air from step 1 2) Heat it up to 120 C 3) Find I Step 3: 1) Take air from step 2 2) Find its adiabaac saturaaon temperature

13 ProperAes of wet solids Equilibrium moisture sorpaon isotherm Same material, different temperatures DVS (Dynamic Vapour SorpAon) Same temperature, different materials sacky point temperature!

14 Process parameters! Feed concentraaon! Droplet size (atomisaaon pressure)! Choice of solvent*! Choice of addiaves ParAcle size and morphology! Feed flowrate! Drying gas flowrate! Drying gas humidity! Drying gas temperature* Product temperature and residual moisture

15 Single droplet drying VOLATILE CONTENT Drying curve POWDER TEMPERATURE 1 st period of drying: EvaporaAon from free surface Wet bulb temperature 2 nd period of drying: Diffusion across solid shell FormaAon of hollow core Time

16 Single droplet drying Wet bulb temperature mass transfer droplet boundary layer heat transfer evaporaaon rate m A = k m S p sat bulk ( A (T surf ) p A ) heat-transfer rate Q = k q S( T bulk T ) surf = m A Δh vap,a Ranz-Marshall correlaaon Sh = Re 1 2 Sc 1 3 Reynolds number Sherwood number Nusselt number Re = udρ η Sh = k md D Nu = k q d λ Schmidt number Prandtl number Nu = Re 1 2 Pr 1 3 Sc = η ρ D Pr = η λ c p

17 Droplet morphology evoluaon Fig. 1. Example of the evolution of RH and sample mass of physical mixture of amorphous Valsartan and PVP during a single DVS measurement. 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. nuclea7on The rotational speed was 75 rpm at ph 6.8 and 100 rpm at ph 2. The! dissolution profile was obtained at 37 C by the paddle method from the powder. The concentration of Valsartan in the solution was non-skin forming determined 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 for measurements. 3. Results and discussion 3.1. Characterisation of solid dispersions smooth par7cles 3.2. Sorption of water strong skin SEM micrographs of spray dried solid dispersions and physical mixtures of microparticles are shown in Fig. 2. SEM analysis revealed a particle size distribution between 2 mm and 30 mm and skin forming a hollow spherical particle shape of the spray dried particles. The amorphous form of Valsartan in the solid dispersions was buckling weak skin confirmed by XRD porous par7cles analysis as shown in Fig. 3. The spray drie samples were compared with the reference sample of semicrys talline Valsartan. The stability of the amorphous form unde storage conditions was also measured after 45 days. No crystallin form of the API was noticed in the stability study of the soli dispersion after this period. Pure Valsartan used in the physica mixtures was prepared by milling step and the volume-mea particle diameter of the amorphous semi-crystalline particles wa 34 mm and 82 mm, respectively. puffing A water sorption isotherm provides information about th affinity between the material and water. The water sorptio isotherms of pure polymers are shown in Fig. 4. From the teste polymers, the most hygroscopic character was revealed by PVP K3 (87.7% change of mass at 95% RH). The polymer Soluplus also show a hygroscopic character with 37.6% change of mass at 95% RH However, the water sorption of Eudragit EPO shows a hydrophobi collapsed shells

18 Droplet morphology evoluaon Skin forming vs. Non skin forming Strong vs. weak shell CompeAAon: - EvaporaAon rate - Internal diffusion rate α = ds dt D eff TECHNOLOGICAL BREAKTHROUGH Direct observaaon: - AcousAc levitaaon - High-speed camera - Contactless thermometer - Raman spectroscopy baascafo equaaon condiaon for shell buckling GEA Niro DRYNETICS TM Building a better spray dryer drop by drop GEA/Niro DryneAcs TM