PROCESS DEVELOPMENT AND MODELLING FOR PARTICLE FORMATION OF EDIBLE FATS USING SUPERCRITICAL MELT MICRONISATION (ScMM)

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1 PROCESS DEVELOPMENT AND MODELLING FOR PARTICLE FORMATION OF EDIBLE FATS USING SUPERCRITICAL MELT MICRONISATION (ScMM P. Münüklü *, F. Wubbolt, P. J. Janen Delft Univerity of Technoloy Laboratory for Proce Equipment Leehwatertraat 44, 68 CA Delft, The Netherlan Thi work eal with the evelopment of a microniation proce for eible fat bae on Supercritical Melt Microniation- technoloy (ScMM, alo known a Particle from Ga Saturate Subtrate-technoloy (PGSS an the evelopment of a moel to ecribe the heat tranfer an phae chane urin rapi oliification of an atomize fat roplet containin iolve CO. In the PGSS proce a mixture of molten eible fat i aturate with upercritical CO an ubequently expane over a nozzle. In thi way micro particle can be prouce with a narrow ize itribution an, vital for foo application, free of olvent. A erie of Experiment were performe in a continuou unit. Without CO in the fat melt oli phere were obtaine. Unitorte hollow phere to pone like morpholoie were obtaine at CO concentration from 5-5wt%, an a contant atomization preure of bar. The variation in melt temperature how pherical an hollow particle at temperature between 6 an o C at contant CO concentration of 5wt% an an atomiation preure of 7 bar. A numerical moel wa evelope, which ecribe the oliification of one pherical roplet urin the ScMM proce. The ubequent tep are the iothermal oliification, unercoolin an oliification of the unercoole roplet. In thee tep the heat tranfer influence an aeroynamic principle are moelle an preente in iaram. INTRODUCTION The prouction of particle in micro ize are traitionally prouce uin liqui nitroen to make the material brittle, which i an expenive an enery conumin technique. With the PGSS metho it i poible to obtain ifferent morpholoie like pherical an pone like particle without any ue of olvent or other aitive except CO, which i a reen an inexpenive olvent []. The evelope moel ecribe the oliification of a inle roplet, by heat removal by CO evaporation an entrainment of ambient air. MATERIALS AND METHOD The ue component in thi project i an eible fat an the proce, which ha been ue i upercritical melt microniation (ScMM alo known a PGSS (particle from a aturate olution.

2 RESULTS AND DISCUSSIONS In Table the experimental winow for experiment performe uner the influence of CO concentration i iplaye. The reult of experiment at ifferent atomization preure an melt temperature are not inclue an will be preente elewhere. Table : Experimental Winow of execute experiment Exper. Nr. Patom. Tmelt Bulk-enity wt.%co o bar C /m3 a 5, b 39,5 5 c 355, 43,9 e 63,6 3 f 3, 5 a wt% b 5wt% c wt% wt% e 3wt% f 5wt% Fiure: Particle obtaine at ifferent CO-concentration. a Completely oli pherical particle, at wt% CO b Hollow particle at 5wt% CO, c pone-like Particle at wt % CO, Spherical hollow an alomerate at wt% CO, e Spherical hollow but mainly alomerate at 3wt% CO, f Spone-like particle at 5wt.% CO Effect of CO conc. on PS a 6 bar/`c Denity [/m3] Number bae mean ize [µm] bar/`c CO conc.(wt% b CO conc. [wt%] Fiure: a Number bae mean particle ize veru CO concentration, b Denity veru CO concentration Obviouly the CO concentration ha an influence on the particle morpholoy. With increain the CO concentration the morpholoy of the particle tranform from pherical to alomerate, itorte or pone like particle. From the particle ize an enitie meaurement it can be conclue that with increain CO concentration hiher than wt% the CO oe not have any inificant contribution on the particle ize an enity. It eem to

3 have only a coolin effect. Experiment one at increain melt temperature how a clear increae in enity. The influence of melt temperature on the particle ize an morpholoy wa not inificant. The atomization preure ha no inificant influence on particle ize or enity. The only effect of atomization preure wa een in the morpholoy, which how with an increae in atomization preure morpholoie from pherical hollow to alomerate pone like particle. Thee roplet cool own an tart to oliify ue to expanion, convective coolin an CO evaporation. The oliification bein at the urface of the roplet. In the abence of CO completely oli particle are forme. In the preence of CO inflation of the roplet occur an hollow particle with a oli crut are forme. At relatively low melt temperature, immeiately after the roplet are forme, oliification bein an a oli crut i forme before all of the CO can ecape. Uner uch conition, epenent on the permeability an the flexibility of the crut the roplet/particle will be eforme or even hattere leain to the oberve hollow itorte or pone like morpholoie. At relatively hih melt-temperature, oliification will procee more lowly, which on the one han facilitate the formation of pherical (primary particle an on the other han promote alomeration ince the wet roplet/particle are more likely to tick toether when they collie. Similarly the effect of the CO -concentration in the melt can be explaine in term of competition between the oliification rate of the melt an the ecape rate of CO. Both temperature an CO -concentration alo have an inirect effect on the particle formation proce in the ene that they have a tron effect on relevant phyical propertie of the melt (like vicoity, urface tenion an conuctivity. MODEL A imple moel wa evelope to ecribe the heat tranfer an phae chane urin rapi oliification of an atomize fat roplet containin iolve CO. Central to thi moelin i the metho of moment. The treatment have then concentrate on the imulation of thoe procee, which are reconize a the key factor controllin the ultimate reult. Thee inclue external an internal heat tranfer, nucleation an crytal rowth kinetic [5]. The moment equation applicable are [3]: N t L t V ( t I N L ( T ( t G( T ( (3 M t A k t 3ρ a ( f L ( t G( T kv A t k a ( G( T ( (4 A the roplet fliht continue in the power collection veel, the ambient air temperature chane a a reult of convective heat tranfer from the roplet an evaporation of CO. The eneral heat tranfer equation for air of ma m air i [6]: m air p T t If we introuce χ, uch that, c mco ( T T + C ( T T ha p, CO m m i the air-to-roplet ma ratio, we et after implification of equation (5, t air χ (6 (5

4 T t χ 6h [ ρ ( f ] ( T T C p, CO ( T T χc p x ( x t (7 With the rivin force expree in concentration of CO, nelectin the concentration of CO in air compare to that in roplet, the rate of evaporation of CO from the roplet i written a: m (8 CO km A M CO ( C CO t The rate of evaporation of CO can be re-written in term of the rate of chane of ma fraction of CO a: x m m ( x CO x m (9 t t ( x t Similarly, concentration i expree in term of ma fraction a: nco mco x m x CCO ρ ( f V M V x V M x Subtitutin the reult of equation(9 an ( in equation(8 an rearranin, we et: The ma tranfer coefficient i calculate bae on the two-film theory, whereby the limitin x km 6 x( x t ( ma tranfer reitance etermine the evaporation rate. The liqui (roplet ie ma tranfer coefficient, k L i that reultin from the penetration theory. k L D πt ( Thi relation i applicable in the rane, Dt Fo <.. (3 An the outie (air ie ma tranfer coefficient, k V i calculate from the relation [4]: Sh +.79 Re Sc kv η Where, Sh, i the Sherwoo number, an Sc i the Schmit number [4]. D ρ D V CO The mot inificant reult of the olution of the ifferential equation icue o far are preente a raph in fi.3 an 4, where the air to roplet temperature profile an the roplet oliification rate at ifferent CO concentration are hown. V [ ] CO M CO 3 ( (4 Temperature, [K] Time, [] Air temperature profile Droplet temperature profile Meltin Point Fiure 3: Air to Droplet temperature profile ifferent Temperature,[K] Time,[] %(w/w CO %(w/w CO %(w/w CO Meltin Point Fiure 4: Droplet oliification rate at CO concentration

5 Fi.3 how a typical reult of the relationhip between the thermal profile of the roplet an the ambient air. It hown that there i a rapi ecreae in roplet temperature aociate with a relatively rapi increae in ambient air temperature at the beinnin of the proce. Thi rapi ecreae in roplet temperature may be attribute to two factor. Firt, the CO evaporate very fat at the beinnin which reult in rapi coolin of the roplet a it take heat from the roplet for it evaporation. Secon, there i a hih convective heat tranfer from the roplet to the ambient air ue primarily to the hiher rivin force for heat tranfer a a reult of hiher roplet temperature couple with lower ambient air temperature. However, thi initial ituation i almot brouht to a halt a the two temperature profile come cloe to each other leavin little rivin force for heat tranfer. Thi reult in a temporary iothermal conition with repect to both the roplet an the ambient air. It can be ai there i a brief balance between rie in heat enery of the roplet a a reult of initial, low level oliification, an heat lo to the ambient air throuh the little remainin rivin force. However, after e certain time the number of nuclei increae, which increae the oliification rate. Thi reult in a relatively rapi increae in roplet temperature. Thi increae will have two notable effect. Firt, the unercoolin i ecreain the nucleation an rowth rate of crytal; econly, the rivin force for heat tranfer between the roplet an the air increae. Thee two ituation have oppoite effect on the thermal tate of the roplet an a certain temperature i etablihe after ome time. Thi ituation become evient from the contant roplet temperature, which i cloe to the normal meltin, point. A the oliification proce i complete, there will be no more latent heat releae an the roplet temperature only cool a any oli from which heat i continuouly bein withrawn. Finally, the temperature of the roplet an that of the ambient air come toether after all poible heat i extracte from the roplet. A een from the fiure 4, a the initial CO concentration increae, the rate of rop in roplet temperature at the beinnin of the proce increae which reult in both in hiher coolin rate an eeper unercoolin. Thi hiher unercoolin i in turn reflecte in hiher recalecence rate, an the temperature of roplet tartin with more CO are hown to overtake thoe tartin with le CO. The overall effect i lower oliification time in roplet tartin with more CO. CONCLUSION The hape an the ize of the forme particle can be manipulate by the temperature of the melt an by the CO /melt ratio. The temperature in the collection veel houl be kept low to uppre alomeration. Uin a novel equipment confiuration it ha become poible to control the particle morpholoy propoe. A continuou ScMM-proce for eible fat wa uccefully evelope which yiel hollow or oli phere, in the ize rane 4 9 micron an a power bulk enity between 5 5 /m 3. The moel how u the influence of certain parameter. Hiher initial CO concentration, lower initial roplet temperature, an lower initial air temperature are hown to facilitate the rapi coolin an oliification of roplet. The CO concentration in the fee mixture turne out to be the overnin operatin variable. A imple moel for the particle oliification wa preente but it i not (yet poible to link moel-preiction to experimental reult irectly. REFERENCES: [] P. MUNUKLU, F.E. WUBBOLTS, P.J. JANSENS, ASC Sympoium Serie 86, 3 [] LAVERNIA, E.J., AND WU, Y., Spray atomization an epoition, 996

6 [3] F.E, WUBBOLTS, E.E., Supercritical Crytallization: Volatile Component A (anti- Solvent, [4] SKELLAND, A.H.P., Diffuional ma tranfer, 95 [5] CLYNE, T.W., Numerical treatment of Rapi oliification, Metall.Tran. B, 5 B, 369, 984 [6] PERRY, R.H., Perry Chemical Enineerin Hanbook, 6 th eition, 984 Symbol Decription Unit A Total external area of crytal entitie in the roplet m C p, Contant preure heat capacity of roplet J/(mol.K C p, Contant preure heat capacity of Ga J/( mol.k Droplet Diameter m m The effective molecular iameter m D v Diffuivity of CO in air m / f(θ Nucleate potency [-] f Soli fraction [-] G Crytal rowth rate M/ h Convective heat tranfer coefficient W/(m K I Nucleation rate #/(m 3. k a Surface hape factor of crytal [-] k Thermal Conuctivity of atomization Ga W/(m.K k L Droplet ie coefficient of ma tranfer m/ k m Ma tranfer coefficient m/ k V Air ie coefficient of ma tranfer m/ L Total lenth of crytal entitie m m CO Total ma of CO in the roplet k m Total ma of roplet k m air Ma of ambient air k N Total number of crytal ite (nuclei [#] n CO Number of mole of CO mole t Time S T Temperarture K T Droplet temperature K T Temperature of Atomization Ga K A Volume of Droplet m 3 v o Releae velocity of roplet from the nozzle m/ V m Volume of molecule m 3 /molecule V L Volume of the liqui portion of a roplet m 3 χ Ambient air-to-roplet ma ratio [-] ρ Denity of atomization Ga k/m 3 ρ Denity of roplet k/m 3 η Dynamic Vicoity of Ambient Ga Pa. T Unercoolin K