ADAMI, RENATA

CAPUTO G.

REVERCHON, Ernesto

English

Archivio della Ricerca - Università di Salerno

Supercritical Assisted Atomization:a Performance Comparison between Laboratory and Pilot ScaleErnesto Reverchon*, Renata Adami*#, Giuseppe Caputo**Dipartimento di Ingegneria Chimica e Alimentare, Università di Salerno, I-84084, ItalyE-mail: ereverchon@unisa.it, FAX: 089964057#Department of Biochemistry & Food Chemistry, University of Turku, FIN-20014, FinlandSummaryThe SAA (Supercritical Assisted Atomization) process has been developed up to pilot scale.Some experiments have been performed on laboratory and pilot apparatuses to compare theperformance of the process on different scales. Zyrconil nitrate and rifampicin have been usedas model compounds. Different concentrations of zyrconil nitrate in water and rifampicin inmethanol have been tested. Particles of zyrconil nitrate with mean diameters ranging between0.3 and 0.6 µm and of rifampicin ranging between 0.5 and 2.5 µm have been obtained on bothapparatuses.IntroductionSupercritical assisted atomization has been recently proposed for the generation of particles offine chemical compounds in the micronic range and with controlled particle size distributions.It is based on the solubilization of controlled quantities of supercritical CO2 in liquid solutionscontaining a solid solute and on the subsequent atomization of the ternary solution through anozzle. SAA process efficiency is based on a two-step atomisation mechanism: primarydroplets are formed at the exit of the nozzle. Then, CO2 is released from the primary dropletsand secondary, smaller droplets are produced. Several compounds have been succesfullymicronized on the laboratory scale: superconductor and catalyst precursors, ceramics, andpharmaceutical compounds, using some different liquid solvents such as water, methanol, andacetone1. Particles ranging between about 0.5 and 4 µm have been as a rule obtained;amorphous or crystalline particles have been produced depending on the chemical nature ofthe solid product and on the temperature of the precipitation vessel. In this work, a pilot scaleplant has been developed to assess if SAA large scale processing is feasible. The design of thenew plant has been finalized to obtain a ten times increase of the production rate.ExperimentalThe apparatus used for SAA experiments mainly consists of three feed lines used to deliversupercritical CO2, the liquid solution and an inert gas. CO2 and the liquid solution are sent to ahigh-pressure vessel (saturator), loaded with stainless steel perforated saddles using two high-pressure pumps. An adequate residence time produces the dissolution of the gaseous stream inthe liquid. Then, a spray is produced delivering the ternary mixture to an 80 µm diameterstainless steel nozzle in the case of the laboratory scale plant and a 200 µm diameter nozzle incase of the pilot plant. Droplets are formed in the precipitator (I.V. 3 dm3 blench scale, 12dm3 pilot scale) that operates at atmospheric pressure. A flow of heated N2 is also delivered tothe precipitator with the scope of favouring the evaporation of the liquid solvent. Samples ofthe processed powder were observed by Scanning Electron Microscopy (SEM). Particle SizeDistributions (PSDs) were measured considering about 1000 particles in each calculation.More details on the SAA apparatus and experimental procedures were previously published2.Results and discussionSystematic experiments were performed to micronize zyrconil nitrate, a catalyst precursor, inH2O at different concentrations of the solute using the bench plant and repeating the sameexperiments on the pilot plant at the same operating conditions. The main difference betweenthe two apparatuses is the heating system of the precipitation vessel. In the case of the benchplant we used electric heaters bended around the vessel, in the case of the pilot plant we useda water jacket. This arrangement assures a better heating efficiency and a smoothertemperature distribution in the precipitator. Both apparatuses yield amorphous sphericalparticles with a relatively narrow particle size distribution (Figure 1).a bFigure 1 : Comparison of SEM image of zyrconil nitrate particles precipitated from H2O at 100mg/mL(a) laboratory scale plant, (b) pilot scale plantWe observed only a slight broadening of the particle size distribution in the case of the pilotplant (see Figure 2). This behaviour has been observed in all the experiments. Varying thesolution concentration from 50 to 100 mg/mL we observed an increase of the particle sizefrom 0.63 to 0.78 µm in the case of the bench scale plant and from 0.63 to 0.87 µm in the caseof the pilot plant.0 1 2 3 4010203040pilot scaleLaboratory scaleparticles, %diameter, µmFigure 2 : PSDs in terms of particle number percentages of zyrconil nitrate from H2O at 100mg/mLThe good results obtained for the system zyrconil nitrate-H2O were confirmed micronizing acompound of different chemical nature, rifampicin, a pharmaceutical principle, usingmethanol as liquid solvent. For what concerns the pilot plant productivity, the bestperformance has been 200g/h of precipitated material.References1. E. Reverchon, Ind. Eng. Chem. Res., 41, 2405 (2002)2. E. Reverchon, G. Della Porta, J. Supercrit. Fluids, 26, 243 (2003)

Supercritical Assisted Atomization:a Performance Comparison between Laboratory and Pilot Scale

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Supercritical Assisted Atomization:a Performance Comparison between Laboratory and Pilot Scale

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