Chemical Engineering Journal 168 (2011) 896–902 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Imaging the supersaturation in high-pressure systems for particle generation Stefan Dowy a,b , Enza Torino b,c , Sebastian Klaus Luther a,b , Matthias Rossmann b,d , Andreas Braeuer a,b,∗ a Lehrstuhl für Technische Thermodynamik, Universität Erlangen-Nürnberg, Am Weichselgarten 8, 91058 Erlangen, Germany b Erlangen Graduate School in Advanced Optical Technologies (SAOT), Universität Erlangen-Nürnberg, Paul-Gordan-Str. 6, 91052 Erlangen, Germany c Chemical and Food Engineering Department, University of Salerno, Via Ponte Don Melillo 1, 84084 Fisciano, Salerno, Italy d Lehrstuhl für Prozessmaschinen und Anlagentechnik, Universität Erlangen-Nürnberg, Cauerstrasse 4, 91058 Erlangen, Germany article info Article history: Received 23 July 2010 Received in revised form 11 November 2010 Accepted 22 November 2010 Keywords: Supersaturation Particle nucleation Particle precipitation High-pressure Elastic light scattering Supercritical antisolvent process SAS abstract The supersaturation which is the driving force for particle precipitation was quantified in situ for the injection of a solution into a supercritical antisolvent. Firstly, saturation mole fractions of the solute yttrium acetate were measured via elastic light scattering in the homogeneous ternary system, which is composed of the solute itself, the solvent dimethylsulfoxide and the antisolvent carbon dioxide. The saturation experiments were carried out at pressures of 8.5, 12 and 16 MPa and at a temperature of 313 K. Secondly, applying a Raman based optical measurement technique the actual solute mole fraction was imaged in situ during the injection of the solution (solute dissolved in solvent) into the antisolvent. The injection experiments were carried out at pressures of 12 and 16 MPa and at a temperature of 313 K. Finally, the ratio of the actual solute mole fractions and the saturation solute mole fractions, which were measured during the injection experiment and during the saturation experiment, respectively, quantifies the supersaturation. High supersaturation values are evidenced already close to the nozzle exit. For the first time, an optical method was developed to measure the supersaturation in situ in a dynamic process under high-pressure. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The field of nanomaterials is a fascinating area of research that has found many applications of technological interest in diverse fields such as pigments, drugs, metal oxides, pharmaceuticals and inorganic materials [1,2]. In recent years, significant progress has been made in supercritical fluid technology, particularly in the generation of a large number of nano-sized particles by precip- itation [3–6]. Therefore, an important question that needs to be satisfactorily addressed in supercritical particle precipitation is the mechanism of particle formation. A significant factor that mainly influences the particle formation process is the degree of supersaturation of the solution which can be influenced by the process conditions. There are several methods to measure supersaturation for liquid and vapour phase processes at ambient conditions [7], but the experimental data concerning supersatu- ration in high-pressure processes is fairly poor [8]. As there is an increasing interest in the application of supercritical fluid technolo- gies to generate different kinds of particles at different operative ∗ Corresponding author at: Lehrstuhl für Technische Thermodynamik, Universität Erlangen-Nürnberg, Am Weichselgarten 8, 91058 Erlangen, Germany. Fax: +49 9131 8525853. E-mail address: andreas.braeuer@aot.uni-erlangen.de (A. Braeuer). conditions, the principles of these processes need to be further enlightened. Several advantages must be considered using supercritical flu- ids compared to conventional routes. Among them, supercritical carbon dioxide (scCO 2 ) is preferred because of its extremely mod- erate critical parameters ( c = 7.4 MPa, T c = 304 K) [9]. In the last years, different antisolvent processes based on the antisolvent CO 2 have been proposed to produce micro or nanoparticles. Besides, in the post-processing step, the solid particles can be separated from the fluid phase (solvent and antisolvent) on a filter and the antisol- vent CO 2 can be separated from the solvent easily by reducing the pressure [10]. Supercritical precipitation techniques have the capa- bility to produce several different kinds of particles with controlled morphology and a very narrow size distribution [11]. At differ- ent operation conditions, nanoparticles, microparticles, balloons or crystals can be produced [2,12,13]. Among the numerous particle formation processes, the supercritical antisolvent (SAS) technol- ogy is especially useful to gently treat thermo-labile particulate, mechanical sensitive and other high purity materials which must not be spoiled with residuals of harmful organic solvents. In this work, the supersaturation measurements have been applied to the supercritical antisolvent process (SAS). The solute to be precipitated is dissolved in the liquid organic solvent to form a solution. Most suitable, the solute is totally insoluble in the anti- solvent/solvent mixture while the solvent is completely miscible in 1385-8947/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2010.11.088