Chemical Engineering Science 60 (2005) 805 – 814 www.elsevier.com/locate/ces New method for the determination of precipitation kinetics using a laminar jet reactor Mousa Al-Tarazi ∗ , A. Bert M. Heesink, Geert F. Versteeg Faculty of Chemical Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands Received 29 April 2004; received in revised form 21 September 2004; accepted 27 September 2004 Available online 18 November 2004 Abstract In this paper a new experimental method for determining the kinetics of fast precipitation reactions is introduced. Use is made of a laminar jet reactor, which is also frequently applied to determine the kinetics of homogeneous gas–liquid reactions. The liquid containing one or more of the precipitating reactants passes a gas-filled reactor as a stagnant jet in which no mixing occurs. The remaining reactant needed for precipitation is supplied in gaseous form and causes the precipitation reaction to occur while it is diffusing into the jet. Hydrodynamics as well as transport phenomena are precisely known for this system, whereas agglomeration can be minimized by adjustment of the concentration of the solute supplied by the gas. The kinetics of the different crystallization steps can be determined by analyzing the size distribution of the produced particles. This new method is experimentally demonstrated for the precipitation of CuS using H 2 S gas. The obtained data were successfully used to simulate a packed bed absorber in which H 2 S is absorbed by a CuSO 4 solution.  2004 Elsevier Ltd. All rights reserved. Keywords: Absorption; Mass transfer; Multiphase reactor; Precipitation kinetics; Gas–liquid; Laminar jet 1. Introduction In a precipitation process, two or more reactants form a solid product (Mersmann et al., 1994). In many cases, the solubility of this product is very low. So when the re- actants are brought together, a high degree of supersatu- ration occurs, which leads to the nucleation of new crys- tals and subsequent crystal growth. These processes proceed simultaneously in a given system. Secondary processes such as agglomeration and Ostwald ripening may also occur. All processes together determine ultimate product quality such as particle size distribution. In almost all industrial cases, precipitation is followed by a separation process that prefers coarse over fine parti- cles. In most crystallizers, it is therefore desired to produce coarse particles of narrow size distribution. Although pre- cipitation is a common operation in the chemical industry, it ∗ Corresponding author. E-mail address: m.y.m.al-tarazi@utwente.nl (M. Al-Tarazi). 0009-2509/$ - see front matter  2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2004.09.043 remains very difficult to predict the size distribution of the produced particles. Particle size is a complex function of nu- cleation rate, crystal growth and agglomeration of the crys- tals (Mersmann, 1993). Knowledge of intrinsic precipitation kinetics is of crucial importance for the design and con- trol of a precipitator. Such kinetic data have been measured for better soluble solids such as calcium carbonate, silver nitrate and calcium oxalate using the conventional mixed suspension mixed product removal (MSMPR) method, us- ing a more or less ideally stirred vessel. For determining the crystallization kinetics of very fast precipitating solids, the MSMPR method is less suited since (local) precipitation rates may be much faster than (local) mixing rates. The pre- cise hydrodynamics inside the crystallizer should be known then, but this is hardly the case with the MSMPR method. Nevertheless, because of the lack of alternative methods, many researchers have applied the MSMPR method to mea- sure the precipitation kinetics of sparingly soluble solids (e.g. Rodgers and Bertherton, 1998; Palosaari et al., 1996; Graber et al., 1996; Al-Tarazi et al., 2004b; Narayan et al., 1992).