A wide variety of industrially or biologically relevant chemical processes, e.g. Grignard chemistry or the respiration of living organisms involve multiphase reactions systems. There is no doubt that the understanding of these systems is of considerable importance.
Consider the dissolution of a solid powder into a chemically reactive liquid. Compared to homogeneous reactions in solution the kinetics of solid/liquid biphasic systems are more complex due to the mass transfer of the solid into the reactive liquid. This mass transfer is known to be dependent on the particle size [1] and it is desirable to measure the time resolved particle size distribution (PSD) during the course of a reaction.
Over the past few years, we have developed high performance small scale reaction calorimeters (50mL, -70 to 180°C, up to 70bar) based on the combined principles of heat balance and power compensation [2,3]. The reactor comprises a well defined environment for the kinetic analysis of chemical reactions via the reaction heat and various analytical hyphenated in situ devices such as mid-IR and UV-Vis ATR spectroscopy. Importantly, our latest generation reactor was designed to perfectly accommodate a probe for focused beam laser reflectance measurements (FBRM). FBRM provide information on the particle size distribution (PSD) via the measured chord length distribution (CLD). The combination of these analytical devices is ideally suited to study the reaction kinetics from the perspective of both the solid and the liquid phase.
While Beer's law defines a simple linear relationship between spectroscopic absorbance measurements and concentrations in solution there is unfortunately no physical model that extracts quantitative information on the solid particles from FBRM. Few empirical methods have been proposed [4].
For our well defined reactor environment, we investigate the possibilities to quantitatively use the FBRM device. For this, the device is studied under various experimental conditions, such as hydrodynamics, solid particle types, device settings, etc. Results are compared to those obtained from the manufacture's reference setup and/or available literature data. Important issues to be considered include for example reproducibility and sensitivity. From this, we propose a calibration method most suitable for our reactor environment relating the CLD to the amount of mass depending on the mean particle size.
On our path towards a kinetic analysis of solid/liquid biphasic reactive systems, we ultimately intend to incorporate the additional analytical signals from FBRM into our existing established methods for the multivariate non-linear optimisation of kinetic data from time resolved absorbance spectroscopy and calorimetry [5,6].
This project is funded by the Swiss National Science Foundation (SNF) no. 200021-113473.
[1] LeBlanc S.E., Fogler H.S. Population balance modelling of the dissolution of polydisperse solids: rate limiting regimes. AIChE (1987) 33: 54-63
[2] Visentin F., Gianoli S.I., Zogg A., Kut O.M., Hungerbühler K. A pressure-resistant small-scale reaction calorimeter that combines the principles of power compensation and heat balance (CRC.v4). Organic Process Research & Development (2004) 8: 725-737.
[3] Zogg A., Fischer U., Hungerbühler K. A new small scale reaction calorimeter that combines the principles of power compensation and heat balance. Industrial and Engineering Chemistry Research (2003) 42: 767-776
[4] Clarke M.A., Bishnoi P.R. Determination of the intrinsic rate constant and activation energy of CO2 gas hydrate decomposition using in-situ particle size analysis. Chemical Engineering Science (2004) 59: 2983–2993
[5] Puxty G., Fischer U., Jecklin M., Hungerbühler K. Data-oriented process development: determination of reaction parameters by small-scale calorimetry with in situ spectrospcopy. Chimia (2006) 60: 605–610
[6] Maeder M. and Neuhold Y.M. Practical Data Analysis in Chemistry. Elsevier, Amsterdam 2007.