(376e) Towards the Kinetic Analysis of Solid/liquid Reaction Systems from Focused Beam Laser Reflectance Measurements (FBRM) In a High Performance Small Scale Reaction Calorimeter

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.