Abstract :
[en] This thesis aims to analyse potential improvement pathways for the sodium dithionite
production process, with a specific focus on the first step of the process: the reaction
leading to the production of zinc dithionite. This work was carried out under the supervision
of Professor Dominique Toye (University of Liège – Department of Chemical
Engineering – PEPs), with the technical support of the company SILOX Belgium, located
at the PRAYON s.a. industrial site in Engis, Belgium.
The introductory chapter, Chapter 1, provides a detailed description of the batch process
used at SILOX Belgium for zinc dithionite production and introduces mesofluidic
reactors. These reactors offer several advantages compared to conventional batch systems,
including enhanced heat transfer due to a high surface-to-volume ratio, more
precise control of reaction conditions (temperature, concentration), and the possibility
of continuous operation, which improves reproducibility. Industrial scale-up relies on
the parallelisation of reactors in order to maintain a high surface-to-volume ratio. Nevertheless,
several challenges remain, such as the handling of solids in flow (maintaining
homogeneous suspensions and preventing fouling) as well as the implementation of reliable
online monitoring.
The first stage of this work focuses on developing a fundamental understanding of
the reaction mechanisms involved. Chapter 2 is dedicated to this aspect. The quantification
methods used are also presented, including iodometric titration, ATR-FTIR
spectroscopy, and monitoring of hydrogen production in batch operation. This work
also led to a scientific publication in Chemical Engineering Journal[1], in which some
preliminary results were presented in dimensionless form for confidentiality reasons related
to industrial data.
Chapter 3 details the design and implementation of the continuous-flow experimental
setup, including reactor geometry, heat exchange, and instrumentation used to monitor
concentrations and temperatures under steady-state conditions. The experimental
results obtained enabled the development and validation of a numerical reactor model.
This model allowed the determination of reaction kinetics and was subsequently used in
Chapter 4 to numerically optimise the reactor configuration and operating parameters
with a view toward industrial application.
Chapter 5 explores improvements in reaction control for the industrial batch reactor
without major modifications to the existing installation. Based on the batch reactor
modelling, the investigated strategies include increasing the initial feed rate to reduce
reaction time, as well as adding acid during the reaction to improve selectivity and
conversion.
Finally, Chapter 6 presents the general conclusions and perspectives, including a synthesis
of the experimental and modelling results, proposals for future improvements,
and possible pathways toward industrial implementation.
