Studies in process analysis and control in batch reactors
This work is part of a number of projects dealing with the development of novel techniques for better analysis and control of chemical processes carried out in batch reactors. The problems of pH measurement and sampling, linked to the implementation of NMR and HPLC on-line analysers, are presented as key areas in this development work. Also, part of the engineering work summarised in this thesis assisted the work of other researchers who participated in the project. In the area of sampling, the difficulties associated with the collection of representatives samples from agitated vessels are introduced. Also, the ideas of calibration and modelling of sampling systems are presented. Modelling tests were used to optimise the design and development of a fast sampling loop system to obtain representative samples from stirred vessels. In addition to this, the modelling studies also assisted the work of other researchers in the project who needed the kinetic and heat-exchange parameters for the process of esterification of crotonic acid. The fast sampling loop was shown to be adequate for the implementation of a low-field NMR system for on-line analysis. The development of discrete samplers designed to collect, dilute and deliver representative samples for LC analysis is also covered in this work. A Mark IV prototype of LC sampler was tested and developed to acceptable levels. In the area of pH measurement the advantages and disadvantages of the use of thermally grown iridium-oxide electrodes are introduced. Their response was compared to that of standard glass electrodes and found to be faster, more stable at high temperatures and no alkaline error was observed. However, the problem of drift of the signals was not fully overcome and it is presented as the limiting factor in the use of the sensors for on-line industrial measurements. Finally, a new type of total iridium-oxide probe is presented.