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In this thesis the control of the reactive distillation of dimethyl ether from methanol is investigated. This process presents challenges from a control standpoint. On top of challenges inherent to control of reactive distillation columns, the high product quality requirements and catalyst degradation must be considered during controller design.
To meet these challenges a novel Process Analytical Technology is developed. After a thorough analysis of existing technologies used for composition analysis the gas phase FT(M)IR is identified as the best technology to meet the requirements. The developed system can be used for real time composition analysis for high product purities in the presented process and can also be applied to other processes in chemical engineering. In dedicated experiments the performance characteristics of the Process Analytical Technology are determined. By extracting small amounts of sample from the column it is robust to changes within the process and can be calibrated offline. The system also the analysis of liquid and gas samples at multiple locations within the column without diminishing the performance characteristics using a single composition analyzer.
After the system was developed and tested in a stirred tank reactor it is implemented into a pilot plant. The pilot plant in combination with the measurement system is used to experimentally validate a dynamic model of the process. The developed model is used to accurately simulate the dynamic column behavior from a cold state to steady state operation. This model is extended to depict a plant with conditions expected in an industrial sized plant, with a high product purity and conversion, operating close to the degradation temperature of the catalyst.
The model is also used to analyze the multiplicity behavior of the plant, multiplicities were detected outside the operating window of the plant but could not be validated experimentally.
Different control schemes are subsequently investigated and it is found that a linear cascading controller can be used to safely operate the plant and meet the control objectives. Additionally, the controller robustness and optimality are evaluated and the implementation of advanced process control schemes is found to only slightly improve controllability.
To conclude the analysis the startup procedure is investigated. The maximal catalyst temperature is found to heavily influence the time optimal startup procedure. A heuristic startup procedure is suggested, and it is shown that it is robust to deviations from optimal procedures. This strategy can be used to reduce the startup duration by one order of magnitude compared to the conventional startup.
The findings in this thesis will help the implementation of the reactive distillation of dimethyl ether into industrial practice. For the first time, it is demonstrated how safe and robust operation of such plants can be ensured under consideration of all relevant characteristics of this process. The developed Process analytical technology can be used for control and quality assurance in this and other processes in the chemical industry.