Developing fundamental understanding of thermal processing of (catalyst) formulations

Gibson, Rebecca Louise ORCID: 0000-0002-0061-6150 (2022). Developing fundamental understanding of thermal processing of (catalyst) formulations. University of Birmingham. Eng.D.

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Thermal processes are key steps in the manufacture of catalysts and functional materials. These large-scale processes are often scaled-up using empirically or experientially derived rules, which result in inefficiently sized assets and longer than necessary processing times. A model-based approach to interrogating thermal processes allows for safer, more informed scale up, resulting in optimised product quality.

A statistically rigorous modelling methodology based on the Sestak-Berggren equation has been developed to quantitatively interpret the results of thermal analysis experiments. This allows the kinetic modelling of multiple overlapped thermal events/reactions, without a priori peak deconvolution. Akaike weights, a statistical metric, allows the comparison of multiple potential models, allowing the optimal number of thermal events occurring during an experiment to be identified. Verification of the internal consistency of the method was completed using in silico (computer generated) data. The impact of experimental noise was also investigated, and it was concluded that this modelling technique could still extract meaningful physical parameters in the presence of up to 10% white noise, although additional experiments may be required if noise levels are this high.

This modelling methodology was applied to multiple experimental systems; temperature programmed reduction (TPR) of a Fischer-Tropsch (FT) catalyst, ammonia temperature programmed desorption (TPD) from SAPO-34, ammonia TPD from ZSM-5 and the temperature programmed decomposition (TPDecomp) of a zinc nitrate catalyst precursor and of calcium carbonate. All derived models were subject to criticism, checking the plausibility of estimated mechanisms and parameters, and also checking for systematic error and overfit. The modified methodology produced good quality models for both the TPR and the ammonia TPD from SAPO-34 . However, fitting of data from both the ammonia TPD from ZSM-5 and the TPDecomp of the zinc nitrate catalyst precursor demonstrated systematic trends in residuals and implausible kinetic mechanisms. The study of calcium carbonate TPDecomp showed a dependence on weight hourly space velocity (WHSV). This raised issues with the data quality, implying transport limitations or reverse reactions could be present within some of the data.

These findings led to an investigation into the bulk heat and mass transport occurring within thermal analysis equipment. Pan-style and tubular reactors were compared using dimensionless analysis (Damköhler and Bodenstein numbers) based on the results of computational fluid dynamics (CFD) simulations. It was concluded that pan-style reactors are susceptible to heat and mass transport limitations and are not suitable for the collection of kinetic data. Tubular reactors of constant diameter are suitable for kinetic experimentation. However, not all thermal analysis experiments can be conducted in tubular equipment. Recommendations were made around conducting experiments to obtain data suitable for kinetic studies: where possible, tubular reactors with high carrier gas flow rates should be used.

Type of Work: Thesis (Doctorates > Eng.D.)
Award Type: Doctorates > Eng.D.
Licence: All rights reserved
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Chemical Engineering
Funders: Engineering and Physical Sciences Research Council
Subjects: T Technology > TP Chemical technology


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