Abstract
The topic of present work was the epoxidation of light olefins on titanium silicate catalysts. Epoxidation of single olefins (ethene, propene, 1-butene and iso-butene) and mixtures of them were investigated. A material study allowed an extensive comparison of titanium silicate catalysts (TS-1 and Ti-MWW) and active sites, revealing the reactant-catalyst interactions present in the activation of the active titanium sites.
The epoxidation of olefins was performed in a laboratory-scale trickle bed reactor operating under transient and stationary states. An extensive set of conditions was screened for each case in these gas-liquid-solid systems. Hydrogen peroxide was the epoxidation agent, while methanol and acetonitrile were used as solvents. The reactants and products were analyzed by gas chromatography. The single olefin epoxidation experiments in the trickle bed reactor revealed the changes in the dynamic behavior depending of the alkene chain length and the molecular structure. The epoxidation of olefin mixtures demonstrated to improve the catalyst stability. Nonetheless, the product selectivity was strongly affected by the number of olefins in the mixtures. Ternary mixtures displayed to be highly selective compared to binary olefin mixtures.
The comparison of titanium silicates demonstrated important differences between these otherwise similar materials. Both materials displayed to be active under comparable mild conditions. However, Ti-MWW exhibited a better performance as acetonitrile was used as solvent, allowing a higher selectivity to the epoxide. TS-1 displayed to be more active, nevertheless, the utilization of methanol as the solvent generated a higher concentration of methoxy species as by-products. The analysis of the synthesis conditions of Ti-MWW demonstrated important changes with the calcination temperature. The acidity and surface areas demonstrated to be affected by this synthesis parameter.
The analysis of reactant-catalyst interactions indicated differences in the titanium active site response depending on the material. The spectroscopic analysis of the materials was carried out in an ATR-FTIR system allowing the contact of the reactants and the catalyst under controlled conditions. The ex-situ analysis allowed the observation of changes in the framework titanium vibration, and the utilization of in-situ modulation excitation spectroscopy permitted the observation of changes in the vibration due to time dependent concentration gradients.
The present study is a broad approach to the epoxidation on titanium silicates, being the reactants, materials and active sites studied. The utilization of transient techniques as step responses demonstrated to be a highly valuable tool to understand the behavior of reactive systems.
The epoxidation of olefins was performed in a laboratory-scale trickle bed reactor operating under transient and stationary states. An extensive set of conditions was screened for each case in these gas-liquid-solid systems. Hydrogen peroxide was the epoxidation agent, while methanol and acetonitrile were used as solvents. The reactants and products were analyzed by gas chromatography. The single olefin epoxidation experiments in the trickle bed reactor revealed the changes in the dynamic behavior depending of the alkene chain length and the molecular structure. The epoxidation of olefin mixtures demonstrated to improve the catalyst stability. Nonetheless, the product selectivity was strongly affected by the number of olefins in the mixtures. Ternary mixtures displayed to be highly selective compared to binary olefin mixtures.
The comparison of titanium silicates demonstrated important differences between these otherwise similar materials. Both materials displayed to be active under comparable mild conditions. However, Ti-MWW exhibited a better performance as acetonitrile was used as solvent, allowing a higher selectivity to the epoxide. TS-1 displayed to be more active, nevertheless, the utilization of methanol as the solvent generated a higher concentration of methoxy species as by-products. The analysis of the synthesis conditions of Ti-MWW demonstrated important changes with the calcination temperature. The acidity and surface areas demonstrated to be affected by this synthesis parameter.
The analysis of reactant-catalyst interactions indicated differences in the titanium active site response depending on the material. The spectroscopic analysis of the materials was carried out in an ATR-FTIR system allowing the contact of the reactants and the catalyst under controlled conditions. The ex-situ analysis allowed the observation of changes in the framework titanium vibration, and the utilization of in-situ modulation excitation spectroscopy permitted the observation of changes in the vibration due to time dependent concentration gradients.
The present study is a broad approach to the epoxidation on titanium silicates, being the reactants, materials and active sites studied. The utilization of transient techniques as step responses demonstrated to be a highly valuable tool to understand the behavior of reactive systems.
| Original language | English |
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| Place of Publication | Turku |
| Publisher | |
| Print ISBNs | 978-952-12-4293-9 |
| Electronic ISBNs | 978-952-12-4294-6 |
| Publication status | Published - 2023 |
| MoE publication type | G5 Doctoral dissertation (article) |