Katalytische Conversie van Duurzame Grondstoffen met behulp van Gedragen en Bulk Titanium Dioxide

In this dissertation, we aim to expand on the topic of titanium dioxide catalysis with particular focus on applications in the valorization of bio-derived materials. Utilization of these bio-derived feedstocks for the production of useful chemicals is critical towards minimizing the environmental impact of the chemical industry by reducing the usage of petrochemicals, for which there is growing social demand. This concept acts as an over-arching theme throughout the dissertation, as is emphasized in Chapter 1 where the broad goals of this work are outlined. In Chapter 2 of this work, we present an overview on the (non-photocatalytic) catalytic applications of both bulk and dispersed titanium dioxide. Here, the polymorphs of titanium dioxide are discussed and their applications in aminolysis, dehydration, esterification, and nitrilation are compared, demonstrating how polymorphism is a critical aspect to considering during catalysis. Chapter 3 acts as a continuation of previous work performed by this lab on the gas phase cyclic dimerization of alkyl lactates to L-lactide, the key precursor to polylactic acid, using a dispersed titania on silica catalyst. This previous work performed focused on catalyst and reaction optimization, with the potential economic and environmental impacts remaining unexplored. In efforts to remedy this, a techno-economic analysis and life cycle assessment were sought after for comparison to the current state-of-the-art utilized in industry for lactide synthesis, the oligomerization-depolymerization (OD) technology. While previous kinetic models were developed for the formation of lactide over the dispersed titania on silica catalyst, a critical limitation was its inability to predict the respective ratios of L-lactide and meso-lactide. Due to the similarity in physical properties of the stereoisomers, the purification step to obtain the pure L-lactide is one of the most cost intensive segments in the process chain, and vital to model accurately when using kinetic modelling. Therefore, an extensive set of experiments were performed using diverse reaction conditions, by adjusting partial pressures, temperatures, and catalyst loadings to understand how these affected the productivity of the catalyst and obtained product yields. The resulting information was utilized in the development of a state-of-the-art kinetic model which was able to accurately predict changes in product yields in accordance to altering reaction conditions. This kinetic model was used in the simulation of a novel industrial sized plant, being used to predict the productivity of plug flow fixed-bed reactor units. This plant incorporated the esterification of lactic acid before being fed into said reactor units to undergo cyclic dimerization. For an apt comparison to our novel esterification-cyclic dimerization (ECD) technology, the current state-of-the-art OD technology was also modelled and underwent the same techno-economic and life cycle analyses. Simulations of the respective plants revealed that the ECD technology was capable of outperforming the currently established OD technology, producing a substantial 16% more L-lactide. Techno-economic analysis of these plants revealed the ECD technology required a significantly lower initial investment for building the plant, while operational costs were comparable between the technologies. Coupling the lower capital required with the higher productivity, a reduction in manufacturing cost price of 19% was realized compared to the current state-of-the-art technology. Furthermore, the life cycle assessment of the respective plants displayed an environmental advantage in lowering equivalent CO2 emissions by 15% per kg of L-lactide produced. Integrating these technologies into the full process chain from fermentation of sugars to ring-opening polymerization displayed that our technology was capable of reducing the minimum selling price of poly-lactic acid by 18%. Chapter 4 marks the beginning of a new investigation into catalyst optimization, focusing on the nitrilation reaction as catalyzed by bulk phase titanium dioxide. Previous studies on the topic displayed the potential of this reaction through the mixed polymorph titania catalyzed nitrilation of ethyl acrylate to acrylonitrile (a key monomer used in many plastics), performing a techno-economic analysis to display competitive prices with petrochemical based acrylonitrile. However, the reaction suffered from substantial catalyst deactivation, acting as a core limitation. Therefore, an investigation into this topic was instigated with two core focal points: determination of the cause of catalyst deactivation, and the role polymorphism plays in the nitrilation reaction for potential reaction optimization. Using time-of-flight secondary ion mass spectroscopy, it was inferred that the deactivation noted was a result of polymerization of the formed acrylonitrile on the catalyst surface, with said polymerization occurring through the unsaturated bonds on the carbon tail. This was further evidenced by the reaction being stabilized when using the saturated equivalent to ethyl acrylate, ethyl propionate. Comparing the catalytic activity of the anatase and rutile polymorphs using the stable nitrilation of ethyl propionitrile to propionitrile, it was revealed that the anatase polymorph exhibited substantially higher activity towards this nitrilation reaction than the rutile polymorph. Catalytic activity correlated well with the acid number and acid site densities. Critically, these correlations were independent per polymorph, emphasizing the role the surface structure plays in the reaction. As a continuation of the previous chapter, Chapter 5 focuses on investigating the mechanism of the nitrilation reaction over the anatase surface in order to understand the optimal route for rational catalyst design. The nitrilation of ethyl acetate to acetonitrile was used as a case study. It is typically understood that this reaction occurs through a sequential aminolysis of the ester to form the respective amide before dehydration occurs to form the end product nitrile. Utilizing infrared spectroscopic analysis, it was indicated that the ester dissociated on the surface in conjunction to the consumption of hydroxyl groups. The formation of ethanol as a result of this dissociation was confirmed via temperature programmed desorption coupled mass spectroscopy, further evidencing the formation of a reactive carboxylate species on the surface. Through pulse testing, the formation of the carboxylate species was revealed to be integral to the formation of the respective nitrile. This displayed the presence of the hydroxyl group on the surface of the catalyst as a critical aspect to facilitate the reaction, providing guidance towards future catalyst design. Density functional theory was used to compare reaction routes between the carboxylate species and ammonia, where it was shown the carboxylate was more likely to react with gas phase ammonia than adsorbed ammonia, indicating the formation of an intermediate amide (before dehydration to the nitrile) occurs through an Eley-Rideal mechanism. Further infrared spectroscopic studies between acetonitrile and the anatase surface revealed the formation of bridged intermediate species, which allowed for the deduction of a sequential dehydration reaction to obtain the nitrile end product. From the information gathered in this chapter, it can be determined that further catalyst optimization for this reaction should focus on increasing the precedence of hydroxyl groups on the catalyst surface to induce more active sites for the required ester activation step.