Femtochemie vibronisch gekoppelter, elektronisch angeregter Zustände von Carbonylverbindungen und hoch fluoriertem Benzol

In this Thesis, the femtochemistry of vibronically coupled excited electronic states of the carbonyl compounds acetone and cyclohexanone and the highly fluorinated benzene-derivative pentafluorobenzene was investigated after optical excitation under jet-cooled conditions using femtosecond time-resolved time-of-flight mass spectrometry and photoelectron imaging spectroscopy. After photoexcitation of the first excited electronic state of acetone, no signs for an α-CC bond cleavage were observed for up to one nanosecond, thereby indicating a bond dissociation in the corresponding triplet state in accordance with the established photochemical picture of a Norrish type I reaction. The two-photon excitation of acetone and cyclohexanone to high-lying Rydberg states induced ultrafast dynamics mediated by the vibronic coupling to the ππ* valence state. After internal conversion to the ππ* state, the α-CC bond of acetone was observed to break in 50-90 femtoseconds. After femtosecond excitation of pentafluorobenzene to the optically bright ππ* excited electronic state, pronounced and long-lived transient oscillations of the parent ion yield were observed. The combination of ab initio electronic structure calculations and quantum dynamics simulations revealed the physical mechanism at the origin of the phenomenon in the shape of very large vibronic coupling strengths with the energetically higher-lying πσ* state along several out-of-plane molecular vibrations. The excited wavepacket periodically oscillates on the ππ* electronic potential energy surface for several picoseconds, thus strongly mixing the initial electronic character with πσ* character near the outer turning points. The probe laser pulse maps this vibrational motion into the observed signal oscillations.In dieser Dissertation wurde die Femtochemie vibronisch gekoppelter, angeregter Elektronenzustände der Carbonylverbindungen Aceton und Cyclohexanon sowie des Benzol-Derivats Pentafluorbenzol im Molekularstrahl mittels femtosekunden-zeitaufgelöster Flugzeit-Massenspektrometrie und Photoelektronen-Geschwindigkeitskartographie untersucht. Nach optischer Anregung des ersten angeregten elektronischen Zustands von Aceton konnten innerhalb von einer Nanosekunde keine Anzeichen eines Bruchs der α-CC Bindung beobachtet werden, was auf den Bruch dieser Bindung in dem entsprechenden Triplett-Zustand nach dem anerkannten photochemischen Mechanismus einer Norrish Typ I Reaktion hindeutet. Die Zwei-Photonen-Anregung von Aceton und Cyclohexanon in hochenergetische Rydbergzustände induzierte eine ultraschnelle Dynamik, die durch die vibronische Kopplung mit dem ππ* Valenzzustand verursacht wird. Nach interner Konversion in den ππ*-Zustand wurde der Bruch der α-CC Bindung von Aceton in 50-90 Femtosekunden beobachtet. Nach Femtosekunden-Anregung des optisch hellen, elektronisch angeregten ππ*-Zustands von Pentafluorbenzol wurden ausgeprägte und langlebige Oszillationen der transienten Ionenausbeute des Stammmolekülions beobachtet. Durch die Kombination von elektronischen ab initio-Strukturrechnungen sowie Quantendynamiksimulationen wurde der dahinterstehende physikalische Mechanismus in Form von sehr großen vibronischen Kopplungen mit dem energetisch höherliegenden πσ*-Zustand entlang von out-of-plane-Molekülschwingungen aufgeklärt. Das angeregte Wellenpaket oszilliert für mehrere Picosekunden periodisch auf der elektronischen Potentialfläche des ππ*-Zustands, wobei der ursprüngliche elektronische Charakter an den äußeren Wendepunkten stark mit πσ*-Charakter gemischt wird. Der Abfrage-Laserpuls bildet diese Schwingungsbewegung in die beobachteten Signaloszillationen ab

Continuous sugar upgrading using Lewis acid catalysts

Sugar upgrading to commodity chemicals has become prevalent over the last decades, owing in part to the potential of Lewis acid catalysts, in particular Sn-Beta zeolites. Sn-Beta has shown to possess high activity for the conversion of glucose to fructose as well as smaller molecules such as α-hydroxy esters (methyl lactate and methyl vinyl glycolate) and trioses (dihydroxyacetone, glyceraldehyde, pyruvaldehyde). Despite its promising kinetic potential, drawbacks that hinder it from being an industrially-used catalyst include the relatively low amount of Sn capable of being incorporated and the requirement of fluoride media to successfully synthesise Sn-Beta. Thus, top-down methods such as solid-state incorporation (SSI) has been of great interest for hard-to-incorporate heteroatoms such as Sn at higher wt. %. With this in mind, this thesis begins with an in-depth mechanistic study in the SSI of Sn-Beta, observing the acetate-zeolite interaction/evolution from the initial mechanochemical step to the ramp rate, both in inert gas flow and air using in situ spectroscopic techniques (Chapter 3). Furthermore, an optimised protocol for the heat treatment is obtained, having no negative impact in the kinetic performance of the zeolite. Chapter 4 investigates the influence of using different initial precursor (B, Fe, Ga, Al) for the zeolites’ subsequent SSI. Tests were done with glucose isomerisation as well as retro-aldol fragmentation in continuous flow. Following this, Chapter 5 demonstrates the application of a different type of Lewis acid catalyst: metal-organic frameworks (MOFs). The MOFs i.e., UiO-66(Zr) were studied in different polar solvents under continuous flow to understand their stability and were subsequently tested for disaccharide (lactose) isomerisation, a substrate which would typically not be possible to upgrade using conventional zeolites. Lactose isomerisation was done using binary mixtures of alcohol/water to successfully carry out the reaction. Chapter 6 sets out to carry out the SSI protocol, conventionally done in hydroxide-assisted zeolites, in fluoride-assisted zeolites. Tests were conducted firstly in a commercial, hydroxide-assisted zeolite using an alkaline media along with a pore directing agent at various temperatures. Thereafter, SSI protocol was conducted for three fluoride zeolites (Hf-, Sn-, Zr-) using the same conditions. Lastly, Chapter 7 discusses the results acquired as well as any pertaining challenges which might have been left open due to aforementioned results

Refinery Integration of By-Products from Coal-Derived Jet Fuels

The final report summarizes the accomplishments toward project goals during length of the project. The goal of this project was to integrate coal into a refinery in order to produce coal-based jet fuel, with the major goal to examine the products other than jet fuel. These products are in the gasoline, diesel and fuel oil range and result from coal-based jet fuel production from an Air Force funded program. The main goal of Task 1 was the production of coal-based jet fuel and other products that would need to be utilized in other fuels or for non-fuel sources, using known refining technology. The gasoline, diesel fuel, and fuel oil were tested in other aspects of the project. Light cycle oil (LCO) and refined chemical oil (RCO) were blended, hydrotreated to removed sulfur, and hydrogenated, then fractionated in the original production of jet fuel. Two main approaches, taken during the project period, varied where the fractionation took place, in order to preserve the life of catalysts used, which includes (1) fractionation of the hydrotreated blend to remove sulfur and nitrogen, followed by a hydrogenation step of the lighter fraction, and (2) fractionation of the LCO and RCO before any hydrotreatment. Task 2 involved assessment of the impact of refinery integration of JP-900 production on gasoline and diesel fuel. Fuel properties, ignition characteristics and engine combustion of model fuels and fuel samples from pilot-scale production runs were characterized. The model fuels used to represent the coal-based fuel streams were blended into full-boiling range fuels to simulate the mixing of fuel streams within the refinery to create potential 'finished' fuels. The representative compounds of the coal-based gasoline were cyclohexane and methyl cyclohexane, and for the coal-base diesel fuel they were fluorine and phenanthrene. Both the octane number (ON) of the coal-based gasoline and the cetane number (CN) of the coal-based diesel were low, relative to commercial fuels ({approx}60 ON for coal-based gasoline and {approx}20 CN for coal-based diesel fuel). Therefore, the allowable range of blending levels was studied where the blend would achieve acceptable performance. However, in both cases of the coal-based fuels, their ignition characteristics may make them ideal fuels for advanced combustion strategies where lower ON and CN are desirable. Task 3 was designed to develop new approaches for producing ultra clean fuels and value-added chemicals from refinery streams involving coal as a part of the feedstock. It consisted of the following three parts: (1) desulfurization and denitrogenation which involves both new adsorption approach for selective removal of nitrogen and sulfur and new catalysts for more effective hydrotreating and the combination of adsorption denitrogenation with hydrodesulfurization; (2) saturation of two-ring aromatics that included new design of sulfur resistant noble-metal catalysts for hydrogenation of naphthalene and tetralin in middle distillate fuels, and (3) value-added chemicals from naphthalene and biphenyl, which aimed at developing value-added organic chemicals from refinery streams such as 2,6-dimethylnaphthalene and 4,4{prime}-dimethylbiphenyl as precursors to advanced polymer materials. Major advances were achieved in this project in designing the catalysts and sorbent materials, and in developing fundamental understanding. The objective of Task 4 was to evaluate the effect of introducing coal into an existing petroleum refinery on the fuel oil product, specifically trace element emissions. Activities performed to accomplish this objective included analyzing two petroleum-based commercial heavy fuel oils (i.e., No. 6 fuel oils) as baseline fuels and three co-processed fuel oils, characterizing the atomization performance of a No. 6 fuel oil, measuring the combustion performance and emissions of the five fuels, specifically major, minor, and trace elements when fired in a watertube boiler designed for natural gas/fuel oil, and determining the boiler performance when firing the five fuels. Two different co-processed fuel oils were tested: one that had been partially hydrotreated, and the other a product of fractionation before hydrotreating. Task 5 focused on examining refining methods that would utilize coal and produce thermally stable jet fuel, included delayed coking and solvent extraction. Delayed coking was done on blends of decant oil and coal, with the goal to produce a premium carbon product and liquid fuels. Coking was done on bench scale and large laboratory scale cokers. Two coals were examined for co-coking, using Pittsburgh seam coal and Marfork coal product. Reactions in the large, laboratory scaled coker were reproducible in yields of products and in quality of products. While the co-coke produced from both coals was of sponge coke quality, minerals left in the coke made it unacceptable for use as anode or graphite grade filler