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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Two approaches to green chemistry in industrially driven processes: aluminum tert-butoxide as a rate enhancing Meerwein-Ponndorf-Verley reduction catalyst applied to the technological transfer from batch to continuous flow and structural modifications of functionalized trialkylsilylamines as energy efficient carbon dioxide capture solvents

Flack, Kyle M. 14 June 2012 (has links)
Green chemistry principles have been applied to the enhancement of two industrial chemistry problems. An industrially used reaction to form alcohols from aldehydes and ketones, the Meerwein-Ponndorf-Verley reduction, was improved by introducing a new catalyst Al(OtBu)₃. Due to the lower state of aggregation of this catalyst versus the conventional Al(OiPr)₃ catalyst, reduction rates were found to be faster in both pure iPrOH and mixed solvent systems for three model compounds: benzaldehyde, acetophenone, and a complex, chiral ketone, (S)-CMK. This allowed for the successful implementation of two important milestones; lowering the amount of catalyst needed necessary to complete the reactions (an economic benefit and lower waste) and the conversion from traditional batch reactions to continuous flow (a processing benefit) whereby reactions can be scaled-out rather than scaled-up. Another industrially important field of research that was focused on was CO₂ capture. High energy demands from current CO₂ capture methods such as aqueous amine solvents, specifically from coal-fired power plant flue gas, led to the development of non-aqueous reversible ionic liquids based on silylated amines. Structural modifications of the substitution around the silicon atom, the length of the alkyl chain bonding the silicon and amine, branching along the alkyl backbone, and investigating secondary and primary amines within this class of silylated amines were completed. These amines were reacted with CO₂ and the CO₂ capacity, the ionic liquid viscosity, reversal temperature and reaction enthalpy were all considered as a function of structure. In all cases the capacity was found to be not only greater than that of monethanolamine, an industrial standard, but higher than theoretical predictions through the formation of carbamic acid. Viscosity, reversal temperature, and reaction enthalpy were all found to be tunable through structure. These modifications gave significant insight into the necessary direction for optimization of these solvents as energy-efficient replacements of current CO₂ capture technology.
2

Phosgenfreie Synthese von Isocyanaten unter Verwendung von CO2 und N-silylierten Aminen

Gründler, Franziska 30 May 2024 (has links)
Isocyanate sind wichtige Zwischenstufen bei der Herstellung zahlreicher Alltagsprodukte, von Matratzen über Lacke und Beschichtungen bis hin zu Kosmetika. Die industrielle Herstellung erfolgt mit Hilfe des reaktiven und giftigen Gases Phosgen. Im Rahmen der vorliegenden Dissertation wird ein vierstufiger Prozess zur phosgenfreien Synthese von Isocyanaten untersucht. Ausgehend von Aminen werden N-Silylamine erzeugt, die im Anschluss mit CO2 zur Reaktion gebracht werden. Dabei bilden sich O-Silylcarbamate, die bereits die NCO-Einheit der Isocyanate tragen. Durch eine N-Silylierung werden N,O-Bis(silyl)carbamate gebildet. Die Stoffklassen der silylierten Carbamate werden durch diese Dissertation um mehrere, bislang unbekannte Vertreter erweitert. Die anschließende thermische Zersetzung liefert erfolgreich die gewünschten Isocyanate. Als Spaltprodukt bildet sich das ungiftige, inerte Hexamethyldisiloxan. Mit diesem patentierten Verfahren gelingt es, CO2 als Kohlenstoff- und Sauerstoffquelle in industriell wichtige Monoisocyanate zu überführen. Die Anwendung auf Diisocyanate wird beleuchtet und erzeugt Potenzial für fortführende Arbeiten.

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