I fenomeni di trasferimento di massa sono un fattore limitante soprattutto nelle reazioni di chimica organica gas-liquido. Questo problema può essere superato sfruttando l'enorme aumento del rapporto superficie-volume quando si nebulizza una soluzione. Ogni goccia generata in questo modo reagirà come un singolo reattore. In questa tesi sono ampiamente studiate sia la foto-ossidazione selettiva di solfuri organici a solfossidi, sia l'utilizzo di CO2 per la sintesi di carbonati ciclici partendo dai corrispondenti epossidi. Una reazione modello è stata scelta per lo studio dell'ossidazione fotochimica di un solfuro solubile in acqua al corrispondente solfossido mediata dall’ ossigeno di singoletto: Per questa reazione sono stati costruiti diversi setup strumentali con l'obiettivo di migliorare la conversione finale e il recupero di massa del processo. Un reattore aerosol fotochimico è stato quindi progettato e costruito in collaborazione con l'Università di KULeuven, permettendo di raggiungere il 95% di conversione finale e la completa selettività verso il solfossido. Il fattore di accelerazione della cinetica di reazione è 144 rispetto alle condizioni di reazione classica. L'espansione metodologica della reazione modello verso solfuri organici non solubili in acqua è stata poi portata avanti in condizioni bulk ponendo le basi per ulteriori esperimenti in aerosol. In questo caso una miscela acqua:etanolo è stata scelta come solvente verde per questioni di sicurezza e sostenibilità ambientale. I cambiamenti climatici rappresentano una minaccia per la vita umana, e i loro effetti sull'ambiente e sullo sviluppo economico e sociale sono ampiamente studiati. Evidenze scientifiche inequivocabili collegano il cambiamento climatico alle emissioni di gas a effetto serra ed identificano la CO2 come uno di questi gas. Per questo motivo si è pensato di utilizzare la CO2 come gas reattivo nella sintesi dello stirene carbonato partendo dallo stirene ossido: Questa sintesi è stata identificata come la reazione modello per studi futuri. Senza alcuna esperienza precedente in questo campo è stato necessario effettuare un ampio studio della letteratura scientifica con l'obiettivo di identificare il miglior catalizzatore adatto ad un reattore aerosol. Il complesso KI/tetraetilen glicole è stato scelto come catalizzatore per il confronto tra la reazione bulk e quella aerosol per le sue caratteristiche, ideali per questa tipologia di sintesi. Lo studio cinetico a diverse temperature della reazione modello in condizioni di bulk e aerosol ha permesso di ottenere fattori di accelerazione fino a 1,85. Sfortunatamente non è stato possibile, durante il periodo di dottorato, lavorare con un reattore a flusso di aerosol per la reazione con la CO2 a causa della configurazione inadeguata dei reattori a disposizione e alla bassa reattività del gas. Per ovviare a questa mancanza è stato progettato e costruito un reattore aerosol modulare potenzialmente in grado, nel prossimo futuro, di sfruttare pienamente i vantaggi dell'aerosol: Nonostante la difficile raccolta dati, dettata del nuovo approccio scelto sulle tecnologie CCU, i risultati raggiunti sono stati sufficienti per ottenere un partenariato in un progetto NATO chiamato TANGO. Il gruppo di ricerca si concentrerà quindi sulla sintesi di nuovi catalizzatori supportati su nanoparticelle magnetiche che, si spera, possano convertire lo stirene ossido in stirene carbonato con un alta resa e tempi di reazione più rapidi. Tutti gli esperimenti necessari andranno a sfruttare il reattore modulare recentemente progettato e costruito a partire dall'esperienza maturata sulla reazione modello. La reazione modello riportata in questa tesi sarà anche il benchmark per le reazioni future.

Overcoming light and mass transfer phenomena in gas-liquid biphasic reactions: introduction of the aerosol methodological paradigm Mass transfer phenomena are a limitation factor especially in gas-liquid organic chemistry reaction. This issue can be overcome by exploiting the huge increase of the surface to volume ratio when spraying the reaction solution. Each droplet generated this way will react as a single reactor. In this thesis the selective photo-oxidation of organic sulfides to sulfoxides and the utilization of CO2 for the synthesis of cyclic carbonates from the corresponding epoxides are both widely studied. A model reaction has been chosen for the study of the photochemical oxidation of a water soluble sulfide to the corresponding sulfoxide mediated by singlet oxygen: For this reaction several setup were built with the aim of enhancing the final conversion and the mass recovery of the process. A photochemical aerosol reactor was design and built in collaboration with the University of KULeuven to obtain allowing us to reach 95% conversion and complete selectivity toward the sulfoxide. The acceleration factor of the reaction kinetic is 144 compared to the bulk reaction. The scope expansion of the model reaction towards organic sulfides that are not soluble in water was then carried on to place the foundation for further aerosol experiments. In this case a water:ethanol mixture is choose as green solvent for safety and environmental issues. Severe climate change represents a threat for human life, and its effects on environment, economic and social development is widely studied. Unequivocally scientific evidences link climate change to greenhouse gases emissions, and identify CO2 as a greenhouse gas. For this reason we thought of using CO2 as a reactive-carrier gas to carry out the synthesis of styrene carbonate from styrene oxide: This synthesis was identified as the model reaction for further studies. Without any previous experience in this field an extensive study of the scientific literature was done with the aim of identifying the best catalyst suitable for an aerosol reactor. KI/tetraethylene glycol is choose as catalyst for the comparison between bulk and aerosol reaction due to its features. The kinetic study at different temperature of the model reaction in bulk and aerosol batch condition was carried on giving an acceleration factor up to 1,85. Unfortunately it was impossible during the PhD period to work with an aerosol flow reactor for CO2 reaction due to inadequate reactor setup and low reactivity of the gas. For this purpose a modular aerosol reactor has been design and built to being able, in the forthcoming future, to fully exploit microdroplets environment: Even if several data were collected with extreme difficulties, due to the novel approach choose on CCU technologies, those were sufficient to obtain a partnership for a NATO project call TANGO. The research group will now focus on the synthesis of new catalysts supported on magnetic nanoparticles that, hopefully, can convert styrene oxide into styrene carbonate with high yield and faster reaction time. All the experiments necessary are going to be exploiting the modular reactor designed and built with the experience gained on the strictly homogeneous reaction. The model reaction reported in this thesis will be the benchmark for future reactions.

Overcoming light and mass transfer phenomena in gas-liquid biphasic reactions: introduction of the aerosol methodological paradigm

URBANI, DANIELE
2022-06-10T00:00:00+02:00

Abstract

Overcoming light and mass transfer phenomena in gas-liquid biphasic reactions: introduction of the aerosol methodological paradigm Mass transfer phenomena are a limitation factor especially in gas-liquid organic chemistry reaction. This issue can be overcome by exploiting the huge increase of the surface to volume ratio when spraying the reaction solution. Each droplet generated this way will react as a single reactor. In this thesis the selective photo-oxidation of organic sulfides to sulfoxides and the utilization of CO2 for the synthesis of cyclic carbonates from the corresponding epoxides are both widely studied. A model reaction has been chosen for the study of the photochemical oxidation of a water soluble sulfide to the corresponding sulfoxide mediated by singlet oxygen: For this reaction several setup were built with the aim of enhancing the final conversion and the mass recovery of the process. A photochemical aerosol reactor was design and built in collaboration with the University of KULeuven to obtain allowing us to reach 95% conversion and complete selectivity toward the sulfoxide. The acceleration factor of the reaction kinetic is 144 compared to the bulk reaction. The scope expansion of the model reaction towards organic sulfides that are not soluble in water was then carried on to place the foundation for further aerosol experiments. In this case a water:ethanol mixture is choose as green solvent for safety and environmental issues. Severe climate change represents a threat for human life, and its effects on environment, economic and social development is widely studied. Unequivocally scientific evidences link climate change to greenhouse gases emissions, and identify CO2 as a greenhouse gas. For this reason we thought of using CO2 as a reactive-carrier gas to carry out the synthesis of styrene carbonate from styrene oxide: This synthesis was identified as the model reaction for further studies. Without any previous experience in this field an extensive study of the scientific literature was done with the aim of identifying the best catalyst suitable for an aerosol reactor. KI/tetraethylene glycol is choose as catalyst for the comparison between bulk and aerosol reaction due to its features. The kinetic study at different temperature of the model reaction in bulk and aerosol batch condition was carried on giving an acceleration factor up to 1,85. Unfortunately it was impossible during the PhD period to work with an aerosol flow reactor for CO2 reaction due to inadequate reactor setup and low reactivity of the gas. For this purpose a modular aerosol reactor has been design and built to being able, in the forthcoming future, to fully exploit microdroplets environment: Even if several data were collected with extreme difficulties, due to the novel approach choose on CCU technologies, those were sufficient to obtain a partnership for a NATO project call TANGO. The research group will now focus on the synthesis of new catalysts supported on magnetic nanoparticles that, hopefully, can convert styrene oxide into styrene carbonate with high yield and faster reaction time. All the experiments necessary are going to be exploiting the modular reactor designed and built with the experience gained on the strictly homogeneous reaction. The model reaction reported in this thesis will be the benchmark for future reactions.
MASSI, Alessandro
BORTOLINI, Olga
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11392/2491034
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact