Nowadays, the reduction of CO2 emissions is among the primary challenges that humanity has to face to limit the rising global temperature. The chemical industry is the second largest contributor to these emissions, therefore new technologies are being investigated, such as Carbon Capture and Utilization (CCU). In this sense, the synthesis of lower olefins (C=2 - C=4 ) from CO2 conversion represents an interesting possibility. In particular, the methanol-mediated pathway (CTO) converts CO2 to methanol, which is further transformed by producing olefins, and it can be performed in a single reactor, combining two catalysts. In this thesis work, the focus is concentrated on the reactivity of SAPO-34 zeolites in the second step of the so-called one-pot process, converting methanol at high pressure (20-38 barg) and co-feeding H2 and CO2. Two SAPO-34 zeolites from different manufacturers were characterized using N2 physisorption, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), temperature-programmed desorption of ammonia (NH3- TPD), and temperature-programmed desorption (MeOH-TPD) and reduction (MeOH-TPR) of methanol. Subsequently, they have been tested under pressure, studying the influence of temperature, pressure, and Gas Hourly Space Velocity (GHSV) and trying to clarify the reaction pathways referring also to information in the literature. The H2 co-feed led to a prolonged catalyst lifetime as a complete methanol conversion was maintained for days, however, the Olefins-to-Paraffins ratio was affected due to alkenes hydrogenation. Furthermore, the influence of CO2 was investigated obtaining a peculiar effect on the O/P ratio, which decreased when the CO2 co-feed was stopped, despite its null conversion. The production of CO and methane was measured over time, observing an increasing by-product concentration with the ToS. Working on a fresh catalyst at the optimal conditions, i.e. 400°C, 30 barg, 3 Nl/h/gcat, an olefin carbon selectivity of 77% has been reached. Finally, the experimental results obtained with the two zeolites have been compared to find the most promising catalyst in the operative conditions of the one-pot process.
La riduzione delle emissioni di CO2 rappresenta oggigiorno una delle sfide principali per limitare l’aumento della temperatura globale. L’industria chimica è il secondo maggior contribuente a tali emissioni, pertanto sono in via di sviluppo nuove tecnologie, come la Carbon Capture and Utilization (CCU). In questo ambito, la sintesi di olefine leggere (C=2 - C=4 ) tramite conversione di CO2 rappresenta una possibilità interessante. Tra gli altri, il processo CTO converte la CO2 in metanolo, il quale viene successivamente trasformato in olefine, e può essere effettuato in un unico reattore, combinando due catalizzatori. In questa tesi, l’attenzione è incentrata sulla reattività delle zeoliti SAPO-34 nel secondo step reattivo del cosiddetto processo "one-pot", ovvero sulla conversione del metanolo ad alta pressione (20-38 barg) ed in presenza di H2 e CO2. Due zeoliti SAPO-34, acquistate da produttori differenti, sono state caratterizzate mediante fisisorbimento di azoto (N2), microscopia elettronica a scansione (SEM), diffrazione a raggi X (XRD), desorbimento a temperatura programmata dell’ammoniaca (NH3-TPD) e desorbimento (MeOH-TPD) e riduzione (MeOH-TPR) a temperatura programmata del metanolo. Successivamente sono state testate ad alta pressione, studiando l’influenza di temperatura, pressione, velocità spaziale (GHSV) e cercando di chiarire i meccanismi di reazione. L’alimentazione di idrogeno ha prolungato la vita del catalizzatore, che è così stato in grado di mantenere una conversione completa di metanolo per giorni. Tuttavia, anche il rapporto tra olefine e paraffine ne è stato influenzato a causa dell’idrogenazione delle olefine stesse. Inoltre, è stata investigata l’influenza della CO2, ottenendo un inaspettato effetto sul rapporto O/P, il quale è diminuito quando l’alimentazione di CO2 è stata interrotta, nonostante essa non venga convertita. La produzione di CO e metano è stata monitorata nel tempo, osservando un aumento della concentrazione di sottoprodotti al variare del tempo di reazione. Utilizzando un catalizzatore fresco nelle condizioni ottimali, ovvero 400°C, 30 barg, 3 Nl/h/gcat, è stata raggiunta una selettività al carbonio di olefine del 77%. Infine, i risultati sperimentali ottenuti con le due zeoliti sono stati confrontati per individuare il catalizzatore più promettente nelle condizioni operative del processo "one-pot".
CO2-to-Olefins: investigation of methanol reactivity over SAPO-34
Belotti, Davide;Böbel, Guido
2022/2023
Abstract
Nowadays, the reduction of CO2 emissions is among the primary challenges that humanity has to face to limit the rising global temperature. The chemical industry is the second largest contributor to these emissions, therefore new technologies are being investigated, such as Carbon Capture and Utilization (CCU). In this sense, the synthesis of lower olefins (C=2 - C=4 ) from CO2 conversion represents an interesting possibility. In particular, the methanol-mediated pathway (CTO) converts CO2 to methanol, which is further transformed by producing olefins, and it can be performed in a single reactor, combining two catalysts. In this thesis work, the focus is concentrated on the reactivity of SAPO-34 zeolites in the second step of the so-called one-pot process, converting methanol at high pressure (20-38 barg) and co-feeding H2 and CO2. Two SAPO-34 zeolites from different manufacturers were characterized using N2 physisorption, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), temperature-programmed desorption of ammonia (NH3- TPD), and temperature-programmed desorption (MeOH-TPD) and reduction (MeOH-TPR) of methanol. Subsequently, they have been tested under pressure, studying the influence of temperature, pressure, and Gas Hourly Space Velocity (GHSV) and trying to clarify the reaction pathways referring also to information in the literature. The H2 co-feed led to a prolonged catalyst lifetime as a complete methanol conversion was maintained for days, however, the Olefins-to-Paraffins ratio was affected due to alkenes hydrogenation. Furthermore, the influence of CO2 was investigated obtaining a peculiar effect on the O/P ratio, which decreased when the CO2 co-feed was stopped, despite its null conversion. The production of CO and methane was measured over time, observing an increasing by-product concentration with the ToS. Working on a fresh catalyst at the optimal conditions, i.e. 400°C, 30 barg, 3 Nl/h/gcat, an olefin carbon selectivity of 77% has been reached. Finally, the experimental results obtained with the two zeolites have been compared to find the most promising catalyst in the operative conditions of the one-pot process.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/210392