The widespread use of fossil fuels has been questioned in recent years and biomass could be one of the solutions. However, the widespread use of bio-liquids is hampered by their negative characteristics: poor stability, acidity, tendency to coking, limited calorific value. These negative factors are caused by the presence of C2-C4 oxygenates. The aim of the following work is therefore the experimental study of the catalytic processes of C-C coupling aimed at converting these oxygenates. An existing lab-scale plant was revamped. A great effort was put in the preparation of the experimental plant as well as the tuning of the various methods and procedures to be used during the experiments. In particular, the ketonization reaction of acetic acid was investigated, chosen as the simplest carboxylic acid which wells simulates the acidic behaviour of the bio-oil. The experiments were performed in a packed bed reactor, where TiO2 and Ru/TiO2 were used as catalyst in the powder form. The experimental campaign was divided into two parts. At the beginning, experiments were run in such a way that only ketonization reaction was taking place. To avoid secondary reactions, the maximum conversion achieved during the experiments was 50%. Here both the effect of the space velocity and the effect of the inlet composition were investigated. In the second part of the work, the behaviour of the catalyst in much higher conversion conditions were studied. Under these operative conditions, both secondary reaction pathways and deactivation phenomena were present. The effect the Ru loading and of H2 co-feed were deeply investigated. TPO tests were also carried out to analyse the formation of carbon deposits. In conclusion, it has been shown that the TiO2 catalysts are able to successfully catalyse acetic acid ketonization reaction. Unexpectedly further condensation and cyclization reactions are activated when temperature and acetic acid conversion are sufficiently high, thus producing fuel-like C6-C9 species. Challenges in terms of catalyst deactivation and difficult control of process selectivity also emerged.
L'uso diffuso delle fonti fossili è stato messo in discussione negli ultimi anni e la biomassa potrebbe essere una delle soluzioni. Tuttavia, l'uso diffuso di bio-liquidi è ostacolato dalle loro caratteristiche negative: scarsa stabilità, acidità, tendenza al coking, potere calorifico limitato. Questi fattori negativi sono causati dalla presenza di ossigenati C2-C4. Lo scopo del seguente lavoro è quindi lo studio sperimentale dei processi catalitici di C-C coupling volti a convertire questi ossigenati. Un impianto esistente su scala di laboratorio è stato rinnovato. Un grande sforzo è stato posto nella preparazione dell'impianto e nella messa a punto dei metodi e delle procedure utilizzate durante gli esperimenti. È stata studiata la reazione di chetonizzazione dell'acido acetico, scelto in quanto semplice acido carbossilico che ben rappresenta il comportamento acido del bio-olio. Gli esperimenti sono stati condotti in un reattore a letto impaccato, dove TiO2 e Ru/TiO2 sono stati utilizzati come catalizzatori sotto forma di polveri. La campagna sperimentale è stata divisa in due parti. Inizialmente, gli esperimenti sono stati condotti in modo tale che la sola reazione di chetonizzazione avesse luogo. Per evitare reazioni secondarie, la conversione massima ottenuta durante gli esperimenti è stata del 50%. Qui è stato studiato l'effetto della velocità spaziale e l'effetto della composizione in ingresso. Nella seconda parte del lavoro è stato osservato il comportamento del catalizzatore in condizioni di conversione molto più elevate. In queste condizioni operative erano presenti sia reazioni secondarie che fenomeni di disattivazione. L'effetto del carico di Ru e della co-alimentazione di H2 è stato studiato. Sono stati anche condotti dei TPO-test per analizzare la formazione di depositi carboniosi. In conclusione, è stato dimostrato che la TiO2 è in grado di catalizzare con successo la reazione di chetonizzazione. Ulteriori reazioni di condensazione e ciclizzazione vengono attivate, producendo specie C6-C9 simili a combustibili. Sono emerse anche sfide in termini di disattivazione del catalizzatore e di difficile controllo della selettività del processo.
Catalytic upgrade of bio-vapours : experimental analysis of acetic acid ketonization on TiO2 catalyst
CAREMOLI, FRANCESCO
2020/2021
Abstract
The widespread use of fossil fuels has been questioned in recent years and biomass could be one of the solutions. However, the widespread use of bio-liquids is hampered by their negative characteristics: poor stability, acidity, tendency to coking, limited calorific value. These negative factors are caused by the presence of C2-C4 oxygenates. The aim of the following work is therefore the experimental study of the catalytic processes of C-C coupling aimed at converting these oxygenates. An existing lab-scale plant was revamped. A great effort was put in the preparation of the experimental plant as well as the tuning of the various methods and procedures to be used during the experiments. In particular, the ketonization reaction of acetic acid was investigated, chosen as the simplest carboxylic acid which wells simulates the acidic behaviour of the bio-oil. The experiments were performed in a packed bed reactor, where TiO2 and Ru/TiO2 were used as catalyst in the powder form. The experimental campaign was divided into two parts. At the beginning, experiments were run in such a way that only ketonization reaction was taking place. To avoid secondary reactions, the maximum conversion achieved during the experiments was 50%. Here both the effect of the space velocity and the effect of the inlet composition were investigated. In the second part of the work, the behaviour of the catalyst in much higher conversion conditions were studied. Under these operative conditions, both secondary reaction pathways and deactivation phenomena were present. The effect the Ru loading and of H2 co-feed were deeply investigated. TPO tests were also carried out to analyse the formation of carbon deposits. In conclusion, it has been shown that the TiO2 catalysts are able to successfully catalyse acetic acid ketonization reaction. Unexpectedly further condensation and cyclization reactions are activated when temperature and acetic acid conversion are sufficiently high, thus producing fuel-like C6-C9 species. Challenges in terms of catalyst deactivation and difficult control of process selectivity also emerged.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/180024