Catalytic conversion of syngas to alcohols and hydrocarbons over transition metal-based micro/mesoporous catalysts
- Autores: Jordi Plana Pallejà
- Directores de la Tesis: Daniel Montané Calaf (dir. tes.), Sònia Abelló Cros (codir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Pilar Ramírez de la Piscina Millán (presid.), Sandra Contreras Iglesias (secret.), Lucía García Nieto (voc.)
- Programa de doctorado: Programa de Doctorado en Nanociencia, Materiales e Ingeniería Química por la Universidad Rovira i Virgili
- Materias:
- Enlaces
- Tesis en acceso abierto en: hdl.handle.net TDX
- Resumen
Due to the rising concerns regarding global warming and climate change, new laws and regulations have been proposed in the European Union to promote the development of clean energy technologies, in order to reduce the dependency on fossil fuels.
Synthesis gas (syngas) can be obtained from the gasification of biomass. This mixture of carbon monoxide and hydrogen offers great versatility, and several reaction processes can be used to obtain a variety of liquid fuels and oxygenated products.
Fischer-Tropsch Synthesis (FTS) is the most extensively used process for the synthesis of linear hydrocarbons from syngas. Lighter products can be used a diesel fuel, and heavier ones can be used as waxes. The most commonly used metals for FTS are Iron and Cobalt. Iron offers high levels of conversion, and the capacity to alter the H2/CO ration of the syngas feed. Cobalt has improved selectivity towards long chain paraffins, and low selectivity towards oxygenated products.
Higher Alcohols Synthesis (HAS) is a reaction process to obtain alcohols containing two or more carbon atoms. These alcohols can be used as intermediates for the synthesis of lubricants, detergents and cosmetics. This process uses a combination of FTS catalysts and methanol synthesis (MS) catalysts (mainly Copper and Chromium), as it involves a combination of both reaction mechanisms (FTS and MS). Common HAS catalysts usually contain a combination of Iron, Cobalt, Chromium and Copper, in order to have both active sites required for the synthesis of higher alcohols.
The objective of this thesis is the study of CO hydrogenation using different types of supported catalysts to obtain fuel-range hydrocarbons via FTS, or to produce higher alcohols via HAS. These experiments were performed in a laboratory-scale reactor, and the catalysts and reaction products were characterized using a variety of techniques.
The first block of the thesis studies the effect of zeolite acidity and mesoporosity in FeCuMgK catalysts supported on ZSM-40 and ZSM-240. The results show that zeolite acidity is responsible for the cracking of heavy hydrocarbons and the formation of aromatic products through oligomerization, cyclization and dehydrogenation of primary short olefins. The Si/Al ratio induced changes in the composition of the aromatic products, with increased acidity resulting in increased complexity of aromatic products. The formation of mesoporosity resulted in a slight increase in C2-C4 paraffins due to an improved access to the acidic sites through the mesopores, due to the overcracking of heavier molecules. The defining factor towards improved gasoline-range products was acidity, with higher Si/Al ratios offering the best selectivity, with mesoporosity having little to no influence.
The second block evaluates the influence of metal loading on binary and ternary FeCoCu catalysts supported on mesoporous silica SBA-15 for the production of higher alcohols. The results pointed out that ternary catalysts offered improved selectivity towards higher alcohols without compromising CO conversion values. Further analysis of different ternary catalysts showed that catalyst FeCoCu 9/9/18 had the best selectivity towards higher alcohols, with the best chain growth probability towards them. The final part evaluated several reaction conditions, and it was found that moderate temperatures were key to facilitate alcohol selectivity. High contact times and stoichiometric ratios of syngas feed were also beneficial towards alcohols selectivity. Alkaline doping showed an improvement of selectivity towards higher alcohols, but reduced overall CO conversion.
