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Title

Valoración de biogás mediante descomposición catalítica para la producción de gas de síntesis y nanofibras de carbono

AuthorsLlobet, Saúl de
AdvisorSuelves Laiglesia, Isabel CSIC ORCID; Moliner Álvarez, Rafael
KeywordsCatálisis
Biogás
Producción gas de síntesis
Nanofibras de carbono
Issue DateDec-2015
PublisherCSIC - Instituto de Carboquímica (ICB)
Universidad de Zaragoza
AbstractBiogas is a renewable energy source that can be used as feedstock in different processes. Among them, the dry reforming of CH4, to produce synthesis gas, is very interesting due to biogas composition. Nevertheless, CH4:CO2 ratios in biogas are generally higher than one and therefore, avoiding carbon deposition is a difficult task. However, this problem can be tackled from a completely different point of view. Instead of trying to avoid carbon formation, it can be promoted as carbon nanofilaments. These carbon structures are not directly responsible of catalyst deactivation and have interesting properties that make them high added value materials. This process, in which syngas and carbon nanofilaments are simultaneously produced from biogas, has been studied for the first time during the course of this thesis and it has been named “Catalytic Decomposition of Biogas (CDB)”. During the study of the CDB, different active phases have been considered as long as different supports or synthesis methods. Besides, the effect of the operating conditions (temperature, space velocity and CH4:CO2 ratio) on the catalyst activity and stability and the amount and quality of the carbonaceous material produced during the reaction has been analysed. Generally, by increasing the value of any of the operating conditions the catalytic activity is improved. Nevertheless, at the same time, surface carbon concentration raises up and it is transformed into encapsulating carbon that reduces catalyst stability. It has been found that there is a compromise between the catalytic activity and stability that maximizes the production of carbon. However, with increasing reaction time, the catalyst stability turns into the most decisive factor. Carbon type and carbon nanofilaments structure greatly depend on the operating conditions, being the temperature the most determining variable. An increase of its value considerably reduces the proportion of carbon nanofilaments as compared to encapsulating carbon and therefore, working at 800 and 900 °C is inadvisable. In addition, the effect of two of the minor components of biogas in the behaviour of the catalysts in the CDB has been studied. Results obtained imply that cleaning stages associated with these compounds could be probably eliminated if the CDB is scaled-up, thereby reducing process costs. Finally, the scaling-up of the process using a rotary reactor and a fluidized bed reactor has been considered. Results show that from the technical point of view the scale-up of the process is feasible. Besides, the preliminary economic study suggests that the use of biogas in the CDB is a very interesting alternative to energy production through its direct combustion. Incomes from synthesis gas are reduced about a 30 %. However, benefits from the simultaneous production of a carbonaceous material with high added value could be two orders of magnitude higher than earnings from energy production. From research conducted in this thesis work, it can be concluded that the catalytic decomposition of biogas for the production of synthesis gas and carbon nanofibres is a feasible alternative, both technically and economically, to the production of energy from biogas combustion.
Description2105-10-15 .-- Tesis llevada a cabo para conseguir el grado de doctor en la Universidad de Zaragoza .-- Sobresaliente "cum laude"
URIhttp://hdl.handle.net/10261/125584
Appears in Collections:(ICB) Tesis
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