Catalytic decomposition of biogas to produce H2-rich fuel gas and carbon nanofibers. Parametric study and characterization

Abstract

One of the main problems that our society must deal with in a near future is the progressive substitution of traditional fossil fuels by different energy sources, such as renewable energies. In this context, biogas will play a vital role in the future. Nowadays, one of the most important uses of biogas is the production of heat and electricity from its direct combustion in co-generation plants. An interesting alternative consists on its direct valorisation to produce a syn-gas that can be further processed to produce chemicals, liquid fuels, or hydrogen. Results showed in this work evidenced that catalytic decomposition of biogas (CH 4 /CO 2 mixtures) can be carried out with a Ni/Al 2 O 3 catalyst obtaining simultaneously a syn-gas with high H 2 content together with carbonaceous nanostructured materials with high added value. The parametric study revealed that temperature, WHSV (Weight Hourly Space Velocity, defined here as the total flow rate at normal conditions per gram of catalyst initially loaded) and CH 4 :CO 2 feed ratio influence directly in CH 4 and CO 2 conversion, H 2 :CO ratio and carbon generation (gC/g cat). It was also evidenced that carbon structure depends on temperature. At 600ºC, fishbone like nanofibers with no hollow core are obtained while at 700ºC a mixture of fishbone and ribbon like nanofibers with a clear hollow core are formed.

Graphitic nanomaterials from biogas-derived carbon nanofibers

“…Nevertheless, the exploitation of biogas for different applications appears as an interesting option, particularly when considering its renewable origin. In this context, the Catalytic Decomposition of Biogas (CDB) to simultaneously produce syngas (SG) with high hydrogen contents and bio-carbon nanofibers (BCNFs) has been studied in detail [18,19]. As CNFs, BCNFs from biogas have initially a certain degree of structural order and therefore, they are classified within graphitic carbons.…”

CH4 and CO2 partial pressures influence and deactivation study on the Catalytic Decomposition of Biogas over a Ni catalyst

“…The nickel domain size of the calcined fresh catalyst was 19 nm while after the reduction pre-treatment (under a H 2 flow at 550 °C) and passivation (under a 1% O 2 -99% N 2 flow at room temperature) was 31 nm. This catalyst has been extensively used and a thorough characterization can be found in previous works of our research group [19,24].…”

Relationship between carbon morphology and catalyst deactivation in the catalytic decomposition of biogas using Ni, Co and Fe based catalysts

“…Operating conditions as temperature or feedstock composition (CH 4 :CO 2 ratio) are key factors [17,18]. Thermodynamic analysis revealed that high temperatures and/or CH 4 :CO 2 ratios below the unity are necessary to avoid carbon formation [19], even though from an industrial point of view the opposite conditions are more convenient.…”

“…Depending on the previous relative rates, catalyst deactivation could be prevented if steps ii) and iii) are faster than iv) [30]. Under these conditions, the front face of catalyst particles remain free of carbon, leaving accessible active sites to CH 4 and CO 2 and allowing the formation of NFC without catalyst deactivation [12,17,31]. With this background in mind, we recently addressed a novel approach to the decomposition of CH 4 /CO 2 mixtures (the so-called catalytic decomposition of biogas (CDB)) which consisted in the simultaneous production of syngas (H 2 and CO mixture) and bio-nanostructured filamentous carbon (BNFC) [32].…”

“…Corthals et al [43] reported the formation of multiwall carbon nanotubes (MWCNT) over a NiMgTiO 3 catalyst and fishbone-like CNF over a NiMgAl 2 O 4 catalyst. Our previous studies with a Ni/Al 2 O 3 catalyst [17,32,44] revealed the formation of fishbone-like CNF at 600 ºC and a mixture of fishbone and parallellike CNF at 700 ºC. In the previous studies, NFC were produced employing different metal-based catalysts.…”