Conversion of lignocellulose into transportation fuels can be attempted through several different routes. However, this is not a simple task due to its chemical complexity, elevated stability and high oxygen content. Among the various thermochemical transformation processes, biomass pyrolysis has been shown to be a very promising option for producing liquid biofuels. Pyrolysis implies the treatment of biomass in an inert atmosphere to yield three fractions: non-condensable gases, liquids (bio-oil) and a solid residue (char). The CASCATBEL project developed a cost-efficient process for converting lignocellulosic feedstock into second-generation liquid biofuels, using tailored nano-catalysts to give products with properties like those found in petroleum-derived fuels. “We began by investigating biomass with the sequential coupling of three catalytic steps to achieve the controlled conversion of biomass into upgraded liquid biofuels (bio-oils),” says project coordinator Dr David Serrano Granados. “These steps were catalytic pyrolysis, intermediate deoxygenation and hydrodeoxygenation.” A large part of the oxygen contained in the pyrolysis bio-oil is removed in the first two catalytic steps. This minimises the hydrogen consumed in the last treatment, which has very positive effects in terms of both process economy and environmental impact. “In addition to advanced biofuels, the process designed will generate renewable electricity from the combustion of the char formed in the first pyrolysis step” Dr Serrano explains. “Likewise, in relation to climate change mitigation, the estimated GHG reduction of the process developed is in most of the considered scenarios higher than 90% compared to fossil fuels.” Bio-oil used in transportation fuels The bio-oil finally produced contained little oxygen and improved properties, such as higher heat value, larger stability and enhanced miscibility with hydrocarbons. “This enables the bio-oil to be used in the formulation of transportation fuels by blending it with conventional gasoline and diesel fractions,” comments Dr Serrano. Scaling-up of the process allowed researchers to fully explore and understand the catalytic and reaction dynamics, and assess the catalyst behaviour in a relevant environment. The experimental work was performed at three different scales (laboratory, bench and pilot plant scales), using both model compounds and real biomass feedstock. Dr Serrano claims: “This was not straightforward, as many catalysts, which showed a good performance with model substrates, exhibited poor catalytic activity when feeding real biomass materials. Moreover, with real biomass feedstock, catalyst deactivation problems were made worse due to the extensive deposition of carbonaceous residues and/or leaching of the active phases in the catalysts.” These challenges were overcome by screening a wide range of catalytic materials, operation modes and reaction conditions. “Researchers found that the modification of microporous-based catalysts, like zeolite, by addition of selected components was very effective for attenuating non-desired secondary reactions, leading to a better yield of upgraded bio-oil,” observes Dr Serrano. CASCATBEL project is expected to have a range of impacts, mainly within the European advanced biofuels market. Other industrial sectors will also be interested in developments like the catalytic system designed for promoting in a single step both catalytic pyrolysis and intermediate deoxygenation reactions of the bio-oil vapours. “Thus, this material, consisting of a modified zeolite, could be used for the co-processing of other feedstock in addition to lignocellulose, such as waste plastics,” Dr Serrano concludes.
CASCATBEL, deoxygenation, biomass, advanced biofuels, nanocatalyst