Waste from food production or wood processing can be turned into a biofuel for more sustainable air travel. The raw oil, however, is unstable and difficult to use. A Swedish research team is working on optimising the refining process.
Biofuel has the potential to make transport and air travel more sustainable, but only if it is produced in a certain way. The research team behind the study includes members of CESTAP, a competence centre for biofuels for turbines, which focuses on sustainable fuels for air travel and power generation. The sustainability of biofuels is a complex issue with many factors to consider. The raw products used should be waste from other processes, and all other fuels required to produce them must be accounted for.
The first step in biofuel production is to heat the waste in a process called pyrolysis, turning it into a liquid called pyrolysis oil. However, pyrolysis oil should not be used directly. It is unstable, viscous and not very efficient as a fuel. Therefore, a second refining step is needed, and that is where the recent research comes in. The pyrolysis oil is mixed with materials that combine to form particles, then heated again in a hydrogen atmosphere. The goal is to reduce its oxygen content, making it easier and more efficient to use.
The particles that form act as catalysts, meaning they are added to speed up a chemical process that would otherwise be too slow to be practical. Forming the most efficient, or active, catalytic particles is quite a finicky task, where even their atomic-scale structure plays a role. X-ray methods are essential for understanding how the particles work and how they can be further optimised.
“The study provided a detailed characterisation under realistic process conditions, and demonstrated that both the biomass composition and the process conditions play a crucial role in determining the structure of the active particles,” says Sara Blomberg, one of the researchers. “Since the particles are formed inside the reactor, knowing which reactor conditions generate maximally active catalyst particles is important for further optimising the industrial process.”
One important process the researchers are looking into is whether there are circumstances under which the catalyst deactivates and stops working.
“We were interested in characterising feedstock contaminants that might potentially contribute to catalyst deactivation,” says Sara Blomberg. “We were able to map contaminants in the nanoparticles with high sensitivity, and the analysis provided important insights into possible catalyst deactivation.”
The researchers compared catalyst particles formed in a model hydrocarbon fuel to those formed in the real industrial process to see what differences would result from the more complex conditions.
“The most important finding from the study was that the active particles differed significantly when the particles were formed in biomass-derived feedstock. Both the biomass itself and the large-scale pilot plant conditions appeared to strongly influence the particle formation and resulting morphology,” concludes Blomberg. “Our findings highlight the importance of characterising catalysts not only under ideal laboratory conditions, but also in scaled-up processes where the catalyst is exposed to more complex environments.”
