Pyrolysis of Posidonia oceanica fibrous spheres: A comparative evaluation of conventional and microwave-assisted pyrolysis

Abstract

Posidonia oceanica debris naturally accumulates on the coastline, negatively affecting the pleasantness of the beaches, whilst it could be advantageously exploited as a source of novel biofuels and bioproducts. In this work, grinded Posidonia oceanica fibrous spheres have been subjected to thermal pyrolysis, comparing conventional and microwave technologies, working under mild similar conditions, aimed at the integrated production of biochar, bio-oil and syngas. The microwave heating favored the cracking reactions, thus promoting the aromatization path, even more so by including a dephlegmator unit. On the other hand, conventional pyrolysis system reduces such degradation reactions, as demonstrated by the chemical composition of the corresponding bio-oil, which includes more aliphatic compounds. Remarkably, the use of the same biochar as both a microwave absorber and a reducing agent was effective for improving the selective syngas production (63 wt%), mainly composed of H₂ and CO (46 and 53 vol%, respectively). The production of higher quality syngas with microwave technology is due to the occurrence of gasification reactions, through the formation of local hot spots. LCA data processing was specifically considered and developed, showing that on the laboratory scale the environmental impact of both technologies is similar, whereas on larger scale microwave-assisted pyrolysis still presents some drawbacks, mainly those associated with energy supply/management. In this context, some specific solutions were provided for making microwave-assisted pyrolysis more competitive with the conventional one, already in the next future, which is a desirable aspect to promote the intensification development of this technology.