Algae characterization and multistep pyrolysis mechanism

Abstract

This paper presents a new characterization method and a multistep kinetic mechanism for describing the pyrolysis process of algae fuels. Since third generation biomasses are still largely unexplored, we first organized a database by collecting literature information on the nature and main features of algal biomass. The algal species, both macro- and micro-algae, are constituted by proteins, carbohydrates and lipids, present in various amounts depending on the taxonomy and growing conditions. Noteworthy, algae contain higher levels of proteins, lipids, nitrogen and ashes compared to vegetal biomasses. Starting from the ultimate analysis and ash content, the biochemical composition of each algal species is defined in terms of proteins, carbohydrates, and lipids. To this aim, a limited number of representative reference species is first defined, based on atomic mass balances. The predicted biochemical compositions fairly agree with experimental information. Then, a multi-step semi-detailed kinetic mechanism of algae pyrolysis has been developed for the different reference components, following the same approach successfully applied for lignocellulosic biomasses. Moreover, a further release of ammonium, nitrates, and carbonates groups is estimated and related to the ash content. Despite the reduced number of reference species and the rough assumptions to reduce the complexity of the overall problem, the model is already able to satisfactorily predict the pyrolysis behavior of micro- and macro-algae. To our knowledge, and despite all the strong simplifications, this is the first method to characterize algae species, as well as the first kinetic model able to predict the algae pyrolysis process.