Thermal conversion of macroalga Macrocystis pyrifera for production of carbon-negative hydrogen

Abstract

In recent years, third-generation--or algae-based biofuels--have been studied extensively in order to reduce the risks of compromised food security, solve biofuel issues from past generations and supply continuous feedstock from energy crops. With the goal of a zero-carbon future, bioenergy with carbon capture and storage (BECCS) is a technology that extends to multiple areas--including algae-based biofuels that avoid greenhouse emissions from biomass processing.

Algae are aquatic plants or microorganisms, classified as micro and macroalgae; they are of considerable scientific interest because they are fast-growing, with a photosynthetic metabolism that generates carbon sources from atmospheric CO$_2$. Macroalgae (seaweed) can be cultivated in aquaculture farms and collected through mechanical devices; the macroalga selected for this study is Macrocystis pyrifera, a giant brown seaweed characterized by its size and its carbon and oxygen-rich composition.

Conventional methods for thermal conversion into potential fuels, such as biomass carbonization, pyrolysis, and gasification are not efficient for biomass with high moisture. For this reason, the research community has introduced new methods like hydrothermal carbonization, liquefaction, and gasification.

This project focuses on the process simulation in Aspen plus® V12 to produce green hydrogen from macroalgae biomass by pyrolysis, gasification, and hydrothermal gasification. Hydrogen production was maximized through sensitivity analysis, achieving a hydrogen yield of 2.08% in hydrothermal gasification, 2.06% for pyrolysis, and 1.85% for gasification.