Unraveling the chemistry of microalgae pyrolysis: Connecting macromolecules to diverse high-value products

The extensive reliance on fossil resources for fuels and platform chemicals has raised critical concerns over resource depletion and increasing greenhouse gas emissions. To address these challenges, microalgae offer a promising sustainable alternative, recognized for their high productivity, efficient CO2 sequestration, and significant capacity to accumulate lipids. Among various conversion strategies, pyrolysis stands out as an effective method for transforming microalgae-derived macromolecules (carbohydrates, proteins, and lipids) into energy-dense products and valuable chemicals. This study provides a detailed mechanistic analysis of pyrolysis pathways, elucidating the formation of nine key product categories: oxygen heterocycles, nitrogen heterocycles, nitrogenous compounds (amines, amides, and nitriles), aldehydes and ketones, carboxylic acids and esters, alcohols, phenols, hydrocarbons, and sulfur-containing compounds. These products are traced to specific macromolecules, with carbohydrates yielding anhydrosugars, furans, and light oxygenates; proteins forming nitrogen-containing compounds; and lipids producing carboxylic acids, esters, and hydrocarbons. Furthermore, synergistic reactions between distinct macromolecules or their derivatives result in unique product distributions, highlighting the complex interplay of reaction pathways. These insights lay the groundwork for optimizing pyrolysis processes, improving product selectivity, and designing advanced catalysts informed by Density Functional Theory (DFT) to address rate-limiting steps. By elucidating these mechanisms, this study advances the sustainable conversion of microalgae into renewable fuels and chemicals, contributing to the development of a more sustainable and environmentally friendly future.