Iron-catalyzed fast hydrothermal liquefaction of Cladophora socialis macroalgae into high quality fuel precursor

Fast hydrothermal liquefaction of acid-washed Cladophora socialis macroalgae has been studied over homogeneous (KOH, K₂CO₃, H₃PO₄, HCOOH) and heterogeneous (H-ZSM-5, Raney Ni, Ru/C, Fe metal) catalysts in a batch reactor at 350 °C. Biocrude with maximum yield (36.2%) and energy density (37.1 MJ kg^-1) and minimum heteroatom contents (3.8% N and 10.1% O) were achieved with metallic Fe. GC-MS indicates reduction in content of carbonyls, acids and N-containing substances and increase in levels of phenols and hydrocarbons in biocrude while ¹H NMR suggests the enhanced formation of oxygenated/nitrogenous compounds in aqueous phase over Fe catalyst compared to non-catalytic test. Such carbonyls and acids removal was proposed to occur via hydride reduction and decarboxylation pathways, respectively. GPC and TAN confirm vast improvement in stability and corrosiveness properties of Fe-catalyzed biocrude. Regeneration of used catalyst has been conducted and the regenerated catalyst exhibited slight deactivation, likely due to sintering of Fe particles.