Cleaner production of bio-oil from macroalgae and low-rank coal mixture by pyrolysis in a microwave reactor integrated with a distillation column

In recent years, biofuels have advanced significantly, progressing from the first to the third generation. Macroalgae, a third-generation biofuel, provides distinct advantages over other biomass, such as abundant availability, minimal space requirements, and little to no competition with arable land. This study explores the cleaner production of bio-oil from a blend of Eucheuma cottonii macroalgae and low-rank coal (LRC) using microwave-assisted pyrolysis (MAP) integrated with a distillation column. This integrated system enhance (C₅-C₁₂), kerosene (C₁₂-C₂₀), and diesel (C₂₁-C₃₈) fractions, suitable for various fuel applications. A 30 g mixture of macroalgae, LRC, and 2 wt% HZSM-5 catalyst was processed in MAP under vacuum (−10 mmH2O) to minimize oxygen content. Pyrolysis was conducted at 620 °C, with microwave power ranging from 0 to 800 W. Optimal conditions—a 1:1 macroalgae-to-coal ratio, 450 W microwave power, and a 135-min reaction time—produced a bio-oil yield of 61.7 wt%. FTIR and GC-MS analyses confirmed the bio-oil's wide hydrocarbon range and diverse functional groups, underscoring its potential across multiple fuel grades. While the process reduces carbon footprints by combining macroalgae's renewable properties with LRC's energy density, challenges such as high oxygen, ash, and sulfur contents require further refining processes like hydrotreatment. This study demonstrates the potential of MAP technology integrated with a distillation column as a scalable, sustainable biofuel production method, offering a promising pathway to cleaner energy solutions and global net-zero emission goals.