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Abstract The removal of nitrogen (N) and sulphur (S) from biocrude oil produced using hydrothermal liquefaction (HTL), is important for the production of high quality renewable fuels. Here the effect of co-liquefaction of bagasse and algae was analysed. Algae (Chlorella vulgaris and Cyanobacteria) were mixed with bagasse (1:1) subjected to HTL at 250–350 °C for 10–60 min. Higher HTL temperatures had a positive effect in increasing the biocrude yield and slightly reduced N content; S did not show a consistent trend. Most of the nitrogen (~66%) and sulphur (~80%) were recovered in the aqueous phase rather than in the biocrude phase, opening the opportunity to recycle these nutrients for algae cultivation. Co-liquefying bagasse with algae improved the biocrude yield (54 wt%) compared to pure Cyanobacteria (47.5 wt%). It also reduced N content from 7 wt% (Cyanobacteria biocrude) to 4.2 wt% (Cyanobacteria: Bagasse) and S from 0.7 wt% to 0.4 wt%. Principal Component Analysis (PCA) analysis identified that biocrude yield is positively correlated with the initial lipid content and anti-correlated with the carbohydrates fraction. Biocrude N content is closely related to the initial amount of proteins in the algae. The Preference Ranking Organization METHod for Enrichment of Evaluations and its descriptive complement Geometrical Analysis for Interactive Aid (PROMETHEE and GAIA) analysis ranked the co-liquefaction of Chlorella vulgaris and bagasse (1:1) at 350 °C and 60 min as one of the best overall combination in terms of biocrude yield, N and S content.

Abstract Hydrothermal liquefaction (HTL) biocrude is a promising source of energy with potential for co-processing with conventional fuels or as a drop-in fuel. However, it needs upgrading to reduce heteroatoms (e.g., N, S, O), improve physical properties, stability, and miscibility with hydrocarbons. Distillation is a conventional physical upgrading method that has not been studied extensively for biocrude using an industry-accepted procedure on a large scale. In this study, an algae-based biocrude was distilled into four fractions using ASTM D2892 standard method: Fraction 1 (

Abstract Generating green-based liquid fuels using hydrothermal liquefaction is a promising method for fossil fuel replacement. This study investigates the impact of recycling the aqueous phase in hydrothermal liquefaction processing on fuel yield, quality and energy efficiency using algae as the feedstock. Recycling the aqueous phase in algal hydrothermal liquefaction increased biocrude production yield by 18.9% at 350 °C, although a 12.2% increase in the biocrude nitrogen content was observed. In the second recycling, the nitrogen content increased to 17.6%, which is not environmentally favourable for direct usage in diesel engines due to the possible increase in Nitrogen Oxides (NOx) emissions. Recycling the aqueous phase in Spirulina Platensis feedstock liquefaction led to a 19–30% increase in yields for different recycling numbers, which was influenced by increasing the temperature and by applying catalysts. The heterogeneous catalyst showed a considerable increase (17.8%) in yield, a decrease (9.5%) in nitrogen content, and an improved energy consumption recovery by 30.8% after single recycling. However, a slight increase (2.7%) in nitrogen content was observed after recycling twice. It is vital to reduce the amount of energy used in the hydrothermal liquefaction process to be comparable with conventional fuels. Recycling the aqueous phase reduced the energy usage considerably. Applying the homogeneous catalyst and recycling the aqueous phase twice had the highest energy efficiency (36.8%) and production yield (51.4%) for the hydrothermal liquefaction process. The generated aqueous phase in single and double recycling experiments had up to 77% and 166% more phosphate, which may be of interest for agricultural applications.