A sequenced batch process for integrated hydropyrolysis and hydrotreatment of a microalgae and used engine oil blend

A sequenced batch process for integrated hydropyrolysis and hydrotreatment (IHP-T) of microalgae and used engine oil (UEO) was examined to produce sulfur-free diesel-like fuel. Four sequenced runs were performed. In the first run, the microalgae and UEO blend was processed at 673 K for 4 h with 6 MPa H₂ and 5 wt% kg_Pt/C/kg_feed to obtain the first-run light oil (FR-LO) and first-run heavy oil (FR-HO) by centrifugation. Next, the same procedure as that employed in the first run was used to treat the LO recovered from a previous run in a new run until the fourth run. The oils obtained in the second, third, and fourth run were named the second-run light oil (SR-LO), second-run heavy oil (SR-HO), third-run light oil (ThR-LO), third-run heavy oil (ThR-HO), fourth-run light oil (FR-LO), and fourth-run heavy oil (FR-HO). LO was always the dominant product fraction in the four runs, and the yields of FR-LO, SR-LO, ThR-LO, and FoR-LO were 83.33, 89.24, 89.29, and 88.34 wt%, respectively. The N, O, and S contents of the LOs always decreased during the sequenced IHP-T process. Zero S content was observed for both the ThR-LO and FoR-LO. The N content of the FoR-LO decreased to 2 ppm (w/v), which is below the requirement for China V gasoline (10 ppm). The total acid number of the LOs decreased from 21.62 for the FR-LO to 1.89 for the FoR-LO. The FoR-LO mainly consisted of saturated hydrocarbons (~47%), unsaturated hydrocarbons (37%), and aromatic compounds (36%) and had a higher heating value (HHV) of 46.37 MJ/kg, a density of 0.80 kg/m³, and a kinematic viscosity of 1.89 × 10⁻³ m²/s. The properties of the FoR-LO are very similar to those of market gasoline. Thus, sequenced IHP-T is a very promising process for producing S-free diesel-like fuel from microalgae and UEO.