Sustainable drop-in biofuel (hexyl levulinate) production through energy-efficient biomass conversion employing waste derived silica-hydroxyapatite supported nano-CuO-TiO2 photocatalyst: Engine performance, exhaust emission and LCA analyses

The present article addresses the concerns of sustainable production of renewable drop-in biofuel namely Hexyl levulinate (HL). This is the first report encompassing energy-efficient conversion of lignocellulosic biomass viz. waste bamboo leaves (WBL) to HL, its engine performance and exhaust emission profile as diesel-biodiesel additive. HL could not only be produced with high yields (74.43 mol%) but also the process severity could be reduced (30 min reaction time,70°C temperature) as compared to previous reports (170°C temperature; 7 h time) employing a novel energy-efficient microwave-UV irradiations assisted batch reactor (MWUVBR) and indigenously prepared waste derived dual supported i.e. silica and HAp supported nano CuO-TiO 2 (SHNCT) photocatalysts. Wastes namely printed-circuit-board and fish scales were utilized to derive silica and hydroxyapatite (HAp) supports. Remarkably, the dual supported i.e. SHNCT photocatalyst exhibited improved properties like higher surface area (156.692 m 2 ) and lower nano-crystallites (1.6 nm TiO 2 ; 2.6 nm CuO) as compared to literature reports. Also, SHNCT photocatalyst rendered higher yield of HL as compared to individual i.e. HAp supported and silica supported photocatalyst. Notably, the MWUVBR-SHNCT synergy delivered an energy-efficient (12.66% energy savings), cost-effective (5.97% cost saving) and eco-friendly (37% GWP mitigation as obtained from LCA analyses) HL synthesis process as compared to conventional process. Furthermore, the present research was successful in establishing optimal HL-biodiesel-diesel blend that could reduce NOx emission alongside significant reduction in HC and CO emissions by 4.28%, 77.27% and 70% respectively. Also, noticeable improvement in brake-power (7.14%) and brake-thermal-efficiency (17.6%) was achieved conforming to SDG7. • Employment of energy efficient (12.66% energy savings) MW-UV irradiations assisted batch reactor. • High Hexyl levulinate (HL) yield (74.43 mol%) from biomass at mild process conditions (30 min,70°C). • High-efficiency low-cost e-waste and fish scale derived dual-supported nano-photocatalyst. • Remarkable GWP mitigation (37%) and cost savings (5.97%) as compared to conventional heating. • First report on HL blending rendering HC (77.27%), CO (70%) and NOx (4.28%) reductions.