Continuous drop-in-biofuel production from pretreated sugarcane bagasse in a microwave-visible irradiated continuous stirred slurry reactor: reaction kinetics & techno-enviro-economic sustainability analyses†

Abstract

This work utilizes an innovative microwave-visible irradiated continuous stirred slurry reactor (MWVIS-CSSR) for sustainable continuous production of a drop-in biofuel, namely, ethyl levulinate (EL), from pretreated sugarcane bagasse (PSCB). Besides, a novel realistic kinetic model, considering MWVIS intensified EL production through parallel non-catalytic and homogeneous–heterogeneous catalytic pathways in the presence of a magnetic Ni_0.5Zn_0.5Fe₂O₄ (NZF) photocatalyst in conjunction with an oxalic acid–choline chloride based acidic deep eutectic solvent (DES2), was also formulated and validated (R² adj. ≥ 0.95). The 5 liter volume MWVIS-CSSR could render maximum 54.7 mol% EL yield (selectivity: 97.85%) at a feed flow rate of 35 ml min⁻¹ under optimized conditions (temperature: 100 °C, NZF loading: 6 wt% PSCB, stirring speed: 500 rpm). Remarkably, the synergistic impact of MW and VIS irradiation substantially elevated the EL yield (54.7 mol%) compared to those of the individual MW (29.45 mol%) and VIS (20.1 mol%) systems. The optimally produced EL when blended at 5 vol% with B10 and B20 (10% and 20% biodiesel–diesel blends) could enhance the brake thermal efficiency (1–2%) besides mitigating 21–22% HC and 7.5–20% CO engine exhaust emissions in comparison with reference blends (B10 and B20). Notably, the reactor scale-up study based on the penetration depth of the MW and VIS energy of NZF and DES2 showcased the potential to upscale the 5 liter MWVIS-CSSR to a 1 m³ volume, allowing EL production to reach 689 kg h⁻¹ with a sugarcane bagasse processing capacity of 2000 kg h⁻¹. Moreover, the process simulation conducted in Aspen Plus software, utilizing COSMO-based property estimation with DFT calculations, alongside the techno-economic analysis, revealed a robust internal rate of return (IRR) of 54.25% and a net present value (NPV) of 8.22 × 10⁵ US$ with a payback period of 4.91 years. Additionally, the environmental impact analysis study for the scaled-up EL production process in the MWVIS-CSSR revealed a reduction of 40–60% in marine ecotoxicity and 39–61% in human toxicity compared to the separate MW-CSSR and VIS-CSSR systems.