Selective synthesis of oxygenated fuel derivative from microwave assisted acetalization of glycerol: Optimization and mechanistic investigations

Glycerol contains 52 wt% oxygen content, therefore unable to be directly used as fuel due to its poor combustion ability. Thus, the catalytic conversion of glycerol into various oxygen-containing fuel additives is grabbing more attention nowadays. This work provides a novel, sustainable, and eco-friendly method for synthesizing heterogeneous acid carbon catalysts from pearl millet cob (PMC) waste. The hydrothermal carbonization process was carried out at different temperatures to fabricate the series of sulfonated pearl millet cob (SPMC) catalysts. XRD, FT-IR, SEM-EDS, XPS, BET, TGA, and CHNSO analyses were performed to characterize fabricated catalysts. The synthesized catalyst, SPMC-70 (catalyst synthesized at 70 °C temperature), possesses OH, COOH, and SO3H functional groups and a significant total acid density (2.03 mmol/g) with 37 m2/g surface area. The SPMC catalysts were employed for the microwave-assisted acetalization reaction of glycerol with acetone for solketal production. The optimization process was carried out using various reaction parameters, including catalyst dosage (2–6 wt.%), reaction temperature (30–60 °C), glycerol to acetone (GL to AC) molar ratio (1:3–1:9), and reaction time (4–13 min). The SPMC-70 catalyst showed the highest catalytic activity among all the synthesized catalysts and provided 99.11 ± 0.3 % GL conversion with 100 % selectivity of solketal under optimal reaction conditions. Additionally, the recyclability test was performed, and it found that the best catalyst was reusable for up to five reaction cycles. These results showed the effectiveness of carbon-based heterogeneous acid catalysts in deriving a fuel additive, solketal.