AlCl₃·6H₂O was used as a catalyst in the esterification reaction of levulinic acid with 1-hexanol for producing hexyl levulinate, a compound that finds applications in several industrial sectors and represents an excellent candidate to be used in diesel fuel blends. A kinetic and thermodynamic study of the esterification reaction was performed, considering four different temperatures (338, 348, 358, and 368 K), an acid: alcohol: catalyst 1:1:0.01 molar ratio, and a reaction time of 72 h. An optimization study was then carried out, evaluating the effect of alcohol and catalyst amounts, and, in the best reaction conditions (acid:alcohol:catalyst 1:2:0.1), a very high levulinic acid conversion (92.5%) was achieved. By using AlCl₃·6H₂O, alongside the high reaction yield, the product purification was also simplified, being such a catalyst able to trap most of the water in a different phase than hexyl levulinate, and, furthermore, it was found to be completely recoverable and reusable for several reaction cycles, without losing its catalytic effectiveness. The use of AlCl₃·6H₂O, therefore, represents a promising effective green route for obtaining hexyl levulinate.

In this work, the transesterification of methyl estolides (ME) extracted from the lipid component present in the sewage scum was investigated. Methyl 10-(R)-hydroxystearate (Me-10-HSA) and Fatty Acid Methyl Esters (FAMEs) were obtained in a single step. A three-level and four factorial Box–Behnken experimental design were used to study the effects of methanol amounts, catalyst, temperature, and reaction time on the transesterification reaction using aluminum chloride hexahydrate (AlCl₃·6H₂O) or hydrochloric acid (HCl) as catalysts. AlCl₃·6H₂O was found quite active as well as conventional homogeneous acid catalysts as HCl. In both cases, a complete conversion of ME into Me-10-HSA and FAMEs was observed. The products were isolated, quantified, and fully characterized. At the end of the process, Me-10-HSA (32.3%wt) was purified through a chromatographic separation and analyzed by NMR. The high enantiomeric excess (ee > 92%) of the R-enantiomer isomer opens a new scenario for the valorization of sewage scum.

The environmental and economic challenges stemming from fossil fuel dependence and climate change highlight the urgent need for sustainable biofuels. Wastewater treatment byproducts, such as sewage sludge (SS), represent a promising, yet underutilized, feedstock for biodiesel production within a circular economy. This research proposes a closed-loop valorization strategy for wastewater treatment byproducts, integrating solventless lipid extraction with the pyrolysis (at 400, 550, and 750 °C) of lipid-free residual biomass to produce the relevant biochars (BC). BCs can be functionalized (sulfonation run at 175 °C, 24 h), characterized (CHNS, FTIR, XRD, SBET, TPD, SEM), and used as catalysts for the esterification reaction of the previously extracted lipids with methanol to produce biodiesel. The extracted lipids were reacted with methanol (1:10 molar ratio, 80 °C, 5 h) using 3 wt.% of sulfonated catalysts per gram of grease, producing fatty acid methyl esters in high yield and conversion (>96%). Catalysts were easily and efficiently recoverable through centrifugation, rendering them stable and reusable for five cycles without losing their catalytic properties. This approach aims to transform SS into a valuable resource, fostering a more sustainable and efficient biofuel production system.