Thermochemical and catalytic processes for the sustainable production of biofuels through biomass conversion

Fossil fuels continue to dominate the global energy supply, particularly in the transport sector, where around 70% of petroleum is used for fuel production. In response, growing research efforts are concentrated toward sustainable alternatives. Among these, biomass, especially waste biomass from industrial, municipal, or lignocellulosic sources, stands out as a low-cost, abundant, and sustainable feedstock for the production of biofuels and value-added chemicals via catalytic or thermochemical conversion processes. This work investigates the production of biofuel through the valorisation of low-value biomass, focusing on both catalytic and thermochemical conversion processes. The catalytic pathway centres on the synthesis of ethyl levulinate (EL), a promising bio-blendstock that can be used in both diesel and gasoline engines. EL can be obtained via acid-catalysed alcoholysis of the polysaccharide fraction of biomass and easily purified. The study initially explored the conversion of model sugar compounds, achieving yields above 50 mol%. Then, the focus shifted towards real waste materials as potential low-value feedstock for an industrial EL production. Moreover, special emphasis was placed on the practical use of EL as diesel and gasoline additive. In particular, engine tests were also carried out to evaluate the impact of various gasoline-EL blends on engine performance and emissions. As a thermochemical approach, the study focused on the gasification of pulp and paper mill sludge (PPMS), a typical paper industry waste mainly composed of cellulose and CaCO₃. Experiments were carried out in a ≈100 kWTH downdraft fixed-bed reactor using either an O₂/H₂O mixture or air as the gasifying agent. Specifically, key process parameters (temperature, substrate loading, and gas flow rates) were carefully optimised to maximise gasification efficiency and improve syngas composition, allowing to reach a high hydrogen-rich syngas composition (~40 mol%), ideal for energy recovery. In conclusion, this work explored the production of a high-potential EL biofuel from low-value raw materials and evaluated its application as a bio-additive in gasoline engines. Additionally, it investigated gasification as an innovative and efficient method for valorising PPMS waste, leading to the generation of hydrogen-rich syngas suitable for energy production.