Enhanced conversion of dairy waste oil to biodiesel via novel and highly reactive UiO-66-NH2/ZnO/TiO2 nano-catalyst: Optimization, kinetic, thermodynamic and diesel engine studies

Abstract

This study focuses on developing a novel UiO-66-NH2/ZnO/TiO2 nano-catalyst for efficient biodiesel generation from dairy waste scum oil (DWSO). UiO-66-NH2, UiO-66-NH2/TiO2, and UiO-66-NH2/ZnO/TiO2 nano-catalysts were prepared via the sol–gel approach and their structural features were analyzed by XRD, FT-IR, BET, ED/Map, SEM, TEM, and CO2-TPD approaches. The UiO-66-NH2/ZnO/TiO2 nano-catalyst demonstrated a mesoporous surface with a specific surface area and an average particle size of 568.1 m2/g and 28.35 nm, respectively. The central composite design (CCD) was also utilized to optimize crucial variables. Biodiesel conversion of 98.7 % was achieved under the optimized process circumstances such as the methanol to DWSO ratio of 9.8:1, reaction temperature of 61 °C, and nano-catalyst concentration of 2 wt%. As a novelty, biodiesel conversion is the highest methyl ester achieved from DWSO so far. The survey of the reaction kinetics employing UiO-66-NH2/ZnO/TiO2 indicated that the rate constant, activation energy and Arrhenius factor are 0.1325 min−1, 48.73 kJ mol−1, and 39.6 × 105 min−1, respectively. Besides, the thermodynamic scrutiny implicates that the process is nonspontaneous (ΔG = 88.94 kJ/mol at 338 K) and endothermic (ΔH = 46.01 kJ/mol). Moreover, the impact of adding DWSO-derived biodiesel to diesel on the diesel engine parameters and viscosity alterations was scrutinized. Fuel rheological behaviour appraisal exhibited that biodiesel follows the Newtonian model. The stability of the UiO-66-NH2/ZnO/TiO2 nano-catalyst was assessed in transesterification successive processes. The nano-catalyst could be reused multiple times, and a conversion of 90.14 % was obtained during the 7th consecutive run. It can be concluded that UiO-66-NH2/ZnO/TiO2 nanoparticles can be employed as a highly retrievable nano-catalyst for efficient transesterification of DWSO.