Smart waste management of waste cooking oil for large scale high quality biodiesel production using Sr-Ti mixed metal oxide as solid catalyst: Optimization and E-metrics studies

Abstract

Biodiesel was prepared at laboratory scale via transesterification reaction from waste cooking oil using Sr-Ti mixed metal oxide as a heterogeneous base catalyst. The solid base catalyst was synthesized by polymer precursor method. The most efficient active phase of catalyst was explored by varying the Sr/Ti atomic ratio in mixed metals oxides. The synthesized catalyst underwent for TGA, Powder XRD, SEM, EDX, FT-IR, XPS, and BET surface area analysis to assess its physicochemical characteristics. Additionally, basicity which has been observed as the most process governing factor was also evaluated through Hammett indicator-benzoic acid titration method. The Sr-Ti mixed metals oxide with 4:1 was observed with highest catalytic activity for methanolysis reaction. Its potency was facilitated by fairly acquired BET surface area (43.6 m2/g) and basic strength (2.89 mmol/g). The appreciable values of both the parameters imparted the high catalytic activity in Sr-Ti mixed metals oxide with atomic ratio 4:1. Onward, transesterification reaction was optimized for the maximum FAME conversion through RSM using CCD. The confirmatory tests showed the consistency with the conclusions drawn from RSM study regarding optimized values of concerned process variables. Transesterification reaction turned out 98% FAME conversion exerting catalyst dose (1.0 wt%), methanol to oil molar ratio (11:1), and reaction time (80 min) at reaction temperature (65 °C) and agitation speed (600 rpm) featured by RSM study. The closeness in optimized value of anticipated and confirmatory results perceived the efficiency of CCD and approving its potency as successful tool to estimate the highest FAME conversion. Next, a pseudo-first-order kinetic model of transesterification reaction was established. In addition to this, the thermodynamic functions were also computed through Eyring plot dictating the non-spontaneity and endergonic nature of transesterification reaction. The Environment-factor (E-factor) and Turn Over Frequency (TOF) were enumerated and they approved the prepared Sr-Ti mixed metals oxide as an efficient and sustainable catalyst for biodiesel production through transesterification. Finally, all the important fuel properties of prepared biodiesel from waste cooking oil was discerned within the range laid by ASTM D-6751 standards for biodiesel which coined the compatibility of prepared methyl ester with CI engines as a substitute of diesel fuel.