Intensification of autocatalytic methyl oleate synthesis in continuous flow rotating recycle reactor under hybrid radiation: Process optimization and Scale-up

Abstract

Intensification of the autocatalytic esterification of methanol with oleic acid for producing methyl oleate (biodiesel) was accomplished using a continuous flow rotating reactor under recycle mode. To exaggerate the biodiesel yield, highly efficient hybrid electromagnetic radiation (near-infrared and microwave irradiation) was used as an energy source. Spherical-shaped nano-zinc-titanate photocatalyst (low band-gap energy: 2.01 eV and low recombination rate) was prepared and utilized in the aforementioned novel reactor. Box-Behnken statistical optimization technique was applied to attain the optimum condition (catalyst concentration 30 wt%, reaction temperature 333 K, methanol: oleic acid mole ratio 11:1, LHSV: 0.20 min−1) resulting in maximum biodiesel yield. Moreover, at optimum rotating speed (∼235 rpm), high external and internal mass transfer coefficients were achieved which rendered a remarkably augmented reaction rate under ideal reactor behavior (Dispersion number: 6.42 × 10−7). A geometric-based COMSOL model was simulated which confirmed uniformity of hybrid irradiation and temperature distribution within the rotating catalytic packed bed; which was applied for the development of a parallel-autocatalytic reaction kinetic model. Langmuir Hinshelwood kinetics of the parallel autocatalytic esterification is well represented in the experimental data (RSSQ=1.52×10-7). Without recycle stream, the reaction exhibited a non-autocatalytic reaction with a lower yield of 79.04 % biodiesel within 0.20 min−1 LHSV, whereas, under recycle mode, the biodiesel yield was increased up to 93.55 % even at a higher LHSV of 0.25 min−1. For larger-scale production of the methyl oleate, the ASPEN PLUS simulator has been deployed for a throughput scale-up factor of 1000 (geometric similarity), which corroborates well with lab-scale yield/reactor performance.