Molecular products, thermal emissions, and radical kinetics from the thermal degradation of croton megalocarpus biodiesel and binary transport fuels

Abstract

There is an urgent interest initiated to develop clean energy resources with the aim of reducing exposure to environmental pollutants and explore model fuels that can hasten the achievement of clean energy combustion. In order to optimize the pyrolysis of binary transport fuels, diesel blends of ratios 1:1, 3:2 and 2:3 were each pyrolyzed at a contact time of 5 seconds in a quartz reactor at 1 atmosphere pressure, at a model temperature of 500 ºC. The surface morphology of the particulate emission was imaged using a field emission gun scanning electron microscope (FEG SEM) while free radical characteristics such as radical intensities and radical kinetics was investigated using an X-band electron paramagnetic resonance spectrometer (EPR). Surface bound functional groups on thermal char were studied using Fourier Transform infra-red spectrometer (FTIR). Optimized molecular structures were performed using the quantum level of theory incorporated in Gaussian ‗16 and CHEMISSIAN computational codes. The charcoal content for pure fossil diesel was compared with the binary diesel residue. Gas-phase molecular components were determined using Gas chromatography (GC) coupled to a mass selective detector (MSD). Elemental composition of thermal char was determined using Smart Elemental Analyzer. It was noted that at a ratio of 2:3 (Biodiesel: Fossil diesel), harmful molecular products reduced significantly, 76 – 99%. Elemental analysis data indicated that the carbon content from commercial diesel was very high (≈ 70.61%) as compared to approximately 53% for biodiesel-fossil diesel mixture in the same ratio 2:3. Interestingly, the free radical content was reduced by nearly 50% in favour of the biodiesel/fossil diesel mixture. Electron paramagnetic resonance (EPR) results gave a g-value of 2.0024 and a narrow ΔHp-p of 3.65 G. The radical concentration for the first EPR experiment was 9.12 × 1019 spins/g and 4.19 × 1017 spins/cm. The decay rate constant for the radicals was low ( while the half-life was ≈ 431 days. Fourier transform infrared (FTIR) results showed the presence of aromatic hydrocarbons, methyl and methylene groups on the surface of biochar while scanning electron microscopy (SEM) images indicated the existence a polymeric structure believed to be highly carbonaceous. The low g-values and low decay rate constant suggest that the free radicals in the biochar are carbon-based and stabilized by a strong π-π conjugated system. This study reports that a binary biodiesel – fossil diesel ratio of 2:3 is a future promising transport fuel because of reduced molecular emissions and decreased free radicals in