Abstract

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A reformed transesterification process for biofuel production using crown ethers was developed and proved to be successful in restricting accumulation of toxic species in the biodiesel phase. Combining crown ethers (18-crown-6; 15-crown-5) with conventional catalysts (KOH/NaOH) in generating neem biodiesel resulted in reduction in the levels of Cr⁶⁺ and As³⁺ in the biodiesel fraction. Converse results were obtained for Cr³⁺ and As⁵⁺ under the same conditions. Toxicity of biofuels is receiving widespread attention, and suppressing hazardous chemical toxins in biodiesel and glycerol waste products is beneficial to sustainable development. A Perkin Elmer SCIEX DRC-e ICP-MS was coupled with a liquid chromatographic system (HPLC) for high performance studies. Elution of the toxic species followed by mass spectrometry for simultaneous detection was conducted for convenient resolution of all four species. A C-8 reinforced silica column formed the stationary phase (150 mm in length; internal diameter: 4.6 mm; particle size: 5.0 μm). The mobile phase was a special mixture of tetrabutylammonium hydroxide (TBAH) blended with the potassium salt of ethylenediaminetetraacetic acid (EDTA) in 5% methanol and water to a pH of 7.2. The elution rate was ~1.2 mL/min; and associated retention times (min) were: As³⁺: 1.61; As⁵⁺:4.06; Cr³⁺: 3.71; and Cr⁶⁺: 5.80. The system is equipped with a dynamic reaction cell (DRC) to facilitate mass detection. The oxygen flow in the DRC was controlled to give a rate of ~ 4.0 mL/min. Following mass detection m/z values of 52 characterized the Cr³⁺/ Cr⁶⁺ species; while the arsenic components were detected as adduct ions, AsO⁺, m/z 91, in affiliation with oxygen. Certified reference materials were used for purposes of calibration. In the biodiesel phase Cr³⁺ levels were most pronounced reaching levels of ~2000 μg/L; Cr⁶⁺ and As³⁺ occurred mainly at ~5 μg/L; whereas As5+ reflected minimal levels at 0.8 μg/L. Certain trends in the results were observed on comparing levels in the glycerol and biodiesel fractions. For instance, retention of Cr³⁺ in the glycerol phase was consistently lower, while for As³⁺ it was relatively higher. In the other two cases of Cr6+ and As5+ the results varied and showed no obvious trend. The study revealed that definite environmental hazards accompanying biofuel production could be curbed by combining crown ethers with conventional catalytic treatment.

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