Biodiesel Synthesis from Milk Thistle (Silybum marianum (L.) Gaertn.) Seed Oil using ZnO Nanoparticles as a Catalyst

Abstract

Biodiesel is considered valuable to reduce dependency on petrofuels. This work aimed to synthesize biodiesel from Silybum marianum using synthesized ZnO nanoparticles as a catalyst. The synthesized ZnO nanoparticles were examined by scanning electron microscopy and X-ray diffraction for confirmation. The synthesized biodiesel was confirmed by ASTM D-6751, H and C-NMR, GC-MS, and FT-IR spectroscopy. The optimum biodiesel yield of 91% was obtained with an oil-to-methanol ratio of 1:24, 15 mg of catalyst concentration, 60 °C temperature, and 45 min of reaction time. Fuel properties were determined according to the ASTM-defined methods and found within the defined limits of ASTM D-6751. 1H-NMR and 13C-NMR showed characteristic peaks at 3.667 ppm, 2.000–2.060 ppm, 0.858–0.918 ppm, 5.288–5.407 ppm, 24.93–34.22 ppm, 172.71, 173.12, 130.16 ppm, and 128.14 ppm, respectively, which confirm biodiesel synthesis. The FAMEs composition of biodiesel was determined by GC-MS, which recognized 19 peaks for different types of FAMEs. FT-IR spectroscopy showed two main peaks, first in the range of 1725–1750 cm−1 and second in the range of 1000–1300 cm−1, which confirmed that the transesterification process had completed successfully. The physicochemical characteristics of Silybum marianum confirm that it is a suitable source to produce biodiesel on an industrial scale.