Heterogeneous transesterification of extracted oil from sweet orange (<i>Citrus sinensis</i>) seed using modified eggshell as catalyst

Abstract

The environmentally sustainable production of biodiesel is important for providing a renewable alternative transportation fuel and a fuel for diesel engines. This research evaluates the use of low-cost catalysts derived from waste materials (eggshell) for converting  triglycerides in seeds oil (sweet orange seed oil) into biodiesel composed of fatty acid methyl esters. The oil extracted was first characterised for its physicochemical parameters viz; yield (38.88 %), moisture content (6.50 %), relative density (0.89 g/cm³), specific gravity (0.90), refractive index (1.46), iodine value (55.80 gI₂/100 g), acid value (5.64 mgKOH/g), free fatty acid (2.82 mgKOH/g), saponification value (179.90 mgKOH/g), and viscosity (0.04 Pa. S). The parameters were within the AOAC (1990) standard except for moisture content and saponification values which were slightly below while acid and free fatty acid values were slightly higher than the AOAC (1990) standard. Further treatment of the oil for suitability for transesterification for biodiesel production was carried out. The GC-MS analysis of the oil shows that triglycerides and other organic functional groups were evident. The eggshells were calcined (750°C) and modified with H₂SO₄ (20 %) to improve its surface for catalytic activity. Transesterification conditions were; oil to methanol ratio of 1:9, reaction time of 2 h and temperature of 65°C while the catalyst dosage was 10 %. The physicochemical parameters of the biodiesel were obtained to be; yield (39.03 %), refractive index (1.47), acid value (1.12 mgKOH/g) and free fatty acid (0.56 mgKOH/g) were all within the accepted range specified by American Society for Testing and Materials, (ASTMD6751). The GC-MS result of the separated biodiesel showed different methyl esters implying that, there was conversion of the triglycerides to methyl esters. Thus, orange seeds and eggshells can be harnessed for biodiesel production.