CaO contained in ash from waste possess

CaO contained in ash from waste, possess excellent catalytic properties such as high basic strength and tolerance of high FFA oil, less environmental hazard impacts due to its low solubility in methanol (Suppes et al., 2004; Liu et al., 2008; Lee et al., 2009; Adewuyi et al., 2012; Khemthong et al., 2012; Rezaei et al., 2013; Tang et al., 2013). CaO as heterogeneous catalyst can be produced from different sources such as chicken eggshell, mollusk shell, golden apple snail shell, mussel shell, oyster shell, meretrix venus shell and mud crab shell (Boey et al., 2011; Jazie et al., 2013). Calcium oxide (CaO) does not occur naturally, it is made from calcination of Rapamycin Supplier at high temperatures [Reaction (1)]. Calcination of limestone to produce lime has been practised since antiquity by cultures all around the world. Calcination of CaCO3 takes place at 500–600 °C but using higher temperature above 700 °C at atmospheric pressure improves the performance of the catalyst and leads to a complete decomposition of CaCO3 (Wei et al., 2009; Krithiga and Sastry, 2011; Sharma et al., 2011; Birla et al., 2012; Navajas et al., 2013). Eggshells, which constitute about 10–11% of the total weight of the whole egg, are composed of approximately 85–95% of CaCO3, weighing 5.5 g of mass and the remaining 5% contains calcium phosphate (0.3%) and magnesium carbonate (0.3%) (Keith-Lucas, 2001; Nakano et al., 2003; Boucher et al., 2008; Krithiga and Sastry, 2011; Jazie et al., 2013). Calcium oxide (CaO) is a basic anhydride, which makes it to have a good catalytic activity and can react easily with water. Chouhan and Sarma (2011) reported that CaO derived from waste eggshell was an effective catalyst for the transesterification of soybean oil, resulting in 97–98% biodiesel yield at 65 °C with alcohol/oil ratio 9:1. Viriya-Empikul et al. (2010) employed eggshell with palm oil, a 95% biodiesel yield was reached within 2 h at 12:1 methanol to oil ratio. The high yield was attributed to high surface area exhibited by the eggshell ash catalyst. Olutoye et al. (2011) studied transesterification of biodiesel from palm oil using eggshell ash as a heterogeneous catalyst. The result revealed that eggshell can be utilised as a low cost heterogeneous catalyst after modification with magnesium and potassium nitrate for biodiesel production, a yield of 95% at alcohol/oil molar ratio of 8:1 was obtained. Furthermore, Khemthong et al. (2012) demonstrated that CaO as catalyst from eggshell and waste bones in biodiesel production with palm olein oil, resulted in a >90% biodiesel yield. Huaping et al. (2006) used non-edible jatropha cursas oil with chemical CaO as a base catalyst, the FAME (Fatty acid methyl ester) yield obtained was 94%, with a relative lower methanol/oil ratio of 9:1, catalyst concentration of 1.5 wt%, at a reaction temperature of 70 °C. Sharma et al. (2011) obtained 95% biodiesel yield from karaja oil using chicken eggshell ash at a methanol to oil molar ratio of 9:1, within 2 h. Boey et al. (2011) reported that CaO catalysed the transesterification of waste oil characterised with high FFA (6.6–6.8%) yielding ∼90% biodiesel as compared to the use of NaOH and KOH which yielded 46% and 61% biodiesel respectively. The abovementioned suggest the robustness of eggshell ash as heterogeneous catalyst. The current study investigated biodiesel production from low quality oil (WVO), employing eggshell ash as heterogeneous catalyst. The process reaction conditions were optimised via response surface method. The experiments were designed using Design-Expert® Software Version 10 by applying 23 full central composite design with 6 star points and 6 centre points. Response surface methodology (RSM) was used by employing central composite design (CCD) to evaluate the stability and variability of the process (Amosa et al., 2015). CCD is a standard RSM design tool used to study the transesterification reaction parameters and predict the variables. CCD is suitable for sequential experiments and fit a quadratic surface, which usually works well for process optimisation (Jazie et al., 2013). Omar and Amin (2011) employed RSM to study the interaction of methanol to oil ratio, reaction temperature, reaction time, catalyst loading and FFA conversion using CCD by applying 24 full factorial design, in the production of biodiesel from waste cooking palm oil with Sr/ZrO2. Boey et al. (2011) applied mud crab shell as catalyst in Biodiesel production and performed a statistical analysis using CCD. Based on the experimental and predicted results, the most important factors affecting biodiesel yield were catalyst concentration, reaction temperature and methanol to oil molar ratio, with 93% yield. Based on the aforementioned studies, the parameters selected for optimisation in the current study are temperature, oil to methanol ratio and catalyst loading.