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The depletion of fossil fuels, increasing demands for diesel and uncertainty in their availability, depletion rate of energy source, emission of very dangerous pollutants, rapid industrialization and increasing price that make petroleum no longer economically sustainable have necessitated the search for cheap raw material cost. A sustainable and economical supply of raw material is the key factor for biodiesel to be competitive commercially (Fazal et al., 2011; Zeng et al., 2008; Su et al., 2009; Lei et al., 2010). Waste cooking oil presents a promising choice as an alternative feedstock for biodiesel production and to reduce production cost (Gnanaprakasam et al., 2013). In addition, the utilization of waste frying oils diminishes the problems of contamination, because the reusing of these waste greases can reduce the burden of the government in disposing of the waste, maintaining public sewers, and treating the oil wastewater (Encinar et al., 2007). Arora et al. (2012) reported that significant amount of organic waste from agriculture, industries, and community sources is collected annually; it can be convertible to useful energy forms like biohydrogen, biogas, bioalcohols, etc., through various Waste-To-Energy Routes (WTERs) for sustainable development. Urooj et al. (2013) remarked that usage of bio-energy is becoming more and more prominent due to the peak oil crisis.
The reaction is affected by several parameters such as the concentration of catalyst, oil to methanol ratio, reaction temperature, moisture, presence of free fatty acids (FFA) and agitation intensity (Encinar et al., 2005). This process involves many parameters that affect the reaction and optimizing so many reaction factors require large number of experiments, which is laborious, time consuming, and economically non-viable. Response surface methodology (RSM) is a useful statistical technique for the optimization of complex processes, as it reduces the number of experiments required to achieve ample data for a statistically pertinent result (Jeong & Park, 2009). Abhang and Hameeddullah (2012) hinted that optimization of process parameters is the key step in response surface methods to achieve high quality without cost inflation.
Yang et al. (2012) investigated the optimal production of biodiesel from waste deep frying oil by using different amount of catalyst and different amount of oil to methanol ratio. Seecharan et al. (2009) reported of their investigation on a laboratory scale production from used cooking oil in Trinidad and Tobago. Abdalla and Oshaik (2013) explained the concept of converting recycled oils to clean biodiesel. They further hinted that the use of waste cooking oil can go a long way in improving biodiesel economics. Conversion of waste frying oil into a valuable biodiesel after acid- pre treatments process is necessary in order to lower its FFA below 1% (Syam et al., 2013). Canakci and Van Gerpen (2001) developed a process by employing acid catalyst to pretreat the high FFA feedstocks until their FFA level was below 1%, allowing the subsequent use of alkaline catalysts to convert the triglycerides. Production of biodiesel from three mixtures of vegetable oil and used cooking oil by alkali-catalyzed transesterification was investigated and remarked that supplementary oil feedstock for biodiesel production can be recommended if engine performance tests provide satisfactory results (Nakpong & Wootthikanokkhan, 2009). Owolabi et al. (2011) reported that the properties of waste cooking biodiesel were not only comparable with that of others but also within standard limits. Utlu and Kocak (2008) concluded that frying oil methyl ester as alternative diesel engine fuel can be used successfully to operate a turbocharged direct injection diesel engine without modifications to engine or injection system. Phan and Phan (2008) reported that blend of 20 vol. % waste cooking biodiesel and 80 vol. % diesels (B20) could be applied in engines without major modification. Ketlogestswe and Gandure (2011) reported that performance of the engine when powered by biodiesel and its blends with petroleum diesel is very comparable to its performance when powered by 100% petroleum diesel.