Literature Review
1. Waste Cooking Oil (WCO)
Recently, the generation of huge amount of waste cooking oil is increasing, as the human population is increasing, and the need of the food preparation is increased. Improper disposal of these waste has become a serious environmental problem. It was reported that approximately 50,000 tons of WCO per year is generated and disposed to the environment only in Malaysia that might affect the quality of soil and water (Kabir, Yacob, &Radam. 2014).
Waste cooking oil is the byproducts of frying dishes with cooking oil that has been prepared from plant or animal fats. Cooking oil is a glycerol ester made up of various essential fatty acids that can only be dissolved in organic solvents. the initial sources of cooking oil such as coconut oil, palm oil, olive oil, and canola oil, as well as lipid-based animals (Aliasa, et all. 2018).
2. Characteristic of Biodiesel
Biodiesel produced from waste cooking oil has several chemical and physical properties. These properties are collected based on literatures which shown in the following table.
3. Process of the production
Production of biodiesel must be specified carefully with best choosing of optimum parameters in order to get maximum yield. It was reported that the optimum ratio of methanol to WCO is 6.5/1 mol%. Moreover, sodium hydroxide (NaOH) flakes which are inexpensive and easy to handle in transportation and storage. They are preferred by small producers. Alkyl oxide solutions of sodium methoxide or potassium methoxide in methanol, which are now commercially available, are the preferred catalysts for large continuous flow production processes. However, it was observed that KOH is the catalyst that gives the best conversion which was used as ratio of 1% at 50 °C to give conversion of 99%. The time is also a very important parameter in the process, it was deduced that increasing the time more than the necessary will not increase the conversion, but it will favour to reversible reaction (Rafaat. 2009).
The stoichiometric ratio for transesterification requires three moles of alcohol and one mole of triglyceride to yield three moles of fatty acid alkyl esters and one mole of glycerol. However, transesterification is an equilibrium reaction in which an excess of alcohol is required to drive the reaction to the right. Transesterification of pretreated waste rapeseed oil carried out by Yuan et al. (2008) showed a maximum conversion at 6.5:1 of methanol to oil ratio, whereas an earlier study by Leung and Guo (2006) found a maximum conversion at a ratio of 7:1. With further increase in molar ratio the conversion efficiency more or less remains the same, but the energy required for the recovery of methanol becomes higher (Demirbas, 2009)
In the case of the alkaline catalysis, the literature presents many works relating to this issue. In most of the literature reviewed the results showed that the best suited catalyst concentrations giving the best yields and viscosities of the esters are between 0.5 and 1.0 wt %. For higher values the yields were lower. As shown in the following figures, KOH catalyst performed the best yield of biodiesel compared to NaOH, CH3OK, and CH3Na. Additionally, KOH catalyst concentration 1% gives the best yield (Rafaat. 2009).
References
Ibrahim, K., et al. (2014). Households’ Awareness, Attitudes and Practices Regarding Waste Cooking Oil Recycling in Petaling, Malaysia.
Aliasa, N., et al. (2018). Characterization of Waste Cooking Oil for Biodiesel Production.
Park, S., et al. (2019). Biodiesel production from locally sourced restaurants waste cooking oil and grease: Synthesis, Characterization, and performance. Retrieved from https://pubs.acs.org/doi/10.1021/acsomega.9b00268
Gnanaprakasam, A., et all. (2013). Recent strategy of biodiesel production from waste cooking oil and process influencing parameters. Retrieved from https://www.hindawi.com/journals/jen/2013/926392/
Refaat, A. (2009). Different techniques for the production of biodiesel from waste vegetable oil. International Journal Of Environmental Science & Technology, 7(1), 183-213. doi: 10.1007/bf03326130
Yuan, X.; Liu, J.; Zeng, G.; Shi, J.; Tong, J.; Huang, G., (2008). Optimization of conversion of waste rapeseed oil with high FFA to biodiesel using response surface methodology. Renew. Energ., 33 (7), 1678-1684
Leung, D. Y. C.; Guo, Y., (2006). Transesterification of neat and used frying oil: Optimization for biodiesel production. Fuel Process Tech., 87 (10), 883–890
Demirbas, A., (2009). Biodiesel from waste cooking oil via base-catalytic and supercritical methanol transesterification. Energ. Convers. Manage., 50 (4), 923- 927