Production of Biodiesel Using Alkaline Based Catalysts From Waste Cooking Oil: A Case Study

Waste cooking oil (WCO) is typically cheaper than diesel and has much less impact on food-chain, so its use as biodiesel can reduce the cost of diesel run operations. Air-conditioned fast food restaurants (FFR) in Bangladesh generate lot of WCO, but due to frequent load shedding they also need to burn lot of diesel for captive power generation. Recycling part of the waste oils in the form of biodiesel can reduce the need of diesel fuel and increase profitability of the establishment. The techno-economic feasibility of such operation in case of a FFR in Dhaka has been investigated. CH3OH (methanol) and NaOH (sodium hydroxide) as base catalyst are mostly used in this process because of their lowest costs, higher reaction rates and higher yields. From the WCO generation of about 80 lites per week, yield for biodiesel production is considered in the range of 80-90%. Single-stage transesterification (SST) process is the cheapest and the easiest of the different methods. The cost of chemicals can be further minimized by recycling of CH3OH and NaOH in this SST process. The possible 35-40% CH3OH and 80-90% NaOH recoveries were considered for a alcohol to oil molar ratio of 5:1 of the reactants. It is found from the study that a small scale processing plant could be developed with reactant recovery units for producing biodiesel to supplement diesel fuel needed to run the generators. The monthly savings was equivalent to only 4% of the diesel cost for standby power, with a payback period of about one year. However this can increase up to 50% of the fuel cost and less than six months of payback period if the cost of dumping WCO in considered. The study reveals that even in the case of a FFR where WCO is available at almost no cost, the processing cost for biodiesel does not make it very feasible unless the cost associated with properly dumping the WCO is high enough.