Biodiesel production from sunflower oil using microwave assisted transesterification
Magida, Nokuthula Ethel
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Biofuels are becoming more attractive worldwide because of the high energy demands and the fossil fuel resources that are being depleted. Biodiesel is one of the most attractive alternative energy sources to petroleum diesel fuel and it is renewable, non toxic, biodegradable, has low sulphur content and has a high flash point. Biodiesel can be generated from domestic natural resources such as coconuts, rapeseeds, soybeans, sunflower, and waste cooking oil through a commonly used method called transesterification. Transesterification is a reaction whereby oil (e.g. sunflower oil) or fats react with alcohol (e.g. methanol) with or without the presence of a catalyst (e.g. potassium hydroxide) to form fatty acid alkyl esters (biodiesel) and glycerol. The high-energy input for biodiesel production remains a concern for the competitive production of bio-based transportation fuels. However, microwave radiation is a method that can be used in the production of biodiesel to reduce the reaction time as well as to improve product yields. Sunflower oil is one of the biodiesel feedstocks that are used in South Africa and is widely used in cooking and for frying purposes. This study aims to use microwave irradiation to reduce the energy input for biodiesel production. The effect of various reaction variables, including reaction time (10 – 60 seconds), microwave power (300 – 900 watts), catalyst (potassium hydroxide) loading (0.5 – 1.5 wt%) and methanol to oil molar ratio (1:3 – 1:9) on the yield of fatty acid methyl ester (biodiesel) was investigated. The quality of biodiesel produced was analysed by Gas Chromatography (GC), Fourier Transform Infrared Spectroscopy (FTIR) and viscometry. The FTIR results confirmed the presence of functional groups of the FAME produced during transesterification. The results showed that transesterification can proceed much faster under microwave irradiation than when using traditional heating methods. The interaction between the alcohol and oil molecules is significantly improved, leading to shorter reaction times (seconds instead of hours) and improved diesel yields. The highest biodiesel yield obtained was 98% at 1:6 oil-to-methanol molar ratio for both 1 wt% and 1.5 wt% potassium hydroxide (KOH) at a reduced reaction time (30 seconds). The chemical composition of FAME (biodiesel) obtained from different conditions contained palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1) and 70% linoleic acid (C18:2). The physical properties (cetane number, viscosity, density and FAME content) of biodiesel produced met the SANS 1935 specification. The energy consumption was reduced from 1.2 kWh with the traditional transesterification to 0.0067 kWh with the microwave transesterification. Microwave irradiation was shown to be effective in significantly lowering the energy consumption for production of biodiesel with good quality for small scale producers.
- Engineering