Biodiesel Production from Selected Non-Edible Feedstocks using Unsupported Potassium Carbonate

The dwindling reserve of fossil fuel and their associated geo-political and environmental problems have increased the need to seek alternative renewable and sustainable sources for fuel production. Biodiesel, mostly produced from vegetable oils, is mono-alkyl ester and is perceived to replace/supplement fossil diesel fuel. Both edible and non-edible vegetable oils can be used as feedstock in the production of biodiesel. The use of edible oils for fuel production is a concern as the global food demand rises. There are also sustainability issues on deforestation and ecological imbalance with large scale biofuel production. The high supply cost of feedstocks which account for more than 80 % of the overall biodiesel production cost coupled with their competition as food sources have turned the attention to the exploitation of non-edible feedstocks such as Jatropha, Castor bean oil, Neem oil, Pongame oil and Sea mango oil. In this study, biodiesel was produced from non-edible vegetable oil sources namely Jatropha curcas oil and waste vegetable oils (Soya bean and Cottonseed). Fresh Soya bean and Cottonseed oils were transesterified to serve as control. Unsupported potassium carbonate (K2CO3) was used as a catalyst to assess its technical feasibility and process conditions for transesterification of the oils. Various qualitative and quantitative analytical techniques were employed for the characterization of the oil feedstocks prior to transesterification. Such techniques were also used to access the completeness of reactions based on the purity of FAME produced. They include gravimetric, volumetric, potentiometric, mass spectrometric and chromatographic techniques. A single-step alkali transesterification process was used to convert four oil samples (fresh Soya bean oil, waste Soya bean oil, fresh Cottonseed oil and waste Cottonseed oil) to fattyacid methyl esters (FAME) because they contained relatively low percentage free fatty acid (% FFA < 1 %). The Jatropha curcas oil contained high free fatty acid (5.70 %) which was reduced to 1.31 % in an acid pre-treatment esterification process prior to transesterification; hence, a two-step transesterification process was employed. The experimental results suggest that K2CO3 is a better alternative to other known alkali catalysts such as NaOH, KOH, NaOCH3 and KOCH3 since it provides practically complete alcoholysis with least amount of soap production. It was observed that a catalyst amount of 4 wt. % K2CO3 with 60 oC reaction temperature and 600 rpm reaction speed was the optimum conditions for the transesterification of the non-edible vegetable oils. Also, the optimum oil to methanol molar ratio for the conversion of both Cottonseed waste vegetable oil (CWVO) and Soya bean waste vegetable oil (SWVO) to FAME was 1:6 whilst that for the Jatropha curcas oil (JCO) was 1:8. The optimum reaction periods were 40 min, 80 min and 120 min respectively for the conversion of CWVO, SWVO and JCO to FAME. The combination of the optimum parameters of catalyst amount, oil: methanol molar ratio, reaction temperature as well as reaction time gave a FAME yield of about 99.5 % for both CWVO and SWVO but 94.8 % for JCO. K2CO3 as a catalyst has been shown to have great potential for transesterification in this work. Biomass such as cocoa pods and plantain peels contain this mineral compound in substantial amounts and readily abound in Ghana. K2CO3 can easily be extracted from such biomass ash using classical economic extraction technology. Given the viability of waste vegetable to produce biodiesel, research to assess the quantity of waste vegetable oil generated in Ghana should be encouraged in the match to realizing the actual production of biodiesel through such routes.

Source: KNUST