Technical noteFuel properties of biodiesel produced from selected plant kernel oils indigenous to Botswana: A comparative analysis
Graphical abstract
Introduction
The environmental impact of petroleum fuels, coupled with the depletion of known petroleum reserves, make renewable energy sources more attractive and justify the continued search for alternative renewable fuels. Biodiesel is among the renewable energy resources that has attracted considerable attention in recent times. Biodiesel is highly favoured as alternative to petroleum-based diesel because it is renewable, non-toxic, biodegradable, non-flammable and environmentally friendly [1]. Other strengths of biodiesel fuel include its relatively high heat of combustion (lower but closely comparable to that of petroleum diesel), high oxygen value, contributing to combustion efficiency, and minimal contribution to global warming due to its closed carbon cycle [2].
Biodiesel fuel is derived from vegetable oils or animal fats [3]. The transesterification of an oil or fat with a monohydric alcohol, in most cases methanol, yields the corresponding mono-alkyl esters, which are defined as biodiesel. Biodiesel has been produced from various sources that include palm oil [4], rapeseed oil [5], soybean oil [6], and sunflower seed oil [7]. Biodiesel has been characterized according to its properties that include density, viscosity, heating value, acid value, cetane number, cloud and pour points, and flash point. The viability of biodiesel from particular feedstock seed oil depends on such factors as availability of the raw material in commercial quantity, ease of oil extraction, the oil content (yield) of the plant seeds as well as their product (biodiesel) meeting the basic fuel characteristics for diesel fuels.
The successful introduction and commercialization of biodiesel in many countries around the world has been accompanied by the development of standards to ensure high product quality and user confidence. Some of the major biodiesel standards are ASTM D 6751 and the European standard EN 14214.
In the current study, fuel characteristics of biodiesel produced through alkali transesterification of three plant oils indigenous to Botswana and J. curcas oil grown under Botswana's natural conditions are compared with those of petroleum diesel.
Section snippets
Extraction of plant seed oil
Materials used for experimentation include matured seeds (obtained from ripened fruits) of Sclerocarya birrea, Tylosema esculentum, Schiziophyton rautanenii and J. curcas plant species harvested from Botswana's indigenous woodlands. In order to maintain oil for experimentation as close to its natural state as possible, mechanical cold press extraction method was used to generate crude oil for subsequent analyses. The mechanism for the extractor consists mainly of a piston, a multi-perforated
Results
Oil yields for different plant species, fatty acid profiles of studied plant oils, ester composition of biodiesel fuels and physicochemical property analyses results are presented in Table 1, Table 2, Table 3, Table 4 respectively, while Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7 present comparative fuel properties of the biodiesel fuels and petroleum diesel.
Oil yield levels
The oil yield regarded as the actual oil content in this study is the one determined using solvent extraction method and not press
Conclusions
The following conclusions can be made from the work discussed in this manuscript;
- 1.
The results of this work has established that the oil bearing seeds of S. birrea, T. esculentum, S. rautanenii and J. curcas plants that are native to Botswana are potential feedstock for the production of quality biodiesel since fuel properties of their derived biodiesel meet major international standards for biodiesel.
- 2.
Of the four biodiesel fuels, S. rautanenii has the best cold flow properties. Other fuel
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