Cold flow properties of biodiesel obtained from corn oil
Introduction
The energy need of the world increases because of the growing population and increasing energy consumption as a result of the industrial developments in worldwide. The most consumed energy source in the world is fossil fuels today. 85% of the energy need of the world is met by fossil fuels [1]. In addition, about 40% of the fossil energy consumption worldwide is composed of oil despite the fact that it showed a decline in 2009 because of the worldwide economic recession [2]. Diesel fuel is the most consumed oil product among all petroleum distillates although its contribution to global air pollution is the one of the highest. It is an important source for air pollutants such as NOx, SOx, CO, CO2, particulate matter, and VOCs (volatile organic compounds) which have serious potential to give damage to health of any living being [3]. It is evident that alternative diesel fuels have a vital importance to be able to reduce air pollution worldwide.
Biodiesel is an alternative and environmentally friendly diesel fuel which can be obtained from renewable biological resources such as vegetable oils and animal fats. The main production method of biodiesel is transesterification of oils and fats, in which vegetable oils or fats react with a monohydric alcohol along with an acidic or basic catalyst to yield a mixture of fatty acid alkyl esters and glycerol [4]. Basic transesterification is used wider because of the shorter reaction period and higher product yield. Use of some excess alcohol is required because of reversible nature of the reaction in both methods.
Properties of biodiesel such as exhaust gas emissions, internal lubricity, and its renewability nature are comparable with petroleum diesel; however, poor cold flow properties of biodiesel are one of the obstacles hindering its common use [5]. Biodiesel contains saturated fatty acyl esters in considerable amounts. They are mainly responsible for high CP (cloud point), PP (pour point) and CFPP (cold filter plugging point) temperatures. Cloud point is the temperature by which liquid lipid material begins to have a cloudy appearance because saturated esters get solidify and become crystallized. This causes blockages in the pipes and filters of the fuel systems of the vehicles. If the temperature decreases further, it solidifies increasingly and finally liquid flow will completely stop. The lowest temperature it can continue to flow is called as pour point. Cold filter plugging point is defined as the highest temperature at which a given amount of a fuel sample cooled under certain experimental conditions cannot pass through a standard filter in a specific time [6]. Cold flow properties of biodiesel and diesel fuels are specified by ASTM (American Society for Testing and Materials) D6751 in US and EN (European Standards) 14214 in Europe. In both standards, the cold flow properties of biodiesel such as CP, PP and CFPP are specified to be reported in degrees Celsius depending on the season and the location.
Although minor constituents such as saturated monoacylglycerols or free steryl glucosides may cause clogging problems in fuel pipes and filters of the vehicles, it is clearly known that cold flow properties of biodiesel are mainly affected by fatty acid mono-alkyl ester composition of the biodiesel [5], [7]. Many studies have been lately focused on improving cold flow properties of biodiesel. Of these, blending biodiesel with different improving agents [5], [8], [9], [10], winterization [11], use of different alcohols in transesterification and use of oils with modified fatty acid profile [12] are noticeable examples. But one important problem with all these solutions is that it is not possible to obtain a biodiesel sample having favorable cold flow properties without causing a negative effect in another property such as cetane number or oxidative stability. The reason is that biodiesel characteristics such as cold flow properties, kinematic viscosity and density are improved with the increasing unsaturated fatty acid content while some others, such as cetane number and oxidative stability, are improved with the increasing saturated fatty acid content. It is also concluded that monounsaturated fatty acid methyl esters such as oleic acid methyl esters are the most appropriate biodiesel components [13], [14].
In this study, it is aimed to investigate the effects of transesterification parameters on the cold flow properties of a biodiesel sample obtained from corn oil. The target of the study is to obtain optimum transesterification conditions giving as low as possible cold flow temperatures.
Section snippets
Experimental
The edible corn oil used in the experiments was supplied from a local grocery store. The density of the corn oil was 0.868 g/mL at 15 °C. Corn oil has a good oxidative stability in spite of its high unsaturated fatty acid content [15]. The fatty acid content of the corn oil used in the study is given in Table 1. The corn oil sample was analyzed by a gas chromatograph (Agilent 6890N gas chromatograph, Waldbronn, Germany) with a DB-23 capillary column (60 m × 250 μm × 0.15 μm). Column temperature
Results and discussions
Each experiment has been repeated at least 3 times and standard deviations in the measurements of cold flow temperatures were at the range of ±0.33 the parameters. The change in the cold flow properties of biodiesel at different parameter levels was plotted as the cold flow properties versus the parameter tested.
Conclusion
As a result, it is suggested from the study that it is possible to improve cold flow properties of biodiesel by manipulating parameter levels of transesterification reaction. In addition, reaction times longer than 10 min, reaction temperatures higher than 20 °C and stirring speeds higher than 300 rpm have no considerable effect on the transesterification reaction in terms of cold flow properties of the biodiesel. Alcohol-to-oil ratios higher than 5.03:1 (in moles) and amount of alkali
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