Elsevier

Biomass and Bioenergy

Volume 18, Issue 6, 1 June 2000, Pages 515-527
Biomass and Bioenergy

Catalytic production of biodiesel from soy-bean oil, used frying oil and tallow

https://doi.org/10.1016/S0961-9534(00)00014-3Get rights and content

Abstract

Three fatty materials, soy-bean oil, used frying oil and tallow, were transformed into two different types of biodiesel, by transesterification and amidation reactions with methanol and diethylamine respectively. The ignition properties of these types of biodiesel were evaluated calculating the cetane index of the transesterification products, and the blending cetane number of the amide biodiesel blended with conventional diesel. Amide biodiesel enhances the ignition properties of the petrochemical diesel fuel, and it could account for the 5% market share that should be secured to biofuels by 2005.

Introduction

Biodiesel, defined as “a substitute for, or an additive to diesel fuel that is derived from the oils and fats of plants and animals” [1] is finding favour in the markets of Europe and US. The European Union has set an objective to secure for motor biofuels a market share of 5% of total motor fuel consumption by 2005. It is expected that a significant portion of this amount will be biodiesel, and a council directive that sets down its specifications is currently under discussion [2]. In a similar way, the US Department of Energy estimated that up to 50% of the total diesel fuel consumption could be replaced with biodiesel [3].

The main advantages of using this alternative fuel are its renewability, better quality exhaust gas emissions (as it does not contain sulphur, except biodiesel derived from canola oil that has a significant sulphur content), its biodegradability and, given that all the organic carbon present is photosynthetic in origin, it does not contribute to a net rise in the level of carbon dioxide in the atmosphere, and consequently to the greenhouse effect [4] (if the carbon dioxide emitted from fertilizer production is not taken into account).

Fatty acid methyl esters (FAME) from vegetable oils have shown promise as biodiesel, as the result of improved viscosity, volatility and combustion behaviour relative to triglycerides, while maintaining their cetane number (around 50). FAME biodiesel is also compatible with conventional diesel, and the two can be blended in any proportion although the ignition quality of the blends remains essentially the same as that of the conventional diesel [5]. Transesterification (also called alcoholysis) of triglycerides for soap manufacture has been studied intensively [6], and more than a dozen US patents, the most mentioned being that of Bradshaw and Meuly [7], and five European processes have been issued [4].

The first objective of this paper is to describe the application of the current FAME biodiesel production technology to the transesterification of soy-bean oil and two residual fatty materials, used frying oil and tallow. Soy-bean oil has been extensively studied as a raw material for FAME biodiesel production [8], and, in our study, it served as a test for the optimization of the production of biodiesel from the two fatty materials, the transformation of which would alleviate a disposal problem. In Spain the edible oils are used in frying pans or fryers (except the oil consumed in salads) and after a variable time of use are discarded. The used frying oil is mostly thrown through the home drains, leading to water pollution. Moreover, as more than 80% of the oil is consumed at home, the control of this disposal behaviour is very difficult. The Council of Tres Cantos (population 28,000), a residential village in the outskirts of Madrid, has launched a pioneering programme to recover all the used frying oil in waste oil containers (capacity 500 l). The containers are emptied and cleaned twice a week, and the used oil is transported to a factory for processing. On the other hand, the consumption of animal fats such as tallow is in decline as the result of a change in the feeding habits of the population and the soap industry cannot take up all the excess animal fats produced.

The cetane index (ASTM D-4737-87) was used to check the ignition quality of the FAME biodiesel from soy-bean oil, used frying oil and tallow.

This paper also describes laboratory studies regarding other derivatives of fatty acids which can be blended with diesel fuel, and that could account for the 5% market share which should be given to biofuels by 2005. Amide biodiesel enhances the ignition quality and other characteristics of the fuel. This amidation reaction of soy-bean oil, used frying oil and tallow was carried out with diethylamine to produce “amide biodiesel”. In order to check its ignition quality the blending cetane number [1] of the amide biodiesel of used frying oil blended with petrochemical diesel was calculated.

Section snippets

General Procedure [8]

In a 2 l glass reactor (see Fig. 1) equipped with a glass anchor-shaped stirrer, a type K thermocouple, a water condenser and funnel, and surrounded by a heating mantle controlled by a proportional integral derivative (PID) temperature controller device, 873 ml (702 g, 0.80 mol) of used frying oil and 244 ml (6 mol) of methanol were placed. The temperature was raised to 60°C and the mixture was stirred at 600 rpm. When this temperature was reached, sodium methoxide (7 g, 0.13 mol, 1% w/w of

Results and discussion

The fatty acid composition and acidity index of the soy-bean oil, used frying oil and tallow are given in Table 1. The oils show a high grade of unsaturation (oleic+linoleic acids ∼80% w/w), while in the tallow the predominance of the saturated acids is higher. The acidity indices of the soy-bean oil and the used frying oil were around 0.5%, which allows the use of basic catalysts in the transesterification process [8]. The tallow had an acidity index of 6.8% which is a limiting condition for

Conclusions

Three fatty materials, soy-bean oil, used frying oil (∼50% mixture of olive and sunflower oil) and tallow were transformed into biodiesel by transesterification reaction with methanol. The operating conditions for this chemical transformation were studied and the analysis of these biodiesels was given. The ignition quality of these biodiesels was evaluated calculating their cetane indices using the ASTM D-4737 method, based in the measure of the density (method ASTM D-1298) and in the

Acknowledgements

We are very grateful to the Laboratory of Petroleum Products of the School of Mines (Madrid) for the determination of the cetane indices of the FAME biodiesels, and to Dr. Juan A. Delgado of Repsol Petróleo (Madrid) for the determination of the blending cetane number of amide biodiesel blended with petrochemical diesel.

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