Elsevier

Applied Energy

Volume 87, Issue 7, July 2010, Pages 2356-2359
Applied Energy

Production of ethyl ester from esterified crude palm oil by microwave with dry washing by bleaching earth

https://doi.org/10.1016/j.apenergy.2009.12.006Get rights and content

Abstract

The production of ethyl ester from a feed material of esterified crude palm oil with 1.7 wt% of free fatty acid (FFA) content using microwave heating was investigated. Parametric studies were carried out to investigate the optimum conditions for the transesterification process (amount of ethanol, amount of catalyst and reaction time). As a result, optimum reaction parameters for the transesterification process aided by microwave heating have been identified: a molar ratio of oil to ethanol of 1:8.5, 1.5 wt% of KOH/oil, a reaction time of 5 min and a microwave power of 70 W. Glycerin from the ester phase was separated by adding 10 wt% of pure glycerin. The ethyl ester was purified with 1.2 wt% of bleaching earth to remove the residual catalyst and residual glycerin. This transesterification process provided a yield of 85 wt% with an ester content of 98.1 wt%. The final ethyl ester product met the specifications stipulated by ASTM D6751-02.

Introduction

The price of fossil diesel has soared during the past 2 years, and the supply will be exhausted some day. Thus, looking for an alternative way to develop a substitute for diesel (biodiesel) is imperative. Biodiesel is a replacement for, or an additive to, diesel fuel, and is derived from the vegetable oils or animal fats [1]. The main advantages of using this alternative fuel are its renewability, better quality of exhaust gas emissions, 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 [2].

Vegetable oil remains the major feedstock for biodiesel production. Animal fat and waste cooking oil have also been used. Soybean (US), rapeseed (Europe) and oil palm (South-east Asia) [2], to mention a few, have been successfully used as renewable vegetable oil sources to generate biodiesel with superior qualities to petroleum-based fuels. The oil palm (Elaeis guineensis Jacq.) produces fruit, about 70–80 wt% of which is constituted by the mesocarp, and about 45–50 wt% of this mesocarp is oil. The rest of the fruit is composed of the shell, kernel, moisture, and other non-fatty fiber. The extracted oil is known as crude palm oil (CPO), and consists of more than 90 wt% of triglycerides and 3–7 wt% of free fatty acids (FFA). A pretreatment process for CPO is an esterification process with alcohol, which changes FFA to esters; this process also commonly uses a strong liquid acid catalyst, such as sulfuric acid. This esterified CPO then reacts with an alkaline catalyst and alcohol by transesterification.

Generally, biodiesel is produced by transesterification. Transesterification is the reaction of triglycerides with an alcohol to form esters and glycerin. Alcohols such as methanol and ethanol are the most frequently employed. Although the use of different alcohols results in some differences in terms of the reaction kinetics, the final yield of esters remains more or less the same [3]. Therefore, selection of the alcohol is largely based on cost and performance considerations. Ethanol can be produced from renewable agricultural resources and is non-toxic, so it is often used as an alcohol for the transesterification of vegetable oils. However, the formation of an emulsion after transesterification with ethanol makes the separation of esters very difficult. In the case of methanol, the emulsion quickly and easily breaks down to form a lower glycerin-rich layer and an upper methyl-ester-rich layer. With ethanol, the emulsion is more stable, which severely complicates the separation and purification of esters [4]. The addition of extra glycerin to the reaction mixture was found to be helpful in glycerin separation [5].

Generally, biodiesel production uses heating coils to heat the raw material, but this method consumes a large amount of energy. By using a microwave for preparative chemistry, it is often possible to accelerate reactions and improve their selectivity [6], [7], [8]. Microwave heating has been proven to prepare biodiesel rapidly and with good conversion results.

Wastewater from biodiesel production contains soap, glycerin and oil, so treatment of the wastewater is necessary. However, the methods of doing so are not described in most instruction-manuals because the process is very difficult. Biodiesel wastewater purified using the water washing method still contains a substantial amount of effluents, as shown in Table 1. Significant product loss also can occur via retention during the water washing phase. Furthermore, emulsions can form when processing used cooking oils or other feeds with high FFA content, due to soap-formation. In refined vegetable oil production bleaching earth is commonly used, due to its high absorption capacity, for de-coloring vegetable oils and removing soap from vegetable products. Bleaching earth can also be used in the cleaning step of biodiesel production to improve the quality of the waste water [9].

In this paper, we describe the development of a transesterification process for the production of ethyl ester from esterified crude palm oil which uses ethanol for an alcohol, and a microwave heating system. Bleaching earth is then applied to purify the ethyl ester.

Section snippets

Materials

Crude palm oil, bleaching earth and ethanol (99.5%) were acquired from the Specialized R&D Center for Alternative Energy from Palm Oil and Oil Crops at Prince of Songkla University. Phenolphthalein of analytical reagent grade was obtained from LabChem (Pittsburgh, PA, USA). Potassium hydroxide (95%), sulfuric acid (98%) and pure glycerin (98%) were commercial grade.

Microwave system

All batch microwave tests were conducted with a Sharp model R235 compact microwave oven working at 2.45 GHz with a power of 800 W.

Transesterification process

A study case of alkaline-catalyzed transesterification was run using esterified CPO that had 1.7 wt% of FFA content and a molar ratio of oil to ethanol of 1:4.5. Important variables affecting the ester content in the transesterification process are the molar ratio of oil to ethanol, the amount of alkaline catalyst, and the reaction time.

Conclusions

The production of ethyl ester from esterified CPO containing 1.7 wt% of FFA content and an oil to ethanol molar ratio of 1:4.5, under microwave assistance, was investigated. It was found that microwave irradiation facilitated the synthesis of ethyl ester from esterified CPO. The optimum conditions for producing ethyl ester from esterified CPO were a molar ratio of oil to ethanol of 1:8.5; 1.5% wt/wt KOH/oil as a catalyst; a reaction time of 5 min; and a microwave power of 70 W. The problem of

Acknowledgments

The author gratefully acknowledges financial support from a Prince of Songkla Graduate Studies Grant and the Graduate School of Prince of Songkla University, and the provision of equipment by the Specialized R&D Center for Alternative Energy from Palm Oil and Oil Crops at Prince of Songkla University.

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