Biodiesel production from waste cooking oils Anh N. Phan a, * , Tan M. Phan b a School of Chemical Engineering and Advanced Materials, Newcastle University, NE1 7RU, UK b Department of Science and Technology, HCMC, Viet Nam article info Article history: Received 12 May 2008 Received in revised form 3 July 2008 Accepted 8 July 2008 Available online 15 August 2008 Keywords: Transesterification Biodiesel Waste cooking oil Boiling range Carbon residue abstract Alkali-catalyzed transesterification of waste cooking oils, collected within Ho Chi Minh City, Vietnam, with methanol was carried out in a laboratory scale reactor. The effects of methanol/waste cooking oils ratio, potassium hydroxide concentration and temperature on the biodiesel conversion were investi- gated. Biodiesel yield of 88–90% was obtained at the methanol/oil ratios of 7:1–8:1, temperatures of 30–50 °C and 0.75 wt% KOH. Biodiesel and its blends with diesel were characterized for their physical properties referring to a substitute for diesel fuel. The results showed that the biodiesel experienced a higher but much narrower boiling range than conventional diesel. Carbon residue content was up to 4 wt%. Blends with a percentage of the biodiesel below 30 vol% had their physical properties within EN14214 standard, which indicated that these could be used in engines without a major modification. Crown Copyright Ó 2008 Published by Elsevier Ltd. All rights reserved. 1. Introduction Increasing concerns regarding environmental impacts, the soar- ing price of petroleum products together with the depletion of fos- sil fuels have prompted considerable research to identify alternative fuel sources. Biofuel has recently attracted huge atten- tion in different countries all over the world because of its renew- ability, better gas emissions and its biodegradability. It is estimated that biodiesel/bio-ethanol could replace approximately 10% of die- sel fuel consumption within Europe and 5% of Southeast Asia’s to- tal fuel demand. Biodiesel is superior to conventional diesel in terms of its sul- phur content, aromatic content and flash point. It is essentially sul- phur free and non-aromatic while conventional diesel can contain up to 500 ppm SO 2 and 20–40 wt% aromatic compounds. These advantages could be a key solution to reduce the problem of urban pollution since transport sector is an important contributor of the total gas emissions. Amongst vehicle fuels, diesel is dominant for black smoke particulate together with SO 2 emissions and contrib- utes to a one third of the total transport generated greenhouse gas emissions [31]. According to Utlu and Kocak [42], there was on average of a decrease of 14% for CO 2 , 17.1% for CO and 22.5% for smoke density when using biodiesel. Biodiesel production from vegetable oils has been extensively studied in recent literature reviews. There were more than 50 papers cited relating to biodiesel production from vegetable oils in the Fukuda et al.’s work [17]. Many researchers have reported the biodiesel production in several ways: (a) the effect of operating parameters [3,15,16,29,36]; (b) the effect of the type of catalysts such as enzyme catalysts [17,20,32,33,38], heterogeneous catalysts [21,39] and acidic catalysts [4,28]. However, the raw material costs and limited availability of vegetable oil feedstocks are always crit- ical issues for the biodiesel production. The high cost of vegetable oils, which could be up to 75% of the total manufacturing cost, has led to the production costs of biodiesel becoming approximately 1.5 times higher than that for diesel [30,44]. Nevertheless, the price of waste cooking oils (WCO) is 2–3 times cheaper than virgin vegetable oils. Consequently, the total manu- facturing cost of biodiesel can be significantly reduced [44]. In addi- tion, a similarity in the quality of biodiesel derived from WCO and from vegetable oils could be achieved at an optimum operating condition [6]. Increasing food consumption has increased the pro- duction of a large amount of waste cooking oils/fats. It was, for example, 4.5–11.3 million litres a year in USA or 4  10 5 –6  10 5 ton/year in Japan [34]. The conversion of this amount of WCO into fuel also eliminates the environmental impacts caused by the harmful disposal of these waste oils, such as into drains [41]. Bio- diesel from WCO (or used frying oils) has been recently investigated [6,11–13,18,24,27,37,41,45]. However, the optimum conditions for biodiesel production (methanol/oils ratio and concentration of catalyst) are inconsis- tent. They strongly depend on the properties of WCO. Dorado et al. [10] found that the ester yield reached 90% at the methanol/oil ratio of 3.48:1 and 1.26 wt% KOH; while Encinar et 0016-2361/$ - see front matter Crown Copyright Ó 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2008.07.008 * Corresponding author. Tel.: +44 (0) 191 222 5747; fax: +44 (0) 191 222 5292. E-mail address: a.n.phan@ncl.ac.uk (A.N. Phan). Fuel 87 (2008) 3490–3496 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel