Aceite de cocina

Fuel 89 (2010) 360–364

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Fuel
journal homepage: www.elsevier.com/locate/fuel

Conversion of waste cooking oil to biodiesel using ferric sulfate and supercritical methanol processes
Prafulla Patil a, Shuguang Deng a,*, J. Isaac Rhodes b, Peter J. Lammers b
a b

Chemical Engineering Department, New Mexico State University, Las Cruces, NM 88003,USA Chemistry and Biochemistry Department, New Mexico State University, Las Cruces, NM 88003, USA

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In this comparative study, conversion of waste cooking oil to methyl esters was carried out using the ferric sulfate and the supercritical methanol processes. A two-step transesterification process was used to remove the high free fatty acid contents inthe waste cooking oil (WCO). This process resulted in a feedstock to biodiesel conversion yield of about 85–96% using a ferric sulfate catalyst. In the supercritical methanol transesterification method, the yield of biodiesel was about 50–65% in only 15 min of reaction time. The test results revealed that supercritical process method is probably a promising alternative method to the traditionaltwo-step transesterification process using a ferric sulfate catalyst for waste cooking oil conversion. The important variables affecting the methyl ester yield during the transesterification reaction are the molar ratio of alcohol to oil, the catalyst amount and the reaction temperature. The analysis of oil properties, fuel properties and process parameter optimization for the waste cooking oilconversion are also presented. Ó 2009 Elsevier Ltd. All rights reserved.

Article history: Received 29 December 2008 Received in revised form 15 May 2009 Accepted 26 May 2009 Available online 13 June 2009 Keywords: Waste cooking oil Supercritical methanol Ferric sulfate Biodiesel

1. Introduction Biodiesel is a mono-alkyl ester of long chain fatty acids produced from renewable feedstocks. It is anon-toxic, biodegradable, relatively less inflammable fuel compared to the normal diesel and has significantly lower emissions than petroleum-based diesel [1]. In addition, biodiesel is better than diesel fuel in terms of sulfur content, flash point, aromatic content and cetane number [2]. Edible vegetable oils such as canola, soybean, and corn have been used for biodiesel production and found to be adiesel substitute [3,4]. However, a major obstacle in the commercialization of biodiesel production from edible vegetable oil is its high production cost, which is due to the higher cost of edible oil. Waste cooking oil, which is much less expensive than edible vegetable oil, is a promising alternative to edible vegetable oil [5]. Waste cooking oil and fats set forth significant disposal problems inmany parts of the world. This environmental problem could be solved by proper utilization and management of waste cooking oil as a fuel. Many developed countries have set policies that penalize the disposal of waste cooking oil the waste drainage [6]. The Energy Information Administration in the United States estimated that around 100 million gallons of waste cooking oil is produced per day in USA,where the average per capita waste cooking oil was reported to be 9 pounds [7]. The estimated amount of waste cooking oil collected in Europe is about 700,000–100,000 tons/year [8].
* Corresponding author. Tel.: +1 575 646 4346; fax: +1 575 646 7706. E-mail address: sdeng@nmsu.edu (S. Deng). 0016-2361/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2009.05.024Biodiesel production by transesterification reaction can be catalyzed with alkali, acid or enzyme. Alkali and acid transesterification processes require less reaction time and lower costs as compared to the enzyme catalyst process [9,10]. Alkali process gives high purity and yield of biodiesel in shorter reaction time [11]; however, this process cannot handle feedstocks with high free fatty acid...