Purification of biodiesel by dry washing, employing starch and cellulose as natural adsorbents Michelle Garcia Gomes a,1 , Douglas Queiroz Santos b,2 , Luís Carlos de Morais c,3 , Daniel Pasquini a,⇑ a Federal University of Uberlândia, Chemistry Institute, Av. João Naves de Ávila, 2121, Bloco 1D, Campus Santa Mônica, Uberlândia, Minas Gerais 38400-902, Brazil b Federal University of Uberlândia, Technical School of Health, Av. Prof. José Inácio de Souza, s/n°, Bloco 6X, 1° andar, Campus, Uberlândia, Minas Gerais 38400-902, Brazil c Federal University of Triângulo Mineiro, Institute of Exact Sciences, Natural and Education, Av. Dr. Randolfo Borges, 1400, Univerdecidade, Uberaba, Minas Gerais 38064-200, Brazil highlights  Biodiesel from sunflower oil was successfully purified with natural adsorbents.  Starch from different sources and cellulose fibers were used as adsorbents.  Dry washing has removed more impurities than the wet washing.  Was reduced the acidity index, alkalinity, free glycerine and turbidity of biodiesel. article info Article history: Received 12 January 2015 Received in revised form 31 March 2015 Accepted 3 April 2015 Available online 13 April 2015 Keywords: Sunflower oil Biodiesel Purification Natural adsorbents abstract This work describes a study of the purification of biodiesel produced from sunflower oil by dry cold washing using natural adsorbents as cellulose and starch from different sources (corn, potato, cassava and rice), and the comparison with dry cold washing with a commercial adsorbent Select 450 Ò and with the conventional wet washing with hot water. The purification by dry washing was carried out by varying the amount of adsorbents in 1%, 2%, 5% and 10% (w/v) at 25 °C for 10 min. For the purification by wet washing, the biodiesel was successively washed with acidified water and pure water at 85 °C until neutralisation. The efficiency of the processes for the removal of biodiesel impurities was evaluated by determining the acidity index, combined alkalinity, free glycerine and turbidity of the biodiesel. All adsor- bents studied presented good efficiency in the removal of the impurities and showed similar behaviour independent of the kind or amount of adsorbent employed. The use of natural adsorbents for the purifi- cation of biodiesel have been shown to be a promissory process to be applied as an industrial stage of the purification of biodiesel during their production. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The most common way to produce biodiesel is by transesteri- fication. Transesterification is the general term used to describe a class of important organic reactions in which an ester is trans- formed into another by the exchange of alkoxide groups. Among all of the alternatives, the transesterification can be considered the best choice because this process is relatively simple [1]. Additionally, depending on oil origin (ester) used, it is possible to obtain biodiesel with physicochemical characteristics similar to diesel. The resulting products of this reaction are divided into two phases, the first one composed mainly of esters (biodiesel), fatty acids and certain amounts of glycerides, and the second phase, the denser, constituted mainly by glycerol and residues of transesterified triglycerides. Phase separation is by settling and/or centrifugation [2]. After the removal of glycerine, biodiesel may present traces of alcohol, catalyst, free fatty acids, glycerine, water, etc. However, it is essential to use the purification and drying pro- cesses so that biodiesel becomes acceptable in the market; i.e., it is essential that certain specifications are complied with to ensure the quality of biodiesel. In this way, it is necessary to establish quality standards, aiming to set limits for the levels of contaminants that will not harm the quality of emissions from burning, as well as per- formance, integrity and security of the engine [2–4]. http://dx.doi.org/10.1016/j.fuel.2015.04.012 0016-2361/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Federal University of Uberlândia, Chemistry Institute, Av. João Naves de Ávila, 2121, Bloco 1D, Campus Santa Mônica, Uberlândia, Minas Gerais 38400-902, Brazil. Tel.: +55 34 32394143; fax: +55 34 32394208. E-mail addresses: pasquini@iqufu.ufu.br, danielpasquini2013@gmail.com (D. Pasquini). 1 Tel.: +55 34 32394143. 2 Tel.: +55 34 32182773. 3 Tel.: +55 34 96890357. Fuel 155 (2015) 1–6 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel