Novel Nanoparticle-Assisted Room-Temperature Synthesis of Methyl Esters from Aloe vera Seed Oil Puran Singh Rathore, † Poonam Mangalorkar, ‡ Padamanabhi S. Nagar, ‡ M. Daniel, ‡ and Sonal Thakore* ,† † Department of Chemistry and ‡ Department of Botany, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara 390002, Gujarat, India * S Supporting Information ABSTRACT: Aloe vera has been used as a cosmetic and medical remedy since ancient times and has gained increasing popularity in recent years. Despite its widespread use, reports on biodiesel from Aloe vera seeds are lacking. The present investigation reports the fatty acid composition of Aloe vera seed oil (AVSO) and addresses the feasibility of using AVSO as a source of biodiesel. A novel ecofriendly catalyst was developed using triacetin as a model. Interestingly, the room-temperature conversion of AVSO and other nonedible oils to methyl esters could be achieved using this novel catalytic system consisting of ethylene diamine in the presence of nickel nanoparticles (NiNPs). The metal core, capping agent, and amine concomitantly contribute to make the system an effective catalyst. 1. INTRODUCTION Biodiesel prepared by the transesterification of vegetable oil with methanol is an alternative fuel that can be used directly in any existing unmodified diesel engine. Because its properties are similar to those of diesel fuel, biodiesel can be blended at any ratio with diesel fuel. Among the various vegetable oil sources, nonedible oils are suitable for biodiesel production, as edible oils are already in demand for food and are much more expensive than diesel fuel. Among nonedible oil sources, Jatropha curcas 1 and Derris indica are some of the species identified as potential biodiesel sources suitable for tropical and subtropical regions of the world. 2 However, a species already having a high potential market can provide an extra edge to its selection. Aloe vera is one such species that has been exploited for medicinal, nutraceutical, and cosmetic purposes. Today, mostly the aloe gel from the center of the leaves is processed. It primarily consists of polysaccharides to which many medical properties have also been attributed. However, the potential of Aloe vera seed oil (AVSO) from a biodiesel prospective has not yet been established. We have investigated the fatty acid composition of a number of oil species in the past. 3a,b In the present study, we investigated the potential of AVSO for the production of biodiesel. The use of a strong base such as KOH and mineral acids leads to the wastage of water and the large-scale generation of effluents. 4 Hence, extensive research has been carried out for the development of suitable catalysts for biodiesel production. Solid catalysts such as ZnAl hydrotalcite, 5 sulfated zirconia, 6 KF/ZnO, 7 hydrous zirconia-supported 12-tungstophosphoric acid, 8 zinc dodecatungstophosphate (Zn 1.2 H 0.6 PW 12 O 40 ; ZnPW) nanotubes, 9 and acid catalyst 10 have some short- comings including high costs and easy deactivation. Solid organic bases have also been used as catalysts for the production of biodiesel. 11 However, the recovery of the catalyst was tedious and expensive. Instead, it is advantageous to use low-boiling amines, which have also exhibited good catalytic activity and have a simpler recovery process. 12,13 However, the vigorous conditions reported previously for such catalysts are not commercially and economically feasible. Because our group has been actively engaged in the synthesis and applications of metal nanoparticles, 14a-d we decided to develop an easy method for the nanoparticle-assisted organic-amine-catalyzed synthesis of methyl esters. Currently, metal nanoparticles (NPs) are used widely in many reactions, 15 with advantages such as higher specific surface, lower mass-transfer resistance, easy separation, and less fouling than for other catalysts. The high efficiency of a nanoparticle system relies mainly on the approach to the metal core and the structure of the surface. Although a number of organic reactions have been catalyzed, the use of NPs in transesterification reactions has not been extensively reported. In an effort to identify catalyst characteristics that would be ideal for biodiesel synthesis, this study compared the catalytic activities of some organic amines in presence of nickel nanoparticles (NiNPs) with that of the conventional catalyst KOH. Initially, triacetin was used as the model system to simplify the analysis and to accelerate the screening for suitable amine-NP catalytic systems. Consequently, the optimized conditions were used for the synthesis of biodiesel from some recognized oils 16a-e,17 and finally applied to AVSO. The products of the new catalyst system were also compared against those obtained from conventional KOH-catalyzed reactions. To our knowledge, this is the first report on the synthesis of biodiesel from AVSO using a novel catalytic system that works at room temperature. 2. EXPERIMENTAL SECTION 2.1. Materials. Nickel acetate [Ni(CH 3 COO) 2 ·4H 2 O], soluble starch, sodium borohydride (NaBH 4 ), liquid ammonia, triacetin, KOH, H 2 SO 4 , triethylamine (TEA), ethylenediamine (EDA), diethyl- Received: November 29, 2012 Revised: April 8, 2013 Published: April 8, 2013 Article pubs.acs.org/EF © 2013 American Chemical Society 2776 dx.doi.org/10.1021/ef301950j | Energy Fuels 2013, 27, 2776-2782