Branched chain derivatives of alkyl oleates: Tribological, rheological, oxidation, and low temperature properties Bryan R. Moser * , Sevim Z. Erhan United States Department of Agriculture, Agricultural Research Service, National Center for Agricultural Utilization Research, 1815 N. University Street, Peoria, IL 61604, USA Received 10 January 2007; accepted 12 January 2008 Available online 4 February 2008 Abstract We report the evaluation of four previously prepared oleochemical branched chain ethers (1–4) and soybean oil methyl esters (SME) against cloud point, pour point, oxidation stability, kinematic viscosity, specific gravity, lubricity, and surface tension. Ethers 1–4 exhib- ited excellent low temperature, oxidation stability, and lubricity behavior; however, at low blend levels (0.5, 1.0, 2.0 wt%) in SME, 1–4 had minimal impact on cloud point and pour point of SME. The specific gravity and surface tension behavior of 1–4 are nearly identical to SME. Ethers 1–4 displayed increased viscosity when compared to SME, but were still within ASTM D 6751 specifications at low blend levels in SME. Conversely, ethers 3 and 4 at 2.0% in SME were out of specification for kinematic viscosity in EN 14214. Both SME and 1–4 exhibited excellent tribological properties, as evidenced by HFRR wear scar behavior well within prescribed ASTM and CEN pet- rodiesel specifications. Published by Elsevier Ltd. Keywords: Additives; Biodiesel; Branched chain ethers 1. Introduction Biodiesel (BD), an alternative fuel obtained from vege- table oils or animal fats, has a number of technical advan- tages over petrodiesel (PD), which include reduction of most exhaust emissions, improved lubricity and biodegrad- ability, higher flash point, reduced toxicity, derivation from a renewable feedstock, and domestic origin [1–4]. In the case of viscosity, gross heat of combustion, and cetane number, BD and PD exhibit essentially similar behavior [1,2]. However, BD is inferior to PD when considering oxi- dation stability, nitrogen oxides (NO x ) emissions, energy content, and cold weather operability [4,5]. Strategies to improve one or more of the deficiencies of BD include the use of blends with PD, fractionation, feedstock modifi- cation, and the employment of additives [6]. The additive approach has attracted a great deal of interest; however, additives as developed for PD are generally ineffective when used in BD fuel [6–10]. Consequently, the develop- ment of effective additives for BD fuel is an important area of current research. We report the evaluation of previously prepared [11,12] novel, oleochemical branched chain ethers (1–4, Fig. 1) against a number of relevant fuel parameters, such as cloud point (CP), pour point (PP), oxidation onset temperature (OT), signal maximum temperature (SMT), kinematic vis- cosity (t), specific gravity (SG), lubricity (lub), and surface tension (c). Further evaluation of the low temperature and viscosity properties of blends of 1–4 in soybean oil methyl esters (SME) will also be presented. A comparison of these results with relevant BD standards, such as ASTM D 6751 (Table 1) [13] and EN 14214 (Table 2) [14], will be included where applicable. The aim of this study is to aid in the development of bio-based materials for potential use as additives in biodiesel fuel (SME). 0016-2361/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.fuel.2008.01.005 * Corresponding author. Tel.: +1 309 6816511; fax: +1 309 6816340. E-mail address: Bryan.Moser@ars.usda.gov (B.R. Moser). www.fuelfirst.com Available online at www.sciencedirect.com Fuel 87 (2008) 2253–2257