Mitigating crystallization of saturated FAMES (fatty acid methyl esters) in biodiesel. 3. The binary phase behavior of 1,3-dioleoyl-2-palmitoyl glycerol e Methyl palmitate e A multi-length scale structural elucidation of mechanism responsible for inhibiting FAME crystallization Athira Mohanan, Bruce Darling, Laziz Bouzidi, Suresh S. Narine * Trent Centre for Biomaterials Research, Departments of Physics & Astronomy and Chemistry, Trent University,1600 West Bank Drive, Peterborough, Ontario K9J 7B8, Canada article info Article history: Received 14 September 2014 Received in revised form 23 February 2015 Accepted 13 April 2015 Available online 21 May 2015 Keywords: Biodiesel Fatty acid methyl ester (FAME) Triacylglycerol (TAG) Binary phase behavior Polymorphism Microstructure abstract The thermal behavior, microstructure and crystal structure of 1,3-dioleoyl-2-palmitoyl glycerol (OPO); an additive demonstrated to improve the cold flow behavior of biodiesel, and methyl palmitate (MeP); a saturated FAME (Fatty acid methyl ester) implicated in the high melting temperature of common bio- diesel, were investigated by DSC (Differential Scanning Calorimetry), PLM (polarized light microscopy) and XRD, respectively. Very complex and rich concentration dependent phase behavior was revealed attributed to specific intermolecular interactions between OPO and MeP. OPO delayed crystallization effectively and disrupted nucleation and growth altering crystal structure and microstructure profoundly. A steep drop in melting temperature accompanied a dramatic decrease of crystal size upon addition of OPO. A complete pseudo-equilibrium phase diagram of OPO/MeP including the thermal transitions below the liquidus line, polymorphism and microstructure development has been achieved. The study provides a comprehensive fundamental understanding that can help optimize the formulation of bio- sourced structured additives that would suppress crystallization and reduce crystal size of biodiesel effectively. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Various factors including fossil fuel depletion and environmental concerns have resulted in an increasing demand for renewable and environmentally responsible fuels. Biodiesel is sought as a viable alternative to petroleum based fuel as it is renewable and less harmful to the environment. The most common biodiesel is a fuel derived from the transesterification of vegetable oil/animal fat and is constituted of FAMEs (fatty acid methyl esters) of these lipids [1]. It is particularly attractive as it has many of the conventional diesel characteristics and can be used neat or in blends with petroleum diesel in unmodified existing diesel engines. Definition and detailed specifications of biodiesel are outlined in standards such as ASTM D 6751 in the United States and EN 14214 of the European Committee for Standardization, in Europe. The poor low temperature performance of biodiesel, indicated by relatively high cloud points (CP, ASTM D2500) and pour points (PP, ASTM D97), is a serious limitation to its wider use, particularly in cold climates [2]. Several approaches to mitigate the low- temperature problems of biodiesel have been investigated over the past decade and are reported in the literature. They include blending with conventional diesel fuel, winterization, and use of synthetic additives [3e5]. The current most popular approach is the use of crystallization depressant additives which generally sup- press the crystallization and retards the rate of nucleation and/or crystal growth [6]. The changes in the crystallization behavior of biodiesel due to the additives can be appreciated at different length scales through the modification introduced to the crystal structure, polymorphism, and microstructure. The present work is part of a series of investigations triggered by promising cold flow results obtained with self-MSBO (metathe- sized soybean oil) additives to commercial biodiesel [7]. It has been found that particular components of MSBO such as TAGs and * Corresponding author. Tel.: þ1 705 748 1011; fax: þ1 705 748 1652. E-mail address: sureshnarine@trentu.ca (S.S. Narine). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy http://dx.doi.org/10.1016/j.energy.2015.04.011 0360-5442/© 2015 Elsevier Ltd. All rights reserved. Energy 86 (2015) 500e513