Article pubs.acs.org/est
Partitioning Behavior of Petrodiesel/Biodiesel Blends in Water Mohamad H. Yassine,†,# Shuyun Wu,† Makram T. Suidan,‡,* and Albert D. Venosa§ †
Environmental Engineering Division, School of Energy, Environmental, Biological, and Medical Engineering, University of Cincinnati, Ohio 45221, United States ‡ Faculty of Engineering and Architecture, American University of Beirut, P.O. Box 11-0236 Riad El-Solh, Beirut, Lebanon 1107 2020 § U.S. Environmental Protection Agency, 26 W. Martin Luther King Drive, Cincinnati, Ohio 45268, United States S Supporting Information *
ABSTRACT: The partitioning behavior of six petrodiesel/soybean− biodiesel blends (B0, B20, B40, B60, B80, and B100, where B100 is 100% unblended biodiesel) in water was investigated at various oil loads by the 10-fold dilution method. Five fatty acid methyl esters (FAMEs), C10− C20 n-alkanes, and four monoaromatic compounds were targeted for analysis. Only the aromatic compounds were partitioned according to Raoult’s law at all oil loads. The partitioning of the FAMEs and n-alkanes at higher oil loads was found to be orders of magnitude higher than the reported aqueous solubilities of these compounds, and directly correlated with the amount of oil load applied. Depth filtration of the wateraccommodated fractions (WAFs) significantly reduced the observed concentrations of the FAMEs and n-alkanes, but did not appreciably affect the aromatic compounds. The FAMEs and n-alkanes concentrations in the filtered WAFs agreed with the aqueous solubilities of those compounds reported in the literature, but the n-alkanes showed progressive deviations from those solubilities with the increase in the amount of biodiesel in the blends. Further dilution experiments on pure n-hexadecane confirmed the presence of a metastable colloidal phase that seems to be controlled by hydrophobic interactions and surface phenomena. The addition of biodiesel to the oil blend appeared to have a positive impact on the dissolved concentrations and the colloidal accommodation of the n-alkanes. Autoxidation of the biodiesel constituents was found to be significant, and increased with increasing oil loads. Chemical products such as hexanal, n-butyl acetate, diethylene glycol monobutyl ether, and diethylene glycol monobutyl ether acetate were positively identified among the FAMEs’ autoxidation byproducts. Our data suggest a positive enhancement for biodiesel on the formation of the oil in water colloidal phase, possibly by forming a surfactant-cosurfactant-like pair of the FAMEs and their autoxidation byproducts.
1. INTRODUCTION Biodiesel has been attracting special attention in the sustainable energy arena because of its potential in transforming the automotive and transportation industries. The renewable and versatile feedstock sources as well as the positive impact on reducing global emissions make biodiesel a very attractive investment for policymakers, market developers, and researchers. The need to understand the behavior and physical interactions of petrodiesel/biodiesel blends in the aquatic environment cannot be overemphasized. Recent attempts to investigate physical interactions and behavior of petrodiesel/ biodiesel blends in the aquatic environment have been very modest.1,2 In contrast, physical interactions and rheological behavior of petrodiesel/biodiesel blends in combustion engines have been heavily investigated.3,4 The fundamentally different molecular structures of petrodiesel and biodiesel result in very different macroscopic physicochemical properties for both fuels. Biodiesel primarily consists of C16−C22 fatty acid methyl esters (FAMEs) with various degrees of unsaturation.5 Petrodiesel, however, is composed of 80−90% saturated hydrocarbons (primarily © 2012 American Chemical Society
normal, branched, and cycloalkanes), 10−20% aromatic hydrocarbons (mainly alkylbenzenes), and
