Article Cite This: Energy Fuels 2019, 33, 5110−5115
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Improvement of Diesel Lubricity by Chemically Modified Tung-OilBased Fatty Acid Esters as Additives Zengshe Liu,*,† Jing Li,†,‡ Gerhard Knothe,† Brajendra K. Sharma,§ and Jiangchung Jiang‡
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†
Bio-Oils Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, United States Department of Agriculture, 1815 North University Street, Peoria, Illinois 61604, United States ‡ Institute of Chemical Industry of Forestry Products, Chinese Academy of Forestry (CAF), Nanjing, Jiangsu 210042, People’s Republic of China § Illinois Sustainable Technology Center, University of Illinois at Urbana−Champaign, 1 Hazelwood Drive, Champaign, Illinois 61820, United States ABSTRACT: Diesel fuel lubricity has been a concern of diesel fuel injection equipment manufacturers for many years. The problem has drawn attention because of the reduction in lubricity associated with the extreme hydrogenation needed to reach the low sulfur levels required in modern diesel fuels. Ultralow-sulfur diesel (ULSD) fuels require higher concentrations of additives or blending with other materials of sufficient lubricity, thereby increasing the cost. Here, we communicate the synthesis of tung-oil-based fatty acid methyl ester [eleostearic acid methyl ester (EAME)] and the maleation compound (EAME/MA) by reacting with maleic anhydride (MA) via the Diels−Alder reaction. EAME/MA reacts with short-chain alcohols, such as methanol and butanol, by opening the cyclic anhydride to form esters, i.e., EAME/MA/ME and EAME/MA/ BU. The EAMA/MA/ME and EAME/MA/BU compounds effectively enhanced the lubricity of ULSD. The lubricity of ULSD at low additive levels (500−1000 ppm) of those two compounds resulted in great improvement in the high-frequency reciprocating rig lubricity tests. For instance, by adding low additive levels of 500 ppm and 1000 ppm to the ULSD fuel, sufficient lubricity was induced and the wear scar and friction of ULSD were reduced by 40 and 46−47%, respectively. The additive concentrations were 20 and 40 times lower than blending ULSD with biodiesel at 1−2% (w/w). Further, by adding EAME/MA/BU at a level of 1000 ppm to other kinds of petrodiesel, such as 0150H GP1 base oil and 166 POA, wear scar values were reduced by 25 and 26%, respectively.
1. INTRODUCTION The use of ultralow-sulfur diesel (ULSD) fuels, as required by regulations in the United States, Europe, and elsewhere, has led to the failure of diesel engine parts, such as fuel injectors and pumps, because they are lubricated by the fuel itself.1−10 The poor lubricity of ULSD requires additives or blending with another material of sufficient lubricity to regain lubricity.1−11 Blending with another fuel, such as biodiesel, increases the cost because the recent price of biodiesel is > $4/gallon compared to < $3/gallon for petrodiesel [in most locations in the United States in 2014; data from U.S. Energy Information Administration (EIA)]. Improvement of lubricity by blending with biodiesel typically requires at least 1% (10 000 ppm) or even 2% (20 000 ppm) of such fuel. Therefore, economically, it is better to enhance the lubricity of ULSD using additives at low additive levels. There is currently a need for efficient additives with relatively low cost for ULSD fuels. Renewable biobased lubricant and biodegradable nanolubricant are gaining growing attention as a means against fossil fuel dependence and toward greener forms of energy resource. Zainala et al. and Darminesh et al. have reviewed the recent development of these areas.12,13 In the past few years, we have worked on development of tung-oil-based materials.14−16 Here, we report the synthesis of new compounds based on eleostearic acid obtained from tung oil because of its three conjugated double bonds with more active reactivity. Another reason to select tung oil as a starting material is that tung oil is non-edible oil; therefore, there is not © 2019 American Chemical Society
an issue with the food−fuel debate. These new compounds can serve as lubricity-improving additives for ULSD. Thus, as shown in Scheme 1, eleostearic acid methyl ester (EAME) Scheme 1. Synthesis Route of EAME/MA and Its Esters
from tung oil gave EAME/MA via a Diels−Alder reaction with maleic anhydride (MA) and subsequent esterification of the MA moiety with a short-chain alcohol, methanol or butanol, gave the compounds termed EAME/MA/ME and EAME/ MA/BU. The lubricity of neat ULSD and other petrodiesel fuels additized with EAME/MA/ME and EAME/MA/BU were evaluated using the high-frequency reciprocating rig (HFRR) lubricity test. Received: March 21, 2019 Revised: May 3, 2019 Published: May 3, 2019 5110
DOI: 10.1021/acs.energyfuels.9b00854 Energy Fuels 2019, 33, 5110−5115
Article
Energy & Fuels
gravity of 0.935−0.940 g/mL at 25 °C. MA, p-toluenesulfonic acid monohydrate (PTS), and sodium methoxide solution (25%, w/w, in methanol) were obtained from Sigma-Aldrich, Inc. (St. Louis, MO, U.S.A.). Tung oil fatty acid esters (EAME) were prepared using a transesterification process reported to convert a vegetable oil into biodiesel,18 also reported in section 2.2. Polyalphaolefin (PAO-6, Durasyn 166) was received from Ineos Oligomers (League City, TX, U.S.A.) with a specific gravity of 0.828 g/mL (ASTM D4052), kinematic viscosity at 40 and 100 °C of 31.13 and 5.91 cSt, respectively (ASTM D445), and pour point of −66 °C (ASTM D97). Hydrotreated heavy paraffinic mineral oil (Kendex 0150H), a Group I base oil, was obtained from American Refining Group (Bradford, PA, U.S.A.) with a specific gravity of 0.864 g/mL (ASTM D4052), kinematic viscosity at 40 and 100 °C of 27 and 5.2 cSt, respectively (ASTM D445), pour point of < −9 °C (ASTM D97), and sulfur content of
