Improvement of Diesel Lubricity by Chemically Modified Tung-Oil-Based Fatty Acid Esters as Additives

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.