Surface tensions of biodiesel blends with pentanol and octanol isomers at different conditions: measurement and new correlation

•Experimental surface tensions of liquid mixtures of biodiesel + pentanol, and + octanol isomers at different temperatures.•A new equation to correlate the surface tension of biodiesel mixtures as a function of the temperature and mole fraction.•The new equation correlates the surface tension better than commonly used equations. Surface tension is an important biodiesel property, its calculation and prediction are fundamental because high values of surface tension significantly difficult proper atomization, and it can cause a poor engine performance. Surface tensions have been measured for binary liquid blends of pentan-1-ol, pentan-2-ol, 2-methylbutan-1-ol, octan-1-ol, octan-2-ol and 2-ethylhexan-1-ol with biodiesel using a Du Noüy ring tensiometer from (288.15 to 338.15) K at 0.1 MPa over the whole composition range. The measured surface tension data for the pure components shows a good agreement for the six alcohols when it is compared with reported values in the literature, showing an average absolute percentage deviation of 0.93%. Surface tension deviations show positive deviations from the average mole fraction of the pure components and they are correlated using the Redlich-Kister equation over the whole concentration range. Surface entropy and surface enthalpy have been estimated from experimental surface tension values of biodiesel mixtures. A new equation has been developed to correlate the surface tension of biodiesel + alcohols mixtures considering the effects of both temperature and mole fraction. This equation is based upon a quadratic mixing rule for the Gibbs free energy. Our model demonstrates to correlate the surface tension of biodiesel mixtures with an average absolute percentage deviation of 0.4%. The correlative capability of the proposed model is compared with Li et al., Fu et al., Myers and Scott, Wang-Chen, Hoke and Patton, and Jouyban et al. equations. [Display omitted]