A comparative study on the fuel properties of biodiesel from woody essential oil depending on terpene composition

Abstract

The essential oils from four Korean domestic gymnosperm species (red pine, white pine, cypress, and cedar) were examined in this study to understand the fuel characteristics based on their terpene compositions. The elemental composition, heating value, density at 20 °C, energy density, flash point, and kinematic viscosity at 40 °C of each woody essential oil were analyzed based on their terpene composition. The major elements in all woody essential oils investigated in this study were carbon, hydrogen, and oxygen. The woody essential oils were composed of more than 80% carbon and less than 10% oxygen due to the presence of terpene derivatives (terpene alcohols and terpene acetates). With respect to minor elements, sulfur contents did not satisfy the quality standard (10 ppm). Among the four woody essential oils, both red pine oil and white pine oil showed slightly lower higher heating values (HHVs; 44.09 MJ/kg and 44.13 MJ/kg, respectively) than diesel fuel. There was a negative correlation between oxygen content and HHV. Density was raised by an increase in the average number of carbon atoms and/or the terpene derivative contents and ranged from 0.875 g/mL for red pine oil to 0.924 g/mL for cedar oil. Based on their higher densities than diesel fuel and although they had lower HHVs, higher energy densities (38.59–39.18 MJ/L) were observed, with the exception of cypress oil. All the woody essential oils satisfied the quality standard for flash point (>40 °C). These flash points should consider both the average number of carbon atoms and terpene derivatives. In contrast, the kinematic viscosity of the essential oils was only affected by the number of carbon atoms. Cedar oil (6.1 mm2/s) had the largest kinematic viscosity followed by cypress oil (2.7 mm2/s), white pine oil (1.6 mm2/s), and red pine oil (1.4 mm2/s). By considering all assessed properties, a terpene mixture similar to the essential oil from red pine oil or white pine oil was deemed the most appropriate alternative biodiesel candidate though its viscosity and sulfur content must be improved.