Supercritical extracts of forest fuels in Great Xing'an Mountains

Extracts are important components of fuels. Fatty-extracts with high heating value (HV) are hypothesized by researchers as positively related to the HV of fuels. The Soxhlet extractor is typically used to extract fatty-extracts but it has shortcomings, including long processing time (8-10 h) and the requirement for large amounts of organic solvent. Supercritical extraction is an alternate and useful technique for extraction of natural products. However, published studies rarely discuss the relationship between extracts and HV. In this study, we assessed the supercritical extracts (SuE) of forest fuels in the Great Xing'an Mountains. Our results indicated that the optimum conditions for extraction of SuEs were 40-60 mesh, 40-50 MPa, 45 degrees C, 80 min and a CO2 flow rate of 1.5-2.0 dm(3)/min. The Soxhlet extracts contents and the SuE contents were all related to HV. However, R-2 of the coniferous samples (0.8499) and needle samples (0.9722) demonstrated that the correlation between HV and the SuE content was closer. We conclude that supercritical fatty-extracts provide a useful index of the HV of fuels, especially coniferous fuels. SuE data can be used in fire management, for example to estimate the rate of fire spread or fire intensity.