Sustainable and efficient extraction of montan wax from lignite using bio-based 2-methyltetrahydrofuran: Performance and kinetics

Bio-based 2-MTHF is a green alternative for efficient lignite wax extraction. • 2-MTHF achieved 7.9 wt% yield, a 58% increase over toluene extraction. • Crude wax yield reached 5.3%, approaching China's National Grade II standard. • Low activation energy (9.02 kJ·mol −1 ) confirms efficient matrix disruption. Lignite, which is rich in high-value montan wax, is currently mostly burned directly, resulting in a waste of resources. At the same time, traditional toluene extraction methods are facing increasingly stringent regulations due to their toxicity and environmental risks, which hinders the efficient utilization of resources and the adoption of environmentally preferable production routes. This study proposes the bio-based solvent 2-methyl tetrahydrofuran (2-MTHF) as a greener and more efficient alternative to toluene. 2-MTHF can effectively penetrate the pores of the lignite matrix, disrupting non-covalent interactions (such as hydrogen bonds) between wax molecules and the coal matrix, thereby achieving selective and efficient dissolution. Under mild conditions (140 °C, 60 min, solid-to-liquid ratio 1:10, particle size 0.15–0.25 mm), the 2-MTHF extract rate reached 7.9 wt%, a 58% increase compared to toluene (5.0 wt%) under the same conditions; the defatted montan wax yield was 5.3%, also higher than that of toluene (3.3%) (an increase of approximately 61%), and the crude wax product approaches China's National Grade II standard, with a resin content of 33.3% slightly above the 27% limit, while its acid value and saponification value comply with the Grade II requirements. Kinetics and mass transfer analysis indicated that the process follows a first-order kinetic model, with an apparent activation energy of only 9.02 kJ·mol −1 , and is controlled by intraparticle diffusion, further confirming that 2-MTHF can effectively weaken non-covalent interactions within lignite and promote the selective leaching of wax. Download: Download high-res image (128KB) Download: Download full-size image