Bio-solubilization of Chinese lignite II: protein adsorption onto the lignite surface

Lignite bio-solubilization is a promising technology for converting solid lignite into oil. This study concerns the adsorption of lignite-solubilizing enzymes onto the lignite surface. Adsorption capacity, infrared spectral analysis and driving forces analysis are studied as a way to help understand the bio-solubilization mechanism. The results show that the amount of lignite bio-solubilization is proportional to the amount of adsorbed lignite-solubilizing enzymes. An increase in lignite-solubilizing enzyme adsorption of 10% leads to a 7% increase in lignite bio-solubilization. However, limited amounts of enzymes can be adsorbed by the lignite, thus resulting in low percentages of bio-solubilization. Infrared spectral analysis shows that side chains, such as hydroxyl and carbonyl, of the lignite structure are the main, and necessary, structures where lignite-solubilizing enzymes attachto the lignite. Furthermore, driving force analysis indicates that the electrostatic force between lignite and enzymes is the main adsorption mechanism. The forces are influenced by solution pH levels, the zeta potential of the lignite and the isoelectric points of the enzymes.