Enzymatic treatment of brown coal following ionic liquid pretreatment

As a low-rank coal, lignite (brown coal) is usually well treated by chemical or enzymatic methods prior to its utilization for energy and materials. Following ionic liquids (ILs)-pretreatment, this study focuses on the treatment of lignite by oxidoreductase-type of enzymes including horseradish peroxidase (HRP), alcohol dehydrogenase (ADH), and laccase. We observed some synergistic effects of IL-pretreatment and enzymatic actions on lignite coal. The combination of IL-pretreatment and HRP-/ADH-treatment enabled smaller and more uniform coal particles than IL-pretreatment alone or that without HRP. However, laccase-treatment led to large coal aggregates likely due to the crosslinking effect. Both HRP- and ADH-treatments induced a lower aliphatic and a higher aromatic content of lignite, particularly when the coal was pretreated by an IL prior to the enzymatic process. Both ADH- and laccase-treatments produced more hydrogen bonds in the coal. Therefore, the combined treatments of lignite by ILs and oxidoreductases dedicate low-rank coal structures.