Improved biological delignification of wood biomass via Ionic liquids pretreatment: A one step process

Abstract

The enzymatic pretreatment of wood biomass for degrading lignin, a complex aromatic polymer, has received much attention as an environmentally safe or “green” process. However, this process for lignin degradation has been found to be very slow, even needed several months. To overcome this limitation, this study reports a new approach for enhanced enzymatic delignification of wood biomass using room temperature ionic liquids (RTILs)- a potentially attractive “green” and “designer” solvent- as (co)solvents or/and pretreated agents. The method comprised pretreatment of wood biomass prior to enzymatic delignification in ILs-aqueous systems with the aim of overcoming low delignification efficiency associated with the difficulties in enzyme accessibility to the solid substrate and the poor substrate and products solubility in aqueous system. The results showed that IL [emim] [OAc] (1-ethyl-3-methylimidazolium acetate) was better solvent for wood delignification than IL [bmim][Cl] (1-butyl-3-methylimidazolium chloride). The recovered cellulose rich materials obtained from combination effects of IL and biological pretreatment contained significantly lower amounts of lignin as compared to the amounts found when each method applied alone. The produced cellulose rich materials were characterized by acid hydrolysis, Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), and X-ray diffractometry (XRD). SEM and XRD revealed considerable microstructural and crystallinity index changes in the pretreated cellulose rich materials.  We believe that this newly developed process will play a great role in converting cellulosic biomass- the most abundant renewable biomaterials in the world- to biomaterials, biopolymers, biofuels, bioplastics and hydrocarbons.

Keywords: ionic liquids, wood biomass, cellulose, lignin, laccase, enzymatic delignification.