Process Optimization And Mechanism Analysis Of Ionic Liquid Pretreatment On Oil Palm Empty Fruit Bunch

Oil palm empty fruit bunch(OPEFB)is the major waste from the oil palm industry in Southeast Asia,and its abundance and carbohydrate-rich nature are adaptable for biofuel production.However,the complex inner structure of lignocellulose itself and the protective action of the exterior wax hinder the degradation and utilization of OPEFB.In this study,ionic liquid(IL)pretreatment and dewaxing process were adopted to enhance enzymatic digestibility of OPEFB.The pretreatment conditions were optimized at a deeper level,and the complex mechanism of wax in the IL pretreatment was analyzed.Firstly,type of IL and temperature conditions of pretreatment were optimized.1)Among the used five ILs([BMIM]Cl,[EMIM]Cl,[EMIM][DEP],[BMIM][Ac],and [EMIM][Ac]),anions had a greater effect on IL pretreatment performance than cations.[BMIM]Ac and [EMIM]Ac with acetic anion exhibited superior performance due to its better ability in dissolving biomass and changing the internal structure of OPEFB.They exhibited significant component removal,morphological changes,reduction of ineffective cellulase adsorption,change in the thermal stability,removal of acetyl groups of hemicellulose,breakage of lignin bond,decrease of crystalline cellulose content,change from cellulose I to cellulose II,and decrease of measured crystallinity,leading to the increase of glucose yield via enzymatic hydrolysis.2)As referred to temperature,all ILs showed better pretreatment performance at a higher temperature of 140°C because of the improved dissolving capacity of ILs.Secondly,the effect of dewaxing on IL pretreatment was quite complex.1)The results showed that dewaxing can further boost the dissolution of OPEFB in [BMIM]Ac and rearrangement after adding anti-solvent which increased the exposure of amorphous cellulose.The dissolution and rearrangement not only increased the total adsorption of cellulase but also reduced the ineffective cellulase adsorption on lignin,jointly improving the effective cellulase adsorption.2)The change of thermal stability also reflected the more change of internal structure.3)What's more,XRD results proved that dewaxing promoted the conversion of cellulose I to cellulose II with a decrease of crystallinity.All these brought from the dewaxing process benefited the enzymatic hydrolysis when using [BMIM]Ac pretreatment.However,the effect using [BMIM]Cl was not improved by dewaxing because of its poor solubility of OPEFB.Finally,a clustering method was used to analyze the 16 index parameters as a whole,and the mechanism of dewaxing combined with IL pretreatment on OPEFB was explored.The results showed that among a series of factors that affected enzymatic hydrolysis,the most directly related factor was the structure of cellulose,including the bareness degree of cellulose,i.e.the accessibility of the cellulase and the internal crystalline structure.When cellulose was not covered by other components and had a more amorphous structure,it was most favorable to be hydrolyzed by cellulases.The effects of dewaxing on different ILs were inconsistent,and the fundamental reason was that the ILs themselves had different effects on OPEFB.This work not only deeply explored the mechanism of IL pretreatment on the typical lignocellulosic biomass OPEFB in Southeast Asia,optimizing the pretreatment conditions,laying a foundation for efficiently and cost-effectively obtaining fermentable sugars,but also provided an important reference for degradation treatment of biomass contained wax.