Evaluation of the two-step treatment with ionic liquids and alkali for enhancing enzymatic hydrolysis of Eucalyptus: chemical and anatomical changes

Abstract

BackgroundThe biomass recalcitrance resulting from its chemical compositions and physical structures impedes the conversion of biomass into fermentable sugars. Pretreatment is a necessary procedure to increase the cellulase accessibility for bioconversion of lignocelluloses into bioethanol. Alternatively, ionic liquids, a series of promising solvents, provide unique opportunities for pretreating a wide range of lignocellulosic materials. In this study, a two-step treatment including ionic liquids pretreatment and successive alkali fractionations was performed on Eucalyptus to achieve a high enzymatic digestibility. The compositional and structural changes of Eucalyptus cell walls and their possible effect on saccharification ratio were comprehensively investigated.ResultsAfter the ionic liquids pretreatment, the cell walls became loose and even swelled, accompanying with the decrease of cellulose crystallinity. As compared to the simplex ionic liquids pretreatment, the integrated process resulted in the significant removal of hemicelluloses and lignin, enhancing the disruption of the cell walls and increasing the exposure of cellulose, which led to a higher conversion of cellulose to glucose. The glucose yield of Eucalyptus underwent the combination of [Bmim]OAc and alkali treatments reached the maximum (90.53 %), which was 6.6 times higher than that of the untreated Eucalyptus. The combination of chemical compositions and physical structure of Eucalyptus affected the efficiency of cellulose enzymatic hydrolysis. Especially, the changes of cellulose crystallinity played a major role in enhancing the enzymatic digestibility of Eucalyptus in this study.ConclusionsThe two-step treatment with ionic liquids pretreatment and successive alkali fractionation can be considered as a promising method to improve the conversion of cellulose to glucose. The detailed information obtained about chemical and anatomical changes was helpful to understand the underlying mechanism of the integrated treatment process acting on Eucalyptus for enhancing enzymatic digestibility.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0578-y) contains supplementary material, which is available to authorized users.

Multi-Scale Structural Studies of Sequential Ionic Liquids and Alkali Pretreated Corn Stover and Sugarcane Bagasse

“…The same effect could be observed in case of IL and IL+NaOH pretreated CS as compared to the untreated CS spectra. The another lignin aromatic skeletal vibrational peak at 1505 cm IL+NaOH pretreated CS and SB substrates possibly indicating the removal of amorphous cellulose [6]. The peak at 1373 cm −1 corresponding to C-H deformation in cellulose and hemicelluloses showed slight decrease in intensities in case of IL+NaOH pretreated SB compared to the increase in SB-Na whereas in case of CS, no prominent change was observed at the same frequency [32].…”

“…Similarly, Li et al [6] showed the decreased roughness of Eucalyptus cell wall after [Bmim][OAc] pretreatment. The re-location of lignin in case of [Emim][OAc]+Na pretreated CS could also be co-related with the increased enzymatic saccharification as shown in Figure 4(a).…”

“…Functional assignment of the respective absorbance bands has been mentioned in the Supplementary file 1: Table S1. It was critically observed that after IL+NaOH pretreatments in CS as well as SB, the peak at 1732 cm −1 band almost disappeared as compared to the IL pretreated ones [6] [27].…”

Effect of Enzymatic Beech Fagus Sylvatica Wood Hydrolysate on Chlorella Biomass, Fatty Acid and Pigment Production

“…A promising replacement for citrate buffer could be a sodium acetate buffer, which is also used during enzymatic hydrolysis of lignocellulose biomass [18,19]. This buffer contains acetate, which was shown in our previous study to greatly improve microalgae growth [13], and therefore can constitute an additional carbon source for microalgae cultivated on lignocellulosic hydrolysates.…”

“…Therefore, alkaline pretreatment, instead of diluted acid pretreatment, was applied before enzymatic hydrolysis. Alkaline pretreatment with the use of NaOH was reported as an effective method to remove hemicellulose and Klason lignin from birch [17], cedar [18] and eucalyptus [18,19] wood, resulting in the increase in cellulose exposure and improvement of cellulose conversion to glucose during enzymatic hydrolysis [18,19]. Temperature of pretreatment and NaOH concentration are crucial parameters determining removal rate of hemicellulose and lignin from wood, and subsequent cellulose hydrolysis.…”