A novel hybrid organosolv: steam explosion method for the efficient fractionation and pretreatment of birch biomass

Abstract

BackgroundThe main role of pretreatment is to reduce the natural biomass recalcitrance and thus enhance saccharification yield. A further prerequisite for efficient utilization of all biomass components is their efficient fractionation into well-defined process streams. Currently available pretreatment methods only partially fulfill these criteria. Steam explosion, for example, excels as a pretreatment method but has limited potential for fractionation, whereas organosolv is excellent for delignification but offers poor biomass deconstruction.ResultsIn this article, a hybrid method combining the cooking and fractionation of conventional organosolv pretreatment with the implementation of an explosive discharge of the cooking mixture at the end of pretreatment was developed. The effects of various pretreatment parameters (ethanol content, duration, and addition of sulfuric acid) were evaluated. Pretreatment of birch at 200 °C with 60% v/v ethanol and 1% w/wbiomass H2SO4 was proven to be the most efficient pretreatment condition yielding pretreated solids with 77.9% w/w cellulose, 8.9% w/w hemicellulose, and 7.0 w/w lignin content. Under these conditions, high delignification of 86.2% was demonstrated. The recovered lignin was of high purity, with cellulose and hemicellulose contents not exceeding 0.31 and 3.25% w/w, respectively, and ash to be < 0.17% w/w in all cases, making it suitable for various applications. The pretreated solids presented high saccharification yields, reaching 68% at low enzyme load (6 FPU/g) and complete saccharification at high enzyme load (22.5 FPU/g). Finally, simultaneous saccharification and fermentation (SSF) at 20% w/w solids yielded an ethanol titer of 80 g/L after 192 h, corresponding to 90% of the theoretical maximum.ConclusionsThe novel hybrid method developed in this study allowed for the efficient fractionation of birch biomass and production of pretreated solids with high cellulose and low lignin contents. Moreover, the explosive discharge at the end of pretreatment had a positive effect on enzymatic saccharification, resulting in high hydrolyzability of the pretreated solids and elevated ethanol titers in the following high-gravity SSF. To the best of our knowledge, the ethanol concentration obtained with this method is the highest so far for birch biomass.

Interaction of enzymes with lignocellulosic materials: causes, mechanism and influencing factors

“…Some enzyme and substrate pairs are given in Table 7 with the effect of increasing substrate concentration. The agricultural residues (corn stover, Kumar and Wyman (2008) GC-220 Cellulose Increased with increase in conc Kumar and Wyman (2008) Cellulase Avicel Decreased with increase in conc Eckard et al (2013) Cellulases Pretreated forest wood Increased with increase in conc Matsakas et al (2018) Celluclast 1.5 L T. reesei Corn stover and corn fiber Increased with increase in conc Arantes and Saddler (2011) Cellic CTec 2 High CrI cellulose Increased with increase in conc Li et al (2018) corn fiber, rice husk, wheat straw, etc.) needs considerably lower protein loadings to achieve optimum adsorption than the forestry residues (poplar, Douglas fir and lodgepole pine).…”

Biorefining Oat Husks into High-Quality Lignin and Enzymatically Digestible Cellulose with Acid-Catalyzed Ethanol Organosolv Pretreatment

“…A review on the use of organosolv pretreatment for the delignification of lignocellulosic materials in the last two years showed that an S/L ratio of 1:10 predominated [8]. Exceptions include the works carried out by Matsakas et al [36] using silver birch wood chips, by Patel et al [37] using Norway spruce, and by Yuan et al [38] using corn stover, wherein an S/L ratio of 1:2 was used. Research works in the literature reported lignin-rich fractions containing >90% lignin [8] achieved via different organosolv pretreatment strategies, namely HCl-catalyzed tetrahydro-2-furanmethanol pretreatment of eucalyptus [39], auto-catalyzed ethanol pretreatment of Eucalyptus nitens bark [40], and oxalic acid-catalyzed glycerol pretreatment of sugarcane trash [41].…”

Future prospects of delignification pretreatments for the lignocellulosic materials to produce second generation bioethanol

“…Steam explosion has been demonstrated to be more effective than other pretreatments. Some of the researches are showing a combination of pretreatment methods to improve delignification . Some examples of effectiveness are commented in Table .…”

“…Some of the researches are showing a combination of pretreatment methods to improve delignification. 63,64 Some examples of effectiveness are commented in Table 4.…”