Organosolv pretreatment assisted by carbocation scavenger to mitigate surface barrier effect of lignin for improving biomass saccharification and utilization

Qiulu Chu,Shufang Wu,Jinguang Hu,Kai Song,Jianqiang Chen,Yongcan Jin,Wenyao Tong

doi:10.1186/s13068-021-01988-w

Qiulu Chu, Shufang Wu + Show 5 more

Open Access

https://doi.org/10.1186/s13068-021-01988-w

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Abstract

BackgroundEthanol organosolv (EOS) pretreatment is one of the most efficient methods for boosting biomass saccharification as it can achieve an efficient fractionation of three major constituents in lignocellulose. However, lignin repolymerization often occurs in acid EOS pretreatment, which impairs subsequent enzymatic hydrolysis. This study investigated acid EOS pretreatment assisted by carbocation scavenger (2-naphthol, 2-naphthol-7-sulfonate, mannitol and syringic acid) to improve biomass fractionation, coproduction of fermentable sugars and lignin adsorbents. In addition, surface barrier effect of lignin on cellulose hydrolysis was isolated from unproductive binding effect of lignin, and the analyses of surface chemistry, surface morphology and surface area were carried out to reveal the lignin inhibition mitigating effect of various additives.ResultsFour different additives all helped mitigate lignin inhibition on cellulose hydrolysis in particular diminishing surface barrier effect, among which 2-naphthol-7-sulfonate showed the best performance in improving pretreatment efficacy, while mannitol and syringic acid could serve as novel green additives. Through the addition of 2-naphthol-7-sulfonate, selective lignin removal was increased up to 76%, while cellulose hydrolysis yield was improved by 85%. As a result, 35.78 kg cellulose and 16.63 kg hemicellulose from 100 kg poplar could be released and recovered as fermentable sugars, corresponding to a sugar yield of 78%. Moreover, 22.56 kg ethanol organosolv lignin and 17.53 kg enzymatic hydrolysis residue could be recovered as lignin adsorbents for textile dye removal, with the adsorption capacities of 45.87 and 103.09 mg g−1, respectively.ConclusionsResults in this work indicated proper additives could give rise to the form of less repolymerized surface lignin, which would decrease the unproductive binding of cellulase enzymes to surface lignin. Besides, the supplementation of additives (NS, MT and SA) resulted in a simultaneously increased surface area and decreased lignin coverage. All these factors contributed to the diminished surface barrier effect of lignin, thereby improving the ease of enzymatic hydrolysis of cellulose. The biorefinery process based on acidic EOS pretreatment assisted by carbocation scavenger was proved to enable the coproduction of fermentable sugars and lignin adsorbents, allowing the holistic utilization of lignocellulosic biomass for a sustainable biorefinery.Graphic abstract

Highlights

Ethanol organosolv (EOS) pretreatment is one of the most efficient methods for boosting biomass saccharification as it can achieve an efficient fractionation of three major constituents in lignocellulose
When the raw biomass consisting of 43.81% cellulose, 23.33% hemicellulose and 28.92% lignin (Fig. 1) was directly subjected to enzymatic hydrolysis, cellulose hydrolysis yield was found to be lower than 10% (Fig. 2), indicating a poor hydrolysis on the raw biomass
As a result of lignin removal and carbohydrate solubilization, cellulose accessibility evaluated as DR28 adsorption increased from 84.83 of the raw biomass to 175.19 mg g−1, contributing to the greater ease of cellulose hydrolysis (Fig. 2)

Summary

Introduction

Ethanol organosolv (EOS) pretreatment is one of the most efficient methods for boosting biomass saccharification as it can achieve an efficient fractionation of three major constituents in lignocellulose. Cellulose and hemicellulose are considered as the economical constituents which are amenable to produce fermentable sugars and further be converted to biofuels and chemicals [3, 4]. The presence of lignin in lignocellulosic biomass and the resulting complex lignocellulosic matrix make it highly resistant towards saccharification by microorganisms or enzymes to produce fermentable sugars [5]. It is suggested that ethanol organosolv (EOS) pretreatment, in particular with acid catalyst, can effectively remove lignin and hemicellulose together through the cleaving of the lignin–carbohydrate complex, yielding cellulose-enriched solids with improved ease of enzymatic hydrolysis [1, 3]. After acid organosolv pretreatment and subsequent enzymatic hydrolysis, lignocellulosic biomass can be effectively fractionated into cellulosic sugars, hemicellulosic sugars and organosolv lignin [10]. In the case of derived lignin, it offers promising opportunities to use lignin as antioxidants [11], adsorbents [12] and other bio-based materials [13, 14]

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