CELF significantly reduces milling requirements and improves soaking effectiveness for maximum sugar recovery of Alamo switchgrass over dilute sulfuric acid pretreatment

Abhishek S Patri,Charles E Wyman,Charles M Cai,Laura Mcalister,Rajeev Kumar

doi:10.1186/s13068-019-1515-7

Abhishek S Patri, Charles E Wyman + Show 3 more

Open Access

https://doi.org/10.1186/s13068-019-1515-7

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Abstract

BackgroundPretreatment is effective in reducing the natural recalcitrance of plant biomass so polysaccharides in cell walls can be accessed for conversion to sugars. Furthermore, lignocellulosic biomass must typically be reduced in size to increase the pretreatment effectiveness and realize high sugar yields. However, biomass size reduction is a very energy-intensive operation and contributes significantly to the overall capital cost.ResultsIn this study, the effect of particle size reduction and biomass presoaking on the deconstruction of Alamo switchgrass was examined prior to pretreatment by dilute sulfuric acid (DSA) and Co-solvent Enhanced Lignocellulosic Fractionation (CELF) at pretreatment conditions optimized for maximum sugar release by each pretreatment coupled with subsequent enzymatic hydrolysis. Sugar yields by enzymatic hydrolysis were measured over a range of enzyme loadings. In general, DSA successfully solubilized hemicellulose, while CELF removed nearly 80% of Klason lignin from switchgrass in addition to the majority of hemicellulose. Presoaking and particle size reduction did not have a significant impact on biomass compositions after pretreatment for both DSA and CELF. However, presoaking for 4 h slightly increased sugar yields by enzymatic hydrolysis of DSA-pretreated switchgrass compared to unsoaked samples, whereas sugar yields from enzymatic hydrolysis of CELF solids continued to increase substantially for up to 18 h of presoaking time. Of particular importance, DSA required particle size reduction by knife milling to < 2 mm in order to achieve adequate sugar yields by subsequent enzymatic hydrolysis. CELF solids, on the other hand, realized nearly identical sugar yields from unmilled and milled switchgrass even at very low enzyme loadings.ConclusionsCELF was capable of achieving nearly theoretical sugar yields from enzymatic hydrolysis of pretreated switchgrass solids without size reduction, unlike DSA. These results indicate that CELF may be able to eliminate particle size reduction prior to pretreatment and thereby reduce overall costs of biological processing of biomass to fuels. In addition, presoaking proved much more effective for CELF than for DSA, particularly at low enzyme loadings.

Highlights

Pretreatment is effective in reducing the natural recalcitrance of plant biomass so polysaccharides in cell walls can be accessed for conversion to sugars
Co-solvent Enhanced Lignocellulosic Fractionation (CELF) is a recently developed advanced pretreatment that utilizes dilute acid in a miscible mixture of tetrahydrofuran (THF) and water to recover about 80–90% of the lignin and > 95% hemicellulose sugars in solution and achieve nearly theoretical sugar yields from the glucan and hemicellulose left in the resulting carbohydrate-rich solids at low enzyme loadings [20]
The pretreatment step alone was termed Stage 1, and the sugars released were expressed in terms of equivalent glucan and xylan by taking into account the water added during hydrolysis

Summary

Introduction

Pretreatment is effective in reducing the natural recalcitrance of plant biomass so polysaccharides in cell walls can be accessed for conversion to sugars. Lignocellulosic biomass must typically be reduced in size to increase the pretreatment effectiveness and realize high sugar yields. Due to the complex nature of plant cell walls, pretreatment is typically required prior to enzymatic and biological conversion to expose carbohydrates from the lignin shield [9]. Co-solvent Enhanced Lignocellulosic Fractionation (CELF) is a recently developed advanced pretreatment that utilizes dilute acid in a miscible mixture of tetrahydrofuran (THF) and water to recover about 80–90% of the lignin and > 95% hemicellulose sugars in solution and achieve nearly theoretical sugar yields from the glucan and hemicellulose left in the resulting carbohydrate-rich solids at low enzyme loadings [20]

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