Abstract
BackgroundFlowthrough pretreatment is capable of removing much higher quantities of hemicellulose and lignin from lignocellulosic biomass than batch pretreatment performed at otherwise similar conditions. Comparison of these two pretreatment configurations for sugar yields and lignin removal can provide insights into lignocellulosic biomass deconstruction. Therefore, we applied liquid hot water (LHW) and extremely dilute acid (EDA, 0.05%) flowthrough and batch pretreatments of poplar at two temperatures and the same pretreatment severity for the solids. Composition of solids, sugar mass distribution with pretreatment, sugar yields, and lignin removal from pretreatment and enzymatic hydrolysis were measured.ResultsFlowthrough aqueous pretreatment of poplar showed between 63 and 69% lignin removal at both 140 and 180 °C, while batch pretreatments showed about 20 to 33% lignin removal at similar conditions. Extremely dilute acid slightly enhanced lignin removal from solids with flowthrough pretreatment at both pretreatment temperatures. However, extremely dilute acid batch pretreatment did realize greater than 70% xylan yields largely in the form of monomeric xylose. Close to 100% total sugar yields were measured from LHW and EDA flowthrough pretreatments and one batch EDA pretreatment at 180 °C. The high lignin removal by flowthrough pretreatment enhanced cellulose digestibility compared to batch pretreatment, consistent with lignin being a key contributor to biomass recalcitrance. Furthermore, solids from 180 °C flowthrough pretreatment were much more digestible than solids pretreated at 140 °C despite similar lignin and extensive hemicellulose removal.ConclusionsResults with flowthrough pretreatment show that about 65–70% of the lignin is solubilized and removed before it can react further to form low solubility lignin rich fragments that deposit on the biomass surface in batch operations and hinder enzyme action. The leftover 30–35% lignin in poplar was a key player in biomass recalcitrance to enzymatic deconstruction and it might be more difficult to dislodge from biomass with lower temperature of pretreatment. These results also point to the possibility that hemicellulose removal is more important as an indicator of lignin disruption than in playing a direct role in reducing biomass recalcitrance.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0660-5) contains supplementary material, which is available to authorized users.
Highlights
Flowthrough pretreatment is capable of removing much higher quantities of hemicellulose and lignin from lignocellulosic biomass than batch pretreatment performed at otherwise similar conditions
Flowthrough pretreatments displayed different trends in solid yields than batch pretreatments in that those from batch pretreatments dropped with increasing temperature and with addition of acid while solid yields from liquid hot water (LHW) flowthrough pretreatments at both 140 and 180 °C remained at 53% and only changed from 51 to 49% when the temperature was increased from 140 to 180 °C for Extremely dilute acid (EDA) flowthrough pretreatments
The results from this study point to the likelihood that the more recalcitrant 30–35% of the lignin that could not be removed by flowthrough pretreatment or relocated by batch operation is likely a primary contributor to biomass recalcitrance which require higher temperatures to affect such lignin properties as surface spread on cellulose, strength of association with cellulose, and hydrophobicity
Summary
Flowthrough pretreatment is capable of removing much higher quantities of hemicellulose and lignin from lignocellulosic biomass than batch pretreatment performed at otherwise similar conditions. Comparison of these two pretreatment configurations for sugar yields and lignin removal can provide insights into lignocellulosic biomass deconstruction. Enzyme driven deconstruction typically requires prior pretreatment to achieve commercially viable product yields, which, inter alia, may remove or alter the hemicellulose and lignin in biomass to increase the surface area of polysaccharides accessible to enzymes [2]. It is vital to understand and advance pretreatment and enzymatic hydrolysis technologies for biomass deconstruction and their integration to devise new approaches to reduce the amount of enzyme required to achieve high sugar yields
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
