Flowthrough pretreatment with very dilute acid provides insights into high lignin contribution to biomass recalcitrance

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.

Cellulose hydrolysis byClostridium thermocellumis agnostic to substrate structural properties in contrast to fungal cellulases

“…The Accellerase® 1500 cellulase enzyme cocktail was kindly provided by DuPont Industrial Biosciences (Palo Alto, CA). The BCA protein content of Accellerase® 1500, as reported elsewhere, 72 was 82 mg mL −1 . C. thermocellum DSM 1313 wild type was kindly provided by Prof. Lee Lynd at Dartmouth College, Hanover NH.…”

Recent advances in understanding the pseudo-lignin formation in a lignocellulosic biorefinery

“…28 Similarly, the flowthrough dilute acid pretreatment is also capable of removing substantial amounts of lignin from lignocellulosic biomass, indeed more lignin could be solubilized in a flowthrough pretreatment than in a batch pretreatment performed under similar conditions. 29 For example, nearly 36% of lignin was removed from poplar in a flowthrough dilute acid pretreatment at 180°C while the lignin content in the batch pretreated poplar remained at the same level compared to that in the untreated sample. 29 On the other hand, the majority of the literature results reported that the percentage of K-lignin content of acid-pretreated biomass to be much higher than that of the untreated material as shown in Table 1.…”

“…29 For example, nearly 36% of lignin was removed from poplar in a flowthrough dilute acid pretreatment at 180°C while the lignin content in the batch pretreated poplar remained at the same level compared to that in the untreated sample. 29 On the other hand, the majority of the literature results reported that the percentage of K-lignin content of acid-pretreated biomass to be much higher than that of the untreated material as shown in Table 1. This phenomenon has been reported for hardwood, softwood, and herbaceous energy crops.…”

Multi-Step Exploitation of Raw Arundo donax L. for the Selective Synthesis of Second-Generation Sugars by Chemical and Biological Route

“…However, the employment of mineral acids has some disadvantages, such as the expensive catalyst recovery and the possible corrosion of the stainless steel equipment. About the last issue, it is reported that the use of H 2 SO 4 concentration higher than 0.05 wt% can rapidly corrode a Type 316 stainless steel (widely used for the construction of autoclaves), even at moderate temperature and time, typical of the hydrothermal pretreatments [36]. Therefore, common stainless steels cannot be adopted for the acid hydrothermal treatments, which instead require special alloys, such as various grades of Hastelloy, zirconium or other corrosion-resistant alloys, which ensure excellent corrosion resistance to acids, even at high severity conditions [37].…”