Abstract
BackgroundLignocellulosic biomass is a renewable, naturally mass-produced form of stored solar energy. Thermochemical pretreatment processes have been developed to address the challenge of biomass recalcitrance, however the optimization, cost reduction, and scalability of these processes remain as obstacles to the adoption of biofuel production processes at the industrial scale. In this study, we demonstrate that the type of reactor in which pretreatment is carried out can profoundly alter the micro- and nanostructure of the pretreated materials and dramatically affect the subsequent efficiency, and thus cost, of enzymatic conversion of cellulose.ResultsMulti-scale microscopy and quantitative image analysis was used to investigate the impact of different biomass pretreatment reactor configurations on plant cell wall structure. We identify correlations between enzymatic digestibility and geometric descriptors derived from the image data. Corn stover feedstock was pretreated under the same nominal conditions for dilute acid pretreatment (2.0 wt% H2SO4, 160°C, 5 min) using three representative types of reactors: ZipperClave® (ZC), steam gun (SG), and horizontal screw (HS) reactors. After 96 h of enzymatic digestion, biomass treated in the SG and HS reactors achieved much higher cellulose conversions, 88% and 95%, respectively, compared to the conversion obtained using the ZC reactor (68%). Imaging at the micro- and nanoscales revealed that the superior performance of the SG and HS reactors could be explained by reduced particle size, cellular dislocation, increased surface roughness, delamination, and nanofibrillation generated within the biomass particles during pretreatment.ConclusionsIncreased cellular dislocation, surface roughness, delamination, and nanofibrillation revealed by direct observation of the micro- and nanoscale change in accessibility explains the superior performance of reactors that augment pretreatment with physical energy.
Highlights
Lignocellulosic biomass is a renewable, naturally mass-produced form of stored solar energy
Corn stover biomass pretreats differently under the same nominal conditions (2 wt% H2SO4, 160°C, 5 min) in differently designed pretreatment reactors The motivation for the rest of the analysis presented here is based on the large range in digestibility of the pretreated corn stover samples from different pretreatment reactors
After 96 h of enzymatic digestion, biomass treated in the steam gun (SG) reactor and horizontal screw (HS) reactors achieved much higher cellulose conversions (88% and 95%, respectively), compared to 69% for the ZC pretreated material
Summary
Lignocellulosic biomass is a renewable, naturally mass-produced form of stored solar energy. We demonstrate that the type of reactor in which pretreatment is carried out can profoundly alter the micro- and nanostructure of the pretreated materials and dramatically affect the subsequent efficiency, and cost, of enzymatic conversion of cellulose. As we demonstrate in this study, the type of reactor in which pretreatment is carried out can profoundly alter the micro- and nanostructure of the pretreated materials and dramatically affect the subsequent efficiency, and cost, of enzymatic conversion of cellulose. All three reactors facilitate high temperature, pressurized, dilute acid catalyzed processes, but employ distinct operational modes: the ZC and SG are batch-type reactors wherein the biomass is pretreated and discharged at the end of pretreatment; the HS reactor is a flow-through process in which acid-impregnated biomass is continuously fed into the reactor With both the SG and HS reactors, the pressurized biomass is explosively decompressed to ambient conditions at the end of pretreatment, while the ZC releases steam pressure into a heat exchanger gradually through a globe valve
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