Kinetics and Rheological Behavior of Higher Solid (Solids >20%) Enzymatic Hydrolysis Reactions Using Dilute Acid Pretreated, Deacetylation and Disk Refined, and Deacetylation and Mechanical Refined (DMR) Corn Stover Slurries

Abstract

Many potential biochemical pathways producing advanced hydrocarbon fuels from renewable lignocellulosic biomass require hydrolysates with high sugar concentrations and low toxicity, enabling flexible fermentation strategies, such as fed-batch fermentations capable of producing high product titers and production rates during fermentation. High sugar concentrations also increase the osmotic pressure in the hydrolysates, thus helping to decrease contamination issues. We have shown the production of high sugar concentrations directly from biomass without the need for energy/ capital intensive concentration, conditioning, and/or purification steps. In our previous work, we successfully demonstrated high biomassderived sugar concentrations (over 230 g/L fermentable sugars) in enzymatic hydrolysis from high solid (>20 wt % insoluble solids) digestions of dilute alkali deacetylated and mechanically refined (DMR) corn stover slurries. The goal of this work was to understand the effects of initial solid loadings on differently pretreated corn stover substrates on the rheological property changes of enzymatic-hydrolyzed slurries as well as the rates and yields of the enzymatic hydrolysis reactions. We performed high-solid enzymatic hydrolysis using deacetylated and disk refined (DDR), DMR, and dilute acid pretreated (DAP) corn stover substrates at four different initial total solid loadings, 17, 22, 27, and 32%. Slurry samples were collected at regular intervals for measurements of monomeric and oligomeric sugar concentrations (glucose and xylose), particle size distributions, viscosities, and yield stresses. We produced over 270 g/L of fermentable, monomeric sugars (157 g/L of glucose and 114 g/L of xylose) at 32 wt % total insoluble solid during enzymatic hydrolysis of the DMR substrates. The pumpabilities of the digested, high-solid enzymatic hydrolysates were shown to be comparable to other commercially relevant slurry streams, such as honey, peanut butter, and ketchup from the food industry. The conversion and rheological results indicate that high-solid enzymatic hydrolysis (∼33 wt %) of DMR substrates is a promising and scalable technology for producing high sugar concentration slurries from lignocellulosic biomass.

Improving Enzymatic Saccharification and Ethanol Production from Hardwood by Deacetylation and Steam Pretreatment: Insight into Mitigating Lignin Inhibition

“…9 The high severities of pretreatment result in the loss of hemicellulose-derived sugars and the formation of inhibitory compounds, which is reported to restrain the sugar yield or ethanol production from lignocellulosic biomass. 10 A deacetylation step with a dilute alkali solution prior to steam pretreatment is suggested to free acetyl groups from the xylan backbone, 11,12 improving the ease of enzymatic hydrolysis. The reasons for the improved biomass saccharification by deacetylation have been previously investigated.…”

“…A deacetylation step with a dilute alkali solution prior to steam pretreatment is suggested to free acetyl groups from the xylan backbone, , improving the ease of enzymatic hydrolysis. The reasons for the improved biomass saccharification by deacetylation have been previously investigated.…”

“…The reasons for the improved biomass saccharification by deacetylation have been previously investigated. It is shown that: (1) deacetylation decreases the degradation of hemicellulose and the formation of inhibitors, − thus imposing less inhibition on cellulose hydrolysis; (2) deacetylation enhances the susceptibility of xylan to enzymatic degradation, ,, which could reduce biomass recalcitrance; (3) the partial removal of lignin and ash in deacetylation plays a role in increasing the biomass-specific surface area or introducing the substantial nanoscale porosity to biomass, ,, thus promoting the cellulose accessibility; , (4) deacetylation decreases the formation of acetic acid in pretreatment, which reduces the generation of pseudolignin and lignin droplets on the fiber surface. , Based on these advantages, significantly improved biomass saccharification could be anticipated after deacetylation–steam pretreatment and subsequent enzymatic hydrolysis for efficient bioethanol production from lignocellulosic biomass …”

Rheology of enzyme liquefied corn stover slurries: The effect of solids concentration on yielding and flow behavior

“…The persistent reduction of yield stress for the untreated 15% slurry sample was likely due to the solid particles retaining some alignment from the previous flow curve tests. Indeed, shear‐induced alignment may be more lasting for untreated corn stover particles due to their overall larger size and greater aspect ratios relative to enzyme‐treated particles 17,35,36 …”

“…The magnitude of a slurry's yield stress is positively correlated to the packing efficiency of solid particles and, ultimately, the number of frictional contacts 32–34 . Following enzymatic liquefaction, the biomass slurry will contain a reduced concentration of insoluble solids, and the remaining solid particles will become negatively buoyant and settle if processing operations (e.g., mixing, pumping) are halted 35–37 . The static yield stress of the slurry is the necessary amount of stress to disrupt the frictional contacts between settled particles as required for the onset of flow while the dynamic yield stress is the minimum amount of stress necessary to maintain flow.…”