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BCRL Publications

AFEX Pretreatment and Enzymatic Conversion of Black Locust (Robinia pseudoacacia L.) to Soluble Sugars

Abstract:

Black locust (Robinia pseudoacacia L.), like willow and poplar, is a hardwood species which can be grown in coppice for bioenergy production, and because of its nitrogen-fixing ability, it can be cultivated with higher yields on less productive land. For these experiments, we examined the feasibility of using ammonia fiber expansion (AFEX) pretreatment to increase the saccharification yields from black locust grown for bioethanol production, as well as examine the impact of posttreatments (hot-water washing and additional size reduction) on sugar yields. The optimal AFEX conditions for black locust were 180°C, 1.0 g NH3/g dry biomass, 2.5 g H2O/g dry biomass, for 30 min residence time, and of the parameters tested, temperature had the greatest impact on yields. Yields from the sample without posttreatment and hydrolyzed at the standard enzyme loading were very low: <30% glucose and ∼50% hemicellulose. Both hot-water washing and size reduction improved yields; however, size reduction had a more significant effect indicating that increasing enzyme accessibility is more important for digestibility as opposed to the removal of soluble inhibitors. The effect of size reduction was comparable to that obtained by quadrupling the enzyme loading, increasing glucose yields by ∼20–30% and hemicellulose yields by ∼20%. Untreated black locust is known to contain compounds which are inhibitory to both enzymes and microorganisms and AFEX pretreatment neutralizes this inhibitory effect to some extent.

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Advanced Regional Biomass Processing Depots: a key to the logistical challenges of the cellulosic biofuel industry

 Abstract:

Interest in commercially viable cellulosic biofuel production has greatly increased due to concerns regarding the sustainability of petroleum fuels. While research into solving the technical issues surrounding cellulosic biofuels is ongoing, much less attention has been paid to solving supply chain challenges such as low bulk density of cellulosic biomass, compositional variability and seasonality of the feedstock, food vs fuel issues, and local environmental concerns. To address these supply chain problems, we explore the concept of Regional Biomass Processing Depots (RBPDs), strategically distributed facilities that procure, pre-process /pre-treat and densify biomass into stable intermediate products that are compatible with existing bulk commodity logistical systems. In this perspective, we discuss the fundamental concept of RBPDs, their functionality, advantages, and potential challenges. We then extend the analysis of depots to include enhanced confi gurations and discuss some technologies that might be deployed in RBPD networks and the valuable coproducts that might be produced via synergies among these technologies.

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Indirect land use change for biofuels: Testing predictions and improving analytical methodologies

Abstract:

Current practices for estimating indirect land use change (iLUC) due to United States biofuel production rely on assumption-heavy, global economic modeling approaches. Prior iLUC studies have failed to compare their predictions to past global historical data. An empirical approach is used to detect evidence for iLUC that might be catalyzed by United States biofuel production through a “bottom-up”, data-driven, statistical approach. Results show that biofuel production in the United States from 2002 to 2007 is not significantly correlated with changes in croplands for corn (coarse grain) plus soybean in regions of the world which are corn (coarse grain) and soybean trading partners of the United States. The results may be interpreted in at least two different ways: 1) biofuel production in the United States through 2007 (the last date for which information is available) probably has not induced any indirect land use change, and 2) this empirical approach may not be sensitive enough to detect indirect land use change from the historical data. It seems clear that additional effort may be required to develop methodologies to observe indirect land use change from the historical data. Such efforts might reduce uncertainties in indirect land use change estimates or perhaps form the basis for better policies or standards for biofuels.

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Influence of physico-chemical changes on enzymatic digestibility of ionic liquid and AFEX pretreated corn stover

Abstract:

Ionic liquid (IL) and ammonia fiber expansion (AFEX) pretreatments were studied to develop the first direct side-by-side comparative assessment on their respective impacts on biomass structure, composition, process mass balance, and enzymatic saccharification efficiency. AFEX pretreatment completely preserves plant carbohydrates, whereas IL pretreatment extracts 76% of hemicellulose. In contrast to AFEX, the native crystal structure of the recovered corn stover from IL pretreatment was significantly disrupted. For both techniques, more than 70% of the theoretical sugar yield was attained after 48 h of hydrolysis using commercial enzyme cocktails. IL pretreatment requires less enzyme loading and a shorter hydrolysis time to reach 90% yields. Hemicellulase addition led to significant improvements in the yields of glucose and xylose for AFEX pretreated corn stover, but not for IL pretreated stover. These results provide new insights into the mechanisms of IL and AFEX pretreatment, as well as the advantages and disadvantages
of each.

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Application of cellulase and hemicellulase to pure xylan, pure cellulose, and switchgrass solids from leading pretreatments

Abstract:

Accellerase 1000 cellulase, Spezyme CP cellulase, b-glucosidase, Multifect xylanase, and beta-xylosidase were evaluated for hydrolysis of pure cellulose, pure xylan, and switchgrass solids from leading pretreatments of dilute sulfuric acid, sulfur dioxide, liquid hot water, lime, soaking in aqueous ammonia, and ammonia fiber expansion. Distinctive sugar release patterns were observed from Avicel, phosphoric acid swollen cellulose (PASC), xylan, and pretreated switchgrass solids, with accumulation of significant amounts of xylooligomers during xylan hydrolysis. The strong inhibition of cellulose hydrolysis by xylooligomers
could be partially attributed to the negative impact of xylooligomers on cellulase adsorption. The digestibility of pretreated switchgrass varied with pretreatment but could not be consistently correlated to xylan, lignin, or acetyl removal. Initial hydrolysis rates did correlate well with cellulase adsorption capacities for all pretreatments except lime, but more investigation is needed to relate this behavior to physical and compositional properties of pretreated switchgrass.

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Comparative material balances around pretreatment technologies for the conversion of switchgrass to soluble sugars

Abstract:

For this project, six chemical pretreatments were compared for the Consortium for Applied Fundamentals and Innovation (CAFI): ammonia fiber expansion (AFEX), dilute sulfuric acid (DA), lime, liquid hot water (LHW), soaking in aqueous ammonia (SAA), and sulfur dioxide (SO2). For each pretreatment, a material balance was analyzed around the pretreatment, optional post-washing step, and enzymatic hydrolysis of Dacotah switchgrass. All pretreatments + enzymatic hydrolysis solubilized over two-thirds of the available glucan and xylan. Lime, post-washed LHW, and SO2 achieved >83% total glucose yields. Lime, post-washed AFEX, and DA achieved >83% total xylose yields. Alkaline pretreatments, except AFEX, solubilized the most lignin and a portion of the xylan as xylo-oligomers. As pretreatment pH decreased, total solubilized xylan and released monomeric xylose increased. Low temperature-long time or high temperature-short time pretreatments are necessary for high glucose release from late-harvest Dacotah switchgrass but high temperatures may cause xylose degradation.

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Surface and ultrastructural characterization of raw and pretreated switchgrass

Abstract:

The US Department of Energy-funded Biomass Refining CAFI (Consortium for Applied Fundamentals and Innovation) project has developed leading pretreatment technologies for application to switchgrass and has evaluated their effectiveness in recovering sugars from the coupled operations of pretreatment and enzymatic hydrolysis. Key chemical and physical characteristics have been determined for pretreated switchgrass samples. Several analytical microscopy approaches utilizing instruments in the Biomass Surface Characterization Laboratory (BSCL) at the National Renewable Energy Laboratory (NREL) have been applied to untreated and CAFI-pretreated switchgrass samples. The results of this work have shown that
each of the CAFI pretreatment approaches on switchgrass result in different structural impacts at the plant tissue, cellular, and cell wall levels. Some of these structural changes can be related to changes in chemical composition upon pretreatment. There are also apparently different structural mechanisms that are responsible for achieving the highest enzymatic hydrolysis sugar yields.

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Corn Harvest Strategies for Combined Starch and Cellulosic Bioprocessing to Ethanol

Abstract:

Conventional harvest and ethanol conversion strategies for corn (Zea mays L.) grain and corn stover involve multiple trips across the field and separate bioprocessing of the grain and stover. The objective of this study was to compare bioethanol yield between a traditional source separated corn harvest coupled with conventional separate starch and cellulosic bioprocessing streams, and novel whole-plant harvest strategies coupled with a whole-plant (starch plus cellulosic) bioprocessing platform. Composition analysis showed immature cut whole-plant fractions whether fresh processed (ImF) or ensiled (ImS), and mature cut whole-plant fraction (MWP) had higher glucan (56.0 ± 8.0% kg kg–1 dry biomass), lower xylan (13.3 ± 2.7%), arabinan (2.9 ± 0.6%) and acid-insoluble lignin (11.8 ± 2.6%) contents than mature cut source separated fractions of stover (MSep-S) and cob (MSep-C). Averaged across locations MWP corn had significantly higher bioethanol yield on a land area basis (6446 ± 974 L ha–1) than the other harvest strategies. There was no difference in ethanol yield on a land area basis between ImF (5679 ± 1046 L ha–1) or ImS (5294 ± 1052 L ha–1) indicating that conventional ensiling is a viable feedstock storage method for bioethanol production in future biorefineries. The results suggest that whole-plant corn harvesting coupled with whole-plant bioconversion to ethanol is a viable alternative to the convention of separate grain and stover harvesting and bioprocessing.

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Investigation of enzyme formulation on pretreated switchgrass

Abstract:

This work studied the benefits of adding different enzyme cocktails (cellulase, xylanase, b-glucosidase) to pretreated switchgrass. Pretreatment methods included ammonia fiber expansion (AFEX), dilute-acid (DA), liquid hot water (LHW), lime, lime + ball-milling, soaking in aqueous ammonia (SAA), and sulfur dioxide (SO2). The compositions of the pretreated materials were analyzed and showed a strong correlation between initial xylan composition and the benefits of xylanase addition. Adding xylanase dramatically improved xylan yields for SAA (+8.4%) and AFEX (+6.3%), and showed negligible improvement (0–2%) for the pretreatments with low xylan content (dilute-acid, SO2). Xylanase addition also improved overall yields with lime + ball milling and SO2 achieving the highest overall yields from pretreated biomass (98.3% and 93.2%, respectively). Lime + ball milling obtained an enzymatic yield of 92.3 kg of sugar digested/kg of protein loaded.

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Rapid quantification of major reaction products formed during thermochemical pretreatment of lignocellulosic biomass using GC–MS

Abstract:

Accurate quantification of reaction products formed during thermochemical pretreatment of lignocellulosic biomass would lead to a better understanding of plant cell wall deconstruction for production of cellulosic biofuels and biochemicals. However, quantification of some process byproducts, most notably acetamide, acetic acid and furfural, present several analytical challenges using conventional liquid chromatography methods. Therefore, we have developed a high-throughput gas chromatography based mass spectrometric (GC–MS) method in order to quantify relevant compounds without requiring time-consuming sample derivatization prior to analysis. Solvent extracts of untreated, ammonia fiber expansion (AFEX) treated and dilute-acid treated corn stover were analyzed by this method. Biomass samples were extracted with acetone using an automated solvent extractor, serially diluted and directly analyzed using the proposed GC–MS method. Acetone was the only solvent amongst water, methanol and acetonitrile that did not contain detectable background levels of the target compounds or facilitate a buildup of plant-derived residues in the GC injector, which decreased analytical reproducibility. Quantitative results were based on the method of standard addition and external standard calibration curves.

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Biomass Conversion Research Laboratory
Michigan State University
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