Abstract:

This paper compares environmental and profitability outcomes for a centralized biorefinery for cellulosic ethanol that does all processing versus a biorefinery linked to a decentralized array of local depots that pretreat biomass into concentrated briquettes. The analysis uses a spatial bioeconomic model that maximizes predicted profit from crop and energy products, subject to the requirement that the biorefinery must be operated at full capacity. The model draws upon biophysical crop input-output coefficients simulated with the EPIC model, as well as input and output prices, spatial transportation costs, ethanol yields from biomass, and biorefinery capital and operational costs. The model was applied to 82 cropping systems simulated across 37 sub-watersheds in a 9-county region of southern Michigan in response to ethanol prices simulated to rise from $1.78 to $3.36 per gallon. Results show that the decentralized local biomass processing depots lead to lower profitability but better environmental performance, due to more reliance on perennial grasses than the centralized biorefinery. Simulated technological improvement that reduces the processing cost and increases the ethanol yield of switchgrass by 17% could cause a shift to more processing of switchgrass, with increased profitability and environmental benefits.

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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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Abstract:

One solution to the supply chain challenges of cellulosic biofuels is a network of local biomass processing depots (LBPDs) that can produce stable, dense, intermediate commodities and valuable co-products prior to shipping to a refinery. A techno-economic model of an LBPD facility that could incorporate multiple technologies and products was developed in Microsoft Excel to be used to economically and environmentally evaluate potential LBPD systems. In this study, three technologies (ammonia fiber expansion or AFEX™ pretreatment, fast pyrolysis, and leaf protein processing) were assessed for profitability. Pyrolysis was slightly profitable under the base conditions, leaf protein processing was highly unprofitable, and AFEX was profitable if biomass drying was not required. This model can be adapted to multiple feedstocks and end uses, including both economic and environmental modeling.

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Abstract:

Development of environmentally sustainable and economically viable technologies for plant cell wall deconstruction to fermentable sugars has been impeded due to native plant cell wall recalcitrance to thermochemical and biological based processing. Lower severity alkaline based pretreatments processes like Ammonia Fiber Expansion (AFEX) can overcome
several limitations of traditional pretreatment approaches (e.g., acidic pretreatments) to producing cellulosic biofuels and biochemicals. Here, we give an overview of chemical reactions taking place during alkaline pretreatments including reactions
between ammonia and polysaccharides/lignin (e.g., ammonolysis, hydrolysis and maillardtype reactions). AFEX based
pretreatments enhance enzymatic digestibility and fermentability of lignocellulosic biomass through various chemical and ultra-structural modifications within the cell wall. An improved mechanistic understanding of the AFEX process has led to develiop
novel alkaline pretreatments that are briefly discussed in this review.

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Abstract:

The authors of this paper have been involved in contentious discussion of the EROI of biomass-based ethanol. This contention has undermined, in the minds of some, the utility of EROI for assessing fuels. This paper seeks to understand the reasons for the divergent results.

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Abstract:

Switchgrass is a North American grass that is considered to be a highly promising herbaceous bioenergy
feedstock. Differences in processing conditions and yields specifically related to switchgrass cultivar or
cytotype (upland or lowland) can be confounded by differences in harvest date or region of growth.
For this research, AFEX™ pretreatment conditions and hydrolysis enzyme mixtures were statistically
optimized for Alamo (lowland) and Shawnee (upland) switchgrass that had been harvested in December
in Oklahoma. Optimal pretreatment conditions and enzyme mixtures were almost identical for both varieties
and gave similar mass sugar yields. Inclusion of hemicellulases in the enzyme mixture maintained
total sugar yields with 50% reduction in enzyme loading. Regardless of variety, the biorefinery should be
able to obtain high sugar yields using the same pretreatment and hydrolysis conditions to process
switchgrass grown under the same environmental conditions, in the same location, and harvested at
the same time of the year.

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Abstract:

In this quantum chemical study, we explore hydrogen bonding (H-bonding) and stacking interactions in different crystalline cellulose allomorphs; namely, cellulose Iβ and cellulose IIII. We consider a model system representing a cellulose crystalline core made from six cellobiose units arranged in three layers with two chains per layer. We calculate the contributions of intrasheet and intersheet interactions to the structure and stability in both cellulose Iβ and cellulose IIII crystalline cores. Reference structures for this study were generated from molecular dynamics simulations of water-solvated cellulose Iβ and IIII fibrils. A systematic analysis of various conformations describing different mutual orientations of cellobiose units is performed using the hybrid density functional theory with the M06-2X with 6-31+G(d,p) basis sets. We dissect the nature of the forces that stabilize the cellulose Iβ and cellulose IIII crystalline cores and quantify the relative strength of H-bonding and stacking interactions. Our calculations demonstrate that individual
H-bonding interactions are stronger in cellulose Iβ than in cellulose IIII; however, the totalH-bonding contribution to stabilization is larger in cellulose IIII because of the highly cooperative nature of the H-bonding network. In addition, we observe a significant contribution from cooperative stacking interactions to the stabilization of cellulose Iβ. The theory of atoms-in-molecules (AIM) has been employed to characterize and quantify these intermolecular interactions. AIM analyses highlight the role of nonconventional
CH3 3 3O H-bonding in the cellulose assemblies. Finally, we calculate molecular electrostatic potential maps for the cellulose allomorphs that capture the differences in chemical reactivity of the systems considered in our study.

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A letter to the editor of Biomass & Bioenergy by Dr. Bruce Dale and Seungdo Kim.

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Abstract:

Leaf protein (LP) produced as a coproduct of cellulosic ethanol production can be utilized by livestock. Effects of conservation method on protein extraction efficiency from orchardgrass (OG) and switchgrass (SG); effects of grass maturity, chemical and heat treatment, and conservation method on protein degradation of LP from OG; and amino acid profiles of OG and LP from OG before and after degradation were evaluated. Two maturities of OG and SG were harvested in 2008 with crude protein (CP) concentrations of 171 and 44 g/kg dry matter (DM; immature) and 131 and 24 g/kg DM (mature) for OG and SG, respectively. Grasses (fresh, stored, or wilted) were chopped, juice extracted with a screw press and adjusted to a pH of 3.3 with concentrated HCl, and treated with or without zinc and with heat (100 or 140 ◦C for 1 h) or without heat (21 ◦C; control) followed by centrifugation to harvest precipitated LP. Efficiencies of extraction were similar for fresh and stored, which were both higher than wilted grass (P < 0.01). Crude protein concentrations (g/kg DM) of LP were approximately twice that of the original grass for all chemical and heat treatment combinations. In vitro protein degradation ofOGLP was evaluated using enzymes extracted from rumens of lactating dairy cows. FreshOGLP treated with HCl + Zn 140 ◦C had the greatest reduction in CP degradation compared to HCl control. An interaction (P < 0.05) between maturity and zinc was observed with zinc decreasing CP degradation of immature OG LP more than mature OG LP after 4 h incubation. Interactions (P < 0.10) were also detected between maturity and temperature and between chemical and temperature after 12 h incubation. Heat decreased CP degradability with temperatures of 100 ◦C and 140 ◦C resulting in similar degradation (42.9 and 39.5 g/kg CP, respectively), which were lower than control (112.9 g/kg CP; P < 0.05) after 4 h incubation. There was an effect of conservation method on HCl + Zn 140 ◦C treated OG LP with similar degradability for stored (51.5 g/kg CP) and wilted (83.0 g/kg CP), which were higher than fresh (16.8 g/kg CP; P < 0.05) after 4 h incubation. The amino acid patterns of OG LP before and after degradation were similar. In summary, LP from fresh grass is most suitable because proteolysis during storage or wilting likely decreases protein recovery and increases ruminal degradation, and both zinc and
heat treatments decrease degradability of OG LP within the rumen.

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Abstract:

Six biomass pretreatment processes to convert switchgrass to fermentable sugars and ultimately to cellulosic ethanol are compared on a consistent basis in this technoeconomic analysis. The six pretreatment processes are ammonia fiber expansion (AFEX), dilute acid (DA), lime, liquid hot water (LHW), soaking in aqueous ammonia (SAA), and sulfur dioxide-impregnated steam explosion (SO2). Each pretreatment process is modeled in the framework of an existing biochemical design model so that systematic variations of process-related changes are consistently captured. The pretreatment area process design and simulation are based on the research data generated within the Biomass Refining Consortium for Applied Fundamentals
and Innovation (CAFI) 3 project. Overall ethanol production, total capital investment, and minimum ethanol selling price (MESP) are reported along with selected sensitivity analysis. The results show limited differentiation between the projected economic performances of the pretreatment options, except for processes that exhibit significantly lower monomer sugar and resulting ethanol yields.

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