BCRL Publications
An integrated paradigm for cellulosic biorefineries: utilization of lignocellulosic biomass as self-sufficient feedstocks for fuel, food precursors and saccharolytic enzyme production
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- Category: Journal Articles
- Published on 23 August 2012
Abstract:
Simultaneously achieving economic, environmental and social sustainability is a major challenge for the emerging renewable fuel industry. We approach this problem by demonstrating a cellulosic biorefinery paradigm which produces ethanol and food precursors using lignocellulosic biomass as the exclusive source for carbohydrates and minerals. Enzymatic hydrolysate from Ammonia Fiber Expansion (AFEX)-pretreated corn stover at 18% w/w solids loading was found to be nutrient-rich. This hydrolysate was fermented completely within 48 h in two stages to produce ethanol and native yeast cells. An in-house saccharolytic enzyme production using AFEX-pretreated corn stover as carbohydrate source greatly reduces the dependence on commercial enzymes. The inducer mixture is 2.5–7 times more potent than lactose, a common enzyme inducer. Economic analysis indicates that the proposed paradigm is substantially more cost-effective relative to the 2005 NREL model. This improvement is largely attributed to the native yeast cells co-production and the reduction of enzyme cost through the in-house production.
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A novel integrated biological process for cellulosic ethanol production featuring high ethanol productivity, enzyme recycling and yeast cells reuse
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- Category: Journal Articles
- Published on 23 August 2012
Abstract:
High enzyme loading requirements, slow xylose fermentation and low ethanol productivity are three of the major issues impeding commercial biochemical production of cellulosic ethanol. We report here a novel integrated biological process to overcome these problems. Enzymatic hydrolysis was performed for only 24 h to avoid the slow rate period which begins at about that time. Unhydrolyzed recalcitrant solids with adsorbed enzymes were recycled to the subsequent cycles. By this approach, easily digestible biomass was processed first and recalcitrant biomass was given enough residence time to get hydrolyzed during subsequent processing steps. Fermentation was conducted using a high yeast inoculation level and was also completed in 24 h. The yeast cells were then recycled. With this novel processing approach, the enzyme loading was reduced from 36 to 22.3 and 25.8 mg protein per gram glucan, respectively, for separate hydrolysis and fermentation (SHF) and for simultaneous saccharification and co-fermentation (SSCF) on AFEX™ pretreated corn stover. The process ethanol productivity was enhanced by 2 to 3 fold due to both fast enzymatic hydrolysis and fast fermentation.
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Comparative life cycle assessment of centralized anddistributed biomass processing systems combined withmixed feedstock landscapes
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- Category: Journal Articles
- Published on 20 August 2012
Abstract:
Lignocellulosic biofuels can help fulfill escalating demands for liquid fuels and mitigate the environmental impacts of petroleum-derived fuels. Two key factors in the successful large-scale production of lignocellulosic biofuels are pretreatment (in biological conversion processes) and a consistent supply of feedstock. Cellulosic biomass tends to be bulky and difficult to handle, thereby exacerbating feedstock supply challenges. Currently, large biorefineries face many logistical problems because they are fully integrated, centralized facilities in which all units of the conversion process are present in a single location. The drawbacks of fully integrated biorefineries can potentially be dealt by a network of distributed processing facilities called ‘Regional Biomass Processing Depots’ (RBPDs) which procure, preprocess/pretreat, densify and deliver feedstock to the biorefinery and return by-products such as animal feed to end users. The primary objective of this study is to perform a comparative life cycle assessment (LCA) of distributed and centralized biomass processing systems. Additionally, we assess the effect that apportioning land area to different feedstocks within a landscape has on the energy yields and environmental impacts of the overall systems. To accomplish these objectives, we conducted comparative LCAs of distributed and centralized processing systems combined with farm-scale landscapes of varying acreages allocated to a ‘cornsystem’ consisting of corn grain, stover and rye (grown as a winter double crop) and two perennial grasses, switchgrass and miscanthus. The distributed processing system yields practically the same total energy and generates 3.7% lower greenhouse gas emissions than the centralized system. Sensitivity analyses identified perennial grass yields,
biomass densification and its corresponding energy requirements, transport energy requirements and carbon sequestration credits for conversion from annual to perennial crops as key parameters that significantly affect the overall results.
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Can Dispersed Biomass Processing Protect the Environment and Cover the Bottom Line for Biofuel?
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- Category: Journal Articles
- Published on 15 December 2011
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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Indirect land use change for biofuels: Testing predictions and improving analytical methodologies
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- Category: Journal Articles
- Published on 10 December 2011
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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Developing a model for assessing biomass processing technologies within a local biomass processing depot
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- Category: Journal Articles
- Published on 06 December 2011
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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Overview to Ammonia Pretreatments for Lignocellulosic Biorefineries
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- Category: Journal Articles
- Published on 01 December 2011
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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Seeking to Understand the Reasons for Different Energy Return on Investment (EROI) Estimates for Biofuels
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- Category: Journal Articles
- Published on 24 November 2011
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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Optimization of AFEX™ pretreatment conditions and enzyme mixtures to maximize sugar release from upland and lowland switchgrass
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- Category: Journal Articles
- Published on 09 November 2011
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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Insights into Hydrogen Bonding and Stacking Interactions in Cellulose
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- Category: Journal Articles
- Published on 24 October 2011
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.
