Cellulosic Biofuel Industry Research Articles

Optimization models for integrated biorefinery operations

Variations of physical and chemical characteristics of biomass lead to an uneven flow of biomass in a biorefinery, which reduces equipment utilization and increases operational costs. Uncertainty of biomass supply and high processing costs increase the risk of investing in the US’s cellulosic biofuel industry. We propose a stochastic programming model to streamline processes within a biorefinery. A chance constraint models system’s reliability requirement that the reactor is operating at a high utilization rate given uncertain biomass moisture content, particle size distribution, and equipment failure. The model identifies operating conditions of equipment and inventory level to maintain a continuous flow of biomass to the reactor. The sample average approximation method approximates the chance constraint and a bisection search-based heuristic solves this approximation. A case study is developed using real-life data collected at Idaho National Laboratory’s biomass processing facility. An extensive computational analysis indicates that sequencing of biomass bales based on moisture level, increasing storage capacity, and managing particle size distribution, increases utilization of the reactor and reduces operational costs.

Advanced Hardwood Biofuels Northwest: Commercialization Challenges for the Renewable Aviation Fuel Industry

A bioenergy summit was organized by Advanced Hardwood Biofuels Northwest (AHB) to debate the barriers to the commercialization of a hybrid poplar biofuels industry for the alternative jet fuels market from the perspective of five years of AHB research and development and two recent surveys of the North American cellulosic biofuels industry. The summit showed that: (1) Growing and converting poplar feedstock to aviation fuels is technically sound, (2) an adequate land base encompassing 6.03 and 12.86 million respective hectares of croplands and rangelands is potentially available for poplar feedstock production, (3) biofuel production is accompanied by a global warming potential that meets the threshold 60% reduction mandated for advanced renewable fuels but (4) the main obstruction to achieving a workable poplar aviation fuels market is making the price competitive with conventional jet fuels. Returns on investment into biomass farms and biorefineries are therefore insufficient to attract private-sector capital the fact notwithstanding that the demand for a reliable and sustainable supply of environmentally well-graded biofuels for civilian and military aviation is clear. Eleven key findings and recommendations are presented as a guide to a strategic plan for a renewed pathway to poplar alternative jet fuels production based upon co-products, refinery co-location with existing industries, monetization of ecosystem services, public-private financing, and researching more efficient and lower-costs conversion methods such as consolidated bioprocessing.

Why the cellulosic biofuels mandate fell short: a markets and policy perspective

AbstractThe revised Renewable Fuel Standard's cellulosic biofuels mandate requires the USA to consume 16 000 million gallons of cellulosic biofuel per year by 2022. The cellulosic biofuels industry has fallen far short of reaching the production targets needed to achieve this volume, and it has even struggled to achieve the greatly reduced revised volumes that were created by the US Environmental Protection Agency despite the subsequent inclusion of landfill gas within the mandate. This article examines the underlying causes of this shortfall from the perspectives of markets and policy. It examines how the cellulosic biofuels production environment has not been conducive to the cost‐competitiveness of pioneer, first‐of‐their‐kind facilities and pathway buildout, and how recent techno‐economic analyses have used uncertainty to quantify the impacts of this environment. It further examines how the cellulosic biofuels mandate has actually hindered commercialization despite being intended to support it. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd

Genome-Wide Association Study Reveals Novel Genes Associated with Culm Cellulose Content in Bread Wheat (Triticum aestivum, L.).

Plant cell wall formation is a complex, coordinated and developmentally regulated process. Cellulose is the most dominant constituent of plant cell walls. Because of its paracrystalline structure, cellulose is the main determinant of mechanical strength of plant tissues. As the most abundant polysaccharide on earth, it is also the focus of cellulosic biofuel industry. To reduce culm lodging in wheat and for improved ethanol production, delineation of the variation for stem cellulose content could prove useful. We present results on the analysis of the stem cellulose content of 288 diverse wheat accessions and its genome-wide association study (GWAS). Cellulose concentration ranged from 35 to 52% (w/w). Cellulose content was normally distributed in the accessions around a mean and median of 45% (w/w). Genome-wide marker-trait association study using 21,073 SNPs helped identify nine SNPs that were associated (p < 1E-05) with cellulose content. Four strongly associated (p < 8.17E-05) SNP markers were linked to wheat unigenes, which included β-tubulin, Auxin-induced protein 5NG4, and a putative transmembrane protein of unknown function. These genes may be directly or indirectly involved in the formation of cellulose in wheat culms. GWAS results from this study have the potential for genetic manipulation of cellulose content in bread wheat and other small grain cereals to enhance culm strength and improve biofuel production.

Developing a cellulosic aviation biofuel industry in Indiana: A market and logistics analysis

With the non-advanced portion of the US Renewable Fuel Standard having been largely met by corn ethanol, many states are looking to cellulosic crops as the next source of biofuels. In Indiana, attention is turning to biojet fuels and renewable diesel as forming the demand for these crops. This paper seeks to determine the optimal manufacturing site locations and supply chain logistics for the conversion of biomass sources to jet fuel and renewable diesel within Indiana. A sequential start-up model is developed for this application, using a mixed integer non-linear (quadratic) program, in which firms sequentially optimize unit costs by choosing the conversion site location, scale, and feedstocks. The results indicate that firms wish to locate conversion sites near biomass sources as opposed to fuel destinations, and that early entrants to the industry gravitate towards counties rich in corn stover, a less expensive residue. However, even with existing subsidies firms would barely break even. Finally, the benefits of the sequential model are elucidated in contrast to a social planner's model, with the key benefit being that the sequential model can generate supply curves independent of demand levels.

The greenhouse gas intensity and potential biofuel production capacity of maize stover harvest in the US Midwest

AbstractAgricultural residues are important sources of feedstock for a cellulosic biofuels industry that is being developed to reduce greenhouse gas emissions and improve energy independence. While the US Midwest has been recognized as key to providing maize stover for meeting near‐term cellulosic biofuel production goals, there is uncertainty that such feedstocks can produce biofuels that meet federal cellulosic standards. Here, we conducted extensive site‐level calibration of the Environmental Policy Integrated Climate (EPIC) terrestrial ecosystems model and applied the model at high spatial resolution across the US Midwest to improve estimates of the maximum production potential and greenhouse gas emissions expected from continuous maize residue‐derived biofuels. A comparison of methodologies for calculating the soil carbon impacts of residue harvesting demonstrates the large impact of study duration, depth of soil considered, and inclusion of litter carbon in soil carbon change calculations on the estimated greenhouse gas intensity of maize stover‐derived biofuels. Using the most representative methodology for assessing long‐term residue harvesting impacts, we estimate that only 5.3 billion liters per year (bly) of ethanol, or 8.7% of the near‐term US cellulosic biofuel demand, could be met under common no‐till farming practices. However, appreciably more feedstock becomes available at modestly higher emissions levels, with potential for 89.0 bly of ethanol production meeting US advanced biofuel standards. Adjustments to management practices, such as adding cover crops to no‐till management, will be required to produce sufficient quantities of residue meeting the greenhouse gas emission reduction standard for cellulosic biofuels. Considering the rapid increase in residue availability with modest relaxations in GHG reduction level, it is expected that management practices with modest benefits to soil carbon would allow considerable expansion of potential cellulosic biofuel production.

How much are wood-based cellulosic biofuels worth in the Pacific Northwest? Ex-ante and ex-post analysis of local people's willingness to pay

The National Institute of Food and Agriculture (NIFA) provided a grant to establish a wood-based cellulosic biofuels industry in the US Pacific Northwest. Whether the industry will be sustainable depends largely on social acceptability in general and market acceptability of the biofuels among the public in particular. We conducted contingent valuation surveys of general public in the US states of Oregon and Washington to determine people's willingness to pay (WTP) for wood-based cellulosic biofuels and the factors that influence their WTP decisions. Oregon has an existing cellulosic biorefinery, while Washington's biorefineries are only being planned, allowing us to conduct an ex-ante (Washington) versus ex-post (Oregon) WTP comparison. We sent out mail surveys to 2828 valid mailing addresses between May and July of 2015 and received 757 completed surveys. We used the distribution-free Turnbull estimator to estimate the expected WTP and logistic regression to determine the relative strength of predictors on WTP. About one fifth (18.8%) of the respondents were willing to pay some premium for wood-based cellulosic biofuels. The mean WTP amount was $0.19±$0.03/gal. (95% confidence interval: $0.17 to $0.21), which equates to a 6.4% price premium on top of the market price for gasoline. Logistic regression results showed that the offered bid price, knowledge on biofuels, age and religious affiliation of respondents were statistically significant predictors of WTP decisions. No significant differences in ex-ante versus ex-post WTP were observed. We also discussed the policy implications of these results for sustainable management of the wood-based cellulosic biofuels industry.

The U.S. cellulosic biofuels industry: Expert views on commercialization drivers and barriers

The continued growth of U.S. first generation biofuels, mostly corn-grain ethanol, is facing increased pressure from the “food-vs.-fuel” and ethanol “blend wall” debates. Second generation (cellulosic) biofuels avoid the uncertainties about impact on food security and land competition, but have yet to become widely commercialized. No previous studies were found quantifying the relative importance of factors driving or constraining the commercialization of the U.S. cellulosic biofuels industry. Respondents to this study's online and paper-based surveys, administered between July and November, 2015, included 228 experts throughout the biorefinery supply chain from seven USDA National Institute of Food and Agriculture (NIFA) Coordinated Agricultural Projects (CAPs) and two industrial conferences. Government policies were rated as the most important driver for the commercialization of cellulosic biofuels. The second most importance driver was added value from non-fuel co-products, followed by carbon emission reduction and volatile oil prices. High production costs, policy uncertainty, and competition vs. petro-fuels were identified as the top three barriers to the commercialization of cellulosic biofuels. This paper also identified significant differences in the rating of drivers and barriers among four self-described expert groups (Feedstock, Processing, Economic/Business, and Sustainability), thus underscoring the importance of examining issues from multiple perspectives and highlighting the value of the USDA NIFA CAPs. Finally, participants were significantly more optimistic about the success of the integrated production of both cellulosic biofuels and biochemicals by the year 2020 vs. cellulosic biofuels alone (at the p = 0.001 level), underscoring the perceived advantages of the integrated biorefinery model.

Genome sequence and physiological analysis of Yamadazyma laniorum f.a. sp. nov. and a reevaluation of the apocryphal xylose fermentation of its sister species, Candida tenuis.

Xylose fermentation is a rare trait that is immensely important to the cellulosic biofuel industry, and Candida tenuis is one of the few yeasts that has been reported with this trait. Here we report the isolation of two strains representing a candidate sister species to C. tenuis. Integrated analysis of genome sequence and physiology suggested the genetic basis of a number of traits, including variation between the novel species and C. tenuis in lactose metabolism due to the loss of genes encoding lactose permease and β-galactosidase in the former. Surprisingly, physiological characterization revealed that neither the type strain of C. tenuis nor this novel species fermented xylose in traditional assays. We reexamined three xylose-fermenting strains previously identified as C. tenuis and found that these strains belong to the genus Scheffersomyces and are not C. tenuis. We propose Yamadazyma laniorum f.a. sp. nov. to accommodate our new strains and designate its type strain as yHMH7 (=CBS 14780 = NRRL Y-63967T). Furthermore, we propose the transfer of Candida tenuis to the genus Yamadazyma as Yamadazyma tenuis comb. nov. This approach provides a roadmap for how integrated genome sequence and physiological analysis can yield insight into the mechanisms that generate yeast biodiversity.

A dynamic programming approach for modeling low-carbon fuel technology adoption considering learning-by-doing effect

Promoting the adoption of low-carbon technologies in the transportation fuel portfolio is an effective strategy to mitigate greenhouse gas emissions from the transportation sector worldwide. However, as one of the most promising low-carbon fuels, cellulosic biofuel has not fully entered commercial production. Governments could provide guidance in developing cellulosic biofuel technologies, but no systematic approach has been proposed yet. We establish a dynamic programming framework for investigating time-dependent and adaptive decision-making processes to develop advanced fuel technologies. The learning-by-doing effect inherited in the technology development process is included in the framework. The proposed framework is applied in a case study to explore the most economical pathway for California to develop a solid cellulosic biofuel industry under its Low Carbon Fuel Standard. Our results show that cellulosic biofuel technology is playing a critical role in guaranteeing California’s 10% greenhouse gas emission reduction by 2020. Three to four billion gallons of cumulative production are needed to ensure that cellulosic biofuel is cost-competitive with petroleum-based fuels or conventional biofuels. Zero emission vehicle promoting policies will discourage the development of cellulosic biofuel. The proposed framework, with small adjustments, can also be applied to study new technology development in other energy sectors.

A Spatial Real Options Approach for Modeling Land Use Change: Assessing the Potential for Poplar Energy Plantations in Alberta

Land use change models based on historical behavior have proven useful in predicting and understanding determinants of change. Such approaches are not possible where land use change data are absent. In this paper, we develop a normative spatial model that considers option values associated with land conversion between agriculture and forestry and their differing time scales. The model is applied in a case study regarding the potential for a cellulosic biofuel industry in Alberta. Results indicate the importance of future patterns of prices in influencing decisions to switch from agriculture to bioenergy production, and suggest that cellulosic plantations are not likely to prevail over agricultural land uses. Les modèles de changement d'affectation des terres basés sur les comportements historiques se sont avérés utiles pour la prédiction et la compréhension des facteurs de changements. Ces approches sont impossibles là où les données concernant les changements d'affectation des terres sont absentes. Cet article présente un modèle normatif spatial qui tient compte des valeurs d'option associées à la conversion des terres agricoles en terres forestières et à leurs différentes échelles de temps. L'application du modèle se fait dans une étude de cas au sujet du potentiel pour une industrie du biocarburant cellulosique en Alberta. Les résultats montrent l'importance de l'influence des futures structures de prix sur le choix de passer de l'agriculture à la production de bioénergie, et suggèrent que les plantations cellulosiques ne l'emporteront pas sur les affectations agricoles des terres.

Estimation of economic impacts of cellulosic biofuel production: a comparative analysis of three biofuel pathways

AbstractThe development of a cellulosic biofuel industry utilizing domestic biomass resources is expected to create opportunities for economic growth resulting from the construction and operation of new biorefineries. We applied an economic input‐output model to estimate potential economic impacts, particularly gross job growth, resulting from the construction and operation of biorefineries using three different technology pathways: (i) cellulosic ethanol via biochemical conversion in Iowa, (ii) renewable diesel blendstock via biological conversion in Georgia, and (iii) renewable diesel and gasoline blendstock via fast pyrolysis in Mississippi. Combining direct, indirect (revenue‐ and supply‐chain‐related), and induced effects, capital investment associated with the construction of a biorefinery processing 2000 dry metric tons of biomass per day (DMT/day) could yield between 5960 and 8470 full‐time equivalent (FTE) jobs during the construction period, depending on the biofuel pathways. Fast pyrolysis biorefineries produce the most jobs on a project level thanks to the highest capital requirement among the three pathways. Normalized on the scale of $1 million of capital investment, the fast pyrolysis biorefineries are estimated to yield slighter higher numbers of jobs (12.1 jobs) than the renewable diesel (11.8 jobs) and the cellulosic ethanol (11.6 jobs) biorefineries. While operating biorefineries is not labor‐intensive, the annual operation of a 2000 DMT/day biorefinery could support between 720 and 970 jobs when the direct, indirect, and induced effects are considered. The major factor, which results in the variations among the three pathways, is the type of biomass feedstock used for biofuels. Unlike construction jobs, these operation‐related jobs are necessary over the entire life of the biorefineries. Our results show that indirect effects stimulated by the operation of biorefineries are the primary contributor to job growth. The agriculture/forest, services, and trade industries are the primary sectors that will benefit from the ongoing operation of biorefineries. Copyright © 2016 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Optimal contracting structure between cellulosic biorefineries and farmers to reduce the impact of biomass supply variation: game theoretic analysis

AbstractThere is considerable year‐to‐year variability in the supply of cellulosic biomass used in the production of cellulosic biofuels, yet strategies to mitigate these variations in biofuel development are not well understood. Biorefineries and farmers venturing into the cellulosic biofuel industry will require biomass supply and contracting strategies that can minimize the impact of these large variations. Some studies have proposed biomass pre‐treatment and storage to address biomass supply variations. Other studies have used transportation modeling approaches to manage supply variations and select the optimal location of a cellulosic biorefinery. However, storage, pre‐treatment, and similar engineering approaches lead to higher costs and have other limitations such as additional infrastructural requirements. There is a gap in understanding how contracting strategies between biorefineries and the biomass suppliers (farmers) can reduce the risks with biomass supply variations. In this study, the contracting structure between biorefineries and biomass suppliers is studied under different market structures for the US Corn Belt. A theoretical framework is then developed to use contracting strategies for mitigating the impact of biomass supply variations. First, the trade‐offs between intricately linked components of biomass cost, such as biomass transport, biomass price (incentive) to suppliers, variation in biomass supply, biorefinery size, and alternative feedstock availability are examined. Next, an optimal contracting structure is developed between biorefineries and biomass suppliers using game theoretic analysis. Results show that both the impact of biomass supply variations and the overall biomass cost can be significantly reduced through the use of the optimal contracting strategy between biorefineries and suppliers. © 2016 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Optimal Mix of Vertical Integration and Contracting for Energy Crops: Effect of Risk Preferences and Land Quality

Long‐term contracts are likely to be critical to induce the production of perennial energy crops as a feedstock for the emerging cellulosic biofuel industry. This paper develops a framework to analyze the determinants of landowner choice among a land‐leasing contract, a fixed‐price contract, and a revenue‐sharing contract for energy crop production. We examine the effect of heterogeneous landowners' risk and time preferences and land quality on the optimal mix and equilibrium terms of these contracts, which jointly maximize the net benefits of the refinery and landowners in a region; this has implications for the extent to which energy crop production is likely to be vertically integrated or independently contracted by a biorefinery. We find that the refinery can potentially earn a higher profit by offering a choice of these three types of contracts rather than a single type of contract only; by allowing self‐selection of contract type based on landowner risk and time preferences, the contractual terms needed to induce production of energy crops are reduced. Although it is optimal for vertically‐integrated and contracted production to co‐exist, we find that the share of the former is predominant across a range of assumptions about the distribution of risk preferences, time preferences, and relative riskiness of conventional and energy crop production. We also find that the impact of having multiple contract types to choose from on landowners' welfare is ambiguous.

Potential job creation in the cellulosic biofuel industry: the effect of feedstock price

AbstractA large‐scale biofuel industry based on cellulosic materials would provide many new job opportunities. We model potential direct jobs generated by a cellulosic ethanol industry in the United States. These job projections are estimated via a bottom‐up approach based on the cellulosic feedstock supply chain systems as a function of the price farmers receive for the feedstock. The cellulosic feedstock types involved in the feedstock supply chain system are crop residues, perennial grasses, annual energy crops, and coppiced and non‐coppiced woody crops. Results show that the feedstock transportation sector is where most of the jobs are created, followed by the feedstock production sector. Jobs generated by the feedstock transportation sector account for around one‐third of total new jobs generated, while jobs generated by cellulosic feedstock production account for about one‐quarter of the new jobs. In the United States, most of the new jobs are created in Iowa, Kansas, Missouri, Oklahoma, and Texas. At feedstock prices over US$ 55 per dry ton, more than 100 000 new direct full‐time equivalent jobs are potentially generated. The number of jobs potentially generated by the cellulosic ethanol fuel production system is highly sensitive to the feedstock price. At $60 per ton, a 50% increase in feedstock price, the system generates over 6 times more jobs than it does at a feedstock price of $40 per ton. Many more farmers produce cellulosic feedstock for ethanol production at higher feedstock prices, and thus more ethanol production leads to more job creation. © 2015 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Validation of a novel sequential cultivation method for the production of enzymatic cocktails from Trichoderma strains.

The development of new cost-effective bioprocesses for the production of cellulolytic enzymes is needed in order to ensure that the conversion of biomass becomes economically viable. The aim of this study was to determine whether a novel sequential solid-state and submerged fermentation method (SF) could be validated for different strains of the Trichoderma genus. Cultivation of the Trichoderma reesei Rut-C30 reference strain under SF using sugarcane bagasse as substrate was shown to be favorable for endoglucanase (EGase) production, resulting in up to 4.2-fold improvement compared with conventional submerged fermentation. Characterization of the enzymes in terms of the optimum pH and temperature for EGase activity and comparison of the hydrolysis profiles obtained using a synthetic substrate did not reveal any qualitative differences among the different cultivation conditions investigated. However, the thermostability of the EGase was influenced by the type of carbon source and cultivation system. All three strains of Trichoderma tested (T. reesei Rut-C30, Trichoderma harzianum, and Trichoderma sp INPA 666) achieved higher enzymatic productivity when cultivated under SF, hence validating the proposed SF method for use with different Trichoderma strains. The results suggest that this bioprocess configuration is a very promising development for the cellulosic biofuels industry.

Economics and Uncertainty of Lignocellulosic Biofuel Production from Energy Cane and Sweet Sorghum in South Texas

Government support uncertainty, scarce yield information, and the inherent risk in bioeconomic phenomena are some of the deterrents faced by investors in the nascent cellulosic biofuel industry. A financial probabilistic model was developed to contrast the economic feasibility of producing cellulosic biofuels from energy cane and sweet sorghum using three technologies: hydrolysis, pyrolysis, and gasification. Hydrolysis and pyrolysis proved feasible (showed possibilities of a positive net present value) without government support and conditioned to stochastic feedstock yields and biofuel prices. Gasification was feasible with government support. Improved feedstock and biofuel productivity would considerably raise the feasibility probabilities for hydrolysis and pyrolysis without government support.

Distribution of Structural Carbohydrates in Corn Plants Across the Southeastern USA

Quantifying lignin and carbohydrate composition of corn (Zea mays L.) is important to support the emerging cellulosic biofuels industry. Therefore, field studies with 0 or 100 % stover removal were established in Alabama and South Carolina as part of the Sun Grant Regional Partnership Corn Stover Project. In Alabama, cereal rye (Secale cereale L.) was also included as an additional experimental factor, serving as a winter cover crop. Plots were located on major soil types representative of their respective states: Compass and Decatur soils in Alabama and a Coxville/Rains-Goldsboro-Lynchburg soil association in South Carolina. Lignin and structural carbohydrate concentrations in the whole (above-ground) plant, cobs, vegetation excluding cobs above the primary ear (top), vegetation below the primary ear (bottom), and vegetation from above the primary ear including cobs (above-ear fraction) were determined using near-infrared spectroscopy (NIRS). The distribution of lignin, ash, and structural carbohydrates varied among plant fractions, but neither inclusion of a rye cover crop nor the stover harvest treatments consistently affected carbohydrate concentrations within locations. Total precipitation and average air temperature during the growing season were strongly correlated with stover composition indicating that weather conditions may have multiple effects on potential biofuel production (i.e., not only yield but also stover quality). When compared to the above-ear fractions, bottom plant partitions contained greater lignin concentrations. Holocellulose concentration was consistently greater in the above-ear fractions at all three locations. Data from this study suggests that the above-ear plant portions have the most desirable characteristics for cellulosic ethanol production via fermentation in the southeastern USA.

A highly efficient dilute alkali deacetylation and mechanical (disc) refining process for the conversion of renewable biomass to lower cost sugars

The deconstruction of renewable biomass feedstocks into soluble sugars at low cost is a critical component of the biochemical conversion of biomass to fuels and chemicals. Providing low cost high concentration sugar syrups with low levels of chemicals and toxic inhibitors, at high process yields is essential for biochemical platform processes using pretreatment and enzymatic hydrolysis. In this work, we utilize a process consisting of deacetylation, followed by mechanical refining in a disc refiner (DDR) for the conversion of renewable biomass to low cost sugars at high yields and at high concentrations without a conventional chemical pretreatment step. The new process features a low temperature dilute alkaline deacetylation step followed by disc refining under modest levels of energy consumption. The proposed process was demonstrated using a commercial scale Andritz double disc refiner. Disc refined and deacetylated corn stover result in monomeric glucose yields of 78 to 84% and monomeric xylose yields of 71 to 77% after enzymatic hydrolysis at process-relevant solids and enzyme loadings. The glucose and xylose yields of the disc refined substrates in enzymatic hydrolysis are enhanced by 13% and 19%, respectively. Fermentation of the DDR substrates at 20% total solids with Z.mobilis utilized almost all sugars in 20hrs indicating the sugar hydrolyzate produced from the DDR process is highly fermentable due to low levels of chemical contaminants. The ethanol titer and ethanol process yield are approximately 70 g/L and 90% respectively. The proposed new process has been demonstrated using pilot scale deacetylation and disc refiners. The deacetylated and disc refined corn stover was rapidly deconstructed to monomeric sugars at 20% wt solids with enzymatic hydrolysis. High process sugar conversions were achieved, with high concentrations of monomeric sugars that exceeded 150 g/L. The sugar syrups produced were found to have low concentrations of known major fermentation inhibitors: acetic acid, furfural and HMF. The low levels of these fermentation inhibitors lead to high fermentation yields. The results suggest that this process is a very promising development for the nascent cellulosic biofuels industry.

The value of native, warm-season perennial grasses grown for pasture or biofuel in the southern Great Plains, USA

The Renewable Fuel Standard under the Energy Independence and Security Act of 2007 mandated the production of 60.5 GL (1 GL = 1 × 109 L) of cellulosic biofuel by 2022. Switchgrass (Panicum virgatum) has been identified as a primary feedstock because it is a perennial adapted to a wide environmental range and produces high yields. Development of the cellulosic biofuel industry has been slow, one reason being a lack of available feedstock driven by lack of a developed market. Rather than considering it only as a dedicated biofuel feedstock, we examined switchgrass potential for both grazing and biofuel feedstock. In a series of experiments testing dry matter yield, grazing preference and animal bodyweight gain, switchgrass (cv. Alamo) was found to produce greater total yield (17.7 kg ha–1) than 15 other warm-season perennial grasses, was the most preferred by stocker cattle in a grazing preference study, and produced good average daily gains in a grazing study (0.84–1.05 kg head–1). These results demonstrate the potential of switchgrass for both grazing and biofuel feedstock. However, the feedstock price would need to increase above US$83 Mg–1 before the economics of dedicated switchgrass feedstock production would surpass that of a combination of switchgrass grazing and feedstock production.