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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Center for Lignocellulose Structure and Formation (CLSF)

Lignocellulose is the carbon- and energy-rich material synthesized by plants when they make secondary cell walls, e.g. in woody tissues. Plants annually convert gigatons of atmospheric CO 2 into these complex and useful biomaterials that comprise over half of all biological carbon on Earth. This biological conversion helps to reduce atmospheric CO 2 that contributes to climate change while generating renewable plant cell walls that are used commercially on a massive scale in the paper, timber and textile industries. Recent technical developments open new possibilities for use of modified wood and cellulose fibers as large-scale alternatives to steel, plastics, and other nonrenewable materials with high carbon footprints and energy inputs, as well as for generation of biofuels and bio-hydrogen. Despite the utility of plant-based biomaterials, many physical and biological aspects of cell wall structure and formation remain obscure, and this limits the current scope for engineering these renewable resources for greater utility.

09 BIOMASS FUELS↗
DOE OSTI2023

Supply chain system for a centralized biorefinery system based on switchgrass grown on marginal land in Michigan

The feedstock supply chain of a biorefinery is critical in determining the economic and environmental performance of biofuels. This study investigated various feedstock supply chains for a centralized biorefinery based on different objective functions and how the biorefinery responds to supply chain volatility. For the analysis, a hypothetical centralized biorefinery was supplied by switchgrass grown on marginal lands in Michigan. From an economic standpoint, the minimum biofuel selling price is an important metric of the objective function, and the greenhouse gas mitigation potential is a similarly important metric for global warming impact. A trade-off therefore exists between the economic and environmental performance of biofuels under this system configuration. However, when a carbon tax credit is applied to soil organic carbon sequestration in switchgrass production, the metric of the objective function may not be the key factor in establishing a supply chain as long as it is associated with biorefinery capacity as well as economic or environmental values. Year-to-year fluctuations in cellulosic biomass yield (supply chain volatility) might also prevent the biorefinery from operating at full capacity. Cellulosic biomass pellets can serve as an auxiliary feedstock for the centralized cellulosic biorefinery system to minimize the impacts of supply chain volatility.

09 BIOMASS FUELS↗
DOE OSTI2020

Nitrogen fixation and resorption efficiency differences among twelve upland and lowland switchgrass cultivars

In nitrogen (N)-limited terrestrial ecosystems, plants employ various strategies to acquire and conserve N, including translocation of N in perennial tissues and stimulation of N fixation in roots and soils. Switchgrass (Panicum virgatum L.) is a genotypically and phenotypically diverse perennial grass with two distinct ecotypes (lowland and upland) and numerous genotypes. It grows well in low-N soils, likely because of its ability to translocate N and to associate with N-fixing microbes, but little is known about variation in these traits among cultivars or even ecotypes. We measured N translocation, N fixation potential in roots and soils, soil net N mineralization, soil net nitrification, and biomass yields in 12 switchgrass cultivars grown in a replicated block experiment in southwestern Michigan, USA. Lowland cultivars had higher yields, rates of N translocation, soil net N mineralization, and N fixation potentials on washed, non-sterile roots, while upland cultivars exhibited higher N fixation potentials in root-free soil. N resorption efficiencies averaged 53±5 [SE] % for lowland versus 29±3% for upland cultivars. Additionally, there were significant among-cultivar differences for all response variables except mineralization and nitrification, with differences likely explained by cultivar-specific physiologies and microbial communities. Here, the ideal cultivar for biofuels is one that can maintain high yields with minimal fertilizer addition and there appear to be several cultivars that meet these criteria. In addition, results suggest substantial N cycle differences among cultivars that might be exploited by breeders to create new or improved high-yielding, N-conserving switchgrass lines.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Global warming intensity of biofuel derived from switchgrass grown on marginal land in Michigan

Energy crops for biofuel production, especially switchgrass (Panicum virgatum), are of interest from a climate change perspective. Here, we use outputs from a crop growth model and life cycle assessment (LCA) to examine the global warming intensity (GWI; g CO 2 MJ –1 ) and greenhouse gas (GHG) mitigation potential (Mg CO 2 year –1 ) of biofuel systems based on a spatially explicit analysis of switchgrass grown on marginal land (abandoned former cropland) in Michigan, USA. We find that marginal lands in Michigan can annually produce over 0.57 hm 3 of liquid biofuel derived from nitrogen-fertilized switchgrass, mitigating 1.2–1.5 Tg of CO 2 year –1 . About 96% of these biofuels can meet the Renewable Fuel Standard (60% reduction in lifecycle GHG emissions compared with conventional gasoline; GWI ≤37.2 g CO 2 MJ –1 ). Furthermore, 73%–75% of these biofuels are carbon-negative (GWI less than zero) due to enhanced soil organic carbon (SOC) sequestration. However, simulations indicate that SOC levels would fail to increase and even decrease on the 11% of lands where SOC stocks >>200 Mg C ha –1 , leading to carbon intensities greater than gasoline. Results highlight the strong climate mitigation potential of switchgrass grown on marginal lands as well as the needs to avoid carbon rich soils such as histosols and wetlands and to ensure that productivity will be sufficient to provide net mitigation.

09 BIOMASS FUELS↗
DOE OSTI2021

Principles and practice of designing microbial biocatalysts for fuel and chemical production

Abstract The finite nature of fossil fuels and the environmental impact of its use have raised interest in alternate renewable energy sources. Specifically, nonfood carbohydrates, such as lignocellulosic biomass, can be used to produce next generation biofuels, including cellulosic ethanol and other nonethanol fuels like butanol. However, currently there is no native microorganism that can ferment all lignocellulosic sugars to fuel molecules. Thus, research is focused on engineering improved microbial biocatalysts for production of liquid fuels at high productivity, titer, and yield. A clear understanding and application of the basic principles of microbial physiology and biochemistry are crucial to achieve this goal. In this review, we present and discuss the construction of microbial biocatalysts that integrate these principles with ethanol-producing Escherichia coli as an example of metabolic engineering. These principles also apply to fermentation of lignocellulosic sugars to other chemicals that are currently produced from petroleum.

09 BIOMASS FUELS↗
DOE OSTI2021

Hydrothermal pretreatment for valorization of genetically engineered bioenergy crop for lipid and cellulosic sugar recovery

Lipids accumulated in the vegetative tissues of cellulosic feedstocks can be a potential raw material for biodiesel and bioethanol production. In this work, bagasse of genetically engineered sorghum was subjected to liquid hot-water pretreatment at 170, 180, and 190°C for different reaction time. Under the optimal pretreatment condition (170°C, 20 min), the residue was enriched in glucan (57.39 ± 2.63 % w/w) and xylan (13.38 ± 0.49 % w/w). The total lipid content of the pretreated residue was 6.81% w/w, similar to that observed in untreated bagasse (6.30% w/w). Pretreatment improved the enzymatic digestibility of bagasse, allowing a recovery of 79% w/w and 86% w/w of glucose and xylose, respectively. The pretreatment and enzymatic saccharification resulted in a 2-fold increase in total lipid in enzymatic residue compared to the original bagasse. Furthermore, pretreatment and enzymatic hydrolysis enabled high sugar recovery while concentrating triglycerides and free fatty acids in the residue.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Deacetylation and Mechanical Refining Pathway for the Bioconversion of Sugarcane Bagasse

Advancing lignocellulose biorefining is imperative for the deployment of cellulosic (2G) biofuels. This work investigates the tailoring of the alkaline deacetylation and mechanical refining (DMR) pathway for the bioconversion of sugarcane bagasse. Experiments are conducted at laboratory and pilot scales, varying the pretreatment conditions (70–92 °C; 48–100 g NaOH /kg) and the mechanical refining technologies (PFI and disk refining). The pretreatments selectively solubilize acetyl groups (> 86%) and lignin (10–63%) while mostly preserving structural carbohydrates in the solid phase. Enzymatic hydrolysis generates hydrolysates of clean sugars (glucose and xylose), with sugar yields increasing up to 81% for glucose and 89% for xylose in response to delignification and mechanical refining. Biochemical methane potential assays reveal specific methane productions of up to 568 NmL CH₄ gVS⁻¹ for alkaline liquor monodigestion and 344 NmL CH₄ gVS⁻¹ for co-digestion with sugarcane vinasse from the conventional (1G) sugarcane ethanol, indicating a strong potential for bioenergy recovery from this process stream. Synergies are identified in integrating 1G ethanol, 2G DMR processing of bagasse, and anaerobic co-digestion of 1G vinasse and 2G DMR alkaline liquor. This technology enables sugarcane biorefineries to enhance the co-production of ethanol, methane, and concentrated streams of CO 2 .

09 BIOMASS FUELS↗
DOE OSTI2021

Adoption of perennial energy crops in the US Midwest: Causal and heterogeneous determinants

The success of a bioenergy policy relies largely on the wide adoption of perennial energy crops at the farm-scale. This study uses survey data to examine potential adoption decisions by farmers in the US Midwest and the causal effects of various direct and indirect influencing factors, especially heterogeneous preferences of farmers. A Bayesian network (BN) model is developed to delineate the causal-relationship between farmers adoption decisions and the influencing factors. Here, we find a dominating role of economic factors and a non-negligible impact of non-economic factors, such as the perceived environmental benefits and the extent of familiarity with perennial energy crops. To examine the effect of heterogeneity in farmer preferences, we classify the surveyed farmers into four categories based on their attitudes toward the economic, social, and environmental dimensions of perennial energy crops. We identify statistically significant between-group differences in the responses of the four types of farmers to the various influencing factors. Our findings contribute to disentangling the complicated motivations that will influence perennial energy crop adoption decisions and provide implications for more targeted policy development that need to consider the heterogeneous drivers of farmer decisions about land use.

09 BIOMASS FUELS↗
DOE OSTI2022

Combustion dynamics of crude and upgraded Thermal DeOxygenation oils in a compression ignition engine

Thermal DeOxygenation (TDO) is a robust thermochemical conversion scheme to produce hydrocarbons from biomass feedstock. The process targets the carbohydrate fraction of biomass to yield a broad mixture of primarily aromatic hydrocarbons within a boiling point range of 348–798 K with low oxygen content (<4 wt%). The resulting materials are amenable to traditional hydrotreating and distillation processes with approximately 70% by mass in the distillate fuel range. The simple conversion scheme combined with commercially viable upgrading routes makes TDO oils a feasible alternative fuel for transportation applications. Here this paper is the first systematic treatment of fit-for-purpose testing of TDO oils in a compression ignition engine. Blends of partially upgraded TDO oils (e.g. whole oil, distilled oil, hydrotreated oil and hydrotreated-distilled oil) are prepared with certified ultra-low sulfur diesel at 5%, 10%, 15% and 20% by volume. The resulting fuels are analyzed for fuel characteristics and combustion dynamics in an instrumented single-cylinder compression ignition engine. All fuel blends at 10% blend level by volume exhibited adequate engine performance. Hydrotreating of the oils is a necessary step to meet cetane number and EPA soot emissions requirements at 20% blend volume. Combined distillation and hydrotreatment meet or exceed all fuel specification and engine performance benchmarks. Partially upgraded TDO oils are suitable fuel options for compression ignition applications.

42 ENGINEERING↗
DOE OSTI2026

Cost and Carbon Intensity Implications of Coprocessing Sustainable Aviation Fuel at Petroleum Refineries

Sustainable aviation fuel (SAF) will play a critical role in decarbonizing the aviation industry. Among SAF production pathways, alcohol-to-jet (ATJ) stands out for its scalability, supported by abundant feedstock availability and a well-established bioethanol industry. However, significant reductions in SAF carbon intensity (CI) require the use of future feedstocks (e.g., cellulosic) whose adoption is hindered by high capital costs for feedstock processing and ethanol upgrading. Here, we evaluate the financial viability and environmental implications of integrating an ATJ SAF biorefinery within a petroleum refinery, utilizing miscanthus and switchgrass as example feedstocks. Three scenarios are evaluated: standalone (benchmark), colocated, and repurposing (coprocessing SAF within the petroleum refinery). Results show repurposing reduces baseline capital costs by 36% and SAF minimum selling price (MSP) by 12% to 8.14 USD·gal −1 ; the superior performance of repurposing is consistent across both feedstocks. Integration has a limited effect on SAF CI, which remains stable across scenarios, whereas using cellulosic feedstocks reduces CI by over 70% relative to corn, with baseline values of 17.01 g CO 2 e· MJ −1 for miscanthus and 12.23 g CO 2 e·MJ −1 for switchgrass. Global sensitivity analysis reveals MSP declines with greater coprocessing levels.

09 BIOMASS FUELS↗
DOE OSTI2021

Effective Biomass Fractionation through Oxygen-Enhanced Alkaline–Oxidative Pretreatment

The high recalcitrance of plant cell walls is an obstacle for effective chemical or biological conversion into renewable chemicals and transportation fuels. Here, we investigated the utilization of both oxygen (O 2 ) and hydrogen peroxide (H 2 O 2 ) as co-oxidants during alkaline-oxidative pretreatment to improve biomass fractionation and increase enzymatic digestibility. The oxidative pretreatment of hybrid poplar was studied over a variety of conditions. Employing O 2 in addition to H 2 O 2 as a co-oxidant during the two-stage alkaline pre-extraction/copper-catalyzed alkaline hydrogen peroxide (Cu-AHP) pretreatment process resulted in a substantial improvement in delignification relative to using H 2 O 2 alone during the second-stage Cu-AHP pretreatment, leading to high overall sugar yields even at H 2 O 2 loadings as low as 2% (w/w of original biomass). The presence of H 2 O 2 , however, was both critical and synergistic. Performing analogous reactions in the absence of H 2 O 2 resulted in approximately 25% less delignification and a 30% decrease in sugar yields. Here, the lignin isolated from this dual oxidant second stage had high aliphatic hydroxyl group content and reactivity to isocyanate, indicating that it is a promising substrate for the production of polyurethanes. To test the suitability of the isolated lignin as a source of aromatic monomers, the lignin was subjected to a sequential Bobbitt’s salt oxidation followed by formic-acid catalyzed depolymerization process. Monomer yields of approximately 17% (w/w) were obtained, and the difference in yields was not significant between lignin isolated from our Cu-AHP process with and without O 2 as a co-oxidant. Thus, the addition of O 2 did not lead to significant lignin crosslinking, a result consistent with the two-dimensional heteronuclear single-quantum coherence (2D HSQC) NMR spectra of the isolated lignin.

09 BIOMASS FUELS↗
DOE OSTI2021

Substitution of distal and active site residues reduces product inhibition of E1 from Acidothermus Cellulolyticus

Abstract Cellulases are largely afflicted by inhibition from their reaction products, especially at high-substrate loading, which represents a major challenge for biomass processing. This challenge was overcome for endoglucanase 1 (E1) from Acidothermus cellulolyticus by identifying a large conformational change involving distal residues upon binding cellobiose. Having introduced alanine substitutions at each of these residues, we identified several mutations that reduced cellobiose inhibition of E1, including W212A, W213A, Q247A, W249A and F250A. One of the mutations (W212A) resulted in a 47-fold decrease in binding affinity of cellobiose as well as a 5-fold increase in the kcat. The mutation further increased E1 activity on Avicel and dilute-acid treated corn stover and enhanced its productivity at high-substrate loadings. These findings were corroborated by funnel metadynamics, which showed that the W212A substitution led to reduced affinity for cellobiose in the +1 and +2 binding sites due to rearrangement of key cellobiose-binding residues.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Effective Biomass Fractionation through Oxygen-Enhanced Alkaline-Oxidative Pretreatment

The high recalcitrance of plant cell walls is an obstacle for effective chemical or biological conversion into renewable chemicals and transportation fuels. Here, we investigated the utilization of both oxygen (O 2 ) and hydrogen peroxide (H 2 O 2 ) as co-oxidants during alkalineoxidative pretreatment to improve biomass fractionation and increase enzymatic digestibility. The oxidative pretreatment of hybrid poplar was studied over a variety of conditions. Employing O 2 in addition to H 2 O 2 as a co-oxidant during the two-stage alkaline pre-extraction/coppercatalyzed alkaline hydrogen peroxide (Cu-AHP) pretreatment process resulted in a substantial improvement in delignification relative to using H 2 O 2 alone during the second-stage Cu-AHP pretreatment, leading to high overall sugar yields even at H 2 O 2 loadings as low as 2% (w/w of original biomass). The presence of H 2 O 2 , however, was both critical and synergistic. Performing analogous reactions in the absence of H 2 O 2 resulted in approximately 25% less delignification and a 30% decrease in sugar yields. The lignin isolated from this dual oxidant second stage had high aliphatic hydroxyl group content and reactivity to isocyanate, indicating that it is a promising substrate for the production of polyurethanes. To test the suitability of the isolated lignin as a source of aromatic monomers, the lignin was subjected to a sequential Bobbitt’s salt oxidation followed by formic-acid catalyzed depolymerization process. Monomer yields of approximately 17% (w/w) were obtained, and the difference in yields was not significant between lignin isolated from our Cu-AHP process with and without O 2 as a co-oxidant. Thus, the addition of O 2 did not lead to significant lignin crosslinking, a result consistent with the twodimensional heteronuclear single-quantum coherence (2D HSQC) NMR spectra of the isolated lignin.

09 BIOMASS FUELS↗
DOE OSTI2020

In Vivo Thermodynamic Analysis of Glycolysis in Clostridium thermocellum and Thermoanaerobacterium saccharolyticum Using 13 C and 2 H Tracers

Clostridium thermocellum and Thermoanaerobacterium saccharolyticum are thermophilic anaerobic bacteria with complementary metabolic capabilities that utilize distinct glycolytic pathways for the conversion of cellulosic sugars to biofuels. We integrated quantitative metabolomics with 2 H and 13 C metabolic flux analysis to investigate the in vivo reversibility and thermodynamics of the central metabolic networks of these two microbes. We found that the glycolytic pathway in C. thermocellum operates remarkably close to thermodynamic equilibrium, with an overall drop in Gibbs free energy 5-fold lower than that of T. saccharolyticum or anaerobically grown Escherichia coli . The limited thermodynamic driving force of glycolysis in C. thermocellum could be attributed in large part to the small free energy of the phosphofructokinase reaction producing fructose bisphosphate. The ethanol fermentation pathway was also substantially more reversible in C. thermocellummthan in T. saccharolyticum. These observations help explain the comparatively low ethanol titers of C. thermocellum and suggest engineering interventions that can be used to increase its ethanol productivity and glycolytic rate. In addition to thermodynamic analysis, we used our isotope tracer data to reconstruct the T. saccharolyticum central metabolic network, revealing exclusive use of the Embden-Meyerhof-Parnas (EMP) pathway for glycolysis, a bifurcated tricarboxylic acid (TCA) cycle, and a sedoheptulose bisphosphate bypass active within the pentose phosphate pathway. Thermodynamics constitutes a key determinant of flux and enzyme efficiency in metabolic networks. Here, we provide new insights into the divergent thermodynamics of the glycolytic pathways of C. thermocellum and T. saccharolyticum, two industrially relevant thermophilic bacteria whose metabolism still is not well understood. We report that while the glycolytic pathway in T. saccharolyticum is as thermodynamically favorable as that found in model organisms, such as E. coli or Saccharomyces cerevisiae , the glycolytic pathway of C. thermocellum operates near equilibrium. The use of a near-equilibrium glycolytic pathway, with potentially increased ATP yield, by this cellulolytic microbe may represent an evolutionary adaptation to growth on cellulose, but it has the drawback of being highly susceptible to product feedback inhibition. The results of this study will facilitate future engineering of high-performance strains capable of transforming cellulosic biomass to biofuels at high yields and titers.

59 BASIC BIOLOGICAL SCIENCES↗