Browsing by Subject "Biofuels"

Now showing 1 - 7 of 7
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    Biofuels and sustainable development: Perspectives on the farm and around the globe
    (2014-03) Sheehan, John Joseph
    The idea that biofuels can be sustainable has long been controversial. This research considers three land-related aspects of biofuels sustainability:1. The effect of local farm management practices on the sustainability of land used to produce corn grain as a biorefinery feedstock. 2. The relative sustainability of land used for producing corn and sugarcane as a function of latitude. 3. The land use implications for biofuels of global pasture-based livestock production systems. Local corn farm management choices can make the difference between net negative and net positive carbon footprints for grain delivered to biorefineries. Carbon footprints reported here are based on full life cycle assessments of each farm, including modeled soil emissions of greenhouse gases. For a cohort of farmers surveyed in southwest Minnesota, avoiding excess fertilizer use, adopting no till practices and replacing commercial fertilizer with animal manure leads to negative carbon footprints of up to -117 gCO2eq per ha. Globally, the choice of land managed for corn or sugarcane versus land maintained to support natural ecosystems is highly dependent on latitude. On average sugarcane produces three times more energy per unit area than does maize. Latitudes closer to the equator have higher net primary productivity (NPP), so there is a greater trade-off between biofuel production and ecosystem productivity in the equatorial zones. Sugarcane is still twice as productive on average compared to maize in the amount of biofuel energy produced per unit of NPP. Global pasture systems could reduce their land footprint by several-fold simply by closing the gap between poor performing and high performing pasture systems across climatically-similar parts of the world. Because pasture's global land footprint is so large, closing the performance gap could make vast amounts of land available for biomass feedstocks, with no new land clearing.
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    Describing The Catalytic Role Of Alkaline Earth Metals On The Thermal Activation Of Cellulose
    (2020-05) Facas, Gregory
    Biomass fast pyrolysis has considerable potential for the production of renewable fuels and chemicals. Despite pyrolysis being studied for more than a hundred years, only a few commercial pyrolysis processes exist as the optimal feedstock composition and reaction conditions for this process remain unknown. The lack of process optimization can be attributed to the multiscale complexity of the process. During pyrolysis the constituents of biomass are fragmented in a matter of seconds through thousands of chemical reactions, that occur in multiple phases, and are simultaneously competing with various heat and mass transfer processes. All of these fundamental phenomena are understood poorly within pyrolysis literature. Pyrolysis is further complicated by alkali and alkaline earth metals that are naturally present in lignocellulosic biomass. These metals are known to alter pyrolysis chemistry and catalyze the initial breakdown of the polymer constituents of biomass. The main objective of this thesis was to investigate the mechanistic role of alkaline earth metals on the initial fragmentation of cellulose, the main component of biomass. Fundamental knowledge into pyrolysis chemistry has been limited previously due to an inability to obtain intrinsic kinetic, a critical tool used to validate reaction mechanisms. The requirements for proper measurement of high temperature (>400 °C) biomass pyrolysis kinetics are presented. Most importantly, these requirements mandate that for proper measurement of kinetic data, experimental techniques must heat and cool reaction samples sufficiently fast to elucidate the evolution of reaction products with time, while also eliminating substantial reaction during the heating and cooling phases. The ability of the PHASR (Pulse Heated Analysis of Solid Reactions) micro-reactor technique and other common pyrolysis reactor techniques to satisfy these requirements was discussed. PHASR can thoroughly satisfy all the requirements for measuring pyrolysis kinetics unlike other conventional reactor techniques. The PHASR technique was then utilized to study the kinetics of calcium assisted activation of cellulose. Conversion of calcium doped films of α-cyclodextrin, a known cellulose surrogate, was measured over a range of reaction temperatures (370-430 °C) and calcium concentrations (0.1-0.5 mmol Ca2+/g CD). The rate of conversion of α-cyclodextrin was significantly accelerated by the presence of calcium. Activation was shown to have a second order rate dependence on calcium concentration, suggesting the involvement of two calcium ions in the mechanism. First principle density functional theory calculations were performed on calcium catalyzed glycosidic bond cleavage and depict calcium as having two catalytic roles of disrupting hydrogen bonding in the cellulose matrix and stabilizing the transition state. The energetics from experiment and computations agree closely representing the first atomistic mechanism of metal catalyzed activation utilizing both experiments and computations. Kinetics of magnesium assisted activation were then measured with PHASR experiments to discern any effects from the size of the catalytic ion on activation chemistry. PHASR experiments were performed in identical temperature and metal concentrations to the calcium experiments. Magnesium assisted activation exhibited identical behavior to the calcium case with energetics of activation matching within experimental error.
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    Enabling Distributed Renewable Energy and Chemical Production through Process Systems Engineering
    (2018-12) Allman, William
    New renewable energy technologies offer the promise of preserving a sustainable energy supply for future generations. Coupling chemical production with renewable energy production can help to address many of the challenges associated with the large-scale implementation of renewable energy, including short time scale variability of electricity production, potential mismatch of supply and demand, and energy stranded in areas of low population density. However, such co-production systems necessitate considering chemical production at scales smaller than what is typically seen in today's infrastructure due to the geospatially dispersed nature of renewable energy resources. This small scale production is economically prohibitive due to economies of scale, which promote building large scale facilities whenever possible. These economic challenges motivate the use of process systems engineering to develop decision making frameworks which minimize the costs of building and operating new renewable energy and chemical production systems. The application of process systems engineering methods to systems producing renewable energy and chemicals presented in this thesis centers around three major themes. First, decomposition, an approach which breaks down large optimization problems into smaller, easier to solve subproblems, is used to solve a challenging problem which finds the optimal design of a combined biorefinery and microgrid system. By doing so, hydrogen production is identified as a critical cost bottleneck in the combined system design. A method for automatically finding subproblems for decomposition for a broad class of optimization problems is also presented. Second, a framework is proposed for considering where new facilities should be built within an existing chemical supply chain. Here, policies and market conditions, such as a carbon tax, are identified that can have a strong effect on reducing emissions from ammonia production. Finally, the connection between the optimal design and operation of renewable energy and chemical systems is analyzed. Here, a framework which determines operating strategies which minimize cost is developed, and the optimal operation of a wind-powered ammonia system in different electricity market structures is analyzed. This framework is used to generate correlations between system design and operating cost which are embedded in a design optimization problem to improve solution efficiency.
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    Managing conservation grasslands for bioenergy and wildlife
    (2014-02) Jungers, Jacob Michael
    Greenhouse gas emissions continue to rise while native grassland habitat continues to decline. A potential solution to both of these conservation priorities may exist in bioenergy. Various state and federal agencies maintain tracts of conservation grasslands, usually native perennial plants, for recreation and habitat. If biomass from conservation grasslands can be harvested without harming habitat and wildlife, then sales of grassland biomass to bioenergy producers may be the economic catalyst to expand conservation grassland acreage. This dissertation reports the bioenergy potential of conservation grasslands, how that potential can be improved, and possible effects of biomass harvest on grassland plants, ducks, and pheasants. Chapter one quantifies the bioenergy potential of biomass from conservation grasslands and identifies environmental characteristics that influence that potential. Chapter two reports an agronomically optimum nitrogen fertilization rate to increase bioenergy yields from switchgrass (Panicum virgatum) and mixed-species grasslands. Chapter three summarizes the effects of biomass harvest on plant diversity and species composition. Chapter four relates plant diversity and composition to duck and pheasant nest density and survival, and measures the effect of biomass harvest on both metrics of reproduction. Some major conclusion include: (1) Estimates of bioenergy potential suggest that 50% of the conservation grassland acreage within an 80 km radius of southwestern Minnesota could produce 75,700,000 liters of ethanol annually. (2) On average, bioenergy yields are predicted to increase by 52% when fertilized with agronomically optimum nitrogen rates ranging from 61 to 87 kg N ha-1. (3) Biomass harvest did not affect plant species richness, species or functional group diversity, nor change the relative abundance of the main plant functional groups in conservation grasslands. (4) Pheasant and duck nest success rates were similar in harvested and unharvested regions of conservation grasslands, but nest density was greater in unharvested regions. Overall, a substantial amount of renewable energy can be produced from harvested conservation grassland biomass without detrimental effects on plant communities or nesting pheasants and ducks.
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    Optimal supply chain and product design of biofuels
    (2013-08) Marvin, William Alexander
    Growth of a biomass-to-biofuels industry has the potential to reduce oil imports, support agriculture and forestry growth, foster a domestic biorefinery industry, and reduce greenhouse gas emissions compared to gasoline. Successful development of biofuels involves Process Systems Engineering challenges at various scales, including elucidation of complex chemical systems for upgrading biomass in terms of mechanisms, kinetics and thermochemistry, design of novel reactors and reactor networks, synthesis and optimization of novel process flow sheets, and supply chain optimization at the enterprise level. None of these aspects exist in isolation; each choice impacts the others and has an important role in the overall economic potential. The aim of this thesis has been to approach these multi-scale challenges by developing optimization models for biofuel supply chain and product design problems, specifically mixed integer linear programs. The biofuel supply chain optimization problems were formulated to determine economical and environmentally efficient biomass processing facility locations and capacities, simultaneously with biomass harvest and distribution. Focus was put on the production of biofuels in the Midwestern United States from grain, agricultural residues, energy crops and wood resources, and the feasibility of meeting governmental biofuel mandates in 2015. The product design problem investigated was for the production of blended gasoline with biomass-derived components. The strategy consists of i) constructing an exhaustive network of reactions consistent with an input set of chemistry rules and ii) using the network information to formulate and solve an optimization problem that yields an optimal product distribution and the sequence of reactions that synthesize them. This was applied to identify potential renewable oxygenates and hydrocarbons obtained from heterogeneous catalysis of biomass that can be blended with gasoline to satisfy ASTM specifications.
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    Responses of songbirds and small mammals to harvests of native grasslands for biofuels in Western Minnesota
    (2014-01) Dunlap, Robert Michael
    Some grassland birds and small mammals exhibit changes in abundance following vegetation removal in the previous year, but it is unknown to what extent these organisms respond to harvests of diverse, native grasslands. This thesis examines the effects of harvesting such grasslands on songbirds and small mammals, representing an important step in evaluating the conservation value of grasslands used for biofuel harvest. I analyzed abundance data collected from area-based bird surveys in grassland biofuel plots harvested via different pattern and percentage in western Minnesota, USA, from 2009 to 2013 (Chapter 1). Small mammal trapping was conducted in the same plots from 2009 to 2012, and abundance and occupancy data collected from these surveys was also analyzed (Chapter 2). I estimated relative abundance of 11 species of grassland birds and 7 species/genera of small mammals among the different harvest intensities and years of study. Four bird species and species richness showed declines in abundance following harvests, whereas two species showed increases in abundance. Harvests also resulted in negative impacts on two small mammals. The removal of vegetation in fall results in shorter, less dense vegetation the following spring, which creates largely unsuitable habitat for tall-grass songbirds (e.g., sedge wren) but more optimal habitat for species that prefer shorter vegetation (e.g., grasshopper sparrow). Additionally, the reduction in ground litter is detrimental to small mammals that prefer thicker vegetation (e.g., voles of the genus Microtus). At the community level, harvesting native grasslands appears to have little impact on grassland birds and small mammals, but it is nonetheless important to identify what species are present prior to harvesting so that harvesting activities do not result in detriment to these species.