Bioenergy crops have attracted increasing interest over the last two decades as their potential to 1) improve national energy security, 2) substitute finite fuels with renewable alternatives, 3) reduce carbon (C) intensity of energy generation, and 4) remove CO2 from the atmosphere and sequester it in soils. In light of climate change predominantly caused by rising atmospheric greenhouse gas concentrations, the potential importance and value of bioenergy cannot be underestimated. This research used data from a single site in Lincolnshire, UK, in combination with new experimental techniques to examine the C dynamics associated with Miscantus x giganteus. The net C budgets were examined using long term eddy-covariance data alongside measurements of C stocks within the soil and litter layer. Results indicated that using a cradle-to-grave lifecycle analysis, and based on the productivity of this site, Miscanthus as an energy feedstock was marginally better than coal but more C intensive than natural gas. Further, soil C stocks were not seen to change significantly over the first 7 years of cropping. Consequently, a combination of soil fractionation and in combination with natural abundance stable C isotope techniques allowed rates of soil C gain or loss to be estimated over time. Soil C was observed to accumulate at fast rates in stable fractions, those that relate to model pools with turnover times well beyond the lifetime of a Miscanthus plantation – a result not predicted by model simulations performed with the systems models ECOSSE and DayCent. A review of six models parameterised for Miscanthus showed a number of factors that contribute to model uncertainty. The results from this thesis are a crucial first step to helping to define model parameters and improve model performance, and therefore to accurately predict the impacts of Miscanthus on C sequestration in a given location for given environmental conditions.

Carbon dioxide capture and storage will be necessary to mitigate the effects of global climate change. Mineral carbonation - converting carbon dioxide gas to carbonate minerals - is a permanent and environmentally benign mechanism for storing carbon dioxide. The peridotite section of the Samail Ophiolite is host to exceptionally well-developed, naturally occurring mineral carbonation and serves as a natural analog for an engineered carbon dioxide storage project. This work characterizes the geochemistry and hydrogeology of peridotite aquifers in the Samail Ophiolite. Water samples were collected from hyperalkaline springs, surface waters, and boreholes in peridotite, and recent mineral precipitates were collected near hyperalkaline springs. Samples were analyzed for chemical composition. Geochemical data were used to delineate water-rock-CO₂ reactions in the subsurface and constrain a reaction path model for the system. This model indicates that mineral carbonation in the natural system is limited by the amount of dissolved carbon dioxide in water that infiltrates deep into the aquifer. The amount of carbon dioxide stored in the system could potentially be enhanced by carbon dioxide injection into the aquifer. Reaction path modeling suggests that injection of water at saturation with carbon dioxide at 100 bars pCO₂ and 90⁰C could increase the carbonation rate by a factor of up to 16,000 and bring carbonation efficiency to almost 100%. Dissolved gas samples from boreholes were collected at in situ conditions and analyzed for chemical composition. Boreholes with pH > 10 contain millimolar levels of dissolved hydrogen and/or methane, indicating these boreholes are located near areas of active low temperature serpentinization. Serpentinization rates were calculated using groundwater flow estimates and dissolved gas concentrations, and range from 3x10⁻⁸ to 2x10⁻⁶ volume fraction peridotite serpentinized per year. Additionally, laboratory incubation experiments show dissolved hydrogen can be stored in sealed copper tubes for at least three months with neither diffusive loss nor production of hydrogen from oxidation of the copper. These experiments demonstrate that copper tubes can be practical containers for collecting and storing dissolved hydrogen in freshwater. Groundwater ages in the peridotite section of the Samail Ophiolite are investigated through analysis of tritium, dissolved noble gases, and stable isotopes. Tritium-³Helium dating was used to estimate the age of modern groundwaters (< 60 years old), and helium accumulation was used as relative age indicator for pre-bomb groundwaters (> 60 years old). Waters with pH < 9.3 have ages from 0-40 years, while waters with pH > 9.3 are all more than 60 years in age. Helium accumulation indicates pH < 10 waters contain only atmospheric and tritiogenic helium, while pH > 10 waters have accumulated 30-65% of their helium from radiogenic production or mantle helium. pH > 10 waters are thus significantly older than pH < 10 waters. Noble gas temperatures are generally around 32⁰C, close to the current mean annual ground temperature. One hyperalkaline borehole has noble gas temperatures 7⁰C cooler than the modern ground temperature, indicating the water at that site may have recharged during a glacial period. Stable isotope data (Δ¹⁸O and Δ²H) for waters with pH < 11 plot between the northern and southern local meteoric water lines, in the typical range for modern groundwater. Hyperalkaline boreholes and springs are enriched in Δ¹⁸O, which suggests they recharged when the southern vapor source dominated, perhaps during glacial periods. Lastly, the potential for in situ mineral carbonation in peridotite is investigated through reactive transport modeling of dissolved CO₂ injection into a peridotite aquifer. Injection was simulated at two depths, 1.25 km and 2.5 km, with reservoir conditions loosely based on the peridotite section of the Samail Ophiolite. The dependence of carbonation extent (mass of carbon dioxide sequestered as carbonate minerals per unit volume) on different factors - such as permeability, reactive surface area, and temperature - was explored. Carbonation extent is strongly controlled by reactive surface area (RSA), with geometric RSA models producing 10 to 770 times more carbonation than conservative RSA models with the same initial permeabilities and temperatures. The ratio of carbon dioxide supply to RSA is also a key factor. The ideal relationship between CO₂ supply and RSA appears to be from 5x10⁻⁴ to 0.2 kg CO₂ /day per m²/m³ RSA. Temperature has also has an impact on carbonation rate: for the same initial permeability, carbonation is 7-35% faster at 90⁰C than at 60⁰C. Simulations of a 50-year carbon dioxide injection show that fracture porosity and permeability do not become overly clogged and carbonation continues at a more or less constant rate. We estimate that one dissolved CO₂ injection well in peridotite could store 1.4 Mtons CO₂ in 30 years with a storage cost of $6/ton. This suggests that an engineered carbon dioxide storage project in peridotite could be both feasible and economical. In situ mineral carbonation in peridotite should continue to be investigated as a safe and permanent mechanism for carbon dioxide storage.

In order to address the global challenges of climate change caused by the increasing concentration of carbon dioxide (CO2), Carbon Capture, Utilization and Storage (CCUS) has been proposed as a promising strategy in carbon management. In parallel with the target of zero emission in fossil-fired power plants, negative emission has also drawn a great deal of attention in other chemical sectors, including cement making and steel production industries. Thanks to the recent reduction in the cost of renewable energy sources, such as wind and solar, a paradigm shifting concept has emerged to directly convert the captured carbon into chemicals and fuels. In this way, decarbonization in various chemical sectors can be achieved with a reduced carbon footprint. A variety of carbon dioxide conversion pathways have been investigated, including thermochemical, biological, photochemical, electrochemical and inorganic carbonation methods. Electrochemical conversion of carbon dioxide has been thoroughly investigated with great progress in electrocatalysts and reaction mechanisms. However, fewer studies have been taken to tackle the constraint of the low solubility of CO2 in conventional aqueous electrolytes. In an effort to improve the solubility of CO2, various novel electrolytes have been designed with a higher uptake of CO2 and a compatibility with electrochemical conversion, including Nanoparticle Organic Hybrid Materials (NOHMs)-based fluids. NOHMs are a unique liquid-like nanoscale hybrid material, comprising of polymers grafted onto nanoparticles (e.g., silica). NOHMs have demonstrated an excellent thermal stability and a high chemical tunability. Two types of NOHMs with ionic bonding (I) between the polymers and nanoparticles were selected in this study: NOHM-I-PEI incorporating polyethylenimine polymer (PEI) and NOHM-I-HPE consisting of polyetheramine polymer (HPE), illustrative of two modes of carbon capture (e.g., chemisorption and physisorption). The NOHMs-based fluids were synthesized with different secondary fluids and salt to tune the viscosity and conductivity. As the first liquid hybrid solvent system for combined carbon capture and conversion, the physical, chemical and electrochemical properties of NOHMs-based fluids were systematically investigated. It was found that NOHMs-based aqueous fluids have exhibited a lower specific heat capacity than that of the 30 wt.% monoethanolamine (MEA) solvents. In addition, upon CO2 loading, the increase in specific heat capacity and the reduction of the viscosity of the NOHM-I-PEI based aqueous fluids can be attributed to the formation of intra-molecular hydrogen bonds. The different chemistries of the two NOHMs can be reflected by the viscosity-based mixing behavior. The smaller critical concentration and the higher intrinsic viscosity of NOHM-I-HPE based aqueous fluids implied a more significant contribution of viscosity to the system by the addition of NOHM-I-HPE. The viscosity of NOHM-I-HPE (30 wt.%) in water was measured to be 395 cP, an order of magnitude higher than that of NOHM-I-PEI (30 wt.%) in water, which was determined to be 22.6 cP. It was also discovered that the addition of N-methyl-2-pyrrolidone (NMP) has resulted in a dramatic increase of the viscosity of NOHM-I-PEI based aqueous fluids, hypothesized to be due to a possible formation of a complex between NMP and NOHM-I-PEI. On the other hand, the presence of 0.1 M potassium bicarbonate (KHCO3) salt greatly reduced the viscosity of NOHM-I-HPE based aqueous fluids. The electrochemical properties of NOHMs-based fluids were also characterized and an excellent electrochemical stability has been demonstrated. The conductivities of NOHMs-based fluids witnessed an unexpected enhancement from the corresponding untethered polymer-based solutions. At 50 wt.% loading, the conductivity was 15 mS/cm for NOHM-I-PEI based aqueous fluids doped by 1 M bis(trifluoromethylsulfonyl)amine lithium salt (LiTFSI), while it was 0.91 mS/cm for PEI based aqueous solutions. Even after the viscosities of the two solutions were converted to the same value, there was still a large gap between the conductivities of the NOHMs-based fluids and polymer-based fluids. The relative tortuosity of ion transport in NOHMs-based fluids compared to untethered polymer-based solutions was less than 1. This result was indicative of a shorter pathway of ion transport in NOHMs-based fluids than in polymer-based fluids. Thus, it is suggested that in addition to a viscosity effect, unique multi-scale structures were also formed, enabling an enhanced ion transport in the NOHMs-based fluids. With this hypothesis, ultra-small-angle X-ray scattering (USAXS) technique was utilized to construct the structures of NOHMs morphology in secondary fluids, from agglomerates at large scale to aggregates at mid-scale, and to the interparticle distance at small scale. The sizes of the aggregates and the interparticle distance were highly tunable by varying the concentrations of NOHMs, and the types of NOHMs and secondary fluids. For example, the aggregate size was (32.30 ± 0.3) nm and (153.9 ± 1.5) nm for 50 wt.% loading of NOHM-I-PEI and NOHM-I-HPE in mPEG, respectively. This hierarchical structure was hypothesized to give ions unique channels and pathways to migrate, resulting in the surprising conductivity enhancement. Cryogenic electron microscopy (CryoEM) was also employed to image such multi-scale fractal structures. The diffusion behavior under this hierarchical structure was studied subsequently. To our surprise, in certain NOHMs-based fluids, such as 10 wt.% NOHM-I-HPE in water at 25℃, the diffusion coefficient of water was 3.43×(10)^(-9) m2/s, higher than that of deionized water, 2.99×(10)^(-9) m2/s. This is evident of the channels created by NOHMs in the secondary fluids to allow faster local diffusion of water and ions. Meanwhile, the diffusion coefficient of NOHM-I-HPE was higher with the presence of 0.1 M KHCO3 salt compared to the salt-free case in water. Though counter-intuitive, this was because salt would interact with the ionic bonding sites of NOHMs, facilitating the dynamic hopping of polymers on the nanoparticle surface, and thus improving the fluidity of the NOHM-I-HPE based aqueous fluids. This investigation of multi-scale structures and diffusion behavior of NOHMs-based fluids was insightful in understanding how the ions move in the system, and in explaining the enhanced conductivity of NOHMs-based fluids compared to the corresponding untethered polymer-based solutions. It is believed that ions move in two regions of the NOHMs-based fluids, the NOHMs-rich region and secondary fluids-rich region, in the mechanisms of translational movement, and coupled and decoupled ion migration with structural relaxation of NOHMs and secondary fluids. With the understanding of the fundamental properties and the construction of hierarchical structures, the carbon capture performance was evaluated for NOHMs-based fluids. The carbon capture behavior can be tuned by the concentration of NOHMs, and the presence of salt and physical solvents. The carbon capture kinetics was determined by both the amount of the capture material and the viscosity of the fluids. It was determined that 30 wt.% NOHM-I-PEI based aqueous fluids exhibited an optimal balance between capture capacity and sorption kinetics. As the concentration of NOHMs further increased, the elevated viscosity of the system limited the mass transfer of carbon capture. It was also found that salt induced a minimal impact on carbon capture in the initial 100 min for 5 wt.% NOHMs loading, but would negatively impact the capture capacity and kinetics at higher NOHMs loadings. Meanwhile, the addition of physical solvent (NMP) reduced carbon capture capacity and kinetics. Various existing forms of CO2 have been identified in NOHMs-based fluids, including carbamate, bicarbonate, and physisorbed CO2. Carbamate came from the reaction between CO2 and the amine functional groups on NOHM-I-PEI. Physisorbed CO2 was identified as the electroactive species for electrochemical conversion of CO2. In the combined carbon capture and conversion experiments using 5 wt.% NOHM-I-HPE based aqueous electrolyte, carbon monoxide (CO) production was enhanced on polycrystalline silver by 60%, and selectivity was changed on a pyridinic-N doped carbon-based electrode, in comparison with conventional 0.1 M KHCO3 electrolyte. The roles of NOHMs in carbon capture and conversion were also explored. The addition of NOHMs was able to improve the solubility of CO2 with a tunable pH change. It is hypothesized that NOHMs can complex with the electrochemical reaction species,CO2 (CO2^-), and this complex formation can be tunable by the concentration and types of NOHMs. In the end, an alternative approach of utilizing NOHMs-based fluids has also been proposed through encapsulation. The encapsulation of NOHMs-based fluids has enabled a higher specific surface area for CO2 uptake, and an enhancement in capture kinetics has been observed compared to the non-encapsulated NOHMs-based fluids. In summary, a novel nanoscale hybrid solvent system has been developed for combined carbon capture and conversion. The insight into the chemistry of this hybrid solvent system is not beneficial to the advancement in carbon capture and conversion, but it is also enlightening for the interdisciplinary development of various areas involving nanoscale hybrid materials.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 129-137).

Thesis (M.E.S.)--York University, 2001. / Typescript. Includes bibliographical references (leaves 172-183). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ71712.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 62-77). Also available on the World Wide Web.

Carbon capture, utilization and storage (CCUS) aims to reduce CO₂ emissions by capturing CO₂ from sources and injecting it into geologic reservoirs for enhanced hydrocarbon recovery and storage. One concern is that unintentional CO₂ and reservoir gas release to the surface may occur through seepage pathways such as fractures and/or improperly plugged wells. We hypothesize that CO₂ and CH₄ migration into the vadose zone and subsequent O₂ dilution and Eh and pH changes could create an increased potential for metal mobilization, which could potentially contaminate ground and surface waters. This potential has not been addressed elsewhere. Goals of this study are to understand how the potential for metal mobilization through soil pore water may increase due to CO₂ and CH₄ and to assess potential impact to aquifers and/or the biosphere. The study was conducted at a CCUS site in Cranfield, MS, where localized seepage of CH₄ (45%) from depth reaches the surface and oxidizes to CO₂ (34%) in the vadose zone near a plugged well. Four sediment cores (4.5-9m long) were collected in a transect extending from a background site through the area of anomalously high soil gas CO₂ and CH₄ concentrations. Sediment samples were analyzed for Eh and pH using slurries (1:1 vol. with DI water) in the field and for occluded gas concentrations, metal (Ba, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) concentrations, moisture content, organic carbon content, and grain size in the laboratory. Data from the background reference area (no gas anomaly: occluded gas ~21% O₂, <1% CO₂, 0% CH₄) showed oxidized conditions (Eh from 464-508mV) and neutral pH (7.0-7.8) whereas samples collected near the gas anomaly (13-21% O₂, 0.1-5% CO₂, <0.1% CH₄) were more reducing (Eh 133-566mV) and more acidic (pH = 5.3-8.0). Significant correlations were found between Eh and O₂ (r = 0.95), pH and CO₂ (r = -0.88), and between these parameters and acid-leachable metals in samples from within the soil gas anomaly. Correlations quickly weaken away from the anomaly. Statistically, total metal concentrations, except for Ba, are similar in all cores. Acid-mobile metal concentrations, above 5m, increase toward the gas anomaly. The percent of water-mobile metals is very low (<2%) for all metals in all cores, indicating freely-mobile metals are not affected by elevated CO₂/CH₄. Conclusions are: 1) oxidation of CH₄ to CO₂ depletes O₂ causing reducing conditions; 2) high CO₂ and low O₂ affect Eh and pH of sediments which in turn alters mineralogy and bond strength between sediments and adsorbed ions; 3) intrusion of strongly acidic fluids (pH of acid used was 0.39) into these sediments could potentially remove weakly bonded metals or dissolve minerals. Implications from this study are that Eh needs to be considered along with pH when analyzing contamination potential, and that exposure of sediments to reducing, followed by acidic conditions, increases the potential for metal mobilization in the vadose zone. More research is needed to determine the concentration of gases (CO₂, CH₄ and O₂) that will create Eh and pH levels that could affect the mineralogy and sorption mechanism potentially leading to metal mobilization. Methods for assessing potential metal mobilization may be useful for site characterization and risk assessment. / text

The Cranfield field, located in southwest Mississippi, is an enhanced oil recovery and carbon sequestration project that has been under a continuous supercritical CO₂ injection by Denbury Onshore LLC since 2008. Two 3D seismic surveys were collected in 2007, pre-CO₂ injection, and in 2010 after > 2 million tons of CO₂ was injected into the subsurface. The goal of this study is to characterize a time-lapse response between two seismic surveys to understand where injected CO₂ is migrating and to map the injected CO₂ plume edge. In order to characterize a time-lapse response, the seismic surveys were cross equalized using a trace-by-trace time shift. A normalized root-mean-square (NRMS) difference value was then calculated to determine the repeatability of the data. The data were considered to have “good repeatability,” so a difference volume was calculated and showed a coherent seismic amplitude anomaly located through the area of interest. A coherent seismic amplitude anomaly was also present below the area of interest, so a time delay analysis was performed and calculated a significant added velocity change. A Gassmann-Wood fluid substitution workflow was then performed at two well locations to predict a saturation profile and observe post-injection expected changes in compressional velocity values at variable CO₂ saturations. Finally, acoustic impedance inversions were performed on the two seismic surveys and an acoustic impedance difference volume was calculated to compare with the fluid substitution results. The Gassmann-Wood fluid substitution results predicted smaller changes in acoustic impedance than those observed from acoustic impedance inversions. At the Cranfield field, time-lapse seismic analysis was successful in mapping and quantifying the acoustic impedance change for some seismic amplitude anomalies associated with injected CO₂. Additional well log data and refinement of the fluid substitution workflow and the model-based inversion performed is necessary to obtain more accurate impedance changes throughout the field instead of at a single well location. / text

The injection operator for a carbon dioxide sequestration project must control the reservoir and associated pore space within the project boundaries to allow for orderly development of the storage facility. A large number of interest owners within a project area is likely to make reaching unanimous agreement among all owners of pore space unlikely, and thus control of the reservoir difficult. In order to facilitate geologic sequestration of carbon dioxide on privately owned land in the United States, or on land for which the minerals or pore space are privately owned, a scheme for aggregating the ownership of pore space is needed. To allow geologic sequestration projects to move forward with less than unanimous consent of interest owners, states can employ various methods of aggregating pore space ownership. This paper examines oil and gas unitization statues and statutes creating groundwater districts to find legislative regimes useful for achieving pore space ownership aggregation. Among the approaches discussed, aggregation of pore space ownership through a unitization model is the most likely choice. Taking that one step further and setting up new unit operating agreements for enhanced oil recovery to serve as a repository for incremental geologic sequestration, and eventual full sequestration activities, provides a firm path toward reducing carbon dioxide emissions while respecting property rights. This paper also compares the few existing pore space aggregation statutes in the United States, which achieve aggregation of pore space ownership through either unitization or eminent domain. The state that appears to be the best equipped to deal with aggregation of pore space ownership is Wyoming. Wyoming has been a leader in developing legislation to deal with pore space ownership before other states. North Dakota and Utah are also very well situated to move forward with carbon sequestration activities. / text

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