No abstract

Carbonic anhydrase (CA) was previously proposed as a green alternative for biomineralization of carbon dioxide (CO2). However, enzyme’s fragile nature when in synthetic environment significantly limits such industrial application. Herein, we hypothesized that CA immobilization onto flexible and hydrated “bridges” that ensure proton-transfer at their interfaces leads to improved activity and kinetic behavior and potentially increases enzyme’s feasibility for industrial implementation. Our hypothesis was formulated considering that water plays a key role in the CO2 hydration process and acts as both the reactant as well as the rate-limiting step of the CO2 capture and transformation process. To demonstrate our hypothesis, two types of user-synthesized organic metallic frameworks [metal–organic frameworks (MOFs), one hydrophilic and one hydrophobic] were considered as model supports and their surface characteristics (i.e., charge, shape, curvature, size, etc.) and influence on the immobilized enzyme’s behavior were evaluated. Morphology, crystallinity and particle size, and surface area of the model supports were determined by scanning electron microscopy, dynamic light scattering, and nitrogen adsorption/desorption measurements, respectively. Enzyme activity, kinetics, and stability at the supports interfaces were determined using spectroscopical analyses. Analysis showed that enzyme functionality is dependent on the support used in the immobilization process, with the enzyme immobilized onto the hydrophilic support retaining 72% activity of the free CA, when compared with that immobilized onto the hydrophobic one that only retained about 28% activity. Both CA–MOF conjugates showed good storage stability relative to the free enzyme in solution, with CA immobilized at the hydrophilic support also revealing increased thermal stability and retention of almost all original enzyme activity even after heating treatment at 70 °C. In contrast, free CA lost almost half of its original activity when subject to the same conditions. This present work suggests that MOFs tunable hydration conditions allow high enzyme activity and stability retention. Such results are expected to impact CO2 storage and transformation strategies based on CA and potentially increase user-integration of enzyme-based green technologies in mitigating global warming.

a b s t r a c tSeveral studies suggest that CO 2 -based geothermal energy systems may be operated economically when added to ongoing geologic CO 2 sequestration. Alternatively, we demonstrate here that CO 2 -Plume Geothermal (CPG) systems may be operated long-term with a finite amount of CO 2 . We analyze the performance of such CO 2 -limited CPG systems as a function of various geologic and operational parameters. We find that the amount of CO 2 required increases with reservoir depth, permeability, and well spacing and decreases with larger geothermal gradients. Furthermore, the onset of reservoir heat depletion decreases for increasing geothermal gradients and for both particularly shallow and deep reservoirs.

DOE NETL), the Japan Oil, Gas, and Metals National Corporation (JOGMEC), and the U.S. Geological Survey (USGS) successfully drilled and logged the Hydrate-01 Stratigraphic Test Well (STW) in the greater Prudhoe Bay oil field on the Alaska North Slope. The logging-while-drilling (LWD) data confirmed the presence of gas hydrate-bearing reservoirs within sand reservoirs in Units D and B that are suitable targets for future testing. The deeper "B1-sand" is considered to be the most favorable for reservoir response testing due the following factors: confirmed high gas hydrate saturation in sediments of high intrinsic permeability; isolated from direct communication with saline aquifers; and located in the proximity of the base of gas hydrate stability, thus allowing efficient gas hydrate decomposition by the depressurization method. The interpreted log data and side-wall core sample measurements were used to create reservoir models for the Prudhoe Bay Unit (PBU) Kuparuk 7-11-12 site. The vertical heterogeneity in porosity, gas hydrate saturation, irreducible water saturation, and permeability distributions for reservoir and nonreservoir units was implemented using fine mesh discretization. To induce gas hydrate destabilization, the depressurization of the B1 sand was carried out using scenarios with constant bottom hole pressure (BHP) and staged multistep decrease of BHP values. Three simulators, MH21-HYDRES, TOUGH+Hydrate, and CMG STARS were engaged to conduct various sensitivity cases to determine the impact of the lateral extension of the reservoir models, uncertainty in in situ reservoir permeability, and water influxes from seal on productivity. Water and gas production rates and volumes predicted using three simulators reveal overall agreement. At the most probable case, gas and water production rates of up to 2.6 MMSCF/day and 8000 fluid bbl/day, respectively, should be accounted for well test designs, surface facility requirements, and field test activities. The full consideration of the multiple cases and scenarios indicates significant uncertainty in simulation results due to uncertainties in key reservoir properties. This underscores the need for acquisition of extended duration production field test data as a means to clarify true reservoir potential.