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Direct air capture (DAC) of CO2 is becoming increasingly important for reducing greenhouse gas concentrations in the atmosphere. However, the cost and energy requirements associated with DAC make it less economically feasible than carbon capture from flue gases. While various methods like solid sorbents and gas–liquid absorption have been explored for DAC, membrane processes have only recently been investigated. The objective of this study is to examine the separation performance of a membrane unit for capturing CO2 from ambient air. The performance of a membrane depends on several factors, including the composition of the feed gas, pressure ratio, material selectivity, and membrane area. The single‐stage separation process with the co‐current flow and constant permeability flux model is evaluated using a commercial module integrated with a process simulator to separate a binary mixture of carbon dioxide and nitrogen to assess the sensitivity of selectivity on purity and recovery of CO2 in permeate, and power requirement. Additionally, three levels of CO2 reduction from the feed stream to the retentate stream (25%, 50%, and 75%) are studied. A trade‐off between purity and recovery factor is observed, and achieving high purity in permeate requires high concentration in the retentate. [ABSTRACT FROM AUTHOR]

The solvent scrubbing method is one of the promising technologies to capture CO2 from flue gas. In this technology, CO2 is absorbed from flue gas using a liquid solvent in an absorption column and subsequently, solvent and CO2 are separated in a stripper column. The recovered solvent from the stripper unit is recycled to an absorption unit along with the makeup of the fresh solvent. Aqueous monoethanolamine (MEA) is widely used as the solvent in this method. The cost of solvent for continuous makeup in the absorber is one of the major operating costs. The goal of this study is to minimize the flow rate of the MEA stream to capture the specified amount of CO2 from flue gas to reduce the operating cost. Various scenarios are simulated in commercial process plant simulator by varying the CO2 loading in lean MEA stream and absorber height. Flue gas compositions are obtained from the Rocky Mountain Hunter Power Plant (coal-fired), Utah, USA. We have shown that more than 80% CO2 is captured using absorber heights of 25–40 m and CO2 loading in MEA of 0.2 and less using the minimum flow rate of MEA. An insignificant amount of MEA (<0.2%) is lost from the absorption and stripper units. Other than the purchasing cost of the solvent, operating costs related to pumping, cooling, handling, etc. can be significantly reduced using the method developed in this study. [ABSTRACT FROM AUTHOR]

The pressure-driven flow of long-chain hydrocarbons in nanosized pores is important in energy, environmental, biological, and pharmaceutical applications. This paper examines the flow of hexane, heptane, and decane in carbon nanotubes (CNTs) of pore diameters 1–8 nm using molecular dynamic simulations. Enhancement of water flow in CNTs in comparison to rates predicted by continuum models has been well established in the literature. Our work was intended to observe if molecular dynamic simulations of hydrocarbon flow in CNTs produced similar enhancements. We used the OPLS-AA force field to simulate the hydrocarbons and the CNTs. Our simulations predicted the bulk densities of the hydrocarbons to be within 3% of the literature values. Molecular sizes and shapes of the hydrocarbon molecules compared to the pore size create interesting density patterns for smaller sized CNTs. We observed moderate flow enhancements for all the hydrocarbons (1–100) flowing through small-sized CNTs. For very small CNTs the larger hydrocarbons were forced to flow in a cork-screw fashion. As a result of this flow orientation, the larger molecules flowed as effectively (similar enhancements) as the smaller hydrocarbons. [ABSTRACT FROM AUTHOR]

A novel semianalytical production predictive tool for tight reservoirs based on the application of material balance on a transient linear flow system is developed in this paper. This method considers two important regions during transient production of oil reservoirs: the saturated region where gas evolves and flows with oil, and the undersaturated region where only oil flows. A zonal moving boundary approach is used to evolve the two regions as the reservoir pressure gradually decreases. A semianalytical method is used to calculate pressures in the various regions and volumetric expansions. For both black oil and volatile oil scenarios, calculations from this analytical framework are able to match reservoir pressures, oil and gas rates, and cumulative gas–oil ratios determined using a reservoir simulator. The model was also applied to wells in tight reservoirs around the United States such as the Bakken (ND) and the Eagle Ford (TX) with reasonable success. [ABSTRACT FROM AUTHOR]

Advances in imaging have made it possible to view nanometer and sub-nanometer structures that are either synthesized or that occur naturally. It is believed that fluid dynamic and thermodynamic behavior differ significantly at these scales from the bulk. From a materials perspective, it is important to be able to create complex structures at the nanometer scale, reproducibly, so that the fluid behavior may be studied. New advances in nanoscale-resolution 3D-printing offer opportunities to achieve this goal. In particular, additive manufacturing with two-photon polymerization allows creation of intricate structures. Using this technology, a creation of the first nano-3D-printed digital (shale) rock is reported. In this paper, focused ion beam-scanning electron microscopy (FIB-SEM) nano-tomography image dataset was used to reconstruct a high-resolution digital rock 3D model of a Marcellus Shale rock sample. Porosity of this 3D model has been characterized and its connected/effective pore system has been extracted and nano-3D-printed. The workflow of creating this novel nano-3D-printed digital rock 3D model is described in this paper. [ABSTRACT FROM AUTHOR]

Nanoconfined water plays a pivotal role in a vast number of fields ranging from biological and materials sciences to catalysis, nanofluidics and geochemistry. Here, we report the freezing and melting behavior of water (D2O) nanoconfined in architected silica-based matrices including Vycor glass and mesoporous silica SBA-15 and SBA-16 with pore diameters ranging between 4–15 nm, which are investigated using differential scanning calorimetry and 2H nuclear magnetic resonance spectroscopy. The results provide compelling evidence that the extreme dynamical heterogeneity of water molecules is preserved over distances as small as a few angstroms. Solidification progresses in a layer-by-layer fashion with a coexistence of liquid-like and solid-like dynamical fraction at all temperatures during the transition process. The previously reported fragile-to-strong dynamic transition in nanoconfined water is argued to be a direct consequence of the layer-by-layer solidification. [ABSTRACT FROM AUTHOR]

Porosity and permeability are the key factors in assessing the hydrocarbon productivity of unconventional (shale) reservoirs, which are complex in nature due to their heterogeneous mineralogy and poorly connected nano- and micro-pore systems. Experimental efforts to measure these petrophysical properties posse many limitations, because they often take weeks to complete and are difficult to reproduce. Alternatively, numerical simulations can be conducted in digital rock 3D models reconstructed from image datasets acquired via e.g., nanoscale-resolution focused ion beam–scanning electron microscopy (FIB-SEM) nano-tomography. In this study, impact of reservoir confinement (stress) on porosity and permeability of shales was investigated using two digital rock 3D models, which represented nanoporous organic/mineral microstructure of the Marcellus Shale. Five stress scenarios were simulated for different depths (2,000–6,000 feet) within the production interval of a typical oil/gas reservoir within the Marcellus Shale play. Porosity and permeability of the pre- and post-compression digital rock 3D models were calculated and compared. A minimal effect of stress on porosity and permeability was observed in both 3D models. These results have direct implications in determining the oil-/gas-in-place and assessing the production potential of a shale reservoir under various stress conditions. [ABSTRACT FROM AUTHOR]

North‐American tight oil production has been on the rise due to the introduction of new drilling and hydraulic fracturing technologies. Such advances have dramatically changed the conventional understanding of the hydrocarbon recovery process. A dimensionless study of tight oil production across the United Sates in plays such as the Bakken, Niobrara, Eagle Ford, Woodford, Bone Spring, and Wolfcamp shed light on some of these recovery processes. Production from any well, regardless of geologic attributes and operating conditions, fits into a universal curve during its initial productive period. Subsequently, production becomes a strong function of hydrocarbon thermodynamics and multiphase flow. Results from this analysis help rank important parameters that affect oil recovery in terms of how wells are operated and the reservoir's intrinsic geological and fluid properties. Furthermore, production results are combined with a simple dimensionless economic analysis to determine optimal fracture configurations independent of oil price environment. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1479–1484, 2018 [ABSTRACT FROM AUTHOR]

The relative amounts of oil and gas produced in prolific plays like the Eagle Ford are affected by the oil bubble point. The oil and kerogen (organic matter) are found in the same rock and the oil may remain in contact with the kerogen. Bulk experiments and molecular simulations clearly show that kerogen preferentially absorbs hydrocarbons. The absorbed oil phase remains in multi-component equilibrium with the expelled oil produced at the surface. Results from a model proposed to calculate the bubble points (at 400 K) of in situ oils (absorbed + free) in the presence of kerogen indicate suppression of about 4150-16,350 kPa from the original value of 28,025 kPa of produced Eagle Ford oil. These calculations depend on the type and level of maturity of kerogen. The prediction of accurate saturation pressures has key implications on volumes of recovery and rates of production from liquid rich shales. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3083-3095, 2017 [ABSTRACT FROM AUTHOR]

A many-body dissipative particle dynamics model, namely, MDPD, is applied for simulation of pore-scale, multi-component, multi-phase fluid flows in fine-grained, nanoporous shales. Since this model is able to simultaneously capture the discrete features of fluid molecules in nanometer size pores and continuum fluid dynamics in larger pores, and is relatively easy to parameterize, it has been recognized as being particularly suitable for simulating complex fluid flow in multi-length-scale nanopore networks of shales. A remarkable feature of this work is the integration of a high-resolution FIB-SEM (focused ion beam scanning electron microscopy) digital imaging technique to the MDPD model for providing 3D voxel data that contain the invaluable geometrical and compositional information of shale samples. This is the first time that FIB-SEM is seamlessly linked to a Lagrangian model like MDPD for fluid flow simulation, which offers a robust approach to bridging gaps between the molecular- and continuum-scales, since the relevant spatial and temporal scales are too big for molecular dynamics, and too small for computational fluid dynamics with known constitutive models. Simulations ranging from a number of benchmark problems to a forced two-fluid flow in a Woodford shale sample are presented. Results indicate that this model can be used to deliver reasonable simulations for multi-component, multi-phase fluid flows in arbitrarily complex pore networks in shales. [ABSTRACT FROM AUTHOR]

Spark plasma sintering (SPS) was used to compact chemically synthesized mesoporous silica powders with ordered hexagonal nanopore channels (~5 nm). Solid compact disks (~19 mm diameter) densified at processing temperatures from 600 to 1000 °C were characterized at multiple length scales using scanning electron microscopy, transmission electron microscopy, Vickers hardness tests, and Brunauer-Emmett-Teller gas adsorption measurements. Microscopy revealed both micro- and nanoporosity in the compacted disks and the hexagonal mesopore channels in the starting powders were retained during SPS at temperatures up to 850 °C under a uniaxial pressure of 10.6 MPa. The degree of macroporosity in SPS samples was correlated to the mechanical properties, surface area, and pore morphology. The macroporosity is retained up to 950 °C under the same pressure, and the degree of macroporosity increases when the mesopores collapse due to individual particle shrinkage. The results of multi-scale characterization of the mesoporous silica compacts were used to shed light on the role of nanostructure and microstructure on the mechanical and physical properties of SPS processed compacted disks. [ABSTRACT FROM AUTHOR]

There are significant resources of oil shale in the western United States, which if exploited in an environmentally responsible manner would provide secure access to transportation fuels. Understanding the kinetics of kerogen decomposition to oil is critical to designing a viable process. A dataset of thermogravimetric analysis (TGA) of the Green River oil shale is provided and two distinct data analysis approaches-advanced isoconversional method and parameter fitting are used to analyze the data. Activation energy distributions with conversion calculated using the isoconversional method (along with uncertainties) ranged between 93 and 245 kJ/mol. Root mean square errors between the model and experimental data were the lowest for the isoconversional method, but the distributed reactivity models also produced reasonable results. When using parameter fitting approaches, a number of models produce similar results making model choice difficult. Advanced isoconversional method is better in this regard, but maybe applicable to a limited number of reaction pathways. © 2011 American Institute of Chemical Engineers AIChE J, 2012 [ABSTRACT FROM AUTHOR]

Paraffinic crude oils in pipelines may form waxy gels during flow shutdowns. These gels can be dislodged by applying pressure if the wall shear stress, proportional to the local pressure gradient, exceeds the gel yield stress. The simplest models assume that the axial pressure profile becomes linear immediately after a jump in upstream pressure, but this fails to account for gel time-dependent rheology or the effect of gel voids on pressure wave propagation. To investigate the former factor, pressure profile and particle imaging velocimetry (PIV) measurements were performed on a model oil gelled under pressure to reduce void formation. After a jump in upstream pressure to a value insufficient to restart flow, the axial pressure profile becomes linear in a two-step process, with an immediate small rise in downstream pressure followed by a time-delayed jump. The local downstream gel deformation measured by PIV exhibits similar two-step time dependence. © 2011 American Institute of Chemical Engineers AIChE J, 2012 [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses articles within the journal on topics including conference on rock mechanics, shale plasticity, and hydraulic fracturing.