Urea removal from an aqueous solution is considered a challenge in the biological process. The state of complete kidney destruction is known as an end-stage renal disease (ESRD). Kidney transplant and hemodialysis are the most common methods for confronting ESRD. More recently, wearable artificial kidney (WAK) devices have shown a significant improvement in urea removal performance. However, low efficiency in physical adsorbents is a barrier in developing them. For the first time, the urea adsorption capacity of five types of last-generation covalent organic framework (COF) nanosheets (NSs) was investigated in this study by applying molecular dynamics (MD) simulation tools. To this end, different analyses have been performed to evaluate the performance of each nanoparticle. The MD all-atom (AA) results demonstrated that all introduced COF NSs had urea removal capacity. Among the five NSs, TPA-COF was shown to have the best outcomes. Moreover, coarse-grained (CG) and density functional theory (DFT) simulations were conducted, and the results show that the TPA-COF nanoparticle modified with –OH functional group has even better properties for urea adsorption. The present molecular study sheds new light on COF NSs as an adsorbent for urea removal.
The convection–diffusion process of carbon dioxide (CO2) dissolution in a saline reservoir is investigated to shed light on the effects of the permeability heterogeneity. Using sequential Gaussian simulation method, random permeability fields in two and three-dimension (2D and 3D) structures are generated. Quantitative (average amount of the dissolved CO2 and dissolution flux) and qualitative (pattern of the dissolved CO2 and velocity streamlines) measurements are used to investigate the results. A 3D structure shows a slightly higher dissolution flux than a 2D structure in the homogeneous condition. Results in the random permeability fields in 2D indicates an increase in the standard deviation of the permeability nodes enhances the dissolution efficiency, fluctuations in CO2 dissolution flux, separation between the different realizations from the same input parameters, and tendency toward more jagged convective fingers’ shape. Furthermore, the distance between the permeability nodes increases the convective fingers’ dissolution efficiency and jagged structure. The degree of freedom in 3D structures results in a higher chance of escaping from the low permeability zones and reduces the interactions between convective fingers in 3D systems. With the same variance and correlation length between permeability nodes, connectivity between high permeable zones in 3D cases are less than that of 2D cases; therefore, 2D realizations overestimate the dissolution flux of real heterogeneous 3D structures, which should be considered carefully.
Article Highlights
CO2 sequestration in two and three dimensional heterogeneous saline aquifers are investigated.
3D structures in homogeneous conditions show higher dissolution than 2D structures.
2D realizations overestimates the dissolution flux over real heterogeneous 3D reservoirs.
The high cost of the CO 2 sequestration in saline aquifers is a barrier to the implementation of them. However, a large portion of the cost is invested to purify and transport the CO 2 from the flue gas stream of the emission sources. Therefore, the possibility of injecting impure CO 2 will reduce the costs strongly. The diffusion coefficient is an important factor that plays a significant role in different aspects of the process. In spite of its importance, it is got less attention due to complex experimental procedures and low range of temperature and pressure applicability in the experimental conditions. To shed light on the effects of the impurity on the diffusion coefficient of CO 2 -water systems, two types of impurities (SO 2 and N 2 ) in two levels are considered in this study through the molecular dynamics simulation approach. Simulations are done on a wide range of pressure and temperature conditions to cover a wide range of operational conditions for CO 2 sequestration projects. The outcomes of these simulations were used in the direct numerical simulations to analyze the effect of the diffusion coefficient matrix changes on the CO 2 dissolution process such as dissolution flux, the motion and shape of convective fingers, and their patterns. Results indicate that impurity has a great impact on the
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