Search

Highlights • Adsorption separation of CO 2 from dry and humid CO 2 /N 2 mixture is carried out under ambient conditions. • Experimentally validated model is applied by a user-defined-function in ANSYS Fluent. • 13X and Mg-MOF-74 are tested for breakthrough and cyclic CO 2 separations. • Dehydration process before CO 2 adsorption processes is strongly recommended. • Cycling separation is recommended to be used instead of breakthrough tests. Abstract Carbon dioxide and storage is an efficient method to reduce the emitted CO 2 from the burning of fossil fuels. Zeolite-based materials are conventional adsorbents used to adsorb some gasses involving carbon dioxide. Mg-MOF-74 is an eminent reticular material among adsorbents due to its good CO 2 capacity at low pressures (10–20 kPa). In this study, an experimentally validated model is used to report the H 2 O effect on CO 2 separation using 13X and Mg-MOF-74 under ambient conditions. A computational model has been developed using ANSYS Fluent program linked by user-define-function (written in C). The adsorption breakthrough results show that a humid CO 2 /N 2 mixture, under 300 K, 86% RH, 101.3 kPa, could slightly reduce the CO 2 adsorption capacity by about 0.05% and 6% for 13X and Mg-MOF-74, respectively (at CO 2 adsorption breakthrough saturation). Regardless of these reductions, Mg-MOF-74 has better adsorption capacity, even under humid ambient conditions, by about 5.77 mmol/g in a comparison to 2.27 mmol/g for 13X, respectively. Cycling stability over more than 90 cycles is also simulated; and shows that, a dehydration process is recommended to be carried out before the CO 2 separation process for efficient energy consumption and sustainable adsorbents. The total recyclable amounts of adsorbed CO 2 are about 0.94 and 3.07 mmol/g for 13X and Mg-MOF-74, respectively, under 101.3 kPa adsorption, 2 kPa desorption, 86% relative humidity, and 298 K. The cyclic CO 2 separation is found to be a robust method more than the breakthrough separation to evaluate the real adsorption capacities. [ABSTRACT FROM AUTHOR]

In this study, we report the effect of water vapor on CO 2 uptake using Mg-MOF-74 via adsorption breakthrough modeling and lab experiments. Carbon dioxide is the most influencing gas that significantly expedites global warming. Therefore, it is ultimately necessary to reduce the rapid increase of CO 2 concentration in the atmosphere by means of Carbon Capture and Storage (CCS). CO 2 separation by physical adsorption is an interesting technology to achieve CO 2 capture with minimum energy penalties. Metal-organic framework (MOF) adsorbents forms a class of adsorbents with much higher specific surface areas than conventional porous materials such as activated carbons, and zeolites. However, most MOFs show notable hydro instability for CO 2 separation from humid flue gas. Mg-MOF-74 is a superior adsorbent amongst other adsorbents owing to its high CO 2 uptake at flue gas conditions. A model is developed using User-Defined-Function in an ANSYS Fluent program. Two and three-dimensional models are validated by comparing their results with experimental work carried out by the authors, at ambient temperature, and published experimental data for high temperature conditions. The effect of water vapor is studied at different temperatures and various relative humidity values for Mg-MOF-74. Results indicate that CO 2 uptake has been significantly reduced with the existence of more than 5% water vapor when Mg-MOF-74 is used as an adsorbent. [ABSTRACT FROM AUTHOR]

Quantitatively, carbon dioxide is the main gas emitted from the burning of fossil fuels; thus, it is the primary contributor to global warming. However, climate change could be mitigated using “carbon capture and storage” (CCS) methods. CO 2 separation by physical adsorption is a promising technology to achieve CO 2 capture with minimum energy costs. Mg-MOF-74 is a distinguished adsorbent amongst porous materials owing to its high CO 2 uptake under flue gas conditions. In this study, a vacuum pressure swing adsorption (VPSA) process composed of five steps (pressurization, feed, rinse, blowdown, and purge) for separating CO 2 from a CO 2 /N 2 mixture using Mg-MOF-74 was mathematically modeled. Two- and three-dimensional computational fluid dynamics (CFD) models were developed using a user-defined-function (UDF, written in C) linked to the ANSYS Fluent program. The models have been validated against published pressure swing adsorption experimental data. The regeneration (blowdown and purge) time has been tuned to explore the performance improvement for the VPSA process. The key optimum performance indices for VPSA in terms of CO 2 purity, recovery, productivity, and process power consumption were found to be 95.3%, 94.8%, 0.50 kg_CO 2 h −1 kg_MOF −1 , and 68.71 kW h tonne_CO 2 −1 , respectively. The corresponding operating carbon capture cost has been evaluated as $6.87 tonne_CO 2 −1 for a 500-MW post-combustion power plant. These CO 2 productivity and power consumption performances represent a significant enhancement in CO 2 separation using physical adsorption technology compared to those reported in the literature. [ABSTRACT FROM AUTHOR]

Carbon dioxide is quantitatively the most significant component which facilitates in the global warming, it is utmost necessary to suppress the rapid increase of CO 2 concentration in the atmosphere by means of Carbon Capture and Storage (CCS). Metal-organic framework (MOF) MOFs has recently been developed with the primary objective of CO 2 capture from flue gases with minimum energy penalties. MIL-101(Cr) holds the supreme importance amongst such types of MOFs owing to its extraordinary thermal and hydro stability. In this study, a novel composite composed of multi-walled carbon nanotubes (MWCNTs) incorporated in a MIL-101(Cr) framework has been synthesized using a molecular-level mixing process in order to enhance the thermal properties of the base framework as well as augment the CO 2 adsorption capacity and separation. The synthesized and activated MWCNT/MIL-101(Cr) composites have been characterized for degree of crystallinity, microstructure, thermal stability, and CO 2 and N 2 equilibrium adsorption capacity. Actual dynamic behavior of adsorption breakthrough tests have been conducted under ambient conditions (297 K and 101.325 kPa) to address the real adsorptive behavior and to quantify the level of the CO 2 adsorption capacity and breakpoint enhancements. Results demonstrate that a substantial improvement in the CO 2 adsorption capacity and breakpoint over pristine MIL-101(Cr) is achievable with the 2 wt% MWCNT/MIL-101(Cr) composite with measured optimal enhancements of about 35.94% and 32.11%, respectively. [ABSTRACT FROM AUTHOR]

• A novel combined sCO 2 cycle and ejector refrigeration cycle is suggested. • Five refrigerants are evaluated to identify the best-suited one for this novel integration. • Sensitivity analysis is performed to identify the most important parameters influencing the combined cycle performance. • Parametric study is performed to study the effect of the most important parameters on system performance. • Multi-objective optimization is performed to compromise between the exergy efficiency and cost. Supercritical CO 2 cycle has an optimal performance when the cycle minimum temperature is around the critical temperature (31 °C), which is impossible at hot climatic conditions. To solve this problem, this work hybridizes a supercritical CO 2 cycle with an ejector refrigeration cycle (ERC) to cool the minimum temperature of the cycle to be about 31 °C and hence achieving the highest possible performance. Comprehensive energy, exergy, and economic analyses are carried out to explore the mechanisms of performance improvement of the novel combined plant. Sensitivity analysis is performed to recognize the most influencing parameters on the performance of the combined plant. Based on the sensitivity analysis, the effect of different operating and design parameters on the system performance is investigated. Furthermore, a multi-objective optimization study is performed to find the trade-off between exergy efficiency and cost-saving. Among the different the five refrigerants used for ERC, the results illustrate that R717 is the most efficient one for the present hybridization. The exergy destruction in the precooler reduces from 15.5% to 0.7% when ERC is combined with the sCO 2 cycle. Thus, the energy efficiency (η th) and exergy efficiency (η ex) increase by 9.5%, while the levelized cost of energy (LCOE) declines by 10.7%. Compared with the standalone sCO 2 cycle, the produced power, η th , η ex , and LCOE of the optimized plant improve by 94.3%, 36.2%, 28.6%, and 18.3%, respectively. [ABSTRACT FROM AUTHOR]

A novel crosslinked microporous polymer was synthesized via a modified acid-catalyzed Friedel-Crafts polycondensation reaction. By virtue of the rigid and polarizable monomers (aniline and pyrrole), the polymer, termed KFUPM-4, was proven permanently porous (Brunauer-Emmett-Teller surface area = 650 m2 g−1) with a high CO 2 capacity (33 cm3 g−1 at 760 Torr and 298 K) and selectivity (CO 2 :CH 4 selectivity = 15:1 at 298 K). As a result of these properties, KFUPM-4 was subjected to breakthrough measurements, whereby the material's ability to selectively capture CO 2 under dynamic conditions from both dry and wet mixed gas streams was clearly demonstrated. Image 1 • A new highly rigid crosslinked porous polymer termed KFUPM-4 for CO 2 capture. • KFUPM-4 exhibited a high selectivity toward CO 2 in comparison to CH 4. • KFUPM-4 showed stability and enhanced CO 2 uptake in the presence of water. [ABSTRACT FROM AUTHOR]