We simulate a moving bed temperature swing adsorption (MBTSA) process to capture CO2 in postcombustion context using zeolite 13X as adsorbent. Experimental adsorption isotherms for CO2 and N2 were ...performed gravimetrically to obtain the equilibrium input data for the model. The need of the flue gas drying was demonstrated by pure water and binary water/CO2 experimental adsorption isotherms, and the energy penalty of the water removal was accounted for within the energetic duty of the unit. The model consists of three sections (adsorption, regeneration, and cooling) each with its own model and integrated by a composite model that simulates the entire unit. Given the large number of variables and parameters in a MBTSA process, which can be arranged in different input data sets, a parametric study of the effect of several variables (feed gas flow rate, regeneration temperature, adsorbent residence time in the adsorption section, feed temperature, solid loading) on the key performance parameters of the process was performed. The results showed that, under the studied conditions, values up to 99% and 91% mol of CO2 recovery and purity could be achieved, respectively. The specific energy consumption, which included an energy recovery in the cooling section, was found to be competitive against reported values for commercial amine absorption separation processes suggesting that the MBTSA process might be a potential separation process candidate for large-scale postcombustion CO2 capture by adsorption.
Despite the great industrial importance of zeolite LTA, there is still a gap in characterization methods, based on adsorption related to hindered diffusion of standard probe gases, such as N2 and Ar. ...LTA has a three-dimensional porous structure with a high degree of symmetry; however, variations in the location of cations, notably S2 and S3 sites, lead to different energy levels in supercages. Herein, we propose to extend the pore type distribution (PTD) methodology, recently applied for metal–organic frameworks, to zeolite materials. As an application example, we selected Na-LTA (4A) zeolite. Structural properties accessed by molecular simulation methods combined with experimental adsorption isotherms of CO2 at 273 K determine the individual contribution of supercages, with different energy levels, to the total adsorption uptake. Using eight local isotherms from the supercages, we developed a kernel that estimates the most likely energy distribution levels among supercages from the best fits of experimental isotherms. The method was applied in detail for LTA samples synthesized in laboratory and supplied by an industrial manufacturer. As an extension of the approach, we also analyze the use of the average local isotherm in the determination of imperfections found in the synthesis of LTA from unconventional raw materials or its deactivation in industrial processes. The proposed methodology generates detailed and relevant information not accessed by existing methods and allows the use of adsorption to characterize this class of very small pore sieves.
•Isotherms of N2 at 77 K (−196 °C) are not suitable to evaluate clinoptilolite textural properties.•Clinoptilolite presents high selectivity for CO2 over CH4 and N2.•The force field parameters used ...for FAU zeolites can be transferred to the clinoptilolite model.•IAST model in predicting the adsorption of mixtures in clinoptilolite.•Molecular simulation confirms the influence of the cation species on the selectivity inversion of CH4/N2 mixtures.
Clinoptilolite is a low-cost and abundant natural zeolite with a high CO2 selectivity, which is abundant in many regions around the world, but with limited industrial use. By combining experimental and theoretical (molecular simulation) approaches, the present work aims at contributing with fundamental data to assist the design of adsorption processes based on this zeolite. A sample of naturally occurring (raw) clinoptilolite was characterized by TGA, XRD, XRF, N2 adsorption isotherms at −196 °C and CO2 at 0 °C. Single-component (CO2, N2, CH4 and O2) and binary (CO2/CH4 and CO2/N2) equilibrium isotherms were measured gravimetrically. Column dynamics experimental data were obtained in order to validate a fixed-bed model, which was then used to evaluate the performance of separation processes. Molecular simulation (MS) was used to build a predictive zeolite model validated with experimental data for CO2, N2, CH4 and O2 able to investigate adsorption of mixtures and gas diffusion. TGA results demonstrated structural stability up to 600 °C with the X-ray diffraction pattern revealing clinoptilolite as the main phase, together with cristobalite and other silicon phases as contaminants. The textural properties obtained from N2 adsorption isotherms at −196 °C of the studied sample were comparable to those reported in the literature, though inaccurate for the actual clinoptilolite structure, which poses significant diffusional resistance for N2 at such temperature. IAST combined with Sips model was used to predict the behavior of mixtures. The proposed clinoptilolite MS model was used to verify the suitability of IAST in predicting mixture equilibrium on clinoptilolite and to predict the selectivity of CO2 over O2. The MS model was able to assess the equilibrium effects in the adsorption of the CH4-N2 mixture and to confirm the relationship between the diffusivity of gases and the positioning and nature of cations in the structure. The fixed-bed model highlighted the different performances of the raw and exchanged clinoptilolite samples, including the theoretical Na-clinoptilolite crystal predicted by the MS model. Together with experimental data, the MS model can be used to aid the design of separation processes of such gas stream with multiple components using clinoptilolite.
Adsorption equilibria of CO2, N2, and the CO2/N2 binary system on AQSOA FAM Z02 grains were measured over a temperature range of 295 to 348 K and over a wide range in pressure from 0.2 to 20 bar ...using a gravimetric method. CO2 and N2 single-component experimental equilibrium measurements were regressed using the Toth equation. CO2 adsorption on AQSOA FAM Z02 reported higher loadings compared to N2 adsorption at all measured temperatures, with an adsorption capacity of 6.1 mmol g–1. The adsorption of the CO2/N2 binary mixture at different gas-phase compositions (0.15/0.85, 0.50/0.50, and 0.80/0.20 mole fractions) was studied. The experimental data were compared with the prediction of ideal adsorbed solution theory (IAST), which also included the nonidealities in the bulk gas phase. The IAST model has shown agreement with the experimental data with <4% average relative error in the absolute adsorbed amount.
•Adsorption microcalorimetry may be used to estimate mass transport properties.•Proposed heat/mass transfer models were able to accurately reproduce the microcalorimetric peaks.•Parametric ...sensitivity analysis provides accurate estimation of diffusion parameters.•The novel method allows the evaluation of both equilibrium and kinetics of adsorption.
A novel method to estimate mass transfer kinetics in porous adsorbents using gas adsorption microcalorimetry is described. By fitting an appropriate model to experimental microcalorimetric peaks, both the LDF constant and the effective diffusion time constant could be estimated. Results are shown for an activated carbon and zeolite 13X. The experimental apparatus consisting of a microcalorimeter coupled to a controlled gas dosing system was described in the model by four control volumes: the dosing vessel, the dead volume, the measuring cell and the composite wall surrounding the cell. The proposed model was able to accurately describe the microcalorimetric peaks obtained upon each gas injection. The sensitivity of the model solution to the diffusion parameters was analyzed and adequate ranges of experimental conditions allowing for accurate parameter estimation could be determined. Mass transfer parameters found by this technique are in agreement with those reported in the literature by other experimental techniques.
The anaerobic decomposition in landfills produces a gas mixture known as landfill biogas. This biogas consists mainly of CH4 and CO2. The CO2 removal can be carried out by means of adsorption. In ...order to promote CO2 removal, zeolite type 4A was used as solid adsorbent. The synthesized zeolite was characterized by scanning electron microscopy and X-ray diffraction. CH4/CO2 mixture isotherms were obtained in a magnetic suspension balance equipped with a gas dosing unit and Extended Langmuir and Extended Sips models were used to predict mixture isotherms from monocomponent data. Three biogas emissions drains in a sanitary landfill in Caucaia (Ceará State, Brazil) - ASMOC - were chosen to test the performance of zeolite as CO2 adsorbent under real conditions. Zeolite 4A has proven to be very selective for CO2 even in the presence of H2S.
This study presents experimental data of storage and delivery tests of methane on activated carbon carried out in a prototype vessel at pressures up to 40 atm. Adsorption equilibrium data at high ...pressure were measured using a gravimetric apparatus. Experimental data obtained from the storage/delivery tests are compared to those obtained from process simulation using a dynamic model. The simulation model was run using the measured equilibrium data as input parameters. A good agreement was observed between experimental and simulated results. Histories of pressure and stored mass were satisfactorily well predicted. Despite heat effects, not precisely taken into account in the model, there was a reasonably good agreement between simulation and experiment for the average temperature inside the vessel.
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