Adsorption Equilibrium Of CO2 Research Articles

Effects of activation on the properties of electrospun carbon nanofibers and their adsorption performance for carbon dioxide

Microporous carbon nanofibers were prepared by stabilization, carbonization, and activation of electrospun polyacrylonitrile-based nanofibers. The average fiber diameters of activated electrospun carbon nanofibers (AECNF) samples, ranging from 280 to 500 nm, generally decreased with increasing activation degree. The evolution of nitrogen was observed during the fabricated processes, and the predominant nitrogen functionalities were shifted to those at higher binding energies when the activation degree increased. The N/C ratios on the surface of the samples were affected significantly by the activation temperature and activation time. The AECNF samples were featured with microporosity and the ultramicropores were also newly formed with increasing activation degree. It was expected that the activation process involved a three-step predominant reaction: the transformation from ultramicropores to submicropores, the micropore enlargement reaction followed by the micropore formation reaction. The equilibrium CO2 adsorption capacities could achieve 1.2 mmole/g (0.15 atm) and 3.2 mmole/g (1 atm) at 298 K. The CO2 uptake at low partial pressure and ultramicroporosity of the adsorbents were related to the isosteric heat of adsorption. The AECNF samples for CO2 adsorption had an energetically heterogeneous surface and Freundlich equation provided a satisfactory fit. Synergetic effects of microporosity and nitrogen content of AECNF on CO2 uptakes at low pressure were observed.

Accelerated CO2 capture on adsorbent coated finned tube: An experimental study

In this study, the external surface of a finned tube was coated by 13X zeolite powder, and the CO2 adsorption equilibrium and dynamics were investigated experimentally. A slurry consisting of dionized water, 13X zeolite powder, and Acrylic latex emulsion (ALE) was used to coat the finned tube. The finned tube was coated by deep coating method. The equilibrium isotherms were measured at the range of 20–90 °C and fitted well by the dual-site Langmuir model. The average difference between the model and the results obtained from the experiments is about 2.5%. The nitrogen adsorption/desorption at 77 K was used for characterization of adsorbents. A 11% reduction was observed in pore volume and surface area. The dynamic test showed that the desorption of adsorbed CO2 takes place in about 14 s which is an order of magnitude faster than the fastest developed method. A conservative criterion was developed for estimating adsorbent working capacity. This criterion showed that the working capacities of the adsorbent are about 80% of its ideal values.

Enrichment of low-grade methane gas from nitrogen mixture by VPSA with CO2 displacement process: Modeling and experiment

To upgrade efficiently the low-concentration methane gas from nitrogen mixture, CO2 displacement was employed into the traditional vacuum pressure swing adsorption (VPSA) process to form the VPSA-CO2DIS process. Non-isothermal and non-isobaric mathematical model for the VPSA-CO2DIS process was developed, where ternary competitive adsorption equilibrium of CH4, N2 and CO2 was calculated using IAST-Sips formulation, and bi-pore diffusion model was used to describe adsorption kinetics. Experiments were carried out to enrich the low-grade methane gas using one-bed four-step VPSA-CO2DIS process with the home-made granular activated carbons (GACs), and results compared to process simulation predictions. Both experimental and simulated results confirmed that a high purity CH4 product gas (75.40% CH4) could be obtained continuously from 10% CH4 feed gas with 89.02% recovery. The combustion heat of the enriched CH4 product gas was estimated higher than the power consumption of this process, and carbon emissions penalty in this process was evaluated to be activated, so this VPSA-CO2DIS process was technically feasible.

The feasibility of cost-effective manufacturing activated carbon derived from walnut shells for large-scale CO2 capture.

The economic potential of activated carbon (AC) synthesis from walnut shell biomass for CO2 capture was evaluated in the present study. For this purpose, the chemical activation was employed to manufacture ACs and the effect of different impregnation ratios of activation agents, comprising KOH (KH) and H3PO4 (HP), onto the properties of fabricated ACs was examined. The obtained results demonstrated that the synthesized AC by HP activation with an impregnation ratio of 1:2.5, which was identified as HP2.5, possesses the highest surface area (1512.6m2/g), micropore volume percentage (74.65%), and CO2 adsorption (3.55mmol/g) at 1bar and 30°C. Moreover, the equilibrium CO2 adsorption data for HP2.5 were better fitted with the Freundlich model, indicating the multilayer CO2 adsorption onto the heterogeneous AC surface dominantly through a physisorption process. In addition, the economic estimations revealed a cost of about $1.83/kg for the ultimate production that was significantly lower than the most of available CACs in the market. Therefore, walnut shells can be considered as a cost-effective and promising biomass source from a scale-up point of view.

Prediction of CO2 adsorption on different activated carbons by hybrid group method of data-handling networks and LSSVM

ABSTRACTCO2 is a ubiquitous species that has received much attention recently. The adsorption of CO2 by means of activated carbons is a well-tried technology that can be used on a large scale. Improvements of the prediction models with more accurate results and lower error are necessary for future development of the projects and the economic dispatch sector. The least square support vector machine, a relatively unexplored neural network known as group method of data handling (GMDH), were implemented to forecast the CO2 adsorption on different activated carbons. This work aims to provide new methods to predict the adsorption equilibrium of pure CO2 on a set of commercial activated carbons and to express it regarding textural properties such as Brunauer–Emmett–Teller (BET) surface area, total pore volume, and micropore volume. Results indicated that the utilized models are very accurate in predicting CO2 adsorption on different activated carbons. Comparison of the outcomes of the two models shows that the GMDH model is more accurate with R2 and mean squared error values of 0.8915 and 0.0001425, respectively.

Simulation of CO2/CH4 high pressure separation on microporous activated carbon

Pure component adsorption equilibrium of CH4 and CO2 on activated carbon have been studied at three different temperatures, 298, 323, and 348 K within a pressure range of 10–2000 kPa. Binary adsorption equilibrium isotherm was described using extended Sips equation and ideal adsorbed solution theory (IAST) model. Experimental breakthrough curves of CO2/CH4 (40:60 in a molar basis) were performed at four different pressures (300, 600, 1200, and 1800 kPa). The experimental results of binary isotherms and breakthrough curves have been compared to the predicted simulation data in order to evaluate the best isotherm model for this scenario. The IAST and Sips models described significantly different results for each adsorbed component when higher pressures are set. These different results cause a significant discrepancy in the estimation of the equilibrium selectivity. Simulated and experimental equilibrium selectivity data provided by IAST presented values of around 4, for CO2/CH4, and extended Sips presented values of around 2. Also, simulated breakthrough curves showed that IAST fits better to the experimental data at higher pressures. According to the simulations, in a binary mixture at total pressure over 800 kPa, extended Sips model underestimated significantly the CO2 adsorbed amount and overestimated the CH4 adsorbed amount.

Effect of volatile organic compounds on carbon dioxide adsorption performance via pressure swing adsorption for landfill gas upgrading

During the landfill gas (LFG) upgrading process of carbon dioxide (CO2) separation by pressure swing adsorption (PSA), if the non-harmful volatile organic compounds (VOCs) are not removed completely, they would cause a rapid failure of the adsorbents due to irreversible adsorption. This point was not given enough concern previously, and no special procedures were generally adopted for VOC removing in practical LFG upgrading engineering. The aim of this study is to demonstrate the harmfulness of VOCs to the adsorbents in PSA process, thereby, five typical VOCs in LFG, including toluene, ethylbenzene, p-xylene, cyclohexane, and butanone were selected and their effect on CO2 adsorption performances of zeolite 13X, 5A and activated carbon were studied for the first time through different adsorption experiments, i.e. the measurement of CO2 equilibrium adsorption isotherm on the adsorbents with or without VOC-loaded, CO2 adsorption experiment simulating the practical PSA operation, and CO2 diffusion coefficient measurement in the dynamic adsorption process. Results of these adsorption experiments demonstrated that all the VOCs adsorbed on the adsorbents irreversibly and lead to CO2 adsorption performances deteriorating. Therefore, conclusion could be drawn that all the VOCs should be removed sufficiently to keep high efficient operation of PSA for LFG upgrading.

Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 5. Impacts of the NH3-H2O Coadsorption on the Coverage of Sulfated TiO2-Based Solids

The present study is a part of an experimental microkinetic approach of the selective reduction of NOx to N2 with NH3 in excess of O2 on V2O5/WO3/TiO2 catalysts (NH3-selective catalytic reduction (NH3-SCR) reaction). Water is always present either in the reactive gas mixtures representative of industrial processes or produced by the reaction. This suggests that H2O may modify the coverage of the pivotal adsorbed NH3 intermediate of the reaction by either a competitive adsorption or reactions (i.e., formation of NH4+). In the temperature range of interest for NH3-SCR (T ≥ ≈423 K), Fourier transform infrared spectroscopy and volumetric measurement using a mass spectrometer are used to study the impacts of the NH3-H2O coadsorption on the coverages of adsorbed NH3 (molecular adsorption) and H2O (molecular and dissociative adsorption) species on two sulfated solids: a 0.7% V2O5/9% WO3/TiO2 NH3-SCR catalyst and its TiO2 support. Regardless of the solid, it is shown that at the NH3-H2O coadsorption equilibrium, ...

CO2 and CO adsorption equilibrium on ZSM-5 for different SiO2/Al2O3 ratios

ABSTRACTCO2 and CO adsorption on MFI type zeolites with different SiO2/Al2O3 ratios (ZSM-5(30), ZSM-5(50), ZSM-5(280), and silicalite) were investigated in this study by a static gravimetric analyzer for pure isotherms at 30°C, 65°C, 100°C, and 135°C over the pressure range of 0–10 atm. Adsorption capacity of CO increases with decreasing SiO2/Al2O3 ratios within ZSM-5. The adsorption of CO2 for decreasing SiO2/Al2O3 ratios, showed stronger adsorption at lower pressures and at higher pressures, the highest capacity varied from ZSM-5(50) to ZSM-5(30). ZSM-5(280) was found to have the highest selectivity for CO2 within the widest range of pressures and temperatures tested.

Measurement and modeling of adsorption equilibria of cobalt (III) acetylacetonate on MCM-41 mesoporous silica in the presence of supercritical carbon dioxide with methanol co-solvent

Adsorption equilibria of cobalt (III) acetylacetonate (Co(acac)3) in the presence of supercritical carbon dioxide (scCO2) with methanol co-solvent on MCM-41 mesoporous silica were studied at 313–353 K and 12.5–20.0 MPa from experimental and model calculation viewpoints. The measured data indicated that the amount of the adsorbed metal precursor decreased with increasing pressure and decreasing temperature, which could be explained by CO2 density effects. Correlation by the Dubinin-Astakhov equation was applicable for examining the adsorption equilibria of the metal precursor on the mesoporous silica in scCO2 while considering the molecular size of the precursor, affinity for the adsorbent, and CO2 density effects. Simulated results with the DA equation implied that the methanol co-solvent can affect the adsorption equilibria of Co(acac)3 on the MCM-41 adsorbent in scCO2.

CO2 gas-adsorption calorimetry applied to the study of chemically activated carbons

In this work, the microporous structure of a series of H3PO4 chemically activated carbons from peach stones with increased activation degree were investigated. CO2 Adsorption equilibrium isotherms and differential enthalpy curves were simultaneously measured at 300K using a Tian-Calvet microcalorimeter coupled to an adsorption manometric setup. Temperature programmed decomposition experiments were used to assess density of oxygen functional groups and determine the impact of surface chemistry on CO2 adsorption capacity. Computer based theoretical calculations were also performed to attempt to predict the adsorption enthalpy profiles. The most activated sample (Xp=0.90) has an average adsorption enthalpy which is approximately 8kJ/mol lower than that of the non-activated samples carbonized under the same conditions. The combination of techniques enabled a better understanding of the pore filling regimes with increasing coverage, since the use of CO2 as a probe gas allows accessing small pores, which otherwise would not be identified from N2 isotherms at 77K. The oxygen content on the carbon surface decreased almost 80% with the increasing degree of activation and did not influence in the CO2 adsorption. Besides providing information about carbon chemistry, CO2 adsorption calorimetry can also be successfully applied to the screening of carbons intended for CO2 capture.

Experimental Determination of the CH4 and CO2 Pure Gas Adsorption Isotherms on Different Activated Carbons

The aim of this work is to provide new experimental data of the adsorption equilibrium of pure CH4 and CO2 on a set of commercial activated carbons and to express it in terms of textural properties...

CO₂ Capture with Mesoporous Silicas Modified with Amines by Double Functionalization: Assessment of Adsorption/Desorption Cycles.

CO2 adsorption on mesoporous silica modified with amine by double functionalization was studied. Adsorption microcalorimetry was used in order to investigate the influence of increasing the nitrogen surface density on double functionalized materials with respect to the only grafted materials. The distribution of sites and the rate-controlling mechanism of adsorption were evaluated. A Tian Calvet microcalorimeter coupled to a manometric setup was used to evaluate the energy distribution of adsorption sites and to calculate the thermokinetic parameters from the differential enthalpy curves. CO2 and N2 adsorption equilibrium isotherms at 50 and 75 °C were measured with a magnetic suspension balance, allowing for the computation of working capacity and selectivity at two temperatures. With these data, an Adsorbent Performance Indicator (API) was calculated and contrasted with other studied materials under the same conditions. The high values of API and selectivity confirmed that double functionalized mesoporous silica is a promising adsorbent for the post combustion process. The adsorption microcalorimetric study suggests a change in active sites distribution as the amine density increases. Maximum thermokinetic parameter suggests that physisorption on pores is the rate-controlling binding mechanism for the double-functionalized material.

Facet effect on CO2 adsorption, dissociation and hydrogenation over Fe catalysts: Insight from DFT

Periodic density functional theory (DFT) calculations were performed to investigate the facet effect on CO2 adsorption, dissociation and hydrogenation over Fe catalysts. The energetically most stable configurations of CO2 and H2 adsorption over different Fe facets were identified from which we observed that CO2 adsorption on Fe(211) and Fe(111) is much stronger than other facets, indicating more sufficient activation of CO2 on these two surfaces. CO2 adsorption stability was found to be impacted by the surface coverage of H* on these Fe facets, showing that when surface H* coverage exceeds to certain percentage, CO2 adsorption is largely weakened whilst the electrons transfer from the Fe surface to CO2 becomes decreased. These results suggest that an appropriate H2-CO2 co-adsorption equilibrium is important for effective activation of reactants. Based on the examination of CO2 dissociation and hydrogenation on these Fe facets, the Fe(111) is potentially the most active facet for CO2 conversion due to a lower barrier for HCOO* formation via CO2 hydrogenation while this facet is also catalytically more active for activating CO2. Fe(110) and Fe(100) exhibit more facile ability to dissociate CO2 to CO* while kinetically competitive formation of CO* and HCOO* was observed over Fe(211). The present work demonstrates that the facet of Fe catalysts can impact the molecular adsorption, activation and conversion path in CO2 hydrogenation and thus can alter the product selectivity.

Evaluating isotherm models for the prediction of flue gas adsorption equilibrium and dynamics

We evaluated isotherm models for the precise prediction of adsorption equilibrium and breakthrough dynamics. Adsorption experiments were performed using pure N2, CO2 and their binary mixture with an activated carbon (AC) material as an adsorbent. Both BET and breakthrough measurements were conducted at various conditions of temperature and pressure. The corresponding uptake amount of pure component adsorption was experimentally determined, and parameters of the four different isotherm models, Langmuir, Langmuir-Freundlich, Sips, and Toth, were calculated from the experimental data. The predictive capability of each isotherm model was also evaluated with the binary experimental results of binary N2/CO2 mixtures, by means of sum of square errors (SSE). As a result, the Toth model was the most precise isotherm model in describing CO2 adsorption equilibrium on the AC. Based on the breakthrough experimental result from the binary mixture adsorption, non-isothermal modeling for the adsorption bed was performed. The breakthrough results with all of the isotherm models were examined by rigorous dynamic simulations, and the Toth model was also the most accurate model for describing the dynamics.

Pure and Binary Adsorption of Carbon Dioxide and Nitrogen on AQSOA FAM Z02

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.

Effect of water onto porous CaO for CO2 adsorption: Experimental and extended isotherm model

Tremendous increment of carbon dioxide in atmosphere has posed devastating impacts to global climate change. The phenomenon has become one of the great challenges need to be considered for achieving techno-economic system. This paper presents an alternative approach for capturing high concentration of CO2 by combination of two separation processes, adsorption and gas hydrate. Potentials of waste seashell from cockle for producing low cost porous calcium oxide for CO2 capture were investigated. The adsorption equilibrium of CO2 on porous calcium oxide with presence of water was measured using a static volumetric technique at 2 °C for pressures up to 36 bar. The CO2 uptakes of 9.1 mmol/g and 11.3 mmol/g were obtained for commercial and synthesized CaO at 36 bar. At optimum water ratio, the equilibrium data were simulated first with three different isotherm models: Langmuir, Freundlich and Redlich-Peterson. The Freundlich model adequately describe the CO2 adsorption on dry samples and Redlich-Peterson gives the best fitted for wet samples at optimum water ratio. The Redlich-Peterson model having the highest R2 was further extended by incorporating water isotherm model to determine the occurrence of water inside the sample. The curve obtained from the extended isotherm model shows an increment of coefficient from 0.94 to 0.99 and 0.94 to 0.98 for commercial and synthesized CaO. The findings revealed the potential of waste cockle shell as a viable and sustainable materials for preparation of calcium oxide for gas adsorption applications. This novel technology will go a long way in amassing the impacts of water in CO2 adsorbent for gas adsorption applications.

Equilibrium and Kinetic Behaviour of CO2 Adsorption onto Zeolites, Carbon Molecular Sieve and Activated Carbons

This study was carried out to characterize CO2 adsorption equilibrium and kinetics of commercial adsorbents that have potential for use in the pressure swing adsorption (PSA) process and also to provide a better understanding of CO2 adsorption behaviour under wide ranges of operating conditions. A comprehensive set of data and the analysis for CO2 adsorption equilibrium and kinetics are presented for six commercial adsorbents, i.e. zeolite 13x, zeolite 5A, zeolite 4A, carbon molecular sieve (MSC-3R), and activated carbons (GCA-830 and GCA-1240). The adsorption equilibrium and the kinetic data were taken at a temperature range of 293-333 K and pressure up to 35 atm. The CO2 adsorption isotherm was found to follow typical a type-I isotherm classification according to IUPAC, representing a monolayer adsorption mechanism. Among the six commercial adsorbents tested, activated carbon GCA-1240 offered the highest adsorption capacity, and zeolite 4A provided the lowest capacity. The obtained isotherm data were correlated as a function of temperature and pressure to fit with different model equations (i.e. Langmuir, Toth, Sips, and Prausnitz). The Sips model showed the best fit with the equilibrium data for zeolite 13X, zeolte 5A, zeolite 4A, and carbon molecular sieve (MSC-3R) while the Prausnitz model provided an excellent fit with the data for activated carbons (GCA-830 and GCA-1240). The isosteric heat of CO2 adsorption was also estimated for individual adsorbents according to the Clausius-Clapeyron equation. The CO2 adsorption kinetic, presented in terms of mass transfer coefficients (k), were analyzed from the plots of CO2 uptake rate using the well-recognized linear driving force (LDF) model. The k values were correlated by non-linear regression to reveal effects of adsorption temperature and pressure. Activation energies of CO2 adsorption on the individual adsorbents were also calculated and correlated according to the Arrhenius equation.

Effect of pore size, aminosilane density and aminosilane molecular length on CO2 adsorption performance in aminosilane modified mesoporous silica

Mesoporous silicas with different pore size were modified by aminosilanes with different molecular length. CO2 adsorption capacity was improved by all aminosilane modification, and the CO2 adsorption capacity was further improved with increasing the aminosilane density. However, CO2 adsorption capacity and the amine efficiency of (3-trimethoxysilylpropyl)diethylentriamine (TA) modified mesoporous silicas with small pores such as MCM-41(2.9 or 3.1 nm) and SBA-15(6.2 or 7.1 nm) were significantly decreased at high aminosilane density. In contrast, TA modified SBA-15 with a large pore (10.6 nm) exhibited further improvement of CO2 adsorption capacity and amine efficiency. N2 adsorption desorption measurements suggested that the pore plugging occurred at high aminosilane density in TA modified mesoporous silicas with small pores. In situ FT-IR spectra and the half-value period of CO2 equilibrium adsorption capacity clearly shows the CO2 adsorption kinetics in these adsorbents with small pores were significantly lower than that in the adsorbent with large pores. To develop the CO2 adsorbents with high adsorption performance, the correlation between aminosilane molecular length, pore size of mesoporous silica and aminosilane density should be considered.

CO2 adsorption properties of ion-exchanged zeolite Y prepared from natural clays

Ordered microporous Y zeolite was successfully synthesized by hydrothermal treatment using metakaolin and Ludox (40% SiO2) as an aluminum and silica source respectively. The metakaolin was obtained by thermal treatment of Algerian kaolin. The obtained Y zeolite was exchanged by different cations such as Cu2+, Ni2+, Ca2+, Na+ and used for the CO2 adsorption at 0 °C. The structural features of the materials were determined by various physico-chemical techniques such as x-ray diffraction, nitrogen sorption at 77 K, Fourier transform infrared spectroscopy and scanning electronic microscopy. The CO2 adsorption at 0 °C was carried using a volumetric method. The adsorption isotherms of CO2 exhibit nonlinear concave curves and showed a high adsorption capacity for CO2 from the M-Y zeolites. The equilibrium CO2 adsorption capacity increase in the following order of Cu2+ < Ni2+ < Ca2+ < Na+. The experimental isotherm data of the CO2 adsorption was best described by the Langmuir model giving a maximum adsorbed amount qm = 77.57 cm3 · g−1 STP for Na-Y zeolite.