Equilibrium Adsorption Studies of CO2, CH4, and N2 on Amine Functionalized Polystyrene

Adsorption of CO₂, CH₄, and N₂ has been investigated using amine functionalized polymeric resins having diethanolamine, imidazole, dimethylamine, and N-methyl piperazine covalently attached to the styrene-divinyl benzene copolymer (PS) matrix. The equilibrium adsorption of CO₂, CH₄, and N₂ was examined on these functionalized polymers at pressures from atmospheric to 40 atm for CO₂ and N₂ while up to 10 atm for CH₄ at 303 K. PS-Imidazole showed the highest adsorption capacity for CO₂ as compared to other functionalized polymers. No significant uptake of CH₄ and N₂ was observed at low pressures by any of the functionalized polymers. The adsorption isotherms were analyzed using dual mode sorption model and Ideal Adsorbed Solution Theory (IAST).     

Analyses of Adsorption Behavior of CO2, CH4, and N2 on Different Types of BETA Zeolites

The adsorption equilibrium and kinetics of CO₂, CH₄, and N₂ on three types of BETA zeolites were investigated at different temperatures and a defined partial pressure range from dynamic breakthrough experiments. The adsorbed amount followed the decreasing order of CO₂ > CH₄ > N₂ for all studied materials. For the same ratio of SiO₂/Al₂O₃, the Na‐BETA‐25 zeolite showed a higher uptake capacity than H‐BETA‐25, due to the presence of a Na⁺ cationic center. Comparing the same H⁺ compensation cation, zeolite H‐BETA‐25 expressed a slightly higher adsorption capacity than H‐BETA‐150. Regarding the selectivity of gases, based on their affinity constants, H‐BETA‐150 displayed the best ability. The adsorption kinetics was considered using the zero‐length‐column (ZLC) technique. Response surface methodology (RSM) was applied to evaluate the interactions between adsorption parameters and to describe the process.     

Adsorption of H2, CO2, CH4, CO,N2 and H2O in Activated Carbon and Zeolite for Hydrogen Production

Abstract

The design of a layered pressure swing adsorption unit to treat a specified off-gas stream is based on the properties of the adsorbent materials. In this work we provide adsorption equilibrium and kinetics of the pure gases in a SMR off-gas: H₂O, CO₂, CH₄, CO, N₂, and H₂ on two different adsorbents: activated carbon and zeolite. Data were measured gravimetrically at 303–343 K and 0–7 bar. Water adsorption was only measured in the activated carbon at 303 K and kinetics was evaluated by measuring a breakthrough curve with high relative humidity.     

Adsorption separation of N2, O2, CO2 and CH4 gases by β-zeolite

In the present study, adsorption equilibrium and kinetic separation potential of β-zeolite is investigated for N₂, O₂, CO₂ and CH₄ gases by using concentration pulse chromatography. Adsorption equilibrium and kinetic parameters have been studied. Henry’s Law constants, heat of adsorption values, micro-pore diffusion coefficients and adsorption activation energies are determined experimentally. The three different mass transfer mechanisms, that have to take place for adsorption to occur, are discussed. From the equilibrium and kinetic data, the equilibrium and kinetic selectivities are determined for the separation of the gases studied.With β-zeolite, carbon dioxide has the highest adsorption Henry’s Law constant at all the temperatures studied, followed by methane, nitrogen and oxygen. Carbon dioxide separation from oxygen, nitrogen and methane has good equilibrium separation factors. This factor is not very high for methane/nitrogen and methane/oxygen systems and is the lowest for nitrogen/oxygen system. Micro-pore diffusion is the dominant mass transfer mechanism for all the systems studied, except CH₄, with β-zeolite. The kinetic separation factors are very small at high temperatures for all the systems studied. Nitrogen/carbon dioxide and oxygen/carbon dioxide can be separated in kinetic processes with reasonable separation factors at low temperatures. Both equilibrium and kinetic separation factors decrease as column temperature increases. Considering all the observations from this study, it was concluded that β-zeolite is a good candidate for applications in flue gas separations, as well as natural gas and landfill gas purifications.     

Adsorption of CO2 from dry gases on MCM-41 silica at ambient temperature and high pressure. 2: Adsorption of CO2/N2, CO2/CH4 and CO2/H2 binary mixtures

Adsorption equilibrium capacity of CO₂, CH₄, N₂, H₂ and O₂ on periodic mesoporous MCM-41 silica was measured gravimetrically at room temperature and pressure up to 25 bar. The ideal adsorption solution theory (IAST) was validated and used for the prediction of CO₂/N₂, CO₂/CH₄, CO₂/H₂ binary mixture adsorption equilibria on MCM-41 using single components adsorption data. In all cases, MCM-41 showed preferential CO₂ adsorption in comparison to the other gases, in agreement with CO₂/N₂, CO₂/CH₄, CO₂/H₂ selectivity determined using IAST. In comparison to well known benchmark CO₂ adsorbents like activated carbons, zeolites and metal-organic frameworks (MOFs), MCM-41 showed good CO₂ separation performances from CO₂/N₂, CO₂/CH₄ and CO₂/H₂ binary mixtures at high pressure, via pressure swing adsorption by utilizing a medium pressure desorption process (PSA-H/M). The working CO₂ capacity of MCM-41 in the aforementioned binary mixtures using PSA-H/M is generally higher than 13X zeolite and comparable to different activated carbons.     

Comprehensive analysis of thermodynamic models for CO2 absorption into a blended N,N-diethylethanolamine-1,6-hexamethyl diamine (DEEA-HMDA) amine

In this work, CO₂ equilibrium solubility of 1M N,N-diethylethanolamine (DEEA):2M 1,6-hexamethyl diamine (HMDA), 1.5M DEEA:1.5M HMDA and 2M DEEA:1M HMDA was studied with a temperature range of 298–333 K and CO₂ partial pressure range of 8–100 kPa. Seven thermodynamic models including Empirical model, Kent and Eisenberg (KE) model, Hu–Chakma model, Austgen model, Helei Liu model, Liu et al. model, and Li–Shen model were developed by correlating reaction equilibrium constants with observed equilibrium solubility of CO₂ in mixed amine solvents. The evaluation of those models was conducted in terms of the average absolute relative deviation (AARD). The results indicated that Liu et al. model considering T, [Amine], P_total and [CO₂(aq)] can better represent this complex system with an AARD of 8.06%. Meanwhile, comprehensive comparison and analysis were also performed to identify the contribution of parameters to develop models, which could provide a guideline for the development of accurate thermodynamic models for representation of thermodynamic behaviors.     

Greenhouse Gas Adsorptivity of Horn-Shaped Carbon Nanotubes over Nitrogen: Equilibrium Study

The synthesis of horn-shaped carbon nanotubes using carbon tetrachloride as carbon source was carried out by solvothermal method at 200°C for 2 h. The scanning and transmission electron microscopic characterization of the obtained product showed the formation of horn-shaped carbon nanotubes with irregular wall structure having inner diameter of ～105 nm and length of ～1 µm. The equilibrium gas adsorption properties of horn-shaped carbon nanotubes derived from carbon tetrachloride were successfully investigated for CO₂, CH₄, and N₂ at 288, 303, and 318 K. Horn-shaped carbon nanotubes possess better CO₂ adsorption capacity (2.53 mmol/g) with high capacity selectivity (14.7) and equilibrium selectivity (59.1) over N₂ at 288 K. The detailed adsorption study with estimation of physical parameters such as Henry's constant and heat of adsorption identifies the horn-shaped carbon nanotubes as a potential adsorbent material in the field of CO₂ storage and separation.     

CO2 adsorption performance of polyethyleneimine-modified ion-exchange resin

A series of solid amine adsorbents were prepared by the template method with ion-exchange resin (D001) as the carrier and polyethyleneimine (PEI) as the modifier. The absorbents were characterized by energy disperse spectroscopy (EDS), scanning electron microscope (SEM), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) techniques. The effects of PEI loading, adsorption temperature and influent velocities on CO₂ adsorption capacity in a fixed-bed reactor were investigated. The results show that the solid amine adsorbent prepared by the template method had a better PEI dispersion, stability and CO₂ adsorption capacity. The maximum CO₂ adsorption capacity was 3.98 mmol·g^?1 when PEI loading was 30%, the adsorption temperature was 65°C and the influent velocity was 40 mL·min^?1. The CO₂ adsorption capacity decreased only by 9.50% after 10 cycles of adsorption–desorption tests. The study of kinetics indicates that both chemical adsorption and physical adsorption occurred in the CO₂ adsorption process. The CO₂ adsorption process included fast breakthrough adsorption and gradually approaching equilibrium stage. The particle internal diffusion process was the control step for CO₂ adsorption.     

Potentiometric,kinetic, and thermodynamic investigations into Cu2+ ion binding properties of vinyl imidazole containing IMAC adsorbent

In this study, the use of the potentiometric method for the determination of the protonation constant of vinyl imidazole (VIM) and the stability constant of the Cu²⁺ ion complex of VIM used in the immobilized metal ion affinity chromatography (IMAC) was investigated. For this purpose, poly(ethylene glycol dimethacrylate‐n‐vinyl imidazole) [poly(EGDMA–VIM)] microspheres (average diameter 150–200 μm) were prepared. The microspheres were characterized by elemental analysis, N₂ adsorption/desorption isotherms, elemental analysis, energy dispersive spectroscopy (EDS). Protonation constants of vinyl imidazole and the metal‐ligand stability constant of vinyl imidazole with Cu²⁺ ions have been determined potentiometrically in 0.1M NaCl aqueous solution at 298, 318, and 338 K, respectively. The corresponding thermodynamic parameters of protonation and complexation processes (ΔG, ΔH, and ΔS) were derived and discussed. The formation kinetics of Cu²⁺‐vinyl imidazole complex were also investigated, and the process obeyed the pseudo‐second‐order kinetic model. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39751.     

CO2/CH4/N2在沸石13X-APG上的吸附平衡

采用磁悬浮热天平测量了CO₂、CH₄与N₂在沸石13X-APG上的吸附等温线,温度为293、303、333和363 K,压力为0～500 kPa。对吸附平衡实验数据采用multi-site Langmuir模型和Sips模型进行拟合,均得到良好的拟合效果,非线性回归得到吸附热等模型参数,可为变压吸附工艺过程的开发提供基础热力学数据。将沸石13X-APG吸附分离性能与文献中报道的吸附材料(如沸石分子筛、活性炭、金属有机骨架材料和介孔硅分子筛)性能相比较。通过比较CO₂、CH₄与N₂吸附容量以及相对分离系数,探讨CO₂/CH₄(垃圾填埋气或者CO₂强化煤层甲烷回收气)体系、CO₂/N₂(燃煤电厂、水泥厂以及焦炭厂烟道气)体系以及CH₄/N₂(煤层气)体系吸附分离的高效材料,为未来二氧化碳吸附捕集和甲烷吸附回收提供基础数据。     

Sorption studies of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript>, N<Subscript>2</Subscript>, CO,O<Subscript>2</Subscript> and Ar on nanoporous aluminum terephthalate [MIL-53(Al)]

Aluminum terephthalate, MIL-53(Al), metal–organic framework synthesized hydrothermally and purified by solvent extraction method was used as an adsorbent for gas adsorption studies. The synthesized MIL-53(Al) was characterized by powder X-Ray diffraction analysis, surface area measurement using N₂ adsorption–desorption at 77 K, FTIR spectroscopy and thermo gravimetric analysis. Adsorption isotherms of CO₂, CH₄, CO, N₂, O₂ and Ar were measured at 288 and 303 K. The absolute adsorption capacity was found in the order CO₂>CH₄>CO>N₂>Ar>O₂. Henry’s constants, heat of adsorption in the low pressure region and adsorption selectivities for the adsorbate gases were calculated from their adsorption isotherms. The high selectivity and low heat of adsorption for CO₂ suggests that MIL-53(Al) is a potential adsorbent material for the separation of CO₂ from gas mixtures. The high selectivity for CH₄ over O₂ and its low heat of adsorption suggests that MIL-53(Al) could also be a compatible adsorbent for the separation of methane from methane–oxygen gas mixtures.     

Fluidized bed hydrodynamic modeling of CO2 in syngas: Distorted RTD curves due to adsorption on FCC

Bubbles rising through fluidized beds at velocities several times superficial velocities contribute to solids backmixing. In micro-fluidized beds, the walls constrain bubble sizes and velocities. To evaluate gas-phase hydrodynamics and identify diffusional contributions to longitudinal dispersion, we injected a mixture of H₂, CH₄, CO, and CO₂ (syngas) as a bolus into a fluidized bed of porous fluid catalytic cracking catalyst while a mass-spectrometer monitored the effluent gas concentrations at 2 Hz. The CH₄, CO, and CO₂ trailing RTD traces were elongated versus H₂ demonstrating a chromatographic effect. An axial dispersion model accounted for 92% of the variance but including diffusional resistance between the bulk gas and catalyst pores and adsorption explained 98.6% of the variability. At 300°C, the CO₂ tailing disappeared consistent with expectations in chromatography (no adsorption). H₂ and He are poor gas-phase tracers at ambient temperature. We recommend measuring RTD at operating conditions.     

Single and Multicomponent Sorption of CO2, CH4 and N2 in a Microporous Metal-Organic Framework

Abstract

Single and multicomponent fixed-bed adsorption of CO₂, N₂, and CH₄ on crystals of MOF-508b has been studied in this work. Adsorption equilibrium was measured at temperatures ranging from 303 to 343 K and partial pressures up to 4.5 bar. MOF-508b is very selective for CO₂ and the loadings of CH₄ and N₂ are practically temperature independent. The Langmuir isotherm model provides a good representation of the equilibrium data. A dynamic model based on the LDF approximation for the mass transfer has been used to describe with good accuracy the adsorption kinetics of single, binary and ternary breakthrough curves. It was found that the intra-crystalline diffusivity for CO₂ is one order of magnitude faster than for CH₄ and N₂.     

Enthalpy of absorption of CO2 with alkanolamine solutions predicted from reaction equilibrium constants

Differential enthalpies of absorption of CO₂ in aqueous solutions of 2-aminoethanol (MEA) and N-methyldiethanolamine were predicted from reaction equilibrium constants using the Gibbs-Helmholtz equation. Correlations for the reaction equilibrium constants and enthalpies of reaction found in the literature for each of the individual reactions taking place at CO₂ absorption were compared to experimental data, and from this, a set of equations was selected for the Deshmukh-Mather model in this work. The carbamate dissociation constant for MEA was fitted to experimental P_CO2 and ΔH_abs data. Heat contributions from each of the individual reactions taking place in the systems MEA+H₂O+CO₂ and MDEA+H₂O+CO₂ were calculated and presented as functions of loading and temperature. Predicted enthalpies of absorption agree well with the data from literature and with experimental data from this work. The calculation procedure described in this work may be used for the adjustment of reaction equilibrium constants by fitting the equilibrium model also to experimentally measured heats of absorption data in addition to P_CO2 data.     

Investigation of the Phase Equilibria of CO2/CH3OH/H2O and CO2/CH3OH/H2O/H2 Mixtures

The storage of excess electricity from renewable energy sources is nowadays a crucial topic. One promising technology is the methanol (CH₃OH) synthesis from H₂/CO₂ mixtures. The achievable one‐pass conversion is limited within this exothermic equilibrium reaction. A possibility to overcome this limitation would be withdrawing CH₃OH and H₂O from the gas phase through in situ condensation under reaction conditions. In this work, the phase equilibrium for mixtures representative for different degrees of conversion was studied. A view cell was employed to determine systematically the single‐ and two‐phase regimes and obtain phase envelopes for mixtures of H₂, CO₂, CH₃OH, and H₂O from 66 to 305 °C and 61 to 233 bar. Furthermore, the densities in the single‐phase area were determined and quantified by an empirical model.     

Simultaneous Adsorption of SO2, NO,and CO2 by K2CO3‐Modified γ‐Alumina

The simultaneous adsorption of SO₂, NO, and CO₂ on K₂CO₃‐modified γ‐alumina under different operating conditions was studied in a fixed‐bed reactor. The experimental results showed that the influence of a temperature increase on the simultaneous adsorption of the three gases was complex and different from the effects seen when both chemical adsorption and competitive adsorption existed. An increase in O₂ concentration and small amounts of water could enhance the adsorption of SO₂ and NO while the adsorption of CO₂ was not influenced. The breakthrough curves of the simultaneous adsorption experiments suggested that the investigated adsorbent may be a good candidate for the simultaneous adsorption of SO₂, NO, and part of the CO₂ while the adsorption capacity for CO₂ still needs to be enhanced.     

On the CO2 absorption kinetics,loading capacity,and catalytic desorption of aqueous solutions of N-methyl-D-glucamine

CO₂ separation with harmful chemicals will damage the environment. It is essential to explore greener solvents that are producible from renewable resources such as biomass. The suitability of N-methyl-D-glucamine (MG), also known as meglumine, for capturing CO₂, was explored in this work. This nontoxic amino sugar, which is derived from sorbitol, represents a renewable bio-solvent. It was found that MG is especially reactive with CO₂. Trials were performed in a stirred cell reactor with a flat gas–liquid interface between 303 and 313 K. The values of the pseudo-first-order reaction rate constant, reaction orders, and activation energy were found. The loading capacity (α) of 0.5 M MG solution was measured at T = 308 K. For a typical value of α = 0.524 mol CO₂/mol MG, the corresponding equilibrium partial pressure of CO₂ was 22 kPa. Finally, it was found that the catalyst Al₂O₃ aided in the desorption of CO₂-loaded MG solutions. Desorption efficiency using Al₂O₃ was higher (74%) than that achieved without this catalyst (45%). It is thus clear that MG represents a potential solvent for improved CO₂ separation from gases.     

The analysis of solubility,absorption kinetics of CO2 absorption into aqueous 1‐diethylamino‐2‐propanol solution

In this present work, the CO₂ absorption performance of aqueous 1‐diethylamino‐2‐propanol (1DEA2P) solution was studied with respect to CO₂ equilibrium solubility, absorption kinetics, and absorption heat. The equilibrium solubility of CO₂ in 2M 1DEA2P solution was measured over the temperature range from 298 to 333 K and CO₂ partial pressure range from 8 to101 kPa. The absorption kinetics data were developed and analyzed using the base‐catalyzed hydration mechanism and artificial neural network models (radial basis function neural network [RBFNN] and back‐propagation neural network [BPNN] models) with an acceptable absolute average deviation of 10% for base‐catalyzed hydration mechanism, 2.6% for RBFNN model and 1.77% for BPNN model, respectively. The CO₂ absorption heat of 1DEA2P was estimated to be ?43.6 kJ/mol. In addition, the ions (1DEA2P, 1DEA2PH⁺, , CO₃^2?) speciation plots of the 1DEA2P‐CO₂‐H₂O system were developed to further understand the reaction process of 1DEA2P with CO₂. Based on a comparison with conventional amines (e.g., MEA, DEA, MDEA) and alternative amines (i.e., 1DMA2P and 4‐(diethylamino)?2‐butanol [DEAB]), 1DEA2P exhibited good performance with respect to CO₂ equilibrium solubility, reaction kinetics, and CO₂ absorption heat. Meanwhile, the overall evaluation of 1DEA2P for application in CCS in terms of absorption and desorption is presented, giving helpful information for the screening of these novel amines. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2694–2704, 2017     

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

Abstract

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.     

Extra-framework charge and impurities effect,Grand Canonical Monte Carlo and volumetric measurements of CO2/CH4/N2 uptake on NaX molecular sieve

In this work, Monte Carlo simulation of CO₂, N₂, and CH₄ adsorption on zeolite 13X is carried out in grand canonical ensemble. FAU framework was used to reproduce the structure of zeolite 13X. Universal force field was used to calculate the interactions between adsorbates and 13X. Metropolis method was used for calculating adsorption isotherm. Volumetric measurements were carried out to confirm the simulation results. The simulation results using Universal force field showed good agreement with experimental results. Highest CO₂ uptake for this zeolite was found as 5.67 mol/kg from GCMC. Isosteric heat of adsorption was investigated to find the heat released during adsorption of each gas. The simulation result of isosteric heat of adsorption for CO₂, N₂, and CH₄ was utmost 17.00, 4.37, and 6.14 kcal/mole, respectively. Radial distribution graphs were used to find affinity of constituents of zeolite for CO₂. Henry’s constant evaluation was also performed at low pressure to find the selectivity of the structure. Henry’s constant of CO₂ in an equimolar mixture of N₂ and CH₄ was calculated 3.49 and 1.49 mol/kg.kPa, respectively. Finally, simulation results were fitted to Toth and dual-site Langmuir isotherms to find the best fit that belongs to dual-site Langmuir.