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In the present study, some commercially available activated carbons were evaluated towards the methyl iodide (CH3I) capture in the context of nuclear industry. A specific methodology was implemented in order to establish structure-activity relationships between adsorbent characteristics and its adsorption behavior towards CH3I. On the one hand, the investigated adsorbents were characterized by a combination of physico-chemical techniques. On the other hand, CH3I retention performance from batch sorption tests under different conditions (temperature and relative humidity) was studied using an original experimental setup. In this work, two conditions were investigated: (i) T = 35°C, R.H. = 26 % ([H2O] ∼15,000 ppmv); (ii) T = 75°C, R.H. = 30 % ([H2O] ∼130,000 ppmv). Different trends were obtained depending on the investigated scenario. At ambient conditions (i), CH3I adsorption performance was affected after KI/TEDA impregnation because of partial pore blockage phenomena induced by the of impregnants presence within the microporosity. However, TEDA impregnation was found to be required to enhance the trapping stability and to capture CH3I with superior efficiency at higher temperature (ii).

An experimental and simulation study using a packed column for CO2 sorption was conducted. The adsorption data of CO2 sorption from CO2/N2 mixture using activated carbon (NORIT RB1) were obtained at different operating conditions. The sorption equilibrium and breakthrough profiles were produced with a total pressure of 1.25 bars. The breakthrough and saturation time decreased with increasing temperature, feed rate, and inlet CO2 concentration. A linear driving force (LDF) model for mass transfer was used to calculate the mass transfer coefficient and reproduce the breakthrough curves. The findings of the LDF model were compared with experimental data produced at various operating conditions to predict the breakthrough curves. The experimental and predicted findings were analyzed by ascertaining the determination coefficient and mean error. The model consistently reproduced all the breakthrough curves and may be considered adequate for predicting the CO2 separation from a CO2/N2 mixture with R2 > 0.97 and mean error less than 5% under all the operating conditions. [ABSTRACT FROM AUTHOR]

The performance of porous carbon materials as sorbents is often compromised by the presence of humidity. Studying the kinetics of water vapour adsorption on activated carbons will undeniably help to overcome this issue. This has been approached in this work by evaluating the influence of several operational factors on the dynamic adsorption of water vapour in these materials. Specifically, different carbon types, particle sizes, air flows and ambient conditions (temperature and relative humidity (RH)) were systematically investigated. The impact of each isolated parameter on both the maximum water uptake and the uptake rate was analyzed by fitting the experimental data to the Linear Driving Force (LDF) kinetic model. The results show that except for the particle size, the studied variables play a role in the water sorption kinetics, although to a different extent. It was also confirmed that the LDF model can adequately describe the kinetics of water vapour adsorption independently of the experimental conditions. Finally, the complete water vapour adsorption process can be described by this model, obtaining a different value of the kinetic constant for the sequential stages, involving different adsorption mechanisms.

The performance of porous carbon materials as sorbents is often compromised by the presence of humidity. Studying the kinetics of water vapour adsorption on activated carbons will undeniably help to overcome this issue. This has been approached in this work by evaluating the influence of several operational factors on the dynamic adsorption of water vapour in these materials. Specifically, different carbon types, particle sizes, air flows and ambient conditions (temperature and relative humidity (RH)) were systematically investigated. The impact of each isolated parameter on both the maximum water uptake and the uptake rate was analyzed by fitting the experimental data to the Linear Driving Force (LDF) kinetic model. The results show that except for the particle size, the studied variables play a role in the water sorption kinetics, although to a different extent. It was also confirmed that the LDF model can adequately describe the kinetics of water vapour adsorption independently of the experimental conditions. Finally, the complete water vapour adsorption process can be described by this model, obtaining a different value of the kinetic constant for the sequential stages, involving different adsorption mechanisms. [ABSTRACT FROM AUTHOR]

CO2 emissions from flue gases can be restricted via a promising post-combustion capture technique, namely, adsorption. In the present work, behavior of adsorbents, prepared from PET (polyethylene terephthalate) waste, for CO2 capture studies was investigated to understand the fixed bed adsorption dynamics. The effect of activation on textural properties, surface functional groups and elemental composition was studied through nitrogen adsorption/desorption, XPS, FTIR, and EDX analysis. Thermal stability of adsorbent samples was also evaluated. The kinetics of the adsorption process was studied using Lagergren's pseudo-first-order model, pseudo-second, fractional order, Elovich, and Avrami models. Freundlich isotherm fit confirmed the heterogeneous nature of adsorbent's surface. Adsorption column breakthrough profiles were modeled using linear driving force (LDF) approximation for mass transfer. Model equations were solved using the Method of lines in MATLAB environment. Results show that the model closely approximated the column breakthrough curves for different CO2 concentrations (5–12.5%) and different adsorption temperatures (30–100 °C). [ABSTRACT FROM AUTHOR]

In this work, high-pressure H 2 S adsorption data in equilibrium and fixed bed conditions using NaY zeolite as adsorbent were determined. Adsorption and desorption isotherms for different temperatures and H 2 S partial pressures up to 1.2 bar were obtained experimentally and modelled with Tóth and Dubinin-Astakhov equations in order to give information about adsorbate/adsorbent and adsorbate/adsorbate interactions. H 2 S adsorption in a fixed bed column was achieved for different inlet volumetric flow rates and breakthrough curve data were evaluated considering adsorbed amount, length of mass transfer zone, contributions of internal and external mass transfer resistances and were modelled with Linear Driving Force (LDF) model to estimate adsorbent particle's effective mass transfer coefficient. Equilibrium results indicate maximum uptake capacities are above 6.0 mol kg−1 for highest partial pressures. Isotherms' modeling suggests the predominance of physisorption of H 2 S in NaY zeolite. However, a hysteresis effect was observed for desorption curves and attributed to H 2 S chemisorption on zeolite surface, as pointed out by strongly favorable isotherms obtained. Fixed bed adsorption data showed breakthrough curves were nonsymmetrical, which indicated the presence of internal resistance mainly, probably due to the microporosity of adsorbent particle. In accordance, mass transfer zones did not vary significantly with inlet flow rate. Effective intraparticle mass transfer coefficients obtained with LDF model increases as flow rate increases, due to a higher availability of H 2 S molecules at adsorbent surface, which increases the driven force necessary for mass transfer in the intraparticle region. Image 1 • Strongly favorable H 2 S isotherms on NaY were determined by high pressure gas adsorption using the partial pressure of this gas on a mixture with helium. • Tóth and Dubinin-Astakhov models can be used together to give information about adsorbate/adsorbent and adsorbate/adsorbate interactions. • Heats of adsorption for H 2 S adsorption on NaY zelite were calculated. • H 2 S desorption indicated interaction between H 2 S and NaY is due to dissociation chemisorption. • H 2 S adsorption on NaY zeolite fixed bed suggests the presence of internal and external mass transfer resistances. [ABSTRACT FROM AUTHOR]

Bioethanol produced from lignocellulosic sources still faces problems related to the feasibility of this technological route. Within the biorefinery concept and clean technology, subcritical water hydrolysis (SWH) is efficient for dissociating lignocellulosic biomass. The solid co-products can be used for other applications to become SWH a more feasible process. The potential use of subcritical water hydrolyzed soybean husks (SWHSH) as a biosorbent to remove basic Red 9 dye (BR9) from aqueous solutions was evaluated in this study. SWHSH was efficient in the uptake of BR9, mainly at a pH of 8.0. The Langmuir model satisfied the biosorption equilibrium profile with a biosorption capacity of 56.8 mg g−1. The thermodynamic parameters indicate that the biosorption is spontaneous, with the ΔG0 ranging from − 22.08 to − 24.88 kJ mol1, with an endothermic nature (ΔH0 = 5.59 kJ mol−1). The biosorption equilibrium was in 60 min for all the initial concentrations studied. The Linear Driving Force (LDF) model fitted the data well, furnishing diffusivity values from 1.41 to 2.00 × 10−8 cm2 s−1. Desorption was also possible under acid conditions, and SWHSH could be effectively used 3 times. Last, the fixed-bed biosorption showed that the SWHSH could remove the BR 9 dye up to 180 min without regeneration, presenting a biosorption capacity of 46.1 mg g1 for 900 mL of treated effluent with an initial concentration of 200 mg L1. The characterization and biosorption results indicate that the BR9 tends to be adsorbed by physical forces, possibly by hydrogen bonds, electrostatic interaction, ππ interaction, and cation-π interaction. Overall, the SWHSH demonstrated potential application as a biosorbent for the removal of BR9. [Display omitted] • Subcritical water hydrolyzed soybean husk (SWHSH) as an alternative biosorbent. • SWHSH was efficient in the uptake of BR9, mainly at a pH of 8.0. • The maximum biosorption capacity was 56.8 mg g−1. [ABSTRACT FROM AUTHOR]

Abstract: The efficiency of Ba2+ removal from aqueous solutions by means of an ion exchange process was investigated. More specifically, a natural zeolitic tuff, namely a Campanian ignimbrite containing both chabazite and phillipsite as exchanger phases was used, and the effect of Ba2+ concentration was studied. The selected material, previously converted into its Na+ form, was used in a laboratory scale fixed bed column, and the kinetics of Ba2+ removal were studied at different concentrations, ranging from 50 to 500g/m3. In all the experiments a very high selectivity of the tuff material towards Ba2+ was observed. The experimental data were interpreted using a diffusional model, based on the Linear Driving Force (LDF) approximation. The model accounted for the presence of two zeolitic phases in the tuff and for mass transfer limitations in both the liquid phase and tuff particles. The model interpreted the data satisfactorily, enabling it to be established that both the internal and external mass transfer resistances played a key role in the kinetics of the ion exchange process. [Copyright &y& Elsevier]

Abstract: In this study, a mathematical model was developed to simulate an adsorption process for dehydration of a gas stream. In deriving the model, the following assumptions were made. Variation of the gas velocity along the bed length was accounted for and the bed pressure drop was calculated by the Ergun equation. Mass and heat transfer outside the solid particles were assumed to be convective and those inside the particle were assumed to be diffusive. The dual site Langmuir isotherm was employed in predicting adsorption equilibrium and the Peng–Robinson equation was used as the PVT relation. The resulting mathematical model was solved by the finite volume method and the results were verified against experimental data reported by Mohamadinejad et al. [2000. Separation Science and Technology 35,1] and Gorbach et al. [2004. Adsorption 10,1]. Good agreement was observed between the predictions of the model and the experimental data. The developed model was used to perform parametric study. Our results suggest that the break-through time decreases linearly with the square of particles diameter. It also decreases linearly with the inverse of particles tortuosity. A similar trend appears to exist for variations of the bed percent saturation. The bed pressure drop increases linearly with the inversed diameter of particles. [ABSTRACT FROM AUTHOR]

An experimental and theoretical study is performed for bulk separation of H/CO mixture (70/30 volume %) by PSA process with zeolite 5A, a process widely used commercially in conjunction with the catalytic steam reforming of natural gas or naphtha. For the optimized adsorption conditions of PSA, the characteristics of adsorption/desorption characteristics have been studied through breakthrough and desorption experiments under various conditions. The purge-to-feed ratio is important to the H product purity only at a long adsorption step time. H could be concentrated from 70% in the feed to 99.99% at H recovery of 67.5%. The results of all five steps in PSA are successfully predicted by the LDF model considering an energy balance and nonlinear isotherm. For the model, the effective diffusivities (D,) are obtained separately from the uptake curves of H and CO. The Langmuir-Freundlich isotherm is used to correlate the experimental equilibrium data and is very well fitted to the results. [ABSTRACT FROM AUTHOR]

• Good separation was obtained between alkali lignin (AL) and NaOH on Mn270 resin. • Separation mechanism was size exclusion, AL promotes adsorption of NaOH on resin. • The interaction energy between AL and NaOH was calculated by molecular simulation. • LDF coupled with the extended Langmuir isotherm was chosen as a suitable model. Alkali lignin and NaOH are two main components in the black liquors from alkaline pulp. Adding sulfuric acid directly to precipitate lignin results in high consumption of acid as well as production of waste salts (Na 2 SO 4). In this work, a benign process was proposed to separate alkali lignin and NaOH using ultra-high crosslinked non-ionic microporous resin Mn270 as an adsorbent and water as an eluent. Special attention was paid to explore the separation mechanism and establish a proper chromatographic model for this process. First, the adsorption isotherms showed the presence of alkali lignin increased the adsorption capacity of NaOH on the Mn270 resin. The separation mechanism was assumed to be size exclusion. Simultaneously, the alkali lignin promotes the adsorption of NaOH on the resin, which was verified by analysis of the interaction energy among NaOH-resin-Alkali lignin from a molecular dynamics simulation point of view. Afterwards, a linear driving force model combined with binary isotherms was used to predict the breakthrough / elution profiles of the two components on the column system fairly well. Finally, the alkaline pulp was used as a feed solution and got a good separation effect. After removal of NaOH, the amount of sulfuric acid and the corresponding salts were reduced by 37.86% in subsequent acid precipitation process. [ABSTRACT FROM AUTHOR]

• We have developed a new two-temperature model of water vapor adsorption in the zeolite 13X. • An advanced numerical scheme based on mixed-hybrid finite element method and operator splitting is used. • Convergence of the numerical scheme is verified. • The model is applied to simulation of charging and discharging cycles of a thermochemical battery. • Behaviour of the two temperatures - the fluid temperature and the zeolite temperature - is studied. In this paper, we present a new two-temperature mathematical model for a thermo-chemical energy storage based on the adsorption and desorption of the water vapor in zeolite 13X. The adsorption process is modelled using the Linear Driving Force (LDF) model and the Langmuir-Freundlich isotherms. A numerical solver based on the mixed-hybrid finite element method and operator splitting technique is proposed. Furthermore, we present a computational study of the charging and discharging processes of the thermo-chemical energy storage emphasising the behaviour of the two temperatures: fluid temperature and zeolite temperature. [ABSTRACT FROM AUTHOR]

lants, the removal of natural organic matter (NOM) is an essential aim to improve the final water quality and to reduce the formation of disinfection by-products. The objective of the present study was to compare the performance of different macroporous anion exchange resins (AERs) with regard to their NOM removal under drinking waters conditions. NOM removal at neutral pH was assessed by measuring the decrease of the dissolved organic carbon concentration in equilibrium experiments. Further, the fictive component approach (adsorption analysis) was applied to describe the competitive adsorption equilibria of the complex NOM system. Due to their relevance for fixed-bed filter design, breakthrough curves (BTCs) were measured and modelled by the homogeneous surface diffusion model with the linear driving force approach for surface diffusion combined with the ideal adsorbed solution theory for competitive adsorption. These model approaches, well known from activated carbon adsorption, were used in the present study to describe NOM adsorption onto AERs. The required mass transfer coefficients were obtained by empirical correlations. The applicability of the BTC model was verified with the experimental data of NOM uptake onto one selected AER. [ABSTRACT FROM AUTHOR]