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Adsorption: Journal of the International Adsorption Society (v.19, #1)

Effect of synthesis conditions of polyallylamine-beads-glucose (PAA-Glu) on boron adsorption by Atsuhiro Harada; Toshiyuki Takagi; Akiko Kawai; Akira Endo (pp. 1-9).

In this study, we assessed the boron adsorption characteristic of our synthesized adsorbent: polyallylamine-beads-glucose (PAA-Glu) by using the adsorption amount and adsorption site availability (ASA), and determined the optimum conditions for PAA-Glu synthesis. ASA is our proposed indicator and it expresses the percentage of the experimental equilibrium adsorption in relation to the theoretical equilibrium adsorption and indicates the availability of adsorption sites (hydroxyl groups) on adsorbents. We investigated the effects of the degree of cross-linking (20, 40 and 60 %), the introduction amount of α-D-glucose (40, 60 and 80 %), and the introduction temperature (30–150 °C) as regards PAA-Glu on the boron adsorption amount. The boron adsorption amount for PAA-Glu (20 % cross-linked, 30 °C) was superior to that for another degree of cross-linked PAA-Glu. However, the ASA for PAA-Glu (60 % cross-linked, 30 °C) exhibited the best value in this synthesized PAA-Glu. Furthermore, we examined the introduction temperature at which glucose was introduced to PAA-Glu (20 % cross-linked) in the 30–150 °C range, and we confirmed that the optimum temperature range for the synthesis of PAA-Glu was 60–80 °C. We found that controlling the space between the main chains of the polymer by using a spacer such as a cross-linker allowed boron molecules to come and go and led to an improvement in the boron adsorption amount and ASA.

Keywords: Boron; Removal; Adsorption; Polyallylamine (PAA); Saccharide

Carbon monoxide isotope enrichment and separation by pressure swing adsorption by Shubhra J. Bhadra; Armin D. Ebner; James A. Ritter (pp. 11-23).

Simulations of three different 3-bed 3-step pressure swing adsorption (PSA) cycles were carried out to study the enrichment and recovery of ¹⁴CO from an isotopic mixture of ¹⁴CO, ¹³CO and ¹²CO using NaX zeolite. Each PSA cycle included feed pressurization/feed (FP/P), heavy reflux (HR) and countercurrent depressurization (CnD) steps; they differed only in the way the CnD step was carried out: PSA Cycle I was carried out under total reflux (i.e., with no ¹⁴CO heavy product production); PSA Cycle II was carried out with discontinuous ¹⁴CO heavy product production; and PSA Cycle III was carried out with continuous ¹⁴CO heavy product production. The effects of the CnD step valve coefficient (c v), heavy reflux ratio (R R), and cycle time (t cyc) on the PSA process performance were determined in terms of the ¹⁴CO enrichment, ¹⁴CO recovery and CO feed throughput. The results showed that there was essentially no limit to the extent of the ¹⁴CO enrichment, despite the inherently low ¹⁴CO/¹²CO (1.05) and ¹⁴CO/¹³CO (1.12) separation factors for these isotopes on NaX zeolite. Under total reflux an optimum c v was found for the CnD step and ¹⁴CO enrichments as high as 152 were obtained. Using the optimum c v under finite reflux, a ¹⁴CO enrichment approaching 20 and a ¹⁴CO recovery approaching 100 % were easily achieved with discontinuous (PSA Cycle II) or continuous (PSA Cycle III) ¹⁴CO heavy product production. There was essentially no difference in the performance of PSA Cycles II and III, a counterintuitive result. The ¹⁴CO enrichment and the ¹⁴CO recovery both increased with decreasing CO feed throughputs and higher R R, which were always very close to unity.

Keywords: Isotope separation; PSA; Pressure swing adsorption; Carbon isotope separation; Nuclear waste

Experimental and molecular simulation studies of CO₂ adsorption on zeolitic imidazolate frameworks: ZIF-8 and amine-modified ZIF-8 by Defei Liu; Yongbiao Wu; Qibin Xia; Zhong Li; Hongxia Xi (pp. 25-37).

ZIF-8 has been rapidly developed as a potential candidate for CO₂ capture due to its low density, high surface area, and robust structure. Considering the electron-donating effect of amino functional groups, amino-modification is expected to be an efficient way to improve CO₂ adsorption of ZIF-8. In this work, grand canonical Monte Carlo (GCMC) simulation was performed to study the CO₂ adsorption isotherm based on ZIF-8, ZIF-8-NH₂, and ZIF-8-(NH₂)₂. ZIF-8 was synthesized and CO₂ adsorption isotherms based on ZIF-8 was measured. The experimental surface area, pore volume, and CO₂ adsorption isotherm were used to validate the force field. Adsorptive capacity of ZIF-8-NH₂, and ZIF-8-(NH₂)₂ were first estimated. The GCMC simulation results indicated that the order of increasing CO₂ capacity of the ZIF-8 in the lower pressure regime is: ZIF-8 < ZIF-8-NH₂ < ZIF-8-(NH₂)₂, and in the high pressure is: ZIF-8 < ZIF-8-(NH₂)₂ < ZIF-8-NH₂. New adsorption sites can be generated with the existence of-NH₂ groups. In addition, for non-modified and amino-modified ZIF-8, it was the first time to use density functional theory (DFT) calculations to investigate their CO₂ adsorption sites and CO₂ binding energies. The present work indicates that appropriate amine-functionalized can directly enhanced CO₂ capacity of ZIF-8.

Keywords: Molecular simulation; Amino-modification; ZIF-8; CO₂ adsorption

High-temperature hydrothermal synthesis of magnetically active, ordered mesoporous resin and carbon monoliths with reusable adsorption for organic dye by Fujian Liu; Hao Zhang; Longfeng Zhu; Yanmei Liao; Faisal Nawaz; Xiangju Meng; Feng-Shou Xiao (pp. 39-47).

Magnetically active, thermally stable, and ordered mesoporous resin (MOMR-200) and carbon (MOMC-200) monoliths were prepared by one-pot hydrothermal synthesis from resol, copolymer surfactant, and iron cations at high-temperature (200 ^∘C), followed by calcination at 360 ^∘C and carbonization at 600 ^∘C. X-ray diffraction results show that both MOMR-200 and MOMC-200 have ordered hexagonal mesoporous symmetry, and N₂ isotherms indicate that these samples have uniform mesopores (3.71, 3.45 nm), high surface area (328, 621 m²/g) and large pore volume (0.31, 0.43 cm³/g). Transmission electron microscopy shows that iron nanoparticles, which are superparamagnetic in nature, are dispersed in the network. More importantly, the high temperature (200 ^∘C) products exhibit much better stability than the samples synthesized at low temperature (100 ^∘C). Interestingly, MOMC-200 has higher adsorption capacity for organic dyes when compared with commercial adsorbents (activated carbon and macroporous resin: XAD-4). Combining the advantages such as magnetically active, thermally stable networks, ordered and open mesopores, high surface area, large pore volume, adsorption of pollutants in water and desorption in ethanol solvent, MOMC-200 is potentially important for water treatments.

Keywords: High temperature synthesis; Ordered mesoporous carbon; Magnetically active; Adsorption; Stability

Preparation and characterization of double metal-silica sorbent for gas filtration by Ebenezer Twumasi Afriyie; Peter Norberg; Christer Sjöström; Mikael Forslund (pp. 49-61).

This paper presents the preparation of a porous (Mg, Ca) silicate structure, which could be employed as sorbent filter media. The sorbents have been prepared using sodium silicate precipitated with various ratios of magnesium and calcium salts. The sorbents obtained were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD) and nitrogen physisorption isotherm. Further, the applicability and performance of the sorbent impregnate with potassium hydroxide for removal of sulphur dioxide (SO₂) has been demonstrated. From the isotherms, specific surface area, pore diameter and volume of pores were estimated. Results show that the chemical composition and textural properties of the resultant sorbents were highly dependent on Mg/Ca molar ratio. It was found that sorbents made with 68 mol% Mg and 32 mol% Ca (PSS-MgCa-68/32); and 75 mol% Mg and 25 mol% Ca (PSS-MgCa-75/25) exhibited even higher specific surface area and pore volume than the sorbents containing a single metal. The Mg/Ca-silica sorbents obtained contains interconnected bimodal porosity with large portions being mesopores of varied sizes. The pore size distribution (PSD) results further indicate that PSS-MgCa-68/32 sorbent exhibits wide PSD of interconnected pores in the size range of 1 to 32 nm while PSS-MgCa-50/50 and PSS-MgCa-75/25 exhibits narrow PSD of 1 to 5 nm. Using SO₂ as model contaminate gas, it was shown that the dynamic adsorption performance of the PSS-MgCa-sorbents impregnated with 8 wt% KOH exhibits SO₂ uptake, with impregnated PSS-MgCa-68/32 showing better performance. This shows that the materials prepared can be used as adsorbent for gas filtration.

Keywords: Mg/Ca-silica sorbent; Gas filtration; Characterization; Textural properties; Impregnate Mg/Ca-silica sorbents

2D-SAFT-VR approach to study of the adsorption isotherms for binary mixtures by Martin Castro; Alejandro Martínez (pp. 63-70).

In this article we present results of approximating molecular modeling of the gas mixtures methane-nitrogen, methane-carbon dioxide, and nitrogen-carbon dioxide adsorbed on activated carbon at a temperature of 318.2 K, based on the Statistical Associating Fluid Theory for potentials of Variable Range. Unlike the previous work (Castro et al.) showing the results in rescaled units, in this work the results obtained are shown in real units as obtained in the experiments.

Keywords: Adsorption; Isotherms; 2D-SAFT-VR; Mixtures; Carbon actived

Application of mass spectrometry for study of the adsorption of multicomponent surfactant mixtures at the solid/solution interface by Mária Benkő; Sándor Puskás; Zoltán Király (pp. 71-76).

The selective adsorption of the components of a polydisperse gemini surfactant blend (alkylbenzenesulfonate-Jeffamine salt, ABSJ) in aqueous solution onto Berea sandstone, a reference material in enhanced oil recovery (EOR), was investigated. The individual adsorption isotherms of the four, benzene-ring containing ABSJ components with different alkyl chain lengths (ranging from decyl to tridecyl of the alkyl chain length) were simultaneously determined by using a four-channel electrospay ionization mass spectrometer (ESI-MS) for concentration analysis. This analytical device provided selective information (based on the differences in the mass to charge ratio) on the adsorption of each component in the mixed surfactant system. The overall isotherm obtained from the superposition of the individual isotherms determined by ESI-MS agreed well with the isotherm determined by UV spectrometry; the UV equipment is benzene-ring sensitive, irrespective of the alkyl chain length. The S-shaped isotherms reached a plateau at the critical micelle concentration. Longer-chain surfactants adsorbed preferentially over the short chain homologs, independently of solution concentration. This analytical device provided the net adsorption isotherm. Most analytical methods are not component selective, and thus they are not able to measure the individual isotherms in multicomponent solutions. Here, we report on a novel method which describes the selective determination of the individual adsorption isotherms of surfactants in a multicomponent mixture. The theoretical background of the method is described in detail.

Keywords: Gemini surfactants; Multicomponent solutions; Adsorption; Berea sandstone; Mass spectrometry; Enhanced oil recovery

A new intraparticle mass transfer rate model for cyclic adsorption and desorption in a slab, cylinder or sphere by Chuncai Yao (pp. 77-81).

A new intraparticle mass transfer rate model for cyclic adsorption and desorption in a slab, cylinder or sphere is proposed on the basis of the asymptotic behaviors of the adsorption rate for short and long cycle periods. Through comparison with the exact solution and the linear driving force (LDF) model, the new model is shown to provide a very good approximation for the instantaneous amount adsorbed as well as the adsorption rate for dimensionless half-cycle period τ c=0.001∼1 and is much better than the LDF model.

Keywords: Cyclic adsorption; Rate model; Diffusion; Mass transfer; Mathematical modeling; Approximation

The effect of small micropores on methane adsorption of coals from Northern China by Feng-Hua An; Yuan-Ping Cheng; Dong-Mei Wu; Liang Wang (pp. 83-90).

In this study, the effect of coal micropores on the adsorption properties, especially the Langmuir pressure (P L), was investigated by testing 11 coal samples from Northern China. The adsorption of CO₂ at 273 K was utilized to analyze the pore size distribution. The results of these coals show that micropore volume and micropore surface area are the major factors affecting the Langmuir volume (V L) but have weaker effects on P L. Micropore filling theory considers that some smaller micropores with an obvious overlapping adsorption force cause volume filling adsorption. These micropores firstly reach saturated adsorption, controlling the adsorption volume at the low-pressure stage and thus have a great effect on P L. Four times the methane molecular diameter, 1.5 nm, was assumed as the critical pore size with obvious overlapping adsorption force. The relationship between P L and the proportion of the pore volume below 1.5 nm to the micropore volume was investigated, and it was found that the higher the volume proportion of these small micropores was, the smaller the P L was, though two data points deviated from this trend. The reason for the anomalous coal samples could be the deviation from the assumed critical pore size of 1.5 nm for volume filling and the effects of the various micropore surface properties, which await further study.The micropore surface increases with increasing coal rank, as does V L. The proportion of pore volume below 1.5 nm increases with coal rank, and P L reverses. However, these relationships are discrete.

Keywords: Langmuir volume; Langmuir pressure; Micropore filling theory; Pore size distribution; Coal rank

Adsorption of methyl parathion on PAC from natural waters: the effect of NOM on adsorption capacity and kinetics by Jingyi Zhang; Baoyou Shi; Tao Li; Dongsheng Wang (pp. 91-99).

Source water pollution by agricultural chemicals poses great threat to drinking water safety and the removal of such contaminants is a challenge to the water treatment industry. In this work, the adsorption behaviors of methyl parathion (MP) from different natural waters onto different kinds of powdered activated carbons (PAC) were investigated systematically. On the basis of the characterization of the PACs and natural organic matter (NOM), the suitability of PAC with NOM for effective removal of MP was proposed, and the effect of competitive adsorption on MP removal under two PAC dosing patterns was evaluated. The results indicated that NOM adsorption was dependent on the molecular weight (MW) distribution of organic compounds and the pore size distribution of PAC. The mesopore surface area with pore size>3 nm was dominant for the adsorption of the NOM fraction in the range of 500 Da

Keywords: Powdered activated carbon (PAC); Natural organic matter (NOM); Suitability; Competitive adsorption; Pore blockage

Pure and binary adsorption isotherms of ethylene and ethane on zeolite 5A by Masoud Mofarahi; Seyyed Milad Salehi (pp. 101-110).

Pure and binary adsorption equilibrium data of ethylene and ethane on zeolite 5A were collected with a volumetric method for the temperature range 283 K to 323 K and pressure up to 950 kPa. The applicability of the binary adsorption prediction by the vacancy solution theory (VST) was investigated. Further individual adsorption and selectivity were obtained by VST prediction. According to the experimental results, zeolite 5A has a high adsorption capacity and selectivity for ethylene in the ethylene/ethane system. VST predicts that ethylene selectivity increases with pressure; it also shows that the amount of ethylene separated by zeolite 5A increases as the temperature decreases at a specified pressure.

Keywords: Adsorption; Zeolite 5A; Ethylene/ethane separation system; Vacancy solution theory

Experimental study on coking, deactivation, and regeneration of binderless 5A zeolite during 1-hexene adsorption by Hui Sun; Benxian Shen (pp. 111-120).

Coking, deactivation, and regeneration of 5A zeolite during 1-hexene adsorption were studied on a fixed-bed adsorber and a themogravimetric analyzer. Adsorption activity measurement, scanning electron microscope (SEM) analysis, X-ray diffraction (XRD) analysis, FT-IR analysis, ¹H NMR analysis, and porosity measurement were used to reveal the mechanism of coking and deactivation of 5A zeolite, and evaluate the influences of binder on them. There are distinct increases in both coke content and deactivation degree with increasing the adsorption temperature. Deactivation degrees of zeolite increase as coke contents rise, however, they display smaller increasing rate at higher coke content. The rates of coke formation and deactivation of 5A zeolite are significantly enhanced by the binder mainly due to the fact that the activity sites offered by the amorphous compounds contained in the binder catalyze the formation of coke precursors. As compared to the coke formed in zeolite with binder, the coke in binderless zeolite is more aromatic. The coke which consists of inflammable part and nonflammable part can be oxidatively removed completely while the temperature approaches 787 K. No destruction in 5A zeolite crystal structure was observed in the regenerated binderless sample. The formation of coke during 1-hexene adsorption on zeolite can be explained using the carbonization-cyclization reaction mechanism. Furthermore, the kinetics models for formation and removal of coke were developed.

Keywords: 5A zeolite; 1-Hexene; Coke formation; Deactivation; Regeneration

Multilayer adsorption equilibrium model for gas adsorption on solids by Sébastien Thomas; Pierre Schaetzel (pp. 121-129).

Adaptation of the ENSIC model to physisorption of nitrogen or argon on a solid surface first led to a 3 parameters model called multilayer adsorption equilibrium model (MAE model). One of these parameters is related to the formation of a multilayer of adsorbate on the solid surface. Exploitation of data from the literature pointed out that this parameter does not depend on the nature of the solid surface and an average value was calculated in the case of N₂ and Ar. As a consequence, the MAE model can be considered as a 2 parameters model. Linearization of the model was established allowing an easy determination of surface areas of macroporous and some mesoporous solids. Fitting of isotherms of meso and macroporous solids has led to promising results compared to the ones obtained with the BET model. Moreover, adaptation of this model to microporous solids can also be used for an uncomplicated determination of porous volume and external surface. Results obtained from data of the literature were close to those obtained with the t-plot model.

Keywords: Adsorption isotherm; Surface area; Pore volume; Mesoporous solid; Microporous solid

On the description of isotherms of CH₄ and C₂H₄ adsorption on graphite from subcritical to supercritical conditions by Mus’ab Abdul Razak; D. D. Do; Toshihide Horikawa; Keita Tsuji; D. Nicholson (pp. 131-142).

Different potential models for methane and ethylene are tested for their suitability for the description of bulk phase behavior, including coexistence, and adsorption on a graphite surface under sub- and super-critical conditions using GCMC simulation. Under sub-critical conditions, those intermolecular potential models that describe correctly the vapor–liquid equilibria were found to be adequate for the description of surface adsorption. These potential models can also give a good account of adsorption under supercritical conditions or near-critical conditions, provided the experimental data (in terms of excess) are correctly obtained with the reliably determined void volume as illustrated in this paper with methane adsorption.

Keywords: Adsorption; Graphon; Methane; Ethylene; Supercritical

Adsorption of ammonia and water on functionalized edge-rich carbon nanofibers by Yusuke Takahashi; Hirotaka Fujita; Akiyoshi Sakoda (pp. 143-159).

The preparation, characterization and ammonia and water adsorption properties of edge-rich carbon nanofibers (CNFs) were studied, including platelet CNFs (PCNFs) and cup-stacked CNFs (CSCNFs). Since PCNFs and CSCNFs have many chemically active exposed edges, functionalization by oxidizing the edges was carried out by ozone stream and by nitric acid. Transmission electron microscopy, N₂ adsorption isotherms and temperature-programmed desorption analysis showed that the nitric acid treatment partly destroyed the graphite structure of the PCNFs and created acid functional groups and micropores, whereas the ozone treatment created functional groups without damaging the structure. Ammonia adsorption isotherms clarified that NH₃ adsorption on PCNFs and CSCNFs occurred mainly on oxygen-containing groups, whereas the adsorption on activated carbon fibers (ACFs) occurred on both oxygen-containing groups and the carbon surface without the functional groups, and the CSCNFs showed larger amounts of adsorbed ammonia compared to the PCNFs. Especially at a relatively low pressure range (<0.2 atm), the PCNFs/CSCNFs/ACFs showed the same ammonia adsorption mechanism; that is, the one-to-one interaction between oxygen atoms in the functional groups and hydrogen atoms in ammonia molecules. In addition, the adsorption on the ACFs appeared to occur mainly by interaction with the carbon surface at relatively high pressure (0.3–1.0 atm). Our experimental results and previous findings suggest that NH₃ adsorption on PCNFs is due mainly to NH…O hydrogen bonding between oxygen-containing groups and ammonia rather than to chemical bonding.

Keywords: Carbon nanofiber; Adsorption; Ammonia; Water

A review on reactive adsorption for potential environmental applications by Manisha Sharma; Raj K. Vyas; Kailash Singh (pp. 161-188).

The aim of this paper is to present a critical review on reactive adsorption processes. The impact of surface modification on adsorption behavior of various adsorbents in context of reactive adsorption has been reviewed. Various characterization and detection methods involved to access and verify the surface morphology of adsorbent, presence of surface functionalities on adsorbent, and concentration of adsorbate have been concisely presented. The paper also delves into the inadequately researched grey areas of reactive adsorption which require further attention such as modeling and adsorbent regeneration so as to make the process more economic. The applicability of reactive adsorption to ensure a cleaner environment has also been briefly discussed. This article also underlines the areas, in which reactive adsorption can be implemented on a pilot scale.

Keywords: Reactive adsorption; Adsorbent modification; Modeling; Adsorbent regeneration; Process intensification

A comparison on efficiency of virgin and sulfurized agro-based adsorbents for mercury removal from aqueous systems by Neda Asasian; Tahereh Kaghazchi (pp. 189-200).

Mercury adsorption by sulfur impregnated adsorbents seems to be one of the most efficient ways for removal of this toxic metal ion from wastewater and atmosphere. The aim of this work was to develop a method for preparation of low-cost sulfurized adsorbent from agricultural wastes; this approach combines two stages of (i) chemical activation with phosphoric acid and (ii) impregnation with powdered sulfur, in one step only. The physico-chemical properties of sulfurized adsorbent (AC-S) were determined with BET, FT-IR, Eschka method and pH_PZC measurements, and compared with those of the virgin sample (AC). It was found that sulfurization according to this method can introduce about 8 wt.% sulfur into the structure of adsorbent, in the forms of C–S, S–H, S–S and S=O functional groups. Although during the sulfur introduction processes, a decrease in surface area and micropore volume of the sulfurized adsorbent is to be expected, not only such decrease did not occur in this work, but a large increase in microporosity was seen. Thereupon, both the sulfur functionalities and extended microporosity of AC-S lead to higher capability of this sample for mercury adsorption rather than AC. Finally, the kinetics and equilibrium of mercury adsorption from aqueous solutions were studied for AC and AC-S.

Keywords: Activated carbon; Sulfur impregnation; Sulfurized adsorbent; Mercury; Kinetics; Isotherm

Diffusion of n-alkanes in mesoporous 5A zeolites by ZLC method by Zhiping Liu; Weiming Fan; Zhaoteng Xue; Jinghong Ma; Ruifeng Li (pp. 201-208).

Diffusion properties of mesostructured zeolite 5A were investigated by employing n-alkanes as probe molecules using the zero length column (ZLC) method. The mesopores were found to enhance molecule diffusion. Moreover, the effective diffusion time constant (D _eff/R ²) increased with mesoporosity in the zeolites between 308 K and 393 K, whereas the activation energy decreased with increasing mesopore volume. The effective diffusivity values of n-alkanes in mesoporous zeolite 5A were generally higher than that the microporous zeolite 5A sample. This clearly implied the important role of the mesopore in zeolites crystals in facilitating the transport of reaction molecules due to shorter average diffusion path length and less steric hindrance.

Keywords: Mesoporous zeolite; 5A zeolite; ZLC method; Diffusion; Activation energy

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Adsorption: Journal of the International Adsorption Society (v.19, #1)

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Adsorption: Journal of the International Adsorption Society (v.19, #1)