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Adsorption: Journal of the International Adsorption Society (v.17, #5)

Special issue of FOA10 in honor of our colleagues in Japan and New Zealand (pp. 765-765).

Preface by Minoru T. Miyahara (pp. 767-768).

Modelling relaxation processes for fluids in porous materials using dynamic mean field theory: application to pore networks by J. R. Edison; M. Ganz; B. Novello; P. A. Monson (pp. 769-776).

We present an application of a recently developed dynamic mean field theory to the study of relaxation dynamics in adsorption and desorption from pore networks. The theory predicts the evolution of density distribution in the system, based on an underlying free energy functional from static mean field theory and the system evolves to equilibrium or metastable equilibrium states consistent with the static theory. The theory makes it possible to follow the evolution of the density distribution with time in response to a change in the bulk pressure or chemical potential. We compare uptake dynamics for a 2D slit pore network with that in a single slit pore. We see more rapid uptake dynamics in the pore network in some cases, due to the greater access of the pore space to the bulk. We also observe that the formation of liquid bridges can slow down the mass transfer in the pore network in certain situations.

Keywords: Porous materials; Dynamics; Mean field theory; Pore networks

Adsorption equilibrium of methane and carbon dioxide on porous metal-organic framework Zn-BTB by Bin Mu; Krista S. Walton (pp. 777-782).

Porous metal-organic frameworks (MOFs) have emerged over the past decade as an important new class of materials possessing permanent porosities, uniform pore structures, high surface areas, and low crystal densities. MOFs are regarded as promising solid adsorbents for gas storage and separation but have not reached an applied level yet. One impediment to MOF applications is incomplete adsorption information and lack of structure-property relationships. In this paper, we present pure-component adsorption equilibrium data for methane and carbon dioxide at different temperatures on a new three-dimensional Zn-MOF material built from the ligand 1,3,5-tris(4-carboxyphenyl)benzene (H₃BTB) with Zn metal. The data are described by Toth’s equation and Dubinin-Astakhov (D-A) equation. Thermodynamic properties including isosteric heat of adsorption are estimated based on the two models and comparisons are made with other adsorbents. The smaller pore diameters of Zn-MOF compared to related structures MOF-177 and UMCM-1 lead to greater adsorption loadings at 1 bar.

Keywords: Adsorption; Metal-organic frameworks; Methane; Carbon dioxide

In situ measurement of gas adsorption processes using Flux Response Technology by Candice Palmer; Ayodeji Sasegbon; Klaus Hellgardt (pp. 783-794).

Flux Response Technology (FRT) is being developed as a powerful in situ perturbation technique to facilitate detailed characterisation of heterogeneous catalysts. FRT works by measuring minuscule changes in flowrate between two gas streams for potentially any gaseous process involving a change in volume (dV/dt). FRT functions analogous to an electrical Wheatstone bridge assembly whereby gas molecules represent electrons and flow capillaries represent resistors. A perturbation of pressure, temperature, but particularly of concentration causes an imbalance in the system, which is measured directly by a very sensitive differential pressure transducer (DPT). It is demonstrated how FRT can provide a simple, inexpensive, highly accurate means of quantifying the acidic sites of zeolites using ammonia ad/desorption as well as determining the dynamically available surface areas of catalysts using nitrogen adsorption at liquid nitrogen temperature. Temperature programmed experiments (temperature perturbations) can also be employed with FRT to rapidly compare catalyst activity directly (for catalyst development but also for quality control) without the need for much calibration.

Keywords: Flux Response; Transient; Technique; In situ; Zeolite

Zeolite synthesis from waste fly ash and its application in CO₂ capture from flue gas streams by Liying Liu; Ranjeet Singh; Penny Xiao; Paul A. Webley; Yuchun Zhai (pp. 795-800).

Zeolite A and A + X mixtures were prepared from coal-fly ash procured from China by using an alkali fusion method. X-ray diffraction showed that both the materials were crystalline and reproducible. Scanning Microscopy revealed that pure zeolite A particles have cubic morphology while the mixture shows intergrowth of cubic and pyramidal crystals. The surface area for A + X mixture was around 330 m²/g which is higher than zeolite A, however, lower than typical X zeolite. CO₂ and N₂ adsorption isotherms were measured and the data was fitted by the Dual Site Langmuir equation. These zeolites were then tested for CO₂ capture at different temperatures in a process with a nine step cycle. When compared with 13X zeolites at higher temperature (∼90 °C), both the zeolite A + X mixture and zeolite A prepared from fly ash showed better performance in CO₂ capture from flue gas because they have higher selectivity of CO₂ over N₂.

Keywords: CO₂/N₂ adsorption; Flue gas; Fly ash; Zeolite A; Zeolite A + X

Adsorption properties of BEA zeolites and their aluminum phosphate extrudates for purification of isomaltose by Manuel Holtkamp; Stephan Scholl (pp. 801-811).

The disaccharide isomaltose is produced via an enzymatic reaction and is adsorbed to BEA zeolite. This reaction integrated adsorption can be achieved as fluidized bed as well as fixed bed. We investigated isotherms, adsorption enthalpies and sorption kinetics of BEA zeolite and extrudates with a novel aluminum phosphate sintermatrix. These extrudates contain 50% (w/w) of BEA 150 zeolites (Si/Al = 75) as primary crystals. BET-surface for extrudates is 245 m²⋅g⁻¹ and 487 m²⋅g⁻¹ for zeolite. Extrudates show a monomodal macropore structure with a maximum at 90 nm. All isotherms show a type I shape. For lower equilibrium concentrations, which occur during the enzymatic reaction, Henry’s law is applied and compared to a Langmuir model. Adsorption equilibrium constant K i,L calculated from Langmuir for extrudates at 4 °C is 64.7 mL⋅g⁻¹ and more than twice as high as obtained from Henry’s law with K i is 26.8 mL⋅g⁻¹. Adsorption on extrudates at 4 °C is much stronger than on zeolite crystals where the Henry coefficient K i is 17.1 mL⋅g⁻¹. Adsorption enthalpy Δh _Ad calculated from van’t Hoff plot with the Henry equation is −44.3 kJ⋅mol⁻¹ for extrudates and −29.6 kJ⋅mol⁻¹ for zeolite crystals. Finally, the kinetics for ad- and desorption were calculated from the initial slope. The diffusion rate for ad- and desorption on extrudates were in the same range while adsorption on zeolites is three orders of magnitudes faster than desorption.

Keywords: Zeolite; Extrudates; Isomaltose; Ad- and desorption kinetics; Isotherms

Effects of a non-ionic surfactant, Tween 20, on adsorption/desorption of saccharification enzymes onto/from lignocelluloses and saccharification rate by Dong-June Seo; Hirotaka Fujita; Akiyoshi Sakoda (pp. 813-822).

In this work, we examined the role of a non-ionic surfactant, Tween 20, on enzymatic hydrolysis of lignocelluloses. Delignified lignocelluloses (pine wood chip) were used as model substrates. Effects of Tween 20 on adsorption/desorption onto/from lignocelluloses with and without hydrolysis were evaluated respectively. Tween 20 lowered the non-biospecific adsorption of β-glucosidase and enhanced the bio-specific adsorption of cellulase. Tween 20 did not affect the liquid phase reaction (cellobiose hydrolysis). However, for the solid surface reaction (cellulose hydrolysis), cellulose conversion for 72 hrs was increased 9–21% and 1–8.5% for samples with high lignin contents (PI) and low lignin contents (PIII) by injection of Tween 20 (0.024–0.24 mM), respectively. Moreover, Tween 20 increased the cellulose conversion rate substantially. It is suggested that the increase of cellulase amount adsorbed due to the increase of effective cellulose surface by Tween 20 contribute to the enhancement of cellulose conversion.

Keywords: Lignocelluloses; Tween 20; Cellulase; β-glucosidase

About the limits of regularization and the ansatz method by Steffen Arnrich; Grit Kalies; Peter Bräuer (pp. 823-831).

The well-known adsorption integral equation (AIE) for calculating pore size and adsorption energy distributions from adsorption isotherms on porous solids is, from the mathematical point of view, a linear Fredholm integral equation of the first kind and therefore an ill-posed problem. What can we realistically expect from the solution of such an ill-posed problem by regularization? Does it make sense to restrict the number of possible solutions by the so-called ansatz method? In this paper, the two methods for solving ill-posed problems are from scratch explained and illuminated by concrete examples. Their relevance and fundamental limitations are discussed.

Keywords: Ill-posedness; Unstable operators; Regularization; Ansatz method; Adsorption integral equation; Pore size and adsorption energy distributions

Characterisation and improvement of sorption materials with molecular modeling for the use in heat transformation applications by S. K. Henninger; F. P. Schmidt; H.-M. Henning (pp. 833-843).

In this paper, several materials for sorption heat transformation applications are evaluated on basis of experimental characterisation and molecular simulation methods. With regard to the application, classical zeolites, ion exchanged zeolites, aluminophosphates as well as silica-aluminophosphates have been analysed. Furthermore samples of metal organic frameworks (MOF) have been evaluated for the use in sorption heat transformation applications with very promising results. In order to understand the fundamental relationship between adsorbent microstructure and water adsorption equilibrium, molecular simulation of water adsorption in various adsorbents are employed. As a result of these simulations within the grand canonical ensemble, the number of water molecules adsorbed in thermodynamic equilibrium under given conditions of temperature and chemical potential (resp. pressure) are obtained. These data are compared with adsorption data from thermogravimetric measurements.

Keywords: Water adsorption; Heat pump; Molecular modelling; Heat transformation; Zeolite; AlPO; MOF

On the influence of heterogeneity of graphene sheets in the determination of the pore size distribution of activated carbons by J. C. Alexandre de Oliveira; R. H. López; J. P. Toso; Sebastião M. P. Lucena; C. L. Cavalcante Jr.; D. C. S. Azevedo; G. Zgrablich (pp. 845-851).

We model carbon-based microporous materials, such as activated carbons, taking into account surface defects in the form of geometrical rugosity in the inner surface of each graphitic slit pore. The used model is a simplified variation of the randomly etched graphite (REG) pore model (Seaton et al., Langmuir 13:1199–1204, 1997).When subcritical Ar or N₂ is used as probe-gas to simulate the adsorption process in slit pores assembled with ideally perfect graphene walls, the resulting pore size distribution (PSD) rather consistently shows a relatively low population of pores around 12–13 Å. This feature is supposed to be an artifact introduced by the perfect graphene sheets modeling assumptions.In this study, we particularly examine to which extent the gap of the PSD around 12–13 Å is linked to the perfect graphene sheet model and the effects of surface rugosity in the determination of the PSD. Adsorption isotherms of nitrogen at 77 K and local density distributions are studied simultaneously in the simulation. We found that, by mixing a complete series of heterogeneous pores with 25% of repulsive sites, a noticeable improvement in the fitting between the theoretical and the experimental isotherms was achieved and the PSD gap was eliminated. The mixed model with 25% of repulsive sites provided a more realistic estimate of the internal structure of microporous carbons.

Keywords: Pore size distribution; Slit geometry; Heterogeneity; Monte Carlo simulation

Characterization of the PSD of activated carbons from peach stones for separation of combustion gas mixtures by Débora A. Soares Maia; J. C. Alexandre de Oliveira; Juan Pablo Toso; Karim Sapag; Raul H. López; Diana C. S. Azevedo; Célio L. Cavalcante Jr.; Giorgio Zgrablich (pp. 853-861).

Controlled series of microporous carbons were prepared through chemical activation with phosphoric acid from peach stones as the precursor material, corresponding to different preparation conditions. Adsorption isotherms of N₂ at 77 K and of CO₂ at 273 K were measured to be used in the characterization of the samples. The recently proposed mixed-geometry model (MGM), which assumes that the activated carbon is better represented by a mixture of slit and triangular geometry pores, is used to obtain the PSDs of the samples, on the basis of Grand Canonical Monte Carlo (GCMC) simulated ideal isotherms, both for N₂ at 77 K and of CO₂ at 273 K. Our results emerging from the analysis of two families of activated carbons reveal a consistent picture supporting the thesis that the PSDs of the same sample obtained trough N₂ and CO₂ adsorption are different, a still controversial issue in the literature. Comparison of predictions from the MGM with those of the pure slit geometry model (PSGM) shows that the former gives a more consistent picture and more similar PSDs for the two adsorbates used.

Keywords: Activated carbon; Pore size distribution; Slit geometry; Triangular geometry

Synthesis and characterization of zeolites NaA and NaY from rice husk ash by Wan-Cheng Tan; Sing-Yoh Yap; Akihiko Matsumoto; Radzali Othman; Fei-Yee Yeoh (pp. 863-868).

In this study, both zeolites NaA and NaY were synthesized from rice husk ash (RHA) by a simple conventional hydrothermal route. Rice husk (RH) was used as a silicate source to produce various zeolites. The hydrothermal route was conducted via a seeding technique involving the preparation of two separate gels, i.e. colloidal seed and feedstock gel. The zeolite was first produced using commercially available chemicals and followed by the replacement of the commercial silicate sources with RHA derived silicate. The RHA silicate was obtained by combusting the RH at different temperatures and durations i.e. 450 °C for both 2 and 6 hours, as well as 750 °C for 6 hours. Zeolite NaY (faujasite) was successfully synthesized with commercial chemical seed and RHA derived feedstock gel. On the other hand, using RHA silicate in both colloidal seed and feedstock gel would give only zeolite NaA. Elemental, structural and morphological analyses of RHA and zeolites were carried out with X-ray fluorescence (XRF) spectrometer, X-ray diffractometer (XRD) and scanning electron microscopy (SEM).

Keywords: Zeolite NaA; Zeolite NaY; Rice husk ash; Silicate sources

Isolation of ethanol from its aqueous solution by liquid phase adsorption and gas phase desorption using molecular sieving carbon by Hirotaka Fujita; Qingrong Qian; Takao Fujii; Kazuhiro Mochizuki; Akiyoshi Sakoda (pp. 869-879).

A novel bioethanol separation process was proposed in this study employing molecular sieving carbon (MSC) as an adsorbent, whose pore diameter is close to molecular size of ethanol. In the proposed process, fermentation broth is first introduced to the adsorption bed packed with MSC. In this step, ethanol is selectively adsorbed onto MSC, with highly enriching ethanol in the micropore of MSC. Subsequently, the concentrated ethanol is desorbed from MSC to gaseous phase, resulting in further purification of ethanol owing to a considerable difference in desorption rate between water and ethanol; Because of molecular sieving effect of MSC, the desorption rate of ethanol is much smaller than that of water. To establish this process, adsorption equilibrium and kinetics of ethanol on various MSCs were investigated in aqueous phase as the first step. Also, desorption kinetics of ethanol and water in gaseous phase were investigated. As a result, it was suggested that highly concentrated ethanol could be obtained with high recovery ratio through these simple operations, meaning the proposed process is quite promising.

Keywords: Bioethanol; Adsorption; Desorption; Separation

Lithium extraction/insertion process on cubic Li-Mn-O precursors with different Li/Mn ratio and morphology by Shu-Ying Sun; Xingfu Song; Qin-Hui Zhang; Jin Wang; Jian-Guo Yu (pp. 881-887).

The cubic phase LiMn₂O₄ precursors are prepared by high-temperature calcinations (1003 K) of LiOH⋅H₂O and MnO₂ mixture with Li/Mn molar ratio = 0.55. The Li₄Mn₅O₁₂ precursors are synthesized via low-temperature solid-phase reaction (673 K) of LiNO₃ and MnO₂ mixture with Li/Mn molar ratio = 1.0. The ion-sieves counterparts (named SMO-H and SMO-L, respectively) are obtained by the acid treatment of Li-Mn-O precursors. The structure, chemical stability, morphology, ion-exchange property and mechanism of Li-Mn-O precursors and MnO₂ ion-sieve were systematically examined via X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), Infrared Spectroscopy (IR), X-ray photoelectron spectroscopy (XPS) and lithium ion selective adsorption measurements. The result shows the more compact Mn-O lattice makes the Li₄Mn₅O₁₂ spinel more stable after the Li⁺ is extracted. The results of IR and XPS show adsorption process of SMO-H exists ion-exchange between the Li⁺ and protons, and redox reaction, but only exists ion-exchange between the Li⁺ and protons in SMO-L. Agglomeration is well-improved by low calcination temperature and the morphology of the Li₄Mn₅O₁₂ precursor and final MnO₂ ion-sieve are effectively controlled within low-dimensional structure. The maximum pH titration capacity of SMO-L for Li⁺ is 6.76 mmol⋅g⁻¹, but only 3.47 mmol⋅g⁻¹ for SMO-H. The ion-sieve obtained from Li₄Mn₅O₁₂ precursor is promising in the lithium extraction from brine or seawater.

Keywords: Lithium; Spinel Li-Mn-O precursor; Adsorption; Ion-sieve; Morphology

A model for enhanced coal bed methane recovery aimed at carbon dioxide storage by Ronny Pini; Giuseppe Storti; Marco Mazzotti (pp. 889-900).

Numerical simulations on the performance of CO₂ storage and enhanced coal bed methane (ECBM) recovery in coal beds are presented. For the calculations, a one-dimensional mathematical model is used consisting of mass balances describing gas flow and sorption, and a geomechanical relationship to account for porosity and permeability changes during injection. Important insights are obtained regarding the gas flow dynamics during displacement and the effects of sorption and swelling on the ECBM operation. In particular, initial faster CH₄ recovery is obtained when N₂ is added to the injected mixture, whereas pure CO₂ allows for a more effective displacement in terms of total CH₄ recovery. Moreover, it is shown that coal swelling dramatically affects the gas injectivity, as the closing of the fractures associated with it strongly reduces coal’s permeability. As a matter of fact, injection of flue gas might represent a useful option to limit this problem.

Keywords: ECBM; Simulation; Permeability; Sorption; Swelling

Bioaccumulation of heavy metals on adapted Aspergillus foetidus by W. Ge; D. Zamri; H. Mineyama; M. Valix (pp. 901-910).

The development of the organisms extracellular and intracellular mechanisms for the uptake of heavy metals were conducted by using the natural detoxification strategies of the organism to toxicity. Aspergillus foetidus was used as a test case organism to examine these processes. Aspergillus foetidus was adapted to multi-metals (Al, Co, Cr, Cu, Fe, Mg, Mn, Ni and Zn) by a sequential method for tolerance development. The detoxification strategies of A. foetidus occurred by two mechanisms. The first mechanism is the production of extracellular metabolites that is capable of adsorbing and precipitating the metal ions on the cell surface. The second mechanism for the detoxification of metals is the intracellular binding of heavy metals to thiol containing compounds such as GSH and sequestering these metal–thiol complexes into sub-cellular compartments or vacuoles. These detoxification strategies resulted in adapted organisms with tolerance to multi-heavy metals concentrations and significantly higher metal uptake with adaptation.

Keywords: Bioaccumulation; Aspergillus foetidus; Multi-heavy metals; Adaptation; Intracellular and extracellular mechanisms

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Adsorption: Journal of the International Adsorption Society (v.17, #5)

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Adsorption: Journal of the International Adsorption Society (v.17, #5)