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Adsorption
[SJR: 0.774] [H-I: 52] [4 followers] Follow

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1572-8757 - ISSN (Online) 0929-5607
Published by Springer-Verlag

[2355 journals]

Selection of a stationary phase for the chromatographic separation of
organic acids obtained from bioglycerol oxidation
- Authors: Lucas C. D. Coelho; Nelson M. L. Filho; Rui P. V. Faria; Ana M. Ribeiro; Alírio E. Rodrigues
  Pages: 627 - 638
  Abstract: A screening study of the chromatographic separation of Glyceric Acid (GCA) and Tartronic Acid (TTA) was performed using three different polystyrene-divinylbenzene ion-exchange resins in hydrogen form (Dowex® 50WX-8, Dowex® 50WX-4, Dowex® 50WX-2). The experiments were described by the axial dispersion flow model with the LDF approximation incorporated into the software gPROMS. From the three investigated adsorbents differing by the crosslinking, Dowex® 50WX-2 has presented the higher adsorption capacity, as well as the highest bed efficiency expressed by the number of theoretical plates. The adsorption equilibrium constants were determined from single breakthrough experiments, and a very good agreement between experimental and simulated data was achieved for both single components and binary mixtures. Therefore, the fundamental data determined within this work represents a key contribution to the design of continuous chromatographic processes for the purification of GCA and TTA.
  PubDate: 2017-07-01
  DOI: 10.1007/s10450-017-9882-5
  Issue No: Vol. 23, No. 5 (2017)
Adsorption of laterally interacting gas mixtures on homogeneous surfaces
- Authors: F. O. Sanchez-Varretti; P. M. Pasinetti; F. M. Bulnes; A. J. Ramirez-Pastor
  Pages: 651 - 662
  Abstract: The adsorption of binary mixtures containing particles A and B on homogeneous substrates is studied by Monte Carlo (MC) simulations, quasi-chemical approximation (QCA), and exact counting of states on finite cells (we call this approach cluster approximation, CA). The energies involved in the adsorption model are five: (1) \(\epsilon_A,\) interaction energy between an A particle and a lattice site; (2) \(\epsilon_B,\) interaction energy between a B particle and a lattice site; (3) \(w_{AA},\) nearest-neighbor interaction energy between two A particles; (4) \(w_{AB}\) (= \(w_{BA}\) ), nearest-neighbor interaction energy between an A particle and a B particle and (5) \(w_{BB}\) , nearest-neighbor interaction energy between two B particles. The process is monitored by following the coverage of both species with the simultaneous increasing of the individual chemical potentials of each mixture component. A non-trivial interdependence between the partial adsorption isotherms was observed and discussed in the context of the lattice-gas theory. The theoretical formalism is used to model experimental data of methane-carbon dioxide mixtures adsorbed on activated carbon. In addition, an excellent agreement was obtained between theoretical and MC simulation results. This finding evidences the usefulness of CA and QCA as a starting point to predict the behavior of a system governed by a large number of parameters.
  PubDate: 2017-07-01
  DOI: 10.1007/s10450-017-9885-2
  Issue No: Vol. 23, No. 5 (2017)
A robust dynamic column breakthrough technique for high-pressure
measurements of adsorption equilibria and kinetics
- Authors: Thomas Saleman; Gongkui Xiao; Gang Li; Eric F. May
  Pages: 671 - 684
  Abstract: Adsorption equilibria and kinetics of N2 and CH4 on four adsorbents, namely commercial activated carbon Norit RB3, zeolite 13X, zeolite 4A and molecular sieving carbon MSC-3K 172, were measured at temperatures of (273 and 303) K in the pressure range of (25–900) kPa using an improved dynamic breakthrough apparatus. Equilibrium adsorption measurements were performed with breakthrough experiments, and sorption kinetics were measured with a chromatographic pulse technique to eliminate undesirable systematics such as buoyancy and limitations imposed by heat transfer in conventional breakthrough techniques. The differential equations governing the spreading of a pulse passing through the column were solved in the Laplace domain to reduce numerical dispersion and artefacts associated with solving these equations for adsorption in the time domain on a finite grid. A method for identifying the reliable measurement range of sorption rates (mass transfer coefficients) from 10−4 to 1 s−1 was proposed and demonstrated with the four adsorbents. The sorption rates for Norit RB3 and zeolite 13X had values above the upper resolvable limit of 1 s−1. The measured sorption rates for MSC-3K 172 and zeolite 4A were compared with values obtained independently using a static volumetric method on the same adsorbents at the same temperatures but over a lower pressure range (0–110 kPa) (Xiao et al., Adsorption 23 (2017) 131–147). The sorption rates obtained for the two adsorbents via these two independent techniques were consistent within the measurement uncertainty of each method, which significantly increases the confidence with which these values can be used in simulations of industrial PSA processes.
  PubDate: 2017-07-01
  DOI: 10.1007/s10450-017-9884-3
  Issue No: Vol. 23, No. 5 (2017)
Orthogonal numerical simulation on multi-factor design for rapid pressure
swing adsorption
- Authors: XinGang Zheng; Hua Yao; Yun Huang
  Pages: 685 - 697
  Abstract: A two-dimensional model is established to simulate the rapid pressure swing adsorption (RPSA) process used for air separation with single bed. The model considers the transport phenomena occurring in both axial and radial direction. The decision variables include five factors (two heights of dead zone, durations of pressurization and adsorption steps, product extraction ratio), and the performance indexes consist of four variables (product purity, product recovery, bed size factor and average volume product yield). Based on an L16 (45) orthogonal design, 16 cases are arranged and the corresponding simulations are performed until the cycle steady states are reached from a given initial state. Range analysis is used to investigate the relative importance of the five factors on each performance index. Each factor’s optimal level and the corresponding combination is found out for each performance index successively.
  PubDate: 2017-07-01
  DOI: 10.1007/s10450-017-9886-1
  Issue No: Vol. 23, No. 5 (2017)
Roll-up effect of sulfur dioxide adsorption on zeolites FAU 13X and LTA 5A
- Authors: Guanghui Li; Qishuai Wang; Tao Jiang; Jun Luo; Mingjun Rao; Zhiwei Peng
  Pages: 699 - 710
  Abstract: The roll-up effect occurs as a result of the displacement of SO2 with H2O(g) when sulfur dioxide from humid flue gas is adsorbed by zeolites. It is mainly affected by SiO2/Al2O3 ratio (S/A) of zeolites, despite lack of detailed studies on use of hydrophilic zeolite. In this study, two zeolites of FAU 13X (S/A of 1.77) and LTA 5A (S/A of 1.51) were used to explore their roll-up effects using the breakthrough curve method. It is shown that the zeolite structure significantly influences the roll-up effect. The roll-up effect of FAU 13X is more significant than that of LTA 5A at the same water vapor content. The maximum roll-up ratio (η) for LTA 5A and FAU 13X are, respectively, 1.23 and 2.55 within the water vapor content range of 0.9–2.4%. Moreover, η of FAU 13X tends to decrease more rapidly than that of LTA 5A with increasing temperature or decreasing adsorption gas pressure. The presence of oxygen inhibits the roll-up effect and increases the breakthrough time of SO2. For the acid-modified zeolite, there is a positive correlation between η and concentration of Ca2+ or Na+ on zeolite surface, indicating obvious impact of cations on the roll-up effect.
  PubDate: 2017-07-01
  DOI: 10.1007/s10450-017-9887-0
  Issue No: Vol. 23, No. 5 (2017)
Adsorption of Human Serum Albumin (HSA) on a mixed-mode adsorbent:
equilibrium and kinetics
- Authors: Pedro Ferreira Gomes; José Miguel Loureiro; Alírio E. Rodrigues
  Pages: 491 - 505
  Abstract: The adsorption equilibrium and kinetics of Human Serum albumin (HSA) onto a novel high particle density multimodal adsorbent were studied by batch adsorption experiments. MabDirect MM, from Upfront Chromatography A/S, is an agarose-tungsten carbide composite adsorbent with an anionic mixed mode ligand. The effects of ionic strength (by addition of salt) and of pH are assessed. Langmuir isotherms parameters are obtained along with pore diffusivity values by fitting the batch experiments using a pore diffusion model. Under the studied conditions for pH 5.0, without salt, it was obtained the largest adsorption capacity (36.0 ± 3.5 mg·gadsorbent,dry −1) a typical behavior for a mixed mode adsorbent. Effective pore diffusivity (Dpe) was estimated as (2.2 ± 0.1) × 10−6 cm2·min−1 for this condition. Additionally, the lowest adsorption capacity (8.6 ± 2.1 mg·gadsorbent,dry −1) and an estimation of Dpe equal to (2.4 ± 0.6) × 10−6 cm2·min−1 were obtained for pH 7.0 without salt. An alternative method of Dpe estimation is used and validate the results obtained by simulations. Furthermore, several experiments were carried out in a fixed bed column with the aim to understand the kinetics and hydrodynamics, and to validate the batch adsorption results. For a feed concentration of ±0.92 g·L−1, pH 5.0, without salt, for cleaned and fresh adsorbent, fixed bed dynamic binding capacities of 13.84 and 14.37 mg·gadsorbent,dry −1 were obtained, respectively, representing near 50% of saturation capacity.
  PubDate: 2017-05-01
  DOI: 10.1007/s10450-017-9861-x
  Issue No: Vol. 23, No. 4 (2017)
Adsorption of propylene, propane, ethylene and ethane in an isoreticular
series of MOF-74 structures
- Authors: Mohammad Gholami; Saeid Yeganegi
  Pages: 507 - 514
  Abstract: Alkene/alkane separation is the most expensive stage in the process of propylene or ethylene producing. Adsorptive separation with porous solid adsorbents is an alternative way to currently used cryogenic distillation process. In this work by GCMC simulation we investigate propane, propylene, ethane and ethylene adsorption in an isoreticular series of IRMOF-74-I (Mg-MOF-74) structures with different pore size. The adsorption isotherms of pure components as well as the selectivity of binary mixtures of propylene/propane and ethylene/ethane at the pressure fixed at 1 bar with variable composition are determined at 318 K. Also, the snapshots of guest adsorption are used to elucidate the adsorption mechanisms. At low pressure, ethane uptake is the same for all studied structures. IRMOF-74-I has the highest ethylene uptake at low pressure and also ethylene/ethane selectivity among studied MOFs. Open metal site is the first preferential site for adsorbing the guest in all structures. IRMOF-74-II, IRMOF-74-III and IRMOF-74-IV have additional site for adsorbing guest molecules. This additional adsorption site makes propylene and propane uptakes higher than that of IRMOF-74-I at low pressure. The second preferential site of IRMOF-74-II, IRMOF-74-III and IRMOF-74-IV, organic linker, interact with propane and propylene as the same and can’t separate them so IRMOF-74-II, IRMOF-74-III and IRMOF-74-IV have lesser selectivity than IRMOF-74-I. At high pressure, IRMOF-74-IV with largest pore size has the highest uptake for all studied hydrocarbons.
  PubDate: 2017-05-01
  DOI: 10.1007/s10450-017-9862-9
  Issue No: Vol. 23, No. 4 (2017)
Monosaccharide separation from ZnCl 2 molten salt hydrates by zeolite beta
- Authors: Johan van den Bergh; Wouter Wiedenhof; Dorota Siwy; Hans Heinerman
  Pages: 563 - 568
  Abstract: Solvent based processes using ionic liquids or molten salt hydrates provide very efficient cellulose dissolution and hydrolysis from lignocellulosic biomass. Efficient separation of sugars from the solvent is very challenging and a hurdle regarding industrial application. Now it is demonstrated that a microporous zeolitic sorbent can provide a very efficient separation of monosugars from a molten salt hydrate containing hydrolysates. Specific details are presented for the separation of glucose from a ZnCl2 molten salt hydrate using Zeolite beta. The molten salt hydrate is promoting the separation in this specific solvent/sorbent combination through a type of salting out adsorption mechanism, leading to a process based on a solvent that allows both efficient cellulose dissolution and hydrolysis and very efficient glucose isolation from the solvent afterwards.
  PubDate: 2017-05-01
  DOI: 10.1007/s10450-017-9868-3
  Issue No: Vol. 23, No. 4 (2017)
Net, excess and absolute adsorption in mixed gas adsorption
- Authors: Stefano Brandani; Enzo Mangano; Mauro Luberti
  Pages: 569 - 576
  Abstract: The formulation of a thermodynamic framework for mixtures based on absolute, excess or net adsorption is discussed and the qualitative dependence with pressure and fugacity is used to highlight a practical issue that arises when extending the formulations to mixtures and to the Ideal Adsorbed Solution Theory (IAST). Two important conclusions are derived: the correct fundamental thermodynamic variable is the absolute adsorbed amount; there is only one possible definition of the ideal adsorbed solution and whichever starting point is used the same final IAST equations are obtained, contrary to what has been reported in the literature.
  PubDate: 2017-05-01
  DOI: 10.1007/s10450-017-9875-4
  Issue No: Vol. 23, No. 4 (2017)
Experimental and modelling studies of CO 2 /N 2 mixture separations using
amine functionalised silicas
- Authors: E. Tsalaporta; N. Brady; J. M. D. MacElroy
  Abstract: A combined experimental and mathematical investigation of amine modified mesoporous silicas as adsorbent materials for carbon dioxide removal from CO2/N2 gaseous mixtures is undertaken. The experiments are designed to permit the determination of CO2 adsorption equilibria and, as appropriate, the assessment of transport and adsorption/desorption reaction kinetic parameters for CO2 interacting with immobilised mono-, di- and triamine moieties. Both forward and reverse breakthrough analysis techniques and cyclic Pressure Swing Adsorption are employed to highlight the significant importance of the role of adsorbent heterogeneity in the separation process.
  PubDate: 2017-06-26
  DOI: 10.1007/s10450-017-9896-z
Adsorption of nutrients on natural Spanish clays for enriching seed
coatings
- Authors: Aránzazu Peña; Antonia Gálvez; José Antonio Rodríguez-Liébana; Concepción Jiménez de Cisneros; Alberto López Galindo; César Viseras; Emilia Caballero
  Abstract: Coating seeds with nutrients remains an effective way of supplying fertilizers for the establishment and development of seedlings. Clays have been proposed, among other coating materials, because of their low price and favorable properties. Nine natural clays (R1-R9), collected in the eastern Andalusian region (south of Spain), were evaluated for the retention of P, Mn and Zn, with the ultimate goal of designing enriched seed coatings. The clays were similar in composition, with high Ca content. Various equations were used for the fitting of kinetic and adsorption data. Adsorption rates of Mn were higher with R2, R6 was the clay in which Zn exhibited the most rapid kinetics, while P was adsorbed on R7 at the highest rate. Slower adsorption rates corresponded in all cases to Zn. The pseudo-second order model adequately explained the experimental kinetic data of Mn, Zn and P on the different sorbents. Adsorption isotherms indicated that the maximum adsorption capacity on the analyzed clays was ranged as Zn > Mn > > P. Clays were able to retain nutrients for long periods of time (up to 96 days) and desorption was inversely related with adsorption. Simultaneous addition on selected clays of Zn and Mn led to significantly higher nutrient desorption. The co-presence in clays of various compounds (nutrients and/or pesticides) affected their release, so this aspect deserves special attention in coating design. Results obtained suggest the feasibility of using these clay materials enriched with nutrients for seed coating.
  PubDate: 2017-06-20
  DOI: 10.1007/s10450-017-9897-y
Gas adsorption effect on the graphene nanoribbon band structure and
quantum capacitance
- Authors: Ali H. Pourasl; Mohammad Taghi Ahmadi; Razali Ismail; Niayesh Gharaei
  Abstract: Graphene nanoribbons (GNRs) as a quasi-one dimensional (1D) narrow strip of graphene hold great potential for applications in variety of sensors because of π-bonds that can react with chemical elements. Despite outstanding properties, graphene nanoribbons have not fully exploited for variety of application in nanoelectronic and nanosensors due to poor understanding of their physical, electrical properties and basic limitations on the synthesis. Therefore, in order to achieve analytical understanding on the interaction of the gas molecules with GNR surface and gas sensing mechanism, a theoretical method using tight binding model based on nearest neighbour approximation is developed in this study. Additionally, the adsorption effects of NO2 and CO2 gas molecules on the band structure and electrical properties of the GNRFET based gas sensor are investigated. Based on the proposed model numerical simulation is carried out which emphasizes the significant effect of the gas adsorption on the band structure and electrical properties of GNRs. On the other hand, quantum capacitance created between metal gate and channel as a sensing parameter is considered and its variations when GNR exposed to the NO2 and CO2 molecules are analytically modelled. Moreover, the adsorption energy and charge transfer occurred during gas molecules interaction with GNR surface are calculated. Also band structure and I–V characteristics are analysed using first principle calculation based on density functional theory. The current–voltage analysis clearly indicates the changes of the quantum capacitance when exposed to the gas molecules. The results of the proposed model are compared with the available experimental data or data obtained by density functional theory (DFT) calculations and good agreements are observed.
  PubDate: 2017-06-16
  DOI: 10.1007/s10450-017-9895-0
Adsorption isotherms of carbon dioxide and methane on CHA-type zeolite
synthesized in fluoride medium
- Authors: Zahra Pourmahdi; Hafez Maghsoudi
  Abstract: High-silica CHA-type zeolite was synthesized in fluoride medium using fumed silica as silica source. Adsorption isotherms of CO2 and CH4 were measured over pressure range of 0–1100 kPa and at temperatures of 298, 323, 353, and 393 K. The isotherms follow a typical Type-I shape according to the BDDT classification. All adsorption isotherms are well described by Langmuir, Toth and Sips isotherms. Adsorptive performance of the zeolite was compared with other CHA-type zeolites, i.e. SAPO-34, Si-CHA and SSZ-13 using ideal adsorption solution theory. The modeling results revealed that the zeolite has a high CO2/CH4 selectivity, e.g. 6.70 for an equimolar mixture at 298 K and 100 kPa. Isosteric heats of adsorption for both CO2 and CH4 were reasonably constant (20.6 and 24.1 kJ mol−1 at loading of 0.02 mol kg−1 for CH4 and CO2, respectively) showing that the adsorbent is energetically homogenous.
  PubDate: 2017-06-13
  DOI: 10.1007/s10450-017-9894-1
Oscillometric–gravimetric measurements of pure gas adsorption equilibria
without the non-adsorption of helium hypothesis
- Authors: J. U. Keller; M. U. Goebel; Th. Seeger
  Abstract: The adsorption of gaseous carbon dioxide (CO2) at near ambient conditions (297 K, 995 mbar) on activated carbon BAX 1100 (Ingevity), has been measured by a new oscillometric-gravimetric method. The method consists of combined gravimetric and dynamic measurements, namely observations of the frequency of small and nearly adiabatic oscillations of the sorptive gas being in equilibrium with the adsorbed phase of adsorbate. The oscillations observed are actually eigenoscillations of a sorptive gas–sorbate–sorbent system. They are initiated by small oscillations of a sphere or a cylinder positioned in a vertical tube above the vessel containing the gas and the sorbent material reversion of experiment by Rüchardt (Phys. Zeitschr XXX:58, 1929)–Flammersfeld (Z. Naturforsch. 23a:3, 1972). Experiments show that the adsorbate includes two different phases consisting respectively of molecules which are only weakly bound to sorbent’s atoms so that they can participate in the low frequency gas oscillations (<10 Hz), and other molecules being strongly bound to sorbent’s atoms so they are “stiff”, i.e. cannot participate in the gas oscillations, eigenfrequencies being in the range of (1010–1012) Hz. The theory of these measurements is outlined and data of adsorption equilibria of carbon dioxide gas on activated carbon BAX 1100 at near ambient conditions which have been measured by three different methods are presented and compared to each other.
  PubDate: 2017-06-10
  DOI: 10.1007/s10450-017-9893-2
In silico investigation of the ozone (O 3 ) binding behavior to the B 36
bowl-shaped structure
- Authors: Elham Tahmasebi; Zeinab Biglari; Ehsan Shakerzadeh
  Abstract: The binding of ozone molecule to the B36 bowl-shaped structure is scrutinized using the density functional theory (DFT) calculations. The interactions are investigated using B3LYP, B3LYP-D3, WB97XD, M06-2X and TPPSH methods. The ozone binding to the B36 structure is studied in terms of energetical, structural and electronic features. The results indicate that although ozone molecule weakly interacts with concave side of structure, it adds to the convex side and the edge of B36 structure. The ozone binding to the edge of B36 is more efficient than its convex side. The HOMO–LUMO gaps of the stable systems are reduced with respect to pure B36 sheet. This could be applied as a chemical signal. The obtained results introduce the B36 structure as an efficient ozone adsorbent.
  PubDate: 2017-05-31
  DOI: 10.1007/s10450-017-9891-4
High capacity and energy-efficient dehydration of liquid fuel 2-dimethyl
amino ethyl azide (DMAZ) over chromium terephthalic (MIL-101)
nanoadsorbent
- Authors: Zeinab Noorpoor; Shahram G. Pakdehi; Alimorad Rashidi
  Abstract: Nanoadsorbents from MIL-101(Cr) metal-organic framework were prepared via hydrothermal method with different additives (hydrofluoric acid, sodium acetate, acetic acid, expanded graphite and without additive) under different synthesis conditions. The samples were characterized by XRD, SEM and nitrogen sorption at 77 K. The frameworks were used for dehydration of liquid fuel DMAZ containing 3 wt% water, for several consecutive cycles between adsorption (at ambient temperature and atmospheric pressure) and desorption at 343 K. Water stability and recyclability of the frameworks were almost similar but the MIL-101 using acetic acid attribute to the higher pore volume and surface area, with \({\text{1}}{\text{.3 g}}_{{{\text{H}}_{{\text{2}}} {\text{O}}}} /{\text{g}}_{{{\text{ads}}}}\) had the most capacity for water capture. Also, adsorption capacity of MIL-101 was compared with commercial zeolite adsorbents (3A and 4A) for dehydration of aforementioned solution. The uptake capacity of MIL-101 with \({\text{1}}{\text{.3 g}}_{{{\text{H}}_{{\text{2}}} {\text{O}}}} /{\text{g}}_{{{\text{ads}}}}\) was 7–8.5 times higher than commercial 3A and 4A zeolites with 0.18 and \({\text{0}}{\text{.15 g}}_{{{\text{H}}_{{\text{2}}} {\text{O}}}} /{\text{g}}_{{{\text{ads}}}}\) respectively. MIL-101 was almost fully dehydrated at 343 K, in contrast to conventional porous zeolites requiring high temperature dehydration (573 K). MIL-101 was shaped and used in an adsorption column with \({\text{1}}{\text{.1 g}}_{{{\text{H}}_{{\text{2}}} {\text{O}}}} /{\text{g}}_{{{\text{ads}}}}\) capacity. Shaped MIL-101 showed robust cyclic performance in the dehydration tests.
  PubDate: 2017-05-31
  DOI: 10.1007/s10450-017-9892-3
Atom–surface scattering: a comparative study considering real and
complex absorbing potentials
- Authors: Maryam Mansoori Kermani; Ali Maghari
  Abstract: In this paper a low density atomic gas colliding on a solid surface was modelled using the quantum scattering theory. The surface has discrete trapping/scattering centers in its lattice. In the model, a harmonic potential for the surface atoms interaction and a constant effective mean field for the gas atoms interactions were considered. The projectile atoms were assumed to be interacted with a solid surface atoms by two different potential models: (i) the Morse potential model, which is a real absorbing potential; and (ii) the Scarf II potential, which is a complex absorbing potential. The scattering probability densities for both models were calculated analytically via the first Born approximation. The effect of the incident atom energies as well as the distance of gas atoms from the surface on the probability densities were studied for both real and complex absorbing potentials. Comparisons have been made between these two types of potentials using the Lippmann–Schwinger quantum scattering equation. It was found that in addition to the competition between repulsive and attractive parts of the potentials, the imaginary part of the complex Scarf II potential has a significant effect on the distance of gas atoms from the surface. The adsorption probabilities of incident atoms on the surface considering the Morse model as well as Scarf II potential were obtained analytically as a function of distance from surface and kinetic energy of projectiles. Comparison our calculated adsorption coefficient with the simulation data of isothermal density distribution for nitrogen and argon adsorbed on the graphite surface shows that the maximum adsorption positions for both potential models provide a good agreement with simulation results.
  PubDate: 2017-05-24
  DOI: 10.1007/s10450-017-9890-5
Experimental study on the effect of inherent moisture on hard coal
adsorption–desorption characteristics
- Authors: Liang Wang; Er-tao Chen; Shimin Liu; Yuan-ping Cheng; Long-biao Cheng; Ming-yi Chen; Hai-jun Guo
  Abstract: Coal is a complex geological body that is composed of organic material, gas, and water. Generally, coal with high hardness is commonly considered to be a non-outburst risk; however, several coal mines with hard coal seams in China have experienced coal and gas outbursts. Coals with different degrees of metamorphism have different inherent moisture ranges, which has a strong influence on gas adsorption and desorption. Currently, inhomogeneous moisture wetting remains an issue in traditional preparation methods for preparing coal samples with different moisture levels. In this paper, we chose three typical hard coals with different degrees of metamorphism and systematically studied their pore structure characteristics, effect of approximate inherent moisture on the gas adsorption–desorption characteristics, and gas diffusion of hard coals. The results show that all of the coal samples have an open pore structure, but each coal sample has different development characteristics of their pore structure. The higher the moisture, the shorter the adsorption equilibrium time required and the lower pressure drop. All of the adsorption isotherm curves fit the Langmuir equation well. The gas adsorption capacity of the same coal sample decreases gradually and the amplitude of the gas adsorption capacity decreases with increasing moisture. This relationship indicates that the existence of moisture occupies a certain space of the pore structure and reduces the gas adsorption sites of coal, reducing the adsorption and desorption amount of the coal samples. Moreover, low and middle rank coal can use the bidisperse model to calculate the diffusion coefficient, while high rank coal can use the unipore model. Increasing moisture causes the macropore diffusion coefficient D a,e and micropore diffusion coefficient D i,e of the YZG and YJ samples to decrease. The effective diffusion coefficient D e of the WLH samples also reduced gradually, which suggests that moisture has an influence on the gas migration and diffusion channels of coal, reducing the gas adsorption equilibrium time, desorption rate, and diffusion rate of coal seam.
  PubDate: 2017-05-22
  DOI: 10.1007/s10450-017-9889-y
Modification of the surface chemistry of microdispersed sintered
detonation nanodiamonds and its effect on the adsorption properties
- Authors: S. N. Lanin; S. A. Rychkova; A. E. Vinogradov; K. S. Lanina; O. N. Obrezkov; P. N. Nesterenko
  Abstract: Microdispersed sintered detonation nanodiamonds (MSDN) with different surface chemistry were characterized using X-ray diffraction method, energy dispersive spectroscopy (EDS) and adsorption of ionogenic and nonionogenic compounds in static and dynamic (with HPLC instrumental design) conditions. It was shown that for MSDN, conditioned with 3 × 10−3 M H3PO4, adsorption of substances with basic properties increases by 13.5–22.0, while washing of MSDN with 1.3 × 10−5 М ammonium hydroxide decreases adsorption of bases as a result of modification of ionic state of functional groups at the surface. It is found that concentration of H3PO4 solution significantly effects on adsorption of ionogenic organic substances. The effect of organic solvent is investigated by obtaining of isotherms of excessive adsorption of pyridine on MSDN from solutions in water and acetonitrile under static conditions. It is found that the equilibration of MSDN with acid solution activates its surface for adsorption of pyridine that may be due to desorption of substances blocking acidic adsorption centers. It was shown that usage of buffers containing additives of ammonium, potassium and sodium electrolytes results in decrease of adsorption of basic molecules, which is explained by competitive adsorption of cations on dissociated carboxyl functional groups on the surface of MSDN.
  PubDate: 2017-05-16
  DOI: 10.1007/s10450-017-9883-4
Role of chemical structures in coalbed methane adsorption for anthracites
and bituminous coals
- Authors: Yongshuai Fu; Xianfeng Liu; Boqing Ge; Zhenghong Liu
  Abstract: An in-depth investigation was conducted on four bituminous coals and three anthracites regarding the chemical structural characteristics using Fourier transform infrared spectroscopy (FTIR). The FTIR spectra of coals can be well approximated by the combination of Gaussian/Lorentzian peaks. FTIR parameters, including aromatic structures, aliphatic structures and oxygen-containing groups (C=O), were determined from curve-fitting analysis. Methane adsorption measurements were carried out through an equilibrium volumetric method, and the Langmuir equation was applied to fit the experimental data. Correlations were established for these FTIR structural parameters and methane adsorption parameters (V L and P L). From the results obtained, it can be seen that rapid changes occur for bituminous coals with the vitrinite reflectance, R o = 1.1–2.1%. The sharp variations of the apparent aromaticity, f a, and A(CH2)/A(CH3) indicate the significant intensive aromatization and the decrease of aliphatic methylene groups, respectively. As a consequence, the size of aromatic clusters is greatly enhanced with increasing coalification. However, the oxygen-containing functional groups, ´C´, varying from 0.43 for sample WJD to 0.10 for sample ZZ, presents a negative linear relationship with R o. Once R o > 2.1% (anthracite), both f a and A(CH2)/A(CH3) tend to be steady. The defects and degree of disorder in coal structure have been reduced to a large extent, and the graphite microcrystalline structure in coal is gradually perfected for anthracites. Coals with higher f a provide more adsorption sites for methane occupation on coal surface, thus demonstrating stronger adsorption capacities. However, the aliphatic methylene groups and oxygen-containing functional groups can decrease the CH4 adsorption amount at low pressure stage (<5 MPa), further reducing the adsorption properties. These findings may have great significance for accurate estimation reserves of coalbed methane and the prevention of gas disasters underground coal mine.
  PubDate: 2017-05-03
  DOI: 10.1007/s10450-017-9888-z