Modeling of the equilibrium moisture content (EMC) of Miscanthus (Miscanthus × giganteus)

The desorption isotherms of miscanthus, Miscanthus × giganteus (stems and leaves) were determined separately by using the saturated salt solutions method at three temperatures (25, 50 and 70 °C) within a range from 5 to 90% relative humidity. Experimental curves of desorption isotherms were fitted to Modified Henderson, Modified Halsey, Modified Oswin and Modified Chung-Pfost models and evaluated by Residual Sum of Squares (RSS), Standard Error Estimation (SEE) and Mean Relative Deviation (MRD) methods. The Modified Oswin model was found to be the most suitable for describing the correlation between equilibrium moisture content, relative humidity and temperature.     

Removal of Phenol Using TDTAB- and HDTAB-Bentonites

Abstract

In this study, the use of modified bentonites for the removal of phenol was investigated. Two alkylammonium derivatives, tetradecyl trimethyl bromide (TDTAB) and hexadecyl trimethylammonium bromide (HDTAB), were used in the modification in amounts equivalent to 100% of CEC. Crude and modified bentonites were subjected to XRD analyses to see the changes in basal spacing (d _L ) depending on modification. The increases observed in basal spacing are 8.93 Å and 8.55 Å for TDTAB- and HDTAB-bentonites, respectively. Batch adsorption studies were carried at pH of 5.5 and 20°C. Adsorption isotherms of TDTAB- and HDTAB-bentonites have similar shape, and two regions are observed in isotherms. Adsorption behavior was modelled using Langmuir, Freundlich, BET, Bradley, Halsey, Henderson, Oswin, and Smith equations. The equations fitted better when the isotherm was divided into two concentration ranges. Adsorption efficiencies were defined in terms of relative increase in adsorbed amounts, and HDTAB-bentonite was found to be better.     

Adsorption Isotherms of Hydrogen on Granular Activated Carbon Derived From Coal and Derived From Coconut Shell

ABSTRACT

The development of adsorption-based storage systems requires a basic understanding of the isotherms over a wide range of pressure and temperatures for various types of adsorbents. This research is to generate experimental isothermal adsorption data for the adsorption of hydrogen gas on activated carbon. The adsorption apparatus is based on a volumetric method, and the experiments were conducted at temperatures ranging from 273 to 308 K and pressures up to 4 MPa. Two types of activated carbon, (i) a granular coal from Indonesia and (ii) a coconut-shell activated carbon that is produced in the laboratory, were used in the experiments. The experimental data are analyzed using the Langmuir, Toth, and Langmuir–Freundlich isotherm models.     

High-Pressure Adsorption Isotherms of Carbon Dioxide and Methane on Activated Carbon From Low-Grade Coal of Indonesia

ABSTRACT

Adsorption isotherms data of methane and carbon dioxide gases on the activated carbons were measured experimentally using a volumetric method with pressure and temperatures ranging from 0 to 3.5 MPa and 27 to 65°C, respectively. Two types of activated carbons, namely, (1) Kalimantan Timur type activated carbon, which is lab-produced from Indonesian low-grade coal and (2) a commercial (Carbotech) activated carbon were used. The adsorption isotherms obtained were found to belong to type 1 of the International Union of Pure and Applied Chemistry classification. The adsorption uptakes for both carbon dioxide and methane on commercial activated carbon are higher than for the Kalimantan Timur activated carbon. This is due to higher Brunauer–Emmet–Teller surface area and pore volume of the former. Langmuir and Tóth isotherm models are correlated to predict the experimental data with acceptable accuracy.     

Isotherms and thermodynamics for the adsorption of n-butane on pitch based activated carbon

The adsorption isotherms of n-butane on pitch based activated carbon (type Maxsorb III) at temperatures ranging from 298 to 328 K and at different equilibrium pressures between 20 and 300 kPa have been experimentally measured by a volumetric technique. The porous properties such as, the density, Brunauer–Emmett–Teller (BET) surface area, pore size, pore volume along with pore size distribution (PSD) of Maxsorb III have been determined. The Dubinin–Astakhov (DA) adsorption isotherm model describes all of the isotherm experimental data within the acceptable error ranges. The present isotherm data are compared with other published data of activated carbon (AC)/n-butane and showed the superiority of the present findings in terms of uptake capacity. The isosteric heat of adsorption (ΔH_ads) of n-butane on Maxsorb III is calculated for different loading. Using the adsorption isotherms and ΔH_ads, the thermodynamic property maps as a function of pressure, temperature and adsorbate amount are also presented.     

Phosphorus sorption,desorption and resorption by soils of the Brazilian Cerrado supporting eucalypt

Oxisols of the Brazilian Cerrado are highly weathered phosphorus deficient soils, on which eucalypt is increasingly being grown as a source of carbon and energy for steel manufacturing. Phosphorus (P) fertilization is a necessary practice to assure adequate eucalypt production; therefore, an understanding of cycling by inorganic soil P should lead to efficient P management and more accurate modeling of P bioavailability. Since sorption and desorption reactions control inorganic P bioavailability, the purpose of this study was to contrast P sorption, desorption and subsequent resorption for a range of Cerrado soils. Its specific objectives were to determine (i) if desorption and resorption show the same hysteresis shown by sorption and desorption, (ii) if K_d values of resorption and desorption for Cerrado soils are dependent on the soil's clay content and (iii) if resorption and desorption K_d values are a function of the amount of labile P on the soil surface. Three levels of P were sorbed onto four Cerrado soils with clay contents between 13% and 81%. Phosphorus desorption was measured using anion-exchange membranes. Sorption was a function of soil clay content, and a pedotransfer function for the soil partition coefficient was calculated with an r²=0.99. Desorption and resorption were dependent on both the clay content of the soil (r²=0.59–0.99) and the amount of sorbed labile P. Pedotransfer functions for each of these processes depend on accurate measurement of the inorganic P that responds to disequilibria exchange. Desorption and resorption were not hysteretic; yet desorption was hysteretic with the original sorption isotherm. This suggests the question: how useful are commonly produced sorption isotherms?     

Water and phosphoric acid uptake of poly [2,5-benzimidazole] (ABPBI) membranes prepared by low and high temperature casting

Phosphoric acid-doped membranes based in poly[2,5-benzimidazole] (ABPBI) were obtained by a new low temperature casting procedure and by the classical high temperature casting from methanesulfonic acid. These membranes, which can be suitable for application in direct methanol proton exchange membrane (PEM) fuel cells, were studied in relation with their phosphoric acid doping level by measuring the free and bonded acid. The water isotherms were also determined for the low and high temperature casted ABPBI membranes. Both, acid and water sorption properties, were compared with those determined in poly [2-2′-(m-fenylene)-5-5′ bibenzimidazole] (PBI) membranes. The water sorption of the ABPBI membranes over the range of all water activity is described by the modified BET equation, commonly known as Guggenheim–Anderson–de Boer (GAB) and a two-parameters empirical isotherm. The acid uptake behaviour of the membranes prepared by low and high temperature casting are related with differences in their supramolecular structure.     

Effect of cycling on hydrogen storage properties of Ti2CrV alloy

In the present work, we have studied the hydrogen absorption–desorption properties of the Ti₂CrV alloy, and effect of cycling on the hydrogen storage capacity. The material has been characterized for the structure, morphology, pressure composition isotherms, hydrogen storage capacity, hydrogen absorption kinetics and the desorption profile at different temperatures in detail. The Ti₂CrV crystallizes in body centered cubic (bcc) structure like TiCrV. The pressure composition isotherm of the alloy has been measured at room temperature and at 373K. The Ti₂CrV alloy shows maximum hydrogen storage capacity of 4.37 wt.% at room temperature. The cyclic hydrogen absorption capacity of Ti₂CrV alloy has been investigated at room temperature upto 10th cycle. The hydrogen storage capacity decreased progressively with cycling initially, but the alloy can maintain steady cyclic hydrogen absorption capacity 3.5 wt.% after 5th cycle. To get insight about the desorption behavior of the hydride in-situ desorption has been done at different temperatures and the amount of hydrogen desorbed has been calculated. The TG (Thermo gravimetric) and DTA analysis has been done on uncycled hydride shows that the surface poisoned sample gives a desorption onset temperature of 675K. The DSC measurement of uncycle and multi-cycled saturated hydrides shows that the hydrogen desorption temperature decreasing with cycling.     

Evaluation of hydrogen sorption models for AB5-type metal alloys by employing a gravimetric technique

This paper is concerned with hydrogen absorption and desorption in AB₅-type hydrogen storage metal alloys. We give a brief overview on models which have been proposed for hydrogen sorption in metals over the past decades. We choose three models based on different perspectives, i.e. thermodynamics, reaction kinetics, and mere observation (empiricism), and evaluate their applicability in order to describe the sorption behaviour. Additionally, we propose a model which is based on a cumulative distribution function. In order to evaluate the models, the hydrogen absorption and desorption isotherms of LaNi₅ and LaNi_4.5Co_0.5 are measured by means of a gravimetric technique. A nonlinear regression is performed to fit the models to experimental data. The computed model parameters are compared to values reported in the literature. The emphasis is given to the applicability of the models with respect to describing the non-ideality of the plateau region and the continuity/smoothness of phase transition regions.     

Solvothermal synthesis,nanostructural characterization and gas cryo-adsorption studies in a metal–organic framework (IRMOF-1) material

A nanoporous metal–organic framework material, exhibiting an IRMOF-1 type crystalline structure, was prepared by following a direct solvothermal synthesis approach, using zinc nitrate and terephthalic acid as precursors and dimethylformamide as solvent, combined with supercritical CO₂ activation and vacuum outgassing procedures. A series of advanced characterization methods were employed, including scanning electron microscopy, Fourier-transform infrared radiation spectroscopy and X-ray diffraction, in order to study the morphology, surface chemistry and structure of the IRMOF-1 material directly upon its synthesis. Porosity properties, such as Brunauer–Emmet–Teller (BET) specific area (～520 m²/g) and micropore volume (～0.2 cm³/g), were calculated for the activated sample based on N₂ gas sorption data collected at 77 K. The H₂ storage performance was preliminary assessed by low-pressure (0–1 bar) H₂ gas adsorption and desorption measurements at 77 K. The activated IRMOF-1 material of this study demonstrated a fully reversible H₂ sorption behavior combined with an adequate gravimetric H₂ uptake relative to its BET specific area, thus achieving a value of ～1 wt.% under close-to-atmospheric pressure conditions.     

A mass transfer model for the adsorption of pesticide on coconut shell based activated carbon

The adsorption isotherms of HCH on coconut shell based activated carbon type NP-5 at constant temperature have been experimentally measured. The porous properties such as, the density, BET surface area, pore size, pore volume along with pore distribution of NP-5 have been determined. The Freundlich’s, Langmuir’s, Temkin, Jovanovic and BET’s adsorption isotherm models describe of experimental data within the acceptable error ranges. The Freundlich, Jovanovic and Langmuir models were fitting better the experimental data. The shape of these isotherms indicates that the HCH is adsorbed as a monolayer and that there is no strong competition between the pesticide molecules and water to occupy the adsorption surface sites.     

Preparation and characterization of PEI-loaded MCM-41 for CO2 capture

MCM-41, a molecular sieve, was prepared using tetraethoxysilane and cetyltrimethylammonium bromide and used as an effective adsorbent for CO₂. By using the wet impregnation method, various weights of poly(ethyleneimine) (PEI) were modified on mesoporous silicate MCM-41 for increasing the CO₂-adsorption capacity. The samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and nitrogen adsorption/desorption isotherms. Thermal gravimetric analysis (TGA) was conducted to investigate the CO₂ capture behaviors. PEI was successfully dispersed into the channels of MCM-41, shifting the (110) diffraction peaks in the XRD patterns. The specific surface area and total pore volume of the PEI-loaded MCM-41 adsorbent decreased when the weight of PEI loading increased. From the results, it was concluded that PEI loading influences the CO₂ capture performance, resulting from the enhancement of the basic functional groups on MCM-41.     

On the application of standard isotherms to hydrogen adsorption in microporous materials

A mathematical framework for simulating equilibrium hydrogen adsorption isotherms in porous materials and estimating the values of key parameters associated with the adsorption process is developed. Explicit expressions for the excess, adsorbed, compressed and absolute masses, for any model isotherm, are derived. The modelling framework is used in combination with five standard equilibrium isotherm models to simulateexperimental data for Prussian blue analogues, nitropussides and metal-organic frameworks via nonlinear regression. The surface areas, the affinity and heterogeneity factors, and the pressure-dependent adsorption volumes are calculatedand compared to values available in the literature and the sensitivity of the results to the number of data points is quantified. The consistency of the results using different isotherm models is evaluated.     

Hydrogen uptake of reduced graphene oxide and graphene sheets decorated with Fe nanoclusters

Graphene oxide (GO) has been prepared by employing modified Staudenmaier's method through thermal exfoliation of graphite oxide. High pressure hydrogen sorption isotherms up to 50 bar of GO, reduced by thermal reduction (TR-GO), chemical reduction (CR-GO) and graphene sheets decorated with Fe nanoclusters (Fe-GS) have been investigated. Thermal reduction of GO at 623 K under high vacuum yields TR-GO. Chemical reduction of GO using hydrazine forms CR-GO. Fe-GS was synthesized through arc-discharge between the ends of two graphite rods with one rod carrying Fe nanoparticles. The surface areas of these graphene samples were determined from the nitrogen adsorption isotherm employing Brunauer, Emmett and Teller (BET) method. Kelvin's equation was used to determine the pore size distribution of all graphene based samples. Hydrogen pressure-composition isotherms (PCI) were determined at 300 K and at 77 K, between 0.1 and 50 bar. Further, in this paper, we present a comparative adsorption isotherm analysis of hydrogen and helium on TR-GO. This reveals that the volume of hydrogen and helium adsorbed by TR-GO is nearly equal. The similar uptake volume determined for both hydrogen and helium indicates the possibility of monolayer adsorption of hydrogen and also nearly similar binding energy between TR-GO and H₂/He.     

Effects of Ca additions on some Mg-alloy hydrides

The hydrogenation of the alloy of composition CaMg_1.8Ni_0.5 containing CaMg₂ and MgNi₂ shows fast activation kinetics. The Mg₂Ni phase is observed in the dehydrided samples. The three plateaus on the hydrogen desorption isotherms correspond to the most stable magnesium hydrides observed up to now in Mg-alloy (ΔH = 20–24 kcal/mol H₂). The effects of Ca additions on the hydrogen storage capacity and desorption rates of some Mg-rich alloys have been studied.     

Effect of Ni content on the hydrogen storage behavior of ZrCo1−xNix alloys

ZrCo_1−xNi_x (x = 0, 0.1, 0.2 and 0.3) alloys were prepared and their hydrogen storage behavior were studied. ZrCo_1−xNi_x alloys of compositions with x = 0, 0.1, 0.2 and 0.3 prepared by arc-melting method and characterized by X-ray diffraction analysis. XRD analysis showed that the alloys of composition with x = 0, 0.1, 0.2 and 0.3 forms cubic phase similar to ZrCo with traces of ZrCo₂ phase. A trace amount of an additional phase similar to ZrNi was found for the alloy with composition x = 0.3. Hydrogen desorption pressure–composition–temperature (PCT) measurements were carried out using Sievert's type volumetric apparatus and the hydrogen desorption pressure–composition isotherms (PCIs) were generated for all the alloys in the temperature range of 523–603 K. A single sloping plateau was observed for each isotherm and the plateau pressure was found to increase with increasing Ni content in ZrCo_1−xNi_x alloys at the same experimental temperature. A van't Hoff plot was constructed using plateau pressure data of each pressure–composition isotherm and the thermodynamic parameters were calculated for desorption of hydrogen in the ZrCo_1−xNi_x–H₂ systems. The enthalpy and entropy change for desorption of hydrogen were calculated. In addition, the hydrogen absorption–desorption cyclic life studies were performed on ZrCo_1−xNi_x alloys at 583 K up to 50 cycles. It was observed that with increasing Ni content the durability against disproportionation of alloys increases.     

Pressure artifacts at isothermal operation of a metal hydride tank

The paper presents the results of experimental investigations on hydrogen absorption and desorption in the metal hydride reactor RS-1 containing 81 kg of La_0.5Nd_0.5Al_0.1Fe_0.4Co_0.2Ni_4.3 intermetallic compound at 60 °C isothermal conditions. During the reactor-scale measurements of pressure-composition isotherms we observe pressure artifacts; pressures for absorption are higher and for desorption are lower than equilibrium pressures obtained after cooling down and reheating of the reactor. This thermal relaxation procedure removes the pressure artifacts. The observed effect is similar to the large aliquot effect, and mostly affects the desorption isotherm. The highest measured pressure difference is 0.7 bar (11%).     

Hydrogen isotope absorption amount and rate of Pd–Al2O3 pellets

A special type of Pd–Al₂O₃ pellet, which included Pd in high weight percent as a hydrogen isotope separation material was prepared by a compression molding method. The pressure–composition isotherm and the plateau pressure of the Pd–Al₂O₃ hydrogen isotope system were determined by a volumetric method. The pellet has high hydrogen absorption ability even at 196 K, and the reaction rate is controlled by surface reaction. The hydrogen absorption capacity and the rate of the Pd–hydrogen system were unchanged by the addition of Al₂O₃. It was found that the Pd–Al₂O₃ pellet has high durability against repeated absorption–desorption cycles. There is no change in the absorption amount and the rate up to 1000 times of absorption–desorption cycles.     

Nanocrystalline MgO supported nickel-based bimetallic catalysts for carbon dioxide reforming of methane

Nanocrystalline magnesium oxide with high surface area and plate-like shape was employed as catalyst support for preparation of nickel-based bimetallic catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), Temperature programmed oxidation and desorption (TPO–TPD), Thermal gravimetric and differential thermal gravimetric (TGA–DTG), H₂ chemisorption and Transmission and electron microscopies (TEM and SEM) analyses. CO₂–TPD data showed the high CO₂ adsorption capacity of catalysts which improves the resistance of catalysts against the carbon formation. The H₂ chemisorption results also indicated that the addition of Pt to nickel catalyst improved the nickel dispersion. The obtained results revealed that the prepared catalysts showed a high activity and stability during the reaction with a low amount of deposited carbon. Addition of Pt to nickel catalyst improved both the activity and resistivity against carbon formation.     

Effects of pore sizes of porous silica gels on desorption activation energy of water vapour

In this work, the effects of pore sizes of silica gel on desorption activation energy and adsorption kinetics of water vapour on the silica gels were studied. The isotherms and adsorption kinetic curves of water vapour on three kinds of silica gels with average pore diameters of 2.0 nm, 5.28 nm and 10.65 nm, respectively, were measured by the method of static adsorption, the desorption activation energies of water vapour on silica gels were estimated by using the TPD technique, and the effects of pore sizes of silica gel on adsorption kinetics and desorption activation energy were discussed. Results showed that the isotherm of water vapour on the A-type silica gel with the average pore diameter of 2 nm was of type I, which can be well described by the Langmuir model; the isotherms of water vapour on the B-type and the C-type mesoporous silica gels with the average pore diameters of 5.28 nm and 10.65 nm, respectively, were of type V; and at lower RH, the smaller the average pore size of the silica gel was, the smaller the adsorption rate constant was due to the diffusion resistance in the pores of the silica gels, while at a higher RH, the smaller the average pore size of the silica gel was, the larger the adsorption rate constant was. The desorption activation energies of water on the A-type, the B-type and the C-type silica gels were respectively 35.54 kJ/mol, 31.41 kJ/mol and 26.16 kJ/mol, which suggested that the desorption activation energy of water on the silica gels increased as the pore sizes of the silica gels decreased.