Nitrogen Adsorption Isotherms Research Articles

Experimental Study of the Adsorption of Nitrogen and Phosphorus by Natural Clay Minerals

Nitrogen and phosphorus are commonly recognized as causing eutrophication in aquatic systems, and their transport in subsurface environments has also aroused great public attention. This research presented four natural clay minerals (NCMs) evaluated for their effectiveness of NH4 + and PO4 3- adsorption from wastewater. All the NCMs were fully characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), BET analysis, and adsorption kinetics and isotherms to better understand the adsorption mechanism-property relationship. The results show that the adsorption efficiency of the four NCMs for phosphate was better than that for ammonia nitrogen. The removal rate of phosphate was higher than 65%, generally in the range of 80%-90%, while the removal rate of ammonia nitrogen was less than 50%. The adsorption kinetic behavior followed the pseudo-second-order kinetic model. The ammonia nitrogen adsorption isotherm was in good agreement with the Freundlich isotherm equilibrium model, and the phosphate adsorption isotherm matched the Langmuir model. Among all the NCMs studied, bentonite (7.13 mg/g) and kaolinite (5.37 mg/g) showed higher adsorption capacities for ammonia nitrogen, while zeolite (0.21 mg/g) and attapulgite (0.17 mg/g) showed higher adsorption capacities for phosphate. This study provides crucial baseline knowledge for the adsorption of nitrogen and phosphate by different kinds of NCMs.

Zinc(ii) and cadmium(ii) amorphous metal-organic frameworks (aMOFs): study of activation process and high-pressure adsorption of greenhouse gases.

Two novel amorphous metal–organic frameworks (aMOFs) with chemical composition {[Zn2(MTA)]·4H2O·3DMF}n (UPJS-13) and {[Cd2(MTA)]·5H2O·4DMF}n (UPJS-14) built from Zn(ii) and Cd(ii) ions and extended tetrahedral tetraazo-tetracarboxylic acid (H4MTA) as a linker were prepared and characterised. Nitrogen adsorption measurements were performed on as-synthesized (AS), ethanol exchanged (EX) and freeze-dried (FD) materials at different activation temperatures of 60, 80, 100, 120, 150 and 200 °C to obtain the best textural properties. The largest surface areas of 830 m2 g−1 for UPJS-13 (FD) and 1057 m2 g−1 for UPJS-14 (FD) were calculated from the nitrogen adsorption isotherms for freeze-dried materials activated at mild activation temperature (80 °C). Subsequently, the prepared compounds were tested as adsorbents of greenhouse gases, carbon dioxide and methane, measured at high pressures. The maximal adsorption capacities were 30.01 wt% CO2 and 4.84 wt% CH4 for UPJS-13 (FD) and 24.56 wt% CO2 and 6.38 wt% CH4 for UPJS-14 (FD) at 20 bar and 30 °C.

The adsorption removal of tannic acid by regenerated activated carbon from the spent catalyst of vinyl acetate synthesis

Activated carbon can remove humic acid organic pollutants to reduce trihalomethanes carcinogens generated in the chlorination disinfection process. In this study, regenerated activated carbon (RAC) was recycled from the spent catalyst of vinyl acetate synthesis via a thermal regeneration method. The influences of regeneration temperature and time on the regeneration rate and iodine adsorption value of the RAC samples were determined, the nitrogen adsorption isotherms and pore structure characteristics of RAC samples were characterised, and the effects of RAC additive amount, pH, adsorption temperature, and time on tannic acid removal rate were investigated. Results indicated that regeneration time and temperature presented pronounced influences on the regeneration rate and iodine adsorption performance of RAC samples. For the RAC sample optimally prepared at 900 °C for 2 h, the iodine adsorption value, BET surface area, and the regeneration rate were 817 mg/g, 1346 m2/g, and 65.9%, respectively. Under the optimal conditions including RAC additive amount of 3.5 g, temperature of 25 °C, adsorption time of 200 min and pH of 4.0, and tannic acid concentration of 50 mg/L, the tannic acid removal rate reached 89.96%. The adsorption kinetic characteristics for tannic acid onto RAC matched to Pseudo-second-order model, meanwhile the analysis of Boyd dynamic equation and Intraparticle diffusion model denoted the absorption process was mainly controlled by film diffusion. This work provides a technology aiming at the joint treatment of hazardous waste resources, which involve the regeneration activated carbon from spent catalysts and the absorption removal of tannic acid organic pollutants.

Rheological properties and sedimentation stability of magnetorheological fluid based on multi-walled carbon nanotubes/cobalt ferrite nanocomposites

In this investigation, nanocomposites of cobalt ferrite (CoFe2O4) nanoparticles grown on multi-walled carbon nanotubes (MWCNTs) were developed by a ultrasonic-assisted co-precipitation technique. The as-prepared MWCNTs/CoFe2O4 nanocomposites were characterized in detail using transmission electron microscope (TEM), Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra, thermogravimetric analysis (TGA), superconducting quantum interference device (SQUID) magnetometer and nitrogen adsorption and desorption isotherms. The obtained MWCNTs/CoFe2O4 was adopted as the advanced dispersed phase for the fabrication of a uniform magnetorheological (MR) fluid, and its rheological properties and sedimentation stability were comprehensively examined. It had been revealed that the designed MR suspension exhibited typical MR features with increasing viscosity, shear stress, yield stress, storage modulus and loss modulus depending on the applied magnetic fields. It was worthy to note that the sedimentation stability of MR fluid was improved significantly, which was primarily attributed to the special three-dimensional network structure of MWCNTs/CoFe2O4 and the reduced density mismatch between the dispersed phase and carrier fluid.

Sorption of Methylene Blue for Studying the Specific Surface Properties of Biomass Carbohydrates

The surface area is an important parameter in setting any biorefining technology. The aim of this study was to investigate the applicability of sorption of methylene blue to characterize the surface of the main biomass carbohydrates: α-cellulose, sigmacell cellulose, natural gum, β-glucan, and starch. The morphology of particles of the model objects was studied by scanning electron microscopy. Nitrogen adsorption isotherms demonstrate that the selected carbohydrates are macroporous adsorbents. The monolayer capacities, the energy constants of the Brunauer–Emmett–Teller (BET) equation, and specific surface areas were calculated using the BET theory, the comparative method proposed by Gregg and Sing, and the Harkins–Jura method. The method of methylene blue sorption onto biomass carbohydrates was adapted and mastered. It was demonstrated that sorption of methylene blue proceeds successfully in ethanol, thus facilitating surface characterization for carbohydrates that are either soluble in water or regain water. It was found that the methylene blue sorption values correlate with specific surface area determined by nitrogen adsorption/desorption and calculated from the granulometric data. As a result of electrostatic attraction, the presence of ion-exchanged groups on the analyte surface has a stronger effect on binding of methylene blue than the surface area does. Sorption of methylene blue can be used in addition to gas adsorption/desorption to assess the accessibility of carbohydrate surface for binding large molecules.

Изменение поверхностных характеристик цинкмодифицированного цеолита типа H-ZSM-5 в процессе трансформации метанола в синтетические углеводороды

The t-plot method is a well-known method for determining the volumes of micro- and/or mesoporous materials and the specific surface area of a sample by comparison with a reference adsorption isotherm of a non-porous material having a similar surface chemical composition. The article describes the applicability of the t-graph method to the analysis of the surface properties of zinc modified samples of zeolite H-ZSM-5 before and after the reactions of methanol transformation into hydrocarbons occur on them. Zeolites are widely used as catalysts in the petrochemical and refining industries. These materials contain active Bronsted acid sites, distributed within the microporous structure of zeolites, which leads to selective catalysis due to the difference in the pore shape of the zeolites used. The size, shape of the zeolite catalyst determines the catalytic performance in terms of both product selectivity and catalyst deactivation. In most zeolite catalyzed hydrocarbon conversion reactions, catalyst activity is lost due to carbon deposition. In this connection, the determination of the surface properties of zeolites is an important task that contributes to the disclosure of the physicochemical essence of the process of deactivation of zeolites. The recalculation of nitrogen adsorption isotherms using the t-plot model made it possible to determine the volume of micro and mesopores. Based on the t-graph data, it can be concluded that during the transformation of methanol into hydrocarbons, carbon accumulates on the surface of the zeolite. In this case, the predominant deposition of carbon on the surface of mesopores, due to the fact that in the process of decontamination, from 61 to 73% of the volume of mesopores is lost. The number of micropores also decreases, but the share of losses is 42–54%, which is 10–15% lower compared to the loss of mesopore volume.

Adsorptive-Oxidative Removal of Sulfides from Water by MnO2-Loaded Carboxylic Cation Exchangers.

Hybrid ion exchangers (HIX) containing manganese(IV) oxide (MnO2) based on macroporous and gel-type carboxylic cation exchangers as supporting materials were obtained. The hybrid materials were characterized using scanning electron microscopy with energy dispersive spectrometry (SEM/EDS), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and nitrogen adsorption isotherms at 77 K and mercury porosimetry. HIX with introduced MnO2 (20.0–32.8 wt% Mn) were tested for removal of dissolved sulfides from anoxic aqueous solutions with 100–500 mg S2−/dm3 concentrations. The process proceeded effortlessly at pH 10–13 despite unfavorable electrostatic interactions of the reactants. The highest exhibited sorption capacity was 144.3 ± 7.1 mg S2−/g. Approximately 65% of dissolved sulfides were oxidized to S2O32− ions and repelled from HIX structure. On average, 13% of sulfide removal products were adsorbed by the MnO2 surface. The impact of MnO2 load and the ionic form of HIX functional groups on removal of sulfides and resulting products was examined. The mechanism of the process is suggested.

Inorganic matter in rice husk derived carbon and its effect on the capacitive performance

Porous carbons were obtained from rice husk using two different chemical activation methods and they were investigated as supercapacitors. Their properties were studied using X-ray photoelectron spectroscopy, thermal analysis, potentiometric titration, and nitrogen adsorption isotherm. The specific capacitance measured in both H2SO4 and KOH electrolytes in two-electrode cell was up to ~150 F/g. The activation method used affected the resulting carbons' features. As expected, the dependence of the capacitance on porosity was found. The ash content reached 36 wt.% and that inorganic mater blocked some pores and limited their accessibility to electrolyte ions and increased the charge transfer resistance. Nevertheless, the main ash constituents such as CaCO3, MgCO3, Ca3(PO4)2 (or P2O5), and Fe- and Zn- containing species did not affect the specific capacitance to a large extent. Especially SiO2, even in a relatively large amount (~20 wt.%), did not play a detrimental role in the capacitance behavior. The results showed that in spite of a high ash content, carbon can exhibit a good capacitive performance provided that it has a favorable porosity and is rich in sp2 configurations.

Entropy in multiple equilibria. Argon and nitrogen adsorption isotherms of nonporous, microporous, and mesoporous materials

Analysis of multiple equilibria of compounds with different coordination sites is extended to the description of adsorption isotherms with focus on the low relative pressure range. The entropy evolution is described using the particle distribution theory which also holds for adsorbents consisting of materials bearing more than one type of sites and applies for the condition that the adsorptive-adsorbent binding strength is larger than the adsorptive-adsorbate binding strength, so that monolayer coverage is favored. This allows to accurately determine the adsorption enthalpy. No assumption concerning the growth mechanism and specifics regarding the structure of the surface is needed. We find on a rigorous basis that this leads to Langmuir's equation for each site independently, that the total fractional amount of bound adsorptive can be described as a linear combination of individual Langmuir isotherms, and that such a linear combination has never the shape of the original Langmuir isotherms. The results are successfully applied to argon and nitrogen adsorption isotherms of nonporous, microporous, and mesoporous adsorbents which allows comparing systems for which the properties of the active surface span a large range. We observe that all experimental data can accurately be described by means of a linear combination of two Langmuir isotherms in the low relative pressure range up to a coverage of 60%–95%. This means that the shape of all adsorption isotherms is essentially determined by the entropy decrease with increasing coverage. The two site interactions involved exhibit substantially different adsorption enthalpies. Interestingly the Ar enthalpy of adsorption Δ a d s H 1 ∅ of the sites 1 for the Stöber-type silica and of the three investigated MCM-41 adsorbents (with pore size of 2.7 nm, 4.1 nm, and 4.4 nm) are similar, namely −11 kJ/mol. The situation is analogous for the enthalpy of adsorption Δ a d s H 2 ∅ for the sites 2, which amounts to −8 kJ/mol. A significantly larger enthalpy of adsorption Δ a d s H 1 ∅ for the sites 1, namely −14.3 kJ/mol, and Δ a d s H 2 ∅ = − 11.7 kJ / mol for the sites 2 is measured for potassium zeolite L thus reflecting the more polar nature of this adsorbent. The measured specific surface area for these samples ranges from 14 m 2 /g for the Stöber-type silica up to 1100 m 2 /g for the MCM-41(4.1 nm) adsorbent. The information provided by the lc2-L (linear combination of 2 Langmuir functions) analysis allows calculating the evolution of the coverage of site 1 and of site 2 as a function of increasing pressure. The inflection points of the isotherms, which mark the point where the curvature changes sign, were determined by numerically evaluating the second derivatives which vanish at this point and are compared with values obtained using BET analysis.

Nitrogen-doped macro-meso-micro hierarchical ordered porous carbon derived from ZIF-8 for boosting supercapacitor performance

Nitrogen-doped carbon materials with large specific surface area and high porosity show a promising application in supercapacitors due to the excellent mass and electron transfer. Zeolitic imidazolate framework (ZIF-8) derived porous carbon usually exhibit sizeable specific capacity and admirable stability for supercapacitors, whereas the macroporous-free structure limits the electrochemical performance. Herein, we report a nitrogen-doped hierarchical ordered porous carbon (NHOPC), which is derived from a novel single-crystal ordered macroporous ZIF-8. Electron microscopy and nitrogen isothermal adsorption experiment identify the three-dimensional interconnected macro-meso-micropores of the NHOPC. By combining structural and electrochemical characterization, the effects of annealing temperature on the physical-chemical structure and electrochemical performance are discussed carefully, thus establishing a reasonable structure-activity relationship. The optimized NHOPC-900 exhibit an ultra-high specific capacity of 475.5 F g−1 at the current density of 0.5 A g−1 and excellent cyclical stability, which attributes to a synergistic effect of large specific surface area, fast mass transfer, and nitrogen-doped matrix of the material.

Preparation and characterization of activated carbon developed from cotton cloth residue activated with phosphoric acid: adsorption of clofibric acid.

Cotton cloth waste was used as a precursor to prepare activated carbon (ACCs) chemically activated with phosphoric acid. Adsorption behavior of prepared ACCs was correlated with physicochemical proprieties. The pore volume and BET surface of ACCs were determined by nitrogen adsorption isotherms and scanning electron microscopy was used to observe their surface morphologies. Fourier transform infrared (FTIR) spectroscopy analysis and pH point zero charge (pHPZC) were conducted to determine chemical properties. Under the optimal conditions: 50% impregnation ratio and thermal treatment under N2 flow at 600 °C during 60 min, the activated carbon prepared exhibits a high surface area 1,150 m2/g, 0.501 cm3/g micropore volume and an excellent adsorption performance. The adsorbed amount of clofibric acid is found to be 9.98 and 83 mg/g at, respectively, initial CA concentration of 10 and 100 mg/L at pH 3.0 and 20 °C. Diffusion and chemisorption are the steps controlling the adsorption of CA onto ACC 50% and the equilibrium data were well described by Freundlich isotherm.

Reexamining supercritical gas adsorption theories in nano-porous shales under geological conditions

Adsorption is an important phenomenon in surface chemistry, especially for nano-porous shales. In the shale gas-in-place, adsorbed gas could contribute up to 85%. However, adsorption is hard to quantitatively characterize due to different adsorption mechanisms, patterns, surfaces, and pore sizes. Moreover, key thermodynamic parameters, such as the enthalpy of adsorption, are challenging to determine due to uncertainties in adsorbed gas densities used in constructing absolute isotherms. In this paper, we revisit the Brunauer, Emmett, and Teller (BET) model, analytically simplify Ono-Kondo (OK) models for subsurface shales, and compare commonly used mono- and multilayer adsorption models (e.g., Langmuir, supercritical Dubinin-Radushkevich (SDR), supercritical BET (SBET), and simplified OK (OKs) models) with recently proposed pressure-dependent adsorption densities to develop a practical and reliable methodology that can be used in the supercritical state, typical for subsurface black shale conditions.Three independent data sets were used for nitrogen and methane adsorption isotherms at different temperatures. We demonstrate that adsorption predicted by the SDR model is comparable or lower than that predicted by the SBET model, but higher than the amounts predicted by Langmuir and OK models. The nitrogen BET method tends to underestimate the accessible SSA for methane. Measurement of isosteric heat of adsorption is suggested instead of the experimental fitting method, due to the significant difference between the calculated results by two commonly used methods. Experimental fitting and simulation methods are also briefly reviewed to guide future research on shale gas adsorption.

Key parameters to improve zeolites hierarchization in direct synthesis

In this study, we propose the generation of micro/mesoporous zeolites with ZSM-11 structure by hydrothermal treatment using tetrabutylammonium hydroxide (TBAOH) as micropore structure directing agent and cetyltrimethylammonium bromide (CTAB) as mesotemplate. From many synthesis parameters evaluated (crystallization time, hydrothermal temperature, CTAB content), the type of base employed in the synthesis gel showed notorious influence in the structure, textural properties and morphology of the micro/mesoporous ZSM-11 zeolites. The samples were characterized by different techniques such as X-ray diffraction, nitrogen adsorption and desorption isotherms, Brunauer–Emmett–Teller surface area, scanning electron microscope, ICP-AES and 27Al MAS NMR. The characterization results revealed that the crystallization time, CTAB content and type of base (NaOH, KOH, Ca(OH)2 and NaCO3) played a dominant role in controlling the formation of both microporous and mesoporous structures. The base employed in the synthesis and its concentration showed important effects on the structure and textural properties of the composite materials. It was found that to obtain the best characteristics in terms of crystallinity and textural parameters, NaOH and KOH should be employed.

MgSO4 composites in a ferroaluminophosphate for enhancement of volumetric heat storage capacity at a low charging temperature

SummaryFerroaluminophosphate (FAPO4‐5)/MgSO4 composites were prepared as a series of new materials with low charging temperatures and improved volumetric heat storage capacities. A microporous zeolithic compound FAPO4‐5 was used as an adsorbent of water vapor and a matrix of MgSO4 salt particles. Composites with various MgSO4 contents (5‐40 wt%) were then prepared using a wet impregnation method. The MgSO4 salt particles were impregnated into the micropores and textural pores of FAPO4‐5 without the crystal structure of the host material, confirmed by XRD patterns. Although nitrogen adsorption isotherms of the composites showed approximately a half of FAPO4‐5 pore was blocked by MgSO4, the water uptake of the composites reached the sum of those from FAPO4‐5 and MgSO4. The dehydration temperature of MgSO4 in the FAPO4‐5 matrix decreased with its decreasing content due to the easier dehydration of FAPO4‐5. The heat storage recovery of the 25 wt% loaded sample at 80°C was 85.5% while that of MgSO4 was 52.2%. The swelling and agglomeration of the composites containing 25 wt% and less salt were suppressed by the micro and textural pores of FAPO4‐5. The composite at 25 wt% of MgSO4 loading exhibited a total volumetric heat storage capacity of 174 kW h m−3 based on the volume in the hydrated state.

Preparation of Fe-doped NaBi(MoO4)2 nanorods and their improved gas-sensing properties

NaBi(MoO4)2 nanorods and nanoparticles were prepared by a facile solvothermal method with or without nitric acid. The crystal phase, morphology, and microstructure of the samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and the nitrogen adsorption isotherms. The NaBi(MoO4)2 nanorods and nanoparticles were tetragonal scheelite nanocrystals, and the nanorods were composed of 4–6 spheritic nanograins which were about 19 nm in diameter. The nanoparticles were aggregated randomly by 25 nm NaBi(MoO4)2 crystallites. Both NaBi(MoO4)2 nanorods and nanoparticles were mesopore structure. The sensors based on NaBi(MoO4)2 nanorods and nanoparticles exhibited high gas-sensing response (30.5 and 24.7) to 100 ppm n-butanol at optimal operating temperature of 370 °C.The composites of Fe-doped NaBi(MoO4)2 nanorods were prepared, and they showed better gas-sensing performances than pure NaBi(MoO4)2 nanorods due to promoting oxygen adsorption and catalysis by Fe doped. The highest sensitivity of the sensor based on 1 wt% Fe-doped NaBi(MoO4)2 nanorods was 48.4 to 100 ppm n-butanol at 300 °C.

A high-efficiency and plane-enhanced chitosan film for cefotaxime adsorption compared with chitosan particles in water

It is well known that the adsorption capacity of particles is stronger than that of film due to the high specific surface area. Nonetheless, it is a bit different in some cases because of the plane enhancement effect of film. The third-generation cephalosporin are commonly used for either prevention or treatment of bacterial infections. These antibiotics, which have been discharged into various water environment, have created a lot of serious problems in our world. Adsorption of cefotaxime (CTX) in water by the chitosan particles (CSp) and films (CSf) were explored. The samples were characterized by scanning electron microscopy, the nitrogen adsorption isotherms, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and others. Various experimental conditions (pH, adsorption time, molecular weight of CSf, initial antibiotic concentrations, the number of films and foreign ions) presented an important influence on CTX removal. The pseudo-second-order kinetics and Freundlich isotherm models better illustrated the adsorption behavior of CTX on CSf, and the highest adsorption capacity was 1003.64 mg g−1, far above CSp (648.05 mg g−1) and these reported adsorbents. The reusability experiments revealed that CSf had passable regeneration and continuous usage performance. Multiple analysis factors suggested that the mechanism of CTX adsorption on CSf was mainly based on plane strengthening effect, electrostatic attraction, nucleophilic addition reaction and hydrogen bonding. These findings showed that CSf was an efficient and reusable adsorbent for antibiotics elimination in water.

Ethylene adsorption on chitosan/zeolite composite films for packaging applications

• A film of chitosan and natural zeolite has been evaluated for ethylene release control. • Ethylene equilibrium of adsorption was measured gravimetrically. • Ethylene adsorption capacity was affected by zeolite amount and film drying process. • Chitosan/zeolite film chose for ethylene is based on the product to be packed. Ethylene is the hormone responsible for the development and ripening of fruits and vegetables. Thus, in order to extend the postharvest shelf life, its accumulation should be avoided. Films, dense and porous, composed of chitosan/zeolite (CZ), were obtained using chitosan as support for clinoptilolite zeolites. These films were characterized by nitrogen and carbon dioxide adsorption isotherms, water vapor permeability and ethylene adsorption capacity. Zeolites distribution and the development of the pores were observed by scanning electron microscopy. Films were dried (partially or totally) by a convective process, followed or not by lyophilization. Lyophilized-CZ (with 93 % zeolite (CZ93 L) showed adsorption capacity similar to that of pure zeolite regenerated at 90 °C (ZR90) and higher than CZ93. Dense-chitosan films (DCF), porous-chitosan films (PCF) and CZ33 (33 % zeolite) exhibited small amounts of adsorbed ethylene when compared to the other materials. Based on these results, the chitosan/zeolite films may be viable for packaging applications.

Copper (I)–Organic Frameworks for Catalysis: Networking Metal Clusters with Dynamic Covalent Chemistry

Metal clusters exhibit diverse structures, emerging functions, and applications; thus, incorporating clusters into metal–organic frameworks (MOFs) brings tremendous merits. Although the constructio...

Vacuum pressure swing adsorption process for coalbed methane enrichment

The enrichment of low concentration coalbed methane using adsorption process with activated carbon adsorbent was studied in this work. Adsorption isotherms of methane, nitrogen and carbon dioxide on activated carbon were measured by volumetric method, meanwhile a series of breakthrough tests with single component, binary components and three components feed mixture has been performed for exploring dynamic adsorption behaviors. Moreover, a rigorous mathematical model of adsorption bed containing mass, energy, and momentum conservation equation as well as dual-site Langmuir model with the Linear driving force model for gas–solid phase mass transfer has been proposed for numerical modeling and simulation of fixed bed breakthrough process and vacuum pressure swing adsorption process. Furthermore, the lumped mass transfer coefficient of methane, nitrogen and carbon dioxide on activated carbon adsorbent has been determined to be 0.3 s −1 , 1.0 s −1 and 0.06 s −1 by fitting the breakthrough curves using numerical calculation. Additionally, a six bed VPSA process with twelve step cycle sequence has been proposed and investigated for low concentration coalbed methane enrichment. Results demonstrated that the methane molar fraction in feed mixture ranged from 10% to 50% could be enriched to 32.15% to 88.75% methane in heavy product gas with a methane recovery higher than 83% under the adsorption pressure of 3 bar (1 bar = 10 5 Pa) and desorption pressure of 0.1 bar. Energy consumption of this VPSA process was varied from 0.165 kW·h·m − 3 CH 4 to 0.649 kW·h·m − 3 CH 4 . Finally, a dual-stage VPSA process has been successfully developed to upgrade a low concentration coalbed methane containing 20% methane to a target product gas with methane purity higher than 90%, meanwhile the total methane recovery was up to 98.71% with a total energy consumption of 0.504 kW·h·m − 3 CH 4 .

Characterization of the physicochemical, structural and thermodynamic properties of encapsulated garlic extract in multilayer wall materials

Garlic extract (GE) was encapsulated into the matrices of two types of multilayer walls composed of whey protein isolate (WPI)/chitosan (CH)/polydextrose (POL) and gum Arabic (GA)/CH/POL. Fourier transform infrared spectroscopy (FTIR) indicated that the compounds of GE were encapsulated within the matrices of the wall materials by physical interactions. The water adsorption isotherms of the powders were determined at 30, 40 and 50 °C. The GAB model was the most suitable to fit the adsorption data. The adsorption sorption of the powders was enthalpy-controlled and the thermodynamic functions demonstrated that the WPI/CH/POL powders had hydrophilic surface with higher number of polar sites available to binding with water molecules than GA/CH/POL powders. The experimental data of water and nitrogen adsorption isotherms were used to determine the surface areas and pore sizes of the powders. All the results can be used to improve the processing, handling, and storage conditions of the powders.