Sorption Hysteresis Research Articles

Sorption Hysteresis Characterization of CH4 and CO2 on Anthracite, Bituminous Coal, and Lignite at Low Pressure

Sorption hysteresis characterization of CH4 and CO2 on lignite, bituminous coal, and anthracite were studied to improve the understanding of the interaction between gas molecules and different ranks of coal and further improve the precision of the adsorption methods in characterizing pore structure at low pressure. Pore structure of three ranks of coal was investigated with scanning electron microscopy (SEM) and nitrogen (N2) adsorption. Then, CH4 and CO2 sorption isotherms were measured using the gravimetric method under 288, 308, and 328 K. The N2 sorption isotherms show that a wide distribution of pore size existed in three coal samples, and with the process of coalification, the specific surface area (SSA) decreased and then increased, while the pore size of coal monotonically decreased. This is confirmed by SEM observation. The measured sorption isotherms were then decomposed into simultaneously running adsorption and absorption branches based on the assumption that the former is totally reversible and the latter completely irreversible. The reconstructed adsorption branches can be well described by both Langmuir model and Dubinin–Radushkevich (D–R) equation. The absorption, which represents the sorption hysteresis portion, increased with pressure, but decreased with temperature. The absorbed amount of gas increased with pressure, but the absorption of CO2 increased concavely with gas pressure while CH4 followed an upward exponential function. Also, the absorption varied with coal rank, following a U-shaped function. This study can provide new insights to CH4 and CO2 sorption hysteresis on coal and other organic geomaterials.

Erratum to: Water sorption hysteresis in wood: II mathematical modeling – functions beyond data fitting

Erratum to: Water sorption hysteresis in wood: II mathematical modeling – functions beyond data fitting

Undesorbable residual gas in coal seams and its influence on gas drainage

The definition of “residual gas” can be found in different scenarios, such as the “fast” and “slow” desorption methods of measuring gas content and the sorption hysteresis test and gas management of coal mines, however, its meaning varies a lot in different contexts. The main aim of this paper is to discuss the existence of truly undesorbable residual gas in coal seam conditions and its impacts on sorption model and gas drainage efficiency. We believe the undesorbable residual gas does exist due to the observation of the extended slow desorption test and the sorption hysteresis test. The origin of undesorbable residual gas may be because of the inaccessible (closed or semi-closed) pores. Some gas molecules produced during coalification are stored in these inaccessible pores, since the coal is relatively intact in the coal seam condition, these gas molecules cannot escape during natural desorption and then create the undesorbable residual gas. Based on the existing adsorption models, we propose the improved desorption versions by taking into consideration the role of residual gas. By numerically simulating a gas drainage case, the gas contents after different drainage times are studied to understand the influence of residual gas content on gas drainage. The results indicate that the influence starts to be obvious even when the total gas content is at a high level, and the impact becomes more and more apparent with increasing drainage time. Our study shows that the existence of residual gas will impede the gas drainage and the total amount of recoverable coal seam methane may be less than expected.

Fast response and highly sensitive humidity sensors based on CaCl2-doped sulfonated poly (ether ether ketone)s

This study presented a novel polymeric humidity sensor based on CaCl2-doped sulfonated poly (ether ether ketone) (SPEEK). For the first time, we developed a crosslinking procedure to modify SPEEK for humidity sensors application. SPEEKs with fixed value of sulfonation degree were synthesized by a direct aromatic nucleophilic substitution polymerization of sulfonated monomers. The obtained polymer was used to prepare humidity sensitive composites by doping CaCl2, and then they were fabricated by spin coating on a ceramic substrate to use as a novel polymeric humidity sensor. Humidity-sensing performances were investigated by varying both CaCl2 concentration and relative humidity. Comparing with the pristine polymer, CaCl2-doped SPEEK showed improved humidity sensing properties and the 10wt%- CaCl2/SPEEK sensor showed the best sensing properties for high sensitivity, little hysteresis (1.14%), fast response (2s)/recovery time (65s) and outstanding stability. Additionally, the morphology and thermal properties of composites and the humidity sensing mechanism of the sensors were discussed in detail. Most importantly, CaCl2 was employed not only as dopant to significantly improve the sensitivity, but also as cross-linker to reduce the sorption hysteresis. This study demonstrated that these humidity sensors could offer a great potential for applications.

The influence of extractives on the sorption characteristics of Scots pine (Pinus sylvestris L.)

The sorption behaviour of extracted and un-extracted Scots pine (Pinus sylvestris L.) heartwood was analysed using dynamic vapour sorption apparatus. In addition to the sorption isotherm and hysteresis, the moisture increments and decrements were determined as well as the rate of sorption. Parallel exponential kinetics model was used for further analysis. The effect of cyclic humidity loading on the sorption characteristics was studied by exposing samples to ten repeated sorption cycles and by determining the amount of accessible hydroxyl (OH) groups before and after the cyclic humidity loading. Removal of extractives led to an increase in EMC both in adsorption and in desorption. Hysteresis decreased due to the removal of extractives. Cyclic humidity loading reduced the sorptive capacity of wood material for both extracted and un-extracted wood, but was more pronounced in un-extracted wood. However, despite the decrease in the sorptive capacity, the amount of accessible OH groups increased after ten repeated dry-humid cycles.

Water sorption hysteresis in wood: III physical modeling by molecular simulation

AbstractMolecular simulation has been successfully applied to sorption and hysteresis studies of various nanoporous materials, revealing underlying mechanisms that neither theoretical nor experimental approaches can achieve. In this work, the grand canonical Monte Carlo approach is used in a simplified wood-water system to simulate sorption isotherms and hysteresis at 25°C and 40°C. Wood is represented by a cell wall model composed of a solid substance and evenly distributed independent cylindrical nanopores with diameters in the range of 0.6–2.2 nm. Polysaccharides and lignin pore-wall compositions are considered. Hydroxyl groups are modeled as negative energy pits attached to walls and water is represented by the extended simple point charge model. Capillary condensation in the wide hygroscopic range and metastable states are well demonstrated in the simulations, thus supporting the independent domain model discussed in the first paper of this series. The size of simulated hysteresis loops increases with pore size, less hydrophilic lignin composition and reduced temperature. The trends shown by the model are consistent with experimental findings. The larger hysteresis can be explained by more metastable states due to weaker wall-water interaction or smaller thermal fluctuation.

Sorption of sulfathiazole in the soil treated with giant Miscanthus-derived biochar: effect of biochar pyrolysis temperature, soil pH, and aging period

Agricultural soil was treated with biochar (5% w/w) produced from two pyrolysis temperatures (400 and 700°C) of giant Miscanthus (GMC-400 and GMC-700, respectively), and the subsequent sorption of sulfathiazole (STZ) was evaluated as a function of pH (2, 5, and 7) and aging period (0, 3, and 6months). Because sorption was nonlinear, with 0.51<N<0.75, the linearized sorption coefficient (K d*) was used for the comparison across samples. The K d* of GMC-400 treatment (3.96-9.96Lkg-1) was higher than that of GMC-700 treatment (1.27-3.38Lkg-1). In laps of aging period over 6months, the sorption of GMC-400-treated soil had gradually increased to be 3.3 times higher than that of untreated soil, whereas there was no statistical difference for GMC-700 treatment. Results of FTIR and SEM analyses revealed that the number of O-containing functional groups in the GMC-400 treatment increases and the micropores of GMC-700 are deformed over time. Sorption was also pH-dependent in the order of pH2>pH5>pH7. The sorption hysteresis (H) index for the GMC-400 treatment was higher at pH7 (3.99) than at pH5(2.53), and both values had increased after 6months (4.18 and 3.17, respectively). The results of this study clearly demonstrate that the sorption of STZ on GMC-treated soils is greatly enhanced, mainly through the greater micropore surfaces, the abundance of hydrophilic functional groups over time, and π+-π electron donor-acceptor interaction at low pH.

Rapid estimation of cation exchange capacity from soil water content

SummaryEstimates of cation exchange capacity (CEC) for soil or earth materials are vital for several applications in agriculture and geotechnical engineering. The time‐consuming and laborious nature of standard methods of CEC determination prompted the development of regression‐based techniques and more sophisticated methodologies, such as artificial neural networks (ANNs), to estimate CEC from other soil properties (e.g. clay, organic matter and pH). The present study proposes regression relations for estimating CEC from soil water content at different relative humidity (RH) values that range from 10 to 90% and considering sorption hysteresis. For model development, water adsorption and desorption isotherms were measured for 203 soil samples from different parts of the world with a vapour sorption analyser within an RH range from 3 to 93%. Regression models were developed for both adsorption and desorption for nine RH values (10, 20, 30, 40, 50, 60, 70, 80 and 90%). For 35 independent soil samples, the models predicted CEC accurately (root mean squared error (RMSE): adsorption = 2.47 (0.04) cmol(+) kg−1; desorption = 2.52 (0.09) cmol(+) kg−1) with no clear effect of RH value or sorption direction on the accuracy of prediction. The new models were superior to three models from the literature based on clay, organic matter and pH; the smallest RMSE from these models was 4.13 cmol(+) kg−1 for the same 35 soil samples. Furthermore, the water sorption‐based models performed better than literature models based on data mining tools (ANNs, support vector machines) and visible near infrared spectroscopy when standardized RMSE values were compared. Thus, a simple measure of soil water content at a known RH can serve as an accurate substitute for measuring soil CEC.Highlights A simple method to estimate cation exchange capacity (CEC) accurately is needed. Regression models for estimating CEC from soil water contents were developed and tested. Models predicted CEC accurately with no effect of relative humidity or sorption direction. Proposed models performed better than existing models based on the validation dataset.

Paper-based printed impedance sensors for water sorption and humidity analysis

The hygroscopic nature of cellulose-based materials poses a challenge in utilising paper for printed electronics. Adsorbed moisture strongly modulates the conductive and dielectric properties of paper. While affecting the function of printed electronic elements, this behaviour is beneficial for low-cost humidity sensing. Here we describe a simple, sensitive paper-based sensor with a pair of inkjet-printed interdigitated electrodes for analysing water sorption of cellulose over a wide range of relative humidity from 10% to 90%. Impedance spectroscopy between 100 Hz and 1 MHz reveals the humidity-dependent electrical properties of paper. We show in particular that measurements at 1 MHz provide reliable information about the water adsorption and desorption of paper. In contrast, testing at frequencies below 200 kHz is dominated by ionic electrode polarisation, masking the water sorption kinetics of the sensor. Transient adsorption follows nearly an exponential function, while desorption is described by a stretched exponential law. At equilibrated conditions, the effective paper permittivity measured during adsorption and desorption is characterised by a Guggenheim–Anderson–de Boer sorption isotherm which allows for a quantitative evaluation of the sorption hysteresis. Our means of sensing provides a simple and practical method of recording and analysing simultaneously conductivity and permittivity as well as wetting and drying of moist paper.

Microscopic Origin of Hysteresis in Water Sorption on Protein Matrices.

Despite the importance of water sorption isotherms for a fundamental understanding of protein-water interactions, the microscopic origin of hysteresis between the adsorption and desorption branches is not well understood. Using our recently developed simulation technique, we compute the water sorption isotherms of two proteins, lysozyme and Trp-cage, a miniprotein. We explicitly compare protein-water interactions in adsorption and desorption processes, by analyzing local hydration in terms of hydrogen bonding, water density, and solvent-accessible surface area. We find that significant differences in hydration behavior between adsorption and desorption manifest themselves at the individual amino acid level, in particular around polar or charged residues. We confirm this observation by demonstrating that Trp-cage's hysteresis can be significantly reduced by mutating charged residues to alanine, a neutral and nonpolar amino acid.

Clinoptilolite and palygorskite as sorbents of neutral emerging organic contaminants in treated wastewater: Sorption-desorption studies

Water reuse for aquifer recharge could be an important route for the introduction of emerging organic contaminants (EOCs) into the environment. The installation of a Horizontal Permeable Reactive Barrier (H-PRB) could constitute a tertiary treatment process to remove EOCs from treated domestic wastewater prior to recharge activities. The sorption-desorption behaviour of six neutral EOCs present in treated domestic wastewater (acetaminophen, caffeine, carbamazepine, cotinine, 4-acetamidoantipyrine (4-AAA) and 4-formylaminoantipyrine (4-FAA)) has been evaluated. Clinoptilolite and palygorskite have been studied as sorbents to be installed in the H-PRB. Batch tests were carried out using an EOC initial concentration ranging from 5 to 100 μg L−1. Apart from acetaminophen and caffeine, both materials showed a limited sorption capacity of neutral EOCs (Kd = 0.63–5.42 L kg−1). In general, the experimental results show that EOCs exhibit a higher sorption affinity for clinoptilolite than for palygorskite. With the exception of carbamazepine, the sorption of the compounds occurs mainly by interactions with mineral surfaces as indicated by the comparison of the partition coefficients into organic matter and into mineral surfaces. According to the molecular geometry of the compounds and the sorption sequences observed, it appears that the dimensions of the organic molecules play a key role in the sorption process. All the studied EOCs exhibit irreversible sorption and sorption-desorption hysteresis.

Changes of chemical properties and the water vapour sorption of Eucalyptus pellita wood thermally modified in vacuum

The aim of this study was to evaluate the chemical composition and the dynamic water vapour sorption properties of Eucalyptus pellita wood thermally modified in vacuum. For this purpose, wood samples were thermally modified in a vacuum oven at 160–240 °C for 4 h. Chemical composition were investigated by wet chemical analysis, elemental analysis, as well as Fourier transform infrared (FTIR) analysis, and dynamic water vapour sorption properties were evaluated by dynamic vapour sorption apparatus. The results showed that holocellulose and alpha-cellulose contents decreased and lignin and extractives contents relatively increased during the heat process. Elemental analysis showed a reduction in hydrogen content and an increase in carbon content. FTIR analysis indicated that the degradation of hemicellulose and condensation reactions of lignin occurred. In addition, the thermo-vacuum resulted in a reduction in the equilibrium moisture content of wood during the adsorption or desorption process. And the sorption hysteresis had a decreasing trend with increasing treatment temperature. The development of the hygroscopicity was related to the increase in the relative content of lignin, the degradation of the carbonyl groups in xylan and the loss of carbonyl group linked to the aromatic skeleton in lignin after heat treatment.

Synthesis of mesoporous nanoparticles of TiO2 from ilmenite

In this study, a surfactant assisted hydrometallurgical procedure was proposed for preparation of mesoporous nanoparticles of titanium dioxide (TiO2) from ilmenite concentrate. Initially, Fe was removed from ilmenite concentrate using HCl and then the titanium was dissolved from the remaining solid in an alkaline condition of NH3 or NaOH in assistance of H2O2 as oxidizing agent in order to prepare the titanium solution (Ti-sol). Afterwards, the prepared Ti-sol was used as titanium source for preparation of a mesoporous nanoparticles of TiO2 in assistance of hexadecyltrimethyl ammonium bromide (HDTMA-Br) as structure directing agent. Different methods were used to characterize the mesoporous nanoparticles of TiO2 structures such as XRD, SEM, and BET. The results showed that the HDTMA helps the formation of slit-shaped mesopores in the range of 1.5 nm when the synthesis was carried out at room temperature despite the media which Ti-sol was prepared, NH3 or NaOH. When a hydrothermal treatment was added to the synthesis process similar mesoporous structure was formed when the Ti-sol was prepared in NH3 with nitrogen sorption hysteresis of H3 type. However, when the NaOH prepared Ti-sol was used the nitrogen sorption hysteresis loop changed to H4 type showing existence of large mesopores (12 nm) in addition to smaller mesopores (2–5 nm). The HRTEM results showed mesoporous structure with nano-rod like particles with particle size around 30–60 nm.

Investigation on performance of multi-salt composite sorbents for multilevel sorption thermal energy storage

Novel bi-salt and tri-salt composite sorbents are developed, and expanded natural graphite treated with sulfuric acid (ENG-TSA) is integrated as the matrix with different mass ratios for heat transfer intensification. Tri-salt composite sorbent is mainly composed of Manganese chloride (MnCl2), Calcium chloride (CaCl2) and Ammonium chloride (NH4Cl) whereas bi-salt composite sorbent comprises Calcium chloride (CaCl2) and Ammonium chloride (NH4Cl). Sorption characteristics under non-equilibrium condition are investigated and compared with that under equilibrium condition. Results show that the sorption hysteresis can be alleviated by bi-salt composite sorbent and even eliminated by tri-salt composite sorbent. Based on testing results, multilevel sorption thermal energy storage (STES) is analyzed, which can greatly enhance the versatility and working reliability. It is also worth noting that the highest energy storage density of reaction heat is 1802kJ/kg and 1949kJ/kg for tri-salt and bi-salt composite sorbents, respectively. Performance of bi-salt composite sorbent is relatively close to the theoretical data, which indicates three main stages. Comparably, performance of tri-salt composite sorbent shows continuous variation with the increment of reaction temperature. The promising multilevel STES reveals the great potential for energy utilization of variable heat source such as solar power when compared with conventional heat storage methods.

Water sorption hysteresis in wood: I review and experimental patterns – geometric characteristics of scanning curves

AbstractThe origin of sorption hysteresis in the wood-water system is still under debate. In nanoporous-fluid systems, in general, hysteresis is explained as the manifestation of metastable states in a single pore-fluid system and that is further complicated by the pore connectivity. Cell walls are considered as micro-mesoporous materials and capillary condensation in the entire hygroscopic region is proposed as an alternative sorption mechanism. In the present work, the woods of Douglas-fir, aspen and western red cedar were in focus and the pore connectivity has been investigated by observing five experimentally generated hysteresis patterns comprised by up to 4thscanning curves at 25 and 40°C. Special attention was given to the congruency property from one pattern as it is known from the literature that deviation from this property can reveal the extent of pore connectivity. Consistent patterns were found for the species-temperature combinations. Further, the high extent of congruency property indicated the dominance of independent cell wall pores.

Water sorption hysteresis in wood: II mathematical modeling – functions beyond data fitting

Abstract The Preisach model, the mathematical form of the independent domain model, has been used to describe water sorption hysteresis in wood for over 20 years, however, its geometric interpretation has not been fully explored. In this work, it is demonstrated that the geometric interpretation can be used to explain the five experimental hysteresis patterns identified in the first paper of this series. Additionally, a modification to the aforementioned model is suggested that involves a numerical implementation, which avoids the use of unknown parameters. Our approach was evaluated at 25 and 40°C by comparing the predicted 1st to 4th order scanning curves with experimental data for Douglas-fir, western red cedar and Aspen. The low prediction errors and well-maintained wiping-out property support the suitability of our approach. Compared to other models found in literature, the presented model has the advantage of high accuracy and easy implementation due to its nonparametric nature.

Experimental and theoretical characterization of methane and CO2 sorption hysteresis in coals based on Langmuir desorption

Sorption hysteresis is important for primary gas production and CO2 sequestration in coalbed methane (CBM) reservoirs. We represent the degree of hysteresis using an areal hysteresis index (AHI) method incorporating a hysteresis parameter β, representing the ratio of available sorption sites for desorption relative to adsorption. This approach was applied to quantify the gas-coal sorption hysteresis to both methane and CO2 on sub-bituminous and bituminous coals and on anthracite. A theoretical desorption model describes hysteresis based on the molecular dynamic equilibrium between gas adsorption and desorption rates. Volumetric excess ad-/desorption isotherms of methane and CO2 show that adsorption capacities for anthracite are higher than those for the sub-bituminous and bituminous coals over the entire experimental pressure range. Hysteresis for CO2 is greater than for methane for all four coal samples investigated. The relationships between β and Langmuir pressure, Langmuir volume and final equilibrium pressure are weakly negative with null relationships between β and coal properties. Sorption hysteresis is caused by Langmuir pressure and gas type based on theoretical and experimental analyses although its physical mechanism remains unclear. A βCH4−βCO2 plot is proposed as a screening tool to determine likely gas substitution contents for enhanced coalbed methane (ECBM) and CO2 sequestration in coals.

Dynamic behaviours of a rationally prepared flexible MOF by postsynthetic modification of ligand struts

Through postsynthetic modification of ligand struts, controllable conversion of a Zr MOF between rigidity and flexibility is realized. The rationally prepared flexible MOF exhibits interesting dynamic behaviours, such as reversible structural deformation, vapour sorption hysteresis and unexpected adsorption of bulky guest molecules.

Simulation Experiment: Effect of Organic Colloid on Carbamazepine Transport in Porous Media

The behavior of organic contaminants in subsoil can be affected by their interactions with organic colloids. In order to explore the impact of organic colloids on the mobility of emerging contaminants in porous media, especially pharmaceutical and personal care products (PPCPs), column experiment was conducted to investigate the migration behavior of target compound carbamazepine (CBZ). In the experiments, quartz sand, standard soil and natural field-collected soil were selected as three types of porous media respectively, and organic colloids were prepared with commercial humic acid. The results showed that, the two-site chemical nonequilibrium model in CXTFIT could better describe the migration behavior of CBZ in all soil columns. This results demonstrated that chemical nonequilibrium adsorption happened in CBZ's migration process. After colloid was added to the sand column, results of CBZ's adsorption process had no significant changes, however, desorption hysteresis was weaker. The reason for that can be explained as the formation of colloid-CBZ complexes by the combination of colloid with CBZ. These complexes could not significantly influence CBZ's adsorption process, however, they could accelerate CBZ's desorption process by solubilization. When organic colloids existed, the migration of CBZ in natural soil and standard soil columns was more hysteretic than sand column, indicating that the sorption capacity of soil column was higher than sand column. The soil organic matter and clay should play a crucial role in the transportation: low/high energy adsorption sites in organic matter and clay surface all could bond with CBZ. Compared with standard soil, the magnitude of sorption and desorption hysteresis of CBZ in natural soil was higher. It was mainly because of the higher organic content in natural soil. Based on the migration behavior of the contaminant in this study, a concept model for various interactions during the transport of hydrophobic organic contaminants in porous media in the presence of organic colloids was then proposed.

Influence of temperature on water vapour sorption isotherms and kinetics of hardened cement paste and concrete

Water vapour sorption isotherms (WVSIs) have contributed significantly towards current knowledge of the porous nanostructure of cementitious materials and are an important component in modern durability calculations. In this paper, two newly developed multi-chamber testing apparatus for determining WVSIs of hardened cementitious materials are described. The adsorption, desorption and scanning behaviour of hardened cement paste and concrete are studied in detail over temperatures of 23°C to 80°C. Experiments provide confirmation of a monotonic reduction in sorption hysteresis with increasing temperature and show a disappearance of low humidity hysteresis by 60°C. Time and history dependence of apparent isosteric enthalpy of adsorption is demonstrated. Typically overlooked anomalous (non-Fickian) sorption kinetics are observed to significantly influence the equilibrium process. The magnitude and effect of temperature and humidity on kinetics is examined. Evidence supporting the role of microstructural change in observed size-independent kinetics and WVSI changes with temperature are discussed.