Water Vapor Adsorption Characteristics Research Articles

Effect of the pore structure characteristics of coal samples on the dynamic adsorption of water vapor

In order to study the dynamic adsorption process of water vapor in the pore structure of different coal samples (YJL for lignite, SEK for bituminous coal and BJ for anthracite). The pore structure characteristics of the three coal samples were analyzed by mercuric pressure method, liquid nitrogen adsorption method and infrared spectroscopy. Further, the water vapor adsorption capacity of the three coal samples under different humidity conditions was determined by dynamic water vapor sorption (DVS) experiments. In addition, the monolayer adsorption and multilayer adsorption at different humidity were calculated using the Dent model. The results showed that YJL had the largest surface pore volume and oxygen functional group parameter (IO = 12.41), and its water vapor adsorption capacity was also the highest. However, under high humidity conditions, the presence of a large number of pore throats in the YJL coal samples hindered multilayer adsorption, resulting in a water vapor adsorption percentage of only 18.07 %. On the other hand, SEK has a small oxygen functional group parameter (IO = 5.81), poor pore connectivity, and a certain pore throat structure, resulting in a low water vapor adsorption capacity of SEK coal samples, with a water vapor adsorption proportion of only 23.76 %. BJ coal has a large pore volume and a large number of oxygen functional groups on the surface (IO = 8.84), which has a good pore connectivity and the least number of pore throats structure, resulting in a water vapor adsorption ratio is higher at 87.38 %. On this basis, cylindrical and wedge-shaped pore models of coal samples were constructed, and molecular dynamics simulations were carried out to investigate the adsorption characteristics of water vapor in these pore models. The results show that the adsorption process of water molecules in coal develops continuously with “initial-water chain-water bridge-water lock”. By summarizing and analyzing the above experimental results, four control mechanisms of coal pore characteristics affecting water vapor adsorption were clarified. These findings are of great significance for studying the movement of water vapor in coal seams and understanding the degree of water confinement caused by hydraulic control measures.

Alkaline Treatment of Straw for Composite Material Production and Its Impact on Water Vapor Adsorption Characteristics

Alkaline Treatment of Straw for Composite Material Production and Its Impact on Water Vapor Adsorption Characteristics

Thermodynamic parameter analysis of water vapor adsorption process of fly ash concrete material

Experimental research on water vapor adsorption performance of concrete with different class Ⅱ fly ash contents is carried out in this paper. Time-varying response curves of water vapor adsorption of fly ash concrete in five different humidity environments were obtained. According to the empirical formula of the thermodynamic parameters of water vapor adsorption of cement-based materials, the thermodynamic parameters of the water vapor adsorption process of fly ash concrete materials are calculated. The calculation method of the thermal kinetic parameters of water vapor adsorption for fly ash concrete materials is proposed; Influence of different fly ash contents with 10%, 20% and 30% mass percentage of cement and water-cement ratio on the water vapor adsorption characteristics of concrete materials is analyzed; The error between the second-layer adsorption energy and the condensation enthalpy of water vapor is calculated, and the rationality of the approximate calculation is analyzed. It is noted that (1) Water vapor adsorption characteristics of concrete materials are related to the water-cement ratio. With the water-cement ratio decreases, the adsorption capacity of concrete material increases. (2) Reasonable formula for calculating the number of saturated adsorption layers n of water vapor suitable for concrete materials is recommended. (3) Taking the condensation enthalpy of water vapor as the adsorption enthalpy of the second layer and subsequent layers reasonable to determine the dynamic parameters of the water vapor adsorption process of concrete.

Combined effects of pore structure and surface chemistry on water vapor adsorption characteristics of coal: Equilibrium, thermodynamic and kinetic studies

The combined effects of surface chemistry and pore structure on water vapor adsorption characteristics of coal were studied by evaluating the equilibrium, thermodynamic and kinetic properties. Four coal samples of different rank were fully characterized with gas (N2 and CO2) sorption and Fourier Transform infrared spectroscopy (FTIR) methods. Then measurements of water vapor adsorption equilibrium and kinetics were undertaken at elevated temperatures. Equilibrium and kinetic data were fitted by the modified BET model and the unipore model, respectively. The thermodynamic parameters, as well as diffusion activation energy were estimated based on the adsorption data. The results demonstrate that water vapor adsorption depends on the surface chemistry but unrelated to the pore structure, because the pore space is not completely filled by water molecules even at the saturation pressure. The monolayer adsorption capacity decreases with increasing coal rank. Moreover, water vapor needs lower work to attain equilibrium on high-ranked coal. Also, the binding affinity of water molecule with primary sites is stronger than secondary sites. Furthermore, the diffusion coefficient decreases with coal rank, and the diffusion activation energy for high-volatile bituminous is higher than the other coals, as a result of the complexity and poor connectivity of its pore network.

Toluene and water vapor adsorption characteristics and selectivity on hydrophobic resin-based activated carbon

The competitive adsorption between volatile organic compounds (VOCs) and water vapor seriously decreases the adsorption capacity of adsorbents. In this paper, a series of hydrophobic spherical resorcinol-formaldehyde resin-based activated carbons (CRFs) were prepared and characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmet-Teller (BET) techniques. The adsorption equilibrium and selectivity of toluene and water vapor on CRFs were investigated systematically. Compared to other adsorbents, HCRF800 treated by hydrogen reduction exhibited the highest toluene uptake (8.64 mmol/g at 293 K) and the strongest hydrophobicity, which was much superior to commercial activated carbon. The results of isosteric heats showed that toluene on HCRF800 was higher than that of water vapor, indicating a stronger interaction between the adsorbent and toluene than water vapor. The adsorption selectivity of toluene/water vapor on CRFs was estimated by the Difference of Isosteric Heats (DIH) equation, and the results suggested that HCR800 possessed the highest selectivity, and the value was in the range of 9.5–52.3. Furthermore, HCRF800 also displayed good toluene uptake at different humidities and faster intra-particle diffusion behavior due to its lower content of surface oxygen groups. Temperature-programmed desorption experiments and Density Functional Theory calculations further revealed that surface oxygen groups had a negative effect on the selectivity of toluene/water, and the negative effect followed the order as O-CO > C-O > CO. Moreover, HCRF800 possessed excellent reversibility. These results demonstrated that HCRF800 would be a superior adsorbent for VOCs recycling from a humid atmosphere.

Study on the water vapor adsorption Characteristics of Carbon materials in HTGR

High-temperature gas-cooled reactor (HTGR) is the first kind of power plant with fourth-generation features in the world, and a large amount of graphite and carbon material is adopted as structural material and fuel matrix material, including boron-containing carbon (BC) and isostatic pressure graphite (IG-110). As a kind of porous material, the carbon material contains a certain amount of moisture, which will impose negative effects on reactor safety. Therefore, this paper studies the water vapor adsorption characteristics of carbon materials in HTGR. The adsorption isotherms of BC and IG-110 were obtained by experimental measurements. Experiments show that the moisture adsorption of IG-110 is much lower than that of BC at various relative humidity. The experimental data is analysed by the BET, GAB, DA, Oswin adsorption models.

Adsorption Isotherm Model for Analyzing the Adsorption Characteristics of Water Vapor to Commercially Available Silica Gel Adsorbents for Adsorption Desalination Applications

In adsorption desalination applications, adsorption isotherms are considered to be a crucial factor, significantly impacting performance. From this perspective, a number of isotherm models have bee...

Influence of Fluorine Doping of Activated Carbon Fibers on Their Water Vapor Adsorption Characteristics.

The characterization of fluorinated carbon fibers by water sorption has been broadly investigated in this work. In brief, a pitch-based activated carbon fiber (ACF) was submitted to a fluorination process under different conditions of partial pressure (F2:N2 ratio) and temperature. This led to samples with varied fluorine content and C-F type bonding. The effect of the fluorination treatment on the textural properties of the ACF was studied by means of nitrogen and carbon dioxide adsorption at −196 and 0°C, respectively, while the changes induced in the surface chemistry of the materials were analyzed by XPS. Also, the affinity and stability of the materials toward water was evaluated by single and cycling isotherms. The obtained results show that a mild fluorination not only can preserve most of the textural properties of the parent ACF, but enhance the water uptake at the first stages of the water sorption process, together with a shift in the upswing of the water isotherms toward lower relative humidities. This indicates that fluorination under certain conditions can actually enhance the surface hydrophilicity of carbon materials with specific properties. On the contrary, higher partial pressures led to highly fluorinated fibers with lower porosity and more hydrophobic character. Moreover, they presented a lower chemical stability as demonstrated by a change in the shape of the water isotherms after two consecutive measurements. The kinetics of water sorption in the ACFs provided further insights into the different sorption phenomena involved. Hence, water sorption can definitely help to tailor the water affinity, stability and performance of fluorinated porous carbon materials under humid conditions.

Microscopic Mechanism of Water Vapor Adsorption Experimennts on Deep Soft Rock Water Vapor

At present, research on the influence of water on the physical properties of rocks is mostly focused on the macroscopic angle. Studies on nanoscale pore structure changes caused by water are few. Shale is characterized by good pore structure and high content of hydrophilic clay minerals susceptible to water. Based on this, in this paper the shale samples were obtained from underground layers 3000 m deep in Songliao Basin, Jilin Province, China. The sample parameters are measured by steam adsorption and nitrogen adsorption experiments under different soaking time conditions. The study shows that the pore structure of shale depends mainly on mineral composition and soaking time. With increase in soaking time, the amount of water vapor adsorption first decreases by 10% and then gradually increases. With water migration in the rock some pore structures are filled with shale particles. As the bubble time increases, the ion diffusion causes development of new pores and micro-cracks, and the adsorbed water vapor amount increases. At the microscopic scale, it is of great practical significance to study the nanoscale pore structure and adsorption characteristics of water vapor in the soft for different soaking time, and to further explore the stress characteristics, adsorption law, and gas migration in shale.

Characterization of silica gel-based composites for adsorption cooling applications

Abstract In this study, adsorption characteristics of water vapor onto several silica gel-based composites have been investigated experimentally. Adsorbent samples under investigation are silica gel powder (SGP), 98wt% SGP with 2wt% Polyvinylpyrrolidone (PVP) binder, 93wt% SGP, 2wt% PVP binder with 5wt% EG500 and 93wt% SGP, 2wt% PVP binder with 5wt% EG100. The three composite samples have been named as (S1-PVP), (S2-EG500) and (S3-EG100), respectively. Porous properties and thermal conductivity of S2-EG500 and S3-EG100 have been measured and compared with that of SGP. Experimental results showed that S2-EG500 has higher effect on enhancing the thermal conductivity of the composites where its thermal conductivity reached about 2.8 times that of SGP whilst thermal conductivity of S3-EGP100 is found to be about 2.3 times that of SGP. Adsorption isotherms of composite samples/water pairs have been measured gravimetrically at 30, 50 and 70 °C. The Toth and Dubinin-Astakhov (D-A) equations have been used to fit adsorption uptake measurements, Toth equation shows a better fitting. Isosteric heat of adsorption of the studied pairs have been extracted from the experimental measurements using Clausius-Clapeyron equation. The Linear Driving Force (LDF) model is found to be able to present adsorption kinetics of the studied pairs through a good agreement with the experimental data.

Water adsorption characteristics of organic-rich Wufeng and Longmaxi Shales, Sichuan Basin (China)

Water is ubiquitously present within organic-rich shale and can exert an important effect on the gas-in-place and gas adsorption capacity of shale reservoirs. Thus, understanding the water adsorption characteristics of gas shale reservoir is critical for optimizing shale-gas productivity. In this work, the water vapor adsorption characteristics of organic-rich Wufeng and Longmaxi Shales in the Sichuan Basin were studied over a wide range of relative humidities (RHs, 5–95%) utilizing a gravimetric method. All the water vapor adsorption isotherms are categorized as type II, suggesting similar water adsorption behaviors between samples. Being pronounced at approximately 70–80% RH, hysteresis loops from water adsorption curves are characterized by calculating areal hysteresis index (AHI) values. The Wufeng Shales have higher AHI values than those of Longmaxi Shales, which are mainly related to the variation of TOC content and pore structure characteristics. Pore size distribution obtained from water vapor adsorption show unimodal distribution of pore sizes, which are generally comparable to that derived from nitrogen physisorption. The mineral content (e.g., quartz and clay contents) and pore structure characteristics (e.g., pore type, porosity and surface area) have great effects on the water vapor uptake in the Wufeng and Longmaxi Shales. Compared to the shales with low surface area and porosity, Wufeng and Longmaxi Shale samples with higher surface area and porosity exhibit much higher water vapor uptake, suggesting that moisture sorption is mainly controlled by the amount of adsorption sites and volumes. When RH increases from low to high values, methane capacity of partially moisture-equilibrated shale could have experienced rapid decline, moderate decrease and slow decrease stages, finally reaching the minimum adsorption capacity for full moisture-equilibrated shale.

Water vapor adsorption on poly(N-isopropylacrylamide) gel cross-linked with N, N′-methylenebisacrylamide

Water vapor adsorption characteristics and the thermosensitivity for vapor adsorption of poly(N-isopropylacrylamide) gel (NIPA gel) cross-linked with N, N′-methylenebisacrylamide (MBAA) (cross-linked NIPA gel) were investigated for application in desiccant humidity control systems. The cross-linked NIPA gels were prepared via copolymerization of NIPA monomers and MBAA monomers, which were used as crosslinkers, at various reagent concentrations and polymerization temperatures in the range of 283–323 K. The water vapor adsorption isotherms of NIPA homopolymer, MBAA homopolymer, and cross-linked NIPA gels were obtained at adsorption temperatures in the range of 298–323 K using a volumetric gas adsorption apparatus. The water vapor adsorptivity of the cross-linked NIPA gel increased with increasing MBAA monomer concentration and decreasing NIPA monomer concentration. NIPA homopolymer under dry conditions showed weak thermosensitivity for water vapor adsorption between 298 and 313 K. Meanwhile, MBAA homopolymer showed almost no change in water vapor adsorptivity above adsorption temperatures of 298 K. The cross-linked NIPA gels had a similar thermosensitivity to NIPA homopolymer, but its sensitivity might be shifted to higher temperature than NIPA homopolymer. Thermosensitivity of the cross-linked NIPA gel was effective in improving polymer water adsorptivity, necessary for desiccant humidity control systems; however, the adsorption performance of the polymer gel systems investigated require further improvements before practical application will be possible.

Water vapor adsorption characteristics of starch−albumen powder and rheological behavior of its paste

ABSTRACT This paper concerns the water vapor adsorption properties of starch-albumen powder (SAP), as a new product with many potential food processing applications. The adsorption data were generated at some practical storage temperatures (27, 35 and 40 °C) and water activities, a w (0.11–0.86) using gravimetric method. The data were fitted to some isotherm models (GAB, Peleg, DLP and BET). The values of some thermodynamic parameters based on the Clausius–Clapeyron equation were also calculated. The rheological behavior of SAP paste was also studied at 20, 30, 45 and 60 °C. SAP was found to have type II isotherm shape and is highly hygroscopic. The adsorption data were better fitted by Peleg and DLP models ( r 2 =0.987–0.999). Monolayer moisture capacity ranged between 4.9 and 6.8 g/100 g solid. The water vapor sorption process in SAP is thermodynamically non-spontaneous and enthalpy-driven. SAP paste showed a characteristic shear-thinning behavior. Activation energy of flow ( E a ) was found to be 31.63 kJ/mol.

Adsorption Characteristics of Water Vapor on Gear-Pellet and Honeycomb-Pellet Types of Adsorbents Containing A-Type Zeolite

It is necessary to recover or process tritiated species that are extensively coexistent in nuclear fusion installations. A conventional way to recover tritium release to atmosphere is catalytic oxidation of tritiated species and adsorption of tritated water vapor on adsorbents with high surface areas. However, pressure loss would become more serious with increase in the size of adsorbent beds, which could lead to greater power needs for ventilation systems. Therefore, new adsorbents with low pressure loss and high surface areas need to be developed and utilized for such large-scale adsorption systems. Thus, the authors tested new types of adsorbents, which are gear-type and honeycomb-type pellet adsorbents. The experimental results reveal that the gear-type pellet adsorbents have larger adsorption capacity than the honeycomb-type pellet adsorbent. It was also found that the gear-type MS4A adsorbent possesses larger adsorption capacity than other adsorbents tested in this work. Furthermore, it was found that new types of adsorbents are lower pressure than conventional-type of adsorbents. Among the new adsorbents studied in this work, the gear-type MS4A adsorbent appears to be most promising for the application to the adsorption systems in terms of adsorption capacity and adsorption rate.

Adsorption characteristics of water vapor on ferroaluminophosphate for desalination cycle

The adsorption characteristics of microporous ferroaluminophosphate adsorbent (FAM-Z01, Mitsubishi Plastics) are evaluated for possible application in adsorption desalination and cooling (AD) cycles. A particular interest is its water vapor uptake behavior at assorted adsorption temperatures and pressures whilst comparing them to the commercial silica gels of AD plants. The surface characteristics are first carried out using N2 gas adsorption followed by the water vapor uptake analysis for temperature ranging from 20°C to 80°C. We propose a hybrid isotherm model, composing of the Henry and the Sips isotherms, which can be integrated to satisfactorily fit the experimental data of water adsorption on the FAM-Z01. The hybrid model is selected to fit the unusual isotherm shapes, that is, a low adsorption in the initial section and followed by a rapid vapor uptake leading to a likely micropore volume filling by hydrogen bonding and cooperative interaction in micropores. It is shown that the equilibrium adsorption capacity of FAM-Z01 can be up to 5 folds higher than that of conventional silica gels. Owing to the quantum increase in the adsorbate uptake, the FAM-Z01 has the potential to significantly reduce the footprint of an existing AD plant for the same output capacity.

Surface Design and Water Vapor-Adsorption Characteristics of Biomimetic Composite Materials Derived from Salmon Resource

Biomimetic composites of hydroxyapatite (HAp) and collagen with fast bio-absorption and good biocompatibility were designed utilizing salmon bone and skin at 283-293 K and pH 7.5-7.9 by a dissolution-precipitation method. Simultaneously, dissolved-precipitated HAp (dp-HA) was prepared at pH 9-10 using the calcined bone. The HAp/collagen composites (HA-C) were constituted by Ca2+-deficient HAp, I type-collagen and gelatin. At the synthetic temperature of 283 K, collagen fiber and HAp microcrystals were seen, while at 293 K, frock like-agglomerated particles or fiber like-oriented columnar ones were observed depending on the composition ratio (H/C) of HAp to collagen. Specific surface areas and total pore volumes for the HA-C synthesized at 293 K clearly increased with increasing the H/C, although there were micro-and-meso-pores in the pore diameters of 3-30 nm. Concerning water vapor-adsorption isotherms at 298 K for the HA-C powders, hysteresis-curves of the amounts of water vapor adsorbed (V) were recognized in the adsorption-desorption processes. The V values increased with increasing the H/C under the low relative pressures (P/PS) of 0-0.3 that mean monolayer-adsorption of water molecule. However, for H/C=2.2, the V values were the highest under the high P/PS of 0.70-0.90 that mean multilayer-adsorption and the biggest hysteresis-curve was found under the P/PS of 0.45-0.60, suggesting that the HA-C (H/C=2.2) powder not only adsorb water molecule on the surfaces but also absorb one into the crystal structure. Accordingly, the biomimetic HA-C powders will be applied as water-absorbable adsorption materials for cosmetic products or bone-regeneration therapy.

A new model for water adsorption in porous ceramics

This research proposes a new isotherm model that is derived for adsorption of clustering and condensable vapors on mesoporous ceramics. The adsorption characteristics of water vapor on both experimental data and isotherm model were investigated over the relative pressure ranging from 0 to 0.95. The applicability of the model was evaluated by significance of fitting parameters. For each adsorption isotherm there are five parameters (m, qf, Kf, qm and Km). The comparison of modeling fit with experimental data was used as the methodology for selecting the most informative and the best-fitting model. The experimental testing results showed that this model is able to describe all possible behaviors of the water adsorption isotherm displaying type IV classification. The model is based on the forming and growth of the water molecule clusters and capillary condensation mechanism in mesopore. The findings suggest a significant tool for understanding the behavior of water adsorption in humidity-control porous ceramics.

Adsorption characteristics of water vapor on the hypercrosslinked polymeric adsorbent

Hypercrosslinked polymeric adsorbent is finding increased application as sorbents for removing the VOCs from gas steam. Due to the competitive adsorption between the water and VOCs, hence, it is important to understand the adsorption characteristics of water vapor on hypercrosslinked polymeric adsorbent. In this paper, the adsorption of water vapor on hypercrosslinked polymeric adsorbent with poly (styrene-divinylbenzene) matrix (HY-1) was investigated and compared with a commercial activated carbon (m-GAC) and activated carbon fiber (ACF). The results showed that HY-1 had minimal uptake of water until P/ P 0 was raised to 0.6, which is an indication of an extremely hydrophobic surface. Moreover, increasing the temperature induced the decrease of the water uptake and a rightward shift in the isotherm heel. The adsorption isotherms of water vapor on three adsorbents were fitted by the Cluster Formation Induced Micropore Filling model (CIMF model). The results indicated that the experimental data can be well-fitted by CIMF model. Based on this semiempirical modeling, the adsorptive contributions of primary sites and micropores were estimated qualitatively. In addition, the effect of water vapor on the adsorption of benzene onto three adsorbents was investigated. The breakthrough time of benzene on HY-1 decreased by 10.4% even if the relative humidity was 80%, while that of m-GAC and ACF decreased by17.2% and 38.9%, respectively. Therefore, HY-1 would be a particularly efficient and competitive adsorbent for VOCs recovery from the humid gas streams.

Adsorption Characteristics of Water Vapor on Zeolitic Materials for Honeycomb-Type Adsorbent

Tritium release in nuclear fusion power plants must be recovered as efficiently as possible in air cleanup system (ACS). In conventional ACS, the tritium gas is oxidized by catalysts, and then tritiated water vapor is collected by adsorbents, whereas which has a problem related to large ventilation force required to overcome high pressure drop in catalyst and adsorbent beds. Honeycomb-type catalyst and adsorbent offer a useful advantage in terms of their low-pressure drop, and honeycomb-type adsorbent using sepiolite-binder is feasible ability for application of ACS. In this study, we examined adsorption characteristics of water vapor on the building material, zeolitic materials using sepiolite-binder, for honeycomb-type adsorbent by changing temperature and concentration of water vapor, in comparison with those for conventional pebble-type adsorbent, and the experimental data were evaluated using Langmuir and Freundlich isotherm models. Each type of adsorbent includes mainly zeolite-4A. Adsorption capacity of zeolitic materials for both adsorbents gradually decreased with decreasing partial pressure of water or increasing temperature, and experimental data are found to fit Langmuir than Freundlich. The maximum adsorption capacity of water vapor on zeolitic material for honeycomb-type adsorbent, which was calculated by Langmuir isotherm model, is comparable to that for pebble-type adsorbent, and heat of water adsorption on zeolitic material for honeycomb-type adsorbent was higher than that for pebble-type adsorbent. These results indicate that honeycomb-type adsorbent using sepiolite-binder is applicable to ACS.

Adsorption characteristics of water vapor on honeycomb adsorbents

Recovery of tritium released into working areas in nuclear fusion plants is a key issue of safety. A large volume of air from tritium fuel cycle or vacuum vessel should be processed by air cleanup system (ACS). In ACS, tritium gas is oxidized by catalysts, and then tritiated water vapor is collected by adsorbents. This method can remove tritium effectively, whereas high throughput of air causes high-pressure drop in catalyst and adsorbent beds. In this study, the applicability of honeycomb-type adsorbents, which offers a useful advantage in terms of their low-pressure drop, to ACS was examined, in comparison with conventional pebble-type adsorbent. Honeycomb-type adsorbent causes far less pressure drop than pebble-type adsorbent beds. Adsorption capacity of water vapor on a honeycomb-type adsorbent is slightly lower than that on a pebble-type adsorbent, while adsorption rate of water vapor on honeycomb-type adsorbent is much higher than that of pebble-type adsorbent.