Water Vapor Adsorption Capacity Research Articles

Water Vapor Adsorption Behavior in Shale Under Different Temperatures and Pore Structures

In this paper, fractal dimension analysis was used to describe pore structure. We proposed a shale water vapor multi-layer adsorption model that considers the control of pore structures. In this respect, the change curve of the water vapor adsorption capacity was found to be consistent with a type II curve. In addition, water vapor adsorption in shale occurs at primary and secondary adsorption sites. When the relative pressure was low, water vapor adsorption in shale occurs at primary adsorption sites. Thus, primary adsorption capacity is greater than secondary adsorption capacity, and changes in the primary adsorption capacity conformed to the characteristics of a type I curve. However, with increasing relative pressure, secondary adsorption sites began to be occupied. The adsorption capacity curves of the two types of adsorption sites intersected. In addition, temperature changes altered the pore structures, and the pore structure had a controlling effect on the adsorption capacity of shale. Temperature was also found to be one of the important factors affecting shale adsorption. Then, we introduced a shale water vapor multi-layer adsorption model that considers both pore structure and temperature. With increasing relative pressure, the water vapor adsorption capacity of shale still maintained the characteristics of a type II curve. However, temperature had an inhibitory effect on the adsorption characteristics in shale. Based on analysis of the changes in shale adsorption at different temperatures, the sorption-induced deformation mechanism caused by water vapor adsorption in shale was further analyzed.

Thermal stability evaluation of selected zeolites for sustainable thermochemical energy storage

ABSTRACT In recent times, the thermochemical energy storage (TCES) method is gaining prominence due to its high energy storage density and minimal heat losses compared to the conventional thermal energy storage (TES) methods. This paper presents the cyclability behavior of selected zeolites for the TCES applications. The zeolites were subjected to sequential desorption and adsorption processes for five times using a differential thermogravimetric analyzer (DTG-60H). To investigate their suitability for the commonly available sources of thermal energy (e.g. solar energy, industrial waste heat), the samples were heated up to 150°C. These zeolites were also tested on Brunauer–Emmet–Teller (BET) analyzer for total surface areas and pore volumes, thus to read their sorption behavior. A field emission scanning electron microscope (FESEM) equipped with an energy dispersive X-ray (EDX) analyzer was used to examine the surface morphology and elemental composition of zeolite sorbents before and after the multi-cycle test run. The changes in the mass of a material during a process, either desorption or adsorption, were notably almost the same across the cycles tested, which confirms the cyclability of the materials tested. Amongst the tested materials, Zeolite-NaY and Zeolite-HY exhibited relatively better process enthalpies owing to their active water adsorption capacities. Of the six materials tested, Zeolite-NaY has offered better results and its enthalpies range from 287.5 J g−1 to 348.5 J g−1 for the desorption and from 81 J g−1 to 292.1 J g−1 for the adsorption. A mass gain was noticed for each of the tested materials as they undergo the cooling process, thus affecting water vapor adsorption capacity negatively.

A Rare 3D Porous Inorganic-Organic Hybrid Polyoxometalate Framework Based on a Cubic Polyoxoniobate-Cupric-Complex Cage with a High Water Vapor Adsorption Capacity.

A rare 3D porous inorganic-organic polyoxoniobate framework based on the cubic polyoxoniobate-cupric-complex cage {[Cu(en)2]@{[Cu2(en)2(trz)2]6(Nb68O188)}} (1a), has been successfully synthesized by a hydrothermal method. The cubic cages 1a are connected with 4-(tetrazol-5-yl)pyridine to form a 1D pillar-like chain structure, and every 1D pillar-like chain is further linked with four adjacent pillar-like chains by the [Cu(en)2]2+ complex to form a 3D porous inorganic-organic polyoxoniobate framework with 4-connected CdSO4-type topology. To our knowledge, it is the first time that three different types of organic ligands are simultaneously introduced into one polyoxoniobate. This material also exhibits a high vapor adsorption capacity and good ionic conductivity properties.

Effect of carbonization temperature on characterization and water vapor adsorption of coffee-shell activated carbon

Coffee shells, which are abundant in cellulose and lignin, are good raw materials to prepare activated carbon. In this paper, coffee shells were selected as raw materials for activated carbon preparation by KOH chemical activation. Influence of carbonization temperature on adsorption capacity of water vapor over activated carbon was researched. Thermogravimetric analysis was employed to select the scope of carbonization temperature. Activation energies of coffee shells pyrolyzed at different heating rates were calculated. Nitrogen adsorption/desorption isotherm and scanning electron microscopy (SEM) were adopted to characterize the activated carbon. And water vapor adsorption isotherms were simulated by the finite simplification model of Do-Do adsorption model. The results show that activation energies of coffee shells pyrolysis process with heating rates of 5, 10 and 20 K/min are 17.21, 18.01 and 57.52 kJ/mol, respectively. The optimal carbonization temperature of coffee shells is 923 K. The adsorption amount of water vapor can reach about 702.3 mg/g under experiment temperature of 298 K and relative humidity of 70%. The highest total pore volume and Brunauer–Emmett–Teller (BET) specific surface area are 1.41 cm3/g and 2817 m2/g, respectively. The simulation results of the finite simplification model are consistent well with water vapor adsorption experiment results. The results show that activated carbon prepared at the optimal condition would be the potential candidate for solar drying system.

Water Vapor Adsorption and Main Controlling Factors of Deep Shale

Water is one of the causes of softening of soft rocks in deep strata. Water absorption in soft rock with high clay content may cause strength softening and deformation. In this paper, soft rock samples from three deep strata are investigated, and the stratigraphic characteristics such as stratum physical parameters, mineral composition, and pore structure are systematically analyzed. The characteristics of water vapor adsorption curves of deep strata soft rock are obtained by water vapor adsorption experiments. The authors analyzed the main factors controlling water vapor adsorption capacity of the rock samples. The experimental results show that the water vapor adsorption capacity increases with increase in humidity. When the humidity exceeds 0.8, the adsorption of water vapor by soft rock increases rapidly. The adsorption capacity of shale is significantly higher than that of conglomerate samples, and the difference between coarse conglomerate and fine conglomerate samples is insignificant. It is shown that water vapor adsorption correlates positively with clay mineral content, particularly minerals with high specific surface area. Under low humidity the temperature has little effect on the adsorption of soft rock water vapor. As the humidity increases, a rise in temperature can significantly increase the water vapor adsorption capacity The results also show that the soft rock water vapor adsorption capacity correlates negatively with initial moisture content, porosity, and permeability. This study is of great significance for understanding the hydrological characteristics and catastrophic processes of deep strata soft rocks.

Adsorption isotherm and kinetics of water vapors on novel superporous hydrogel composites

Abstract A promising and highly efficient new solid desiccant material composted of superporous hydrogel (SPHs) of polyacrylamide (PAM) and AQSOA-Z02 zeolite was fabricated to capture water vapor from moist air. The synthesis method of PAM-SPHs involved the gas blowing and foaming technique which insured a uniform distribution of zeolite particles throughout the polymer matrix. The presence of three dimensional porous structure, interconnected macropores in SPHs and the highly hydrophilic functional groups of AQSOA-Z02 particles enabled the synthesized SPHs composite to exhibit excellent water vapor adsorption capacity. The introduction of AQSOA-Z02 zeolite in the polymer matrix increased the water vapor adsorption capacity from 0.77 gw/gads to 0.89 gw/gads. Both materials exhibited type-III isotherm and followed Frenkel-Halsey-Hill and Guggenheim, Anderson and Boer (GAB) adsorption isotherm models. The high adsorption capacity was attributed to the combined effects of capillary condensation in interconnected macropores and the attachment of water molecules to the hydrophilic functional groups present in the zeolite structure. The water vapor adsorption capacity was found to decrease with increasing temperature. Adsorption kinetics studies suggested that the water vapor adsorption followed first-order kinetics models and the mechanism of water molecules diffusion into the internal structure of SPHs was case-II type of diffusion mechanism.

Preparation and water vapor adsorption of “green” walnut-shell activated carbon by CO2 physical activation

In this study, activated carbons without any chemical residue were prepared from walnut shells. The preparation method in a tube furnace included a pyrolysis carbonization process and a CO2 activation process. The influences of activation temperature and holding time on the specific surface area, yield, and pore structure were investigated. Adsorption performance of water vapor was also examined in details. Thermogravimetric analysis, N2 adsorption–desorption isotherm, and scanning electron microscope were used to characterize samples. The result shows that the activation energy at different heating rates varies from 30.16 to 64.86 kJ/mol. The highest water vapor adsorption capacity of the sample is 0.3824 g/g and it takes only 30 min to realize regeneration. And the maximum Brunauer–Emmett–Teller specific surface area of 1228 m2/g also occurs in this optimal preparation condition. CO2 physical activation method was found to have a positive effect on pore structure development of activated carbon for water vapor adsorption.

Enhanced Ice Nucleation and Growth by Porous Composite of RGO and Hydrophilic Silica Nanoparticles

A porous composite of 3-dimensional (3D) reduced graphene oxide (rGO) and silica dioxide nanoparticles (PrGO-SN) was synthesized via a single-step hydrothermal process, which can initiate facile ice nucleation and growth starting from temperature as high as −8 °C and 5–8% RH supersaturation and sustain rapid ice crystal growth. The excellent ice nucleation activity of the PrGO-SN composite demonstrates a novel means of ice nucleation relative to known materials, attributed to not only the lattice match between the ice and crystalline structure of the PrGO-SN composite but also higher specific surface area, larger water vapor adsorption capacity, better porosity, and more hydrophilic surface of the composite than rGO. Moreover, environmental scanning electron microscope (E-SEM) in situ observation confirmed detailed growth patterns of ice crystals on the composite, which were affected by the regions with different surface roughness. These findings enabled further understanding of the factors that affected the heterogeneous ice nucleation process and shed light on the design and fabrication of more efficient functional porous ice nucleation materials for many practical applications such as cloud seeding.

A Series of 3D Porous Lanthanide-Substituted Polyoxometalate Frameworks Based on Rare Hexadecahedral {Ln6W8O28} Heterometallic Cage-Shaped Clusters.

A series of 3D porous lanthanide-substituted polyoxometalate frameworks, Na2[Ln2(H2O)11]2[Ln3(H2O)3(α-SiW11O39)2]2·69H2O (1-Ln, Ln = Sm, Eu, Gd, Tb, and Dy), are built from novel hexadecahedral {Ln6W8O28} heterometallic cage-shaped clusters. Intriguingly, every tetrameric {[Ln3(H2O)3(α-SiW11O39)2]2}14- cage-cluster is linked with another eight tetrameric cage-clusters by Ln3+ cations, leading to a novel 3D inorganic porous framework, which exhibits good thermal and chemical stability, excellent water vapor adsorption capacity, and moderate proton conductive properties. Furthermore, the solid state luminescence spectra demonstrate that 1-Sm, 1-Eu, 1-Tb, and 1-Dy display the lanthanide characteristic emission bands. The temperature-dependent magnetic susceptibility indicates that there are antiferromagnetic interactions in 1-Tb and 1-Dy.

Novel porous ultrathin NiO nanosheets for highly efficient water vapor adsorption-desorption

Exploiting humidity-buffering materials for air humidity control is of vital necessities. Novel porous ultrathin NiO nanosheets as effective humidity-buffering materials were successfully synthesized with a simple, low-cost and high-yield method. It exhibits ultrahigh water vapor adsorption-desorption performance at room temperature, which is superior to both commonly used conventional materials and most reported novel ones. The excellent water vapor adsorption capacity can be attributed to its unique porous ultrathin structures. Numerous mesopores with relatively large diameter and volume can largely decrease water molecules diffusion resistance and increase adsorption space. Moreover, the ultrathin structure can lead to more sufficient contact between water vapor and adsorbents and provide great specific surface area, which can further facilitate water vapor adsorption. The potential of ultrathin nanosheets to be humidity-buffering materials has been explored carefully for the first time and this work also sheds light on the rational design of adsorbents with superior water capacity for efficient humidity control.

Preparation of coffee-shell activated carbon and its application for water vapor adsorption

Coffee-shell activated carbon was prepared by a two-step activation method including carbonization process and potassium hydroxide (KOH) activation process. The influences of activation temperature, activation time and mass ratio of KOH to char on activated carbon water vapor adsorption performance were investigated by single factor design. The optimum preparation conditions of activated carbon with large adsorption capacity were determined. The water vapor adsorption experiments of activated carbon were carried out under 70% relative humidity and adsorption temperature of 298 K. Pore structure characteristics were studied via N2 adsorption-desorption isotherm. The results show that the optimum preparation conditions are activation temperature of 1073 K, activation time of 10 min and mass ratio of KOH to char of 3:1. The Brunauer–Emmett–Teller (BET) specific surface area, total pore volume and water vapor adsorption capacity of the optimum coffee-shell activated carbon are 2349 m2/g, 1.036 cm3/g and 0.7409 g/g, respectively. All isotherms are type I with narrow pore size distributions in micropore region. Moreover, the obtained activated carbon was characterized by pH, elemental analysis and Fourier transform Infrared (FT-IR) spectroscopy. The results show that the obtained activated carbon would be one of the potential adsorbents for dehumidification in solar energy drying system.

Experimental study of water vapor adsorption behaviors on shale

Understanding water distribution behaviors plays an essential role in shale gas development due to the hydraulic fracturing technology. In this study, water vapor adsorption isotherms were measured for Upper Triassic Yanchang and Lower Silurian Longmaxi samples at 288.15 K, 298.15 K and 308.15 K to investigate the adsorption behaviors of water on shale. For a description of adsorption process, a Dent’s model provides an estimate of primary and secondary adsorption sites of water adsorption. The effects of temperature, shale mineralogy, and water distribution were discussed. The results show that temperature has a negative effect on water vapor adsorption. Adsorption capacities of primary and secondary sites decrease with increasing temperature. Water vapor adsorption capacity is tightly associated with clay content, whereas water vapor adsorption has no significant relationship with total organic carbon (TOC). Normalized water vapor adsorption content also has no significant relationship with TOC, which indicates no obvious correlation between water vapor adsorption and TOC content. The inter-crystal pores of clay minerals provide significant specific surface for gas adsorption in shale. At low relative pressure, a large number of water molecules adsorb on the primary sites. At high relative vapor pressure, most of the primary sites have been occupied, so that the secondary adsorption sites will be utilized. Therefore, due to relative weak binding energies in secondary adsorption sites, water cluster are formed in micro-pores of shale. As relative vapor pressure increases, capillary condensation gradually predominates over the adsorption. The study will reveal mechanism of water adsorption and distribution characteristics on shale and provide some foundation for geological reserve estimation and shale gas recovery prediction.

Preparation of tobacco-stem activated carbon from using response surface methodology and its application for water vapor adsorption in solar drying system

Tobacco-stem activated carbons (TACs) were prepared by ZnCl2 activation and used for water vapor adsorption in solar drying system. The effects of activation temperature, activation time, and ZnCl2 impregnation ratio on water vapor adsorption performance and BET specific surface area of TACs were carried out and the preparation conditions were analyzed by surface response methodology. Pore structure and morphology of the samples were characterized by N2 adsorption-desorption isotherm and scanning electron microscope. Water vapor adsorption and desorption isotherms of TACs were carried out. A six subsequent adsorption-regeneration cycle of water vapor was investigated. The result shows that BET specific surface area of 1893.6 m2/g, water vapor adsorption capacity of 563.4 mg/g are obtained in the optimum preparation conditions of activation temperature 621 °C, activation time 73 min and ZnCl2 impregnation ratio of 1.70. Pore structure and surface area analysis shows that TAC21 is prepared as a microporous activated carbon and suitable for water vapor adsorption application. Both TAC18 and TAC21 possess an excellent reversibility of water vapor adsorption under the tested condition. The result confirms that the TAC adsorbents would be the potential candidates for dehumidification and heat recovery in solar drying system.

Water Vapour Storage Capacity of Masonry Renovation Plasters Contaminated with Chlorides

The effect of sodium chloride presence on the water vapour storage capacity was studied for six types of plasters designed for application in masonry restoration. Sorption isotherms were measured using a static climate chamber method. The researched materials were characterised by their bulk density, matrix density, and total open porosity. For the studied materials, measurement of chloride binding isotherms by an adsorption method was done in order to reveal their capacity to accumulate salts and relate the adsorbed water vapour to the amount of contained salt. The experimental sorption data measured for salt contaminated samples were analysed using relation expressing the dependence of the mass equilibrium moisture content (EMC) of plasters saturated with salt solution of given molality on relative humidity of the environment. For relative humidity up to 70 %, good agreement between measured and calculated data was obtained. For higher relative humidity, the water vapour adsorption capacity of studied materials was not fully exploited especially for lower chloride concentrations. The type of binder together with physical parameters of examined materials was found to have a decisive role in chloride binding. One of the tested materials can be possibly classified as WTA renovation plaster, considering its total open porosity, bulk density and high binding capacity for chlorides. On the other hand, one must take into account its hygroscopicity, especially in case of a higher salt contamination. DOI: http://dx.doi.org/10.5755/j01.ms.24.4.19434

Efficient prediction of water vapor adsorption capacity in porous metal–organic framework materials: ANN and ANFIS modeling

Optimum design of water vapor separation process (dehumidification) using adsorption process mostly depends on the selection of appropriate porous materials or adsorbents with the highest equilibrium storage capacity of the vapor. Equilibrium capacity is generally evaluated through cost-demanding experiments via direct measurement of the vapor isotherm. Reliable prediction of the vapor adsorption capacity in porous materials provides a robust tool to a quick screening of porous materials appropriating for dehumidification process. In this article, adsorption capacity of water vapor in metal–organic framework (MOF) materials is predicted using two robust “artificial neural network (ANN)” and “Adaptive network-based fuzzy inference system (ANFIS)” methods. The three parameters of the surface area, pore volume and pore diameters are selected as input and the water vapor adsorption capacities of MOFs were computed as the output of the models. Comparison of the obtained results and real experimental data implied the superiority of the ANFIS and ANN models to predict the water vapor adsorption capacity into MOFs with a mean squared error (MSE) of 0.005 and 0.002, respectively. This clearly indicates a great potential for the application of both ANN and ANFIS methods to rapid screen MOFs suitable for water vapor adsorption.

Iron doped aluminophosphate molecular sieve with improved adsorption capacity for water vapor

With a characteristic of S-shape isotherms for water vapor adsorption, aluminophosphate molecular sieve with AFI type (AlPO-5) has been considered as an up-and-coming adsorbent for the utilization in the adsorption cooling and heating (ACH) system. In order to improve its adsorption performance, iron doped AlPO-5 (FeAPO-5) with variable Fe loading was synthesized by microwave hydrothermal method. The effects of the iron doping content on the structure and adsorption performance were systematically investigated. The analysis results of X-ray diffraction (XRD), UV–visible spectroscopy (UV–Vis-DR) and scanning electron microscopy (SEM) showed that the iron ion was incorporated into aluminophosphate molecular sieves with a typical AFI structure as that of AlPO-5 through the isomorphous substitution. As the iron content of FeAlPO-5s increased, the isolated FeIII decreased, while oligonuclear FeIII and nanosized FeIII increased, besides, the static adsorption curves showed that the adsorption capacity of FeAlPO-5 increased first and then decrease. After iron modifying, the crystallinity and morphology of crystals was improved, and the adsorption performance increased from 0.185 g/g (AlPO-5A) to 0.235 g/g (FeAlPO-5), while the desorption performance of FeAlPO-5 (95.69 kJ/mol) was close to that of AlPO-5A (81.59 kJ/mol).

Structural, mechanical and hygrothermal properties of lightweight concrete based on the application of waste plastics

Three different types of plastic waste replacing up to 50% of natural aggregates are used in concrete mix design. A wide set of basic physical, mechanical, thermal, and hygric properties of developed concretes is determined and their assessment is made using a comparison with reference data. The mechanical parameters, though decreasing with the increasing amount of plastic aggregates, are found satisfactory for non-bearing concrete structures. The up to seven times lower thermal conductivity, as compared with the reference material, provides an evidence of greatly improved thermal insulating capabilities. The hygric properties of designed concretes are characterized by an increase of water and water vapor transport parameters and a decrease of water vapor adsorption capacity with the increasing amount of plastic aggregates. Based on the obtained experimental results, a conclusion can be made that the designed lightweight concretes containing plastic waste aggregates present a prospective solution from the points of view of both plastic waste disposal and improvement of buildings' energy efficiency.

Adsorption desalination-cooling system employing copper sulfate driven by low grade heat sources

In this study benefits of employing copper sulfate salt hydrate with water vapor as a new adsorption pair in thermally driven adsorption desalination-cooling systems (ADCSs) have been investigated. Adsorption characteristics (isotherm and kinetic) of copper sulfate/water vapor pair have been presented in this study within temperature range of 25–55 °C. Sun-Chakraborty (S-C) and Dubinin-Astakhov (D-A) models have been used for fitting isotherms results, while linear driving force (LDF) model has been used for the kinetics results. Experimental adsorption capacity of water vapor onto copper sulfate is found to be around 0.51 kg/kg at 25 °C. Activation energy (Ea) and the pre-exponential coefficient (Dso) are estimated to be 25.053 kJ/mol and 1.89 × 10−7 m2/s respectively. A theoretical model for an ADCS has been investigated employing copper sulfate as adsorbent material. The proposed system can produce specific daily water production about 8.2 m3 per ton of copper sulfate, 227 W/kg of copper sulfate specific cooling power and 0.57 coefficient of performance. The performance of the modeled system indicates that the proposed system can be driven efficiently by renewable energy such as solar energy.

Silver-Exchanged Mordenite for Capture of Water Vapor in Off-Gas Streams: A Study of Adsorption Kinetics

Reduced silver-exchanged mordenite (Ag0Z) has been recognized as the benchmark adsorbent for radioactive iodine removal from the nuclear fuel reprocessing off-gases. It has also been shown to have a considerable adsorption capacity for water vapor, which is a major component (tritiated water) in the off-gases of spent nuclear fuel reprocessing facilities. Therefore, understanding the kinetics of water vapor adsorption on Ag0Z is necessary for a better design of off-gas treatment systems. The adsorption kinetics were studied through adsorption experiments of water vapor on Ag0Z pellets and analyses of the kinetic data with adsorption models that describe processes of mass transfer and inter/intracrystalline diffusion. Uptake curves of water vapor on Ag0Z pellets were obtained with a continuous-flow adsorption system at temperatures of 25, 40, 60, 100, 150, and 200 °C and dew points from −53.6 °C to 12.1 °C. The diffusion-controlling factors were determined experimentally and analytically. It was found that the diffusion process of water vapor in Ag0Z pellets was controlled by macropore diffusion. Gas film mass-transfer resistance also contributed to the adsorption process of the 0.9 mm Ag0Z pellets, but it could be minimized with a high gas velocity and small pellet radius. Kinetic models including macropore diffusion (MD), linear driving force (LDF) and shrinking core (SC) were used to fit the uptake curves. The macropore diffusivity for water vapor adsorption on Ag0Z pellets was determined using the three models. It was found that the LDF and SC models could well describe the kinetic process, while the fitting with the MD model was not quite as good due to the existence of external mass-transfer resistance for the 0.9 mm Ag0Z pellets.

Development of MIL-101(Cr)/GrO composites for adsorption heat pump applications

Adsorption heat pumps can be used for generating heating, cooling, seasonal energy storage and water desalination applications. Metal-organic frameworks (MOFs) are hybrid porous materials with high surface area and superior adsorption characteristics compared to conventional adsorbents. MIL-101(Cr) has a large pore size with water vapour adsorption capacity up to 1.5 gH2O gads−1 and high cyclic stability, and thus has the potential to be used in adsorption heat pumps. This work investigates the enhancement of the thermal conductivity and water adsorption characteristics of MIL-101(Cr) using hydrophilic graphene oxide. Two methods have been used to develop MIL-101(Cr)/GrO composites. The first method was through the physical mixing of GrO and MIL-101(Cr) while the other was through incorporating the GrO during the synthesis process of MIL-101(Cr). The composites and neat MIL-101(Cr) were characterized in terms of their structure, water adsorption uptake, BET surface area, particle size, thermal gravimetric analysis, SEM images and thermal conductivity measurements. Results showed that introducing low amounts of GrO (2%) to the neat MIL-101(Cr) enhanced the water adsorption characteristics at high relative pressure but enhanced the heat transfer properties by 20–30% while using more than 2% of GrO reduced the water adsorption uptake but significantly enhanced the thermal conductivity by more than 2.5 times.