Water Vapor Adsorption Isotherms Research Articles

Structural and Rheological Characterization of Vegetable Crispbread Enriched with Legume Purée.

Crispbread is gaining popularity as a healthy snack or bread substitute. This is a lightweight dry type of flat food that stays fresh for a very long time due to its lack of water and usually contains different types of grain flour, including gluten-containing wheat or rye flour. The incorporation of legume purée into crispbread represents an innovative approach to enhancing the nutritional profile and taste of the product. The rheological properties of various legume purées (chickpea, white bean, black bean, and red bean) mixed with citrus pectin were examined, revealing significant differences in fluid behavior and viscosity. Crispbread formulations were analyzed for water content and activity, color, structure, FT-IR spectra, water vapor adsorption isotherms, and sensory evaluation. The results showed the possibility of obtaining crispbread based on the purée of legumes and citrus pectin. Crispbread enriched with red bean purée exhibited low water activity (0.156) and water content (3.16%), along with a continuous porous structure, and received the highest sensory evaluation score among the products. These findings can be treated as a basis for the development of other innovative recipes and combinations using legumes.

Simultaneous impregnation and microencapsulation of CaCl2 using silica gel and methyl cellulose for thermal energy storage applications

Thermal energy storage utilizing the adsorption of moisture from air is a promising energy storage technology due to its high energy density and minimum heat losses. Salt hydrates and salt hydrate composites, such as calcium chloride (CaCl2) and CaCl2-based composites, have shown favourable energy storage properties in this area of research. However, these materials have shown issues with stability due to swelling and deliquescence. In this work, CaCl2 was stabilized using three methods: impregnation into silica gel, encapsulation in methyl cellulose, and both impregnation and encapsulation stabilization techniques used simultaneously. Therefore, three CaCl2-based composites were synthesized. For the first composite, silica gel was impregnated with CaCl2. For the second composite, CaCl2 was encapsulated by methyl cellulose. For the third composite, silica gel was impregnated with CaCl2 and the CaCl2 was encapsulated with methyl cellulose. These samples were structurally characterized using scanning electron microscopy as well as Brunauer-Emmett-Teller (BET) to determine surface area, pore size distribution and nitrogen adsorption isotherms at 77 K. Water vapour adsorption isotherms were also determined at 25 °C for different relative humidities by dynamic vapor sorption (DVS). Similarly, LiCl-based composites were also synthesized and examined in this work, but issues of deliquescence, swelling, and agglomeration made the materials impractical to work with. To determine the prepared materials’ thermal energy storage performance, 2–6 g of each sample was tested in a lab-scale apparatus. This process uses the exothermic adsorption of moisture from ambient air in an open thermal energy storage system. The CaCl2 impregnated silica gel that was encapsulated in methyl cellulose showed reasonably high stability and energy storage performance after 3 hydration and dehydration cycles with minimum agglomeration. An energy storage density of 241 kWh/m3 (0.87 GJ/m3) and specific energy of 630 Wh/kg (2268 kJ/kg) was achieved with this material for 90% inlet relative humidity after a regeneration at 90 °C.

Statistical physics modelling of adsorption isotherms of water vapour on shale: Stereographic, energetic and thermodynamic investigations

AbstractUnderstanding the mechanisms of shale–water interaction by water vapour adsorption is crucial for predicting shale gas productivity. In this study, equilibrium adsorption data of water vapour on four different shales of the Sichuan Basin at three temperatures (298, 308, and 318 K) were measured using static gravity techniques. The water vapour adsorption isotherms were simulated by three statistical physics models. Steric parameters, including the number of water vapour molecules adsorbed per site (n), monolayer adsorption amount (q0), and adsorption energy (ΔEa), and thermodynamic parameters such as configuration entropy (Sa), internal energy (Eint), and free energy (Ga) derived from the selected model were used to explain the adsorption mechanism. The model analyses suggest that the adsorbed water vapour molecules are attached to the shale surface in a multi‐anchorage manner. The adsorption of the first layer shows a Type I characteristics, while the adsorption of the subsequent layer is of Type III. The calculated adsorption energies indicate that the physical adsorption takes place on the water vapour molecules on the shale, and the main interaction forces are hydrophilic bonding forces and van der Waals forces. Negative Eint and Ga values indicate that the spontaneous properties are for water vapour adsorption and that the system requires the release of energy to capture the water vapour molecules.

Dimensions, microstructure, chemical, and hygroscopic analysis of steam-exploded bamboo fibers at different ages

Bamboo fibers (BFs) at different ages (1, 3, and 5 years old) were prepared by pretreatment and steam explosion. The results demonstrated that the separation degrees of BFs increased with the age of the bamboo. The combined effects of pretreatment and steam explosion partially removed the hemicellulose and lignin from BFs, while the crystalline structure of cellulose remained unaltered. The water vapor adsorption isotherms of BFs at different ages all showed a typical S-shape and could be classified as type II, and the hysteresis of BFs increased with the age of the bamboo. After pretreatment and steam explosion, the tissues in the vascular bundle were effectively crushed, and the parenchyma tissues were dislodged and separated from the fiber sheath. During the steam explosion process, hot steam penetrated the bamboo’s pores, including the pores induced by pretreatment. This caused fractures and delamination in the interface between the vascular bundle and the parenchyma tissues. These cracks progressed layer by layer along the vascular bundle interface, leading to the fracture of the bamboo.

Estimating the hydratable surface area of building materials from water vapour sorption

The specific surface area of a building material controls its physical, chemical, and biological functions and services, including its moisture regulating potential. The Hydratable Specific Surface Area (H-SSA) of a building material can be estimated from its primary water vapour adsorption and desorption isotherm at a given relative humidity (RH) value or range of RH. The concept is illustrated for 12 mineral and bio-based building materials. The estimated H-SSA for only 1 kg of some building materials can approach the area of a typical agricultural field (500,000 m2, 50 ha.), which helps explain and illustrate the great moisture regulating properties of many bio-based materials. The H-SSA appears useful to help characterize and classify building materials.

Use of K2CO3 to Obtain Products from Starch-Oil Mixtures by Extrusion.

Mixtures of potato starch with oils (rapeseed and sunflower) were extruded. To improve the complexation of edible oils, a catalyst was added in amounts of 3 g, 6 g, and 9 g per 100 g of sample. The aim was to obtain potato starch extrudates with a high degree of complexation and edible oils during physical modification (extrusion) with the innovative use of K2CO3 as a catalyst. Selected functional properties (water solubility index and fat absorption index) and technological properties of the obtained extrudates (radial expansion index); color in the L*, a*, and b* systems, and the specific surface area was determined from the water vapor adsorption isotherm (SBET). The fat content was determined as external, internal, or bound, and complexed by amylose to assess the degree and manner of fat complexation during extrusion. Iodine-binding capacity and the complexing index were determined to confirm the formation of amylose-lipid complexes. The incorporation of edible oils resulted in a decrease in the radial expansion index and water solubility index compared to control samples. The extrudates were dark orange. Extrudates obtained at the temperature profile L: 80/80/80/60/60/50 °C, depending on the cooking oil, complexed from 48-79% of the introduced rapeseed oil and from 36-40% of the sunflower oil. The extrusion temperature profile (H: 100/100/100/75/75/60 °C) reduced the amount of bound lipid fractions. Using potassium carbonate in the extrusion of starch-lipid systems gives hope for further increasing the share of lipids in extruded mixtures.

Experimental investigation of innovative composite Maxsorb III adsorbent for cooling and water desalination

This study presents an innovative composite Maxsorb III/CaCl2 (70 wt % of Maxsorb III to 30 wt % of CaCl2) for a relatively high adsorption capacity, cooling capacity, and freshwater production. The raw Maxsorb III (Max) has undergone acid treatment (2 mol HCl) as a pretreatment then it is impregnated with salt hydrates (Max/CaCl2). Raw and composite Max is characterized using XRD, adsorption isotherm utilizing nitrogen, and water vapor adsorption kinetics and isotherm. The isotherm outcomes showed that Max/CaCl2 had a water uptake of 1.35 kgH2O/kgMax/CaCl2. A simulation model of a desalination system employing the adsorption technique, either with or without heat recovery, has been conducted using MATLAB software to show the performance of an adsorption system utilizing the innovative composite adsorbent material. The results showed that Max/CaCl2 attained SDWP of 25.4 m3/tonMax/CaCl2 per day with SCP 717.4 W/kgMax/CaCl2 and COP 0.704 at 85 °C. Additionally, water productivity utilizing condenser-evaporator heat recovery can reach 36.7 m3/tonMax/CaCl2 at 85 °C and 43 m3/tonMax/CaCl2 at 95 °C. The results indicated that the innovative composite material has a promising performance within the AD system and overcomes traditional adsorbents such as activated carbon, silica gel, and zeolite.

Modeling of monolayer water adsorption on surface of cement minerals by molecule simulation and adsorption isotherm

The performance of water on the pore surface governs the mechanical properties and durability of cementitious materials and structures. As a fundamental mechanism, the interaction between water and cementitious mineral micropore surfaces behaves differently under various circumstances, which can be investigated by molecular simulation methods in detail. Molecular simulations based on Grand Canonical Monte Carlo method were performed to obtain the water vapor adsorption isotherms on the surface of tricalcium silicate (C3S) and calcium hydroxide (CH), which are selected as typical cement mineral and hydration product respectively. The adsorption behavior of C3S and CH is compared by the adsorption energy and adsorption isotherm model. The condensation processes were explained by the Kelvin equation. The critical pore sizes of C3S and CH for condensation are 19 Å and 15 Å respectively. Beyond the critical pore size, water adsorption shows monolayer adsorption performance. The water adsorption process on the surface includes three stages: rapid adsorption, stable adsorption and slightly condensed adsorption, which are related to the surface interaction of minerals with water molecules. The Langmuir model is more suitable for the CH with homogeneous surface, while the Freundlich model is more suitable for the C3S model with nonhomogeneous surface. The adsorption heat of the first layer of water film and adsorption energy on the surface of CH are higher.

Change of the surface and structure of activated carbon as a result of HNO3 modification

In the paper the chemical modification of activated carbon was presented. The activated carbon was modified by nitric acid. For the tested activated carbons, the following physical and chemical properties were determined: bulk density, pH of the water extract, and effective diameter of the grains. Elemental and technical analyses were performed. The pore distribution was determined using mercury porosimetry. Low-temperature nitrogen isotherms were used to analyze the microporous structure. The chemical properties of the surfaces of the tested adsorbents were interpreted by means of the Boehm method. The water vapor adsorption isotherms at 303 K were determined and the adsorption capacity towards methanol was tested using the desiccator method. Thermogravimetric tests were used and, at the same time, the released oxidizing gases from the tested samples were analyzed using a mass spectrometer. As a result of the modification, activated carbon enriched with acidic oxygen functional groups was obtained. The resulting modified activated carbon showed worse structural parameters (when compred to umodified activated carbon), however it was characterized by a higher adsorption capacity in relation to polar adsorbates such as water and methanol, especially in the low pressure range.

A Modified Dent-Fractal Mathematical Model to Investigate the Water Vapor Adsorption on Nanopore Structure Heterogeneity from the Longmaxi Shale, Sichuan Basin, China

The study of water vapor adsorption (WVA) isotherms on shales is crucial to comprehend the adsorption–desorption behavior and deposit mechanism of water in shale pore systems. To systematically investigate the relationship between fractal dimension and WVA in shale reservoirs, a new Dent-fractal (DF) model was developed and the ability of different adsorption models to match with WVA experimental data was evaluated. The role of shale pore structure heterogeneity controlling the amount of WVA is also discussed. The results indicate that WVA on shale involves the monolayer–multilayer adsorption and capillary condensation. On the one hand, the GAB and Dent and DF models were found to be the best models for fitting and predicting WVA isotherms in Longmaxi shale. On the other hand, the DLP and DS models had the worst fitting qualities for WVA adsorption data. The pore structure of micropores has a more significant effect on WVA adsorption than that of meso-macropores. The larger surface and pore volume of micropores can provide more adsorption sites and space, which is favorable for WVA. In low-Rh conditions, the higher surface area, the pore surface complexity rises, resulting in higher water vapor monolayer adsorption. Under high-Rh conditions, for shale reservoirs with a highly heterogeneous pore structure, the relationship between the heterogeneous pore structure of the shale and the amount of water adsorbed in multiple layers is not obvious due to the formation of clusters of water molecules.

Adsorption behavior of Mo-MEL zeolites for reducing VOCs from cooking oil fumes

Based on the increasing public awareness of the pollution and hazard of cooking oil fume, MEL-type zeolite with Mo incorporation via a self-developed recrystallization method was developed for the reduction of non-methane hydrocarbon (NMHC) in cooking oil fumes via adsorption process. Mo species is proved to exist both in the MEL zeolitic framework and MoO3 clusters through XRD, IR, N2 adsorption–desorption, SEM and UV–vis characterization. Water vapor adsorption isotherms and 29Si NMR results indicate Mo-MEL owns superior hydrophobicity because of its high level of atoms coordination and lack of silanols. Toluene-TPD and dynamic adsorption results reveal the enhanced affinity to VOCs molecular on Mo-MEL, superior than Si-MEL and Al-MEL. The Mo-contained sample shows a considerable VOCs capacity under different humid conditions, suggesting its application potential for the adsorption and enrich of cooking VOCs, especially in humid condition.

Development and performance evaluation of novel silica gel-coated heat exchanger with high durability and conductivity to improve adsorption water treatment

Adsorption water treatment (AWT) has received considerable attention because it can be used to produce freshwater using low-grade heat sources. Furthermore, owing to its nearly consistent desalination performance and high-water recovery rate (>80 %), it has a high potential for use as a minimal liquid discharge process. However, a low freshwater production yield per unit volume of the AWT system is observed because the AWT system uses an adsorbent-packed heat exchanger (APHE), which has a high thermal resistance. In this study, the development and performance evaluation of a novel adsorbent-coated heat exchanger (ACHE) with high durability and conductivity is presented to enhance the heat and mass transfer rates during the adsorption and desorption processes. Binders and spray coating methods are utilized to achieve a uniform coating thickness and highly durable ACHE, and the adhesion strength is investigated using a pull-off test. The physical properties of the composite adsorbent are then examined using argon and water vapor adsorption isotherms, and the thermal conductivity is determined using the transient plane source method. Finally, the performance of the AWT process is evaluated considering the hot-water temperature and cycle time and achieves a significant superiority in the ACHE compared with the APHE.

Experimental and molecular investigation of water adsorption controls in marine and lacustrine shale reservoirs

The restriction of hydrocarbon migration within shale reservoirs by pre-adsorbed water necessitates an investigation into water adsorption control mechanisms within shales. In this study, water vapor adsorption isotherms obtained from marine and lacustrine shale samples along with isotherms from their organic matter and experimentally verified kerogen molecular models were used to evaluate water adsorption mechanisms, with simulated wet kerogen-quartz nanocomposites. Furthermore, these were also used to investigate organic matter-inorganic interaction controls on water adsorption. Pore size distribution (PSD) controls on water distribution in organic matter were obtained via water vapor adsorption and low-pressure nitrogen adsorption analysis, along with small angle neutron scattering (SANS) analysis. The results reveal water adsorption is linked to changes in mesopore volume within organic matter and porosity in kerogen models. PSD obtained from the shales only reveal mesopore controls at high RH, with water adsorption mainly controlled by oxygen functional groups in organic matter pores and swelling clays. Inorganic controls on water adsorption are also observed in adsorbed water not tightly bound to the shale surface due to a high montmorillonite content in clay interlayers, and organic matter interaction with quartz with a negative relationship between the adsorbed water and the quartz content. Collectively, these findings indicate that CO2 migration in shale reservoirs could be inhibited by water that is distributed in potential CO2 adsorption sites within organic matter pores and montmorillonite.

Modeling of multi-temperature IV and V-type water vapor adsorption isotherms on activated carbons for chemical protection

A static volumetric method measured the water vapor adsorption isotherms on porous activated carbons (AC and ASC-T) at 278.15 K ～ 308.15 K. Because of the difference in surface oxygen-containing functional groups, a Type-V isotherm represented water vapor adsorption on AC, whereas a Type-IV isotherm characterized ASC-T. The applicability of seven classical adsorption equilibrium models was analyzed and compared systemically. Results show that the Dual-sites Langmuir-Freundlich equation had the lowest residual errors (< 6 ml/g). Further, based on the linearization DA equation, a new partitioned segment-fitting strategy was first developed to describe multi-temperature adsorption isotherms. Two sets of the division points (P/P0) and parameters (n) were acquired. For AC and ASC-T, the best division point (P/P0) and parameter (n) were equal to 0.1 and 0.9, 0.2 and 2, respectively. The fitted results of multi-temperature adsorption isotherms show that the R2 values of AC and ASC-T both were bigger than 0.93, showing that the new fitting strategy has very good applicability. It offers the possibility to address the problem of the accurate description for multi-temperature water vapor adsorption data on porous activated carbons.

Mathematical modeling of adsorption isotherms of water vapour on polymeric ionites used in agrochemical practice

Polymeric ion-exchange materials (ionites) are used in agriculture to make substrates for complete and long-term plant nutrition. The main nutrients in bound form are contained on the ion-exchange groups of the ionite. The degree of dissociation of these groups, and thus the release of ions into the soil, depends on the moisture content. In case of heavy rainfall and during drought, the exchange properties of the ionite will be different. Therefore, the study of water adsorption in such ionites is a rather urgent problem. In this work, the water vapour adsorption by ionites is studied using a thermodynamic model that incorporates the interplay between changes in the energy of dissociation of ion-exchange groups and the osmotic effect. Within the framework of this approach adsorption isotherms are built in the range of air humidity from 0,1 to 1 at physically reasonable values of system parameters. Isotherms have a characteristic inflection point in the area of medium humidity, which allows them to be attributed to isotherms of the fifth type. The obtained model isotherms describe adsorption in mesoporous and microporous materials, which are ionites, and fully correspond to experimental adsorption isotherms of this type.

Composite material-based a clay for adsorption desalination and cooling applications

This paper studies improving the performance of an adsorption system by improving raw bentonite as an adsorbent. Acid treatment has been used for the pretreatment of raw bentonite. Then, a composite and activated adsorbents are prepared by bentonite impregnated in salt hydrates (CaCl2 and (NH4)2CO3). XRD, nitrogen adsorption isotherm, water vapor adsorption isotherm and kinetics are used to characterize raw and modified bentonite. Experimental results of adsorption isotherms and kinetics have been fitted using Dubinin–Astakhov equilibrium model and linear driving force model. MATLAB software has been used to solve a simulation model of an adsorption desalination system with and without heat recovery (HR). The effect of the modified adsorbents on the adsorption system performance has been investigated. The results illustrated that the surface area and pore volume of Bent/CaCl2 increased by about 200% and 500%, respectively, compared to raw bentonite. The Bent/CaCl2 was predicted to have the highest water uptake (0.82 kgH2O.kg−1). Bent/CaCl2 was predicted to have a SDWP of 11.5 m3.ton−1 per day with SCP 326 W.kg−1 and COP 0.52 at 85 °C desorption temperature. Also, the SDWP was predicted to achieve 26 m3.ton−1 per day with HR under the same conditions. The SDWP can be increased to 29 m3.ton−1 at 95 °C desorption temperature.

Novel ultrasonic dynamic vapor sorption apparatus for adsorption drying, cooling and desalination applications

Adsorption systems for desalination, drying, and cooling applications could be powered by renewable energy sources. Thus, it is a promising technology for solving energy and water problems. Designing an efficient adsorption system and evaluating its performance depend mainly on the adsorption isotherms and kinetics of nanoporous materials. The present work designs and manufactures a precise gravimetric sorption apparatus to measure the adsorption isotherms and kinetics of water vapor onto porous materials. It is equipped with a high-precision mass balance to record the change in mass of the tested sample. The main feature of the present apparatus is using an ultrasonic device to generate water vapor allowing easy control of the water vapor flow rate and operating pressure. This novel approach leads to a significant reduction in the apparatus capital cost. To confirm the accuracy and reliability of the proposed instrument, the adsorption kinetics and isotherms of water vapor onto three different materials are measured using the proposed apparatus and compared to the corresponding data in literature. The maximum deviation is found to be less than 4%, indicating the high accuracy of the proposed instrument. During the repeatability tests, a maximum uncertainty of 1.1% is observed at a relative pressure of 0.8, which is within the accuracy of the electronic mass balance. Accordingly, it is confirmed that the developed apparatus could measure the adsorption isotherm and kinetics of water vapor onto nanoporous materials with high accuracy and reliability.

Modeling of equilibrium water vapor adsorption isotherms on activated carbon, alumina and hopcalite

A static volumetric method measured the equilibrium adsorption isotherms of water vapor on commercial activated carbon, alumina and hopcalite adsorbents. A type II isotherm represents water vapor adsorption on alumina and hopcalite, whereas a type V isotherm characterizes activated carbon. A method based on the sensitivity analysis of parameters is used to evaluate the estimability of unknown parameters involved in the Toth-Aranovich–Donohue (type II) and Mahle (type V) adsorption isotherm equations. The estimable parameters are then identified using experimental water vapor measurements at three different temperatures, i.e., 293, 303 and 313 K and pressures up to the saturated concentration, simultaneously. The isotherm modeling methodology is implemented and solved within COMSOL Multiphysics®. The results of the isotherm model using the fitted parameters show excellent agreement with the experimental measurements. Thus, this is confirmed by the performance indices such as the Pearson correlation coefficient and the mean square error. In addition, the isosteric water vapor heat of adsorption is estimated using the Clausius-Clapeyron equation and the temperature-dependent models developed for each adsorbent.

Disagreements Between Calorimetric and Van't Hoff Enthalpies of Adsorption: A New Langmuir-like Model to Account for the Effect of Solvent Displacement Stoichiometry

The reported inconsistencies between calorimetry and the van't Hoff equation hinder the utility of thermodynamics in pharmaceutical research. In ligand binding or adsorption assays, it is believed that the van't Hoff equation falls short because of the lack of stoichiometric treatment in the equilibrium constant. A new modified Langmuir-Like equation that accounts for the stoichiometry of solute adsorption and solvent displacement is proposed in this work. The performance of the model was evaluated by studying the adsorption of phenobarbital from aqueous solutions by commercial activated carbon. The amount of water occupying the adsorption sites was estimated by graphical analysis of the ‘knee point’ of water-vapor adsorption isotherms and was found to correlate well with the relative percentage of hydroxyl and carbonyl surface groups. It was found that one phenobarbital molecule displaces 2-6 water molecules from the adsorption site. It is shown that adsorption enthalpy was not affected by the adjustment for stoichiometry, supporting the notion that the van't Hoff enthalpy is intrinsic and is independent of the stoichiometry of solvent displacement in Langmuir-based binding. The widely reported disparities between the van't Hoff and calorimetric enthalpies are unlikely to be from a stoichiometric origin.

Thermodynamic analysis and modeling of water vapor adsorption isotherms of roasted specialty coffee (Coffee arabica L. cv. Colombia)

The experimental assessment and computer modeling of the water vapor adsorption isotherms of roasted specialty coffee is addressed in this study. Thus, both coffee beans and ground coffee of medium (850 μm) and fine (600 μm) particle sizes were analyzed over a range of water activities of between 0.1 and 0.9 and at temperatures of 25, 35, and 45 °C. The adsorption isotherms were determined using the dynamic dew point (DDI) method. The computer modeling of adsorption isotherms was addressed in order to describe the influence of the water activity and temperature on the equilibrium moisture content. Furthermore, the hygroscopic capacity of roasted coffee was analyzed by differential thermodynamic analysis. Experimental results and modeling showed that the high level of moisture adsorption found in the ground coffee was related to a large adsorption area, suggesting that specialty coffee should preferably be stored as beans. The Peleg empirical model was the most suitable at representing both type III upward concave adsorption behavior and the effect of temperature on the adsorption isotherms. Differential thermodynamic analysis revealed an increase in the water adsorption energy at low equilibrium moisture content, while negative Gibbs free energy values revealed the spontaneity of the adsorption process.