Water Vapor Adsorption Research Articles

Dynamic variation of bed parameters and time optimisation of solar adsorption refrigeration system based on CFD simulation

One major reason for the limited application of adsorption refrigeration systems is their lower refrigeration efficiency and performance compared to other alternatives. Additionally, there is limited research focused on optimizing the system performance over time. This paper presents a numerically validated thermodynamic model to analyse the effect of adsorption time on the performance efficiency enhancement of a solar adsorption refrigeration system. The adsorption rate model proposed by Sokoda and Suzuki has been used to evaluate the adsorption and desorption characteristics of water vapor on silica gel and the solar collector system has been fitted to a heat flow density equation based on measured concentrated solar heating. The water vapor adsorption capacity on silica gel as a function of temperature and pressure in the adsorption bed has been numerically evaluated during the four stages of the cooling cycle, namely adsorption, preheating, desorption, and cooling. The coefficient of performance and specific cooling power have been utilized as the major performance indicators, in the context of the influence of adsorption time on the refrigeration performance of the system. The simulation results revealed that, although increasing the adsorption time increased the system's cooling capacity, it also prolonged the cycle time and adversely affected the dynamics of preheating and desorption processes (due to increased solar input). As a result of the numerical simulation, an optimum value of adsorption time has been predicted to be 71 min corresponding to a coefficient of performance equal to 0.476 and a specific cooling power equal to 28.6 W/kg.

Anion exchange material based on polyvinylchloride and urea for the removal of chromium(vi) ions from aqueous solutions

AbstractIn this study, an anion exchange material obtained by chemically modifying granulated polyvinyl chloride with urea was examined. To study the structural morphology of the anion exchanger, polymer PVC‐based anion exchange resin second type (PPE‐2), we applied different characterization techniques including X‐ray diffraction (XRD), Fourier‐transform infrared (FTIR), scanning electron microscopy (SEM), and water vapor adsorption analysis. Moreover, PPE‐2 was used to remove hexavalent chromium ions from aqueous media. A pseudo‐second order model was used to describe sorption kinetics as well as the adsorption mechanism. The Langmuir isotherm and the pseudo‐second order kinetic model led to the most consistent results in describing ion removal from solution. In the case of hexavalent chromium ions, the maximum adsorption capacity was 148.4 mg g−1. The Dubinin‐Radushkevich (D‐R) free energy of adsorption (ED) was >16 kJ mol−1, which indicates chemical interaction between the ion exchange material and Cr(VI) ions. The Gibbs energy ΔG, enthalpy ΔH, and entropy ΔS changes during binding showed that the sorption process is spontaneous and involves chemical sorption through endothermic ion exchange reactions. In addition, the results demonstrate that the anion exchanger (PPE‐2) very efficiently removed hexavalent chromium ions from industrial wastewater.

Synthesis of Aluminum-Based Metal-Organic Framework (MOF)-Derived Carbon Nanomaterials and Their Water Adsorption Isotherm.

The characteristics of water vapor adsorption depend on the structure, porosity, and functional groups of the material. Metal-organic framework (MOF)-derived carbon (MDC) is a novel material that exhibits a high specific area and tunable pore sizes by exploiting the stable structure and porosity of pure MOF materials. Herein, two types of aluminum-based MOFs were used as precursors to synthesize hydrophobic microporous C-MDC and micro-mesoporous A-MDC via carbonization and activation depending on the type of ligands in the precursors. C-MDC and A-MDC have different pore characteristics and exhibit distinct water adsorption properties. C-MDC with hydrophobic properties and micropores exhibited negligible water adsorption (108.54 mgg-1) at relatively low pressures (P/P0~0.3) but showed a rapid increase in water adsorption ability (475.7 mgg-1) at relative pressures of about 0.6. A comparison with the isotherm model indicated that the results were consistent with the theories, which include site filling at low relative pressure and pore filling at high relative pressure. In particular, the Do-Do model specialized for type 5 showed excellent agreement.

Recycling of cathode ray tubes and stone sludge for the synthesis of Al-MCM-41 grafted amine functional group and environmental humidity control material applications

There is a growing need for economical methods by which to reuse industrial waste. This paper reports on the recycling of industrial waste in the preparation of amine functionalized mesoporous molecular sieves (Al-MCM-41), for use as a building material applicable to the energy-free regulation of indoor humidity. The preparation of amine functionalized Al-MCM-41 for experiments involved combining stone sludge, cathode ray tube panel waste glass, an alkali agent (sodium hydroxide), and cetyltrimethylammonium bromide with aminopropyltriethoxysilane in various proportions. The water vapor adsorption of amine functionalized Al-MCM-41 (42.85 g/m2) far exceeded of amine functionalized Al-MCM-41 without surface grafting (28.64 g/m2). Al-MCM-41 with 2.5 vol% amine functional groups achieved the highest 24-h water vapor adsorption performance in compliance with JIS A 1470 standards. This research provides an economical approach to the recovery and recycling of industrial waste that is rich in silicon and aluminum.

Thermodynamic analysis of water vapor adsorption onto freeze-dried ora-pro-nobis (Pereskia aculeata Miller) mucilage

The mucilage of Pereskia aculeata Miller is a hydrocolloid with the potential to be used as a food additive. Thus, data on its physical, chemical and microbiological stability are necessary to evaluate the storage stability of the product. This study aimed to determine the thermodynamic properties of water vapor adsorption onto freeze-dried ora-pro-nobis mucilage (OPNM) and to interpret the mechanisms that govern water adsorption onto powder particles through the study of enthalpy-entropy compensation. In addition, OPNM was characterized in terms of moisture, ash, ether extract, protein, fiber and carbohydrates beyond the functional chemical groups by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Thermodynamic analysis showed that water adsorption onto OPNM powder was characterized as a spontaneous process with strong attractive forces in the water and OPNM mixture. The water sorption mechanism for OPNM at the studied adsorption range was regulated by energy interactions related to the chemical composition of the product.

Modeling of Water Vapor Adsorption and Desorption in an Industrial Medical Air Dryer

Modeling of Water Vapor Adsorption and Desorption in an Industrial Medical Air Dryer

Water Vapor Adsorption on Desiccant Materials for Rotary Desiccant Air Conditioning Systems

In order to determine the water vapor adsorption performance of a rotary desiccant-based air conditioning system, the behavior of water adsorption on cylindrical pores of different sizes was studied by using classical density functional theory (CDFT) based on perturbated chain statistical associating fluid theory (PC-SAFT). Firstly, the structural parameters of the desiccant material were characterized by scanning electron microscopy (SEM), X-ray Energy Dispersive Spectrum (EDS), and N2 adsorption/desorption isotherms, as well as adsorption equilibrium measurements of water vapor at temperature range 293–308 K. Secondly, the potential energy equation of water molecules in cylindrical pores was determined, and contribution of various terms of PC-SAFT for simulating fluid in cylindrical pores were established. Finally, the pore size distribution (PSD) of the desiccant materials is determined by the PC-SAFT kernel. Moreover, water vapor condensation was investigated with the PC-SAFT model in micropores. The results indicate that the rotary desiccant materials have a large number of micropores with a volume of 0.3669 cm3/g and the amount of water adsorption is about 0.285 g/g. The condensation pressure and the pore width corresponding to the saturated pressure P0 grow with an increase in the temperature, signifying that adjusting the PSD of the material has a significant effect on improving the dehumidification performance. The research concludes that the PSD range of the oxide cylindrical pore between 1.09 and 1.53 nm is particularly beneficial for dehumidification. This study provides valuable theoretical guidance for optimizing dehumidification materials.

Competitive adsorption characteristics of VOCs and water vapor by activated carbon prepared from Fe/N-doped pistachio shell.

Various materials have been developed to capture volatile organic compounds (VOCs) to mitigate air pollution. However, sorbent materials with excellent resistance to water are rare. Here, several Fe/N-doped activated carbons (ACs) have been prepared to capture VOCs in humid environments. The ACs were analyzed by various characterization techniques, such as BET, SEM, XPS, XRD, FTIR, and Raman. The results showed that Fe/N doping resulted in the specific surface area of the ACs increasing by 500 to 1000 m2g-1, the average pore size increasing to approximately 2nm, improved mesoporous structure, higher graphitization, lower hydrophilicity, and polarity. The VOCs adsorption performance of the ACs was evaluated by static and dynamic adsorption experiments. The uptake of toluene and ethyl acetate by ACs was enhanced to 224mgg-1 and 135mgg-1, respectively. And ACs were able to maintain 70 to 80% VOCs adsorption capacity for VOCs at 80% relative humidity. Furthermore, the microscopic mechanisms were investigated by the grand canonical Monte Carlo method (GCMC). The highly graphitized structure and the N functional groups favored the VOC adsorption process and discouraged the adsorption of water vapor. This work affirmed the dominance of Fe/N-doped carbon, which will contribute to the evolution of water-resistant VOCs adsorbent materials.

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.

A universal strategy for efficient synthesis of Zr‐based MOF nanoparticles for enhanced water adsorption

AbstractZr‐based metal‐organic framework (Zr‐MOF) nanoparticles (NPs) have attracted extensive research thanks to their outstanding thermal and chemical stability, but their efficient synthesis is still challenging. Here, high‐quality Zr‐MOF NPs with tunable and uniform particle sizes can be successfully fabricated within 30 min by high‐gravity technology with high yields. Significantly, the rapidly milder preparation of UiO‐66 NPs can also be achieved at 90 or 70°C. This strategy has been extended to the synthesis of other Zr‐MOF NPs. Furthermore, the water vapor adsorption properties of obtained UiO‐66 NPs display a size‐dependent effect. The 70 nm UiO‐66 NPs have the highest adsorption capacity of 625 mg g−1 among unmodified UiO‐66 reported so far, and manifest 2.0–2.8 times faster water adsorption rate than the micron ones. This study provides a feasible method for the efficient and mild preparation of MOFs nanoparticles, which may promote the synthesis and applications of nano‐sized MOFs.

Characterizing water vapor adsorption on coal by nuclear magnetic resonance: Influence of coal pore structure and surface properties

Steam injection is a novel and promising technology for enhancing coalbed methane (CBM) recovery. Accurate descriptions of the migration and adsorption of water vapor on coal is crucial for determining the occurrence state of the CBM and improving CBM production. This study quantitatively characterized the dynamic transport and adsorption processes of water vapor in coal pores and fractures using nuclear magnetic resonance (NMR). The results demonstrated that water vapor was preferentially adsorbed in the coal micropores, which was mainly related to capillary condensation, whereas liquid water filled a wide range of pores and fractures. Due to the differences in the microstructure and surface properties among different coals, the water vapor adsorption behaviors varied significantly. Among the coals used in this study, water vapor was most easily adsorbed on the bitumite with the biggest specific surface area, pore volume, pore area, the highest content of oxygen-containing functional groups, and the strongest wettability. Additionally, the coal pore structure had a greater impact on the water vapor adsorption capacity than the oxygen functional groups and the wettability. This research is of great significance for understanding the flow behaviors of water vapor in porous media and the interactions between coal and water.

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.

Adsorption behaviour and thermodynamics of water on deep reservoir and its influence on CO2 sequestration

In this study, the adsorption experiments of water vapour on deep reservoir were conducted. The thermodynamics for water vapour adsorption were analysed. Results illustrate that primary binding centres have stronger affinity than secondary binding centres. Water molecule will be preferentially trapped at primary binding centres in low-pressure region. In high-pressure region, secondary adsorption predominates. Primary adsorption spontaneity increases with pressure. At secondary binding centres and total binding centres, the spontaneity degree quickly improves and then slowly decreases as pressure increases. The transfer of water molecules from the more energetic binding centres to the less binding centres leads to the initial reduction in entropy loss (ΔS) and isosteric heat of adsorption (Q st). The late enhancement in ΔS and Q st is caused by the growing water clusters. Water vapour adsorption can promote CH4 desorption. By occupying adsorption sites and reducing pore connectivity, water vapour adsorption causes an unfavourable effect on CO2 sequestration.

Adsorption of Water Vapors on Magnetite Powders Prepared by Chemical Precipitation and Thermolysis Methods

Adsorption of Water Vapors on Magnetite Powders Prepared by Chemical Precipitation and Thermolysis Methods

Change of polymeric gel structure of several foamed plastic insulations deteriorated by moisture

Foamed plastic insulations require long-term performance under sustainable development goals. However, in recent years, it has been reported that foamed plastic insulations installed in high-humidity environments, such as under waterproof sheets on a rooftop, absorb moisture and subsequently increase thermal conductivity.The study aims to estimate both moisture absorption and changes in physical properties of foamed plastic insulations after exposure to high humidity and discuss the moisture-induced deterioration based on the results of several experiments.We observe what changes occur in three types of foamed plastic insulation, phenolic foam, polyurethane foam, and extruded polystyrene foam, in a deterioration condition with moisture. In the first step, we verify that the moisture exists in what form and whether moisture condenses inside or blends with the material after deterioration occurs. Precisely, comparing weight changes before and after high-temperature humidity deterioration with two test results. One is changing a polymeric gel structure of the deteriorated insulation with X-ray CT, and another is the amount of adsorbed water vapor on the surface of each insulation with the gas adsorption method. Results from these studies refer that the deteriorated phenolic foam and moisture are assumingly miscible to transform polymeric gel structure.The second step compares how moisture deterioration affects insulation’s thermal characteristics. We evaluated in our previous study when insulations are exposed to the seasonal humidity cycle to apply typical seasonal fluctuation in Northeast Asian countries, affecting more critical damage than a persistent condition to samples. Therefore, we examine the relationship between thermal characteristics and moisture deterioration effect in humidity fluctuations. Resultantly, the phenolic foam’s polymeric gel structure is changed, and its thermal property is affected by humidity swings.The results provide a part of the moisture deterioration mechanism, miscible behavior between moisture and foamed plastic insulations to change polymeric gel structure, which shifts thermal properties.

Thermodynamic behavior of water vapor adsorption in shale and its dependence on organic matter and clay minerals

Isothermal adsorption experiments of water vapor in shale samples with differing TOC (total organic carbon content) and differing clay content were conducted at three set temperatures to reveal the adsorption mechanism, and to determine the thermodynamic dependence of primary and secondary adsorption processes on the content of organic matter and clay minerals. The adsorption of water vapor in shale is spontaneous with the Gibbs free energy change is minus ranging from −0.28 - −5.15 KJ/mol, the adsorption changes from entropy driven to enthalpy driven as the adsorption amount increases (enthalpy change turns from plus to minus ranging from −1.25–––6.72 KJ/mol, and the entropy change is opposite ranging from −0.0031–––0.035 KJ/mol), and the primary adsorption amount increases with higher experimental temperature but secondary adsorption amount decreases. Fitting results and their relying theories indicate that micropore filling and monolayer adsorption occur in primary adsorption mainly though strong hydrogen bonding and electrostatic forces between water vapor and the pore surface, and multilayer adsorption and capillary condensation dominate secondary adsorption mainly through weak hydrogen bonding among water vapor. There are positive correlations of adsorption amount versus both clay content and TOC. Clay minerals are strongly hydrophilic because of their exchangeable cations and polar groups, providing primary and secondary adsorption sites, and enhancing the spontaneity of adsorption. OFGs (oxygen functional groups) in organic matter are hydrophilic, other pore surfaces are hydrophobic or weak hydrophilic, which also develop many adsorption sites. Results from this work provide new insights about the influence of organic matter and clay minerals on the adsorption thermodynamic behavior of water vapor in shale.

Physical and chemical changes to commercial sodium phosphate glasses after aging or dynamic vapor sorption

Commercial sodium phosphate glasses are used as reference materials for polyphosphate chain length analysis. Water can spontaneously hydrolytically degrade the characteristic polyphosphate P-O-P bond, and reduce the polyphosphate chain length. XRD, Raman spectroscopy, and SEM were used to characterize glasses stored for two weeks, six months and >10 years, and three commercial sodium phosphate glasses after controlled water vapor adsorption and desorption. Rapid water vapor absorption was measured above 50 % relative humidity. The chain length distribution for a dissolved commercial sodium phosphate glass with an average chain length of 45 PO3− units was analyzed with polyacrylamide gel electrophoresis. A distribution of linear polyphosphates, interrupted with a population spike of ∼13 PO3− units, trimetaphosphate rings, and orthophosphates were identified. 31P-MAS NMR suggested that the linear polyphosphate population spike could be the product of large ring polyphosphate scission upon dissolution. This study confirms the importance of dry storage for chain length reference phosphate glasses.

WO3 boosted water tolerance of Pt nanoparticle on SO42--ZrO2 for propane oxidation

H2O poisoning of platinum-based catalysts for VOCs oxidation is a long-standing problem due to H2O strongly competitive adsorption on active sites. In this work, it is found that the H2O competitive adsorption on Pt active sites is effectively weakened by enhancing strong metal-support interaction (SMSI) in Pt-based catalyst. SMSI between WO3 and Pt species occurs in the WO3 supported Pt catalyst (Pt/WO3) but disappears in Pt-3W/ZrO2 due to monolayer dispersed WO3 on ZrO2. The formation of aggregated WO3 species in Pt-3W/SO42--ZrO2 leads to the SMSI which is further enhanced by SO42--ZrO2. The enhanced SMSI plays critical role on weakening water vapor adsorption on active sites, thus Pt-3W/SO42--ZrO2 exhibits both highest activity (T90 = 200 °C) and water tolerance which is much superior than Pt/ZrO2, Pt/WO3, Pt-3W/ZrO2 and Pt/SO42--ZrO2 under wet condition (5% H2O). Our primary results provide a promising strategy for designing superior platinum catalysts for VOCs complete oxidation.

Study of Dynamic Sorption in Adsorption Refrigeration Cycle

This paper shows the characteristics of temperature and adsorbed (water vapor) mass rate distribution in the adsorber unit which is the key part to any adsorption refrigeration system. The temperature profiles of adsorption/desorption phases (Dynamic Sorption) are measured experimentally under the operating conditions of 90oC hot water temperature, 30oC cooling water temperature, 35oC adsorption temperature and cycle time of 40 min. Based on the temperature profiles, The mass transfer equations for the annulus adsorbent bed are solved to obtain the distribution of adsorption velocity and adsorbate concentration using non-equilibriummodel. The relation between the adsorption velocity with time is investigated during the process of adsorption. The practical cycles of adsorption and desorption were stated dependent on the variables obtained from the experiment and equations calculations.The results show that the adsorption velocity is diminished after a period of 20 min. The maximum value of the adsorbed water vapor concentration on silica gel is 0.12 kg water/kg adsorbent (adsorption phase) and the minimum value of the water content into silica gel is 0.04 kg water/kg adsorbent (desorption phase) producing a dynamic sorption of kg water/kg adsorbent.