Affinity For Water Vapor Research Articles

Recent Advances in Desiccant Materials for Energy‐Efficient and Sustainable Heat Transfer Systems

The expanding prevalence of heating, ventilation, and air conditioning (HVAC) systems, currently reliant on fossil fuel‐derived energy, necessitates energy‐saving measures to address climate change concerns. Implementing desiccants with high water vapor affinity reduces latent heat input, impacting the heat exchanger's functionality based on system and desiccant characteristics. This review analyzes the materials in solid desiccants, binders, and substrates, emphasizing advancements for enhanced heat transfer efficiency. Some notable materials explored include metal–organic frameworks, activated carbon, silica gel, polymers, and zeolite. In system level, the article discusses about the dual‐channel heat exchanger which emerges as a solution to drawbacks in existing dehumidification systems, offering higher performance and lower latent heat load in modern solid desiccant‐coated heat exchangers. Despite the environmental impact of material usage, future research should focus on sustainable materials, such as those derived from biomass or recycled sources, to maintain efficiency while minimizing waste in HVAC systems.

Building extra transport channels in mixed-matrix membrane for air dehumidification

Membrane separation is a promising technology relative to the mature distillation technique due to its high energy efficiency. Incorporating nanoparticle to polymer matrix to fabricate mixed-matrix membranes (MMMs) is one of effective ways to overcome the typical trade-off relationship between gas permeability and selectivity. Although silica based MMMs were studied for natural gas dehydration and desalination, it is rarely been investigated for air dehumidification. Herein, membrane material with high water vapor affinity of Pebax 1074 was applied as polymer matrix and silica was incorporated as filler to fabricate MMMs. The embedded silica filler can simultaneously enhance water vapor permeability (13–33% up) and H2O/N2 selectivity (40–60% up) at an optimal loading of 1 wt%. The relatively hydrophobic form improved water vapor permeability due to the pronounced enlarged d-spacing and the resultantly enhanced diffusivity coefficient. The more hydrophilic filler enhanced more H2O/N2 selectivity than that of the counterpart because of the largely improved water vapor solubility coefficient. The concomitant improvement of both water vapor permeability and its selectivity makes it stand out from the various previously reported membranes, demonstrating its potential for scale-up application.

Investigation of the Side Chain Effect on Gas and Water Vapor Transport Properties of Anthracene-Maleimide Based Polymers of Intrinsic Microporosity.

In the present work, a set of anthracene maleimide monomers with different aliphatic side groups obtained by Diels Alder reactions were used as precursors for a series of polymers of intrinsic microporosity (PIM) based homo- and copolymers that were successfully synthesized and characterized. Polymers with different sizes and shapes of aliphatic side groups were characterized by size-exclusion chromatography (SEC), (nuclear magnetic resonance) 1H-NMR, thermogravimetric (TG) analysis coupled with Fourier-Transform-Infrared (FTIR) spectroscopy (TG-FTIR) and density measurements. The TG-FTIR measurement of the monomer-containing methyl side group revealed that the maleimide group decomposes prior to the anthracene backbone. Thermal treatment of homopolymer methyl-100 thick film was conducted to establish retro-Diels Alder rearrangement of the homopolymer. Gas and water vapor transport properties of homopolymers and copolymers were investigated by time-lag measurements. Homopolymers with bulky side groups (i-propyl-100 and t-butyl-100) experienced a strong impact of these side groups in fractional free volume (FFV) and penetrant permeability, compared to the homopolymers with linear alkyl side chains. The effect of anthracene maleimide derivatives with a variety of aliphatic side groups on water vapor transport is discussed. The maleimide moiety increased the water affinity of the homopolymers. Phenyl-100 exhibited a high water solubility, which is related to a higher amount of aromatic rings in the polymer. Copolymers (methyl-50 and t-butyl-50) showed higher CO2 and CH4 permeability compared to PIM-1. In summary, the introduction of bulky substituents increased free volume and permeability whilst the maleimide moiety enhanced the water vapor affinity of the polymers.

Surface Structuring and Water Interactions of Nanocellulose Filaments Modified with Organosilanes toward Wearable Materials.

Colloidal dispersions of cellulose nanofibrils (CNFs) are viable alternatives to cellulose II dissolutions used for filament spinning. The porosity and water vapor affinity of CNF filaments make them suitable for controlled breathability. However, many textile applications also require water repellence. Here, we investigated the effects of postmodification of wet-spun CNF filaments via chemical vapor deposition (CVD). Two organosilanes with different numbers of methyl substituents were considered. Various surface structures were achieved, either as continuous, homogeneous coating layers or as three-dimensional, hairy-like assemblies. Such surface features reduced the surface energy, which significantly affected the interactions with water. Filaments with water contact angles of up to 116° were obtained, and surface energy measurements indicated the possibility of developing amphiphobicity. Dynamic vapor sorption and full immersion experiments were carried out to inquire about the interactions with water, whether in the liquid or gas forms. Mechanical tests revealed that the wet strength of the modified filaments were almost 3 times higher than that of the unmodified precursors. The hydrolytic and mechanical stabilities of the adsorbed layers were also revealed. Overall, our results shed light on the transformation of aqueous dispersions of CNFs into filaments that are suited for controlled interactions with water via concurrent hydrolysis and condensation reactions in CVD, while maintaining the moisture buffering capacity and breathability of related structures.

Desiccant materials for air conditioning applications - A review

Desiccants are a group of adsorbent materials that have a great affinity for water vapour. Due to this merit, desiccant material can produce hot and dry air which can be used for the drying process as well as in air-conditioning applications to minimize the latent heat load. A good desiccant must have better moisture absorption capability as well as lower regeneration temperature. The moisture absorption capability basically depends upon the desiccant characteristics like pore volume, apertures size and void fraction. Depending upon normal physical state, desiccants can be either solids or liquids. Solid desiccant materials such as silica gel, natural zeolites, molecular sieves, activated alumina, synthetic polymers are highly porous in nature and adsorb water by using mechanisms of chemical adsorption. Liquid desiccants such as Calcium chloride, tri-ethylene glycol, and lithium chloride are generally very strong solutions of ionic salts and their behaviour is controlled by changing its temperature and concentration. This paper presents a detailed study on different solid, liquid and composite desiccant which combine two or more desiccant materials for better properties and performance. This review has a great significance for the research and technical development in the field of desiccant dehumidification and air-conditioning technology.

Recrystallization and Water Absorption Properties of Vitrified Trehalose Near Room Temperature.

To provide the physicochemical properties of vitrified trehalose for predicting its recrystallization. Thin films of vitrified trehalose solutions were prepared at room temperature and exposed to various humid and temperature atmospheres. The in-situ amount of retained water in the vacuum-dried trehalose thin film during exposure was determined using its FTIR spectrum by quantifying the extremely infinitesimal amount of retained water in the trehalose solution. Recrystallization of the sample was also assessed by the FTIR spectrum of trehalose dihydrate. The effective water absorption coefficient, h meff , exponentially increased to the water activity of the trehalose sample, A w , at 25°C and 40°C at which the increasing rates are comparable. The surface energy of trehalose dihydrate, γ, was found to be lower than the value calculated from the reported equation, neglecting the effects of the activity of the solute and solvent water. The retained water in trehalose considerably increases its affinity for water vapor, and the change in this affinity with regard to the water activity is nearly independent of temperature. The dihydrate nucleation rate of trehalose-water system is maximal when trehalose weight ratio is ~0.8 at 25°C and is slightly higher (~0.85) at 40°C.

Starch Particles, Energy Harvesting, and the "Goldilocks Effect".

This study reports on the unique water vapor adsorption properties of biomass-derived starch particles (SPs). SPs offer an alternative desiccant for air-to-air energy exchangers in heating, ventilation, and air conditioning systems because of their remarkable adsorption–desorption performance. SP15 has a particle diameter (dp) of 15 μm with a surface area (SA) of 2.89 m2/g and a pore width (Pw) of 80 Å. Microporous starch particles (SP15) were compared with high amylose starch (HAS15; SA = 0.56 m2/g, dp = 15 μm, Pw = 46 Å) and silica gel (SG13; SA = 478 m2/g, dp = 13 μm, Pw = 62 Å). Transient water vapor tests were performed using a customized small-scale energy exchanger coated with SP15, HAS15, and SG13. The water swelling (%) for SP15 was ca. 2 orders of magnitude greater with markedly higher (ca. three- and six-fold) water vapor uptake compared to HAS15 and SG13, respectively. At similar desiccant coating levels on the energy exchanger, the latent effectiveness of the SP15 system was much improved (4–31%) over the HAS15 and SG13 systems at controlled operating conditions. SP15 is a unique desiccant material with high affinity for water vapor and superior adsorption properties where ca. 98% regeneration was achieved under mild conditions. Therefore, SPs display unique adsorption–desorption properties, herein referred to as the “Goldilocks effect”. This contribution reports on the utility of SPs as promising desiccant coatings in air-to-air energy exchangers for ventilation systems or as advanced materials for potential water/energy harvesting applications.

Model-based Process Design of Adsorption Processes for CO2 Capture in the Presence of Moisture

Separation processes based on adsorption show potential in the field of carbon dioxide capture and utilization or storage. Model- based process design is a powerful tool to fully exploit this potential. In order to get an accurate description of the behavior of the processes in a fixed bed, a reliable description of the equilibrium adsorption is necessary. In this work the potential of two types of zeolites, 13X and ZSM-5, is investigated in regards to their use in a temperature swing adsorption process for a post- combustion capture application. To this end, the single component adsorption equilibrium of CO2, N2, and H2O vapor is presented along with appropriate isotherms describing the data. This allows for a comparison of the two sorbents with respect to their cyclic CO2 adsorption capacity and selectivity for CO2. Additionally, the competition for adsorption sites between CO2 and N2 is investigated by applying the ideal adsorbed solution theory (IAST) to predict the binary adsorption equilibrium on both sorbents. These predictions indicate a very high selectivity of 13X for CO2, making this a very promising sorbent for temperature swing adsorption in a post-combustion capture environment, with the caveat that it also strongly adsorbs water vapor. This strong affinity for water vapor may imply that a flue gas stream would have to be dried before it enters the adsorption unit.

Corrections for measurements of tritium in subterranean vapor using silica gel

Hazardous contaminants buried within vadose zones can accumulate in soil gas. The concentrations and spatial extent of these contaminants are measured to evaluate potential transport to groundwater for public risk evaluation. Tritium is an important contaminant found and monitored for in vadose zones across numerous sites within the US nuclear weapons complex, including Los Alamos National Laboratory. The extraction, collection, and laboratory analysis of tritium from subterranean soil gas presents numerous technical challenges that have not been fully studied. Particularly, the lack of moisture in the soil gas in the vadose zone makes it difficult to obtain enough sample (e.g., > 5 g) to provide for the required measurement sensitivity, and often, only small amounts of moisture can be collected. Further, although silica gel has high affinity for water vapor and is prebaked prior to sampling, there is still sufficient residual moisture in the prebaked gel to dilute the relatively small amount of sampled moisture; thereby, significantly lowering the "true" tritium concentration in the soil gas. This paper provides an evaluation of the magnitude of the bias from dilution, provides methods to correct past measurements by applying a correction factor (CF), and evaluates the uncertainty of the CF values. For this, 10,000 Monte Carlo calculations were performed, and distribution parameters of CF values were determined and evaluated. The mean and standard deviation of the distribution of CF values were 1.53 ± 0.36, and the minimum, median, and maximum values were 1.14, 1.43, and 5.27, respectively.

An adsorption model of insoluble particle activation: Application to black carbon

We present a model of insoluble particle activation based on a modification of the Köhler equation in which we introduce a term based on the activity of water adsorbed on the particle surface. We illustrate the model by application to activation data from black carbon (BC) particles. We parameterize the model using a free energy of adsorption that reflects the relative affinity for water vapor adsorbing on either the BC surface or the adsorbed water layer. This enables the parameterization of either chemically modified (hydrophilic) or graphitic (hydrophobic) BC. Several features of a suite of carbon activation data are captured by the model. In particular, upper and lower bounding curves are predicted for activation supersaturation as a function of diameter. We show a large body of recent activation data that all fall within these bounds. The model also predicts that activation of BC aerosol leads to activation diameters from 3 to 10 times smaller than activation of soluble particles of identical dry diameter. The activation of smaller particles may be expected to impact the size distribution of resulting cloud droplets and thus the aerosol first indirect effect on climate. Finally, we compare activation of BC aerosol as calculated with this model to activation of mixed particles of BC and ammonium sulfate. It is shown that for some range of the adsorption free energy a hydrophilic BC aerosol is predicted to activate at lower supersaturation than comparable mixed aerosol of low mass fraction in the soluble component, indicating the utility of a model of mixed particle activation based on the adsorption of water to form an interfacial solution.

Wettability of fine silica powder surfaces modified with several normal alcohols

The chain length effects of chemical modification with various normal alcohols on the wettability of silica have been studied. The modifications were carried out by chemical reaction of alcohol molecules with surface silanols. The amount of silanols on sample surface was obtained by the Grignard method, and the amount of modifiers was determined by thermal analysis. As a result, surfaces were designed to have various concentrations of normal alkoxyl groups. The wettability of these well-defined samples for water were investigated by water vapor adsorption, heat of immersion and various preferential dispersion tests. The results are summarized as follows: (1) the wettability of samples with modifiers of carbon number above eight markedly changes at the modification ratio of about 20%; (2) the samples chemisorbed alcohol with less than eight carbon atoms, the modification ratios of above 20% are required to give hydrophilic surfaces. Because the bulkiness effect of modifiers on wettability decreases with reduction of chain length; (3) in the cases of hydrophobic samples, cooperative water adsorption takes place at the first stage of adsorption. With the occurrence of multilayer adsorption, a continuous two dimensional water layer is formed at the latter stage of adsorption. In the cases of the hydrophobic samples, the adsorbed amount was less than theoretical monolayer capacity in spite of high relative pressure at about P/ P 0=1. Therefore, such a continuous two dimensional water layer is not formed as a result of the steric hindrance of the modifiers. In this case, multilayer adsorption dose not occur. The surface property is estimated to be hydrophobic; (4) the results of preferential dispersion tests as the evalution of macroscopic wettability are in agreement with the results of water vapor affinity and heat of immersion as the nanoscopic wettability.

The change in the water vapor affinity of fine silica particles loaded with trimethylsilyl groups

Microscopic and macroscopic wettabilities of fine silica powder surfaces loaded with trimethyl-silyl groups (TMS) were studied. The modification was carried out by the chemical reaction of hex-amethyldisilazane (HMDS) molecules with surface silanols and the TMS coverage was determined by elemental analysis of carbon. The microscopic wettability was investigated by water vapor adsorption and IR spectroscopic methods. The macroscopic wettability was examined by various preferential dispersion tests. The results are summarized as follows. (1) HMDS molecules preferentially reacted with free type surface silanols. (2) The macroscopic wettability drastically changed at a TMS coverage of about 40%. (3) The effect of steric hindrance appeared clearly at a TMS coverage above 40%. Hence, a part of the residual surface silanols is shielded by TMS and water molecules will not access these sites. (4) In the case of TMS coverage below about 40%, cooperative adsorption takes place at the first stage of adsorption. Then by the occurrence of multilayer adsorption, a continuous two-dimensional water layer is formed at the latter stage of adsorption. On the other hand, in the case of coverage above about 40%, the adsorbed amount was about 65% of the theoretical monolayer capacity in spite of a high relative pressure at about P/P 0 = 1. Therefore, such a continuous two-dimensional water layer is not formed on account of the steric hindrance of the TMS and multilayer adsorption will not occur in this case. The surface property is estimated to be hydrophobic. (5) The results of preferential dispersion tests as the macroscopic wettability are in agreement with the results of water vapor affinity as the microscopic wettability.

トリメチルシリル基を導入したシリカ微粉体の水蒸気吸着特性

The wettabilities of fine silica powder surfaces loaded with trimethylsilyl groups (TMS) were studied microscopically and macroscopically. Modification was carried out by the chemical reaction of hexamethyldisilazane (HMDS) molecules with surface silanols, and the TMS coverage was determined by the elemental analysis of carbon. The microscopic wettability was investigated by water vapor adsorption and the IR spectroscopic method. The macroscopic wettability was examined by various preferential dispersion tests. The results are summarized as follows: (1) HMDS molecules preferentially reacted with free type surface silanols. (2) The macroscopic wettability drastically changed at a TMS coverage of about 40%. (3) The effect of steric hindrance appeared clearly at a TMS coverage above 40%. Hence, a portion of residual surface silanols is shielded by TMS, and water molecules cannot access these sites. (4) In the case of TMS coverage below about 40%, cooperative adsorption takes place durring the first stage of adsorption. Then, by the occurrence of multilayer adsorption, a continuous two dimensional water layer is formed during the latter stage of adsorption. On the other hand, for the samples whose coverages are above about 40%, the adsorbed amount was about 65% of theoretical monolayer capacity in spite of high relative pressure at about P/P0=1. Therefore, such a continuous two-dimensional water layer is not formed due to the steric hindrance of the TMS, and multilayer adsorption cannot occur in this case. The surface property is estimated to be hydrophobic. (5) The results of preferential dispersion tests on macroscopic wettability were in agreement with the results of the water vapor affinity of microscopic wettability.

Adsorption of nitrogen and water vapour by activated Kevlar ® chars

Fibrous activated carbons were prepared from Kevlar ® (i.e. poly ( p-phenylene terephthalamide), in the form of a commercially available woven textile. The cloth was carbonised in nitrogen and activated in either steam or carbon dioxide to varying burn-offs at 1123 K. The resultant activated chars were characterised by nitrogen adsorption, water sorption, and elemental analysis. It was found that significant differences existed between the chars activated in steam and carbon dioxide. Kevlar ® chars were found to have a greater affinity for water vapour than comparable rayon chars. The pore volume developed in Kevlar ® chars tended towards a maximum value as the burn-off increased.

The Use of Textile Yarns in Separation Processes

A new method has been developed for preparing chromatography columns quickly, uniformly, and with high reproduci bility, using textile yarns as the solid adsorbent. Gas-chromatography experiments using columns packed in this way have revealed that rayon yarns have a high affinity for water vapor but allow other species, even those quite similar to water in size and chemistry, to pass through essentially unretarded. The degree of water retardation by rayon yam- filled columns has been found to depend on a number of controllable factors: charge volume and frequency of injection, column pressure and temperature, and yarn packing density. To demonstrate the usefulness of the rayon-water specificity for removing water from mixtures, two novel devices have been built that are capable of producing dry ethanol from aqueous mixtures on a laboratory scale at modest energy cost. One of these designs, taking advantage of the high tensile strength of yarn, makes use of a moving yarn loop to achieve almost continuous separation and a high yield of ethanol. Even if such processes do not turn out to be economically practicable for large-scale ethanol production, the concept of gas or liquid chromatography using bundles of yarns with suitable chemical properties should find application in many practical separation problems.

Water Vapor Affinity of Potassium Bromide Coated with Potassium Oleate

Abstract The amounts of adsorbed water and the isosteric heats for water vapor adsorption on fine crystals of KBr treated with various amounts of potassium oleate (KOI) were measured. In the adsorption isotherm of untreated KBr, a slight stepped rise of the amount adsorbed was observed, and this step is considered to be due to the two-dimensional condensation of water molecules adsorbed on the uniform surfaces of KBr particles. The monolayer capacity, determined from the adsorption isotherm of KBr by the point B method, agreed with the value calculated according to an adsorptive structure based on the two assumptions that all the surfaces of the KBr particles consist of (100) planes and that one water molecule is adsorbed per regularly distributed Br− site. A small amount of pre-adsorbed KOI was recognized to prevent the water vapor adsorption on KBr, and conversely, this effect disappeared with increasing KOI content while the hygroscopicity of the sample increased markedly. This abnormal increase in the adsorbed amount suggests that the adsorbed water molecules penetrate into the multilayer films of KOI on the KBr.

Sorption of water, carbon dioxide and nitrogen by sol—gel thorium oxide

Sol gel thoria is an agglomerate of microcrystallites held together in a semirigid matrix. A layer of sorbed water bridges the intercrystalline contacts. Prolonged evacuation is required to remove this sorbed layer. Prizing penetration can occur by again introducing a high relative pressure of water vapor. Stringent outgassing (<500°C) removes the chemisorbed species to permits stronger intercrystalline bonding. The semirigid matrix network yields to the capillary forces of water when multiplex layers are sorbed in the intercrystalline network at 22°C, whereas nitrogen (−196°C) condenses in the interconnected cavities or capillaries of fixed geometry. These crystalline surfaces chemisorb water and/or carbon dioxide to the exclusion of nitrogen due to the close proximity of adjacent surfaces. High temperature studies show that the surfaces in these intracrystalline voids have a tenacious affinity for water vapor. Considerable water chemisorption prevails even at temperatures in excess of 500°C in vacuum. The pore structure dictates the amount of supercritical physical sorption. Almost all of the sorption capacity is in the porous voids surrounding the crystallites in the matrix. The size of these voids range upward from the molecular micropores to the large capillary range. Intraparticulate sintering is nearly complete at 1000°C with adsorption thence limited to the nonporous exterior of the particle.

Some properties of molybdenite cleavage surfaces

Low energy electron diffraction, Auger electron spectroscopy and photoemission studies have been carried out on surfaces of molybdenite prepared by cleavage. Surfaces cleaved in ultra high vacuum are extremely inert. There is some evidence that surfaces containing adsorbed oxygen have a weak affinity for water vapour and the significance of the result for some of the mechanical properties of MoS2 is discussed. Low energy electron diffraction measurements are consistent with a surface structure not differing greatly from that of the bulk, and the energy analysis of back scattered electrons confirms the existence of two valence bands in MoS2.

The Graft Copolymerization of a Vinyl Monomer Containing a Glucose Residue onto Polypropylene Fiber

Abstract The graft copolymerization of 3-O-methacryloyl 1,2; 5,6-diisopropylidene-α-d-glucofuranose (MDG) onto polypropylene fibers was carried out by the γ-ray pre-irradiation technique in the presence of oxygen. The isopropylidene groups of the glucose residue grafted on the copolymer were removed by hydrolysis in aqueous formic acid, and the hydroxyl and hemiacetal groups were regenerated. The deacetonated fibers exhibited a considerable affinity for water vapor and could be dyed with a reactive dye.

A study of the structure of milk crumb

AbstractAn indication of the structure of milk crumb has been obtained by studying its water sorption isotherm together with those of its components.During the vacuum drying of a sucrose‐milk mixture, a proportion of a material is formed with a greater affinity for water vapour. There is no evidence of complex formation between the other ingredients of milk crumb.A preliminary examination of the mixture containing the sucrose‐milk complex was made. There was no evidence of any effect on the flavour or the viscosity of milk chocolate containing such material.It is deduced that there is no interaction involving hydrophilic groups between milk and chocolate liquor during milk crumb manufacture.