Water Vapor Sorption Experiments Research Articles

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

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

Hollow Filaments from Coaxial Dry-Jet Wet Spinning of a Cellulose Solution in an Ionic Liquid: Wet-Strength and Water Interactions.

Hollow tubing and tubular filaments are highly relevant to membrane technologies, vascular tissue engineering, and others. In this context, we introduce hollow filaments (HF) produced through coaxial dry-jet wet spinning of cellulose dissolved in an ionic liquid ([emim][OAc]). The HF, developed upon regeneration in water (23 °C), displays superior mechanical performance (168 MPa stiffness and 60% stretchability) compared to biobased counterparts, such as those based on collagen. The results are rationalized by the effects of crystallinity, polymer orientation, and other factors associated with rheology, thermal stability, and dynamic vapor sorption. The tensile strength and strain of the HF (dry and wet) are enhanced by drying and wetting cycles (water vapor sorption and desorption experiments). Overall, we unveil the role of water molecules in the wet performance of HF produced by cellulose regeneration from [emim][OAc], which offers a basis for selecting suitable applications.

A modified Guggenheim-Anderson-Boer model for analyzing water sorption in coal

The presence of water can alter the mechanical properties of coal, which may not only cause roof falls during the coal mining process but also affect the hydraulic fracturing of coalbed methane (CBM) reservoirs. The nature of water adsorption properties in unconventional reservoir rocks has been the subject of several recent papers. However, the adsorption properties and adsorption mechanism of water in coal have not been thoroughly investigated. In this study, we carried out water vapor sorption experiments on four coal samples of different maturities. We found no linear relationship between maturity and water adsorption capacity. Furthermore, we proposed that the water adsorption mechanism in coal can be divided into two types: attached to oxygen functional groups and pore filling, which occur in hydrophilic pores and hydrophobic pores, respectively. Based on the above hypothesis, a modified Guggenheim-Anderson-Boer model was proposed to interpret water adsorption isotherms. It was concluded that the differences in the water adsorption characteristics of different coals under high humidity conditions were caused by the pore volume and the proportion of hydrophilic pores. We further analyzed the influence mechanism of water adsorption on methane adsorption under high relative humidity conditions. We found that the influence of water adsorption on methane adsorption in coal can be attributed to the water adsorption amount and proportion of hydrophilic pores.

Materials on Plant Leaf Surfaces Are Deliquescent in a Variety of Environments.

Materials on plant leaf surfaces that attract water impact penetration of foliar-applied agrochemicals, foliar water uptake, gas exchange, and stomatal density. Few studies are available on the nature of these substances, and we quantify the hygroscopicity of these materials. Water vapor sorption experiments on twelve leaf washes of sample leaves were conducted and analyzed with inductively coupled plasma-optical emission spectroscopy (ICP-OES) and X-ray diffraction. All leaf surface materials studied were hygroscopic. Oils were found on the surface of the Eucalyptus studied. For mangroves that excrete salt to the leaf surfaces, significant sorption occurred at high humidity of a total of 316 mg (~0.3 ml) over 6–10 leaves and fitted a Guggenheim, Anderson, and de Böer sorption isotherm. Materials on the plant leaf surface can deliquesce and form an aqueous solution in a variety of environments where plants grow, including glasshouses and by the ocean, which is an important factor when considering plant-atmosphere relations.

New Insight into Sorption Cycling Stability of Three Al-Based MOF Materials in Water Vapour.

Three porous aluminium benzene-1,3,5-tricarboxylates MIL-96(Al), MIL-100(Al) and MIL-110(Al) materials were studied for their hydrothermal stability. The 40-cycles water vapour sorption experiments for the three samples were performed by varying the temperature between 40 and 140 °C at 75% relative humidity to simulate working conditions for materials used in water sorption-based low-T heat storage and reallocation applications. The materials were characterized by powder X-ray diffraction, N2 physisorption, and Nuclear Magnetic Resonance and Infrared spectroscopies before and after the cycling tests. The results showed that the structure of MIL-110(Al) lost its crystallinity and porosity under the tested conditions, while MIL-96(Al) and MIL-100(Al) exhibited excellent hydrothermal stability. The selection of structures, which comprise the same type of metal and ligand, enabled us to attribute the differences in stability primarily to the known variances in secondary building units and the shielding of potential water coordination sites due to the differences in pore accessibility for water molecules. Additionally, our results revealed that water adsorption and desorption at tested conditions (T, RH) is very slow for all three materials, being most pronounced for the MIL-100(Al) structure.

Water vapour sorption and moisture transport in and across fibre direction of wood

Water vapour sorption experiments are frequently used to characterise the absorption and desorption of water in wood. To evaluate whether water vapour transport—compared to sorption and sorption related processes—can be neglected in small wood samples, this study investigates the sorption kinetics of Norway spruce (Picea abies) samples with different lengths of transport pathways in and across fibre direction. Water vapour sorption experiments were performed under identical climatic conditions at ambient air pressure and ambient standard temperature. Along the whole tested range of relative humidity sample thickness was shown to have an impact on the sorption kinetics. At low relative humidity, the initial uptake and release of water was considerably influenced by the diffusion of water vapour through the lumen-pit-ray system. Differences between the sorption kinetics for samples in and across fibre direction were thus considerable. With increasing moisture content, the initial uptake and release of water increased for samples across fibre direction, while it decreased for samples in fibre direction. Moisture transport across fibre direction thus seems to be increasing and cell wall processes seem to be more relevant. At high relative humidity, differences between the sorption kinetics for samples in and across fibre direction started to disappear while the impact of sample thickness was still considerable. Therefore, an additional or modified process, which depends on the number of sorption sites but not on the anatomical orientation must be considered at an increased moisture content of wood.

Water sorption and transport in Silurian shales

We have studied the transport of water in shales through gravimetric water vapour sorption experiments. Kinetic data have been evaluated and several kinetic models have been compared, with emphasis on time-dependent diffusivity models. The effective diffusivities as a function of relative pressure show an initial increase corresponding to the sorption to primary adsorption centres, followed by water cluster formation. The final decrease in effective diffusivity is connected with flattening of the pore-mouth meniscus. Introducing the flow rate kinetic parameter enables samples with different amounts of adsorbed water to be compared, showing that the highest value of the flow rate kinetic parameter is connected with the sample with largest surface area and the greatest micropore volume.

Sorption and diffusion properties of untreated and thermally modified beech wood dust

Dynamic water vapor sorption experiments were carried out using beech wood dust (from untreated and thermally modified wood) of two-particle sizes, (< 25 and 80–250 µm), obtained from abrasive sanding. Sorption isotherms were parameterized with the GAB and GDW models. Dust from thermally modified wood had significantly lower equilibrium moisture content compared to dust from untreated material, due to the reduction in primary sorption sites in treated material. The observed changes were quantified by the coefficients of the GAB and GDW models. Thermal modification and size of wood dust particles had no influence on binding energy of water molecules being linked to the secondary sorption sites. Water diffusivity decreased significantly with increasing moisture content, but only for monolayer sorption. For higher moisture content values, water diffusivity was practically independent of moisture content. These results were found for untreated and thermally modified material as well as for both dust size fractions. The influence of thermal modification on water diffusivity was unclear, which is attributed to the diffusion model, which represents dust particles as spheres and assumes instant hygroscopic equilibrium. Overall, this study indicates that the effectiveness of filtration processes likely depends strongly on sorption and diffusion properties of wood dust only at low moisture contents within the hygroscopic range.

The Study of Bound Water Status and Pore Size Distribution of Chinese Fir and Poplar Cell Wall by Low-Field NMR

With the increasing shortage of timber resources and the advancement of environmental protection projects, many artificial fast-growing forests are planted and used as raw materials in China. There are significant differences in the properties of natural forest wood and artificial fast-growing forest wood, and the properties of wood mainly depend on the change in the status of bound water in the cell wall. In this study, the fiber saturation point (FSP) and pore size distributions within the cell wall of six species of fast-growing forest wood were studied by low-temperature nuclear magnetic resonance (NMR) technology. The effects of species, growth rings, and extractives on the FSP and pore structure were analyzed. The water vapor sorption experiments were performed, and the adsorption isotherms of the samples were fitted through the Guggenheim-Anderson-de Boer (GAB) equation. According to the least-square regression of the adsorption isotherms and combined with the low-temperature NMR experiments, the content and proportion of the different types of bound water were analyzed. The results showed that the average FSP of each Chinese fir was about 40% and that of each poplar was about 35%. There is about a 10% difference between the FSP measured by NMR technology and the adsorption bound water content obtained by adsorption isothermal. The pore size distribution results show that in all samples, the proportion of pores larger than 10.5 nm is very low, about 10%; the proportion of 1.92-10.5 nm pores is about 30%; and the proportion of pores smaller than 1.92nm is more than 50%. This work will be helpful to the study of the wood moisture status and provide reference data for wood modification.

Influence of Environmental Factors on the Swelling Capacities of Superabsorbent Polymers Used in Concrete.

Superabsorbent polymers (SAP) are of major interest as materials to control the cement hydration process. The swelling behavior of the SAPs significantly influences the performance of the resulting concrete by slowly releasing polymer-bound water in order to maintain a consistent w/c value. A round-robin test conducted by the RILEM Technical Committee 260-RSC showed that the same batch of polymer can lead to large deviations in concrete performance and this was assumed to originate in different storage conditions of the SAP. In this contribution the change in the performance of two SAPs, a crosslinked poly(acrylate) and a crosslinked poly(acrylate-co-acrylamide), was assessed after ageing in standard climate, at 50 °C, and under UV irradiation. During storage in standard climate or 50 °C, ageing led to dehydration of the SAP, and this subsequently led to a higher water uptake during swelling. By contrast, UV irradiation reduced the water uptake, most likely as a result of photo-crosslinking. Dynamic water vapor sorption experiments indicated a strong dependence of the water uptake on both the ambient humidity and the temperature. As a result, cement mixtures containing SAP must be calculated on the dry mass of the SAP rather than the actual weight on site. A standard procedure of how to pack and handle SAP to be used in concrete is also provided.

The impact of wheat (Triticum aestivum L.) bran on wheat starch gelatinization: A differential scanning calorimetry study

The effect of wheat bran on starch gelatinization temperature was investigated. Dynamic water vapour sorption and water retention capacity experiments showed that bran bound up to 3 times more water than starch. However, examining starch gelatinization in starch-bran-water mixtures with differential scanning calorimetry showed that the effect of substituting starch by bran differed from that of moving into a regime of limiting water. Modelling the effect of the mixture composition on starch gelatinization behavior indicated that the onset (To) and peak (Tp) gelatinization temperatures were positively impacted by the bran concentration in water. The conclusion temperature (Tc) was negatively affected by the water content. Fractionation experiments demonstrated that the increased To and Tp were mainly caused by the extractable wheat bran components, such as potassium and phosphorus, which decrease the plasticization capacity of the solvent. The mechanism behind our observations was explained with the side-chain liquid-crystalline polymeric model for starch.

The Relevance of Water Vapour Transport for Water Vapour Sorption Experiments on Small Wooden Samples

To characterise the sorption behaviour of wood or other hygroscopic materials with the use of water vapour sorption experiments, an accurate understanding of water vapour transport both to and through the sample material is necessary. Within the last decades, various modelling approaches on the sorption kinetics were developed, but there seems to be no general agreement on the relevance of water vapour transport. Using small amounts of grained wood, this study aims to estimate the influence of water vapour transport in sorption experiments on small sample sizes. A theoretical analysis based on a diffusion equation including a simplified sink/source term was carried out and compared with corresponding experiments. Nonlinear isotherm and temperature were shown to have a major impact on the effective diffusion of water vapour, whereas step size in humidity seems to mainly influence processes within the cell wall (e.g. relaxation and reorganisation of microstructure). Considering the paths of stagnant air above sample surface, the anomalous behaviour for a variation in sample thickness of grained wood can be explained. In conclusion, water vapour transport appreciably influences the sorption kinetics of small sample sizes and has to be considered in the modelling and interpretation of water vapour sorption experiments.

Novel Dual-Action Plant Fertilizer and Urease Inhibitor: Urea·Catechol Cocrystal. Characterization and Environmental Reactivity

The mechanochemical reaction of urea and catechol affords the quantitative formation of a 1:1 urea·catechol (URCAT) cocrystal that can act simultaneously as a urease inhibitor and as a soil fertilizer. The novel compound has been characterized using solid-state methods, and its environmental activity has been assessed using the inhibition of Canavalia ensiformis urease and water vapor sorption experiments at room temperature. The urea molecules within the cocrystal were organized in hydrogen-bonded dimers bridged by two catechol molecules, with the OH groups interacting via hydrogen bonds with the urea carbonyl groups. The inhibition of jack bean urease enzyme by URCAT led to the complete loss of urease activity after a 20 min incubation period. A large difference of water vapor adsorption was observed between urea and URCAT, with the latter adsorbing 3.5 times less water than urea. Our results suggested that cocrystal engineering strategies can be successfully applied to tackle sustainability problems at the food–energy–water nexus.

Gas and water vapor sorption and diffusion in a triptycene-based polybenzoxazole: effect of temperature and pressure and predicting of mixed gas sorption

Fundamental gas transport properties of a novel thermally rearranged polymer (TPBO) prepared from a co-polyimide precursor with controlled triptycene molar content are discussed. He, N2, CH4, CO2 and C2H6 sorption isotherms were experimentally measured in the range 5–50 °C and up to 32 atm and analyzed with the dual mode model. Water vapor sorption and diffusion at 35 °C was also investigated. TPBO exhibits larger gas and vapor sorption capacity relative to previously reported thermally rearranged polymers. The dual mode parameters retrieved from the analysis of single gas sorption isotherms were used to estimate a priori the sorption behavior in mixed gas conditions. The predicted mixed gas solubility-selectivity is significantly higher than ideal solubility-selectivity and it is comparable to that exhibited by other glassy polymers. Gas and vapor diffusion coefficients in TPBO were estimated from the solution-diffusion model and from sorption kinetics, respectively, and are larger than in previously reported thermally rearranged polymers. The dual sorption-mobility model indicates that the polymer rigidity significantly affects gas diffusion coefficients. CO2/CH4 diffusivity-selectivity was larger than in other glassy polymers, pointing out the superior size-sieving ability provided by triptycene units. Water vapor sorption experiments revealed that TPBO is more hydrophilic relative to previously reported thermally rearranged polymers: theoretical models were exploited to speculate water vapor distribution in the polymer matrix.

Comparison of water vapour transmission rates of monolayer films determined by water vapour sorption and permeation experiments

Abstract The water vapour transmission rate (WVTR) of packaging materials and edible coatings is one of their critical parameters for the shelf life of many food products. The water vapour transmission rates of flat bodies such as films are determined by permeation measurements which are a steady-state method. Another method is based on water vapour sorption measurements which is a non-steady-state method. It can be used only for mono-material flat bodies. It allows using smaller sample areas compared to permeation measurements. However, not much is known about how well both methods correlate with each other. Therefore, the aim of this study was to compare the WVTR results of different materials determined by both methods. The results of both methods differed by up to factor of three, measured at identical samples. In a few cases the difference was up to factor five. The exact reasons for these differences are unknown. Nonetheless, the water vapour sorption method is a suitable method to determine the magnitue of order of the water vapour transmission rate but not its exact value.

Analysis on the influence of grain size and grain layer thickness on the sorption kinetics of grained wood at low relative humidity with the use of water vapour sorption experiments

Water vapour sorption (WVS) experiments on grained Norway spruce wood (Picea abies) at low relative humidities were carried out to test the influence of grain size and grain layer thickness on the sorption kinetics. Samples were compared under identical climatic conditions (i.e. humidity and temperature), and the kinetic behaviour was analysed with selected modelling approaches existing in the literature. Both, grain size and grain layer thickness influenced the initial kinetics, with the latter showing a larger impact. This confirms the notion of a transport limited initial mass increase with diffusion of water vapour/H2O-molecules to the sorption sites being a possible candidate. In contrast, the long-time behaviour was only slightly affected, supporting the concept of a relaxation and reorganisation dominated long-time behaviour. An analysis on the WVS kinetics of cut and grained wood with comparable sample material has further shown a very similar behaviour, which allows to draw some conclusions for cut wood. Regarding the modelling approaches, the parallel exponential kinetics model provided the best fitting results as the predictive models could not properly capture the split-up for a variation in grain size or grain layer thickness.

Effect of humidity and nanocellulose content on Polyvinylamine-nanocellulose hybrid membranes for CO2 capture

In order to address the need for more efficient technologies for carbon capture applications, a novel type of nanocellulose based hybrid membrane has been successfully prepared by blending the commercial Polyvinylamine solution Lupamin® 9095 (BASF) with Nano Fibrillated Cellulose (NFC) to improve its mechanical and separation capabilities. Self-standing films with different nanocellulose loading (from 30 to 70wt%) have been prepared and characterized at 35°C through water vapor sorption experiments and humid gas permeation tests.As expected, membrane permeability consistently increased with increasing water vapor and a higher presence of Lupamin in the film resulted in an increment of both gas permeability and selectivity. In particular blends with a NFC content of 70wt% Lupamin reached an ideal selectivity of 135 for the separation of CO2/CH4 and 218 for CO2/N2, at 60 RH%, while the maximum permeability in the order of 187 Barrer was instead reached at 80% RH.Water vapor solubility was also measured and modeled through Park Model to correlate the gas separation properties with the effective content of water present in the membrane matrix. As expected, a higher content of the hydrophilic polymer resulted in a larger water uptake, which at medium to high humidity appeared to trigger a water clustering phenomenon in the matrix. This fact was accompanied by a substantial relaxation of the polymer network, causing a marked reduction of selectivity, which dropped, at the highest RH investigated, to values in the order of 30 and 80 towards CH4 and N2 respectively. Despite this loss in performance, most materials tested still showed very interesting properties, well above Robeson's 2008 Upper Bound, making them an interesting alternative for traditional gas separation processes.

Effect of Sodium Sulfite, Sodium Dodecyl Sulfate, and Urea on the Molecular Interactions and Properties of Whey Protein Isolate-Based Films.

Whey protein coatings and cast films are promising for use as food packaging materials. Ongoing research is endeavoring to reduce their permeability. The intention of this study was to evaluate the effect of the reactive additives sodium sulfite, sodium dodecyl sulfate (SDS), and urea on the oxygen barrier, water vapor barrier, and protein solubility of whey protein cast films. The concentration of the reactive additives was 1 to 20 wt.-%. Dried whey protein cast films were used as substrate materials. The water vapor transmission rate, the oxygen permeability, and the protein solubility were measured. Effective diffusion coefficients and effective sorption coefficients were calculated from the results of the water vapor sorption experiments. The presence of sodium sulfite resulted in an increased number of hydrophobic interactions and hydrogen bonds and a slightly decreased number of disulfide bonds. The oxygen permeability decreased from 68 to 46 cm3 (STP/standard temperature and pressure) 100 μm (m2 d bar)−1 for 1 wt.-% SDS in the whey protein cast film. The water vapor transmission rate decreased from 165 to 44 g 100 μm (m2 d)−1 measured at 50 to 0% r. h. for 20 wt.-% SDS in the whey protein cast film. The reduction in the water vapor transmission rate correlated with the lower effective diffusion coefficient.

Nanocellulose-based membranes for CO2 capture

A new type of hydrophilic polymeric membrane based on microfibrillated cellulose (MFC) has been investigated to determine its potential in the field of gas separation, with special reference to carbon capture and natural gas sweetening. In particular, pure MFC films and MFC/Lupamin® (a commercial polyvinylamine produced by BASF) nanocomposite membrane have been synthesized and characterized. The effect of relative humidity on gas permeability was considered and independent water vapor sorption experiments were also carried out in order to correlate the permeation results to the actual water content in the materials. The experimental results showed that very good CO2/N2 and CO2/CH4 selectivity (in the order of 500 and 350 respectively) could be reached by using pure MFC films, which however showed limited CO2 permeability, never exceeding 25Barrer, even at the highest relative humidity investigated. To increase the transmembrane flux, a hydrophilic polyvinylamine (Lupamin®) has been added to the pure MFC: the addition caused a marked increase in permeability of up to one order of magnitude but decreased the selectivity to about the same extent, thus decreasing the overall membrane performance. The reason of such behavior seems to be related to the amount of water absorbed by the membrane as the MFC/Lupamin nanocomposite resulted to be highly swollen by water vapor.Nonetheless, both the investigated materials showed separation performances that are above the 2008 Robeson's upper bound for CO2/N2 and CO2/CH4 systems, disclosing an attractive potential for the production of advanced gas separation membranes.

Analysis of the CO2–H2O Chemisorption in Lithium Silicates at Low Temperatures (30–80 °C)

Li8SiO6 and Li4SiO4 were synthesized by a solid-state reaction. Then, dynamic and isothermal thermogravimetric water vapor sorption experiments were performed using two carrier gases: N2 and CO2. Initially, the Li8SiO6–H2O–(N2 or CO2) systems were analyzed. It was evidenced that Li8SiO6 can trap water physically and chemically, producing Li–OH superficial species. When CO2 was used as the carrier gas, Li8SiO6 continued chemisorbing H2O but CO2 was trapped as well, forming Li2CO3 and Li4SiO4 as secondary phases. On the basis of these results, the Li4SiO4–H2O–CO2 system was also analyzed. The experimental results and different theoretical thermodynamic calculations confirmed that Li8SiO6 can chemisorb 2 moles of CO2 per mole of ceramic at a low temperature range (30–80 °C). Finally, different CO2 chemisorption kinetic experiments were performed to analyze and quantify the trapped CO2.