Water Vapor Adsorption Research Articles

Porous and conductive cellulose nanofiber/carbon nanotube foam as a humidity sensor with high sensitivity

In this study, we developed a humidity sensor with high sensitivity based on cellulose nanofiber/carbon nanotube (CNF/CNT) hybrid foam. The porous structure of the foam not only provides more contact interface for water molecules adsorption, but also tunes the conductivity of the CCF closed to the point where the sensor is most sensitive to the change in humidity. With this porous structural design, the obtained foam sensor shows a high humidity sensitivity of 87.3% (ΔI/I0, and the response limit is 100%), excellent linearity (R2 = 0.996) within the humidity range from 29 to 95% relative humidity (RH), and good long-time stability (more than two months). Furthermore, the water vapor adsorption behavior of the CNF/CNT foam sensor can be well described by the pseudo-first-order kinetic model. Finally, a simple humidity measuring device based on the CNF/CNT foam is presented, which can find good applications for human breath and fingertip humidity monitoring.

Exploring an electric-aid ozone decomposition mode to enhance water resistance over manganese oxide monolith catalyst under high humidity

In this work, a facile, green, and effective reaction mode of electric-aid ozone decomposition (EAOD) was developed over a manganese-based monolith catalyst for eliminating ozone under high humidity. The catalyst was prepared by directly growing α-MnO2 nanorods on Al honeycomb substrate (MnO2/Al) via a simple hydrothermal process, and the EAOD mode was performed just by connecting the MnO2/Al monolith catalyst with a DC power supply during ozone decomposition reaction. In the EAOD mode reaction, the MnO2/Al catalyst exhibited a stable ozone conversion efficiency of over 82 % and excellent stability over 720 min under a relative humidity of 90%, well beyond the performance of catalyst in the conventional ozone decomposition reaction without the help of electric aid. Here, the water evaporation by the external electric field generated from the EAOD mode hinders the competitive adsorption of water vapor on the active sites of MnO2/Al catalyst, consequently enhances its water resistance. Moreover, increasing input electric current of the DC power supply could further improve the catalytic activity and stability of the monolith catalyst for ozone decomposition in EAOD mode reaction.

Formation of Adsorbent Particles Layer on Aluminum and Its Water Vapor Adsorption Properties

Formation of Adsorbent Particles Layer on Aluminum and Its Water Vapor Adsorption Properties

Experimental investigation of dehumidification and regeneration of zeolite coated energy exchanger

Zeolite desiccant particles are well known for their strong affinity to adsorb water vapor molecules; however, they require significant regeneration energy to be created. This paper presents an experimental study of the adsorption and regeneration processes of a monolayer zeolite for indoor dehumidification to the 13X zeolite beads with a 4 × 8 mesh bead size and a pore opening 10 A⁰ were used as this monolayer. An experimental investigation was conducted to determine the effects of the relative humidity, temperature, and air flow rate on the adsorption and regeneration processes. The results show the effectiveness of the monolayer coating method and the relative humidity significantly affects the adsorption process, and that the airflow rate surrounding and through the zeolite beads increases the adsorption and desorption of the water vapor molecules. In the absence of the meniscus radius formation due to the monolayer arrangement prevents external condensation. With an airflow rate of Re = 1773, the full adsorption process at a relative humidity of 99% was obtained within 37 min; meanwhile, the regeneration process proceeded at 100 °C within 66 min. The adsorption time was reduced by 27% and 43% as the Reynold number increases to 2586 and 3325, respectively. Likewise, the effectiveness of the regeneration time is decreased by 0.07% and 14% within the same Reynold number increases. Results obtained from this research can be used to guide the future development of polymer-coated energy exchangers.

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.

Discrete Arsonate-Grafted Inverted-Keggin 12-Molybdate Ion [Mo12O32(OH)2(4-N3C2H2-C6H4AsO3)4]2- and Formation of a Copper(II)-Mediated Metal-Organic Framework.

The discrete inverted-Keggin ion [Mo12O32(OH)2(4-N3C2H2-C6H4AsO3)4]2- (1) has been prepared in an aqueous acidic (pH 0.8) medium by the reaction of MoO3 with the (4-triazolylphenyl)arsonic acid 4-N3C2H2-C6H4AsO3H2 under hydrothermal conditions and was isolated as a sodium salt in 21% yield. The exact same reaction in the presence of Cu2+ ions resulted in the neutral metal-organic framework (MOF) Cu2[Mo12O34(4-N3C2H2-C6H4AsO3)4] (Cu-1) in 68% yield. The inverted-Keggin ion 1 comprises a metal-oxo core, which is capped by four organoarsonate groups, and in Cu-1, individual polyanions are linked in the solid state by coordination of the Cu2+ ions with the triazolyl groups. The discrete ion 1 was characterized by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and atomic absorption (AA) spectroscopy, as well as thermogravimetric analysis (TGA), and the POM-MOF Cu-1 was characterized by single-crystal and powder XRD, FT-IR, TGA, and gas sorption. Cu-1 has channels with a diameter of around ∼0.9 nm and exhibits a water-vapor adsorption capacity of 89.7 cm3 g-1 (p/p0 = 0.95).

Scaling analysis of large pressure jump driven adsorption of water vapour in columnar porous silica gel bed

Adsorption process can be initiated either by Large Temperature Jump (LTJ) or Large Pressure Jump (LPJ). In this study, a theoretical analysis of coupled heat and mass transfer process during LPJ driven adsorption has been carried out using scaling principles of the governing conservation equations. A columnar domain consisting of silica gel (adsorbent) and water vapour (adsorbate) pair has been considered with heat and mass transfer directions orthogonal to each other. This domain is subjected to a sudden LPJ with isothermal boundary condition. Adsorption process has been divided into three phases for scaling analysis viz. i) pressure equalization ii) adsorption accompanied by heat generation and iii) heat removal phase. From order of magnitude arguments, various important physical scales for each phase have been derived and validated with a 2-dimensional computational fluid dynamics (CFD) study. The temperature rise in the adsorber bed is found to be 14.5 K, and the time scale to attain peak temperature is ~100 s from the initiation of adsorption. This justifies the short cycle time deployed in practical PSA systems to operate near isothermal condition. The outcomes of this investigation serve as a fundamental insight into LPJ driven adsorption process and help identify the various factors which practically effect this mode of adsorption.

Dynamic model for the simultaneous adsorption of water vapor and methane on shales

Water is almost ubiquitous in shale gas reservoirs. To analyze simultaneous water vapor and methane adsorption in shales, a dynamic model with a time-dependent boundary and diffusivity and a noninstantaneous adsorption mechanism was proposed. The analytical solution of the model was obtained via integral transformation method. The model was applied to match the dynamic data of simultaneous CH4–H2O adsorption. The results suggest that the strength for gas adsorption to shale is characterized by adsorption rate coefficient and desorption rate coefficient, where the adsorption strength of shale to water vapor is stronger than that to methane, and the conversion rate from water vapor to adsorbed water on adsorption sites is larger. The methane and water vapor diffusion coefficients first increase to a maximum and then decrease with time. The maximum methane diffusion coefficient ranges from 5.83 × 10−13–1.08 × 10−11 m2/s; the maximum water vapor diffusion coefficient ranges from 2.06 × 10−19–4.53 × 10−13 m2/s. The methane diffusivity and its variation rate are larger than those of water vapor. The methane and water vapor diffusion coefficients first increase with the density of free gases in pores and then decrease in the late period of the adsorption process. Water vapor reduces the adsorption strength of shale to methane and free methane-to-adsorbed methane conversion rate on adsorption sites. The methane diffusion coefficient in dry shale increases with time, and its growth rate reaches zero at adsorption equilibrium, which ranges from 6.60 × 10−14–4.82 × 10−11 m2/s; the methane diffusivity increases exponentially with the methane adsorption amount and free methane density in pores.

Study on activated carbon/silica gel/lithium chloride composite desiccant for solid dehumidification

An activated carbon/silica gel/lithium chloride composite desiccant (AC-SL) for air dehumidification is proposed. Lithium chloride and silica gel are impregnated into activated carbon pores to improve the density, thermal conductivity and water vapor adsorption capacity of AC-SL. Nitrogen isothermal adsorption lines, SEM images and Fourier Transform Infrared showed that impregnation significantly reduced AC-SL is specific surface area and pore parameters and increased the content and types of oxygen-containing functional groups on its surface. The sorption kinetics study shows that the equilibrium adsorption capacity of AC-SL is 6.8 times that of activated carbon. The Dubinine-Astakhov equation based on Polanyi potential theory is used for nonlinear fitting of the water vapor isotherms adsorption, and the correlation coefficients of the fitting equations are all above 0.98. When the relative humidity is 60%, the water vapor adsorption capacity of AC-SL reached 0.81 kg kg−1, 4.5 times that of pure activated carbon. The simulation results show that the AC-SL coated heat exchanger's dehumidification capacity is 3.13 kg h−1, which has a higher cost performance than other materials.

The effect of water vapor on methane adsorption in the nanopores of shale

Water plays an essential role in shale gas migration and adsorption, and most studies on the influence of water on shale gas adsorption refer only to moisture-equilibrated shales. To investigate the impact of water vapor on methane adsorption in shales, three experiments were conducted and compared: (1) pure methane adsorption onto dry shale (PMD), (2) pure methane adsorption onto moisture-equilibrated shale (PMMS), and (3) simultaneous adsorption of water vapor and methane (SAWM) onto shale. The experimental results reveal that the detrimental impact of water vapor on methane adsorption is inferior to that of preadsorbed water. Two mechanisms, water blocking and adsorption competition, are responsible for the reduction and difference in the methane adsorption capacity and adsorption rate between PMMS and SAWM. Compared to PMD, the methane adsorption capacity decreases by 81–96% in PMMS and by 20–49% in SAWM. Methane adsorption equilibrium is achieved the fastest in PMD. Before the equilibration degree reaches 95%, methane adsorption during SAWM progresses more rapidly, while the reverse occurs when the equilibration degree exceeds 95%. Water vapor can impact micropores more easily during the premoistening process, which obviously lowers methane adsorption. The adverse effect of water vapor on micro-to mesopores is inhibited by high methane partial pressure in SAWM. In PMMS, adsorbed water mainly occupies micropores (0.3–1.5 nm), and methane is adsorbed in pores larger than 1.5 nm. In SAWM, methane preferentially occupies micropores; the competition between methane and water vapor is mainly concentrated in mesopores (1.5–20 nm).

Metal@COFs Possess High Proton Conductivity with Mixed Conducting Mechanisms

The inherent porous structures and aligned functional units inside the skeleton of covalent organic frameworks (COFs) provide an extraordinary promise for post-modification and deservedly expand their application in the field of proton conduction. Herein, we tactfully introduced copper ions into a two-dimensional COF (TpTta) furnished with ample N,O-chelating sites by a post-modification strategy to achieve two copper(II)-modified products, namely, CuCl2@TpTta-3 and CuCl2@TpTta-10. Inspiringly, the two modified COFs demonstrated the higher conductivities of 1.77 × 10-3 and 8.81 × 10-3 S cm-1 under 100 °C and 98% relative humidity, respectively, among the previously reported COFs with higher σ values. In comparison to the pristine COFs, the σ values of CuCl2@TpTta-3 and CuCl2@TpTta-10 are boosted by 2 orders of magnitude. On the basis of structural analyses, nitrogen and water vapor adsorption tests, and proton conduction mechanism analysis, we deeply analyzed the reason why the conductivity of the modified COFs was significantly increased. To the best of our knowledge, it is the first time to employ the CuCl2-modified strategy to boost the conductivity of COFs, which offers a wise idea for the fabrication of highly conductive materials in the field of fuel cells.

Preparation and modulation of Cu-BTC-(n)Br/MCFs with water stability and its application for CO2 capture

In this study, a novel composite Cu-BTC-(n)Br/MCFs was successfully synthesized by solvothermal method. The composites were characterized by XRD, N2 adsorption and desorption, SEM, FT-IR, TG, and water vapor adsorption technologies. Meanwhile, the CO2 adsorption isotherms were obtained using the static adsorption instrument which could be well fitted by the Langmuir-Freundlich model. The Cu-BTC-0.05Br/MCFs exhibited a good CO2 adsorption capacity of 2.44 mmol/g which was basically maintained after five adsorption-desorption cycles. More importantly, the Cu-BTC-0.05Br/MCFs also showed remarkable adsorption effectivity that was an increase of 8.7% than the Cu-BTC/MCFs at 35 °C and 1 bar after water treatment. The Cu-BTC-(n)Br/MCFs were promising candidate materials for effectively CO2 capture in practical application.

Comparative evaluation of MIL-101(Cr)/calcium alginate composite beads as potential adsorbents for removing water vapor from air

Recently, MIL-101(Cr) as a porous coordination polymer is of great interestin water adsorption due to its water stability and excellent water uptake capacity. However, its microcrystalline nature puts limitations on its practical applications. Therefore, achieving an efficient method to produce the desired shaped forms while preserving the intrinsic properties of the powder has been a challenge. In this study, the MIL-101(Cr) powder material was produced in >300 g quantities with an overall yield of around 65% and an average SBET = 3101 m2 g−1 and it was shaped into spherical beads with mean size of 2.1 ± 0.2 mm by using sodium alginate and calcium chloride solution through an ionotropic gelation technique. The water vapor adsorption and the breakthrough behavior of prepared adsorbent were investigated in comparison with commercial adsorbents. In addition, hydrothermal stability, optimized regeneration temperature and mechanical strength of the adsorbent beads were examined. The results showed that at 25 °C and 1 bar the shaped adsorbent affording of water uptake of 1.1 g/g at 75% relative humidity, which is 290, 250 and 350 % more than activated alumina, 13X and 3A molecular sieves, respectively. Furthermore, it showed a breakthrough time as high as that for activated alumina and 3A molecular sieve. The complete regeneration was achieved at as low as 80 °C and the adsorbent showed stable performance after 20 consecutive water adsorption/desorption cycles. The outcome of this study suggests the high potential of the ionotropic gelation to shape MIL-101(Cr) powder material into bead form and use in water adsorption applications.

Pressure- and temperature-initiated adsorption of water vapour in a finned flat-tube adsorber

Adsorption heat transformation is an environmentally friendly and effective method of using low-temperature heat from renewable, industrial and domestic sources. The transformation can be initiated by changing either adsorptive pressure (pressure-initiated, PI) or adsorbent temperature (temperature-initiated, TI). This work aims to elucidate how the initiation pathway affects the dynamics of water adsorption for silicoaluminophosphate AQSOA-FAM-Z02 loaded inside a commercial finned flat-tube heat exchanger. The main findings of this study are as follows: (a) all kinetic curves can be represented as a superposition of fast and slow exponentials associated with the process rate limitation by vapour transfer or heat transfer, respectively; (b) at a short time (<150–200 s), the PI adsorption is faster than the TI one by a factor of 3; (c) at a long time (>100–150 s), the PI desorption is slower than the TI one. From the practical point of view, the revealed differences between the PI and TI dynamics could allow the specific power of adsorption heat transformers to be improved through a better organization of the working cycle.

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.

Experimental investigation into the permeability of water vapor in shales

The transport of water vapor in shale (mudrocks) plays an important role in many natural and engineering issues, such as the global water cycle and shale gas production. However, the permeability of water vapor in shale is not well understood. An experimental approach to investigate the water vapor permeability in shale is presented in this paper. Water vapor sorption was conducted under the dynamic relative humidity condition in which the vapor evaporation was generated from the liquid distilled water at different gas (helium) pressures. Three crushed samples of Carboniferous shale from the eastern Qaidam Basin, China, were obtained and tested. In the experiments, the adsorption process of water vapor into the crushed shale was observed, and the permeability of water vapor through shale was calculated with the data collected during the dynamic water vapor adsorption process. The results show that the permeability decreases with increasing water vapor adsorption. The relationship between permeability and water vapor adsorption amount fits an exponential equation well. The permeability at the equilibrium of water vapor adsorption is 3–4 orders of magnitude lower than that in the initial stage of water vapor adsorption. The decrease in pore size and resulting pore throat blockage cause this permeability reduction. The water film thickness and water saturation in the shale pores at adsorption equilibrium were estimated. The permeability reduction is closely related to the maximum water film thickness. The larger the range of pores blocked by the water film is, the more obvious the permeability reduction.

Modeling the effect of humidity and temperature on VOC removal efficiency in a multistage fluidized bed adsorber

The competitive adsorption of volatile organic compounds (VOCs) and water vapor onto beaded activated carbon (BAC) in a fluidized bed adsorber is developed in the form of a two-phase model using the Manes method. The Manes method uses as input single component adsorption isotherms described by the Langmuir model for adsorption of VOCs and the Qi-Hay-Rood (QHR) model for adsorption of water vapor. The effect of temperature is accounted for using the linear van’t Hoff relationship for Langmuir affinity coefficient. The effects of relative humidity (RH) and temperature in the simulations are validated using experimental data, with very good agreement observed (e.g. R2 = 0.98 comparing overall removal efficiencies). Humidity begins to have an effect on the adsorption of 1,2,4-trimethylbenzene (TMB) on BAC starting at 70% RH in the form of a reduction in overall removal efficiency due to fewer available adsorption sites. The overall removal efficiency decreases from 93.0% at 70% RH to 85.4% at 90% RH, and then plateaus with further increase in RH up to 100%. In dry air, temperature variation has a small effect on removal efficiency, showing a reduction in modeled overall removal efficiency from 93.0% to 90.2% when the adsorption temperature increases from 22 to 50 ˚C. On the other hand, at high RH values, temperature has a larger and positive effect on removal efficiency due to RH change. Increasing the temperature of a stream of humid air (RH = 95%) from 22 to 27 °C increases the TMB removal efficiency by 6.9% from 85.3% to 92.2%. Taking into account the effect of humidity and temperature, the model can be used to help optimize fluidized bed adsorber operations in industrial applications.

Hydrophobic shell structured NH2-MIL(Ti)-125@mesoporous carbon composite via confined growth strategy for ultra-high selective adsorption of toluene under highly humid environment

• NH 2 -MIL(Ti)-125 was confined grown into via ‘ship-in-the-bottle’ synthesis approach by Ti-clusters anchored OMC. • Hydrophobic shell (OMC) enhanced surface non-polar and humidity resistance on MIL(Ti)@OMC Ti. • MIL(Ti)@OMC Ti achieved interconnected micro-/mesoporous networks and accelerated mass transfer. • MIL(Ti)@OMC Ti showed high moisture-resistance and adsorption affinity for toluene at ultra-low pressure. • the mechanism of selective toluene adsorption and recycling performance were deeply investigated. Competitive adsorption of volatile organic compounds (VOCs) under high humidity is a critical but challenging issue in the applications of metal–organic frameworks (MOFs). In this work, hydrophobic-shell structured NH 2 -MIL(Ti)-125@mesoporous carbon composite was designed to enhance selective adsorption towards VOCs under humid conditions via confined growth strategy. Ti-clusters were first anchored into pores of ordered mesoporous carbon (OMC), and then confined grown into NH 2 -MIL(Ti)-125 via ‘ship-in-the-bottle’ approach. Hydrophobic shell of OMC concurrently protected the adsorption sites on NH 2 -MIL(Ti)-125 from H 2 O occupation and enhanced affinity towards non-polar toluene. Moreover, the resulting composited supplied abundant diffusion channels for toluene thereby accelerated the mass transfer though mesopores (OMC) and micropores (MOFs). As expected, the hydrophobic-shell NH 2 -MIL(Ti)-125@OMC composite efficiently enhanced hydrophobic property and toluene adsorption affinity. It obtained a dramatical increase in toluene adsorption capacity (3.86 mmol/g at 0.001 P / P 0 ) about 7.4 times of NH 2 -MIL(Ti)-125, and a 29% decrease in water vapor adsorption capacity (0.30 g/g at 1 mbar), which much superior than many reported expensive adsorbents. In addition, the composite induced more confined micropores to mesopores interconnected structure in MIL(Ti)@OMC Ti , and hence facilitated toluene diffusion. The toluene rate constant of pseudo-second-order adsorption ( k a ) on the MIL(Ti)@OMC Ti was up to 0.12 g/(mmol∙min), which was 1.2–2.0 times higher than those of the MIL(Ti) species. Moreover, breakthrough curve indicated that MIL(Ti)@OMC Ti showed 1.5 times of toluene working capacity with faster diffusivity at 80% RH compared to pure NH 2 -MIL(Ti)-125, while the latter exhibited much lower value of Q w / Q e than that of the former. This work provides a novel composite strategy for hydrophobic MOFs construction, and deeper understanding for VOCs/H 2 O competitive adsorption on MOFs composites in large scale applications.

Toluene and water vapor adsorption characteristics and selectivity on hydrophobic resin-based activated carbon

The competitive adsorption between volatile organic compounds (VOCs) and water vapor seriously decreases the adsorption capacity of adsorbents. In this paper, a series of hydrophobic spherical resorcinol-formaldehyde resin-based activated carbons (CRFs) were prepared and characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmet-Teller (BET) techniques. The adsorption equilibrium and selectivity of toluene and water vapor on CRFs were investigated systematically. Compared to other adsorbents, HCRF800 treated by hydrogen reduction exhibited the highest toluene uptake (8.64 mmol/g at 293 K) and the strongest hydrophobicity, which was much superior to commercial activated carbon. The results of isosteric heats showed that toluene on HCRF800 was higher than that of water vapor, indicating a stronger interaction between the adsorbent and toluene than water vapor. The adsorption selectivity of toluene/water vapor on CRFs was estimated by the Difference of Isosteric Heats (DIH) equation, and the results suggested that HCR800 possessed the highest selectivity, and the value was in the range of 9.5–52.3. Furthermore, HCRF800 also displayed good toluene uptake at different humidities and faster intra-particle diffusion behavior due to its lower content of surface oxygen groups. Temperature-programmed desorption experiments and Density Functional Theory calculations further revealed that surface oxygen groups had a negative effect on the selectivity of toluene/water, and the negative effect followed the order as O-CO > C-O > CO. Moreover, HCRF800 possessed excellent reversibility. These results demonstrated that HCRF800 would be a superior adsorbent for VOCs recycling from a humid atmosphere.

Water Vapor Adsorption Capacity Loss of Molecular Sieves 4A, 5A, and 13X Resulting from Methanol and Heptane Exposure.

Zeolite-based molecular sieves are applied in industrial dehydration units for their high water uptake capacities and extremely low equilibrium pressure of water vapor. During their operational life, they tend to lose their water vapor adsorption capacity slowly. To optimize the usage of molecular sieves in dryer units, it is vital to understand the mechanism(s) leading to deactivation. In this work, the capacity loss was studied by exposing LTA- and FAU-type zeolites to methanol and heptane vapors under relatively harsh conditions using repetitive adsorption/regeneration cycles. A simple microflow unit was designed and used for the deactivation experiments. The water vapor adsorption capacity of the resulting samples was measured using a gravimetric analyzer. In addition, they were characterized by classic XRD, 13C NMR, and TGA techniques. The crystallinity of fresh and spent zeolite XRD patterns was not drastically affected even after exposure to the contaminants. It was found that methanol easily gave rise to a severe loss of water vapor adsorption capacity, much more so than heptane. Water vapor uptake in the methanol exposed samples is ∼50% lower than that for the fresh zeolites. This is attributed to nonvolatile, residual hydrocarbons.