Ethanol Vapor Adsorption Research Articles

An investigation of the influence of nanofibers morphology on the performance of QCM-based ethanol vapor sensor utilizing polyvinylpyrrolidone nanofibers active layer

Quartz crystal microbalances (QCMs) coated by polyvinylpyrrolidone (PVP) nanofibers with controlled morphology have been made for ethanol vapor detection. We used electrospinning to deposit PVP nanofibers of different morphologies (spherical-beaded, spindle-beaded, and pure nanofiber) on a QCM surface to study the effect on sensor performance. BET characterization revealed that the spherical-beaded nanofiber had the highest BET-specific surface area than the other morphologies, which improves the QCM sensor sensitivity, limit of quantification (LOQ), limit of detection (LOD), and sensor response. QCM coated with spherical-beaded nanofiber showed improved sensitivity of 2.632 Hz/ppm, lower LOD and LOQ of 0.018 ppm and 0.061 ppm, and better response compared to those coated with spindle-beaded and pure nanofiber. Based on adsorption isotherm models, Freundlich adsorption isotherm was found to be the most suitable for describing ethanol vapor adsorption on the sensor. The high sensitivity of the sensor to ethanol vapor was attributed to hydrogen bonding interactions between the sensor and the ethanol molecules. This study shows that the QCM-based sensor performance can be improved by modifying the morphology of nanofibrous coating layer.

Thermal kinetics on adsorption heat transformation based on activated biocarbon and ethanol as working pairs

Cooling systems and refrigerators based on adsorption heat transformation processes (AHT) are a green alternative to compression cooling systems. Considering the increasing demand for human comfort, there is a crucial need for next-generation energy-efficient technologies, where the modeling and understanding of all parameters is a milestone. The viability and performance of the technology rely on the selected pair adsorbent/working fluid, but further from their pure thermodynamic performance, processing, and its derivates kinetic factors are depicted high relevant. In this work, ethanol adsorption kinetics on classic commercial adsorbents (activated carbon, AC) are predicted and further determined. The adsorptive phenomenon was investigated by means of computational simulation based on implemented Linear Driving Force (LDF) and the results were compared with experimental adsorption isotherms modeled by using Dubinin-Astakhov equation. The specific cooling effect (SCE) was studied by temperature monitoring during ethanol vapor adsorption experiments in a transient regime.

Experimental Study on Activated Carbon-MIL-101(Cr) Composites for Ethanol Vapor Adsorption.

In this study, the hydrothermal method was used to synthesize MIL-101(Cr), and activated carbon (AC) with different content was incorporated in to MIL-101(Cr), thereby obtaining AC-MIL-101(Cr) composite material with a huge specific surface area. The physical properties of MIL-101(Cr) and AC-MIL-101(Cr) were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), nitrogen adsorption and desorption and specific surface area testing, and ethanol vapor adsorption performance testing. The results show that with the increase of activated carbon content, the thermal stability of AC-MIL-101(Cr) is improved. Compared with the pure sample, the BET specific surface area and pore volume of AC-MIL-101(Cr) have increased. In the relative pressure range of 0–0.4, the saturated adsorption capacity of AC-MIL-101(Cr) to ethanol vapor decreases slightly. It is lower than MIL-101(Cr), but its adsorption rate is improved. Therefore, AC-MIL-101(Cr)/ethanol vapor has a good application prospect in adsorption refrigeration systems. The exploration of AC-MIL-101(Cr) composite materials in this paper provides a reference for the future application of carbon-based/MOFS composite adsorbent/ethanol vapor working fluid in adsorption refrigeration.

Universal spatio-topological control of crystallization in sessile droplets using non-intrusive vapor mediation

The present work showcases a mechanism of asymmetric solvent depletion using vapor-mediated interaction that can non-intrusively regulate the site of crystal precipitation. In general, the flow pattern inside a drying sessile saline droplet leads to circumferential deposition of salt crystals at the end of evaporation. Instead, we show that our proposed approach can manipulate the spatial location of crystal precipitation. The introduction of a pendant ethanol droplet near the sessile saline droplet’s vicinity creates an asymmetric ethanol vapor gradient around the sessile drop. The differential adsorption of ethanol vapor on the surface of the saline droplet gives rise to a spatial surface tension gradient. This, in turn, enhances the internal convection [∼O (102–103)] within the saline droplet. The vigorous and non-uniform flow promotes targeted contact line depinning, ensuring preferential segregation of the salt crystals. Using this methodology, we can inhibit crystal formation at selected locations and favorably control its deposition in definite regions. The interplay of flow hydrodynamics and the associated contact line motion governs this phenomenon marked by the inception and growth of crystals at a preferential site. The universal character of such a phenomenon is verified for a variety of salt solutions on the glass substrate. Tweaking of contact line motion using vapor mediation can be used as a strategic tool for controlling the salt crystallization sites for various potential applications starting from water purification to portable diagnostics, fouling, and scaling, particularly in cases that require the separation of unwarranted solutes from solvents.

Water-Soluble Flexible Organic Frameworks That Include and Deliver Proteins.

Four water-soluble hydrazone-based three-dimensional (3D) flexible organic frameworks FOF-1-4 have been synthesized from a semirigid tetracationic tetraaldehyde and four flexible dihydrazides. 1H NMR spectroscopy indicated the quantitative formation of FOF-1-4 in D2O, while dynamic light scattering experiments revealed that, depending on the concentration, these porous frameworks display hydrodynamic diameters ranging from 50 to 120 nm. The porosity of the frameworks is confirmed by ethanol vapor adsorption experiments of the solid samples as well as the high loading capacity for a 2.3 nm porphyrin guest in water. The new water-soluble frameworks exhibit low cytotoxicity and form inherent pores with diameters of 5.3 or 6.7 nm, allowing rapid inclusion of proteins such as bovine serum albumin and green and orange fluorescent proteins, and efficient delivery of the proteins into normal and cancer cells. Flow cytometric analysis reveals percentages of the delivered cells up to 99.8%.

Ethanol sensing with pure and boric acid doped eectrospun CuInS2 nanofibers in the presence of relative humidity

The influence of boric acid doping on ethanol vapor sensing performance of electrospun copper indium disulfide (CuInS2) nanofibers in the presence of various levels of relative humidity was examined for the first time. Pure and boric doped CuInS2 nanofibers are prepared through electrospinning method and characterized by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy and Thermogravimetric analysis techniques. It was found that not only the ethanol sensing performance but also base line current of the CuInS2 nanofiber based sensors are greatly influenced by the boric acid doping level. Maximum sensitivity was obtained with pure CuInS2 under humid conditions. Kinetic studies indicated that ethanol vapor adsorption kinetics strongly depend on level of the relative humidity and the ethanol concentration.

Selection of binder recipes for the formulation of MOFs into resistant pellets for molecular separations by fixed-bed adsorption

Abstract The formulation of metal-organic frameworks (MOFs) materials into resistant structures is a key step towards their use in adsorptive separation processes. In this study, ZIF-8 crystals have been formulated into resistant pellets with various binders by a simple extrusion-crushing-sieving (ECS) approach. 55 recipes were evaluated with a series of stability tests – mechanical stability upon friction, acid/base stability, hydrothermal stability and long-term stability for storage over several years – as well as with a set of adsorption and separation experiments. The stability tests have highlighted that PVF (polyvinylformal) is the most promising binder to generate resistant pellets with ZIF-8 crystals for the adsorptive recovery of n-butanol in the acetone-butanol-ethanol (ABE) fermentation process, while other binders, including methylcellulose, may find their use in gas/vapor adsorption processes. Adsorption of ethanol vapor has shown that the formulation results into a decrease of adsorption capacity, which is proportional to the binder fraction, while having no effect on the adsorption kinetics. On the other hand, packed bed experiments in liquid phase have indicated that ZIF-8 composite materials maintain the separation ability of the unformulated ZIF-8, but also that the binder results into an unfavorable additional mass transfer resistance. These results have been supported by complementary porosimetry measurements with Ar and Hg, indicating that the composite materials are very porous with narrow pore-size distributions. From this experimental work, various formulation recipes have been identified, which may lead to resistant MOF composite materials for adsorptive separations.

Enhanced pervaporation performance of PDMS membranes based on nano-sized Octa[(trimethoxysilyl)ethyl]-POSS as macro-crosslinker

A homogeneous distribution of inorganic fillers and their integration with polymer matrix is the primary challenge for advancement of mixed matrix membranes (MMMs) in pervaporation. Due to well-defined structure and multi-functional groups attached to the apex silicon atoms, polyhedral oligomeric silsesquioxane (POSS) provides a high possibility of good compatibility with diverse polymer matrix at the molecular level. In this work, soluble and reactive octa[(trimethoxysilyl)ethyl]-POSS(OPS) was synthesized, which was used as macro-crosslinker and reinforced porous fillers of polydimethylsiloxane (PDMS) synchronously to prepare a series of OPS/PDMS MMMs. The OPS/PDMS MMMs were characterized by FT-IR, XRD, SEM, TGA, DSC, PALS, vapor adsorption measurement and tensile test. It was found that OPS dispersed homogeneously in PDMS matrix and achieved good integration with PDMS based on SEM and DSC characterization. PALS results indicated that compared with pure PDMS membrane, OPS/PDMS MMMs with proper OPS loading showed much larger radii of free volume cavities (r3, r4) and fractional free volumes (fv3, fv4 and fv). The numerous hydrophobic POSS cages and enlarged PDMS’ free volume would effectively improve the diffusion selectivity towards ethanol. Vapor adsorption results showed that the chemical incorporation of moderate amount OPS into PDMS not only improved ethanol vapor adsorption amount, but also depressed water adsorption amount in PDMS, which would obviously improve PDMS’ sorption selectivity to ethanol. As applied to the bio-ethanol recovery from aqueous solutions, the prepared OPS/PDMS MMMs exhibited a simultaneous increase in permeation flux and separation factor, breaking the permeation flux-separation factor trade-off limitation. As OPS loading was 7.5 wt%, the separation factor of OPS/PDMS MMMs reached the maximum value of 16.4 (109% higher than that of pure PDMS membrane), with permeation flux of 253.1 g/m2h (32% higher than that of pure PDMS membrane). Experimental results showed that an increase in operation temperature resulted in an increase in permeation flux, but decrease in permeability, separation factor and selectivity. The pervaporation performance of OPS/PDMS MMMs kept stable during two days operation time. This work may provide useful insights of high-performance MMMs with a POSS embedded selective layer for biofuel separation.

An Organoselective Zirconium‐Based Metal–Organic‐Framework UiO‐66 Membrane for Pervaporation

A UiO‐66 membrane was synthesized on an Al2O3 support by an in situ solvothermal method with a coordination modulation technique. We first confirmed the organic selectivity of the UiO‐66 membrane for methanol, ethanol, and acetone in mixtures with water. The membrane displayed highly stable pervaporation performance during the test and exhibited a separation factor of approximately 4.3 and a flux of 1.28 kg m–2 h–1 in ethanol/water. From the water and ethanol vapor adsorption measurement, the water uptake was lower in a binary system than that in a single system, although the ethanol uptake was similar for the binary and single systems. Therefore, the ethanol selectivity of the UiO‐66 membrane can be attributed to the preferential adsorption of the organic compound rather than water, as confirmed by a binary‐vapor adsorption measurement.

Vapor sensing using a bio-inspired porous silicon photonic crystal

Naturally occurring photonic crystals present on the wing scales of Papilio butterflies are known to exhibit vivid iridescent coloration as well as various optical properties, including vapor sensing properties. This work reports the fabrication of a periodic array of concave multilayers in porous silicon mimicking the Papilio blumei nanostructure and its application as an optical vapor sensor. We compared the variations in the reflectance spectrum due to ethanol vapor adsorption and condensation inside the bio-inspired concave porous silicon multilayer structure to the variations of a standard flat porous silicon Bragg mirror. This results in an enhanced response time in the case of the bio-inspired concave structure.

Sensing Properties of WO<sub>3</sub> as Thin Film Prepared by PVD towards Ethanol Vapor

Three thin films were prepared by PVD starting from WO3 powder with thicknesses ( 998.7, 1620, 2240 nm ) respectively on glass substrates under limited thermal and pressure conditions, studied their I-V characteristics and calculated the sensitivity for 100 ppm of ethanol vapor adsorption (The temperature of the films have been changed from 25°C to 350°C). A comparison among them was achieved at 300 °C as an operating degree and found that the 1620 nm WO3 has more sensitivity and has more power to adsorb for ethanol vapor on it.

Sensing Properties of WO<sub>3</sub> as Thin Film Prepared by PVD towards Ethanol Vapor

Three thin films were prepared by PVD starting from WO3 powder with thicknesses ( 998.7, 1620, 2240 nm ) respectively on glass substrates under limited thermal and pressure conditions, studied their I-V characteristics and calculated the sensitivity for 100 ppm of ethanol vapor adsorption (The temperature of the films have been changed from 25°C to 350°C). A comparison among them was achieved at 300 °C as an operating degree and found that the 1620 nm WO3 has more sensitivity and has more power to adsorb for ethanol vapor on it.

Adsorption of Ethanol Vapor on Mica Surface under Different Relative Humidities: A Molecular Simulation Study

The adsorption of ethanol vapor on a mica surface at 298 K and different relative humidities (RHs) are studied using grand canonical Monte Carlo and molecular dynamics simulations. The simulations show that the adsorbed ethanol molecules form a monolayer on the mica surface, sharply contrasting the behavior of water, which forms multiple adsorption layers on the mica surface. Simulations of an ethanol and water mixture reveal that the adsorbed molecules are segregated into a water-rich domain near the mica surface and an ethanol-rich domain on top of the water-rich domain. The water-rich domain exhibits multilayers unless the RH is extremely low (<1%), whereas the ethanol-rich domain exhibits a monolayer. These findings are supported by calculations of the isosteric heats of adsorption and analyses of configurations, concentrations, and diffusivities of molecules in different layers.

Adsorption of Water and Ethanol in MFI-Type Zeolites

Water and ethanol vapor adsorption phenomena are investigated systematically on a series of MFI-type zeolites: silicalite-1 samples synthesized via both alkaline (OH(-)) and fluoride (F(-)) routes, and ZSM-5 samples with different Si/Al ratios as well as different charge-balancing cations. Full isotherms (0.05-0.95 activity) over the range 25-55 °C are presented, and the lowest total water uptake ever reported in the literature is shown for silicalite-1 made via a fluoride-mediated route wherein internal silanol defects are significantly reduced. At a water activity level of 0.95 (35 °C), the total water uptake by silicalite-1 (F(-)) was found to be 0.263 mmol/g, which was only 12.6%, 9.8%, and 3.3% of the capacity for silicalite-1 (OH(-)), H-ZSM-5 (Si/Al:140), and H-ZSM-5 (Si/Al:15), respectively, under the same conditions. While water adsorption shows distinct isotherms for different MFI-type zeolites due to the difference in the concentration, distribution, and types of hydrophilic sites, the ethanol adsorption isotherms present relatively comparable results because of the overall organophilic nature of the zeolite framework. Due to the dramatic differences in the sorption behavior with the different sorbate-sorbent pairs, different models are applied to correlate and analyze the sorption isotherms. An adsorption potential theory was used to fit the water adsorption isotherms on all MFI-type zeolite adsorbents studied. The Langmuir model and Sircar's model are applied to describe ethanol adsorption on silicalite-1 and ZSM-5 samples, respectively. An ideal ethanol/water adsorption selectivity (α) was estimated for the fluoride-mediated silicalite-1. At 35 °C, α was estimated to be 36 for a 5 mol % ethanol solution in water increasing to 53 at an ethanol concentration of 1 mol %. The adsorption data demonstrate that silicalite-1 made via the fluoride-mediated route is a promising candidate for ethanol extraction from dilute ethanol-water solutions.

A New Series of Nanoporous Ionic Crystals Based on Polyoxometalates – Synthesis, Crystal Structures, and Adsorption Properties

AbstractBased on polyoxometalate cluster anions and macrocations, KH2[Cr3O(OOCCH3)6(H2O)3][α‐GeMo12O40]·10H2O (1), K1.5H1.5[Cr3O(OOCCH3)6(H2O)3][α‐GeW12O40]·9.5H2O (2), NaH2[Cr3O(OOCCH3)6(H2O)3]3[α‐P2W18O62]·32H2O (3), and Na3[Cr3O(OOCCH3)6(H2O)3]3[α‐As2W18O62]·34H2O (4) have been prepared by a conventional method and characterized by single‐crystal X‐ray diffraction, IR and UV/Vis spectroscopy, elemental analysis, thermogravimetric analysis (TGA) and powder X‐ray diffraction (PXRD). In addition, the gas adsorption properties of these four compounds for methanol and ethanol have been investigated. The adsorption studies display an apparent difference between methanol and ethanol vapor adsorption and demonstrate that such microporous materials could be applied as new molecular sieves for selective sorption from a mixture of C1 and C2 alcohols.

Recovery of Ethanol from Carbon Dioxide Stripped Vapor Mixture: Adsorption Prediction and Modeling

Carbon dioxide stripping of ethanol and adsorption can be used in a bioethanol fermentation system to reduce product inhibition. To gain a better understanding of the bioethanol adsorption process, a mathematical model was used to predict the adsorption performance of activated carbon WV-B 1500 for ethanol vapor adsorption in the presence of carbon dioxide and water. The model takes into account changes in velocity due to adsorption, heat effects during adsorption, and heat losses to the surroundings. The model, developed without resorting to fitting parameters, was validated successfully by comparing the model predictions with experimental adsorption data. Finally, the model was used to predict the adsorption working capacities to assess the performance of the adsorption process in an industrial process.

Effect of ethanol on optical and electrical parameters of porous silicon

The effect of ethanol vapor adsorption on the properties of porous silicon-based structures was studied by Raman scattering, infrared spectroscopy, and I–V characteristics. A decrease in the resistance of porous silicon layers and a simultaneous increase in the intensity of the band of infrared absorption caused by the presence of (OH)−…x(OH)− (x = 1, 2, …) groups upon exposure to ethanol vapor and vice versa in the case of degassing were detected. The observed effect is attributed to a change in the depletion region in por-Si skeleton elements due to the electrostatic interaction of (OH)− groups with positively charged surface defects. The effect of hydrogen-bonded Si-OH…OH-C2H5 centers on the increase in the silicon conductivity is discussed.

The synthesis, characterization of oxidized multi-walled carbon nanotubes, and application to surface acoustic wave quartz crystal gas sensor

Intermetallic alloy catalysts had been prepared by the polyol method, and used for the growth of the individual- or bundle-shaped multi-walled carbon nanotubes (MWCNTs) by thermal chemical vapor deposition method. The purified MWCNTs catalyzed by Mg 28-Ni 68-Mo 4 alloy catalyst were oxidized with the nitric acid/hydrogen peroxide solution (volume ratio = 2/1) to generate carboxylic acid groups. The oxidized MWCNTs (MWCNT-COOH) were further modified with different molecular weights of polyethylene glycols and chloromethyl styrene, respectively, to verify carboxylic acid groups and achieve higher hydrophobic property. Contents of organic functional groups grafted on MWCNTs were estimated with thermogravimetric analysis experiments. In addition, the MWCNT-COOH and poly( n, n-dimethylamino propylsilsesquioxane) (SXNR) were mixed in the THF solvent, and sprayed onto the surface of SAW crystal gas sensor. The MWCNT-COOH were employed to the 156 MHz surface acoustic wave (SAW) quartz crystal sensor for the adsorption of ethanol vapor. The SAW quartz crystal gas sensor coated with the MWCNT-COOH/SXNR was exhibited a high response for ethanol vapor efficiently.

A thermogravimetric analyzer for condensable gas adsorption under subatmospheric conditions

We have developed a thermogravimetric system (TG system) for condensable gas adsorption by modifying a standard thermogravimetric analyzer Cahn TG 2121 and performed isotherm measurements of water vapor adsorption on Fuji Davison type RD silica gel and ethanol vapor adsorption on Maxsorp II activated carbon. For the water vapor-silica gel data, our results compare favorably with the data reported by the manufacturer and those obtained from a volumetric method. This confirms the reliability of our TG system for adsorbents which do not swell significantly. In addition, our isotherm data also provide useful design information for the development of adsorption chillers.

Chemical characterization of plasma-polymerized films from acetylene and nitrogen-containing mixtures and their ethanol vapor sensitivity

In this study, plasma-polymerized thin films were prepared from plasma enhanced chemical vapor deposition (PECVD) of acetylene (C 2H 2), acetylene/nitrogen (C 2H 2/N 2), or acetylene/ammonia (C 2H 2/NH 3). When N 2 or NH 3 was mixed with C 2H 2 in the feed, the films were identified to contain all elements of the mixture and the properties of the films were implied by the C–H bonds and nitrogen functionalities. As shown by X-ray photoelectron spectroscopy (XPS) the [N]/[C] atomic ratio varies by changing the mixture composition and reaches a maximum of 0.12 for mixing C 2H 2 with NH 3. It is found that the resistance of the thin film sensors prepared from C 2H 2, C 2H 2/N 2, and C 2H 2/NH 3 is distinctly decreased by over 2 orders of magnitude by the adsorption of ethanol vapor.