Adsorption Of Organic Vapors Research Articles

Adsorption and electrothermal desorption of organic vapors using activated carbon adsorbents with novel morphologies

Novel morphologies of activated carbons such as monolith, beads and fiber cloth can effectively capture organic vapors from industrial sources. These adsorbent materials are also unique because they can undergo direct electrothermal regeneration to recover the adsorbed organic vapors for potential re-use. This investigation compares and contrasts the properties of these adsorbents when using electrothermal–swing adsorption. The adsorption systems consisted of an organic vapor generation system, an electrothermal–swing adsorption vessel, a gas detection unit, and a data acquisition and control system. The activated carbon monolith (ACM) had the lowest pressure drop, highest permeability, highest electrical resistivity and lowest cost as compared to the activated carbon beads (ACB) and the activated carbon fiber cloth (ACFC). ACB had the largest throughput ratio and lowest length of unused bed as compared to the other adsorbents. However, ACFC had the largest adsorption capacity for toluene when compared to ACM and ACB. ACFC was also faster to regenerate and had a larger concentration factor than ACM and ACB. These results describe relevant physical, electrical, adsorption and cost properties for specific morphologies of the adsorbents to more effectively capture and recover organic vapors from gas streams.

Performance evaluation of wash-coated MCM-48 monolith for adsorption of volatile organic compounds and water vapors

The adsorption equilibrium and column dynamics of five organic molecules (acetone, benzene, n-hexane, toluene, trichloroethene) and water vapors on the wash-coated MCM-48 were studied to investigate the applicability of a monolithic adsorber in the adsorption based areas. The wash-coated samples were characterized by using X-ray diffraction (XRD), scanning electron microscopic (SEM) images and nitrogen adsorption–desorption isotherms. To obtain the pure component adsorption equilibrium data at different temperatures (300.15–322.15 K), a gravimetric method was used. The wash-coated MCM-48 showed the unique feature of mesoporous media without any defects although the adsorption capacities for selected adsorbates decreased. The hybrid adsorption isotherms, presented in our recent works [J.W. Lee, J.W. Lee, W.G. Shim, S.H. Suh, H. Moon, J. Chem. Eng. Data 48 (2003) 381–386; J.S. Oh, W.G. Shim, J.W. Lee, J.H. Kim, H. Moon, G. Seo, J. Chem. Eng. Data 48 (2003) 1458–1462; J.W. Lee, W.G. Shim, H. Moon, Micropor. Mesopor. Mater. 73 (2004) 109–119; W.G. Shim, J.W. Lee, H. Moon, Micropor. Mesopor. Mater. 88 (2006) 112–125] satisfactorily correlated the adsorption equilibrium data obtained. The adsorption equilibrium amounts for water vapor were about 5–6 times higher than those of the corresponding organic compounds. To examine the behavior of adsorption breakthrough curves, we employed axi-symmetric model with hybrid isotherms for single component and a simple extended hybrid Langmuir–Sips (EHLS) equation for multicomponent. The current work demonstrates that the adsorption breakthrough patterns are significantly dependent on the equilibrium adsorption isotherm shape. In the case of multi-component mixture systems, we found that there are cooperative and competitive relationships between soluble chemicals and water vapor. Moreover, considering the prediction works, the hybrid isotherm model agrees well with the single component experimental data while the EHLS model fails to explain the multi-component systems.

Theoretical and Experimental Investigation of Morphology and Temperature Effects on Adsorption of Organic Vapors in Single-Walled Carbon Nanotubes

Hexane adsorption on single-walled carbon nanotube (SWNT) bundles is studied by both simulation and experimentally using a previously developed computer-aided methodology, which employed a smaller physisorbed probe molecule, nitrogen, to explore the porosity of nanotube samples. Configurational-bias grand canonical Monte Carlo simulation of hexane adsorption on localized sites of the bundles is carried out to predict adsorption on their external surface and in their internal sites. These localized isotherms are then combined into a global isotherm for a given sample by using knowledge of its tube-diameter distribution and structural parameters, such as the fraction of open-ended nanotubes and the external surface area of bundles in samples, which have been independently determined from the standard nitrogen adsorption isotherm. The near-perfect replication of experimental isotherms demonstrates the validity of our method for structural characterization of SWNT samples. The effect of temperature on adsorption is also studied and the simulation results are extrapolated to predict the limiting hexane adsorption capacity of the samples. The similarity between the hexane adsorption isotherms and those of other organic molecules demonstrates that the adsorption mechanisms explored here are not specific to hexane, and that the proposed methodology can be potentially applicable to other sorbates with equal success.

Fine organic particulate matter dominates indoor-generated PM2.5 in RIOPA homes

Residential indoor and outdoor fine particle (PM(2.5)) organic (OC) and elemental carbon (EC) concentrations (48 h) were measured at 173 homes in Houston, TX, Los Angeles County, CA, and Elizabeth, NJ as part of the Relationship of Indoor, Outdoor and Personal Air (RIOPA) study. The adsorption of organic vapors on the quartz fiber sampling filter (a positive artifact) was substantial indoors and out, accounting for 36% and 37% of measured OC at the median indoor (8.2 microg C/m(3)) and outdoor (5.0 microg C/m(3)) OC concentrations, respectively. Uncorrected, adsorption artifacts would lead to substantial overestimation of particulate OC both indoors and outdoors. After artifact correction, the mean particulate organic matter (OM=1.4 OC) concentration indoors (9.8 microg/m(3)) was twice the mean outdoor concentration (4.9 microg/m(3)). The mean EC concentration was 1.1 microg/m(3) both indoors and outdoors. OM accounted for 29%, 30% and 29% of PM(2.5) mass outdoors and 48%, 55% and 61% of indoor PM(2.5) mass in Los Angeles Co., Elizabeth and Houston study homes, respectively. Indirect evidence provided by species mass balance results suggests that PM(2.5) nitrate (not measured) was largely lost during outdoor-to-indoor transport, as reported by Lunden et al. This results in dramatic changes with outdoor-to-indoor transport in the mass and composition of ambient-generated PM(2.5) at California homes. On average, 71% to 76% of indoor OM was emitted or formed indoors, calculated by (1) Random Component Superposition (RCS) model and (2) non-linear fit of OC and air exchange rate data to the mass balance model. Assuming that all particles penetrate indoors (P=1) and there is no particle loss indoors (k=0), a lower bound estimate of 41% of indoor OM was indoor-generated (mean). OM appears to be the predominant species in indoor-generated PM(2.5), based on species mass balance results. Particulate OM emitted or formed indoors is substantial enough to alter the concentration, composition and behavior of indoor PM(2.5). One interesting effect of increased indoor OM concentrations is a shift in the gas-particle partitioning of polycyclic aromatic hydrocarbons (PAHs) from the gas to the particle phase with outdoor-to-indoor transport.

Adsorption of Ethylmethylamine Vapor by Activated Carbon Filters

The adsorption of high concentrations of ethylmethylamine (EMA) vapor from a humid air stream by an activated carbon bed has been studied. The adsorption behavior is quite different from the adsorption of trace quantities from an aqueous solution. The introduction of surface groups has no apparent direct effect on EMA adsorption. However, because these surface groups enhance water adsorption from the air stream and because adsorbed water hinders organic vapor adsorption, the modified carbons exhibit a lower apparent capacity and slower adsorption kinetics for EMA than the untreated ones. EMA is adsorbed from the vapor phase by a different mechanism than it is adsorbed from the liquid phase. The effect of humidity was evaluated and shown to influence the breakthrough time.

Relationships between organic vapor adsorption behaviors and gas sensitivity of carbon black filled waterborne polyurethane composites

Vapor adsorption behavior and its influence on the gas sensitivity of conductive carbon black filled waterborne polyurethane composites were studied. It was found that the traditional swelling model that was applicable for the reversible variation in the composites electrical resistance induced by the solvent uptake was challenged. That is, the higher adsorption quantity was not bound to result in higher sensitivity to the vapor. On the basis of a detailed study on thermodynamics of adsorption, selective swelling of the segmented microstructure of the composites’ matrix and the preferred distribution of the conductive fillers in the matrix were found to take the responsibility. The solvent–matrix polymer interaction and the chemical characteristics of the solvents determined the relationship between the vapor adsorption behavior and the electrical responsivity of the composites.

Preparation and characterisation of carbon-coated ceramic foams for organic vapour adsorption

Ceramic foam substrates of various porosities were coated with novolak resin, which was then subsequently carbonised and activated to develop a pore structure. The carbon forming the layer was characterised by thermal analysis, TPD and N 2, CO 2 and hexane vapour adsorption. It was found to be microporous with a high surface area (up to 1400 m 2 g −1), which made it a good adsorbent for hexane vapour at ambient temperature. The carbon–ceramic interface was examined using SEM. The coated foams displayed a reduced pressure drop compared to carbon granules and had good dynamic hexane vapour adsorption characteristics. Depending on the foam architecture, hexane breakthrough was delayed for up to 78 min.

Adsorption equilibrium of organic vapors on single-walled carbon nanotubes

Gravimetric techniques were employed to determine the adsorption capacities of commercially available purified electric arc and HiPco single-walled carbon nanotubes (SWNTs) for organic compounds (toluene, methyl ethyl ketone (MEK), hexane and cyclohexane) at relative pressures, p/ p 0, ranging from 1 × 10 −4 to 0.95 and at isothermal conditions of 25, 37 and 50 °C. The isotherms displayed both type I and type II characteristics. Adsorption isotherm modeling showed that SWNTs are heterogeneous adsorbents, and the Freundlich equation best describes the interaction between organic molecules and SWNTs. The heats of adsorption were 1–4 times the heats of vaporization, which is typical for physical adsorption of organic vapors on porous carbons.

On the prediction of adsorption isotherms of methanol/water vapour mixtures on microporous activated carbon

It is well known that the adsorption of organic vapours on activated carbons (AC) can be disturbed in the presence of water vapour. When the adsorbed solutions are miscible, different theories, based on the pioneering Dubinin–Radushkevich (D–R) and Dubinin– Astakhov (D–A) equations are used to describe the experimental data. Among recent works, Linders et al. [1] showed that the isotherm of multicomponents can be modeled by using the ideal adsorbed solution theory (IAST), D–R and D–A equations. This model fits well with the experimental data up to a relative pressure of 0.1 (methanol adsorption at 60% RH) but shows discrepancies beyond these value. No explanation was given by the authors. Taqvi et al. [2] proposed to estimate the binary equilibria using the virial mixture coefficient approach (VMC). The observed trends are explained in terms of molecular interactions and, in particular, water was found to promote the adsorption of methanol. This is explained by the ability of alcohol to form H bond with water. To sum up, it seems that if some points such as the state of the phase adsorbed (homogeneous solution) are well established, other points such as the over-adsorption of methanol or the lack of models for the high methanol relative pressures, need further explanation. In this work, we report our results obtained for the co-adsorption of methanol and water vapours on a commercial activated microporous carbon (AC). The relative humidity (RH) ranges from 25% to 74% and the methanol concentration from 0% to saturation. The obtained results lead us to propose a thermodynamical approach that explains the isotherms of methanol adsorption at constant RH. Furthermore, our approach fits well with several results in the literature. Adsorption isotherms were collected in dynamic flow conditions at 298 K using an intelligent gravimetric analyzer (IGA) supplied by Hiden Analytical Ltd. This apparatus is fully computer controlled and measures gravimetric adsorption on a microbalance. The sample temperature was constantly monitored throughout the experiment, and the variation was found to be ±0.05 K. Further details about the acquisition procedure can be found elsewhere [3]. The AC studied has been obtained by activation of coconut shell in steam at 1123 K. The porosity characterization was determined by benzene adsorption using a procedure described elsewhere [4]. The sample is mainly considered as microporous (Vmic = 0.585 cm 3 /g; Vmes = 0.082 cm 3 /g) with specific surface area close to 1500 m 2 /g and having a poor surface chemistry (acidic groups = 0.06 meq/g and basic groups = 0.5 meq/g as determined by Boehm titration). The isotherms of pure methanol and water adsorption are presented in Fig. 1. The adsorption of methanol, that exhibits type I isotherm, is characterized by strong dispersive interactions of the methyl groups with the carbon pore walls [3]. As a result, a large part of the pore volume is already filled at low relative pressures. The water isotherm is of type V. Then the carbon surface is evaluated to be extremely hydrophobic. The sharp increase of the adsorbed water is attributed to the condensation of water into the micropores. The adsorption isotherms of binary mixtures, presented in Fig. 2, were obtained for a relative humidity of 25%, 50%, 60% and 74% respectively. It should be noted that the number of data for each isotherm decreases with increasing RH due to limitations of our experimental set-up. Moreover, all the isotherms are of type I. The slope at low partial pressure in methanol increases with increasing RH before reaching a plateau that corresponds to the capacity near saturation. The total mass uptake is higher when RH = 25% than for pure methanol, and it then decreases with increasing RH.

Effect of Temperature on the Adsorption of Organic Vapours on Activated Carbon Fibres

Viscose rayon-based activated carbon fibre (ACF) was prepared by CO2 activation and the pore structure of all samples characterized via nitrogen adsorption at −196 ° C. The influence of temperature on the adsorption of organic vapour onto ACF was studied by gravimetric methods. The results showed that the adsorption capacity towards organic vapour decreased with increasing temperature at a given concentration. The larger the specific surface area of the ACF, the greater the extent to which its vapour adsorption performance was affected by temperature. It is suggested that an ACF of a relatively low burn-off would be suitable for adsorption at higher temperatures.

Dynamic Analysis of Diffusion and Adsorption of Water‐Miscible and Water‐Immiscible Organic Vapors in Soil

AbstractA dynamic analysis of the diffusion and adsorption of water‐miscible volatile organic compounds (methanol and acetone) and water‐immiscible volatile organic compounds (benzene and toluene) in a soil pellet has been performed experimentally by using the single pellet moment technique. The experiments were conducted in a one‐sided single pellet adsorption cell at a temperature of 30 °C and varying relative humidities (0, 20, and 40 %). The results obtained with dry and wet systems showed that volatile organic tracers were adsorbed reversibly onto the soil. The overall adsorption equilibrium constants of both water‐miscible and water immiscible volatile organic compounds decreased with relative humidity. The sorption of water‐immiscible VOCs (benzene) onto soil was found to be much less than that of water‐miscible VOCs (methanol). The effective diffusivity of water‐immiscible volatile organic vapor (benzene) in the soil did not show a considerable change with relative humidity. In contrast, there was an appreciable change in the effective diffusivity for water‐miscible VOCs (methanol) with moisture.

Impedance analysis of the thickness shear mode resonator for organic vapour sensing

The impedance analysis of thickness shear mode (TSM) resonator coated with calixarene films was successfully exploited for the registration of organic solvent vapours of relatively high (pre-explosive) concentrations. The impedance analysis consisted of fitting the experimental admittance spectra of TSM resonators to the equivalent circuit model using a highly accurate and reliable least squares algorithm. This approach allowed simultaneous monitoring of the changes in mass and viscoelastic properties of the sensitive membrane caused by adsorption of organic vapours and therefore enables both quantification and discrimination between the vapours of different types of organic solvents, such as hexane and toluene.

An Extended Equation for Rate Coefficients for Adsorption of Organic Vapors and Gases on Activated Carbons in Air-Purifying Respirator Cartridges

Organic vapor adsorption rates in air-purifying respirator cartridges (and other packed beds of activated carbon granules) need to be known for estimating service lives. The correlation of Lodewyckx and Vansant [AIHAJ 61:501–505 (2000)] for mass transfer coefficients for organic vapor adsorption onto activated carbon was tested with additional data from three sources. It was then extended to better describe all the data, including that for gases. The additional parameter that accomplished this was the square root of molar equilibrium capacity of the vapor or gas on the carbon. This change, along with skew corrections when appropriate, resulted in better correlations with all experimental rate coefficients.

New Method of Vapour Discrimination Using the Thickness Shear Mode (TSM) Resonator

The Impedance analysis technique complimented with curve fitting software was used to monitor changes in film properties of Thickness Shear Mode (TSM) resonator on vapour exposure. The approach demonstrates how sensor selectivity can be achieved through unique changes in film viscosity caused by organic vapour adsorption.

An extended equation for rate coefficients for adsorption of organic vapors and gases on activated carbons in air-purifying respirator cartridges.

Organic vapor adsorption rates in air-purifying respirator cartridges (and other packed beds of activated carbon granules) need to be known for estimating service lives. The correlation of Lodewyckx and Vansant [AIHAJ 61:501-505 (2000)] for mass transfer coefficients for organic vapor adsorption onto activated carbon was tested with additional data from three sources. It was then extended to better describe all the data, including that for gases. The additional parameter that accomplished this was the square root of molar equilibrium capacity of the vapor or gas on the carbon. This change, along with skew corrections when appropriate, resulted in better correlations with all experimental rate coefficients.

Organic vapor adsorption behavior of poly(3-butoxythiophene) LB films on quartz crystal microbalance

In this work, poly(3-butoxythiophene) (P3BOT) mixed with stearic acid (SA) in different ratios have been used to form LB films. The incorporation of the ether group increases the hydrophilicity of the molecules. The mixed films on water subphase undergo a phase transition at the evaluated pressure. The adsorption behavior of the mixed films with a P3BOT/SA ratio of 2:1 on quartz crystal microbalance (QCM) as sensing materials to two series of chemical analyte vapors was investigated. The interaction mechanisms involving dipole/dipole or hydrogen bonding interaction were proposed to explain the frequency response during the adsorption. The sensitivity of the film on QCM increases with film thickness and the concentration of the analyte vapor. Moreover, this work indicates that the control of sensitivity and selectivity of polymer film sensor to chemical vapor can be achieved through functionalization of the polymer.

Pressure Swing Adsorption of Organic Vapors: Experimental and Theoretical Results

Chemie Ingenieur TechnikVolume 73, Issue 6 p. 735-736 Article Pressure Swing Adsorption of Organic Vapors: Experimental and Theoretical Results W.-D. Sußebach Dipl.-Ing., W.-D. Sußebach Dipl.-Ing. Lehrstuhl für Verfahrens- und Umwelttechnik, Ruhr-Universität Bochum, D-44780 BochumSearch for more papers by this authorH.-J. Röhm Prof. Dr., H.-J. Röhm Prof. Dr. Lehrstuhl für Verfahrens- und Umwelttechnik, Ruhr-Universität Bochum, D-44780 BochumSearch for more papers by this author W.-D. Sußebach Dipl.-Ing., W.-D. Sußebach Dipl.-Ing. Lehrstuhl für Verfahrens- und Umwelttechnik, Ruhr-Universität Bochum, D-44780 BochumSearch for more papers by this authorH.-J. Röhm Prof. Dr., H.-J. Röhm Prof. Dr. Lehrstuhl für Verfahrens- und Umwelttechnik, Ruhr-Universität Bochum, D-44780 BochumSearch for more papers by this author First published: 12 July 2001 https://doi.org/10.1002/1522-2640(200106)73:6<735::AID-CITE7355555>3.0.CO;2-TAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume73, Issue6Juni 2001Pages 735-736 RelatedInformation

Adsorption and Electrothermal Desorption of Hazardous Organic Vapors

In 1997, 6.04 x 10\u8 kg of hazardous air pollutants were emitted into the atmosphere from the United States. A bench-scale activated-carbon fiber-cloth adsorption, electrothermal desorption, and condensation system was designed, built, and operated to demonstrate its ability to capture and recover organic hazardous air pollutants from airstreams. The annular-cartridge configuration of the activated carbon fiber cloth allows low pressure drop and rapid electrothermal regeneration. Adsorption and electrothermal desorption cycling of the system with an airstream containing 1,000 ppmv methyl ethyl ketone (MEK) resulted in closure within 8% by mass. Competitive adsorption between water vapor and MEK reduced MEK adsorption capacity 43% as relative humidity of the gas increased from 4 to 90% at 22°C dry-bulb temperature. Increasing the dry-bulb temperature of the gas stream by 10°C at a constant dew-point temperature resulted in a 37% increase in MEK adsorption compared to the high relative humidity test case, while allowing the water vapor to penetrate the adsorber. The automated system achieves MEK capture efficiency >99.9% by mass while recovering the liquid MEK for reuse.

Carbon Fiber Adsorption Using Quantitative Structure-Activity Relationship

Adsorption capacities of adsorbents are necessary for selecting and designing adsorption systems for separation and removal processes, such as air quality control devices, because they are indicators of service life. This paper describes the use of the Dubinin-Radushkevich (DR) equation and the quantitative structure-activated relationship to predict the equilibrium adsorption of select organic vapor by activated carbon fiber (ACF) adsorbents. The DR isotherm parameter, k, depends on the adsorbate as well as the adsorbent, and the prediction for k can be obtained indirectly from the affinity coefficient. A correlation is developed to compute the affinity coefficient from the modified, first-order, valence molecular connectivity index. This method provides an improved way to predict equilibrium adsorption capacities for select volatile organic compound adsorbates and activated carbon fiber adsorbents.

Application of polymer-coated quartz crystal microbalance (QCM) as a sensor for BTEX compounds vapors

A sensor based on the technique of a quartz crystal microbalance (QCM) was developed for the detection of organic vapors such as benzene, toluene, ethylbenzene, and xylenes (BTEX compounds). Detection was based on the adsorption of organic vapors on a thin layer of polydimethylsiloxane (PDMS) coated at the surface of AT-cut gold-coated quartz crystal electrodes. The frequency shifts due to the sorption of BTEX compounds were measured. Calibration graphs were constructed by plotting the frequency changes (ΔF/Hz) against the concentration of organic compounds. Using this method, the detection of these organic vapors was carried out at the ppm level. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1062–1066, 2001