Adsorption Of Organic Vapors Research Articles

Adsorption of Gas Phase Organic Compounds by Swellable Organically Modified Silica

Swellable organically modified silica (SOMS) is a sol–gel derived material that spontaneously expands >2.5× upon contact with organic liquids, absorbing 7.8 mL/g. Adsorption of gas-phase volatile organic compounds by SOMS was measured to examine how the capability to swell affects capacity and rate of organic vapor absorption. Static adsorption capacities of SOMS for organic vapors at saturated vapor pressure ranged from 0.7 to 1.05 g/g, which was higher than values for other sorbents (powdered activated carbon, Amberlite XAD-4, Tenax TA, OptiPore, and organophilic zeolite). Rates of adsorption by SOMS were similar to those of XAD-4, a porous polymer with similar surface chemistry, and slower than that of activated carbon. Sequential coadsorption of multiple compounds by SOMS was measured, yielding enhanced adsorption capacity attributed to adsorption-induced pore expansion. The sequential adsorption of phenol and acetone vapor (p = p0) led to a total capacity of 5.7 g/g. Adsorption of organic vapors was ...

Adsorption of volatile organic vapors by activated carbon derived from rice husk under various humidity conditions and its statistical evaluation by linear solvation energy relationships

The adsorption of sixteen volatile organic compounds (VOCs) in the gas phase by activated carbon (AC) generated from waste rice husk was investigated under two different levels of relative humidity (RH) by inverse gas chromatography (IGC). R850 AC had the largest surface area and was characterized. Linear solvation energy relationship (LSER) was employed to understand the interactions between R850 AC and VOCs. The major functional groups on the surface of R850 AC were CC, SiOSi, OH, and CO(H). IGC indicated that the gas/solid adsorption coefficients (log Kd) for the 16 VOCs lied in the range 4.0–6.1 (g g−1)/(g mL−1) under medium RH (around 55%), but decreased under high RH (90%). Moreover, the log Kd value predicted from our LSER equations was highly correlated to the experimental log Kd of the R850 AC. This study demonstrates that R850 AC is a promising material for VOC removal and the established LSER equations are useful to estimate VOC adsorption.

Systematic evaluation of the adsorption of organic vapors onto a miniaturized cartridge device using breakthrough tests in parallel experiment with a full size respirator cartridge

Breakthrough experiments are essential for the characterization of the adsorption capacity and micropore volume of activated carbon respiratory cartridges and for the validation and determination of cartridge service life models. In an effort to gain better control over environmental conditions in breakthrough tests and to obtain reliable data, a novel experimental approach using a miniaturized (Mini) cartridge was designed to replicate a small section of a respiratory cartridge. The Mini device and the organic vapor respiratory cartridge were tested in single and parallel experiments where in the former, one filter was tested one at a time and in the latter both devices were exposed simultaneously to the same conditions. The Mini device gave comparable results to the 10% breakthrough times and adsorption capacities of the organic vapor cartridges. The reproducibility of the packed carbon bed of the Mini provided strong support for using the Mini in breakthrough experiments for the characterization of the activated carbon adsorption capacity and estimation of cartridge service life.

The role of beaded activated carbon’s surface oxygen groups on irreversible adsorption of organic vapors

The objective of this study is to determine the contribution of surface oxygen groups to irreversible adsorption (aka heel formation) during cyclic adsorption/regeneration of organic vapors commonly found in industrial systems, including vehicle-painting operations. For this purpose, three chemically modified activated carbon samples, including two oxygen-deficient (hydrogen-treated and heat-treated) and one oxygen-rich sample (nitric acid-treated) were prepared. The samples were tested for 5 adsorption/regeneration cycles using a mixture of nine organic compounds. For the different samples, mass balance cumulative heel was 14 and 20% higher for oxygen functionalized and hydrogen-treated samples, respectively, relative to heat-treated sample. Thermal analysis results showed heel formation due to physisorption for the oxygen-deficient samples, and weakened physisorption combined with chemisorption for the oxygen-rich sample. Chemisorption was attributed to consumption of surface oxygen groups by adsorbed species, resulting in formation of high boiling point oxidation byproducts or bonding between the adsorbates and the surface groups. Pore size distributions indicated that different pore sizes contributed to heel formation – narrow micropores (<7Å) in the oxygen-deficient samples and midsize micropores (7–12Å) in the oxygen-rich sample. The results from this study help explain the heel formation mechanism and how it relates to chemically tailored adsorbent materials.

Characterization of sampling artifacts in the measurement of carbonaceous particles using high- and low-volume samplers in Daejeon, Korea

This study investigates the influence of positive sampling artifacts on the determination of atmospheric organic carbon (OC) and elemental carbon (EC) by undenuded high-volume (HV) and low-volume (LV) samplers. The samples, which were collected in Daejeon, Korea during the spring and fall of 2014, were analyzed for OC and EC using a thermal optical transmittance (TOT) technique. Positive artifacts for OC using the undenuded LV and HV samplers were determined to be ∼12.2% and ∼7.2%, respectively. The adsorption of organic vapors on quartz filters and the analytical artifacts of thermal-optical method contributed equally to the positive artifact for the HV sampler, whereas that of the undenuded LV sampler was caused primarily by the adsorption of organic vapors on quartz filters with a relatively small contribution from the analytical artifacts of thermal-optical method. The analytical artifacts of thermal-optical method was closely related to the additional formation of pyrolyzed OC (POC) during the analysis, resulting in an underestimation of EC (HV sampler: 15.6 ± 15.6%; undenuded LV sampler: 9.1 ± 7.6%). The POC that formed during the analysis was related to the adsorption of organic vapors (in both the HV and undenuded LV samplers) and high particle loading on the quartz filters (HV sampler only). OC concentrations determined using the undenuded LV sampler and corrected using backup filter measurements correlated well with those of the denuded LV sampler (R2 = 0.98), suggesting that the backup filter correction method can be applied to particulate OC measurements using an undenuded LV sampler under conditions typical of those in Daejeon, Korea.

The role of beaded activated carbon’s pore size distribution on heel formation during cyclic adsorption/desorption of organic vapors

The effect of activated carbon’s pore size distribution (PSD) on heel formation during adsorption of organic vapors was investigated. Five commercially available beaded activated carbons (BAC) with varying PSDs (30–88% microporous) were investigated. Virgin samples had similar elemental compositions but different PSDs, which allowed for isolating the contribution of carbon’s microporosity to heel formation. Heel formation was linearly correlated (R2=0.91) with BAC micropore volume; heel for the BAC with the lowest micropore volume was 20% lower than the BAC with the highest micropore volume. Meanwhile, first cycle adsorption capacities and breakthrough times correlated linearly (R2=0.87 and 0.93, respectively) with BAC total pore volume. Micropore volume reduction for all BACs confirmed that heel accumulation takes place in the highest energy pores. Overall, these results show that a greater portion of adsorbed species are converted into heel on highly microporous adsorbents due to higher share of high energy adsorption sites in their structure. This differs from mesoporous adsorbents (low microporosity) in which large pores contribute to adsorption but not to heel formation, resulting in longer adsorbent lifetime. Thus, activated carbon with high adsorption capacity and high mesopore fraction is particularly desirable for organic vapor application involving extended adsorption/regeneration cycling.

The cost-effective synthesis of furan- and thienyl-based microporous polyaminals for adsorption of gases and organic vapors.

This work reveals that furfural and 2-thenaldehyde can readily react with melamine via "one-step" polycondensation to yield hyper-cross-linked sulfur-, nitrogen- and oxygen-rich microporous polyaminals with promising applications in adsorption of gases and toxic organic vapors.

Microporous polyimides with functional groups for the adsorption of carbon dioxide and organic vapors

Microporous polyimides containing a high density of trifluoromethyls or benzophenone with uniform pores are synthesized, which possess high uptakes for CO2and aromatic and aliphatic vapors, exhibiting potential in gas storage and recovery of toxic organic vapors.

Tetraphenyladamantane-Based Microporous Polybenzimidazoles for Adsorption of Carbon Dioxide, Hydrogen, and Organic Vapors

Tetraphenyladamantane-based microporous polybenzimidazoles were prepared through condensation polymerizations of 1,3,5,7-tetrakis(4-formyphenyl)adamantane with 3,3′-diaminobenzidine and 1,2,4,5-tetraaminobenzene tetrachloride, respectively, which exhibit large BET surface area up to 1023 m2 g–1 and narrow pore size distribution with pore size locating at about 0.6 nm. The sorption measurements show that they can uptake 17.3 wt % CO2 (273 K/1 bar), 1.6 wt % H2 (77 K/1 bar), 98.0 wt % benzene, and 53.6 wt % cyclohexane (298 K, P/P0 = 0.95). Moreover, according to the Henry’s law initial slope method and ideal adsorbed solution theory, the resultant polymers possess high CO2/N2 selectivity (71) and CO2/CH4 selectivity (12). The influences of porous structures, that is, porous size and distribution of the polymers, on the adsorption properties of gases and organic vapors are interpreted in terms of the pore-size-exclusive effect as well as variations of physicochemical parameters such as Henry’s constants, first virial coefficients, enthalpies of adsorption, and kinetic diameters, critical temperatures of adsorbates.

Guest editorial: Special issue on science of friction

Tribology involves not only two-body contacts of two solid materials—a substrate and a counter-surface; it often involves three-body contacts whether the third body is intentionally introduced or inevitably added during the sliding or rubbing. The intentionally added third body could be lubricant oil or engineered nanomaterial used to mitigate the friction and wear of the sliding contact. The inevitably added third body could be wear debris created from the substrate or the counter surface during sliding. Even in the absence of any solid third-body between the sliding surfaces, molecular adsorption of water or organic vapors from the surrounding environment can dramatically alter the friction and wear behavior of solid surfaces tested in the absence of lubricant oils. This review article covers the last case: the effects of molecular adsorption on sliding solid surfaces both inevitably occurring due to the ambient test and intentionally introduced as a solution for engineering problems. We will review how adsorbed molecules can change the course of wear and friction, as well as the mechanical and chemical behavior, of a wide range of materials under sliding conditions.

Vapors in the ambient—A complication in tribological studies or an engineering solution of tribological problems?

AbstractTribology involves not only two-body contacts of two solid materials—a substrate and a counter-surface; it often involves three-body contacts whether the third body is intentionally introduced or inevitably added during the sliding or rubbing. The intentionally added third body could be lubricant oil or engineered nano-material used to mitigate the friction and wear of the sliding contact. The inevitably added third body could be wear debris created from the substrate or the counter surface during sliding. Even in the absence of any solid third-body between the sliding surfaces, molecular adsorption of water or organic vapors from the surrounding environment can dramatically alter the friction and wear behavior of solid surfaces tested in the absence of lubricant oils. This review article covers the last case: the effects of molecular adsorption on sliding solid surfaces both inevitably occurring due to the ambient test and intentionally introduced as a solution for engineering problems. We will review how adsorbed molecules can change the course of wear and friction, as well as the mechanical and chemical behavior, of a wide range of materials under sliding conditions.

Chemical and toxicological evolution of carbon nanotubes during atmospherically relevant aging processes.

The toxicity of carbon nanotubes (CNTs) has received significant attention due to their usage in a wide range of commercial applications. While numerous studies exist on their impacts in water and soil ecosystems, there is a lack of information on the exposure to CNTs from the atmosphere. The transformation of CNTs in the atmosphere, resulting in their functionalization, may significantly alter their toxicity. In the current study, the chemical modification of single wall carbon nanotubes (SWCNTs) via ozone and OH radical oxidation is investigated through studies that simulate a range of expected tropospheric particulate matter (PM) lifetimes, in order to link their chemical evolution to toxicological changes. The results indicate that the oxidation favors carboxylic acid functionalization, but significantly less than other studies performed under nonatmospheric conditions. Despite evidence of functionalization, neither O3 nor OH radical oxidation resulted in a change in redox activity (potentially giving rise to oxidative stress) or in cytotoxic end points. Conversely, both the redox activity and cytotoxicity of SWCNTs significantly decreased when exposed to ambient urban air, likely due to the adsorption of organic carbon vapors. These results suggest that the effect of gas-particle partitioning of organics in the atmosphere on the toxicity of SWCNTs should be investigated further.

The Effects of Aging on the Dynamic Adsorption of Hazardous Organic Vapors on Impregnated Activated Carbon

The effects of an eight-year natural aging of ASC impregnated activated carbon on the adsorption capacity and breakthrough times of model organic vapors and of the nerve agent sarin were investigated. Aging delayed methanol breakthrough from dry air on pre-dried carbon, but shortened the breakthrough time of both methanol and hexane under relative humidity (RH) of 30–85% on pre-humidified carbon. Aging also shortened the breakthrough time of the less volatile model compound 2-methoxyethanol, especially under RH of 60–85%. Aging significantly reduced the protection capacity against sarin at RH of 85%. The effects of aging on physisorption are attributed to enhanced hydrogen-bonding capability and strength of the interaction between water and adsorption sites on the carbon surface.

Synthesis of 1,3,5,7-tetrakis(4-cyanatophenyl)adamantane and its microporous polycyanurate network for adsorption of organic vapors, hydrogen and carbon dioxide.

This report presents the synthesis of a tetraphenyladamantane-based microporous polycyanurate network with a BET surface area of 843 m(2) g(-1) and a pore size of 7.8 Å. It uptakes 98.0 wt% benzene (298 K, P/P0 = 0.9), 1.49 wt% H2 (77 K/1 bar) and 12.8 wt% CO2 (273 K/1 bar) with CO2/N2 selectivity of up to 112.

Novel activated cotton as eco-adsorbent for solvent vapor

The potential of activated cotton (AC) as a low cost eco-absorbent for the recovery of organic solvent vapor was studied in this study. Its pore structure and chemical structure were characterized. Its adsorption speed, saturated adsorption volume and desorption process of solvent vapor were also evaluated. Its organic vapor adsorption process is fast enough to reach equilibrium within 10min. It adsorbs more solvent vapor than other activated carbons due to its high microporosity. Finally, less than 200°C is required for the complete desorption of adsorbed species.

Microporous Poly(Schiff Base) Constructed from Tetraphenyladamantane Units for Adsorption of Gases and Organic Vapors

A new microporous poly(Schiff base) (PSN-3) is constructed from 1,3,5,7-tetrakis(4-formylphenyl)adamantane and 1,3,5,7-tetrakis(4-aminophenyl)adamantane through an A4 -A4 ' reaction. The surface and internal morphologies of porous PSN-3 are examined by FE-SEM and HR-TEM. PSN-3 exhibits a BET surface area of 865 m(2) g(-1) with a major pore size around 0.6 nm. Moreover, PSN-3 can uptake 1.32 wt% H2 (77 K/1 bar), 13.6 wt% CO2 (273 K/1 bar), 80.5 wt% benzene, and 63.7 wt% cyclohexane (298 K/0.9 bar). The adsorption selectivities for CO2/N2, CO2/CH4, benzene/N2, and benzene/H2O are 88, 16, 267, and 19, respectively. The high adsorption capacities and selectivities for gases and vapors make PSN-3 a promising candidate for H2 storage, CO2 capture, and recovery of organic pollutants.

Tetraphenyladamantane-based microporous polyimide for adsorption of carbon dioxide, hydrogen, organic and water vapors

Tetraphenyladamantane-based microporous polyimide was synthesized. It can uptake 14.6 wt% CO2 at 273 K and 1 bar, 99.2 wt% benzene and 59.7 wt% cyclohexane at 298 K and 0.9 bar, exhibiting potential applications in gas storage and recovery of organic pollutants.

Removal of elemental mercury from Bayer stack gases using sulfur-impregnated activated carbons

The Bayer refining process can generate flue gases that contain elemental mercury, volatile organic carbons (VOCs) and water vapor creating a unique and challenging environment for the development of mercury adsorption technologies. Three sulfur impregnated activated carbons (SIACs) were tested under a range of conditions to assess each as a potential candidate for use in pilot scale fixed bed adsorber trials.All materials tested met or exceeded the mercury loading capacities specified by the respective suppliers and were therefore not significantly impeded by the addition of toluene into the gas phase. Of the SIACs, Pica/Alcoa Selexorb HG showed the lowest affinity to adsorption of organic vapors (toluene) and the highest affinity to the adsorption of mercury vapors (over a wide range of operating temperatures). Alcoa/Pica Selexorb HG is the preferable sulfur impregnated carbon for the removal of mercury vapors and is recommended for use in pilot trials.

Effect of the adsorbate kinetic diameter on the accuracy of the Dubinin–Radushkevich equation for modeling adsorption of organic vapors on activated carbon

This paper investigates the effect of the kinetic diameter (KD) of the reference adsorbate on the accuracy of the Dubinin–Radushkevich (D–R) equation for predicting the adsorption isotherms of organic vapors on microporous activated carbon. Adsorption isotherms for 13 organic compounds on microporous beaded activated carbon were experimentally measured, and predicted using the D–R model and affinity coefficients. The affinity coefficients calculated based on molar volumes, molecular polarizabilities, and molecular parachors were used to predict the isotherms based on four reference compounds (4.3≤KD≤6.8Å). The results show that the affinity coefficients are independent of the calculation method if the reference and test adsorbates are from the same organic group. Choosing a reference adsorbate with a KD similar to that of the test adsorbate results in better prediction of the adsorption isotherm. The relative error between the predicted and the measured adsorption isotherms increases as the absolute difference in the kinetic diameters of the reference and test adsorbates increases. Finally, the proposed hypothesis was used to explain reports of inconsistent findings among published articles. The results from this study are important because they allow a more accurate prediction of adsorption capacities of adsorbents which allow for better design of adsorption systems.

Effects of pore structure and surface chemical characteristics on the adsorption of organic vapors on titanate nanotubes

Effects of pore structure and surface chemical characteristics of titanate nanotubes (TNTs) on their adsorptive removal of organic vapors were investigated. TNTs were prepared via a hydrothermal treatment of TiO2 powders in a 10 M NaOH solution at 150 °C for 24 h, and subsequently washed with HCl aqueous solution of different concentrations. Effects of acid washing process (or the sodium content) on the microstructures and surface chemical characteristics of TNTs were characterized with nitrogen adsorption-desorption isotherms, FTIR, and water vapor adsorption isotherms. For the adsorption experiments, gravimetric techniques were employed to determine the adsorption capacities of TNTs for four organic vapors with similar heats of vaporization (i.e., comparable heats of adsorption) but varying dipole moments and structures, including n-hexane, cyclohexane, toluene, and methyl ethyl ketone (MEK), at isothermal conditions of 20 and 25 °C. The experimental data were correlated by well-known vapor phase models including BET and GAB models. Isosteric heats of adsorption were calculated and heat curves were established. Equilibrium isotherms of organic vapors on TNTs were type II, characterizing vapor condensation to form multilayers. The specific surface area (and pore volume) and hydrophilicity of TNTs were the dominating factors for the determination of their organic vapors adsorption capacity. The GAB isotherm equation fitted the experimental data more closely than the BET equation. The heats of adsorption showed that the adsorption of organic vapors on TNTs was primarily due to physical forces and adsorbates with larger polarity might induce a stronger interaction with TNTs.