Adsorption of carbon dioxide on microporous carbon adsorbents

Adsorption isotherms of carbon dioxide on microporous carbon adsorbents prepared by activation with potassium sulfide in water vapor were measured. The measurements were carried out in the pressure interval from 1 Pa to 0.1 MPa at temperatures from 216.2 to 293.15 K. Based on the theory of volumetric filling of micropores, the main structural and energetic parameters of the microporous carbon adsorbents were calculated. The adsorption isosters of carbon dioxide were calculated from the adsorption isotherms in the same pressure and temperature ranges and approximated by linear dependences. The plots of the differential mole isosteric heats of adsorption vs amount adsorbed were constructed by using the adsorption isosters.     

Dilatometric measurements on carbon adsorbents

Conclusion The dilatometric changes of carbon adsorbents as a result of water vapor adsorption-desorption cycles are irreversible and depend on the temperature of the initial dehydration. After an adsorption-desorption cycle, the granules remain expanded if the evacuation is carried out at 293 K and are irreversibly compressed if the dehydration is carried out at 623 K.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 927–929, April, 1987.     

Preparation and modification of complex pyrolytic carbon-silica adsorbents

Summary The surface properties of complex adsorbents prepared through the pyrolysis of dichloromethane on the surface of silica gel were investigated. The reaction was carried out in a specially constructed reactor at 400–500°C. The construction and performance of the reactor are described. The modification of the silica gel surface by pyrogenic carbon results in its chemical but not energetical homogeneity. Such adsorbents usually show strong adsorptive properties which limits their use in chromatography. A simple method of homogenizing the porous structure and energetic properties of the adsorptive centers of such adsorbents is presented. The method consists of an additional pyrolysis of an alcohol or other substances on the surface of the carbon-silica adsorbent. Such reactions were carried out under both static and dynamic conditions. The properties of the modified adsorbent depend on the reaction conditions and on the type of the additionally pyrolysed substance.     

Adsorption of proteins on mesoporous carbon adsorbents

A study of the sorption of bull serum albumin (BSA) on carbon adsorbents with different porous structures has shown that, for adsorbents with globular structures, sorption depends on the size of the adsorbent particles. An assumption has been made concerning the nonequilibrium nature of BSA sorption on mesoporous adsorbents associated with irreversible adsorption of the protein and the nonuniform distribution of the adsorbed protein within the adsorbent particles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1737–1740, August, 1991.     

Storage stability of ketones on carbon adsorbents

Activated coconut carbon constitutes the more widely used sorbent for preconcentration of volatile organic compounds in sampling workplace air. Water vapour is always present in the air and its adsorption on the activated carbon surface is a serious drawback, mainly when sampling polar organic compounds, such as ketones. In this case, the recovery of the compounds diminishes; moreover, ketones can be decomposed during storage. Synthetic carbons contain less inorganic impurities and have a lower capacity for water adsorption than coconut charcoal. The aim of this work was to evaluate the storage stability of various ketones (acetone, 2-butanone, 4-methyl-2-pentanone and cyclohexanone) on different activated carbons and to study the effect of adsorbed water vapour under different storage conditions. The effect of storage temperature on extraction efficiencies was significant for each ketone in all the studied sorbents. Recovery was higher when samples were stored at 4 degrees C. The results obtained for storage stability of the studied ketones showed that the performance of synthetic carbons was better than for the coconut charcoals. The water adsorption and the ash content of the carbons can be a measure of the reactive sites that may chemisorb ketones or catalize their decomposition. Anasorb 747 showed good ketone stability at least for 7 days, except for cyclohexanone. After 30-days storage, the stability of the studied ketones was excellent on Carboxen 564. This sorbent had a nearly negligible ash content and the adsorbed water was much lower than for the other sorbents tested.     

Adsorption of hydrogen on nanoporous carbon adsorbents

Four samples of active carbons with specific micropore volumes of 0.4—1.33 cm³g^-1 at 77 K and pressures up to 5 MPa were used to study hydrogen adsorption. The highest amount of of hydrogen adsorbed on these active carbons at the boiling point 20.38 K and pressure 0.101 MPa was calculated by methods derived from the theory of volumetric filling of micropores (TVFM). The adsorbent FAS-1-05 prepared by the liquid-phase polymerization of furfurol was shown to have the highest adsorption capacity. The amounts of hydrogen adsorbed on FAS-1-05 at temperatures 77, 196, and 300 K and pressures 7 and 20 MPa were calculated using the TVFM methods with allowance for linearity of the isosters. The results were compared with the experimental values obtained at 77 K and pressure below 5.1 MPa and at 293 K and pressures up to 16.1 MPa. The highest amounts of hydrogen adsorbed (6.2 wt.% for the adsorbent FAS-1-05) were obtained under pressures below 5.1 MPa and at 77 K.     

The solvent eluotropic strength on carbon adsorbents

Summary Two theoretical approaches are discussed to calculate the solvent strength () on carbon materials. One is based on the adsorbate-adsorbent interfacial tension and the other uses the theory of solubility parameters. It is shown that there is good agreement between these approaches. Experimental values are compared with theoretical ones and there is again a good agreement. Solvents having small and highly polar molecules have small values. Solvents having large and aromatic molecules have high values. Binary solvent mixtures can be classified in two groups depending on the rate of change of with the mole fraction of the strongest solvent in the mixture.Dedicated to Professor Dr. István Halász for his 60th birthday.     

Radiative-thermal modification of dispersed and fibrous adsorbents by metal compounds

The investigation of solid-phase reaction in salt-oxide systems has a promising future for radiative modification of the surface by metallic clusters and oxides.     

Features of sulfur hexafluoride adsorption on carbon adsorbents

The isotherms describing excess adsorption of SF₆ and N₆I₆ on carbon adsorbents with different pore structures were measured at pressures of 0.001—2.4 and 0.0001—0.1 MPa, respectively, and temperatures of 298—408 E. A linear dependence of Henry"s constant on temperature in the lnK—10³/O coordinates was found for all the samples. The specific surface areas of the samples determined by the BET method from the SF₆ adsorption are lower than those derived from benzene adsorption. The most pronounced difference was found for the grafitized carbon black. When SF₆ was adsorbed on supermicroporous carbon AC-71 and on microporous carbons PAC and CMS, a hysteresis was found, which, unlike that on mesoporous carbon adsorbents, is observed in the initial region of the equilibrium pressures.     

Energetic aspects of micropore adsorption in carbon adsorbents

Russian Chemical Bulletin -     

Adsorption of sodium dodecylsulfate on modified carbon adsorbents

The adsorption of anionic surfactants on carbon adsorbents modified with water-soluble derivatives of natural polymers, cellulose and chitin, is considered with sodium dodecylsulfate taken as an example. It is shown that such modification leads to changes in the adsorption structural characteristics and the particle size distribution of carbon-water suspensions of the original adsorbent, and to the emergence of new functional groups on its surface that are able to interact selectively with adsorbate molecules. It is assumed that adsorption of anionic surfactant on carbon adsorbents under equilibrium conditions proceeds via stepwise filling of the carbon??s porous structure: we first observe volume filling of micropores according to their sizes, and then the formation of a surfactant??s monolayer in mesopores and on the outer surface of the adsorbate. It is established by thermal analysis that the thermal stability of carbon adsorbents is enhanced through the preferential localization of anionic surfactants in micropores. The filling of mesopores and the outer carbon surface by surfactant molecules leads to a regular decrease in thermal stability and an increase in the adsorbent surface??s hydrophilicity.     

The adsorption of water isotopomers on carbon adsorbents

Adsorption isotherms were measured by the gas chromatography method over the temperature range 50–80°C, and isosteric heats of adsorption of water isotopomers were calculated in the region of low coverages on two active carbons (Norit and FAS) with similar volumes of micropores (0.38 and 0.37 cm³/g) but different chemical properties of the surface (the surface of active carbon (AC) Norit is hydrophilic and that of AC FAS, hydrophobic). The isotherms on AC Norit were convex and those on AC FAS concave toward the axis of adsorption. At all equilibrium pressures, the adsorption of H₂O and D₂O on AC Norit was much higher than on AC FAS. The isotherms of adsorption of H₂O and D₂O were quite similar on both adsorbents, but the isotherms and heats of adsorption of D₂O were slightly higher than those of H₂O because of small differences in adsorbate-adsorbent and adsorbate-adsorbate interactions and the structure of adsorbate molecules. Original Russian Text ? S.N. Lanin, N.V. Kovaleva, L.A. Litvincheva, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 2, pp. 351–355.     

Surface modification of chromatography adsorbents by low temperature low pressure plasma

In this study we show how low temperature glow discharge plasma can be used to prepare bi-layered chromatography adsorbents with non-adsorptive exteriors. The commercial strong anion exchange expanded bed chromatography matrix, Q HyperZ, was treated with plasmas in one of two general ways. Using a purpose-designed rotating reactor, plasmas were employed to either: (i) remove anion exchange ligands at or close to the exterior surface of Q HyperZ, and replace them with polar oxygen containing functions (‘plasma etching and oxidation’); or (ii) bury the same surface exposed ligands beneath thin polymer coatings (‘plasma polymerization coating’) using appropriate monomers (vinyl acetate, vinyl pyrrolidone, safrole) and argon as the carrier gas. X-ray photoelectron spectroscopy analysis (first ∼10 nm depth) of Q HyperZ before and after the various plasma treatments confirmed that substantial changes to the elemental composition of Q HyperZ's exterior had been inflicted in all cases. The atomic percent changes in carbon, nitrogen, oxygen, yttrium and zirconium observed after being exposed to air plasma etching were entirely consistent with: the removal of pendant Q (trimethylammonium) functions; increased exposure of the underlying yttrium-stabilised zirconia shell; and introduction of hydroxyl and carbonyl functions. Following plasma polymerization treatments (with all three monomers tested), the increased atomic percent levels of carbon and parallel drops in nitrogen, yttrium and zirconium provided clear evidence that thin polymer coats had been created at the exteriors of Q HyperZ adsorbent particles. No changes in adsorbent size and surface morphology, nor any evidence of plasma-induced damage could be discerned from scanning electron micrographs, light micrographs and measurements of particle size distributions following 3 h exposure to air (220 V; 35.8 W L⁻¹) or ‘vinyl acetate/argon’ (170 V; 16.5 W L⁻¹) plasmas. Losses in bulk chloride exchange capacity before and after exposure to plasmas enabled effective modification depths within hydrated Q HyperZ adsorbent particles to be calculated as 0.2–1.2 μm, depending on the conditions applied. The depth of plasma induced alteration was strongly influenced by the power input and size of the treated batch, i.e. dropping the power or increasing the batch size resulted in reduced plasma penetration and therefore shallower modification. The selectivity of ‘surface vs. core’ modification imparted to Q HyperZ by the various plasma treatments was evaluated in static and dynamic binding studies employing appropriate probes, i.e. plasmid DNA, sonicated calf thymus DNA and bovine serum albumin. In static binding studies performed with adsorbents that had been exposed to plasmas at the 5 g scale (25 g L⁻¹ of plasma reactor), the highest ‘surface/core’ modification selectivity was observed for Q HyperZ that had been subjected to 3 h of air plasma etching at 220 V (35.8 W L⁻¹). This treatment removed ∼53% of ‘surface’ DNA binding at the expense of a 9.3% loss in ‘core’ protein binding. Even more impressive results were obtained in dynamic expanded bed adsorption studies conducted with Q HyperZ adsorbents that had been treated with air (220 V, 3 h) and ‘vinyl acetate/argon’ (170 V, 3 h) plasmas at 10.5 g scale (52.5 g L⁻¹ of plasma reactor). Following both plasma treatments: the 10% breakthrough capacities of the modified Q HyperZ adsorbents towards ‘surface’ binding DNA probes dropped very significantly (30–85%); the DNA induced inter-particle cross-linking and contraction of expanded beds observed during application of sonicated DNA on native Q HyperZ was completely eradicated; but the ‘core’ protein binding performance remained unchanged cf. that of the native Q HyperZ starting material.