Gas-solid Adsorption Research Articles

Biofilter Efficiency In Odor Abatement At Composting Plants

In the present work, five composting facilities have been examined for odor abatement efficiency of the gaseous emissions control devices, mainly scrubbers and biofilters. A correlation between olfactory nuisance and chemical composition was tried, using for the chemical analysis the same samples collected for the olfactometric experiments. The odor units were determined by the dynamic method (olfactometer). For the chemical analysis, the volatile organic compounds were first enriched by gas-solid adsorption and analyzed by gas chromatography-flame ionization detection and gas chromatography-mass spectrometry. The results evidenced the role of limonene as masking agent and the discontinuous performance of the biofilters. The formation of sesquiterpenes as by-products of limonene biodegradation was highlighted.

ChemInform Abstract: Air Pollution Controls

This chapter focuses on the requirement for air pollution control, principles of air cleaning, selection of suitable control methods, and economic and energy resources needed to install and operate emission control systems of various types. Keywords: Workplace air quality; Recirculated air Emission control requirements; Economic impact; Process control; System control; Elimination; Air-cleaning methods; Classification of controls; Gravitational separation; Inertial separation; Filtration; Liquid scrubbing; Gas-solid adsorption; Combustion; Selection; Application

Gas phase chemistry of technetium and rhenium oxychlorides

The chloride and oxychloride chemistry of the group 7 elements Tc and Re was investigated in order to develop an experimental approach to a gas chemical characterisation of bohrium (Bh, element 107). In thermochromatography experiments with trace amounts of101,104Tc and183,184Re the formation of one volatile compound was observed in O2/HCl containing carrier gas, which was attributed to MO3Cl (M = Tc, Re). From the measured deposition temperatures the adsorption enthalpies on quartz surfaces ΔHads(TcO3Cl) = -51 ± 3 kJ/mol and ΔHads(ReO3Cl) = -62 ± 3 kJ/mol were evaluated. The sublimation enthalpies were derived using an empirical correlation between Δ Hadsand ΔHsubl: ΔHsubl(TcO3Cl) = 49±10 kJ/mol and ΔHsubl(ReO3Cl) = 67±10 kJ/mol. A fast gas chemical separation technique for highly volatile compounds of short-lived isotopes based on isothermal gas solid adsorption chromatography (OLGA-principle) was developed. With a modified OLGA device, model studies with the short-lived nuclides106,107,108Tc and169,170,174,176Re were carried out in preparation of an experimental gas chemical investigation of bohrium (Bh, element 107). Separation times of less than 3 s were achieved. A good separation of the oxychlorides of group 7 elements from chloride and oxychloride compounds of152-155Er,151-154Ho (as models for actinide elements),98-101Nb,99-102Zr (as models for light transactinide elements),218Po, and214Bi was accomplished in this chemical system.

Modified van der Waals Equation for the Prediction of Multicomponent Isotherms

A modified two-dimensional van der Waals equation model was proposed for the prediction of multicomponent gas–solid adsorption isotherms from corresponding single-component adsorption equilibrium data. The model was used to predict adsorption isotherms of CO–CO2mixtures and CO2–N2mixtures on Cu(I)–NaY zeolite. Experimental adsorption equilibrium data of the two systems were compared with results calculated from the model and three other models in the literature: the ideal adsorbed solution model, the vacancy solution theory of adsorption using the Flory–Huggins activity coefficient equation, and the two-dimensional van der Waals equation. The results indicated that the modified van der Waals equation predicted the experimental results better than the three other models for the two systems studied, especially for the CO–CO2system, which involved chemical reaction during adsorption and exhibited azeotropic behavior.

The influence of relative humidity on the adsorption of toluene by soils — Interpretation with the adsorption energy distribution functions

It has been shown that the VOC adsorption capacity of soil decreases significantly with increasing relative humidity levels in the vapor phase. It might be due to the competition of adsorption sites by water molecules on the soil surfaces. Generally, the surface of nature adsorbents, such as soil and clay mineral, is highly heterogeneous owing to their complex chemical composition and irregularities of physical structure. It is necessary to describe the adsorption phenomena of nature adsorbent microscopically. Based on gas-solid adsorption isotherm, the energy distribution function of sorbing sites on soil surface were constructed. The variation of adsorption energy distribution function reveals that the adsorption energy for water was higher than that for toluene and, therefore, the soil surface would prefer to adsorb water vapor rather than toluene vapor. In addition, the adsorption energy of water vapor shifts towards the lower side at higher relative humidity level. It appears that the water vapor is condensed onto the surface. It is found that the previously adsorbed water molecules modified the soil surface and changed the energy spectrum of the adsorption sites. The shift of the adsorption energy spectrum to lower adsorption energy is the reason of the suppression of the soil uptake of organic vapors by water vapor.

Classification of Gibbs adsorption isotherms

The current IUPAC classification of gas–solid adsorption isotherms has two deficiencies: it is incomplete and it gives the incorrect impression that adsorption isotherms are always monotonically increasing functions of pressure. However, there are many isotherms that are not monotonic and show maxima. The reason for this deficiency is that the IUPAC classification is based conceptually on ideas about the `absolute' adsorption rather than on the Gibbs adsorption. It is shown here that supercritical gases show adsorption isotherms which are fundamentally different from those in the IUPAC classification. There are experimental data for hydrocarbons, inert gases, nitrogen, carbon oxide, carbon dioxide, nitrogen oxides, and others on microporous and macroporous adsorbents for supercritical temperatures showing nonmonotonic isotherms with maxima. It also is shown that the Ono–Kondo lattice model is able to predict all known types of adsorption behavior. By changing two energetic parameters (energies for adsorbate–adsorbate and adsorbate–adsorbent interactions), one can obtain smooth or stepped multilayer adsorption isotherms for macroporous adsorbents. It also is possible to describe adsorption on microporous adsorbents by imposing the appropriate boundary conditions. The Ono–Kondo model also predicts steps in isotherms similar to those observed in high resolution measurements for nitrogen and oxigen on zeolites. The monolayer version of the Ono–Kondo theory gives all known types of monolayer adsorption isotherms.

The multiple equilibrium model for characterizing porous materials

In this work, a multiple-process equilibrium model was used to analyze gas-solid adsorption equilibria in the porous carbonaceous material, BPL. Methane was used as a non-polar gaseous probe molecule to study the adsorption process. This analysis provided adsorption capacities, n i , along with the associated equilibrium constants, K i , for the three processes needed to fit the isotherms. The temperature dependence of the K i allowed determination of the enthalpies of the adsorption processes, Δ H i . These enthalpies were greater than the heat of vaporization for methane but less than that usually associated with chemisorption processes. Simulated adsorption data were generated based on the methane analysis to determine the effect of pore size distribution on the analysis. It is concluded that, given a continuous distribution of pore sizes, a large number of adsorption processes is necessary to describe accurately the total adsorption. For heterogeneous distributions, as is observed in activated carbon materials, it is possible to resolve discontinuities in the distribution.

Two-Surface Virial Analysis of Alkane Adsorption on Carbopack C with and without Hydrogen Treatment

Second gas–solid virial coefficients for propane, butane, pentane, and hexane were found for Carbopack C and Carbopack C-HT (Supelco Inc.) within the temperature range of 323 to 471 K using gas–solid chromatography in the Henry's law region of adsorption. Carbopack C and Carbopack C-HT are both graphitized carbon black powders. Treatment of Carbopack C with hydrogen at 1273 K converts it to Carbopack C-HT and is believed to remove certain high energy sites or “hot spots” from the carbon surface. These two surfaces provide appropriate model systems to test a two-surface virial analysis. Surface areas for both powders were calculated using a uniform single-surface model and a two-surface model. Only the two-surface virial model which is based on gas–solid interaction parameters determined by an iterative process and numerical integration gave reasonable areas for the two surfaces: 13.2 and 13.9 m2/g for Carbopack C and Carbopack C-HT, respectively. The percentage of high energy sites on the Carbopack C was found to be 2.6% and for Carbopack C-HT was found to be 1.5%. The gas–solid interaction energy for the high energy sites was found to be 1.80 times greater than the corresponding value for the low energy portion of the surface. In addition, the gas–solid adsorption energies for the four alkane adsorbates were found to have a linear correlation with their boiling points and with the ratio of their critical temperatures divided by the square root of their critical pressures.

The effects of pretreatment on the surface properties of soils

The specific surface areas of soil particles pretreated by sieving and degassing were measured with porosimeter to study whether these pretreatment procedures would result in changes on the surface properties of soil particles or not. It was found that different particle size and degassing temperature did not change the magnitude of specific surface area. The results revealed that the surface area of soil particles was contributed predominantly by internal surface and the degassing temperature did not affect the surface area till 250°C. And an indirect method, based on the gas-solid adsorption isotherm data, was used to estimate the adsorption energy distribution function for these soil-nitrogen system of different pretreaments. The results showed that the normalized distribution function was nearly similar for these two soils.

Theoretical study of cluster models and molecular hydrogen interaction with SnO 2 [110] surface

Cluster models representing the SnO 2 [110] surface were studied using MNDO, AM1 and PM3 semiempirical methods. The geometries of these clusters were optimized and the dependence of geometric and electronic properties upon cluster size was investigated. The geometric parameters for the cluster model Sn 15O β0 indicates a slight deviation from the experimental results whereas its energy gap of 3.76 eV is in close agreement with the experimental value. The interaction between H 2 and the [110] surface was also investigated in order to analyse the gas-solid adsorption process on the surface of the hydrogen sensor SnO 2. The geometry of the adsorbed gas on the tin oxide surface was also optimized. The H 2 interaction energy with the tin oxide surface is smaller than the corresponding interaction energy of the dissociative process which also indicates a charge transfer towards the bare cluster. Our results are compared with experimental data and the reliability of the different semiempirical methods is discussed.

Numerical procedure for calculating the gas-solid adsorption energy from molecular properties. Some comments on surface irregularities and adsorption site topography

Numerical procedure for calculating the gas-solid adsorption energy from molecular properties. Some comments on surface irregularities and adsorption site topography

COMPUTER SIMULATIONS OF FRACTAL SURFACES: APPLICATION IN ADSORPTION

A computer program which is able to simulate adsorption on fractal surfaces was developed. The fractal surfaces are generated as Takagi surfaces. The computer program is based on a DLA-algorithm. Adsorption was simulated in different conditions: 1. equivalent active sites (homogeneous surfaces); 2. active sites with different adsorption probabilities; the probability associated with every active site is computed using a van der Waals potential. Our simulation allows us to explore the actual structure of the gas-solid interface and to study the sensitivity to energetic disorder. The fractal dimension of gas-solid interface vs. adsorption coverage curves are computed.

Application of a new numerical method for characterizing heterogeneous solids by using gas-solid chromatographic data

A new numerical method for calculating the adsorption energy distribution function from retention volume data obtained by gas-solid adsorption chromatography is introduced. The method, which considers the ill-posed character of the problem, is applicable to all physico-chemical models that describe the local adsorption on one kind of sites. Using Langmuir and Jovanovic local isotherms the distribution functions are determined for n-hexane and 1-hexene on a glass and for cyclohexane and cyclohexene on two silica gels with different pore sizes.

High added value products from difficult wastes

The residual fly ash produced by coal combustion in thermoelectric power plants was mixed with vegetation water obtained from an olive mill. The aim of this research was to increase the adsorptive capacity of fly ash, by means a new way of aggregation, using residues from the food industry, namely the concentrate of the vegetation water from olive mills. In particular we tried up to obtain a solid product with the following characteristics: good mechanical strength; wet strength; high porosity and high specific surface area; good adsorptive properties. The product of the aggregation was submitted to a pyrolysis and activation process in order to obtain an adsorbent material. The pyrolysis produced an oily liquid fraction, with a good calorific value, a high hydrogen content gaseous fraction and a carbonaceous matrix dry residue. As the latter present good microstructural characteristics, it was utilized in adsorption processes, on laboratory apparatus, in order to evaluate its adsorptive capacity for organic vapours. The results obtained with gas-solid adsorption experiments in fixed-bed bench scale plant, using toluene vapours as the adsorbed gas, verified the possibility of getting useful products at a high added value from waste materials of difficult disposal qualities.

Simulation studies of adsorption in rough-walled cylindrical pores

A model is developed for porous materials in which the atomic nature of the solid is explicitly included. The result is a gas-solid interaction law for molecules in rough-walled pores of arbitrary shape. Simulations of adsorption isotherms and energies are reported for methane at 300 K in several model porous solids. The methane-solid interaction was obtained from a summation over solid atoms using parameters for the pairwise energies appropriate for methane in coal. Rough-walled cylindrical pores were considered in this work with radii equal to 6.5, 10.0, and 13.4 [angstrom]; for reference, adsorption on the flat adsorbent surface was also studied. Calculations of the average gas-solid adsorption energy which show the effects of variable pore radius are shown. The average methane-methane energy on these heterogeneous surfaces is shown to be non-negligible. The isotherm data are subjected to a simple analysis that allows one to fit their dependence on pore radius in a straightforward way. 15 refs., 12 figs., 4 tabs.

Precision and accuracy of the gas—solid adsorption isotherms derived by the elution-by-characteristic-points method

The influence of the fluctuations of the experimental parameters of the reproducibility of the overloaded band profiles used to determine the isotherms by the elution-by-characteristic-points (ECP) method was investigated using two new tools. A parameter measuring the difference between two similar curves, such as overloaded elution profiles or adsorption isotherms, was defined. The band profiles measured were compared with those calculated from the derived isotherm, using models from the theory of non-linear chromatography. The agreement between both profiles was defined as a distance lower than twice the average distance between two profiles measured on the same day on the same column. The degree of validity of the various assumptions made in the ECP method was assessed.

Analytical Scaling of Thermal Swing Adsorption

Abstract With many applications of fixed-bed gas-solid adsorption systems, it is not surprising to find a considerable amount of work reported in the literature, presented in conferences, and summarized in a number of textbooks. Reviews of different adsorption systems are available from Ruthven (5), Wankat (9), Yang (11), and Suzuki(7). The oldest adsorption process for gas purification employs thermal swing adsorption (TSA) cycles. Strongly adsorbed species are desorbed by raising the temperature of the adsorbent and sweeping the strongly adsorbed species out of the void space with a purge gas which is frequently the direct heating medium.

Gas phase retention volume behavior of organic compounds on Carbotrap graphitized carbon

The graphitized carbon material Carbotrap is often used for sampling gaseous organic compounds. Knowledge of the retention volumes of the compounds of interest on Carbotrap is required to design sampling protocols. Published data are examined here to develop correlation equations between retention volume and both vapor pressure and boiling point. The 38 compounds considered included ethane, butane, 1,2-dichloroethane, benzene, trichloroethene, 1,1,2-trichloroethane, phenol, toluene, chlorobenzene, n-butylamine, 4-heptanone, p-dichlorobenzene, decane, n-butylbenzene, biphenyl, n-dodecane, n-tetradecane. The correlation equations are examined in terms of gas—solid adsorption theory. They allow prediction of retention behavior for compounds for which experimental retention data are not yet available.

A new method of evaluation of specific surface area of solids using inverse gas chromatography at infinite dilution

A new method is proposed for the determination of specific surface areas of solids using gas solid adsorption inverse chromatography at infinite dilution. It is shown that this method is valuable especially for low surface area solids.

Application of Gas-Solid Adsorption Chromatography for Characterizing Adsorbent Heterogeneity

Abstract A new equation for the total net retention volume is used to describe pressuredependent retention measurements for cyclohexane and cyclohexene on wide-pore and narrow-pore silicas. This equation gives a good representation of the above experimental data. Parameters of this equation permit evaluation of the distribution functions that characterize the energetic heterogeneity of solid adsorbents.