Adsorption Of Aromatic Compounds Research Articles

Adsorption of Aromatic Compounds by Activated Carbon: Effects of Functional Groups and Molecular Size

The adsorption of three aromatic compounds on to an untreated carbon was investigated. The solution pH was lowered in all experiments so that all the solutes were in their molecular forms. It was shown that the difference in the maximum adsorption of the solutes was mainly a result of the difference in the sizes of the molecules and their functional groups. Furthermore, it was illustrated that the packing arrangement was most likely edge-to-face (sorbate–sorbent) with various tilt angles. On the other hand, the affinity and heterogeneity of the adsorption systems were apparently related to the pKa values of the solutes.

Effects of the Solute Ionization on the Adsorption of Aromatic Compounds from Dilute Aqueous Solutions by Activated Carbon

Adsorption of four dissociating aromatic compounds and one nondissociating compound on a commercial activated carbon is investigated systematically. All adsorption experiments were carried out in pH-controlled aqueous solutions. The adsorption isotherms are fitted to the binary homogeneous Langmuir model, where the concentrations of the molecular and the ionic species in the liquid phase are expressed in terms of the sum of the two and the degree of solute ionization. Examination of the relationships between the solution pH, the degree of ionization of the solutes, and the model parameters is found to give new insights into the adsorption process. Furthermore, this is used to correlate the variation of the monolayer capacity with the solution pH.

Factors affecting the adsorption of fatty acids, alcohols and aromatic compounds on to carbon black pigments (flow micro-calorimetry studies)

The surface activity of different types of carbon black with fatty acids, alcohols and aromatic compounds, is examined using flow micro-calorimetry (FMC), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Significant differences in the overall adsorption activity of fatty acids and aromatic compounds are observed. The differences in behaviour between the various types of carbon black are evident and show that the specific surface area, as well as, their chemical nature are integral factors affecting the adsorption activity. Essentially, four factors were found to affect the adsorption activity of the fatty acids and alcohols: the presence of carboxylic and hydroxyl groups (which are found to form the strongest interactions with carbon black), the length and linearity of the hydrocarbon chain and the presence of unsaturation in the structure. Presence of aromatic ring type of functionality and size are also determinant factors in the adsorption of aromatic compounds. In order to characterise different carbon blacks, FTIR and XPS analysis have been used in an attempt to determine the nature of functional groups present on the surface of the carbon blacks. This provides valuable information regarding the adsorption mechanisms onto carbon black surfaces. Other techniques include thermogravimetric analysis (TGA), N 2 BET adsorption studies and Karl Fisher analysis. The latter tests were performed in order to determine differences in the volatile and water contents, respectively, of the carbon black samples.

Adsorption of aromatic compounds on C xN-coated activated carbon

C x N-coated activated carbons have been prepared by deposition of C x N on activated carbon at 600, 700 and 1000°C, and the adsorption of four aromatic compounds (nitrobenzene, benzoic acid, phenol and aniline) on the C x N-coated samples has been investigated. The C x N-coated samples were characterized by XPS, Raman spectroscopy and N 2 adsorption measurement at 77 K. The amount of nitrogen atoms bonded to three carbon atoms in graphene layers increased with increasing deposition temperature, while the surface areas of C x N-coated activated carbons decreased with increasing deposition temperature and duration. Molecular orbital calculation has suggested that the chemical interaction of C x N with aromatic compounds is enhanced due to low SOMO (Singly-Occupied Molecular Orbital) energy levels induced by nitrogen incorporation in graphene layers. The amounts of the adsorbed aromatic compounds per weight (g) of C x N-coated activated carbon were lower than those for original and heat-treated activated carbons, however, those per unit surface area (m 2) of the C x N-coated samples were larger than those for the uncoated ones as suggested by molecular orbital calculation.

Qualitative analysis of complex mixtures of VOCs using the inside needle capillary adsorption trap

An alternative sampling technique for fingerprint analysis of complex mixtures of petroleum-based products is presented. Fingerprint chromatograms of the volatile organic compounds (VOCs) for class 0-5 accelerants can be readily obtained using the recently developed inside needle capillary adsorption trap (INCAT) device. The concentration of VOCs from the static headspace of these complex mixtures, onto the adsorbing carbon coating of the INCAT device, avoids some problems associated with conventional headspace gas chromatography (HS-GC). The INCAT sampling method is a solventless extraction technique in which the analytes adsorbed inside the device are thermally desorbed inside the heated injection port of a gas chromatograph (GC), or a gas chromatograph coupled with a mass spectrometer (GC-MS). The presented method of active sampling with the INCAT device was used to obtain fingerprint chromatograms of the headspace of various gasolines, paint thinners, and lighter fluids. The static headspace chromatograms, from active sampling with the INCAT device, were compared with direct liquid injection of the samples. The INCAT chromatograms showed preferential adsorption of aromatic compounds over lighter, more volatile, but less polar compounds. Each class of the accelerant can be positively identified from the fingerprint chromatogram using only a few characteristic peaks. In addition, the ability to detect these volatile components of gasoline in aqueous samples at environmentally significant levels was also investigated.Key words: VOC, fingerprinting, INCAT, petroleum, headspace GC.

Qualitative analysis of complex mixtures of VOCs using the inside needle capillary adsorption trap

An alternative sampling technique for fingerprint analysis of complex mixtures of petroleum-based products is presented. Fingerprint chromatograms of the volatile organic compounds (VOCs) for class 0-5 accelerants can be readily obtained using the recently developed inside needle capillary adsorption trap(INCAT) device. The concentration of VOCs from the static headspace of these complex mixtures, onto the adsorbing carbon coating of the INCAT device, avoids some problems associated with conventional headspace gas chromatography (HS-GC). The INCAT sampling method is a solventless extraction technique in which the analytes adsorbed inside the device are thermally desorbed inside the heated injection port of a gas chromatograph (GC), or a gas chromatograph coupled with a mass spectrometer (GC-MS). The presented method of active sampling with the INCAT device was used to obtain fingerprint chromatograms of the headspace of various gasolines, paint thinners, and lighter fluids. The static headspace chromatograms, from active sampling with the INCAT device, were compared with direct liquid injection of the samples. The INCAT chromatograms showed preferential adsorption of aromatic compounds over lighter, more volatile, but less polar compounds. Each class of the accelerant can be positively identified from the fingerprint chromatogram using only a few characteristic peaks. In addition, the ability to detect these volatile components of gasoline in aqueous samples at environmentally significant levels was also investigated.

ChemInform Abstract: Adsorption of Aromatic Compounds and Molecular Structure: Experimental and Theoretical Descriptors

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Liquid-Phase Hydrogenation Kinetics of Aromatic Hydrocarbon Mixtures

The liquid-phase hydrogenation kinetics of one multiaromatic mixture and five binary aromatic mixtures of toluene, ethylbenzene, xylenes, and mesitylene were determined in a semibatch reactor operating at a pressure of 40 bar and a temperature of 125 °C. Commercial preactivated catalyst particles of nickel−alumina were used in the experiments. In mixtures, the aromatic compounds reacted in queues so that the most reactive components started to react immediately while the least reactive components did not react until the most reactive components had been hydrogenated completely. This type of reactivity decreased with the increasing number of substituents, i.e. in the order monosubstituted > disubstituted > trisubstituted. The relative positions of the substituents affected the reaction rate so that the reactivity decreased in the order ortho > para > meta. The queue effect was described with a kinetic model based on the rapid adsorption of aromatic compounds and hydrogen and sequential addition of hydrogen...

Monte Carlo simulations on adsorptions of benzene and xylenes in sodium-Y zeolites

The structures of benzene and C8 isomers ( o-xylene, m-xylene, p-xylene) in NaY simulated by the canonical Monte Carlo method were in good agreement with the experimental data of the available neutron diffraction analysis. All these sorbed compounds are stacked through the aromatic π-electron interaction on the cation of the SII site in the Sodium-Y. The experimental adsorption order ( m-xylene > o-xylene > p-xylene) of xylene isomers in the faujasite was also in good agreement with the order obtained from calculated heats of adsorption. It was shown that the difference in the interaction between the 4-ring sites and the methyl groups of xylene caused the better adsorption of m-xylene compared to those of the others. From these results, our conclusion is that the adsorption of the C8 isomers in the faujasite can be explained by considering only the interaction between the zeolite framework and the adsorbate approximated as a rigid model. Moreover, this type of simulation proved to be very useful to understand the mechanism of the adsorption of aromatic compounds in zeolites like faujasites.

Reversibility of adsorption of aromatic compounds onto powdered activated carbon (PAC)

Desorption of sorbed compounds is an important process in the powdered activated carbon-activated sludge (PAC-AS) wastewater treatment system, where sorption and biodegradation interact. To assess the extent of desorption to be expected in the PAC-AS system, reversibility of adsorption was investigated using isotherm studies and a leaching technique under the conditions prevalent in the PAC-AS system. Two aromatic compounds, o-cresol and 3-chlorobenzoic acid (3-CB), and two types of powdered activated carbon (PAC) were used to study desorption. High degrees of irreversible adsorption were observed with both desorption techniques, depending on the type of PAC and the compound. The thermally activated, peat-based PAC (SA4) showed a high degree of irreversible adsorption compared to the chemically activated, wood-derived PAC (CA1). The phenolic compound, o-cresol, could be desorbed to a lesser extent than 3-CB from both types of PAC. Contact time between the PAC and the compound was found to affect the desorption of o-cresol adversely. Oxygen availability enhanced the adsorptive capacity of SA4 for o-cresol. Sorption of 3-CB proved unaffected by either contact time or oxygen. Oxidative polymerization as a probable mechanism for the irreversible adsorption observed is also discussed. Desorption kinetics from SA4 showed a first phase of rapid desorption followed by a second phase of slow desorption. CA1 displayed the first rapid desorption phase only.

Desorption Characteristics of Aromatic Compounds in Aqueous Solution on Solid Adsorbents

Adsorption and desorption equilibria of 11 kinds of aromatic compounds were measured in their aqueous solution on an activated carbon and synthetic adsorbents. In the adsorption of aromatic compounds substituted by electron-donating groups in aqueous solution, the hysteresis between adsorption and desorption, which suggested the appearance of irreversible adsorption, was observed on activated carbon. Desorption isotherms coincided with adsorption isotherms on synthetic adsorbents. The electronic state of adsorbents and adsorbates was determined by the semiempirical molecular orbital calculation. It was found that irreversible adsorption appeared when the energy difference between HOMO of adsorbate and LUMO of adsorbent was small. An influence of acidic surface oxides of activated carbon was experimentally studied on the desorption characteristics of aromatic compounds. Although the amount adsorbed decreased by the wet oxidation of the carbon, the desorption characteristics were improved and the hysteresis disappeared. The results were supposed to be attributed to the change of the LUMO energy of carbon by wet oxidation.

Adsorption of aromatic compounds in large MFI zeolite crystals

Very large (180 × 40 × 40 µ3) and well defined crystals have been used in a gravimetric system to investigate the adsorption of aromatic compounds in MFI (silicalite) zeolite. The isotherms and isosteric heats of adsorption (Qst) were reported for future comparison with various adsorption models. Three types of phase transition were found. Isotherms of p-xylene showed a sharp step rise from ca. 4 to 8 molecules uc–1. A clear phase boundary could be outlined. Adsorbed benzene behaved as a dual-phase system in the range between 4.6 and 6 molecules uc–1. There were more phase transitions above 6 molecules uc–1 but it was not possible to outline the phase boundary. Molar entropy changes of 210 and 180 J mol–1 K–1 were found for the observed p-xylene–MFI and benzene–MFI phase transitions. For ethylbenzene and toluene, a dual-phase region was also observed but the transition was less pronounced. Isosteric heats, calculated from isotherms, showed a complex variation with loading and a strong dependence on temperature. It was also found that the adsorption kinetics are strongly influenced by the previous adsorption history. For freshly calcined samples the uptake rate was relatively fast. However, re-calcination after the adsorption of p-xylene created a diffusion barrier inside the crystalline material and subsequent adsorption of other aromatic compounds became much slower and displayed two-step kinetics.

Hydrophobic adsorption of aromatic compounds on polyurethane foam as carbon source for Pseudomonas growth

Hydrophobic adsorption of aromatic compounds on polyurethane foam as carbon source for Pseudomonas growth

Hydrophobic adsorption of aromatic compounds on polyurethane foam as a carbon source for Pseudomonas growth.

The use of polyurethane foam appears to be efficient to extract hydrophobic pollutants from aqueous media. Their adsorption is the result of spontaneous hydrophobic interactions with the foam, The rate of adsorption is a function of the diffusion of the molecules into the foam as well as their hydrophilic/lipophilic balance. A mixture of different molecules modifies the adsorption capacities of each type of molecule on the foam, probably resulting from stacking phenomena between the molecules. The Pseudomonas species can grow in the presence of the polyurethane foam and be adsorbed on it. Moreover, a strain of Pseudomonas pseudoalcaligenes tested in this study can use adsorbed biphenyl as the sole carbon source. Polyurethane foam therefore shows favorable characteristics for being chosen as a method of concentrating aromatic compounds and optimizing the rate of degradation of these molecules by bacteria.

Interpretation of Adsorptive Interaction in Aqueous Solution by Frontier Orbital Theory.

Adsorption equilibria of eighteen kinds of organic compounds in their aqueous solution were measured on activated carbon and synthetic adsorbents. Affinity coefficients for adsorption were determined by applying the DR equation to measured isotherms. It was found that the affinity coefficient depended on substituent groups of aromatic compounds.The adsorptive interaction on the activated carbon and the synthetic adsorbents was studied based on the frontier orbital theory. Electronic states of adsorbent, adsorbate and solvent were calculated using the semiempirical molecular orbital method. Then, the characteristic energy of adsorption in aqueous solution was estimated. Affinity coefficients were correlated by the characteristic energy ratio to the energy of the reference adsorbate. It was found that charge transfer interaction played an important role in the adsorption of aromatic compounds in aqueous solution. A correlation procedure of adsorption isotherm was proposed based on the DR equation and the characteristic energy.

The comparative reactivity of various organic adsorbates with Cu(II) in CuH-SAPO-5 and CuH-SAPO-11 molecular sieves studied by electron spin resonance

The adsorption rates of various organic adsorbates on CuH-SAPO-5 and CuH-SAPO-11 molecular sieves have been studied from changes in the electron spin resonance (e.s.r.) spectra of Cu(II). The adsorption rate for hydrazine is much faster than for ethylene, and hydrazine coordinates to Cu(II) through its π-bond. The room-temperature adsorption of aromatic compounds (benzene; o-, m-, and p-xylene; toluene; ethylbenzene; and aniline), saturated nonpolar hydrocarbons ( n-hexane, cyclohexane, methylcyclohexane, 1,2-dimethylcyclohexane, and 1,3-dimethylcyclohexane), and polar cyclohexylamine on dehydrated CuH-SAPO-5 and CuH-SAPO-11, heat-treated at 65–200°C, is evaluated. With increased pretreatment temperature, the original Cu(II) e.s.r. intensity ( I A ) decreases and the intensity of a sharp singlet at g = 2.003 ( I B ), associated with adsorbate decomposition, increases. From the variation of the I A I B ratio as a function of pretreatment temperature, the relative reactivity of Cu(II) in CuH-SAPO-5 and CuH-SAPO-11 toward the various organic adsorbates is determined. It is of particular interest that the order of reactivity differs between the SAPO-5 material with a 12-ring channel and the SAPO-11 material with a 10-ring channel.

Adsorption of benzoic acid from organic solvents on calcite and dolomite: Influence of water

A study has been carried out of the adsorption of benzoic acid from cyclohexane solution onto the hydrophilic surface of calcite. We determined initially the chemical and mineral composition of the solid, its specific surface area and its granulometry. This was followed by the determination of the enthalpies of immersion of calcite in different solvents. These thermodynamic properties gave information on the energetics of calcite—solvent interactions. In this way, we could construct a scale of affinities of the different organic molecules and water for the calcite surface. It was noted that the enthalpies were higher in unsaturated than in saturated organic solvents, and higher in water than in the organic solvents. The adsorption isotherms and the differential molar enthalpies of displacement were determined in the presence and the absence of water. The role played by water in the adsorption of polar organic molecules from the oil phase has not been clearly explained previously. In this paper, we indicate how the presence of water can modify the adsorption of aromatic compounds on the surface of calcite. As regards the adsorption isotherms, the presence of water essentially increases the amount of adsorption. The results of the calorimetric studies were found to be surprising; we observed that the differential molar enthalpies of displacement were endothermic. Similar experiments were carried out with dolomite and n-heptane solution and the results compared with those obtained with calcite and cyclohexane, leading to the formulation of a general model concerning the adsorption of small polar organic molecules from organic solvents onto the surfaces of the carbonates.

Adsorption of organic substances at electrodes: Recent advances

Recent developments concerning four areas in the field of adsorption of organic compounds at electrodes are critically examined and discussed. The topics are: (1) possibility of experimental determination of the molecular size factor, n; (2) effect of the nature of the metal on the Gibbs energy of adsorption; (3) effect of the crystallographic orientation of the metal surface; (4) effect of functional groups in the adsorption of aromatic compounds from non-aqueous solvents. Results show: (1) the value of n appears to be ⋍ 1 for all substances irrespective of the molecular size; (2) the nature of the metal is mainly seen through the desorption of the preadsorbed water molecules; (3) the effect of the atomic density of the metal surface cannot be assessed unambiguously from the few data available; (4) functional groups can change the adsorbate—solvent interactions as well as the aromaticity of the benzene ring. The combined effects can turn a physical interaction with the metal surface into a strong, specific chemical interaction via the π-electron system, as a consequence of changes in the interfacial orientation.

Partitioning and adsorption of aromatic compounds on microporous Silica gel

Partitioning and adsorption of aromatic compounds on microporous Silica gel

Retention times and heats of adsorption of aromatic compounds on carbon adsorbents

A high-performance liquid chromatographic method was applied to the determination of the adsorption isotherms and heats of benzene, toluene, ethylbenzene, o-xylene, pseudocumene, p-diethylbenzene and anisole from n-heptane on carbon adsorbents. The retention times of these compounds were determined at 20, 40 and 60°C. Comparison of the results of chromatographic and static investigations allowed the character of the dynamic process to be established. The heats of adsorption of aromatic compounds on carbon and silica adsorbents were compared. The mechanism of the adsorption interaction is discussed.