Adsorption Isotherms Of Benzene Research Articles

An inverse gas chromatography study of the adsorption of organics on zeolite and zeolite/iron oxyhydroxide composite at the infinite and finite surface coverage

The surfaces of natural (NZ) and zeolite/iron oxyhydroxide composite (ZFe) samples were analysed by means of inverse gas chromatography (IGC) using the adsorption data of organic non-polar and polar probes, in the infinite and finite-dilution regimes, in the temperature range 483?513 K. The dispersive components of the free energy of adsorption, ?S, determined by the Gray method, decreased with increasing temperature for both zeolites. The specific interactions were characterised by the specific free adsorption energy change, ?Ga S, the specific enthalpy change of adsorption, ?Ha S, as well as the donor and acceptor interaction parameters (KA, KD) and the basic character of the NZ and ZFe was evidenced. The adsorption isotherms of n-hexane, benzene, chloroform and tetrahydrofuran (THF) were determined under finite surface coverage and used to estimate the specific surface area and the adsorption energy distribution. The adsorption capacity of the ZFe was higher than for NZ for all the investigated adsorbates. The specific surface areas and pore size distributions were also determined using nitrogen adsorption?desorption isotherms, i.e., the BET method. It was observed that the nature of the adsorbate and the properties of the solid surface of the initial and modified samples governed the uptake of adsorbates.

Adsorption equilibrium of activated carbon amid fluctuating benzene concentration in indoor environments

Adsorption is commonly employed to remove volatile organic compounds (VOCs) from indoor air. However, the reversibility of this process has been rarely explored in prior research. Meanwhile, some previous research indicated partial reversibility in adsorption and desorption processes, which has not been described in traditional adsorption equilibrium models. In this study, we measured benzene adsorption and desorption isotherms on 6 activated carbons within two concentration ranges: 0–3 ppm and 0–6 ppm. The results showed that the adsorption process was partially reversible and the desorption isotherm was hysteretic for all the samples. Different carbons exhibited distinct isotherm patterns, yet the desorption isotherms in the experimental concentration range can be calculated from the adsorption isotherms using the same empirical equation. In addition, we measured the breakthrough curves using the oscillating benzene concentration (6 ppm to background) on the test columns. Reversible adsorption was observed at low degrees of saturation of the test column. Especially for microporous activated carbon, desorption could be sustained for several hours with purging even at the breakthrough rate of about 10%. An adsorption equilibrium model incorporating partially reversible adsorption and hysteretic desorption isotherm was developed based on the experimental data, which allows a preliminary interpretation of the measured breakthrough curves at fluctuating inlet concentrations.

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Process analysis of temperature swing adsorption and temperature vacuum swing adsorption in VOCs recovery from activated carbon

• The adsorption process of TSA and TVSA for VOCs in waste gas was studied, and the parameters of process purification and recovery of VOCs were discussed. • The dynamic adsorption experiment was completed,The adsorption isotherm of benzene on activated carbon was determined. • A mathematical model was established to simulate the process of TSA and TVSA. • The initial range of the optimal hot-cold purge ratio is determined. • The influence of vacuum step on adsorption and desorption step is discussed. • Under the condition of low grade heat source, TVSA will be an environmental protection process. In order to better guide the design of industrial process for purification and recovery of VOCs, Temperature swing adsorption (TSA) and Temperature vacuum swing adsorption (TVSA) process for VOCs purification and recovery were studied systematically with activated carbon adsorbent. The adsorption and desorption behaviors of benzene on activated carbon in above two processes were investigated systematically. Effects of operating parameters on process performances were further analyzed, including as regeneration temperature, purging feed ratio and hot-cold purging ratio. The results showed that the increase of hot-cold purging ratio (HP/CP) could obtain the same regeneration effect as the increase of desorption temperature. Increasing the feed purge ratio without increasing the hot-cold purging ratio is not conducive to bed regeneration, because a large number of cold purge gases cannot utilize the residual heat of temperature wave, thus reducing the desorption effect of the cooling step on the bed. In addition, the vacuum step can enhance the regeneration ability of hot nitrogen to the bed at the same regeneration temperature, making the bed regeneration of TVSA process more thorough. Temperature in the middle and lower part of the bed in TVSA process was higher and the regeneration was more thorough. In conclusion, TVSA has more obvious advantages than TSA in terms of energy consumption, hot or cold purge volume and bed regeneration.

Adsorption energetics of benzene vapors on activated adsorbent based on glycyrrhiza glabra root extract residues

Glycyrrhiza glabra root plant is mainly used in the pharmaceutical industry to obtain drugs. However, one of the important tasks is to obtain coal adsorbents with effective use of the remaining residues. We will have the opportunity to determine the full thermodynamic properties of the activated carbon adsorbent enriched with additional substances from the residues of the licorice root and to fully determine the adsorption properties of the obtained porous coal adsorbents using capillary and volumetric methods in a high-vacuum adsorption device and a high-sensitivity DAK 1-1 calorimetric apparatus. By determining the benzene adsorption isotherm, differential heat, entropy and equilibrium time of the obtained coal, the adsorption capacity of the new adsorbent, the location of the active centers, and the pore sizes can be described in detail.

Computer Analysis of the Porous Structure of Activated Carbons Derived from Various Biomass Materials by Chemical Activation.

In this study, the preparation of activated carbons from various materials of biomass origin by activation with potassium hydroxide and a comprehensive computer analysis of their porous structure and adsorption properties based on benzene (C6H6) adsorption isotherms were carried out. In particular, the influence of the mass ratio of the activator’s dry mass to the char mass on the formation of the microporous structure of the obtained activated carbons was analysed. The summary of the analyses carried out based on benzene adsorption isotherms begged the conclusion that activated carbon with a maximum adsorption volume in the first adsorbed layer and homogeneous surface can be obtained from ebony wood at a mass ratio of the activator to the char of R = 3. The obtained results confirmed the superiority of the new numerical-clustering-based adsorption analysis (LBET) method over simple methods of porous structure analysis, such as the Brunauer–Emmett–Teller (BET) and Dubinin–Raduskevich (DR) methods. The LBET method is particularly useful in the evaluation of the influence of the methods and conditions of production of activated carbons on the formation of their porous structure. This method, together with an appropriate economic analysis, can help in the precise selection of methods and conditions for the process of obtaining activated carbons at specific manufacturing costs, and thus makes it possible to obtain materials that can successfully compete with those of other technologies used in industrial practice and everyday life.

Benzene Adsorption on Nanoporous Silica Gels with Grafted Polyfluoroalkyl Layers and the Wettability

Features of the benzene adsorption in polyfluoroalkyl layers of different structures grafted on surfaces of silica gel (SG) are studied using gas chromatography, static adsorption, and diffuse reflectance IR spectroscopy. After modification, Henry’s law constants determined from the gas chromatography data and the static benzene adsorption values fall in the order SG > SG–F(III) > SG–F > SG–iso-F(III), where samples SG–F(III), SG–F, and SG–iso-F(III) are produced using silanes n‑C6F13(CH2)2SiCl3, n‑C6F13(CH2)2Si(CH3)2Cl, and iso-C3F7(CH2)2SiCl3, respectively. It is found that the energy characteristics of adsorption of benzene and other hydrocarbons on the SG–F(III) sample with the linear trifunctional modifier are 3–7 kJ/mol higher than the respective characteristics determined on the initial support. The contact angles for nanoporous silica gels with polyfluoroalkyl layers are calculated from desorption data in the region of the capillary condensation hysteresis of the benzene adsorption isotherms.

Assessing benzene and toluene adsorption with peat depth: Implications on their fate and transport.

After a hydrocarbon spill in a peatland, dissolution of water-soluble compounds including benzene and toluene introduces a dissolved-phase plume to the peatland groundwater system, while the adsorption of these solutes onto the peat matrix restrains their distribution velocity. The adsorption of benzene and toluene and its dependency on peat depth, thus degree of decomposition, are investigated. The batch adsorption experiments revealed that benzene and toluene adsorption isotherms in peat are linear, with adsorption coefficients ranging from 16.2 to 48.7L/kg and 31.6-48.7L/kg, respectively. In a vertical peat profile benzene adsorption decreased with depth, while toluene adsorption increased. Considering toluene adsorption onto cellulose is significantly less than toluene adsorption onto humic substance, the increase in toluene adsorption was attributed to decreasing cellulose and increasing humic substances with depth. Negligible competition for adsorption was observed between benzene and toluene at the measured concentrations. The retardation factors of benzene and toluene ranged respectively from 3.5 to 10.7 and from 5.4 to 17.7, both increasing with depth. Higher retardation in deeper peat coupled with lower hydraulic conductivity will lead to a weaker solute velocity in deeper peat, thus preferential migration of these dissolved-phase contaminants in shallow layers. The results can help predict the behavior of dissolved hydrocarbons in peatlands after a hydrocarbon spill.

Adsorption properties of benzene vapors on activated carbon from coke and asphalt

The industry produces a variety of wastes in production processes. This has a negative impact on the state of ecological balance. Today, in the oil industry, many different types of oil waste are accumulated as reserves. Focusing them on targeted production is one of the most pressing issues today. The use of a high-vacuum adsorption device is important in producing adsorbents from coke and asphalt from residual oil products and in the complete determination of the sorption properties of the obtained adsorbents. Benzene and toluene adsorption isotherms, the sorption volume, and properties of the new adsorbent can be described in detail by studying the adsorption heat.

Influence of Pyrocarbon Deposition in the Porous Structure of Activated Carbons

Deposition of pyrolytic carbon from the vapor phase onto the surface of various activated carbons, i.e., industrial (SKT and AG-3) and specially prepared via addition of KOH to a composition of carbon black with petroleum pitch followed by carbonization and washing, was studied. The deposition was carried out by passing benzene vapor in a stream of N2 through heated activated carbon. The obtained modified samples were studied using molecular probes by measuring adsorption isotherms of benzene and CCl4 at 20°C on the same samples. The results showed that the weight gain increased from 3% to 15% depending on the sample and the volume of micropores of width 0.4-0.6 nm increased to 0.07-0.15 cm3/g as the deposition time increased from 60 to 450 min. The modified activated carbons obtained in this manner could be used further to obtain carbon molecular sieves with pore sizes from 0.3 to 0.4 nm.

Interaction between Hydrocarbons C6 and Modified Activated Carbons: Correlation between Adsorption Isotherms and Immersion Enthalpies.

Adsorption isotherms of benzene, cyclohexane, and hexane were determined from the gas phase on microporous activated carbons with Brunauer–Emmett–Teller areas between 816 and 996 m2 g–1. The Dubinin–Radushkevich equation was used to calculate the parameters of characteristic energy Eo and micropore volume Wo. Also, immersion enthalpies of activated carbons in solvents were obtained (benzene: −95.0 to −145.1 J g–1; cyclohexane: −21.2 to −91.7 J g–1; and hexane: −16.4 to −66.1 J g–1), and they were used to calculate the product EoWo with the Stoeckli and Kraehenbuehl equations. Subsequently, values of EoWo from the two techniques (between 512 and 2223 J cm3 mol–1 g–1 for the adsorption isotherms; between 1204 and 12008 J cm3 mol–1 g–1 for immersion enthalpies) were correlated with some characteristics of the adsorbate such as molecular size, the molar volume, and the dielectric constant. It was found that modifying the activated carbon affected the adsorption process, being favored by temperature changes and restricted by oxidation processes. The adsorbate, which showed the highest values for EoWo, was benzene, because it had a smaller molecular size and a higher dielectric constant.

Trace benzene removal from vinyl acetate with ZIFs: A computational study

The removal of trace benzene from vinyl acetate with zeolitic imidazolate frameworks (ZIFs), a kind of metal-organic frameworks (MOFs) with formula unit M(IM)2 is studied. ZIF-2, ZIF-3, ZIF-6, ZIF-8, ZIF-10, and ZIF-68 are selected to study the adsorption of benzene and vinyl acetate. Density functional theory (DFT) method is used to study the interaction of the adsorbed molecules with the metal and organic linkers of ZIFs. Various adsorption positions are examined and the preferred configurations are obtained. The adsorption isotherms of benzene and vinyl acetate in pure components and benzene/vinyl acetate mixtures (0.01%/99.99%) in ZIFs at 373 K are obtained by molecular simulation. The calculation results showed that ZIF-68 has the highest selectivity for benzene.

The effect of diverse metal oxides in graphene composites on the adsorption isotherm of gaseous benzene

The effective removal technique is necessary for the real world treatment of a hazardous pollutant (e.g., gaseous benzene). In an effort to develop such technique, the adsorption efficiency of benzene in a nitrogen stream (5 Pa (50 ppm) at 50 mL atm min−1 flow rate and 298 K) was assessed against 10 different metal oxide/GO composite materials (i.e., 1: graphene oxide Co (GO-Co (OH)2), 2: graphene oxide Cu (GO-Cu(OH)2), 3: graphene oxide Mn (GO-MnO), 4: graphene oxide Ni (GO-Ni(OH)2), 5: graphene oxide Sn (GO-SnO2), 6: reduced graphene oxide Co (rGO-Co(OH)2), 7: reduced graphene oxide Cu (rGO-Cu(OH)2), 8: reduced graphene oxide Mn (rGO-MnO), 9: reduced graphene oxide Ni (rGO-Ni(OH)2), and 10: reduced graphene oxide Sn (rGO-SnO2)) in reference to their pristine forms of graphene oxide (GO) and reduced graphene oxide (rGO). The highest adsorption capacities (at 100% breakthrough) were observed as ~23 mg g−1 for both GO-Ni(OH)2 and rGO-SnO2, followed by GO (~19.1 mg g−1) and GO-Co(OH)2 (~18.8 mg g−1). Therefore, the GO-Ni(OH)2 and rGO-SnO2 composites exhibited considerably high capacities to treat streams containing >5 Pa of benzene. However, the lowest adsorption capacity was found for GO-MnO (0.05 mg g−1). Alternately, if expressed in terms of the 10% breakthrough volume (BTV), the five aforementioned materials showed values of 0.50, 0.46, 0.40, 0.44, and 0.39 L g−1, respectively. The experimental data of target sorbents were fitted to linearized Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich isotherm models. Accordingly, the non-linear Langmuir isotherm model revealed the presence of two or more distinct sorption profiles for several of the tested sorbents. Most of the sorbents showed type-III isotherm profiles where the sorption capacity proportional to the loaded volume.

Analysis of the microporous structure of the low-cost activated carbon fibres obtained from flax and jute cloth

The paper presents the results of research devoted to obtaining the low-cost activated carbon fibres from waste flax and jute cloth by carbonisation in inert atmosphere and activation with air as well as to the analysis of the microporous structure of materials obtained on the basis of the nitrogen, argon and benzene adsorption isotherms, using among others, the unique LBET method with implemented of the new models of the multilayer adsorption on the heterogeneous surfaces of the carbonaceous adsorbents. As part of the research conducted, imaging of the surface of the low-cost activated carbon fibres obtained has also been done using scanning electron microscopy.

Computer simulations of the structure and properties of organic pillared MFI zeolite catalyst

Multifunctional porous hybrid materials have recently received a lot of attentions because they combine the advantages of incorporating both inorganic oxides and organic species into the structure to solve the limitation of sole component material. This paper reports a type of model of organic pillared MFI zeolite catalyst, in which the full-atom mimetic model is constructed by using molecular modeling technique. Dreiding force field is used to calculate the interactions between sorbate–sorbate and sorbate–sorbent in the organic pillared MFI zeolite. The optimized model is characterized by calculating low-angle and high-angle X-ray diffraction patterns. Besides, the adsorption behavior of benzene and toluene is also investigated through the mimetic model. Simulated adsorption isotherms of benzene and toluene are agreement with the experimental data at low pressure. Density distributions of benzene and toluene show that toluene adsorbs preferentially in the region of interlayer space of lamellar MFI zeolite while benzene tends to adsorb in the area of micropores at low pressure. With increasing pressure, the guest molecules gradually fill in the area of micropores and mesopores of the organic pillared MFI zeolite. Moreover, the developed strategy in the present work can be applied to build other model for organic pillared zeolite catalyst by arranging different zeolite frameworks or organic species.

An analysis of the porous structure of activated carbons obtained from hazelnut shells by various physical and chemical methods of activation

This paper presents the results of the research analysing the microporous structure of carbonaceous adsorbents obtained from hazelnut shells by various physical and chemical methods of activation. The calculations were carried out with the use of the procedure of fast multivariant identification of adsorption systems with implemented LBET class adsorption models, which is generally referred to as the LBET method, as well as by DR and BET methods on the basis of adsorption isotherms of benzene and nitrogen. Porosimetry measurements, as well as imaging with the use of scanning electron microscopy and an EDX elemental analysis were also conducted.

Evaluation of Activated Carbon-Coated Electrode in Electrostatic Precipitator and Its Regeneration for Volatile Organic Compounds Removal

Activated carbon-coated electrode was developed and applied in electrostatic precipitator to remove volatile organic compound gases simultaneously with dust particles from a contaminated air. The activated carbon coating mixture was made up of powdered activated carbon (AC), carbon black (CB), and polyvinyl acetate (PVA), and methanol was added as a solvent to control the thickness of the mixture for best coating performance. During the coating process, the Brunauer-Emmett-Teller (BET) surface decreased to 86% of the original AC while pore volume percentages of macro pore increased, compared to micro- and meso-sized pores. The adsorption isotherm of benzene, toluene, ethyl benzene, and xylene (BTEX) gases onto the original AC and AC coating mixture (AC thoroughly mixed with PVA and methanol for coating and powdered again after dry) were tested and compared to each other, and it was found that both isotherm were best fitted to Freundlich and Langmuir isotherm with the order of adsorption capacities; ethyl benzene > m-xylene > toluene > benzene. The difference between adsorption capacities was clearer with the absorbent AC but became little with the AC coating mixture. In removing BTEX at increasing linear velocities up to 6.7 cm/s, it appeared that the surface area of AC electrode was directly proportional to its removal rate of BTEX. The thermal desorption was applied to regenerate the AC electrode, and 200 °C was found to be most efficient for benzene desorption, but higher temperature would be required for entire BTEX gases desorption.

A quartz crystal microbalance study of the adsorption of benzene and acetone vapors onto coumarin-substituted manganese phthalocyanine film

A novel coumarin-substituted manganese phthalocyanine (5) was successfully synthesized and used as sensing element for benzene and acetone vapor detection. The effects of water vapor on the benzene and acetone vapor-sensing properties and adsorption isotherms on thin film of 5 were also studied. Our preliminary results indicated that the presence of humidity modifies the baseline frequency but not the sensitivity of the sensor toward benzene and acetone vapors. Two isotherm models, Langmuir and Jovanovic isotherms, were selected to describe the adsorption process. Linear regression analysis, which is the most basic and commonly used predictive analysis method, was used to estimate the suitability of the selected isotherm models. The Jovanovic model was found to be adequate for describing benzene and acetone adsorption onto compound 5.

Adsorption isotherms of some alkyl aromatic hydrocarbons and surface energies on partially dealuminated Y faujasite zeolite by inverse gas chromatography

Adsorption isotherm data of some alkyl aromatic hydrocarbons (benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene) measured in the temperature range of 423–523K on a partially dealuminated faujasite type DAY F20 zeolite by inverse gas chromatography are presented in this work. The temperature dependent form of Tóth's equation has been fitted to the multiple temperature adsorption isotherms of benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene with standard deviations of 4.6, 5.0, 5.9, 4.3, 5.1 and 6.3mmolkg−1 and coefficients of determinations (r2) of 0.977, 0.971, 0.974, 0.975, 0.991 and 0.991, respectively. The gas–solid equilibria and modeling were interpreted on the basis of the interfacial properties of the zeolite, by dispersive, specific and total surface energy heterogeneity profiles and distributions of the adsorbent measured by surface energy analysis.

Surface oxidation of activated electrospun carbon nanofibers and their adsorption performance for benzene, butanone and ethanol

Carbon nanofibers prepared by electrospinning and subsequent steam activation were oxidized by treatment in HNO3 and HNO3/H2SO4 mixture. Surface morphology and degree of graphitic structure of oxidized nanofibers are affected mildly by acid oxidation according to SEM and Raman measurement. Nitrogen adsorption/desorption isotherms demonstrate decrease in specific surface area and pore volume of carbon nanofibers after oxidation. XPS spectra exhibit that oxidized nanofibers possess higher surface oxygen content than pristine nanofibers. Higher water adsorption capacities on oxidized nanofibers determined by water adsorption isotherms suggest the improvement of surface polarity and hydrophilicity. Furthermore, adsorption isotherms of benzene, butanone and ethanol show that surface oxidation enhances the adsorption tendency for butanone and ethanol on nanofibers due to increased surface polarity, indicating that the adsorption selectivity to polar organic compounds is improved.