Adsorption and thermo desorption characteristics of hydrocarbons on single walled carbon nanotubes

We investigated the heterogeneous adsorption and thermal desorption behaviors of acetone, n-hexane and trichloroethylene (TCE) on single walled carbon nanotubes (SWCNTs). Adsorption isotherms for selected molecules on SWCNTs were measured using a quartz spring balance at temperatures ranging from 303.15 to 323.15 K. Thermal gravimetric desorption experiments were also conducted at different heating rates (2-10 K/min) to obtain information about the interaction strength of hydrocarbons with SWCNTs surfaces. The adsorption isotherm data were analyzed successfully with the temperature dependent Toth equation. To obtain the adsorption and desorption energy distribution functions (AED/DED) for hydrocarbons and nitrogen, the integral equation with Fowler-Guggenheim isotherm (for AED) and first order desorption rate equation (for DED) were solved using the generalized nonlinear regularization method. It was found that Henry's constants, the isosteric heats of adsorption, and the pattern of energy distribution function were highly dependent on the polarizability.     

Surface energy heterogeneity and heterogeneous adsorption of benzene on double-walled carbon nanotubes

We examined the adsorption properties of double walled carbon nanotubes (DWCNTs) synthesized by using a catalytic chemical decomposition vapor method. To analyze the structural and energetical surface characteristics of the DWCNTs, nitrogen and benzene adsorption isotherms were measured. The Toth isotherm equation was used to correlate the adsorption data and evaluate the thermodynamic properties such as Henry's constant and the adsorption second virial coefficient. The existence of heterogeneous surface in DWCNTs was confirmed by the analysis of pore size distribution, the isosteric heat of adsorption, and the adsorption energy distribution determined for nitrogen and benzene.     

Adsorption and thermodesorption characteristics of benzene in nanoporous metal organic framework MOF-5

This study has been prepared and characterized a highly nanoporous metal organic framework (MOF-5). The nitrogen adsorption isotherm, gravimetric adsorption and thermodesorption method that utilize a quartz spring balance are used to examine the unusual adsorption behavior. Especially, the hybrid Langmuir–Sips isotherm equation is employed to correlate the experimental isotherm data. Moreover, the unusual adsorption behavior in MOF-5 is discussed in relation to its isosteric enthalpy of adsorption, adsorption energy distribution and desorption energy distribution calculated from benzene adsorption and thermodesorption measurements.     

Comparative experimental study of methane adsorption on multi-walled carbon nanotubes and granular activated carbons

In this study, methane storage capacity of granular activated carbons (GACs) and two types of multi-walled carbon nanotubes (MWCNTs) was investigated and compared. An experimental apparatus consisting a dual adsorption vessel was set up for measurement of equilibrium adsorption of methane on adsorbents using volumetric technique at pressure range of 0–50?bar at different temperatures. The first type of MWCNs has shown lower methane uptake (4.5?mmol?g^?1) compared to GACs (6.5?mmol?g^?1) at the temperature of 283.15?K and the pressure of 50?bar, while 33?mmol?g^?1 of methane storage capacity was achieved using the second type of MWCNTs that is much higher than methane storage on GACs at the same operating conditions. The superior uptake performance for the second type of MWCNTs can be attributed to its specific characteristics such as smaller pore size and higher pore volume. The experimental data of adsorption were almost equally well described by Langmuir, Freundlich and Sips equations to determine the model isotherms. The isosteric heat of methane adsorption on the adsorbent was calculated based on Clausius–Clapeyron and the Sips isotherm model using the experimental data at different temperatures. Results revealed that the isosteric heat of methane adsorption on MWCNTs was lower than the heat of methane adsorption on GACs. Low values obtained for isosteric heats of adsorption indicated dominance of physisorption mechanism for all adsorbents. In general, the obtained data indicated that some well-structured MWCNTs with uniform and narrow size distribution as well as higher pore volume are potential materials for methane storage and deserve further study.     

Adsorption characteristics and heat of adsorption measurements of R-134a on activated carbon

This paper presents adsorption isotherms of R-134a (HFC-134a) on highly porous pitch based activated carbon (Maxsorb III) in the temperature range of 5–70 °C and pressures up to 12 bar, using desorption method. The experimental data have been fitted with the Dubinin–Astakhov (D–A) isotherm equation. The adsorption isotherms of R-134a on Maxsorb III obtained from the present study are compared with the adsorption isotherm results of R-134a on similar type of adsorbents obtained by other researchers and they are found to be fairly consistent. The isosteric heat of adsorption of the assorted adsorbent–refrigerant pair has also been extracted from the present experimental data.     

Adsorption of Hydrogen in Graphitic Slit Pores

Molecular simulations of adsorption isotherms for hydrogen on graphite and graphitic slit pores are presented. The simulations employ the path integral isomorphism of Feynman to rigorously account for the quantum nature of the adsorbate. The isosteric heat of adsorption of para-hydrogen on planar graphite is computed from several different solid–fluid potential models and compared with experiment. The adsorption isotherm for hydrogen on the graphite basal plane was computed at 20 K and compared with experiment. Agreement with experiment is very good. Adsorption isotherms for hydrogen in slit pores of two different pore widths are computed at 20 K and compared with results from classical simulations. Quantum and classical isotherms exhibit qualitatively different behavior.     

ZSM-5沸石分子筛的高压吸附储氢特性

研究了ZSM-5沸石分子筛对氢的超临界吸附特性．结果表明,在77K／5MPa、195K／7MPa、293K／7MPa条件下,ZSM-5沸石分子筛的储氢质量分数分别为1．97％、0．65％和0．4％．用Clausius-Clapeyron方程求得的等量吸附热（3．8kJ／mol）与吸附量无关,表明该分子筛是一种表面势场均匀的吸附剂．将表面过剩吸附理论与描述Ⅰ型等温线的诸理论模型结合,分析了超临界吸附等温线,发现基于Toth方程的等温线模型在整个实验范围内与实验数据吻合较好,由该模型计算出的氢吸附相密度在77K达到55．6kg／m^3．根据回归参数讨论了超临界条件下氢在微孔沸石分子筛中的吸附机理,确认了氢在微孔沸石分子筛中的吸附为物理吸附．     

超高交联树脂对氯酚类化合物的吸附性能

通过静态吸附研究,比较了Am berlite XAD-4和ZH-01吸附树脂对水溶液中2-氯苯酚、2,4-二氯苯酚、2,4,6-三氯苯酚的吸附热力学特性。结果表明,在288 K~318 K和研究的浓度范围内,ZH-01、XAD-4对氯酚类化合物的吸附平衡数据符合F reund lich和L angm u ir吸附等温方程。2-氯苯酚在两树脂上的吸附为放热过程,是单分子层的物理吸附;而2,4-二氯苯酚和2,4,6-三氯苯酚在XAD-4吸附是单分子层物理吸附,在ZH-01的吸附属单分子层吸热过渡化学吸附,主要是毛细管凝聚和微孔填充作用造成的吸附。并计算了氯酚类化合物在两树脂上的吸附焓变、自由能变、吸附熵变,对吸附行为进行了合理的解释。     

Adsorption of trichloroethylene and benzene vapors onto hypercrosslinked polymeric resin

In this research, the adsorption equilibria of trichloroethylene (TCE) and benzene vapors onto hypercrosslinked polymeric resin (NDA201) were investigated by the column adsorption method in the temperature range from 303 to 333 K and pressures up to 8 kPa for TCE, 12 kPa for benzene. The Toth and Dubinin–Astakov (D–A) equations were tested to correlate experimental isotherms, and the experimental data were found to fit well by them. The good fits and characteristic curves of D–A equation provided evidence that a pore-filling phenomenon was involved during the adsorption of TCE and benzene onto NDA-201. Moreover, thermodynamic properties such as the Henry's constant and the isosteric enthalpy of adsorption were calculated. The isosteric enthalpy curves varied with the surface loading for each adsorbate, indicating that the hypercrosslinked polymeric resin has an energetically heterogeneous surface. In addition, a simple mathematic model developed by Yoon and Nelson was applied to investigate the breakthrough behavior on a hypercrosslinked polymeric resin column at 303 K and the calculated breakthrough curves were in high agreement with corresponding experimental data.     

Removal of anionic surfactants from aqueous solutions by adsorption onto high area activated carbon cloth studied by in situ UV spectroscopy

The removal of anionic surfactants, benzene sulfonate (BS), p-toluene sulfonate (TS), 4-octylbenzene sulfonate (OBS) and 4-dodecylbenzene sulfonate (DBS) from water and 0.01 M H(2)SO(4) solutions by adsorption onto high area activated carbon cloth (ACC) were studied by in situ UV-spectroscopic technique. The various properties of the ACC were given and the in situ UV-spectroscopic technique was described. Both kinetic and isotherm data were obtained for the adsorption of surfactants. Kinetic data were treated according to intraparticle diffusion, pseudo-first-order, pseudo-second-order and Elovich models. They were found to fit the pseudo-second-order model best. Isotherm data were treated according to well-known Langmuir and Freundlich models. The regression analysis of the data showed that Freundlich model represents the isotherm data of the surfactants better. The rate and extent of adsorption of surfactants were found to increase in the order BS相似文献   

Extension of the model of associated adsorbate to adsorption on patchwise heterogeneous surfaces

Isotherms and isosteric heats for adsorption on patchwise heterogeneous surfaces were studied numerically. The Berezin-Kiselev equation, which describes localized adsorption with interactions in the adsorbed phase, was assumed for the local adsorption isotherm. The numerical calculations were made by using the Dubinin-Radushkevich and the exponential energy distributions.     

Zeolite heat pump — adsorption of methanol in synthetic zeolites 13X, 4A and 5A

The adsorption isotherms for methanol adsorption in synthetic zeolites 13X, 4A and 5A were measured gravimetrically at various temperatures. The model of Langmuir and the potential theory were used for correlating the equilibrium data. The monolayer capacity was calculated using these two models. A small deviation at elevated temperatures was observed. The differential heat of adsorption was measured calorimetrically for all three zeolites. The isosteric heat of adsorption was calculated for zeolite 13X using measured equilibrium data. The log p, 1/T equilibrium diagram for zeolite 13X was computed using the Langmuir equation.     

Amine-impregnated MCM-41 in post-combustion CO2 capture: Synthesis,characterization, isotherm modelling

In this study, a composite mesoporous silica material MCM-41 (Mobil composite matter) is impregnated with monoethanolamine (MEA) as primary linear amine, benzylamine (BZA) as primary cyclic amine and N-(2-aminoethyl) ethanolamine (AEEA) as secondary diamine and the effects of amine loading, amine type, CO₂ partial pressure and adsorption temperatures on the CO₂ adsorption are investigated. The CO₂ adsorption performances of MCM-41 and amine impregnated MCM-41 samples are studied up to 1 bar of CO₂ partial pressure and the temperature range of 25–60 °C. The amine loadings (% impregnation) are optimized for maximum CO₂ uptake. The materials are characterised using N₂ adsorption/desorption isotherm, Fourier Transform Infrared (FT-IR) Spectroscopy, Thermogravimetric (TGA) and Elemental (CHNS) analysis. The materials have shown good structural and thermal stability. The MCM-41-40%AEEA, MCM-41-40%BZA and MCM-41-50%MEA samples are exhibited the CO₂ adsorption capacity of 2.34 mmol/g (102.98 mg/g), 0.908 mmol/g (39.96 mg/g) and 1.47 mmol/g (64.69 mg/g) respectively. The CO₂ uptake of MCM-41-40%AEEA is 3.5 times higher than that of in MCM-41 (0.68 mmol/g) and it is also the highest reported value as di-amine impregnated MCM-41. The results indicated that the adsorption capacities of the materials (MCM-41 and MCM-41-40%AEEA) are decreased with an increase of adsorption temperature in the range of 25–60 °C. The Freundlich, Langmuir, Sips and Toth isotherm models are used to correlate and predict experimental CO₂ adsorption data. The Sips and Toth isotherm models are found to be better fitted with the experimental data. The isosteric heat of adsorption of MCM-41 and MCM-41-40%AEEA samples are also calculated from Van’t Hoff plot using iSorbHP-win instrumental analysis software in the experimental temperature range.     

The adsorbate-adsorbate association model in localized adsorption of gases on random heterogeneous surfaces

In this paper we discuss the adsorbate-adsorbate association model, which assumes the formation of higher associates parallel to a heterogeneous surface with a random distribution of adsorption sites. The model calculations of the adsorption isotherms and isosteric heats were made using quasi-gaussian and exponential energy distributions. The critical properties of the adsorption isotherm equations, involving energetic heterogeneity and dispersion and association interactions in the surface phase, were also studied.     

4He adsorption isotherms on Na-plated Pyrex glass

We present ⁴ He volumetric adsorption isotherm measurements on small area cells made out of Pyrex glass, and the same cells coated with partial platings of evaporated sodium. Isotherms at 4.2K and 3.99K are used to obtain quanititative results for the isosteric heat of adsorption (q_st) on bare glass and qualitative results for q_st on the Na-plated portion of the cells.On leave from Instituto de Fisica, Universidade Federal do Rio de Janeiro, Brazil, supported by CNPq.     

Cryogenic adsorption of nitrogen on activated carbon: Experiment and modeling

A cryo-sorption device was built based on a commercial gas sorption analyzer with its sample chamber connected to the 2nd stage of the Gifford-McMahon (GM) cryocooler (by SUMITOMO Corporation), which could provide the operation temperature ranging from 4.5 K to 300 K; The nitrogen adsorption isotherms ranging from 95 to 160 K were obtained by volumetric method on the PICATIF activated carbon. Isosteric heat of adsorption was calculated using the Clausius–Clapeyron equation and was around 8 kJ/mol. Conventional isotherm models and the artificial neural network (ANN) were applied to analyze the adsorption data, the Dual-site Langmuir and the Toth equation turned out to be the most suitable empirical isotherm model; Adsorption equilibrium data at some temperature was used to train the neural network and the rest was used to validate and predict, it turned out that the accuracy of the prediction by the ANN increased with increasing hidden-layer, and it was within ±5% for the three-hidden-layer ANN, and it showed better performance than the conventional isotherm model; Considering large time consumption and complexity of the adsorption experiment, the ANN method can be applied to get more adsorption data based on the already known experimental data.     

Adsorption of Direct Red 80 dye from aqueous solution onto almond shells: effect of pH, initial concentration and shell type

The adsorption of Direct Red 80 (DR 80) dye from aqueous solution on almond shells as an eco-friendly and low-cost adsorbent was studied. The effect of shell type (internal, external and mixture shells), pH and initial dye concentration were considered to evaluate the sorption capacity of almond shell adsorbent. The mixture type of almond shell showed to be more effective. The adsorption studies revealed that the mixture type of almond shells remove about 97% of the DR 80 dye from aqueous phase after 1h of the adsorption process in a batch system. Although, pH changes did not appreciably affect the adsorption process but the maximum adsorption capacity of different types of almond shells (20.5, 16.96 and 16.4 mg/g for mixture, external and internal shells) were obtained at pH 2. However, in order to have a better control on the experimental conditions, pH 6 was selected for conducting all adsorption experiments. Initial dye concentration was varied from 50 to 150 mg/L. Higher concentrations of dye in aqueous solution reduced DR 80 dye adsorption efficiency of almond shells. Equilibrium data were attempted by various adsorption isotherms including Langmuir, Freundlich and Brunauer-Emmett-Teller (BET) models. It was found that the adsorption process by mixture type of almond shells follows the Langmuir non-linear isotherm. Furthermore, the experimental data by internal and external almond shells could be well described by the BET and Freundlich isotherm models, respectively. The pseudo-second-order kinetics provides the best correlation of the experimental data.     

Kinetics and equilibrium studies for the adsorption of Acid Red 57 from aqueous solutions onto calcined-alunite

The adsorption of Acid Red 57 (AR57) onto calcined-alunite was examined in aqueous solution in a batch system with respect to contact time, pH and temperature. The first-order, pseudo-second-order kinetic and the intraparticle diffusion models were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted very well the pseudo-second-order kinetic model and also followed the intraparticle diffusion model up to 90 min. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The equilibrium data are successfully fitted to the Langmuir adsorption isotherm. The Langmuir isotherm constant, K(L), was used to evaluate the changes of free energy, enthalpy and entropy of adsorption for the adsorption of AR57 onto calcined-alunite. The results indicate that calcined-alunite could be employed as low-cost material for the removal of acid dyes from textile effluents.     

Removal of fluoride from aqueous solution using granular acid-treated bentonite (GHB): batch and column studies

Removal of fluoride from aqueous solution using granular acid-treated bentonite (GHB) was studied by batch and column adsorption experiments. The results of the batch adsorption experiments demonstrated that the maximum fluoride removal was obtained at pH of 4.95 and it took 40 min to attain equilibrium. Kinetics data fitted pseudo-second-order model. Batch adsorption data was better described by Redlich-Peterson and Freundlich isotherm models than Langmuir isotherm model. The adsorption type of GHB was ion exchange. Column experiments were carried out at different influent fluoride concentrations and different flow rates. The capacities of the breakthrough and exhaustion points increased with the decrease of flow rate and the increase of initial fluoride concentration. The experimental results were well fitted with Thomas model. Exhausted GHB was regenerated by alkali/alum treatment. The total sorption capacity of GHB was increased after regeneration and activation.     

Thermodynamic analysis of single-stage and single-effect two-stage adsorption cooling cycles using indigenous coconut shell based activated carbon-CO2 pair

The CO₂ adsorption pressure concentration isotherms of indigenous coconut shell based activated carbon are measured using Sievert's type experimental setup. The thermodynamic properties viz. isosteric heat of adsorption at surface loading, Gibbs free energy, entropy and specific heat capacity are estimated using measured adsorption isotherms data. These measured adsorption isotherms data and thermodynamic properties are used for the thermodynamic analysis of single-stage and single-effect two-stage adsorption cooling system. The performance of the adsorption cooling cycle in terms of the maximum theoretical specific cooling effect and coefficient of performance at different driving heat source temperatures (80 °C for single-stage and 65 °C for single-effect two-stage) and evaporator temperatures (0, 5, 10 and 15 °C) is estimated. The maximum values of specific cooling effect and coefficient of performance are obtained as 9.26 kJ kg⁻¹ and 0.06 for single-stage and 8.85 kJ kg⁻¹ and 0.04 for single-effect two-stage cooling system respectively.