Preparation of active carbons from corn stalk for butanol vapor adsorption

Active carbons(ACs) were prepared through chemical activation of biochar from whole corn stalk(WCS)and corn stalk pith(CSP) at varying temperatures using potassium hydroxide as the activating agent. ACs were characterized via pore structural analysis and scanning electron microscopy(SEM). These adsorbents were then assessed for their adsorption capacity for butanol vapor. It was found that WCS activated at900 °C for 1 h(WCS-900) had optimal butanol adsorption characteristics. The BET surface area and total pore volume of the WCS-900 were 2330 m2/g and 1.29 cm3/g, respectively. The dynamic adsorption capacity of butanol vapor was 410.0 mg/g, a 185.1% increase compared to charcoal-based commercial AC(143.8 mg/g).

PROPERTIES AND THERMODYNAMICS OF ADSORPTION OF BENZOIC ACID ONTO XAD-4 AND A WATER-COMPATIBLE HYPERCROSSLINKED ADSORBENT

The adsorption behavior of benzoic acid onto a water-compatible hypercrosslinked polymeric adsorbent NJ-8 wascompared with that onto macroporous Amberlite XAN-4. This paper focuses on the static equilibrium adsorption behaviors,the adsorption thermodynamics and the column dynamic adsorption profiles. Five isotherm models are used to fit the results.This shows that the Freundlich equation can give a perfect fit. The specific surface area of NJ-8 is about as high as that ofAmberlite XAD-4, but the adsorbing capacity for benzoic acid on NJ-8 is about 14.9%-64.8% higher than that on AmberliteXAD-4, which is attributed to its microporous mechanism and partial polarity. The negative values of the adsorptionenthalpy are indicative of an exothermic process. Both enthalpy and free energy changes of adsorption manifest a physicalsorption process. The negative values of the adsorption entropy indicate that adsorption is well consistent with the restrictedmobilities and the configurations of the adsorbed molecules on the surface of the studied adsorbents with superficialheterogeneity. Both adsorbents were used in mini-column experiments to demonstrate the higher breakthrough adsorbing capacity of the hypercrosslinked polymeric adsorbent NJ-8 to benzoic acid, as compared with that of Amberlite XAD-4.

Kinetics and Thermodynamics of Adsorption of VB12 onto Mesoporous Carbon Coated with PMMA

Ordered mesoporous carbons CMK-3, CMK-I coated with poly（methyl methacrylate）（PMMA）（CMK-3- PMMA and CMK-1-PMMA） and pristine mesoporous carbons CMK-3, CMK-1 were employed to adsorb vitamin B12（VB12） from water solution. Adsorption isotherm and kinetics of adsorption were investigated via batch experiments. It was found that the adsorption capacity of VB 12 at 30, 40 and 50 ℃ can reach 688.2, 572.4 and 428.7 mg/g, respectively. The adsorption isotherm can be described by Langmuir model. The pseudo first- and second-order kinetic models were employed to fit the dynamic adsorption. It was found that the dynamic adsorption follows the pseudo second-order model. The thermodynamic equilibrium coefficients obtained at different temperatures were used to evaluate the thermodynamic constants △G^0, △H^0 and △S^0. The negative value of Gibbs free energy, △G^0 indicates that the adsorption occurred via a spontaneous process. The increase in the value of-△G^0 with increasing temperature indicates that higher temperatures were favourable to the sorption process. The enthalpy values of △H^0〉40 kJ/mol（66.36 kJ/mol and 56.43 kJ/mol） for CMK-3-PMMA and CMK-1-PMMA confirm that chemisorption were involved in the adsorption process. This is consistent with the IR spectra and is another evidence for the formation of hydrogen bond between PMMA in the pore of CMK-3 and VB 12.

Kinetics and Thermodynamics of Adsorption Methylene Blue onto Tea Waste/CuFe₂O₄Composite

Tea waste/CuFe2O4 (TW/C) composite was prepared by co-precipitation method. The TW and TW/C samples are characterized by FTIR, XRD, SEM and N2 physical adsorption. The results showed that specific surface area of 350 and 570 m2·g?1 for TW and TW/C, respectively. The average pore size of TW/C is ca. 100 nm. Adsorption of methylen blue onto TW/C composite has been studied. Measurements are performed at various contact time, pH and adsorbent dosage. The adsorption kinetics of methylen blue (MB) could be described by the pseudo-second order kinetic model. The adsorption isotherms are described by means of Langmuir and Freundlich isotherms. It was found that the Freundlich model fit better than the Langmuir model. The thermodynamic constants of the adsorption were calculated to predict the nature of adsorption. The values of thermodynamic parameters indicate that a spontaneous and endothermic process was occurred.

Elimination, Kinetics and Thermodynamics of Fe(II) Ions by Adsorption in Static and Dynamic Conditions on Activated Carbons in Aqueous Media

This work investigated the removal, kinetics and thermodynamics of iron(II) ions (Fe(II)) by adsorption in static and dynamic conditions in aqueous media on activated carbons (AC-i30min, AC-i1h, and AC-i24h), prepared from palm nut shells collected in the city of Franceville to Gabon, using potassium hydroxide (KOH) as the activating agent. Results on the elimination of Fe(II) in static and dynamic adsorption on prepared activated carbons (ACs) showed that the AC-i24h adsorbent has the best Fe(II) adsorption capacities at saturation (Qsat). The Qsat obtained on AC-i24h in static and dynamic conditions (17.87 and 10.38 mg/g, respectively) were higher than those of AC-i30min (13.89 and 5.54 mg/g respectively) and AC-i1h (14.92 and 8.64 mg/g respectively). Moreover, the static adsorption was more effective in the removal of Fe(II) ions in aqueous media in our experimental conditions. The percentage removal (%E) of Fe(II) obtained on prepared activated carbons in static conditions was better than those obtained in dynamic conditions, especially on AC-i24h, where the %E was 89.27% in static and 61.56% in dynamic. In kinetics, results showed that the pseudo-second-order kinetic model best described the adsorption mechanisms of Fe(II) on prepared activated carbons in static adsorption, with mainly of chemisorption on the solid surfaces. However, in dynamic conditions, the pseudo-first-order kinetic model was more suitable. In addition to the weak interactions between Fe(II) and the activated carbon surfaces, strong interactions (chemisorption) were also observed. Also, thermodynamic data obtained on AC-i24h in static adsorption indicated that the adsorption of Fe(II) was spontaneous and increased with temperature (ΔG˚ H˚ = 503.54 KJ/mol).

Investigations of methane adsorption characteristics on marine-continental transitional shales and gas storage capacity models considering pore evolution

Methane adsorption is a critical assessment of the gas storage capacity(GSC)of shales with geological conditions.Although the related research of marine shales has been well-illustrated,the methane adsorption of marine-continental transitional(MCT)shales is still ambiguous.In this study,a method of combining experimental data with analytical models was used to investigate the methane adsorption characteristics and GSC of MCT shales collected from the Qinshui Basin,China.The Ono-Kondo model was used to fit the adsorption data to obtain the adsorption parameters.Subsequently,the geological model of GSC based on pore evolution was constructed using a representative shale sample with a total organic carbon(TOC)content of 1.71%,and the effects of reservoir pressure coefficient and water saturation on GSC were explored.In experimental results,compared to the composition of the MCT shale,the pore structure dominates the methane adsorption,and meanwhile,the maturity mainly governs the pore structure.Besides,maturity in the middle-eastern region of the Qinshui Basin shows a strong positive correlation with burial depth.The two parameters,micropore pore volume and non-micropore surface area,induce a good fit for the adsorption capacity data of the shale.In simulation results,the depth,pressure coefficient,and water saturation of the shale all affect the GSC.It demonstrates a promising shale gas potential of the MCT shale in a deeper block,especially with low water saturation.Specifically,the economic feasibility of shale gas could be a major consideration for the shale with a depth of<800 m and/or water saturation>60%in the Yushe-Wuxiang area.This study provides a valuable reference for the reservoir evaluation and favorable block search of MCT shale gas.

Thermodynamics and kinetics of adsorption of molybdenum blue with D301 ion exchange resin

The adsorption behavior of D301 for molybdenum blue was investigated.The thermodynamics parameters in adsorption process were calculated and the adsorption kinetics was studied.The experimental results show that the adsorption characteristic of D301 for molybdenum blue fits well with the Freundlich adsorption isotherm equation.In the adsorption process of D301 for molybdenum blue,both the enthalpy change ΔH and entropy change ΔS are positive,while the free energy change ΔG is negative when temperatures are in the range of 303-333 K.It is indicated that the adsorption is a spontaneous and endothermic process,and the elevated temperatures benefit to the adsorption.Kinetic studies show that the kinetic data are well described by double driving-force model,and the adsorption rate of molybdenum blue on D301 is controlled by the intraparticle diffusion during the adsorption process.The total kinetic equation is determined.

Thermodynamics and kinetics of adsorption for heavy metal ions from aqueous solutions onto surface amino-bacterial cellulose

Amino-bacterial cellulose（amino-BC） was prepared by chemical modification of bacterial cellulose（BC）.The adsorption characteristics and mechanism of amino-BC were studied.The results show that adsorption data can be fitted well by Langmuir equation and the pseudo-second order kinetics,indicating that the adsorption of amino-BC would obey monolayer molecule adsorption and the main action was chemisorption.Meanwhile,the adsorption process was studied by the Elovich equation and the intra-particle diffusion model,indicating that the absorption characteristics of metal ions on amino-BC is controlled by both film diffusion and particle diffusion.The increase of reaction temperature will accelerate the adsorbing rate because of endothermic reaction.

THERMODYNAMICS ADSORPTION OF MANGANESE ION ON 1-(2-PYRIDYLAZO)-2-NAPHTHOL-6-SULPHONIC ACID IMPREGNATED RESIN

An ion-exchange resin of type 201×7 was impregnated with the reagent 1-(2-Pyridylazo)-2-naphthol-6-sulphonic Acid (PAN-S). The adsorption characteristics of PAN-S resin for manganese ion were studied on the static equilibrium adsorption. Within temperature range of 288K^313K and the concentration range investigated, equilibrium data for the adsorption of manganese ions from aqueous solutions by PAN-S resin were obtained and correlated with Freundlich and Langmuir equation. The results showed that the process of the adsorption of manganese ions from aqueous solution by PAN-S was an exothermic process. Estimations of the isothermic enthalpy change of adsorption,free energy change and entropy of adsorption are reported,and the adsorption behaviors are reasonably interpreted.

Thermodynamics and kinetics of cadmium adsorption onto oxidized granular activated carbon

Cadmium sorption behavior of granular activated carbon oxidized with nitric acid was systematically studied by sets of the equilibrium and time-based experiments under various conditions. The cadmium adsorption capacity of oxidized granular activated carbon enlarged with an increase in pH, and reduced with an increase in ionic strength. Experimental data were evaluated to find out kinetic characteristics. Adsorption processes were found to follow pseudo-second order rate equation. Adsorption isotherms correlate well with the Langmuir isotherm model and the maximum sorption capacity of cadmium evaluated is 51.02 μmol/g. Thermodynamic parameters were calculated based on Van＇t Hoff equation. Equilibrium constant Kd was evaluated from Freundlich isotherm model constants, Langmuir isotherm model constants, and isotherms, respectively. The average change of standard adsorption heat ΔH^0 was -25.29 kJ/mol. Negative ΔH^0 and ΔG^0 values indicate the adsorption process for cadmium onto the studied activated carbon is exothermic and spontaneous. The standard entropy ΔS^0 was also negative, which suggests a decrease in the freedom of the system.

Study on the Irreversible Thermodynamics of a Marine Engine Exhaust-powered Adsorption Refrigerating System

This study investigates the heat and mass transfer mechanism of a marine engifie exhaust-powered adsorption refrigerating system by using irreversible thermodynamics. The equations of entropy-production rate and the linear phenomenological equations of thermodynamic flux and force are established. The conventional experimental facilities of unit tube are developed and the phenomenological coefficients are obtained by fitting the experimental data. It is concluded that the thermodynamic process in the adsorbent bed is determined by the coupling effect of the heat and mass transfer; furthermore, the mass transfer is determined by the heat transfer. Taking some measures to increase heat transfer can improve the performance of the adsorption refrigerating system. The conclusions presented in this paper may be of value to the engineering applications of the system.

Characteristics of Phosphorus Adsorption with Boiler Slag and Process Optimization

[Objective] This study aimed to investigate the characteristics of phosphorus adsorption on boiler slag and optimize the adsorption process. [Method] Boiler slag was used as an adsorbent in the single-grade adsorption process to dispose the rural domestic sewage. During the course, phosphorus adsorption kinetics and thermodynamics, adsorption operating curve and the minimum boiler slag dosage were analyzed and calculated. [Result] Langmuir adsorption isotherm could be applied to describe the absorption of phosphorus with boiler slag, and the absorption kinetics was confirmed with the pseudo second-order equation. The maximum absorption quantity and the initial absorption rate increased with the rise of temperature, reaching up to 0.159 1 mg/g and 0.169 8 mg/(g·min) respectively at 40 ℃. Thermodynamic variables ΔG0<0 and ΔH0>0 indicated that the entire process was a spontaneous endothermic reaction, and high temperature would facilitate the reaction of absorption. In the single grade adsorption, the minimum adsorbent dosage decreased as the temperature rose; at 40 ℃ the optimum mass ratio of boiler slag to wastewater was 3.31 kg/m3. [Conclusion] The adsorption process with boiler slag as adsorbent is an economical and effective approach for treating rural domestic sewage.

A New Competitive Adsorption Isothermal Model of Heavy Metals in Soils

A new competitive adsorption isothermal model(CAIM)was developed for the coexistent and competitive binding of heavy metals to the soil surface.This model extended the earlier adsorption isothermal models by considering more than one kind of ion adsorption on the soil surface.It was compared with the Langmuir model using different conditions, and it was found that CAIM,which was suitable for competitive ion adsorption at the soil solid-liquid surface,had more advantages than the Langmuir model.The new competitive adsorption isothermal model was used to fit the data of heavy metal(Zn and Cd)competitive adsorption by a yellow soil at two temperatures.The results showed that CAIM was appropriate for the competitive adsorption of heavy metals on the soil surface at different temperatures.The fitted parameters of CAIM had explicit physical meaning.The model allowed for the calculation of the standard molar Gibbs free energy change,the standard molar enthalpy change,and the standard molar entropy change of the competitive adsorption of the heavy metals,Zn and Cd,by the yellow soil at two temperatures using the thermodynamic equilibrium constants.

Thermodynamic and Kinetic Studies of Effective Adsorption of 2,4,6-trichlorophenol onto Calcine Mg/Al-CO_3 Layered Double Hydroxide

Adsorption of 2, 4, 6-trichlorophenol（TCP） onto the calcined Mg/Al-CO_3 layered double hydroxide（CLDH） was investigated. The prepared Mg/Al-CO_3 layered double hydroxide（LDH） and CLDH were characterized by powder X-ray diffraction（XRD） and thermo gravimetric analyzer-differential scanning calorimeters（TG-DSC）. Moreover, 2,4,6-trichlorophenol（TCP） was removed effectively（94.7% of removal percentage in 9h） under the optimized experimental conditions. The adsorption kinetics data fitted the pseudosecond-order model well. The Freundlich, Langmuir, and Tempkin adsorption models were applied to the experimental equilibrium adsorption data at different temperatures of solution. The adsorption data fitted the Freundlieh adsorption isotherm with good values of the correlation coefficient. A mechanism of the adsorption process is proposed according to the intraparticle diffusion model, which indicates that the overall rate of adsorption can be described as three steps.

Study on Adsorption Behavior of P-nitroaniline from Aqueous Solution by Amphiphilic Hollow Carbonaceous Microspheres

[Objective] The research was aimed to study the adsorption behavior of p-nitroaniline from aqueous solution by porous hollow carbonaceous spheres （PHCSs）.[Method] The effects of pH,temperature and amount of carbonaceous microspheres on adsorption behavior of p-nitroaniline were investigated.[Result] The adsorption amount was affected by temperature slightly,and it decreased with the increase of temperature within a certain range.PHCSs had a higher adsorption capacity as pH was in the range of 2.0-8.0.The adsorption amount of p-nitroaniline was proportional to PHCSs amount within a certain range until it reached a saturation level.The adsorption isotherms of p-nitroaniline appeared to be nonlinear and obeyed to Freundlich equation very well.[Conclusion] The amphiphilic property and the specific chemical functional groups of PHCSs enable them to be a potentially excellent sorbent.

THE ADSORPTION BEHAVIORS OF 2,6-DICHLOROPHENOL ONTO HYPERCROSSLINKED RESINS

Experimental investigations were conducted on the adsorption characteristics of 2,6-dichlorophenol by two hypercrosslinked resins ZH-01 and XAD-4. The static adsorption was studied. Within temperature range of 288K-313K, the equilibrium adsorption date was fitted to freundlich adsorption isotherm models to evaluate the model parameters. The enthalpies, free energy, entropy were indicative of an exothermic, a spontaneous and disorder decreasing process. The magnitudes for 2,6-dichlorophenol on ZH-01 showed a chemisorption＇s transitions while on XAD-4 shows a physical adsorption process. The results showed that the ZH-01 adsorbents were better than the Amberlite XAD-4 for removing the 2,6-dichlorophenol in aqueous solutions.

Removal of heavy metals from aqueous solution by sawdust adsorption

The adsorption of lead, cadmium and nicel from aqueous solution by sawdust of walnut was investigated. The effect of contact time, initial metal ion concentration and temperature on metal ions removal has been studied. The equilibrium time was found to be of the order of 60 min. Kinetics fit pseudo first-order, second-order and intraparticle diffusion models, hence adsorption rate constants were calculated. The adsorption data of metal ions at temperatures of 25, 45 and 60~C have been described by the Freundlich and Langmuir isotherm models. The thermodynamic parameters such as energy, entropy and enthalpy changes for the adsorption of heavy metal ions have also been computed and discussed. Ion exchange is probably one of the major adsorption mechanisms for binding divalent metal ions to the walnut sawdust. The selectivity order of the adsorbent is Pb（I1）~Cd（II）〉Ni（I1）. From these results, it can be concluded that the sawdust of walnut could be a good adsorbent for the metal ions from aqueous solutions.

Recovery of rare earth element ytterbium(Ⅲ) by dried powdered biomass of spirulina: Adsorption isotherm, kinetic and thermodynamic study

The adsorption characteristics and mechanisms of spirulina powder were investigated when it was used as adsorbent to recover ytterbium(Ⅲ) from wastewater solution. Surface structure and element valence of the adsorbent were analyzed by SEM and XPS for the exploring of its adsorption mechanism for ytterbium(Ⅲ). The adsorption characteristics of ytterbium(Ⅲ) on spirulina powder was analyzed through assessing adsorption isotherm, kinetics and thermodynamic models. The adsorption isotherm data were best explained by Langmuir model, and the adsorption capacity of spirulina powder for ytterbium(Ⅲ) was 72.46 mg/g when adsorption temperature was 318 K. The kinetic experiment results showed that the pseudo-second order kinetic model can better simulate the adsorption process of spirulina powder to ytterbium(Ⅲ), indicating that the rate-controlling step was chemical adsorption. Spirulina can be an efficient and economical ytterbium(Ⅲ) recycling material, because it showed good adsorption stability and reusability from the adsorption-desorption cycle experiment results.

Thermodynamic study of adsorption of phenolic compounds onto Amberlite XAD-4 polymeric adsorbents and its acetylized derivative MX-4

Adsorption equilibrium isotherms of phenolic compounds, phenol, p cresol, p chlorophenol and p nitrophenol, from aqueous solutions by Amberlite XAD 4 polymeric adsorbent and its acetylized derivative MX 4 within temperature range of 283 323K were obtained and fitted to the Freundlich isotherms. The capacities of equilibrium adsorption for all four phenolic compounds from their aqueous solutions increased around 20% on the acetylized resin, which may be contributed to the specific surface area and the partial polarity on the network. Estimations of the isosteric enthalpy, free energy, and entropy for the adsorption process were reported.

Static and dynamic studies of adsorption by four macroporous resins to enrich oridonin from Rabdosia rubescens

Oridonin,one of the active ingredients in Rabdosia rubescens(R.rubescens),has been reported to induce cell apoptosis and cell cycle arrest in many cancers.Conventional extraction methods tend to result in unsatisfied enrichment and poor quality of oridonin present in a given biomass.This paper aims to evaluate the performance and separation characteristics of four different macroporous resins to arrive at the most suitable methodology for the isolation and purification of highquality oridonin.Static absorption kinetics,thermodynamic and dynamic adsorption were evaluated.HP20 was selected for further study due to its high adsorption capacity of 32 mgg 1 and desorption ratio with 98.5%.The pseudosecondorder model was considered to be the most suitable for kinetic results,and Langmuir model was chosen to better describe the absorption thermodynamics.Under optimum conditions(flow rate of 4 ml min 1,bed depth with 6 cm and initial concentration of 2.15 mg·ml^1),the effective content of oridonin increased from 33.9%to 79.1%in the dry extract with a recovery of 81%and the purity of oridonin improved from 76%to 93%.The results confirm that HP20 provides an efficient method to purify most oridonin from R.rubescens.