Characterization and Methanol Adsorption of Walnutshell Activated Carbon Prepared by KOH Activation

Walnut-shellactivated carbons（WSACs）were prepared by the KOH chemicalactivation.The effects of carbonization temperature,activation temperature,and ratio of KOH to chars on the pore development of WSACs were investigated.Fourier transform infrared spectroscopy（FTIR）,X-ray powder diffraction（XRD）,and scanning electron microscopy（SEM）were employed to characterize the microstructure and morphology of WSACs.Methanoladsorption performance onto the optimalWSAC and the coal-based AC were also investigated.The results show that the optimalpreparation conditions are a carbonization temperature of 700 ℃,an activation temperature of 700 ℃,and a mass ratio of 3.The BET surface area,the micropore volume,and the micropore volume percentage of the optimalWASC are 1636 m^2/g,0.641 cm^3/g and 81.97%,respectively.There are a lot of micropores and a certain amount of meso-and macropores.The characteristics of the amorphous state are identified.The results show that the optimalWSAC is favorable for methanoladsorption.The equilibrium adsorption capacity of the optimalWSAC is 248.02mg/g.It is shown that the equilibrium adsorption capacity of the optimalWSAC is almost equivalent to that of the common activated carbon.Therefore the optimalWSAC could be a potentialadsorbent for the solar energy adsorption refrigeration cycle.

Performance of an Activated Carbon-Ammonia Adsorption Refrigeration System

An experimental study of the adsorption performances of NH3 on several commercial activated carbons was described. Firstly, the specific surface area, pore size distribution and morphological structure of the activated carbons have been characterized by N2 adsorption, Scanning Electron Microscope (SEM), and X-ray diffraction (XRD). The adsorption capacities of four kinds of activated carbons were compared based on adsorption isotherms at 30℃. Results show that a type of activated carbon MSC30 with high adsorption capacity of NH3 is a promising adsorbent for NH3 because of its large specific surface area and high pore volume. Secondly, the effect of adsorption temperature on the adsorption capacity of NH3 on MSC30 was investigated. A modified Dubinin-Astakhov equation was employed to describe the adsorption isotherms, with the reliability and accuracy evaluation. The isosteric heat of adsorption of MSC30-NH3 as a function of the amount adsorbed was calculated applying the Clausius-Clapeyron equation with isotherms obtained at 20℃ and 30℃. Thirdly, a packed-bed type adsorber was used to evaluate the influence of cycle time on the system cooling performance (coefficient of performance, specific cooling performance, and volumetric cooling performance) of the MSC30-NH3 pair at the evaporating temperatures of 5℃, 10℃ and 15℃ with a fixed adsorption/condensing temperature and desorption temperature of 30?C and 80℃, respectively. Finally, a long term operation without degradation for MSC30-NH3 adsorption was experimentally demonstrated from the 80 consecutive adsorption-desorption cycles.

Adsorption onto Activated Carbon Fiber Cloth and Electrothermal Desorption of Volatile Organic Compound(VOCs):A Specific Review

A general research program, focusing on activated carbon fiber cloths （ACFC） and felt for environmental protection was performed. The objectives were multiple： （i） a better understanding of the adsorption mecha- nisms of these kinds of materials; （ii） the specification and optimization of new processes using these adsorbents; （iii） the modeling of the adsorption of organic pollutants using both the usual and original approaches; （iv） applications of ACFC in industrial processes. The general question was： how can activated carbon fiber cloths and felts be used in air treatment processes for the protection of environment. In order to provide an answer, different approaches were adopted. The materials （ACFC） were characterized in terms of macro structure and internal porosity. Specific studies were performed to get the air flow pattern through the fabrics. Head loss data were generated and modeled as a fi.mction of air velocity. The performances of ACF to remove volatile organic compounds （VOCs） were approached with the adsorption isotherms and breakthrough curves in various operating conditions. Regenera- tion by Joule effect shows a homogenous heating of adsorber modules with rolled or pleated layers. Examples of industrial developments were presented showing an interesting technology for the removal of VOCs, such as dichloromethane, benzene, isopropyl alcohol and toluene, alone or in a complex mixture.

Adsorption characteristics of carbon tetrachloride from aqueous solution onto polyacrylonitrile-based activated carbon fiber

The isotherm,mechanism and kinetics of carbon tetrachloride(CT) adsorption by polyacrylonitrile-based activated carbon fiber(PAN-ACF) were investigated in batch reactors and a continuous flow reactor,and the regeneration of PAN-ACF was also studied.Freundlich and Dubinin-Radushkevich(D-R) adsorption equations can well describe the adsorption isotherm.CT is mainly adsorbed on the exterior surface of PAN-ACF with low boundary layer effect and rate-controlling step of intra-particle diffusion.The adsorption dynamics in the batch reactor well fits with the pseudo-first-order model,and the breakthrough curves in the continuous flow reactor can be well described by the Yoon-Nelson model.The ACF can be recycled through thermal regeneration,whereas the adsorption capacity decreases from 7.87 to 4.98 mg/g after the fourth regeneration.78%-94%of CT can be removed from the wastewater of a fluorine chemical plant on a pilot scale,which confirms the efficacy of ACF under industrial conditions.The results indicate that PAN-ACF is applicable to CT removal from wastewater.

Plasma Modification of Activated Carbon Fibers for Adsorption of SO_2

Viscose-based activated carbon fibers （VACFs） were treated by a dielectric-barrier discharge plasma under the feed gas of N2. The surface functional groups of VACFs were modified to improve the adsorption and catalysis capacity for SO2. The surface properties of the untreated and plasma-treated VACFs were diagnosed by SEM, BET, FTIR, and XPS, and the adsorption capacities of VACFs for SO2 were also compared and discussed. The results show that after the plasma treatment, the external surface of VACFs was etched and became rougher, while the surface area and the total pore volume decreased. FTIR and XPS revealed that nitrogen atoms were introduced onto the VACFs surface and the distribution of functional groups on the VACFs surface was changed remarkably. The adsorption characteristic of SO2 indicates that the plasmatreated VACFs have better adsorption capacity than the original VACFs due to the nitrogen functional groups and new functional groups formed in modification, which is beneficial to the adsorption of SO2.

STUDY ON THE PROPERTIES OF DIFFERENT ACTIVATED CARBON FIBERS AND THEIR ADSORPTION CHARACTERISTICS FOR FORMALDEHYDE

Porous structure and surface chemistry of activated carbon fibers obtained by differ-ent precursors and activation methods were investigated. Adsorption isotherms werecharacterized by nitrogen adsorption at 77K over a relative pressure range from 10 6to 1. The regularization method according to Density Functional Theory (DFT) wasemployed to calculate the pore size distribution in the samples. Their specific surfaceareas were calculated by BET method, micropore volume and microporous specificsurface area calculated by t-plot method and MPD by Horvath-Kawazoe equation. Mi-cropore volume of rayon-based ACF was higher than that of other samples. The staticand dynamic adsorption capacity for formaldehyde on different ACFs was determined.The results show that steam activated Rayon-based A CFs had higher adsorption capac-ity than that of steam and KOH activated PAN-A CFs. Breakthrough curves illustratedthat Rayon-ACFs had longer breakthrough time, thus they possessed higher adsorp-tion capacity for formaldehyde than that of PAN-ACFs. The entire sample had smalladsorption capacity and short breakthrough time for water. Rayon-A CFs had exccl-lent adsorption selectivity for formaldehyde than PAN-ACFs. And the samples withhigh surface areas had relatively high adsorption capacity for formaldehyde. Elementaicontent of different A CFs were performed. Rayon-based A CFs contained more oxygenthan PAN-ACFs, which may be attributed to their excellent adsorption capacity forformaldehyde.

Effects of Pre-oxidation Conditions on Adsorption Performance of Activated Carbon Fibers

In order to investigate the effects of pre-oxidation conditions on adsorption performance of activated carbon fibers （ ACFs ）, electrospun polyacrylonitrile （ PAN ） fiber webs were adopted as precursors for preparing ACFs. Firstly, the webs were stabilized under different pre-oxidation conditions; secondly, the pre-oxidative fibers were chemically activated by high temperature treatment in nitrogen. Pre-oxidation temperature, heating rate, and treatment time are the main factors on affecting the adsorption performance of the ACFs. Scanning electron microscope （ SEM）, differential scanning calorimeter （DSC）, and Fourier transform infrared spectroscopy （FTIR） were used to characterize the structure and property of the pre-oxldatlve fibers, and the dynamic benzene adsorption capacity of benzene of ACFs was measured. The results indicate that the moderate pre-oxidation condition is necessary to prepare the ACFs with better adsorption capacity, and the optimal oxidation conditions are to increase from room temperature to 230 ~C with a heating rate of 0.75 ~C ~ min -1 held at the peak temperature for 30min.

ORGANIC CHELATING REAGENT ON REDOX ADSORPTION OF ACTIVATED CARBON FIBER TOWARDS Au^(3+)

Organic chelating reagent influences upon the redox adsorption of activated carbon fiber towards Au3+ were systematically investigated. The experimental results indicated that the presence of organic chelating reagent on activated carbon fiber strongly affects adsorption capacity of activated carbon fiber towards Au3+. The reduction-adsorption amount of Au3+ increased three times by the presence of 8-quinolinol. Furthermore, The reduction-adsorption amount of Au3+ depended on the pH value of adsorption and temperature.

STUDIES ON THE DYNAMIC COMPETITIVE ADSORPTION OF ORGANIC VAPORS ON THE ACTIVATED CARBON FIBERS ACTIVATED WITH PHOSPHORIC ACID

The dynamic competitive adsorption behaviors of different binary organic vapor mixtures on ACF-Ps under different operation conditions were investigated by gas chromatography in this paper. The studied mixtures included benzene/toluene, toluene/xylene, benzene/isopropylbenzene, ethyl acetate/toluene and benzene/ethyl acetate. Experimental results show that various ACF-Ps, as with ACF-W, can remove both vapors in binary vapor mixtures with over 99% of removal efficiency before the breakthrough point of the more weakly adsorbed vapor. In dynamic competitive adsorption, the more weakly adsorbed vapor not only penetrates early, but also will be displaced and desorbed consequently by stronger adsorbate and therefore produces a rolling up in the breakthrough curve. The ACF-Ps prepared at different temperatures have somewhat different adsorption selectivity. The feed concentration ratio of vapors, the length/diameter ratio and the thick of bed have effect on competitive adsorption. The competitive adsorption ability of a vapor is mainly related to its boiling point. Usually, the higher the boiling point, the stronger the vapor adsorbed on ACF-P.

PREPARATION OF ACTIVATED CARBON FIBER AND THEIR XENON ADSORPTION PROPERTIES (II)-XENON ADSORPTION PROPERTIES

The adsorption of xenon from air has an interest in the monitoring of nuclear explosion or accident, or in the treatment of nuclear waste gas. In this paper, the pore structure of several series of activated carbon fibers has been characterized. The adsorption properties of xenon on these activated carbon fibers under different temperatures have been studied in details. The results show that the xenon adsorption amount on activated carbon fibers do not increase with specific surface area of adsorbents, but are closely related to their pore size distribution. Pores whose radius equal to or narrow than 0.4nm would be more advantageous to the adsorption of xenon.

ADSORPTION OF DYES ON ACTIVATED CARBON FIBERS

The adsorplion behavior of dyes on a variety of sisal based activated carbonfibers (SACF) has been studied in this paper The results show that this kind of ACFhas excellent adsorption capacities for some organic (dye) molecules. SACF canremove nearly all methylene blue, crystal violet, bromophenol blue and Eriochromeblue black R from water after static adsorption for 24 h. at 30℃ The adsorptionamounts can reach more than 400 mg/g when adding 50 mg SACF into 50 ml dyesolution. Under the same conditions, the absorption amounts of xylenol orangefluorescein and Eriochrome black T were lower On the other hand, the adsorptionamounts change along with the characteristics of adsorbents. The SACFs activatedabove 840 ℃ which have higher specific surface areas and wider pore radii, havehigher adsorption amounts for the dyes. The researching results also show that foeadsorption rates of dyes onto SACFs decrease by the order of methylene blue,Eriochrome blue black R and crystal violet.

Adsorption performances and refrigeration application of adsorption working pair of CaCl_2-NH_3

The adsorption performance of CaCl2?NH3 is studied under the condition of different expansion spaces for adsorbent, and the relationships between adsorption performance of CaCl2?NH3 and the phenomena of swelling and agglomeration during adsorption are researched. It is found that the performance stability is related to the ratio of expansion space to the volume of adsorbent r as, and the performance attenuation is serious in the case of large r as. Severe adsorption hysteresis exists in the process of adsorption and desorption at the same evaporating and condensing temperatures, which is related to the stability constant of chemical reaction. This phenomenon cannot be explained by the theory of physical adsorption. Moderate agglomeration will be beneficial to the formation of ammoniate complex; the magnitude of expansion space will affect adsorption performance. Analysis shows that the activated energy needed in the process of adsorption for the sample with r as. of 2∶1 is less than that for the sample with r as of 3∶1. The refrigeration performance of CaCl2?NH3 is predicted from experiments. The cooling capacity of one adsorption cycle is about 945.4 kJ/kg for the adsorbent with an r as of 2∶1 at the evaporating temperature of 0°C. Keywords chemical adsorption - attenuation - adsorption hysteresis - ammonia - activated carbon - refrigeration

Multiscale Simulation Starting at the Molecular Level for Adsorption Process Development

This article presents a multiscale simulation approach starting at the molecular level for the adsorption process development. A grand canonical Monte Carlo method is used for the prediction of adsorption isotherms of methanol on an activated carbon at the molecular level. The adsorption isotherms obtained in the linear region （or adsorption constant） are exploited as a model parameter required for the adsorption process simulation. The adsorption process model described by a set of partial differential equations （PDEs） is solved by using the conservation element and solution element method, which produces a fast and an accurate numerical solution to PDEs. The simulation results obtained from the adsorption constant estimated at the molecular level are in good agreement with the experimental results of the pulse response. The systematical multiscale simulation approach addressed in this study may be useful to accelerate the adsorption process development by reducing the number of experiments.

Dynamic Simulation of Absorber for Solar Adsorption Refrigerator: A Validated Numerical Model

In this work, a numerical model is presented that describes the transfer of heat and mass inside a cylindrical regenerator of a solar adsorption refrigerator that uses the methanol/activated-carbon refrigerant pair. This model is based on the equations of mass conservation, energy conservation, Darcy’s law and the balance model between sorbate and sorbent given by the Dubinin-Astak- hov’s equation. On the other hand, the linear driving force (LDF) model is used to describe the rate of desorption. In the developed model, the spatial variation of methanol vapor pressure within the activated carbon bed is taken into account and, as one of the boundary conditions, the temperature is used at the external surface of the absorber measured experimentally along the day. Using the developed model, the temperature, pressure and concentration of methanol were calculated;both inside the grains of carbon and in the space between the grains, as a function of time. The algorithm was validated comparing the numerical results with the experimental data, obtaining a satisfactory concordance.

Study of Static Adsorption Capacity of ACF for Xenon at 201 K

The static adsorption performances of a series of active carbon fiber(ACF)for xenon at 201 K were measured with a model ASAP2010M specific surface area and aperture distribution instrument by changing the working gas of instrument from N 2 to Xenon. Compared with grain active carbon(GAC): (1) the adsorption performance of Viscose based ACF(VACF) adsorbents is better than that of GAC; (2) owing to the difference of aperture distribution, the adsorption performance of ACF with different radicales is different under the same experiment conditions though the specific surface area is similar; (3) there is no definite relationship between adsorption performance and specific surface area; (4) the VACF A2 is the superior xenon adsorbent at the experimental temperature.

Static Adsorption of Xenon on ACF at 257 K

The static adsorption of xenon on active carbon fiber (ACF) at 257 K was measured with ASAP2010 specific surface area and pore diameter distribution instrument by changing the working gas from nitrogen to xenon. Compared with grain activated carbon (GAC), the results were as follows: (1) The adsorption performance of Viscose-based ACF (VACF-As) was the best among all absorbents tested. VACF-A3 was the superior xenon absorbent. The performance of pitch-based ACF (PACF-Cs) approached that of GAC, (2) Due to the difference of aperture distribution, the adsorption performances of ACF with different radics were different under the same experiment conditions even though the specific surface area was similar, (3) There were some differences of adsorptive capacity among ACF absorbents which had the same radic, however there was not definite relationship between their specific surface area and adsorptive capacity, (4) The adsorption of xenon on all kinds of ACF agrees with Langmuir equation, (5) The adsorptive curves can be fitted with a binomial equation.

ADSORPTION CHARACTERISTICS OF SACFs FORA VARIETY OF DYES

The isothermal adsorption of dyes on a variety of sisal based activated carbonfibers (SACFs), and the influence of PH and temperature on absorption are discussedin this paper The results indicate that the adsorption of methylene blue, crystal violetand Eriochrome blue black R on SACFs shows type I isotherms and can be describedby the Langnuir equation or the Freudlich equation. The acidity of solution hasgreatly ifluence over the adeorption amounts of methylene blue, crystal violet andEriochrome blue black R. As PHs of the solutions were adjusted to increase ordecrease from the original acidity of the solution (4. 7. 4. ) and 4. 0 for methylene blue,crystal violet and Eriochrome blue black R. respectively), the amounts of dyesadsorbed on SACFs increased. The adsorption temperature (in the range of 25~50℃)exerts little influence on the adsorption amount of methylene blue, crystal violet andfluorescein. For azo dyes (Eriochrome blue black R and Eriochrome black T), howeverthe absorption amount increases slightly with the elevation of temperature.

Adsorption and photocatalytic degradation of phenol over TiO_2/ACF

The adsorption and photocatalytic degradation of phenol in water were investigated in a cylindrical borosilicon glass photoreactor with a cooling water jacket using TiO 2/ACF as photocatalyst. A 15 W UV lamp(254 nm) was used as central light source. The effects of the temperature and initial concentration of phenol solution on adsorption and photocatalytic process were studied, and the comparison of adsorption, photolysis and photocatalysis was conducted. The results show that the classical model of Langmuir gives a good description of the adsorption of phenol on TiO 2/ACF and low temperature can improve the adsorption of phenol on photocatalyst; increasing temperature can increase the photocatalytic degradation rate of phenol; and the adsorption enhances the photocatalytic removal of phenol.

Adsorption Models and Structural Characterization for Activated Carbon Fibers

The nitrogen adsorption isotherms at 77.69 K were measured for two samples of activated carbon fibers and their microstructures were investigated. Among established isotherm equations, the Dubinin-Radushkevieh equation showed the best agreement with the experimental data, while the Langmuir equation showed a large deviation when employed at low relative pressures. The MP method, t-method and as-method were used to analyze the pore size distribution. The calculated average pore widths and BET （Brunauer-Emmett-Teller） surface areas for the sample A-13 were 0.86 nm and 1 286.60 m^2/g, while for the sample A-16, they were 0.82 nm and 1 490.64 m^2/g. The sample with larger pore width was more suitable to be used as additive in chemical heat pumps, while the other one could be used as adsorbent in adsorption refrigeration systems .

TiO_2-loaded activated carbon fiber:Hydrothermal synthesis,adsorption properties and photo catalytic activity under visible light irradiation

TiO2-loaded activated carbon fibers （ACF） were prepared by a hydrothermal method. The samples were characterized by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, Fourier transform infrared （FTIR） spectrometry and UV-vis diffuse reflectance spectra （DRS）. SEM images showed that the TiO2 nanoparticles were deposited on the surface of ACF, and the particle size and loading amount of TiO2 were varied by changing the initial concentration of tetrabutyl titanate （TBOT）. The results of an ash experiment showed that the loading amounts of TiO2 were 18.4%, 43.3%, 52.5%, 75.1%, and 91.1% for initial concentrations of TBOT of 0.07,014, 0.21,0.28, and 0.35 tool/L, respectively, Physical interactions played an important role in the formation of TiO2/ACF composite fibers that absorb UV and visible light. Compared with those of ACF, improved adsorption and photocatalytic activity toward Rhodamine B （RhB） were observed for TiO2/ACF composite fiber. The Rhodamine B could be removed efficiently by TiO2/ACF composite fibers, and the TiO2 loading amount had a significant effect on the photocatalytic activity of TiO2/ACF composite fibers.