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Adsorption: Journal of the International Adsorption Society (v.15, #5-6)
Analysis of n-C4∼n-C10 mixtures in 5A molecular sieves using IAS theory with multi-site Langmuir isotherms by Ji-chang Liu; Ben-xian Shen; Ji-hong Dong (pp. 423-428).
The Constant-capacity Adsorption Solution (CAS) model for n-C4∼n-C10 mixture was built. Based on the adsorption experimental data, the Multi-site Langmuir (MSL) model was selected to describing the adsorption isotherms of n-C4∼n-C10 monocomponent. The CAS model was derived based on the IAS theory. The adsorption capacities predicted by the CAS model were compared with the experiment data of mixed gas adsorption. The results show the consistency. From the viewpoint of thermodynamics, the interactions between the normal paraffins of different carbon numbers were discovered. CAS model is applicative for the mixed gas in which the monocomponents have the similar adsorption capacities in the adsorbent.
Keywords: Normal paraffins; Molecular sieves; Adsorption model
Adsorption of CO2 on mesocellular siliceous foam iteratively functionalized with dendrimers by Zhijian Liang; Bandar Fadhel; Caspar J. Schneider; Alan L. Chaffee (pp. 429-437).
Melamine-type dendrimers are grafted to mesocellular siliceous foam (MCF) with ultralarge mesopores by stepwise alternating treatments of the substrate with 2,4,6-trichlorotriazine and ethylenediamine. MCF grafted dendrimers up to 4th generation are prepared and characterized. Very high organic loadings (55 wt% at the 4th generation) are achieved, with half of the initial substrate mesopores volume remaining unoccupied—leaving room for the rapid ingress and egress of small gas molecules. The product materials possess relatively high thermal stability—their decomposition starts at around 300 °C. Adsorption measurements suggest that only the primary amine groups of these melamine type structures are active for CO2 chemisorption. The CO2 adsorption capacities of these adsorbents are improved relative to the unfunctionalized MCF, especially when considered on a wt% substrate basis.
Keywords: Mesoporous material; Mesocellular siliceous foam; Melamine dendrimer; Functionalization; CO2 adsorption
Removal of phenols from water and petroleum industry refinery effluents by activated carbon obtained from coconut coir pith by T. S. Anirudhan; S. S. Sreekumari; C. D. Bringle (pp. 439-451).
Coir pith obtained from the coir industry as waste biomass was used to prepare activated carbon by chemical activation using phosphoric acid (H3PO4). The influences of activation temperature and lasting time of activation on specific surface areas (SSA) of the activated carbons were observed. Physical characteristics of the activated carbon were investigated using X-ray diffraction (XRD), infra-red spectroscopy (IR), surface area analyzer, scanning electron microscopy (SEM), thermal analysis and potentiometric titration. The feasibility of using activated carbon for the removal of phenol (P), p-chlorophenol (PCP) and p-nitrophenol (PNP) from water and petroleum refinery industry effluents was investigated. The effects of contact time, adsorbent dose, ionic strength and initial concentration on the adsorption of phenols onto the activated carbon were investigated. The optimum pH for the maximum removal of phenols was 6.0. The equilibrium adsorption data of phenols were correlated to Langmuir and Freundlich isotherm models, the latter being the best fit of the experimental data. Dynamics of the sorption process and mass transfer were investigated using McKay and Urano-Tachikawa models. Adsorption kinetic data fits the Urano-Tachikawa kinetic model. The utility of the adsorbent was tested by using petroleum refinery industry effluent. The adsorbed phenols can be recovered by treatment with 0.1 M NaOH solution.
Keywords: Coir pith; Activated carbon; Adsorption isotherm; Phenols; Mass transfer studies; Desorption
Sulfur fixation on bagasse activated carbon by chemical treatment and its effect on acid dye adsorption by M. Valix; W. H. Cheung; G. McKay (pp. 453-459).
Heteroatoms are known to introduce specific surface functionalities that can enhance the adsorption properties of carbons. Sulfur fixation on bagasse-activated carbon was conducted by a low temperature chemical treatment with sulfuric acid followed by physical activation with CO2 at 900 °C. The effect of sulfur fixation on the surface chemical properties of bagasse-activated carbons were investigated and on their subsequent acid dye removal (CIBA AB80) behavior. Surface chemical development were examined and followed using Fourier transform infrared spectroscopy (FTIR), heteroatom analysis and carbon surface acidity. Functional group stability with thermal treatment was also investigated. The textural properties of the activated carbons were characterized by nitrogen adsorption. Chemical pre-treatment and gasification was able to fix up to 0.2 wt% of sulfur on the activated carbon. Although the sulfur fixed by chemical treatment is low, this method introduced several advantages in comparison to fixation by thermal methods. The chemical method did not interfere with the textural development of the carbon, as found in thermal methods. In addition, the surface chemistry generated by these levels of sulfur groups was sufficient to increase the uptake of acid blue dyes by more than 700% based on adsorption capacities normalized by the surface area of the carbon.
Keywords: Bagasse; Sulfur fixation; Activated carbon; Adsorption
Adsorption of toluene and 1,1,1-trichloroethane on selected adsorbents under a range of ambient conditions by W. S. Bouhamra; C. G. J. Baker; A. S. Elkilani; A. A. Alkandari; A. A. A. Al-Mansour (pp. 461-475).
The effects of ambient temperature (25°C to 40°C) and relative humidity (0% to 30%) on the adsorption of toluene, and 1,1,1 trichloroethane on silica alumina, silica alumina impregnated with KMnO4, and activated carbon granules and pellets were determined. VOC concentrations in the range 1–1000 ppm were studied. Measurements of the weight of the adsorbed VOCs as a function of time were made in a thermogravimetric analyzer (TGA). Linear isotherms were tested in all cases. Values of the Henry coefficient H were in the range 0.01–0.10 mm3 air/mm2 BET area; they decreased with both increasing temperature and relative humidity. The highest values of H were consistently observed with KMnO4-impregnated silica alumina. Empirical correlations relating H to the parameters employed in this study were derived. There was good agreement between the values of H calculated from equilibrium and kinetic data obtained in the TGA and corresponding values measured in a glass test chamber. Improved correlation of the data was obtained using the nonlinear Freundlich, Toth and Dubinin isotherms. The determined fitting parameters for toluene and 1,1,1-trichloroethane on activated carbon were in good agreement with data published in the literature.
Keywords: Adsorption; VOC; Activated carbon; Silica alumina; Activated silica alumina; Relative humidity; Isotherms
Enhanced removal of hydrogen sulfide from a gas stream by 3-aminopropyltriethoxysilane-surface-functionalized activated carbon by Senlin Tian; Hong Mo; Renfeng Zhang; Ping Ning; Tinghua Zhou (pp. 477-488).
A commercial activated carbon was functionally modified by silylation with 3-aminopropyltriethoxysilane (APTES). The silylation led to the fixation of weakly basic functional groups, –NH2, on the surface as indicated by pH titration, Boehm titration, N $_{2^{-}}$ BET analysis and X-ray photoelectron spectroscopic (XPS) analysis. Despite reducing the specific BET area and the pore volume, silylation improved the H2S removal capacity so that APTES modified activated carbon (APTES-AC) was 3.55 times more effective than the original activated carbon. XPS results indicate that H2S removal may be associated with the amino (–NH2) group and the presence of sulfur in the four oxidation states S2−, S0, S4+ and S6+. The effects of moisture, oxygen content and temperature on the performance of APTES-AC for H2S removal were investigated. The presence of moisture in the gas stream was found to have an adverse effect on the H2S removal, whilst the presence of oxygen favored the removal of H2S by APTES-AC. The higher removal capacity of APTES-AC relative to the original activated carbon indicates that APTES-AC is a potential candidate for the removal of H2S from gas streams. The H2S removal efficiency of APTES-AC was proved be superior to that of Na2CO3-impregnated AC by the pilot-scale test of purification H2S containing industrial waste gas, yellow phosphorus off-gas.
Keywords: Activated carbon; Silylation; 3-Aminopropyltriethoxysilane; Hydrogen sulfide; Removal
Preparation of carbon molecular sieves from palm shell: effect of benzene deposition conditions by M. A. Ahmad (pp. 489-495).
Application of carbon molecular sieve (CMS) for gas separation has been found much attention recently. In this work, CMS was prepared from locally available palm shell through carbonization, steam activation and carbon vapour deposition (CVD) technique. After carbonization step, the char produced was subjected to steam activation at various activation times. The activated carbon obtained at 53.2% burn-off, which contain the highest amount of micropore volume was further used in CVD step by using benzene vapour at various deposition conditions. The performance of CMSs produced was examined by assessing the adsorption kinetics of O2, N2, CO2 and CH4 gases. All CMS samples showed a small N2 and CH4 uptake compared to the O2 and CO2. The suitable conditions for CVD were found at 800°C, 30 min and 30 vol% benzene of deposition temperature, time and benzene concentration, respectively. At this point the O2/N2 and CO2/CH4 uptake ratios arrived 7.1 and 16.0, respectively.
Keywords: Adsorption; Palm shell; Carbon molecular sieves; Uptake ratio
Adsorption of CO2 and N2 on synthesized NaY zeolite at high temperatures by Wei Shao; Luzheng Zhang; Liangxiong Li; Robert L. Lee (pp. 497-505).
NaY zeolite particles with a high surface area of 723 m2/g were synthesized by a hydrothermal method. Adsorption isotherms of pure gases CO2 and N2 on the synthesized NaY particles were measured at temperatures 303, 323, 348, 373, 398, 423, 448 and 473 K and pressures up to 100 kPa. It was found that the adsorption isotherm of CO2 on the synthesized zeolite is higher than that on other porous media reported in the literature. All measured adsorption isotherms of CO2 and N2 were fitted to adsorption models Sips, Toth, and UNILAN in the measured temperature/pressure range and Henry’s law adsorption equilibrium constants were obtained for all three adsorption models. The adsorption isotherms measured in this work suggest that the NaY zeolite may be capable of capturing CO2 from flue gas at high temperatures. In addition, isosteric heats of adsorption were calculated from these adsorption isotherms. It was found that temperature has little effect on N2 adsorption, while it presents marked decrease for CO2 with an increase of adsorbate loading, which suggests heterogeneous interactions between CO2 and the zeolite cavity.
Keywords: Adsorption isotherm; Isosteric heat of adsorption; Zeolite; CO2 capture
Porosity characteristics and pore developments of various particle sizes palm kernel shells activated carbon (PKSAC) and its potential applications by S. M. Mak; B. T. Tey; K. Y. Cheah; W. L. Siew; K. K. Tan (pp. 507-519).
The adsorption behaviour and the micro- and mesopore size distributions of commercial palm kernel shell activated carbons (PKSAC) and other commercial activated carbon are characterized. The results showed that PKSAC are predominantly microporous materials, where micropores account 68–79% of total porosity. On the other hand, commercial activated carbons: Norit SX Plus, Calgon 12×40, and Shirasagi “A” activated carbons contained high mesopore fraction ranging from 33 to 52%. The analysis showed that the degree of mesoporosity of PKSAC is increased steadily with the decrease of particle size. This is due to the presence of channels interconnect the smaller pores in the interior of smaller particle size PKSAC. The smaller size PKSAC particle that is highly mesoporous has preformed better on the adsorption of larger molecules such as methylene blue. On the other hand, bigger size PKSAC particle has better performance on the adsorption of smaller adsorbates such as iodine.
Keywords: Palm kernel shell activated carbons; Nanoporous; Mesoporosity; Particle size; Adsorption; Diffusion
Sorbate densities on 5A zeolite above and below the critical conditions: n alkane data evaluation and modeling by Kevin F. Loughlin; Dana Abouelnasr (pp. 521-533).
The sorbate densities of n-alkanes C1–C20 in 5A zeolite are modeled. For validation of this model, the n-alkane adsorption data for gases and liquids on 5A zeolite is critically evaluated using the concept of sorbate densities. The adsorbed phase critical temperatures appear to occur at a reduced temperature of 0.975 different from the vapor-liquid critical reduced temperatures of 1.0 for C3 to C20 n-alkanes. For methane and ethane species, the critical adsorbate reduced temperatures T CAR occur earlier at reduced temperatures of 0.83 and 0.96 respectively. The modified Rackett equation of Spencer and Danner (1972) is satisfactorily used to calculate the adsorbate loading for q max below adsorbed phase critical reduced temperature, T CAR.Above the critical adsorbate reduced temperatures, the saturated loading appears to be constant and equal to 8±1 g/100 gZ for all the alkanes. The data in this region is scarce however, as there are not many isotherms above a T r of 1.15. However the available isotherms appear to have a fairly equal and constant saturation loading between T r=T CAR and T r=1.652.
Keywords: n-alkanes C1–C20 ; 5A zeolite; Sorbate densities; Sorbate molar volumes; Critical conditions
Bioadsorption and ion exchange of Cr3+ and Pb2+ solutions with algae
by Maria das Graças Nunes Matos; Vivian Gouveia Diniz; Cesar Augusto Moraes de Abreu; Augusto Knoechelmann; Valdinete Lins da Silva; Edmilson Santos de Lima (pp. 535-535).