Kinetics and equilibrium of dissolved oxygen adsorption on activated carbon

The macroscopic adsorption behavior of dissolved oxygen on a coconut shell-derived granular activated carbon has been studied in batch mode at 301 and 313 K for initial dissolved oxygen concentrations of 10-30 mg/l and oxygen/carbon ratios of 2-180 mg/g. BET (Brunauer, Emmett, and Teller) surface area, micropore volume, and pore size distribution were determined from N₂ isotherm data for fresh and used samples of carbon. The surface groups were characterized using Boehm titrations, potentiometric titrations, and FTIR study. The material is characterized by its high specific surface area , microporocity (micropore volume ), its basic character ( total basic groups) and its high iron content (15,480 ppm Fe). BET n-layer isotherm describes adsorption equilibrium suggesting cooperative adsorption and important adsorbate-adsorbate interactions. Kinetic data suggest a process dependent on surface coverage. At low coverage a Fickian, intraparticle diffusion rate model assuming a local equilibrium isotherm (oxygen dissociation reaction) adequately describes the process. The calculated diffusion coefficients (D) vary between and for initial oxygen concentration of 10 and 20 mg/l, respectively. Sensitivity analysis shows that the oxygen dissociation equilibrium constant determines the equilibrium concentration, whereas the diffusion coefficient controls the kinetic rate of the adsorption process having no effect at the final equilibrium concentration. A combined kinetic mass transfer model with concentration-dependent diffusion (parabolic form) has been developed and successfully applied on the dissolved oxygen adsorption system at high surface coverage. For equilibrium uptake of the estimated mean mass transfer coefficient and adsorption rate constant are and , respectively.     

Removal of metal ions from aqueous solution by adsorption onto activated carbon cloths: adsorption competition with organic matter

Activated carbon cloths are recent adsorbents whose adsorption properties are well known for monocomponent solutions of organics or metal ions. However, to treat wastewaters with these materials, their performance has to be determined in multicomponent solution. This work studies adsorption competition between metal ions (Cu²⁺, Pb²⁺) and organic matter (benzoic acid). The first part investigates adsorption equilibrium of monocomponent metal ions solutions and shows the dependence of adsorption capacities on adsorbent porosity and metal ions chemical properties (molecular weight, ionic radius and electronegativity). The influence of pH is also demonstrated. The second part focuses on adsorption competition: (1) between both metal ions (a decrease of adsorption capacities is observed, whose value is related to adsorption kinetics of metal ions); (2) between metal ions and organic matter, in solution or adsorbed onto the activated carbon cloth (a strong influence of pH is shown: when benzoic acid is under benzoate form, in both cases adsorption is increased due to the formation of ligands between adsorbed benzoate ions and metals).     

The performance of two adsorption ice making test units using activated carbon and a carbon composite as adsorbents

The available adsorption working pairs applied to adsorption refrigeration system, which utilize activated carbon as adsorbent, are mainly activated carbon-methanol, activated carbon-ammonia, and composite adsorbent-ammonia. The adsorption properties and refrigeration application of these three types of adsorption working pairs are investigated. For the physical adsorbents, consolidated activated carbon showed best heat transfer performance, and activated carbon-methanol showed the best adsorption property because of the large refrigerant amount that can be adsorbed. For the composite adsorbents, the consolidated composite adsorbent with mass ratio of 4:1 between CaCl₂ and activated carbon, showed the highest cooling density when compared to the granular composite adsorbent and to the merely chemical adsorbent. The physical adsorption icemaker that employs consolidated activated carbon-methanol as working pair had the optimum coefficient of refrigeration performance (COP), volume cooling power density (SCP_v) and specific cooling power per kilogram adsorbent (SCP) of 0.125, 9.25 kW/m³ and 32.6 W/kg, respectively. The composite adsorption system that employs the consolidated composite adsorbent had a maximum COP, SCP_v and SCP of 0.35, 52.68 kW/m³ and 493.2 W/kg, respectively, for ice making mode. These results are improved by 1.8, 4.7 and 14 times, respectively, when compared to the results of the physical adsorption icemaker.     

Adsorption and electrothermal desorption of organic vapors using activated carbon adsorbents with novel morphologies

Novel morphologies of activated carbons such as monolith, beads and fiber cloth can effectively capture organic vapors from industrial sources. These adsorbent materials are also unique because they can undergo direct electrothermal regeneration to recover the adsorbed organic vapors for potential re-use. This investigation compares and contrasts the properties of these adsorbents when using electrothermal-swing adsorption. The adsorption systems consisted of an organic vapor generation system, an electrothermal-swing adsorption vessel, a gas detection unit, and a data acquisition and control system. The activated carbon monolith (ACM) had the lowest pressure drop, highest permeability, highest electrical resistivity and lowest cost as compared to the activated carbon beads (ACB) and the activated carbon fiber cloth (ACFC). ACB had the largest throughput ratio and lowest length of unused bed as compared to the other adsorbents. However, ACFC had the largest adsorption capacity for toluene when compared to ACM and ACB. ACFC was also faster to regenerate and had a larger concentration factor than ACM and ACB. These results describe relevant physical, electrical, adsorption and cost properties for specific morphologies of the adsorbents to more effectively capture and recover organic vapors from gas streams.     

Preparation of powdered activated carbon from rice husk and its methane adsorption properties

Success of adsorbed natural gas (ANG) storage process is mainly based on the characteristics of the adsorbent, so various synthesized adsorbents were analyzed for methane adsorption on a thermodynamic basis. Activated carbon from rice husk (AC-RH) was synthesized and its methane adsorption capacities were compared with phenol based activated carbons (AC-PH₂O and AC-PKOH). The adsorption experiments were conducted by volumetric method under various constant temperatures (293.15, 303.15, 313.15 and 323.15 K) and pressure up to 3.5MPa. Maximum methane adsorption was observed in AC-RH as its surface area is higher than the other two adsorbents. The experimental data were correlated well with Langmuir-Fruendlich isotherms. In addition, isosteric heat of adsorption was calculated by using Clausius-Clapeyron equation.     

Systematic Approach to Quantify Adsorption and Biodegradation Capacities on Biological Activated Carbon Following Ozonation

The goal of this research was to develop a systematic approach to quantify adsorption and biodegradation capacities on biological activated carbon (BAC). The role of absorption and biodegradation on BAC was studied using a continuous column. Several media, i.e., granular activated carbon (GAC), seeded glass bead and seeded GAC, and a target compound (p-hydroxybenzoic acid) were selected. Before breakthrough, the effluent of the GAC column contained a small amount of p-hydroxybenzoic acid that contributed the greatest amount of organic carbon to the effluent of the glass bead column, which suggests that adsorption should be the prevailing mechanism for removal the p-hydroxybenzoic acid, and biodegradation should be responsible for reducing the ozonation intermediates. Also, the bioactivity approach (biomass respiration potential, BRP) of BAC can not only reveal the importance of biodegradation mechanisms for the intermediates of ozonation, but also quantify the extent of the adsorption or biodegradation reaction occurring on BAC.     

Comparative study of methylene blue dye adsorption onto activated carbon,graphene oxide,and carbon nanotubes

Three different carbonaceous materials, activated carbon, graphene oxide, and multi-walled carbon nanotubes, were modified by nitric acid and used as adsorbents for the removal of methylene blue dye from aqueous solution. The adsorbents were characterized by N₂ adsorption/desorption isotherms, infrared spectroscopy, particle size, and zeta potential measurements. Batch adsorption experiments were carried out to study the effect of solution pH and contact time on dye adsorption properties. The kinetic studies showed that the adsorption data followed a pseudo second-order kinetic model. The isotherm analysis indicated that the adsorption data can be represented by Langmuir isotherm model. The remarkably strong adsorption capacity normalized by the BET surface area of graphene oxide and carbon nanotubes can be attributed to π–π electron donor acceptor interaction and electrostatic attraction.     

Effect of pH on adsorption of 2,4-dinitrophenol onto an activated carbon

The adsorption characteristics of 2,4-dinitrophenol from water onto a granular activated carbon, F-400, were studied at pH 4.3, 7 and 10. Adsorption equilibria of 2,4-dinitrophenol on GAC could be represented by Sips equation. Equilibrium capacity increased with decreasing pH. The differences in the rates of adsorption are primarily attributable to the differences in the equilibrium at the various pHs. Intraparticle diffusion was explained by surface diffusion mechanism. An adsorption model based on the linear driving force approximation (LDFA) was used for simulating the adsorption behavior of 2,4-dinitrophenol in a fixed bed adsorber. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8-10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

Performance analysis of an adsorption refrigerator using activated carbon in a compound adsorbent

To improve the performance of the adsorption refrigeration of CaCl₂-ammonia adsorption system, activated carbon has been distributed uniformly in the mass of CaCl₂, thereby helping to enhance mass transfer and uplift the cooling power density. A multifunctional heat pipe adsorption refrigerator, in which activated carbon-CaCl₂ is used as compound adsorbent and ammonia as refrigerant, is designed. Water and acetone are used as working liquids for the heat pipe. This paper presents a study on the adsorption refrigeration performances of this adsorption refrigerator under two different working conditions, ice-maker for fishing boat driven by the waste heat from exhaust gases, and solar ice-maker driven by solar water heating. The obtained average SCP (specific cooling power) and the COP (coefficient of performance) of the refrigerator were measured to be 770.4 W/kg and 0.39 at about −20 °C of evaporating temperature for the former working condition, and they were 161.2 W/kg and 0.12 at about −15 °C of evaporating temperature for the later working condition.     

The role of adsorbent pore size distribution in multicomponent adsorption on activated carbon

The impact of adsorbent pore size distribution (PSD) on adsorption mechanism for the multi solute system was evaluated in this study. Anoxic and oxic adsorption equilibrium for the single solute (phenol), binary solute (phenol/2-methylphenol) and ternary solute (phenol/2-methylphenol/2-ethylphenol) systems on one granular activated carbon (GAC) F400 and two types of activated carbon fibers (ACFs), namely, ACC-10 and ACC-15, were determined. F400 has a wide PSD, while ACC-10 and ACC-15 have narrow PSD and their critical pore diameters are 8.0 Å and 12.8 Å, respectively. In single solute adsorption, the increase of adsorptive capacity under oxic conditions as compared to anoxic ones was related to the PSD of the adsorbent. Binary solute adsorption on ACC-10 and ternary solute adsorption on ACC-15 indicated no impact of the presence of molecular oxygen on the adsorptive capacity and the adsorption isotherms were well predicted by the ideal adsorbed solution theory (IAST). Significant differences between oxic and anoxic isotherms were noticed for other multicomponent adsorption systems. The narrow PSD of ACFs was effective in hampering the oligomerization of phenolic compounds under oxic conditions. Such a phenomenon will provide accurate predictions of fixed bed adsorbers in water treatment systems.     

Prediction of breakthrough curves for adsorption on activated carbon fibers in a fixed bed

A new model is proposed to describe the removal of volatile organic compounds (VOC) from a gas stream passing through a bed packed with activated carbon fibers (ACFs). Toluene was used as the test compound. Both pore diffusion and surface diffusion are considered in the model. The equilibrium behavior is shown to fit the Dubinin–Radushkevich isotherm with the values of parameters K and W₀ of 1.101 × 10⁻⁹ and 57.73 kg/m³, respectively. The experimental results show that this model can predict VOC breakthrough curve very well.     

Characterization procedure for adsorption of DOC (Dissolved Organic Carbon) from synthetic wastewater

A characterization method to evaluate the composition of background organic matters in terms of adsorbability was presented and applied to synthetic and domestic wastewater. The binomial distribution of DOC (Dissolved Organic Carbon) fraction in relation of a characterizing variable, the Freundlich coefficient, k, was proposed to describe the initial composition of wastewater by a finite number of pseudospecies. This method was tested for removal of DOC by using granular and powdered activated carbons. These experiments enable us to get information on the distribution function of species in the solution. From the results obtained in this work, kinetic experimental data were predicted on the assumption that the diffusion coefficients were unchanged during the experiments. It was confirmed to be effective in determining the initial composition and describing the equilibria of the DOC. From the experiments, it was found that this synthetic solution has a sigmoid type isotherm on activated carbons. This implies that there are two different adsorption regions in a system, favourable and unfavourable cases, depending on the solution concentration. This unfamiliar problem can be solved by using a characterization method based on IAST-Freundlich model.     

Effects of activated carbon surface chemistry and pore structure on the adsorption of organic contaminants from aqueous solution

The objective of this research was to develop activated carbon selection criteria that assure the effective removal of trace organic contaminants from aqueous solution and to base the selection criteria on physical and chemical adsorbent characteristics. To systematically evaluate pore structure and surface chemistry effects, a matrix of activated carbon fibers (ACFs) with three activation levels and four surface chemistry levels was prepared and characterized. In addition, three granular activated carbons (GACs) were studied. Two common drinking water contaminants, relatively polar methyl tertiary-butyl ether (MTBE) and relatively nonpolar trichloroethene (TCE), served as adsorbate probes. TCE adsorbed primarily in micropores in the 7-10 Å width range while MTBE adsorbed primarily in micropores in the 8-11 Å width range. These results suggest that effective adsorbents should exhibit a large volume of micropores with widths that are about 1.3 to 1.8 times larger than the kinetic diameter of the target adsorbate. Hydrophobic adsorbents more effectively removed both TCE and MTBE from aqueous solution than hydrophilic adsorbents, a result that was explained by enhanced water adsorption on hydrophilic surfaces. To assure sufficient adsorbent hydrophobicity, the oxygen and nitrogen contents of an activated carbon should therefore sum to no more than about 2 to 3 mmol/g.     

Comparison of vapor adsorption characteristics of acetone and toluene based on polarity in activated carbon fixed-bed reactor

Adsorption characteristics according to polarity of acetone and toluene vapors on coconut based activated carbon were investigated by using a fixed bed reactor. Single vapor and binary vapor adsorption of acetone and toluene were conducted. In the single vapor system, the equilibrium adsorption capacity of toluene vapor on activated carbon was five times higher than that of acetone vapor because of polarity difference between adsorbent and adsorbate. The breakthrough curve of acetone vapor in the binary vapor was quite different from that of single acetone vapor. Acetone adsorbed in the binary vapor was substituted with toluene due to the affinity difference during adsorption process and its outlet concentration increased to 1.6 times than inlet concentration. The temperature changes in activated carbon bed during adsorption of acetone vapor and toluene vapor occurred in the time ranges of 10–30 min. The temperature change for acetone vapor adsorption was about 3 °C; however, that for toluene vapor adsorption was increased to 33 °C maximally.     

Hydrogen adsorption characteristics of activated carbon

Hydrogen adsorption on activated carbons was investigated in the present works up to 100 bars at 298 K. Coconut-shell was activated by potassium hydroxide, resulting in activated carbons with different porosities. All of prepared activated carbons are microporous and show the same adsorption properties. The complete reversibility and fast kinetics of hydrogen adsorption show that most of adsorbed quantity is due to physical adsorption. A linear relationship between hydrogen adsorption capacity and pressure is obtained for the all samples regardless of their porosities. Hydrogen adsorption capacities are linear function of porosities such as specific surface area, micropore surface area, total pore volume, and micropore volume. The maximum hydrogen adsorption capacity of 0.85 wt.% at 100 bars, 298 K is obtained in these materials.     

Electrochemically enhanced adsorption of aniline on activated carbon fibers

For adsorptive separation processes, the adsorption rate and capacity are two important factors affecting the costs. This study describes the anodic polarization of activated carbon fibers (ACFs), which can enhance the adsorption rate and capacity of aniline. The electrosorption kinetics and the affecting factors (bias potential, electrolyte, and pH) of isotherms for aniline on ACFs were investigated. The adsorption/electrosorption of aniline on ACFs follow pseudo-first-order adsorption kinetics, and the adsorption rate improves with increasing bias potential. The electrosorption isotherms, which exhibit a variety of responses depending on bias potential, electrolyte and pH, follow the two classical models of Langmuir and Freundlich. With electrosorption of aniline from aqueous solution, a two-fold enhancement of adsorption capacity is achievable. The initial and saturated ACFs were characterized using scanning electron micrograph (SEM) and Fourier transform infrared spectroscopy (FT-IR). The SEM micrographs show that the surface of ACFs is not oxidized, which is also verified by cyclic voltammetry results. The FT-IR spectroscopy suggests that the interaction between aniline and ACFs is main weak physisorption instead of chemisorption. These experimental results suggest that the electrochemical polarization of ACFs can effectively improve the adsorption rate and capacity of aniline, which may be due to the enhanced affinity between aniline and ACFs instead of the oxidation on the surface of ACFs or in the solution.     

Determination of assimilable organic carbon (aoc) in ozonated water with acinetobacter calcoaceticus

The effect of ozone application in drinking water on the production of assimilable organic carbon (AOC) was evaluated. The typical procedure to determine AOC is suggested by van der Kooij, which is the method of bacterial growth measurement by colony‐forming units using the strain P17 and/or NOX. The bacterial indicator species used for this study is Acinetobacter calcoaceticus which was isolated and identified while ozonating Nakdong river water. This strain could never be isolated from the raw water, but this strain was the predominant isolate in the ozonated water. Within a short incubation time, this organism was found to replicate well on acetate and oxalate as the sole carbon sources. The yield coefficients of this organism for acetate and oxalate are the same order of magnitude as the value of P17 and NOX. With full‐scale experiments, A. calcoaceticus concentration was found to increase after ozonation, but did not decrease upon chlorination. In laboratory‐scale experiments with Yongsan river water, aldehyes were found to be produced in proportion to the ozone dose. The raw water contains low concentrations of aldehydes, but has a high AOC concentration. A correlation between aldehyde production and AOC production was observed in the tested water with ozonation.     

Influence of solvent type on dibenzothiophene adsorption onto activated carbon fiber and granular coconut-shell activated carbon

The adsorption behavior of dibenzothiophene (DBT) on an activated carbon fiber (ACF) and a granular coconut-shell activated carbon (GCSAC) in the solvents n-hexane, n-decane, toluene, and mixture of n-decane and toluene was investigated. The DBT adsorption onto both samples was more active in n-hexane than in n-decane. The lowest DBT adsorption was observed in toluene. Regardless of the type of activated carbons and solvents, all the isotherms fit the Freundlich equation better than the Langmuir equation. At low equilibrium concentrations of <2 mass ppm-S, GCSAC displayed greater capacity for DBT adsorption than did ACF in all the tested solvents. The adsorption kinetics of ACF and GCSAC in all the tested solvents were governed by a pseudo-second-order model.