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Adsorption: Journal of the International Adsorption Society (v.17, #4)

Characteristics of sulfur removal by silver-titania adsorbents at ambient conditions by Sachin Nair; Bruce J. Tatarchuk (pp. 663-673).

Sulfur capacity of SiO₂, TiO₂ and γ-Al₂O₃ structures was investigated. Thermal treatment of TiO₂ and γ-Al₂O₃ in air increased their respective sulfur capacity by 67 and 43%. Sulfur capacity was associated with surface acidity and the improvement attributed to the formation of bronsted acid sites. Addition of 4wt% transition metals further enhanced the sulfur capacity of TiO₂ with Ag indicating the highest increase. Comparison of sulfur capacity of Ag/TiO₂ with other adsorbents was made using JP5 fuel with sulfur concentration of 1172 ppmw. Ag/TiO₂ adsorbent demonstrated a saturation sulfur capacity of 8.20 mg/g. A significant loss in sulfur capacity was observed between real and model fuel compositions. Various factors resulting in this loss was investigated such as the effect of additives, competitive adsorption and the structure of sulfur heterocycles.

Keywords: Adsorptive desulfurization; Fuel additives; Surface acidity; Competitive adsorption

Improvement of water vapor adsorption ability of natural mesoporous material by impregnating with chloride salts for development of a new desiccant filter by Saya Nakabayashi; Katsunori Nagano; Makoto Nakamura; Junya Togawa; Asami Kurokawa (pp. 675-686).

The aim of this study is the development of a new adsorbent for the desiccant material which can be regenerated by the domestic exhaust heat by using natural mesoporous material, Wakkanai siliceous shale. To improve this shale’s performance to adsorb/desorb the water vapor, lithium chloride, calcium chloride or sodium chloride was supported into the mesopores by impregnating with each chloride solution. Especially sodium chloride was effective to increase the water vapor adsorption amount 5–7 times of that of natural shale in the relative humidity range from 50 to 70%. Moreover, the appropriate impregnating concentrations were determined as 5wt% from the relationship between the maximum water vapor adsorption amount and the mesopore volume. Based on these results, a new desiccant filter has been developed by impregnated original paper with lithium chloride and sodium chloride. This paper contained shale powder in the synthetic fibers. The dehumidification performance of this filter was evaluated under the simulated summer condition in Tokyo. From the cyclic adsorption/regeneration test, this shale and chlorides filter could adsorb and desorb 60 g/h water vapor repeatedly at the regeneration temperature of 40°C. On the other hand, a silica gel filter and a zeolite filter adsorbed and desorbed only 10 g/h and 25 g/h, respectively. These results suggested that the shale impregnated with the chlorides has the best dehumidification ability as a new desiccant material. Further, the desiccant filter made from the shale will achieve the effective use of the low temperature exhaust heat.

Keywords: Water adsorption; Siliceous shale; Desiccant; Impregnation; Sodium chloride

Flowrate correction for the determination of isotherms and Darken thermodynamic factors from Zero Length Column (ZLC) experiments by Huidan Wang; Stefano Brandani; Guiping Lin; Xiayi Hu (pp. 687-694).

The ZLC method is a simple and rapid approach to measure adsorption equilibrium isotherms. When extending this technique to the measurement of large concentration steps, the primary problem is how to estimate the outlet flowrate from the measured concentration signal. In this paper, two different corrections to calculate the outlet flowrate are introduced. Based on simulations of the ZLC system that are in good agreement with reported experimental results, a series of desorption cases were simulated. Isotherms were calculated using the two approximations of the outlet flowrate. The comparisons are used to identify the range in which the approximations are applicable. Darken’s thermodynamic correction factors were also calculated to verify the validity of the flow corrections.

Keywords: Adsorption equilibrium; Mathematical model; Numerical simulation; ZLC

Solidification in weakly attractive cylindrical nanopores under tensile condition by Hideki Kanda (pp. 695-699).

The authors clarified freezing points of the Lennard-Jones (LJ) condensate for strongly attractive cylindrical nanopores by using molecular dynamics (MD), and by thermodynamically predicting the results without using any adjustable parameters. In contrast to the Clapeyron equation, the obtained freezing points exhibited a significant dependence on the equilibrium bulk phase pressure, forming a remarkably skewed curve on a p–T diagram. In this paper, for weakly attractive cylindrical nanopores, freezing point depression under tensile conditions, similar to the authors previous study. The MD results show that the authors previous thermodynamic model successfully predicted freezing point depression for a bigger pore. However, for a smaller pore, obtained freezing points (liquid-solid coexistence curve) remarkably close to the bulk vapor-solid coexistence curve, and could not be predicted by the thermodynamic model.

Keywords: Solidification; Thermodynamic model; Pore wall interaction; Molecular dynamics

Multi-component adsorptive separation: use of lumping in PSA process simulation by Pramathesh R. Mhaskar; Arun S. Moharir (pp. 701-721).

Being a discrete-continuous process, approach to a cyclic steady state in computer simulation of Pressure Swing Adsorption is through iterative procedures and simulation itself is quite computation-intensive. Considering the fact that simulation based design itself is an iterative process, it is imperative that simulation be computationally very efficient and phenomenologically as close to the physics of adsorption-desorption as possible. Utility of lumping the components of a gas mixture into fewer pseudo-components was computationally examined in the simulation of a representative multi-step cycle of a pressure swing based adsorptive separation process applied to natural gas treatment. The actual feed had six components competing for adsorbent sites. Five different lumping alternatives were studied and compared with the simulation results for a full six-component simulation under identical equipment dimensions and operating conditions. Lumping could reduce the number of equations to be solved by more than half and the corresponding reduction in CPU time was about 90%. The six component mixture of Natural Gas was found to be sufficiently represented by two pseudo-components. The predicted recovery (in terms of Methane and Ethane) and quality (in terms of content of higher hydrocarbons) of the raffinate differed by not more than 0.8% and 0.02% respectively. The paper discusses possible heuristics for decision-making regarding appropriate lumping as verified by extensive simulation studies.

Keywords: Lumping into pseudo-components; Adsorptive separation; Natural gas treatment; Simulation; Pressure-swing; Heuristics

Improving the equilibrium performance of active carbons for separation processes by co-adsorption with low pressure solvent: application to carbon capture by Martin B. Sweatman (pp. 723-737).

The equilibrium performance of a novel gas separation process described quite recently (Sweatman in Chem. Eng. Sci. 65:3907, 2010) called ‘pressure-swing wetting layer absorption’ here is investigated by means of molecular Monte-Carlo simulation. This process is very similar to pressure-swing adsorption except that solvent, in the form of low pressure vapour, is added to the gas to be separated in order to improve equilibrium performance. Earlier work, based on relatively simple density functional theory models, suggests that this process could be significantly more efficient than the analogous pressure-swing adsorption process when tetrahydrofuran (THF) is used as the solvent, although this conclusion is based only on equilibrium behaviour and does not take into account the effect of any dynamical processes. The aim of this work is to provide more detailed molecular simulation results to help understand this behaviour and guide experiments towards suitable solvents and conditions so that the process can experimentally tested. It is found that using acetonitrile as the solvent could be over nine times more effective than THF, which was modelled in previous work, for the particular carbon capture application studied here. These simulation results also demonstrate that, due to the effect of confinement on fluid structure, bulk solubility data cannot be used to reliably predict equilibrium performance in this context, and that the equilibrium performance is especially enhanced for pores that exhibit a bilayer phase transition.

Keywords: Carbon capture; Porous media; Adsorption; Absorption; Molecular simulation; Monte-Carlo; Ternary mixture

Influence of the exchangeable cations on SO₂ adsorption capacities of clinoptilolite-rich natural zeolite by Meryem Sakizci; Burcu Erdoğan Alver; Ertuğrul Yörükoğullari (pp. 739-745).

The sulfur dioxide adsorption on clinoptilolite-rich tuff from Bigadiç region of Western of Turkey and its modified forms (Na⁺, K⁺, Ca²⁺ and Mg²⁺) have been studied at 273 K and 293 K up to 100 kPa. The structural properties of clinoptilolites were studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR). The quantitative XRD analysis demonstrated that the Natural-B sample is mainly constituted by clinoptilolite (80–85%) with minor contents of quartz (7–8%), feldspar (5–6%) and mica-illit (4–5%). It was found out that the adsorption capacity and the affinity of SO₂ with clinoptilolite samples depended mainly on the type of exchanged cations and decreased as Na-B > K-B > Mg-B > Natural-B > Ca-B for both temperature. These results show that clinoptilolite-rich zeolites are considered potentially good adsorbents for SO₂ removal.

Keywords: Adsorption; Clinoptilolite; Sulphur dioxide; XRD; FT-IR

Selective adsorption of 2,3-DCDD and 1,2,3,4-TCDD on *BEA, EMT, FAU and MFI-type zeolites as alternative adsorbents for on-line dioxin monitoring by M. Mercury; R. Denoyel; A. Simon-Masseron; M. Carette; Y. Zerega; J. Patarin; M. Soulard; C. Reynard; A. Janulyte (pp. 747-758).

The aim of this study is to evaluate the capabilities of zeolites as selective sorbents for on-line dioxin monitoring. The adsorption isotherms of 2,3-DCDD and 1,2,3,4-TCDD from isooctane on several zeolites with different pore sizes (*BEA, EMT, FAU and MFI-type zeolites) are determined. Selective adsorption is shown for FAU and EMT-type zeolites. 2,3-DCDD is adsorbed by FAU with the highest adsorption capacity and affinity while 1,2,3,4-TCDD is not adsorbed whatever the zeolites. The adsorption of 2,3-DCDD inside the pores of FAU is qualitatively confirmed by diffuse reflectance UV spectrometry and thermogravimetry measurements.

Keywords: Dioxin; Zeolite; Selective adsorption; Adsorption from solution

The downsizing of a TSA system for an air purification unit using a high flow rate method by T. Hidano; M. Nakamura; A. Nakamura; M. Kawai (pp. 759-763).

A high flow rate type air purification unit to reduce the size of adsorption vessel was developed. The setting area of air purification unit and the cost of adsorption vessel were reduced to 65% and 70% respectively. The downsizing was achieved by the way that a mass transfer zone (MTZ) was formed in the whole region of adsorbent layer and by the development of adsorbent for the high flow rate process. As regards the adsorbent, the adsorption performance to realize the process was investigated. Then the adsorbent which has larger size and higher adsorption performance was developed and TSA process experiment was carried out. As the result, the realization of the high flow rate process was made sure experimentally.

Keywords: Adsorption; TSA; MTZ; Air; Purification; NaX; Carbon dioxide

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Adsorption: Journal of the International Adsorption Society (v.17, #4)

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Adsorption: Journal of the International Adsorption Society (v.17, #4)