Transport and sorption of water vapour in activated carbons

Cossarutto, L.; Zimny, T.; Kaczmarczyk, Jan; Siemieniewska, T.; Bimer, J.; Weber, J.V.

doi:10.1016/s0008-6223(01)00065-3

Cited by 99 publications

(93 citation statements)

References 18 publications

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“…Such a lower shift of the uptake pressure due to N-doping has already been reported for ACF and activated carbon. 74,78 It is well-known that the uptake pressure and the shape of the H 2 O isotherm are functions of both micropore size and surface chemical properties. In this case, however, the influence of micropore size can almost be excluded and the observed difference in the uptake pressure be attributed solely to carbon surface chemistry.…”

Section: Synthesis Of Ordered Microporous Carbons Using Zeolite Templatementioning

confidence: 99%

Synthesis of Various Types of Nano Carbons Using the Template Technique

Kyotani¹

2006

Bulletin of the Chemical Society of Japan

101

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Using uniform nanochannels of an aluminum anodic oxide film as a template, uniform and unique multiwalled carbon nanotubes can be synthesized with a selectivity of 100%. This technique allows one to precisely control the diameters and the length of nanotubes. Moreover, it is possible to chemically modify only the inner surface of carbon nanotubes and to prepare carbon nanotubes with a double coaxial structure of heteroatom-doped multiwalls. The test tube like carbon prepared by this technique was found to be dispersible in water without any post treatment. In addition to this one-dimensional approach, unique microporous carbon can be prepared by the template technique using zeolite Y. The resulting microporous carbons are characterized by their regular ordering, originating from the regularity of the parent zeolite. When the synthesis conditions were optimized, the specific surface area and the micropore volume of the zeolitetemplated carbon reach more than 4000 m 2 g À1 and 1.8 cm 3 g À1 , respectively. This review introduces such a templatemediated approach and highlights how useful and versatile the template technique is for the production of nano carbons.Carbon is an element with a unique ability to bond with itself principally via sp 3 (diamond-like) and sp 2 (graphite-like) hybridization. This versatility gives rise to a rich diversity of structural forms of solid carbon. Most of the materials dealt with in carbon science and industry are considered to be composed of mainly large polycyclic aromatic molecules. The differences in the shape of such macromolecules and the way the molecules assemble (how they stack and how they are connected to one another) again lead to an immense variety of possibilities. If one could control the shape of the macromolecules and the state of their assemblage at the nanometer level, it would be possible to prepare carbon materials with a unique nano structure, thereby expecting novel and useful characteristics from the structure. Such control is, however, a very difficult task, because the nano structure of carbon materials is not uniform by nature, except for perfect graphite and diamond. To illustrate, a drawing of the molecular structure of activated carbon is shown in Fig. 1, where many curved polycyclic aromatic molecules with different sizes and shapes are stacked and connected in very complicated ways, which is quite different from the uniform ordered porous structure of zeolite materials. It is easily understood from this molecular model that control of the shape and the position of each macromolecule in the model is very difficult and essentially impossible. For the ultimate control of the carbon nano structure, it is desirable to build up a carbon structure from small building blocks, i.e., synthesize the structure from small organic molecules using techniques developed in the field of organic synthesis. However, the organic syntheses of fullerenes and carbon nanotubes have not been achieved yet, even by using cutting-edge technology. One of the most powerful and pro...

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Section: Synthesis Of Ordered Microporous Carbons Using Zeolite Templatementioning

confidence: 99%

Synthesis of Various Types of Nano Carbons Using the Template Technique

Kyotani¹

2006

Bulletin of the Chemical Society of Japan

101

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“…Particularly, the rate constant for the final desorption step is much slower than that for the corresponding adsorption increment. This result is attributed to the difficulty in removing adsorbate from ultramicropores in adsorbents, which is caused by the overlap of potential fields from pore walls [34].…”

Section: Adsorption and Desorption Kineticsmentioning

confidence: 99%

Adsorption and desorption performance of benzene over hierarchically structured carbon–silica aerogel composites

Dou

Wang

et al. 2011

Journal of Hazardous Materials

106

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a b s t r a c tHierarchically structured carbon-silica aerogel (CSA) composites were synthesized from cheap water glass precursors and granulated activated carbon via a post-synthesis surface modification with trimethylchlorosilane (TMCS) and a low-cost ambient pressure drying procedure. The resultant CSA composites possess micro/mesoporous structure and hydrophobic surface. The adsorption and desorption performance of benzene on carbon-silica aerogel composite (CSA-2) under static and dynamic conditions were investigated, comparing with pure silica aerogel (CSA-0) and microporous activated carbon (AC). It was found that CSA-2 has high affinity towards aromatic molecules and fast adsorption kinetics. Excellent performance of dynamic adsorption and desorption observed on CSA-2 is related to its higher adsorption capacity than CSA-0 and less mass transfer resistance than AC, arising from the well-developed microporosity and open foam mesostructure in the CSA composites.

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“…53 -55 Harding et al 56 analysed the existence of diffusion barriers in the kinetics of water adsorption/desorption on activated carbons. Others 30,57 have studied the kinetics of adsorption with relative water vapour pressure, in terms of a rate constant. Figure 8 represents the water vapour adsorption kinetics at 298 K at different relative pressures for D22G41 carbon, where M t is the amount of water adsorbed at time t and M e is the equilibrium amount of absorbed water.…”

Section: Adsorption Of Water Vapourmentioning

confidence: 99%

“…This behaviour agrees fairly well with the results obtained in the literature. 30,56,57 In the low relative pressure region, the rate constant value decreases as the adsorption over the active centres proceeds and extent of covering increases, due to diffusion limitation of water molecules through the narrow micropores partially filled after adsorption on primary centres. D22G98 shows the highest rate constants at low relative pressure (up to p/p o < 0.4), probably due to the absence of the effect of diffusion of water vapour throughout the micropores, given the lack of porous structure of this sample.…”

Section: Adsorption Of Water Vapourmentioning

confidence: 99%

“…4 -6 Although many studies have been made to understand the influence of surface oxygen groups in the water vapour adsorption on activated carbon, 3 -27 very little effort has been focused on carbon surfaces with nitrogen groups or metal cations. Cossarutto et al 30 found that the addition of nitrogen to a carbon surface results in an enhancement of adsorption at low relative pressures and a decrease in the maximum amount of water adsorbed. Manhajan et al 7 used modified carbons with high amounts of metal cations (Li, Na, K, Ca) on the carbon surface.…”

Section: Introductionmentioning

confidence: 99%

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Water vapour adsorption on lignin‐based activated carbons

Bedia

Rodríguez-Mirasol

Cordero

2007

J of Chemical Tech & Biotech

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Lignocellulosic wastes are interesting precursors for carbon products. The high amount of Na observed in kraft lignin makes it a promising precursor for the preparation of activated carbons for desiccant applications. Water adsorption capacity and kinetics of kraft lignin-based chars and activated carbons with different burn-off and inorganic matter content have been studied. CO 2 partial gasification of lignin char develops a wide porous structure. An increase of the micropore volume can be observed at low to medium burn-offs. At degrees of higher activation the mesoporous structure develops. For very high burn-off the porous structure is destroyed by coalescence of the pores and reduction of the carbon material. The carbons obtained show atomic surface concentrations of sodium from 7.6-15.4%, as revealed by XPS analysis. Water vapour adsorption isotherms have been obtained in a thermogravimetric system and have been fitted by a DS model, which properly represents the experimental data. The kinetics of water vapour adsorption follows a linear driving force mass transfer (LDF) model. The presence of sodium and oxygen surface groups on the carbon surface enhances water vapour adsorption at low relative pressure. Activated carbon produced at 41% burn-off shows the highest water vapour adsorption at low relative pressures, as a consequence of the high sodium dispersion on its surface. The sodium dispersed over the carbon surface undergoes clustering as gasification proceeds, decreasing the number of active centres. For burn-off higher than 41%, this behaviour produces a decrease in the water adsorbed at low relative pressures.  2007 Society of Chemical Industry Keywords: water vapour adsorption; lignin; CO 2 gasification; chars; activated carbon; sodium INTRODUCTION Activated carbons can be obtained from many raw materials, including carbonaceous wastes; they present a high capacity for water vapour adsorption at medium to high relative pressures, due to their large specific surface area and high porosity. Unfortunately, they show mostly a type V isotherm for water vapour adsorption, with very low uptake at low relative pressures. For desiccant applications, as in sorption cooling/heating systems, low-cost porous solids with relatively large water vapour adsorption at low relative pressures (type I moderate isotherms) are preferred.

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Transport and sorption of water vapour in activated carbons

Cited by 99 publications

References 18 publications

Synthesis of Various Types of Nano Carbons Using the Template Technique

Synthesis of Various Types of Nano Carbons Using the Template Technique

Adsorption and desorption performance of benzene over hierarchically structured carbon–silica aerogel composites

Water vapour adsorption on lignin‐based activated carbons

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