Activated carbon fibers fiber diameters

KoTHmex activated carbon fiber fabrics AW-1101 (BET specific surface area of 880m /g, average pore diameter of 2nm) was provided by Taiwan Carbon Technology Co. Ltd. The support is pretreated in a boiling aqueous solution of 6.5wt.% HNO3 for 1 h. Then the support is rinsed with distilled water, air-dried for 12h at room temperature and for 5h at 393 K. BET specific surface area of the ACF is 950m /g. 

FIGURE 4.20 Volume corrected invariant versus beam position for the chemically activated carbon fiber prepared from pitch-based carbon fiber (samples CFK60 and CFNa65). The vertical lines indicate the fiber diameter (CFK60—dashed lines andCFK65—full lines). (From Lozano-Castello, D., et al., Carbon, 44, 1121, 2006. With permission.)... 

The study of methane adsorption on activated carbon fibers has demonstrated, as was previously explained, that these carbonaceous materials, because of their cylindrical morphology and smaller diameter, have higher packing density than activated carbons with similar micropore volumes [191]. Subsequently, the higher adsorption capacity for the powdered activated carbons against the higher packing density for the fibers helps both kinds of materials reach similar, maximum adsorption values [191]. 

In this sense, the main objective of this work is to show the usefulness of the Microfocus Beamline (ID 13) in the characterization of activated carbon fibers. Thus, examples with activated carbon fibers with different bum-off degree obtained with different activating agents, and different fiber diameter will be presented. 

In order to show the suitability of the pSAXS technique to characterize activated carbon fibers, the examples have been divided in two sections i) experiments at the center of the fiber, and ii) experiments across the fiber diameter. 

The examples presented in this work illustrate the suitability of pSAXS technique to characterize activated carbon fibers. It has been shown the isotropy features in activated carbon fibers prepared from different precursors and using different activating agents. In addition, this technique is able to obtain scattering measurements across the fiber diameter, which has allows us to obtain maps of pores distribution. The present results show that... 

Activated carbon fibers (ACFs) offer a choice of other carbon forms for VOC removal. As discussed earlier, the narrow diameter of the fibers provides ready access of adsorptive species to the adsorbent surface. The incorporation of ACF into permeable forms such as felt, paper, and rigid monoliths helps to surmount the disadvantages of using loose fibers. Rigid ACF composites have been prepared at the University of Kentucky and examined for their potential for the removal of low concentrations of VOCs [31]. 

In the case of activated carbon fibers, pore size is small compared to GACs. Moreover, the external diameter of activated carbon fibers is at least two orders of magnitude smaller than GACs. A mesh of well-interconnected micropores from the core to the external surface of an activated carbon fiber reduces the intraparticulate diffusion time. This results in the superior adsorption dynamics of activated carbon fibers as compared to GACs (Hayes and Akamatsu 2000). 

Although they are specifically treated in Chapter 17, activated carbon fibers (ACFs) and derived cloths and felts deserve special mention here due to their uniform pore size distribution (PSD) and small and uniform fiber diameter, which confer on them, respectively, both size selectivity and rapid... 

In a comprehensive study of the adsorption of MTBE onto a range of activated carbon fibers, Knappe et al. [51] related the capacity of the adsorbents to the volume of pores in the range 0.8—1.1 run. This corresponded to pores approximately 1.6 times the kinetic diameter of the MTBE molecule. It was also found that, if the requirement for pores in the correct size range was met by the carbons, the more hydrophobic carbon showed the highest capacity. 

Knappe et al. [51] tested the range of activated carbon fibers mentioned above for the removal of TCE, and found the carbons with a higher volume of pores in the range 0.7-1.0nm were the most effective for removing the compound. These pores are approximately 1.5 times the kinetic diameter of TCE. Also similar to MTBE, given a similar pore volume in the appropriate range, the more hydrophobic carbon demonstrates the higher adsorption of MTBE. 

Activated carbon fibers (ACF) and nano fibers (ACNF) are a relatively modem form of porous carbon material with a number of significant advantages over the more traditional powder or granular forms. Advantages include high adsorption and desorption rates, thanks to the smaller fiber diameter and hence very low diffusion limitations, great adsorption capacities at low concentrations of adsorbates, and excellent flexibility [18, 19]. 

The diameters are retained after activation. Most commercial activated carbon fibers have a diameter of nearly 10 xm, although other sizes in the range of 8-20 xm are also available. Figure 5.18 shows a SEM image of a commercial ACF. The fiber diameters of ACFs derived from various precursors are shown in Figure 5.19. 

The AFM image of the original activated carbon fiber at magnification of 5 X 5 pm is shown in Fig. 15.1. From this image it is clear that nonmod-ified carbon fiber consists of a thin 7-8 micron diameter fibers composed of microfibrils 400-600 nm. The observed block structure fiber indicates the location of microfibrils along the fiber axis, in good agreement with literature data on the structure of carbon fibers [7]. 

Hollow Fiber with Sorbent Walls. A cellulose sorbent and dialy2ing membrane hoUow fiber was reported in 1977 by Enka Glan2stoff AG (41). This hoUow fiber, with an inside diameter of about 300 p.m, has a double-layer waU. The inner waU consists of Cuprophan ceUulose and is very thin, approximately 8 p.m. The outer waU, which is ca 40-p.m thick, consists mainly of sorbent substance bonded by ceUulose. The advantage of such a fiber is that it combines the principles of hemodialysis with those of hemoperfusion. Two such fibers have been made one with activated carbon in the fiber waU, and one with aluminum oxide, which is a phosphate binder (also see Dialysis). 

Detailed accounts of fibers and carbon-carbon composites can be found in several recently published books [1-5]. Here, details of novel carbon fibers and their composites are reported. The manufacture and applications of adsorbent carbon fibers are discussed in Chapter 3. Active carbon fibers are an attractive adsorbent because their small diameters (typically 6-20 pm) offer a kinetic advantage over granular activated carbons whose dimensions are typically 1-5 mm. Moreover, active carbon fibers contain a large volume of mesopores and micropores. Current and emerging applications of active carbon fibers are discussed. The manufacture, structure and properties of high performance fibers are reviewed in Chapter 4, whereas the manufacture and properties of vapor grown fibers and their composites are reported in Chapter 5. Low density (porous) carbon fiber composites have novel properties that make them uniquely suited for certain applications. The properties and applications of novel low density composites developed at Oak Ridge National Laboratory are reported in Chapter 6. 

In gas separation applications, polymeric hollow fibers (diameter X 100 fim) are used (e.g. PAN) with a dense skin. In the skin the micropores develop during pyrolyzation. This is also the case in the macroporous material but is not of great importance from gas permeability considerations. Depending on the pyrolysis temperature, the carbon membrane top layer (skin) may or may not be permeable for small molecules. Such a membrane system is activated by oxidation at temperatures of 400-450 C. The process parameters in this step determine the suitability of the asymmetric carbon membrane in a given application (Table 2.8). 

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