Activated carbon fibers advantages

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. 

Usually the activated carbon granules are employed for chromium removal or for catalysts preparation. However in some previous reports the perspectives and advantages of activated carbon fibers (ACF) utilization for the same employment have been documented [2,4]. It seems from the analysis of the articles that the use of ACF or activated carbon cloth has a great potential. 

There is growing interest in the development and application of activated carbon fibers (ACF), whose unusual properties can be advantageous in certain applica-... 

Y. Q. Fei, F. Derbyshire. M. Jagtoyen, and 1. Mochida, Advantages of producing carbon fibers and activated carbon fibers from shale oils. Proceedings of the Eastern Oil Shale Syniposium Lexington, KY, Nov. 16-19, 1993, pp. 38-45. 

Activated carbon fibers (ACFs) are porous carbons with a fiber shape and a well-defined porous structure that can be prepared with a high adsorption capacity. Although the ACFs are very promising materials, they have not still a market as important as the activated carbons (ACs) due to their difference in production costs. The main characteristics and advantages of the ACFs are as follows [1-3]. 

Sorption capacities of granular activated carbons and activated carbon fibers were measured, but they were relatively low, e.g., 1 g/g for activated carbon granules with llOOm /g surface area and 19g/g for those with 1220m /g, and no relation to the Brunauer, Emmett, and Teller (BET) surface area was observed. Therefore, the experimental results on different carbon materials showed that macropores, which make bulk density lower, are mainly responsible for their large sorption capacity. Fibrous particles of carbon may be advantageous for easy deformation of macropores to be suitable for sorption of heavy oils. 

Fibrous activated carbons, activated carbon fibers, have been prepared recently and developed a new field of applications. They have a number of advantages over granular activated carbons. The principal merit to prepare activated carbon in fibrous morphology is its particular pore structure and a large physical surface area. Differences between ACFs and granular activated carbons are listed in Table 9. 

Other advantage of ACFs is the possibility to prepare woven clothes and nonwoven mats, which developed new applications in small purification systems for water treatment and also as a deodorant in refrigerators in houses, recently reported. In order to give the fibers an antibacterial function and to increase their deodorant fimetion, some trials on supporting minute particles of different metals, such as Ag, Cu and Mn, were performed. Table 5. 2 presented comparison between properties of activated carbon fibers and granular activated carbons [13-46]. 

Rebouillat el al [4] and Suzuki [5] give good reviews of activated carbon fibers. Traditionally, activated carbon granules are made by the carbonization of a product such as coconut shells, which due to their physical granular form, tend to be difficult to handle and the development of an activated woven cloth by the British Chemical Defence Establishment at Porton Down [6,7] via the controlled heat treatment of a woven rayon cloth offers many advantages. The activated charcoal cloth (ACC) product was made under licence in 1977, by Charcoal Cloth Ltd. One such process used a 1.8 m wide fabric, reducing to about 1.0 m at the end of the process. To aid carbonization, the cloth was treated with a solution of chemicals to confer a measure of flame retardancy. As explained in Chapter 6, there are two forms of flame retardant—one where the flame retardant acts as a catalyst and promotes removal of the —OH groups and the other form, which actually reacts with the —OH... 

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]. 

As a result activated carbon fiber is produced through a series of process consisting of stabilization, carbonization, and activation of precursor fibers. It is important to improve the efficiency of the production process as well as to select low cost precursors [42]. The stabilization process, air oxidation of precursor fibers at 200-300 °C, is the process required to prevent the precursor fibers from melting during the subsequent carbonization process [61, 62]. It is essential for PAN and pitches, but is not essential for phenolic resin and cellulose, because the latter precursors are thermosetting resins. Phenolic resin is known to produce higher surface area ACF as compared with other precursors. It is, therefore, very advantageous if we could improve the production efficiency of phenol resin based ACF by, possibly, simple and cost effective methods. 

Activated carbon fiber (ACF) offers several advantages over traditional granular and powdered carbons as an absorbent material. Rayon-based ACFs (80) possess... 

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). 

These Deloxan beads have an inert siloxane matrix which is advantageous over other adsorbents such as activated carbon or organic polymer-based resins and fibers because (1) valuable API product is not adsorbed and lost as is the case when activated carbons are used and (2) they are chemically resistant to most solvents and stable over a wide pH range (0-12). 

Another method to improve the structural order of CMs is the conversion of the precursors to fibers prior to the pyrolysis step [377]. The precursor polymer may be stretched in addition. Carbon fibers are manufactured in large quantities as reinforcements in composite materials, after Bowen [403] and Fitzer [404]. Surface and bulk activation can be accomplished by anodic oxidation in dilute aqueous electrolytes (cf. Besenhard et al. [405, 406]). But carbon fibers with various degrees of graphitization have also been employed recently in rechargeable batteries [407-411] and in electrochemical double layer capacitors [18, 412-416]. This takes advantage of two fiber specific effects, namely... 

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