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Isotropic pitch-based ACFs
DFT Pore size distributions of UTSI ACFs illustrating that not only larger surface area but also pore volumes and pore size distribution can be controlled
Iodine numbers comparing UTSI ACFS with commercial ACFs.
MB adsorption comparing UTSI ACFS with commercial ACFs.
These novel adsorbents are expected to take advantage of some of the features offered by the new fabrication process. Advantages include:
Over the past decade it has become abundantly clear that water contamination and green house gases are of increasing concern in the United States and throughout the world[1-3]. They have prompted industry to develop advanced new materials and improve the performance of existing processes to address these problems. In many cases, adsorbents have been determined to provide the best available technologies for the removal of trace contaminants from water and air. However, the current state-of-art has many limitations including inadequate adsorption/ion exchange capacity, kinetics, selectivity, and scalability. The current generations of ion exchange/carbon adsorbents are primarily in the form of beads or granules, which limit contact efficiency (both the available surface area and the path length to active sites). Increasing surface area by decreasing particle size is counterproductive as the ensuing increase in pressure drop makes scalability impractical for removing trace contaminants from water and air. Thus, design of new, well-characterized, advanced adsorbents represents a unique approach to solving these problems.
Research on the UTSI activated carbon fibers is expected to impact adsorbent technology, which could have profound effects within the field of water and air purification, catalyst support, separation of chemical and biochemical, medicine, fuel cell and hydrogen storage.
Traditionally, adsorbents have been the primary materials used for removal of impurities for both water and air, since they usually have high surface areas. It is well known that small pores, such as micropores (< 2 nm) and mesopores (2 - 50 nm), result in the large surface areas responsible for adsorption; Pore size, pore size distributions, and surface area, as well as pore surface chemistry are the major factors in the adsorption process.
Granular activated carbon (GAC), one of widely used conventional adsorbents, has been commercially available since the early 1900's and is used extensively for air and water clean-up primarily due to their low cost. The raw material for activated carbon can be any organic material with a high char yield (i.e. coal, peat, coconut shells, or certain polymers). Activation occurs when the carbon layers are etched away through an oxidation reaction resulting in the formation of a porous carbon network with high surface area. GACs have been accepted as the industry standard for adsorbing unwanted chemical compounds from water and air. As a result, they have become ubiquitous throughout industry, wastewater treatment facilities and even in households for point-of-use drinking water purification. However, GACs display disadvantages such as slow kinetics, bad selectivity and less than 100% working capacity, since a significant portion of their porosity is relatively inaccessible (the working capacity is affected by the very small micropores in the interior of the GAC that do not easily desorb). They also have other drawbacks including costly reactivation and limited design flexibility.
Fibrous activated carbons (ACFs) offer a number of advantages over GACs, including greatly improved contact efficiency with the media leading to greater rates of adsorption, much higher surface areas (up to 2500 m2/g) and the potential for greatly simplified in situ regeneration through electrical resistance heating. Unfortunately the commercially available ACFs are very expensive (~$100/lb), in part because they suffer from huge weight losses during activation, and are very brittle and susceptible to wear and tear during their handling.
1. Vörösmarty C, Green J. P, Salisbury J. and Lammers R. B. "Global water resources: vulnerability from climate change and population growth". Science 2000, 289, 284-288.
2. Aldhous P. "The world's forgotten crisis - Over a billion people cannot get clean water, and things are getting worse". Nature. 2003, 422, 251.
3. Kerr R. A. “How hot will the greenhouse world be?”. Science. 2005, 309(5731), 100.
4. Najm I. N, Snoeyink V. L, Lykins B. W. and Adams J. Q. “Using powdered activated carbon: a critical review”. JAWWA. 1991, 83, 65-76.
Dr. Ahmad (Adam) Vakili
Professor Mechanical, Aerospace and Biomedical Engineering
Address inquiries to:
Advanced Carbon Based Materials
The Univ. of TN Space Inst.
411 B.H. Goethert Parkway
Tullahoma, TN 37388-9700