Regeneration, of activated carbon

Polymeric adsorbents have also been found to be very useful, and even highly water-loving undesired materials like p-toluene sulphonic acid from waste streams can be recovered via ad.sorption and regeneration with solvents like fv -propanol. In such instances, the regeneration of activated carbons is not satisfactory, even with aqueous sodium hydroxide. Solutes like phenols, substituted phenols, aromatic amines, heterocyclic amines (pyridine, picolines, etc.) can be recovered, in a rewarding way, from aqueous solutions. 

Adsorption. Some organic materials are not removed in biological systems operating under normal conditions. Removal of residual organic material can be achieved by adsorption. Both activated carbon and synthetic resins are used. As described earlier under pretreatment methods, regeneration of activated carbon in a furnace can cause carbon losses of perhaps 5 to 10%. 

Eppig, C. P. deFilippi, R. P. Murphy, R. A. "Supercritical Fluid Regeneration of Activated Carbon Used for Volatile-Organic-Compound Vapor Adsorption, EPA Report 600/2-82-067, 1982. 

Another area where microwave heating is nsed to heat carbon is in the regeneration of activated carbons. When spent activated carbon is snbject to a microwave field, the heat generated within the particles prodnces rapid temperatnre rises and the release of other componnds adsorbed on the carbon [19-23], In a similar process, carbon nsed as adsorbent to remove NO and SO from gas streams can be regenerated with microwaves prodncing CO2 and N2 as gases and elemental snlphnr [24],... 

The simultaneous decomposition of pentachlorophenol and regeneration of activated carbon, using microwaves was reported [46], claiming that the quality of the carbon was maintained or actually increased after several adsorption/microwave-regeneration cycles. Carbon, in graphite form, has also been used as a microwave absorbent for the microwave pyrolysis of urea [47]. 

S. Bradshaw, E. J. van Wyk and G. du Toit. Microwave regeneration of activated carbon adsorbents. Proceedings from the International Conference on Microwave Cftem/slry,Prague, Czech Republic 1998. 

S. M. Bradshaw, E. J. VanWyk and J. B. deSwardt, Preliminary economic assessment of microwave regeneration of activated carbon for the carbon in pulp process. Journal of Microwave Power and Electromagnetic Energy, 32, 131-144 (1997). 

Apart from obvious dry cleaning applications, potential applications of C02-based microemulsions include (i) printed circuit board cleaning, (ii) extraction of contaminants from soils, (Hi) cleaning of polymers, foams, aerogels, porous ceramics, and laser optics, (iv) regeneration of activated carbon beds or catalysts, and (v) the separation of dyestuffs from textiles. 

The regeneration of activated carbon beds used in gas phase adsorption requires less severe conditions than for liquid phase processes. Regeneration can be conducted in situ by stripping with steam. Newer and more efficient systems use regeneration by hot inert gas, nominally at 350°F, to recover a greater portion of contaminants with their subsequent recovery. This is particularly attractive if the disposal of condensate from steam regeneration becomes a problem [73]. 

Numerous challenges remain in the refinement of contemporary design and operation of carbon adsorption treatment systems. Those currently in the forefront include the transfer and regeneration of activated carbon, competitive effects on adsorption, the production of intermediate organic species in activated carbon systems, and bioactivity on activated carbon. 

Modell, M., de Filippi, R., and Krukonis, V. (1980). Regeneration of activated carbon with supercritical carbon dioxide. In Activated Carbon Adsorption of Organics from the Aqueous Phase, Vol. 1 (I. H. Suffet and M. J. McGuire, eds.). Ann Arbor Science, Ann Arbor, MI, pp. 447-461. 

To overcome calcium catalysis, a methodology has been assessed that uses specific reactivation parameters in terms of temperature ramp and duration [39, 40]. In any case, an acid washing seems to be a good way to remove the majority of metal ions before thermal regeneration of activated carbon [43]. 

Pilard, M., Dagois, G., Montagnon, P., and Chesneau, M. (1996). Influence of minerals on the regeneration of activated carbon used in drinking water treatment. Water Supply, 14, 263-70. 

Magne, P. and Walker, P.L., Jr (1986). Phenol adsorption on activated carbons application to the regeneration of activated carbons polluted with phenol. Carbon, 24, 101-7. 

Ferro-Garcia, M.A., Utrera-Hidalgo, E., Rivera-UtriUa, et al. (1993). Regeneration of activated carbons exhausted with chlorophenols. Carbon, 31, 857-63. 

Alvarez-Trevit, J. A. Steam Regeneration of Activated Carbon Adsorbents, Ph.D. diss.. The University of Texas at Austin, 1995. 

The forerunner of all the recent applications of SCF technology reported in the United States is the SCF regeneration of activated carbon first described at an American Chemical Society meeting in 1978 (Modell, de Filippi, and Krukonis, 1978). The phenomena in operation during adsorption of organics from wastewater and the desorption of organics from the activated carbon using supercritical carbon dioxide are similar to those active in other supercritical fluid extraction processes. Therefore, we examine the technical details here. 

Figure 8.3 shows the molecular structure of six pesticides that were tested and their solubility levels in supercritical CO2 at one set of test conditions, 275 bar (4,000 psia) and 100°C. Also included in this figure is the solubility of phenol, which was studied because it is a raw material in the production of some of the pesticides and thus might be found in pesticide plant wastewaters. The solubility of these compounds varies over a one hundredfold concentration range, but the regenerability of activated carbon is not necessarily related solely to the solubility level. Specifically, a high solubility in supercritical CO2... 

In this chapter the SCF processing of two natural products, coffee and edible oils, is described in some detail. The principles involved in the coffee decaffeination process are similar to those described for the regeneration of activated carbon and the extraction of ethanol from water. In the remainder of the chapter a variety of other SCF applications are presented. 

When the activated carbon becomes saturated with ethanol, it is regenerated by passing CO2 at 200 °C and 10 atm through the bed. The hot gas stream is cooled to 75 °C in column 11 which causes the ethanol to condense. Ethanol of 98.5% concentration is recovered from the condenser. The C02/feed ratio in the extractor is 7 Ib/lb, and the regeneration of activated carbon requires 7 lb C02/lb activated carbon. 

Modell, M., R. J. Robey, V. J. Krukonis, R. P. de Filippi, and D. Oestereich. 1979. Supercritical fluid regeneration of activated carbon. Paper presented at National AIChE Meeting, Boston, MA. 

Monocrotaline, a pyrrolizidine alkaloid of chemotherapeutic interest, has been extracted from the seeds of Crotalaria spectabilis using supercritical carbon dioxide and carbon dioxide-ethanol mixtures (29). Other alkaloids that have been extracted using SFE include nicotine and caffeine. Environmental applications of supercritical fluids include regeneration of activated carbon, extraction of organic contaminants like polynuclear aromatic hydrocarbons and polychlorinated biphenyls from water and soils, and the newly emerging field of supercritical water oxidation. 

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