Regeneration of powdered activated carbon. Part II: Steam‐carbon reaction kinetics

Chihara, Kazuyuki; Matsui, Isao; Smith, J. M.

doi:10.1002/aic.690270208

Cited by 19 publications

(9 citation statements)

References 17 publications

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“…Again a loss in adsorption capacity occurred, this time due to loss of base carbon. The gasification time for maximum retention of capacity corresponded closely to the state where the weight of carbon gasified was equal to the weight of residual carbon.Rates of gasification evaluated from our fluidized-bed data agreed well with kinetics results obtained earlier (Chihara et al, 1981b) in a thermal gravimetric apparatus. This suggests that the kinetics data are suitable for designing regeneration equipment.…”

supporting

confidence: 86%

“…The kinetics results of Chihara et al (1981b) should be applicable for predicting the extent-of-gasification vs. time relation. The measurements reported here of adsorption capacity in cyclic operation complete the data needed for design.…”

Section: Results and Discussion Effects Of Cyclic Operationmentioning

confidence: 99%

“…The sucrose-steamcarbon system was chosen because kinetics had been studied (Chihara et al, 1981b). Then the predicted results using the known kinetics could be compared our observed data obtained by cyclic regeneration in the fluidized-bed reactors.…”

Section: Scopementioning

confidence: 99%

“…Various weights of virgin carbon particles were added to the tubes and the reaction rate (g carbon/s) measured by weighing the tube after a reaction time of 2400 to 6OOO s at 1088°K with a steam concentration of 4.9%. Chihara et al (1981b) determined reaction rates in a TGA apparatus with the same virgin carbon (Type BPL, Pittsburgh Activated Carbon) and including the same temperature and steam concentration. In the TGA apparatus complete mixing was attained.…”

Section: Regenerationmentioning

confidence: 99%

“…Chihara et al (1981a) investigated the thermal decomposition of adsorbed sucrose and proposed rate equations for a simple two-reaction sequence of decomposition processes. Also, Chihara et al (1981b), using a thermal gravimetric apparatus, measured the kinetics of the third step employing steam for gasifying the residual carbon from sucrose adsorption.There appears to be no information on the optimum conditions for regeneration when the activated carbon is to be used repeatedly in adsorption-regeneration cycles. The key factor is the extent of carbon gasification.…”

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confidence: 99%

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Cyclic regeneration of activated carbon in fluidized beds

1982

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Cyclic thermal regeneration of powdered activated carbon containing adsorbed sucrose was studied in fluidized beds at 1151°K and 101.3 kPa (1 atm). The regeneration process consists of three steps: 1) drying, Z), thermal decomposition, and 3), gasification of residual carbon with steam. The maximum restoration of adsorption capacity (98.5% recovery after each regeneration) was obtained when gasification removed an amount of carbon equal to the residual adsorbed carbon after thermal decomposition. It was verified that the time required to attain optimum regeneration could be determined from available kinetics data for the steamcarbon reaction. For our sucrose-activated carbon system this time was about 180 s at 1151°K. SCOPEActivated carbon is widely used for removing organic pollutants from waste water. Economic considerations require regeneration of the spent carbon and the thermal process is most widely used. Also, powdered carbon is less expensive than the granular type so that fluidized-bed regeneration has some attraction. Thermal regeneration consists of three steps: l), drying of the wet, spent carbon, Z), heating to temperatures of the order of l l O O O K where thermal decomposition occurs rapidly, and 3) gasification of residual carbon. The second step is chemically complex, involving decomposition of original adsorbates, desorption of low-molecular weight products, and leaving residual adsorbed carbon. A major fraction of the original adsorbate is removed in this step. However, unless the residual carbon is removed, continued cycling operation results in buildup of residual carbon and reduction in adsorption capacity.Effective design of regeneration processes for both powdered and granular carbon has been handicapped by lack of kinetics data for the regeneration reactions, and only recently have efforts been made to obtain such information. Suzuki et al. (1978) and Hashimoto et al. (1979) have studied the second step and given rate equations for the loss in weight due to decomposition reactions. Chihara et al. (1981a) investigated the thermal decomposition of adsorbed sucrose and proposed rate equations for a simple two-reaction sequence of decomposition processes. Also, Chihara et al. (1981b), using a thermal gravimetric apparatus, measured the kinetics of the third step employing steam for gasifying the residual carbon from sucrose adsorption.There appears to be no information on the optimum conditions for regeneration when the activated carbon is to be used repeatedly in adsorption-regeneration cycles. The key factor is the extent of carbon gasification. The objective of our research was to determine the optimum extent of gasification in cyclic operation. Experimentally, powdered carbon with adsorbed sucrose was regenerated in a fluidized bed at 1151OK and 1 atm using steam.If the optimum gasification and the kinetics of the reaction are known, the time of the third step can be calculated. The sucrose-steamcarbon system was chosen because kinetics had been studied (Chihara et al., 1981b). Then the ...

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supporting

confidence: 86%

Section: Results and Discussion Effects Of Cyclic Operationmentioning

confidence: 99%

Section: Scopementioning

confidence: 99%

Section: Regenerationmentioning

confidence: 99%

mentioning

confidence: 99%

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Cyclic regeneration of activated carbon in fluidized beds

1982

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Regeneration of activated carbon. Part I: Thermal decomposition of adsorbed sodium dodecylbenzene sulfonate

1983

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Equilibrium adsorption isotherms and rates of thermal decomposition were measured for sodium dodecyl-benzene sulfonate (DBS) adsorbed on powdered activation carbon. The rate data were obtained in a thermal gravimetric apparatus operated both at constant temperature (522 to 666 K) and with a constant rate of temperature increase from 298 to 1023 K.About 50% of the adsorbed material could be removed at temperatures up to 748 K and only a small amount of the remaining 50% could be eliminated by further heating to 1,023 K. The residual adsorbate at 1,023 K was considerably greater than could be accounted for by inorganic materials such as NaeSOr.The kinetics of the decomposition up to 748 K could be explained by a two-reaction sequence, either parallel or consecutive reactions. Rates of decomposition were slower than found in earlier studies (Chihara et al., 1981) SCOPERegeneration of activated carbon normally requires drying of the spent carbon at temperatures up to 378 K, followed by heating and gasification at temperatures up to 1,073 K. The gasification process with an oxidizing gas is usually necessary to retain most of the original adsorption capacity. A large fraction of the deposited material can be removed by thermal decomposition prior to gasification (oxidation). For an adsorbate such as sucrose with no inorganic residue, nearly all of the adsorbed material is volatilized by heating alone. With more refractory materials such as DBS, heating to 1,073 K leaves significant carbonaceous material in addition to the inorganic residue.For design of regenerators, rate equations are necessary for both thermal decomposition and gasification. In a prior study (Chihara et al., 1981), kinetics were measured for these two processes with carbon containing adsorbed sucrose. For this easily decomposed adsorbate, the overall thermal decomposition process could be explained by separate, single, rate-controlling steps, the first for 298 K < T < 428 K and the second occuring at 428 < T < 773 K. The objective of the current work was to measure rates of thermal decomposition and gasification for a refractory adsorbate, and DBS was considered to be r e p resentative of such components found in wastewaters.First, equilibrium isotherms were measured at 303 and 308 K. Then thermal decomposition data were obtained in a TGA apparatus operated at constant temperatures up to 666 K and with a constant rate of temperature rise up to 1,023 K, all at atmospheric pressure in a stream of helium. These results are reported in Part I. In Part I1 rates of gasification of residual adsorbed material are reported and analyzed. CONCLUSIONS AND SIGNIFICANCEEquilibrium isotherms for DBS on BPL activated carbon (bituminous coal base) indicate capacities of 0.28 to 0.60 kg adsorbed per kg of activated carbon over a range of solution concentrations (aqueous) from 20 to 9, OOO ppm. These capacities are more than twice those for sucrose on the same carbon.No thermal decomposition was observed below about 490 K for DBS, while for sucrose more than 30% of...

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Regeneration of activated carbon. Part II: Gasification kinetics with steam

1983

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The kinetics of the reaction between steam and thermally‐regenerated activated carbon containing DBS residue was studied at 973 to 1,062 K and atmospheric pressure. The results fit a Langmuir‐Hinshelwood rate equation originally developed for the oxidation of other types of carbon with steam. The rates of reaction were relatively high. Auxiliary experiments with added Na2SO4 indicated that the non‐volatile inorganic residue from DBS has a catalytic effect.Readsorption measurements on regenerated samples demonstrated that thermal regeneration alone resulted in considerable loss (35%) in adsorption capacity but that thermal regeneration followed by steam gasification could completely restore the adsorption capacity for DBS on the remaining virgin carbon.

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Regeneration of powdered activated carbon. Part II: Steam‐carbon reaction kinetics

Cited by 19 publications

References 17 publications

Cyclic regeneration of activated carbon in fluidized beds

Cyclic regeneration of activated carbon in fluidized beds

Regeneration of activated carbon. Part I: Thermal decomposition of adsorbed sodium dodecylbenzene sulfonate

Regeneration of activated carbon. Part II: Gasification kinetics with steam

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