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

Abstract

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...

Kinetics of spent activated carbon regeneration

“…Thus, the sodium salts increased the rate twwthree fold, but the separate effects on the residue and on the base carbon were not determined. A similar effect of sodium sulfate on the gasification rate was noted by Umehara et al (1983b). Chemisorption measurements at 240-300°C for the sodium-containing residue showed a severalfold increase in adsorption rate over the base carbon and a slightly lower activation energy of 10 kcal/mol.…”

Additively Manufactured Zinc Oxide Thin-Film Transistors Using Directed Assembly

“…The results showed that glycerol can be completely decomposed at a relative low temperature of 290.8 °C, 59 while the decomposition of SDBS requires a much higher temperature. 60 No thermal decomposition happens for SDBS below 217 °C. Even at a high temperature of 800 °C, 40% of SDBS is still not decomposed.…”

“…Employing thermogravimetric analysis, the thermal decomposition of SDBS and glycerol has been investigated previously. The results showed that glycerol can be completely decomposed at a relative low temperature of 290.8 °C, while the decomposition of SDBS requires a much higher temperature . No thermal decomposition happens for SDBS below 217 °C.…”

Thermal desorption behavior of aliphatic and aromatic hydrocarbons loaded on activated carbon

“…"After drying at 150 °C for 3 h. sucrose and sodium decylbenzenesulfonate desorption in nitrogen were examined by Chibara et al (1981) and Umehara et al (1983), respectively. A two-step decomposition, which was first-order in the adsorbates, provided a good description of the observed TGA weight losses.…”