Kinetic and regeneration aspects of the adsorption of phenol on activated carbon
Cassidy, Edward King
Busch, A. W.
Master of Science
Physical-chemical treatment of liquid wastes is becoming widespread. One promising physical treatment process is contaminant adsorption on activated carbon. Units are frequently operated with the inclusion of carbon reactivation or' regeneration. In order to design adsorption processes both the kinetics of removal and the effects of regeneration require quantification. This study was conducted to establish the kinetics of phenol removal in non-flow, well-mixed reactors where cocoanut charcoal was the adsorbent. The batch system consisted of a Phipps-Bird six place paddle stirrer run at 162 RPM. Reactor volumes were 1000 ml and fluid volumes were 900 ml. Reactors were buffered to pH of 6.8 to 7.0. Phenol was measured by light absorbance on a Beckman DBG spectrophotometer. Removal rate was found to follow a film diffusion limitation description, where concentration gradient across the proposed film was the driving force. Effective concentration at the surface of the particle was calculated by applying the isotherm equation of Weber and Morris, for which the parameters were established for the system studied. The proportionality between driving gradient and removal rate was determined. When the ratio of phenol to carbon was in excess of approximately 40 mg/gm intraparticle diffusion limitation was indicated. Regeneration effects on carbon were studied in four phases. The first phase established, for a single high temperature regeneration of carbon, initially loaded to 1 % by weight, that uptake rate was decreased upon redose, relative to virgin carbon. The second phase showed that virgin carbon at equilibrium with the atmosphere underwent mass loss and eventual destruction at regeneration temperatures of 550 °C and 950 °C, whereas, at 170 °C, mass loss stabilized at 3 %. The third phase separated, partially, the mechanisms operative in capacity change during regeneration at a single temperature (550 °C). The final phase of the regeneration study established, for the temperatures and loadings studied, the desirability of high temperature of regeneration and heavy loading of the carbon prior to regeneration. More capacity was recovered, and carbon destruction was retarded, when the carbon was initially heavily loaded and the regeneration temperature was the highest studied.