W.T. Tsai

Adsorption of acid dye onto activated carbons prepared from agricultural waste bagasse by ZnCl2 activation.

A series of activated carbons were prepared from agricultural waste sugarcane bagasse by chemical activation with zinc chloride (ZnCl2) as an activating agent at 500 degrees C and 0.5 h soaking time. The Langmuir surface area and total pore volume were used to estimate the average pore diameter of the carbon products. The values of the surface area and pore volume increased linearly with increase in the impregnation ratio (IR) up to 100 wt%. The adsorption capacities of the derived adsorbents for Acid Orange 10 were measured at 20 degrees C and 40 degrees C to gain further insights into the acidic surface oxides of the adsorbent from the results of Fourier transform infrared (FTIR) spectroscopy analysis and pH measurement. Adsorption isotherms of the acid dye on adsorbents prepared were determined and correlated with common isotherm equations. It was found that the Langmuir model appears to fit the isotherm data better than the Freundlich model. The physical properties of these adsorbents were consistent with the parameters obtained from the isotherm equations.

Preparation of activated carbons from corn cob catalyzed by potassium salts and subsequent gasification with CO2

In the present study, granular activated carbons were prepared from agricultural waste corn cob by chemical activation with potassium salts and/or physical activation with CO2. Under the experimental conditions investigated, potassium hydroxide (KOH) and potassium carbonate (K2CO3) were effective activating agents for chemical activation during a ramping period of 10 degrees C/min and subsequent gasification (i.e., physical activation) at a soaking period of 800 degrees C. Large BET surface areas (>1,600 m2/g) of activated carbons were thus obtained by the combined activation. In addition, this study clearly showed that the porosity created in the acid-unwashed carbon products is substantially lower than that of acid-washed carbon products due to potassium salts left in the pore structure.

Regeneration of spent bleaching earth by pyrolysis in a rotary furnace

Abstract A spent bleaching earth (SBE) from an edible oil refinery has been thermally regenerated by a rotary furnace under inert atmosphere (i.e. N 2 ). Under the experimental conditions investigated, pyrolysis temperature (500–660°C) is an important operating parameter. The effects of processing parameters such as pyrolysis temperature (>660°C), holding time and flowing gas (N 2 vs. CO 2 ) on the characterizations of the resulting solids are negligible compared to the fresh bleaching earth. Results showed that these samples are type IV with hysteresis loops corresponding to type H3 from nitrogen adsorption isotherms, indicating slit-shaped mesoporous characteristics. The regenerated clays have smaller surface areas (≈100 vs. 268 m 2 g −1 ) and pore volumes (≈0.214 vs. 0.359 cm 3 g −1 ) than the fresh bleaching earth. In addition, this study clearly demonstrated that the porosities created in the samples without acid-washing are lower than those with acid washing due to the residues left in the pores. Thus, smaller pores, accompanied by an increase in surface area, were also obtained for all samples after acid washing treatments.

Characterization of activated carbons prepared from sugarcane bagasse by ZnCl2 activation.

Activated carbons were prepared from the agricultural waste of sugarcane bagasse by the chemical activation with zinc chloride (ZnCl2) at the activation temperature of 500°C with soaking time of 0.5 hour. The influence of activation parameters on the final carbon products was examined by varying the impregnation ratio (i.e., mass ratio of added ZnCl2 to bagasse) and bagasse size. The physical properties of carbon products were characterized by nitrogen adsorption/desorption isotherms (at 77 K) and helium displacement method. The surface area and pore volume of carbons were thus obtained by the BET equation and t-plot method. Also, the particle density and porosity of carbons were estimated by the total pore volume and true density. The increases of the values of surface area and pore volume are approximately proportional to the impregnation ratio. The microporous carbon product with the BET surface area of 905 m2/g and total pore volume of 0.44 cm3/g was obtained in the present study. Further, the adsorption isotherms of two acid dyes from aqueous solutions onto the carbon products were performed at 30°C. The results show that the adsorption isotherms of acid dyes with high molecular weight or large molecular size on the microporous adsorbents of activated carbons are plateau forms, indicating multilayer adsorptions, which may be attributed to the steric hindrance of the adsorbate molecules.

ADSORPTION OF PARAQUAT ON THE PHYSICALLY ACTIVATED BLEACHING EARTH WASTE FROM SOYBEAN OIL PROCESSING PLANT

A series of regeneration experiments with physical activation were carried out on bleaching earth waste from the soybean refining process in a rotary reactor. The influence of activation parameters on the spent clay by varying the holding time of 1∼4 hours and temperature of 700∼900°C was determined. The variations of pore properties as well as the change of chemical characteristics in the resulting solids were also studied. Results showed that the resulting samples were type IV with hysteresis loops corresponding to type H3 from nitrogen adsorption–desorption isotherms, indicating slit-shaped mesoporous characteristics. However, the regenerated clays had smaller surface areas (70∼117 m2/g) than that (245 m2/g) of fresh bleaching earth. Under the physical activation conditions investigated, the holding time of 1 hour and temperature of 700°C were found to be optimal conditions for producing mesoporous clay with physical activation. The adsorption of paraquat on regenerated sample was also evaluated. The isotherm showed that the regenerated sample still had a high affinity for this herbicide. Thus, the regeneration of this agro-industrial waste is one option for utilizing the clay resource, and it may be used for water treatment applications to remove organic contaminants.

Regeneration of Bleaching Clay Waste by Chemical Activation with Chloride Salts

Abstract Spent bleaching earth (SBE) was regenerated by chemical activation with low cost and low pollution chlorides as activating agents. Under the conditions of activation temperature of 600°C and holding time of 1 h investigated, results show that fresh bleaching earth and regenerated bleaching earth are type IV with hysteresis loops corresponding to type H3 from nitrogen adsorption–desorption isotherms, indicating slit-shaped mesoporous structure. It is also found that the effect of the regeneration treatment studied in the present work on the pore structures and chemical properties of the resulting solids is negligible compared to the fresh bleaching earth. On the other hand, the pore properties of these chemically activated solids are higher than those of the sample regenerated from heat regeneration, but only approximate 45% of surface area are reclaimed. It implies that the carbon residues could be retained within pores and/or clogs the entrance of pores, resulting in a decrease in pore properties.