Augustine Quek

Thermogravimetric investigation of hydrochar-lignite co-combustion

Co-combustion of hydrochar with lignite was investigated by means of thermogravimetric analysis. Hydrochars were produced from coconut fibers and eucalyptus leaves under hydrothermal conditions at 250°C. The hydrochar was added in varying amounts to lignite for combustion. The results indicated that hydrothermal treatment decreased the volatile matter content and increased the fixed carbon content of the biomaterials. The elevated energy density and decreased ash content of the hydrochar improved its combustion behavior when co-fired with lignite for energy production. The hydrochars derived from coconut fiber and eucalyptus leaves had similar chemical compositions and showed similar influences on lignite combustion. Hydrochar addition increased the burnout and shortened the combustion range of the hydrochar-lignite blends. High combustion efficiency was observed due to the synergistic interactions between hydrochar and lignite during the co-combustion process. A kinetic study showed that the combustion process of hydrochar-lignite blends followed first-order reaction rates.

Low-Energy and Chemical-Free Activation of Pyrolytic Tire Char and Its Adsorption Characteristics

Abstract It is generally known that the solid char obtained from pyrolysis of scrap rubber tires can be used as an adsorbent for several applications such as wastewater treatment. In this study, scrap tires were first pyrolyzed under nitrogen (N2) or carbon dioxide (CO2) gas under various temperatures to produce char. The char was activated in situ by post-pyrolysis oxygenation (PPO) at different temperature ranges as soon as the pyrolysis process was completed. Elemental and spectroscopic analyses showed significant zinc content in the char after PPO. Batch-mode removal of aqueous copper (Cu) using the chars revealed that, for N2 and CO2, the optimum condition for pyrolysis was at 550 °C and for activation was from 550 to 250 °C. Although CO2-pyrolyzed char had lower Cu and lead (Pb) removal than N2-pyrolyzed char, it had higher char yields. For both N2- and CO2-pyrolyzed char, activation with PPO improved their heavy metal removal efficiencies significantly compared with unactivated char. PPO chars had much faster removal rates and higher Cu removal compared with both pyrolyzed, unactivated char and commercial activated carbons.

Removal of copper by oxygenated pyrolytic tire char: Kinetics and mechanistic insights

The kinetics of copper ion (Cu(II)) removal from aqueous solution by pyrolytic tire char was modeled using five different conventional models. A modification to these models was also developed through a modified equation that accounts for precipitation. Conventional first- and second-order reaction models did not fit the copper sorption kinetics well, indicating a lack of simple rate-order dependency on solute concentration. Instead, a reversible first-order rate reaction showed the best fit to the data, indicating a dependence on surface functional groups. Due to the varying solution pH during the sorption process, modified external and internal mass transfer models were employed. Results showed that the sorption of copper onto oxygenated chars was limited by external mass transfer and internal resistance with and without the modification. However, the modification of the sorption process produced very different results for unoxygenated chars, which showed neither internal nor external limitation to sorption. Instead, its slow sorption rate indicates a lack of surface functional groups. The sorption of Cu(II) by oxygenated and unoxygenated chars was also found to occur via three and two distinct stages, respectively.

Methylene blue sorption onto oxygenated pyrolytic tire char: equilibrium and kinetic studies.

A novel method is presented for pyrolyzing and activating waste tires for adsorptive removal of aqueous contaminants. The adsorption characteristics of a cationic dye (methylene blue, MB) by pyrolytic tire char were evaluated. Mechanistic insights into the adsorption of MB onto char made from pyrolyzed tires are discussed on the basis of equilibrium and kinetic studies. A comparative evaluation of the performance of unoxygenated, pyrolyzed chars (NoPPO) and oxygenated chars (P550250) is reported. Despite having similar surface areas between the oxygenated and unxoygenated chars, the adsorption capacity of the former was much higher than that of the latter. However, adsorption of MB is thermodynamically unfavorable (ΔG>0) although oxygenation lowers the free energy of adsorption. MB sorption onto P550250 is inhibited by an external film, which was not observed in the case of NoPPO. An increase in the solution temperature was found to reduce the adsorption rates of MB onto P550250 but increase the sorption ...