Search

A series of calcium oxide–magnesium oxide (CaO–MgO) catalysts were prepared under the effects of different precipitating agents and using varied Mg/Ca ratios. The physiochemical characteristics of the prepared catalysts were analyzed using XRD, FE-SEM, BET, FTIR, and TG/DTA techniques. Quantification of basic active sites present on the surface of the CaO–MgO catalysts was carried out using the Hammett indicator method. The as-prepared mixed oxide samples were tested for propylene carbonate (PC) synthesis through the alcoholysis of urea with propylene glycol (PG). The effects of the catalyst composition, catalyst dose, reaction temperature, and contact time on the PC yield and selectivity were investigated. The maximum PC yield of 96%, with high PC selectivity of 99% and a urea conversion rate of 96%, was attained at 160 °C using CaO–MgO catalysts prepared using a Mg/Ca ratio of 1 and Na2CO3 as a precipitating agent. The best-performing catalysts also exhibited good reusability without any significant loss in PC selectivity. It is expected that the present study will provide useful information on the suitability of different precipitating agents with respect to the catalytic properties of the oxides of Ca and Mg and their application in the synthesis of organic carbonates.

The aim of the present study is to analyze the competitive adsorption of cadmium (Cd(II)), nickel (Ni(II)), and zinc (Zn(II)) ions onto rice husk ash (RHA) from ternary metal ion mixtures. RHA is a waste material obtained from the flue gas of the rice husk fired boilers. The equilibrium adsorption data were obtained at different initial concentrations (C0= 10 to 100 mg·dm−3), 5 h contact time, 30 °C temperature, and RHA dosage of 10 mg·dm−3at pH = 6. The Freundlich and the Redlich−Peterson models represent the single ion equilibrium adsorption data better than the Langmuir model. The equilibrium metal removal decreases with increasing concentrations of the other metal ions, and the combined action of Cd(II), Ni(II), and Zn(II) ions on RHA is found to be antagonistic. The competitive Sheindorf−Rebuhn−Sheintuch (SRS) model fits the ternary adsorption equilibrium data satisfactorily. [ABSTRACT FROM AUTHOR]

The present study reports the simultaneous adsorption of cadmium (Cd(II)), nickel (Ni(II)), and zinc (Zn(II)) ions from aqueous solution onto bagasse fly ash (BFA). BFA is a waste material collected from the particulate collection equipment attached to the flue-gas line of bagasse fired boilers in sugar mills. The equilibrium adsorption data were obtained with a BFA dosage of 10 g/dm3at varying initial concentrations (C010−100 mg/dm3), 5 h contact time, 30 °C temperature, and initial pH 6. The single metal ion equilibrium adsorption data were fitted to the noncompetitive Langmuir, Freundlich and Redlich−Peterson (R−P) models. The R−P and Freundlich models represent the equilibrium data better than the Langmuir model over 10 ≤ C0≤ 100 mg/dm3. The adsorption capacity of Zn(II) is found to be higher than that of Ni(II) or Cd(II) for the ternary metal solutions, and is in agreement with the single-component adsorption data. The equilibrium metal removal decreases with an increase in the concentration of the other metal ion and the combined action of Cd(II), Ni(II), and Zn(II) ions on BFA is generally found to be antagonistic. Equilibrium isotherms for the ternary adsorption of Cd(II), Ni(II), and Zn(II) ions on BFA have been analyzed by using nonmodified, modified, and extended Langmuir models; nonmodified and modified R−P models; and the Sheindorf−Rebuhn−Sheintuch (SRS) model. The competitive SRS model fits the ternary adsorption equilibrium data satisfactorily and adequately, and has been used to simulate the equilibrium sorption behavior of the ternary metal ion system through three-dimensional plots. [ABSTRACT FROM AUTHOR]