Adsorption of Basic Magenta II onto H2SO4 activated immature Gossypium hirsutum seeds: Kinetics, isotherms, mass transfer, thermodynamics and process design

Abstract

The adsorption of Basic Magenta II onto H2SO4 activated immature Gossypium hirsutum seeds was analysed using Ho, modified Freundlich, Sobkowsk–Czerwi, Blanchard, Elovich, Avrami, and modified Ritchie kinetic models by nonlinear regression-sum of normalized errors analysis. The goodness of fit was evaluated with coefficient of determination and root mean square error. The good agreement of experimental data to Avrami second-order model indicated that the mechanism of adsorption followed multiple kinetic orders. The Avrami second-order mechanism was applied to predict the rate constant of sorption and the equilibrium capacity and subsequently the obtained equilibrium adsorption capacities were utilized to find the equilibrium concentrations. Langmuir, Freundlich, Temkin, Sips and Hill isotherms were investigated to understand the nature of adsorption with the help of nonlinear regression analysis. Both Sips and Hill isotherms were best fit to the adsorption equilibrium data showing the homogeneous adsorption on the heterogeneous surface of carbon and the positive co-operative manifestations of the Basic Magenta II molecules. The mass transfer study depicted the details such as mass transfer coefficient, intra-particle diffusion rate, pore diffusion coefficient, and film diffusion coefficient. The adsorption process was found to be controlled by film diffusion. The thermodynamic parameters like, Gibbs free energy change, enthalpy change, entropy change and isosteric heat of adsorption confirmed the endothermic, feasible and spontaneous nature of adsorption. A single stage batch adsorber was designed using Sips isotherm constants to estimate the amount of carbon required for desired purification. Keywords: Gossypium hirsutum seeds, Isotherms, Kinetics, Mass transfer, Thermodynamics, Process design