Preparation and characterization of distillers’ grain based activated carbon as low cost methylene blue adsorbent: Mass transfer and equilibrium modeling

Abstract

In this study, an orthogonal array design method was employed to optimize carbon preparation from distillers’ grain (DGAC). The physical and chemical properties of the produced DGAC were characterized using scanning electron microscopy (SEM), N2 adsorption–desorption technique (Brunauer-Emmett-Teller, BET), and fourier transform infrared spectroscopy (FTIR). The BET surface area of DGAC was found to be 1430 m2/g, with average pore diameter of 2.19 nm. Batch experiments were carried out to study the adsorption of methylene blue (MB) onto DGAC. External mass transfer model, internal diffusion model, Boyd model and pseudo-second-order model were used to fit the adsorption kinetic process of MB adsorption onto DGAC. The results shows the external mass transfer model could only describe the adsorption for the initial 5 min, and later the internal diffusion in the pores of the carbon particles became a main resistance, chemisorption was also involved in the adsorption process. The adsorption equilibrium was described best by Langmuir isotherm with maximum adsorption capacity of 934.6 mg/g of MB at 55°C, thermodynamic studies confirmed that the adsorption of MB onto DGAC was spontaneous and thermodynamically favourable. These findings support the potential of using distillers’ grain as raw material to prepare well-developed porous texture adsorbent with huge MB removal capacity.