A new modified walnut shell by grafting l‐aspartic acid: Synthesis and kinetics

Abstract

AbstractA new modified walnut shell was prepared by grafting l‐aspartic acid (ASP) to walnut shell (WNS) in the hydrochloric acid solution (1.0 M). The effects of stirring speed, particle size, solid‐liquid ratio, temperature, and modifying agent concentration on grafting yield were studied. The grafting process conditions were optimized, and the grafting yield of WNS reached ∼14 wt%. The kinetics of the grafting reaction was investigated in the temperature range of 348‐368 K. A three‐step hypothesis was proposed to describe the grafting process: The ASP molecules diffuse to the out surface of WNS through the liquid film, then attend to the internal surface and react with WNS. The shrinking core models with different controlling steps were used to fit the kinetic data of the grafting process, and the results showed that the model controlled by a product layer fitted well with the experimental data. The internal diffusion coefficient DA of ASP in WNS has been calculated, and it was applied to predict the grafting yield at different ASP concentrations by a shrinking core model. The results showed that the shrinking core model controlled by internal diffusion is suitable.