Mass Transfer Mechanisms for Decolorizing Resin Adsorption of Alkaline Degradation Products of Hexose

Alkaline degradation products of hexose (HADP) were prepared as a representative colorant in remelt syrup to evaluate their adsorption performance onto a decolorizing resin. Four novel phenomenological adsorption mass transfer models, namely, external mass transfer resistance (EMTR), internal mass transfer resistance (IMTR), combined EMTR-IMTR, and adsorption on active sites (AAS), were used to decipher the mass transfer mechanisms for the resin adsorption of HADP. At the initial colorant concentrations of 60, 90, and 120 mg/L, the equilibrium adsorption capacities of the resin for HADP were 190, 270, and 326 mg/g, and the corresponding decolorization rates were 95%, 90%, and 82%, respectively. EMTR combined with IMTR was the rate-limiting step for HADP adsorption onto the resin, and AAS could not be neglected. The dynamic characteristics of HADP adsorption through the liquid film around the resin and the pores inside the resin could be described well using the combined EMTR-IMTR model. The AAS model could accurately calculate the physisorption and chemisorption rates during the whole adsorption process. These models can help provide new insights into the mass transfer behaviors of the adsorption system.