Adsorption behaviors and kinetics studies of chitooligosaccharides with specific degree of polymerization on a novel ion-exchange resin

Abstract Physiological activities of chitooligosaccharides (COSs) are related to their intrinsic structure and purities of products. However, the efficient preparation method of COSs with a specific degree of polymerization (DP) is still lacking, which limits the in-depth research and application of COSs. This work focused on the adsorption characters of COSs on the ion-exchange resin. Static adsorption experiments were conducted to study the effects of initial solution pH and ionic strength on the adsorption behaviors of chitobiose, chitotriose, chitotetraose, chitopentaose, and chitohexaose (COS 2–6). The adsorption equilibrium, thermodynamics, and kinetics of adsorption were investigated, and the molecular dynamics method was used to calculate the interaction energy of COS 2–6 with the resin and the diffusion coefficients of COS 2–6 in solution. The results show that the adsorption equilibrium data of COS 2–6 are satisfied with the Langmuir model, while the adsorption equilibrium capacities decrease with the increase of COSs DP. The COS 2–6 adsorption kinetic data are well fitted to the pseudo-second-order kinetic model. Liquid-film diffusion and intra-practical diffusion are both the adsorption rate-limiting steps. Thermodynamic parameters show that the adsorptions of COS 2–6 on HX-7 resin are spontaneous and feasible. With the increase of DP, the diffusion coefficients of COS 2–6 in solution decrease while the interaction force with resin become stronger, thus leading to more favorable adsorption.