Synthesis of Resins with Ionic Liquids for Purification of Flavonoids from Hippophae rhamnoides L. Leaves

The efficient purification method of high-purity flavonoids from Hippophae rhamnoides L. (sea buckthorn) is reported. A novel room temperature ionic liquid-based macroporous adsorption resin (MAR), N-methylimidazole/MARs (Mim/MARs), was prepared on the basis of the Friedel-Crafts-catalyzed and surface-modified technique. The material exhibited favorable characteristics for adsorption application, including high pore volume (1.90 cm(3)/g, 3 times as big as the optimal commercial adsorbent), good pore structure (type IV isotherm with an HI hysteresis loop, the most favorable structure for adsorption purposes), narrow particle size and pore size distribution (1.2 mm with a standard deviation of 0.106 mm), and excellent chemical stability. This paper also presents the first experimental evidence that the functional groups of the modified materials and composite action of certain molecular interactions between the adsorbent and flavonoids affected the adsorption process. Moreover, a new sphere-size adsorption kinetics model in which the adsorption process contained three or more compartments and detailed parameters of sphere size was developed according to the multicompartment kinetics model and Karichhoff's theory by investigating the regression of the experimental results. The conclusion that the first compartment of the adsorption process onto Mim/MARs mainly occurred on spheres larger than 0.83 mm and the second and third ones mainly occurred on spheres of 0.46-0.83 and 0.22-0.46 mm, respectively, was drawn from this new sphere-size adsorption kinetics model.