Free Glycerol Removal from Biodiesel Using Anion Exchange Resin as a New Type of Adsorbent

Anion exchange resins, as a new class of adsorbents for glycerol removal, were proposed and compared with cation exchange resins and macroporous resins. These kinds of resins exhibited excellent adsorption properties to free glycerol in biodiesel, and the maximum adsorption capacity of anion exchange resins for glycerol even reached 439.31 mg/gdry resin. To further examine the effects of functional groups and ion types of anion resins on the removal of glycerol, four kinds of anion resins, including strongly and weakly basic anion exchange resins in chloride and free hydroxyl types, were synthesized. Compared with weakly basic anion exchange resins in two different types, strongly basic anion exchange resins all displayed better adsorption effects for glycerol. Kinetic and thermodynamic studies of strongly basic anion exchange resin with a quaternary ammonium group in the chloride type were performed to reveal the adsorption mechanism of the resin for glycerol. The results showed that the adsorption of this resin for glycerol was a spontaneous, exothermic process accompanied by a gradual decrease in entropy. Besides intraparticle diffusion, the adsorption mechanism also involved the hydrogen bond force between free glycerol and glycerol molecule adsorbed onto the active sites of the resin as well as the hydrogen bond attraction between glycerol molecules adsorbed onto the adjacent active sites, and the dipole bond force between glycerol and a quaternary ammonium group.