Solid-phase extraction of long-chain fatty acids from aqueous solution

Microbially derived long-chain free fatty acids are useful precursors for biofuel production. However, effective and biocompatible methods for their separation from aqueous solutions do not presently exist. The overall and relative efficacy of several commercially available hydrophobic, anion exchange, and mixed-mode adsorbents for the recovery of laurate, a model 12-carbon saturated fatty acid, was compared according to both equilibrium and kinetic studies. Mixed-mode adsorbents exhibited the greatest adsorption capacity and affinity, with Amberlite IRA-402 able to adsorb up to 430 g-laurate/kg. Meanwhile, the anion exchange resin Amberlite IRA-67 adsorbed up to 426 g-laurate/kg, while the hydrophobic resin Dowex Optipore L-493 adsorbed a maximum of only 106 g-laurate/kg. Polymer gel adsorbents, which display the greatest aqueous swelling, achieved the fastest rates of laurate recovery. Adsorption kinetics were well represented by a pore-diffusion model for all adsorbents. Estimated pore diffusion coefficients were as high as 7.2 × 10^-10 m²/s for Amberlite IRA-402.