(633d) Application of Polymer Resins for Solid Phase Extraction of Long Chain Fatty Acids From Aqueous Solutions

In light of exhausting fossil fuel reserves and global climate change, there is an increasing interest in the development of microbial biocatalysts with the ability to synthesize liquid fuel replacements.  For such purposes, long chain fatty acids (which constitute both biodiesel and jet fuel feed stocks) have recently been photosynthetically-synthesized by genetically-modified Cyanobacteria from sunlight and CO₂ [1].  Although the newly-synthesized fatty acid products can be extracellularly secreted, their efficient recovery from culture medium represents a new separation challenge which is complicated by the formation of fatty acid salts with medium components, as well as pH effects.  We here present on the in situ recovery of long chain fatty acids from culture medium via solid-phase extraction using polymer resins.  Polymer materials were specifically selected for their high level of biocompatibility with Cyanobacteria cultures,  efficacy over a wide range of pH and ionic strength conditions, and isolation following dispersion in biphasic cultures.  The relative utility of both anion exchange (from weak to strong base)and hydrophobic resins for the adsorption of ampihphilic fatty acid molecules have been characterized and comparatively analyzed with respect to both their equilibrium and kinetic performance.  High levels of product recovery is possible via adsorption  according to both potential mechanisms, with high loading capacities (up to 425 mg/g wet resin) having been achieved.  These result distinguishes the effect between relative strengths between electrostatic attractions and Van der Waals interactions as potential driving forces for the adsorptive recovery of free fatty acids from aqueous media. Pseudo first and second order kinetic models, as well as a general rate law expression were used to study the fatty acid adsorption kinetics as a function of different culture environments (e.g., pH, ionic strength, aqueous composition). A pore diffusion model was lastly employed to investigate the diffusion of laurate in both anion exchange and hydrophobic resins. Finally, by employing an efficient and tunable elution protocol, purified fatty acids can be recovered from culture media at high yields and in the preferred form (salt or free acid).

[1] Xinyao Liu, Jie Sheng, Roy Curtiss III, Fatty acid production in genetically modified cyanobacteria, PNAS, early edition, 2011