Treatment of Anion-Exchange Membranes with an Anti-Organics Fouling Coating for Use in Bio-Oil Separations

Electrodialysis (ED) has been looked at as a means of carboxylic acid, salt, and alkali metal removal from bio-oil. With the use of ED, organic acids can be recovered from pyrolysis products, pre-hydrogenation, and add value to the process. Typical anion-exchange membranes used in ED are not compatible with bio-oil and are easily blinded by the oil and foul. In addition, the mostly organic system does not have enough water activity to conduct ions. The anion-exchange membranes must be modified in order to resist fouling by organics and also allow for high ionic transfer in a low water system. This can be accomplished through the surface functionalization of the membranes. This research used polyethylenimine (PEI) to passivate the surface of  an AMX membrane. The positively charged amine groups both allow for passivation and create a hydrophilic layer at the membrane surface. Both the modified and unmodified membranes were exposed for an extended period to pyrolysis-produced bio-oil and the level of fouling was determined using FTIR-ATR spectroscopy. The results showed that the functionalized membrane has a much lower level of fouling than the unmodified membrane. By the functionalization of anion-exchange membranes, this research supports ED as a possible method for bio-oil separations.