2.4 Lignin recovery
Lignin was recovered from the liquid fraction using an Amicon stirred ultrafiltration cell (UFSC20001, Amicon Corporation) with a 1 kDa membrane disc. Nitrogen gas was connected to the stirred cell at 207 kPa with the magnetic stirrer set at 300 rpm. The liquid fraction (30 ml) was mixed with 70 ml of ethanol/water solution, loaded to the stirred cell, and filtered. Additional 40 ml of ethanol/water solution was added and filtered to completely remove the free choline chloride, DHBA, and the third constituent. The retained lignin on the membrane disc was air-dried for further characterization.