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.