Delignification and Membrane Fabrication from Birch Biomass

Debarked birch chips (Betula pendula) with an average size of 5 × 1 × 0.1 cm were used as source material for all described operations. DES treatment was applied for partial delignification of the biomass. Utilised DES consisted of choline chloride (ChCl, CAS # 67-48-1, Merck KGaA, Darmstadt, Germany), acting as a hydrogen bond acceptor (HBA), and lactic acid (LAc, CAS # 79-33-4, Merck KGaA, Darmstadt, Germany), acting as hydrogen bond donor (HBD). Deionised (DI) water mixed with ethanol at a 1:9 ratio was used for washing residual DES from treated biomass. Consequent bleaching of biomass was completed using acetic acid (CAS # 64-19-7, Merck KGaA, Darmstadt, Germany) and sodium chlorite (CAS # 7758-19-2, Acros Organics, Geel, Belgium). Ionic liquid (95% 1-ethyl-3-methylimidazolium acetate; C₁C₂ImOAc, CAS # 143314-17-4, Iolitec Ionic Liquids Technologies GmbH, Heilbronn, Germany) mixed with dimethylsulphoxide (CAS # 67-68-5, Merck KGaA, Darmstadt, Germany) at a 2:8 mass ratio was used for the preparation of the casting solution.
Non-woven polyester was used as a support material for the membrane preparation and was taken from used reverse osmosis (RO) membranes and cleaned mechanically and chemically. CENTRA-R 60\120 system (Elga purification system, Veolia Water, Lane End, UK) was used to produce ultra-pure DI water (15 MΩ, 0.5–1 µS/cm), which was used for the washing process, preparation of water-based solutions, and as a non-solvent in the coagulation bath. Anhydrous LiCl (CAS # 7447-41-8, Merck KGaA, Darmstadt, Germany) was used as an additive. Polyethylene glycol (PEG, approx. M_w 35 000 g/mol, CAS # 25322-68-3, Merck KGaA, Darmstadt, Germany) was used to prepare a model solution for the membrane retention study.