Xie Y., Björkmalm J., Ma C., Willquist K., Yngvesson J., Wallberg O., Ji X. Techno-economic evaluation of biogas upgrading using ionic liquids in comparison with industrially used technology in Scandinavian anaerobic digestion plants. 2018. Applied Energy. 227. 742-750. 10.1016/j.apenergy.2017.07.067.