has a complicated structure (Tolesa et al. 2019; Dai et al.
2007), and sometimes relying on the conventional methods
may not yield much improved results (Chio et al. 2019). The
use of ILs, however, has proven to be a better alternative to
the foregoing (Wang and Qian 2020; Zhang et al. 2015).
4.1 Ionic Liquids in Lignin Depolymerization
ILs are being used to solve varieties of challenges associated
with the treatment and deconstruction of lignin to
mono-cyclic aromatic such as sugars, polyols, organic acids,
furans, and phenolics (Singh et al. 2017; Yang et al. 2018;
Thierry et al. 2017). ILs have shown greater advantages over
the thermal approach which requires metal supports such as
Cu, Ni, Rh, and Pd,. as catalysts that employ high temperatures beyond 200 °C and heightened pressure. Employing a
versatile catalyst like methyltrioxorhenium (MTO) may be
efficient for catalyzing the C–O bond cleavage of the b-O-4
model compounds in lignin (Szalaty et al. 2018; Scott et al.
2015; Gregorio et al. 2006); however, the heterogeneous
nature of the lignin still limits its application.
The main purpose of lignin depolymerization is to convert the complex lignin into renewable fuels and chemicals
(Wang et al. 2017; Prado et al. 2015). Other methods have
altogether yielded low due to the lack of effective conversion
methods. Lignin conversion into value-added (aromatic)
products is a laborious task. The depolymerization of lignin
in ILs has been studied under oxidative and reductive conditions. The use of ionic liquids in lignin depolymerization
helps to optimize the process hence, minimizing waste
generation and resource underutilization.
Wang et al. revealed various sources of lignin that is
produced in varying proportions. Organosolv beech, one of
the commonest forms of lignin was reacted in
1-ethyl-3-methylimidazolium-trifluoromethane
sulfonate
([emim][CF 3 SO 3 ]) ionic liquid which in turn produced
2,6-Dimethoxy-1,4- benzoquinone at an 11.5 wt% yield.
Eugenol when subjected to a temperature of 200 °C produced a 7.9% Guaiacol.
4.1.1 Protic ILs on Lignin
Protic ILs (PILs) can greatly reduce reaction pathways and
minimize cost. However, due to the—interaction in
lignin-derived molecules, the further application of ILs may
be limited. Three PILs with different cations were utilized to
demonstrate the extraction of lignin in a study by Achinivu
et al., pyridinium [Py]
+
, 1-methylimidazolium [Mim]
+ and
pyrrolidinium [Pyrr]
+
.
They showed that [Py][Ac] and [Mim][Ac] can dissolve
large amounts of lignin components except for Xylan, which
dissolved only in [Pyrr][Ac]. The ability that [Py]
+ and
[Mim]
+ presence is selective is an advantage since it is a
necessary measure in selective extraction (partitioning).
References
Adams, C. J., Earle, J., & Seddon, K. R. (2000). Catalytic cracking
reactions of polyethylene to light alkanes in ionic liquids. Royal
Society of Chemistry Journal, pp. 21–23.
Al-sabagh, A. M., Yehia, F. Z., Eshaq, Gh., Rabie, A. M., &
ElMetwally, A. E. (2015). Greener routes for recycling of
polyethylene terephthalate. Egyptian Journal of Petroleum. https://
doi.org/10.1016/j.ejpe.2015.03.001.
Anastas, P., & Eghbali, N. (2010). Green chemistry: Principles and
practice. Chemical Society Reviews, 301–312. https://doi.org/10.
1039/b918763b.
Berthod, A., Ruiz-Ángel, M. J., & Carda-Broch, S. (2018). Recent
advances on ionic liquid uses in separation techniques. Journal of
Chromatography A, 1559, 2–16.
Bicak, N. (2005). A new ionic liquid: 2-hydroxy ethylammoniumformate. Journal of Molecular Liquids, 116, 15–18. https://doi.org/10.
1016/j.molliq.2004.03.006.
Broderick, E. M., Serban, M., Mezza, B., & Bhattacharyya, A. (2017).
Scientific approach for a cleaner environment using ionic liquids.
ACS Sustainable Chemistry & Engineering, 5, 3681–3684.
Cao, Y., & Mu, T. (2014). Comprehensive investigation on the thermal
stability of 66 ionic liquids by Thermogravimetric analysis. ACS
Sustainable Chemistry & Engineering. https://doi.org/10.1021/
ie5009597.
Chio, C., Sain, M., & Qin, W. (2019). Lignin utilization: A review of
lignin depolymerization from various aspects. Renewable and
Sustainable Energy Reviews Elsevier Ltd, 107, 232–249.
Clarke, C. J., Tu, W. C., Levers, O., Brohl, A. & Hallett, J. P. (2018).
Green and sustainable solvents in chemical processes. Chemical
Reviews, 118, 747 − 800.
Dai, A. J., Patti, A., Longe, L., Garnier, G., & Saito, K. (2007).
Oxidized lignin depolymerisation using formate ionic liquid as
catalyst and solvent. ChemCatChem. https://doi.org/10.1002/cctc.
201700632.
Gregorio, G. F., Weber, C. C., Grasvik, J., Welton, T., Brandt, A., &
Hallett, J. (2006). Green Chemistry. https://doi.org/10.1039/
C6GC01295G.
Holbrey, J. D., & Rogers, R. D. (2002). Green chemistry and ionic
liquids: Synergies and ironies green chemistry approach—process
management. In R. Rogers, et al. (Eds.), Ionic Liquids (pp. 2–14).
Washington, DC: ACS Symposium Series. American Chemical
Society.
Hong, S. M., Chen, E. Y., & Chem., G. (2017). Chemically recyclable
polymers: A circular economy approach to sustainability. Green
chemistry, 19, 3692.
Iannone, F., Casiello, M., Monopoli, A., Pietro, C., Sportelli, M. C.,
Picca, R. A., et al. (2017). Ionic liquids/ZnO nanoparticles as
recyclable catalyst for polycarbonate depolymerization. Journal of
Molecular Catalysis A: Chemical, 426, 107–116. https://doi.org/10.
1016/j.molcata.2016.11.006.
Applications of Ionic Liquids in Plastic and Lignin Waste Recycling
335
2007), and sometimes relying on the conventional methods
may not yield much improved results (Chio et al. 2019). The
use of ILs, however, has proven to be a better alternative to
the foregoing (Wang and Qian 2020; Zhang et al. 2015).
4.1 Ionic Liquids in Lignin Depolymerization
ILs are being used to solve varieties of challenges associated
with the treatment and deconstruction of lignin to
mono-cyclic aromatic such as sugars, polyols, organic acids,
furans, and phenolics (Singh et al. 2017; Yang et al. 2018;
Thierry et al. 2017). ILs have shown greater advantages over
the thermal approach which requires metal supports such as
Cu, Ni, Rh, and Pd,. as catalysts that employ high temperatures beyond 200 °C and heightened pressure. Employing a
versatile catalyst like methyltrioxorhenium (MTO) may be
efficient for catalyzing the C–O bond cleavage of the b-O-4
model compounds in lignin (Szalaty et al. 2018; Scott et al.
2015; Gregorio et al. 2006); however, the heterogeneous
nature of the lignin still limits its application.
The main purpose of lignin depolymerization is to convert the complex lignin into renewable fuels and chemicals
(Wang et al. 2017; Prado et al. 2015). Other methods have
altogether yielded low due to the lack of effective conversion
methods. Lignin conversion into value-added (aromatic)
products is a laborious task. The depolymerization of lignin
in ILs has been studied under oxidative and reductive conditions. The use of ionic liquids in lignin depolymerization
helps to optimize the process hence, minimizing waste
generation and resource underutilization.
Wang et al. revealed various sources of lignin that is
produced in varying proportions. Organosolv beech, one of
the commonest forms of lignin was reacted in
1-ethyl-3-methylimidazolium-trifluoromethane
sulfonate
([emim][CF 3 SO 3 ]) ionic liquid which in turn produced
2,6-Dimethoxy-1,4- benzoquinone at an 11.5 wt% yield.
Eugenol when subjected to a temperature of 200 °C produced a 7.9% Guaiacol.
4.1.1 Protic ILs on Lignin
Protic ILs (PILs) can greatly reduce reaction pathways and
minimize cost. However, due to the—interaction in
lignin-derived molecules, the further application of ILs may
be limited. Three PILs with different cations were utilized to
demonstrate the extraction of lignin in a study by Achinivu
et al., pyridinium [Py]
+
, 1-methylimidazolium [Mim]
+ and
pyrrolidinium [Pyrr]
+
.
They showed that [Py][Ac] and [Mim][Ac] can dissolve
large amounts of lignin components except for Xylan, which
dissolved only in [Pyrr][Ac]. The ability that [Py]
+ and
[Mim]
+ presence is selective is an advantage since it is a
necessary measure in selective extraction (partitioning).
References
Adams, C. J., Earle, J., & Seddon, K. R. (2000). Catalytic cracking
reactions of polyethylene to light alkanes in ionic liquids. Royal
Society of Chemistry Journal, pp. 21–23.
Al-sabagh, A. M., Yehia, F. Z., Eshaq, Gh., Rabie, A. M., &
ElMetwally, A. E. (2015). Greener routes for recycling of
polyethylene terephthalate. Egyptian Journal of Petroleum. https://
doi.org/10.1016/j.ejpe.2015.03.001.
Anastas, P., & Eghbali, N. (2010). Green chemistry: Principles and
practice. Chemical Society Reviews, 301–312. https://doi.org/10.
1039/b918763b.
Berthod, A., Ruiz-Ángel, M. J., & Carda-Broch, S. (2018). Recent
advances on ionic liquid uses in separation techniques. Journal of
Chromatography A, 1559, 2–16.
Bicak, N. (2005). A new ionic liquid: 2-hydroxy ethylammoniumformate. Journal of Molecular Liquids, 116, 15–18. https://doi.org/10.
1016/j.molliq.2004.03.006.
Broderick, E. M., Serban, M., Mezza, B., & Bhattacharyya, A. (2017).
Scientific approach for a cleaner environment using ionic liquids.
ACS Sustainable Chemistry & Engineering, 5, 3681–3684.
Cao, Y., & Mu, T. (2014). Comprehensive investigation on the thermal
stability of 66 ionic liquids by Thermogravimetric analysis. ACS
Sustainable Chemistry & Engineering. https://doi.org/10.1021/
ie5009597.
Chio, C., Sain, M., & Qin, W. (2019). Lignin utilization: A review of
lignin depolymerization from various aspects. Renewable and
Sustainable Energy Reviews Elsevier Ltd, 107, 232–249.
Clarke, C. J., Tu, W. C., Levers, O., Brohl, A. & Hallett, J. P. (2018).
Green and sustainable solvents in chemical processes. Chemical
Reviews, 118, 747 − 800.
Dai, A. J., Patti, A., Longe, L., Garnier, G., & Saito, K. (2007).
Oxidized lignin depolymerisation using formate ionic liquid as
catalyst and solvent. ChemCatChem. https://doi.org/10.1002/cctc.
201700632.
Gregorio, G. F., Weber, C. C., Grasvik, J., Welton, T., Brandt, A., &
Hallett, J. (2006). Green Chemistry. https://doi.org/10.1039/
C6GC01295G.
Holbrey, J. D., & Rogers, R. D. (2002). Green chemistry and ionic
liquids: Synergies and ironies green chemistry approach—process
management. In R. Rogers, et al. (Eds.), Ionic Liquids (pp. 2–14).
Washington, DC: ACS Symposium Series. American Chemical
Society.
Hong, S. M., Chen, E. Y., & Chem., G. (2017). Chemically recyclable
polymers: A circular economy approach to sustainability. Green
chemistry, 19, 3692.
Iannone, F., Casiello, M., Monopoli, A., Pietro, C., Sportelli, M. C.,
Picca, R. A., et al. (2017). Ionic liquids/ZnO nanoparticles as
recyclable catalyst for polycarbonate depolymerization. Journal of
Molecular Catalysis A: Chemical, 426, 107–116. https://doi.org/10.
1016/j.molcata.2016.11.006.
Applications of Ionic Liquids in Plastic and Lignin Waste Recycling
335