Depolymerisation of lignin using Brönsted acidic ionic liquids
S. K. Singh,1 P. L. Dhepe *1
1
Catalysis Division, National Chemical Laboratory, Pune 411008, India
*
E-mail: [email protected],
1. Introduction:
The limited reserves of fossil feedstocks and their fluctuating prices force researchers to identify the use of
eco-friendly and renewable resources as an alternative to produce chemicals, fuels and materials. In view of this,
plant derived biomass (crop waste) containing cellulose (40-50%), hemicellulose (20-30%), lignin (20-25%) etc. are
useful.1,2 Since India is an agricultural country, huge quantity of crop waste (624 MMT per year) is produced which
can be used for chemicals, fuels and materials synthesis.3 It will be beneficial to use lignin, the only naturally
occurring polymer of phenolic compounds linked together via C-O-C (60-75%) and C-C (20-30%) bonds for the
production of chemicals and fuel additives. In this report, we present results on the catalytic conversion of lignin
into chemicals using homogeneous Brӧnsted acidic ionic liquids (BAILs) catalysts (Scheme 1).
2. Materials and Methods:
Synthesis of BAILs is done by a known process.4 Characterization of the catalysts was carried out using
1
NMR ( H, 13C), FT-IR, CHNS, TGA, and UV-Vis techniques. Catalytic reactions were carried out in autoclave at
various temperatures (80-170oC) for desired time (10-180 min). The reaction mixture was analyzed by FT-IR, DSC,
GPC, GC and GC-MS techniques.
3. Results and Discussion:
Figure 1 summarizes the results on the conversion of lignin into phenolic monomers using BAILs for the
reactions carried out at 120oC. It can be observed that over HC-5 catalyst maximum of 96 % yield for organic
solvent soluble products is possible. Other BAILs were also active but showed lower yields (8-78%). The activity of
BAILs was also compared with mineral acid, H2SO4 and solid acid catalysts (HUSY, H-beta etc.). It is observed that
BAILs perform better than these catalysts under similar reaction conditions. The detailed study on time, catalyst
concentration etc. are carried out and their effects on the conversions and product formation were confirmed by GC,
GC-MS and GPC analysis. It was observed that the products have low molecular weight distribution (110-220gmol1
). The complete characterization of lignin and products by various techniques helped in understanding the reaction
mechanism and also presence of various functional groups. The details on this will be discussed during presentation.
Scheme 1: Conversion of lignin into valuable chemicals
Figure 1: Catalytic depolymerisation of lignin over HC
catalysts
4. Conclusion:
Lignin depolymerisation using BAILs is presented under mild reaction conditions (120 oC) to achieve ca.
78% yield for low molecular weight aromatic products. Details about catalytic activity, substrate and products
characterization will be discussed during presentation.
[1] R. Sahu, P.L. Dhepe, A One-Pot Method for the Selective Conversion of Hemicellulose from Crop Waste into
C5 Sugars and Furfural by Using Solid Acid Catalysts, ChemSusChem, 5 (2012) 751-761.
[2] A.B. Pandey, S. ; Sukumaran, R.; Kausik, N, Study on Availability of Indian Biomass Resource for Exploitation,
in: Exploitation (Ed.: R. Chidamabaram), Technology Information and Forecasting and Assessment Council
(TIFAC) Report India, 2009.
[3] B. M. Matsagar and P. L. Dhepe, Bronsted acidic ionic liquid-catalyzed conversion of hemicellulose into sugars,
Catal. Sci. Technol., 5 (2015) 531-539.