(261i) Macroalgae Pretreatment Using Peg-Linked Dicationic Acidic Ionic Liquids

Macroalgae has become a sustainable source of carbohydrates for the production of bio-fuel and bio-based chemicals. Compared with lignocellulosic biomass, macroalgae has higher photosynthetic efficiency, higher yields, lower lignin content and requires a simpler environment for its cultivation. Saccharification of macroalgae is commonly performed in a pressurized system in the presence of an acid catalyst. But ionic liquids (ILs) have been gaining popularity as effective and environmentally benign solvents for biomass as it enables hydrolysis to be performed at atmospheric conditions.

Task specific ILs are currently being explored in biomass processing owing to their versatility and multi-functionality (Olivier-Bourbigou et al., 2010). Particularly, Bronsted acidic ILs could replace traditional mineral acids such as sulfuric and hydrochloric acids. Typically, mono-cationic ILs are used to initially dissolve the biomass forming a homogeneous solution which is subsequently hydrolyzed using either enzymes or an acid catalyst. Meanwhile, dicationic ILs have various advantages over mono-cationic ILs such as higher thermal stability, decreased toxicity and multi-functionality. Particularly, ether-functionalized ILs tend to exhibit lower viscosities than their aliphatic counterparts. Moreover, the oxygen atoms embedded in the ether chains could act as hydrogen bond acceptors promoting biomass dissolution (Zhao et al., 2008). Dicationic ILs with acidic counter-anions are scarcely reported in biomass processing.

In this work, dicationic acidic ILs (DAILs) with varying poly-ethylene glycol (PEG) linker chains were synthesized, characterized and utilized for the conversion of Gelidium amansii, a red macroalgae into its corresponding monomeric sugars. The structures of PEG-DAILs having an acidic counter-anion (i.e. [2HSO₄]^-) were confirmed using spectroscopic techniques. Results showed the liquid form of PEG-DAILs, which are thermally stable up to T_peak < 350 ºC. PEG-DAILs with short ether chains (e.g. Di-, Tri- and Tetra-ethylene glycol) exhibited faster reaction rates than those with long ether chains (e.g. PEG400 and PEG600). Parameters such as particle size, biomass loading, reaction temperature and time were varied to achieve optimal sugar yields. Results showed [Tri-EG-(MIm)₂] 2HSO₄ as the best PEG-DAIL for maximum sugar release from G. amansii. Overall findings show the potential of PEG-DAILs for one-pot dissolution and hydrolysis of macroalgae to sugars.This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (No. 2009-0093816) and by the Ministry of Science, ICT & Future Planning (No. 2015R1C1A2A01054605).

References:

Olivier-Bourbigou, H., Magna, L., Morvan, D., Appl. Catal. A-Gen., 373 (2010) 1.

Zhao, H., Baker, G. A., Song, Z., Olubajo, O., Crittle, T., Peters, D., Green Chem., 10 (2008) 696.