Oxidation of Organosolv Lignin in a Novel Surfactant-free Microemulsion Reactor

Abstract

Lignin is considered as a promising substitute for fossil resources, but the efficient conversion of the lignin remains a huge challenge due to its structural complexity and immiscibility with typical solvents. Herein, a series of surfactant-free microemulsion reactors comprised of octane, water and n-propanol were designed and their corresponding phase behaviors alongside their ability to intensify oxidative depolymerization of lignin was explored. Experimental results show that the phenolic monomer yield improves substantially (40-500 wt.%) when the novel microemulsion systems are employed by comparison with processes performed in a single solvent. Detailed characterizations also suggest that the above intensification is rationalized by the solubilization effect of the microemulsion system, which arise as a consequence of directional aggregation of lignin at the microemulsion interface.

Production of 4-Ethylphenol from Lignin Depolymerization in a Novel Surfactant-Free Microemulsion Reactor

“…15 However, when the W OA value increases from 7.5 to 31.4 wt %, the increasing number of O/W microemulsion droplets can increase the probability of collision between themselves, and they may start forming hydrophobic and hydrophilic channels, decreasing the κ value of the system. 20,26 As a result, the microstructure transforms from the O/W to bicontinuous (B.C) microregion at this range. With the further increase in W OA (more than 31.4 wt %), the water-in-oil (W/O) microemulsion is formed with noctane as the continuous phase.…”

“…There are two distinct regions in the phase diagram. 20 In particular, the colored region is described as a single-phase microemulsion region, which is optically isotropic and transparent. By contrast, the other one is assigned to a multi-phase region, which is turbid under the stirring condition.…”

“…This observation can be attributed to the aggregation of amphipathic lignin at its surface. 20 As a result, it can improve the contact between the lignin and water-soluble IL catalyst for the following lignin depolymerization. Besides, considering the comparison of the microemulsion droplets with and without lignin, the size distribution of the former is more dispersed than that of the latter, which is attributed to the high dispersion degree of the lignin macromolecule (Table S1), resulting in a wider size distribution of droplets in the microemulsion containing lignin.…”

“…In our previous work, a novel SFME system for bagasse lignin oxidation was constructed, achieving a 40−500 wt % increase in phenolic monomers' yield with comparison to those in single-solvent systems. 20 Therefore, an SFME system would be a good choice to improve the 4-ethylphenol production from lignin depolymerization.…”

An efficient solution to determine surface energy of powders and porous media: Application to untreated and treated lignin

“…As an amorphous copolymer, lignin is mainly composed of phenolic groups such as phydroxyphenyl (H-unit), guaiacyl (G unit) and syringyl (S Unit) that are residues from three monolignols (p-coumaryl, coniferyl and sinapyl alcohols) as lignin precursors [11,12]. Lignin, in powder form, has a wide set of applications as filler in composites, such as UV blocker [13][14][15][16][17], antioxidant [18][19][20], charring agent in flame retardancy [21][22][23][24][25][26], mechanical reinforcement [13,27,28] or surfactant [29][30][31]. However, the strong polar nature of lignin, due to the presence of hydroxyl groups, makes it incompatible with the non-polar PLA matrix, resulting in a poor interfacial filler-matrix adhesion [32].…”