Perspective on Technical Lignin Fractionation

Abstract

Technical lignin extracted from pulping and biorefining processes provides a class of complex and polydisperse phenolic polymers. Preparation of lignin with lower structural complexity and polydispersity through lignin fractionation is one of the primary solutions to engineer lignin into a value-added material. Sequential lignin fraction by pH controlled precipitation from 12 to 1 is one of the primary developed methods. Partial solubility of lignin in organic solvents is another promising method for lignin fractionation. Organic solvents with different polarity and solubility factors are able to fractionate lignin, yielding a more homogeneous chemical structure. As a modification of the lignin fractionation process using solvents, water/organic solvents mixture, such as propan-2-one, alcohols, and acetic acid, from room to high temperature has been proposed as a greener method for lignin fractionation. Using membrane technology is another promising method and current results indicate a good potential for lignin recovery and fractionation.

New Opportunities in the Valorization of Technical Lignins

“…Problems related to rather sticky precipitates might occur for some lignin types, and additional efforts are required to overcome such problems during process scale‐up. General process aspects and issues of lignin fractionation were comprehensively reviewed very recently [96] …”

Isolation of Low Dispersity Fractions of Acetone Organosolv Lignins to Understand their Reactivity: Towards Aromatic Building Blocks for Polymers Synthesis

“…Fractionation of lignin allows to obtain well‐defined fractions of low dispersity and more uniform structure, thus potentially improving their use in high value applications. The past few years have seen considerable developments in this area, and recent reviews give an exhaustive overview of the different methods that have been used [23–25] …”

“…The past few years have seen considerable developments in this area, and recent reviews give an exhaustive overview of the different methods that have been used. [23][24][25] A detailed study of the solubility in common organic solvents was first performed to find the best conditions to fractionate the organosolv lignins from beech and birch. Both lignins were then refined into five distinct fractions, which were characterized by 31 P NMR, FTIR spectroscopy, size exclusion chromatography (SEC) and differential scanning calorimetry (DSC).…”

Lignin Fractionation in Segmented Continuous Flow

“…Commonly used techniques include sequential/fractional precipitations, fractional dissolutions, extractions, adsorption-desorption and ultrafiltration; some very recent reviews give more extensive overviews regarding lignin fractionations and manage to bring in context various challenges that would still eventually need to be overcome. [12,13] Fractional precipitation was used in our group to fractionate and investigate both an example for lignins produced in modern versions of traditional paper industries, as well as a lignin generated as by-product in a modern biorefinery process. The first lignin was a softwood kraft lignin, KL, produced via the Lignoboost process; [14] the second lignin was a wheat straw organosolv lignin, WL, isolated as by-product of the CIMV biorefinery process.…”

“…The idea to fractionate the lignin stream generated in the initial biomass fragmentation is not new: fractionation of lignins has been investigated since the early 1950s, and the field has seen recently numerous achievements. Commonly used techniques include sequential/fractional precipitations, fractional dissolutions, extractions, adsorption–desorption and ultrafiltration; some very recent reviews give more extensive overviews regarding lignin fractionations and manage to bring in context various challenges that would still eventually need to be overcome …”