Oxidative Depolymerization of Alkaline Lignin from Pinus Pinaster by Oxygen and Air for Value-Added Bio-Sourced Synthons.

Martin Camus,Olivia Condassamy,Sergio Mastroianni,Henri Cramail,Christelle Michaud,Gérard Mignani,Etienne Grau,Stéphane Grelier,Frédérique Ham-Pichavant

doi:10.3390/polym13213725

Abstract

In this work, an efficient 3-step process targeting the chemical modification and purification of lignin oligomers from industrial alkaline lignin is described. The oxidative depolymerization process of alkaline lignin with O2 or Air pressure, without use of metal catalyst, led to the production of two fractions of lignin oligomers named ‘precipitated lignin’ and ‘hydrosoluble lignin’ with 40% and 60% yield, respectively. These fractions were characterized with a wide range of methods including NMR spectroscopy (31P, 2D-HSQC), SEC (in basic media), FTIR. NMR analyses revealed the presence of carboxylic acid functions at a ratio of 1.80 mmol/g and 2.80 mmol/g for the precipitated and hydrosoluble lignin, respectively, values much higher than what is generally found in native lignin (between 0.2 and 0.5 mmol/g). SEC analyses revealed the formation of low molar masses for the precipitated (2200 g/mol) and hydrosoluble fractions (1500 g/mol) in contrast to the alkaline lignin (3900 g/mol). It is worth noting that the hydrosoluble fraction of lignin is soluble in water at any pH. Both processes (oxygen and air) were successfully scaled up and showed similar results in terms of yield and functionalization.

Highlights

Biomass represents a primary renewable feedstock for the manufacture of polymeric materials
These side species were similar in quantity and composition for kraft lignin (Table 1)
The inorganic compounds were extracted by acidic precipitation, firstly with carbon dioxide and with a mineral acid to the complete precipitation of lignin

Summary

Introduction

Biomass represents a primary renewable feedstock for the manufacture of polymeric materials. The production of lignin is estimated in the range of 50 million tons [1] In this concern, technical lignins represent a very promising resource for the production of aromatic chemicals and phenolic-containing [2,3] polymers. Lignin is a complex polyphenolic biopolymer whose structure and properties basically depend on the raw material, growing conditions of the plant and extraction methods used [4]. Despite this challenge to isolate lignin, pulping industries are developing processes to deconstruct biomass which are classified according to the pH and solvents used as typically acidic, alkaline or organosolv processes [5]

Methods

Results

Conclusion