Antioxidant Additives Produced from Argan Shell Lignin Depolymerization

Zainab Afailal,Noemí Gil-Lalaguna,María Teresa Torrijos,Jesús Arauzo,José Luis Sánchez,Alberto Gonzalo

doi:10.1021/acs.energyfuels.1c01705

Zainab Afailal, Noemí Gil-Lalaguna + Show 4 more

Open Access

https://doi.org/10.1021/acs.energyfuels.1c01705

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Abstract

The present work summarizes the results of an experimental study focused on producing antioxidant additives for biofuels from argan shell lignin. The generation of this waste has noticeably increased in specific regions of Morocco as a result of the upward trend in the production of argan oil. Lignin extracted from argan shells via a semi-chemical pulping process was depolymerized under hydrothermal conditions in a stirred autoclave reactor at a temperature range of 250–350 °C. Lignin conversion to phenolic compounds was conducted in subcritical water together with different reaction medium (H2, CO2, and HCOOH). The organic fraction in the aqueous liquid product was extracted and blended with biodiesel at a dosage of 1 wt % to evaluate its antioxidant potential. According to the obtained results, the biodiesel oxidation stability time was drastically improved up to 400%. The depolymerization temperature was observed as a critical factor in the antioxidant potential of the additives, showing a maximum value at 300 °C, regardless of the reaction medium. An extensive characterization of the produced additives was performed. The phenolic monomers present in the produced additives were identified using gas chromatography–mass spectrometry, finding a notable presence of catechol, especially in the additives obtained at 300 °C, which led to the best results of biodiesel oxidation stability. Gel permeation chromatography analyses of the additives also showed a well dissolution of relatively big molecules (up to 7000 Da) in biodiesel. More efforts are required to verify the actual antioxidant potential of these types of molecules.

Highlights

Lignin is considered one of the most abundant biopolymers in the world
The yield of the lignin fraction extracted from Argan shell (AS) by the semi-chemical pulping treatment was up to 22% with respect to the initial lignin contained in the raw material
Depolymerization of lignin extracted from argan shells to produce added-value chemicals, antioxidant additives, has been studied

Summary

Introduction

Lignin is considered one of the most abundant biopolymers in the world (up to 40% of the dried weight in some types of lignocellulosic biomass[1−3]). Lignin can be extracted from the lignocellulosic biomass by classical chemical methods (kraft and sulfite processes) and semi-chemical methods (organosolv and soda processes), in addition to the new promising methods, such as pretreatments using ammonia[8] or imidazole.[9] as a result of its complicated structure, the extraction of an unaltered state of the native lignin is still not yet possible.[4] A semi-chemical pulping process using soda has been a historically typical process in the production of pulp and paper from non-wood materials, such as some crops (Miscanthus and kenaf) or agricultural residues (straw and bagasse).[10] This process entails separating pulp with a high cellulose content from the original lignocellulosic material, living behind a black liquor, rich in lignin content, as a problematic byproduct to be managed.[10,11]

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