Demethylation of Lignin fromRice-Straw Biorefinery: An Integrated Chemical and Biochemical Approach

Abstract

The efficiency of lignocellulosic biorefineriesis limited because of the high recalcitrance and low reactivity of lignin. Thereactivity of lignin can be enhanced through various chemical and biochemicalapproaches. Demethylation is one of the methods that improve the availabilityof phenolic hydroxyl groups in lignin, thereby enhancing its reactivity andapplication in sustainable adhesives. The goal of this study is to integratemicrobial and chemical approaches to aid in the demethylation of lignin. Towardsthat end, lignin was first extracted and purified from the rice strawbiorefinery solid residue obtained post ethanol fermentation. This rice strawlignin was then subjected to chemical and microbial demethylation. Formicrobial demethylation under alkaline conditions, Pseudomonas putida and Pseudomonasfluorescens were employed, while demethylation under neutral conditions wasconducted using Trametes versicolor.Integrated treatment using Pseudomonasputida followed by hydrogen iodide yielded an increase in the phenolichydroxyl content by approximately 39-43%. Demethylation using chemical methodsand biological methods alone provided approximately 18-27% increases inphenolic hydroxyl content, respectively. Furthermore, to assess the physicaland chemical properties of demethylated lignin, FT-IR, TGA, and morphologicalanalytical tools were employed.

Keywords

Biorefinery valorization / Lignin chemistry / Pseudomonas spp. / Phenolic hydroxylenrichment / Sustainable green chemistry

Supplementary Materials

The following supporting information can be found at: https://www.sciepublish.com/article/pii/787, Figure S1: Thermogravimetric graph of purified lignin (non-demethylated); Figure S2: Thermogravimetric graph of chemically demethylated lignin using HI and (a) DMF as solvent (b) CA as solvent; Figure S3: Thermogravimetric graph of microbially demethylated with (a) Pseudomonas putida (b) Pseudomonas fluorescens; Figure S4: Thermogravimetric graph of microbially demethylated with Trametes versicolor; Figure S5. Thermogravimetric graph of lignin demethylated with the integrated approach, initially with Pseudomonas putida followed by HI with (a) DMF as solvent (b) CA as solvent; Table S1: IC₅₀ values of lignin samples before and after demethylation.

Acknowledgments

We would like to thank Pranita Pawar and Pratiksha Japtap of Praj Matrix for their assistance with analytical equipment.

Author Contributions

Conceptualization, S.P., F.A. and K.V.; Methodology, K.V. and K.R.; Validation, K.V., F.A. and K.R.; Formal Analysis, K.V.; Investigation, K.V.; Resources, K.R.; Data Curation, K.V.; Writing—Original Draft Preparation, K.V.; Writing—Review & Editing, S.P.; Visualization, S.P. and K.V.; Supervision, S.P.; Project Administration, S.P.; Funding Acquisition, S.P.

Ethics Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data provided in this study are included within the article and/or supporting materials.

Funding

This research received no external funding.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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