Solvothermal-Based Lignin Fractionation From Corn Stover: Process Optimization and Product Characteristics

Punjarat Khongchamnan; Wanwitoo Wanmolee; Navadol Laosiripojana; Verawat Champreda; Nopparat Suriyachai; Torpong Kreetachat; Chainarong Sakulthaew; Chanat Chokejaroenrat; Saksit Imman

doi:10.3389/fchem.2021.697237

Solvothermal-Based Lignin Fractionation From Corn Stover: Process Optimization and Product Characteristics

Front Chem. 2021 Aug 5:9:697237. doi: 10.3389/fchem.2021.697237. eCollection 2021.

Authors

Affiliations

¹ School of Energy and Environment, University of Phayao, Muang Phayao, Thailand.
² National Nanotechnology Center, National Science and Technology Development Agency, Thailand Science Park, Pathumthani, Thailand.
³ The Joint Graduate School for Energy and Environment (JGSEE), King Mongkut's University of Technology Thonburi, Bangkok, Thailand.
⁴ BIOTEC-JGSEE Integrative Biorefinery Laboratory, National Center for Genetic Engineering and Biotechnology, Pathumthani, Thailand.
⁵ Intregated Biorefinery Excellent Center (IBC), School of Energy and Environment, University of Phayao, Muang Phayao, Thailand.
⁶ Department of Veterinary Technology, Faculty of Veterinary Technology, Kasetsart University, Bangkok, Thailand.
⁷ Department of Environmental Technology and Management, Faculty of Environment, Kasetsart University, Bangkok, Thailand.

Abstract

Fractionation of lignocellulosic is a fundamental step in the production of value-added biobased products. This work proposes an initiative to efficiently extract lignin from the corn stover using a single-step solvothermal fractionation in the presence of an acid promoter (H₂SO₄). The organic solvent mixture used consists of ethyl acetate, ethanol, and water at a ratio of 30: 25:45 (v/v), respectively. H₂SO₄ was utilized as a promoter to improve the performance and selectivity of lignin removal from the solid phase and to increase the amount of recovered lignin in the organic phase. The optimal conditions for this extraction, based on response surface methodology (RSM), are a temperature of 180°C maintained for 49.1 min at an H₂SO₄ concentration of 0.08 M. The optimal conditions show an efficient reaction with 98.0% cellulose yield and 75.0% lignin removal corresponding to 72.9% lignin recovery. In addition, the extracted lignin fractions, chemical composition, and structural features were investigated using Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, and two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance spectroscopy (2D-HSQC NMR). The results indicate that the recovered lignin primarily contains a β-O-4 linking motif based on 2D-HSQC spectra. In addition, new C-C inter-unit linkages (i.e., β-β, and β-5) are not formed in the recovered lignin during H₂SO₄-catalyzed solvothermal pretreatment. This work facilitates effective valorization of lignin into value-added chemicals and fuels.

Keywords: corn stover; homogeneous catalyst; lignin fractionation; optimization; phenolic compound; solvothermal based.