Microwave-assisted lime treatment and recovery of lignin from hydrothermally treated sweet sorghum bagasse

Abstract

Microwave (MW)-assisted lime treatment was applied for the extraction of lignin from sweet sorghum bagasse (SSB) which was previously subjected to a MW-assisted hydrothermal treatment for the extraction of hemicellulose. Under optimum conditions, lime dosage at a concentration of 10% by weight of the substrate and 78 min of treatment residence time resulted in 68.27 (± 1.19) % by weight of the lignin extracted from the substrate. The residual SSB was composed of 69.41 (± 1.83) % cellulose, 12.14 (± 0.71) % hemicellulose, 12.59 (± 0.31) % lignin and 4.03 (± 0.21) % ash in it. The bulk density of the two-step treated SSB was 3.6 times that of the untreated SSB. The yellow liquor was treated with CO₂ and 60.26 (± 2.11) % by weight of the dissolved lignin was precipitated from it. The physicochemical properties of the treated-SSB and the lignin samples were analysed using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscope (SEM). The mass balance of the MW-assisted fractionation of SSB was conducted and the prospect of the process for on-farm fractionation of lignocellulosic materials was considered.

Keywords:

• microwave-assisted extraction
• lime treatment
• sweet sorghum bagasse
• lignin extraction
• lignin recovery
• on-farm fractionation

Acknowledgements

The authors acknowledge the financial assistance from the Fonds Quebecois de la Recherche sur la Nature et les Technologies (FQRNT) and the Natural Sciences and Engineering Research Council of Canada (NSERC).

Disclosure statement

No potential conflict of interest was reported by the authors.