Mechanistic Investigation in Ultrasound-Assisted (Alkaline) Delignification of Parthenium hysterophorus Biomass

Abstract

Delignification of biomass is a primary step in biomass pretreatment in fermentation based synthesis of alcoholic biofuels. This paper attempts to give mechanistic insight into ultrasound-assisted delignification of biomass. Parthenium hysterophorus (carrot grass) has been used as the model biomass. The approach of study is to couple simulations of cavitation bubble dynamics to the experiments on delignification. Best values of delignification parameters with ultrasound have been identified as temperature = 303 K, NaOH concentration = 1.5% w/v, and biomass concentration = 2% w/v. Characterization of delignified biomass has been carried out using FTIR spectroscopy and XRD and FESEM techniques. Both physical and chemical effects of transient cavitation contribute to delignification. The physical effect of shock waves leads to depolymerization of lignin matrix through homolytic cleavage of phenyl ether α−O−4 and β−O−4 bonds. The chemical effect of radical generation causes hydroxylation/oxidation of the aromatic moieties and side chain elimination. Due to these peculiar mechanisms, ultrasound treatment gives effective delignification at ambient temperature and with lesser requirement of delignifying agents. Cavitation also causes decrystallization of cellulose due to partial depolymerization. Kinetic analysis of delignification at best values of parameters has revealed 2-fold enhancement with ultrasound as compared to mechanically agitated treatment.

Cellulose fibers isolated from energycane bagasse using alkaline and sodium chlorite treatments: Structural, chemical and thermal properties

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Physicochemical characterization of lignin recovered from microwave‐assisted delignified lignocellulosic biomass for use in biobased materials

“…However, the most costly component of alcoholic biofuel synthesis is the pretreatment of the biomass prior to fermentation. The maximum amount of sugar monomers (mainly cellulose and hemicellulose) from raw biomass is necessary for efficient and economic alcoholic biofuel production . Lignin, which fills the space between cellulose and hemicelluloses and crosslinks with hemicellulosic polysaccharides, acts as a barrier for the accessibility of chemicals and enzymes to cellulose .…”

Delignification of intact biomass and cellulosic coproduct of acid‐catalyzed hydrolysis

“…12 An effective lignin removal at ambient temperature with less delignifying agent was attained in a simulation study using ultrasound-assisted delignification of biomass under alkaline condition. 13 In oxygen delignification of pine kraft pulp, the use of a continuous reactor resulted in a significantly higher performance compared with a batch reactor. 14 In a research study evaluating lignocellulose biotreatment, a faster and shorter initial delignification phase was reported in the fungitreated wood.…”