A comparative evaluation of fermentable sugars production from oxidative, alkaline, alkaline peroxide oxidation, dilute acid, and molten hydrate salt pretreatments of corn cob biomass

Augustine O Ayeni,Oluranti Agboola,Rasheed Babalola,Babalola A Oni,Michael O Daramola,Julius O Omodara,Ayodeji A Ayoola,Deinma T Dick

doi:10.3934/energy.2021002

Abstract

Production of high value-added products from lignocelluloses is an economically sustainable alternative to decreasing dependence on fossil fuels and making the chemical processes environmentally friendly. In this study, different methodologies of alkaline (Ca(OH)2 and NaOH), dilute acid (10%w/w H2SO4), hydrogen peroxide (H2O2), alkaline peroxide oxidation (H2O2/Ca(OH)2 and H2O2/NaOH), and molten hydrated salt (MHS) mediated (ZnCl2.4H2O) pretreatments were employed in the hydrolysis of corncob amenable to enzymatic hydrolysis. Optimal enzyme hydrolysis temperature (considering 45 and 50 ℃) and time (2, 24, 72, and 96 h) were investigated for each pretreatment procedure to ascertain the concentrations of glucose, xylose, and total sugar present in the corncob. At 45 ℃ and 96 h, NaOH alkaline pretreatment achieved the best optimum total sugar production of 75.54 mg/mL (about 54% and 88% increments compared to dilute acid pretreatment (35.06 mg/mL total sugars) and MHS (9.32 mg/mL total sugar) pretreatment respectively). In this study, total sugars production increased appreciably at 45 ℃ and longer hydrolysis period (96 h) compared to hydrolysis at 50 ℃ (with maximum total sugars production of 18.00 mg/mL at 96 h). Scanning electron microscopic imaging of the untreated and treated samples displayed cell wall distortion and surface disruptions.

Highlights

With the worldwide increasing energy demand worldwide and the accompanying environmental degradation brought about by conventional energy sources, it is essential that we look inwards for alternative sources of energy and chemicals [1]
Total lignin content was 22.41%(w/w). This high amount of lignin in the biomass provides a strong point for developing an efficient pretreatment methodology that will be able to rupture the lignocellulosic complex thereby exposing the polysaccharides for enzymatic attack in order for the useful compounds to be released from the complex [14]
Pretreatment of lignocellulosic biomass is a critical step in the production of biofuels and other chemicals from them

Summary

Introduction

With the worldwide increasing energy demand worldwide and the accompanying environmental degradation brought about by conventional energy sources, it is essential that we look inwards for alternative sources of energy and chemicals [1]. Lignin is a binding sheath in the lignocellulosic complex It hinders hydrolysis, preventing the release of the polymers for decomposition or degradation. The pretreatment step is required for the rupturing of the lignocellulsic complex, thereby releasing the polymers and lignin before conversion of cellulose and hemicellulose into usable products [2,6]. Biomass pretreatment technologies can be divided into different categories such as mechanical, chemical, physicochemical and biological methods or various combinations of these [7]. The pretreatment methods alter or damage the lignocellulose biomass complex, removing or reducing lignin contents, and expose the polysaccharides to enzymatic attack. A reliable pretreatment process must be able to depolymerize hemicelluloses, decrystallize and preserves the celluloses, remove lignin, have low energy input, reduce the formation of inhibitors, and must be cost effective [12].

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Results

Conclusion