Optimization of Alkaline and Dilute Acid Pretreatment of Agave Bagasse by Response Surface Methodology.

Abimael I Ávila-Lara,Sarah R Messina-Fernández,Claudia E Saldaña-Duran,Edgar I Jimenez-Ruiz,Jesus N Camberos-Flores,Jorge A Mendoza-Pérez,Jose A Pérez-Pimienta,Leticia M Sánchez-Herrera

doi:10.3389/fbioe.2015.00146

Abimael I Ávila-Lara, Sarah R Messina-Fernández + Show 6 more

Open Access

https://doi.org/10.3389/fbioe.2015.00146

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Abstract

Utilization of lignocellulosic materials for the production of value-added chemicals or biofuels generally requires a pretreatment process to overcome the recalcitrance of the plant biomass for further enzymatic hydrolysis and fermentation stages. Two of the most employed pretreatment processes are the ones that used dilute acid (DA) and alkaline (AL) catalyst providing specific effects on the physicochemical structure of the biomass, such as high xylan and lignin removal for DA and AL, respectively. Another important effect that need to be studied is the use of a high solids pretreatment (≥15%) since offers many advantaged over lower solids loadings, including increased sugar and ethanol concentrations (in combination with a high solids saccharification), which will be reflected in lower capital costs; however, this data is currently limited. In this study, several variables, such as catalyst loading, retention time, and solids loading, were studied using response surface methodology (RSM) based on a factorial central composite design of DA and AL pretreatment on agave bagasse using a range of solids from 3 to 30% (w/w) to obtain optimal process conditions for each pretreatment. Subsequently enzymatic hydrolysis was performed using Novozymes Cellic CTec2 and HTec2 presented as total reducing sugar (TRS) yield. Pretreated biomass was characterized by wet-chemistry techniques and selected samples were analyzed by calorimetric techniques, and scanning electron/confocal fluorescent microscopy. RSM was also used to optimize the pretreatment conditions for maximum TRS yield. The optimum conditions were determined for AL pretreatment: 1.87% NaOH concentration, 50.3 min and 13.1% solids loading, whereas DA pretreatment: 2.1% acid concentration, 33.8 min and 8.5% solids loading.

Highlights

Lignocellulosic biomass is the most abundant renewable carbohydrate source in the world and it is proposed to dominate the biofuel production in the future (Avci et al, 2013)
agave bagasse (AGB) was been used with acid and enzymatic hydrolysis followed by a fermentation step using a native microorganism (Pichia caribbica UM-5) obtaining ~57% of theoretical ethanol (w/w) (Saucedo-Luna et al, 2011) or for the production of n-butanol and ethanol from different Agave species (Mielenz et al, 2015)
The need to investigate the use of high solids loading (≥ 15%) in biomass pretreatment has increase offers many advantaged over lower solids loadings, including increased sugar and ethanol concentrations, which will be reflected in lower capital costs (Modenbach and Nokes, 2012; Li et al, 2013); this data is currently limited for dilute acid (DA) and AL pretreatments in AGB (Hernández-Salas et al, 2009; SaucedoLuna et al, 2011)

Summary

Introduction

Lignocellulosic biomass is the most abundant renewable carbohydrate source in the world and it is proposed to dominate the biofuel production in the future (Avci et al, 2013). A pretreatment step is fundamental to alter the structure of cellulosic biomass to make cellulose more accessible to the enzymes that convert the carbohydrate polymers into fermentable sugars (Mosier et al, 2005). Many options exist for pretreatment of biomass, increase saccharification efficiency and improve the yields of monomerics sugars; the leading examples use liquid catalysts, such as sulfuric acid, ammonia, ionic liquid, or water, which penetrate the cell wall and alter its chemistry and ultrastructure (Dadi et al, 2006; Chundawat et al, 2011). Agave bagasse (AGB) byproduct of the Tequila industry that represent 40% of the harvested plant, with an annual generation in Mexico of about 1.12 kg × 108 kg has been studied for biomass conversion using different pretreatment approaches, such as ionic liquid (Perez-Pimienta et al, 2013) and organosolv (Caspeta et al, 2014). AGB was been used with acid and enzymatic hydrolysis followed by a fermentation step using a native microorganism (Pichia caribbica UM-5) obtaining ~57% of theoretical ethanol (w/w) (Saucedo-Luna et al, 2011) or for the production of n-butanol and ethanol from different Agave species (Mielenz et al, 2015)

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