Review of Second-Generation Bioethanol Production from Residual Biomass

Abstract

SummaryIn the context of climate change and the depletion of fossil fuels, there is a great need for alternatives to petroleum in the transport sector. This review provides an overview of the production of second-generation bioethanol, which is distinguished from first-generation and subsequent generations of biofuels by its use of lignocellulosic biomass as raw material. The structural components of the lignocellulosic biomass such as cellulose, hemicellulose and lignin, are presented along with technological unit steps including pre-treatment, enzymatic hydrolysis, fermentation distillation and dehydration. The purpose of the pre-treatment step is to increase the surface area of carbohydrate available for enzymatic saccharification, while minimizing inhibitors. Performing the enzymatic hydrolysis releases fermentable sugars, which are converted by microbial catalysts into ethanol. The hydrolysates obtained after pre-treatment and enzymatic hydrolysis contain a wide spectrum of sugars, predominantly glucose and xylose.Genetically engineered microorganisms are therefore needed to carry out co-fermentation. The excess of harmful inhibitors in the hydrolysate, such as weak organic acids, furan derivatives and phenol components, can be removed by detoxification before fermentation. Effective saccharification further requires using co-acting exogenous hemicellulases and cellulolytic www.ftb.com.hrPlease note that this is an unedited version of the manuscript that has been accepted for publication. This version will undergo copyediting and typesetting before its final form for publication. We are providing this version as a service to our readers. The published version will differ from this one as a result of linguistic and technical corrections and layout editing.enzymes. Conventional species of distillers' yeast are unable to ferment pentoses into ethanol, and only a very few natural microorganisms, including yeast species like Candida shehatae, Pichia stipites, Scheffersomyces and Pachysolen tannophilus, metabolize xylose to ethanol.Enzymatic hydrolysis and fermentation can be performed in a number of ways, by separate saccharification and fermentation, simultaneous saccharification and fermentation or consolidated bioprocessing. Pentose-fermenting microorganisms can be obtained through genetic engineering, by introducing xylose-encoding genes into metabolism of a selected microorganism to optimize its use of xylose accumulated in the hydrolysate.

Non‐Conventional Media as Strategy to Overcome the Solvent Dilemma in Chemoenzymatic Tandem Catalysis

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Evolution toward the utilization of mango leaves as lignocellulosic material in bioethanol production: A review of process parameter and integrated technologies

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Twenty‐first‐century chemical odyssey: fuels versus commodities and cell factories versus chemical plants

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