Advancing 2G Ethanol: Technologies, Pathways, and Sustainability in Modern Biorefineries

Abstract

As the global energy landscape shifts toward decarbonization, the transition from first-generation (1G) to second-generation (2G) biorefineries has become essential to ensure energy security without compromising food supplies. This review examines the architectural evolution of biomass biorefineries, contrasting the established 1G starch-and-sugar-based models with the emerging 2G lignocellulosic frameworks. We provide a detailed technical analysis of the three critical stages of 2G ethanol production: pretreatment (to overcome biomass recalcitrance), hydrolysis (to liberate fermentable sugars), and fermentation (optimizing yeast performance for pentose and hexose sugars). Furthermore, the article evaluates the scope of 2G biorefineries in India, highlighting the nation's ambitious E20 blending targets and the role of agricultural residues in reducing carbon footprints and stubble burning. By analyzing current technological bottlenecks and policy incentives, this review outlines the potential for 2G ethanol to act as a cornerstone of India’s sustainable bio-economy.