BIOBUTANOL PRODUCTION FROM LIGNOCELLULOSIC BIOMASS: ADVANCES AND CHALLENGES IN ACETONE–BUTANOL–ETHANOL(ABE) FERMENTATION

Lignocellulosic biomass represents an abundant, renewable, and non-food-based feedstock for biobutanol production. Composed mainly of cellulose, hemicellulose, and lignin, lignocellulosic materials such as agricultural residues, forestry waste, and energy crops offer significant potential for sustainable biorefinery applications; however, the complex and recalcitrant structure of lignocellulose poses substantial challenges for efficient bioconversion. Cellulose is described as a linear, unbranched polysaccharide built entirely from β-1,4-linked D-glucose units, forming highly ordered crystalline microfibrils through intra- and intermolecular hydrogen bonds, while hemicellulose is a heterogeneous, branched polysaccharide with a random, amorphous structure, and lignin is an amorphous, highly branched, three-dimensional phenolic polymer tightly associated with carbohydrates, forming lignin–carbohydrate complexes (LCCs) that reduce enzymatic accessibility.Pretreatment is required to release fermentable sugars, but pretreating lignocellulosic substrate not only produces assimilable sugars but also various fermentation inhibitors, including furfural, hydroxymethylfurfural (HMF), weak acids, and phenolics, that can significantly impede microbial growth and metabolism.Solventogenic Clostridium species, including Clostridium acetobutylicum and Clostridium beijerinckii, constitute the foundational biocatalysts for acetone–butanol–ethanol (ABE) fermentation and operate through a biphasic growth strategy consisting of acidogenesis and solventogenesis. Biobutanol has gained increasing attention as a next-generation biofuel due to several physicochemical and functional advantages over ethanol; however, low product concentrations, mixed sugar utilization challenges, inhibitory compounds from biomass pretreatment, butanol toxicity to microbial cells, and strain degeneration and process instability represent major limitations in ABE fermentation.Technological advancements for improving butanol yields include genetic engineering of Clostridium strains, metabolic pathway optimization, in situ product recovery (ISPR), co-culture strategies and consolidated bioprocessing, detoxification of lignocellulosic hydrolysates, and emerging biotechnological approaches such as synthetic biology designs and engineering of alternative hosts (e.g., E. coli, yeast). Industrially, biobutanol is recognized as a promising bio-based chemical and fuel with broad commercial potential, but scalability, techno-economic barriers, and sustainability considerations remain critical challenges.Continued technological innovation and system-level optimization are essential for achieving economically viable and environmentally sustainable lignocellulose-based biobutanol production.