Biochemical Conversion Processes of Lignocellulosic Biomass to Fuels and Chemicals – A Review

Abstract

Lignocellulosic biomass - such as wood, agricultural residues or dedicated energy crops - is a promising renewable feedstock for production of fuels and chemicals that is available at large scale at low cost without direct competition for food usage. Its biochemical conversion in a sugar platform biorefinery includes three main unit operations that are illustrated in this review: the physico-chemical pretreatment of the biomass, the enzymatic hydrolysis of the carbohydrates to a fermentable sugar stream by cellulases and finally the fermentation of the sugars by suitable microorganisms to the target molecules. Special emphasis in this review is put on the technology, commercial status and future prospects of the production of second-generation fuel ethanol, as this process has received most research and development efforts so far. Despite significant advances, high enzyme costs are still a hurdle for large scale competitive lignocellulosic ethanol production. This could be overcome by a strategy termed 'consolidated bioprocessing' (CBP), where enzyme production, enzymatic hydrolysis and fermentation is integrated in one step - either by utilizing one genetically engineered superior microorganism or by creating an artificial co-culture. Insight is provided on both CBP strategies for the production of ethanol as well as of advanced fuels and commodity chemicals.

Pilot-scale steam explosion pretreatment with 2-naphthol to overcome high softwood recalcitrance

“…In contrast, steam pretreatments allow for very high biomass loadings and are currently the dominating commercial pretreatment method [24]. Steam pretreatments additionally offer the possibility of a steam explosion.…”

Pretreatment strategies for microbial valorization of bio‐oil fractions produced by fast pyrolysis of ash‐rich lignocellulosic biomass

“…A significant challenge, however, lies in its conversion because lignocellulose is a plant‐based, sturdy and compact biocomposite material consisting of lignin, cellulose and hemicellulose. In the last decades, a number of conversion methods have been developed mainly focusing on the production of second‐generation biofuels (Brethauer & Studer, ; Dahmen et al, ; Maurya, Singla, & Negi, ; Seidl & Goulart, ). One of such a conversion method is fast pyrolysis—a thermochemical method which converts lignocellulosic biomass in the absence of oxygen mainly into an energy‐rich liquid referred to as bio‐oil, also referred as to bio‐oil (Bridgwater, Meier, & Radlein, ).…”

Composting-Like Conditions Are More Efficient for Enrichment and Diversity of Organisms Containing Cellulase-Encoding Genes than Submerged Cultures

“…The carbohydrate constituents (cellulose, pectins and hemicelluloses) are embedded in the hydrophobic lignin matrix that severely limits access to degradation enzymes. Consequently, the enzymatic decomposition step is slow and incomplete, hampering the development of cost efficient production processes for biobased products including biopolymers, chemicals and biofuels [1,2]. To overcome these difficulties, intense research is presently addressing the identification of ever more efficient and robust enzymes for saccharification of cellulose to fermentable sugars.…”