Abstract
Biofuels produced from non-food lignocellulosic feedstocks have the potential to replace a significant percentage of fossil fuels via high yield potential and suitability for cultivation on marginal lands. Commercialization of dedicated lignocellulosic crops into single biofuels, however, is hampered by conversion technology costs and decreasing oil prices. Integrated biorefinery approaches, where value-added chemicals are produced in conjunction with biofuels, offer significant potential towards overcoming this economic disadvantage. In this study, candidate lignocellulosic feedstocks were evaluated for their potential biomass and silica yields. Feedstock entries included pearl millet-napiergrass (“PMN”; Pennisetum glaucum [L.] R. Br. × P. purpureum Schumach.), napiergrass (P. purpureum Schumach.), annual sorghum (Sorghum bicolor [L.] Moench), pearl millet (P. glaucum [L.] R. Br.), perennial sorghum (Sorghum spp.), switchgrass (Panicum virgatum L.), sunn hemp (Crotalaria juncea L.), giant miscanthus (Miscanthus × giganteus J.M. Greef and Deuter), and energy cane (Saccharum spp.). Replicated plots were planted at three locations and characterized for biomass yield, chemical composition including hemicellulose, cellulose, acid detergent lignin (ADL), neutral detergent fiber (NDF), crude protein (CP), and silica concentration. The PMN, napiergrass, energy cane, and sunn hemp had the highest biomass yields. They were superior candidates for ethanol production due to high cellulose and hemicellulose content. They also had high silica yield except for sunn hemp. Silica yield among feedstock entries ranged from 41 to 3249 kg ha−1. Based on high bioethanol and biosilica yield potential, PMN, napiergrass, and energy cane are the most promising biorefinery feedstock candidates for improving biofuel profitability.
Highlights
Acid detergent lignin is the Neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) were residue remaining after sequential digestion of ADF residue with 72% sulfuric acid [58]
Year by feedstock entries interacted across all traits except for hemicellulose
There could be the possibility of recovering other soluble products remaining mineral fraction (Figure 2)
Summary
Production of biofuels as a single revenue source remains economically unprofitable [1]. Conceptual extensions of lignocellulosic feedstocks from current single biofuel platforms to integrated biorefineries involve separation and utilization of compositional fractions of biomass into primary biofuels (ethanol from cellulose and hemicellulose, for example) and additional bioproducts from the remaining lignin (lignosulfonates, bioplastics, etc.) [4] and mineral (biosilica, etc.) fractions. Depolymerization of plant biomass results in primary fractions of cellulose, hemicellulose, and lignin. Most of the lignin is directly combusted for the production of energy during the pulping process, and only small amounts have been utilized for conversion into other chemicals. If different pulp processing methods are used, lignosulfonates can be produced in leu of lignin being directly combusted. The utilization of lignin either directly for biopower or indirectly by producing lignosulfonates has not proven sufficient towards making biofuel refineries profitable. Investigation of additional, value-added co-products that can be obtained from the residual mineral fraction is warranted
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