Silica production across candidate lignocellulosic biorefinery feedstocks

Authors: XU, YIFENG - Texas A&M University; PORTER, NICK - Texas A&M University; FOSTER, JAMIE - Texas A&M Agrilife; MUIR, JAMES - Texas A&M Agrilife; SCHWAB, PAUL - Texas A&M University; Burson, Byron; JESSUP, RUSSELL - Texas A&M University

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2019
Publication Date: 1/7/2020
Citation: Xu, Y., Porter, N., Foster, J., Muir, J., Schwab, P., Burson, B.L., Jessup, R. 2020. Silica production across candidate lignocellulosic biorefinery feedstocks. Agronomy. 10(1):82. https://doi.org/10.3390/agronomy10010082.
DOI: https://doi.org/10.3390/agronomy10010082

Interpretive Summary: During the past several years production of cellulosic ethanol from non-food crops including forage and bioenergy grasses has decreased because hydraulic fracking has increased oil production in the U.S. The amount of cellulosic ethanol previously mandated to be in gasoline by previous government administrations also has been greatly reduced. However, cellulosic ethanol is not the only product that can be obtained from integrated biorefining of these grasses. Several other value-added biomass co-products can be recovered. One of these is amorphous silica, which has the potential of increasing the profitability of biofuel refining. Silica is used in a range of industrial products such as semiconductors, nanotechnology products, reinforcing agents, and specialty chemicals. Most silica today is produced by heating quartz at very high temperatures, which is expensive because of the amount of energy required. Recovering silica from plants by biorefining is more economical. This study was undertaken to determine the amount of biomass and silica produced by eight different grasses (pearl millet, napiergrass, a pearl millet x napiergrass hybrid [PM x N], annual sorghum, perennial sorghum, switchgrass, giant miscanthus, and energy cane) and one legume (sunn hemp). The PM x N hybrid, napiergrass, energy cane, and sunn hemp produced the most biomass. They also had the highest silica yields except for sunn hemp. Because of their high biomass and silica yields, the PM x N hybrid, napiergrass, and energy cane are the most promising biorefinery feedstock candidates for improving biofuel profitability.

Technical 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. x 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 x giganteus J.M. Greef & 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 per ha. Based on high bioethanol and biosilica yield potential, PMN, napiergrass, and energy cane are the most promising biorefinery feedstock candidates for improving biofuel profitability.