Richard Laine

Upcycling/Valorizing a Plentiful Agricultural Waste Rice Hull Ash (RHA)

Global warming provides intense motivation to find ways to supplant commercial-scale CO2 generating processes to offset envisioned catastrophic effects on the environment. Coincidentally, efforts are ongoing to replace fossil fuels, especially coal, with solar, wind and wave sources of energy. One less appreciated energy source is the combustion of agricultural (Ag) waste that generates steam to produce electricity. Combustion of Ag waste such as rice hulls, corn and coconut husks etc. is essentially carbon neutral given plants photosynthetically fix CO2. Often, the combustion of Ag waste generates materials that themselves can be valorized. Early UM work demonstrated that rice hull ash produced worldwide in Mt/yr quantities, can be used to produce solar grade Si using less stringent conditions than used currently. We solved a 90-year-old challenge to silicon chemists, depolymerizing RHA SiO2 forming alkoxysilanes (spirosiloxane, SP) distilled directly from RHA to make silica-depleted RHA, SDRHA40-65 with specific surface areas (SSAs > 40 m2/g). Our teams’ continued efforts on using SP and SDRHA40-65 to access novel materials: SP provides a new source of fumed SiO2 without the intermediacy of SiCl4, which derives from Si metal, produced by carbothermal reduction. SP serves as the basis for new forms of Li+ conducting polymers, especially as solid solutions with PEO. SiC, Si2N2O, and Si3N4 ceramics directly produced from the carbothermal reduction fo SDRHA without external added carbon sources. SDRHA with high surface areas are promising candidates for Li-ion supercapacitors. SDRHA-derived SiC exhibits increases in capacity to ≈ 950 mAh/g on slow cycling (400-600 cycles), potentially serving as new sustainable anode materials for Li-ion batteries.