SusChEM: Carbon Capture and Utilization by Controlled Carbonate Mineralization

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

1335694 (Doherty). One of the defining problems of our time is that levels of CO2 in the atmosphere have increased from 315 ppm in 1958 to 394 ppm in 2012, leading to concerns about changes in climate occurring at a rate that will be difficult to manage. The steady increase in CO2 emissions from stationary sources across a spectrum of industrial processes (e.g., electricity generation, manufacturing of cement, chemicals, plastics) has raised tremendous interest in the process of carbon capture and utilization, ideally without adversely affecting living standards world-wide. But, if CO2 capture is to be economically and environmentally sustainable in the long-term, it is crucial to find ways of turning CO2 from harmful waste into a useful product at an economical price. This project is a high-risk high-reward strategy toward achieving this goal. A novel holistic approach for CO2 capture underpinned by scientific and green engineering foundations that has the potential to transform CO2 into a useful solid product with net positive value will be explored. The current standard approach to dealing with this problem has been to separate CO2 from combustion gases in the form of a highly compressed and almost pure fluid that is then disposed of in one of several ways, most of which will require careful monitoring for re-emission. Instead, pn this project, the combustion gases will be reacted with reagents (Ca2+, OH-, silicates, or saccharides/phosphonates) to form a benign and potentially valuable solid carbonate material with applications in the construction industry. The proposers estimate that the energy penalty for carbonate mineralization technology is significantly less than that for current approaches. They propose to establish and optimize the governing molecular processes that underlie the use of subsurface geological brines or reactive minerals as feedstocks to capture and utilize CO2 in the form of solid carbonates and/or silicates. These feedstocks have high Ca2+ contents, as well as desirable alkalinities, which significantly increase the carbonation rates. The proposes hypothesize that deep molecular understanding of the metastable solid products formed, coupled with state-of-the-art conceptual process design and development (a systems approach), will lead to an effective combined capture and utilization technology for CO2 that will be transformative in its approach and potentially in its societal impact. The intellectual merit of the approach is the novel coupling of fundamental materials science at a molecular level to establish the molecular design rules for the formation and stabilization of reactive metastable carbonate/silicate solids with process design (systems) strategies for implementing these rules at macroscopic scale. This will be achieved by exploiting state-of-the-art techniques of NMR spectroscopy, which have only recently become available for key 43Ca, 25Mg, 13C, 31P and dipolar-coupled 29Si and 1H species in carbonates and cementious materials. The novel use of saccharides/phosphonates or other organic molecules to stabilize reactive carbonates is expected to promote their processability, storage stability, and conversion into valuable structural materials. Based on the molecular insights obtained, materials processing variables (e.g., temperature, pressure, pH, composition, and reactor/separator configurations) will be assessed and optimized to control precipitation and crystallization of carbonate solids with engineered structures, particle morphologies, and surface compositions, including techno-economic considerations. The broader impacts of this research include (1) educating graduate and undergraduate students broadly in state-of-the-art methods of molecular engineering of crystalline solids and process design strategies for their syntheses, (2) fostering broad awareness of greenhouse gas emissions, their impacts, candidate strategies for CO2 utilization, and associated energy and environmental ramifications, and (3) the specific possibility for developing a paradigm-changing approach by which CO2 is converted to a valuable structural material. The insights gained from the proposed project will be general, enabling students and the broader scientific community to develop novel approaches for converting waste products into potentially valuable materials, along with quantifying process design and economic factors through a systems approach to evaluate cost-effectiveness.