Multiscale Process Intensification of Waste Valorization Reactions

ConspectusThe central theme of this Account is the development of intensified and sustainable chemical processes for the sequestration of CO₂ in synergism with the utilization of wastes of industrial, urban, and agricultural origins. A challenge when working with solid waste-fluid reactions is that mass transfer limitations across solid-liquid, solid-gas, and gas-liquid interfaces and unfavorable thermodynamics lead to slow reaction rates, incomplete reaction conversions, high energy expenditure and processing costs, and inadequate product properties. The traditional macroscale approaches to overcoming slurry reaction limitations can be effective; however, they come at a cost to the environment. In the treatment or valorization of low-grade and waste resources, such conventional approaches are often unfeasible on an industrial scale. Sustainable solutions are thus needed.In the last six years, we have been exploring and developing approaches to overcoming reaction rate limitations of slurry reactions of environmental relevance by concurrently applying process intensification strategies and multiscale engineering approaches. The scientific approach has relied on laboratory-scale experiments to test and refine the devised multiscale process intensification strategies, with thermodynamic and computational modeling work supporting the experimental work and with advanced characterization techniques being used to elucidate reaction and transport mechanisms and aid the development of nanoscale reaction models and micro- and macroscale process models. The research streams, associated with the four key references, discussed next are (a) brine carbonation; (b) mineral carbonation and enhanced weathering; (c) process intensification and integration; and (d) characterization techniques.Within the four research streams, a number of mineral carbonation processes have been investigated and can be classified as (i) ambient weathering and carbonation; (ii) gas-(wet) solid accelerated carbonation; (iii) aqueous accelerated carbonation; (iv) supercritical accelerated carbonation; and (v) CO₂ mineralization from brine. In some cases, the research was aimed at producing valuable products with reduced environmental risk or a reduced carbon footprint, such as an organomineral fertilizer and zeolites. In other cases, the aim was to assess the reactivity of minerals to match the right feedstock with the right carbonation process, in view of maximizing net carbon sequestration. There were also cases where the carbonation process was reimagined by the use of innovative reaction conditions, reactors, and reagents. The experience with accelerated weathering and carbonation in engineered processes has been translated into the field of enhanced rock weathering (ERW) in agriculture, where the multidisciplinary approach used has served to advance ERW science and technology in ways that have had a resounding effect on recent commercial deployment.The completed research serves to encourage the adoption of process intensification technologies in place of conventional processes, in industry and among the research community, and to catalyze the development of the types of sustainable processes required by the chemical, metallurgical, and minerals industries (which are critical to the green transition) to reduce their environmental impact and carbon emissions. Moreover, the multiscale process intensification approaches developed may also be extended to other industrial, urban, and agricultural processes where the reduction of energy intensity, carbon intensity, and environmental footprint could be achieved.