EFRI DCheM: Making Cement Green by Low-Temperature Manufacturing of Calcium Hydroxide from Distributed Waste Sources

Cement is arguably the world’s most important building material, but its production is responsible for up to 8% of global carbon dioxide emissions, representing a major impediment to meeting the carbon budget required to reduce the rate of global warming. Decarbonization of the cement industry has been a longstanding environmental challenge because the bulk of the industry’s carbon dioxide emissions result from the chemical reaction that takes place during limestone calcining, the first step in traditional cement production.

Produced by current practices, emissions associated with cement production alone would account for as much as 40% of the world’s carbon budget in 2050, a figure based on emissions allowable for a 50% chance of limiting warming to 1.5°C in 2050. To address this challenge, a novel calcination-free LoTeCH (Low-Temperature Calcium Hydroxide) process will be developed to produce calcium hydroxide that can replace limestone as the key cement precursor from distributed waste streams such as recycled concrete, coal ash, and metal-smelting slag.

The resulting LoTeCH calcium hydroxide can be seamlessly integrated into the existing cement-making infrastructure to replace limestone calcination, reducing CO2 emissions by more than 50% with the added benefit of reduced limestone mining. An extension of this technology to create a distributed and extremely low-carbon cement-making process that would consume carbon dioxide sourced from power-plant flue gas also will be pursued to enable a potentially carbon-negative cement industry.

In addition to developing new technologies to transform cement production into a sustainable industry, the project will train a diverse cohort of students, working collaboratively to solve this environmental problem of global concern, taking a multidisciplinary approach to problem solving. The project will directly engage underrepresented minority undergraduate and graduate researchers from two minority serving institutions (Ft.

Lewis College and University of Illinois at Chicago) within the research tasks and will support their participation in UW-Madison campus programs that offer undergraduate students opportunities to gain research experience. These activities will be used by the project team to recruit and educate underrepresented minority students. This project will also work to increase public scientific literacy and public engagement to understand the ways that the built environment is responsible for carbon emissions.

The proposed project will develop an energy efficient, low carbon-emission calcium hydroxide production process for sustainable cement production. Towards this goal, the project will generate fundamental engineering knowledge enabling a four-step LoTeCH process cycle that uses ammonia and an ion-exchange process to produce Ca(OH)2 from waste material feedstocks under mild pressure (2-3 bar) and sub-boiling temperatures.

The proposed work will generate fundamental insights into dissolution, transport, and precipitation processes using in-situ characterization methods. New covalent organic framework (COF)-based ion-exchangers with tunable exchange characteristics and enhanced capacity and stability will be synthesized to support the key pH-swing process step. Predictive multiscale and multiphysics process modeling will leverage high-throughput characterization data for model validation and will make possible robust process optimization.

Using these modeling methods and simulation techniques, new process intensification schemes will be developed to create an efficient, distributed production process suitable for feedstocks that are expected to be highly variable in their composition. Process development will be guided by techno-economic analysis (TEA), continuous material flow analysis (C-MFA), and life cycle assessment (LCA), including an assessment of the impact of this technology on the existing cement industry and the potential emergence of a low-carbon cement industry in the future.

By integrating expertise in mineral dissolution and precipitation, material synthesis, reactor design and process intensification, and environmental and sustainability engineering, this project will broaden fundamental understanding of a critically important industrial process and create a new paradigm for how cement is produced.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.