UC Berkeley

Abstract: Methane pyrolysis is an emerging technology to produce lower-carbon intensity hydrogen at scale, as long as the co-produced solid carbon is permanently captured. Partially replacing Portland cement with pyrolytic carbon would allow the sequestration at a scale that matches the needs of the H2 industry. Our results suggest that compressive strength, the most critical mechanical property, of blended cement could even be improved while the cement manufacture, which contributes to ~ 9% global anthropogenic CO2 emissions, can be decarbonized. A CO2 abatement up to 10% of cement production could be achieved with the inclusion of selected carbon morphologies, without the need of significant capital investment and radical modification of current production processes. The use of solid carbon could have a higher CO2 abatement potential than the incorporation of conventional industrial wastes used in concrete at the same replacement level. With this approach, the concrete industry could become an enabler for manufacturing a lower-carbon intensity hydrogen in a win–win solution. Impact: Methane pyrolysis is an up-scalable technology that produces hydrogen as a lower carbon-intensity energy carrier and industrial feedstock. This technology can attract more investment for lower-carbon intensity hydrogen if co-produced solid carbon (potentially hundreds of million tons per year) has value-added applications. The solid carbon can be permanently stored in concrete, the second most used commodity worldwide. To understand the feasibility of this carbon storage strategy, up to 10 wt% of Portland cement is replaced with disk-like or fibrillar carbon in our study. The incorporation of 5% and 10% fibrillar carbons increase the compressive strength of the cement-based materials by at least 20% and 16%, respectively, while disk-like carbons have little beneficial effects on the compressive strength. Our life-cycle assessment in climate change category results suggest that the 10% cement replacement with the solid carbon can lower ~10% of greenhouse gas emissions of cement production, which is currently the second-largest industrial emitter in the world. The use of solid carbon in concrete can supplement the enormous demand for cement substitute for low-carbon concrete and lower the cost of the low-carbon hydrogen production. This massively available low-cost solid carbon would create numerous new opportunities in concrete research and the industrial applications.