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Co-Production of Cement and Carbon Nanotubes with a Carbon Negative Footprint

C2CNT (Carbon dioxide to carbon nanotube) cement plants have been introduced and analyzed which provide a significant economic incentive to eliminate the massive CO2 greenhouse gas emissions of current plants and serves as a template for carbon mitigation in other industrial manufacturing processes. Rather than regarding CO2 as a costly pollutant, this is accomplished by treating CO2 as a feedstock resource to generate valuable products (carbon nanotubes). The exhaust from partial and full oxy-fuel cement plant configurations are coupled to the inlet of a C2CNT chamber in which CO2 is transformed by electrolysis in a molten carbonate electrolyte at a steel cathode and a nickel anode. In this high yield 4e- per CO2 process, the CO2 is transformed into carbon nanotubes at the cathode, and pure oxygen at the anode that is looped back in improving the cement line energy efficiency and rate of production. A partial oxy-fuel process looping the pure oxygen back in through the plant calcinator has been compared to a full oxy-fuel process in which it is looped back in through the plant kiln. The second provides the advantage of easier retrofit, while the first maximizes efficiency by minimizing the volume of gas throughput (eliminating N2 from air). An upper limit to the electrical cost to drive C2CNT electrolysis is USD70 based on Texas wind power costs, but will be lower with fuel expenses when oxy-fuel plant energy improvements are taken account. The current value of a ton of carbon nanotubes is substantially in excess of a ton of cement. Hence a C2CNT cement plant consumes USD50 of electricity, emits no CO2, and produces USD100 of cement and USD60,000 of carbon nanotubes per ton of CO2 avoided. As the cement product ages, CO2 is spontaneously absorbed. This is a powerful economic incentive, rather than economic cost, to mitigate climate change through a carbon negative process.