Abstract :
[en] Carbon Capture Storage (CCS) or Utilization (CCU) is nowadays a well-studied and promising field in order to reduce CO2 emissions, main driver of global warming. The CO2 can arise from a wide range of sources, including industrial ones such as flue gas from power, cement or ammonia plants. In particular, CO2 emissions from the cement production represent approximately 5 to 7 % of anthropogenic global CO2 emissions . It is key issue for the cement sector to reduce its emissions via different levers such as modern dry-process technology, co-substitution and carbon capture storage or reuse. Hence, the capture of CO2 from cement plants and its conversion into valuable compounds will be crucial in the long run.
As a multitude of CO2-based processes, including chemical reactions, are described in the literature, a methodological selection was carried out to identify the CO2 conversion routes that are the most suitable to be implemented in the cement sector within a mid-term time period. It highlighted in particular the interest of the production of formic acid (HCOOH), appearing as an energy storage medium, where captured CO2 is electrochemically reduced.
The purpose of this study is therefore to investigate this pathway via techno-economic and environmental assessments. Using process flow modeling, the flowsheet is then implemented in Aspen Plus® in order to evaluate the operational performance as well as the production cost associated with the production of formic acid. The process relies on an electrochemical reactor where carbon dioxide and water are injected. A mixture of CO2, H2O, HCOOH and H2 comes out the cathode while mainly O2 is out of the anode, which can be further compressed to be stored, transported and reused. A separator divides the outlet of the cathode into a gaseous stream containing CO2 and H2, and a liquid stream, H2O and HCOOH. The water-formic acid mixture is then separated in a distillation column to provide a 85%wt formic acid stream, while the water is recycled in the process. The carbon dioxide-hydrogen mixture is separated using a membrane so that the CO2 is recirculated. The hydrogen stream is recovered for later reused. The operating conditions and parameters such as the pressure/temperature in reactor, its size, the nature of the catalyst, the electrolytes, the separation steps pressure levels, etc. have been varied to evaluate their respective influence on the process performances.
As a result, this study proposes an optimization of the conversion unit regarding the technical performances as well as economic indicators such as OPEX and CAPEX. An environmental assessment, based on the Life Cycle Assessment (LCA) method, is finally conducted to ensure the whole positive environmental balance. First results tend to demonstrate that this CO2-based process may have both lower emissions and potential to reduce fossil resource depletion compared to the conventional productions, i.e. both the carbonylation of methanol in sodium hydroxide and the oxidation of hydrocarbons, presenting negative environmental impacts .
