Abstract :
[en] Carbon Capture and Storage (CCS) or Utilization (CCU) is nowadays a well-studied and promising field in order to reduce CO2 emissions, main driver of global warming. 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 a key issue for the cement sector to reduce its emissions through 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.
The purpose of this study is therefore to investigate the electro-reduction of CO2 to formic acid (HCOOH) as a valorisation option, using multi-criteria process optimization. Using process flow modelling, the flowsheet is implemented in Aspen Plus® in order to evaluate the operational performances as well as the production costs 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, formic acid 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 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 reuse.
The operating conditions and parameters such as the pressure/temperature in reactor, its size, the electrolytes, the separation steps pressure levels, etc. have been evaluated to quantify their respective influence on (i) the process performances, (ii) the economic indicators and (iii) the environmental indicators. Life Cycle assessment (LCA) is therefore used to include environmental considerations in order to identify the hotspots of the process and select operating conditions to ensure the whole positive environmental balance and minimize the impacts. The software SimaPro® is used to perform the environmental analysis.
As a result, this study illustrates how process engineering, associated with LCA methodology, proposes a relevant optimization of the conversion unit regarding the techno-economic and environmental performances. First results tend to demonstrate that this CO2-based process may have both lower emissions and higher potential to reduce fossil resource depletion compared to the conventional ways of production, i.e. the carbonylation of methanol in sodium hydroxide and the oxidation of hydrocarbons, that both present negative environmental impacts.
