CO2Fix: A Simple and Efficient Tool for Estimating the Decarbonization Potential for Chemical CO2 Utilization Pathways

A global effort is underway to reduce GHG emissions to address the growing concerns of anthropogenic climate change. Carbon dioxide capture, utilization, and storage (CCUS) has garnered significant attention as a means of reducing GHG emissions and decarbonizing several industries, including the natural gas industry. One means of applying CCU to a process is through the chemical conversion of CO₂ produced from the process _­­into other products. However, a given CCU process will have its CO₂ footprint, which has to be accounted for when analyzing the process’s potential for CO₂ abatement or when comparing such potential to other processes. This is typically done by conducting Life Cycle Assessments (LCA), which involve comprehensive accounting for the CO₂ footprint of a process throughout its various stages.

In this work, we develop a new metric to account for the CO₂ and carbon footprint of chemical processes in addition to the CO₂-fixation probability for CO₂ utilization technologies. This new tool is named CO2Fix, defined as the ratio of CO₂ being fixed chemically from a process while accounting for the CO₂ produced directly or indirectly from the same process through its chemistry, energy requirements and/or other emissions. Leveraging basic thermodynamic concepts and ASPEN^® aided regression analysis, a model was developed for estimating CO2Fix that is a function of easily obtainable reaction parameters such as temperature, pressure, the heat of reaction, CO₂ conversion, and CO₂ intensity of utilized energy sources. The developed model was then used to analyze the CO2Fix and understand its relationship with multiple model parameters over a wide range of reaction conditions using different energy sources (conventional and renewable). The analysis provided insights such as the nonlinear relationship between CO2Fix and the conversion for non-autothermal reactions since the relationship is normally linear for autothermal reactions. The model was then used in several case studies to analyze the CO2Fix of a few known CO₂ utilization processes, such as CO₂ hydrogenation to methanol (which is one of the few commercial CO₂ chemical utilization routes), the Dry Reforming of Methane (DRM) reaction, and the direct synthesis of Dimethyl Carbonate (DMC) using CO₂. In the case of CO₂ hydrogenation to methanol, the CO2Fix was calculated to be 1.6 at a CO₂ conversion of 50% when utilizing gas as an energy source. Analysis of the DRM reaction showed that the reaction has no potential to abate CO₂ (CO2Fix of 1 or below) without utilizing low CO₂ intensity renewable energy sources such as solar power or wind. Even when using biomass-powered electricity, the CO2Fix for the DRM reaction was approximately 1.1 at 100% conversion. The direct synthesis of DMC was found to have the potential for CO₂ abatement over a large range of reaction conditions at CO₂ conversions beyond 30%, giving a CO2Fix >1 even when the process is powered by natural gas. With the current emphasis on CCUS as a means of decarbonizing the natural gas industry, we propose this model as an efficient and straightforward approach to quickly screen out unviable CCUS routes. Furthermore, the CO2Fix model can be applied to compare different CCUS routes in terms of their ability to decarbonize processes through the chemical fixation of CO₂. Additionally, a software tool was developed utilizing the CO2Fix model for rapid analysis of CO₂ reactions with limited information.