(456g) Process Modeling and Sensitivity Studies for Integrated Carbon Capture and Conversion with Ionic Liquids

The continued increase in anthropogenic emissions of CO2, a potent greenhouse gas (GHG), has been associated with the damage to the environment through global warming and climate change. A multi-faceted approach is necessary to limit emissions and achieve the net-zero emissions target set by The Paris Agreement. Reducing CO2 emissions from hard-to-abate sectors such as manufacturing is challenging as they are likely to continue to utilize fossil-based sources as a feedstock and fuel for process heating for the foreseeable future.

Closing the industrial carbon cycle is an economically and environmentally attractive solution to decarbonize industrial production. In this context, CO2 captured from industrial point sources is used as a C1 feedstock and converted to value-added chemicals and fuels. However, the energy penalties associated with the conditioning (chiefly via desorption, compression, transportation and reaction) of CO2 in conventional, sequential capture and conversion (CCC) processes remain a technological and economical barrier to large-scale deployment (Pérez-Fortes et al., 2016). The capital and energy intensity of these operations can be lowered by integrating the carbon capture and conversion steps.

The key innovation of integrated carbon and conversion (ICCC) processes is thus a process intensification approach, whereby the separation of the CO2 from the capture medium is eliminated. Instead, the conversion to a value-added chemical occurs in the capture medium itself. This presents important advantages: first, the heat of reaction can (partially) offset the heat required for CO2 separation, which in conventional capture processes is provided by an external utility. Second, the reaction of the CO2 in the captured medium occurs in the condensed (typically liquid) phase, which can be performed at lower pressures and temperatures.

In spite of these advantages, research on ICCC processes remains limited. Kothandaraman et al. designed and evaluated an ICCC process to produce methane using the 2-EEMPA water-lean capture solvent (Kothandaraman et al., 2021). More recently a similar process producing methanol was analyzed using the same capture solvent by the same authors (Kothandaraman et al., 2022). Hernandez et al. evaluated an ICCC process with ionic liquids (ILs) as a bifunctional capture agent and catalyst to produce propylene carbonate (Hernandez et al., 2022). While significant contributions have been made, a systems-level analysis considering simultaneous material- and process-level for ICCC is still needed.

Motivated by the above, we propose a mathematical modeling and sensitivity study with respect to key material properties for ICCC. In particular, we focus on a prototype process comprising ionic liquid (IL)-based CO2 capture from post-combustion flue gas from an ethylene plant, and direct conversion into methanol. Methanol was chosen as the product as it is an important petrochemical intermediate, functions as a hydrogen carrier, and provides short-term liquid storage at room temperature.

In this prototype process, CO2 is chemically absorbed using aprotic heterocyclic anion ionic liquid solvents (AHA ILs), which were selected due to their superior material properties such as low heat of absorption, improved thermal stability, nonvolatility, and low viscosity of the solvent (Seo et al. 2020, Seo et al., 2021, Seo et al., 2021, Seo et al., 2023, Seo et al., 2023, Seo et al., 2024). Once captured, CO2 is converted into methanol via a thermocatalytic hydrogenation reaction using Cu- and Pt- based catalysts. The solvent is removed from the product stream and recycled to the absorber. Product methanol and water are recovered while unreacted vapor consisting of hydrogen is recycled and compressed to the reactor. Furthermore, the ICCC process is integrated with an ethylene manufacturing plant, which can provide hydrogen and heat for the proposed process.

An equation-oriented, multi-scale, rate-based steady-state flowsheet model for the IL-based ICCC process is developed and implemented in gPROMS. A rate-based model considering kinetics and mass transfer limitations of CO2 capture is used for the absorber. The model is used to evaluate the energetic performance of proposed ICCC process as a function of key material properties. A sensitivity analysis with respect to catalyst performance and target CO2 removal rate from the flue gas is performed.