(244c) Optimal Selection of Solvent and Contactor Technology for Micro-Encapsulated Carbon Sorbent (MECS) Based CO2 Capture

Carbon capture utilization and storage (CCUS) is believed to play a prominent role in combating climate change and global warming issues. Many novel technologies are being developed to make CO₂ capture an economically viable piece of the net-zero carbon framework. There are several potential solvents such as ionic liquids, carbonate solutions, and phase change solvents that have favorable energetics and can achieve high loading with promise of significantly improving the economics of CO₂ capture processes. However, these solvents can suffer from high viscosity and/or solid reaction products that can lead to transport difficulties, clogging of the contactor, and the use of distillation towers impractical. Microencapsulation of such solvents inside a polymer capsule can help alleviate some of these operational difficulties. Microencapsulation of carbon sorbents (MECS) is a technology proposed by Vericella et.al. for CO₂ capture applications [1]. Microcapsules containing the solvent can be produced with diameters ranging from 100-600 microns. The small size of these microcapsules results in a high specific surface area per unit volume, which can enhance mass and heat transfer rates. A few studies [2-4] have reported analysis of MECS in a fixed bed, and fluidized bed reactor configuration for a particular solvent (mainly carbonate solutions and MEA). As the choice of microencapsulated solvents and the type of contactor both have strong impact on the economic feasibility of this technology, detailed modeling and techno-economic analysis is required to properly evaluate this technology.

The present work evaluates different solvents and reactor configuration for MECS using process modeling and techno-economic analysis. The encapsulated solvents considered in this study are Na₂CO₃, ionic liquids, and piperazine. Required thermodynamic, reaction kinetics, and physical properties models of the solvents are developed based on the data obtained from the open literature. First, a rigorous capsule model is developed with an underlying solvent chemistry model that describes heat and mass transfer in the microcapsule. The results from the capsule model are validated with experimental data for the Na₂CO₃solvent [4]. Two contactor technologies are evaluated: a fixed bed and a moving bed. These reactor models are 1-D non-isothermal, first principles-based models with appropriate mass transfer, hydro-dynamic, and momentum sub-models. The multi-scale reactor models incorporating the capsule model and embedded heat exchangers are implemented in Aspen Custom Modeler (ACM) where the method of lines is used to solve the resultant system of partial differential equations. The models simulate both absorption and regeneration stages of the process and study the impact of key design and operating parameters on the performance of MECS technology.

Techno-economic analysis of these reactor types operating with different solvents is carried out by computing their Equivalent Annual Operating Cost (EAOC) and comparing them with the traditional MEA technology [5]. The capital cost of the reactor, compressors, and heat exchangers is estimated using Aspen Process Economic Analyzer (APEA) along with custom correlations. Operating costs include the cooling and heating utilities and compression cost for the flue gas, if any. Each combination of reactor type and solvent type is optimized for a fair comparison. It is observed that both reactor type and specific solvent have large impact on the economics of MECS technology.

References

1. Vericella, J. J. et al. “Encapsulated liquid sorbents for carbon dioxide capture”, Nature Communications, 6:6124, 1-7, 2015.
2. Anggit Raksajati, et al, “Techno-economic Evaluation of CO₂ Capture from Flue Gases Using Encapsulated Solvent”, Industrial & Engineering Chemistry Research 1604-1620, 56 (6), 2017.
3. Hornbostel, et al, Packed and fluidized bed absorber modeling for carbon capture with micro-encapsulated sodium carbonate solution, Applied Energy 1192-1204, 2019.
4. Kotamreddy, et al., Process Modeling and Techno-Economic Analysis of a CO2 Capture Process Using Fixed Bed Reactors with a Microencapsulated Solvent, Energy & Fuels 2019 33 (8), 7534-7549 DOI: 10.1021/acs.energyfuels.9b01255.
5. T, Cost and Performance Baseline for Fossil Energy Plants Volume 1. 2015. DOI: DOE/NETL-2015/1723.