Constantino Mansogo

A Process to Capture Carbon Dioxide by using Amino Acid Solutions and Guanidine Solids in Slurry Bubble Column Reactors

Constantino Mansogo

Mentor: Jorge Gabitto Chemical Engineering Department

Introduction: The absorption of CO2 into aqueous amine solutions is among the most effective technologies for CO2 capture from coal- or natural gas-fired power plants. However, CO2 absorption by pure amines and mixtures of amines still face numerous challenges, such as high energy consumption for solvent regeneration, low capacity to absorb CO2, poor thermal stability, and high corrosivity of materials [1]. Amino acid salt solutions have been proposed as chemical absorbents for CO2 capture. Compared to amine solutions, the amino acid salt solutions are less toxic, cause less corrosion to equipment materials, and show very little degradation by oxidation [1]. Berthromè et al. [2] reported a process for CO2 absorption directly from the air using environmentally friendly aqueous amino acid solutions. The process is completed by the reaction of the CO2-loaded solutions with a simple bis-iminoguanidine chemical compound, which crystallizes as an insoluble carbonate salt and regenerates the amino acid sorbent. This process has great potential for reducing energy demand because the energy required in the regeneration step is used to heat a solid compound and not a liquid solution [3]. Gabitto et al. [4] discussed the application of this process using two-phase batch and bubble column reactors. The amino acid regeneration step is carried out in a separate batch step [2].

Figure 1. Proposed cyclic process for continuous CO2 absorption. Objectives/Goals: The goal of this project is to develop a novel process, which combines the CO2 absorption and the amino acid regeneration steps into a single step to be carried out in a slurry bubble column. The energy required for regenerating the solvent will be significantly reduced. The combined process will also reduce the number of steps and thus the operating cost, compared to a process using independent steps. Other important goals of this project are training undergraduate students and dissemination of knowledge through publications and presentations. Methodology: The proposed single-step project comprises the following sub-steps, see Figure 1: First, a solid guanidine compound is mixed with an alkaline amino acid solution. Second, the solid-liquid mixture (slurry) is pumped from the top of the absorption column, and the exit liquid is recycled using a diaphragm pump. The gas-phase containing the CO2 is injected from the bottom of the column. Once the cycle is finished, the remaining slurry phase is filtered, and the amino acid solution is recovered. The filtered solid is heated up to release the captured CO2 for disposal, and regenerate the guanidine compound for reuse. A reactor operating in this mode will significantly increase the amount of CO2 captured compared to a similar operation using independent steps. Results and Discussion: We have developed a theoretical model to represent the novel single-step process. The theoretical model was implemented by modifying the software codes developed by Gabitto et al. [4] to simulate the CO2 absorption process. The modified computer codes are currently being validated against literature data [2]. The validated codes will be used to optimize operating conditions for the process.

Flue Gas CO2 Absorption + Amino-Acid Regeneration Three-Phase Slurry Column Reactor Slurry

Solid/Liquid Separation

Solid

GBIG Regeneration

Solid GBIG Liquid Recovered Amino-Acid

CO2

Conclusions: The theoretical model has been developed, and a custom-made computer code has been written to simulate the process. There are no simulation data available at this moment, but significant progress has been accomplished. Once the validation process is completed, the theoretical model will be evaluated by comparison with other literature models under similar specific conditions. Evaluation and Dissemination plan: A publication will be submitted to the special issue on ‘Novel CO2 Sequestration Technologies’ from the Energies scientific journal. An abstract has already been submitted, and the guest editor, Dr. Jorge Gabitto, has solicited a full article for peer-reviewing. The results collected in this project will be used to support preparation of bigger proposals to external agencies such as Department of Energy, National Science Foundation, and others.

References

1) Liang, Z., Fu, K., Idem, R., and Tontiwachwuthikul, P. “Review on Current Advances, Future Challenges, and Consideration Issues for Post-Combustion CO2 Capture using Amine-Based Absorbents,” Chinese Journal of

Chemical Engineering, 24, 278–288, 2016. 2) Brethomè, F. M., Williams, N. J., Seip, Ch. A., Kidder, M., and Custelcean, R., “Direct Air Capture of CO2 via Aqueous-Phase Absorption and Crystalline-Phase Release using Concentrated Solar Power,” Nature Energy, 3, 553559, 2018. 3) Garrabrant, K. A.; Williams, N. J.; Holguin, E., Brethome, F. M., Tsouris, C., and Custelcean, R. “Energy-Efficient CO2 Capture from Flue Gas by Absorption with Amino Acids and Crystallization with a Bis-Iminoguanidine,”

ChemRxiv, 2019. doi.org/10.26434/chemrxiv.7663289.v1. 4) Gabitto, J., Custelcean, R., and Tsouris, C. “Simulation of Carbon Dioxide Absorption by Amino Acids in Two-Phase Batch and Bubble Column Reactors,” Sep. Sci. & Tech., DOI: 10.1080/01496395.2019.1609030, 2019.