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].
Slurry
Flue Gas
CO2 Absorption + Amino-Acid Regeneration Three-Phase Slurry Column Reactor
Liquid Solid/Liquid Separation
Recovered Amino-Acid
Solid GBIG Regeneration
CO2
Solid GBIG
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. Page 155 of 3
