Abstract
In this work, sodium aluminate alkaline solution was used to capture CO2 in a continuous bubble column scrubber and aluminum tri-hydrate (ATH) precipitates were produced. As the sodium carbonate could be recycled after the filtrated solution was crystallized by evaporation, a novel CO2 capture process was developed successfully. There were five experimental operation variables, including solution flow rate (A), concentration of the solution (B), gas flow rate (C), CO2 gas concentration (D), and liquid temperature (E), with four levels to each variable. The influence of each variable on absorption efficiency (EF), absorption rate (RA), absorption factor (φ), mass transfer coefficient (KGa), and precipitation rate (RP) in a steady state was explored in this study. The Taguchi experimental design was adopted, and 16 experiments were performed; as the optimum operating conditions found in Taguchi analysis required further verification, there were a total of 21 experiments in the end. According to S/N analysis, the overall order of importance was D > A = B > C > E, meaning D (CO2 concentration) was most important and E (liquid temperature) was least important. In addition, the result also showed that the Rp was 1.25–2.0 times higher than the RA. The obtained powder was mainly ATH according to XRD analysis, with the crystal size ranging between 8.14 and 27.97 nm. However, the BET analysis showed its particle size range being 17.6–283.7 nm, indicating agglomeration for primary particles. The SEM analysis showed that there were flower-like, irregular, urchin-like, elongated, and amorphous particles. The solutions from five groups of optimum conditions were used to recycle the sodium carbonate experiments. After evaporation and crystallization of the filtrated solutions, the energy loading was found to be 1.70–2.56 GJ/t-solvent, illustrating the superiorities of low energy consumption. The precipitated powders were verified to be sodium carbonate by FTIR, which is a valuable constituent.
Highlights
As the greenhouse effect results in climate anomalies, humans are bearing the adverse consequences
Three parts have been explored in the CO2 capture and reuse studies; the first is the Taguchi experiment, the second is the verification of optimum conditions, and the third is the evaporation crystallization tests
The particle size from BET was quite different from those crystal sizes from XRD, and the difference between some groups was over 10 times; this may be because the aluminum tri-hydrate (ATH) powder prepared in this study showed severe agglomeration
Summary
As the greenhouse effect results in climate anomalies, humans are bearing the adverse consequences. The global warming goal requires reducing greenhouse gases (GHG) emissions by 40–70% by 2050 relative to 2010 levels and achieving neutral to negative emissions by the end of the century [1]. Considerable manpower and expenses have been devoted to study the capture, storage, and reutilization of CO2 around the world. The CO2 emitted from fossil fuels is 5–20% according to the literature, so the absorption process is the main choice for capturing CO2 [2]. This is a mature technique, which employs a two-tower plant, including a scrubber and a stripper
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