Optimization of CO2 capture on diatomaceous earth functionalized with cetyltrimethylammonium bromide and tetraethylenepentamine by a statistical experimental approach

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The carbon dioxide (CO2) sorption capacity of diatomaceous earth (DE) modified with cetyltrimethylammonium bromide (CTAB) and functionalized with different loading levels of tetraethylenepentamine (TEPA) was investigated at atmospheric pressure under the influence of operating temperature, TEPA loading level, and water vapor content in the feedstream. The characterization of the sorbent was determined by X-ray diffraction and Fourier transform infrared spectroscopy analyses. Two statistical procedures were performed to minimize the number of experimental runs required to achieve the optimization of the CO2 sorption capacity and the critical factors. A full 2^3 factorial design with three central points was performed at a 95% confidence interval. The operating temperature, TEPA loading level, H2O concentration, and the TEPA loading level-H2O concentration interaction had a positive effect on the CO2 sorption capability. Only the temperature-H2O concentration interaction has a negative influence on the capacity. From a face-centered central composite design response surface model (FCCCD-RSM), the optimum condition for the 40% (w/w) TEPA/CTAB-DE was at a temperature range of 58–68 °C and a water vapor concentration range of 9.5–14% (v/v) with a fixed absorbent weight/total gas flow rate ratio of 1.8 g∙s/mL and an initial CO2 concentration of 10% (v/v) in He. The maximum capacity of the sorbent was about 149.4 mg/g at 63.5 °C with a 12% (v/v) water vapor concentration in the feed. Verification of the statistical FCCCD-RSM was performed after determining the optimization. The estimated capacity fitted well to the experimental data, and so this statistical method has an effective potential for optimizing the CO2 capture processes.