Catalytic CO₂ desorption in CO₂-loaded aqueous MEA solution over so₄^2-/ZrO₂/γ-Al₂O₃ catalysts

Greenhouse gases, especially carbon dioxide (CO₂), have attracted significant focus as one of the predominant contributors to climate change. Chemical absorption of CO₂ using amine solvents is the most commercial mature technology that can be adopted for CO₂ capture. 5 M monoethanolamine (MEA) solvent is the baseline solvent and has been the most frequently investigated. However, this solvent suffers from high energy requirement for the rich solution regeneration process, resulting in its immensely high operating costs of CO₂ capture. A potential approach to greatly reduce energy requirement was proposed by Idem et al. ¹. They demonstrated that the addition of solid acid catalyst into the rich amine solution for CO₂ desorption is an effective method to decrease the heat duty. Several zeolite molecular sieve catalysts such as, H-ZSM5 and gamma-Al₂O₃ have been studied and showed higher catalytic activity for this purpose. To further develop this promising method, in the present work, a composite catalyst SO₄^2-/ZrO₂ (SZ) supported on gamma-Al₂O₃ (SZA) was prepared by the precipitation-impregnation method and used for the first time as a catalyst in a rich anime solvent regeneration process. SZ is a representative solid superacid catalyst, which possesses the superior Br nsted acid sites (BAS), but encounters small surface area and rapid deactivation. gamma-Al₂O₃ is an acid catalyst and the most extensively employed support materials, and has large physical properties, strong Lewis acid sites (LAS), and high thermal stability. Potentially, the composite catalyst SZA may show a superior catalytic CO₂ desorption performance for a CO₂-loaded amine solvent regeneration process. In this work, SZA was prepared and applied for the rich 5 M MEA solvent regeneration process to increase the CO₂ desorption performance. Three SZA catalysts with different ZrO₂ and gamma-Al₂O₃ mass ratios were synthesized. The procedure of catalyst preparation is based on Hua et al. ², with a modification. The SZA with ZrO₂/gamma-Al₂O₃ mass ratio of 0.5, 1, and 2 was marked as SZA1/2, SZA1/1, and SZA2/1, respectively. All the catalysts were measured with XRD, FT-IR, N₂ absorption, Py-IR, and NH₃-TPD techniques. The regeneration experiment was conducted using a batch reactor, which is displayed in Figure 1. Typically, 1 L rich MEA solutions with the CO₂ loading of 0.5 mol CO₂/mol amine were introduced into a 2 L four-necked flask, which was immersed in the oil bath. 12.5 g catalyst was put into the MEA solution. The time was recorded until the amine solvent temperature reached at 338 K. The final temperature of this system was kept at 371K for 540 minutes. The CO₂ loadings of solution at time of at 15, 30, 45, 60, 90, 120, 240, 360 and 540 minutes were measured by Chittick apparatus.