Unraveling the Role of Metal Oxide Catalysts in the CO₂ Desorption Process from Nonaqueous Sorbents: An Experimental Study Carried out with ¹³C NMR

Abstract

The CO2 desorption process from a CO2-saturated nonaqueous sorbent, 2-(2-aminoethoxy)­ethanol (DGA) in diethylene glycol monomethyl ether (DEGMME), was investigated in the absence and presence of four different metal oxides, namely, V2O5, TiO2, WO3, and ZnO, aiming at identifying acid catalysts with the potential to reduce the energy demand for sorbent regeneration. The desorption performances of the DGA-DEGMME solutions with and without catalysts were evaluated in terms of CO2 desorption rate, overall CO2 desorbed, and thermal energy consumption. The desorption mechanism was understood by the 13C NMR speciation study of the solutions during the regeneration experiments. As a result, metal oxide catalysts, depending on the number and types of acidic sites on their surface, can accelerate the carbamate breakdown and the subsequent CO2 release. In particular, WO3 and TiO2 can be considered good candidates for implementation in CO2 capture processes with nonaqueous sorbents, as they greatly improved the desorption performance, and their structures remain unchanged before and after use. The combination of nonaqueous sorbents with catalysts, here reported for the first time, provides an effective strategy that could inspire the design of advanced sorbents for energy-efficient CO2 capture.

Energy-Saving Effect of Low-Cost and Environmentally Friendly Sepiolite as an Efficient Catalyst Carrier for CO2 Capture

“…20 Liang et al 21 reported that the solid catalyst HZSM-5 (Brønsted acid dominated) and γ-Al 2 O 3 (Lewis acid dominated) can reduce the heat duty efficiently in the commercial aqueous monoethanolamine (MEA) solution regeneration process. Recently, Bhatti et al 22 investigated several metal oxide catalysts to improve CO 2 desorption performance in nonaqueous 2-(2-aminoethoxy)ethanolamine (DGA) solution at the desorption temperature of 90 °C; as a result, WO 3 and TiO 2 showed remarkable advantages in enhancing the CO 2 desorption performance. Zhang et al 23 studied SAPO-34 and SO 4 2− /TiO 2 for the catalytic CO 2 desorption from CO 2 -loaded MEA solution under the relatively low temperature of 96 °C; their results revealed that the Brønsted/Lewis acid sites on the catalysts are beneficial to the MEAH + deprotonation and carbamate decomposition, and a high mesopore surface area (MSA) also enhances the catalytic CO 2 desorption performance.…”

Evaluating CO2-Desorption Performance of Solid Acid Catalysts in CO2-Loaded Aqueous Solutions of N-Ethylethanolamine

“…Mostly, hindered and tertiary amines were used to enhance the efficiency of desorption of primary amines because such amines exhibit better desorption capabilities. , On the other hand, different classes of desorption catalysts have been applied in past works. It is evident from recent works that Al 2 O 3 among the metal oxides, H-ZSM-5 among zeolites, MCM-41 among mesoporous silica, and SO 4 2– /ZrO 2 among sulfated metal oxides are the most effective candidates for catalyst-aided amine regeneration. ,− In contrast to zeolite-based catalysts, fewer metal oxides have been used to regenerate amines. − This serves as the basis to investigate the performance of several metal oxides. A brief overview of amine regeneration with metal oxides − is provided in the Supporting Information (Table S1).…”

“…It is evident from recent works that Al 2 O 3 among the metal oxides, H-ZSM-5 among zeolites, MCM-41 among mesoporous silica, and SO 4 2– /ZrO 2 among sulfated metal oxides are the most effective candidates for catalyst-aided amine regeneration. ,− In contrast to zeolite-based catalysts, fewer metal oxides have been used to regenerate amines. − This serves as the basis to investigate the performance of several metal oxides. A brief overview of amine regeneration with metal oxides − is provided in the Supporting Information (Table S1). Especially, Bhatti et al reported that metal oxides do not adversely affect the absorption capacity of amines.…”

Investigating the Performance of Ethanolamine and Benzylamine Blends as Promising Sorbents for Postcombustion CO2 Capture through 13C NMR Speciation and Heat of CO2 Absorption Analysis

“…According to the best technologies identified so far, postcombustion capture (PCC) has become a commonly accepted method for controlling CO 2 emission from energy-related sources. 3,4 Among the various PCC technologies developed, the chemical absorption using amine-based liquid solutions is considered the most mature and functional method and has several advantages in terms of selectivity for CO 2 , absorption rate, and loading capacity 5 compared to other techniques, such as adsorption with solid sorbents 6 or the use of a membrane contactor. 7 It is well known that there are three kinds of amine that can be used to capture CO 2 from a flue gas, namely, primary, secondary, and tertiary amines.…”

“…Unfortunately, the combustion of fossil fuels leads to an inevitable increase in the concentration of carbon dioxide (CO 2 ) in the atmosphere, which is closely related to the so-called global warming, one of the most serious environmental challenges. , As a result, the topic of carbon capture and storage (CCS) has recently attracted a lot of attention from the scientific community and from politicians in every government. According to the best technologies identified so far, postcombustion capture (PCC) has become a commonly accepted method for controlling CO 2 emission from energy-related sources. , Among the various PCC technologies developed, the chemical absorption using amine-based liquid solutions is considered the most mature and functional method and has several advantages in terms of selectivity for CO 2 , absorption rate, and loading capacity compared to other techniques, such as adsorption with solid sorbents or the use of a membrane contactor . It is well known that there are three kinds of amine that can be used to capture CO 2 from a flue gas, namely, primary, secondary, and tertiary amines. , In general, in an aqueous solution, primary and secondary amines can react directly (and rapidly) with CO 2 to form stable carbamates, ensuring efficient separation and a high CO 2 absorption rate but requiring high temperatures (and energy) to regenerate the sorbent.…”