Carbon capture by DEA-infused hydrogels

Highlights

• Aqueous DEA solutions were incorporated into hydrogel particles at low concentrations to prepare DEA infused hydrogels.

• The resulting hydrogels exhibited higher and faster CO₂ absorption compared to DEA solutions under identical DEA contents.

• At a fixed DEA concentration, the overall CO₂ uptake was independent on the crosslinking degree of the hydrogel.

• The absorption kinetics of DEA infused hydrogels was generally enhanced at higher crosslinking degree.

• Breakthrough experiments were conducted to validate the CO2 selectivity of DEA infused hydrogels in a simulated flue gas.

Abstract

Escalating global temperatures have spurred the development of various CO₂ sorbents. Liquid amines are the most widely employed sorbent but they exhibit multiples drawbacks including low absorption capacity, high regeneration energy and degradation of the amine. This work presents the performance of an entirely new CO₂ absorbent that is prepared by simply adding commercial or synthesized hydrogels into a solution of a standard liquid amine, diethanolamine (DEA) solution with a low concentration (5.0 wt. %, 10.0 wt. % and 20.0 wt. %) to generate DEA-infused hydrogels. This new material can rapidly capture CO₂ even with relatively low amounts of DEA Higher overall uptake has been achieved compared to the commonly used DEA solutions. Moreover, hydrogels with various crosslinking degrees were prepared and employed for preparing the DEA infused hydrogels. It was found that the overall CO₂ absorption was largely independent of the crosslinking degree, but the absorption kinetics generally improved with a higher crosslinking degree. In addition, breakthrough experiments demonstrate the outstanding performance of this proposed material for CO₂ removal from flue gas. The absorption capacity of the DEA-infused hydrogels is well maintained after multiple regeneration cycles especially with the addition of polyethylenimine (PEI) so the hydrogels can easily be recovered and reused. This new material shows promise as a new CO₂ absorbent in the CO₂ capture industry.

Introduction

The unprecedented consumption of fossil fuels has escalated the level of carbon dioxide (CO₂) in the atmosphere since the Industrialization Revolution which has caused a change in the global climate (Rochelle, 2009; Pachauri and Meyer, 2014; ESRL, 2016). Consequently, numerous strategies and approaches have been proposed to capture the CO₂ released from various sources such as coal-fired power plants and natural gas processing stations (Saha, 2018; Zhang et al., 2018; Zareiekordshouli et al., 2018; D’Alessandro et al., 2010; Markewitz et al., 2012). Due to its high reactivity, good selectivity and relatively facile operation, “amine scrubbing” has emerged as the most well-established approach. It uses liquid alkanolamines as the absorbent and has become the benchmark technique for CO₂ capture to date (Walters et al., 2016; Kim et al., 2013; Luis, 2016). However, the process suffers from a number of intrinsic drawbacks including the massive energy demands associated with regenerating the liquid amines, low absorption efficiency and severe corrosion on facilities in a long term (Choi et al., 2009; MacDowell et al., 2010; Goeppert et al., 2012). In an attempt to overcome these shortcomings, many researchers have explored the use of solid adsorbents over the past few decades (Wang et al., 2011, 2015; Nugent et al., 2013). Typically, these solid adsorbents are porous materials such as zeolites (Sua and Lu, 2012), silica nanoparticles (Li et al., 2015) or metal organic frameworks (MOFs) (Dasgupta et al., 2012). They possess high surface areas and large pore volumes and are functionalized with various amines using physical (impregnation) or chemical (grafting) approaches so the CO₂ adsorption kinetics and capacity are significantly improved compared to that of the aqueous solutions of amines (Zhang et al., 2014; Hicks et al., 2008). However, fabrication of these supports is often complex and costly which has hindered large-scale operation. In addition, the performance of some of these can be lost in the presence of water vapor that is abundant in the flue gas. Furthermore, they may exhibit poor selectivity towards CO_2, especially for the adsorbents that physically bind CO₂.

In our previous study, we incorporated liquid amines into hydrogel particles and developed a new platform, namely amine infused hydrogels (AIHs), for the post-combustion carbon capture (Xu et al., 2018). The enlarged surface area of AIHs allowed for fast and efficient CO₂ uptake. Moreover, the materials exhibited reasonable regeneration capacity over multiple CO₂ absorption-desorption cycles. The aim of this study is to understand the performance of AIHs more comprehensively by varying the cross-linking degree, amine concentration and gas composition. DEA was selected as the standard amine due to its high reactivity and low volatility. (DEA). The first objective of this work is to investigate how the DEA infused hydrogels would perform at relatively low DEA concentrations (5.0 wt. %, 10.0 wt. % and 20.0 wt. %). In addition to using commercial hydrogels an acrylamide-based hydrogel with varying crosslinking degrees was synthesized to investigate the correlation between the CO₂ uptake and the cross-linking degree. The resulting materials were tested using a simulated flue gas (15.0 vol. % CO₂ in N₂) to determine the capture performance of DEA infused hydrogels. This study broadens the understanding of the behavior of AIHs under various working conditions, and thus may contribute to the large-scale employment of AIHs in the carbon capture industry in the future.