Study of Kinetics, Solubility, Heat of Absorption and Formation of Bicarbonate and Carbamate of Linear and Ring Diamines in CO2 Absorption Process

Study of kinetics, solubility, heat of absorption and formation of bicarbonate and carbamate of linear and ring diamines in CO₂ absorption process

Rui Zhang^a, Zhiwu Liang^a*, Qi Yang^b*, Xiao Luo^a

^aJoint International Center for CO₂ Capture and Storage (iCCS), Provincial Key Laboratory for Cost-effective Utilization of Fossil Fuel Aimed at Reducing Carbon-dioxide Emissions, College of Chemistry and Chemical Engineering, Hunan University, Changsha, Hunan, 410082, P.R. China

^bCSIRO Manufacturing, Clayton Victoria 3168, Australia

Keywords: amines; CO₂ capture; ring amines

* Author for correspondence: Dr. Zhiwu Liang Email: zwliang@hnu.edu.cn

 Tel: +86-13618481627 and +86-73188573033

ABSTRACT

Climate change has caused strong concern worldwide and excessive CO₂ emission is considered to be the main contributor to global warming, therefore CO₂ capture and storage has become an important research subject. Among different CO₂ capture methods, post-combustion capture using chemical absorbents, especially amine absorbents, is regarded as a feasible method for mitigating the CO₂ emissions from many industrial sources. The most commonly studied amine absorbent is monoethanolamine (MEA). Aqueous solutions of other primary, secondary and tertiary amines and amino acid salts have also been studied to investigate their mass transfer performance, reaction kinetics and energy consumption in absorption-desorption processes. All of these absorbents, however, demonstrated some challenges for use in CO₂ capture processes. For example, primary amines such as MEA have a fast reaction rate with CO₂ during absorption but require large energy consumption during CO₂ desorption; a tertiary amine such as N-methyldiethanolamine (MDEA) requires less energy for CO₂ desorption but has a slow reaction rate with CO₂ during absorption. Other challenges for CO₂ capture processes include amine degradation, facility corrosion, and the escape of amine or other substances to the environment. These challenges, in particular high energy consumption, result in high CO₂ capture costs. To address these challenges, it is important to develop better solvents and better processes.

An ideal amine absorbent for CO₂ capture should have fast reaction kinetics during CO₂ absorption, large CO₂ cyclic capacity (the difference between rich amine CO₂ loading and lean amine CO₂ loading), and low energy consumption during desorption. The performance of amines during CO₂ absorption and stripping is strongly related to amine molecular structure. To design and develop better amine absorbents for CO₂ capture, it is necessary to understand the effect of amine molecular structure on amine performance in CO₂ capture. Yang et al. and Conway et al., have studied a number of specifically designed amine absorbents for CO₂ capture^{1, 2}. These designer amines contained two or three amino groups of different types which were spaced by two or three carbons in the same molecules. Their results showed that the designer amines demonstrated a significant improvement in CO₂ cyclic capacity. Especiallly the designer amines contain a ring structure in its molecular structure, so in this work, there are 5 damines (Table 1) were selected to investigated their CO₂ capture performance. The CO₂ equilibrium solubility, the formation of carbamate/bicarbonate, the reaction kinetics and the heat of absorption also was investigated at the corresponding experimental condition. The current results we obtained now shows that the ring amine could produced more bicarbonate and less carbamate than the linear diamines as shown in Figure 1. More bicarbonate vs. less carbamate is benefits to the CO₂ desorption performance.

The other experiments about the CO₂ absorption-desorption performance will be performed in future. Through comparing the solubility, the heat of absorption and the reaction kinetics to get a good understanding on the effect of the molecular structure (ring) on the amine performance for CO₂ capture.

Table 1. The details of each amine used in this work.

Amine	Abbreviation	Mol Wt	Purity (%)	Molecular structure
Monoethanolamine	MEA	61.08	99.0
Ethylenediamine	EDA	60.10	99.5
N1,N2-Dimethylethane-1,2-diamine	DMEDA	88.15	98.0
Piperazine	PZ	86.14	99.0
2-Methylpiperazine	2-MPZ	100.16	95.0
2,6-Dimethylpiperazine	2,6-DMPZ	114.19	97.0

 

Figure 1. The profile of each species with the CO₂ loading changes of each amine. Solid and dash line are the fitted line for different species of each amine.

 

ACKNOWLEDGEMENTS

 

The authors are very grateful for the CSIRO PhD student scholarship to support this research and would like to acknowledge the research contribution to the CO₂ loaded amines test by the CSIRO PCC team in Australia. The authors also would like to express thanks for the financial support from the National Natural Science Foundation of China (NSFC-Nos.21536003, U1362112 and 51521006), National Key Technology R&D Program (MOST-No. 2014BAC18B04), Graduate Student Innovation Project of Hunan Province (CX2016B121). China Scholarship Council and China Outstanding Engineer Training Plan for Students of Chemical Engineering & Technology in Hunan University (MOE-No.2011-40) are also greatly appreciated.

 

Reference

1.            Yang, Q.; Puxty, G.; James, S.; Bown, M.; Feron, P.; Conway, W., Toward Intelligent CO₂ Capture Solvent Design through Experimental Solvent Development and Amine Synthesis. Energy & Fuels 2016, 30, (9), 7503-7510.

2.            Conway, W.; Yang, Q.; James, S.; Wei, C.-C.; Bown, M.; Feron, P.; Puxty, G., Designer Amines for Post Combustion CO₂ Capture Processes. Energy Procedia 2014, 63, 1827-1834.