The Absorption Kinetics of CO₂ into Ionic Liquid—CO₂ Binding Organic Liquid and Hybrid Solvents

Abstract

Carbon dioxide (CO₂) capture is a global concern because of its effect on climate change especially as regards to global warming. Among greenhouse gases, CO₂ is the most abundant with high concentration released from post combustion processes into the atmosphere. For instance, the volume of CO₂ emission from thermal power plants, petroleum refineries, petrochemical plants, hydrogen and cement factories has become one of the top important global concerns nowadays. In order to capture post-combustion CO₂ and securely store it way or to produce useful products from it, it requires separation of CO₂ from flue gas stream. Industrially, it is generally accepted that the most appropriate method that can be applied commercially to capture CO₂ involves absorbing it with a reversible reaction from gas streams into aqueous amine especially monoethanolamine. Although, CO₂-aqueous amine process is accepted as a mature technology but its absorption/desorption systems are the subject of several studies as the process is energy-intensive among other issues. In view of the shortfalls of CO₂-aqueous amine systems and the greater societal concern to control the amount of CO₂ released to the environment from industrial sources to abate its effects, research for alternative viable solvent systems becomes of high interest to researchers as well as industrialists. Hence, this chapter is mainly to focus on highlighting and discussing relevant advanced solvent systems for CO₂ capture. Among the novel solvents or technology worthy of discussion here include use of organic solvents consisting of an amidine or a guanidine and a linear alcohol, such as 1-hexanol, instead of aqueous amines. In this case, CO₂ loaded solvent could be regenerated at 90–100 °C which is much lower than the boiling point of the solvent and as a result, sufficient drop in energy requirements could be achieved. In order to be applicable, CO₂ binding organic liquid systems (“CO₂BOLs”) will react with CO₂ at sufficient rates. In case, the reaction rate is not sufficient it can be upgraded with piperazine derivatives. Another potential novel method is the capture of CO₂ by special liquids which have negligible vapor pressure and high thermal stability known as ionic liquids (ILs). The ILs also have favorable CO₂ solubility and a wide liquid state temperature with tunable physicochemical characteristics. Further advanced approach can be to develop a blended solvent which can also react with CO₂ more efficiently. A blended system is a hybrid that possesses combined benefits of the amines mixture components thereby providing a better alternative than using single component. Other novel solvents for post combustion CO₂ capture are noted and discussed here.