(16b) Tailoring Amine Based Solvents for Reactive CO2 Absorption Using Structure-Property Relationships

The development of new amines for CO₂ absorption for post combustion carbon capture processes to mitigate the climate change has received much attention in the last years. But CO₂ absorption also remains an important task in many established large scale industrial processes like the purification of synthesis gas. Such processes could benefit from tailored new amines.

In the present project novel amines for the removal of CO₂ from synthesis gas by reactive absorption are developed and tested. All studied amines are derivatives of triacetone amine (TAA). These interesting amines have not been considered before as reactive solvents for CO₂ capture. The approach of the present work is new: we have realized a shake-hand between the knowledge-guided synthesis of the new TAA-based amines and their characterization as solvents.

In a first step, a short list of TAA-based amines, that looked promising, was established, and the possibilities to synthetize them were evaluated. Some of the candidates were then synthesized and studied experimentally. Based on the results of these studies, new candidates were identified. In the iterative process, about 50 amines were considered and about 25 of them were actually synthesized and investigated. These amines differ only in the substituent of the basic TAA ring structure. From the results relationships between the structure of the amines and their properties as reactive solvents for CO₂ capture can be established. Some of these structure-property relationships can be generalized.

The experimental methods used for the characterization of the solvents have been described in detail recently [1]. The measurements include: solubility and rate of absorption of CO₂, liquid-liquid and solid-liquid equilibrium and viscosity. Furthermore, basic physico-chemical data like acid constants, and chemical equilibrium constants, namely those of the carbamate formation, were determined. The same procedures were applied for all amines.

Based on this comprehensive data the amines were assessed regarding their performance as solvents. An enhanced version of the method of Notz et al. [2] which allows ranking solvents with respect to the process energy requirement and solvent flow rate was employed. Some of the particularly attractive solvents show a temperature-dependent liquid-liquid phase split, which could be used beneficially in the reactive absorption process. The most promising solvent was successfully tested in pilot scale.

[1] D. Vasiliu, A. Yazdani, N. McCann, M. Irfan, R. Schneider, J. Rolker, G. Maurer, E. von Harbou, H. Hasse: Thermodynamic Study of a Complex System for Carbon Capture: Butyltriacetonediamine + Water + Carbon Dioxide, J. Chem. Eng. Data 61 (2016) 3814–3826

[2] R. Notz, I. Tönnies, H. Mangalapally, S. Hoch, H. Hasse: A short-cut method for assessing absorbents for post-combustion carbon dioxide capture, Greenhouse Gas Control 5 (2011) 413-421