Experimental assessment of the thermophysical properties of Choline Proline and its performance as a post-combustion carbon capture solvent.

Carbon capture technologies are expected to play a significant role in the energy transition, as a powerful tool for the decarbonisation of the already existing power stations and the hard-to-abate industrial sectors, and as part of biogas upgrading systems and blue hydrogen production processes. Nowadays, amine scrubbing stands among the most solid technologies in the carbon sequestration field, though being renowned for the high energy regeneration requirements, the toxicity, the corrosiveness and the fast degradation they undergo. Ionic liquids (ILs) are emerging as a viable alternative to the aqueous amine solutions for post-combustion carbon capture processes. In this regard, recent studies show that choline proline ([Cho][Pro]) has a very good potential, thanks to its ring structure and to the presence of amine functionalities in the amino acid moiety – which promote the physical and the chemical CO2 absorption, respectively. On the downside, the high viscosity values constitute a serious drawback in practical applications, which can be overcome through the use of solutions of [Cho][Pro] in solvents such as DMSO. The present work aims at providing insights into the thermophysical properties and performance of [Cho][Pro]. Firstly, the IL was synthesised according to an innovative procedure which replaces the expensive and corrosive choline hydroxide with choline chloride as a mean of cation source. Next, density and viscosity were measured for solutions of [Cho][Pro] in DMSO at varying concentrations (12.5%wt, 25%wt and 50%wt) in a temperature interval ranging from 25°C to 70°C. The data obtained were correlated with empirical equations to allow subsequent calculations. The absorption process of the same solutions was later investigated through a gravimetric method in a ~5ml volume reactor. At last, the 50%wt solution was employed in a set of tests performed on a bench-scale test plant. The cyclability of the solution was assessed by calculating the capacity loading and the regeneration efficiency for three consecutive absorption/desorption cycles carried out for 90 minutes at 30°C and 80°C, respectively. Then the effect of temperature (from 30°C to 60°C for the absorption step and from 70°C to 110°C for the desorption one) was investigated and discussed. The results were compared to the ones obtained in a former study carried out on the same test bench with a 12.5%wt [Cho][Pro] in DMSO solution – showing the very poor performances of the current solution with respect to the latter.