Masoud Mofarahi

Green processes that use environmentally friendly materials have gained significant attention, in particular in the fuel processing section. Alkaline salts of natural amino acids (NAAs), known as NAA salt solutions (NAASs), have significant potential to replace conventional solvents for achieving greener CO2 capture. Thermophysical properties, including the viscosity of NAASs, are essential for developing processes and their optimization. This study aims to develop a generalized theoretical model derived from free-volume theory (FVT) for estimating the viscosity of NAASs. Four different cases for parameter regression were applied to the largest viscosity databank investigated thus far (19 NAAs, three alkaline compounds, 29 NAASs, and 2039 data points), and the performance of the model using the parameters from the cases was evaluated. The highest accuracy was achieved (average absolute relative deviation percentage (AARD) = 1.54 %, average relative deviation percentage (ARD) = 0.09 %, R-squared (R2) = 0.9969) in the concentration- and solution-specific cases, but many parameters were required for the whole databank. In contrast, the most general case using global parameters resulted in the least number of parameters (six adjustable parameters) and showed reasonable accuracy (AARD = 10.42 %). A specific case in which the model parameters were obtained from each NAAS with a simple modification of the barrier energy parameter (α) yielded a higher accuracy (AARD = 4.12 %, ARD = 0.53 %, R2 = 0.9606) with a smaller number of parameters for the entire databank. The results demonstrated that the FVT is capable of modeling the viscosities of NAASs and can thus be employed for the simulation and optimization of thermophysical properties.