K. Sobala, H. Kierzkowska-Pawlak
Lodz University of Technology, Łódź, PL


The chemical absorption in alkanolamine solutions is the most effective method of removing CO2 from flue gases produced from fossil fuel combustion. The disadvantage of this technology is its high operating cost associated with the energy consumption required to regenerate the solvent. The cost of regeneration is related to the heat of absorption of CO2 in the solution. Therefore, recent research have been focused on development of solvents which are characterized by simultaneous low heat of absorption and fast reaction rate. The above requirements can be achieved by activated aqueous solutions of N,N-diethylethanolamine (DEEA). According to the previous studies, addition of N-methyl-1,3-propanediamine (MAPA) to DEEA-based solutions resulted in the increase in the rate of absorption. The aim of this work is to determine the heat of absorption of CO2 in aqueous solutions of blended amines: DEEA+MAPA. The measurements were conducted in a reaction calorimeter CPA 201 (SyrrisLdt) at a temperature of 313.15 K. The calorimeter allows for continuous measurement of the heat flow which is released during the semi-batch absorption of CO2. The effect of concentration of MAPA activator on the heat of absorption in blended DEEA+MAPA solutions of total concentration of 1, 1.1, 2 M was analyzed. The concentration of MAPA was 0.05, 0.1 and 0.2 M. To determine the differential heat of absorption (ΔHabs,diff ) as a function of CO2 loading (α [mol CO2/mol amine]), the original measurement method was developed. According to the first law of thermodynamics for open systems, the energy balance formulated for the whole system took into account the energy flow associated with the mass of the inflow CO2. For the studied solvent systems, the heat of absorption of CO2 in aqueous solutions of DEEA + MAPA was higher than in the single DEEA solution. For example, for a 1 M DEEA solution, the differential heat of absorption was -ΔHabs,diff = 54.1 kJ/mol, and for the mixture 0.9 M DEEA+0.1 M MAPA it was -ΔHabs,diff = 65.8 kJ/mol, at the same CO2 loading α = 0.46 mol CO2/mole of amine in both cases. The present results demonstrate that as the MAPA concentration increases in DEEA-based solvents, the heat of absorption also increases. These findings may be used to develop an optimal composition of the new CO2 absorbent based on DEEA+MAPA blends.

Keywords: CO2 capture, heat of absorption, reaction calorimeter, DEEA, MAPA