Studies on the effect of addition of piperazine and sulfolane into aqueous solution of N-methyldiethanolamine for CO2 capture and VLE modelling using eNRTL equation

• VLE of CO2 in aq. (MDEA + PZ) and (MDEA + PZ + sulfolane) measured in an equilibrium cell.
• Model validated with literature and experimental data. Estimation of species and pH.
• PZ promotes CO2 absorption while sulfolane acts as physical solvent in aq. medium.
• (MDEA + PZ + sulfolane) blend can be an efficient hybrid solvent for CO2 capture.

In this work, new experimental vapour liquid equilibrium (VLE) data and modelling work of VLE of CO2 in piperazine (PZ) activated aqueous solutions of n-methyldiethylamine (MDEA) are presented. Besides, experimental VLE data of CO2 in a hybrid solvent, containing sulfolane as physical solvent along with aqueous (MDEA + PZ), have also been reported over the temperature range of 308–328 K and CO2 partial pressure range of 1–1400 kPa. The concentrations of MDEA in the aqueous solutions are 22–28 mass% and also 42–48 mass%. PZ is used as a rate activator within a concentration range of 2–8 mass%. The total amine concentration in the aqueous solutions of (MDEA + PZ) has been kept within 30 mass% and also 50 mass%, while for the hybrid solvent the concentration of sulfolane has been maintained at 10 mass% along with total 50 mass% (MDEA + PZ). Electrolyte non random-two liquid (eNRTL) theory has been used to model the VLE. It has been found that there is a good agreement between the experimental and model results of CO2 solubility in PZ activated MDEA solutions. The CO2 cycle capacity is calculated considering a set of lower and higher CO2 partial pressures corresponding to lower (lean solvent) and higher (rich solvent) equilibrium CO2 loadings. For the sulfolane based hybrid solvent, it has been observed that the CO2 cyclic capacity of the solvent decreases with the lower lean-rich partial pressure range of 10–100 kPa, but increases at higher partial pressure ranges of 100–1000 kPa at 323 K. PZ mass% in the hybrid solvent has also been found to have a positive effect on the CO2 cyclic capacity.

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