Densities, viscosities, and liquid diffusivities in aqueous piperazine and aqueous (piperazine + N-methyldiethanolamine) solutions

Densities and viscosities of aqueous solutions containing both piperazine (PZ) and N-methyldiethanolamine (MDEA) have been determined at a temperature range from (293.15 to 323.15) K. The concentrations of MDEA have been kept constant at (1, 2, 3, and 4) mol · dm-3 with the concentration of PZ varying from (0 to 1) mol · dm-3. Liquid diffusivities of aqueous PZ solutions have been determined using the Taylor dispersion technique over a temperature range from (293.15 to 368.15) K and concentrations from (0 to 1.5) mol · dm-3. At infinite dilution, the method proposed by Othmer & Thakar can be used to estimate the liquid diffusivities, and a modified Stokes-Einstein relation can be used to predict the diffusivities at higher concentrations. Liquid diffusivities of both PZ and MDEA have been determined in aqueous solutions containing 4.0 mol · dm-3 MDEA and (0, 0.5, and 1.0) mol · dm-3 PZ at a temperature range from (298.15 to 368.15) K. The liquid diffusivities can be estimated by a modified Stokes-Einstein relation.