Effect of MDEA degradation products on foaming behavior and physical properties of aqueous MDEA solutions

This study has been carried out to investigate the foaming behavior of aqueous methyldiethanolamine (MDEA) in presence of N,N,N-tris-(hydroxyethyl) ethylenediamine (THEED), hydroxyethyl ethylenediamine (HEED), N,N′-bis-(hydroxyethyl) piperazine (bHEP), N,N-bis-(2-hydroxyethyl) glycine (bicine), acetic acid and octanoic acid. This foaming study was combined with physical characterization of the tested solution to enhance the understanding of the foaming behavior. The foaming tendency of aqueous MDEA solution was reported in terms of foam volume. Foam stability was reported on the basis of the time required for the last bubble to break. The effect of THEED, HEED, bHEP, bicene, acetic acid and octanoic acid on solution physical properties i.e., density, surface tension and viscosity were studied. The results of this study showed that the addition of 5 ppm of THEED increased the foam volume by about 17% and the foam stability by about 180%. The addition of 5 ppm of HEED increased the foam volume by about 20% and the foam stability by about 222%. The bHEP and bicene showed minor effect on foam volume, however, bHEP and bicine have immense influence in increasing foam stability. Octanoic acid has much more influence in increasing the foam volume and breaking time than the acetic acid. The addition of THEED, HEED, bHEP, bicine, acetic acid and octanoic acid increased solution viscosity. THEED, HEED, bHEP and bicine increased solution surface tension and did not affect solution density. The addition of 0.8 wt% of octanoic acid decreased the surface tension by about 7.3% and slightly increased the solution density. Finally, a mathematical model on drainage of foaming was proposed to understand the parametric effects behind the foam breaking of aqueous MDEA solutions.