Effect of potassium thiocyanate on the phase diagram of Methyl Ethyl Ketone + secondary Butyl Alcohol + Water: Search for the Quadruple Critical Point

• Published in: Journal of molecular liquids 2019-12, Vol.296, p.111776, Article 111776
• Main Authors: Naseer, A.P., Madhavan Unni, P.K.
• Format: Article
• Language: English
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2019.111776

The effect of addition of small amounts of the ionic impurity Potassium Thiocyanate (KSCN) on the tunnel-like region in the phase diagram of Methyl Ethyl Ketone (MEK) + secondary Butyl Alcohol (sBA) + Water (W) is investigated in detail. The KSCN weight fraction range, 0 ≤ XKSCN ≤ 0.0318, results in a systematic decrease in the diameter of the critical-tunnel from ΔT = 71.416 K at XKSCN = 0, to ΔT = 5.275 K at XKSCN = 0.0315. For 0.03190 ≤ XKSCN ≤ 0.03195 the line of critical points end abruptly at specific values of water weight fractions (XW) resulting in the formation of several critical end points. For XKSCN ≥ 0.0320 the critical-tunnel splits into several pairs of parabolic critical lines, each carrying double critical points (DCPs) at their vertices, with one-phase region in-between. The distance between the DCPs corresponding to the low- and high-MEK regions can be made to approach or recede from each other depending on the KSCN weight fraction. The QCP in this system is pushed into a hypothetical region due to curvature effects of the coexistence surface in MEK + W + sBA + KSCN. •Phase diagram of Methyl Ethyl Ketone + secondary Butyl Alcohol + Water + KSCN.•Search for Quadruple Critical Point.•Several DCPs and Critical End Points seen in the system.•Distance between DCPs tunable using the weight fraction of KSCN.•Phase diagram explained on the basis of unusual solvation dynamics shown by KSCN.