Chair:

Dr. Lei Li, Chemical and Petroleum Engineering Department, University of Pittsburgh

Committee:

Dr. Susan Fullerton, Chemical and Petroleum Engineering Department, University of Pittsburgh

Dr. Sachin Velankar, Chemical and Petroleum Engineering Department, University of Pittsburgh

Dr. Haitao Liu, Chemistry Department, University of Pittsburgh

Title: “Enhanced Liquid-liquid Separation via Surface Engineering”

Abstract: Liquid-liquid separation is critical to the chemical industry in general. Application and adoption of intensified process design and 3D-printing offer the prospect of revolutionizing the separation. A device that takes the advantage of potential reduced size, increased scalability of equipment, and process intensification through faster extraction and phase separation at a lower energy cost could be highly amenable towards modular chemical manufacturing. In this work, we have studied both miscible liquid-liquid extraction and immiscible oil/water separation processes.

Supported liquid membranes (SMLs) are very promising in separating miscible liquid-liquid mixtures, though the poor durability due to the loss of liquid phase is a major concern. In current work, ionic liquids (ILs) with high stability have been impregnated into polyvinylidene fluoride (PVDF) membranes to separate miscible benzene-heptane mixture. The two-imidazolium based ILs, i.e., 1-Butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) and 1-butyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate ([BMIM][FAP]), were tested. Both ILs show successful separation within 48 hours. The stability of IL in SILMs has also been investigated via multiple separation cycles. The SEM, weight change of SILM and separation results indicate that the separation efficiency of [BMIM][PF6] SILM does not degrade for up to 144 hours. The SILM has been further optimized with curvature design (i.e., curved SILM) to increase the interfacial area and thus increase the separation throughput, where the curved SILM separation device was 3D-printed. The findings here have important implications on design and application of SILMs in separating miscible liquid-liquid mixtures.

As for oil/water separation, based upon a 3D printed separation device driven by Laplace pressure gradient, we have developed a surface coating, i.e., hydrophobic/oleophilic alkylsilane, to improve the separation efficiency. Chloro(dodecyl)dimethylsilane solution was reacted with -OH groups on the device surface to achieve chemically crafted alkylsilane. Water contact angles (WCA) of ~102 degrees and hexadecane contact angles (HCA) of ~3 degrees were achieved. Compatibility of the coating with various solvents have been demonstrated by immersion tests in different solvents. The separation results also show that the coating increases the separation efficiency.

Our research shows promising results and has important implications in liquid-liquid extraction and oil/water separation.