Hide/Show Apps

Phase equilibria of binary systems with carbon dioxide and carbon dioxide-philic materials

Dumanlılar, Beril.
Phase behavior investigations in supercritical carbon dioxide (scCO2) permit design and development of new and environmentally friendly supercritical fluid processes. Recently polyhedral oligomeric silsesquioxanes (POSS) modified with certain functional groups have been found to be soluble in supercritical CO2. In this thesis, solubilities of methacrylisobutyl POSS (MIBPOSS) and methacrylisooctyl POSS (MIOPOSS) in scCO2 have been studied. In the structure of these molecules, one of the eight branched alkyl chain functionalities attached to the Si atoms of the cage structure has been replaced with a CO2-philic functional group, methacryl, to improve the enthalpic contribution on their solubility. The cloud or dew points were determined using a high-pressure visible cell at the temperature range of 308-323 K, up to 22.1 MPa. The measured highest solubility of MIBPOSS was 0.006 mol fr. at 323 K and 16.8 MPa, while it was 0.0017 mol fr. at 323 K and 22.1 MPa for MIOPOSS. Both MIBPOSS and MIOPOSS exhibit higher solubilities in scCO2 compared to their counterparts with single type of functionality, octaisobutyl POSS, isooctyl POSS and methacryl POSS. The solubility data were modeled by using six different density-based semi-empirical models, all of which give good correlations. One interesting feature that was observed in the phase behavior studies of the MIBPOSS-CO2 binary system was pressure-induced melting temperature (MT) depression of POSS. The maximum measured decrease in the MT was 77 K degrees under the CO2 pressure of 4.8 MPa. Beside these studies, a model was developed to predict the MT depression of various CO2-philic aromatic molecules including naphthalene, biphenyl and 1, 3, 5-tri-terbutylbenzene (TTBB) in CO2, which sufficiently predicted their MT depression behavior.