Date

2018-09-01

Author

Dumanlılar, Beril
Dilek Hacıhabiboğlu, Çerağ

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Solubility and phase behavior investigations of novel materials in supercritical carbon dioxide (scCO2) permit design and advancement of new and environmentally friendly supercritical fluid processes. Supercritical carbon dioxide (scCO2) is called as a green solvent because it is non-toxic, non-flammable, inexpensive, and abundant. Its use in a process instead of an organic solvent can eliminate the emissions of volatile organic components. Also, due to its nonpolar structure,it can dissolve nonpolar molecules with small molecular weight. On the otherhand, due to its quadrupole moment, it also exhibits specific interactions such as Lewis acid-base with some substances functionalized with certain polar groups, strong enough to dissolve them. Poly (methyl methacrylate) and sugar acetates are among those substances which can interact with scCO2 becauseof their carbonyl groups and be dissolved in scCO2. Certainmaterials such as poly (dimethyl siloxane) (PDMS) which have flexible siloxanegroups can also dissolve in scCO2. In this study, our investigationon the phase behavior of polyhedral oligomeric silsesquioxanes (POSS)-CO2binary systems are continued with different chemical structures of POSS.Earlier, the solubility of various POSS, which are trifluoropropyl, octamethyl,metacryl, isooctyl and octaisobutyl POSS, in scCO2 were studied[1,2]. All of these components were found to be soluble in scCO2,with different levels of solubility, except octamethyl POSS. The commoncharacteristic property of these molecules was that all the functional groupsattached to the Si atom of a certain POSS were identical. However in thisstudy, we report the phase behavior of methacrylisobutyl POSS (MIBPOSS) and methacrylisooctylPOSS (MIOPOSS) with CO2, both of which have two different functional groups intheir chemical structures. High pressure view cell was used to measure the cloudor dew points at the temperature range of 308-323 K, up to 22 MPa. The measuredhighest solubility was exhibited by MIBPOSS, which was 0.006 mol fr. at 323 Kand 16.82 MPa. The solubility of POSS in scCO2 increases with increasingpressure for both POSS at the isothermal conditions. At the isobaric conditions,solubility decreases with increasing temperature due to the decreasing densityof the solvent. On the other hand, at constant CO2 density,solubility of POSS in scCO2 increases with increasing temperaturepossibly due to the increasing vapor pressure of the solutes. An interestingsolubility behavior was observed, which was that the dual functionality allowsboth POSS molecules attain a higher solubility in scCO2 compared to theircounterparts with single functionality. This shows that the entropiccontributions dominate the solubility of the double functional POSS moleculesin scCO2. Due to the lack of the information on the criticalproperties or group contribution constants of these molecules, the solubilitydata was modeled using density-based semi-empirical models, which predicted thesolubility of these molecules in scCO2 with a maximum absoluteaverage relative deviationof 7%.

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https://hdl.handle.net/11511/75977

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