Viscosity Measurements of Two Potential Deepwater Viscosity Standard Reference Fluids at High Temperature and High Pressure

This paper reports high-pressure viscosity measurements for Krytox GPL 102 lot K2391 and tris­(2-ethylhexyl) trimellitate (TOTM). These two viscous liquids have recently been suggested as potential deepwater viscosity standard (DVS) reference fluids for high temperature, high pressure viscosity studies associated with oil production from ultradeep formations beneath the deepwaters of the Gulf of Mexico. The measurements are performed using a windowed, variable-volume, rolling-ball viscometer at pressures between 7 and 242 MPa and temperatures between 314 and 527 K with an expanded uncertainty of 3% at a 95% confidence level. The viscosity results are correlated using an empirical temperature/pressure-dependent function and a modified Vogel–Fulcher–Tammann (VFT) Equation. The present viscosity data for TOTM and Krytox GPL 102 lot K2391 are in good agreement with the available reported data in the literature at lower temperatures and pressures. The viscosity values of TOTM and Krytox GPL 102 lot K2391 are 9.5 mPa·s and 25 mPa·s, respectively, at 473 K and 200 MPa, whereas the desired DVS viscosity value at this condition is 20 mPa·s. Although the viscosity of Krytox GPL 102 lot K2391 is closer to the targeted value, a comparison of the present viscosity results with data obtained for lot K1537 indicates a very large lot-to-lot variation of the viscosity for this polydisperse perfluoropolyether oil, which represents a significant deficiency for a DVS

Small Molecule Cyclic Amide and Urea Based Thickeners for Organic and sc-CO₂/Organic Solutions

A series of cyclic amide and urea materials were prepared and screened as small molecule thickeners for organic solvents, dense CO₂, and mixtures thereof. In addition to a cyclohexane or benzene core, both of which are mildly CO₂-phobic, these molecules contained either ester, amide, or urea groups responsible for establishing intermolecular interactions necessary for increasing solution viscosity. These groups also function to connect siloxane or heavily acetylated CO₂-philic segments to the cyclic core of the thickener molecule. Many of these compounds were shown to thicken conventional organic liquids (e.g., toluene, hexane), usually after heating and cooling the mixture. A propyltris­(trimethylsiloxy)­silane-functionalized benzene trisurea material was also shown to thicken compressed liquid propane and butane. Attaining solubility and self-assembly in CO₂ proved more challenging, however. Several ester, amide, and urea containing compounds were discovered that are soluble in dense CO₂ at low loadings (0.5–2 wt %). For linear siloxane segments, increasing the number of silicon atoms provides greater solubility in dense CO₂. Branched siloxane segments were shown to have superior solubility characteristics in dense CO₂ to linear siloxanes of similar silicon content. However, only the propyltris­(trimethylsiloxy)­silane-functionalized benzene trisurea and trisureas functionalized with varying proportions of propyltris­(trimethylsiloxy)­silane and propyl-poly­(dimethylsiloxane)-butyl groups exhibited remarkable viscosity increases (e.g., 3–300-fold at 0.5–2.0 wt %) in CO₂, although high concentrations of an organic cosolvent (18–48 wt %) such as hexane were required to attain dissolution in CO₂

Effect of Isomeric Structures of Branched Cyclic Hydrocarbons on Densities and Equation of State Predictions at Elevated Temperatures and Pressures

The <i>cis</i> and <i>trans</i> conformation of a branched cyclic hydrocarbon affects the packing and, hence, the density, exhibited by that compound. Reported here are density data for branched cyclohexane (C6) compounds including methylcyclohexane, ethylcyclohexane (ethylcC6), <i>cis</i>-1,2-dimethylcyclohexane (<i>cis</i>-1,2), <i>cis</i>-1,4-dimethylcyclohexane (<i>cis</i>-1,4), and <i>trans</i>-1,4-dimethylcyclohexane (<i>trans</i>-1,4) determined at temperatures up to 525 K and pressures up to 275 MPa. Of the four branched C6 isomers, <i>cis</i>-1,2 exhibits the largest densities and the smallest densities are exhibited by <i>trans</i>-1,4. The densities are modeled with the Peng–Robinson (PR) equation of state (EoS), the high-temperature, high-pressure, volume-translated (HTHP VT) PREoS, and the perturbed chain, statistical associating fluid theory (PC-SAFT) EoS. Model calculations highlight the capability of these equations to account for the different densities observed for the four isomers investigated in this study. The HTHP VT-PREoS provides modest improvements over the PREoS, but neither cubic EoS is capable of accounting for the effect of isomer structural differences on the observed densities. The PC-SAFT EoS, with pure component parameters from the literature or from a group contribution method, provides improved density predictions relative to those obtained with the PREoS or HTHP VT-PREoS. However, the PC-SAFT EoS, with either set of parameters, also cannot fully account for the effect of the C6 isomer structure on the resultant density

Liquids That Freeze When Mixed: Cocrystallization and Liquid–Liquid Equilibrium in Polyoxacyclobutane–Water Mixtures

We show that liquid polyoxacyclobutane −[CH₂–CH₂–CH₂–O]_<i>n</i>– when mixed with water at room temperature precipitates solid cocrystals of the polymer and water. Cocrystals can also be formed by simply exposing the liquid polymer to saturated humidity. This appears to be the only known example of nonreacting liquids combining to form a solid cocrystal, also known as a clatherate, at room temperature. At high temperatures, the same polymer–water mixtures phase separate into two coexisting liquid phases. This combination of cocrystal formation and LCST-type liquid–liquid equilibrium gives rise to an unusual, possibly unique, type of phase diagram

High-Temperature, High-Pressure Volumetric Properties of Propane, Squalane, and Their Mixtures: Measurement and PC-SAFT Modeling

This study reports the high-temperature, high-pressure density data for propane, squalane, and their binary mixtures for five compositions at temperatures to 520 K and pressures to 260 MPa. The density measurements are obtained with a floating-piston, variable-volume, high-pressure view cell. From the density data, the isothermal and isobaric excess molar volumes upon mixing are computed. For the mixture compositions studied here, the excess volume is mostly negative, showing a minimum at 0.6550 mole fraction of propane and becomes less negative as the propane concentration increases. The perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) provides good representation for the experimental data. A mean absolute percent deviation (δ) of 1.4% is obtained with the PC-SAFT EoS when using propane and squalane pure component parameters fit to density data at high-temperature, high-pressure conditions