Effect of isomeric structures of branched cyclic hydrocarbons on densities and equation of state predictions at elevated temperatures and pressures.

The cis and trans 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), cis-1,2-dimethylcyclohexane (cis-1,2), cis-1,4-dimethylcyclohexane (cis-1,4), and trans-1,4-dimethylcyclohexane (trans-1,4) determined at temperatures up to 525 K and pressures up to 275 MPa. Of the four branched C6 isomers, cis-1,2 exhibits the largest densities and the smallest densities are exhibited by trans-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.

Aminosilicone solvents for CO(2) capture.

This work describes the first report of the use of an aminosilicone solvent mix for the capture of CO(2). To maintain a liquid state, a hydroxyether co-solvent was employed which allowed enhanced physisorption of CO(2) in the solvent mixture. Regeneration of the capture solvent system was demonstrated over 6 cycles and absorption isotherms indicate a 25-50 % increase in dynamic CO(2) capacity over 30 % MEA. In addition, proof of concept for continuous CO(2) absorption was verified. Additionally, modeling to predict heats of reaction of aminosilicone solvents with CO(2) was in good agreement with experimental results.

Design and evaluation of nonfluorous CO2-soluble oligomers and polymers.

Ab initio molecular modeling is used to design nonfluorous polymers that are potentially soluble in liquid CO2. We have used calculations to design three nonfluorous compounds meant to model the monomeric repeat units of polymers that exhibit multiple favorable binding sites for CO2. These compounds are methoxy isopropyl acetate, 2-methoxy ethoxy-propane, and 2-methoxy methoxy-propane. We have synthesized oligomers or polymers based on these small compounds and have tested their solubility in CO2. All three of these exhibit appreciable solubility in CO2. At 25 degrees C, oligo(3-acetoxy oxetane)6 is 5 wt % soluble at 25 MPa, the random copolymer (vinyl methoxymethyl ether30-co-vinyl acetate9) is 5 wt % soluble at 70 MPa and random copolymer (vinyl 1-methoxyethyl ether30-co-vinyl acetate9) is 3 wt % soluble at 120 MPa. These oligomers and polymers represent new additions to the very short list of nonfluorous CO2-soluble polymers. However, none of these are more soluble than poly(vinyl acetate), which exhibits the highest CO2 solubility of any known polymer containing only the elements C, H, and O.