Mark C. Thies

Ternary phase equilibria for acetic acid-water mixtures with supercritical carbon dioxide

Abstract Ternary phase equilibrium data are presented for acetic acid-water mixtures with supercritical carbon dioxide at temperatures of 313 and 323 K and pressures of 73, 104 and 139 bar. Selectivities and distribution coefficients were obtained from these data and are also reported. Results indicate that supercritical carbon dioxide is not a suitable solvent for acetic acid-water separations. An experimental flow apparatus equipped with a view cell was used to obtain the experimental measurements. Limited phase equilibrium data for the binary systems water-carbon dioxide and acetic acid-carbon dioxide at 323 K and pressures from 56 to 177 bar are also presented.

MALDI-TOF mass spectrometry: Obtaining reliable mass spectra for insoluble carbonaceous pitches

Abstract The insolubility of high molecular weight (MW) carbonaceous pitches (e.g. mesophases) in even aggressive solvents has always been a significant obstacle to their MW characterization. By using matrix-assisted, laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry with the matrix 7,7,8,8-tetracyanoquinodimethane (TCNQ), we are now able to obtain reproducible, highly resolved mass spectra for insoluble pitches. A solvent-free sample preparation technique was developed in which the matrix and pitch sample are combined and ground together to form a fine powder. We then use the high surface tension of water to create a thin uniform coating of the matrix–pitch mixture on the target cell. Laser power and pulsed ion extraction delay were both found to significantly alter the spectra obtained, and a procedure for optimizing each is described. Three carbonaceous pitches were evaluated: an anthracene pitch produced by thermal polymerization, a petroleum pitch similar to A-240 and produced by heat-soaking decant oil, and a high MW cut of this pitch produced by supercritical extraction. The anthracene pitch contained enough lower MW species to serve as a self-matrix, so no TCNQ addition was required. For the high MW cut of petroleum pitch, the use of TCNQ or dithranol revealed the presence of trimers and tetramers at MWs up to 1250 Da.

Fluid phase equilibria and critical phenomena for the dodecane-water and squalane-water systems at elevated temperatures and pressures

Abstract Stevenson, R.L., LaBracio, D.S., Beaton, T.A. and Thies, M.C., 1994. Fluid Phase Equilibria and critical phenomena for the dodecane-water and squalane-water systems at elevated temperatures and pressures. Fluid Phase Equilibria 93; 317-336. Vapor-liquid and liquid-liquid equilibrium compositions and critical points were measured for the dodecane-water and squalane-water systems at temperatures from 600 to 660 K and pressures up to 310 bar. A continuous-flow apparatus was used for these high-temperature measurements to minimize thermal decomposition of the hydrocarbons of interest. Both systems were found to exhibit Type III phase behavior with the critical curve that starts from the critical point of water passing through both temperature and pressure minima before extending to higher pressures. A limited number of liquid-liquid equilibrium compositions are also reported for the benzene-water system at temperatures from 472 to 523 K.

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.

Phase equilibrium modeling of mixtures of long-chain and short-chain alkanes using Peng–Robinson and SAFT

Abstract Peng–Robinson and selected implementations of the Statistical Associating Fluid Theory (SAFT) equation of state (EoS) were evaluated for their ability to correlate and predict vapor–liquid equilibrium for highly asymmetric mixtures of n-alkanes. Peng–Robinson is surprisingly accurate for fitting such mixtures, but only if the pure component parameters are regressed with vapor pressure and liquid density data, as is normally done with SAFT. Furthermore, these parameters were found to be well-behaved and to increase monotonically with carbon number. In spite of its deficiencies in modeling the near-critical and critical regions, PC-SAFT is recommended for predicting the phase behavior of asymmetric mixtures of n-alkanes for which no data are available. For example, with a binary interaction parameter of zero, PC-SAFT accurately predicts liquid-phase compositions for n-alkane mixtures of C6+C16, C6+C24 and C6+C36 over a wide range of temperatures and pressures.

Fractionation of petroleum pitch by supercritical fluid extraction

Abstract Petroleum pitch has considerable potential as an inexpensive raw material for the economical production of high-performance carbon fibers and carbon-carbon composites. However, current methods for pretreatment of the pitch have several deficiencies that result in inferior fiber and composite properties. A better separation process is needed to improve the reproducibility and quality of the mesophase pitch precursor. A supercritical fluid extraction process is being investigated for this purpose. A flow apparatus is described for measuring phase equilibrium data for mixtures of solvent and pitch at temperatures up to 675 K and pressures to 350 bar. Equilibrium phase compositions are reported for the toluene/Ashland A-240 pitch system at temperatures of 595, 634, and 674 K and pressures ranging from 29 to 76 bar. The molecular weight distributions of the extracted fractions show that the process is effective in separating pitch fractions by molecular weight.

Carbon fibers from mixtures of AR and supercritically extracted mesophases

Abstract Mixtures of two mesophase pitches derived from different raw material sources were investigated for producing high-performance carbon fibers. In particular, a high-melting, supercritically extracted (SCE) mesophase that was hard to spin but produced fibers with excellent properties was combined with AR mesophase, a relatively low-melting material. Mixtures of the SCE and AR mesophases ranging from 25 to 75% SCE were melt-spun into fiber form. The addition of 25% AR to the SCE mesophase dramatically improved its spinnability to the point that fiber yields were similar to those obtained for 100% AR. Surprisingly, fibers produced from the mesophase mixtures all stabilized more rapidly than those produced from either of the pure mesophases, with the fastest weight gain being obtained for the 25% SCE–75% AR mixture. DRIFTS was used to follow the stabilization reactions and confirmed these results. In general, final fiber properties of the mesophase mixtures were also superior to those of the pure mesophases. For example, significant improvements in both the thermal conductivity and Young’s modulus of AR mesophase were obtained with the addition of 25% SCE mesophase.

Control of mesophase pitch properties by supercritical fluid extraction

Abstract Supercritical fluid (SCF) extraction has been used to fractionate an isotropic petroleum pitch and produce a number of pitch fractions, many of which contain 100% mesophase. Toluene was used as the supercritical solvent, and experiments were carried out in a region of liquid-liquid equilibrium that exists for mixtures of pitch and toluene above the critical pressure of toluene. A central composite design was used to investigate the effects of the operating variables of temperature, solubility parameter and solvent-to-pitch ( S P ) ratio on the yield and softening point of the produced mesophase pitch fractions. Temperatures, pressures and S P ratios from 310 to 360 °C, 45 to 155 bar and 2.5 to 4.0, respectively, were investigated. Using the developed statistical models, the effect of operating variables on softening point and mesophase yield can be quantitatively predicted. Chemical analyses of the mesophases by elemental analysis and DRIFT indicate that the extraction process can also be used to alter the chemical composition (e.g. the degree of alkyl substitution) of the produced mesophases. The flexibility of SCF extraction for processing pitches is illustrated by the fact that one can change the operating temperature and pressure and still maintain a constant mesophase yield or softening point.

As-spun orientation as an indication of graphitized properties of mesophase-based carbon fiber

A 100% mesophase produced by supercritical fluid extraction was melt-spun into roundshaped fibers. The spinning temperature was allowed to vary while all other spinning conditions were held constant. The as-spun preferred orientation of the graphene basal planes with respect to the fiber axis was found to change as a result of a change in the spinning temperature. As-spun fibers that had developed a high degree of preferred orientation after spinning were found to have a high degree of preferred orientation, low d(0002)-spacing, and large crystallite size after graphitization. Also, as-spun fibers with a high degree of preferred orientation were found to have high modulus and low electrical resistivity after heat treatment. Scanning electron microscopy results indicate that, regardless of spinning temperature, all fiber sets exhibit a radial-folded transverse texture.

High charge-capacity polymer electrodes comprising alkali lignin from the Kraft process

Advances in materials chemistry are necessary for low-cost energy storage to support energy generation from renewable sources and electric transportation. Renewable biopolymers, such as sodium lignosulfate (SLS), have attracted interest for electrodes when mixed with conducting polymers due to their higher charge-capacity and natural abundance. The availability of SLS is limited and will continue to decrease, while alkali lignin (AL), which accounts for 98% of lignin from paper-pulping, exhibits poor solubility in acidic electrolytes used for electropolymerization of conducting polymers. Here, we utilize organic acid solvents to overcome processing limitations in order to synthesize electrodes comprising polypyrrole (PPy) and SLS. Compared to PPy/SLS, electrodes containing PPy/AL exhibit an increase in capacitance from 312 F g−1 to 444 F g−1, and a decrease in relaxation time constant from 1.7 to 1 s. Furthermore, we showed that the electrochemical performance of PPy/AL electrodes could be further increased by incorporating AL with higher phenolic content that is obtained from an elevated-temperature, pH-driven fractionation process.