Erdogan Kiran

High-pressure viscosity and density of n-alkanes

High-pressure viscosities and densities of n-butane, n-pentane, n-hexane, and n-octane have been measured with a specially designed falling cylinder viscometer. Data cover the pressure range from 10 to 70 MPa at temperatures from 310 to 450 K. When the viscosity is plotted as a function of density, the data at all temperatures and pressures are shown to reduce to a single curve for each alkane. An exponential relationship of the form η = B1 x exp(B2xρ) + B3 is used to describe the density dependence of viscosity. The logarithmic viscosity of the alkanes changes linearly with the inverse temperature at all pressures. The density shows a linear dependence on temperature.

Miscibility, density and viscosity of poly(dimethylsiloxane) in supercritical carbon dioxide

Abstract Phase boundaries, densities and viscosities of solutions of poly(dimethylsiloxane)s (PDMS) in supercritical carbon dioxide have been determined. The demixing pressures of 5 wt% solutions of PDMS of different molecular weights (Mw = 38 900, Mw//Mn = 2.84; MwMn= 93 700, Mw/Mn = 2.99; Mw = 273 500, Mw/Mn = 2.29; Mw = 369 200, Mw/Mn/Mn= 2.19) were determined in the temperature range from 300 to 460 K. At temperatures above 330 K the solutions show typical lower critical solution temperature behaviour and the demixing pressures increase with temperature. Below 330 K, the behaviour is reversed, and demixing pressures show a dramatic increase with decreasing temperature. The phase boundaries and the steep changes in the demixing pressures with temperature are discussed in the framework of the Sanchez—Lacombe model. Evaluation of the demixing pressures along with information on the details of molecular weight distributions obtained by gel permeation chromatography show that the observed demixing pressures are very much influenced by the high-molecular-weight tails of the distributions. Analysis of the density and viscosity data for solutions of PDMS with Mw = 38 900 at 1, 2 and 5 wt% concentrations show that results can be correlated with a free-volume based relationship of the form η = A expB/1 - Cp)]. Analysis of the pressure dependence of viscosity at selected temperatures shows that the apparent activation volumes are in the range of 30 to 60 cm3 mol−1. Analysis of the temperature dependence at different pressures gives activation energies in the range 7–10 kJ mol−1.

Modeling polyethylene solutions in near and supercritical fluids using the sanchez-lacombe model

Abstract Effectiveness of the Sanchez-Lacombe model in predicting the high pressure phase behavior of solutions of polyethylene standards of molecular weights 2,150, 16,400, 108,000, and 420,000 in n-pentane and n-pentane-carbon dioxide binary solvents has been evaluated. It is shown that by proper adjustment of the characteristic temperature for the polymer, which is achieved by using data for one molecular weight sample, variations with respect to concentration and pressure are correctly predicted. The model correctly predicts also the solvent-dependent shift from LCST (Lower Critical Solution Temperature) to UCST (Upper Critical Solution Temperature) type behavior for these solutions upon increase in, the carbon dioxide content of the n-pentane-carbon dioxide binary solvent.

Miscibility, phase separation, and volumetric properties in solutions of poly(dimethylsiloxane) in supercritical carbon dioxide

Miscibility conditions and volumetric properties of solutions of poly(dimethylsiloxane) in supercritical carbon dioxide have been determined as a function of polymer molecular weight, polymer concentration, temperature, and pressure. Measurements have been conducted in a variable volume view cell equipped with an LVDT sensor to identify the position of a movable piston and thus the internal volume of the cell and consequently the density of the solution at a given pressure and temperature. The demixing data (in the form of P-T curves for a given concentration, or as P-x diagrams at a given T) and the density isotherms are presented for solutions of two polymer samples with different molecular weights (Mw = 38,600; Mw/Mn = 2.84 and Mw = 94,300; Mw/Mn = 3.01) at several concentrations in the range from 0.05 to 10 mass % over a temperature range from 302–425 K. Solution densities corresponding to the demixing points also have been identified. Representation of the demixing densities on the density isotherms, i.e., pressure-density plots is a new methodology that gives a direct assessment of the volumetric expansion the solution must undergo before phase separation. The temperature–composition diagrams generated at selected pressures show that the poly(dimethylsiloxane) + CO2 solutions display both lower critical solution and upper critical solution type behavior. The lower critical solution temperature moves to lower temperatures and the upper critical solution temperature moves to higher temperatures with decreasing pressure and they eventually merge together at lower pressures forming an hourglass-shaped region of immiscibility. This behavior is linked to the solvent quality of supercritical carbon dioxide that changes with pressure.

A new experimental system to study the temperature and pressure dependence of viscosity, density, and phase behavior of pure fluids and solutions

Abstract A new apparatus which has been designed to determine viscosity, density, and phase behavior in pure fluids or mixtures is presented. The measurements can be conducted from atmospheric conditions up to 70 MPa and 473 K. Using this apparatus, density and viscosity for n-hexane and n-octane have been measured and the results have been compared with the literature values as a function of pressure from about 7 to 70 MPa at temperatures 323, 348, 373, 398, 423, and 448 K. The densities are observed to be measurable with an accuracy better than ±1% and viscosities with an accuracy better than ±5%.

Polymer Formation, Modifications and Processing in or with Supercritical Fluids

Essential characteristics of chain molecules, their formation, properties and processing aspects are presented with a special focus on solvent dependent features. How supercritical fluids with their tunable characteristics can be put into use as the process or processing solvents in various stages of polymer formation, purification, modification, fabrication, recovery and recycling is discussed. Thermodynamic aspects of polymer solubility and the effects of various factors such as the polymer type, molecular weight and molecular weight distribution, concentration, solvent type, temperature and pressure on the solubility of polymers in supercritical fluids are presented. Modeling of polymer solutions at high pressures with lattice fluid (Sanchez-Lacombe) and perturbation (SAFT) methods is reviewed and their effectiveness is compared. The question of kinetics of phase separation is addressed and a new technique which permits repetitive penetration into the metastable and unstable regions of a polymer-solvent system by multiple slow- or rapid (at rates approaching 1000 MPa/s) pressure drops is described.

High-pressure extraction and delignification of red spruce with binary and ternary mixtures of acetic acid, water, and supercritical carbon dioxide

Abstract High-pressure extractions and delignification of red spruce have been carried out using acetic acid-water, acetic acid-carbon dioxide, and acetic acid-water-carbon dioxide mixtures. Effect of solvent composition (from 0 to 100% acetic acid), pressure (from 1.4 to 25 MPa), temperature (from 120 to 180 °C), and extraction time (from 0.5 to 3 h) has been studied. Extent of delignification has been determined by chemical (acid insoluble fraction), spectroscopic (FTIR), and microscopic (SEM) evaluations. With acetic acid-water binary mixtures containing 73 mol % (90 vol %) acetic acid, high delignification levels (in the range from 70 to 95%) were achieved with relatively high yields (60 to 50%, respectively). The physical properties of the pulp obtained with this mixture were comparable to conventional pulps. Breaking length and burst index were around 7.8 km and 4.3 kPa m 2 g −1 , respectively. In extractions with acetic acid-carbon dioxide and acetic acid-water-carbon dioxide mixtures, extent of dissolution and delignification levels were, however, lower.

High-pressure light scattering apparatus to study pressure-induced phase separation in polymer solutions

A new high-pressure time- and angle-resolved light scattering apparatus has been developed to study the kinetics of phase separation in polymer solutions and other fluid mixtures under pressure at near- and supercritical conditions. The system consists of a high-pressure polymer loading chamber, a solvent charge line, a variable-volume scattering cell (with a built-in movable piston connected to a pressure generator, and an expansion rod driven by an air-actuated diaphragm), and a recirculation pump which are all housed in a temperature-controlled oven. The system is operable at pressures up to 70 MPa, and temperatures up to 473 K. The scattering cell is a short path-length cell made of two flat sapphire windows that are separated by 250 μm. It is designed to permit measurements of transmitted and scattered light intensities over an angle range from 0° to 30°. A linear image sensor with 256 elements is used to monitor the time evolution of the scattered light intensities at different angles. With this sen...

Solubility of polyethylene in n-pentane at high pressures

Abstract The high pressure solubility of polyethylene standards (Mw = 2100, 16400, 108000 and 420000 and M w M n = 1.14, 1.16, 1.32 and 2.66, respectively) in n-pentane has been studied. Concentrations of up to 15 wt% polymer have been investigated. For each polymer sample and concentration, pressures that are required to achieve single-phase solutions have been determined over a range of temperatures. The solutions are found to all show lower critical solution temperatures. Demixing pressures are observed to depend strongly on the molecular weight of the polymer.

Miscibility, density and viscosity of polystyrene in n-hexane at high pressures

Abstract The demixing pressures, densities and viscosities of solutions of nearly monodisperse polystyrene samples ( M w / M n n -hexane have been determined. Measurements were conducted with samples of different molecular weights ( M w = 4000–50 000) at concentrations up to 8 mass% over a pressure range from 5 to 70 MPa and a temperature range from 323 to 423 K. The demixing pressures were observed to increase with molecular weight (from about 10 MPa for M w = 4000 to 50 MPa for M w = 50 000) and show high sensitivity to temperature (Δ P /Δ T being about −1 MPa°C −1 ) in the range investigated. Density and viscosity data were collected in the one-phase homogeneous regions, and viscosity was correlated with an equation of the form η = A exp{ B /(1 − V 0 ρ ), which is based on the free-volume considerations. For a given system, the viscosities increase with solution density (or pressure). At a fixed solution density, viscosity increases with polymer concentration or molecular weight. Depending upon the system, viscosities have ranged from 0.15 to 0.45 mPa s. Flow activation volumes and flow activation energies were about 40 cm 3 mol −1 and 6 kJ mol −1 , respectively. The demixing and viscosity data have been also compared with the results obtained in n -butane and n -pentane for one sample ( M w = 9000). In going from n -butane to n -hexane, the demixing pressures decrease while the viscosities become higher.