Thermal effects in polytetrafluoroethylene at high hydrostatic pressures

The temperature changes as a result of rapid hydrostatic pressure applications are reported for polytetrafluroethylene (PTFE, Teflon) in the reference temperature range from 294° to 381°K and in the pressure range from 13.8 to 200 MN/m². The thermal effects were found to be higher at the reference temperature approximating the transition temperatures of 19° and 30°C than at higher reference temperature. The data were analyzed by determining the predicted thermoelastic coefficients derived from the Thomson equation (?T/?P = αT/ρC_p). A curvefitting analysis showed that the empirical curve, (?T/?P) = ab(ΔP)^b?1, described the experimental thermoelastic coefficients obtained from the experiments. The fact that no agreement was found between the predicted and the experimental coefficients is due to the physical changes in PTFE at the transition temperatures. The relationship between the thermal effects and the chain molecular motion is discussed by including dynamic mechanical analysis and differential scanning calorimetry DSC measurements for the PTFE samples.     

Thermal effects in styrene-butadiene rubber at high hydrostatic pressures

The temperature changes as a result of rapid hydrostatic pressure applications are reported for unvulcanized styrene-butadiene rubber (SBR) in the reference temperature range from 292 to 405 K and in the pressure range from 13.8 to 200 MN m⁻². The thermal effects were found to be a function of pressure and temperature. A curve fitting analysis showed that the empirical curve (∂T/∂P)=ab(ΔP)^b−1, described the experimental thermoelastic coefficients obtained from the experiments. The data were analysed by determining the predicted thermoelastic coefficients derived from the Thomson equation (∂T/∂P)=T_o/C_p. The experimental and the predicted Grüneisen parameter γ_T were also estimated. Close agreement was found at low pressure but differences were observed at higher pressures between the experimental and expected values for the thermoelastic coefficients and the Grüneisen parameter.     

Thermal dissociation of Ca(OH)2 at elevated pressures

The equilibrium Ca(OH)₂ ? CaO+H₂O has been studied at pressures of steam up to 50 bars and at temperatures of up to 800° C. The dissociation pressures determined are in agreement with the data derived by some previous workers at pressures of less than one bar but they conflict with data published for higher pressures. The results can be expressed by the relation over the range 530–800°c.     

Thermal effects in poly(hexamethylene adipamide) and polyoxymethylene at high hydrostatic pressures

The dynamic mechanical properties, transition behavior, and morphology of polycarbonate (PC)-polyurethane (PU) semi-interpenetrating polymer networks (semi-IPNs) and linear blends were studied by means of Rheovibron, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). Two glass transition temperatures corresponding to polycarbonate and polyurethane were observed and microphase separation was further evident with TEM. In PC/PU semi-IPNs, two glass transition temperatures were shifted inwardly indicating that the interpenetrating network of polyurethane increases the mutual miscibility of PC and PU. The average phase domain was 500Å in semi-IPNs and the phase domains were in the range 1000–6000 Å in linear blends of the corresponding polymers. The compatibilities of PC and PU were greatly influenced by the molecular weight of polyols in PU prepolymer and the ratio of NCO/OH; lower molecular weight polyols and higher NCO/OH ratio resulted in better compatibility, and finer phase domains in PC and PU linear blends and semi-IPNs.     

Minimum fluidization velocity at elevated temperatures and pressures

A procedure based on the Ergun equation to predict the minimum fluidization velocity at elevated temperatures and pressures and for different gaseous fluidizing agents has been discussed and shown to be applicable for practical purposes.     

Fuel effects on diffusion flames at elevated pressures

This study addresses the influence of elevated pressures up to 1.6 MPa on the flame geometry and the flickering behavior of laminar diffusion flames and particular attention has been paid to the effect of fuel variability. It has been observed that the flame properties are very sensitive to the fuel type and pressure. The shape of the flame was observed to change dramatically with pressure. When the pressure increases, the visible flame diameter decreases. The height of a flame increases first with pressure and then reduces with the further increase of pressure. The cross-sectional area of the flame (A_cs) shows an average inverse dependence on pressure to the power of n (A_cs ∝ P⁻ⁿ), where n = 0.8 ± 0.2 for ethylene flame, n = 0.5 ± 0.1 for methane flame and n = 0.6 ± 0.1 for propane flame. It was observed that the region of stable combustion was markedly reduced as pressure was increased. High speed imaging and power spectra of the flame chemiluminescence reveal that an ethylene flame flickers with at least three dominant modes, each with corresponding harmonics at elevated pressures. In contrast methane flames flicker with one dominant frequency and as many as six harmonic modes at elevated pressures.     

Kinetics of coal char gasification at elevated pressures

The effects of temperature, pressure, steam flow rate and CO₂/H₂O ratio of gasifying agent on the pressurized gasification of Linnancang coal char were investigated. A correlation of kinetic data was developed for coal chars from coals of different ranks at 30 kg cm ⁻² and 950 °C. The catalytic effects of Ca, Na and Fe catalysts on the gasification activity, activation energy and methane recovery were studied.     

Solubility of methane in glycols at elevated pressures

The solubility of methane in ethylene glycol and in diethylene glycol has been determined at temperatures in the range 25 to 125 °C at pressures up to 20.4 MPa. The experimental results were correlated by the Peng-Robinson (1976) equation of state, and interaction parameters have been obtained for these systems. Henry's constants were derived for comparison with data from the literature.     

Dense phase viscosities of fluidised beds at elevated pressures

The dense phase viscosities of gas-fluidised beds have been measured at pressures up to 20 bar by a falling-sphere technique. Glass powders of mean sizes 64, 101 and 475 μm were fluidised by carbon dioxide or nitrogen. An increase in gas pressure leads to a substantial decrease in the viscosity of the fine powder when fluidised but the viscosity of fluidised beds of powders larger than about 100 μm is almost independent of pressure. The implications of the experimental observations on the stability of bubbles in high-pressure fluidised beds are discussed.     

The catalytic dealkylation of alkyl phenols at elevated pressures

The most successful catalysts previously used in atmospheric pressure experiments were screened for their suitability for hydrodealkylation of o-cresol at elevated pressures. Active charcoal was easily the best, while coke functioned well at higher temperatures, with soda-lime and zinc fluoride on alumina notably less successful; the last named gave rise to a high yield of non-phenolic compounds. Active charcoals from various sources were compared under standard conditions in the hydrodealkylation of o-cresol at 50 atm, and the best two grades were used successfully to dealkylate high boiling acids tar acids derived from low temperature carbonisation of coal. These gave high yields of dealkylated phenols, and unchanged feed stock was recycled such that in two passes 90% of the feed reacted to give over 25 % phenol and cresols. The catalytic activity of the charcoals waned slowly and irreversibly under reaction conditions, and attempts to combat this by alteration of reaction variables and use of impregnating agents only effected marginal improvements.     

Activated diffusion of methane from coals at elevated pressures

Diffusion of methane from three coals ranging in rank from anthracite to HVA bituminous has been studied at initial methane pressures up to about 2.76 MPa (400 psi). Unsteady-state diffusion conditions existed, the methane pressure within the coal particle decreasing with time while the methane pressure outside the particles remained at atmospheric. The diffusion parameter $\text{D}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{r}{}_0$ increased with increasing methane concentration at high values of methane sorption. Diffusion was activated but the exact magnitude of the activation energy is uncertain owing to the suspected contribution of the heat of sorption to the temperature coefficient. $\text{D}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{r}{}_0$ increased with decreasing particle size of coal studied, but r₀ is clearly less than the particle radius.     

Optical rotation of dilute aqueous xanthan solutions at elevated hydrostatic pressure

The optical rotation of dilute aqueous xanthan solutions of ultrasonically depolymerized xanthan have been measured in the pressure range from 0.1 to 50 MPa. This was achieved using a high-pressure cell in a spectropolarimeter of original design. The conformational melting temperature T_m of xanthan was found to decrease with increasing pressure. The pressure coefficients of the melting temperature at constant ionic strengths, I, was found to be (ΔT_m/Δp)_I = ?(9.5 ± 4.0) 10^?8 K Pa^?1 and (ΔT_m/Δp)_I = ?(20 ± 10) 10^?8 K Pa^?1 for solution ionic strengths of 10 mM NaCl and 25mM NaCl, respectively. The largest shift in T_m of xanthan for an increase in hydrostatic pressure from 0.1 to 50 MPa is less than ?10 K. The observed decrease in conformational transition temperature can have significant implications when xanthan is used in polymer or micellar flooding processes in high-salinity, high-temperature oil reservoirs where the reservoir temperature is close to the structural transition temperature at ambient pressure.     

Vapor-liquid equilibrium behavior for the propane-acetone system at elevated pressures

The vapor-liquid phase behavior of the propane-acetone system under equilibrium conditions has been established experimentally at 325, 350, 375, 400 and 425 K. Under these conditions pressures up to 4666.4 kPa (676.8 psia) were obtained. The composition of the vapor and liquid phases in equilibrium, in conjunction with data available in the literature for the critical state behavior of this system, has permitted the establishment of the complete vapor-liquid equilibrium behavior of the propane-acetone system for temperatures ranging from 325 K up to the critical temperature of acetone (T_c = 508.1 K). The K-constants resulting from this experimental study when related to pressure produced isothermal relationships that follow a normal behavior and which do not exhibit any azeotropic tendencies.     

The boiling-point relations of cadmium and zinc at elevated pressures

The boiling points of cadmium and zinc have been determined at elevated pressures by means of an internally heated pressure vessel, used in conjunction with argon as the pressure medium. Vapour pressure-temperature relations have been derived for cadmium in the pressure range 1—103.5 atmospheres and for zinc in the range 1—30.2 atmospheres; heats of vaporisation have been calculated for these metals from these relations. Unusual crystallisation phenomena are exhibited by the condensed droplets of the metals.