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ABSTRACT This paper shows a study about the utilization of recycled aggregates from the construction and demolition wastes. They were used to manufacture concrete kerbs and floor blocks which are [...]

Processing polymer blends in the presence of high-pressure carbon dioxide (CO2) affords numerous advantages over organic solvents and is becoming a commercially viable and environmentally responsible alternative in the development of new multicomponent materials. A prerequisite to such processing is a fundamental understanding of how high-pressure CO2 influences the phase behavior of polymer blends. In this work, we use high-pressure spectrophotometry to measure the cloud point (Tcp) of poly(dimethylsiloxane)/poly(ethylmethylsiloxane) (PDMS/PEMS) blends as a function of CO2 pressure (P) in the vapor phase. Results obtained here at different blend compositions indicate that values of Tcp for this upper critical solution temperature (UCST) blend (i) generally increase with increasing pressure and (ii) collapse onto a master curve of ΔTcp(P) for pressures up to about 35 MPa. These data are analyzed by the Sanchez−Lacombe equation of state to ascertain the temperature dependence of an effective interaction parameter (χ) in terms of A + B/T, where A and B are both pressure-sensitive. We also compare our results with previously reported data to delineate the role of hydrostatic pressure on the phase behavior of these blends.

In this work, we use a molecular based equation of state, the Soft-SAFT equation, to predict complete Joule−Thomson inversion curves for carbon dioxide and the n-alkane series, including heavy n-alkanes up to octatetracontane (n-C48H98). Comparisons with available experimental and correlation data, for carbon dioxide and the lighter n-alkanes, show good quantitative agreement. We observe a strong dependence of the inversion curve on the set of molecular parameters used in the calculations, especially near the inversion point and in the high-temperature region. The equation is able to predict the general trend of inversion curves even for extreme conditions, with reduced pressure, Pr = P/Pc, values up to 40, and reduced temperatures, Tr = T/Tc, of almost 5.

The shape of the Joule−Thomson inversion curve of a fluid at high temperatures is shown to be directly related to its second and third virial coefficients. Experimental values and empirical correlations of the third virial coefficient of carbon dioxide are used to resolve a previously observed conflict between inversion curves obtained from different equations of state for this fluid. In particular, third virial coefficients predicted from the Pitzer−Sterner equation of state are shown to be in error, resulting therefore in an incorrect inversion curve.

Vapor pressures computed from nine cubic equations of state (EOS's) of the van der Waals form are correlated in corresponding states form using the linear Pitzer principle and a simple temperature function anchored at the critical point. The results strongly suggest that cubic equations of state do not conform to the usually assumed linear dependence of fluid properties on acentric factor. The failure of three-parameter cubic equations of state to predict the exact vapor pressure consistent with a specified acentric factor is analyzed, and new correlations are presented for the characteristic parameter in Soave's cohesion function that minimize this intrinsic error over a wider range of acentric factors. Soave's direct procedure for calculation of vapor pressures from EOS is found to be more accurate than all other approximate methods by at least 1 order of magnitude. However, the leading coefficient in Soave's equations is shown to be inconsistent with the limiting slope of the vapor pressure curve predicted by the equations of state. New direct expressions are developed that eliminate this inconsistency and give good representation of vapor pressures with fewer adjustable coefficients.

A new procedure is proposed for the correlation and prediction of vapor pressures of pure fluids. Polynomial regression of experimental saturation data is constrained by anchoring the vapor pressure equation at two or more characteristic points which are to be satisfied exactly. Results for 12 test fluids show that the new expressions correlate experimental data from the triple to the critical point, with precision as good as or better than that given by more complex equations which use more adjustable coefficients. The method can also be used for extrapolation purposes, including prediction of triple or critical points and of hypothetical supercritical saturation states.

Recoveries of different pesticide groups after storage either on C₁₈ cartridges or as dried residues from organic solutions, and their analysis by gas chromatography with electron capture and flame photometric detection, were studied. Two storage temperatures, 4 and −18 °C, and three storage periods, 3, 7 and 30 d, were considered. The effect of storage temperature and storage time on the recovery of 27 pesticides in water was investigated. In general, the pesticide recoveries were ≥70% after 30 d of storage at −18 °C on C₁₈ cartridges. Exceptions included captan and folpet. The storage of the dried residues generally did not affect the pesticide recovery when kept at −18 °C for up to 30 d.