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Właściwości i zastosowania wody pod- i nadkrytycznej

Światła-Wójcik D.

Wiadomości Chemiczne

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2010

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[Z] 64, 3-4

225-242

EN

In the last decades, sub- and supercritical water has received continuously increasing attention as a reaction medium. As safe, non-toxic, readily accessible it is used in chemical synthesis, waste destruction and biomass processing [1–4]. A broad area of technological and industrial applications of sub- and supercritical water arises from its physical and transport properties falling between those of a gas and a liquid. The solvent properties of water can rapidly change with increasing pressure and temperature [2, 5, 10]. Above the critical point (Tc = 647.1 K, Pc = 22.06 MPa) water becomes highly compressible and diffusive. The static dielectric constant approaches values characteristic for low-polar solvent (Fig. 5). Contrary to liquid water at ambient conditions, supercritical water is a poor solvent for ionic species but is well miscible with hydrocarbons and gases (Fig. 6). The ionic product of supercritical water can be a few orders of magnitude higher than in ambient water (Fig. 4) with consequent effect on the kinetics and mechanisms of chemical reactions. By adjustment of thermodynamic conditions one can tune density, viscosity, polarity or pH of water to the desired solvation properties without any change in the chemical composition. An alternation in the character of water solvent near and above the critical point is the consequence of the structural transformations in the hydrogen-bonded network. As evidenced by many experimental and simulation studies the average number of hydrogen bonds per molecule and the lifetime of H-bonds decrease with increasing temperature and decreasing density [2, 10, 19]. With respect to experiment computer simulation plays an equal, and sometimes pivotal role, in quantitative characterization and understanding of water under extreme conditions. Precise definition of an H-bond employed in computer simulation allows one to examine size and topology of clusters of hydrogen-bonded molecules for various thermodynamic states [17, 19]. Such knowledge is invaluable to link features of the hydrogen bonding with the macroscopic properties of water [10, 19]. This article provides an overview of three aspects concerning water from ambient to supercritical conditions. In Chapter 1 the physical and transport properties are reviewed. Features of hydrogen bonding and a relationship between the molecular engagement in hydrogen-bonded clusters and macroscopic properties of water are discussed in Chapter 2. Chapter 3 focuses on technological and industrial applications of sub- and supercritical water. The summary concludes on main research needs.

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Niszczenie substancji organicznych metodą SCWO

Borek H.

Przegląd Papierniczy

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2002

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R. 58, nr 5

308--309

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Nadkrytyczna utylizacja odpadów jako realizacja idei TETF

Rogacki G., Wawrzyniak P., Bartczak Z.

Zeszyty Naukowe. Inżynieria Chemiczna i Procesowa / Politechnika Łódzka

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1998

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Nr 23

222-229

PL

Termiczne metody utylizacji odpadów i zanieczyszczeń organicznych nie mogą spełnić idei TETF ponieważ występują w nich strumienie gorących i rozrzedzonych gazów. Woda w stanie nadkrytycznym stwarza warunki do termicznej utylizacji przy kosztach porównywalnych z innymi metodami.

EN

Thermal methods of organic waste disposal cannot fulfil the TEFT ideas because they deal with hot and dilute streams of gases. Supercritical water provides conditions for thermal methods at costs comparable with other methods.