Hydrothermal and Supercritical Water Processes (eBook)

Gerd Brunner (Autor)

eBook Download: PDF | EPUB

2014 | 1. Auflage
604 Seiten
Elsevier Science (Verlag)
978-0-444-59418-1 (ISBN)

Infos

Hydrothermal and Supercritical Water Processes presents an overview on the properties and applications of water at elevated temperatures and pressures. It combines fundamentals with production process aspects. Water is an extraordinary substance. At elevated temperatures (and pressures) its properties change dramatically due to the modifications of the molecular structure of bulk water that varies from a stable three-dimensional network, formed by hydrogen bonds at low and moderate temperatures, to an assembly of separated polar water molecules at high and supercritical temperatures. With varying pressure and temperature, water is turned from a solvent for ionic species to a solvent for polar and non-polar substances. This variability and an enhanced reactivity of water have led to many practical applications and to even more research activities, related to such areas as energy transfer, extraction of functional molecules, unique chemical reactions, biomass conversion and fuel materials processing, destruction of dangerous compounds and recycling of useful ones, growth of monolithic crystals, and preparation of metallic nanoparticles. This book provides an introduction into the wide range of activities that are possible in aqueous mixtures. It is organized to facilitate understanding of the main features, outlines the main applications, and gives access to further information - Summarizes fundamental properties of water for engineering applications - Compares process and reactor designs - Evaluates processes from thermodynamic, economic, and social impact viewpoints

GERD H. BRUNNER (Prof. em. of Chemical Engineering) Institute for Thermal Separation Processes Hamburg University of Technology (Institut f�r Thermische Verfahrenstechnik Technische Universit„t Hamburg-Harburg), Eissendorfer Strasse 38, D-21073 Hamburg, Germany. Phone: [phone] FAX: [phone] e-mail: [e-mail] Academic qualifications: - 1968 degree in Chemical Engineering by Technische Universit„t M�nchen, Germany. - 1972 doctoral degree (Dr.-Ing.) from Universit„t Erlangen-N�rnberg, Germany. - 1978 Habilitation (Dr.-Ing. habil.) in Technical Chemistry from Universit„t Erlangen-N�rnberg, Germany. - 1980 Assistant Professor at Universit„t Erlangen-N�rnberg - 1982 Full Professor of Chemical Engineering at Technische Universit„t Hamburg-Harburg. - 2008 retired from active service. Industrial experience: - 1982 - 1990 Senior researcher Siemens-KWU (non-nuclear energy activities), from 1983 as consultant. - 1989 - now: Consultant to F. Hoffmann-La Roche AG (supercritical fluids application) - 1982 - now: Consultant to many industrial companies in the field of Supercritical Fluids. Honorary positions: - Chair Member of the Academy of Sciences in Hamburg - Honorary Professor of Chemical Engineering, (Dr. h.c.), Technical University Sofia, 2008 Professional Position 1982 - March 2008 Full Professor, Head of Subdepartment Thermische Verfahrenstechnik Various position in administration of research and teaching at the Hamburg University of Technology Actual position: Prof. em. of Chemical Engineering Regional Editor of The Journal of Supercritical Fluids Scientific interests - Phase equilibria at elevated pressures and temperatures in complex systems - Transfer processes at elevated pressures and temperatures in complex systems - Separation processes with supercritical gases, i.e. extraction from solids, countercurrent separations, separation with chromatographic methods (SFC) - Simulated-moving-bed-separations - Hydrodynamic behaviour of countercurrent columns - Pyrolysis of organic compounds - Hydrolysis of bio-polymers - Supercritical water: destruction of waste, cleaning of soil - Enzymes at high pressures, in particular for separation processes - Electro-Ultra-filtration for biotechnological systems - Membrane separations of gases at high pressures - Biodiesel, bio-refinery Publications: About 290 publications, including about 15 patents.

Textauszug

Chapter 2

Properties of Pure Water

Gerd Brunner

Abstract

The properties of water vary from ambient conditions to critical conditions and above critical conditions over a remarkable wide range. From ambient to supercritical temperature, water changes its character from a solvent for ionic species to a solvent for nonionic species. Electrochemical properties vary substantially. For example, the dipole moment decreases from the high value at ambient conditions to a value common for normal solvents at supercritical conditions. But even in the critical region, water is still as polar as acetone. The pH-value of liquid water decreases by three units with temperature increasing to about T = 250 °C, thus providing many more H+-ions for acid-catalyzed reactions. Just below the critical temperature, the ionic product of water changes tremendously, rendering near-critical and supercritical water a much less ionized compound than at ambient conditions. Reactivity of water increases in the neighborhood of the critical point with or without a catalyst.

This chapter covers first the role of water in general, the main properties of water at standard and hydrothermal conditions, the structure of water, and phase behavior of pure water. Then, individual properties of water are presented. Thermodynamic, transport, and electrical properties are discussed in detail. For thermodynamic properties, the fundamental thermodynamic equations are briefly reviewed, followed by the individual properties like volumetric properties (and P,V,T-behavior), heat capacity, enthalpy, and entropy. Transport properties that are discussed include viscosity, thermal conductivity, and diffusivity. Electrical properties that are covered are ion product, electrical conductivity, and dielectric constant. This chapter is concluded with a brief discussion of refractive index and surface tension. Various tables and diagrams, useful for understanding and first conceptual designs, are included throughout the chapter.

Keywords

Pure water

Steam tables

Thermodynamic properties

Electrical properties

Transport properties

In this chapter, the role of water in general, the main properties of water at standard and hydrothermal conditions, the structure of water, and phase behavior are addressed first. Then, individual properties of water are presented. The thermodynamic, transport, electrical properties are discussed in detail. For thermodynamic properties, the fundamental thermodynamic equations are briefly reviewed, followed by the individual properties like volumetric properties (and P,V,T-behavior), heat capacity, enthalpy, and entropy. Transport properties that are discussed include viscosity, thermal conductivity, and diffusivity. Electrical properties that are covered are ion product, electrical conductivity, and dielectric constant. This chapter is concluded with a brief discussion of refractive index and surface tension. Various tables and diagrams, useful for understanding and first conceptual designs are included throughout the chapter.

2.1 Introduction

Water is the most abundant and ubiquitous compound on planet Earth. It is essential for life and is a major constituent of all known life-forms. Water determines our lives in many aspects such as nurturing, cleaning, and influencing the weather. Water occurs on earth in three states of aggregation: as vapor, as liquid, and as solid, which are a consequence of our planet's orientation to our sun. Water in the form of water vapor is the most important compound for controlling temperatures on earth. The water content of our atmosphere is variable between about 0.5 mol% in cold dry air and 3–4 mol% in humid tropical air [1]. The water cycle, that is, the amount of water transported in the atmosphere, is about 2500 times larger than the carbon cycle. In its liquid form, water comprises more than 96% of the oceans which cover our earth to about 71% with a depth of about 4200 m for more than half of the oceans [2]. Liquid water in fresh water lakes and rivers is a minor contribution of about 0.1% to total liquid water on our planet. Water as solid ice in glaciers and ice-caps around the poles contain only about 1.7% of all water [3] but plays an important role for our climate. Hydrothermal water occurs in nature in thermal baths, in geysers, and in volcanic outlets below water level (black smokers).

Water as the all-time and everywhere-available compound acts as a working fluid in many aspects, for example, from the use of its potential energy in ancient and modern machines to make mechanical and electrical energy available, as cooking fluid for preparing food, as solvent in the extraction of natural compounds, and not least of all, as processing fluid in power plants.

This chapter will concentrate on water at elevated temperatures and pressures, and on the applications of water at hydrothermal and supercritical conditions, as the title of the chapter states. The main area covered in this chapter is water and its applications at temperatures above T > 100 °C (373 K) up to the critical temperature of water (T = 374 °C, 647 K) and far beyond, and pressures above the saturation pressure of water up to around P = 200 MPa. Properties of water at ordinary or ambient conditions will be included for comparison.

The reader will get sufficient insight to understand or realize the effects that the properties of water and their dramatic changes exert on their environment and on other compounds. Data of properties of water will be provided to such an extent that the reader will be able to work with them without being forced to refer to other sources. This holds for understanding the effects and for using data for at least conceptual process design. It may be necessary to refer to fundamental treatises, to more extensive databases, or to other computational resources for detailed design purposes or for special effects. Therefore, the necessary and available sources will be addressed.

Pure water is a tasteless, odorless, colorless, clear liquid. It shimmers lightly blue in thick layers as does its solid form, that is, ice. Water in this chapter refers to the isotopic composition of water defined in the international standard called Vienna Standard Mean Ocean Water (VSMOW) [4]. Heavy water D2O, that is, where hydrogen is 100% deuterium, is beyond the scope of this chapter. For more information, see IAPWS (International Association for the Properties of Water and Steam) releases at http://iapws.org/.

Properties of water are summarized in Table 2.1. A detailed description of the individual properties follows below. The values of properties in Table 2.1 are the recommended values issued by IAPWS. This organization has over several decades dedicated its work to the precise measurement, correlation, and distribution of best values of the properties of water. The IAPWS releases and guidelines are the most reliable data available for the properties of water and should be used in scientific and industrial work. They can be accessed at http://iapws.org/.

Table 2.1

Properties of Water (Hydrogen Oxide) (IAPWS, http://iapws.org/)

Molar mass

18.015268 g/mol

Melting point at 1013 mbar

273.15 K (0 °C)

Boiling point at 1013 mbar

373.13 K (99.98 °C)

Triple point

273.16 K (0.01 °C)

(611.657 ± 0.010) Pa

Densitya

At 273.15 K (ice)

916.8 kg m− 3

273.15 K (water)

999.818 kg m− 3

277.15 K

999.97495 kg m− 3

293.15 K

0.998.231 kg m− 3

Refractive index

0.589 μm, 273.15 K

0.1 MPa

1.33434

Critical pressure

Pc

22.064 MPa

Critical temperature

Tc

647.096 K

Critical density

ρ

322 kg m− 3

Enthalpy of fusiona

285.89 kJ mol− 1

Enthalpy of meltinga

At 0 °C

6.010 kJ mol− 1

Enthalpy of boilinga

At 100 °C

40.651 kJ mol− 1

Dynamic viscosity (liq.)

298.15 K

889.7351 × 10− 6 Pa s

Surface tension

298.15 K

71.98 mN m− 1

Electrical conductivity

298.15 K

0.055 μS cm− 1

Dielectric...

Produkt-Details

• Erscheint lt. Verlag: 4.4.2014
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie ► Physikalische Chemie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Strömungsmechanik
• Themenwelt: Technik
• ISBN-10: 0-444-59418-3 / 0444594183
• ISBN-13: 978-0-444-59418-1 / 9780444594181