Basic Concepts and Processes

Extraction is the selective dissolution, washing, or leaching of certain substances from a solid or liquid mixture by the aid of a liquid solvent. The valuable substance (or with a cleaning process, the pollutant) is transferred by a solvent as the receiving phase from the feed phase. Thus, extraction is a sorption process similar to adsorption and absorption, in which a selective auxiliary substance acts as the receiver phase. 

In contrast to other separation processes, extraction does not lead directly to pure key components. The feed phase after extraction (raffinate phase) contains not only the carrying substance which is inert to the solvent, hut also solvent, and valuable key components. The receiving or extract phase, consists essentially of the solvent and key components. Regeneration of the solvent and purification of the key components requires additional separation processes, for example, rectification. 

It is important to intensively mix the prepared feed phase with the receiving solvent in extraction processes, and to allow sufficient contact time for the transfer of key compo-nent(s) between the phases. After the required degree of mass transfer has been achieved, the raffinate and extract phases must be separated. Mixing and phase separation must be repeated several times in an extraction unit to obtain good extraction yield. 

In solid-liquid extraction (leaching) a certain component is dissolved out from the 

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Having introduced the basic concepts and equations for various energy redistribution processes, we will now... 

In order to operate a process facility in a safe and efficient manner, it is essential to be able to control the process at a desired state or sequence of states. This goal is usually achieved by implementing control strategies on a broad array of hardware and software. The state of a process is characterized by specific values for a relevant set of variables, eg, temperatures, flows, pressures, compositions, etc. Both external and internal conditions, classified as uncontrollable or controllable, affect the state. Controllable conditions may be further classified as controlled, manipulated, or not controlled. Excellent overviews of the basic concepts of process control are available (1 6). 

Although the basic concept and the arrangement of the chapters is this second edition are the same as the first, this new edition includes many minor additions and updates related to the advances in processing and catalysis. 

This book seeks essentially to provide a rigorous, yet lucid and comprehensible outline of the basic concepts (phenomena, processes, and laws) that form the subject matter of modem theoretical and applied electrochemistry. Particular attention is given to electrochemical problems of fundamental significance, yet those often treated in an obscure or even incorrect way in monographs and texts. Among these problems are some, that appear elementary at first glance, such as the mechanism of current flow in electrolyte solutions, the nature of electrode potentials, and the values of the transport numbers in diffusion layers. 

At present there is a sufficiently complete picture of photoelectrochemical behavior of the most important semiconductor materials. This is not, however, the only merit of photoelectrochemistry of semiconductors. First, photoelectrochemistry of semiconductors has stimulated the study of photoprocesses on materials, which are not conventional for electrochemistry, namely on insulators (Mehl and Hale, 1967 Gerischer and Willig, 1976). The basic concepts and mathematical formalism of electrochemistry and photoelectrochemistry of semiconductors have successfully been used in this study. Second, photoelectrochemistry of semiconductors has provided possibilities, unique in certain cases, of studying thermodynamic and kinetic characteristics of photoexcited particles in the solution and electrode, and also processes of electron transfer with these particles involved. (Note that the processes of quenching of photoexcited reactants often prevent from the performing of such investigations on metal electrodes.) The study of photo-electrochemical processes under the excitation of the electron-hole ensemble of a semiconductor permits the direct experimental verification of the applicability of the Fermi quasilevel concept to the description of electron transitions at an interface. 

In this first chapter, we will outline the scope of this book on the kinetics of chemical processes in the solid state. They are often different from the kinetics of processes in fluids because of structural constraints. After a brief historical introduction, typical situations of non-equilibrium crystals will be described. These will illustrate some basic concepts and our approach to understanding solid state kinetics. 

Fifty years have elapsed since the first major surge occurred in the development of the Athabasca oil sands. The main effort has been devoted to the development of the hot water extraction process 13 significant projects utilizing this process are reviewed in this paper. However, many other techniques have also been extensively tested. These are classified into several basic concepts, and the mechanism underlying each is briefly described. A critical review of K. A. Claries theories concerning the flotation of bitumen is presented, and his theories are updated to accommodate the different mechanisms of the primary and secondary oil recovery processes. The relative merits of the mining and in situ approaches are discussed, and an estimate is made of the probable extent of the oil sand development toward the end of this century. 

The aim of this chapter is to describe the process of network formation using qualitative arguments together with simple mathematical tools. The intention is to provide a first approach to the subject that should enable the reader to get acquainted with the basic concepts and definitions of the network structure. 

For a better comprehension of the ED processes it is necessary to refresh a few basic concepts and definitions regarding the electrolytic cell and thermodynamic electrode potential, Faraday s laws, current efficiency, ion conduction, diffusivity, and transport numbers in solution. 

The term electromembrane process is used to describe an entire family of processes that can be quite different in their basic concept and their application. However, they are all based on the same principle, which is the coupling of mass transport with an electrical current through an ion permselective membrane. Electromembrane processes can conveniently be divided into three types (1) Electromembrane separation processes that are used to remove ionic components such as salts or acids and bases from electrolyte solutions due to an externally applied electrical potential gradient. (2) Electromembrane synthesis processes that are used to produce certain compounds such as NaOH, and Cl2 from NaCL due to an externally applied electrical potential and an electrochemical electrode reaction. (3) Eletectromembrane energy conversion processes that are to convert chemical into electrical energy, as in the H2/02 fuel cell. 

Considerable progress has been made during the past decade toward a better insight into the basic concepts and mechanism involved in metallic dissolution and corrosion. More emphasis has been placed on the "fundamental particles (metallic ions, electrons, and electron acceptors) and on the use of current-voltage characteristics. The wide recognition of dissolution and corrosion as electrode processes, and the idea of a polyelectrode exhibiting a mixed potential, have augmented the use of electrochemical techniques in the study and interpretation of corrosion phenomena. There is even some evidence that the phenomenon of passivity may soon be clarified. 

Chapter 7 deals with the basic concepts and properties of very specific technological media, namely, foam systems. Important processes such as surfactant interface accumulation, syneresis, and foam rupture are considered. 

This book is written as a basic framework to introduce the concepts and processes from drug discovery to marketing approval by regulatory authorities. It is particularly suitable for undergraduates pursuing courses in medicine, pharmacy, science and life sciences. Professionals in the pharmaceutical industry will find this book useful as a quick reference guide. 

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