Chemical conversion, definition

Although there is no commonly accepted definition of a membrane reactor (MR), the term is usually applied to operations where the unique abilities of membranes to organize, compartmentalize, and/or separate are exploited to perform a (bio)chemical conversion under conditions that are not feasible in the absence of a membrane. In every MR, the membrane separation and the (bio)catalytic conversion are thus combined in such a way that the synergies in the integrated setup entail enhanced processing and improved economics in terms of separation, selectivity, or yield, compared to a traditional configuration with reactor and separation separated in time and space. When the membrane itself carries the catalytic functions, it is mostly referred to as a reactive membrane. ... 

There is no commonly accepted definition of a membrane reactor but the term is applied to membrane (including liquid membrane) processes and devices whose function is to perform chemical conversion, coupling and combining chemical and transport processes, using the unique contacting features of membranes. As a rule, functional definition of this term includes fermentation, catalysis, separation of the products and their enrichment. A few published reviews at this time are available [98-104]. In most of pubhcations the bioreactors, based on enzymes or whole cells, impregnated into the membrane pores (immobihzed or supported hquid membranes) or deposited on the membrane surfaces are discussed. 

The principle of stationary (or instationary) is also applied to the atmospheric budget of trace species, regarding F+ the source term (emission Q) and F the total removal term R (deposition and chemical conversion). With the definition of the residence time (see Chapter 4.5 for more details) it follows from Eq. (4.96) that ... 

The solvent extraction of coal is, in essence, a mild form of chemical conversion because in addition to the pnrely solvent action, there may also be molecular alterations that are definite and irreversible. Coal-solvent interactions are complex (Szeliga, 1987) but, in more general terms, extraction is usually enhanced by temperature in addition, the presence of hydrogen will significantly alter the molecular changes. 

The selectivity, conversion, and product yield of chemical reactions along with the power inputs, basically determine the practical availability of a chemical process. Definitions of these parameters may be found in [1-6],... 

This reasoning is based on the assumption that a secondary valence bond [...] does not survive chemical conversion unchanged. [...] The secondary valences must disappear at least in the transition state of the reaction [15, p. 342]. K the colloids prove to be resistant even so, i.e. their degree of polymerisation does not change even in such profound chemical conversion processes as esterification or saponificatimi , it is definite that all the basic molecules [...] are bonded to each other via primary valences [10, p. 17] and not by secondary valences, which are definitely destroyed [...] by such chemical intervention [26, p. 482]. In a nutshell, in this case, macromolecules and not micelles must be involved. Such proof [...]... 

The chemical conversion of o-glucose to D-glucono-5-lactone and thence to o-gluconic acid has been used in manufacturing processes. Electrochemical oxidation in the presence of bromide (Isbell et al. 1932) and oxidation with air or oxygen (employing a catalyst deWilt 1972) are examples of methods in use. However, because of the appearance (during chemical production) of unwanted side products that require difficult downstream purification, the more specific microbial fermentations and other biochemical processes are definitely competitive. 

Pericyclic reactions are of stereospecific nature. This trait is of great value to synthetic organic chemists, because through a judicious choice specific chemical conversion can be carried out in which products have definite stereochemistry. Some problems related to these aspects are discussed in this unit. 

Section 2 combines the former separate section on Mathematics with the material involving General Information and Conversion Tables. The fundamental physical constants reflect values recommended in 1986. Physical and chemical symbols and definitions have undergone extensive revision and expansion. Presented in 14 categories, the entries follow recommendations published in 1988 by the lUPAC. The table of abbreviations and standard letter symbols provides, in a sense, an alphabetical index to the foregoing tables. The table of conversion factors has been modified in view of recent data and inclusion of SI units cross-entries for archaic or unusual entries have been curtailed. 

The term feedstock in this article refers not only to coal, but also to products and coproducts of coal conversion processes used to meet the raw material needs of the chemical industry. This definition distinguishes between use of coal-derived products for fuels and for chemicals, but this distinction is somewhat arbitrary because the products involved in fuel and chemical appHcations are often identical or related by simple transformations. For example, methanol has been widely promoted and used as a component of motor fuel, but it is also used heavily in the chemical industry. Frequendy, some or all of the chemical products of a coal conversion process are not isolated but used as process fuel. This practice is common in the many coke plants that are now burning coal tar and naphtha in the ovens. 

Basic Standards for Chemical Technology. There are many numerical values that are standards ia chemical technology. A brief review of a few basic and general ones is given hereia. Numerical data and definitions quoted are taken from References 16—19 (see Units and conversion factors) and are expressed ia the International System of Units (SI). A comprehensive guide for the appHcation of SI has been pubUshed by ASTM (20). 

A catalyst is a substance that iacreases the rate of approach to equiUbrium of a chemical reaction without being substantially consumed itself. A catalyst changes the rate but not the equiUbrium of the reaction. This definition is almost the same as that given by Ostwald ia 1895. The term catalysis was coiaed ia ca 1835 by Ber2eHus, who recognized that many seemingly disparate phenomena could be described by a single concept. For example, ferments added ia small amounts were known to make possible the conversion of plant materials iato alcohol and there were numerous examples of both decomposition and synthesis reactions that were apparendy caused by addition of various Hquids or by contact with various soHds. 

There is a wide range of conversion levels. The term maximum conversion type has no precise definition but is often used to describe a level of conversion, where there is no net fuel oil manufactured. A fuel products refinery with specialities may manufacture lubricating oils, asphalts, greases, solvents, waxes and chemical feed stocks in addition to the primary fuel products. The number and diversity of products will naturally vary from one refinery to another. Refineries produce chemical feed stocks for sale to the chemical affiliates and do not have responsibility for the manufacture of chemical products directly. Both operations may be carried out at the same physical location but the corporate product responsibilities are usually separate. 

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