Contact times functional definition

The yield of a gas-solid heterogeneous reaction depends not on the total time that molecules spend in the reactor but on the time that they spend on the catalyst surface. The contact time distribution provides a standardized measure of times spent in the absorbed state. A functional definition is provided by the following equation applicable to a first-order, heterogeneous reaction in an isothermal reactor ... 

Functionally, the effective dwell time (EDT) at 90% level can be defined as the time it taken by the forcetime curve to traverse the 90% of the peak height. Likewise, the effective contact time (ECT) is the time between points at 10% of the peak height. The shape of the force curve depends, as we know, on the deformation mechanisms of the powder and therefore, all other variables being equal, EDT and ECT will be different for brittle and plastic materials. Although somewhat useful for material characterization, such variables should not be confused with the universally accepted definitions of contact time (time of contact) and dwell time (time of immobility). 

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. 

As a biosensor, by definition, consists of a biological recognition system in intimate physical and functional contact with an artificial transducer, among the possible combinations the most efHcient ones have to be conceived with regard to the demands of the actual analytical problem. The choice will not only be determined by the optimum sensitivity or the response time to be attained, but also by the properties of the matrix and the concentration range of the substance to be monitored. This may be explained by means of an example. 

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