Reaction-Enhanced Extraction

Reactfon-Enhanced Extraction Reaction-enhanced extraction involves enhancement of the partition ratio for extraction through the use of a reactive extractant that forms a reversible adduct or molecular complex with the desired solute. Normally, the extractant compound is dissolved in a diluent liquid such as kerosene or another high-boiling hydrocarbon. Because reactive extractants form strong specific interactions with the solute molecule, they can provide much... 

Extractive Reaction Extractive reaction combines reaction and separation in the same unit operation for the purpose of facilitating a desired reaction. To avoid confusion, the term extractive reaction is recommended for this type of process, while the term reaction-enhanced extraction is recommended for a process involving formation of reversible solute-extractant interactions and enhanced partition ratios for the purpose of facilitating a desired separation. The term reactive extraction is a more general term commonly used for both types of processes. 

T0736 SOUND/epic, Dispersion by Chemical Reaction (DCR) Technology T0745 State University of New York, Oswego, Electrochemical Peroxidation (ECP) T0747 SteamTech Environmental Services and Integrated Water Resources, Inc., Steam-Enhanced Extraction (SEE)... 

One of the first comprehensive studies of the chemical nature of humic substances was carried out by Sprengel (1826, 1837). The procedures he developed for the preparation of humic acids became generally adopted, such as pretreatment of the soil with dilute mineral acids to enhance extraction with alkali. Sprengel concluded that, for soils rich in bases, humic acid was in a bound form consequently, the soil had a neutral reaction (contained mild humus ). This soil was regarded as highly fertile. On the other hand, for soils poor in bases, the humic acid was believed to be in the free form, with the result that the soil was acid and unproductive (contained acid humus ). A major contribution of Sprengel to humus chemistry was his extensive studies on the acidic nature of humic acids. 

Sometimes reaction rates can be enhanced by using multifunctional reactors, i.e., reactors in which more than one function (or operation) can be performed. Examples of reactors with such multifunctional capability, or combo reactors, are distillation column reactors in which one of the products of a reversible reaction is continuously removed by distillation thus driving the reaction forward extractive reaction biphasing membrane reactors in which separation is accomplished by using a reactor with membrane walls and simulated moving-bed (SMB) reactors in which reaction is combined with adsorption. Typical industrial applications of multifunctional reactors are esterification of acetic acid to methyl acetate in a distillation column reactor, synthesis of methyl-fer-butyl ether (MTBE) in a similar reactor, vitamin K synthesis in a membrane reactor, oxidative coupling of methane to produce ethane and ethylene in a similar reactor, and esterification of acetic acid to ethyl acetate in an SMB reactor. These specialized reactors are increasingly used in industry, mainly because of the obvious reduction in the number of equipment. These reactors are considered by Eair in Chapter 12. 

This reasoning for mass transfer and chemical reaction in gas/liquid systems, is equally well applicable to liquid/liquid systems. When mass transfer in a liquid quid system is accompanied by rapid chemical reaction, the term chemically enhanced extraction applies. 

Chemical reactions occur in many commonly practiced separation processes. By chemical reactions, we mean those molecular interactions in which a new species results (Prausnitz et al, 1986). In a few processes, there will he hardly any separation without a chemical reaction (e.g. isotope exchange processes). In some other processes, chemical reactions enhance the extent of separation considerably (e.g. scrubbing of acid gases with alkaline absorbent solutions, solvent extraction with complexing agents). In still others, chemical reactions happen whether intended or unintended estimation of the extent of separation requires consideration of the reaction. For example, in solvent extraction of organic acids, the extent of acid dissociation in the aqueous phase at a given pH should be taken into account (Treybal, 1963, pp. 38-41). Chemical equilibrium has a secondary role here, yet sometimes it is crucial to separation. 

---