Quenching (chemistry)
In the chemical reaction is denoted by quenching (Engl. To quench = delete ) rapidly stopping an ongoing reaction at a given time. This can be done by quickly adding a further reaction partner (sometimes also referred to as a quencher or scavenger ), which removes one of the starting materials from the reaction mixture, by cooling down, which reduces the speed of the reaction so much that it is considered almost stopped, or by rapid and strong dilution, which greatly reduces the probability of the reaction of two reactants .
laboratory
In the laboratory, for example, this technique is used to carry out kinetic studies on reactions. For this purpose, several batches of the same reaction are quickly stopped under the same conditions after different reaction times, in order to then be able to determine the conversion that has taken place up to this point in time using suitable measuring methods . Such a method is always necessary when direct measurement is not possible in the course of the reaction (for example because the product must first be converted into a chemical compound , solution or measuring apparatus suitable for the measurement ).
Synthesis reactions can be quenched by pouring the hot reaction mixture onto ice (or an ice-water mixture). This not only significantly reduces the temperature, but also any acid or base that may be present is greatly diluted and water-insoluble components are precipitated .
technology
In chemical process engineering , special quench coolers are used, which cool the reaction mixture down to such an extent that a further reaction, e.g. to undesired secondary products, is prevented. In gas treatment in particular, gas scrubbers are used to quench gases, for example in a spray scrubber for cleaning and cooling exhaust gases from waste incineration .
A reaction cannot always be slowed down sufficiently by simply cooling it down. A reaction can also be stopped by stirring in special reactants. In the case of batches on a ton-scale, however, analysis, feed and mixing times make it difficult to break off reactions precisely.
Individual evidence
- ↑ John J. McKetta (Ed.): Encyclopedia of chemical processing and design. Vol. 62, Marcel Dekker New York 1998, ISBN 0-8247-2613-8 ( limited preview in Google book search), p. 406.
- ↑ VDI 3679 sheet 2: 2014-07 wet separator; Waste gas cleaning by absorption (scrubbers). Beuth Verlag, Berlin. P. 50.