Adsorbent

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An adsorbent or adsorbent is used to remove trace substances from fluids . These trace substances are adsorptively attached to the surface of the adsorbent due to van der Waals forces .

Basics

The technical adsorbents used in laboratory practice and especially in exhaust gas cleaning technology can be divided as follows:

Because of their porosity , adsorbents have a large internal surface. This can sometimes be more than a thousand square meters per gram. Pore ​​diameter and pore size distribution depend on the particular adsorbent. While zeolites, for example, have a clearly defined pore diameter, a distinction can be made between macro-, meso- and micropores in activated carbons, depending on the pore diameter. The specific volume of the micropores is usually between 0.25 and 1.2 cubic centimeters per gram of adsorbent.

Adsorbents are impregnated for certain separation tasks . The impregnating agent either serves as a reactant ( chemisorption ) or as a catalyst for heterogeneous catalysis . The adsorbents can be impregnated either by immersion and spray processes or by adsorption from the gas phase. The mass fraction of the impregnating agent can be up to 30 percent. Examples of the use of adsorbents are impregnated with sulfuric acid or bromine -treated activated carbons for the separation of mercury from furnace flue gases and with metal oxides, activated carbons, provided for the reduction of nitrogen dioxide in the motor vehicle interior filtration.

application

Adsorbents are used, among other things, in exhaust gas cleaning systems, water treatment systems , extractor hoods , insoles , adsorption chillers and cabin air filters . The selection of the respective adsorbent depends not only on the components to be separated but also on economic aspects and safety aspects. The interaction between the substance to be adsorbed (adsorptive) and the adsorbent is important for the separation task. The economic aspects also include the regenerability of the adsorbent used. This assumes that there is no reaction between the adsorbed substance (adsorpt) and the adsorbent. In terms of safety, the reactivity and flammability of activated carbon play a key role. Likewise, adsorbed hydrocarbons can represent a fire load that can not be neglected .

literature

  • VDI 3674: 2013-04 Exhaust gas cleaning through adsorption; Process gas and waste gas cleaning (Waste gas cleaning by adsorption; Process gas and waste gas cleaning). Beuth Verlag, Berlin. ( Summary and table of contents online )

Web links

Wiktionary: Adsorbent  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ a b Hans Wirth: Properties and selection criteria for adsorbents . In: Dust - cleanliness. Air . 36, No. 7, 1976, ISSN  0949-8036 , pp. 288-292.
  2. ↑ a b VDI 3928: 2017-01 Waste gas cleaning by chemisorption. Beuth Verlag, Berlin, pp. 21-23.
  3. ↑ Wolfgang Esser-Schmittmann, Simone Schmitz: Chemisorption of mercury from combustion exhaust gases. In: Hazardous substances - cleanliness. Air . 74, No. 5, 2014, ISSN  0949-8036 , pp. 175-177.
  4. ↑ Uta Sager, Eckhard Däuber, Christof Asbach, Dieter Bathen, Frank Schmidt, Claudia Weidenthaler, Jo-Chi Tseng, Wolfgang Schmidt: Differences in the adsorption of NO 2 and NO on modified activated carbon. In: Hazardous substances - cleanliness. Air. 74, No. 5, 2014, ISSN  0949-8036 , pp. 181-184.
  5. ↑ Harald Jüntgen: Basics of Adsorption . In: Dust - cleanliness. Air. 36, No. 7, 1976, ISSN  0949-8036 , pp. 281-288.
  6. ↑ Jürgen Klein: Regeneration of adsorbents . In: Dust - cleanliness. Air. 36, No. 7, 1976, ISSN  0949-8036 , pp. 292-297.
  7. ↑ Götz-Gerald Börger: Smoldering fire in activated carbon adsorbers , part 1 and part 2. In: Chem.-Ing.-Techn. ISSN  0009-286X , 69, No. 1 + 2, 1997, pp. 130-132 and 69, No. 3, 1997, pp. 358-361.