Sorption

Sorption is a collective name for processes that lead to an accumulation of a substance within a phase or at an interface between two phases. The accumulation within a stage called precisely absorption, the interface to the adsorption. James William McBain led in 1909 the generic term for sorption processes one of which may not be a clear distinction between adsorption and absorption.

The sorbent material is called a sorbent, the sorbent or sorbent. The not yet sorbed substance is called sorptive while he is named after the sorption of adsorbate, or absorpt. The system on or embedded ( sorbed ) with the sorbent material together is referred to as sorbate.

Classification

The causes of sorption are usually physical interactions between sorbent and sorbate. Sorption is an equilibrium process between uptake and release (desorption ) of a substance. If there is no balance, a balance is sought. Through concentration and temperature changes, and displacement reactions, sorption is influenced and shifted the position of equilibrium. Practical importance of sorption processes in which certain substances preferably be (selectively) was added.

• Absorption indicates an equilibrium process of storage ( and retrieval ) of the sorbate from one phase to the volume of another phase. Thus, For example, ( a gaseous phase ) and water ( a liquid phase ), a balance, for example, with respect to the oxygen content of the two phases, an intermediate air.
• Adsorption is the attachment ( and deposition ) of a substance from one phase to the surface (more precisely, interface ) to another phase. The internal volume of the sorbent remains - as opposed to absorption - uninvolved and can be a solid or liquid phase. Important chromatographic methods ( adsorption chromatography ), as well as many gas filters ( filter respirator ) based on adsorption. Physisorption (physical adsorption) is the general case of adsorption and is based on physical interactions between the adsorbate with the interface.
• Chemisorption (chemical adsorption) is a special case of adsorption. Here it comes to chemical bond between the adsorbate and the interface. This can lead to further chemical reactions and is an important step in heterogeneous catalysis. Chemisorption usually takes place at much higher temperatures than a physisorption and is limited to solid interfaces. The terms physisorption and chemisorption are usually used when certain processes are described to be in which a clear distinction between chemical and physical reactions or can.

The terms and desorption desorbate be used for the delivery of adsorbed and absorbed materials.

Measurement & description

The distribution of a substance between sorbent (eg a solid) and its solution (eg, an aqueous phase ) can be determined by batch experiments. Here arises between sorption and desorption of a substance a state of equilibrium. The ratio of the concentrations in the two phases is strong, inter alia, dependent on the temperature. The mathematical description is made with sorption isotherms.

The sorptive affinity of substances can be simplified with dimensionless and concentration- independent partition coefficients described, for example, the partition coefficient between the organic carbon in the soil and water ( Koc or log Koc ).

Application

Sorption, in particular, the adsorption, the behavior of pollutants in the environment plays an important role, eg of organic pollutants in the air ( attachment to aerosol particles) or underground ( attachment to soil particles or colloids). Pollutants can be bound in the longer term, for example by sorption to soil particles. Heavy-water -soluble and / or non-volatile pollutants can be transported by sorption on dust particles in the atmosphere or to suspended particles in the water ( also ground seepage and groundwater) over long distances.

Sorption is technically used in absorption chillers and air drying with water -attracting substances (see solar air-conditioning ).