ABSORPTION OF GASES ON SOLID
Absorption of gases by solid include; there are other substances other that are porous not only earth, charcoal and membrane of animal cell that can absorb gases but solid metal can do the same function, such metal is the experimental result showing the existence of gaseous hydrogen in meteorites falling on the earth surface and absorbed as they pass through space.
To explain thus theory, we have to define absorption and the aims and mechanism of concurrence.
Absorption is one of the four techniques or unit operation that aims at mass separation which relies on chemical properties and concentration driving forces, these technologies include: membrane technology, absorption, distillation, and adsorption.
Absorption is the process of taking a molecule of a substance directly into another substance. It may either be by physical or chemical process. It is one of the techniques used in separation or removal of small quantities of contaminants in a fluid stream that has several components as well as adsorption and solvent extraction.
For absorption on solids to take place physically depends on the solubility of the substance absorbed, chemical absorption involves reaction between the absorbed substance and the absorbing medium. The success of an absorption process depends on the choice of the solvent added. Normally, the solvent ought to be non-toxic, relatively cheap, non-inflammable, environmental friendly, non-,corrosive non-volatile, and having low viscosity e.g. water.
Adsorption is a process involving the molecules of a substance to the surface of the solids is opposite to absorption in which the molecules of substances enter the absorbing medium. For instance, due to porusness of charcoal, it can absorb large volume of gases including most of the poisonous substance due to its large surface area. Therefore it is applied in gas mask and filters. Absorption started more than 70 years ago for application in petroleum and chemical processing industries.
2.2 AIMS OF ABSORPTION The two main basic purpose of absorption includes:
- The separation or removal of components of gaseous phase: This process may require physical or chemical process. Example is the separation of Carbon(iv)oxide from Ammonia gas production in order to meet the gas specification. In this case, absorption is followed by desorption.
- To recover a particular component in a liquid phase: two gases may absorb each and this may chemical reaction taking place in liquid phase which result in obtaining the desired compound. Sometimes, chemical reaction may occur I the presence of a solid catalyst, example of non catalytic reaction is the absorption of sulphur(Iv)oxide in fatty alcohol which produce detergent. Sometimes, the aforementioned principles above are formulated together for a particular amount of reaction required and certain absorption efficiencies of several gas components
2.3 Absorption equipment
Despite that absorption is an old technique used in selective removal of contaminants from gaseous mixtures and this selective removal is as a result of the economic value of the constituent of the mixture. These equipment includes:
- Agitator vessel: this is used for a batch operation which is employ in the introduction of the gas directly into the liquid or solid and this is done mechanically by the agitator.
- Bubble plate tower: these towers are likened to be in classical bubble cap column distillation that consists of shallow plates over which the liquid and gases flow. The operation of a bubble works in the sample principle as the tray in the distillation column .
- Cooler Absorbers: when this gas is absorbed, there is heat evolution and the cooler absorber removes the generated heat.
- Spray Tower: This has nozzles that spray liquid of various kinds. Other equipment includes
- Packed tower.
- Venturi scrubbers.
Notice that absorption taking place in a particular system can be represented in a rate form as
Rate of Absorption= Absorption CoefficientSurface AreaDriving Force
The basic purpose of wide industrial application of absorbers to ascertain a large mass transfer area and to create conditions under which transfer coefficients are high in both phases and in turn