Liquid-phase adsorptions organic solutes adsorption

Liquid phase adsorption is used mainly to bind turbid substances, to purify and decolor solutions, and to separate organic pollutants. Grained active carbon is employed as an adsorbent, mixed in a pulverized form with the liquid or as particles in a percolation process. 

Applications of liquid-phase adsorption include removal of organic compounds from water or organic solutions, colored impurities from organics, and various fermentation products from fermentor effluents. Separations include paraffins from aromatics and fructose from glucose using zeolites. 

Liquid-phase adsorption methods are also widely used. The adsorption of iodine from potassium iodide solution is the standard ASTM method D1510. The surface area is expressed as the iodine number whose imits are milligrams of iodine adsorbed per gram of carbon blacks. The test conditions such as adsorbate concentration and the amount of carbon black sample used are specified in such a way that the values of iodine numbers turn out to be about the same as the values for surface areas in square meters per gram that is measured by nitrogen adsorption for nonporous and nonoxidized furnace carbon blacks. The iodine number is raised by porosity and decreased by surface oxygen or adsorbed organics. Still it is the most easily measured surface area estimate and is used extensively, especially for process control. 

Methods 3 and 4 are specific to liquid phase adsorption and especially effective when recovery of adsorbate is desirable. Desorption by alkaline solution is often used for recovery of organic acids adsorbed on... 

Two other methods worth discussing are wet air oxidation and regeneration by steam. Wet oxidation may be defined as a process in which a substance in aqueous solution or suspension is oxidized by oxygen transferred from a gas phase in intimate contact with the liquid phase. The substance may be organic or inorganic in nature. In this broad definition, both the well known oxidation of ferrous salts to ferric salts by exposure of a solution to air at room temperature and the adsorption of oxygen by alkaline pyrogallol in the classical Orsat gas analysis would be considered wet oxidations. 

At the beginning stage of dehydrogenation, the substrate organic hydride is adsorbed onto the catalyst surface from the liquid phase directly and easily. Catalytic reaction processes will succeed it, until the surface sites are filled with the adsorbed reactant and products. Once product desorption starts to form and grow a bubble, product readsorption becomes unfavorable due to the increment of translational entropy of the product molecule in the bubble, if compared with that in the solution, shifting the adsorption equilibrium for the product and suppressing its effect of rate retardation. 

The role of hydrogen bonds in liquid or vapour-phase adsorption processes has not hitherto been very clearly defined. The present paper is a brief review of some recent investigations in this laboratory, many of them unpublished, which it is believed may help to define the conditions favouring hydrogen bond adsorption especially from dilute solutions, by inorganic and organic substrates. 

The adsorption of phenol and phenolic compounds is by far the most studied of aU liquid-phase applications of carbon adsorbents [1]. This is because phenol is used as a model aromatic molecule and has been declared a priority pollutant. Therefore, this chapter devotes more attention to the adsorption of phenol and substituted phenols than to the adsorption of other organic solutes. 

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