Application liquid-phase adsorption

The following topics, having an emphasis towards environmental protection, are included in a separate bibliography in Volume 2 PSA and Cyclic Systems, and Applications Liquid-Phase Adsorption Ion Exchange, Chromatography, and Related Separations. 

Chapter 7 gives a review of the technology and applications of zeolites in liquid adsorptive separation of petrochemical aromatic hydrocarbons. The application of zeolites to petrochemical aromatic production may be the area where zeolites have had their largest positive economic impact, accounting for the production of tens of millions of tonnes of high-value aromatic petrochemicals annually. The nonaromatic hydrocarbon liquid phase adsorption review in Chapter 8 contains both general process concepts as well as sufficient individual process details for one to understand both commercially practiced and academic non-aromatic separations. 

Lignite GAC This presents a total surface area of 650 m2/g and an apparent density of 0.50 g/cm3, approximately. It is usually used for liquid-phase adsorption, and specifically, in decolorizing applications because it has a higher percentage of meso (transitional) and macro pores than bituminous GAC, and therefore is appropriate for larger molecules. 

A major application of liquid phase adsorption is to the removal of relatively small amounts of impurities or color bodies in water treating, sugar refining, and other processes. Both batch and... 

The process patterns found in liquid systems are more diverse and frequently much more complex than those in vapor-phase applications. In part, this arises from the greater number of factors that can influence adsorption from solution. The various permutations in which these factors can be joined confer a flexibility that makes liquid-phase adsorption adaptable to many diverse situations.1 2> 3... 

ACNF is an excellent adsorbent and has found usage in applications such as gas-phase and liquid phase adsorption [5, 20, 36] as well as elec-... 

Despite its industrial importance, adsorption from the liquid phase has been studied much less extensively than adsorption from the vapor phase. There is no difference in principle between adsorption from liquid and vapor phases since, thermodynamically, the adsorbed phase concentration in equilibrium with a liquid must be precisely the same as that which is in equilibrium with the saturated vapor. The differences arise in practice because in adsorption from the liquid phase one is almost invariably concerned with high adsorbed phase concentrations close to the saturation limit. The simple model isotherms, developed primarily to describe adsorption from the vapor phase, are at their best at low sorbate concentrations and become highly unreliable as saturation is approached. Such models are therefore of only very limited applicability for the correlation of liquid phase adsorption data. 

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. 

Table 3.3.10 lists application areas of gas and liquid phase adsorption. Figure 3.3.46 shows a typical process. 

The extended Langmuir (Markham-Benton) isotherm has limited applicability especially for liquid phase adsorption, since even singlecomponent isotherms in liquid phase are rarely explained by the Langmuir equation. There have been several trials to extend the Freundlich type equation to mixture isotherms. Fritz and Schliinder (1974) gave the following equation. 

Applications of activated carbons (AC) in liquid-phase adsorptions are extensive, the number running into thousands. This Chapter makes no attempt to summarize such involvements, but concerns itself with explanations of mechanisms of adsorption of inorganic and organic species from the aqueous phase. In this way, an understanding of the factors which control extents of adsorption is made available and can be extended to other systems. This Chapter also highlights applications of major industrial importance. 

The micropore structure can be determined by several methods such as immersion calorimetry, small-angle X-ray scattering (SAXS) high resolution transmission electron microscopy (HRTEM) and s- and liquid-phase adsorption, among which the most widely us is gas adsorption[7]. The pore structure of activated carbon is usually characterised in terms of the pore size distribution (PSD), perhaps die most imporlant aspect of characterization of die structural heterogeneity of porous solids used in industrial applications. This PSD could be obtained as an arbitrarily chosen form such as, for instance, mma or C ssian distribution[8]. For a local isodierm one may choose traditional mmlels, statistical mechanical methods such as DFT, or, most accurate for micropores, methods based on Monte Carlo simulation. 

One further development in adsorption technology which holds some promise, is a cyclic process applicable to the separation of liquids. The separation method depends on concentration changes and is referred to as concentration swing adsorption (Rao and Sircar 1992). Separation of a binary mixture, such as ethanol-water, occurs by the selective liquid phase adsorption of ethanol (the more strongly adsorbed component) onto the surface of a porous adsorbent. The cycle consists of four steps ... 

Material balances, often an energy balance, and occasionally a momentum balance are needed to describe an adsorption process. These are written in various forms depending on the specific application and desire for simplicity or rigor. Reasonably general material balances for various processes are given below. An energy balance is developed for a fixea bed for gas-phase application and simphfied for liquid-phase application. Momentum balances for pressure drop in packed beds are given in Sec. 6. 

The following are some of the typical industrial applications for liquid-phase carbon adsorption. Generally liquid-phase carbon adsorbents are used to decolorize or purify liquids, solutions, and liquefiable materials such as waxes. Specific industrial applications include the decolorization of sugar syrups the removal of sulfurous, phenolic, and hydrocarbon contaminants from wastewater the purification of various aqueous solutions of acids, alkalies, amines, glycols, salts, gelatin, vinegar, fruit juices, pectin, glycerol, and alcoholic spirits dechlorination the removal of... 

Filter aids may be applied in one of two ways. The first method involves the use of a precoat filter aid, which can be applied as a thin layer over the filter before the suspension is pumped to the apparatus. A precoat prevents fine suspension particles from becoming so entangled in the filter medium that its resistance becomes exces-sive. In addition it facilitates the removal of filter cake at the end of the filtration cycle. The second application method involves incorporation of a certain amount of the material with the suspension before introducing it to the filter. The addition of filter aids increases the porosity of the sludge, decreases its compressibility, and reduces the resistance of the cake. In some cases the filter aid displays an adsorption action, which results in particle separation of sizes down to 0.1 /i. The adsorption ability of certain filter aids, such as bleached earth and activated charcoals, is manifest by a decoloring of the suspension s liquid phase. This practice is widely used for treating fats and oils. The properties of these additives are determined by the characteristics... 

Applications of carbon adsorption go far beyond conventional water treatment applications which we will discuss in a general sense shortly. Table 8 provides a summary of the key applications of carbon adsorption systems for liquid phase applications. 

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