ADSORPTION, LIQUID SEPARATION

Nearly every chemical manufacturiag operation requites the use of separation processes to recover and purify the desired product. In most circumstances, the efficiency of the separation process has a significant impact on both the quality and the cost of the product (1). Liquid-phase adsorption has long been used for the removal of contaminants present at low concentrations in process streams. In most cases, the objective is to remove a specific feed component alternatively, the contaminants are not well defined, and the objective is the improvement of feed quality defined by color, taste, odor, and storage stability (2-5) (see Wastes, industrial Water, industrial watertreati nt). 

In contrast to trace impurity removal, the use of adsorption for bulk separation in the liquid phase on a commercial scale is a relatively recent development. The first commercial operation occurred in 1964 with the advent of the UOP Molex process for recovery of high purity / -paraffins (6—8). Since that time, bulk adsorptive separation of liquids has been used to solve a broad range of problems, including individual isomer separations and class separations. The commercial availability of synthetic molecular sieves and ion-exchange resins and the development of novel process concepts have been the two significant factors in the success of these processes. This article is devoted mainly to the theory and operation of these Hquid-phase bulk adsorptive separation processes. 

An adsorbent can be visualized as a porous soHd having certain characteristics. When the soHd is immersed in a Hquid mixture, the pores fill with Hquid, which at equilibrium differs in composition from that of the Hquid surrounding the particles. These compositions can then be related to each other by enrichment factors that are analogous to relative volatiHty in distillation. The adsorbent is selective for the component that is more concentrated in the pores than in the surrounding Hquid. 

The choice of separation method to be appHed to a particular system depends largely on the phase relations that can be developed by using various separative agents. Adsorption is usually considered to be a more complex operation than is the use of selective solvents in Hquid—Hquid extraction (see Extraction, liquid-liquid), extractive distillation, or azeotropic distillation (see Distillation, azeotropic and extractive). Consequentiy, adsorption is employed when it achieves higher selectivities than those obtained with solvents. 

A significant advantage of adsorbents over other separative agents Hes in the fact that favorable equiHbrium-phase relations can be developed for particular separations adsorbents can be produced that are much more selective in their affinity for various substances than are any known solvents. This selectivity is particularly tme of the synthetic crystalline zeoHtes containing exchangeable cations. These zeoHtes became available in the early 1960s under the name of molecular sieves (qv) (9). 

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Ebex process separation [ADSORPTION, LIQUID SEPARATION] (Voll)... 

ADSORPTION,LIQUID SEPARATION] (Vol 1) [ADSORPTION,LIQUID SEPARATION] (Vol 1)... 

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