Adsorption various commercial processes

There are seven commercial processes in operation six operate in the vapor phase. The Universal Oil Products process operates in the Hquid phase and is unique in the simulation of a moving bed. The adsorption unit consists of one vessel segmented into sections with multiple inlet and oudet ports. Flow to the various segments is accompHshed by means of a rotary valve which allows each bed segment to proceed sequentially through all the adsorption/desorption steps. 

Most commercial extraction solvents currently are utilized to produce an improved raffinate. Recently, American Cyanamid announced availability of various dipropio-nitriles which are capable of recovering pure aromatics with exceptional selectivity. Extractive distillation to recover benzene or toluene from petroleum fractions has become an accepted commercial process. The possibilities of utilizing selective adsorption for concentration of aromatics has been receiving serious consideration. 

This case study involves the recovery of highly valued and high demand ethylbenzene (EB) and mixed-xylenes (comprising of p-xylene (PX), m-xylene (MX) and o-xylene (OX)) from a C8-aromatics mixture (C8A). As point out above, C8A is isomers mixture, so their separation (recovery) is not simple, that why there is only one commercial process of liquid-phase adsorptive separation available for EB recovery from C8A. [8] However, this process requires high investment cost and generates huge volume of waste adsorbent that may become an environmental problem. Therefore, another green process should be considered for the EB purification. The ratio of various properties of the key components (EB and PX) were tested to examine the possibly alternatives. The result showed, by vapor pressure ratio, the solvent-based extractive distillation can be employed for their purification. [7]... 

Besides porosity surface chemistry of the carbonaceous matrix, inorganic matter in activated carbon and its chemical specification have shown to be important for the process of MM adsorption/oxidation. In the study of the performance of various commercial carbons it was found that such ash constituents such as potassium and iron can be critical for the feasibilify of MM removal. While potassium, which is the natural component of coconut shell-based carbon enhances capacity by shifting the dissociation of MM to the right via basic environment, iron plays a role for catalytic oxidation via redox reactions. It is almost always present in an inorganic matter of carbons form such natural sources as coal, wood, or peat and its effect on MM adsorption /oxidation can be summarized in the following sequence of reactions (in the presence of moisture and ojQ gen) [139] ... 

Eluxyl A process for separating /7-xylene from its isomers, using an adsorbent-solvent technique. The process is based on simulated countercurrent adsorption where the selective adsorbent is held stationary in the adsorption column. The feed mixture to be separated is introduced at various levels in the middle of the column, as in the Sorbex process. The /r-xylene product can be more than 99.9 percent pure. Developed by IFP and Chevron Chemical. A large pilot plant was built in Chevron s site at Pascacougla, MS, in 1994 and a commercial plant on the site was announced in 1996, Since then, the process has been widely licensed. 

Adsorptive separation is a powerful technology in industrial separations. In many cases, adsorption is the only technology available to separate products from industrial process streams when other conventional separation tools fail, such as distillation, absorption, membrane, crystallization and extraction. Itis also demonstrated that zeolites are unique as an adsorbent in adsorptive separation processes. This is because zeolites are crystalline soUds that are composed of many framework structures. Zeolites also have uniform pore openings, ion exchange abiUty and a variety of chemical compositions and crystal particle sizes. With the features mentioned, the degree of zeoUte adsorption is almost infinite. It is also noted that because of the unique characteristics of zeoHtes, such as various pore openings, chemical compositions and structures, many adsorption mechanisms are in existence and are practiced commercially. 

Separation of gas streams by adsorption is becoming increasingly popular as improved technology comes on the market. Some examples of commercially practiced adsorption processes are shown in Table 1. These processes take advantage of the selective adsorption properties of a number of microporous adsorbents, including activated carbon, silica, alumina, and various synthetic and natural zeolites. 

Many commercial activated carbons have been prepared with various sources of raw materials and different processing conditions. As a result, the micropore structures and specific surface areas of activated carbons, which are the most profound influences on the extent of adsorption, vary, and in general, activated carbons have a surface area of up to 3000 m2/g. The rate of adsorption increases with some function of the inverse of the radius of the activated carbon even though the adsorption capacity (i.e., equilibrium adsorption) is relatively independent of the particle diameter. However, for a highly porous adsorbent such as activated carbon, the... 

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