Ebex process

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

Ethylbenzene Separation. Ethylbenzene [100-41-4] which is primarily used in the production of styrene, is difficult to separate from mixed Cg aromatics by fractionation. A column of about 350 trays operated at a refluxTeed ratio of 20 is required. No commercial adsorptive unit to accomplish this separation has yet been installed, but the operation has been performed successhiUy in pilot plants (see Table 5). About 99% of the ethylbenzene in the feed was recovered at a purity of 99.7%. This operation, the UOP Ebex process, requires about 40% of the energy that is required by fractional distillation. 

The UOP Ebex process has been available for license since the 1970s. This process is a rejective simulated moving bed process where the ethylbenzene is the least adsorbed member of the mixed xylenes and is recovered in high purity in the raffinate stream [47]. Other liquid phase simulated moving bed concepts selective for ethylbenzene have been considered. These would ostensibly require less adsorbent circulation per unit feed because ethylbenzene is typically at <20% concentrahon in mixed xylenes [48, 49]. A process is disclosed by Broughton [50] that produces a pure m-xylene stream along with a pure ethylbenzene stream. 

Although not yet industrialized, the recovery of ethylbenzene contained in these cuts by sdective adsorption is also planned, particidarly by Exxon and UOP (Universal Oil Products). In Exxon s process, e desired hydrocarbon is preferentially adsorbed, while UOP s Ebex process is similar in prindple to the Sorbex type of technique, in whief the ethylbenzene remains in the raffinate. Asahi also has developments under way ii this area. 

The Ebex process for ethylbenzene recovery was developed more recently and, although pilot scale operation has been demonstrated, no full-scale commercial unit has yet been built. ... 

The adsorbents used in the Parex and Ebex processes are all various cationic forms of faujasite (Table 12.6). Due to the effect of liquid hold-up in the macropores, the effective separation factor fot a pelleted zeolite adsorbent is appreciably lower than the separation factor for the same material in unaggregated form. The number of theoretical stages required for any specified product purity decreases as the separation factor increases, but the relationship is highly nonlinear. Simulation studies reveal that for an economic process the minimum acceptable intrinsic separation factor between the extract and raffinate products is about 3. With a separation factor of less than... 

Whereas in the Parex process paraxylene is the most strongly adsorbed species and is removed in the extract, in the Ebex process ethylbenzene is the least strongly held species and is withdrawn as raffinate. Representative steady-state concentration profiles measured in a pilot scale Ebex unit are shown in Figure 12.13. It may be. seen from Table 12.6 that the selectivity of the ethylbenzene adsorbents (NaY, CaX, and Sr-KX) is generally lower than... 

The Parex process for the separation of isomers of xylene is based on the Sorbex configuration as is the Ebex process for the recovery of ethyl benzene. Both these processes utilize cationic forms of X and Y zeolites with toluene or p-diethylbenzene as desorbent in the Parex process and toluene as desorbent for the Ebex process. The Molex process (also based on the... 

Ebex [Ethylbenzene extraction] A version of the Sorbex process, for extracting ethylbenzene from mixtures of aromatic C8 isomers. The adsorbent is a zeolite. It had not been commercialized as of 1984. 

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