Ensorb process

Major commercial processes in n-paraffin separation are U.O.P. s Molex process (2-5), B.P. s process (6-8), Exxon s Ensorb process (9, 10), Union Carbide s IsoSiv process (11-13), Texaco s T.S.F. process (14, 15), Shell s process (16), and VEB Leuna Werke s Parex process (17). Except... 

FIGURE 12 Schematic diagram of the Exxon Ensorb process. (Courtesy of Aromatics Technology Division of Exxon Chemical Company.)... 

FIGURE 1130. Simplified flow sheet of Exxon Ensorb Process for separation of medium-chain... 

ENSORB [ExxoN adSORBtion] A process for separating linear from branched hydrocarbons, using a zeolite molecular sieve. The adsorbed gases are desorbed using ammonia. It operates in a cyclic, not a continuous, mode. Developed by Exxon Research Engineering Company, and used by that company on a large scale at the Exxon refinery in Baytown, TX. Asher, W. J., Campbell, M. L., Epperly, W. R., and Robertson, J. LHydrocarbon Process., 1969, 48(1), 134. 

Description The ExxonMobil Chemical (EMC) process offers commercially proven technologies for efficient recovery and purification of high-purity n-paraffin from kerosine feedstock. Kerosine feedstocks are introduced to the proprietary ENSORB recovery process developed by ExxonMobil Chemical, wherein the long-chain aliphatic normal paraffins are selectively removed from the kerosine stream in vapor phase by adsorption onto a molecular sieve. Isoparaffins, cycloparaffins, aromatics and other components not adsorbed are typically returned to the refinery kerosine pool. The cyclical process uses a low pressure ammonia desorbate to recover the n-paraffins from the sieve for use as LAB-qual-ity product or for further purification. 

The ENSORB adsorbent offers a high recovery of n-paraffins and a tolerance for sulfur and nitrogen that is unparalleled in the industry. Process conditions can be optimized for a targeted range of molecular... 

Several different adsorption processes for the separation of linear paraffins have been developed including Ensorb (Exxon), IsoSiv (Union Carbide), T. S. F. (Texaco), the Shell process, and the Leuna Werke process. The latter has been called Parex (paraffin extraction) but the choice of name is unfortunate because of possible confusion with the UOP Parex process for separation of xylene isomers. All these processes use a 5A molecular sieve, generally in binderless form to minimize nonselective adsorption. The C,o-C,g linear paraffins are strongly adsorbed even at temperatures as high as 350°C. Thermal swing desorption is not feasible since the temperature required for desorption is so high that coking would occur. The alternatives are therefore vacuum desorption, which is used in some versions of the IsoSiv process, or displacement desorption which is used in most if not all of the other processes. 

In the Molex process the Sorbex system is used for the separation of linear and branched hydrocarbons, using as adsorbent 5A molecular sieve. This is the same adsorbent as is used in the cyclic batch processes such as Ensorb and Isosiv. In contrast to the situation with the Cg aromatics, the separation factor is very large and it seems unlikely that for such an easy separation the increased cost of a Sorbex unit is justified by the reduction in adsorbent inventory and/or desorbent circulation rate. Detailed cost comparisons do not appear to have been published, but it seems likely that any economic advantage which the Molex process may have arises more from the energy savings associated with liquid phase operation than from the intrinsic advantages of a countercurrent adsorption system. 

---