IsoSiv process, paraffin separation

Total Isomerization Also called TIP. An integrated process which combines light paraffin isomerization, using a zeolite catalyst, with the IsoSiv process, which separates the unconverted normal paraffins so that they can be returned to the reactor. Developed by Union Carbide Corporation and now licensed by UOP. The first plant was operated in Japan in 1975 by 1992, more than 25 units had been licensed. 

In the TIP process the Hysomer process is combined with the ISOSIV process which separates normal paraffins from branched ones by selectively adsorbing the normal fraction into zeolite CaA (pressure swing adsorption). Ajfter desorption (by applying vacuum) the normal paraffins are recycled. A schematic view... 

Steam stripping, which is widely used in the regeneration of solvent recovery systems using an activated carbon adsorbent, can be considered as a combination of thermal swing and displacement desorption. Vacuum desorption, which is used in some versions of the Union Carbide IsoSiv process for separation of medium-chain linear paraffins as well as in some air separation systems can be considered as a special case of pressure swing. 

One version of the UOP IsoSiv process uses PSA to separate normal paraffins from branched and cycHc hydrocarbons in the to range. 

However, ia some cases, the answer is not clear. A variety of factors need to be taken iato consideration before a clear choice emerges. Eor example, UOP s Molex and IsoSiv processes are used to separate normal paraffins from non-normals and aromatics ia feedstocks containing C —C2Q hydrocarbons, and both processes use molecular sieve adsorbents. However, Molex operates ia simulated moving-bed mode ia Hquid phase, and IsoSiv operates ia gas phase, with temperature swiag desorption by a displacement fluid. The foUowiag comparison of UOP s Molex and IsoSiv processes iadicates some of the primary factors that are often used ia decision making ... 

The IsoSiv process is an isobaric, isothermal adsorption technique used to separate n-paraffins from gas oils. The operation conditions are approximately 370°C and 100 psi. Desorption is achieved using n-pentane or n-hexane. The solvent is easily distilled from the heavier n-paraffins and then recycled. 

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... 

Union Carbide s OlefinSiv Process. Union Carbide s OlefinSiv process is used mainly to separate n-butylenes from isobutylene 31). The basic hardware is the same as for the IsoSiv process for n-paraffin separation, and the process uses a rapid cycle, fixed-bed adsorption. Since this process separates straight-chain olefins from branched-chain olefins, it is reasonable to assume that a 5A molecular sieve is used as the adsorbent. Product purities are claimed to be above 99% for both n-butylene and isobutylene streams. 

The normai isoparaffin separation process used most often is the Union Carbide IsoSiv process. Units with feed capacities of up to 3600 metric tons/day have been built. In the mid-1970 s the Hysomer paraffin-isomerization process, developed by Shell Research B.V., was combined with the IsoSiv process in such a way that normal paraffins are nearly completely isomerized. The combination is t led the Total Isomerization Process (TIP) and is shown schematically in Fig. 12.5-7. Product from a TIP unit has a Research Octane Numter of 88-92, compared to 79-82 for the product from a Hysomer unit alone. 

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. 

The CD step was first used by Union Carbide in the IsoSiv process in a Texas PSA plant in 1961 (Avery and Lee, 1962 Keller, 1983 Cassidy and Holmes, 1984). The process separated 1,000 barrels per day of natural gasoline feed into n-paraffins and branched/cyclic hydrocarbons. The feed contained 54.4% n-paraffins and 45.6% branched/cyclic hydrocarbons (Symoniak, 1980). The n-paraffin (strong adsorptive) product purity was 95-98%, whereas the purity of the isomer was 98-99% (Symoniak, 1980). Additional and larger IsoSiv plants have been built since 1961. The CD step was mentioned, as part of more complex PSA processes, in several patents that were all filed later than its first commercial practice in 1961 (Kiyonaga, 1965 Wagner, 1969). 

---