Processes, commercial Parex

A large number of commercial attd experimental results have beat rqxnted. The products from a truly countercurrem process would be constant. In a simulated countercurrent process, the product concentration varies, but the cycle repeats every few minutes when the valves are swiidied. It is common to pool each product and report the average compositions. Table 14.3-1 gives the results fora commercial Parex purification of p-xylene. A specially formulated molecular sieve adsorbent was used and p-diethylbenzene was the desorbent. The p-xylene is the most strongly adsorbed species. A typical plarrt for producing p-xylene would produce 100,000 metric tons/yr of p-xylene produa. 

Currendy, there are three commercially available PX adsorption processes UOP s Parex, IFP s Eluxyl, and Toray s Aromax (not to be confused with Chevron s Aromax process for reforming naphtha into aromatics). In all of these processes, the feed and desorbent inlets and the product oudet ports are moved around the bed, simulating a moving bed. 

Displacement-purge forms the basis for most simulated continuous countercurrent systems (see hereafter) such as the UOP Sorbex processes. UOP has licensed close to one hundred Sorbex units for its family of processes Parex to separate p-xylene from C3 aromatics, Molex tor /i-paraffin from branched and cyclic hydrocarbons, Olex for olefins from paraffin, Sarex for fruc tose from dextrose plus polysaccharides, Cymex forp- or m-cymene from cymene isomers, and Cresex for p- or m-cresol from cresol isomers. Toray Industries Aromax process is another for the production of p-xylene [Otani, Chem. Eng., 80(9), 106-107, (1973)]. Illinois Water Treatment [Making Wave.s in Liquid Processing, Illinois Water Treatment Company, IWT Adsep System, Rockford, IL, 6(1), (1984)] and Mitsubishi [Ishikawa, Tanabe, and Usui, U.S. Patent 4,182,633 (1980)] have also commercialized displacement-purge processes for the separation of fructose from dextrose. 

Isomar [Isomerization of aromatics] A catalytic process for isomerizing xylene isomers and ethylbenzene into equilibrium isomer ratios. Usually combined with an isomer separation process such as Parex (1). The catalyst is a zeolite-containing alumina catalyst with platinum. Developed by UOP and widely licensed by them. It was first commercialized in 1967 by 1992, 32 plants had been commissioned and 8 others were in design or construction. See also Isolene II. 

Molex A version of the Sorbex process, for separating linear aliphatic hydrocarbons from branched-chain and cyclic hydrocarbons in naphtha, kerosene, or gas oil. The process operates in the liquid phase and the adsorbent is a modified 5A zeolite the pores in this zeolite will admit only the linear hydrocarbons, so the separation factor is very large. First commercialized in 1964 by 1992, 33 plants had been licensed worldwide. See also Parex (2). 

Parex (1) [Para extraction] A version of the Sorbex process, for selectively extracting p-xylene from mixtures of xylene isomers, ethylbenzene, and aliphatic hydrocarbons. The feedstock is usually a C8 stream from a catalytic reformer, mixed with a xylene stream from a xylene isomerization unit. The process is operated at 177°C the desorbent is usually p-diethylbenzene. The first commercial plant began operation in Germany in 1971 by 1992, 453 plants had been licensed worldwide. Not to be confused with Parex (2). 

The Parex, Toray Aromax and Axens Eluxyl processes are the three adsorptive liquid technologies for the separation and purification of p-xylene practiced on a large scale today. The MX Sorbex process is the only liquid adsorptive process for the separation and purification of m-xylene practiced on an industrial scale. We now consider a few other liquid adsorptive applications using Sorbex technology for aromatics separation that have commercial promise but have not found wide application. 

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... 

The Parex and MX-Sorbex processes are both members of UOP s family of Sorbex processes. The MX-Sorbex process for the separation of high-purity meta-xylene was introduced in 1998. Five MX-Sorbex units were commercialized between 1998 and 2001. The market for meta-xylene is expected to grow to 800,000 metric tons per year by 2009 (23). The Parex process was introduced in 1971 for the separation of para-xylene, and 71 units were commercialized by 2001. 

Commercial plants UOP is the world s leading licensor of process technology for aromatics production. UOP has licensed more than 600 separate process units for aromatics production, including over 200 CCR Platforming units, 134 Sulfolane units, 80 Parex units, 61 Isomar units, 44 Tatoray units and 38 THDA units. 

SMB systems were created to exploit some of the countercurrent features of moving-bed systems, but employing fixed beds to avoid attrition. Liquid-phase SMB adsorption systems, such as OOP s Sorbex processes, have been commercialized since the early 1960s. Among the Sor-bex family, the Molex process separates normal paraffins from branched and cyclic isomers the Olex process splits olefins from paraffins the Parex process isolates p-xylens from m-, o-xylene, and ethyl benzene mixtures and the Sarex process splits fructose from com syrup. These are discussed further in Section 14.6. 

Liquid Phase Separation. UOP have pioneered several small-scale processes to fractionate mixtures of liquids. The Parex process was introduced in 1971 and by 2001 71 units were running commercially. The MX-Sorbex process was introduced in 1998 and so far 5 units have been commercialized. Very recently,in 2001, UOP introduced a new Sorbex process, MaxEne, to increase the ethlene yield from Naphtha Crackers. Examples of these are listed in Table 30. 

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