Processes, commercial Molex

In contrast to trace impurity removal, the use of adsorption for bulk separation in the liquid phase on a commercial scale is a relatively recent development. The first commercial operation occurred in 1964 with the advent of the UOP Molex process for recovery of high purity / -paraffins (6—8). Since that time, bulk adsorptive separation of liquids has been used to solve a broad range of problems, including individual isomer separations and class separations. The commercial availability of synthetic molecular sieves and ion-exchange resins and the development of novel process concepts have been the two significant factors in the success of these processes. This article is devoted mainly to the theory and operation of these Hquid-phase bulk adsorptive separation processes. 

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. 

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). 

Figure 6.2 illustrates the separation of n-Csis and non-n-Cs/is in CaA molecular sieves or 5A. The separation mechanism is obvious when the kinetic diameter of the molecules and molecular sieve pore size opening are compared. n-Csjc have kinetic diameters of less than 4.4 A which can diffuse freely into the 4.7 A pores of the CaA molecular sieve, while non-n-Cs/ have kinetic diameters of 6.2A. A commercial example of shape-selective adsorption is the UOP Molex process, which uses CaA molecular sieves to separate Cio-C n-paraffins from non- -parafHns (aromatics, branched, naphthenes). 

In 1998, UOP announced the development of a new Sorbex process called the MMP Sorbex process [15-19] that was capable of simultaneously separating both Cio i6 mono-branched paraffins and Cio i6 normal paraffins from a corresponding kerosene stream or n-paraffin-depleted Molex raffinate stream. Previously, no commercial process existed to isolate significant quantities of mono-methyl paraffin derived from either kerosene or n-paraffin depleted kerosene. Mono-methyl paraffins are desirable because they are needed for a new type of anionic surfactant. 

The MMP Sorbex process has many similarities but also some differences when compared to the detergent Molex process. As with all of Sorbex processes, the MMP Sorbex process operates in the Uquid phase, employing suitable conditions (pressure, temperature) to overcome any diffusion constraints to achieve target performance. Table 8.4 highlights and contrasts the different characteristics of the detergent Molex and MMP Sorbex processes. The process was successfully demonstrated in a continuous countercurrent moving bed separation pilot plant using commercial n-paraffin-depleted kerosene (Molex raffinate) feedstock. A typical gas... 

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 process was demonstrated in a simulated continuous counter-current chromatographic separation pilot plant. Both the primary method of operation and the pre-pulse technique were demonstrated, with the pre-pulse technique showing improved recoveiy. Using commercial n-paraffin depleted kerosene (Molex Raffinate) feedstock we routinely demonstrated the ability to achieve better than 90% mono-methyl and normal paraffin purity with greater than 70% recovery of mono-methyl paraffins. 

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. 

Simulated moving-bed (SMB) processes have been widely nsed for difficult, liquid-phase separations (Ruthven, 1984 Humphrey and Keller, 1997 Juza et al 2000). Sorbex is the generic name used by UOP for these processes. The most important application is the separation of the xylene isomers, named the Parex process. Other commercialized SMB separations include n-paraffins/isoparaffins (Molex), olefins/paraffins (Olex), fructose/glucose (Sarex), and chiral SMB separations (Juza et al., 2000). A host of other separations have been demonstrated (Humphrey and Keller, 1997), although the commercial status of these applications is unknown. These demonsffated separations include separation of hydroxyparaf-finic dicarboxylic acids from olefinic dicarboxylic acids removal of thiophene, pyridine, and phenol from naphtha separation of unsaturated fatty acid methyl esters from saturated fatty acid methyl esters and separation of saturated fatty acids from unsaturated fatty acid (Humphrey and Keller, 1997). 

This process was developed and commercialized by UOP and called the Sorbex process, a general name applied to the separation of p-xylence from C8 reformates (Parex) (Broughton ei al., 1970 deRosset et al, 1978, Broughton, 1984), normal paraffins from isoparaffins and aromatic hydrocarbons (Molex), linear olefins from paraffins (Olex) and fructose from dextrose and polysaccharides (Sarex) and so on. 

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