Processes, commercial Sorbex

Until late 1990s, purified m-xylene was produced predominantly by the HF/BF3 process developed by Mitsubishi Gas Chemical Co. The separation is based on the complex formation between m-xylene and solvent HF/BF3. However, concerns about the process operation, environment, metallurgy and safety render the process commercially unattractive due to its use of HF/BF3. These concerns led to many developments in the adsorptive separation process for m-xylene separation [3-8]. The UOP MX Sorbex process, developed by UOP and commercialized in 1998, already accounts for more than 70% of the world s m-xylene capacity. A 95% m-xylene recovery with 99.5% purity can be achieved by the MX Sorbex process. 

Such a concept was originally used in a process developed and Hcensed by UOP under the name UOP Sorbex (59,60). Other versions of the SMB system are also used commercially (61). Toray Industries built the Aromax process for the production of -xylene (20,62,63). Illinois Water Treatment and Mitsubishi have commercialized SMB processes for the separation of fmctose from dextrose (64—66). The foUowing discussion is based on the UOP Sorbex process. 

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. 

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. 

Eluxyl A process for separating /7-xylene from its isomers, using an adsorbent-solvent technique. The process is based on simulated countercurrent adsorption where the selective adsorbent is held stationary in the adsorption column. The feed mixture to be separated is introduced at various levels in the middle of the column, as in the Sorbex process. The /r-xylene product can be more than 99.9 percent pure. Developed by IFP and Chevron Chemical. A large pilot plant was built in Chevron s site at Pascacougla, MS, in 1994 and a commercial plant on the site was announced in 1996, Since then, the process has been widely licensed. 

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). 

Recognizing the need for a more economically and environmentally friendly citric acid recovery process, an adsorptive separation process to recover citric acid from fermentation broth was developed by UOP [9-14] using resin adsorbents. No waste gypsum is generated with the adsorption technique. The citric acid product recovered from the Sorbex pilot plant either met or exceeded all specifications, including that for readily carbonizable substances. An analysis of the citric acid product generated from a commercially prepared fermentation broth is shown in Table 6.2, along with typical production specifications. The example sited here is not related to zeolite separation. It is intent to demonstrate the impact of adsorption to other separation processes. 

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. 

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... 

Such a concept was originally used in a piocess developed and licensed by UOP under the name UOP Sorbex, The extent of commercial of Sorbcx processes is shown in fable 2. Other versions of file SMB... 

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. 

Only one commercial plant based on UOP s proprietary Cresex Process is operated by Merichem (Now Merisol) at Houston, TX, USA. Cresex is an extension of UOP s well-known Sorbex process based on adsorption and desorption. 

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. 

Other versions of the simulated moving-bed process beve been commercialized by Toray Industries, Inc.27 2 and Mitsubishi Chemical Industries, Ltd.29 These processes vary from the Sorbex techsology in details rather than in their besic concept. 

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. 

Sorbex is the generic name used by UOP for their simulated countercurrent sorption process which has been successfully developed for a variety of large-scale commercial separations. All Sorbex processes in current operation operate in the liquid phase, but in principle the process could also be applied to a vapor phase system. In order to understand the Sorbex process it is simplest to consider a true isothermal countercurrent displacement desorption system, as sketched in Figure 12.11. Such a system is similar in its essential features to the Hypersorption system but without the additional complexity of the thermal swing. 

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