Other Sorbex Processes

Sarex (1) [Saccharide extraction] A version of the Sorbex process, for separating fructose from mixtures of fructose and glucose. The usual feed is com syrup. The adsorbent is either a proprietary zeolite or an ion-exchange resin. Unlike all the other Sorbex processes, the solvent is water. The process depends on the tendency of calcium and magnesium ions to complex with fructose. The patents describe several methods for minimizing the dissolution of silica from the zeolite. The process is intended for use with a glucose isomerization unit, so that the sole product from com syrup is fructose. Invented by UOP in 1976 by 2003, five plants had been licensed. 

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. 

As documented in Chapter 5, zeolites are very powerful adsorbents used to separate many products from industrial process steams. In many cases, adsorption is the only separation tool when other conventional separation techniques such as distillation, extraction, membranes, crystallization and absorption are not applicable. For example, adsorption is the only process that can separate a mixture of C10-C14 olefins from a mixture of C10-C14 hydrocarbons. It has also been found that in certain processes, adsorption has many technological and economical advantages over conventional processes. This was seen, for example, when the separation of m-xylene from other Cg-aromatics by the HF-BF3 extraction process was replaced by adsorption using the UOP MX Sorbex process. Although zeolite separations have many advantages, there are some disadvantages such as complexity in the separation chemistry and the need to recover and recycle desorbents. 

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. 

Figure 8.2 depicts the four main zones and their immediate proximity to each other in the Molex process. As indicated earlier, the Sorbex process operates on a liquid-solid countercurrent contacting principle. Zone 1 is referred to as the... 

Details of the design and performance of other liquid phase adsorptions such as the Sorbex processes are proprietary. 

Large-scale Sorbex processes have been developed for a variety of different bulk separations a brief summary is given in Table IV. In recent years, the same principle has been applied also to a wide range of chiral separations and other difficult separations that are important in the pharmaceutical industry. Several novel system configurations have been developed. In one system, a carousel of 12 small columns rotates between two stationary circular headers, which act as the switch valve, thus effectively incorporating the adsorption and the flow switching functions within a single unit. 

Displacement of the adsorbate with another substance that is in turn displaced in process is practiced, for instance, in hquid phase recovery of paraxylene from other Cg aromatics. In the Sorbex process, suitable desorbents are toluene and paradiethylbenzene. This process is described later. 

The SMB technology was developed by UOP and its major field of application is in the area of binary separations. For example, SMB has been used in the chemical industry for several separations known as SORBEX processes [1-3], which include, among others, the PAREX process for p-xylene separation from a Cs aromatic fraction [4], the OLEX process for the separation of olefins from paraffins, the SAREX process to separate fructose from glucose [4] and the MOLEX process [5]. Simulated moving bed is being used particularly for separation of enantiomers from racemic mixtures or from the products of enantioselective synthesis [6,7]. It has been used for the production of fine chemicals, and petrochemical intermediates, such as Cg-hydrocarbons [8], food chemistry such as fatty acids [2], or certain sugars from carbohydrate mixtures [8] and protein desalination [9]. 

The actual Sorbex process is shown schematically in Figure 12,12. The process operates with a fixed adsorbent bed rather than with a moving bed and the countercurrent process is simulated by moving the feed, desorbent, and product points continuously by means of a rotary valve. The column sketched is divided into 12 segments, each with appropriate flow distributors to allow the introduction of feed or removal of products. In the position indicated, lines 2 (desorbent), 5 (extract), 9 (feed), and 12 (raffinate) are operational and all other lines are closed. When the rotary valve is moved to its next position the desorbent enters at point 3, extract leaves at point 6, feed at point 10, and desorbent at point I. Functionally the bed has no top or bottom and is equivalent to an annulus. The same distance is always maintained between adjacent streams, but this distance may be different for the different segments of the column. 

Citric Acid Separation. Citric acid [77-92-9] and other organic acids can be recovered from fermentation broths usiag the UOP Sorbex technology (90—92). The conventional means of recovering citric acid is by a lime and sulfuric acid process ia which the citric acid is first precipitated as a calcium salt and then reacidulated with sulfuric acid. However, this process generates significant by-products and thus can become iaefficient. 

Expansion of Sorbex technology to the production of m-xylene shows how the process concept can be used for multiple applications in separations that cannot be performed by other means. One can expect that, as demand for new, difficult to separate aromatics increases, the simulated moving bed liquid adsorption processes can provide a means for production. 

There are three liquid-phase adsorption Sorbex technology-based separation processes for the production of olefins. The first two are the UOP C4 Olex and UOP Sorbutene processes and the third is the detergent Olex process(Cio i,5) [25, 26]. The three olefin separation processes share many similarities. The first similarity between the three olefin separation processes is that each one utilizes a proprietary adsorbent whose empirical formula is represented by Cation,([(A102)),(Si02)2] [27]. The cation type imparts the desired selectivity for the particular separation. This zeolite has a three-dimensional pore structure with pores running perpendicular to each other in the x, y and z planes [28]. The second similarity between the three olefin separation processes is the use of a mixed olefin/paraffin desorbent. The specifics of each desorbent composition are discussed in their corresponding sections. The third similarity is the fact that all three utilize the standard Sorbex bed allotment that enables them to achieve product purities in excess of 98%. The following sechons review each process in detail. 

The Sarex process employs the full allotment of Sorbex beds in addition to the four basic Sorbex zones. When a Sarex unit processes corn syrup that has an approximate composition (on a dry basis) of 42% fructose, 53% glucose and 5% other saccharides, it produces a fructose enriched corn syrup with >95% purity at >90% recovery [34, 35]. The Sarex process employs sufficient operating temperature to overcome diffusion limitations with a corresponding operating pressure to maintain liquid-phase operation. 

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... 

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. 

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). 

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