SORBEX process

UOP raffinate process UOP Sarex process UOP Sorbex process UOP Sorbex processes UOP Sorbex separation... 

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. 

The McCabe-Thiele approach has been developed to describe the Sorbex process (76). Two feed components, A and B, with a suitable adsorbent and a desorbent, C, are separated ia an isothermal continuous countercurrent operation. If A is the more strongly adsorbed component and the system is linear and noninteracting, the flows ia each section of the process must satisfy the foUowiag constraints for complete separation of A from B ... 

Fig. 9. Schematic diagram of a UOP Sorbex process. D, E, F, R, and. f represent flow rates for desorbent, extract, feed, raffinate, and net sobds.

UOP has developed a UOP Sorbex process for the recovery and purification of citric acid from fermentation broths. The process provides technical-grade citric acid, C HgOy, which can be further recrystaUized to obtain food-grade citric acid (qv). 

Separation of Fatty Acids. Tall oil is a by-product of the pulp and paper manufacturiag process and contains a spectmm of fatty acids, such as palmitic, stearic, oleic, and linoleic acids, and rosia acids, such as abietic acid. The conventional refining process to recover these fatty acids iavolves iatensive distillation under vacuum. This process does not yield high purity fatty acids, and moreover, a significant degradation of fatty acids occurs because of the high process temperatures. These fatty and rosia acids can be separated usiag a UOP Sorbex process (93—99) (Tables 8 and 9). 

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. 

FIG. 16-59 UOP Sorbex process. Reprinted with permission of John Wiley Liquid Separation, in Kirk-Otbmer Encyclopedia of Gbemical Tecbnology, 4th ed., John Wiley [Pg.1557]

Citric acid (Ruthven, 1997). In the separation of citric acid from fermentation liquors the Sorbex process can be used. In the conventional process neutralization is carried out with lime followed by acidification with sulphuric acid to produce calcium sulphate as waste. The Sorbex technology avoids lime and sulphuric acid wastage and calcium sulphate disposal. 

Separation of fatty acids (Ruthven, 1997). Tall oil from the pulp and paper industry is subjected to separation of rosin acid, linoleic acid, oleic acid, and neutral compounds. Distillation at reduced pressure is u.sed, but this leads to degradation of products. A Sorbex process eliminates this problem. 

Cresex [Cresol extraction] One of the Sorbex processes. This one extracts p- or m-cresol from mixed cresols, and ciesols as a class from higher alkyl phenols. By 1990, one plant had been licensed. 

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). 

MS Sorbex A Sorbex process used in the production of w-xylene from C8 aromatic mixtures. A zeolite is used as the sorbent and toluene is the desorbent. 

Olex A version of the Sorbex process for separating olefins from paraffins in wide-boiling mixtures. It can be used for hydrocarbons in the range C6 - C20. Based on the selective adsorption of olefins in a zeolite and their subsequent recovery by displacement with a liquid at a different boiling point. Mainly used for extracting Cn - C14 olefins from the Pacol... 

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). 

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. 

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. 

The Parex and MX Sorbex processes are quite similar with regard to the adsorbent section mechanics so all of the discussion about the functional zones in the section for the Parex process applies to the MX Sorbex process also. The MX Sorbex process produces m-xylene at 99.5-99.8% purity at a recovery in excess of 95%. The major differences between the two technologies are the choice of adsorbent and desorbent... 

Zeolite/Desorbent Combination A light desorbent, that is a desorbent that boils lighter than the mixed xylene feed, is used in the MX Sorbex process. This means that the energy demand of the distillation columns per unit feed for the MX Sorbex... 

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. 

Since the Sorbex process is a liquid-phase fixed-bed process, the selection of particle size is an important consideration for pressure drop and process hydraulics. The exact particle size is optimized for each particular Molex process to balance the liquid phase diffusion rates and adsorbent bed frictional pressure drop. The Sorbex process consists of a finite number of interconnected adsorbent beds. These beds are allocated between the following four Sorbex zones zone 1 is identified as the adsorption zone, zone 2 is identified as the purification zone, zone 3 is identified as the desorption and zone 4 is identified as the buffer zone. The total number of beds and their allocation between the different Sorbex zones is dependent on the desired performance of the particular Molex process. Molex process performance is defined by two parameters extract normal paraffin purity and degree of normal paraffin recovery from the corresponding feedstock. Details about the zone and the bed allocations for each Molex process are covered in subsequent discussions about each process. 

The third desorbent characteristic is that the desorbent material must be easily separated from the two Sorbex process products extract and raffinate. The adsorbent chamber s composition profile produces extract and raffinate streams comin-gled with desorbent. In order for the process to be economical, the separation of the feed components from the desorbent (achieved through fractionation) is set by the boiling point differences between the species. Depending on the selectivity possessed by the desorbent over that of the feed normals, the subsequent desorbent rates needed to flush feed normal paraffins from the adsorbent s selective volume and the resulting extract or raffinate streams from the Sorbex chambers could contain in some cases more than 50% desorbent. High concentration of desorbent demonstrates the importance of the desorbent characteristics when selecting a desorbent. 

The adsorbent used in the Sorbex process is partitioned into discrete beds within the Sorbex chambers. These beds are then allocated among four main Sorbex zones. Table 8.2 lists these zones and their corresponding function. 

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... 

Table 8.2 Sorbex process zones and their corresponding function.

The first parameter A represents the selective pore rate (m /h). For a set volume of adsorbent contained in the Sorbex chambers, there is a known selective pore volume. This selective volume quantity is divided equally among the various adsorbent beds. Since Sorbex process simulates a moving bed process where adsorbent moves counter current to the process flow, the selective pore rate represents the quantity of selective volume that moves with every step or index of the rotary valve. One step of the rotary valve indexes the feed point from one bed to the next sequential bed position. 

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