The 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 ... 

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. 

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). 

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). 

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 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... 

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

A more sophisticated development of the same general principle is the Sorbex process, developed by UOP, which is illustrated in Fig. 14. In this system a single fixed adsorbent bed is divided into a number of discrete sections, and the feed, desorbent, raffinate, and extract lines are switched through the bed by a rotary valve. The process operates essentially isothermally with regeneration of the adsorbent by displacement desorption. There are four distinct zones in the bed, with changes in liquid flow rate between zones. Each zone consists of several sections (Fig. 14). 

MaxEne A process for increasing the yield of propylene from naphtha crackers without increasing that of propylene. A version of the Sorbex process is used to separate the normal paraffins from the branched paraffins before the cracker. Developed and offered by UOP in 2000, but not reported to have been licensed by 2005. 

MX Sorbex A process for extracting m-xylene from mixed xylene streams, using a variation of the Sorbex process. Five units were operating in 2005. 

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. 

VARICOL A continuous chromatographic process for separating natural products. It generally resembles the Sorbex process, which uses a simulated moving bed, but the column is divided into a larger number of independent sectors. 

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. 

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