Horizontal adsorbers

In the Aromax process, the adsorbent can be easily loaded, unloaded or regenerated at the level of each stage. Its total life is about 10 years. The operation takes place at a temperature below 200 0 at less than 2.10 Pa absolute. The number of stages can be increased by placing two or more horizontal adsorbers in series, depending on tbe type and volume of tbe feed to be treated and the performance required. 

A second criticism is that the model restricts attention to the forces between the adsorbent and the adsorbate molecules—the vertical interactions—and neglects the forces between an adsorbate molecule and its neighbours in the same layer—the horizontal interactions. From the nature of intermolecular forces (p. 5) it is certain that these adsorbate-adsorbate interactions must be far from negligible when a layer is approaching completion and the average separation of the molecules is therefore small in relation to their size. 

The Aromax process was developed in the early 1970s by Toray Industries, Inc. in Japan (95—98). The adsorption column consists of a horizontal series of independent chambers containing fixed beds of adsorbent. Instead of a rotary valve, a sequence of specially designed on—off valves under computer control is used to move inlet and withdrawal ports around the bed. Adsorption is carried out in the Hquid phase at 140°C, 785—980 kPA, and 5—13 L/h. PX yields per pass is reported to exceed 90% with a typical purity of 99.5%. The first Aromax unit was installed at Toray s Kawasaki plant in March 1973. In 1994, IFP introduced the Eluxyl adsorption process (59,99). The proprietary adsorbent used is designated SPX 3000. Individual on-off valves controlled by a microprocessor are used. Raman spectroscopy to used to measure concentration profiles in the column. A 10,000 t/yr demonstration plant was started and successfully operated at Chevron s Pascagoula plant from 1995—96. IFP has Hcensed two hybrid units. 

The channels in zeoHtes are only a few molecular diameters in size, and overlapping potential fields from opposite walls result in a flat adsorption isotherm, which is characterized by a long horizontal section as the relative pressure approaches unity (Fig. 6). The adsorption isotherms do not exhibit hysteresis as do those in many other microporous adsorbents. Adsorption and desorption are reversible, and the contour of the desorption isotherm foUows that of adsorption. 

The heai4 of an adsorbent wheel system is a rotating cyhnder containing the adsorbent. Figure 16-55 illustrates two types horizontal and vertical. In some adsorbent wheels, the adsorbent particles are placed in basket segments (a multitude of fixed beds) to form a hori-... 

FIG. 16-55 Adsorbent wheels for gas separation a) horizontal with fixed beds (h) vertical monolith. Reprinted with permission ofUOF.)... 

The adsorbers are usually built of steel, and may be lagged or left unlagged the horizontal type is shown in Figure 28. The vapor-laden air is fed by the blower into one adsorber which contains a bed of 6- to 8-mesh activated carbon granules 12 to 30 inches thick. The air velocity through the bed is 40 to 90 feet per minute. The carbon particles retain the vapor only the denuded air reaches the exit, and then the exhaust line. The adsorption is allowed to continue until the carbon is saturated, when the vapor-laden air is diverted to the second adsorber, while the first adsorber receives low-pressure steam fed in below the carbon bed. The vapor is reformed and carried out by the steam. The two are condensed and if the solvent is not miscible with water, it may be decanted continuously while the water is run off similarly. After a period which may be approximately 30 or 60 minutes, all the vapor has been removed, the adsorbing power of the charcoal has been restored, and the adsorber is ready to function again, while adsorber No. 2 is steamed in turn. 

FIG. 18 Mean-square displacements gi t) vs time for chains with 7 = 128 in a narrow non-adsorbing sUt (Z)= l,e = 0) at density cp = 1.5. Straight lines show effective exponents = 0.56, and = 0.84, respectively. Broken horizontal lines show (above) and (below), (b) Log-log plot of the relaxation time r 3 vs N for the case (D = 1, e = 0) and various densities (p as indicated. Straight lines show interpretations in terms of effective exponents Zgff (r oc [16]. 

FIGURE 6.4 Horizontal ES chamber 1 — mobile phase reservoir, 2 — capillary siphon, 3 — small cover plate with distributor plate, 4 — base plate, 5 — adsorbent layer, 6 — carrier plate, 7 — main cover plate, 8 — additional cover plate used to close the chamber. (From Soczewinski, E., Planar Chromatography, Vol. 1, Kaiser, R.E., Ed., Huethig, Heidelberg, 1986, pp. 79-117. With permission.)... 

Isocratic linear development is the most popular mode of chromatogram development in analytical and preparative planar chromatography. It can be easily performed in horizontal chambers of all types. The mobile phase in the reservoir is brought into contact with the adsorbent layer, and then the movement of the eluent front takes place. Chromatogram development is stopped when the mobile phase front reaches the desired position. Usually 20 X 20 cm and 10 X 20 cm plates are applied for preparative separations, and this makes the migration distance equal to about 18 cm. Due to the fact that the migration distance varies with time according to the equation Z, = (Z, c, and t are the distance of the solvent front traveled, constant,... 

The procedure described earlier for sample preconcentration can be easily extended for the online extraction of solid samples, e.g., powdered plant materials. Horizontal conbguration of the chromatographic plate in the chamber facihtates this procedure, because the sample to be extracted is then placed on a carrier plate at the begiiming part of the adsorbent layer (or in the scrapped channel of the adsorbent layer), which should be directed upward [15,26]. The chamber is covered with a narrow plate, and the development is started with a snitable extracting solvent. In some cases, it is advantageous to put the narrow plate directly on the adsorbent layer to press the sample to be extracted. Extracted components are preconcentrated on the adsorbent layer at the end of the narrow plate, as shown in Fignre 6.26 [15]. 

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