Solvent extraction packed tower

Solvent Extraction - Solvent extraction uses solvents to dissolve and remove aromatics from lube oil feed stocks, improving viscosity, oxidation resistance, color, and gum formation. A number of different solvents are used, with the two most common being furfural and phenol. Typically, feed lube stocks are contacted with the solvent in a packed tower or rotating disc contactor. Each solvent has a different solvent-to-oil ratio and recycle ratio within the tower. 

One other method of recovering mercury from the vapor phase is to extract mercury using a suitable solvent (e.g. toluene or chloroform) in a scrubber, e.g. a packed tower. The mercury in the solvent can be reprocessed commercially. But, the poor solubility of mercury in such solvents warrants consumption of huge quantities of solvent thus limiting the use of a packed tower process for mercury recovery. It is therefore apparent that a preconcentration step must be used to facilitate the removal and recovery of mercury from the air phase. 

TREATABILITY/REMOVABILITY Process, Removable Range (%), Avg. Achievable Cone. (pg/L)) steam stripping, >99, <48 solvent extraction, 90-95, 16,000 activated sludge, >9, <10, granular activated carbon adsorption, >99, <10 Filtration and Sedimentation indicated negative removal best available technologies granular activated charcoal, packed tower aeration... 

Furfural Process (23, 37/, 41, 94, 103). Furfural as a selective solvent is used at relatively high temperatures, usually in the range from 150 to 250°F. The higher permissible temperatures allow for extraction of oils of high viscosity and waxy fractions even in packed towers without danger of clogging the packing. 

A commercial plant for these processes follows the general scheme of Fig. 11.23 (95). For 200,000 lb./day of degummed soybean oil and a solvent ratio of 8.3 1, two extraction columns each 5.5 ft. in diameter, 87 ft. tall (75 ft. of packing), operate in parallel for the furfural extraction at 120°F. The interface is held between the oil and solvent inlets, so that both phases are dispersed in one section of the tower or the other. The naphtha extraction is carried out in a single packed tower 4.5 ft. in diameter, containing a 50-ft. depth of Raschig rings, at 70 F. Furfural and... 

Almost all countercurrent extraction devices utilize dispersion of one immiscible phase as drops in another immiscible phase we will provide a brief introduction here. At the end, we will introduce porous hollow fiber membrane based nondispersive countercurrent solvent extraction devices. The dispersive devices may involve continuous agitation or no agitation at all. Dispersive devices without any agitation as such are of three types spray towers packed towers perforated plate towers. Spray towers were illustrated in Figure 8.1.2(b). 

Figure 8.1.35. Schematic of various large-scale liquid-liquid extraction devices, (a) Packed tower for solvent extraction (b) sieve-plate extraction column (c) an early Scheibel column extraction design (d) Karr column, in which the plates have reciprocating motions (e) centrifugal extractor (f) porous hollow fiber membrane solvent extraction device (see Figure 8.1.13(a) for a detailed design).

Example 8.1.14 A pharmaceutically active compound present in a low concentration in an aqueous solution is to be extracted into an organic solvent. The m value is known to be 12. The extraction is to be carried out from the feed aqueous solution in a packed tower of diameter 11cm. Earlier experiments in the packed tower indicated that the KiruU value for this compound is 4 x 10 s . The feed... 

The extraction operation proper consists of a series of countercurrent contacts between oil and solvent as in Figs. 11-8 and 11-9 however, vertical packed towers are more widely used than settling tanks. 

Extraction (sometimes called leaching) encompasses liquid-liquid as well as liquid-solid systems. Liquid-liquid extraction involves the transfer of solutes from one liquid phase into another liquid solvent it is normally conducted in mixer settlers, plate and agitated-tower contacting equipment, or packed or spray towers. Liquid-solid extraction, in which a liquid solvent is passed over a solid phase to remove some solute, is carried out in fixed-bed, moving-bed, or agitated-solid columns. 

An important feature in the construction of continuous countercurrent extraction towers is the design of the nozzles through which the solvent and oil feed enter. Nozzles should be designed to distribute the stream evenly over the cross-sectional area of the tower in order to minimize channeling and to make maximum use of the packing near the inlet. Consideration should also be given to the use of intercoolers to enforce a temperature gradient. 

Extractive Distillation. In extractive distillation a fraction comprising compounds of similar volatility is vaporized and passed countercurrent to a liquid solvent stream in a packed or bubble cap tower. The operating conditions of temperature and pressure are regulated so that one or more of the components of the mixture are dissolved in the entrainer and removed in a liquid phase extract, while the remaining vapor is taken overhead and condensed or discharged as gaseous effluent. 

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