Fractionators packed column internals

Figure 8.7 provides fractionation column internal trays that are to be added to the overall pressure vessel cost. A packed-column internal (random packing) cost is also given as cost per cubic foot of column-packed volume. 

In the case of a packed column, the terms on the right-hand side should each be divided by the voidage, ie, the volume fraction not occupied by the soHd packing (71). In unpacked columns at low values of the sHp velocity approximates the terminal velocity of an isolated drop, but the sHp velocity decreases with holdup and may also be affected by column internals such as agitators, baffle plates, etc. The sHp velocity can generally be represented by (73) ... 

Two types of injectors are frequently employed. For packed column SFC, a standard six port rotary valve with an external sample loop of 1-10 pL has proven to be quite reliable. For capillary column SFC, a similar rotary valve with an internal "loop of 0.2 to 0.5 pL is typically employed. Frequently the rotor is pneumatically actuated in a very rapid fashion to allow only a small fraction of sample to be introduced ("time-split ) this is done to avoid column overload. Alternatively, the flow from the injector is split off in the same fashion as in GC. A disadvantage of the latter mode is the potential for sample discrimination. 

Process pressure vessel cost. Process pressure vessels are always designed in accordance with the current ASME code. These major equipment items are always cylindrical metal shells capped with two elliptical heads, one on each end. Installation can be either vertical or horizontal. Vertical is generally a fractionation-type column with internal trays or packing, although the smaller-height vertical vessels (less than 15 ft) are mostly two-phase scrubber separators. The horizontal vessel is generally a two- or three-phase separation vessel. 

Identification of liquid products was carried out mainly by combined high resolution GC/mass spectrometry. Identity of products in most cases was confirmed by comparison of their retention volumes and H NMR spectra with those of reference compounds. Differentiation between the n-paraffin, a-olefin, and internal olefins in each fraction of the product from 1 was likewise based on comparison with available reference samples. Gas chromatographic columns used for quantitative analysis of liquid products included packed columns, e.g., 6% OV-17 on 100-120 mesh Chromosorb W, as well as capillary columns (29). 

The column experiments were carried out in a glass column of l.Scm internal diameter and 30cm length filled with Sg of ion exchange resin. Pd solution was percolated through the packed column at a flow rate of 1.0 ml/min controlled by a peristaltic pump (EYELA SMP-21, Japan). The effluent samples were collected at r ular intervals by the fraction collector (Model Adventec SF-2100) and analyzed for Pd concentration by ICP. 

Supercritical fractionation of a liquid lipid feed material is usually carried out in a packed column. Standard columns are not available commercially and have to be custom built either in-house or by manufacturers of extraction units. Lab-scale and pilot-scale supercritical columns, 0.6-13.6 m high with internal diameters of 14.3-68 mm are available in research labs around the world and have been used for the processing of deodorizer distillates (56, 57, 86-90), vegetable and fish oils (91-105), cocoa butter, and milkfat (106-109). A schematic diagram of a typical SCCO2 fractionation column (2.8 m, 2.54 cm o.d.), which was designed and built... 

The sample is loaded at atmospheric pressure into an external or internal loop, or groove in the valve core and introduced into the mobile phase stream by a short rotation of the valve. The volume of sample injected is normally varied by changing the volume of the sample loop or by partially filling a sample loop with a fraction of its nominal volume. External sample loops have volumes from about 5 p.1 up to about 5 ml, although typical injection volumes for conventional diameter columns are 10-50 xl. Injections from 1 p,l to about 40 nl require micro-injection valves equipped with replaceable internal loops [7,32-34]. Injection volumes less than about 40 nl are performed by positioning a split vent between the injector and the column. Typical injection volumes that preserve column efficiency for packed columns of different internal diameters are summarized in Table 5.1. For packed capillary columns with internal diameters < 0.2 mm direct injection will usually require the use of a split vent to minimize volume overload unless on-column focusing is possible. Injection volumes about 5 times larger than those indicated in Table 5.1 are sometimes used to increase sample detectability but with some decrease in the column separation power. 

A reduction factor <5 has to be introduced for columns with internals reducing the cross-sectional area (Eq. (6-72)). This is the void fraction of packed columns introducing the relative void fraction it is... 

Most distillations conducted commercially operate continuously, with a more volatile fraction recovered as distillate and a less volatile fraction recovered as bottoms or residue. If a portion of the distillate is condensed and returned to the process to enrich the vapors, the Hquid is called reflux. The apparatus in which the enrichment occurs is usually a vertical, cylindrical vessel called a stiU or distillation column. This apparatus normally contains internal devices for effecting vapor—Hquid contact the devices may be categorized as plates or packings. 

The checkers obtained roughly 30 g. of crude product in each run. Freshly opened Woelm silica gel (obtained from ICN Pharmaceuticals, 26201 Miles Ave., Cleveland, Ohio 44128) was deactivated as above, and 1800 g. was wet-packed with petroleum ether in a 65-mm. internal diameter column. In the first run the column was eluted as above, but a considerable amount of solvent was required to collect the product. Therefore, in the second run the crude product was applied to the column as a solution in petroleum ether, and 1-1. portions of 20% v/v ether petroleum ether, 30% ether, 40% ether, 50% ether, 60% ether, and 70% ether were run through. None of these six fractions contained a significant weight of material. Elution with 2 1. of 80% v/v ether petroleum ether then provided the bromohydrin acetate. 

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