Plates, fractionating

Lastly, it is worth mentioning that there are applications of two-or-more-step preparative TLC in solnble organic matter fractionations however, they are rarely described [4,86]. Each plate is developed successively in a series of solvents such as tetrahydrofurane, CHClj/MeOH (4 1 v v), toluene, and pentane such that the solvent front advancers approximately 4 cm with each successive solvent the plate dries up between the solvent, and the development tank atmosphere is allowed to equilibrate for at least 30 min after adding a new solvent, and before inserting the plates. Fractions represented immobile material in tetrahydrofurane (THE) and mobile compounds in successive solvents. 

A mixture of water and ethyl alcohol containing 0.16 mole fraction alcohol is continuously distilled in a plate fractionating column to give a product containing 0.77 mole fraction alcohol and a waste of 0.02 mole fraction alcohol. It is proposed to withdraw 25 per cent of the alcohol in the entering stream as a side stream containing 0.50 mole fraction of alcohol. 

Geddes, R. L. Trans. Am. Inst. Chem. Eng. 42 (1946) 79. Local efficiencies of bubble plate fractionators. 

Figure 9.29 Membrane formation by meteoritic amphiphilic compounds (courtesy of David Deamer). A sample of the Murchison meteorite was extracted with the chloroform-methanol-water solvent described by Deamer and Pashley, 1989. Amphiphilic compounds were isolated chromatographically on thin-layer chromatography plates (fraction 1), and a small aliquot ( 1 p,g) was dried on a glass microscope slide. Alkaline carbonate buffer (15 p,l, 10 mM, pH 9.0) was added to the dried sample, followed by a cover slip, and the interaction of the aqueous phase with the sample was followed by phase-contrast and fluorescence microscopy, (a) The sample-buffer interface was 1 min. The aqueous phase penetrated the viscous sample, causing spherical structures to appear at the interface and fall away into the medium, (b) After 30 min, large numbers of vesicular structures are produced as the buffer further penetrates the sample, (c) The vesicular nature of the structures in (b) is clearly demonstrated by fluorescence microscopy. Original magnification in (a) is x 160 in (b) and (c) x 400.

Reagent-grade chloroform was distilled through a 30-plate, fractional distillation column at a reflux ratio of 10 to 1 and collected over outgassed calcium hydride. The purified solvent then was frozen in liquid nitrogen and outgassed under high vacuum while it warmed slowly to room temperature. 

Plate exchangers, 189,195 Plates, fractionating. See Trays Pneumatic conveying, 71-76 dense phase transfer, 74 equipment, 72,73,75 flow rates, 72 operating conditions, 73 pilot plant, 74... 

Step B. To the aqueous reaction mixture described under Step A is added 1000-1500 ml. of methanol and the mixture is allowed to stand at room temperature for three hours. The dimethylal and methanol are then distilled out, distillation being stopped when the temjierature of the residue reaches 90°. The mixture is cooled and treated with 10 moles of 40% sodium hydroxide. The amine layer is taken up in ether and the aqueous layer extracted three times with 300 ml. of ether. The ether extract is dried Over anhydrous calcium sulfate and the ether is then removed by distillation. Distillation of the amine is carried out from a Claisen flask, b.p. 82° at 17 mm., 1.5615. Further purification can be effected by distillation through a 12-plate fractionating column. 

Procedure. Isobutylene (gaseous) is introduced in a rapid stream to the well-stirred mixture of thiophene and sulfuric acid over a period of about one hour. The temperature is raised to 60-70° before addition of the isobutylene and maintained in that range throughout the addition by means of a water bath. The organic layer is decanted from the catalyst layer and washed with dilute alkali (KOH or NaOH), dried over calcium chloride, and distilled in a 10-plate fractionating column. The cut boiling between 162 and 170° is a mixture of 2- and 3-/rr/-butyl-thiophene. These isomers are best separated in a 60-plate column by a double fractionation. Pure 2-terf-butylthiophene boils at 163.9°,... 

To determine the actual number of plates required, divide the result in step 2 by the overall plate fractional efficiency, typically denoted by E(y Values can range from 0.4 to 0.8. The actual number of plates can be calculated from... 

W. L. Bolles Rapid Graphical Method of Estimating Tower Diameter and Tray Spacing of Bubble-Plate Fractionators, Pet. Refiner, 25(12) 103 (1946). 

Collect HPLC fractions based on time (e.g., 1-2 minutes per fraction) by use of an automated sample collector, kept at 4°C, with 1.5-mL Agilent Well Plate fraction collector (325-pL fractions are typically collected per 1.5-mL microtubes). 

Flooding is usually correlated in terms of the sum of the continuous v, and dispersed v phase superficial velocities (velocities based on the empty column cross-sectional area). Flooding data for a variety of systems was correlated in the range of plate fractional free area e = 0.085 to 0.58 by the following equationfBaird etal.. 19941 ... 

The best possible precision for the determination of VPIE can be obtained by measuring Ap and p simultaneously using a differential technique. Another and quite different approach to determine the VPIE involves a measurement of the separation factor (a) defined by the equilibrium between the liquid phase and its saturated vapor in a one-plate fractionation experiment... 

The results just described demonstrate that the resolution of GC peaks may be very sensitive to changes in retention time resulting from instability in oven temperatures. Since the number of theoretical plates is related to resolution values, significant degradation in column plate values can occur with variations in oven temperatures. When you compare the time and effort required to obtain a two-plate fractional distillation on a 2-mL mixture (see Experiment [3B] and Technique 2) with the speed and ease used to obtain a 500 plate separation on 12.5 (xL of cyclohexanol in this experiment, it is hard not to be impressed with the enormous power of this technique. 

This technique is performed on a 15 theoretical plate fractionation column to obtain a true boiling point curve while maintaining an approximate 5 1 reflux ratio. The still pressure is reduced in order to prevent decomposition... 

The sample is distilled at an accurately controlled pressure between 0.13 and 6.7 kPa (1 and 50 mm Hg) under conditions that are designed to provide approximately one theoretical plate fractionation. Data are obtained from which the initial boiling point, the final boiling point, and a distillation curve relating volume percent distilled and atmospheric equivalent boiling point temperature can be prepared. 

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