Concentric-tube column

Spinning band column Hyper-Cal column Concentric tube column... 

To a distillation flask is added 29.0 gm (0.244 mole) of 3-bromopropyne and 2.5 gm (0.0174 mole) of dry cuprous bromide. The flask is attached to a concentric-tube column (25-30 theoretical plates), and the temperature of the flask is controlled so that the takeoff temperature at the head remains at 72.8°-73.5°C. In 24 hr, 24.4 gm (84 %) of bromopropadiene of 75-85 % purity is obtained. The remaining 3-bromopropyne (propargyl bromide) is removed by washing the product with a 40 % aqueous solution of diethylamine. Three to four moles of diethylamine is used for each mole of propargyl bromide in the product as calculated from VPC or refractive index data. After swirling the mixture (acidified with 15 % hydrochloric acid) for hr, the organic layer is separated, washed with water, dried over potassium carbonate, and distilled quickly under reduced pressure into a Dry Ice-cooled receiver to afford pure bromopropadiene, b.p. 72.8°C (9760 mm), w ° 1.5212, 1.5508. 

Widmer column. A Dufton column, modified by enclosing within two concentric tubes the portion containing the glass spiral. Vapour passes up the outer tube and down the inner tube before entering the centre portion. In this way flooding of the column, especially at high temperatures, is greatly reduced (Widmer HCA 7 59 1924). 

Figure 6.10. Concentric tube heated injection port with adaptor for 1/8 and 1/4-inch columns. Glass liners are used for all-glass systems.

The isomeric oxiranes prepared by ring closure of l-bromo-l-phenyl-2-propan-ol (ref. 9) were separated on a Fischer concentric tube column (theoretical plate number 90) (b.p. cis (1) 355 K/13 mm Hg, trans (2) 361 K/13 mm Hg, ac-... 

After drying (removal of water), the extract is quantitatively transferred into a Kudema-Danish flask equipped with a concentrator tube and a Snyder column for sample concentration. The apparatus is placed in a water bath and ether is evaporated out. Use boiling chips in all heating operations. The volume of the extract is concentrated down to 1 to 2 mL. 

Fig. 4. Schematic diagram of a concentric-tube airlift bioreactor (with working volume of 1.0 1). 1 Reactor column 2 inner draft tube (with its height of 15 cm) 3 sparger B bottom clearance (2.5 cm) d diameter of draft tube (4.5 cm) D reactor diameter (7.0 cm) H column height (40 cm)...

Kudema-Danish (KD) Apparatus. 500 mL evaporating flask, 10 mL graduated concentrator tubes with ground glass stoppers, three ball macro-Synder column. 

Many types of fractionating columns have been designed. However, most of these have proved relatively inefficient, and the principal types presently in use are the Vigreux, bubble-cap, packed, spinning-band, and concentric-tube. Each of these will be considered in turn. 

Two less common, but very useful, columns are the spinning-band and concentric-tube columns. The spiiming-band column consists of... 

A concentric-tube column (F g- 1-33) consists of two concentric tubes with only a small annular space between them ( 0.75 mm). The vapors and descending liquid pass between the tubes, and fractionation results from the liquid-vapor contact on the walls. These columns are characterized by a rapidly decreasing HETP with increasing throughput, and they require a very slow withdrawal of the distillate in order to maintain equilibrium. They have very low holdup and HETP (0.5 to 1 cm). Thus, they are particularly suited for careful distillation of relatively small quantities (2 to 20 ml), in which the low holdup is important and the slow withdrawal rate ( 0.1 ml per hour for a 100-plate column) is not too inconvenient. 

I ig. 1-33. Concentric-tube column. (Courtesy of Dr. E. Naragon and Analytical Chemistry.)... 

The most satisfactory columns are usually the ones with a low pressure drop, since they are much less prone to flood. The spinning-band column appears to be one of the best for this purpose, and a concentric-tube column, except for the slow take-off rate, is also fairly satisfactory. A glass-helix-packed column is usually unsatisfactory because of a great tendency toward flooding. Metal packing is more desirable in this respect. With most columns, it is advisable to hold the jacket at a somewhat higher temperature (5 to 10°) than the vapor temperature because of this increased tendency toward flooding. 

The focus of this entry is limited to the design of aerobic fermenters, i.e., stirred tank and concentric tube airlift fermenters, which are commonly utilized in the bioprocessing industries. Design principles and the basic calculations are described with a couple of industrial examples. Readers with a limited background in mixing technology are referred to the gas-liquid contactor entry of this encyclopedia for a more comprehensive understanding of fluid flow and mass transfer characteristics in stirred tank reactors and bubble columns. 

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