Heated column jacket

Separations achieved with a dedicated gas chromatograph for fast GC (flash gas chromatograph) with a much shorter length of capillary column inserted into a resistively heated column jacket... 

Separation of the hexachlorodisiloxane (b.p. 137°) from unreacted silicon tetrachloride is accomplished by distillation. A 40-cm. fractionating column packed with glass helixes and provided with a heating jacket is suitable. The distillation is started cautiously since much dissolved chlorine is expelled initially. Care. Use a fume hood ) Silicon tetrachloride (b.p. 57°) will pass up the column with little or no heat applied to the jacket. When the bulk of the tetrachloride has passed over, the heat to the flask and the column jacket is increased carefully so that distillation continues steadily. The product passing over at 135 to 138° is collected and redistilled if desired. The recovered silicon tetrachloride may be recirculated. 

The apparatus must be adequately insulated and the column jacket provided with the requisite heat compensation (section 7.7.3). The use of an automatic column head (section 7.5.3) allows the distillation to be performed with a minimum of attention. In the present case it would be useful to place a contact thermometer, connected to a bell via a relay (section 8.2.2), in the column head. The thermometer would be set to the boiling point of benzene, and when a signal was heard, the initial reflux ratio of 9 would be increased, say, to 20. In the same way it would be progressively raised to the final value of 50. The load may conveniently be regulated by means of a contact manometer actuated by the pressure differential (section 8.4.2). In accordance with the amount of the charge the still pot may be a pilot-plant flask (section 7.6.1) or a round-bottomed flask of 4 to 10 litres capacity, heated by a flask heater (section 7.7.1). 

Fischer and Weyand (chap. 8, Ref. [27]) could prove that providing a column with an electric heat-compensating jacket in addition to a vacuum jacket may improve the efficiency considerably (Fig. 341). 

When heating elements are used on the column head care must, of course, be taken that the vapour is not superheated, as this would vitiate the temperature readings. A calibration as described for column jackets must therefore be carried out first. If distillates having a high melting point are produced, they can easily be handled by the use of heating tape on the connections to the receiver and on the receiver itself. 

The steel column was insulated in an electrically heated aluminum jacket and temperature-controlled using a solid-state proportional temperature controller. The latter device contained two potentiometers that could each be preset to provide particular temperatures. Temperature changes were controlled by the programmer. Published precision of the instrument is 5%. Typically, precision of commercial amino acid analyzers lies in the... 

Maintain a temperature below -20°C in the lines of the distillate cooler and receiver as well as in the condenser. Turn on the column mantle heat controller and maintain the column jacket temperature 0 to 5 C below the vapor temperature. 

Fig. II, 17, 2 illustrates a fractional distillation unit f for use with glass helices. The column is provided with an electrically-heated jacket the resistance shown in the Figure may be replaced by a variable transformer. The still head is of the total-condensation variable take-off type aU the vapour at the top of the column is condensed, a portion of the condensate is returned to the column by means of the special stopcock (permitting of...

The efficiency of all the above columns (and also those described below) is increased by lagging with asbestos cloth. The best results are obtained by surrounding each column with two glass jackets and heating the inner jacket electrically to a temperature within 5-10° of the fraction... 

The Stedman-type column is shown in Fig. 11, 56, 25. The characteristic features are (i) the use of a fine stainless steel wire cloth formed into conical discs, and (ii) an accurately fitting Pyrex glass jacket, produced by shrinking Pyrex glass on mandrels to the required inside dimensions. Modifications incorporating a silvered vacuum jacket and an electrically-heated jacket are marketed. This column is said to possess high efficiency but is expensive. It is generally employed in conjunction with a total-condensation variable take-off still head. 

The best results are obtained with a fractionating column surrounded by an electrically-heated jacket (compare Figs. II, 17. 2. and II. 17, 3), but this is not essential for n-caproic anhydride. For the preparation of propionic or n-biityric anhydride, a highly efficient fiactionating column must be used in order to obtain satisfactory results. 

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