Distillation continuous fractional

Mass Transfer and Separation Processes Principles and Applications 

2 Mass and Energy Balances Equimolar Overflow and Vaporization 

There are three balances for the binary system considered here the total mole balance, the component mole balance, and tire heat balance. It is customary to apply these in unison and, in turn, to three separate regions of tire fractionation column. One set each is used to describe conditions above and below the feed tray (i.e., the rectifying and stripping sections). These balances are taken over the entire upper and lower portions and include tiie reboiler and condenser as well as the product stream. A third set of balances is applied to an isolated stage, the feed tray, and includes the flow rates and thermal condihon of the incoming feed. Let us see how this works out in practice. For the rechfying section, we have 

Rate of total moles in - Rate of total moles out = 0 

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If a waste contains a mixture of volatile components that have similar vapor pressures, it is more difficult to separate these components and continuous fractional distillation is required. In this type of distillation unit (Fig. 4), a packed tower or tray column is used. Steam is introduced at the bottom of the column while the waste stream is introduced above and flows downward, countercurrent to the steam. As the steam vaporizes the volatile components and rises, it passes through a rectification section above the waste feed. In this section, vapors that have been condensed from the process are refluxed to the column, contacting the rising vapors and enriching them with the more volatile components. The vapors are then collected and condensed. Organics in the condensate may be separated from the aqueous stream after which the aqueous stream can be recycled to the stripper. 

Modem plants generally produce carbon disulfide of about 99.99% purity. High product quaUty is ensured by closely controlled continuous fractional distillation. Reagent and U.S. Federal specifications, and typical commercial-grade quaUty are Hsted in Table 5. 

Williams et al. (Wl), describe the results of studies of the automatic control of continuous fractional distillation. These studies were made on an analog computer which could simulate a five-plate tower. The effects of column design, varying feed rate, imperfect sampling, and quality of feed and reflux on controllability were evaluated. An earlier article by Rose and Williams (R2) on the same system compares various schemes for controlling fractionation columns. One interesting conclusion is that derivative control action cannot improve the control for any of the various combinations of measurement and regulation that were studied. 

The initial step in the isolation of individual chemicals from coal-tar is continuous fractional distillation (cf. oil) which yields the fractions shown in Table 2.2... 

Example 12-1 Design a continuous fractionating distillation column to separate 3.78 kg/sec of 40 percent benzene and 60 percent toluene into an overhead product containing 97 mass percent benzene and a bottom product containing 98 mass percent toluene. Use a reflux ratio of 3.5 mole to 1 mole of product. Latent molal heat of both benzene and toluene is about 357.1 kJ/kg. 

Add cautiously 15 ml. of concentrated sulphuric acid to 50 ml. of water in a 100 ml. distilling-flask, and then add 10 g. of pinacol hydrate. Distil the solution slowly. When about 40 ml. of distillate (consisting of pinacolone and water) have been collected, and no more pinacolone comes over, extract the distillate with ether. Dry the extract over sodium sulphate. Distil the dry filtered extract carefully, with the normal precautions for ether distillation (p. 164). When the ether has been removed, continue the distillation slowly, rejecting any fraction coming over below 100 . Collect the pinacolone, b.p. 106 , as a colourless liquid having a peppermint odour. Yield, 4 5-5 o g. A small quantity of higher-boiling material remains in the flask. 

Place 80 g, of hydroxylamine sulphate (or 68-5 g. of the hydrochloride), 25 g. of hydrated sodium acetate, and 100 ml. of water in a 500 ml. flask fitted with a stirrer and a reflux water-condenser, and heat the stirred solution to 55-60°. Run in 35 g (42 nil,) of -hexyl methyl ketone, and continue the heating and vigorous stirring for ij hours. (The mixture can conveniently be set aside overnight after this stage.) Extract the oily oxime from the cold mixture twice with ether. Wash the united ethereal extract once with a small quantity of water, and dry it with sodium sulphate. Then distil off the ether from the filtered extract, preferably using a distillation flask of type shown in Fig. 41 (p. 65) and of ca, 50 ml, capacity, the extract being run in as fast as the ether distils, and then fractionally distil the oxime at water-pump pressure. Collect the liquid ketoxime, b.p. 110-111713 mm. Yield, 30-32 g. 

Now distil the contents of C by heating carefully over a gauze. A small initial fraction of unchanged thionyl chloride boiling at 78-80° comes over, and the temperature then rises rapidly to 194°. Directly this happens, stop the distillation, allow the condenser to drain thoroughly, and then replace G by the duplicate receiver. Run the water out of the condenser so that it acts as an air-condenser, and then continue the distillation. Collect the benzoyl chloride as the fraction boiling at 194-198°. Yield, 19 g. 

After the butyl chloride fraction has been collected, change the receiver and continue the distillation untU the zinc chloride commences to crystallise. Allow to cool and stopper the flask. The anhydrous zinc chloride thus obtained may be used in another preparation and recovered repeatedly. This results in considerable economy when the preparation is conducted by a large number of students. 

A. Maleic acid. Assemble the apparatus shown in Fig. Ill, 28, 1. Place 45 g. of dry mahc acid in the 200-250 ml. distilling flask and cautiously add 63 g. (57 ml.) of pure acetyl chloride. Warm the flask gently on a water bath to start the reaction, which then proceeds exothermically. Hydrogen chloride is evolved and the malic acid passes into solution. When the evolution of gas subsides, heat the flask on a water bath for 1-2 hours. Rearrange the apparatus and distil. A fraction of low boiling point passes over first and the temperature rises rapidly to 190° at this point run out the water from the condenser. Continue the distillation and collect the maleic anhydride at 195-200°. Recrystallise the crude maleic anhydride from chloroform (compare Section 111,93) 22 g. of pure maleic anhydride, m.p. 54°, are obtained. 

Manufacture. Trichloromethanesulfenyl chloride is made commercially by chlorination of carbon disulfide with the careful exclusion of iron or other metals, which cataly2e the chlorinolysis of the C—S bond to produce carbon tetrachloride. Various catalysts, notably iodine and activated carbon, are effective. The product is purified by fractional distillation to a minimum purity of 95%. Continuous processes have been described wherein carbon disulfide chlorination takes place on a granular charcoal column (59,60). A series of patents describes means for yield improvement by chlorination in the presence of dihinctional carbonyl compounds, phosphonates, phosphonites, phosphites, phosphates, or lead acetate (61). 

There are two serious problems associated with continuous tar distillation. Coal tar contains two types of components highly corrosive to ferrous metals. The ammonium salts, mainly ammonium chloride, associated with the entrained Hquor remain in the tar after dehydration, tend to dissociate with the production of hydrochloric acid and cause rapid deterioration of any part of the plant in which these vapors and steam are present above 240°C. Condensers on the dehydration column and fractionation columns are also attacked. This form of corrosion is controlled by the addition of alkaU (10% sodium carbonate solution or 40% caustic soda) to the cmde tar in an amount equivalent to the fixed ammonia content. 

Distillation. Distillation separates volatile components from a waste stream by taking advantage of differences in vapor pressures or boiling points among volatile fractions and water. There are two general types of distillation, batch or differential distillation and continuous fractional or multistage distillation (see also Distillation). 

Zirconium and hafnium are separated by fractional distillation of the anhydrous tetrachlorides in a continuous molten solvent salt KCl—AlCl system at atmospheric pressure (56,57). Zirconium and hafnium tetrachlorides are soluble in KCl—AlCl without compound formation and are produced simultaneously. 

Gum turpentine is obtained from wounding living trees to get an exudate containing turpentine and rosin. Turpentine is separated from the rosin by continuous steam distillation and further fractionation. Wood turpentine comes from the extraction of stumps of pine trees using naphtha, and subsequent separation of rosin and turpentine by fractional distillation. Tail-oil turpentine is a byproduct of the Kraft sulphate paper manufacture. Terpenes are isolated from the sulphate terpentine and separated from the black digestion liquor. The composition of turpentine oils depends on its source, although a-pinene and p-pinene are the major components. 

The oxidizing agent is prepared in a 500-ml flask equipped with a magnetic stirrer and cooled in an ice bath as follows In the flask are placed 60 ml of concentrated sulfuric acid and 20 ml of water, and the solution is cooled to 10°. Potassium persulfate (42 g, 0.15 mole) is added slowly to the stirred solution while maintaining the temperature below 10°. The solution is diluted with an additional 65 ml of water maintaining the temperature below 15°. The solution is now cooled to about 7° and 0.08 mole of the ketone is added over 40 minutes. After the addition has been completed, the solution is allowed to come to room temperature and stirring is continued for 20 hours. The solution is diluted carefully with 150 ml of water and extracted twice with 75-ml portions of ether. The ether is washed with sodium bicarbonate solution, followed by water, and the ethereal solution is dried. Removal of the solvent, followed by fractional distillation, affords the product ester. 

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