Still pot contents

In a batch separation the concentration of the still pot contents gradually changes owing to the removal of low-boiling component with the distillate the value of xb shifts towards zero. Let us assume that we have distilled down to a concentration Xb of 10 mol% and let us again carry out the above calculation. We then obtain the data shown in Table 13 where they are compared with those found for the beginning of the distillation. 

About half the still pot contents will therefore remain as residue. The operating hold-up, estimated at 100 ml, wiU be taken off as intermediate fraction and added to the charge in the next distillation, since such a small quantity cannot be separated adequately in the same stiU. 

If foaming occurs to a troublesome extent at the beginning of distillation, an attempt may be made to reduce it by the addition of an anti-foaming agent [16]. Silicone oils have recently been used with success for this purpose. If the material to be distilled is highly viscous it is advisable to keep the still pot contents in constant motion with a magnetic stirrer or the stirrer due to Hiibner [17]. 

V = quantity of vapor, moles W = contents ol still pot, moles... 

W i = Contents of still pot or ketde at any point, 1, after start for components, i, mols Wio = Initial contents of ketde or still pot, mols, for component, i... 

It is important to give the still pot an initial charge which substantially exceeds the volume of the upper reservoir so that the still pot will not go dry. It is veiy important to avoid letting the heated still pot go dry. The heated flask may crack and the solid contents in the pot may decompose to contaminate the system. In some cases an explosion may occur (e.g. when LiAIH4 is used see below). A metal catch pan should be positioned under each distillation apparatus to contain any spills which may occur upon solvent removal. Each still should also be vented to a fume hood. 

Batch distillation (Fig. 16) is often preferable to continuous distillation when small quantities of feed material are processed. A liquid feed is charged to a still pot and heated until vaporization occurs. Vapor leaves the top of the column, and after condensation, part is removed as product and the rest returned to the column as reflux. As distillation proceeds, the contents of the still pot and the overhead product become richer in less volatile components. When operated at a fixed reflux ratio, an overhead product cut is collected until the product composition becomes unaccceptable. As an alternative, the reflux ratio can be gradually increased to hold the product composition constant as the cut is taken. For a fixed rate of heat addition to the still pot, the latter option results in a steadily declining product flow rate. After the first cut, subsequent... 

The apparatus originally attached to the three necks of the reactor is quickly replaced by stoppers (rubber or ground glass) and a Vigreux fractionating column adapted for vacuum distillation. The pressure within the system is slowly reduced to about 25 mm. After the dissolved hydrogen chloride and the unreacted ethanol have been removed, the contents of the still pot are heated slowly. A fraction obtained over the range from room temperature up... 

The contents of the still-pot are then transferred to a beaker (heating gently to melt, if necessary), cooled in an ice-salt mixture to crystallize, filtered, and drained. Melting point, of crude crystals 57-60 C., after recrystallization from ethanol-water or petroleum ether ethyl ether 67° C. Source Bruce 1952... 

The nature of this equilibrium is invariably such that as the concentration of a component increases in the liquid, it also increases in the vapour (or in a certain limiting case, remains constant it never decreases). As the first vapour reaches the condenser at the beginning of a distillation it condenses completely to a liquid of the same composition and starts to return through the column. Now this vapour, at the start of the distillation, is in equilibrium with the contents of the boiler, or still-pot, and contains a greater proportion of the lighter components thus it cannot also be... 

In the case of a batch distillation it is therefore not sufficient to determine the conditions of distillation at the start it is necessary to consider what the final composition of the contents of the still pot is to be, or what is the highest reflux ratio that one is prepared to use, considering the total time required. Suppose that we adopt r = 25 as the limiting reflux ratio, that xb = 80 mol% and that we keep xb and the number of theoretical stages constant at 98% and 10 respectively. The data found for a reduction of the stiU pot concentration from 80 to 5 mol% are then as shown in Table 14. 

Pump the contents of the still pot into the propylene glycol product receiver. 

The distillation of rose oil is an art in itself as not only quality but also quantity plays an important role. It takes two distillation cycles to produce between 200 and 280 g of rose oil. Jean-Fran ois Arnodou describes its manufacture as follows (Arnodou, 1991) the still pot is loaded with 400 kg of rose petals and 1600 L of water. The contents are heated until they boil and steam distilled. Approximately, the quantity of owers used is then distilled. That action will last about 2-3 h. Specially designed condensers are required in order to obtain a good quality. The condensing system comprises a tubular condenser followed by a second cooler to allow the oil to separate. The oil is collected in Florentine-type oil separators. About 300 L of the oil-saturated still waters are then redistilled in a separate still in order to recover most of the oil contained in them. Both oils are mixed together and constitute the rose oil of commerce. BIOLANDES described in 1991 the whole process, which uses a microprocessor to manage parameters such as pressure and temperature, regulated by servo-controlled pneumatic valves. 

It was decided to heat the solution for several hours in an attempt to speed up the process. The jar and it s contents were propped up on a porcelain stand inside a cooking pot. To this pot was added enough water to surround the pickle jar. The lid to the pickle jar was made finger tight so that the contents could not evaporate but still allow pressure to escape. For roughly 3 hours the mixture sat in very warm water (not boiling.) Occasionally one would lift the jar, and shake the contents before placing it back on the stand. Afterwards the heat source was turned off and the water and the pickle jar contents cooled to room temperature. 

A solution of 25 g. of sodium hydroxide in 500 c.c. of water is heated to boiling (porous pot ) in a distilling flask (capacity 1 1.) connected to a downward condenser which is provided with a receiver containing 60 c.c. of 2 A-hydrochloric acid. Through the corked neck of the flask 18-6 g. of nitrosodimethylaniline hydrochloride—preferably the moist reaction product—are added in portions. Each addition is only made after most of the oily drops of the base from the preceding portion have dissolved, and finally the liquid is boiled until it has become reddish-brown. The dimethylamine produced is trapped in the hydrochloric acid in the receiver at the conclusion of the distillation the contents of the receiver must still be acid. They are evaporated to dryness on the wateT bath in a small porcelain or glass basin, and finally the completely anhydrous salt can be recrystallised from a very small amount of absolute alcohol. Yield 5-6 g. 

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