Decanting

In the first class, azeotropic distillation, the extraneous mass-separating agent is relatively volatile and is known as an entrainer. This entrainer forms either a low-boiling binary azeotrope with one of the keys or, more often, a ternary azeotrope containing both keys. The latter kind of operation is feasible only if condensation of the overhead vapor results in two liquid phases, one of which contains the bulk of one of the key components and the other contains the bulk of the entrainer. A t3q)ical scheme is shown in Fig. 3.10. The mixture (A -I- B) is fed to the column, and relatively pure A is taken from the column bottoms. A ternary azeotrope distilled overhead is condensed and separated into two liquid layers in the decanter. One layer contains a mixture of A -I- entrainer which is returned as reflux. The other layer contains relatively pure B. If the B layer contains a significant amount of entrainer, then this layer may need to be fed to an additional column to separate and recycle the entrainer and produce pure B. 

Wastewater leaves the process from the bottom of the second column and the decanter of the azeotropic distillation column. Although both these streams are essentially pure water, they will nevertheless contain small quantities of organics and must be treated before final discharge. This treatment can be avoided altogether by recycling the wastewater to the reactor inlet to substitute part of the freshwater feed (see Fig. 10.36). 

Leaving the refinery, jet fuel has generally no free water and contains only a small quantity of dissolved water. But humidity from the air and tank breathing result in continuous intrusion of water that must be then removed by decanting and filtration. This is why jet fuel needs to be tested for its ability to separate the contained water. 

Water content No decanted water Non-detectable by cobalt bromide test (NF M 41-004) Pass valve freezing test (ASTM D 2713, ISO 13758)... 

During storage, sediments decant with the water phase and deposit along with paraffins and asphalts in the bottoms of storage tanks as thick sludges or slurries (BS W). The interface between the water-sediment and the crude must be well monitored in order to avoid pumping the slurry into the refinery s operating units where it can cause serious upsets. 

These hazards are reduced drastically by desalting crude oils, a process which consists of coalescing and decanting the fine water droplets in a vessel by using an electric field of 0.7 to 1 kV/cm. 

All the process water streams are collected, the entrained hydrocarbons decanted, and the water is sent to the waste water stripper. 

Now decant the dried liquid into a small distilling flask of about 10 ml, capacity (Fig. 36, p. 63). Distil the liquid and collect the fraction b.p. 74-79°. Yield, 3 g. 

The crude acetonitrile contains as impurity chiefly acetic acid, arising from the action of phosphoric acid on the acetamide. Therefore add to the nitrile about half its volume of water, and then add powdered dry potassium carbonate until the well-shaken mixture is saturated. The potassium carbonate neutralises any acetic acid present, and at the same time salts out the otherwise water-soluble nitrile as a separate upper layer. Allow to stand for 20 minutes with further occasional shaking. Now decant the mixed liquids into a separating-funnel, run off the lower carbonate layer as completely as possible, and then pour off the acetonitrile into a 25 ml, distilling-flask into which about 3-4 g. of phosphorus pentoxide have been placed immediately before. Fit a thermometer and water-condenser to the flask and distil the acetonitrile slowly, collecting the fraction of b.p. 79-82°. Yield 9 5 g. (12 ml.). 

Boil the mixture gently on a sand-bath for 4 hours and then decant into a conical flask and cool. Seed the cold solution if necessary with a trace of a-methylglucoside. The glucoside separates as colourless crystals. When crystallisation ceases, filter the glucoside at the pump, drain, wash quickly with a small quantity of methanol, and then recrystallise from a minimum of methanol. For this purpose methanol of good quality, but not necessarily anhydrous, should be used. The a-methylglucoside is obtained as colourless crystals, m,p. 165°. Yield, 6-7 g. 

It is advisable in any case before an experiment to place the weighed aluminium isopropoxide overnight in a shallow dish in a vacuum desiccator over sodium hydroxide. The isopropanol should be dried over anhydrous sodium sulphate, and the clear liquid decanted off before use. 

When the reaction is complete, heat the stirred mixture carefully under reflux over a Bunsen burner and asbestos gauze for I hour if the mixture becomes too thick for efficient stirring, add up to 15 mL of acetic acid. Now decant the hot mixture into 500 ml. of vigorously-stirred ice-cold water wash the residual zinc thoroughly with glacial acetic acid (2 portions each of I -2 ml.), decanting the acid also into the stirred water. 

Gently warm a mixture of 32 g. (32 ml.) of ethyl acetoacetate and 10 g. of aldehyde-ammonia in a 400 ml. beaker by direct heating on a gauze, stirring the mixture carefully with a thermometer. As soon as the reaction starts, remove the heating, and replace it when the reaction slackens, but do not allow the temperature of the mixture to exceed 100-no the reaction is rapidly completed. Add to the mixture about twice its volume of 2A -hydrochloric acid, and stir the mass until the deposit either becomes solid or forms a thick paste, according to the quality of the aldehyde-ammonia employed. Decant the aqueous acid layer, repeat the extraction of the deposit with more acid, and again decant the acid, or filter off the deposit if it is solid. Transfer the deposit to a conical flask and recrystallise it twice from ethanol (or methylated spirit) diluted with an equal volume of water. The i,4-dihydro-collidine-3,5-dicarboxylic diethyl ester (I) is obtained as colourless crystals, m.p. 130-131°. Yield 12 5 g,... 

Urease solution. Place about 5 g. of jack-bean meal in a mortar and grind up with about 10 ml. of water, t hen add about 90 ml. of water, mix thoroughly and allow to stand for some time in order to deposit starch and other insoluble substances. Decant off the supernatant liquid into a conical flask and cork the latter. 

Potassium Hydroxide, Alcoholic. Boil under reflux a mixture of 10 g. of powdered KOH and 100 ml. of rectified spirit for 30 minutes. Cool and if solid material remains, decant through a filter of glass-wool. 

Bromine-water. Shake about 5 ml. of bromine with 100 ml. of water, and decant off the clear aqueous solution as required (concentration about 3%). 

By treatment with anhydrous aluminium chloride (Holmes and Beeman, 1934). Ordinary commercial, water-white benzene contains about 0 05 per cent, of thiophene. It is first dried with anhydrous calcium chloride. One litre of the dry crude benzene is shaken vigorously (preferably in a mechanical shaking machine) with 12 g. of anhydrous aluminium chloride for half an hour the temperature should preferably be 25-35°. The benzene is then decanted from the red liquid formed, washed with 10 per cent, sodium hydroxide solution (to remove soluble sulphur compounds), then with water, and finally dried over anhydrous calcium chloride. It is then distilled and the fraction, b.p. 79-5-80-5°, is collected. The latter is again vigorously shaken with 24 g. of anhydrous aluminium chloride for 30 minutes, decanted from the red liquid, washed with 10 per cent, sodium hydroxide solution, water, dried, and distilled. The resulting benzene is free from thiophene. 

Cuprous chloride. Hydrated copper sulphate (125 g.) and sodium chloride (32-5 g.) are dissolved in water (400 ml.) boiling may be necessary. An allialine solution of sodium sulphite (from 26 5 g. of sodium bisulphite and 17 -5 g. of sodium hydroxide in 200 ml. of water) or the solution of the sodium bisulphite alone is added to the resulting hot solution during about 5 minutes with constant shaking. The solution will be decolourised or nearly so. It is then cooled to room temperature (or in an ice bath), and the supernatant liquid is decanted... 

Red phosphorus. Commercial red phosphorus is usually contaminated with small quantities of acidic products. It should be boiled for 15 minutes with distilled water, allowed to settle, decanted through a Buchner funnel, and then washed two or three times with boiling water by decantation. Finally, the phosphorus is completely transferred to the Buchner funnel and washed with hot water untU the washings are neutral. It is dried at 100°, and kept in a desiccator or in a tightly stoppered bottle. 

Method 2 (Martin, 1942). A mixture of 200 g. of zinc wool, 15 g. of mercuric chloride, 10 ml. of concentrated h3 drochloric acid and 250 ml. of water is stirred or shaken for 5 minutes. The aqueous solution is decanted, and the amalgamated zinc is covered with 150 ml. of water and 200 ml. of concentrated hydrochloric acid. The material to be reduced, usually about 0-3-0-4 mole, is then added immediately, and the reaction is commenced. 

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