Potassium carbonates

Potassium carbonate (poe-TAS-ee-yum KAR-bun-ate) is also known as potash, pearl ash, salt of tartar, carbonate of potash, and salt of wormwood. It is a white, translucent, odorless, granular powder or crystalline material that tends to absorb water from the air. As it does, it is converted into the sesquihydrate ( sesqui = one-and-a-half) with the formula KjCOj i.sHjO. That formula means that three molecules of potassium carbonate share two molecules of water among them. 

Potash is easily produced by pouring water over the ashes of burned plants and then evaporating the solution formed in large pots (hence the name pot ash ). The process has been known since at least the sixth century ce and the resulting product used in the manufacture of soap. Potash was one of the first chemicals to be exported by American colonists, with shipments having left Jamestown as early as 1608. Potassium carbonate is also called pearl ash and salt of tartar, both of which are impure forms of the compound. The impurities present include sodium chloride 

Potassium carbonate. Red atoms are oxygen black atom is carbon and turquoise atoms are potassium. Gray stick indicates a double bond. 

Most of the potassium carbonate made in the United States is produced beginning with potassium chloride (KC1) obtained from seven mines in New Mexico, Michigan, and Utah. The potassium chloride is first converted to potassium hydroxide (KOH) by electrolysis. The potassium hydroxide is then treated with carbon dioxide (C02) to obtain potassium bicarbonate (KHC03). Finally, the potassium bicarbonate is decomposed by heating, yielding water, carbon dioxide, and potassium carbonate. 

Another method of preparation, called the Engel-Precht process, is a modification of this procedure. A mixture of potassium chloride, magnesium carbonate or magnesium oxide, and carbon dioxide is treated under 30 atmospheres 

Applications Potassium hydroxide is utilized in the manufacture of other potassium compounds (potassium carbonate, potassium phosphates e.g. tetrapotassium pyrophosphate, potassium permanganate, potassium bromate, potassium iodate, potassium cyanide etc.), of dyes, special soaps and battery liquids. It is also used in photographic developers, in glass manufacture and as a drying and absorption agent. In many of these applications its use is declining. 

The K2CO3 1.5H2O produced by carbonation is in part calcined in rotary tube furnaces at 250 to 35()°C 

Manufacture Potassium carbonate (potash) was formerly produced by the ashing of wood and other plant raw materials. Since the middle of the nineteenth century, the saline residues from the rock salt industry and salt deposits have been the raw materials for potassium carbonate production. The currently industrially most important process is the carbonation of electrolytically produced potassium hydroxide. 50% potassium hydroxide solution (e.g. from the mercury process) is saturated with carbon dioxide, the solution partially evaporated and the potassium carbonate hydrate K2CO3 1.5H2O which precipitates out is separated. After drying, the product is either marketed as potash hydrate or is calcined in a rotary tube furnace at temperatures of 250 to 350°C to anhydrous potassium carbonate. Anhydrous potassium carbonate is also produced in a fluidized bed process in which potassium hydroxide is 

In other processes similar to the Solvay process (see Section 3.1.1.3.3), potassium carbonate is produced directly from potassium chloride with amines such as isopropylamine via a potassium hydrogen carbonate step, but contaminated calcium chloride brine is produced as a byproduct whose disposal poses environmental problems. In the former States of the USSR potassium carbonate is also produced from alkali aluminosilicate deposits (e.g. nepheline) together with aluminum oxide, cement and sodium carbonate. 

In the former States of the USSR potassium carbonate is also produced from alkali aluminosilicates e.g. nepheline KNai[AlSi04]4 

Hydrated lime is used in the amine process for the production of potassium carbonate from potassium chloride [31.20]. 

Potassium chloride is reacted with carbon dioxide in precarbonated isopropylamine solution under pressure in an autoclave. Potassium hydrogencarbonate precipitates and the amine is converted into isopropylamine chlorohydrate. The potassium salt is isolated by filtration, washed free of amine and heated to convert it to the carbonate. Unreacted amine present in the filtrate is recovered by distillation. Hydrated lime is then added to convert the isopropylamine chlorohydrate back to the amine, which is also recovered by distillation. The main uses of potassium carbonate are the production of glass and sodium silicate. 

MELTING POINT = 891°C BOILING POINT = decomposes DENSITY = 2.3 g/cm3 

Potassium carbonate is used in the chemical industry as a source of inorganic potassium salts (potassium silicates, potassium bicarbonate), which are used in fertilizers, soaps, adhesives, dehydrating agents, dyes, and pharmaceuticals. Potassium carbonate used to make potassium lye produces soft soaps, which are liquids or semisolids rather than solids. Other uses of potassium carbonate includes use as a fire suppressant in extinguishers, as a C02 absorbent for chemical processes and pollution control, an antioxidant in rubber additives, and in pharmaceutical formulations. 

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Benfield process Removal of carbon dioxide from fuel gases, such as those obtained by gasifying coal in the Lurgi process, by countercurrent scrubbing of the gases by hot potassium carbonate solution. 

Catacarb process An extraction process used to remove carbon dioxide from process gases by scrubbing the hot gases with potassium carbonate solution containing additives which increase the hydration rate of the gas in the solution. The Vetrocoke process is similar. See Benfield process. 

In one process the carbon dioxide is removed using potassium carbonate solution, potassium hydrogencarbonate being produced ... 

This reaction can be reversed by heat and the potassium carbonate and carbon dioxide recovered. (Other compounds which absorb carbon dioxide and evolve it again at a lower temperature are also in common usage" ). 

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.). 

Required Sulphuric acid, 27-5 ml. aniline, 24 ml. sodium nitrite, 20 g. dry potassium carbonate, 3-4 g. (To ensure that the potassium carbonate is dry, it should be gently heated in an evaporating-basin over a small Bunsen flame for 4-5 minutes with stirring, and then allowed to cool in a desiccator.)... 

Now transfer the cold distillate to a separating-funnel, and shake vigorously with about 50-60 ml. of ether run oflF the lower aqueous layer and then decantf the ethereal solution through the mouth of the funnel into a 200 ml. conical flask. Replace the aqueous layer in the funnel, and extract similarly twice more with ether, combining the ethereal extracts in the conical flask. Add 3-4 g. of dry powdered potassium carbonate to the ethereal solution, securely cork the flask and shake the contents gently. The ethereal solution of the phenol... 

A) Extract the mixture with about 40 ml. of chloroform, in which the free base is very soluble. Run off the lower chloroform layer, dry it with potassium carbonate as in (a), and then add carbon tetrachloride slowly with stirring to the filtered chloroform solution until the base starts to crystallise out. Allow to stand for a short time (t.e., until the deposition of crystals ceases) and then filter at the pump as the crystals lose the last trace of solvent, they tend as before to break up into a fine powder, the deep green colour becoming paler in consequence. 

Required Aniline, 30 ml. onrhlorobenzoic acid, 8 g. potassium carbonate, 8 g. powdered copper oxide, 0 4 g. 

Prepare a mixture of 30 ml, of aniline, 8 g. of o-chloro-benzoic acid, 8 g. of anhydrous potassium carbonate and 0 4 g. of copper oxide in a 500 ml. round-bottomed flask fitted with an air-condenser, and then boil the mixture under reflux for 1 5 hours the mixture tends to foam during the earlier part of the heating owing to the evolution of carbon dioxide, and hence the large flask is used. When the heating has been completed, fit the flask with a steam-distillation head, and stcam-distil the crude product until all the excess of aniline has been removed. The residual solution now contains the potassium. V-phenylanthrani-late add ca. 2 g. of animal charcoal to this solution, boil for about 5 minutes, and filter hot. Add dilute hydrochloric acid (1 1 by volume) to the filtrate until no further precipitation occurs, and then cool in ice-water with stirring. Filter otT the. V-phcnylanthranilic acid at the pump, wash with water, drain and dry. Yield, 9-9 5 g. I he acid may be recrystallised from aqueous ethanol, or methylated spirit, with addition of charcoal if necessary, and is obtained as colourless crystals, m.p. 185-186°. 

Extract the dimethylaniline by shaking the distillate in a separating-funnel with a few ml. of ether, and then dry the ethereal solution over potassium carbonate distil the filtered ethereal solution from a small distilling-flask e.g, Fig. 36, p. 63) with the usual precautions, and finally the dimethylaniline, b.p. 193°. Yield, almost theoretical. 

Alcohols Anhydrous potassium carbonate anhydrous magnesium or calcium sulphate quicklime. 

Ketones Anhydrous sodium, magnesium or calcium sulphate anhydrous potassium carbonate. 

Higher alcohols. These may be purified by drying with anhydrous potassium carbonate or with anhydrous calcium sulphate, and fractionated after filtration from the desiccant. Bark corks (or ground glass joints) should be used rubber stoppers are slightly attacked. The boiUng points of the fractions to be collected are as follows —... 

Mono-alkyl ethers of ethylene glycol, ROCHjCHjOH. The mono methyl, ethyl and n-butyl ethers are inexpensive and are known as methyl cellosolve, cellosolve, and butyl cellosolve respectively. They are completely miscible with water, and are excellent solvents. The commercial products are purified by drying over anhydrous potassium carbonate or anhydrous calcium sulphate, followed by fractionation after... 

The acetone is refluxed with successive small quantities of potassium permanganate until the violet colour persists. It is then dried with anhydrous potassium carbonate or anhydrous calcium sulphate, filtered from the desiccant, and fractionated precautions are taken to exclude moisture. 

If it is desired to purify an inferior product, 1 litre of it is refiuxed for 6 hours with 85 ml. of acetic anhydride and then distilled through a fractionating column the liquid passing over at 56-57° is collected. The distillate is shaken with 20 g. of anhydrous potassium carbonate for 10 minutes, filtered and redistilled. The resulting methyl acetate has a purity of 99- 9 %. 

Ethyl acetate. Various grades of ethyl acetate are marketed. The anhydrous comjjound, b.p. 76-77°, is of 99 per cent, purity, is inexpensive, and is suitable for most purposes. The 95-98 per cent, grade usually contains some water, ethyl alcohol and acetic acid, and may be ptuified in the following manner. A mixture of 1 litre of the commercial ethyl acetate, 100 ml. of acetic anhydride and 10 drops of concentrated sulphuric acid is refluxed for 4 hours and then fractionated. The distU-late is shaken with 20-30 g. of anhydrous potassium carbonate, filtered and redistilled. The final product has a purity of about 99-7% and boils at 77°/760 mm. 

The chloroform is shaken two or three times with a small volume (say, 5 per cent.) of concentrated sulphuric acid, thoroughly washed with water, dried over anhydrous calcium chloride or anhydrous potassium carbonate, and distilled. 

Hexamethylene glycol, HO(CH2)gOH. Use 60 g. of sodium, 81 g. of diethyl adipate (Sections 111,99 and III,100) and 600 ml. of super-d ethyl alcohol. All other experimental detaUs, including amounts of water, hydrochloric acid and potassium carbonate, are identical with those for Telramelhylene Glycol. The yield of hexamethylene glycol, b.p. 146-149°/ 7 mm., is 30 g. The glycol may also be isolated by continuous extraction with ether or benzene. 

Use the apparatus detailed in Section 111,20. Dissolve 100 g. (123 ml.) of methyl n-butyl ketone (2-hexanone) (Section 111,152) in 750 ml. of ether and add 150 ml. of water. Introduce 69 g. of clean sodium in the form of wire (or small pieces) as rapidly as possible the reaction must be kept under control and, if necessary, the flask must be cooled in ice or in running water. When all the sodium has reacted, separate the ethereal layer, wash it with 25 ml. of dilute hydrochloric acid (1 1), then with water, dry with anhydrous potassium carbonate or with anhydrous calcium sulphate, and distil through a fractionating column. Collect the fraction of b.p. 136-138°. The yield of methyl n-butyl carbinol (2-hexanol) is 97 g. 

Freshly distilled ethyl formate must be used. Commercial ethyl formate may be purified as follows. Allow the ethyl formate to stand for 1 hour with 16 per cent, of its weight of anhydrous potassium carbonate with occasional shaking. Decant the ester into a dry flask containing a little fresh anhydrous potassium carbonate and allow to stand for a further hour. Filter into a di flask and distil through an efficient fractionating column, and collect the fraction, b.p. 53-54° protect the receiver from atmospheric moisture. 

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