Author Topic: Industrial preparations of various chemicals  (Read 706 times)

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Industrial preparations of various chemicals
« on: January 09, 2004, 07:35:00 AM »
I picked up a book at the library recently called "Industrial Chemistry" by R. W. Thomas & Peter Farago.  The whole thing is pretty interesting, but I typed up some of the most relevant parts.  I got less verbose as I went on, summarizing and editing more thoroughly.  There is some stuff on ammonia production I didn't transcribe, but most of it involves heating something to give off ammonia gas.  Not terrifically practical if you don't have an industrial compressor to condense it.

Anyway, I hope that some of this is useful.  Does anyone have more information on the reduction of potassium fluoride with silicon?  The author was far from verbose about it.

p. 45: Sodium
Sodium was formerly produced by the electrolysis of molten sodium hydroxide, but this has now been completely replaced by methods based on the electrolysis of molten sodium chloride.  In most cases the Downs Sodium Cell is used.  Development off an efficient apparatus for the electrolysis of sodium chloride proved difficult for a number of reasons, and it was not until 1924 that the Downs Cell was perfected.

The main problem was that the melting point of sodium chloride is about 800 degrees C, so that large quantities of sodium vapor (which ignites on exposure to air) would be present.  Moreover, the cell was corroded rapidly at this temperature and, most serious of all, some of the sodium dissolved in the electrolyte, so increasing the `metallic' conductivity that electrolytic decomposition soon stopped.

These problems were overcome by the addition of calcium chloride to the salt to reduce its melting point, the electrolyte used containing 60 per cent of calcium chloride and having a melting point of 600 degrees C.

The cell consists of a steel cylinder lined with refractory brickwork.  A typical cell might be 3 metres high by just under 2 metres in diameter.  The anode is a large graphite rod projecting vertically into the electrolyte, and this is enclosed by two semicircular steel cathodes.  During electrolysis, sodium is liberated that the cathodes and rises to the top of the electrolyte, whereas chlorine is given off at the anode.  The anodes and cathodes are separated by a steel gauze so that the sodium rises into the outer circular channel (and up into the pipe attached) and the chlorine passes into the central cone, whence it is led off.  The sodium overflows from the collecting pipe, which contains a movable rod or `ticker' to clear any solidified sodium.

To melt the electrolyte, graphite blocks are used to connect the electrodes so that these blocks become red-hot and melt the mixture.  When this begins to melt they are removed, the heat produced by the passage of electricity maintaining the temperature (the outside of the cell is well lagged).  In a typical cell, a current of 30 000 A may be used with a working voltage of 6.7 V.

p. 59

Potassium is usually made by electrolyzing molten potassium hydroxide or by reducing potassium fluoride with calcium carbide or silicon.

p. 99

Iodine and its derivatives


The mother liquor that remains after the crystallization of the sodium nitrate [in sodium nitrate production in Chile] contains about 2-4 grammes per litre of sodium iodate.  About 10 per cent of the mother liquor is treated for the recovery of iodine.  A spray of the liquor is passed into an absorption tower into which is blown a stream of sulphur dioxide.  This converts the iodate into iodide as follows:

The solution emerging from the tower is then liberated with a small quantity of addition nitrate mother liquor, which liberates free iodine as a fine suspension.

The iodine is extracted from the aqueous suspension in flotation cells in which the pH of the solution is adjusted by addition of sodium carbonate, and the iodine is extracted with kerosene.  The free iodine, containing material from the flotation cells is passed into special sealed reactors where it is heated to 125 degrees C.  This melts the iodine, which forms a heavy layer at the bottom of the reactor.  The molten iodine is tapped off periodically...

In the U.S.A., iodine is obtained from iodides in oil-well brine by displacing the iodine with chlorine, using a method similar to that for bromine extraction [mentioned earlier--essentially bromine is extracted from sea water by passing chlorine gas through it].  The iodine is stripped from the solution by a current of air.

A little iodine is obtained from the residue (kelp) left after burning certain types of seaweed.  This contains iodides, which are left in the liquor remaining after crystallizing other salts.  Iodine can be obtained by displacing it with chlorine, or by treating the solid residues with a mixture of concentrated sulphuric acid and manganese dioxide, and subliming out the iodine.


An interesting modern use is in iodine vapour bulbs for electric lighting.  The tungsten vaporizing from the filament reacts with iodine to form a volatile tungsten iodide.  This can decompose at the heated filament to form iodine and tungsten.  Ultimately tungsten is re-deposited on the filament at the same rate as it evaporates, so that the bulb has a longer life than the old type in which vaporized tungsten recondenses on the glass.

P. 117
Phosphorus and its derivatives
... At one time, phosphorus was obtained by heating the mineral phosphate with concentrated sulphuric acid, so producing phosphoric acid, as described below.
Ca3(PO4)2 + 3H2SO4 --> 3CuSO4 + 2 H3PO4 [sic--presumably he means CaSO4]

The phosphoric acid was the heated for a long time in fireclay vats with charcoal or coke, when the acid became converted first to metaphosphoric acid (HPO3) and finally to phosphorus, which was distilled off.
H3PO4-->HPO3 + H20
4HPO3+12C--> P4+12CO+@H2

Nowadays, however, virtually all of the world's phosphorus is produced in electric-arc furnaces.  The charge for the furnace is rock phosphate (which may be sintered if too fine), coke or anthracite, and silica chippings. [Enormous and complex arc furnace is described, running at 150-300V, 5000-30000A] ... The following equation summarizes the reactions occurring:
2Ca3(PO4)2 + 6SiO2 + 10C --> 6CaSiO3 + P4 +10CO
Because this process is highly endothermic, a temperature of at least 1500 degrees C is required...

... small quantities [of phosphorus] are used for making other phosphorus compounds, and also in the match industry.  Safety matches depend on the reaction between red phosphorus and oxidizing agents such as potassium chlorate, whereas `strike anywhere' matches have a mixture of phosphorus sesquisulphide, P4S3, and potassium chlorate in the head.

[p. 124 describes some useful tidbits about phosphate fertilizers:  Super-phosphate is a mixture of Calcium sulfate and Ca(H4P04)2 (18% P2O5), and triple super-phosphate is just Ca(H2P04)2 (47% P2O5).  Explains why all my attempts to make trimethyl phosphate a la uemura have failed.  Confusing nomenclature to say the least…]

p. 144: Phosphorus compounds

... [Phosphorus oxychloride] is produced by passing chlorine through a solution of phosphorus pentoxide in phosphorus trichloride (made from the action of chlorine on phosphorus).  The phosphorus oxychloride can be distilled off and is used for making alkyl or aryl phosphates, which may be found in some insecticides and placticizers.