Nitro-Cellulose Industrial Waste
KLAUS MUDRACK, Head and Professor
Institute of Sanitary Engineering
College of Technology,
Hannover, Germany
Nitro-cellulose is a nitrate-ester of cellulose and therefore more correctly
called cellulose nitrate. There are per glucose molecule, the basic element of
cellulose, 3 OH-groups for esterification available so that the production of nitrocellulose is possible with different nitrogen quantities. The quantity of nitrogen
and the length of the molecules determine the qualities of the nitro-cellulose and,
because of modifications necessary for the process of production, indirectly the
nature of the waste products.
Nitro-cellulose with a nitrogen content between 12.6 and 13.4 per cent is
known as "gun-cotton." "Collodion" (with a nitrogen content of 10.0 to 12.5
per cent) is made, for example, by adding 20 to 25 per cent camphor. This results in a technical synthetic "celluloid" and, when dissolved in organic solvents,
various "lacquers. "
PRODUCTION OF NITRO-CELLULOSE (1,2,3)
Pure cellulose is treated in the form of cotton-linters or wood-cellulose with
a mixture of sulphuric acid (59-67 per cent), nitric acid (21-23 per cent) and water (10-20 per cent), the so-called "nitrating acid". In order to get favorable
contact between the voluminous cellulose and the nitrating acid about 50 kg of
nitrating acid are needed for each kg of cellulose. After the chemical reaction
the excess nitrating acid is separated by centrifuging. A considerable part ofthe
nitrating acid however is left as "adhering acid", namely 80-100 per cent of the
nitro-cellulose weight in the production of gun-cotton and 150 to 180 per cent in
the production of collodion. This adhering acid has to be washed out of the nitrocellulose by a hundred times greater quantity of water and thus becomes added to
the waste. As the nitric acid adheres more to the nitro-cellulose than the sulphuric
acid, the percentage of the nitric acid is higher in the adhering acid than in the
nitrating acid. Apart from these inorganic substances, the highly acid waste also
contains organic substances in the form of cellulose decomposition products.
In the USA during the last years there has been developed a method of recovery of the adhering acid by using magnesium nitrate instead of sulphuric acid. By
this means the acid content of the waste can be reduced considerably.
NEUTRALIZATION OF THE ACIDS
The sulphuric and nitric acids contained in the sewage must be neutralized
before being discharged into the receiving water. This is normally done with lime
(CaO) or dolomite (CaO.MgO). Assuming a quantity of 1.2 tons excess acid per
ton of nitro-cellulose, about 0.74 tons of dolomite for each ton of nitro-cellulose
is needed for neutralization. The waste is mixed with corresponding quantities of
lime --or dolomite -- milk in reaction tanks. In the settling tank that follows
the insoluble calcium sulphate (gypsum) is retained. The addition of the neutralizing substance must be directed through pH-electrodes in order to be able to adjust the dosage to the varying acid-contents. This method of neutralization is
generally known (4,5) and need not be discussed here.
If a large receiving stream is available, part of its temporary hardness (hy-
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