Question

By which distillation method Glycerine can be purified??

Answer 1

Vacuum distillation method

Answer 2

This practically pure substance is produced by the distillation of crude glycerine, a by-product of the soapmaking and candlemaking industries.

Fats and oils, on saponification with caustic soda, yield a dilute impure solution containing about 5 per cent of glycerine, and this, on treatment and purification, yields a product containing 80 per cent of glycerine and 10 per cent of salts, known as soap lyes crude glycerine.

In the candle industry fats are hydrolysed by the autoclave, Twitchell, or similar process, yielding fatty acids and a solution of glycerine, and this solution on treatment and concentration yields saponification glycerine containing about 90 per cent of glycerine and a small percentage of salts and other impurities.

Approximate analyses of these two crude products are given below, so that the problem of distilling them for the production of glycerine in its purer forms may be understood.

Crude glycerine.

Saponification glycerine.

Glycerine T.A.V...............................................

81.28

86.47

Specific gravity at 20°/20° C.....

1.3010

1.2393

Total residue at 160° C.

12.45

0.80

Ash ................................................................................

9.73

0.42

Organic residue by difference .............................................

2.72

0.38

Arsenic parts per million .............................................

2