This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
On an industrial scale this gas is prepared from alcohol by Ipatiew's catalytic process, for the purpose of making ethane. The alcohol is vaporised, and the vapour passed over amorphous aluminium oxide heated to 360°: -
C2H5 OH = C2H4 + H1O.
The ethylene thus obtained is carefully purified (to obviate "poisoning ' of the catalyst in the further operation), and converted into ethane, C2H6, by passing it mixed with purified hydrogen over freshly-reduced nickel heated to 150-200°. The resulting ethane is used in specially constructed freezing machines.1
On a small scale, it may be prepared as follows. A solution of 60 c.c. of alcohol in 300 grams of strong sulphuric acid is mixed in a flask with about 200 grams of coarse sand and heated to 160-170°. A mixture of 200 c.c. of alcohol and 300 grams of sulphuric acid is dropped into the flask through a tap funnel, the rate being regulated so that a steady stream of the evolved gas is maintained. To purify the gas from ether, alcohol, sulphur dioxide, and carbonic acid, it is passed through a series of wash bottles, of which the first may be empty, and the others contain in succession sulphuric acid and dilute caustic soda solution.
The small quantity of impurity still present can be got rid of by liquefying the gas, and then vaporising it again at a temperature of - 80°. Pure ethylene, however, can be obtained by using boric anhydride to decompose the alcohol, instead of sulphuric acid.
A nearly quantitative yield of ethylene is given by Newth's method,2 in which phosphoric acid heated to 200-220° is used.
1 Sprent, J. Soc. Ghem. Ind., 1913, 32, 171. 2 Trans. Chem. Soc, 1901, 79, 915,
On a small scale, about 50 or 60 c.c. of syrupy phosphoric acid of sp. gr. 1.75 are placed in a small Wurtz flask of about 180 c.c. capacity. The flask is fitted with a cork carrying a thermometer and a dropping-tube, the end of the latter being drawn out to a fine tube, and reaching to the bottom of the flask. Phosphoric acid of the sp. gr. mentioned, 1.75, begins to boil at approximately 160°. It is boiled in the flask for a few minutes until the temperature reaches 200°, when alcohol is allowed to enter drop by drop. Ethylene is immediately disengaged, and by maintaining the temperature between 200° and 220° a continuous supply of the gas can be obtained. Even with so small an apparatus as that described, ethylene is produced at the rate of 10 to 15 litres per hour. It is led through a small Woulfe's bottle (100 to 150 c.c. capacity) standing in a vessel of ice, in which an aqueous liquid collects containing a small quantity of ether, alcohol, and traces of oily impurity. The gas which passes on is practically pure ethylene, free from carbon dioxide, and absorbed completely by fuming sulphuric acid.
For preparation on a larger scale, alcohol may be vaporised and the vapour bubbled through phosphoric acid kept at the temperature stated.
If methyl alcohol is substituted for ethyl in the foregoing process, and the temperature of the acid kept between 200° and 210°, the gas evolved is practically pure methyl ether (CH3)20.