Methyl alcohol is known as Wood Alcohol because it was formerly obtained by the destructive distillation of wood.
Methyl alcohol may be prepared by any of the general methods described before. For large scale production, the following three methods can be used:
From water gas.
Today, methanol is mostly manufactured by this method. Steam is passed through red-hot coke to form water gas. Water gas is a blend of carbon monoxide and hydrogen.
Water-gas is blended with half its volume of hydrogen. The mixture is compressed to 300 atmospheres. It is then passed over a zinc oxide-chromium oxide catalyst at 300ºC. Methyl alcohol vapors are produced which are condensed (Fig. 15.2).
From Natural Gas.
Methyl alcohol is also manufactured from methane obtained from natural gas. A mixture of methane and oxygen (9:1) is passed over the copper catalyst at 250ºC under pressure. Methane is oxidized to methyl alcohol.
Wood is heated to 400ºC in iron retorts in the absence of air (Destructive distillation) to produce:
This is a gaseous mixture which consists of CH4, CH3-CH3,H2,CO2,CO, and N2.
This is an aqueous mixture which consists of 5% methyl alcohol, 0.5% acetone, and 10% acetic acid.
This is a thick black liquid that separates from the aqueous distillate. On further distillation, it gives a mixture of cresols.
This is a solid residue that is left in iron retorts. It consists mainly of carbon and is a popular domestic fuel.
Separation of Methyl Alcohol from Pyroligneous Acid. Pyroligneous acid is a mixture of acetic acid, acetone, and methyl alcohol. Methyl alcohol is isolated from it by the following steps:
Removal of Acetic Acid.
Pyroligneous acid is mixed with Ca(OH)2. This reacts with acetic acid to form calcium acetate. The mixture is distilled. Methyl alcohol and acetone distill over leaving calcium acetate in the flask.
Removal of Acetone.
The mixture of methyl alcohol and acetone is fractionally distilled. Acetone boils at 56ºC. Methyl alcohol boils at 64.5ºC. The methyl alcohol so obtained is not pure. It is treated with CaCl2. Methyl alcohol forms CaCl2.CH3OH, which is a crystalline compound. This is separated and decomposed by boiling with water to give free alcohol. Finally, it is dried over lime (CaO) and redistilled to get pure methyl alcohol.
The wood Distillation method of making methyl alcohol is only of historical importance. It is not used these days.
Methyl alcohol is a colourless liquid, bp 64.5ºC. It is miscible with water in all proportions. When taken internally, methyl alcohol is a poison. As little as 30 ml can cause death, and lesser amounts can cause irreversible blindness. A mixture of methyl alcohol vapour and air is easily ignited by even a small spark. Chemically it behaves like a typical monohydric alcohol. It gives most of the general reactions mentioned before.
Methyl alcohol is used : (1) as a solvent for paints and varnishes : (2) as an antifreeze for automobile radiators : (3) to denature ethyl alcohol : (4) as a motor fuel. A 20% mixture of methyl alcohol and gasoline makes a good motor fuel : and (5) in the manufacture of formaldehyde.