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.
For commercial purposes methyl alcohol is obtained chiefly from the products of wood which has been submitted to dry distillation, or treated with hot producer-gas. Almost any hard wood may be employed for the distillation. The species generally used are beech, birch, maple, oak, and thorn: in this country, the thorn is regarded as one of the best for the purpose, though it is not always obtainable in sufficient quantity. Vinasse, a by-product of beet-sugar manufacture, is also a source of methyl alcohol.
1 Ann. Chym. Phys., 1835, 58, 5; 183G, 61, 193.
A wood-distilling industry of considerable magnitude has been developed in the United States. In Canada, and Australia also, the industry is a growing one; and an important quantity of wood spirit, amounting in 1907-8 to about 6 1/2 million kilos., is produced in Austria-Hungary and Germany. In this country the industry is on a smaller scale.
In the United States, the wood used is thoroughly seasoned for one or two years. Usually it is divested of its bark, and cut into 50-inch lengths. The destructive distillation is carried out in large iron retorts at a temperature of 400° to 500°F. (204° to 260° C). These retorts are usually made of steel, and are provided with outlet tubes about 15 inches in diameter. The retorts are set in pairs in brickwork, and batteries of from 2 to 20 pairs are common. The wood is fed through the door, and carefully stacked so as completely to fill the retort; or in some cases the wood is loaded into steel cars and these run into the retort. In the larger works, the retorts are constructed of brick, and are of 50 cords capacity. They are provided with heavy iron doors, which are tightly closed after the charging is completed, and the retorts are then heated from below with burning wood, coal, or charcoal, supplemented by tar, oil, and gas obtained as by-products of the industry. Natural gas is also used as the fuel in some cases.
The gaseous products of the distillation are passed through condensers. Any gases not condensed are returned and burned under the retorts.
The condensed products are run into tanks, in which the tar settles out; whilst the "pyroligneous acid," containing acetic acid, methyl alcohol, acetone, allyl alcohol, etc., forms the upper layer. The pyroligneous acid is a dark red-brown liquid with a peculiar empyreumatic odour; it is used to a limited extent in making an impure acetate of iron ("black iron liquor"), but is usually treated to separate the methyl alcohol, acetone, and acetic acid. It contains about 4 per cent, of methyl alcohol.1
The separation is effected by fractional distillation. To recover the acetic acid, the vapours are passed into milk of lime, whereby are employed, and from them are obtained distillates containing 15, 42, and 82 per cent, of wood alcohol respectively. The last product - 82 per cent, wood spirit - still contains acetone, in varying amount, as well as other substances.
' grey acetate of lime " is produced. Alternatively, the pyroligneous acid may be neutralised with lime before distilling off the methyl alcohol. Usually three stills of about 2,500 gallons capacity each
1 Baskerville, J. Ind. Eng. Chem., 1913, 5, 768.
The processes may be shown diagrammatically as follows: -
No decomposition occurs below 160° during the distillation. Between 160° and 275°, the pyroligneous acid is formed; about 275°, the yield of gaseous products becomes well marked; between 350° and 450°, liquid and solid hydrocarbons are formed; and above 450° little change occurs.
The crude wood alcohol obtained is generally sent to a central-located refinery in tank-cars, iron drums, or barrels, for purification and rectification. This is accomplished by further distillation from lime or caustic soda, with special methods for removing acetone, as described below. The final product ordinarily obtained is commercial wood alcohol (wood spirit, wood naphtha), which is usually sold at 95 per cent. strength (Tralles), but which may contain from 10 to 20 per cent. of acetone and varying proportions of other impurities. A more highly-rectified and refined product containing 97 to 98 per cent. of actual methyl alcohol is also obtained; this is sold under various trade names, such as "Columbian Spirits," "Colonial Spirits," "Manhattan Spirits." In Canada, a similar product is known as "Green Wood Spirits" and "Standard Wood Spirits."
During the year 1909 there were distilled in the United States 1,150,000 cords of hard woods such as beech, birch, and maple; and 116,000 cords of yellow pine, fir, and other soft woods. From the hard woods, the chief products obtained were, per cord of wood: -
Crude wood alcohol ..............................
Grey and brown acetates .......................
(Mainly grey acetate of lime.)
The soft woods yielded. besides charcoal, chiefly turpentine and wood tar. They are of more value for the production of these than as a source of wood alcohol and acetic acid.
Figures for the relative yields obtained from different kinds of wood in laboratory tests have been given by Hawley and Palmer.1 For the three hard woods commonly used on a large scale for distillation in the United States the average results were as follows;.
(1). Expressed as percentage of the dry weight of wood.
Wood alcohol (100 per cent.).
Acetic acid (100 per cent.).
(2). Expressed in terms of commercial products and referred to the basis of a cord (90 cb. ft.) of air-dried wood (15 per cent. of moisture): -
Gallons of wood alcohol.
82 per cent.
Lb. of calcium acetate, 80 per cent.
- Methyl alcohol is also obtained as a by-product in the manufacture of wood pulp. In the sulphate process for "easy bleaching " pulp, about 13 kilos. of methyl alcohol are formed per 1,000 kilos. of cellulose, and a part of this alcohol is recovered by condensing the vapours discharged from the digesters at pressures between 10 and 4 atmospheres. This is a fairly pure alcohol, containing only about 0 5 per cent. of acetone. A further quantity, of less pure spirit, is obtained from the vapours passing at pressures below 4 atmospheres, and from the evaporation of the lye. In the Ritter-Kellner sulphite process, 8 to 10 kilos. of methyl alcohol are formed per ton of cellulose.2
Methyl alcohol can also be obtained from the ' black liquor ' yielded in the digestion of wood by the "soda-pulp " process,3 and from waste esparto liquors.4
1 Eighth Int. Cong. Appl. Chem., 1912; (Abst.) J. Soc. Chem. Ind., 1912, 31, 865.
2 Bergstrom, Papierfabrikant, 1912, 10, 677.
3 White and Rue (Abst,), J. Soc. Chem. Ind., 1917, 36, 383.
4 Lawrence, ibid.
Fig. 29. - triple-column continuous still.
For wood alcohol, ether, etc. a, supply tank; b, liquor regulator; c, preheater; d, separating column; e, separating column rectifier; f, separating column condenser; g, boiling column; h, boiling column rectifier; k, rectifying column; l,rectifying column rectifier; m, rectifying column condenser; n, rectifying column cooler; o, steam regulators; p, oils condensing tank r, run-off testers (Blair, Campbell & McLean, Ltd., Glasgow),