Pressure Chemistry

In the three processes provision is made for heat interchange between gas entering and leaving the converter, either inside the converter itself or in a separate heat interchanges, so that the heat of reaction maintains the temperature of the catalyst. Nitrogen and hydrogen are prepared as a mixture in the Haber Bosch process from producer gas (a mixture of nitrogen and carbon monoxide) and water gas (a mixture of hydrogen and carbon monoxide). Water gas and producer gas in suitable pro portions are passed with steam over an iron oxide catalyst kept at a correct temperature, when nearly all the carbon monoxide reacts with steam to give a mixture of hydrogen and carbon dioxide; the latter gas is removed by solution in water under high pressure, while any unchanged carbon monoxide is absorbed by a solution of a cuprous salt (e.g., ammoniacal cuprous formate). In the Casale process hydrogen is produced electrolyti cally, and in the Claude process the gas is obtained from coke oven gas by a process in which other constituents are removed by liquefaction. In both processes the nitrogen-hydrogen mixture is produced by burning a calculated amount of air in the hydrogen.

Alcohol Synthesis.

G. Patart has shown that methyl alcohol (methanol) is produced by the interaction of carbon monoxide and hydrogen, under conditions of high temperature and pressure, in the presence of zinc oxide. The activity of zinc oxide as a methanol catalyst is increased by the addition of certain acidic oxides (e.g., oxides of chromium, manganese and uranium). A most efficient catalyst is produced by the reduction of a basic zinc chro mate Two litres of methyl alcohol per hour can be produced for each litre of space occupied by catalyst when a mixture of hydrogen (two parts by volume) and carbon mon oxide (one part) is passed under a pressure of 200 atmospheres over the catalyst kept at 400° C, at a rate corresponding to 20,000 litres per hour (measured at N.T.P.) of gas mixture.

Audibert has found that copper prepared by regulated reduction of cuprous or cupric oxide acts as a methanol-forming catalyst ; both the activity and stability of this catalyst may be increased by the addition of small amounts of oxides of various metals (zinc, manganese, beryllium or cerium) which act as promoters. A catalyst containing o•oi atoms of cerium for each atom of copper is stated to be highly reactive at so low a temperature as 300° C.

Experience in high-pressure practice gained through the develop ment of ammonia syntheses enabled the Badische Anilin and Soda Fabrik to place the methanol synthesis on a manufacturing basis, and in 1925 to export 500,000 gallons of synthetic methanol to the United States.

The possible number of reactions that can be effected between a mixture of carbon monoxide and hydrogen is theoretically almost unlimited, and the course of reaction is largely dependent on the nature of catalyst employed. A catalyst made from zinc

chromate leads to the production of substantially pure methanol from a mixture of carbon monoxide and hydrogen under condi tions detailed above, but if the catalyst is made alkaline by the addition of, e.g., potassium carbonate or chromate, the product contains beside methanol, n-propyl, isobutyl and higher alcohols, together with acids, free or combined as esters. The proportion of the various constituents depends on the rate of passage of the carbon monoxide-hydrogen mixture over the catalyst.

Addition of metallic cobalt to zinc chromate produces a catalyst which brings about the formation of methyl, ethyl, n propyl, isobutyl, n-butyl and higher primary alcohols ; small amounts of aldehydes can also be isolated, but the product con tains no acids free or combined.

Production of Oil from Coal.

Bergius's process for conver sion of coal into oil consists in heating powdered coal, preferably in a liquid medium, to a temperature of C, in the presence of hydrogen under a pressure of about 25o atmospheres. The introduction of 5% of hydrated ferric oxide (bog-iron ore) assists the process by combining with sulphur contained in the coal; the oxide possibly functions also as a catalyst. A large amount of heat is produced by the hydrogenation which may result in rise of temperature and the consequent formation of coke.

The oil-coal mixture has a much better thermal conductivity than powdered coal alone, and it is possible with the assistance of a stirrer to keep the reacting mass within the necessary limits of temperature.

The liquefaction of coal is regarded by Bergius as proceeding in two stages : (I) hydrogen addition, and (2) a splitting up of large molecules into smaller ones, with subsequent further addi tion of hydrogen. Bergius's liquefaction process is applicable to all types of coal, including lignites, except the anthracites and coals which consist chiefly of fusain. A continuously acting plant is usually employed on the works scale. The coal-oil mixture is forced in at one end of a long, cylindrical iron converter down which it is propelled by a mechanically driven stirrer. Hydrogen is circulated through the converter which is partially immersed in a gas-heated lead bath. The products from ioo parts of bituminous coal are as follows: gas (methane and ethane), 20 parts; oil boiling up to 23o° C, 20 parts; oil boiling at 230°-330° C, io parts; and oil boiling above 33o° C, including pitch, 20 parts. The remaining products are ammonia, 0.5 parts; water, 8 parts ; and ash, i o parts. The oily products consist of members of the aliphatic, aromatic and hydroaromatic series. Compounds of a phenolic character, chiefly cresols, are also included. Motor spirit obtained from the products (about 15%) is very rich in aromatic and hydroaromatic hydrocarbons, and may be blended with petrol to give a mixture with good anti-knocking qualities.