Pressure Chemistry

The process of heating materials with hydrogen under pressure is termed berginisation and has been applied to asphalts, coke oven tars, and heavy distillate oils for the production of light boiling oil suitable for use as motor spirit.

High-pressure Plant.

Gases used in high-pressure processes are usually stored at atmospheric pressure in ordinary inverted bell-type, water-sealed gas holders. Gas from the holders is then compressed and passed into the high-pressure system as required. Multiple-stage compressors should be specially designed for the particular gas mixture, since gases vary in their deviation from Boyle's law. The design of the compressor should also guard against leakage of gas to atmosphere and the possibility of air being drawn into the plant.

A large factor of safety must be em ployed in the construction of high pressure vessels, owing to the possibility of blow holes and other structural faults. Vessels for use at ordinary tempera tures are usually constructed of mild steel. When the vessel is to be sub jected to both high pressure and high temperature, mild steel can no longer be used since its tensile strength begins to de crease very appreciably at about 30o° C. If the reacting gases contain hydrogen, the metal may also suffer serious deteriora tion in strength owing to the removal of carbon by the action of hydrogen at the elevated temperature. In practice, a complex form of vessel is constructed in which the outer pressure-resisting shell, made of mild steel, is kept cool and away from the action of the hot gases (compare fig. 2) ; or else some special steel or

alloy is used which retains a high tensile strength at the tempera ture to which it is subjected, and which suffers little deterioration through contact with gases employed in the process. (See fig. 3.) Steels containing chromium and nickel have been found to be best suited to this purpose.

The construction of plant for chemical processes, involving the use of gases at high pressures and temperatures, has presented many difficulties, for example the making of pressure-tight en closures, glands and valves, but the advantages which arise from the reduction in gas volumes and possible efficient heat re covery make such processes in many ways preferable to normal pressure systems.

Fischer, Conversion of Coal into Oil (trans. by R. Lessing) [1925] (includes chapters on hydrogenation of coal and synthetic processes under pressure) ; R. Taylor, High Pressure Chem istry [in the press] ; B. Waeser, Atmospheric Nitrogen Industry [19261 (includes chapters on Haber-Bosch Synthesis of Ammonia, Production of Nitrogen and Hydrogen, also Bibliography) ; H. Wolbling, Die Hydriesung [Halle, 1926] (Technical Application of Catalytic Hydrogenation, including Fischer's Synthol and Bergius's Processes) ; Proceedings of the International Conference of Bitumi nous Coal, Nov. 1926, Carnegie Institute of Technology (includes papers by F. Bergius, F. Fischer and G. Patart). TA.)