Modern Gasworks Practice

616 MODERN GASWORKS PRACTICE The Development of Catalysis There can. be no question that the development of catalysis is likely to have a profound influence on the future of gas production. So far as actual carbonization in the retort is concerned, it is difficult for the moment to foresee how the forces of catalysis can be applied with such discrimination that the production of any particular products may be facilitated and cultivated. With the purification of gas, however, the way is perhaps easier. At the present time the operation of removing the main impurity, sulphuretted hydrogen, is necessarily intermittent owing to the fact that oxidation of the iron sulphides formed cannot be carried out with sufficient rapidity. As it stands, the process is essentially one of delayed catalysis, for alter the completion of sulphidation and oxidation the oxide of iron remains in its original condition. It can, liowever, be only a matter of time before a practical process is developed by means of which both. sulphuretted hydrogen and sulphur compounds are oxidized at high velocity to sulphur or, carrying the process a stage further, to sulphur dioxide. Rideal and Taylor have already gone some way towards the attainment of this ideal. Three main points stand out, namely, the choice of a suitably activated catalyst whicli is unaffected by poisoning influences such as cyanides, the provision of an absolutely tar-free gas, and the provision of an economical source of heat, i.e. waste heat if possible, for carrying on tlie reaction. The liigh.-speed oxidation of sulphur to sulphur dioxide would provide the solution of that will-o’-the-wisp of the gas engineer—complete purification. With sulphur dioxide available it would be a com-paratively easy matter to take the process a stage further and to arrange for the production of ammonium sulphate or at least sulphite, as a matter of course. Absorption Processes The primary objection to hot purification processes is that fuel bas to be con-siimp.d for the purpose of the reaction. For this reason many favour absorptive methods which may be conducted at ordinary temperatures. On the other hand, the objection to the latter processes is that they are comparatively slow in action, the space-velocity ratio being enormous when compared with the high, velocity obtained by intaoducing a catalyst. One of the most promising of absorptive methods is that introduced recently by Gordon. Adam,1 who has taken ad vantage of the relative absorptive power of charcoal for various gases. For instance, if the constituents of coal gas are considered it will be seen that some are more readily absorbed than others. Thus, 1 volume of cliarcoal absorbs approximately 65 volumes of sulphur compounds at normal temperature and pressure, while the same volume of charcoal only retains 1-75 volumes of hydrogen and 9-5 of carbon monoxide. In Adam’s process the coal gas (subsequent to the usual treatment in wet and dry purification plant, and, therefore, with sulphuretted hydrogen and ammonia removed) is passed through animal or wood cliarcoal in a granulated form. The selective action of the charcoal is employed to ensure that only the sulphur constituents and naphthalene are absorbed. This is of importance owing to the fact that ethylene and other unsaturated hydrocarbons would otherwise be removed. The quantity i B.P. 127431/19.