Modern Gasworks Practice

410 MODERN GASWORKS PRACTICE logues decompose under the action of heat, found that, in a stream of nitrogen rieh in benzene, decomposition just started. at a temperature of 550° C. and at this stage a solid resembling naphth alene was deposited. This was identified as diphenyl1 and was produced in increasing quantities, together with. hydrogen, as the temperature was carried higher. At still higher temperatures, however, decomposition went a stage further, diphenyl-benzene being found. These results are a little perplexing in that, altliough benzene is found in some quantity in coal gas and tar, diphenyl is present in quantities scarcely sufficient to be separated. Here is an instance of so-called differences between theory and practice, or, between laboratory and large-scale results, indicating that some important factors had not been taken into account. The discrepancy was, however, ascribed to the prevailing atmosphere. or the state of dilutiou of the benzene by other gases, notably hydrogen and methane. When experiments were repeated, in which the benzene was highly diluted with nitrogen, decomposition was lessened, and the yield of solid condensates, such as diphenyl, decreased. Hydrogen was th.cn employed in lieu of nitrogen as a diluent. By gradually diluting further and further with hydrogen, the quantity of molecular condensates gradually diminished until, when the benzene was rechiced to a proportion. of about 8 per cent, by volume of the mixture, only traces of diphenyl were produced, the benzene being practically undecomposed by the treatment. A reason was, therefore, clearly established for the stability of benzene during carboni-zation at such temperatures as 800° C. At higher temperatures (900° C.) benzene was found to be readily decomposed, even when highly diluted with hydrogen, and deposition of the characteristic grey methane carbon was noticed. When the temperature was raised to 1,100° C. with an atmosphere imitative of car-bonizing conditions, benzene disappeared entirely, as was found in the earlier research. Further experiments were made with toluene. In this case, when decomposition. occurred at 600° C., the solid condeusate produced was found to be stilbene. At the same time an oily substance was formed. At higher temperatures increasing decomposition was notecl and at 750° C. it was quite extensive. The most note-worthy distinction from the behaviour of benzene, however, occurred when a hydrogen atmosphere was employed, for it was found that the decomposition of the toluene was very much accelerated, with the production of large quantities of benzene, and smaller amounts of solid condensates. What happens then, is that the hydrogen atmosphere can act directly on the toluene producing benzene and methane. The decomposition of the xylenes was found to be very similar to that of toluene, yielding, in an atmosphere of hydrogen at 750° C., toluene and benzene by reduction, and a limited quantity of solid condensates. Cresol is also reduced extensively (at 750° C. in hydrogen) to toluene and, necessarily, to benzene also. The conclusions set out above clearly indicate that there is a tendency for hydrogen (which. is the predominant product of carbonization) to reduce the single 1 Compare Haber, p. 409.