The effect of pipe diameter on the thermal decomposition of acetylenes

Abstract

The experimental technique developed in this work differs considerably from methods used in previous investigations of this type. It was possible to essentially duplicate the German data concerning the effect of pipe diameter on the thermal decomposition of acetylene; however, the more detailed investigation disclosed additional information of interest. It was shown that acetylene passes from explosibility to non-explosibility through a pressure range rather than abruptly through a so-called boundary pressure as described in the German data. It was further observed that the explosibility of acetylene, in a given size pipe, apparently passes through a minimum within the minimum decomposition pressure range as defined by the experiments. Since no reasonable explanation is seen for this phenomenon, it is concluded that it may be characteristic of such thermal decompositions of acetylenes. The minimum decomposition pressures obtained with monovinyl acetylene are much higher than the single value reported in the German data. This may indicate a greater degree of stability to thermal decomposition than has heretofore been attributed to the higher acetylenes. Although this work has shown that the probability of thermal decomposition of acetylene and monovinyl acetylene has a statistical dependence on the initial system pressure, in view of the dominant effect of ignition energy on the minimum decomposition pressures, it is concluded that such precise definition is of little practical value in predicting acetylene explosibility unless the energy of ignition can be precisely specified.