Failure of the scaling laws in the thermal explosion of methyl isocyanide

Abstract

Thermal explosions of methyl isocyanide have been studied in spherical reaction vessels with volumes in the range 300–5000 ml. The normal inverse dependence of the explosion limit on the square of the radius appears to hold over limited ranges, e.g. from 300–1000 ml and from 2000–3000 ml, but the explosion limits at 1000 ml and 2000 ml are characterized by markedly different values of the critical parameter δc. Temperature measurements were made at and near the vessel walls, but they do not reveal any abnormalities which could be used to explain these results.An appendix reports measurements of the thermal conductivities of methyl cyanide and methyl isocyanide from 200–350 °C.

A reformulation of the theory of unimolecular reactions

“…Schneider and Rabinovitch estimated the degree of self-heating in their highpressure reactions on the basis of a AH of isomerisation of -15 kcal mol-' and a thermal conductivity of 0.25 mW cm-' deg-'. We have recently remeasured both AH as -23.70 + 0.14 kcal mol-' (65) and the thermal conductivity, about 0.20 mW cm-' deg-' at 230°C (66), which implies that all of the correction factors for self-heating estimated by Schneider and Rabinovitch are too small by about a factor of two. It seems likely that if sufficient raw experimental data are still available to enable these self-heating corrections to be calculated properly, some of the present discrepancies might be eliminated.…”