Aspects of alkane pyrolysis

• Main Author: Booth, G. T.
• Published: Swansea University 1979
• Subjects: 547.4
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636119

The high temperature pyrolysis of butane, in the region 545°C -600°C, has been studied with special emphasis on the effect of reactor wall conditions. The use of a steel reaction vessel, both unpacked, and packed with steel balls, has added the hydrogen atom recombination reaction to the widely accepted, totally homogeneous reaction mechanism. Using this well substantiated, purely homogeneous system as our base the induced heterogeneous component has been, to a great degree, clearly defined. The effects on reaction rate, reaction orders, and Arrhenius parameters have been quantified. Throughout the study the variability of the ratio f C / (C +C )was strongly in evidence; moreover, the Arrhenius equations ~e uc;d 3 from this ratio show remarkable agreement with those derived from homogeneous data, implying that the fundamental chain propagation steps are the same in the homogeneous and heterogeneous environments. Chain lengths under the condition of this work were calculated to be vastly reduced, from those in the purely homogeneous system but not substantially so to totally suppress the homogeneous reaction. A much higher surface to volume ratio than was achieved in this work would seemingly be required to significantly reduce reaction rate further. A computed description of the system has been attempted with encouraging, if not total, success. If we are prepared to accept something approaching unit wall efficiency for the recombination of hydrogen atoms at the reactor surface then the observed reduction in reaction rate can be totally accounted for by the inclusion of this reaction in the homogeneous mechanism. It was noted, however, that under certain conditions of the study the decrease in reaction rate could not be fully explained in this way even if the wall efficiency was assumed to be unity. These results, obtained in the packed vessel at 833 K and at various pressures, have led to the postulation of an additional wall reaction. The observed variability of the ratio fC2/i(C1+C3) points to this reaction being a preferential, possibly selective, reaction of 2-Butyl on the vessel wall.