2. Experimental part
Experiments were conducted at atmospheric pressure in flow quartz reactor with i.d. 14 mm and the length of isothermal zone 200 mm. three independent electrical heaters with automatic regulation of temperature by separate thermocouples inside the rector provide almost uniform temperature profile. Taking into account the surface of quartz pockets for thermocouples, the surface to volume ratio s/v was 5.4 mm⁻¹ to elucidate the influence of the inner surface of the reactor, in some experiments the second reactor with i.d. 8 mm and s/v ratio 13.3 mm⁻¹ was used. In several experiments a thin (~4mm) layer of the industrial catalyst IPM-0.2 for isomerization of pentane-hexane fraction with 0.2 pt/γ -AI₂O₃ (fraction 0.5-0.8 mm ) was placed at the entrance of the reactor. The contact time with catalyst (~0.06 s) was at least 20 times less than the complete reaction time.
Experiments were conducted in the temperature range 500-750 ˚C with the use of three diluting gase: nitrogen, helium or methane. Prepared in advance hydrocarbon-oxygen-buffer gas mixture was fed from cylinder trough the gas controller with a gas flow in a range from 2.4 to 025 ml/s which at 700 ˚C corresponds to the residence time from 0.35 to 3.6 s. The most of experiments were made at alkane concentration in buffer gas 5 mol.% with the mole ratio [o₂]₀/[cnH2n+2]0from 0.2 to 1. But in some experiments aimed on the investigation of the influence of alkane concentration, it was varied from 2 to 9.2 mol. % at constant ratio[o₂]₀/[cnH2n+2]0from= 0.5 . Taking into account the low concentration of hydrocarbon, experimental conditions can be considered as almost isothermal, with experimental heating in the most cases below 5 ˚C
Products were analyzed by GC equipped with several columns and detectors. Carbon was usually balanced within ±4%. The concentration of water was calculated from the oxygen balance. More detailed description of experimental equipment and conditions is given elsewhere
Experimental investigation of the oxidation of ethane was accompanied by the kinetic modeling with the use of the model for partial oxidation of c1-c2 hydrocarbons, specially developed for the temperature rang 600-1200 K and pressures from 1 to 100 atm, according to principles described in. This model includes 454 elementary reactions with all kinetic parameters taken from independent literature sources, predominantly NIST database . These parameters were not varied or adjusted anymore during the course of calculations. All calculations were conducted for isothermal conditions with the use of the package Kintecus V450