Modeling the thermal destruction of toluene (C7H8) as tar-related species for fuel gas cleanup

Thermal destruction of vaporized toluene in the presence of a [N-2 + H2O + O-2] in air and [N-2 + H-2 + H2O] gas mixtures are examined. Toluene (P-[C7H8] = 0.93-1.85 kPa) is used as model species present in tar-related volatile organic compounds from advanced thermochemical conversion technologies. Experiments were performed in a nonisothermal tubular flow reactor at a total pressure of ca. 101.3 kPa, temperature range of 973-1223 K. In presence of oxygen-containing molecules (molar ratios of [H2O + O-2]/C7H8 were varied between 1.78 and 3.52), a first-order reaction rate could express the effects of temperature and residence time. Thermal destruction of toluene in [N-2 + H-2 + H2O] gas mixture ([H-2 + H2O]/C7H8 = 3.52, and 0.40 < tau < 0.90 s) was studied as reference. Activation energies of the thermal destruction of toluene are: 356 +/- 5 kJ mol(-1) in [N-2 + H2O + O-2] atmosphere and 250 +/- 10 kJ mol(-1) in [N-2 + H-2 + H2O] gas mixture. A chemical reaction network and a free-radical mechanism have been suggested to explain the products concentration distribution. The free-radical mechanism has been used to interpret the experimental trends at gas residence times (tau < 5 s).