Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-V-12Kinetic ExperimentsHexadecane, that can be produced from renewable sources and is regarded as a highqualitydiesel [4], was selected as a model compound for the second generation biodiesels.The reaction orders of NO, O 2 and C 16 H 34 were determined by varying the concentration ofthe components in the gas mixture. Concentrations of 300-1500 ppm NO, 150-1000 ppmhexadecane, and 1-8 vol.% O 2 were used, keeping helium as balance gas. The concentrationof H 2 O was kept constant at 12 vol.%. The results were mathematically treated to obtain thereaction orders with respect to NO, C 16 H 34 and O 2 . Typical experimental results obtained inthe SCR of NO X in microchannels are illustrated in Fig. 2. The reduction conversion withoctane is used for comparison purposes, as a representative component for fossil fuels.Conversion, (%)45.040.035.030.025.020.015.010.05.00.0HexadecaneOctane0 100 200 300 400 500 600Temperature, (ºC)Figure 1: SEM picture of a microplatelet – 50XFigure 2: NO to N 2 conversion of hexadecane in amicroreactor for octane and hexadecane. Gas flow:500ppm NO, 187.5ppm C 16 H 34 (or 375ppm C 8 H 18 ) , 6vol.% O 2 , 12 vol.% H 2 O and He balance.Two important reactions in the SCR were found to be as follows: 2 NO + C 16 H 34 + 23.5O 2 N 2 + 16 CO 2 + 17 H 2 O; and C 16 H 34 + 24.5 O 2 16 CO 2 + 17 H 2 O. Based onexperimental data, the reaction orders were calculated. The reaction orders with respect to NOare close to zero at the low temperature range (200-400 ºC), possible due to the NO X speciescoverage of the active sites. The order with respect to NO increased at higher temperatures(400-550 ºC). Oxygen displayed the opposite behaviour: decreasing the order with respect toO 2 while increasing temperature; while hexadecane appeared to have a two-fold behaviour:for temperatures below and above 350 ºC. Apparently, the reaction orders with respect tohexadecane decreased with raising temperature. This was the case at temperatures below 350-400 ºC. At higher temperatures, however, the reaction orders increased again reaching aminimum around 350 ºC. Additionally, the orders with respect to C 16 H 34 were found to behigher than the orders in O 2 and NO, which might suggest that the hydrocarbon-oxidation stepdominates over the NO X -reduction one.190