PNNL

Abstract

Fractional factorial design was used to determine which factors have significant effects on the HCN (hydrogen cyanide) oxidation reaction over 0.5% Pt/Al2O3 under lean conditions. We conclude that the reaction temperature and gas-hourly space velocity (GHSV) have significant effects on the HCN conversion, while no significant effects are caused by the presence of either NO (nitric oxide) or C3H6 (propene). A central composite design was used to study the effects of temperature and GHSV on HCN conversion, C3H6 conversion and NOx selectivity. Based on a second polynomial equation model, regression analysis was used to study the significance of each variable term and derive equations for each response. Our results show that HCN conversion was significantly affected by temperature (X3), GHSV (X4), a temperature polynomial term (X32), and a temperature and GHSV interaction term (X3X4). HCN conversion decreased with increasing values of GHSV and increased with increasing temperature, up to a transition temperature that depends on the GHSV value. The variables of temperature (X3), GHSV (X4), and the temperature polynomial term (X32) have significant effects on both C3H6 conversion and NOx selectivity, but in these two cases the interaction of temperature and GHSV was not significant. Contour plots of HCN conversion, C3H6 conversion, and NOx selectivity versus temperature and GHSV were constructed from an analysis of the measured data, and these plots can be utilized to estimate HCN conversion, C3H6 conversion, and NOx selectivity over the range of temperatures and GHSV investigated. Optimum catalyst operation is described by high HCN conversion and low NOx selectivity. These results show C and o that the highest HCN conversion was achieved at temperatures above 250 relatively low GHSV values, while low NOx selectivity was best achieved at a C.o temperature of 215