Polymer formation during the HDN of indole

During kinetic studies of the hydrodenitrogenation (HDN) of indole (IND) over a NiMo/ P-Al2O3 catalyst, it was found that material balances (representing loss of indole) were often low and varied depending on reaction conditions. Tests of IND with an alumina support, in which no reaction to HDN products occurred, also gave low material balances, which appeared to reach a line out value with space time. UV spectra of a liquid sample from this run showed evidence of species different than IND, which is attributed to a polymer. The low material balances were due to the failure of the GC analysis to detect the polymer in the product sample and possible loss of polymer by condensation in the lines leading to the sample collector. Material balances with the catalyst were related to conversion of IND to HDN reaction products. Low material balances were only obtained with IND, not with reaction products alone. It was concluded that the loss of IND is due to formation of a polymer. At low space time (low IND conversion), the polymer is rapidly formed in competition with conversion of IND to HDN products, while at high space time (high IND conversion), the polymer decreases due to back reaction to IND, followed by conversion to HDN products. The consequence of polymer formation, when it occurs, is that it represents a parallel reaction path to conversion of indole and needs to be accounted for in any kinetic analysis of the HDN of indole.