Formation of nitrogen containing compounds from ammonia co-fed to the Fischer–Tropsch synthesis

Abstract

The effect of ammonia on activity and selectivity of a low temperature, iron-catalyzed slurry phase Fischer–Tropsch process was studied. The ammonia content in the feed was varied systematically from 0 to 10vol% while the total pressure was adjusted simultaneously in order to keep partial pressures constant. In addition to standard Fischer–Tropsch synthesis (FTS) products, long chained aliphatic amines, nitriles and amides were formed; the latter two product classes had not been observed by others before with iron based catalysts. The selectivities toward nitrogen containing compounds increased with increasing ammonia content while the formation rates of alcohols, aldehydes and organic acids were reduced possibly suggesting that nitrogen containing compounds are formed via oxygenates or their precursors. Common FTS descriptors such as methane selectivity, chain growth probability, olefin to paraffin ratio and double bond shift were largely unaffected at the studied levels of ammonia addition, while the activity at ammonia levels above 2vol% decreased over and above the intrinsic deactivation rate. Although this deactivation seems reversible upon removal of ammonia from the feed gas, the selectivity is shifted toward higher water gas shift reactivity.