(124f) Kinetic Study of Thermal Decomposition of N,N-Diethylhydroxylamine (DEHA) in Steam Crackers

Nitrogen compounds such as N,N-Diethylhydroxylamine (DEHA) are used as antifouling additives in crude oil refinery systems and steam cracking furnaces. These compounds are excellent radical scavengers and are proven to prevent fouling resulted from radical reaction mechanisms. However, these processes are commonly run at elevated temperatures as high as 850 °C, which may lead to the thermal decomposition of the nitrogen additives. Possible decomposition products are NOx, which pose a serious safety concern because NOx could lead to gums and/or ammonium nitrite and nitrate in the cold box area of an ethylene plant.

In this study, we developed the thermal decomposition kinetics pathways of DEHA and DEA (Diethylamine is a decomposition product of DEHA). Interestingly, two distinct pathways exist one producing NO and the other producing NH₃. The kinetics, together with thermodynamics, were used to study the decomposition products of the DEHA and DEA under different temperatures by employing the in-house developed kinetic modeling platform. Temperature plays an important role in determining the major decomposition product of DEHA and DEA. At lower temperatures (below 500 °C), appreciable NO is indeed produced, but NH₃ is essentially the only major product at high temperatures typical of steam cracking. DEHA decomposition was also simulated under typical propane steam cracking conditions and found to produce only NH₃ as well. NH3 is very stable once formed and may potentially react with N2O3 in the cold box to produce ammonium nitrite which accumulates in the cold box. In summary, thermal decomposition of nitrogen compounds is a source of NOx formation only at low temperatures.