PNNL

Abstract

Molybdeum sulfide based catalysts, such as nickel–molybdenum on alumina (NiMoS/Al2O3), are widely used in hydrotreating and have potential for catalyzing waste plastic covnersion via hydrogenolysis, yet their performance, such as reaction kinetics and network, for amide-rich polymer feeds is poorly defined. Here we combine Nylon 66 with the amide model compound, N,N-dibutylhexanediamide (DBDAD), to quantify hydrodeoxygenation (HDO) and hydrodenitrogenation (HDN) chemistry in a stirred batch reactor (53 bar H2, 280–320 °C). DBDAD conversion is near-linear with time, indicating strong adsorption of the substrates on the active sites. Time-resolved product identification indicates parallel C-O first-cleavagedeoxygenation (DO) and C-N first-cleavagedenitrogenation (DN) sequences proceeding through amine and diol intermediates, respectively, to C4–C6 alkanes. Increasing temperature shifts selectivity toward DN, decreasing the initial r(DO)/r(DN) from 1.38 (280 °C) to 0.69 (320 °C), with an apparent activation energy of 173 kJ mol?¹ for DBDAD conversion. At 300 °C, nylon 66 converts faster than DBDAD, producing a complex mixture of oxygen- and nitrogen-containing species and an initial rate ratio r(DO)/r(DN) of 1.6. No heteroaromatic nitrogen products are detected. These results provide reaction pathways and product signatures relevant to hydroprocessing catalysts exposed to polyamide-derived streams