Reaction network and kinetics of the vapor-phase catalytic hydrodenitrogenation of quinoline

Abstract

The reaction network and kinetics of quinoline hydrodenitogenation (HDN) were studied in a flow microreactor packed with presulfided NiMo/A1 2 0 3 catalyst. Reactor temperatures were 330 to 420 0 C, and total pressure was either 3.55 or 7.0 MPa (500.or 1000 psig).Partial pressure of the reactant compound (quinoline or one of its hydrogenated derivatives) was 13.3 or 26.7 kPa, and reactant feed rates varied from 41.7 to 667 hr g catalyst/g-mol.The results indicated that the initial ring saturation reactions of quinoline are all reversible over a wide range of HDN conditions; also, saturation of the aromatic ring is thermodynamically (but not necessarily kinetically) more favorable than saturation of the heteroring. Nitrogen removal from quinoline occurred primarily through the decahydroquinoline intermediate, and propylcyclohexane was the major hydrocarbon product. The NiMo/Al?0 3 catalyst exhibited little selectivity for the reaction pathway of minimum hydrogen consumption, due to insufficient hydrogenolysis activity.Adsorptivities of the nitrogen compounds in the quinoline HDN network varied significantly. A Langmuir-Hinshelwood kinetic model, allowing for these different adsorptivities, was developed for the hydrogenolysis and nitrogen removal reactions. On active catalyst sites, the Py-tetrahydroquinoline and decahydroquinoline reaction intermediates appeared to adsorb about six times as strongly as the less basic aromatic amines (quinoline, Bz-tetrahydroquinoline, and o-propylaniline), which in turn showed an adsorption strength approximately four times greater than that of ammonia.

Hydrodenitrogenation of quinoline over carbon-supported transition metal sulfides

“…In the literature it has been reported that for Ni-Mo/AI203 catalysts the ring-opening reactions of THQ I and DHQ are rate limiting (11)(12)(13). However, this is certainly not true for our TMS/C catalysts.…”

“…The relative adsorption coefficients of the reactants and intermediate products are completely different in the liquid and gas phase. For instance, the adsorption coefficient of DHQ is twice as large as those of Q, THQI, and THQ5 in the liquid phase, but six times larger in the gas phase (12,14,17). The H2S/H 2 ratio during the autoclave experiments was 2.5 × 10 -3 and 1.5 × 10 -4 during the flow experiments.…”

“…When the ring opening was eliminated too (CHA-HDN and OPA-HDN) the HDN activity increased strongly but again the periodic trends did not really change (2). Although the ring-opening • reaction is considered to be the rate-limiting step of the Q-HDN reaction over Ni-Mo/ AI203 catalysts (11)(12)(13), our experiments have shown that for the TMS/C catalysts, not the ring opening but the formation of DHQ by the hydrogenation of Q is the slowest step. The CHA-HDN experiments (2) have shown that the trends for the HDN activities remain unchanged even if both slow steps (hydrogenation and ring opening) were removed, the cleavage of the C-N bond in CHA definitely being a fast reaction.…”

“…In contrast to HDS, the hydrogenation of the N-containing ring and in most cases also the hydrogenation of the benzene ring of quinoline are necessary steps in the two reaction pathways of Q-HDN via DHQ and OPA (cf. (11)(12)(13)(14)(15)(16)(17). The differences in the hydrogenation activities between various TMS will be more pronounced in the Q-HDN, which requires 8-14 H atoms to convert Q to hydrocarbons, than in the thiophene HDS which strictly needs only 4 H atoms, but may use up to 8 atoms.…”

Hydrodenitrogenation of quinoline and its intermediates over sulfided NiW/γ‐Al2O3 in the absence and presence of H2S

“…Simultaneous HDN of o-ethyl aniline or DHQ and HDS of thiophene showed that DHQ adsorbs much stronger than o-ethyl aniline [18] . In the presence of DHQ, quinoline, and THQ, the rate of HDN of OPA is considerably suppressed [19,20] . However, the THQ1-OPA reaction path cannot be negligible and amounts to about 40% of quinoline HDN [13] .…”