Catalytic hydrodenitrogenation of quinoline in a trickle-bed reactor. Effect of hydrogen sulfide

Abstract

Studies at 350, 375, and 390 O C and 6.9 MPa showed that the presence of H,S (generated in situ from CS,) in the overall reaction network somewhat inhibits hydrogenation and dehydrogenation reactions but markedly accelerates hydrogenolysis reactions, for a net increase in the overall rate of hydrodenitrogenation (HDN). These effects are similar to those observed previously in vapor-phase reactions. H,S has little effect on the activation energies for the hydrogenation and dehydrogenation reactions, but it significantly reduces those for the hydrogedysis reactions. Certain plugging problems encountered upon reacting 5,6,7,84etrahydroquinoline are attributed to formation of a trimer imine as an intermediate. The presence of Tetralin in the liquid inhibits the overall hydrodenitrogenation reaction, indicating that inhibition by competitive adsorption is more important than the accelerating hydrogen-donor capability that Tetralin exhibits in some homogeneous reactions.In an associated paper (Satterfield and Yang, 1984) we have reported on studies of quinoline HDN in a trickle bed reactor using an NiMo/A120, catalyst which was presulfided but in which no sulfur compound was added to liquid or gas during reaction. In previous vapor-phase studies we have shown that the rate of catalytic hydrodenitrogenation (HDN) of pyridine or quinoline is increased in the presence of H2S (Satterfield and Giiltekin, 1981) and we have interpreted this in terms of the comparative effect of H2S on the hydrogenation vs. the hydrogenolysis reactions that occur in the overall HDN reaction. In the present study we have analyzed the effects of the presence of H2S on the reaction in the liquid phase, in an analogous fashion to our earlier vapor-phase studies. Experimental SectionThe studies reported on here were carried out in the same trickle-bed apparatus, using samples of the same catalyst and procedures previously described, except that CS2 was added to the feed in various concentrations. CS2 rapidly reads with hydrogen to generate HzS in situ. Most of the data here were taken with catalyst charge no. 3. Catalyst charge no. 2 was used here primarily for some comparisons with no. 3. These same two catalyst charges were also used to generate the kinetic data in the absence of H2S, published in the accompanying paper.All the data reported here were obtained after the catalyst charges had reached steady-state activity. Catalyst charge no. 1 was used for sdme preliminary studies and charge no. 4 was used to study the effect of a change in the activation procedure. The time required for steady state to be reached was less, the higher the quinoline concentration in the feed and the lower the space-time (faster flow rates) used. As characterized by a standardized run (see below), steady state was essentially reached in about 150 h. The acronyms for the various compounds present are the same as those used previously and are given in Figure 2 of our accompanying paper (Satterfield and Yang, 1984). ResultsReproducibility. Figure 1 shows the activity...

SUPPORT EFFECT ON CONVERSION OF QUINOLINE OVER ReS2 CATALYST

“…It can be observed that the main reaction product was 1,2,3,4 tetrahydroquinoline (THQ1), and that decahydroquinoline (DHQ) was observed in minor amounts for all the catalysts. The conversion of quinoline by the ReS 2 (x)/supports catalyst can be depicted in the reaction scheme shown in Figure 5, in agreement with previously reported studies by several authors [4,5,6,9,10]. Figure 5 shows that the formation of DHQ compound can be produced through hydrogenation of quinoline (either via THQ1 or THQ5 intermediate compounds).…”

“…Yang and Satterfield [5] studied the effect of hydrogen sulfide on the HDN of quinoline using NiMo/Al 2 O 3 catalyst. They found that the hydrogen sulfide inhibits hydrogenation and dehydrogenation reactions but markedly accelerates hydrogenolysis reactions.…”

Hydrodenitrogenation of quinoline over carbon-supported transition metal sulfides

“…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.…”

“…Before discussing the selectivities of the various TMS catalysts it is useful to point out that the compounds present in the reaction product mixture can be divided into several categories with respect to their adsorption properties (14)(15)(16)(17). Because of their nonpolar character, the adsorption of the solvent and the hydrocarbon products of the Q-HDN can be neglected compared to the double-ring N-compounds.…”

“…This difference might have led to slightly altered catalyst surfaces and thus to altered activities and selectivities. It is known that an increase in the H2S/H2 ratio may lead to an increase in NH3 removal, but a decrease in hydrogenation (14,16). In the autoclave experiments the catalyst activities are measured directly after sulfidation of the catalysts, while in the flow experiments the catalysts were aged during 27 h. The results of the flow experiments at constant (10 and 50%) HDN-conversions of Q to hydrocarbons are presented in Table 3.…”