K-Doped Co–Mn–Al Mixed Oxide Catalyst for N₂O Abatement from Nitric Acid Plant Waste Gases: Pilot Plant Studies

Abstract

The K-doped Co−Mn−Al mixed oxide deN 2 O catalyst was prepared by calcination of Co−Mn−Al layered double hydroxide, subsequent impregnation with KNO 3 , and shaping into tablets of 5 mm × 5 mm. Tablets were tested for N 2 O decomposition in pilot scale reactor connected at the bypassed tail gas from the nitric production plant downstream of the SCR NO x /NH 3 catalyst with the aim to perform kinetic measurements. Special attention was paid to study the changes in the catalytic performance, which was monitored using both the long-term catalytic test and the comparison of physical−chemical properties of the fresh and used catalyst. The changes in the surface composition, caused by the time-on-stream operation for 112 days in the pilot reactor, provided stable catalytic performance; average value of N 2 O conversion of 90 ± 6% at 450 °C was kept (GHSV = 11 000 m 3 m bed −3 h −1 ). The obtained kinetic data were applied in modeling of a fullscale reactor for the N 2 O emissions abatement and can be used for estimation of the amount of the catalyst necessary for obtaining required N 2 O conversion in the target plant.

Must the Best Laboratory Prepared Catalyst Also Be the Best in an Operational Application?

“…Graphite was also found as a minor phase in all industrially prepared catalysts, together with the spinel phase, since graphite was added to the catalyst matter for ease of forming. Graphite line was not observed in the catalysts used in the long-term pilot plant testing (not shown here), confirming combustion of graphite during the catalytic test [4]. Small un-labelled diffractions correspond to the Kbeta line of the used X-ray radiation source.…”

“…Parameters: 390 • C, 150 kPa, mean pore diameter, model gas mixture 1000 ppm N 2 O + 5 mol% O 2 + 2 mol% H 2 O in N 2 , catalysts in tablets 5.1 mm × 5.1 mm. Figure 8 for η evaluated from experimental data mentioned in Table 1 2 Determined from Figure 9 3 Experimental data of N 2 O decomposition over commercial tablets measured in the laboratory at 390 • C and VHSV = 3000 m 3 m bed −3 h −1 (Figure 2) 4 Tortuosity calculated from Equation (10) using experimentally determined porosity (Table 3) Figure 9. Dependence of theoretically achievable N2O conversion on the 1 st order kinetic constant in kinetic regime.…”

“…In the presented work, based on previous extensive laboratory screening tests of N 2 O catalytic decomposition [1][2][3], three cobalt mixed oxide deN 2 O catalysts with optimal content of alkali metals K/Co 4 MnAlO x , Cs/Co 4 MnAlO x, and Cs/Co 3 O 4 were prepared on a large scale, shaped into tablets and tested in the pilot plant reactor connected to the bypassed tail gas from the nitric production plant. Results of pilot plant testing of K/Co 4 MnAlO x for decreasing N 2 O emissions from a nitric acid plant were published in our previous work [4]. Although high efficiency in N 2 O removal (N 2 O conversion of 75-90% at 450 • C, VHSV = 11,000 m 3 m bed −3 h −1 ) were reached; the question is if the prepared tablet catalyst achieved similar catalytic performance to the laboratory catalyst or if it was lower and in the latter case optimization of the pilot catalyst's preparation procedure would then be beneficial.…”

“…The effect of NH 3 on the decomposition of N 2 O in the presence of cobalt catalysts was studied only sporadically; mainly on zeolites and to a lesser extent on oxidic catalysts [10,11]. The influence of NH 3 in the feed gas was also studied in an individual experiment performed under laboratory conditions over K/Co 4 MnAlO x -industry tablets [4]. It was found that ammonia oxidized to N 2 O, NO, NO 2 , and probably N 2 (not measured), which means that ammonia can also contribute to the fluctuations of NO x concentration present in the feed or can also increase N 2 O concentration at the reactor outlet.…”

Bulk, Surface and Interface Promotion of Co3O4 for the Low-Temperature N2O Decomposition Catalysis

“…A literature survey and our previous studies indicate that the structure of the cobalt spinel active phase can be doped with various metal cations [14][15][16][17][18]. Among them, the most promising effect for the deN 2 O reaction has been reported for Zn, Ni, Pb and Bi addition [19][20][21][22].…”