Denitrogenation

Synthetic fuels derived from shale or coal will have to supplement domestic suppHes from petroleum someday, and aircraft gas turbine fuels producible from these sources have been assessed. Shale-derived fuels can meet current specifications if steps are taken to reduce the nitrogen levels. However, extracting kerogen from shale rock and denitrogenating the jet fuel are energy-intensive steps compared with petroleum refining it has been estimated that shale jet fuel could be produced at about 70% thermal efficiency compared with 95% efficiency for petroleum (25). Such a difference represents much higher cost for a shale product. 

Catalyst choice is strongly influenced by the nature of the feedstock to be hydrotreated. Thus, whereas nickel-promoted and cobalt—nickel-promoted molybdenum catalysts can be used for desulfurization of certain feedstocks and operating conditions, a cobalt-promoted molybdenum catalyst is generally preferred in this appHcation. For denitrogenation and aromatics saturation, nickel-promoted molybdenum catalysts usually are the better choice. When both desulfurization and denitrogenation of a feedstock are required, the choice of catalyst usually is made so that the more difficult operation is achieved satisfactorily. 

Open-chain and cyclic compounds containing azo groups (-N2 —), such as azoalkanes, azoarenes, pyrazolines, triazolines, etc. may also eliminate N2, but these reactions are called azo-extrusions (IUPAC, 1989 a). The terms denitrogenation and nitrogen extrusion, both used by Adam et al. (1992, 1993) and by Adam and Sengelbach (1993) should not be used. They are superfluous and ambiguous. 

Some desulfurization occurs thermally but essentially no denitrogenation occurs without the aid of catalysts. ... 

The HDN of pyridine (Fig. 3) proceeds via the hydrogenation of the pyridine ring to piperidine, followed by further hydrogenation to the aliphatic amine [49] or by denitrogenation [50,51],... 

Coke builds up on the catalyst since the start up of operation. In the first weeks of operation, an amount between 5% and 8% of coke accumulates on the catalyst. The rate of deposition decreases with time on stream, a careful monitoring of temperature and of feed/H2 ratio is the basis for controlling deposition. Coke deposition primarily affects the hydrogenation reactions (and so denitrogenation), but the deposition rate determines the catalyst life. As mentioned above, deactivation is compensated by an increase in temperature (and some times in pressure, when denitrogenation has to be adjusted, as well). However, increasing severity, increases coke deposition and shorten catalyst life. 

Schwarz et al. in agreement with Shukla observed the formation of 2-Oxo-l, 2-dihydroquinoline, 8-hydroxy-2-oxo-l, 2-dihydroquinoline, 8-hydroxycoumarin, and 2,3-dihydroxy-phenylpropionic acid were found as intermediates of quinoline transformation by P. fluorescens 3 and P. putida 86 [325], They compared that metabolic pathway with the one obtained for Rhodococcus strain B1 (Fig. 22). This bacterium was unable to yield denitrogenated metabolites (i.e., 2-oxo-l, 2-dihydroquinoline, 6-hydroxy-2-oxo-l, 2-dihydroquinoline, and 5-hydroxy-6-(3-carboxy-3-oxopropenyl)-lH-2-pyridone). 

As can be seen, in both the 5,6- and the 7,8-dihydroxy-2(lH)quinolinone pathways, after initial hydroxylation adjacent to the N-heteroatom, the benzene moiety of the quinoline ring is transformed to a dihydroxy derivative 5,6- or 7,8-, respectively, which subsequently undergoes ring cleavage. However, neither of them involves C—N bond cleavage and consequently do not lead to denitrogenated products. 

The metabolites identified [327] for each of these pathways are collected in Table 15 and once again, it should be emphasized that only the last two, catechol/anthranilate and coumarin pathways (named c and d, in Fig. 23) yield denitrogenated products. In summary, the four metabolic pathways identified for quinoline transformation, as shown in Fig. 23, are ... 

The anthranilate intermediate is believed to be metabolized to denitrogenated products. The list of proposed metabolites is also included in Fig. 25. A consortium of anaerobic and denitrifying bacteria was found to degrade indole via oxindole [341], but further details were not given to ensure if pathway 1 was followed. 

It is important to mention that up to now the isolated, identified and sequenced enzymes from denitrogenating strains correspond to those, for which although the cleavage of the N-ring is observed, it never lead to denitrogenated products. 

IsoQN-l-OR ( 472nm 9.04mM-lcm-l) No reaction towards QN (and substituted QN) and inactivated by 5-OH-isoQN Degrade Iso-QN but denitrogenation not reported, dihydro-pathway. After purification (50% yield), the solid was as 350 times more active than the crude extract. 

Shukla [323] isolated an aerobic Gram-negative motile bacterium from sewage which was identified as a P. stutzeri and was found to degrade quinoline by a different pathway, yielding denitrogenated products. 

Finnerty, W. R. Shockley, K. Attaway, H., Microbial desulfurization and denitrogenation of hydrocarbons., in Microbial Enhanced Oil Recovery, Zajic, J.E., et al Editors. 1983, Penwell Tulsa, Okla. pp. 83-91. 

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