Energy & Fuels 1992,6, 485-493
485
Table VIII. Carbon and Sulfur Content of Spent Catalysts % carbon % sulfur Cold Lake 19.5 13.1 Ni/Mo on y-alumina 11.0 5.3 demetallization 18.1 4.4 Mo on y-alumina 30.7 2.7 y-alumina Athabmca 15.2 11.9 Ni/Mo on y-alumina 21.6 14.2 spent Ni/Mo-before 23.3 17.9 spent Ni/Mo-after Peace River 17.4 4.2 Ni/Mo on y-alumina 15.8 4.6 Mo on y-alumina 26.8 2.8 y-alumina
Conclusions 1. The major role of the catalyst is hydrogen transfer to the heavy fractions, to help suppress coke formation, hydrogenation and heteroatom removal from the distillate fractions. Significant residue conversion as well as some heteroatom removal occurred in the absence of a hydrogenation catalyst, i.e., during runs with y-alumina, but severe coking occurred during these experiments. 2. High activity Ni/Mo on y-alumina catalyst gave the best performance overall because of its high general activity for hydrogenation of the feedstock. The much lower hydrogenation activities of the demetallization, spent Ni/Mo, and Mo on y-alumina catalysts were nevertheless sufficient to suppress the formation of coke in the reactor.
Ni/Mo and Mo on y-alumina catalysts had carbon contents of 15.&19.5%, while the less active demetallization catalyst gave a carbon content of only 11% with CL. The y-alumina, which gave severe coke formation in the reactor, contained 27-31% carbon. The lack of hydrogenation activity for the y-alumina was consistent with the high carbon content; the low carbon level on the demetallization catalyst can be attributed to the low acidity of the support.
Acknowledgment. We are grateful to P. L. Jokuty and L. Nazarewycz for their assistance in analyzing the feed and product samples. Contribution of the coker products from Athabasca bitumen by R. Kirchen is gratefully acknowledged. Financial support wm provided by EMR Canada, Esso Petroleum Canada, Nova Husky Research Corp., Syncrude Canada, and Shell Canada. Registry No. Ni, 7440-02-0;Mo, 7439-98-7;V, 7440-62-2.
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Results of Reactivity Mapping Studies through the Negative Temperature Coefficient Region for Propane at Pressures from 5 to 15 atm D. N. Koert,* D. L. Miller, and N. P. Cernansky Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, Pennsylvania 19104-2884 Received July 9, 1991. Revised Manuscript Received March 31, 1992
A pressurized flow reactor (PFR) has been constructedfor kinetic studies of homogeneous gas-phase hydrocarbon oxidation in the low to intermediate temperature regimes. The design of the flow reactor provides the ability to study gas-phasekinetics free from transport effects and temperature gradients at pressures up to 20 a h . A series of experiments designed to map the reactivity of hydrocarbon/air mixtures over a range of temperatures (600-900 K) and pressures (5-14 atm) has been conducted on the PFR using propane/air mixtures. These mapping experiments examine the effect of pressure on the overall tendency of hydrocarbons to oxidize by using carbon monoxide measurements as an indicator of the degree of oxidation or autoignitiontendency. The reactivity mapping technique using CO concentration has been validated by comparison of results with detailed species measurements. The mapping results indicate a narrow temperature range extending from 640 to 770 K in which the rate of hydrocarbon oxidation reaches a peak and then diminishes. This behavior is consistent with negative temperature coefficient (NTC) behavior, where low-temperature oxidation nearly stops as temperature is increased above a threshold value corresponding to the transition to intermediatetemperature oxidation. The temperature range over which NTC behavior occurs is observed to shift to higher temperatures and to broaden as pressure is increased. NTC region broadening is indicated by a shift of the starting temperature to lower temperatures, and a shift of the ending temperature to higher temperatures as the pressure is increased. Broadening of the NTC region with increasing pressure can be explained by viewing HOz' formation in the R' + O2mechanism as rate limiting to the overall process leading to the formation of the intermediate temperature regime branching agent H202. The experimentally observed pressure-dependent shift in the NTC region temperature range is compared to an analysis of Benson's turnover temperature for the R' + O2mechanism. This analysis is found to account for fuel concentration effects on the NTC region temperature shift rather than pressure-induced kinetic falloff behavior. Introduction There is a need for experimental data on the chemistry of hydrocarbon oxidation at high pressure (>1atm) and
* Author to whom correspondence should be addressed.
low temperature (
