Time on-stream testing

A series of nickel/(rare earth phosphate) catalysts were investigated by Nagaoka et al. [35] for methane ATR. Among them, Ni/(Gd, Ce or Er phosphate) showed good activity, maintaining a stable CH4 conversion during time on-stream tests... 

A similar Pt/Ce02 catalyst, studied by Recupero et al. [58] in the ATR of propane, was found to give high H2 and CO selectivity values in the temperature range 600-700 °C. The catalyst did not show any carbon deposition after time on-stream testing carried out with sequential start-up and shut-down cycles. 

A structured ruthenium catalyst (metal monolith supported) was investigated by Rabe et al. [70] in the ATR of methane using pure oxygen as oxidant. The catalytic activity tests were carried out at low temperature (<800 ° C) and high steam-to-carbon ratios (between 1.3 and 4). It was found that the lower operating temperature reduced the overall methane conversion and thus the reforming efficiency. However, the catalyst was stable during time on-stream tests without apparent carbon formation. 

The whole vapors from peanut shells, which have a unique composition, i.e., high levels of lignin and protein, can be successfully reformed. Over the time on stream tested to date, no significant deactivation of the catalyst was noted. 

After 5 h of time-on-stream the TS-1 catalyst showed a significant decrease in activity (Fig. 39.4), mainly related to the formation of heavy byproducts by PYC condensation on the surface [27,28]. The TG analysis carried out on the catalyst after the tests, showed the presence of two signals corresponding to a weight loss the first one, around 523 K, may refer to residual reagents and/or products adsorbed on the catalyst, while the second one at 743 K may be attributed to the combustion of heavy by-products deriving from PYC condensation, which is the main cause of deactivation. 

The objective of the present study is to develop a cross-flow filtration module operated under low transmembrane pressure drop that can result in high permeate flux, and also to demonstrate the efficient use of such a module to continuously separate wax from ultrafine iron catalyst particles from simulated FTS catalyst/ wax slurry products from an SBCR pilot plant unit. An important goal of this research was to monitor and record cross-flow flux measurements over a longterm time-on-stream (TOS) period (500+ h). Two types (active and passive) of permeate flux maintenance procedures were developed and tested during this study. Depending on the efficiency of different flux maintenance or filter media cleaning procedures employed over the long-term test to stabilize the flux over time, the most efficient procedure can be selected for further development and cost optimization. The effect of mono-olefins and aliphatic alcohols on permeate flux and on the efficiency of the filter membrane for catalyst/wax separation was also studied. 

Recently, mesoporous aluminosilicates with strong acidity and high hydrothermal stability have been synthesized via self-assembly of aluminosilicate nanoclusters with templating micelles. The materials were found to contain both micro- and mesopores, and the pore walls consist of primary and secondary building units, which might be responsible for the acidity and stability (181). These materials were tested in isobutane/n-butene alkylation at 298 K, showing a similar time-on-stream behavior to that of zeolite BEA. No details of the product distribution were given. 

A variety of solid acids besides zeolites have been tested as alkylation catalysts. Sulfated zirconia and related materials have drawn considerable attention because of what was initially thought to be their superacidic nature and their well-demonstrated ability to isomerize short linear alkanes at temperatures below 423 K. Corma et al. (188) compared sulfated zirconia and zeolite BEA at reaction temperatures of 273 and 323 K in isobutane/2-butene alkylation. While BEA catalyzed mainly dimerization at 273 K, the sulfated zirconia exhibited a high selectivity to TMPs. At 323 K, on the other hand, zeolite BEA produced more TMPs than sulfated zirconia, which under these conditions produced mainly cracked products with 65 wt% selectivity. The TMP/DMH ratio was always higher for the sulfated zirconia sample. These distinctive differences in the product distribution were attributed to the much stronger acid sites in sulfated zirconia than in zeolite BEA, but today one would question this suggestion because of evidence that the sulfated zirconia catalyst is not strongly acidic, being active for alkane isomerization because of a combination of acidic character and redox properties that help initiate hydrocarbon conversions (189). The time-on-stream behavior was more favorable for BEA, which deactivated at a lower rate than sulfated zirconia. Whether differences in the adsorption of the feed and product molecules influenced the performance was not discussed. 

The life time of a catalyst is an important criterion for its commercial application. The reforming reactions in most of the cases have been studied only for hours of time on-stream, but not for days or weeks. Superior catalysts need to be evaluated by operating continuously for thousands of hours. Simple accelerated aging test that allows assessment of catalyst life in hours or days rather than the usual priod of months will be helpful. 

All the preliminary measurements of the Rh-3/5/Si02 (denoted as Rh-3-SILP) catalyst discussed so far were initially studied at 100 °C and 10 bar syngas pressure (H2 CO 1 1) over a period of up to 36 h. This time on stream was further extended to 180 hours to test the long-term stabihty of the Rh-3-SILP dehydroxylated catalyst system (Fig. 3). 

Catalytic tests were performed in an isothermal flow quartz reactor apparatus under atmospheric pressure, provided with on-line gas chromatographic (GC) analysis of the reagent and products by two GC instrument equipped with flame ionization and thermoconducibility detectors. The activity data reported refers to the behavior after at least two hours of time on stream, but generally the catalytic behavior was found to be rather constant in a time scale of around 20 hours. 

Silica-supported triflic acid catalysts were prepared by various methods (treatment of silica with triflic acid at 150°C or adsorption of the acid from solutions in trifluoroacetic acid or Freon-113) and tested in the isobutane-1-butene alkylation.161 All catalysts showed high and stable activity (near-complete conversion at room temperature in a continuous flow reactor at 22 bar) and high selectivity to form saturated C8 isomers (up to 99%) and isomeric trimethylpentanes (up to 86%). Selectivities to saturated C8 isomers, however, decreased considerable with time-on-stream (79% and 80% after 24 h). 

This approximation of the energy balance may lead to inaccurate prediction of the temperature profile as a function of time on stream. Thus, at short contact times it may underpredict the temperature, while at long contact times it may overpredict the actual temperature profiles. However, on the average, the model predictions are good, as seen from the comparisons with data in subsequent sections. In our opinion, the above simplifications are reasonable, especially since the reproducibility of the MAT test is somewhat poor. 

Figures 4 and 5 show the effects of varying deactivation order, n and endotherm AH, respectively, on the FFB and MAT conversions. In Figure 4, AH was kept at the base value of 130 Btu/lb and only n was varied. As expected, with increasing n, i.e. lower deactivation rate, the longer time on stream FFB test shows higher conversion relative to MAT. In this specific simulation, for values of n>0.3,...

By decreasing the length of the test, from 240 h to 6 h on stream, it was expected that a set of used catalysts with decreasing coke and metal contents would be obtained. The TS set of used catalysts enables the determination of the variation of carbon content versus time on stream. As reported in Figure 2, the amount of carbon very quickly attains a quasi-steady state as often reported in the literature. In fact, a 11,4 wt % C content is found for the shortest test indicating the extreme rapidity of the initial coking of the catalyst. 

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