Flow-reactor Experiments

Soot samples collected from the engine running on fuel with additive were studied. Printex-U, a flame soot supplied by Degussa, was used as a reference material. 

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Conversion efficiencies of the dynamometer-aged catalysts were measured in a standard A/F sweep test on an engine dynamometer [6]. The sweep experiments were carried out at 450 and 85,000 h space velocity (volumetric basis standard conditions). The sweep ranged from 0.5 A/F lean of stoichiometry to 0.5 A/F rich of stoichiometry with imposed A/F perturbations of+.0.5 A/F at 1 Hz. After sweep evaluation, small samples of catalyst were renrroved from the front region of the brick for chemisorption and flow reactor experiments. 

Process studies are often performed as either batch or flow-reactor experiments. A general and important aspect of laboratory studies is that they can be performed under controlled process conditions. 

Fig. 13.3 Laboratory flow reactor experiments on carbon monoxide oxidation as function of pressure [226]. The initial temperature is 1040 K and the initial mole fractions are 1.0% CO, 0.5% O2, and 0.65% H2O, with the balance N2.

Fig. 13.6 Laboratory flow reactor experiments on selective noncatalytic reduction of nitric oxide by ammonia, with and without hydrogen addition [251]. Inlet composition NO = 225 ppm, NH3 = 450 ppm, O2 = 1.23% balance inert. Residence time 0.075 s atmospheric pressure.

The Flow Reactor In flow reactor experiments designed for chemical kinetic interpretation, the objective is to achieve a plug-flow situation, where composition and temperature are uniform over the cross section of the reactor. This condition may be approximated both in the turbulent [442] and the laminar [233] flow regimes. In the turbulent flow regime, a high linear flow rate secures negligible recirculation flow. Each element of gas reacts as it moves, with the characteristic time scale for heat and mass transfer by... 

Figure 14.3 shows results from flow reactor experiments on NO sensitized oxidation of methane in the 800 to 1200 K temperature range. In the absence of NO, temperatures of about 1100 K are required to initiate rapid oxidation of CH4 [31], but in the presence of NO, reaction occurs at temperatures as low as 850 K. The results indicate three different temperature regimes a low-temperature region (900-1000 K) with partial oxidation of methane, an intermediate-temperature regime with little reaction (1000-1150 K), and a high-temperature regime (>1150 K) with complete oxidation. 

Although the dominating mechanism of the formation of the first ring (benzene) is still in dispute, it is now possible to predict benzene production in hydrocarbon flames and flow reactor experiments with a reasonable degree of accuracy [318,363],... 

In this chapter the performance of plalinum/base metal fuel additive-filter systems is discussed with studies on a pilot engine as a basis. It will be compared to the performance of cerium, iron, and copper base metal additives, the latter two also in combination with platinum. The background of the difference in performance of the platinum/base metal combinations is discussed with results from flow-reactor experiments as a basis. 

A series of batch and mixed flow reactor experiments was performed at pH <3 to determine the effect of SO , Cl , ionic strength, and dissolved O2 on the rate of pyrite oxidation by Fe ". Of these, only dissolved O2 had any appreciable affect on the rate of pyrite oxidation in the presence of Fe. Williamson and Rimstidt (1994) combined their experimental results with kinetic data reported from the literature to formulate rate laws that are applicable over a range panning six order of magnitude in Fe " " and Fe " " concentrations, and for a pH range of 0.5-3.0, when fixed concentrations of dissolved O2 are present ... 

This places a burden on the interpretation of static experiments (or equivalent flow reactor experiments), and conditions should therefore be established which are free of diffusion effects. In connection with these difficulties the advantage of experimental methods such as the Schwab-type reactor system becomes quite apparent, since no variations of pressure or concentration occur during the measurements in this system. 

The achieved TOC destruction efficiency is high although the real gasification efficiency could not be determined because the traces of solid and oily product are not quantitatively recovered. In the aqueous effluent pyrocatechol, methoxyphenol and phenol were identified as the major compounds by GC-MS. Both the low feed concentration and the higher reaction time compared with the tubular flow reactor experiments could explain this fmding. 

Figure 12.3. Typical course of the outlet NO concentration during a flow-reactor experiment. In this case cerium-activated soot mixed with 6 mg of platinum-ASA was oxidised at temperature of 650 K in a gas phase of 300 ppm NO and 10 % Oj in argon.

From Figures 12.2.a and 12.2.b it is clear that in flow-reactor experiments NO does hardly influence the soot oxidation rate in absence of a supported platinum catalyst. From results not shown here it is clear that the same holds for the effect of a supported platinum catalyst the oxidation rate in the absence of NO is the same, with or without supported platinum catalyst. This leads to the conclusion that only... 

From flow-reactor experiments with stacked beds of supported platinum catalyst and Printex-U, discussed in [16], it was concluded that the platinum catalyst does not need to be mixed with the soot to be effective. The combination of platinum catalyst and gas phase NO is effective through the gas phase. 

In engine experiments, the platinum is particularly effective after some period of use or in combination with a platinum treated filter. This leads to the assumption that the role of the platinum in the soot is small and that the platinum collected on the filter is more important for the oxidation of soot. This is confirmed by flow-reactor experiments, that showed that platinum present in the soot did not influence the oxidation rate in any case (not shown). The platinum particles in the soot are too small (atomic dispersion) to contribute to the oxidation of NO and the concentration of platinum is very low. 

In flow-reactor experiments, the effect of NO in the gas phase and a supported platinum catalyst mixed with the soot is twice as large for cerium when compared to that of copper, iron, and Printex-U. All other conditions are similar and, therefore, it is concluded that cerium catalyses the oxidation of soot with NO2. Because there is... 

The amount of CO and COj that is formed is high compared to the amount of NO used in the flow-reactor experiments with cerium activated soot. It is possible to achieve a situation where each NO molecule participates more than once in the oxidation reaction. This confirms an oxidation cycle that was proposed by Mul et al. [18]. This cycle is visualised in Figure 12.4. 

In engine experiments, significant NO reduction, up to 20%, has been observed. Also in flow-reactor experiments, some jeduction was measured, although this was less pronounced. The outlet concentration of NO in the oxidation experiments was only 10 % lower than the inlet concentration of NO during the first 60 % of the oxidation experiments, whereas the oxidation rate was high. This indicates that the... 

The Pt SiC catalyst (Fig. Ic) shows light-off around 220°C and NO reduction in the same temperature range as for the other catalysts. The NjO formation maximises around 235°C and is of similar magnitude as for the Pt/ZSM-5 catalyst. The NOj formation rate increases rapidly around this temperature and shows a maximum at 320°C. Adsorption of neither hydrocarbons nor NOx on the Pt SiC sample is obvious from Fig Ic. In Table 2 the NOx reduction efficiency and the selectivity towards N2 and N2O formation are summarised for the flow reactor experiments. Both the NOx reduction activity and the N2 selectivity of the Pt/SiC and Pt/ZSM-5 system appear to be similar, while Pt/Al203 shows a higher peak reduction value for the heating ramp experiments. 

For example the conversion of cellulose was studied in autoclaves with residence times of up to 1 h at 200-400 °C and 8-18 MPa [138, 139]. It was found that sodium carbonate as a catalyst suppresses the formation of char and oil and mainly water-soluble products were formed. At 400 and with a Ni catalyst, CH4 and CO2 were found as major products in the gas phase. Batch reactor experiments [140, 141] used for the formation of a CH4-rich gas from biomass, waste model compounds and real waste waters, were also carried out at 350 °C, 20 MPa, and reaction times of 60-120 min. It was shown that aromatic and aliphatic hydrocarbons as well as oxygenates are converted to a CH4-rich fuel gas in the presence of hydrogenation catalysts. The results were confirmed in continuous-flow reactor experiments with residence times of 10 min and longer for conversions of 90 % or more. In any case, without the high reactivity of biomass in and with near-critical water, methane formation at low temperatures would not be possible. 

Combination of IR study of adsorbed species with gas phase analyses showed that, in the NO2-C3H6-O2 reaction over Ce-ZSM-5 at 373 - 473 K, organic nitro-compounds were formed from NO 2 and C3H6, and N2 was mainly produced by the reactions of these nitro-compounds with NO2 (or NO2 + O2). Tliese results together with the results obtained previously for flow reactor experiments indicated that these nitrocompounds are the intermediates of the reduction of NO as in the following scheme. The high reactivity of adsorbed CH3NO2 with NO 2 supported this scheme. 

A. Morita, M. Sugiyama, H. Kameda, S. Koda, D. R. Hanson Mass accommodation coefficient of water molecular dynamics simulation and revised analysis of droplet train/flow reactor experiment, J. Phys. Chem. B 108, 9111-9120 (2004). 

Batch and flow reactor experiments were compared. In case of CSTR, fluctuations were periodic whereas in a batch reactor oscillations were more like random noise when the current was 8.0 mA. It has been found that polymer influenced the oscillatory and growth behaviour during electrochemical deposition of lead. Results also indicated a transition from dendritic to DLA/fractal-type structure on the addition of PVA in the solution. 

Table 2.4 lists Fe concentration versns contact time with pyrite from a ping flow reactor experiment (PFRlO) (Rimstidt and Newcomb, 1993). The rate of ferric iron consumption is the time derivative of these data. Finding this derivative for t = 0 is especially useful because the initial conditions of the experiment are accurately known so their effect on the rate can be clearly established. One strategy for finding the initial rate is to fit the first few concentration versus time... 

Table 2.4. Concentration of FC versus contact time between solution and pyrite in a plug flow reactor experiment (PFRlO) (Rimstidt and Newcomb, 1993)...

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