Pulse reactor system

Experiments were carried out in a pulse reactor system based on the TAP-2 reactor described by Cleaves et al. [3]. This consists of a small tubular reactor and a detector housed in a vacujun system pumped by a 1,500 Is" turbomolecular pump to a base pressure of... 

A pulse reactor system similar to that described by Brazdll, et al( ) was used to obtain the kinetic data. The reactor was a stainless-steel U-tube, composed of a l/S" x 6 preheat zone and a 3/8" X 6 reactor zone with a maximum catalyst volume of about 5.0 cm. The reactor was Immersed In a temperature controlled molten salt bath. 

We thank K. S. Patel and D. M. DiCicco for providing the dynamometer-aged catalysts and sweep evaluation data. E. Gulari and C. Sze (U. of Michigan) assisted with the design of the pulsed reactor system. 

The pulse technique may also be conveniently extended to include stages of reactant preparation. Figure 9 shows a schematic representation of a pulse reactor system recently used by Gault et al. (81), which includes stages for alcohol (the reactant precursor) dehydration and subsequent olefin hydrogenation, the resulting saturated hydrocarbon being the material of catalytic interest. A method has been described (82) which allows the use of a pulse reactor at above atmospheric pressure. 

The apparatus. The delay between the moment that the hydrocarbon products reach 50 percent of their maximum value, is expected to be in the order of a few seconds, as follows from figure 1. As we intended to measure these delays directly, we developed a pulse reactor system into which a well shaped pulse could be introduced, and which did not deform too much during its passage through the equipment. This was obtained by paying careful attention to a number of construction details, which were ... 

Gulevich, A. V., etal. (1998). Fast Two-Core Pulse Reactor System with a Thermal Subcritical Laser Module Analysis of Startup Results, Trans. Am. Nucl. Soc. (USA) 78, 193. 

Other microwave-assisted parallel processes, for example those involving solid-phase organic synthesis, are discussed in Section 7.1. In the majority of the cases described so far, domestic multimode microwave ovens were used as heating devices, without utilizing specialized reactor equipment. Since reactions in household multimode ovens are notoriously difficult to reproduce due to the lack of temperature and pressure control, pulsed irradiation, uneven electromagnetic field distribution, and the unpredictable formation of hotspots (Section 3.2), in most contemporary published methods dedicated commercially available multimode reactor systems for parallel processing are used. These multivessel rotor systems are described in detail in Section 3.4. 

A system of N continuous stirred-tank reactors is used to carry out a first-order isothermal reaction. A simulated pulse tracer experiment can be made on the reactor system, and the results can be used to evaluate the steady state conversion from the residence time distribution function (E-curve). A comparison can be made between reactor performance and that calculated from the simulated tracer data. 

Temporal analysis of products (TAP) reactor systems enable fast transient experiments in the millisecond time regime and include mass spectrometer sampling ability. In a typical TAP experiment, sharp pulses shorter than 2 milliseconds, e.g. a Dirac Pulse, are used to study reactions of a catalyst in its working state and elucidate information on surface reactions. The TAP set-up uses quadrupole mass spectrometers without a separation capillary to provide fast quantitative analysis of the effluent. TAP experiments are considered the link between high vacuum molecular beam investigations and atmospheric pressure packed bed kinetic studies. The TAP reactor was developed by John T. Gleaves and co-workers at Monsanto in the mid 1980 s. The first version had the entire system under vacuum conditions and a schematic is shown in Fig. 3. The first review of TAP reactors systems was published in 1988. 

The original TAP system has been modified, resulting in the TAP-2 reactor system. The main difference between the TAP and TAP-2 reactor systems is higher sensitivity and detection efficiency of reactor effluent because the microreactor and the detector are physically much closer in TAP-2 than TAP. Moreover, TAP-2 can perform experiments using much smaller input pulses than the original TAP system. Gleaves et al have identified the next set of adaptations for the TAP-2 reactor system by combining the TAP-2 experimental apparatus with IR and Raman... 

Zhiznevskii et al. chose another group of catalysts for the production of methacrolein, based on the solid solution systems Mo—Te oxides [110,360] and Sb—Te oxides [361] which were investigated in a pulse reactor at 340°C. Selectivities of 70—90% are reported. The Mo—Te catalyst (1 4) has a unique dependence of the activity upon the degree of reduction of the catalyst surface. Initial reduction to 6% increases activity, but further reduction lowered this again. The selectivity changes in a similar manner. X-Ray investigations led the authors to the conclusion that some Te—Mo—P-phase, which is formed with reduction but decomposed if the reduction is taken too far, is responsible. Combinations of Sb2Os and TeOz can likewise be selective catalysts. The relatively low activity at 400°C is much improved by the addition of molybdenum (60 mol.%). 

This correlation corresponds to an exponential decay model, k = koe aY. This expression differs from the conventional exponential model often used in continuous-flow systems 22, 23), k = koe at, in that the analog to time in a pulsed reactor is pulse number or its equivalent, cumulative feed introduced. In our case the correlating quantity is cumulative feed converted, Y. If one assumes that deactivation is caused by coke, the amount of which is proportional to hexane actually converted, this... 

Studies have been made using both continuous flow reactor system and a pulse flow microreactor system with purified helium as the carrier gas similar to that described elsewhere... 

Various reactors can be used for dynamic experiments. The application of recycle reactors to the investigation of the underlying reaction networks has been demonstrated by Bennett [58], who operated a recycle reactor with the dynamic method by superimposing reactant concentration pulses on the inlet stream. To ensure that the amounts of gaseous components adsorbed on the catalyst are appreciable compared to the amounts of measurable components flowing, the ratio of the catalyst to total reactor volume was made as high as possible. A reactor system, designed for transient experiments, has been described by Bennett et al. [43]. 

In order to assign and compare catalyst reactivity rates, measured conversions were "normalized" to 3000 GHSV by multiplying observed conversions by the factor actual GHSV/3000. The normalized conversions were used to specify rates to individual products and rates for overall CO conversion. The reaction has b n shown not to be mass or heat transfer limited (12). CO and irreversible H2 chemisorption were measured at room temperature, the former using a pulse injection system and a thermal conductivity detector, and the latter using a static system. Prior to measurements, catalysts were reduced under the same schedule as for reactor runs. 

Pt/Alumina. A sample (0.5g) of 0.3% Pt/alumina EUROPT-3 was used to promote hexane to benzene conversion in a Micromeritics 2900 flow reactor system which permitted in-situ TPR, TPD, TPO and pulse hydrogen chemisorption etc. The exit stream from the reactor was analysed via a residual gas analyser and an FID gas... 

The TAP-2 reactor system [4] was used to perform transient response experiments under vacuum and at temperatures ranging from 300 to 400°C. A carbon loading of 100 mg was placed between two layers of quartz particles (0.2-0.3 mm particle size). Neon was used as an internal standard for calibration and as a reference for diffusion. Nitric oxide and neon were introduced by pulses in the microreactor (25.4 mm in length and 4 mm in diameter) in a volume ratio of 1 1. The reactor was continuously evacuated and the response of the pulses as a function of time was analysed on -line by a quadrupole mass spectrometer. 

The principal difficulties with the pulse technique lie in the problems connected witlh obtaining a reasonable pulse at a reactor s entrance. The injection must take place over a period which is very short compared with residence times in various segments of the reactor or reactor system, and there must be a negligible amount of dispersion between the point of injection and the entrance to the reactor system, ff these conditions can be fulfilled, this technique represents a simple and direct way of obtaining the RTD. 

Next the reactor system in which the CSTR is preceded by the PFR will be treated. If the pulse of tracer is introduced into the entrance of the plug-flow section, then the same pulse will appear at the entrance of the perfectly mixed section Xp seconds later, meaning that the RTD of the reactor system will be... 

---