Periodic reactor operation

Process intensification can be considered to be the use of measures to increase the volume-specific rates of reaction, heat transfer, and mass transfer and thus to enable the chemical system or catalyst to realize its full potential (2). Catalysis itself is an example of process intensification in its broadest sense. The use of special reaction media, such as ionic liquids or supercritical fluids, high-density energy sources, such as microwaves or ultrasonics, the exploitation of centrifugal fields, the use of microstructured reactors with very high specific surface areas, and the periodic reactor operation all fall under this definition of process intensification, and the list given is by no means exhaustive. 

Effluent Flows. The water flows that the retention basin is required to accommodate are summarized in Table 10.4.A. The normal operating flows are those listed under "Continuous Flows," while the "Intermittent Flows," constitute the flows encountered during periodic reactor operations and during... 

Figure 3.34. The four classes of periodic reactor operation as defined by Bailey (1973) represented by typical reactor responses (r) at different environmental changes (e) and characterized by the ratio of characteristic times respectively as indicated.

Several modes of waste management are available. The simplest is to dilute and disperse. This practice is adequate for the release of small amounts of radioactive material to the atmosphere or to a large body of water. Noble gases and slightly contaminated water from reactor operation are eligible for such treatment. A second technique is to hold the material for decay. This is appHcable to radionucHdes of short half-life such as the medical isotope technetium-9 9m = 6 h), the concentration of which becomes negligible in a week s holding period. The third and most common approach to waste... 

Fig. 16. Variation in a stationary cycling state of catalyst temperature, S03, and complex concentrations in the melt phase and the concentration of gas phase species with time in a half cycle in the forward flow portion of a reactor operating under periodic reversal of flow direction with r = 40 min, SV = 900 h (Csodo = 6 vol%, (Co2)o = 15 vol%, Ta = 50°C. Curves 1, just after switching flow direction 2,1 min 3, 6.6 min 4, 13.3 min, and 5, 20 min after a switch in flow direction. (Figure adapted from Bunimovich et at., 1995, with permission, 1995 Elsevier Science Ltd.)...

In a typical reaction 100 - 200 mg of metal [Cr or Ni] was evaporated from a preformed alumina crucible over a period of 60 - 90 min and deposited into a mixture of 2 in poly(dimethylsiloxane) [Petrarch Systems 0.1 P.] within a rotary solution metal vapor reactor operating at 10 4 torr. The reaction flask was cooled to approximately 270 K by an iced-water bath. For a description of the apparatus see Chapter 3 of reference 4. The product in each case was a dark orange viscous liquid and was characterized as obtained from the reaction vessel. 

The water flow to a chemical reactor cooling coil is controlled by the system shown in Figure 11-4. The flow is measured by a differential pressure (DP) device, the controller decides on an appropriate control strategy, and the control valve manipulates the flow of coolant. Determine the overall failure rate, the unreliability, the reliability, and the MTBF for this system. Assume a 1-yr period of operation. 

The following problem is formulated as an optimization problem. A batch reactor operating over a 1-h period produces two products according to the parallel reaction mechanism A — B, A — C. Both reactions are irreversible and first order in A and have rate constants given by... 

Thermophilic Anaerobic Reactor Applications. Pulp and paper industries typically discharge warm (50°C) effluents, and conventional reactors operating under mesophilic conditions require cooling of such wastewaters. Attempts have been made periodically by various groups to investigate the possibility of applying thermophilic anaerobic processes to pulp and paper discharges, but to date there is no conclusive evidence to prove the superior performances of thermophilic reactors as compared to their mesophilic counterparts. 

The first reaction is the isomerization from a zero-octane molecule to an alkane with 100 octane the second is the dehydrocyclization of heptane to toluene with 120 octane, while the third is the rmdesired formation of coke. To reduce the rate of cracking and coke formation, the reactor is run with a high partial pressure of H2 that promotes the reverse reactions, especially the coke removal reaction. Modem catalytic reforming reactors operate at 500 to 550°C in typically a 20 1 mole excess of H2 at pressures of 20-50 atm. These reactions are fairly endothermic, and interstage heating between fixed-bed reactors or periodic withdrawal and heating of feed are used to maintain the desired temperatures as reaction proceeds. These reactors are sketched in Figure 2-16. 

In the chemistry of the fuel cycle and reactor operations, one must deal with the chemical properties of the actinide elements, particularly uranium and plutonium and those of the fission products. In this section, we focus on the fission products and then chemistry. In Figures 16.2 and 16.3, we show the chemical composition and associated fission product activities in irradiated fuel. The fission products include the elements from zinc to dysprosium, with all periodic table groups being represented. 

Products from the reactor passed through a back-pressure regulator into a separator maintained at 75°F and 200 psig. Tail gas from the separator passed through a second back-pressure regulator and was metered and sampled. Liquid products were drained from the separator after each 24-hr period of operation and washed with water to remove ammonia and hydrogen sulfide before a sample was taken for analysis. At the conclusion of each experiment the oil and hydrogen flows were stopped, the reactor was depressurized, and steam was introduced at the rate of 0.41 lb/lb/hr while the reactor was cooled to 700°F. Air was then introduced at the rate of 1.1 scf/lb/hr, and these conditions were maintained until the coke bumoff was completed. 

Several patents were issued on this topic. For example, Rueter [34] in his patent cited about 120 US patents and about 40 foreign patents in the period 1987-2004. The actual number of patents is higher, but already these numbers indicate that many aspects of catalyst and process technology are covered. Patents in the last five years (2003-2008) were thus focused either on the improvement of catalyst preparation and/or improvement of reaction/reactor operations, particularly with strong attention on the safety of operations. However, often in the cited patents operations are still... 

With the introduction of microreactors, transient reactor operations became interesting due to their low internal reactor volume and, thus, fast dynamic behavior. In 1999, Liauw et al. presented a periodically changing flow to prevent coke development on the catalyst and to remove inhibitory reactants in an IMM microchan-nel reactor [58]. This work was preceded by Emig in 1997, of the same group, who presented a fixed-bed reactor with periodically reversed flow [59]. In 2001, Rouge et al. [14] presented the catalytic dehydration of isopropanol in an IMM microreactor. 

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