Reactor volume catalyst decay

With the demonstration of supercritical fluid extraction, an obvious extension would be to extract or dissolve the compounds of interest into the supercritical fluid before analysis with SFC.(6) This would be analogous to the case in HPLC, where the mobile phase solvent is commonly used for dissolving the sample. The work described here will employ a system capable of extracting materials with a supercritical fluid and introducing a known volume of this extract onto the column for analysis via SFC. Detection of the separated materials will be by on-line UV spectroscopy and infrared spectrometry. The optimized SFE/SFC system has been used to study selected nonvolatile coal-derived products. The work reported here involved the aliphatic and aromatic hydrocarbon fractions from this residuum material. Residua at several times were taken from the reactor and examined which provided some insight into the effects of catalyst decay on the products produced in a pilot plant operation. 

From Figure 2-6. wc note a very important observation The total volume to achieve 80% conversion for five CSTRs of equal volume in series is roughly the same as the volume of a PFR, As wc make the volume of each CSTR smaller and increase the number of CSTRs, the total volume of the CSTRs in series and the volume of the PFR will become identical. That is, we can model a PFR with a large number of CSTRs in series. This concept of using many CSTRs in series to model a PFR will be used later in a number of situations, such as modeling catalyst decay in packed-bed reactors or transient heat effects in PFRs. 

The plot of residuals versus some measure of the time at which experiments were run can also be informative. If the number of hours on stream or the cumulative volume of feed passed through the reactor is used, nonrandom residuals could indicate improper treatment of catalyst-activity decay. In the same fashion that residuals can indicate variables not taken into account in predicting reaction rates, variables not taken into account as affecting activity decay can thus be ascertained. 

Fig. 8.12 shows the setup of a laser beam and microphone for ethylene quantification with a PAS detector [24]. In the array, the eight reaction tubes are arranged linearly. A pulsed laser is passed through each effluent from the reactors to excite ethylene molecules. The pulsed laser used emitted at 943-950 cm-1 (where ethylene has a strong absorption) - a 10 or 100 Hz modulated 25 W laser with a pulse length of 35 or 25 ps. A microphone with a fast response time and decay was used. The ethylene concentration of each effluent was determined by the volume and response time. The signal from the most distant tube is weak so that the signals were accumulated for 2.5 s. Data presented in the reference are shown in Fig. 8.13. Ethylene concentrations were determined for the effluent from the mixed-oxide catalyst consisting of La, Ba, Pb, Th, Mn, Ni and Cu.

The differentia reactor is relatively easy to construct at a low cost. Owing to the low conversion achieved in this reactor, the heat release per unit volume will be small (or can be made small by diluting the bed with inert. solids) so that the reactor operates essentially in an isothermal manner. Vtlien operating this reactor, precautions must be taken so that the reactant gas or liquid does not bypass or channel through the packed catalyst, but instead flows uniformly across the catalyst. If the catalyst under investigation decays rapidly, the differential reactor is not a good choice because the reaction rate parameters at the start of a run will be different from those at the end of the run. In some cases sampling and analysis of the product stream may be difficult for small conversions in multicomponent systems. 

Mass transfer-limited processes favor SRs over monoliths as far as the overall process rates are concerned. Moreover, SRs are more versatile and less sensitive to gas flow rates. However, the productivity per unit volume is not necessarily higher for SRs because of the low concentration of catalyst in such reactors. There is also no simple answer to the selectivity problem, and again each process should be compared in detail for both reactors. For a kinetic regime, monoliths can be more advantageous due to their easier operation. The catalyst does not disintegrate due to the stirrer action, and catalyst separation is avoided. Catalysts are often pyrophoric materials, handling of which is usually a hazardous operation. The benefits of MRs can be achieved only for stable catalysts. For quickly deactivating catalysts, SRs are easier to operate, since replacement of decayed catalysts is simpler. 

The catalytic deactivation is independent of gas-phase concentration and follows a first-order decay rate law, with a decay constant of 0.72 reciprocal minutes. The feedstream is diluted with nitrogen so that as a first approximation, volume changes can be neglected with reaction. The reactor contains 22 kg of catalyst that moves through the reactor at a rate of lOkg/min. The gas oil is fed at a rate of 30mol/min at a concentration of 0.075 mol/dm, Determine the conversion that can be achieved in this reactor. 

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