Outlet reactor mixtures

Table 6.4 Basic physical properties of components in the outlet reactor mixture.

To get an idea about the relative volatilities of components we proceed with a simple flash of the outlet reactor mixture at 33 °C and 9 bar. The selection of the thermodynamic method is important since the mixture contains both supercritical and condensable components, some highly polar. From the gas-separation viewpoint an equation of state with capabilities for polar species should be the first choice, as SR-Polar in Aspen Plus [16]. From the liquid-separation viewpoint liquid-activity models are recommended, such as Wilson, NRTL or Uniquac, with the Hayden O Connell option for handling the vapor-phase dimerization of the acetic acid [3]. Note that SR-Polar makes use of interaction parameters for C2H4, C2H6 and C02, but neglects the others, while the liquid-activity models account only for the interactions among vinyl acetate, acetic acid and water. To overcome this problem a mixed manner is selected, in which the condensable components are treated by a liquid-activity model and the gaseous species by the Henry law. 

In order to secure a continuous quantitative analysis of the outlet gas mixture, including all the species necessary for the evaluation of the nitrogen atomic balance, namely NH3, NO, N02 (reactants), N2 and N20 (products), the gases exiting the reactor were analyzed both by a Mass Spectrometer (MS) (Balzers QMS200) and by a UV analyzer (ABB Limas 11HW) in a parallel... 

In conclusion to this section, research in the RTD area is always active and the initial concepts of Danckwerts are gradually being completed and extended. The population balance approach provides a theoretical framework for this generalization. However, in spite of the efforts of several authors, simple procedures, easy to use by practitioners, would still be welcome in the field of unsteady state systems (variable volumes and flow rates), multiple inlet/outlet reactors, variable density mixtures, systems in which the mass-flowrate is not conserved, etc... On the other hand, the promising "generalized reaction time distribution" approach could be developed if suitable experimental methods were available for its determination. 

The experimental set up has been described in details in an earlier study [10]. Tlie kinetic measurements were performed at 300 C in differential flow reactor conditions by recycling the outlet gas mixture. The reactants (NO, CO) and reaction products (Nj, NjO, COj) were analysed by means of a chromatograph HP5850 equipped with a thennal conductivity detector. Their separation was achieved on a column CTRl supplied by Alltech. 

Note that the auto-thermal PFR reactor (preheat of inlet reactant by the outlet reaction mixture) exhibits similar behaviour with CSTR. Even if the PFR alone is stable, the positive feedback of heat through the recovery heat exchanger makes the system unstable. The stabilisation can be obtained by introducing a heat source that keeps constant the feed reactor temperature (see also the Chapter 13). 

A Mass Spectrometer (MS) (Balzers QMS200) was used for species analysis. This instrument can provide the qualitative and quantitative temporal evolution of the composition of the outlet gas mixture. The following m/e ratios were monitored in order to follow the transient behavior of the most relevant species 15 (NHj), 18 (H2O), 28 (N2), 30 (NO), 32 (O2), 40 (Ar), 44 (NjO), and 46 (NO2). The MS data were elaborated taking into account the species cross-sensitivities and the response factors periodically estimated by means of specific calibration runs in a blank reactor, thus obtaining the outlet concentrations of reactants and products. A UV analyzer (ABB Limas IIHW), which provided accurate continuous simultaneous measurements of ammonia, NO, and NO2, was also coupled in parallel to the MS [10]. 

FIGURE 2.1 Schematic representation and picture of a lab-scale semi-batch reactor used for enzymatic desulfurization of simulated biogas containing SOOOppm of H2S. Outlet gas mixture is analyzed using a GC equipped with a TCD and a FPD for the detection of CH4/CO2 and H2S, respectively. 

A continuous flow stirred tank reactor (CFSTR) differs from the batch reactor in that the feed mixture continuously enters and the outlet mixture is continuously withdrawn. There is intense mixing in the reactor to destroy any concentration and temperature differences. Heat transfer must be extremely efficient to keep the temperature of the reaction mixture equal to the temperature of the heat transfer medium. The CFSTR can either be used alone or as part of a series of battery CFSTRs as shown in Figure 4-5. If several vessels are used in series, the net effect is partial backmixing. 

A promoted nickel type catalyst contained in the reactor tubes is used at temperature and pressure ranges of 700-800°C and 30-50 atmospheres, respectively. The reforming reaction is equilibrium limited. It is favored at high temperatures, low pressures, and a high steam to carbon ratio. These conditions minimize methane slip at the reformer outlet and yield an equilibrium mixture that is rich in hydrogen. ... 

According to [4], the optimum conditions of the sulfonation stage are a reactor temperature of 15°C, an S03/I0 ratio of 1.08, and 2.8 vol % S03 in the gas stream. Such mild conditions lead to sulfonation mixtures consisting of 85% P-sultones (1) 10% alkenesulfonic acids (2) 5% y-sultones (3) and less than 5% unreacted olefins. The authors observe that the reaction has been completed to more than 95% at the outlet of the reactor. This means that the incomplete conversions found by earlier authors [15] must have been due to phenomena occurring after the sulfonation. Of equal importance is the observation that the reactivity of 10 toward gaseous S03 seems similar to that of AO. 

The design equations for a CSTR do not require that the reacting mixture has constant physical properties or that operating conditions such as temperature and pressure be the same for the inlet and outlet environments. It is required, however, that these variables be known. Pressure in a CSTR is usually determined or controlled independently of the extent of reaction. Temperatures can also be set arbitrarily in small, laboratory equipment because of excellent heat transfer at the small scale. It is sometimes possible to predetermine the temperature in industrial-scale reactors for example, if the heat of reaction is small or if the contents are boiling. This chapter considers the case where both Pout and Tout are known. Density and Q ut wiU not be known if they depend on composition. A steady-state material balance gives... 

Fig. 6 shows the evolution of the CO concentration after the introduction of the methanol/water mixture to the reformer, indicating a CO spike at the initial stage of operation. CO concentration of up to 2% (dry basis) was observed at the reformer outlet by gas chromatography, but it was reduced to 0.6% in 20 min as shown in Fig. 6. CO concentration at the outlet of the PROX reactor operating at an 02 CO ratio of 1, increased rapidly to 1 lOOppm...

Catalytic activity tests have been performed in a quartz microreactor (I.D.=0.8 cm) filled with 0.45 g of fine catalyst powders (dp=0 1 micron). The reactor has been fed with lean fiiel/air mixtures (1.3% of CO, 1.3% of H2 and 1% of CH4 in air resp ively) and has been operated at atmospheric pressure and with GHSV= 54000 Ncc/gcath The inlet and outlet gas compositions were determined by on-line Gas Chromatography. A 4 m column (I D. =5mm) filled with Porapak QS was used to separate CH4, CO2 and H2O with He as carrier gas. Two molecular sieves (5 A) columns (I D.=5 mm) 3m length, with He and Ar as carrier gases, were used for the separation and analysis of CO, N2, O2, CH4, and H2, N2, O2 respectively... 

GP 8[ [R 7[ Syngas generation with commercial Pt-Rh gauzes, metal-coated foam monoliths and extruded monoliths has been reported. For similar process pressure, process temperature, and reaction mixture composition, methane conversions are considerably lower in the conventional reactors (CH4/O2 2.0 22 vol.-% methane, 11 vol.-% oxygen, 66 vol.-% inert species 0.14—0.155 MPa 1100 °C) [3]. They amount to about 60%, whereas 90% was reached with the rhodium micro reactor. A much higher H2 selectivity is reached in the micro reactor the CO selectivity was comparable. The micro channels outlet temperatures dropped on increasing the amount of inert gas. 

Hydrolytic Kinetic Resolution (HKR) of epichlorohydrin. The HKR reaction was performed by the standard procedure as reported by us earlier (17, 22). After the completion of the HKR reaction, all of the reaction products were removed by evacuation (epoxide was removed at room temperature ( 300 K) and diol was removed at a temperature of 323-329 K). The recovered catalyst was then recycled up to three times in the HKR reaction. For flow experiments, a mixture of racemic epichlorohydrin (600 mmol), water (0.7 eq., 7.56 ml) and chlorobenzene (7.2 ml) in isopropyl alcohol (600 mmol) as the co-solvent was pumped across a 12 cm long stainless steel fixed bed reactor containing SBA-15 Co-OAc salen catalyst (B) bed ( 297 mg) via syringe pump at a flow rate of 35 p,l/min. Approximately 10 cm of the reactor inlet was filled with glass beads and a 2 pm stainless steel frit was installed at the outlet of the reactor. Reaction products were analyzed by gas chromatography using ChiralDex GTA capillary column and an FID detector. 

The reactor brings the reaction mixture to equilibrium at the outlet temperature. The reaction is exothermic and the equilibrium constant K is given by ... 

This chapter reports the results from transient experiments (mainly, TPD or TPSR) coupled with on-line analysis of reaction mixture at the outlet of a well-stirred reactor. It means that the gas composition detected at the outlet of the reactor is in contact with the catalyst inside the reactor. Catalytic runs in isothermal conditions were also proceeded in order to avoid strong adsorptions of reactants or intermediates. 

The deprotection of carbobenzyloxy protected phenylalanine was carried out in a low-pressure test unit (V= 200 ml) equipped with a stirrer, hydrogen inlet and gas outlet. The gas outlet was attached to a Non Dispersive InfraRed (NDIR) detector to measure the carbon dioxide. During the reaction the temperature was kept at 25 °C at a constant agitation speed of 2000 rpm. In a typical reaction run, 10 mmol of Cbz protected phenylalanine and 200 mg of 5%Pd/C catalyst were stirred in a mixture of 70 ml ethanol/water (1 1). The Cbz protected phenylalanine is not water-soluble but is quite soluble in alcoholic solvents conversely, the water-soluble deprotected phenylalanine is not very soluble in alcoholic solvents. Thus, the two solvent mixture was used in order to keep the entire reaction in the solution phase. Twenty p.1 of the corresponding modifier was added to the reaction mixture, and hydrogen feed was started. The hydrogen flow into the reactor was kept constant at 500 ml/minute and the progress of the reaction was monitored by the infrared detection of C02 in the off-gas. 

A continuous flow reactor vessel contains a liquid reacting mixture with a density of 0.85 g/cm3 and a viscosity of 7 cP at 1 atm pressure. Near the bottom of the vessel is a I i n. outlet line containing a safety relief valve. There is 4 ft of pipe with two 90° elbows between the tank and the valve. The relief valve is a spring-loaded lift check valve, which opens when the pressure on the upstream... 

In Fig. 7, the mixture fractions in each environment and l2 are shown. By definition of the inlet conditions, in the inlet tubes — 0 and 2 = 1. The variations away from the inlet values represent the effect of micromixing. For example, if we set y — 0 in Eqs. (36) and (37) to eliminate micromixing, then and 2 would remain at their inlet values at all points in the reactor. Note that the spatial distributions of 1 and %2 are antisymmetric with respect to the vertical axis (as would be expected from the initial conditions.) In the outlet tube, and 2 are very near the perfectly micromixed value of 1/2. Finally, by comparing Fig. 6 and Fig. 7, we can observe that macromixing occurs slightly faster than micromixing in this reactor (i.e.,pn are closer to their outlet values than are .)... 

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