Laboratory reactors experimental conversions

In kinetic studies it is advised to avoid experimentation in which external transport limitations are experienced. These can be easily avoided by adapting the flow rates. Yet, Koros and Nowak [1967] and Madon and Boudart [1982] have drawn attention to the lack of generality of the usual diagnostic test for external mass and heat transfer limitations. In this experimental test, the conversion (or the rate) is measured at constant space-time, W/Fao, but the flow velocity is varied by adapting simultaneously ITand Fao- If the conversion (or the rate) is not affected, the conclusion is drawn that there are no external transport limitations. At the low Reynolds numbers encountered in laboratory reactors, the mass and heat transfer coefficients are quite insensitive to changes in flow rates, so that these have to be varied over a very wide range. 

Hydrogenation of lactose to lactitol on sponge itickel and mtheitium catalysts was studied experimentally in a laboratory-scale slurry reactor to reveal the true reaction paths. Parameter estimation was carried out with rival and the final results suggest that sorbitol and galactitol are primarily formed from lactitol. The conversion of the reactant (lactose), as well as the yields of the main (lactitol) and by-products were described very well by the kinetic model developed. The model includes the effects of concentrations, hydrogen pressure and temperature on reaction rates and product distribution. The model can be used for optinuzation of the process conditions to obtain highest possible yields of lactitol and suppressing the amounts of by-products. 

Some experimental studies (1-7) have demonstrated the possibility of improving the performance of a catalytic reactor through cyclic operation. Eenken et al. (4) reported an improvement of 70% in conversion of ethylene to ethane under periodic operation. In a later article (2), they concluded that periodic operations can be used to eliminate an excessively high local temperature inside the catalytic reactor for a highly exothermic reaction. In our laboratory, Unni et al. (5) showed that under certain conditions of frequency and amplitude associated with the forced concentration cycling of reactants, the rate of oxidation of SC>2 over catalyst can be increased by as much as 30%. Re-... 

The many factors outlined above which affect reaction rates suggest that considerable caution is advisable when utilising laboratory data for the design of large-scale reactors. It is essential first to locate the reaction volume or volumes. This, in the case of the absorption of CO2 into aqueous ammonia liquid discussed above, the fast reaction between dissolved CO2 and dissolved ammonia occurs in a small volume of liquid close to the gas—liquid interface. The forward reaction rate is, therefore, proportional to the gas—liquid interfacial area. The conversion of the initially fomed NH2COONH4 to (NH4)2COa by hydrolysis is a much slower reaction and takes place throughout the whole volume of the liquid phase. Similarity would therefore dictate that the interfacial area per unit liquid volume should be the same in experimental and full-scale reactors. 

FCC catalyst testing prior to use in commercial reactors is essential for assuring acceptable performance. Purely correlative relations for ranking catalysts based on laboratory tests, however, can be erroneous because of the complex interaction of the hydrodynamics in the test equipment with the cracking kinetics. This paper shows how the catalyst activity, coke-conversion selectivity and other product selectivities can be translated from transient laboratory tests to steady state risers. Mathematical models are described which allow this translation from FFB and MAT tests. The model predictions are in good agreement with experimental data on identical catalysts run in the FFB, MAT and a laboratory riser. 

Several profound theoretical and experimental studies performed on the laboratory scale have been reported which focus on the use of various configurations of membrane reactors as a reactant distributor in order to improve selectivity-conversion performances. In particular, several industrially relevant partial oxidations have been investigated, including the oxidative coupling of methane [56], the oxidative dehydrogenations of propane [57], butane [58], methanol [59, 60], the epoxidation of ethylene [61], and the oxidation of butane to maleic anhydride [62]. 

Figure 7.19 represents schematically a way to determine experimentally whether external mass transfer can be neglected. Transfer effects do not occur when the conversion for a given space-time does not depend on the flow rate. The test is not very sensitive, however. This is caused by the small dependence of the mass transfer coefficient on the flow rate at the low Reynolds numbers prevailing in laboratory fixed bed reactors. 

The products from the pyrolyses of four higher alpha-olefins have been accounted for by an empirical model involving three competing decomposition pathways a molecular decomposition involving a six-membered ring transition state (which yields both propylene and an alpha-olefin with three less carbon atoms than the reactant) and two free radical chain pathways. One free radical channel involves hydrogen abstraction from, the second radical addition to the reactant olefin. The relative contributions of these three paths have been estimated from experimental data from the laboratory pyrolysis of higher alpha-olefins. The pyrolyses were carried out at low conversions in a quartz flow reactor at 475°-550°C. 

The previous examples show that if we know the molar flow rate to the reactor and the reaction rate as a function of conversion, then we can calculate the reactor volume necessary to achieve a specified conversion. The reaction rate does not depend on conversion alone, however. It is also affected by the initial concentrations of the reactants, the temperature, and the pressure. Consequently, the experimental data obtained in the laboratory and presented in Table 2-1 as -ta for given values of X are useful only in the design of full-scale reactors that are to be operated at the same conditions as the laboratory experiments (temperature, pressure, initial reactant concentrations). This conditional relationship is generally true i.e., to use laboratory data directly for sizing reactors, the laboratory and full-scale operating conditions must be identical, Usually, such circumstances are seldom encountered and we must revert to the methods described in Chapter 3 to olrtain — ta as a function of X. 

Gas samples from the reactor were analyzed by mass spectroscopy and gas chromatography and conversions of sulfur dioxide to sulfur vapor were computed from the combined analytical data. In this large-scale test program, effects on catalyst loading of a number of variables were examined in detail. While the laboratory experimentation had been quite extensive, operation of a pilot plant was considered necessary to permit scale-up of the process to the 200-300 ton/day plants conceivably required in the future. 

The system was designed to produce 1,000 [kg/h] of compound C. According to the experimental data, recorded at the laboratory, the reaction has a conversion of 60 % and the molar fraction of compotmd A in the feed stream of the reactor is 0.4. In addition, output stream 3 only contains compotmd C, and stream 4 (the recycle stream) only contains compounds A and B. (a) What is the molar composition of the fresh stream (1) (b) What is the molar composition of the recycle stream ... 

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