Recycle reactor, catalytic reaction

Various experimental methods to evaluate the kinetics of flow processes existed even in the last centuty. They developed gradually with the expansion of the petrochemical industry. In the 1940s, conversion versus residence time measurement in tubular reactors was the basic tool for rate evaluations. In the 1950s, differential reactor experiments became popular. Only in the 1960s did the use of Continuous-flow Stirred Tank Reactors (CSTRs) start to spread for kinetic studies. A large variety of CSTRs was used to study heterogeneous (contact) catalytic reactions. These included spinning basket CSTRs as well as many kinds of fixed bed reactors with external or internal recycle pumps (Jankowski 1978, Berty 1984.)... 

A second source of difficulty is caused by the unavoidable empty space in recycle reactors. This limits their usefulness in some studies. Homogeneous reactions in the empty gas volume may interfere with heterogeneous catalytic measurements. Transient experiments could reveal much more information on various steps in the reaction mechanism but material in the empty space can obscure sharp changes. 

In this work we present results obtained both with batch and continuous flow operation of the gas-recycle reactor-separator utilizing Ag and Ag-Sm203 electrocatalysts and Sr(lwt%) La203 catalysts, in conjunction with Linde molecular sieve 5A as the trapping material, and discuss the synergy between the catalytic and adsorption units in view of the OCM reaction network. 

External recycle reactor Polymerizations, catalytic reactions Very useful for viscous mixtures Equipment cost can be high (for viscous systems and for high pressure operations)... 

A recycle reactor with very high recycle ratio is used to study the kinetics of a particular irreversible catalytic reaction, A R. For a constant flow rate of feed (r = 2 kg sec/liter) the following data are obtained ... 

Catalytic hydrogenation in supercritical carbou dioxide has been studied. The effects of temperature, pressure, and CO2 concentration on the rate of reaction are important. Hydrogenation rates of the two double bonds of an unsaturated ketone on a commercial alumina-supported palladium catalyst were measured in a continuous gra-dient-less internal-recycle reactor at different temperatures, pressures, and C02-to-feed ratios. The accurate control of the organic, carbon dioxide, and hydrogen feed flow rates and of the temperature and pressure inside the reactor provided reproducible values of the product stream compositions, which were measured on-line after separation of the gaseous components (Bertucco et al., 1997). 

The third example (Fig. 4.3-27) is a loop reactor with internal recycle, developed by G. Lull. This reactor can advantageously be used to study kinetics of heterogenous catalytic reactions at pressures up to 40 MPa and temperatures to 500°C. The internal recycle... 

Differential internal recycle reactors have become important tools in recent years for the investigation of catalytic processes and a number of such reactors have been reported in literature with the main emphasis on the actual reactor design [1,2]. In this work a similar reactor, which has been developed by the main investigator for gas-phase reactions under low pressure and high temperature, where it proved its suitability, is described. [3]... 

Zwahlen A. G., Agnew J. Modification of an Internal Recycle Reactor of the Berty Type for Low-Pressure High Temperature Catalytic Gas-Phase Reaction CHEMECA 1987, I, 50.1-50.7, Melbourne, Australia. 

Davis studied the hydrogenation of ethylene to ethane in a catalytic recycle reactor operated at atmospheric pressure (R. J. Davis, Ph.D. Thesis, Stanford University, 1989.) The recycle ratio was large enough so that the reactor approached CSTR behavior. Helium was used as a diluent to adjust the partial pressures of the gases. From the data presented, estimate the orders of the reaction rate with respect to ethylene and dihydrogen and the activation energy of the reaction. 

Liquid propylene, gaseous carbon monoxide and hydrogen, and a soluble cobalt catalyst are fed to a high-pressure catalytic reactor. The reactor effluent goes to a flash tank, where all of the solution constituents are vaporized except the catalyst, which is recycled to the reactor. The reaction products are separated from unconsumed reactants in a multiple-unit process, and the product stream, which contains both butyraldehyde and /i-butanol, is subjected to additional hydrogenation with excess hydrogen, converting all of the butyraldehyde to butanol. 

In Section IV.B the five mathematical BSR models will be discussed. This includes a discussion of the general assumptions or restrictions made in the development of the models and a discussion of the additional assumptions that lead to each of the separate models. The relations that were used to describe momentum and mass transfer have already been discussed in the previous two sections, and will therefore not be repeated here. Furthermore the kinetic model to be implemented in a BSR model is considered to be known. In Section IV.C the adequacy of the models will be illustrated based on the results of validation experiments. For those experiments, the selective catalytic reduction (SCR) of nitric oxide with excess ammonia served as the test reaction, using a BSR filled with strings of a commercial deNO catalyst shaped as hollow extrudates. The kinetics of this reaction had been studied separately in a recycle reactor. 

Tank reactors for solid-catalyzed gaseous or liquid reactions are seen much less frequently than tubular reactors because of the difficulty in separating the phases and in agitating a fluid phase in the presence of solid particles. One type of CSTR used to study catalytic reactions is the spinning basket reactor, which has the catalyst embedded in the blades of the spinning agitator. Another is the Berty reactor, which uses an internal recycle stream to achieve perfectly mixed behavior." These reactors (see Chapter 5) are frequently used in industry to evaluate reaction mechanisms and determine reaction kinetics. 

The case study of vinyl acetate synthesis emphasises the benefits of an integrated process design and plantwide control strategy based on the analysis of the Reactor / Separation / Recycles structure. The core is the chemical reactor, whose behaviour in recycle depends on the kinetics and selectivity of the catalyst, as well as on safety and technological constraints. Moreover, the recycle policy depends on the reaction mechanism of the catalytic reaction. 

The reactor is operating in liquid phase at bubble point conditions. Fresh and recycled ethylene are fed to the liquid phase of the reactor through a gas distributor. The homogeneous catalyst is continuously fed to the reactor section. The dimerization reaction is carried out at about (50-600°C and 20-30 atm.)[14] with a reaction time of about (4-6) hrs. The homogeneous catalytic reaction proceeds at an ethylene conversion of about 80-85 percent per pass with a selectivity to butene-1 approaching 93%. The exothermic heat of reaction is removed by means of external pump-around loop equipped with a cooler. The reactor effluent is withdrawn from the reactor as a liquid containing the catalyst. 

Although the H-Oil reactor is loaded with catalyst, not all of the reactions are catalyzed some are thermal reactions, like thermal cracking, which depend on liquid holdup and not on how much catalyst is present. Thus, the material balance equations need to be divided into two categories, one set for the noncatalytic thermal reactions and another set for the catalytic reactions. A convenient parameter to use is the thermal volume/catalytic volume ratio, T/C, which is the ratio of liquid holdup to catalyst volume. In a commercial ebullated bed, this ratio is close to 1.0 under ebullation conditions. Consequently, the material balance equations for the catalytic reactions with no recycle are given in Eq. (17) ... 

The final set of equations for the H-Oil reactor can now be written to account for the recycle situation, and thermal reactions in concert with catalytic reactions. 

The model for the H-Oil reactor introduces two complications beyond the axial dispersion model. First, the boundary conditions are modified to account for the recycle and second, the catalyst in the reactor means that both thermal and catalytic reactions are occurring simultaneously. The set of equations given in Eq. (18) are solved numerically with a differential equation solver. This allows the reactor size to be... 

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