Recycle Reactor Operation

In considering continuous operation, recycle loops are often included (Herbert, 1964), with improved performance, that is, higher treatment rate, smaller vessel size, higher conversion. As a means for resource conservation and recovery as well as for environmental problems, recycle systems have become increasingly important. 

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Figs. 2a and 2b show typical results obtained with the electrocatalytic YSZ recycle reactor operated in the batch mode. The initial CH partial pressure was 20 kPa, i.e. 20% CH in He at atmospheric pressure. The recirculation... 

It follows from the equation above that c, if Fv.rec Fvj This means that for a recycle stream much larger than the feed stream, the catalyst bed operates as a differential reactor, while the whole system gives an outlet concentration differing significantly from that of the feed. This significantly simplifies problems of chemical analysis. In practice, the recycle reactor operates differentially if the recycle ratio Fv.ret/Fv.f is larger than 25. The rate is then given by the overall rate ... 

A new reactor concept for the study of catalyst deactivation is presented, it consists of the combination of an electrobalance and a recycle reactor. With the electrobalance, the coke content on the catalyst is measured continuously. The recycle reactor operates gradientlessly at high conversion, with on-line gas chromatographic analysis of the effluent. Thus, the catalyst activity and product selectivities may be coupled directly with the coke content and the coking rate on the catalyst. 

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. 

The thermal catalytic route proposed involves heating the fresh reactant feed plus recycle up to 790°C and feeding this material into a M0S2 catalyst fixed-bed reactor operating at 0.1 MPa (1 atm). The route yields a production of H2 almost 50% higher than the decomposition of H2S route. 

In cases where a large reactor operates similarly to a CSTR, fluid dynamics sometimes can be estabflshed in a smaller reactor by external recycle of product. For example, the extent of soflds back-mixing and Hquid recirculation increases with reactor diameter in a gas—Hquid—soflds reactor. Consequently, if gas and Hquid velocities are maintained constant when scaling and the same space velocities are used, then the smaller pilot unit should be of the same overall height. The net result is that the large-diameter reactor is well mixed and no temperature gradients occur even with a highly exothermic reaction. 

A typical reactor operates at 600—900°C with no catalyst and a residence time of 10—12 s. It produces a 92—93% yield of carbon tetrachloride and tetrachloroethylene, based on the chlorine input. The principal steps in the process include (/) chlorination of the hydrocarbon (2) quenching of reactor effluents 3) separation of hydrogen chloride and chlorine (4) recycling of chlorine to the reactor and (i) distillation to separate reaction products from the hydrogen chloride by-product. Advantages of this process include the use of cheap raw materials, flexibiUty of the ratios of carbon tetrachloride and tetrachloroethylene produced, and utilization of waste chlorinated residues that are used as a feedstock to the reactor. The hydrogen chloride by-product can be recycled to an oxychlorination unit (30) or sold as anhydrous or aqueous hydrogen chloride. 

The operational characteristics of the older Berty reactors are described in Berty (1974), and their use in catalyst testing in Berty (1979). Typical uses for ethylene oxide catalyst testing are described in Bhasin (1980). Internal recycle reactors are easy to run with minimum control or automation. 

Of these three, two must be measured experimentally to calculate the stability criteria. In recycle reactors that operate as CSTRs, rates are measured directly. Baloo and Berty (1989) simulated experiments in a CSTR for the measurement of reaction rate derivatives with the UCKRON test problem. To develop the derivatives of the rates, one must measure at somewhat higher and lower values of the argument. From these the calculated finite differences are an approximation of the derivative, e.g. ... 

In previous studies, the main tool for process improvement was the tubular reactor. This small version of an industrial reactor tube had to be operated at less severe conditions than the industrial-size reactor. Even then, isothermal conditions could never be achieved and kinetic interpretation was ambiguous. Obviously, better tools and techniques were needed for every part of the project. In particular, a better experimental reactor had to be developed that could produce more precise results at well defined conditions. By that time many home-built recycle reactors (RRs), spinning basket reactors and other laboratory continuous stirred tank reactors (CSTRs) were in use and the subject of publications. Most of these served the original author and his reaction well but few could generate the mass velocities used in actual production units. 

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. 

Appropriate setting of two on-off valves (Fig. 1) allows the system to be operated either as a batch recycle reactor or as a continuous-flow steady-state recycle reactor. 

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

When produced from natural gas the synthesis gas will be impure, containing up to 5 per cent inerts, mainly methane and argon. The reaction equilibrium and rate are favoured by high pressure. The conversion is low, about 15 per cent and so, after removal of the ammonia produced, the gas is recycled to the converter inlet. A typical process would consist of a converter (reactor) operating at 350 bar a refrigerated system to condense out the ammonia product from the recycle loop and compressors to compress the feed and recycle gas. A purge is taken from the recycle loop to keep the inert concentration in the recycle gas at an acceptable level. 

The first stage of the process is a hydroformylation (oxo) reaction from which the main product is n-butyraldehyde. The feeds to this reactor are synthesis gas (CO/H2 mixture) and propylene in the molar ratio 2 1, and the recycled products of isobutyraldehyde cracking. The reactor operates at 130°C and 350 bar, using cobalt carbonyl as catalyst in solution. The main reaction products are n- and isobutyraldehyde in the ratio of 4 1, the former being the required product for subsequent conversion to 2-ethylhexanol. In addition, 3 per cent of the propylene feed is converted to propane whilst some does not react. 

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