The purpose of this study was to develop the use of semibatch operation of a recirculation reactor in kinetic studies. Ethylene hydrogenation over a supported copper catalyst was studied experimentally. In semibatch operation one of the reactants is fed a t the rate necessary to hold the total pressure in the reactor constant. In ethylene hydrogenation the reaction rate is directly equal to the feed rate, and the kinetics can be studied a t constant partial pressure of either of the reactants. Since ethane is inert, this technique permitted the study of reaction rate as a function of one variable a t a time.Although ethylene hydrogenation has been studied extensively, there is not general agreement regarding the kinetics over a copper catalyst. The results are themselves of interest because they indicate the reasons for the apparently conflicting data in the literature.The design of experiments for the systematic study of the kinetics of a chemical reaction in the gas phase presents a dilemma. Fixed beds of catalyst are commonly employed in flow reactors for studies of heterogeneous reactions, but gas composition and temperature vary over a wide range from inlet to outlet if appreciable conversion is attained. High conversions in the laboratory serve to demonstrate the feasibility of a commercial process, but the data obtained are often difficult to analyze. Differential reactors giving low conversions operate at nearly constant temperature and gas composition, but extremely accurate gas analyses are required if the reaction rate is to be calculated from the necessarily small change in gas composition.The recirculation reactor provides a technique for overcoming these difficulties. A gas is circulated over a small amount of catalyst in a gas circulation loop, and the advantages of the differential reactor are retained. In batch operation the system is closed, and reaction rate is calculated from measurements of gas composition as a function of time. In continuous operation the reactants and products are fed and withdrawn continuously so as to establish a steady state. The overall conversion can be large though the conversion in the differential bed is very small, so extreme analytical precision is not required. The composition of the effluent is essentially the same as that of the gas in contact with the catalyst.Batch operation has the disadvantage that the concentrations of both reactants and products change progressively as the experiment proceeds. With continuous operation each test requires a considerable time to reach a steady state and provides but a single value of reaction rate at a particular gas composition. Neither type of operation makes is possible to carry out a systematic kinetic stud:, in which reaction rate is studied by progressive change of a single variable.For certain types of reactions these difficulties can be overcome by semibatch operation of a recirculation reactor. As employed in this study for the hydrogenation of ethylene the semibatch operation is as follows: the recirculation react...
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