W. KEITH HALL, D. S. MaclVER, and H. P. WEBER Mellon Institute, Pittsburgh, Pa.
Semiautomatic Microreactor for Catalytic Research The innovation in technique made possible by this instrument simplifies microscale evaluations of catalyst activity, an especially desirable feature in catalyst screening studies
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complished using even a manual microcatalytic procedure. Moreover, it has been shown (2) that this method has a number of advantages over more conventional procedure. I t suffers, however, from several limitations, the most important being that when a small slug of the reacting mixture is carried through a bed of catalyst by a stream of inert gas, it is doubtful that equilibrium or steady sIate assumptions can be made with respect to either the condition of the catalyst or the adsorption of the gases present. This may make it difficult, or perhaps impossible, to interpret properly such data as those for the pressure dependence of the reaction rate. Further, the data obtained are integral reaction rates, and the technique is not easily adaptable to the requirements for differential reaction kinetics. These factors have suggested that gas phase chromatography (GPC) be applied as an analytical tool in a more conventional manner-eg., as a means of analyzing the tail gas from a steady state, flow-type reactor. The two types of data may be expected to complement each other nicely.
RESEARCH involving heterogeneous catalysis, obtaining data on catalytic activity is often tedious and time consuming, especially in cases where complex reactions are involved. Often the analyses must be done by specialists outside the laboratory, and a time lag ranging from hours to weeks may occur. The disadvantages of this situation in planning a successive series of experiments are obvious; what is required is a fast simple method of performing analyses of complex mixtures in the worker’s own laboratory. T o solve this problem, an instrument has been devised for putting catalytic kinetic studies on a basis that is nearly automatic, not only for the microcatalytic (slug) technique but also for the use of gas phase chromatography in analyzing the tail gas from steady state reactors. The reactions studied were polymerization of propylene and cracking of 2,3dimethylbutane over silica-alumina cracking catalysts. Earlier reports (2, 3, 6) from this laboratory have dealt with aspects of this problem. I t has been shown that a considerable saving of time can be ac-
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T h e work described shows how catalytic kinetic studies have been put on a nearly automatic basis and demonstrates the utility of the resulting instrument, not only for the microcatalytic (slug) technique but also for the more conventional use of GPC for the analysis of the tail gas from steady state reactors. T h e reactions studied were the polymerization of propylene and the cracking of 2,3-dimethylbutane over silica-alumina cracking catalysts. Experimental
Equipment. A previously designed microcatalytic system ( 2 ) was modified by substituting, for the stopcock arrangement, an automatic dosing device constructed from solenoid valves. Periodic and automatic operation of this device was synchronized with the temperature control of the catalytic reactor. An automatic integrating system (5) was used in the analysis, which allowed the areas of the various chromatographic peaks to “print-out” in digital form. This considerably reduced the calculation time.
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