130
Ind. Eng. Chem. Fundam., Vol. 17, No. 2, 1978
An All-Glass Internal Recycle Reactor William D. Fitzharrls and James R. Katzer' Department of Chemical Engineering, University of Delaware, Newark, Delaware 7971 7
An all-glass (or quartz) internal recycle reactor, designed to eliminate problems of metal-containing reactors, is described. Reactant adsorption on the metal, catalyst contamination from the metal, and undesired metal reactivity are avoided in catalytic studies. Three variations on the reactor concept are examined.
Several reactor concepts for achieving gradientless reactor operation have been described in the literature (Bennett et al., 1972; Berty, 1974; Berty et al., 1969; Brisk et al., 1968, Butt, 1971; Carberry, 1964, Garanin et al., 1967; Gelain, 1969; Langer and Walker, 1954; Perkins and Rase, 1958;Satterfield and Roberts, 1968). Continuous-flow recirculation and stirred-tank reactors have particular advantages for kinetic studies involving broad ranges of reactant and product concentrations (Carberry, 1964; Bennett, 1967). In addition, rates of poisoning and deactivation can be effectively investigated without an assumed poisoning model in such reactors because the entire catalytic surface is exposed to a uniform concentration of poison throughout the reactor. Both the continuous-flow external loop recycle reactor and the continuous-flow stirred-tank reactor (CFSTR) can achieve similar reaction conditions; however, incorporation of the recycle loop into the main reactor body can reduce or eliminate many of the problems resulting from an external recycle loop. The most critical of these problems include a high reactor surface-tovolume ratio and possible difficulties in pumping the fluid uniformly and without contamination. Chambers et al. (1965) and Hanson and Benson (1973) discuss solutions to these problems. The Berty reactor (Berty, 1974; Berty et al., 1969), whose applicability to catalyst deactivation studies has been well documented (Mahoney, 1974; Weekman, 1974), incorporates internal recycle to achieve high gas flow rates past the catalyst. However, the Berty reactor suffers from drawbacks due to its materials of construction. Because of the potential catalytic activity of the metal body of the reactor and because of the potential for adsorption of reactants on and contamination of the catalyst from the reactor, the reactor body can interfere with studies of catalyst kinetics, poisoning, and deactivation. For these reasons we have developed the d-glass internal recycle reactor described below. Figure 1shows the simpler of the two design concepts. The reactor body is a 1300-cm3 heavy-wall resin kettle with a ground-glass flange for closure. T o avoid grease and achieve a leak-free seal, a groove is machined into the face of each ground surface, and seal is achieved by clamping a hightemperature O-ring between the meeting faces. The draft tube is thin-wall tubing, sized so that the annular area is slightly smaller than the center open area, and it is connected to the body of the reactor. Wide slots are formed in the bottom of the draft tube to allow flow of gas into the annular region to form the internal recirculation pattern. Stirring is achieved by a magnetically driven impeller. To avoid the problem of having to seat the impeller in its bearings in the reactor and yet allow easy removal and exchange of impellers, the stirrer is built as a self-contained unit similar to a gyroscope (Figure 2). The stirrer can thus be easily removed from the draft tube. The cage holding the stirrer is made of glass rod with a bearing rest formed into the crosspieces at the top and a t the bottom. The bearings are 0019-7874/78/1017-0130$01.00/0
machined with 60" angles, as shown, and are graphite pieces held between the bearing rest and the stirrer point. Bearing tension is adjusted by softening the glass rods connecting the end rings and cross members and adjusting them relative to one another. At low stirrer speeds the stirrer may require bushings to prevent its rattling in the draft tube; for stirrer speeds greater than 1000 rpm gyroscopic action holds the stirrer upright, and no rattle is observed. Catalyst can be placed in a glass basket resting on the stirring unit. Alternatively, the catalyst may simply be a metal film impregnated or evaporated onto an alumina cylinder which rests directly on the stirring unit. Inlet and exit gas ports are positioned to prevent shortcircuiting of the gas flowing into the reactor. A thermocouple enters via an O-ring seal through a third entry port positioned so that the thermocouple can be moved axially to measure temperatures at any position between the top and the bottom of the reactor. For lower temperature operation (
