@'
ALABORATORYAPPARATUS FORVAPOR PHASE REACTIONS LEO J. SPILLANE and ROBERT D. GOODWIN Allied Chemical & Dye Corporation, Morristown, New Jersey
A REVIEW of the literature for the last twenty years fails ta reveal more than a very few publications describing a laboratory apparatus of general applicability to the study of vapor phase reaction^.'-^ In our experience even these suffer from one or more of the following defects: (a) Elaborate devices for the control of liquid feed; (b) Use of rubber tubing a t points subjected to continuous exposure to reagents; (c) Inconvenience in changing catalyst and in cleaning the system. For the past three years we have been experimenting with various modifications of the apparatus described in this paper. Since it has become reasonably standardized and has demonstrated a wide adaptability, we believe it is worth reporting. The arrangement illustrated in Figure 1 has been used most frequently for the simultaneous introduction of a gas and a liquid to the converter tube. Simple alterations permit considerable variation of the reactants. The ent.ire equipment may be constructed from materials ordinarily available in a well-stocked laboratory. I t is easily assembled and can be conveniently taken apart for cleaning and changing the catalyst. Operation is simple, as is indicated by the fact that several previously unskilled workers have been trained 10 l ~ s~tisfncrury upernrors in It!*.; rhm 3 day's tirnc. .1,1 1r 1rs.irnti:~I ~ p i ~ r t :,rr i in\.olwd in the consrrucrion and operation: the feed system, the converter, and the condensing system. These u-illbe described in detail. THE FEED SYSTEM
The most important function of the feed system is to introduce reactants at a constant rate throughout the experiment. When compressed gases from cylinders are used, littlk difficulty is encountered simply by using good needle valves with simple flowrneters for measurement. Use of liquid reactants, on the other hand, requires considerable care to avoid changes in the rate of addition resulting from such variable factors as unexpected alterations in pressure, clogging of delivery tubes, or back-surge from too rapid vaporization in the converter. In our apparatus the fimt requirement to maintain purposes air from constant liquid feed a t desired rates is a source of inert gas at constant Pressure. the laboratory compressed air supply is satisfactory. A I Hooo, H., J. VERAEUS, AND F. J. ZUIDERWEG, Trans. Far. diaphragm valve4 is attached to the compressed air Sac., 35, 993 (1939). WENDLAND, R., J. CBEM.EDUC..21, 171 (1944). 4 Regulator model CON0 H-10, Conoflow Corporation, Phila-
' O'BANION,E., ibid., 24, 287 (1947).
delphia, Pennsylvania.
FEBRUARY. 1948
supply to minimize the wide variations in pressure delivered from the compressor reservoir. A short section of thermometer capillary inserted in the air line was found to serve equally well. When it isnecessary to use nitrogen in place of air, coarse regulation can be effected by means of a needle valve on the high pressure cylinder. From the coarse regulator the air passes through a controller based on the Cartesian float principle6 (shown schematically in Figure 2).= Air enters the h e controller a t A and part of it passes to the syetem through outlet B. During normal operation the float is held against the capillary tip C so that a small stream of air is allowed to escape. Using x~ateras the float liquid, very delicate pressure adjustments ca6 be made by raising or lowering the leveling bulb D. At the same time protection is obtained against pressure variations in the entire system. Air from the controller is delivered at a constant pressure through capillary A (Figure 1) into the bottom of feed reservoir B. Connection to the reservoir is accomplished through a 19/38 standard taper joint held in place by springs. Liquid is displaced through open stopcock C and capillaries D and E into the reaction tube F. Capillary D (1 mm., I.D.) is sealed to reservoir B and to the 29/42 joint G. Capillary E (0.2 to 1 mm., I.D.) is attached to D through a 10/30 joint and is held in place by springs. The rate of liquid flow from the reservoir is best governed by adjusting the pressure of gas introduced through capillary A and by varying the size of capillary E. Capillaries D and E also serve to minimize liquid hold-up and to reduce the effect of back-surge during vaporization. When a homogeneous liquid can be vaporized in the presence of a gas without reaction, the materials are added to the converter through adapter H. The adapter is connected to the converter either through a neoprene stopper or a 19/38 joint. When mixing of reagents must be prevented until the liquid is vaporized, a more complicated arrangement is necessary. The adapter part I entering the converter is inserted in a larger outer tube by means of a ring seal and is extended nearly to the catalyst zone J. The outer tube is connected to the reagent-gas feed and is of sufficient diarneter to allow filling the preheat zone with packing (alundum granules or glass beads). Through the original gas inlet K a slow stream of inert gas is usually passed to prevent reagent gases from backing into the liquid feed.
Fi-ro
2.
P..luur.
0ont.ou.r
for Liqvld
Fad
the indentations N. This is followed by catalyst; 50 cc. occupies about six inches. Pyrex Raschig rings (6 X 6 rnm.) or, in some instances, alundum (8-10 mesh) serve as packing for vaporizer and preheater 0. The heating furnace P is constructed by winding nichrome wire on a refractory core (I1/, X 18 in.).' The heating units are wound as two separate circuits to function independently as preheater and reactor; temperature control can be effected manually through Variacs. The insulation consists of a two-inch layer of Superex (Johns-Manville) pipe lagging. Raw ends of the lagging are sealed with a layer of magnesia cement. Temperatures as high as 650°C. were used with these furnaces and with a gradient of less than 5" over the length of the catalyst zone. THE CONDENSING SYSTEM
Hot gases from the converter are led first through an efficient water-cooled condenser, usually of the Friedrichs type, which is fitted with a socket to join the ball of the converter tube and held tightly with a clamp (Figure 1). Liquid condensate drops into the receiver Q which is equipped with side tubes and stopcocks so that samples may be withdrawn without interrupting the process or developing any bark pressure. Gases not condensed in the water-cooled condenser pass THE CONVERTER through a series of cold traps R which are cooled as reThe converter F consists of a Pyrex tube (25 mm. quired for the individual operation. In our research O.D.) which is equipped with a sealed-in thermocouple frequently involving the use of ammonia, the first trap, well L and a semi-ball joint M. In filling the tube, cooled with ice and salt, was followed by two cooled by inert packmg (8-10 mesh alundum and Pyrex Raschig dry iceacetone mixture. This series made possible rings) is added to a depth of four inches, measured above nearly quantitative recovery of the excess ammonia for material balance calculations. GILMONT, R.,Ind. Eng. C h m . , A d . Ed., 18,633 (1946). The controller actually used was adapted from a pressure If measurement of noncondensable gas volumes is
regulator purchased from the Emil Greiner Company, New York. The only modification necessary was the outlet E for attachment to the leveling bulb D.
7 Purchased from the Norton Company, Worceakr, Massachusetts.
80
desired, a wet test meter may be attached to the end of the condensing train, being suitably protected against corrosion by the insertion of wash bottles after the cold traps. The entire apparatus is assembled as indicated in Figure 1. It is mounted vertically on a rigid rack over a bench eighteen inches above the floor level. The top of the feed reservoir is about seven feet above the floor and can be reached readily by a person of average height
JOURNAL OF CHEMICAL EDUCATION
although when adjustments a t the top become necessary the operator usually mounts a step. Ordinarily, an entire run can be conducted without requiring attention a t the top, once the feed reservoir has been filled and the rate adjusted. Temperatures are read by manipulating the thermocouple at the bottom of the converter tube. Reactions may be carried out under atmospheric or reduced pressure.
