Simple, Inexpensive-Glass Reactors for High-Temperature Aqueous Kinetics Experiments Peter M. Jeffers SUNY, Cortland, NY 13045 We have devised methods to make, fill, and seal glass bulbs that we subsequently have heated to 200 OC for kinetics studies of hydrolysis reactions'. These bulbs have numerous advantages over other possible reactors including low cost, speedand ease of manufacture, absence of leakage, very small dead volume, and inherent cleanliness. O w raw materials have ranged from soft glass disposable pipets to discarded glass gas chromatograph columns to standard 7-mm0.d. borosilicate laboratory tubing. The only apparatus required is a simple gas-oxygen glass-blowing torch with appropriate propane or standard burner gas and oxygen supplies. The techniques involved require minimal glassblowing skills and can be mastered by a beginner with just a few practice sessions. Bulb Manufacture The burner flame is adjusted to about 10-cm length with the center cone about l-cm long. This flame should soften 7mm borosilicate glass tubing in less than 10 s. The tubing must be rotated slowly and uniformly in the flame. A concerted 1%-revolution to-and-fro motion is easiest to master. When the glass has softened (about 10-12 s), it is removed from the flame and drawn out about 2-3 cm. The process is repeated in increments of about 1cm along the tubing until 10 to 12 bulbs have been formed. The next step is to heat for just a second a t the midpoint of each drawn section, two or three quick touches to the flame will suffice, then to exit the flame auicklv and draw an additional 1 to 1.5 cm. After ahout five of ;hew secondary pulls have been completed, it is easiest to break off the finished work, then to c o m ~ l e t ethe remaining bulhs. After a short cool-down (a minute or so), the individual bulhs can be broken apart with the fingers. The fine capillary tip that results from the second drawing process is important in sealing the bulbs. Filling About 20 of the bulbs can be laced unrieht in adrv50-mL beaker. When about 40 m l , of ;he fill& s h i o n is added to the beaker, immernine all but the u!mer t i ~ s the . bulhs fill simultane&sly and completely by %pilla;y'action, which also holds the liquid in when they are removed for sealing. The filling process is completed in a matter of seconds. Sealing Depending on the solution composition, i t might be advisable to wear latex gloves for the sealing step. The solution must be drained t o allow a small air space a t one end. The thumb and forefinger hold the lower tip and are used to "valve" this drainage. I t is usually necessary to touch the upper capillary tip to the flame to initiate drainage. Alternatively, the lower end can be touched to a moist tissue, which will allow flow to occur. When an appropriate air space has been formed, the upper end is sealed by touching it to the flame. This seal will be secure in less than 1s of heatine. The t,ult,is t h e n i n ~ e r t e d ~ a nthesecondend d issealed by heating thecapillary near theend toexpel the last few millimetersof solution, then touching the t i p t o the hot flame to complete 522
Journal of Chemical Education
Top: len-a completed, empty bulb; right-a filled and sealed bulb. Note the air pocket accupying l z m length of the rlgM stem. Center: EigM bulbs aner me first drawlng step. Bottom: Two completed bulbs shawlng the secondary drawing process result.
the seal. Draining and sealing a single bulb should take no more than 10 s. Dlscusslon Cleanliness of these bulbs is assured since the entire length of tubing is flamed to near the softening point during the drawing process. The tubing can be prerinsed with an appropriate solution to remove any inorganic matter. Making the bulbs is suchaquick and inexpensive process that we make no attempt t o re-use them. The air space is critical. The problem is not the vapor pressure of water, but the thermal expansion of liquid water. We have found that a bulb with total volume of 350 pL must have a 5- to 15-pL air space to avoid rupturing (violently) when it is heated to 150 to 200 'C. Lower temperatures require correspondingly smaller air spaces. We regularly wrap each bulb in aluminum foil so that, if one does explode, the slivers are confined and the neighboring tubes are not also lost. The air space must be kept minimal if the solution contains volatile reactant materials. The distribution of matter between liquid and gas phases can be calculated from the appropriate volumes and the Henry's law constant, but Henry's law constants are not readily available for temperatures above 30 "C2. Our experience1 has demonstrated that the very small vapor volume of these tubes, which becomes even smaller upon heating, leads to a negligible Henry's law correction for experiments on chlorinated methanes, ethanes, and ethenes. On the other hand, we have found that, if a solution of 1,2-dichloroethane, for example, is kept in a tightly stoppered, 250-mL volumetric flask a t 25 "C, the volatile loss of reactant that occurs upon opening for daily
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Jeffers. P. M.; Ward. L. M.; Woytowitch, L. M.; Wolfe, N. L. Envlron. Scl. Technol. 1989. 23, 965. Ashworth, R. A.; Howe, G. 6.; Mullins, M. E.; Rogers, T. N. J. Hazardous Materials 1988, 18, 25.
sampling results in an apparent hydrolysis rate constant too large by a factor of 1000. If the reactants are relatively nonvolatile, the size of the airlexpansion gap is unimportant. The length of the bulbs could be increased to provide a larger volume for analysis, with, of course, an attendant increase in expansion volume. We have made no attempt to discover the upper temperature range possible for these glass bulbs, but we have used them successfully at 200 "C. Our experience has been that any explosions will occur very early in the heating process and that once a final temperature is achieved, the bulbs will survive indefinitely. The bulbs could be filled and drained in an inert gas glove box, held vertical during removal, and sealed with very little air contamination. The very small diameter of the capillary ends would allow little diffusional mixing in the time required for sealing, and these capillary ends could be increased in length to assure that such air contamination was negligible. For our hydrolysis experiments on chlorinated alkanes and alkenes, we sampled by file-scratching and breaking off
one ti^. We then made direct aaueous on-column GC iniections bf 0.1-0.5 pL. A larger syringe could be used to Gthdraw 100300 ULof the solution, inieet it into a small senturn vial containing an extraction solveit, and analyzing tl;e extract in standard fashion. Use of these techniques offer numerous opportunities to devise "highn-temperature kinetics ex~erimentsfor undergraduates,-in addition to research use as we have reported1. We regularly use gas chromatograph ovens for heating the foil-wrapped samples, thus the entire apparatus for kinetics studies is available in essentially all laboratories with little or no additional equipment purchase or construction. Acknowledgment
Useful discussions and encouraeement bv Jackson Ellineton and Lee Wolfe of the ~ t h e n s ~ n v i r o n k e n t~esearFh al Laboratorv are ao~reciated.as are the excellent ~hotomaphy and ehitoriaiEommenti of Hob Ryans. This paperkas DreDared while the author was a National Research Council senior Fellow.
Volume 67
Number 6 June 1990
523
