Sealed tubes safety

CISHC Chem. Safety Summ., 1977, 48, 25 Shaw, A. W., private comm., 1978 During the vacuum fractional distillation of bulked residues (7.2 t containing 30— 40% of the bis(hydroxyethyl) derivative, and up to 900 ppm of iron) at 210—225°C/ 445—55 mbar in a mild steel still, a runaway decomposition set in and accelerated to explosion. Laboratory work on the material charged showed that exothermic decomposition on the large scale would be expected to set in around 210—230°C, and that the induction time at 215°C of 12—19 h fell to 6—9 h in presence of mild steel. Quantitative work in sealed tubes showed a maximum rate of pressure rise of 45 bar/s, to a maximum developed pressure of 200 bar. The thermally induced decomposition produced primary amine, hydrogen chloride, ethylene, methane, carbon monoxide and carbon dioxide. 

With the tap closed, heat the sealed tube at the required temperature taking adequate safety precautions (see above). After the required time, allow the reaction mixture to cool to room temperature before opening the tap carefully. 

Finally, the safety of UFIPTC must also be considered. Rupture or failure of seals, tubing, and fittings can present a potential danger to the user. With proper instrument design and normal safety precautions, however, UHPLC can be safe to use [38]. This is especially true of commercial instruments, which are no more dangerous than any other HPTC. 

As we have mentioned in previous volumes in this series, we consider bulk polymerizations in sealed ampoules or even sealed heavy-walled tubes not merely imsafe, but dangerous. The procedure, in some respects is so trivial, that it is rarely described in any detail. Yet, so much polymer chemistry has been studied by sealed-tube polymerization that the procedure has to be described. Procedure 2-1 is a composite of those described elsewhere [28,34,35,75,76], Safety procedures will have to be designed to conform to OSHA regulations. 

Figure 5.1 The Knowles water electrolysis cell Key A, steel cell tank B, temperature control tubes C, electrodes D, leads E, gas collection bells F, insulating sleeves G, sealing and safety tubes H, J, insulating caps (top, bottom) K, copper connections M, gas take-off pipes N, drain tubes O, S-pipes ...

GG Sealing and Safety Tubes. SS, TT Temperature Control Mains. 

Fig. 4 Sorptive tube by National Institute for Occupational Safety and Health (1) plastic cap (2) sealed tube ends (broken before use) (3) glass sorptive tube, (4) spring (5) glass wool (6) sorbent (7) stopper and (8) protective layer of sorbent.

Bismuth is an ideal reductant for WCle because it is nontoxic, inexpensive, not impeded by a surface oxide, does notreaddy reduce WeClia, and forms volatile but low vapor pressure Bids for greatly improved safety in sealed tube reactions. Bismuth is also easily dispersed in reaction mixtures because it dissolves in molten BiClg. 

In general, the polymerization of vinyl chloride may be carried out in bulk, solution, suspension, and in emulsion. Free-radical initiators are most commonly used although organometallic initiators and radiation initiation have been considered. Since the monomer is a gas at ordinary temperatures and pressures, suitable equipment is required for VCM polymerization. Sealed tubes and capped bottles have been used for this experimental work. In the use of bottles, safety precautions should be considered both from the standpoint of explosion hazards and the problems of exposure of personnel to VCM. 

A sample of 50-100 mg is weighed into a combustion tube, 12 x 120 mm. Two milliliters 85% phosphoric acid is added, and the tube is sealed in a flame such that the wall thickness is maintained in the area of the seal. For safety, the tube is contained within a screw-cap metal tube. The nested tubes are placed in a silicone-oil bath for 15 min at 150 C, then removed and cooled. The contents of the combustion tube are transferred to a test tube of similar dimensions which is equipped with a ground-glass stopper. Two mL of petroleum ether is used to rinse the combustion tube, and the rinsings are added to the test tube. The test tube is shaken, and the petroleum ether layer is pipetted into a second test tube. The contents of the first test tube are extracted with another 2-mL aliquot of petroleum... 

I) Dissolve 2.465 g Na3lrCIg in water and dilute to volume. (2) Transfer 1.000 g Ir sponge to a glass tube, add 20 ml of HCI and 1 ml of HCIO4. Seal the tube and place in an oven at 300°C for 24 hr. Cool, break open the tube, transfer the solution to a volumetric flask, and dilute to volume. Observe all safety precautions in opening the glass tube. 

Proper condensate removal is important. An inverted split cup inside the shell, with the upper capped end above the nozzle and the lower open end -in. above the bottom tubesheet, should be used to cover the oudet nozzle. This can be made by splitting a pipe that is one size larger than the condensate oudet down the centerline. In this case, a 2-in. split is adequate. This cup must be fully seal welded (not tack welded) to force condensate down to the -in. clearance above the bottom tubesheet. A common error is to allow 6 in. or more above the tubesheet for the centerline of the condensate oudet. In this case, 6 in. of tube is 10% of the surface. If the cup is not used, add 10% more tubes to correct for the dead liquid space near the bottom. This is in addidon to the 10% safety factor. 

A satisfactory way to accomplish the introduction of chlorine with minimal loss of the gas is to seal the reaction flask with a two-holed stopper equipped with a gas-inlet tube reaching just above the surface of the reaction mixture and an exit tube connected to a U-tube filled with mineral oil which is used as a gas-flow indicator. Chlorine is then introduced from the cylinder through a safety trap at such a rate as to maintain a small positive pressure in the reaction flask. 

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