Vacuum lines

Adsorption isotherms conventionally have been determined by means of a vacuum line system whereby pressure-volume measurements are made before and after admitting the adsorbate gas to the sample. For some recent experimental papers, see Refs. 24 and 25. 

Molybdenum hexafluoride [7783-77-9] MoF, is a volatile liquid at room temperature. It is very moisture sensitive, hydrolysing immediately upon contact with water to produce HF and molybdenum oxyfluorides. MoF should therefore be handled in a closed system or in a vacuum line located in a chemical hood. The crystals possess a body-centered cubic stmcture that changes to orthorhombic below —96° C (1,2). The known physical properties are Hsted in Table 1. 

Fig. 8. Magnetherm reactor central electrode, A secondary circuit, B grounding electrode, C refractory lining, D carbon lining, E primary material feed, F slag taphole to FeSi recovery, G vacuum line, H water spray ring, I condenser, cmcible, K trap, L filter, M and transformer, N.

The radioactive isotopes available for use as precursors for radioactive tracer manufacturing include barium [ C]-carbonate [1882-53-7], tritium gas, p2p] phosphoric acid or pP]-phosphoric acid [15364-02-0], p S]-sulfuric acid [13770-01 -9], and sodium [ I]-iodide [24359-64-6]. It is from these chemical forms that the corresponding radioactive tracer chemicals are synthesized. [ C]-Carbon dioxide, [ C]-benzene, and [ C]-methyl iodide require vacuum-line handling in weU-ventilated fume hoods. Tritium gas, pH]-methyl iodide, sodium borotritide, and [ I]-iodine, which are the most difficult forms of these isotopes to contain, must be handled in specialized closed systems. Sodium p S]-sulfate and sodium [ I]-iodide must be handled similarly in closed systems to avoid the Uberation of volatile p S]-sulfur oxides and [ I]-iodine. Adequate shielding must be provided when handling P P]-phosphoric acid to minimize exposure to external radiation. 

The first definitive studies of boron hydrides were carried out by Alfred Stock in Germany starting about 1912 (1). Through extensive and now classic synthetic studies, the field of boron hydride chemistry was founded with the isolation of a series of highly reactive, air-sensitive, and volatile compounds of general composition and This accomplishment required the development of basic vacuum line techniques for the... 

Hand and power tool cleaning is used on ships mostly for spot repair of damaged areas. Hand tools include scrapers, wire bmshes, and sanders. Electric and pneumatic power tools, which include grinders and needle guns, clean faster and more thoroughly than hand tools. Most power tools have vacuum lines coimected to collect paint debris. 

Manipulations involving materials sensitive to air or water vapour can be carried out by these procedures. Vacuum-line methods make use of quantitative transfers, and P(pressure)-V(volume)-T(temperature) measurements, of gases, and trap-to-trap separations of volatile substances. 

W-Metbylpbenotbiazine [1207-72-3] M 213.2, a-form m 99.3" and b 360-365", 0-form m 78-79". Recrystn (three times) from EtOH gave a-form (prisms). Recrystn from EtOH/ benzene gave the B-form (needles). Also purified by vacuum sublimation and carefully dried in a vacuum line. Also crystd from toluene and stored in the dark [Guarr et al. J Am Chem Soc 107 5104 1985 Olmsted et al. J Am Chem Soc 109 3297 1987.]... 

Methyl vinyl sulfone [3680-02-2] M 106.1, b 116-118 /20mm, d 1.215, n 1.461. Passed through a column of alumina, then degassed and distd on a vacuum line and stored at -190° until required. 

Styrene is difficult to purify and keep pure. Usually contains added inhibitors (such as a trace of hydroquinone). Washed with aqueous NaOH to remove inhibitors (e.g. rert-butanol), then with water, dried for several hours with MgS04 and distd at 25° under reduced pressure in the presence of an inhibitor (such as 0.005% p-tert-butylcatechol). It can be stored at -78°. It can also be stored and kept anhydrous with Linde type 5A molecular sieves, CaH2, CaS04, BaO or sodium, being fractionally distd, and distd in a vacuum line just before use. Alternatively styrene (and its deuterated derivative) were passed through a neutral alumina column before use [Woon et al. J Am Chem Soc 108 7990 1986 Collman J Am Chem Soc 108 2588 1986]. 

Crystd from EtOH or from benzene/abs EtOH, diethyl ether and pet ether. It was sublimed under vacuum and carefully dried in a vacuum line. Stored in the dark under nitrogen. 

Phosgene [75-44-5] M 98.9, b 8.2 /756mm. Dried with Linde 4A molecular sieves, degassed and distilled under vacuum. This should be done in a closed system such as a vacuum line. HIGHLY TOXIC, should not be inhaled. If it is inhaled operator should lie still and made to breath ammonia vapour which reacts with phosgene to give urea. 

Values listed are guides, and final line sizes and flow velocities must be determined by appropriate calculations to suit circumstances. Vacuum lines are not included in the table, but usually tolerate higher velocities. High vacuum conditions require careful pressure drop evaluation. 

When 5.00 mL of ether has been delivered by the syringe pump, the pump is shut off The reactor is allowed to run an additional 15 min before the fluorine and the mercury arcs ate shut off. The preaerosol furnace, the evaporator heater unit, and the coolant pump are shut off. Once the system approaches ambient conditions, all the helium carriers are shut off and the product trap valves are closed The product trap and its Dewar flask filled with liquid nitrogen are removed to the vacuum line where the trap is evacuated... 

The contents of the trap are transferred to the glass vacuum line by vacuum distillation. The contents are condensed into a 150-mL stainless steel cylinder containing an excess of 20% aqueous sodium carbonate and allowed to react with occasional shaking for 24 h The products are fracbonated through 5, -78, -131, and -196 °C traps under active pumping (3 pm of Hg) The product (8.5 g) is collected in the -131 °C tiap. The remaining vacuum line traps were virtually empty. 

The metal itself, having an appreciable vapour pressure, is also toxic, and produces headaches, tremors, inflammation of the bladder and loss of memory. The best documented case is that of Alfred Stock (p. 151) whose constant use of mercury in the vacuum lines employed in his studies of boron and silicon hydrides, caused him to suffer for many years. The cause was eventually recognized and it is largely due to Stock s publication in 1926 of details of his experiences that the need for care and adequate ventilation is now fully appreciated. 

Figure 2-46. Typical flow velocities for vacuum lines. Note 1 torr = 1.33 mb = 133.3 Pa. 1.0 ft/sec = 0.3048 m/seo. By permission, Ryans, J. L. and Roper, D. L., Process Vacuum System Design Operation, McGraw-Hill Book Co., Inc., 1986 [18].

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