Initial Evacuation

For food and pharmaceutical applications, the microbial count must be reduced to less than 10,000 viable cells per g exopolysaccharide. Treatment with propylene oxide gas has been used for reducing the number of viable cells in xanthan powders. The patented process involves propylene oxide treatment for 3 h in a tumbling reactor. There is an initial evacuation step before propylene oxide exposure. After treatment, evacuation and tumbling are alternated and if necessary the reactor is flushed with sterile nitrogen gas to reduce the residual propylene oxide level below the Food and Drug Administration permitted maximum (300 mg kg 1). The treated polysaccharide is then packaged aseptically. 

TPD studies tend to depopulate the molecular state sites during the Initial evacuation or carrier gas sweep. Thus, they are only sampling the slow sites which may well be dissociative as we have not examined this frequency region. The presence of an Intermediate molecular adsorbate would allow us to easily rationalize the possible change In observed molecularlty of the FRC results as the temperature was raised In that the dissociative sites would become accessible at the higher temperatures. 

The purging cycles for an evacuate-first purge are shown in Figure 7-4. In this case the beginning of the cycle is defined as the end of the initial evacuation. The oxygen mole fraction at this point is the same as the initial mole fraction. Furthermore, the remaining cycles are identical to the vacuum purge operation and Equation 7-6 is directly applicable. However, the number of cycles / is the number of cycles after the initial evacuation. 

Strength County-GIS personnel supported operations through continuous production of maps that were distributed to all agencies. EOC (Emergency Operations Center) staff worked to procure buses for initial evacuation and for transport from decontamination... 

Figure 7. FTIR absorbance spectra, 600-1600 cm of MgTPP thin film (a) initial evacuation and (b) evacuated after exposure to 750 torr of oxygen and light for 48 hours.

Initial evacuation of a vacuum chamber is influenced in the medium-, high-, and ultrahigh vacuum regions by continually evolving quantities of gas, because in these regions the escape of gases and vapors from the walls of the vessel is so significant that they alone determine the dimensions and layout of the vacuum system. 

Fig. 5.9. Toepler pump and gas buret. In this installation a constant-volume" manometer is used for measuring the pressure. Stopcock B allows the attachment of a sampling bulb or a large expansion bulb for use with large volumes of gas. Stopcock A is used for initial evacuation of the calibrated volume and sample bulbs. It is closed during the operation of the pump. When a gas is to be measured, the mercury levels in the right arm of the Toepler pump and in the left arm of the manometer are adjusted to levels (C) for which the gas volume has been calibrated. An excellent version of this pump is manufactured by the Rodder Instrument Co., Los Altos, Calif.

G. Example Initial Pump-Down and Venting the Pumping System. Initial evacuation of the system is accomplished by attaching all... 

Collected in a SUMMA passivated canister under pressure using an additional pump or at subatmospheric pressure by initially evacuating the canister the air transferred into cryogenically cooled trap attached to a GC column the trap heated benzene determined by GC/MS (U.S. EPA Method TO-14). 

Subscript t denotes the contents of the tank H and m refer to the inlet stream. Since the tank is initially evacuated, integration gives... 

A simple method is to measure the increase in pressure (p2) over time in an initially evacuated chamber. Another possibility is the use of sorbents in the chamber so that the partial pressure (p2) is kept practically at zero. The amount of permeating gas can be gravimetrically determined with the help of the sorbent. It is also possible to use... 

It is desirable to have a manometer in the system. The pressure should drop to approximately 30 mm. as the temperature approaches 105°. If, during the initial evacuation, foaming occurs, it will be necessary to loosen the stopper on the reaction... 

Figure 3.4. Differential gas adsorption manometry with capillaries (valves for initial evacuation of equipment or filling of reservoir not represented) (after Schlosser, 1959).

You have 2.4 mol of a gas contained in a 4.0-L bulb at a temperature of 32°C. This bulb is connected to a 20.0-L sealed, initially evacuated bulb via a valve. Assume the temperature remains constant. 

The simulations reported here consisted of pressurizing an initially evacuated adsorber with four mixtures of different compositions. These simulations are very much like the traditional flash calculations of chemical engineering thermodynamics applied to an adsorption system. The first set of runs, which we refer to as set G-NVT, is equivalent to solving Eq. (4) with = 0, qf = 0, = y "AF > 0, closure condition... 

FiC5. 14. NMR spectra of Ru/SiOi. The initial number of silanol protons has been reduced by exchange with deuterium. Both traces are difference spectra with respect to the state after initial evacuation. The continuous line represents a sample under 20 Torr of H, gas, and the dashed line represents a sample after pumping away the reversible hydrogen. There is both reversible and irreversible spillover to the support (signal at. 3 ppm), and ther e is rever sible and irreversible chemisorption on the metal (sigiral at 65 ppm). [Reproduced with permission from Uner et al. (47). ... 

Fig. 17. A plot similar lo that of Fig. 16 but for Rh/SrTiO,j. The open symbols are the adsorption after the initial evacuation. After the highest pressure point was taken, the reversible hydrogen was pumped away, and the intensities Ia and /b decreased to the level indicated by vac. Next, the adsorption experiment was repeated (solid symbols). The increase of Ia with pressure (the spillover) is less marked than indicated in Fig. 16. [Reproduced with permission from Rojo el al (51). CopyTight 1994 American Chemical Society.]...

A fuel gas is known to con tain methane, ethane, and carbon monoxide. A sample of the gas is charged into an initially evacuated 2.000-liter vessel at 25 C and 2323 mm Hg absolute. The vessel is weighed before and after being charged, and the mass difference is found to be 4.929 g. Next, the higher heating value of the gas is determined in a calorimeter to be 841.9 kj/mol. Calculate the molar composition of the gas. 

---