Quench gas

Quench Converter. The quench converter (Fig. 7a) was the basis for the initial ICl low pressure methanol flow sheet. A portion of the mixed synthesis and recycle gas bypasses the loop interchanger, which provides the quench fractions for the iatermediate catalyst beds. The remaining feed gas is heated to the inlet temperature of the first bed. Because the beds are adiabatic, the feed gas temperature increases as the exothermic synthesis reactions proceed. The injection of quench gas between the beds serves to cool the reacting mixture and add more reactants prior to entering the next catalyst bed. Quench converters typically contain three to six catalyst beds with a gas distributor in between each bed for injecting the quench gas. A variety of gas mixing and distribution devices are employed which characterize the proprietary converter designs. 

Adl b tic Converters. The adiabatic converter system employs heat exchangers rather than quench gas for interbed cooling (Fig. 7b). Because the beds are adiabatic, the temperature profile stiU exhibits the same sawtooth approach to the maximum reaction rate, but catalyst productivity is somewhat improved because all of the gas passes through the entire catalyst volume. Costs for vessels and exchangers are generally higher than for quench converter systems. 

Similarly, at lower currents, the volume of arc plasma is loo small I ) and so is the clogging effect. The pressure and volume of the quenching gas can be adjusted to interrupt the current now also at current zero. All these adjustments are pre-set and sealed by the manu-facturer. 

The quenched gas passes to an H2S removal stage where it may be assumed that H2S is selectively scrubbed down to 15 parts per million with substantially nil removal of CO2. Solution regeneration in this process is undertaken using the waste low-pressure steam from another process. The scrubbed gas, at 35°C and saturated, has then to undergo CO conversion, final H2S removal, and CO2 removal to allow it to meet the product specification. 

A quenching gas is added to give up electrons to the chamber gas so that inaccuracies are NOT introduced due to ionizations caused by the positive ion. 

A quenching gas is used in order to prevent a secondary pulse due to ionization by the positive ions. 

Figure 11.5 (cont d) (b) ICI quench converter with axial flow quench gas is injected and mixed by means of lozenges (Twigg 1996, p. 429 reproduced with permission from Catalyst Handbook, ed. M.V. Twigg, Manson Publishing Company, London, 1996.)... 

A proportional counter consists of a tube filled with a gas such as xenon, with positive and negative electrodes. The negative electrode is a thin wire maintained at a potential around -2 kV. Incoming photons ionise gas molecules. These drift towards the negative electrode, until the field enhancement around the thin wire is sufficient to multiply them by the cascade effect, and cause a charge pulse on the wire. The pulse is quenched by the addition of a quench gas, normally a halogen or hydrocarbon which reacts with the ions and stops the cascade. 

Figure 1.4 IR-spectra of soot particles produced by evaporation of graphite under different helium quenching gas pressures. The occurrence of the four additional sharp peaks at elevated helium pressures turned out to originate from [60-/h]fullerene (Cgo) [20].

Figure 7 Log-log plot of Lm for He(2 S) vs. T. (From Ref. 137.) The same symbol indicates the same quenching gas as in Fig. 6.

Clough and Thrush96 extended the intensity measurements to wavelengths of 3 [x which permitted them to determine 70 = 0.26 0.04 sec-1 at 293°K with 02 as the quenching gas. Combination with the above expression for ki3. gives = 6.8 x 10"7 M. In a later... 

Recently quantum yields of O( S) from N20 have been determined as a function of incident wavelength. The yield is near unity at 1290 A [McEwan et al. (680), Black et al. (113)]. Because the photolysis of N20 is a convenient source for the production of O( S), N(2D), N2(A3E), and N2(B3n), their quenching rates by many gases have been measured by monitoring emissions produced by the photolysis of N20 and quenching gas mixtures. Chamber-lain and Simons (203) believe that in the region 1400 to 1550 A NO is produced mostly from two reactions... 

Quenching Gas Quenching Constant a (torr 1) Quenching Gas Quenching Constant a (torr1)... 

Ma and Mq arc masses of the atom A and the quenching gas, respectively. Some workers define the quenching cross section as... 

The atomic fluorescence may be observed under either steady-state or time-dependent conditions. Under steady-state conditions the decrease of fluorescence intensity I is observed when the quenching gas is admixed, and from (II.2a, b) the well-known Stem-Volmer relation is obtained... 

Small carbon grains are assumed to be the carrier of the prominent interstellar ultra violet absorption at 217 nm. To investigate this hypothesis, we produced small carbon particles by evaporating graphite in an inert quenching gas atmosphere, collected the grains on substrates, and measured their optical spectra. In the course of this work - which in the decisive final phase was carried out with the help of K. Fostiropoulos and L. D. Lamb - we showed that the smoke samples contained substantial quantities of C60. The fullerene C60 (with small admixtures of C70) was successfully separated from the sooty particles and, for the first time, characterized as a solid. We suggested the name fullerite for this new form of crystalline carbon. 

Figure 1. Absorption spectra of collected carbon particles produced by evaporating graphite in a quenching atmosphere of helium. The samples were obtained at different quenching gas pressures. Notice the occurrence of additional absorptions in the uv-visible at elevated helium pressures. These features turned out to originate from C60 (buckminsterfullerene). For comparison, the interstellar 217 nm absorption is also shown.

Figure 2. Absorption of carbon particles in the infrared. At elevated helium quenching gas pressures, there are four stronger lines emerging out of the continuum. Theory predicts precisely four ir-active fundamentals for a football structured C60 molecule and they should occur close to the measured positions. Such spectra gave us the first strong hint that we produced C60 in macroscopic quantities. Some of the tiny line features originate from the less abundant fullerent...

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