Space velocity correlation

Today, the modern version of time-lag focusing, or delayed extraction,14 16 is used in almost all MALDI-TOF mass spectrometers. It is in fact a special case of the Wiley and McLaren method, in which the initial spatial distribution (usually a very thin sample and matrix mixture dried on a stainless steel plate) is assumed to be zero. Therefore, after the delay time the velocity and spatial distributions are correlated, i.e. ions of highest velocity have moved the greatest distance. This space velocity correlated focusing has been described by Colby and Riley,17 and provides considerably better focusing than can be obtained from two independent and uncorrelated initial distributions in space and velocity/energy that comprise the general Wiley-McLaren case. 

Figure 13.8 Schematic of (a) space focusing on a dual-stage source and (b) space-velocity correlated focusing from a dual-stage source after delayed extraction.

Colby, S.M. and Reilly, J.P. (1996) Space-velocity correlation focusing. Anal. Chem., 68,1419-1428. 

King, T.B., Colby, S.M., and Reilly, J.P. (1995) High- resolution MALDI-TOF mass-spectra of 3 proteins obtained using space-velocity correlation focusing. Int. J. Mass Spectrom. Ion Processes, 145, L1-L7. 

Figure 10.7. (a) Positions of ions following delayed extraction showing normal mass dependence of space-velocity-correlated focusing, (b) Positions of ions after correction using mass-correlated acceleration. 

The polymerization of light olefins using copper pyrophosphate is licensed by The M. W. Kellogg Co. under patents of the Polymerization Process Corp. The process is essentially the same as the U.O.P. process but instead uses a copper pyrophosphate catalyst (18). The first plant was built in 1939 (22) and several more have been put into operation since that time. A correlation of operating variables for this process was published in 1949 (21) it shows how conversion is influenced by catalyst activity, temperature, ratio of propene plus n-butene to isobutene, and the space velocity of olefins and of total feed when operating at 900 pounds per square inch gage pressure. A catalyst life of 100 to 150 gallons of polymer per pound of catalyst is claimed (15). 

A change in any one of the three included variables which improves the quality of the product will increase the numerical value of the factor hence, the larger the factor, the better the alkylate quality. In ordinary commercial operation F will vary from about 10 to 40. Acid content of the reaction mixture and reaction time, while not directly a part of the factor, are so interrelated that if the acid content is maintained above 40%, the olefin space velocity term correlates the effects of these variables satisfactorily. While reaction temperature has an important effect on product quality, it has not been included in this factor since this variable is ordinarily held constant at an optimum value for any well-... 

Another objective was to determine whether product differences were obtained with the two feedstocks and also to correlate the higher pressure/space velocity results with previous data. 

Catalyst Activity. As discussed previously, the major objective of this work was to determine the effect of varying the operating parameters of volumetric space velocity and total reactor pressure. Since catalyst activity effects the relative comparisons of the data, it must first be established whether catalyst deactivation is also a correlating factor and to what extent. 

The 850°F+ conversion is a correlating parameter for comparing C1-C4 gas yield, C5-500°F liquid yield, 500°F+ conversion, and 650°F+ conversion. Various combinations of the operating parameters of space velocity, total reactor pressure, and temperature achieve the same 850°F+ conversion. Thus, the product distribution can then be related to 850°F+ conversion with only minor variations between specific experimental runs. No difference in product distribution (at a given 850°F+ conversion) was noted for runs made with SRC-I/prehydrogenated KC-Oil at 70/30 and 50/50 nominal weight ratio feed blends. 

A simple Langmuir-Hinshelwood model explains quantitatively the steady-state behavior (4) but it fails to explain the oscillatory phenomena that were observed. The origin of the limit cycles is not clear. Rate oscillations have not been reported previously for silver catalyzed oxidations. Oxidation of ethylene, propylene and ethylene oxide on the same silver surface and under the same temperature, space velocity and air-fuel ratio conditions did not give rise to oscillations. It thus appears that the oscillations are related specifically to the nature of chemisorbed propylene oxide. This is also supported by the lack of any correlation between the limits of oscillatory behavior and the surface oxygen activity as opposed to the isothermal oscillations of the platinum catalyzed ethylene oxidation where the SEP measurements showed that periodic phenomena occur only between specific values of the surface oxygen activity (6,9). 

Mears,53 Paraskos et al.,66 Montagna and Shah,38 and Montagna et al.59 have recently shown that ineffective catalyst wetting can cause the reactor performance to be dependent on the liquid velocity. The y used a correlation of Puranik and Vogelpohl69 for the effectively wetted surface area of the packing to explain the effects ofliquid hourly space velocity and the length of the catalyst bed on the performance of bench-scale HDS reactors. 

The space-time velocity correlation tensor is defined as... 

Weight space velocity has been universally adopted in the case of the fluid-catalyst process because the extent of cracking is dependent upon the amount of catalyst, whereas the volume of a given amount of catalyst may vary considerably with different fluidization conditions. In correlations, it is often more convenient to use reciprocal space velocity, WJWol hour, which is zero with no catalyst, under which condition the conversion and yields of cracked products are likewise essentially zero, whereas space velocity is infinite. 

Correlations of yields and product quality versus conversion, with conversion varied by changing space velocity (other conditions constant), are normally used as standards of comparison to establish the effects of other operating variables. To this extent, it is usually considered that space velocity has no effect on product distribution and quality except as it affects conversion. 

Summary The synthesis of trichlorosilane (TCS) from silicon and HCl produces considerable amounts of less desired chlorosilanes by side reactions, especially silicon tetrachloride (STC). The results of this paper support the view that the undesired STC is formed from TCS in a consecutive reaction, which is probably catalyzed by Si impurities and which is preferred at low space velocity and high temperatures. It seems that TCS selectivity losses are due to regions or spots in the industrial reactor with such conditions. XPS surface concentrations of Si impurities dramatically change with the proceeding synthesis reaction because of the mobility of the impurity species and do not correlate with results of Si bulk analysis. 

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