Yield transverse

Radial density gradients in FCC and other large-diameter pneumatic transfer risers reflect gas—soHd maldistributions and reduce product yields. Cold-flow units are used to measure the transverse catalyst profiles as functions of gas velocity, catalyst flux, and inlet design. Impacts of measured flow distributions have been evaluated using a simple four lump kinetic model and assuming dispersed catalyst clusters where all the reactions are assumed to occur coupled with a continuous gas phase. A 3 wt % conversion advantage is determined for injection feed around the riser circumference as compared with an axial injection design (28). 

Fig, 8.99 Relative resistance to stress-corrosion cracking of three aluminium alloys subjected to different environments. The stress levels employed corresponded to 75, 50 and 25% of the respective transverse yield strengths (after Liflca and Sprowls )... 

There is no reason to believe that the off-diagonal Q integrals which yield this increase in U over I should be equal for longitudinal and transverse polarization but neither is there at present any basis for selecting different values. Hence we assume U1 = U2 and by use of the a values given above for the chlorine atom, the value of —El is calculated to be about 30 per cent smaller than was obtained in Table VI. Since the effect of anisotropy would be expected to be about the same for all of the halogens, the qualitative conclusions drawn from the results in Table VI are not affected. It is clear that anisotropy may be important, however, and must be considered in quantitative work. 

The relaxation rates of the individual nuclei can be either measured or estimated by comparison with other related molecules. If a molecule has a very slow-relaxing proton, then it may be convenient not to adjust the delay time with reference to that proton and to tolerate the resulting inaccuracy in its intensity but adjust it according to the average relaxation rates of the other protons. In 2D spectra, where 90 pulses are often used, the delay between pulses is typically adjusted to 3T] or 4Ti (where T] is the spin-lattice relaxation time) to ensure no residual transverse magnetization from the previous pulse that could yield artifact signals. In ID proton NMR spectra, on the other hand, the tip angle 0 is usually kept at 30°-40°. 

Figure 10.5 shows the FID obtained on a soap sample. The initial points of the FID yield information on the absolute proton signal intensity which is related to the total proton content in the sample. After the initial few points of the FID however, one must be careful with how the data are viewed quantitatively. Protons in different physical environments will have very different relaxation times. In the FID the differences in transverse (T2) relaxation are observed readily. In the case of the soap sample the FID contains a rapidly decaying signal at the beginning of the FID along with a signal that decays at a much slower rate. 

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