Front detection mode

Reduced flow-system lengths and, consequently, reduced flow-mixing generally cause steeper slopes of the peak fronts in the peak detection mode. 

A majority of traditional NIR measurements are made on solid materials and these involve reflectance measurements, notably via diffuse reflectance. Likewise, in the mid-IR not all spectral measurements involve the transmission of radiation. Such measurements include internal reflectance (also known as attenuated total reflectance, ATR), external reflectance (front surface, mirror -style or specular reflectance), bulk diffuse reflectance (less common in the mid-IR compared to NIR), and photoacoustic determinations. Photoacoustic detection has been applied to trace-level gas measurements and commercial instruments are available based on this mode of detection. It is important to note that the photoacoustic spectrum is a direct measurement of infrared absorption. While most infrared spectra are either directly or indirectly correlated... 

Figure 2 shows a theoretical bidimentional polydisper-sity (size and density). The bidimensional Gaussian distribution is shown in Fig. 2A, where (S) is the size axis, (D) is the density, and C represents the number of particles. If such a sample is eluted according to the Hyperlayer elution mode, a broad fractogram is observed, as shown in Fig. 2B. From such a fractogram, every fraction corresponds to particles of different sizes and densities, as qualitatively shown in Fig. 2C. The front of the peak is associated with particles that are very different from the ones at the tail. It is possible to imagine granulometric detection all along the fractogram profile, as shown in Fig. 2D. If the density distribution coinvolved with the size distribution is considered, every fraction is...

The reaction occurs over a relatively small zone in the catalyst bed. As the reaction moves down the catalyst bed, coke deposits deactivate the front part of the bed. The reaction continues down the bed until a substantial part of the catalyst is deactivated and unconverted methanol "breakthrough" is detected in the reactor effluent stream. Use of sufficient catalyst permits reactor onstream periods, or cycles, sufficiently long to avoid excessive regenerations. To enable this to be done onstream, multiple reactors are provided and operated in parallel on a cyclic mode. The New Zealand plant is designed to operate with four reactors onstream, with a fifth reactor in regeneration. 

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