Sampling physical characteristics

The complexity of petroleum products raises the question of sample validity is the sample representative of the total flow The problem becomes that much more difficult when dealing with samples of heavy materials or samples coming from separations. The diverse chemical families in a petroleum cut can have very different physical characteristics and the homogeneous nature of the cut is often due to the delicate equilibrium between its components. The equilibrium can be upset by extraction or by addition of certain materials as in the case of the precipitation of asphaltenes by light paraffins. 

A bitumen sample is oxidized at high temperature under well defined conditions and its physical characteristics are measured before and after this artificiai ageing process. The method is defined in France as AFNOR T 66-032 and in the USA by ASTM D 2872 (Rolling Thin-Film Oven Test). 

The principal requirement of a sampling system is to obtain a sample that is representative of the atmosphere at a particular place and time and that can be evaluated as a mass or volume concentration. Remote monitoring techniques are discussed in Chapter 15. The sampling system should not alter the chemical or physical characteristics of the sample in an undesirable manner. The major components of most sampling systems are an inlet manifold, an air mover, a collection medium, and a flow measurement device. 

Samples of particulate matter can be subjected to many of the above analytical techniques in chemical characterization. The following methods are, however, particularly applicable to analysis of physical characteristics of particulate matter isolated from air sampling. 

For many proteins, especially glycoproteins, the physical characteristics, particularly the hydrophilic nature of Toyopearl HW resins, improve mass and activity recovery rates. Toyopearl HW media do not adsorb proteins, as conventional gels can, and thus do not interfere with sample recovery (39). 

Methods are described for determining the extent to which original natural color is preserved in processing and subsequent storage of foods. Color differences may be evaluated indirectly in terms of some physical characteristic of the sample or extracted fraction thereof that is largely responsible for the color characteristics. For evaluation more directly in terms of what the observer actually sees, color differences are measured by reflectance spectrophotometry and photoelectric colorimetry and expressed as differences in psychophysical indexes such as luminous reflectance and chromaticity. The reflectance spectro-photometric method provides time-constant records in research investigation on foods, while photoelectric colorimeters and reflectometers may prove useful in industrial color applications. Psychophysical notation may be converted by standard methods to the colorimetrically more descriptive terms of Munsell hue, value, and chroma. Here color charts are useful for a direct evaluation of results. 

The objective indication of color differences in foods has usually been attempted in a simplified, indirect way that involves a comparison of some physical characteristic of the samples or, more often, an extracted fraction that is assumed or has been proved to be largely responsible for the associated color characteristics. Although such a method does not measure the actual visual color of the samples, a measure of relative amounts of color-characteristic pigments or a comparison of physical properties of extracts of color-critical fractions (which may be mixtures of several pigments) may prove to be very sensitive indications of differences that are closely related to color. 

The properties of the samples have corresponded to the data of literature. The physical characteristics of the catalysts used are shown in Table 1. 

It is important to divide the sample without discrimination with respect to size, density, or any other physical characteristics of the particles. 

Moving-boundary electrophoretic techniques, originally demonstrated by Tiselius in 1937, employ a U-tube with the sample occupying the lower part of the U and the two limbs being carefully filled with a buffered electrolyte so as to maintain sharp boundaries with the sample. Electrodes are immersed in the electrolyte and direct current passed between them. The rate of migration of the sample in the electric field is measured by observing the movement of the boundary as a function of time. For colourless samples, differences in refractive index may be used to detect the boundary. Such moving-boundary techniques are used mainly in either studies of the physical characteristics of molecules or bulk preparative processes. 

The procedures used to record NIR spectra for samples are much less labor-intensive than those involved in other spectroscopic analytical techniques. NIR spectral information can be obtained from transmission, reflectance and transflectance measurements (Figure 14.1) this allows the measurement process to be adapted to the physical characteristics of the sample and expedites analyses by avoiding the need for sample preparation. 

However, SMV has a relatively low discriminating power, which may require the use of near-unity thresholds in order to distinguish very similar products. It can also result in ambiguous identification of batches of the same substance with different physical characteristics (e.g. samples of the same product with different grain sizes can have very similar correlation coefficients and may be confused) or different substances with high chemical similarity. In these cases, cascading libraries, as previously discussed, can be used. 

The NIR spectrum contains information about the physical characteristics of samples, as well as chemical information, which are the basis of the previously discussed applications. NIR is thus suitable for determining physical parameters. 

A mineral is a naturally occurring, crystalline inorganic compound with a specific chemical composition and crystal structure. Minerals are commonly named to honor a person, to indicate the geographic area where the mineral was discovered, or to highlight some distinctive chemical, crystallographic, or physical characteristic of the substance. Each mineral sample has some obvious properties color, shape, texture, and perhaps odor or taste. However, to determine the precise composition and crystal structure necessary to accurately identify the species, one or several of the following techniques must be employed optical, x-ray diffraction, transmission electron microscopy and diffraction, and chemical and spectral analyses. 

In addition to chemical information, NIR spectra also contain information about the physical characteristics of samples and systems that can manifest itself, for example, as a baseline shift caused by scattering differences. On the one hand, this information is extremely useful in characterising particle size [102],... 

Using the catalyst vendor s equilibrium catalyst report, the physical properties of the circulating catalyst may be monitored for any change. Albemarle routinely analyzes a sample of the circulating catalyst inventory among others for physical characteristics, including surface area (SA), metal content, apparent bulk density (ABD), and particle size distribution (PSD). 

Calibration The process of constructing a model that is used to predict characteristics or properties of unknown samples. The model is constructed from a calibration data set with measured multivariate responses (R) and corresponding known sample concentrations or physical characteristics of interest (O-... 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

A database of chemical, mineralogical, and physical characteristics of North American fly ashes was assembled from the analysis of more than 178 samples of North American fly ash (McCarthy et al 1989). These fly ashes were derived from the combustion of five principal... 

As organic solvents have different physical characteristics, aqueous standards cannot be used for calibration when determining trace metals in oils or petroleum fractions. The sample can either be ashed or diluted in a... 

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