Narrow cut

With the accumulation of results obtained from various and complex analyses of narrow cuts (Waterman method), correlations have been found f ctween refractive index, specific gravity and molecular weight on one hand, and percentages of paraffinic, naphthenic and aromatic carbon on the other. 

This method follows the ASTM D 1159 and D 2710 procedures and the AFNOR M 07-017 standard. It exploits the capacity of the double olefinic bond to attach two bromine atoms by the addition reaction. Expressed as grams of fixed bromine per hundred grams of sample, the bromine number, BrN, enables the calculation of olefinic hydrocarbons to be made if the average molecular weight of a sufficiently narrow cut is known. 

The exacting Hst of specification requirements for aviation gas turbine fuels and the constraints imposed by deUvering clean fuel safely from refinery to aircraft are the factors that affect the economics. Compared with other distillates such as diesel and burner fuels, kerosene jet fuels are narrow-cut specialized products, and usually command a premium price over other distillates. The prices charged for jet fuels tend to escalate with the basic price of cmde, a factor which seriously underrnined airline profits during the Persian Gulf war as cmde prices increased sharply. 

In azeotropic distillation, the added component is a chemical that forms an azeotrope (constant-boiling mixture) which boils at a lower temperature than any of the constituents of the feed. For example, addition of certain ketones to narrow cut mixtures of paraffins, naphthenes, and an aromatic is known to form azeotropes with the paraffins and naphthenes which boil at temperatures low enough to permit relatively easy separation of them from the aromatic. 

Gasoline products are highly volatile products that evaporate quickly (often completely) within one or two days. They are narrow cut fractions with no residue and low viscosity, which spread rapidly to a thin sheen on water or onto the land. They are highly toxic to biota, will penetrate the substrate, and are nonadhesive. 

GPC of charcoal lighter fluid (Figure 9) shows the increase in the linear molecular size of the cut similar to the ASTM distillation pattern. Lubricating oils are narrower cuts. 

Chapman, Pearce, and Avens (4, 20) investigated the relation between chemical composition and insecticidal efficiency of various dormant and foliage spray oils against several common insect pests of deciduous trees, and found it to be positive. They concluded that an oil which is highly paraffinic in character is the most desirable type. Saturated narrow-cut petroleum fractions were used by Pearce, Chapman, and Frear 21) in a study of the influence of molecular weight and structural constitution on the insecticidal efficiency of such oils to eggs of the oriental fruit moth, Grapholitha molesta (Busck). Correlations between efficiency and various properties were compared on the basis of composition. The value of paraffinicity was illustrated, and the importance of other properties was indicated. 

Many publications in the area of protein research are entitled Purification and characterization of..., and describe a purification procedure in sufficient detail that it can be reproduced in another laboratory. The characterization section may include structural, functional, and genetic information, and carrying out such studies is likely to require at least milligram quantities of pure protein. Ideally the purification should involve a small number of steps, with good recovery at each step. If the recovery is poor (<50% at any step), however, there should be some indication of what happened to the missing activity. Has it been discarded in the other fractions for the sake of purity, or does it represent a true loss of activity If the latter, then the end-product may be less than fully active despite apparent homogeneity indicated by standard analysis. The choice between recovery and purification at each step can be problematic taking a narrow cut of a chro-... 

Toluene rose to prominence during WWI as the basis for 2,4,6-Trinitrotoluene (TNT) manuf. The demand became so great that petroleum sources were used to augment coal-tar sources. The petroleum process involved narrow cut naphthas contg small amts of toluene which were subjected to thermal cracking to produce a... 

Narrow cuts of asphaltenes from Kuwait atmospheric residuum with molecular radius ranging from 26 to 153 A (based on size exclusion chromatography) were examined by Baltus and Anderson (1983) in pores... 

The distillation process is not used for the narrow-cut fractionation. However, by passing a second time through the distillation tower the... 

With conventional processes, the specific production of aromatics is facilitated by the treatment of narrow cuts 60-140 for all BTX, 65-85 C for benzene, 85-llfr C for toluene, and 110-I45 C for xylenes. 

Simple distillation cannot separate aromatics from noD -aromatic, because the relative volatilities are very low, and many azeotropes are formed. Azeotropic distillation is based on the formation of an azeotrope betu een the non-aromatic hydrocarbons and a low boiling polar solveat It is select among the hrst terms of the series of alcohols, ketones, aldehydes and nitriles, and is employed pure or mixed with water. If the solvent forms a hetero-azeotrope, its recovery is accordbgly facilitated. The )aeld is not limited in principle. The impurity content of the feedstock and the composition of the azeotrope determine the amount of solvent required. Cuts rich in aromatics can be treated in this way fairly economically. However, any variation in the type of impurity to be removed, and consequently in the composition of the azeotrope, may lead to less perfect purification. Furthermore, this method can be applied only to a narrow cut which contains... 

This analysis for particles of size between and + d g can be easily extended to the feed with wide size distribution. The feed with wide size distribution can be looked upon as the sum of narrow cuts of solids and it will be reasonable to expect the outflow stream to be the sum of outflow streams from these narrow cuts. To achieve this we shall first examine the system using a single size feed. 

Fractionation makes it possible to separate the fatty acid mixtures into narrower cuts or even individual components. The detergent-grade feedstock C12-C18 fraction is separated from the whole cut by topping off the C8-C10 fraction. The middle cut, C12-C14, can be further fractionated from the C12-C18 cut through the use of multistage fractionation employing two or more columns. 

XFor one time purification or with a readily available sample, sacrifice yield for purity by taking a narrow cut from a chromatographic peak during the first purification step. 

In general, to standardize a particular protein, a purified form of that protein is used as a primary calibrator (see Chapter 20). The purified preparation must, however, express the same immunoreactivity as the native protein. Unfortunately, once removed from its natural milieu, apo B-lOO is insoluble in aqueous buffers. This phenomenon is attributed to the very hydrophobic nature of apo B-100. An LDL preparation with density of 1,030 to 1.050 g/mL, often referred to as narrow-cut LDL, is generaUy used as the primary standard for apo B-100. The protein concentration of the purified preparation is determined by amino acid analysis. In contrast, freshly purified apo A-I is soluble in aqueous buffers and is suitable as a primary standard. 

Some of this feedstock was fractionated on a vacuum distillation unit at IFP into four other narrower cuts, centred on an increasing number of carbon atoms from C24 to C27/C28. These cuts cannot be used to accurately determine the reaction kinetics of a given linear paraffin, but may reveal possible mixture effects or steric hindrance. 

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