Light fraction, composition

It is fruitless to attempt detailed study of a phenomenon whose products are not well identified. It is unfortunately frequently noted in the literature, especially in cases of column chromatography, that fractions are only identified as to the chemical operations which brought them to light. Fractions are identified, for example, only by the solvent used. Speculations as to the composition of the radioactive solutes in such solutions can seldom be really reliable, and the presence of an unexpected radioactive species is in such cases undetectable. It is also important in reading the literature to watch out for cases in which the chemical yields of the carriers have not been measured. Extensive decomposition can often occur on silica gel and alumina columns, especially when photosensitive or moisture sensitive compounds are used. For these reasons much of the information now existing in the literature must be regarded as only exploratory, awaiting the development of better analytical methods for separation, purification, identification and determination of the products —known or expected. 

The composition and yield of curcuminoids extracted using the existing techniques, e.g. hydrodistillation, low-pressure solvent extraction, soxhlet and SC-C02 extraction, were compared (Braga et al., 2003). The highest yield was obtained using soxhlet extraction with ethanol and the lowest (2.1%) with hydrodistillation. The best solvent for SC-C02 extraction is a mixture of ethanol and isopropanol. ar-Curcumene, z-(y)-atlantone and ( )-(y)-atlantone constituted about 60% of the light fraction. 

In co-hydropyrolysis experiments without catalysts the degree of pine wood/ polyethylene mixture (1 1 weight ratio) conversion was 80% wt. and yield of the light liquid fraction - 23% wt. The addition of iron ore catalyst activated by mechanochemical treatment increased the degree of mixture conversion by 5-13%. This increase was mainly due to light liquid fraction formation. The variation of catalyst nature (pyrite, pyrrhotite, haematite) influences on the product composition. Pyirhotite catalyst yields the highest amount of the light fraction (about 40% wt.). 

Table 14.9 Polymer Composition of Automotive Shredder Residue Lights Fraction Col- ...

The composition of the remaining part of the light fraction appears to be made mostly of biogenic materials (fibres, skins, feathers and lignocellulosic materials). 

The double-entry separator performance is often characterized for a two-component system by the equilibrium ratio Ki (definition (2.2. If)) as well as by the separation factor ajj (definition (2.2.2a)). Both definitions relate the two product stream compositions and are related to each other by (2.2.2i). The compositional differences between the light fraction and feed stream 1 may be indicated by a heads separation factor... 

After detailed steps involving integration of the first term by parts, the following result has been obtained (see Olander (1972) and Benedict et al. (1981)) for the composition variation of the light fraction with height for the enriching section ... 

Note There is no feed introduction at total reflux (see Section 8.1.3.2) Xu/ merely identifies the composition at the feed location, z = 0.) Multiplying these two equations together, we get an expression for the separation factor between the light fraction end (xnij) and the heavy fraction end (xiiij) at total reflux ... 

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