Oligomer-rich fraction

Crude GSE can be separated into distinct components from monomer-rich to oligomer- and polymer-rich fractions by solvent extraction followed by chromatography on Toyopearl resin. The pre-fractionation of the tannin crude extract by liquid-liquid extraction with ethyl acetate fractionates the monomers into the organic phase and improves the subsequent fractionation of oligomers and polymers on Toyopearl HW 40 resin. This fractionation technique is easy to operate and... 

If procyanidins are to be analyzed quantitatively, ethyl acetate extractions should be omitted because every procyanidin exhibits a specific partition coefficient. For the qualitative analysis of procyanidins one should be aware that procyanidins of lower degree of polymerization are extracted more easily into ethyl acetate than procyanidins of higher degree of polymerization. Therefore, ethyl acetate fractions have already been termed as "dimer rich", whereas ethyl acetate insoluble fractions have been referred to as "oligomer rich" [55]. In any case, the number of extractions as well as the phase volumes should be standardized in order to get reproducible results. Some researchers advocate the use of methylethylketone instead of ethyl acetate because extractability is supposed to be better [188-189]. 

Fast pyrolysis of pine sawdust in a small vortex reactor operating at 10 to 20 kg/h and 480 to 520 °C produces high yields of primary pyrolysis oils (over 55% by weight on a dry basis). The vortex reactor transmits very high heat fluxes to the sawdust, causing primarily depolymerization of the constituent polymers into monomers and oligomers. A preliminary scheme separates the raw oils into a carbohydrate-derived aqueous fraction and a phenolic-rich ethyl acetate (EA) soluble fraction. The EA fraction is washed with water and with aqueous sodium bicarbonate to remove acids yielding 20% to 25% of the feed as phenols and neutrals (P/N) in the EA solution. 

Fractions 8 through 13 in table 9.7 were obtained with propane. Again the polydispersities of the fractions are less than that of the parent material. The concentration of methyl acrylate in the backbone of the fractions is now about 4wt% less than that of the parent. Also, notice that molecular weights of the first few fractions obtained with propane are lower than those of the final fractions obtained with chlorodifluoromethane this indicates that chlorodifluoromethane can remove only fractions rich in acrylate even if the molecular weight is greater than available oligomers that have a higher ethylene content. 

Olefinic oligomers with a reduced degree of branching were produced with a silica-rich ZSM-22 outer layer catalyst in the oligomerization of a feed containing mixed butenes, diluted with butanes, with the approximate proportions 65% olefins and 35% saturates. It was reported that a high viscosity index lubricant was produced by oligomerization of lower olefins, essentially the C3-C4 fractions, with a medium-pore, shape-selective aluminosilicate HZSM-22 catalyst. ... 

Several variations of this process have been described. By the addition of NMP, the reaction mixture separates into a more dense polymer-rich liquid phase, and into a less dense phase, containing the oligomers, and unreacted reactants. The less dense phase can be used for further recovery of a high molecular fraction or reuse in a further polymerization step. ... 

Fractionation is best carried out on the unneutralized oligomer by dissolving the latter in acetone and adding successive portions of n-hexane. Each addition of hexane causes separation of the solution into two phases, of which the heavier is rich in large molecule components. Recovery of oligomer from the isolated heavy fraction is achieved by flashing off the solvent phase under reduced pressure. 

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