Low extract yields

Low extract yields were obtained either by short reaction times at high temperatures or by more extended reaction at low temperatures. The designations of high and low temperature depend upon the individual coal and, more especially upon the coal rank. The evidence accrued in this research has shown that there exists a threshold temperature below which the potential for liquids formation is minimal and above which conversion can proceed at an appreciable rate. 

C.D. Kacher et al. [5] performed some additional chloride extractions into TBP/benzene with Zr, Hf and Ti. The reported low extraction yields of Hfby... 

The yield for the alkaline extraction of tannins fi-om Pirns pinaster barit, is substancially higher than the typical yields obtained by organic or aqueous extraction. However, the specificity of the solvent to phenolics is low. Enforcing that conclusion we observed that the alkaline extract FCPM content represents 95-96 % of the total phenols content of the extract. However, when this fraction is compared to the total mass of extract, we verified that this value is much lower (= 40 % list = 57.3), which confirms the idea that the alkaline extract is relatively poor in phenolic material, presenting a variety of non-phenolic extractives. The most specific solvent is ethanol, that, in spite of revealing a relatively low extraction yield, provides a very rich phenolic extract, in which 96 % of total phenols are condensable with formaldehyde. The aqueous extract presents the lowest extraction yield, with a low content either in phenolic material and FCPM. However, that can be due to the fact that most of the phenolics had already been extracted by... 

Kacher et al. [33] performed some additional chloride extractions into TBP/ benzene with Zr, Hf, and Ti. The reported low extraction yields of Hf in [31] by Czerwinski et al. could not be reproduced by Kacher et al. who reported that they observed that significant amounts of Hf (more than 50% in some cases) stick to Teflon surfaces. (They actually conducted their subsequent experiments with polypropylene equipment, because only negligible adsorption was observed with polypropylene surfaces.) The Hf results from the experiments by Czerwinski et al. [31] were based on on-line data taken at the 88-Inch Cyclotron where the radionuclide was collected on a Teflon disk that, according to [33], accounts for the seemingly low Hf extraction. Surprisingly, a similar loss of Rf due to adsorption in the experiments of Czerwinski et al. [31] was not suspected by Kacher et al. Therefore, the latter authors, based on their new Zr-, Hf-, and Ti-results and on the previous Rf results in [31], suggested a revised sequence of extraction into TBP/ benzene from around 8 M HCl as Zr > Hf > Rf > Ti. In a parallel study of liquid-liquid extractions into TBP/benzene from HBr solutions, extraction of Rf was found to be low and was only increased for bromide concentrations beyond 9 M [33]. The extraction behavior of the group-4 elements into TBP from both HCl and HBr solutions was primarily attributed to their different tendencies to hydrolyze [33]. 

On the other hand, quantitative extraction requires complete and exhaustive extraction and no material can be lost. To assure complete extraction when a food is analyzed for the first time in a laboratory, it is useful to carry out two or three extractions, pool the solvents, and keep separate the next extracts to verify the presence of carotenoids. Usually four to six extractions are enough to remove the carotenoids completely from a sample. The extraction can be carried out in a blender, vortex, or with a mortar and pestle. Accelerated solvent extraction (ASE), an important extraction technique in residue analysis, currently attracts interest due to its short duration, low level of solvent use, and high extraction yield. The average recoveries for all carotenoids with the exception of norbixin ranged from 88.7 to 103.3% using manual extraction and from 91.0 to 99.6% by ASE (70 bar and temperature of 40°C) both extractions were carried out with a mixture of MeOH, EtOAc, and petroleum ether (1 1 1). ... 

In coals alkylated in this manner, the number of acidic sites is substantially reduced, and acid-base associations are virtually precluded. Extracts from alkylated coals should, therefore, be amenable to GPC fractionation. Such fractionation, conducted on Bio Beads S-Xl and S-X2, results in separation by molecular weight and indicates that both benzene and chloroform extracts contain substantial amounts of high ( 6000) and fairly low (560-640) molecular weight fractions (Figure 2). While the extract yields from non-reductively ethylated vitrinite increase in the order benzene extr. chloroform extr. - pyrid. extr > the molecular weights determined by VPO in pyridine, decrease in this order. 

Selection of Solvents. The extraction yield of a low rank coal (Annesley) has been determined after digestion using a selection of solvents (Table II). The results show large variations in solvent power and, in particular, the high extraction yields obtained with hydrogen donor solvents. It is important to differentiate between the ability of a solvent to prevent polymerisation of the dissolved coal by hydrogen transfer, and its ability to retain the dissolved coal in solution. For example, Tetralin is frequently quoted as an... 

The petrological composition is important when considering the solvent extraction of prime coking coals but with lower rank British coals the variations in petrology are less pronounced. A more frequent cause of variations in extraction yield with low rank coals (CRC 802 and CRC 902) results from ageing. The reactivity of a coal decreases substantially as the coal becomes oxidised by exposure to the atmosphere (Table III). 

The yield of glucolimnanthin 1 and nitrile 2 in seed meal by extraction with mixtures of water and MeOH was less critical and maximal at all proportions below 80% MeOH (Fig. 10.4b). For extraction of seed meal we chose 50% aqueous MeOH as the extraction solvent. The extraction yield of glucolimnanthin 1 appears to be poor at 50% aqueous MeOH in Fig. 10.4a, but the low yield in this case is primarily due to enzyme-mediated conversion into its breakdown products 2 and 3. 

In spite of its simplicity and conceptual clearances, the original protocol has suffered from many intrinsic problems in a practical sense. For example, the reaction with the alkyne-cobalt complexes provided low chemical yields and required harsh reaction conditions. In addition, it was also difficult to extract the obtained product from the sticky metallic residue. Those problems can be accounted for based on the widely accepted mechanism given in Scheme 1, which, as proposed by Magnus," is supported by many theoretical studies. ... 

After extraction of the whole paprika, including seed and stems, the obtained colour-value of the extract is relative low, about 350 to 500 ASTA, but the extraction yield can reach 15 to 17 wt.%. High-quality Hungarian paprika species like Sweet Paprika Excelsior give an extract with a colour value between 1,500 and 1,800 ASTA, and a good flavour profile. 

The pure oleoresin produced by solvents normally contains only pure curcumin, in a crystalline form. It is hardly soluble in liquid- and supercritical CO2- Even at an extraction pressure of 450 bar, and with 2 hours extraction time at 65°C, only 20% of the initial curcumin can be extracted. On the other hand, all the volatile oil and fatty oil is extracted, and a fat-free curcumin-starch mixture with a very low flavour-content can be produced. The total extraction yields are between 5 to 12%, with mostly fatty oil and volatile oil, and about 10% curcumin in the extract. 

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