Humic acids from coal

Mkuherjee, P. and Lahiri, A. Studies on the rheological properties of humic acid from coal, Colloid Sci. 11. 240-243 (1956). 

Humic acids from lignitic soft coal (2 samples) 61.2 4.1 34.8 —0.6 —... 

Dr. Steelink. We have not worked with humic acids from bituminous coals. In general, the carbonyl and phenolic content of an oxidized coal would be the most important structural properties in contributing to EPR phenomena such as we have described. 

Humic Acid from Brown Coal from Dudar, Hungary... 

The decomposition of peroxides generally gives rise to light emission, but those without special features are not efficient. The low level of light emission makes certain identification of mechanism difficult. This is particularly the case for very low level light from biological sources such as humic acid, brown coal oxidation and phagocytosis. 

Humic acids are alkaH-extractable materials and total humic acid content is a term that refers to the humic acid content of coal that has had its carboxylate cations removed with sodium pyrophosphate. Values for some typical AustraHan brown coals range from 24—92% (13). Treatment of lignitic coals with mineral acid to release the alkaH and alkaline cations may dissolve up to 20% of the coal. The naturally moist coals are slightly acidic and have a pH of 3.5—6.5. 

Coal with a mean particle size of less than 3 mm is slurried with water and then oxidized with oxygen or mixtures of oxygen and air at temperatures ranging from 100° to 300° C, at partial oxygen pressures ranging from 0.1 to 10 MPa and reaction periods ranging from 5 to 600 minutes [425]. In the absence of catalysts, such as alkaline bases, the main products of oxidation are humic acids. 

Hofrichter, M., and Fritsche, W., Depolymerization of Low-Rank Coal by Extracellular Fungal Enzyme Systems. 3. In Vitro Depolymerization of Coal Humic Acids by a Crude Preparation of Manganese Peroxidase From the White-Rot Fungus Nematoloma Frowardii B19. Applied Microbiology and Biotechnology, 1997. 47(5) pp. 566-571. 

Walia, D. S., and Srivastava, K. C., Biological production of humic acid and clean fuels from coal. Patent No. US5670345. 1997, Sep. 23. 

Commercially Available Humic Acids. A large quantity of the commercially available humic acids was purchased from Fluka AG (Buch, Switzerland) by the Health Effects Research Laboratory (HERL) of the U.S. Environmental Protection Agency (USEPA), Cincinnati, Ohio. This coal-based humic substance is from West Germany. 

Conversely, the coal-based Fluka humic acid may be too different from the aquatic humic matter in terms of molecular weight, solubility, and functional group to serve as the best model for toxicological evaluation of drinking water-derived substances. 

The results of elementary analyses of lignin isolated from fresh (2, 3) and rotted straw and data for different types of coals and humic acids isolated from these and from chernozem are shown in Table III to illustrate further steps of coalification. The following points should be noted ... 

B. K. Mazumdar. Low rank coals like lignites and natural humic acid derived from such coals are known to contain alicyclic structures in their constitution. How does the author envisage the formation of such structures in the transformation of lignin to humic acid-like substances ... 

Jince the time of Berzelius, chemists have proposed structures for the amorphous, black substance known as humic acid. In the past 150 years, much experimental work has appeared on the nature of humic acid, most of it based on classical chemical and microbiological studies. Very little information about the molecular structure of humic add has resulted from these studies however. Some of the problems plaguing investigators in this field have been (a) variation in the source of humic acid, (b) variation in the definition of humic fractions of soil and coal, (c) lack of crystallinity of the samples, (d) uncertainty of molecular weight measurements, (e) variation in extraction techniques, and (f) variation in elemental composition. The little unambiguous information that exists today is based on extensive degradation of the humic acid polymer and represents only a small fraction of the total molecule. 

Cornelius Steelink. It is possible that other systems may give rise to the. radical species. However, one of our models for humic acids is a biradical cr oh whose radical character would not be changed on acetylation. Our humic acids change very little in spin content on methyladon. It IsJw would be interesting to form sodium salts from your coals to see if ho the spin content increased. This would be fairly convincing evidence for oxygen radicals. 

The absorber pump constantly recycled the fluid through the oxygen absorber so that the fluid was always essentially saturated with oxygen. A small side stream was removed from the gas absorber recycle by the reactor pump. The side stream could either flow through the reactor or bypass the reactor. The reactor bypass was used when it was desired to study the decomposition in solution of the humic acids. Down stream from the reactor was a filter to remove any coal fines produced, a sight glass to observe the fluid, a flow colorimeter to measure the rate of production of humic acids, and a flow rate indicator. 

Figure 2 shows the kind of data one can obtain from the apparatus described here. The absorption values from the flow colorimeter are plotted directly vs. time assuming Beer s law, the slope of the locus of this data is the rate of production of humic acids. This rate exhibited a definite induction time. For this experiment, between time zero when the coal was introduced and 10 hours, the rate of production of humic acids increased by a factor of 5. After the induction time of 10 hours the rate of production of humic acids remained constant. 

In liquid phase oxidations diffusivities are about 1/104 times those existing in the gas phase, and from the pores humic acids and benzenoid acids are removed whose mean diameters are very large compared with the average pore diameter in coal and molecules such as nitrogen and methanol. 

Vauquelin (14), A. Klaproth (6), and R. Jameson (5), alkali soluble organic constituents of soil and coal are designated as humic acids/ Collectively, these substances make up an ill-defined series of dark colored, weakly acidic solids which form whenever plant components (such as lignin) are exposed to fungal oxidases, or when coal is allowed to weather or otherwise oxidize. Some evidence now exists that humic acids isolated from these varied sources do indeed contain several common peripheral structures (2, II, 16), but by any more discriminating test, the term possesses little chemical significance or fixed meaning. 

Prevailing uncertainties are perhaps most clearly illustrated by the properties of humic acids obtained from a nominally single source—e.g., oxidized coal. Such humic acids will resemble each other in color and typically have equivalent weights around 250. However, depending upon factors which are... 

Measurements of alkali solubles in these coal samples—conventionally accepted as indices of humic acid concentrations—were initially performed by using Kreulen s method (7). However, even when the most stringent precautions were taken to exclude air, this method yielded markedly time-dependent results (presumably owing to oxidation of the coal by the relatively strong alkali solution), and a more satisfactory colorimetric technique (by J. F. Fryer) was therefore employed. This entailed extracting the coal sample with 0.1 N aqueous sodium hydroxide for 16-20 hours in an inert atmosphere and subsequent photoelectric scanning of the extract solutions. Actual humic acid concentrations were then obtained from specially constructed reference curves which related optical density (at an appropriate wavelength) to humic acid contents. The inherent error in this determination is estimated at less than 10%. 

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