Mean maximum reflectance of vitrinite

The mean maximum reflectance of vitrinite (Ro max) is the mean of one hundred determinations. 

Figure 8 shows the effect of rank, as measured by the mean maximum reflectance of vitrinite, on the overall conversion. 

In this paper, we demonstrate how mean maximum reflectance of vitrinite in oil (hereafter referred to as R ) can be used in place of conventional chemical-rank parameters (volatile matter and fixed carbon) to estimate the relative yields of carbonization products, specific properties of gas produced by carbonization, and chemical properties of coal such as calorific value and free swelling index (FS1). Further, we illustrate that measured R can be used to detect coal oxidation, to categorize coals for certain combustion uses, and to help classify coals by rank. 

The mean maximum reflectance of vitrinite was determined in oil (ca. 1.517 index of refraction) and in 546-nm wavelength green light. A photomultiplier photometer was used to measure vitrinite reflectance. Two glass standards were used to calibrate the equipment. A Leitz MPV2 microscope photometer was used. The reflectance values were determined as designated in ASTM D2798-85 (2 5). Twenty-five vitrinite reflectance values were determined for the Rasa coal. 

In a single coal, vitrinite, which is usually the commonest maceral, has a higher reflectance than the associated liptinite, but a lower reflectance than inertinite. There is, therefore, a correlation between carbon content and reflectance, and this is used to precisely determine rank. The mean maximum reflectance of vitrinite in oil (Romax) as the level of organic maturity, or rank, of a coal sample. 

As described earlier, the optical reflectance of vitrinite depends on its degree of aromatization and, hence, the loss of volatile matter. This natural process can be substituted by artificial heating without oxidant (pyrolysis) in a laboratory furnace. Because of evolving anisotropic reflectance character during such coking processes, the maximum reflectance of vitrinite is reported to be used for temperature tracing [3], but Bunt et al. [8] also demonstrated the applicability of the mean reflectance. 

Figure 2. Noncatalytic hydrogenation—product yields vs. vitrinite + exinite content. Curve a, total conversion (X) Curve b, extract ( ) (10). (Note Lines a and b relate to coals where the mean maximum reflectance (R0 max) of the vitrinite fall in the range 0.43-0.68%. Values in parenthesis refer to R0 max for...

Quring the past several years coal petrography has gained acceptance in certain areas of coal utilization, preparation, and mining as a useful analytical tool. The rapid evolution of this analytical technique can be attributed to the development and subsequent refinement of quantitative methods for measuring the reflectance characteristics of vitrinite in coal (8, 14, 15, 16). Mean maximum reflectance has been shown to be directly related to coal rank (14, 16). Moreover, it is known that rank is important in determining certain carbonization and chemical properties. 

The refractive index of coal can be determined by comparing the reflectance in air with that in cedar oil. A standard test method (ASTM D-2798) covers the microscopic determination of both the mean maximum reflectance and the mean random reflectance measured in oil of polished surfaces of vitrinite and other macerals in coal ranging in rank from lignite to anthracite. This test method can be used to determine the reflectance of other macerals. For vitrinite (various coals), the refractive index usually falls within the range 1.68 (58% carbon coal) to 2.02 (96% carbon coal). 

It should also be noted that the anisotropy of the vitrinite reflectance increases significantly with the coal rank. This means that for one sample, even the random-reflectance readings in nonpolarized light scatter much more for high-rank coals > 2.0%) such as anthracite than do those of lower rank samples. Table 3.1 provides values for minimum, mean, and maximum reflectance measurements. It also clarifies diy only R is not suitable for rank determination [7]. 

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