Liptinite

Because of their hydrocarbon character, liptinites show a lower density and an increased fraction of volatile matter ( 80 wt%). 

It should be noted that fluorescence measurements on different liptinite mac-erak vary with the rank The fluorescence intensity decreases as the red-to-green ratio increases with the rank, finally becoming so weak as to make measurements impossible [2,3]. 

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Macerals. Coal parts derived from different plant parts, are referred to as macerals (13). The maceral names end in "-inite" as do the mineral forms of rocks. The most abundant (about 85%) maceral in U.S. coal is vitrinite, derived from the woody tissues of plants. Another maceral, called liptinite, is derived from the waxy parts of spores and poUen, or algal remains. The liptinite macerals fluoresce under blue light permitting a subdivision based on fluorescence. A third maceral, inertinite, is thought to be derived from oxidized material or fossilized charcoal remnants of early forest fires. 

The elemental composition of the three maceral groups varies. The vitrinite, which frequently is about 85% of the sample in the United States, is similar to the patent coal. The liptinites are richer in hydrogen, whereas the inertinites are relatively deficient in hydrogen and richer in carbon. The liptinites also contain more aliphatic materials the inertinites are richer in aromatics. The term inertinite refers to the relative chemical inertness of this material, making it especially undesirable for Hquefaction processes because it tends to accumulate in recycled feedstock streams. 

Earlier publications have documented the higher reactivities of vitrinite and liptinite group macerals and the lower reactivities of certain inertinite macerals in liquefaction (50,57,68). 

The behavior of macrinite and micrinite in industrial processes is not clearly understood. As stated above, many U.S. petro-graphers treat both of these constituents as MinertM coal constituents. On the other hand, overseas workers have observed that micrinite may not be inert during carbonization. Because some micrinite appears to have been generated during the progressive coalification of the liptinite macerals, it might, instead, be quite reactive. 

The reactive role of liptinite macerals in liquefaction has been partially documented (50,68). However, recent work has shown that unaltered sporinite often is encountered in the residues from both batch and continuous liquefaction runs. For example, sporinite was a common component in the residues of a high volatile A bituminous coal after hydrogen-transfer runs at 400° for 30 minutes (70). In spite of the relative unreactivity of the sporinite in this instance, the vitrinite clearly had reacted extensively because vitroplast was the predominant residue component. The dissolution rate of sporinite from some coals, even at 400°C, may be somewhat less than that of vitrinite. 

Liptinites were made up of hydrogen-rich hydrocarbons derived from spores, pollens, cuticles, and resins in the original plant material. Vitrinites were made up of wood, bark, and roots and contained less hydrogen than the liptinites. Inertinites are mainly oxidation products of the other macerals and are consequently richer in carbon. The inertinite group includes fusinite, most of which is fossil charcoal, derived from ancient peat fires. 

Block coals" are dull coals that break into large blocks because they have fewer vitrain and clarain bands, but have a composition higher in liptinite macerals, which are tough. 

The high-volatile Liddell bituminous coal (Figure 2 (E)) shows little indication of thermally-activated molecular mobility below 500 K. There is some fusion between 500 and 600 K followed by a major fusion transition above 600 K which appears very similar to the high temperature transition of the Amberley coal. This Liddell coal, however, has only 6% liptinite, has a crucible swelling number of 6.5 and exhibits considerable Gieseler fluidity. We therefore attribute this high temperature fusion event to the aromatic-rich macerals of the coal and associate it with the thermoplastic phenomenon. This implies that a stage has been reached in the coalification processes at which aromatic-rich material becomes fusible. 

The low-volatile bituminous Bulli coal which contains no liptinite and has significant thermoplastic properties has a M2J pyrogram (Figure 2 (F)) showing only one fusion transition which is lesser in extent and shifted to higher temperatures than that of the Liddell coal. This transition is, of course, attributed to aromatic-rich macerals. 

Figure 3. Pyrograms of pure liptinite (o), vitrinite (x) and inertinite (+) for coals with < 75% carbon (daf). The vertical bars denote standard errors.

Two distinct types of fusible material occur in coals. One type is aliphatic-rich and associated with the liptinite macerals and the other is contained in the aromatic-rich macerals and particularly the vltrinites of bituminous coals. 

In the case of low rank brown coals the aliphatic-rich extractable material fuses at temperatures well below 600 K. With increasing coallflcatlon rank the thermal stability of this liptinite material Increases and the temperature range of its fusion transition approaches that at which the thermoplastic phenomenon of bituminous vltrinites occurs. The enhanced stability with increasing rank is attributed to greater covalent crosslinking which also would make the material less extractable and resistant to... 

Binder phase continuous solid carbon matrix formed during the thermoplastic deformation of those coal macerals that become plastic during carbonization formed from the thermoplastic deformation of reactive (vitrinite and liptinite) and semi-inert (semi-fusinite) coal macerals of metallurgical bituminous coals (ASTM D-5061). 

Boghead coal nonbanded coal in which the liptinite (the waxy component) is predominantly alginite. 

Cannel coal Nonbanded coal in which the liptinite is predominantly sporinite. Fusain coal layers composed of chips and other fragments in which the original form of plant tissue structure is preserved commonly has fibrous texture with a very dull luster friable and resembles charcoal commonly concentrated in bedding layers or lenses that form planes of weakness in coal and thus is often exposed on bedding surfaces of broken coal. 

Liptinite group of macerals composed of alginite, cutinite, resinite, and spori-nite derived from secretions of plants and distinguished from one another... 

As Stopes seems to have anticipated, a large number of macerals have been identified and named. All macerals, however, can be conveniently grouped into three major subdivisions -vitrinite, liptinite, and inertinite. The vitrinite group of macerals are derived from plant cell wall material (woody tissue) and usually make up 50-90% of most North American coals. Although there are a large number of named varieties of... 

Free Radicals in Macerals. Electron spin resonance (ESR) has been used to study carbon free radicals in coals, and to some extent, separated macerals. The technique provides information on radical density and the environment of the radicals. The resonance position, termed the g-value, is dependent on the structure of the molecule which contains the free electron. The line width is also sensitive to the environment of the unpaired electron. In an early study, Kroger (71) reported that the spin concentration varied between maceral groups with liptinite < vitrinite inertinite. For this limited set of samples the spin concentration increases with rank for liptinites and vitrinites and decreases for the micrinite samples. On the other hand, van Krevelen (72) found the same general results except... 

Direct Characterization Techniques. The in situ analysis of elemental composition of coals by ion microprobe was first demonstrated by Dutcher t al. (85). Raymond (86) has applied this technique to examine the variation in composition of coal macerals which has been especially effective for looking at sulfur distribution. An example of the organic sulfur distribution for two bituminous coals is shown in Table II which is taken from reference (86). Note that the liptinites contain the... 

The technique also yields quantitative spectra that are characteristic of both the individual maceral type and the rank of the coal. It is now also well established that all of the liptinite macerals (coal components derived from the resinous and waxy plant material) and many of the vitrinite macerals (coal components derived from woody tissue of plants) will fluoresce, and that some recently discovered liptinite macerals can only be identified by their fluorescence properties. 

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