Vacuum pyrolysis coals

Temperature-programmed vacuum pyrolysis in combination with time-resolved soft ionization mass spectrometry allows principally to distinguish between two devolatilization steps of coal which are related to the mobile and non-mobile phase, respectively. The mass spectrometric detection of almost exclusively molecular ions of the thermally extracted or degraded coal products enables one to study the change of molecular weight distribution as a function of devolatilization temperature. Moreover, major coal components can be identified which are released at distinct temperature intervals. 

The yields of the reaction of maceral concentrates with pyridine and iodine show some interesting trends and are given in Table V. Unlike the results from the thermal reactions such as vacuum pyrolysis (Table IV) or short contact time liquefaction (29), the vitrinites are more reactive than the spori-nites. The inertinites are less reactive but the magnitude of the difference in the comparison with the other maceral groups from the Indiana and Kentucky coals is much less than what has been found for the yields from the thermal reactions. 

Figure 8. Spectra of chars of PSOC 212 coal chars from 80-sec vacuum pyrolysis at the indicated temperature...

Figure 9. Comparison of tar and heavy aliphatic evolution with diminishing char aliphatic content products from 20-sec vacuum pyrolysis run ofPSOC 170 coal ((H) tar released (O) hydrocarbons released (k) aliphatic C-H in char)...

Figure 10. Hydrogen distribution in char from infrared analysis. The hydrogen in the char is normalized by the amount of hydrogen in the starting coal sample. Chars from 80-sec vacuum pyrolysis of PSOC 212...

The pyrolysis high resolution mass spectrometry (PyHRMS) technique has been described in detail previously (20). Briefly, the coal sample was placed on a platinum rhodium mesh on the end of a probe as a slurry. After the solvent had evaporated, the probe was inserted into the mass spectrometer and positioned within 5 mm of the source. The probe, which had been previously calibrated with an infra-red thermometer, was computer-controlled to give a temperature profile beginning at 100°C and increasing at 50°C/min to 800 C. The precise masses were matched to their corresponding chemical structures by computer programs developed in-house. This technique results in the relatively slow vacuum pyrolysis of the coal sample. 

Figure 30. FTIR spectra of tars from a Pittsburgh seam bituminous coal (PSOC 170). Tars from 10 s vacuum pyrolysis at the indicated temperature.

When pyrolysis of coal is carried out in the mass spectrometer in high vacuum of its ion source compartment, volatilization of broken fragments is likely to occur, unless they are of large molecular size. However, a large molecular size of a fragment would also reduce its rotational ability. 

In the context of the present discussion the term "mobile phase will be used to describe those components which can be thermally extracted ("distilled", "desorbed ) under vacuum at temperatures below the thermal degradation range of the coal. The residue, designated as the nonmobile ("network ) phase, is thermally degraded in the pyrolysis temperature range. Of course, the onset of pyrolysis may vary considerably, depending on heating rate, rank and coal type (10). 

Solvent-Refined Coal Process. In the 1920s the anthracene oil fraction recovered from pyrolysis, or coking, of coal was utilized to extract 35—40% of bituminous coals at low pressures for the purpose of manufacturing low cost newspaper inks (113). Tetralin was found to have higher solvent power for coals, and the I. G. Farben Pott-Broche process (114) was developed, wherein a mixture of cresol and tetralin was used to dissolve ca 75% of brown coals at 13.8 MPa (2000 psi) and 427°C. The extract was filtered, and the filtrate vacuum distilled. The overhead was distilled a second time at atmospheric pressure to separate solvent, which was recycled to extraction, and a heavier liquid, which was sent to hydrogenation. The bottoms product from vacuum distillation, or solvent-extracted coal, was carbonized to produce electrode carbon. Filter cake from the filters was coked in rotary kilns for tar and oil recovery. A variety of liquid products were obtained from the solvent extraction-hydrogenation system (113). A similar process was employed in Japan during Wodd War II to produce electrode coke, asphalt (qv), and carbonized fuel briquettes (115). 

The use of gas chromatography to determine oxygen in coal is considerably faster than the methods just described. The oxygen produced from coal pyrolysis in a vacuum was converted to carbon monoxide catalytically, and the total quantity of gas was measured. Gas chromatography was then used to measure the concentration of carbon monoxide in the gas. 

Other Factors. Several other factors influence, at least to some extent, the course of the pyrolysis process. These include particle size, bed configuration, pressure/vacuum during pyrolysis, nature of the coal ash, secondary reactions, etc.37 It is beyond the scope of this chapter to consider these items, but the interested reader can find additional information in the literature, including reports on pressure effects,21,38 effect of vacuum,23 effect of inorganics,26,39 and effect of a reactive atmosphere.23,40... 

Pyrolysis is an ancient method of decomposing solid matter by heating to high temperatures examples are production of metals, coke furnaces, and obtaining of chemicals from coal prior to petroleum. There are many kinds of pyrolysis batch, semi-batch or continuous catalytic or non-catalytic out under vacuum or at atmospheric or high pressure. Its medium may be inert, oxidative or reductive. Heating rate, temperature, and time are important pyrolysis parameters. 

Thermal cracking of ethane, propane, butane, naphthas, gas oils, and/or vacuum gas oils is the main process employed for the production of ethylene and propylene butadiene and benzene, toluene, and xylenes (BTX) are also produced. Thermal cracking of these hydrocarbons is also called pyrolysis of hydrocarbons. Ethylene is the organic chemical produced worldwide in the largest amoimts and has been called keystone to the petrochemical industry. This technology is well documented in the literature. Somewhat similar thermal cracking processes are used to produce vinyl chloride monomer (VCM) from ethylene dichloride (EDQ, styrene from ethylbenzene, and allyl chloride from propylene dichloride (PDC). Production of charcoal and coke from wood and coal is actually a pyrolysis process, but it is not discussed here. 

Table 10. Products from discharge pyrolysis of coal in vacuum and in the presence of added gases in static systems230, 231i...

The FT-IR spectra for four coals and their vacuum tar are illustrated in Fig 27 For bituminous coals, the two materials are almost identical except for a higher concentration of aliphatic (hydroaromatic) hydrogen (especially methyl) in the tar This extra hydrogen is presumably abstracted from the char to stabilize the free radical sites formed when the bridges were broken Similar arguments were given for pyrolysis of model compounds by Wolfs et al (56) ... 

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