OCR Text |
Show Nature of Trace Elements: Coal contains virtually e\/ery naturally occurring element. However, except for carbon, hydrogen, oxygen, nitrogen, and sulfur, most elements are present in coal in only minor or trace amounts. These elements are often found in the inorganic fraction of coal, even though some trace elements may also be associated with the organic groups. While the nature of minerals of coal is to some extent investigated, little is known about the organically bound trace elements (Gluskoter et al., 1981). During coal liquefaction processes, the trace elements undergo physical and chemical changes, finally appearing in almost e\/ery product stream. Although gross elemental material balance studies have been made for several processes (Filby et al., 1982), our knowledge of the reactions of trace elements of coal during liquefaction processes and the forms of trace elements in coal liquefaction products is very 1imited. At present, trace elements in coal-derived liquids are known to exist in both inorganic and organic forms (Filby et al., 1981). Upon distillation of these coal liquids, the vacuum bottoms residue is the major sink for most nonvolatile, inorganic or organically bound elements, the volatile species being transported into the lighter fractions (Filby et al., 1981; Sandstrom et al., 1982; Squires et al., 1983). Trace elements of coal, under the high temperature (=450°C), high pressure (100 atm), and strong reducing environment of hydrogen and hydrogen-donor solvents are converted to different compounds which, in coal-derived liquids, appear as suspended particles or dissolved 1.5.7 |