AIR OXIDATION OF TURKISH BEYPAZARI LIGNITE .2. EFFECT OF DEMINERALIZATION ON STRUCTURAL CHARACTERISTICS IN OXIDATION REACTIONS AT 150-DEGREES-C

Demineralized (HCl/HF) samples of Beypazari lignite were oxidized in a ir at 150 degrees C for up 120 h in a ventilated oven. Elemental analy ses, diffuse reflectance Fourier transform infrared (DRIFT), solid-sta te C-13 CP/MAS/TOSS NMR, and pyrolysis mass (PY-MS) spectroscopies as well as solvent swelling were used for the characterization of the oxi dized and unoxidized samples. It was found that the removal of 90.1% o f the mineral matter from Beypazari lignite facilitated the access of oxygen into the coal structure and permitted the occurrence of diffusi on-controlled reactions. This was confirmed by the observation of line ar relationships between the decrease in the intensity of aliphatic CH 2 and CH3 groups, the increase of the O/H atomic ratio and the decreas e in the aliphatic factor, and the square root of the duration of oxid ation. It was observed from swelling measurements in pyridine before a nd after the oxidation that aryl esters and anhydrides, which were the major oxidation products, probably acted as covalent cross-links. Ali phatic groups oxidized more rapidly than aromatic structures and, in f act, methylenes oxidized more rapidly than methyls. The decrease in th e intensity of the molecular ion series alkylphenols, alkyldihydroxybe nzenes, alkylbenzenes, and alkylnaphthalenes arising from pyrolysis ma ss spectrometry of oxidized samples was approximately consistent with the corresponding increase in the intensity of CO2+, CH3COOH+, and CO molecular ions.